[ { "text": "Transfer of orbital angular momentum superposition from asymmetric\n Laguerre-Gaussian beam to Bose-Einstein Condensate: In this paper, we have formulated a theory for the microscopic interaction of\nthe asymmetric Laguerre-Gaussian (aLG) beam with the atomic Bose-Einstein\ncondensate (BEC) in a harmonic trap. Here the asymmetry is introduced to an LG\nbeam considering a complex-valued shift in the Cartesian plane keeping the axis\nof the beam and its vortex states co-axial to the trap axis of the BEC. Due to\nthe inclusion of the asymmetric nature, multiple quantized circulations are\ngenerated in the beam. We show how these quantized circulations are transferred\nto the BEC resulting in a superposition of matter vortex states. The calculated\nRabi frequencies for the dipole as well as quadrupole transitions during the\ntransfer process show distinct variability with the shift parameters of the\nbeam. A significant enhancement of the quadrupole Rabi frequency for higher\nvorticity states is observed compared to symmetric single orbital angular\nmomentum (OAM) mode beam at a particular range of the shift parameters. We also\ndemonstrate the variation of superposition of matter vortex states and observe\nits distinct feature compared to the superposition of the LG modes for\ndifferent shift parameters. The first order spatial correlation of the\nsuperposed states supports this feature and highlights asymmetry in degree of\ntransverse coherence along orthogonal directions on the surface.", "category": "physics_atom-ph" }, { "text": "Molecular wave-packet dynamics on laser-controlled transition states: Understanding and controlling the electronic as well as ro-vibrational motion\nand, thus, the entire chemical dynamics in molecules is the ultimate goal of\nultrafast laser and imaging science. In photochemistry, laser-induced\ndissociation has become a valuable tool for modification and control of\nreaction pathways and kinetics. Here, we present a pump-probe study of the\ndissociation dynamics of H$_2^+$ using ultrashort extreme-ultraviolet (XUV) and\nnear-infrared (IR) laser pulses. The reaction kinematics can be controlled by\nvarying the pump-probe delay. We demonstrate that the nuclear motion through\nthe transition state can be reduced to isolated pairs of initial vibrational\nstates. The dynamics is well reproduced by intuitive semi-classical\ntrajectories on a time-dependent potential curve. From this most fundamental\nscenario we gain insight in the underlying mechanisms which can be applied as\ndesign principles for molecular quantum control, particularly for ultrafast\nreactions involving protons.", "category": "physics_atom-ph" }, { "text": "Manipulation of ultracold atomic mixtures using microwave techniques: We used microwave radiation to evaporatively cool a mixture of of 133Cs and\n87Rb atoms in a magnetic trap. A mixture composed of an equal number (around\n10^4) of Rb and Cs atoms in their doubly polarized states at ultracold\ntemperatures was prepared. We also used microwaves to selectively evaporate\natoms in different Zeeman states.", "category": "physics_atom-ph" }, { "text": "Three-dimensional laser cooling at the Doppler limit: Many predictions of Doppler cooling theory of two-level atoms have never been\nverified in a three-dimensional geometry, including the celebrated minimum\nachievable temperature $\\hbar \\Gamma/2 k_B$, where $\\Gamma$ is the transition\nlinewidth. Here, we show that, despite their degenerate level structure, we can\nuse Helium-4 atoms to achieve a situation in which these predictions can be\nverified. We make measurements of atomic temperatures, magneto-optical trap\nsizes, and the sensitivity of optical molasses to a power imbalance in the\nlaser beams, finding excellent agreement with the Doppler theory. We show that\nthe special properties of Helium, particularly its small mass and narrow\ntransition linewidth, prevent effective sub-Doppler cooling with red-detuned\noptical molasses.", "category": "physics_atom-ph" }, { "text": "Photoassociative creation of ultracold heteronuclear 6Li40K* molecules: We investigate the formation of weakly bound, electronically excited,\nheteronuclear 6Li40K* molecules by single-photon photoassociation in a\nmagneto-optical trap. We performed trap loss spectroscopy within a range of 325\nGHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic\nstates and observed more than 60 resonances, which we identify as rovibrational\nlevels of 7 of 8 attractive long-range molecular potentials. The long-range\ndispersion coefficients and rotational constants are derived. We find large\nmolecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be\ncomparable to those for homonuclear 40K_2*. Using a theoretical model we infer\ndecay rates to the deeply bound electronic ground-state vibrational level\nX^1\\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production\nof ultracold bosonic ground-state 6Li40K molecules which exhibit a large\nintrinsic permanent electric dipole moment.", "category": "physics_atom-ph" }, { "text": "Continuous slowing of a gadolinium atomic beam: The article presents the development of a new and innovative experimental\nmethod to fully characterize a solenoidal \"spin-flip\" Zeeman slower (ZS) using\na Quartz Crystal $\\mu$-balance (QCM) as a kinetic energy sensor. In this\nexperiment, we focus a 447.1 nm laser into a counter-propagating beam of\ngadolinium (Gd) atoms in order to drive the dipole transition between ground\n$^{9}$D$^{0}_{2}$ state and $^{9}$D$_{3}$ excited state. The changes in the\nvelocity of the beam were measured using a QCM during this process, as a novel\nand alternative method to characterize the efficiency of a 1 m-long spin-flip\nZeeman slower. The QCM, normally used in solid-state physics, is continuously\nand carefully monitored to determine the change in its natural frequency of\noscillation. These changes reveal a direct relation with changes in the\ndeposition rate and the momentum exchanged between the QCM and Gd atoms. Hence,\nin terms of ultracold atom physics, it might be used to study the\ntime-evolution of the velocity distribution of the atoms during the cooling\nprocess. By this method, we obtain a maximum atom average velocity reduction of\n(43.5 $\\pm$ 6.4)$\\%$ produced by our apparatus. Moreover, we estimate an\nexperimental lifetime of $\\tau_{e}$ = 8.2 ns for the used electronic\ntransition, and then we compared it with the reported lifetime for 443.06 nm\nand 451.96 nm electronic transitions of Gd. These results confirm that the QCM\noffers an accessible and simple solution to take into account for laser cooling\nexperiments. Therefore, a novel and innovative technique can be available for\nfuture experiments.", "category": "physics_atom-ph" }, { "text": "Deterministic strong-field quantum control: Strong-field quantum-state control is investigated, taking advantage of the\nfull---amplitude and phase---characterization of the interaction between matter\nand intense ultrashort pulses via transient-absorption spectroscopy. A sequence\nof intense delayed pulses is used, whose parameters are tailored to steer the\nsystem into a desired quantum state. We show how to experimentally enable this\noptimization by retrieving all quantum features of the light-matter interaction\nfrom observable spectra. This provides a full characterization of the action of\nstrong fields on the atomic system, including the dependence upon possibly\nunknown pulse properties and atomic structures. Precision and robustness of the\nscheme are tested, in the presence of surrounding atomic levels influencing the\nsystem's dynamics.", "category": "physics_atom-ph" }, { "text": "The helion charge radius from laser spectroscopy of muonic helium-3 ions: Hydrogen-like light muonic ions, in which one negative muon replaces all the\nelectrons, are extremely sensitive probes of nuclear structure, because the\nlarge muon mass increases tremendously the wave function overlap with the\nnucleus. Using pulsed laser spectroscopy we have measured three 2S-2P\ntransitions in the muonic helium-3 ion ($\\mu^3$He$^+$), an ion formed by a\nnegative muon and bare helium-3 nucleus. This allowed us to extract the Lamb\nshift $E(2P_{1/2}-2S_{1/2})= 1258.598(48)^{\\rm exp}(3)^{\\rm theo}$ meV, the 2P\nfine structure splitting $E_{\\rm FS}^{\\rm exp} = 144.958(114)$ meV, and the\n2S-hyperfine splitting (HFS) $E_{\\rm HFS}^{\\rm exp} = -166.495(104)^{\\rm\nexp}(3)^{\\rm theo}$ meV in $\\mu^3$He$^+$. Comparing these measurements to\ntheory we determine the rms charge radius of the helion ($^3$He nucleus) to be\n$r_h$ = 1.97007(94) fm. This radius represents a benchmark for few nucleon\ntheories and opens the way for precision tests in $^3$He atoms and $^3$He-ions.\nThis radius is in good agreement with the value from elastic electron\nscattering, but a factor 15 more accurate. Combining our Lamb shift measurement\nwith our earlier one in $\\mu^4$He$^+$ we obtain $r_h^2-r_\\alpha^2 =\n1.0636(6)^{\\rm exp}(30)^{\\rm theo}$ fm$^2$ to be compared to results from the\nisotope shift measurements in regular He atoms, which are however affected by\nlong-standing tensions. By comparing $E_{\\rm HFS}^{\\rm exp}$ with theory we\nalso obtain the two-photon-exchange contribution (including higher orders)\nwhich is another important benchmark for ab-initio few-nucleon theories aiming\nat understanding the magnetic and current structure of light nuclei.", "category": "physics_atom-ph" }, { "text": "Direct Experimental Access to the Nonadiabatic Initial Momentum Offset\n upon Tunnel Ionization: We report on the non-adiabatic offset of the initial electron momentum\ndistribution in the plane of polarization upon single ionization of argon by\nstrong field tunneling and show how to experimentally control the degree of\nnon-adiabaticity. Two-color counter- and co-rotating fields (390 and 780 nm)\nare compared to show that the non-adiabatic offset strongly depends on the\ntemporal evolution of the laser electric field. We introduce a simple method\nfor the direct access to the non-adiabatic offset using two-color counter- and\nco-rotating fields. Further, for a single-color circularly polarized field at\n780 nm we show that the radius of the experimentally observed donut-like\ndistribution increases for increasing momentum in the light propagation\ndirection. Our observed initial momentum offsets are well reproduced by the\nstrong-field approximation (SFA). A mechanistic picture is introduced that\nlinks the measured non-adiabatic offset to the magnetic quantum number of\nvirtually populated intermediate states.", "category": "physics_atom-ph" }, { "text": "$^{87}$Sr lattice clock with inaccuracy below 10$^{-15}$: Aided by ultra-high resolution spectroscopy, the overall systematic\nuncertainty of the $^{1}S_{0}$-$^{3}P_{0}$ clock resonance for lattice-confined\n$^{87}$Sr has been characterized to $9\\times10^{-16}$. This uncertainty is at a\nlevel similar to the Cs-fountain primary standard, while the potential\nstability for the lattice clocks exceeds that of Cs. The absolute frequency of\nthe clock transition has been measured to be 429,228,004,229,874.0(1.1) Hz,\nwhere the $2.5\\times10^{-15}$ fractional uncertainty represents the most\naccurate measurement of a neutral-atom-based optical transition frequency to\ndate.", "category": "physics_atom-ph" }, { "text": "Measuring the polarization of electromagnetic fields using Rabi-rate\n measurements with spatial resolution: experiment and theory: When internal states of atoms are manipulated using coherent optical or\nradio-frequency (RF) radiation, it is essential to know the polarization of the\nradiation with respect to the quantization axis of the atom. We first present a\nmeasurement of the two-dimensional spatial distribution of the electric-field\namplitude of a linearly-polarized pulsed RF electric field at $\\sim 25.6\\,$GHz\nand its angle with respect to a static electric field. The measurements exploit\ncoherent population transfer between the $35$s and $35$p Rydberg states of\nhelium atoms in a pulsed supersonic beam. Based on this experimental result, we\ndevelop a general framework in the form of a set of equations relating the five\nindependent polarization parameters of a coherently oscillating field in a\nfixed laboratory frame to Rabi rates of transitions between a ground and three\nexcited states of an atom with arbitrary quantization axis. We then explain how\nthese equations can be used to fully characterize the polarization in a minimum\nof five Rabi rate measurements by rotation of an external bias-field, or,\nknowing the polarization of the driving field, to determine the orientation of\nthe static field using two measurements. The presented technique is not limited\nto Rydberg atoms and RF fields but can also be applied to characterize optical\nfields. The technique has potential for sensing the spatiotemporal properties\nof electromagnetic fields, e.g., in metrology devices or in hybrid experiments\ninvolving atoms close to surfaces.", "category": "physics_atom-ph" }, { "text": "Gauge-invariant absorption of light from a coherent superposition of\n states: Absorption and emission of light is studied theoretically for excited atoms\nin coherent superposition of states subjected to isolated attosecond pulses in\nthe extreme ultraviolet range. A gauge invariant formulation of transient\nabsorption theory is motivated using the energy operator from Yang's gauge\ntheory. The interaction, which simultaneously couples both bound and continuum\nstates, is simulated by solving the time dependent Schr\\\"odinger equation for\nhydrogen and neon atoms. A strong dependence on the angular momentum and the\nrelative phase of the states in the superposition is observed. Perturbation\ntheory is used to disentangle the fundamental absorption processes and a rule\nis established to interpret the complex absorption behaviour. It is found that\nnon-resonant transitions are the source of asymmetry in energy and phase, while\nresonant transitions to the continuum contribute symmetrically to absorption of\nlight from coherent superpositions of states.", "category": "physics_atom-ph" }, { "text": "Intra- and intercycle interference of electron emission in laser\n assisted XUV atomic ionization: We study the ionization of atomic hydrogen in the direction of polarization\ndue to a linearly polarized XUV pulse in the presence a strong field IR. We\ndescribe the photoelectron spectra as an interference problem in the time\ndomain. Electron trajectories steming from different optical laser cycles give\nrise to intercycle interference energy peaks known as sidebands. These\nsidebands are modulated by a grosser structure coming from the intracycle\ninterference of the two electron trajectories born during the same optical\ncycle. We make use of a simple semiclassical model which offers the possibility\nto establish a connection between emission times and the photoelectron kinetic\nenergy. We compare the semiclassical predictions with the continuum-distorted\nwave strong field approximation and the ab initio solution of the time\ndependent Schr\\\"odinger equation. We analyze such interference pattern as a\nfunction of the time delay between the IR and XUV pulse and also as a function\nof the laser intensity.", "category": "physics_atom-ph" }, { "text": "A model study on a pair of trapped particles interacting with an\n arbitrary effective range: We study the effects of the effective range of interaction on the eigenvalues\nand eigenstates of two particles confined in a three-dimensional (3D) isotropic\nas well as one- or quasi-one dimensional harmonic (1D) traps. For this we\nemploy model potentials which mimic finite-range s-wave interactions over a\nwide range of s-wave scattering length $a_s$ including the unitarity limits\n$a_s \\rightarrow \\pm\\infty$. Our results show that when the range is larger\nthan the 3D or 1D harmonic oscillator length scale, the eigenvalues and\neigenstates are nearly similar to those of noninteracting two particles in the\n3D or 1D trap, respectively. In case of 3D, we find that when the range goes to\nzero, the results of contact potential as derived by Busch {\\it et al.}\n[Foundations of Physics, {\\bf28}, 549 (1998)] are reproduced. However, in the\ncase of 1D, such reproducibility does not occur as the range goes to zero. We\nhave calculated the eigenvalues and eigenstates in 1D harmonic trap taking\none-dimensional finite- range model potential. We have also calculated bound\nstate properties of two particles confined in a highly anisotropic quasi-1D\ntrap taking three-dimensional finite-range model potential, and examined\nwhether these quasi-1D results approach towards 1D ones as the aspect ratio\n$\\eta$ of the radial to axial frequency of the trap increases. We find that if\nthe range is very small compared to the axial size of the trap, then one can\nreach 1D regime for $\\eta \\ge 10000$. However, for large range, one can nearly\nget 1D results for smaller values of $\\eta$. This study will be important for\nexploration of two-body or many body physics of trapped ultracold atoms\ninteracting with narrow Feshbach resonance for which the effective range can be\nlarge.", "category": "physics_atom-ph" }, { "text": "Testing the neutrality of matter by acoustic means in a spherical\n resonator: New measurements to test the neutrality of matter by acoustic means are\nreported. The apparatus is based on a spherical capacitor filled with gaseous\nSF$_6$ excited by an oscillating electric field. The apparatus has been\ncalibrated measuring the electric polarizability. Assuming charge conservation\nin the $\\beta$ decay of the neutron, the experiment gives a limit of\n$\\epsilon_\\text{p-e}\\lesssim1\\cdot10^{-21}$ for the electron-proton charge\ndifference, the same limit holding for the charge of the neutron. Previous\nmeasurements are critically reviewed and found incorrect: the present result is\nthe best limit obtained with this technique.", "category": "physics_atom-ph" }, { "text": "Studies of general relativity with quantum sensors: We present two projects aiming to probe key aspects of the theory of General\nRelativity with high-precision quantum sensors. These projects use cold-atom\ninterferometry with the aim of measuring gravitational waves and testing the\nequivalence principle. To detect gravitational waves, a large multi-sensor\ndemonstrator is currently under construction that will exploit correlations\nbetween three atom interferometers spread along a 200 m optical cavity.\nSimilarly, a test of the weak equivalence principle is currently underway using\na compact and mobile dual-species interferometer, which will serve as a\nprototype for future high-precision tests onboard an orbiting satellite. We\npresent recent results and improvements related to both projects.", "category": "physics_atom-ph" }, { "text": "Comment on \"Dynamics of transfer ionization in fast ion-atom collisions\": We inspect the first-order electron-electron capture scenario for transfer\nionization that has been recently formulated by Voitkiv et al. (Phys. Rev. A\n86, 012709 (2012) and references therein). Using the multichannel scattering\ntheory for many-body systems with Coulomb interactions, we show that this\nscenario is just a part of the well-studied Oppenheimer-Brinkmann-Kramers\napproximation. Accurate numerical calculations in this approximation for the\nproton-helium transfer ionization reaction exhibit no appreciable manifestation\nof the claimed mechanism.", "category": "physics_atom-ph" }, { "text": "Inverted crossover resonance aiding laser cooling of $^{171}$Yb: We observe an inverted crossover resonance in $\\pi$-driven four-level\nsystems, where $F'-F=0,+1$. The signal is observed through saturated absorption\nspectroscopy of the $(6s^{2})$ $^{1}S_{0}$ $-$ $(6s6p)$ $^{3}P_{1}$ transition\nin $^{171}$Yb, where the nuclear spin $I=1/2$. The enhanced absorption signal\nis used to generate a dispersive curve for 556 nm laser frequency stabilisation\nand the stabilised light cools $^{171}$Yb atoms in a two-stage magneto-optical\ntrap, achieving temperatures of 20 $\\mu$K. The Doppler-free spectroscopy scheme\nis further used to measure isotopic frequency shifts and hyperfine separations\nfor the intercombination line in ytterbium.", "category": "physics_atom-ph" }, { "text": "Frequency-modulation saturation spectroscopy of molecular iodine\n hyperfine structure near 640 nm with a diode laser source: In a frequency-modulation spectroscopy experiment, using the radiation from a\nsingle frequency diode laser, the spectra of molecular iodine hyperfine\nstructure near 640 nm were recorded on the transition\n$B^3\\Pi_{0_u^{+}}-X^1\\Sigma^+_{g}$. The frequency reference given by the value\nof the modulation frequency (12.5 MHz in given experiment) allows determination\nof the frequency differences between hyperfine components with accuracy better\nthan 0.1 MHz using the fitting procedure in experiment with only one laser.", "category": "physics_atom-ph" }, { "text": "Exact Keldysh theory of strong-field ionization: residue method vs\n saddle-point approximation: In recent articles [Mishima et al., Phys. Rev. A, 66, 033401(2002); Chao,\nPhys. Rev. A, 72, 053414 (2005)] it was proposed to use the residue theorem for\nthe exact calculation of the transition amplitude describing strong-field\nionization of atomic systems within Keldysh theory. This should avoid the\nnecessity to apply the method of steepest descent (saddle-point approximation).\nComparing the results of both approaches for atomic hydrogen a difference by a\nfactor of 2 was found for the 1s, and an even more drastic deviation for the 2s\nstate. Thus it was concluded that the use of the saddle-point approximation is\nproblematic. In this work the deviations are explained and it is shown that the\nprevious conclusion is based on an unjustified neglect of an important\ncontribution occurring in the application of the residue theorem. Furthermore,\nthe applicability of the method of steepest descent for the ionization of\nRydberg states is discussed and an improvement of the standard result is\nsuggested that successfully removes the otherwise drastic failure for large\nprincipal quantum numbers.", "category": "physics_atom-ph" }, { "text": "Precision Measurement of Time-Reversal Symmetry Violation with\n Laser-Cooled Polyatomic Molecules: Precision searches for time-reversal symmetry violating interactions in polar\nmolecules are extremely sensitive probes of high energy physics beyond the\nStandard Model. To extend the reach of these probes into the PeV regime, long\ncoherence times and large count rates are necessary. Recent advances in laser\ncooling of polar molecules offer one important tool -- optical trapping.\nHowever, the types of molecules that have been laser-cooled so far do not have\nthe highly desirable combination of features for new physics searches, such as\nthe ability to fully polarize and the existence of internal co-magnetometer\nstates. We show that by utilizing the internal degrees of freedom present only\nin molecules with at least three atoms, these features can be attained\nsimultaneously with molecules that have simple structure and are amenable to\nlaser cooling and trapping.", "category": "physics_atom-ph" }, { "text": "Narrow-band hard-x-ray lasing: Since the advent of x-ray free-electron lasers (XFELs), considerable efforts\nhave been devoted to achieve x-ray pulses with better temporal coherence. Here,\nwe put forward a scheme to generate fully coherent x-ray lasers (XRLs) based on\npopulation inversion in highly charged ions (HCIs), created by fast inner-shell\nphotoionization using XFEL pulses in a laser-produced plasma. Numerical\nsimulations show that one can obtain high-intensity, femtosecond x-ray pulses\nof relative bandwidths $\\Delta\\omega/\\omega=10^{-5}$ - $10^{-7}$ by orders of\nmagnitude narrower than in XFEL pulses for wavelengths down to the\nsub-\\aa{}ngstr\\\"om regime. Such XRLs may be applicable in the study of x-ray\nquantum optics and metrology, investigating nonlinear interactions between\nx-rays and matter, or in high-precision spectroscopy studies in laboratory\nastrophysics.", "category": "physics_atom-ph" }, { "text": "Theoretical characterization of the collective resonance states\n underlying the xenon giant dipole resonance: We present a detailed theoretical characterization of the two fundamental\ncollective resonances underlying the xenon giant dipole resonance (GDR). This\nis achieved consistently by two complementary methods implemented within the\nframework of the configuration-interaction singles (CIS) theory. The first\nmethod accesses the resonance states by diagonalizing the many-electron\nHamiltonian using the smooth exterior complex scaling technique. The second\nmethod involves a new application of the Gabor analysis to wave-packet\ndynamics. We identify one resonance at an excitation energy of 74 eV with a\nlifetime of 27 as, and the second at 107 eV with a lifetime of 11 as. Our work\nprovides a deeper understanding of the nature of the resonances associated with\nthe GDR: a group of close-lying intrachannel resonances splits into two\nfar-separated resonances through interchannel couplings involving the 4d\nelectrons. The CIS approach allows a transparent interpretation of the two\nresonances as new collective modes. Due to the strong entanglement between the\nexcited electron and the ionic core, the resonance wave functions are not\ndominated by any single particle-hole state. This gives rise to plasma-like\ncollective oscillations of the 4d shell as a whole.", "category": "physics_atom-ph" }, { "text": "Calculation of atomic spectra and transition amplitudes for superheavy\n element Db (Z=105): Atomic spectra and other properties of superheavy element dubnium (Db, Z=105)\nare calculated using recently developed method combining configuration\ninteraction with perturbation theory (the CIPT method, Dzuba et al, Phys. Rev.\nA, {\\bf 95}, 012503 (2017)). These include energy levels for low-lying states\nof Db and Db~II, electric dipole transition amplitudes from the ground state of\nDb, isotope shift for these transitions and ionisation potential of Db. Similar\ncalculations for Ta, which is lighter analog of Db, are performed to control\nthe accuracy of the calculations.", "category": "physics_atom-ph" }, { "text": "Active and passive stabilization of a high-power UV frequency-doubled\n diode laser: We present a resonantly frequency-doubled tapered amplified semiconductor\nlaser system emitting up to 2.6 W blue light at 400 nm. The output power is\nstable on both short and long timescales with 0.12% RMS relative intensity\nnoise, and less than 0.15%/h relative power loss over 16 hours of free running\ncontinuous operation. Furthermore, the output power can be actively stabilized,\nand the alignment of the input beams of the tapered amplifier chip, the\nfrequency doubling cavity and-in case of fiber output-the fiber can be\noptimized automatically using computer-controlled mirrors.", "category": "physics_atom-ph" }, { "text": "Lorentz force on an electron in a strong plane-wave laser field and the\n low-frequency limit for ionization: A motion of a classical free charge in an electromagnetic plane wave can be\nfound exactly in a fully relativistic case. We have found an approximate\nnon-parameter form of the suitable equations of motion. In a linearly polarized\nwave, in the simplest frame of reference, the charge moves along the well-known\n\"figure-8\" path. We have numerically calculated the Lorentz force acting on the\ncharge as a function of time. In virtue of this, for the low frequency\nionization (or detachment) rate, we discuss a manifestation of nondipole and\nrelativistic effects.", "category": "physics_atom-ph" }, { "text": "Complete-return spectrum for a generalized Rosen-Zener two-state\n term-crossing model: The general semiclassical time-dependent two-state problem is considered for\na specific field configuration referred to as the generalized Rosen-Zener\nmodel. This is a rich family of pulse amplitude- and phase-modulation functions\ndescribing both non-crossing and term-crossing models with one or two crossing\npoints. The model includes the original constant-detuning non-crossing\nRosen-Zener model as a particular case. We show that the governing system of\nequations is reduced to a confluent Heun equation. When inspecting the\nconditions for returning the system to the initial state at the end of the\ninteraction with the field, we reformulate the problem as an eigenvalue problem\nfor the peak Rabi frequency and apply the Rayleigh-Schr\\\"odinger perturbation\ntheory. Further, we develop a generalized approach for finding the higher-order\napproximations, which is applicable for the whole variation region of the\ninvolved input parameters of the system. We examine the general surface in the\n3D space of input parameters, which defines the position of the n-th order\nreturn-resonance, and show that the section of the general surface is\naccurately approximated by an ellipse. We find a highly accurate analytic\ndescription through the zeros of a Kummer confluent hypergeometric function.\nFrom the point of view of the generality, the analytical description of\nmentioned curve for the whole variation range of all involved parameters is the\nmain result of the present paper.", "category": "physics_atom-ph" }, { "text": "Statistics of electromagnetic transitions as a signature of chaos in\n many-electron atoms: Using a configuration interaction approach we study statistics of the dipole\nmatrix elements (E1 amplitudes) between the 14 lower odd states with J=4 and\n21st to 100th even states with J=4 in the Ce atom (1120 lines). We show that\nthe distribution of the matrix elements is close to Gaussian, although the\nwidth of the Gaussian distribution, i.e. the root-mean-square matrix element,\nchanges with the excitation energy. The corresponding line strengths are\ndistributed according to the Porter-Thomas law which describes statistics of\ntransition strengths between chaotic states in compound nuclei. We also show\nhow to use a statistical theory to calculate mean squared values of the matrix\nelements or transition amplitudes between chaotic many-body states. We draw\nsome support for our conclusions from the analysis of the 228 experimental line\nstrengths in Ce [J. Opt. Soc. Am. v. 8, p. 1545 (1991)], although direct\ncomparison with the calculations is impeded by incompleteness of the\nexperimental data. Nevertheless, the statistics observed evidence that highly\nexcited many-electron states in atoms are indeed chaotic.", "category": "physics_atom-ph" }, { "text": "Bohmian mechanics to high-order harmonic generation: This paper introduces Bohmian mechanics (BM) into the intense laser-atom\nphysics to study high-order harmonic generation. In BM, the trajectories of\natomic electrons in intense laser field can be obtained with the Bohm-Newton\nequation. The power spectrum with the trajectory of an atomic electron is\ncalculated, which is found to be irregular. Next, the power spectrum associated\nwith an atom ensemble from BM is considered, where the power spectrum becomes\nregular and consistent with that from quantum mechanics. Finally, the reason of\nthe generation of the irregular spectrum is discussed.", "category": "physics_atom-ph" }, { "text": "Amplified spontaneous emission at 5.23 um in two-photon excited Rb\n vapour: Population inversion on the 5D-6P transition in Rb atoms produced by cw\nexcitation at different wavelengths has been analysed by comparing the\ngenerated mid-IR radiation at 5.23 um originated from amplified spontaneous\nemission and isotropic blue fluorescence at 420 nm. A novel method of detecting\ntwo-photon excitation in atomic vapours using ASE is suggested. We have\nobserved directional co- and counter-propagating emission at 5.23 um. We find\nthat the power dependencies of the backward- and forward-directed emission can\nbe very close, however their spectral dependencies are not identical. The\nmid-IR emission in Rb vapours excited by nearly counter-propagating beams at\n780 and 776 nm does not exactly coincide spatially with the applied laser\nbeams. The presented observations could be useful for enhancing efficiency of\nfrequency mixing processes and new field generation in atomic media.", "category": "physics_atom-ph" }, { "text": "Chiral molecule candidates for trapped ion spectroscopy by ab initio\n calculations: from state preparation to parity violation: Parity non-conservation (PNC) due to the weak interaction is predicted to\ngive rise to enantiomer dependent vibrational constants in chiral molecules,\nbut the phenomenon has so far eluded experimental observation. The enhanced\nsensitivity of molecules to physics beyond the Standard Model (BSM), has led to\nsubstantial advances in molecular precision spectroscopy, and these may be\napplied to PNC searches as well. Specifically, trapped molecular ion\nexperiments leverage the universality of trapping charged particles to optimize\nthe molecular ion species studied toward BSM searches, but in searches for PNC\nonly a few chiral molecular ion candidates have been proposed so far.\nImportantly, viable candidates need to be internally cold and their internal\nstate populations should be detectable with high quantum efficiency. To this\nend, we focus on molecular ions that can be created by near threshold resonant\ntwo-photon ionization and detected via state-selective photo-dissociation. Such\ncandidates need to be stable in both charged and neutral chiral versions to be\namenable to these methods. Here, we present a collection of suitable chiral\nmolecular ion candidates we have found, including CHDBrI$^+$ and CHCaBrI$^+$,\nthat fulfill these conditions according to our \\textit{ab initio} calculations.\nWe find that organo-metallic species have a low ionization energy as neutrals\nand relatively high dissociation thresholds. Finally, we compute the magnitude\nof the PNC values for vibrational transitions for some of these candidates. An\nexperimental demonstration of state preparation and readout for these\ncandidates will be an important milestone toward measuring PNC in chiral\nmolecules for the first time.", "category": "physics_atom-ph" }, { "text": "Investigation of a $^{85}$Rb Dark Magneto-Optical Trap using an Optical\n Nanofibre: We report here measurements on a dark magneto-optical trap (DMOT) of\n$^{85}$Rb atoms using an optical nanofibre (ONF) with a waist of $\\sim$~1\n$\\mu$m. The DMOT is created using a doughnut-shaped repump beam along with a\ndepump beam for efficient transfer of cold atoms from the bright hyperfine\nground state ($F=3$) into the dark hyperfine ground state ($F=2$). The\nfluorescence from the cold $^{85}$Rb atoms of the DMOT is detected by coupling\nit into the fibre-guided modes of the ONF. The measured fractional population\nof cold atoms in the bright hyperfine ground state ($p$) is as low as\n$\\sim$0.04. The dependence of loading rate of DMOT on cooling laser intensity\nis investigated and also compared with the loading rate of a bright-MOT (BMOT).\nThis work lays the foundation for the use of an ONF for probing of a small\nnumber of atoms in an optically-dense cold atomic cloud.", "category": "physics_atom-ph" }, { "text": "Experimental determination of L X-ray fluorescence cross sections for\n elements with 45 < Z < 50 at 10 keV: Synchrotron radiation at 10 keV was used to experimentally determine the Ll,\nL, LI, LII, LI and LII fluorescence cross sections for elements with 45 < Z <\n50, as part of an ongoing investigation at low energies. The measured data were\ncompared with calculated values obtained using coefficients from Scofield,\nKrause and Puri et al.", "category": "physics_atom-ph" }, { "text": "Measurement of 7p$_{1/2}$-state hyperfine structure and\n 7s$_{1/2}$-7p$_{1/2}$ transition isotope shift in $^{203}$Tl and $^{205}$Tl: A two-step, two-color laser spectroscopy technique has been used to measure\nthe hyperfine splitting of the 7p$_{1/2}$ excited state in $^{203}$Tl and\n$^{205}$Tl, as well as the isotope shift within the 7s$_{1/2}$ - 7p$_{1/2}$\ntransition. Our measured values for the hyperfine splittings, 2153.2(7) MHz (in\n$^{203}$Tl) and 2173.3(8) MHz (in $^{205}$Tl), each differ by 20 MHz from\npreviously published values which quoted comparable precision. The transition\nisotope shift of $^{203}$Tl relative to $^{205}$Tl was measured to be 534.4(9)\nMHz. In our experiment, one laser was locked to the thallium ground-state\n6p$_{1/2}$ - 7s$_{1/2}$ 378 nm transition, while the second, spatially\noverlapping laser was scanned across the 7s$_{1/2}$(F=1) - 7p$_{1/2}$(F=0,1)\nhyperfine transitions. To facilitate accurate frequency calibration,\nradio-frequency modulation of the laser was used to create sidebands in the\nabsorption spectrum.", "category": "physics_atom-ph" }, { "text": "Investigation of M1 transitions of the ground-state configuration of\n In-like Tungsten: Three visible lines of M1 transitions from In-like W were recorded using the\nShanghai permanent magnet electron beam ion trap. The experimental wavelengths\nwere measured as 493.84 $\\pm$ 0.15, 226.97 $\\pm$ 0.13 and 587.63 $\\pm$ 0.23 nm\n(vacuum wavelengths). These results are in good agreement with theoretical\npredictions obtained using large-scale Relativistic Many-Body Perturbation\nTheory, in the form of the Flexible Atomic Code.", "category": "physics_atom-ph" }, { "text": "Linear polyatomic molecules with \u03a0 ground state: sensitivity to\n variation of the fundamental constants: In polyatomic molecules with \\Pi\\ electronic ground state the ro-vibrational\nspectrum can be strongly modified by the Renner-Teller effect. The linear form\nof C3H molecule has particularly strong Renner-Teller interaction and a very\nlow lying vibronic \\Sigma+ level, which corresponds to the excited bending\nvibrational mode. This leads to the increased sensitivities of the microwave\nand submillimeter transition frequencies to the possible variation of the fine\nstructure constant alpha and electron to proton mass ratio mu.", "category": "physics_atom-ph" }, { "text": "Role of the Coulomb potential on the ellipticity in atomic high-order\n harmonics generation: The role of the Coulomb potential on the generation of elliptically polarized\nhigh-order harmonics from atoms driven by elliptically polarized laser is\ninvestigated analytically. It is found that the Coulomb effect makes a\ncontribution to the harmonic ellipticity for low harmonic orders and short\nquantum path. By using the strong-field eikonal-Volkov approximation, we\nanalyze the influence of the Coulomb potential on the dynamics of the continuum\nstate and find that the obtained harmonic ellipticity in our simulation\noriginates from the break of symmetry of the continuum state.", "category": "physics_atom-ph" }, { "text": "First-principles simulations for attosecond photoelectron spectroscopy\n based on time-dependent density functional theory: We develop a first-principles simulation method for attosecond time-resolved\nphotoelectron spectroscopy. This method enables us to directly simulate the\nwhole experimental processes, including excitation, emission and detection on\nequal footing. To examine the performance of the method, we use it to compute\nthe reconstruction of attosecond beating by interference of two-photon\ntransitions (RABBITT) experiments of gas-phase Argon. The computed RABBITT\nphotoionization delay is in very good agreement with recent experimental\nresults from [Kl\\\"under et al, Phys. Rev. Lett. 106 143002 (2011)] and\n[Gu\\'enot et al, Phys. Rev. A 85 053424 (2012)]. This indicates the\nsignificance of a fully-consistent theoretical treatment of the whole\nmeasurement process to properly describe experimental observables in attosecond\nphotoelectron spectroscopy. The present framework opens the path to unravel the\nmicroscopic processes underlying RABBITT spectra in more complex materials and\nnanostructures.", "category": "physics_atom-ph" }, { "text": "K-shell ionization of heavy hydrogen-like ions: A theoretical study of the K-shell ionization of hydrogen-like ions,\ncolliding with bare nuclei, is performed within the framework of the\ntime-dependent Dirac equation. Special emphasis is placed on the ionization\nprobability that is investigated as a function of impact parameter, collision\nenergy and nuclear charge. To evaluate this probability in a wide range of\ncollisional parameters we propose a simple analytical expression for the\ntransition amplitude. This expression contains three fitting parameters that\nare determined from the numerical calculations, based on the adiabatic\napproximation. In contrast to previous studies, our analytical expression for\nthe transition amplitude and ionization probability accounts for the full\nmultipole expansion of the two-center potential and allows accurate description\nof nonsymmetric collisions of nuclei with different atomic numbers, $Z_1 \\neq\nZ_2$. The calculations performed for both symmetric and asymmetric collisions\nindicate that the ionization probability is reduced when the difference between\nthe atomic numbers of ions increases.", "category": "physics_atom-ph" }, { "text": "A new setup for experiments with ultracold Dysprosium atoms: In the domain of quantum degenerate atomic gases, much interest has been\nraised recently by the use of Lanthanide atoms with large magnetic moments, in\nparticular Dysprosium and Erbium. These species have been successfully brought\nto quantum degeneracy and are now excellent candidates for quantum simulations\nof physical phenom- ena due to long-range interactions. In this short article,\nwe report on the progresses in the construction of a new experiment on\nBose-Einstein condensation of Dysprosium atoms. After completing the vacuum and\nthe laser setups, a magneto-optical trap on the narrow 626nm 162Dy transition\nhas been realized and characterized. The prospects for future experiments are\nbrie y discussed.", "category": "physics_atom-ph" }, { "text": "Intermediate-energy electron-impact dissociative ionization-excitation\n of molecular hydrogen: We have implemented three variants of the exterior complex scaling procedure\nin prolate spheroidal coordinates (PS-ECS) to study the dissociative electron\nimpact ionization-excitation of hydrogen molecule, where the emerging electrons\nand one of the protons are detected in coincidence for the first time in a\nrecent experiment. In the first variant, designated PSECS-1B, the two target\nelectrons are treated ab initio while the interaction of the incident-scattered\nelectron is taken into account using the first term of the Born series. In the\nsecond, PSECS-2BCD, the second Born term is introduced in the dipole\napproximation. In the third approach, designated PSECS-SW, applied to the\nionization-excitation to the $2p\\sigma_u$ level of H$_2^+$, the\nmulti-configurational single active electron approximation is used for the\ntarget, while the interaction of the incident electron with the target is\ndescribed ab initio. Our results agree partially with those of a recent\nexperiment which is in progress.", "category": "physics_atom-ph" }, { "text": "Optical tuning of the scattering length of cold alkaline earth atoms: It is possible to tune the scattering length for the collision of ultra-cold\n1S0 ground state alkaline-earth atoms using an optical Feshbach resonance. This\nis achieved with a laser far detuned from an excited molecular level near the\nfrequency of the atomic intercombination 1S0--3P1 transition. Simple resonant\nscattering theory, illustrated by the example of 40Ca, allows an estimate of\nthe magnitude of the effect. Unlike alkali metal species, large changes of the\nscattering length are possible while atom loss remains small, because of the\nvery narrow line width of the molecular photoassociation transition. This\nraises prospects for control of atomic interactions for a system without\nmagnetically tunable Feshbach resonance levels.", "category": "physics_atom-ph" }, { "text": "Attosecond Transient Absorption Spectroscopy without Inversion Symmetry: Transient absorption is a very powerful observable in attosecond experiments\non atoms, molecules and solids and is frequently used in experiments employing\nphase-locked few-cycle infrared and XUV laser pulses derived from high harmonic\ngeneration. We show numerically and analytically that in non-centrosymmetric\nsystems, such as many polyatomic molecules, which-way interference enabled by\nthe lack of parity conservation leads to new spectral absorption features,\nwhich directly reveal the laser electric field. The extension of Attosecond\nTransient Absorption Spectroscopy (ATAS) to such targets hence becomes\nsensitive to global and local inversion symmetry. We anticipate that ATAS will\nfind new applications in non-centrosymmetric systems, in which the\ncarrier-to-envelope phase of the infrared pulse becomes a relevant parameter\nand in which the orientation of the sample and the electronic symmetry of the\nmolecule can be addressed.", "category": "physics_atom-ph" }, { "text": "L-MM Auger electron emission from chlorinated organic molecules under\n proton impact: angular distribution and total cross section measurement: We have measured absolute total cross section for LMM Auger electron emission\nof Cl in chlorinated methane and benzene chloride in collision with H+ ion.\nProjectile energy dependence of the total yield as well as the angular\ndistribution has been studied. Incident proton energy has been varied from 125\nkeV to 275 keV in steps of 50 keV. C KLL Auger yield have been compared with\nprevious studies and found to be in agreement within the effect of chemical\nspecies It has been found that the LMM Auger yield of Cl is much more\nsignificantly affected by molecular environment than the C KLL.", "category": "physics_atom-ph" }, { "text": "Efficiency limitation for realizing an atom-molecule adiabatic transfer\n based on a chainwise system: In a recent work we have developed a robust chainwise atom-molecule adiabatic\npassage scheme to produce ultracold ground-state molecules via\nphoto-associating free atoms [J. Qian {\\it et.al.} Phys. Rev. A 81 013632\n(2010)]. With the help of intermediate auxiliary levels, the pump laser\nintensity requested in the atomic photo-association process can be greatly\nreduced. In the present work, we extend the scheme to a more generalized\n(2$n$+1)-level system and investigate the efficiency limitation for it. As the\nincrease of intermediate levels and auxiliary lasers, the atom-molecule\nadiabatic passage would be gradually closed, leading to a poor transfer\nefficiency. For the purpose of enhancing the efficiency, we present various\noptimization approaches to the laser parameters, involving order number $n$,\nrelative strength ratio and absolute strength. We show there can remain a limit\non the population transfer efficiency given by a three-level $\\Lambda$ system.\nIn addition, we illustrate the importance of selecting an appropriate number of\nintermediate levels for maintaining a highly efficient transfer under mild\nexperimental conditions.", "category": "physics_atom-ph" }, { "text": "Temperature and number evolution of cold cesium atoms inside a\n wall-coated glass cell: We report an experimental study on the temperature and number evolution of\ncold cesium atoms diffusively cooled inside a wall-coated glass cell by\nmeasuring the absorption profile of the 62S1/2 (F=4)-62P3/2 (F'=5) transition\nline with a weak probe laser in the evolution process. We found that the\ntemperature of the cold atoms first gradually decreases from 16 mK to 9 mK, and\nthen rapidly increases. The number of cold atoms first declines slowly from\n2.1*10^9 to 3.7*10^8 and then falls drastically. A theoretical model for the\nnumber evolution is built and includes the instantaneous temperature of the\ncold atoms and a fraction p, which represents the part of cold cesium atoms\nelastically reflected by the coated cell wall. The theory is overall in good\nagreement with the experimental result and a nonzero value is obtained for the\nfraction p, which indicates that the cold cesium atoms are not all heated to\nthe ambient temperature by a single collision with the coated cell wall. These\nresults can provide helpful insight for precision measurements based on diffuse\nlaser cooling.", "category": "physics_atom-ph" }, { "text": "Data-Driven Energy Levels Calculation of Neutral Ytterbium ($Z$ = 70): In view of the difficulty in calculating the atomic structure parameters of\nhigh-$Z$ elements, the HFR (Hartree-Fock with relativistic corrections) theory\nin combination with the ridge regression (RR) algorithm rather than the Cowan\ncode's least squares fitting (LSF) method is proposed and applied. By analyzing\nthe energy level structure parameters of the HFR theory and using the fitting\nexperimental energy level extrapolation method, some excited state energy\nlevels of the {Yb~I} ($Z=70$) atom including the $4f$ open shell are\ncalculated. The advantages of the ridge regression algorithm are demonstrated\nby comparing it with Cowan's least squares results. In addition, the results\nobtained by the new method are compared with the experimental results and other\ntheoretical results to demonstrate the reliability and accuracy of our\napproach.", "category": "physics_atom-ph" }, { "text": "Rydberg States of H$_3$ and HeH as Potential Coolants for Primordial\n Star Formation: Current theory and measurements establish the age of the universe as ca. 13.8\nbillion years. For the first several hundred million years of its existence, it\nwas a dark, opaque void. After that, the hydrogen atoms comprising most of the\n\"ordinary\" matter began to condense and ionize, eventually forming the first\nstars that would illuminate the sky. Details of how these \"primordial\" stars\nformed have been widely debated, but remain elusive. A central issue in this\nprocess is the mechanism by which the primordial gas (mainly hydrogen and\nhelium atoms) collected via the action of dark matter cools and further\naccretes to fusion densities. Current models invoke collisional excitation of\nH$_2$ molecular rotations and subsequent radiative rotational transitions\nallowed by the weak molecular quadrupole moment. In this article, we review the\nsalient considerations, and present some new ideas, bases on recent\nspectroscopic observations of neutral H$_3$ Rydberg electronic state emission\nin the mid-infrared.", "category": "physics_atom-ph" }, { "text": "Alignment-dependent fluorescence emission induced by tunnel ionization\n of carbon dioxide from lower-lying orbitals: Study on ionization process of molecules in an intense infrared laser field\nis of paramount interest in strong-field physics and constitutes the foundation\nof imaging of molecular valence orbitals and attosecond science. We show\nmeasurement of alignment-dependent ionization probabilities of the lower-lying\norbitals of the molecules by experimentally detecting alignment-dependence of\nfluorescence emission from tunnel ionized carbon dioxide molecules. The\nexperimental measurements are compared with the theoretical calculations of\nstrong field approximation (SFA) and molecular ADK models. Our results\ndemonstrate the feasibility of an all-optical approach for probing the\nionization dynamics of lower-lying orbitals of molecules, which is still\ndifficult to achieve until now by other techniques. Moreover, the deviation\nbetween the experimental and theoretical results indicates the incompleteness\nof current theoretical models for describing strong field ionization of\nmolecules.", "category": "physics_atom-ph" }, { "text": "Orientational Effects on the Amplitude and Phase of Polarimeter Signals\n in Double Resonance Atomic Magnetometry: Double resonance optically pumped magnetometry can be used to measure static\nmagnetic fields with high sensitivity by detecting a resonant atomic spin\nresponse to a small oscillating field perturbation. Determination of the\nresonant frequency yields a scalar measurement of static field ($B_0$)\nmagnitude. We present calculations and experimental data showing that the\non-resonance polarimeter signal of light transmitted through an atomic vapour\nin arbitrarily oriented $B_0$ may be modelled by considering the evolution of\nalignment terms in atomic polarisation. We observe that the amplitude and phase\nof the magnetometer signal are highly dependent upon $B_0$ orientation, and\npresent precise measurements of the distribution of these parameters over the\nfull 4{\\pi} solid angle.", "category": "physics_atom-ph" }, { "text": "Laser-driven relativistic tunneling from p-states: The tunneling ionization of an electron from a p-state in a highly charged\nion in the relativistic regime is investigated in a linearly polarized strong\nlaser field. In contrast to the case of an s-state, the tunneling ionization\nfrom the p-state is spin asymmetric. We have singled out two reasons for the\nspin asymmetry: first, the difference of the electron energy Zeeman splitting\nin the bound state and during tunneling, and second, the relativistic momentum\nshift along the laser propagation direction during the under-the barrier\nmotion. Due to the latter, those states are predominantly ionized where the\nelectron rotation is opposite to the electron relativistic shift during the\nunder-the-barrier motion. We have investigated the dependence of the ionization\nrate on the laser intensity for different projections of the total angular\nmomentum and identified the intensity parameter which governs this behaviour.\nThe significant change of the ionization rate is originated from the different\nprecession dynamics of the total angular momentum in the bound state at high\nand low intensities.", "category": "physics_atom-ph" }, { "text": "Exploration of the magnetic-field-induced\n $5s5p$~$^3P_0$~-~$5s^2$~$^1S_0$ forbidden transition in bosonic Sr atom: We presented experimental and theoretical studies of the effect of an\nexternal magnetic field on the forbidden transition in the bosonic Sr atom. In\nour ultra-cold atomic system, the excitation fraction of\n$5s5p$~$^3P_0$~-~$5s^2$~$^1S_0$ forbidden transition was measured under the\ncircumstance of the different magnetic field strengths by using the normalized\ndetection method. Based on perturbation theory, we calculated the\nmagnetic-field-induced $5s5p$~$^3P_0$~-~$5s^2$~$^1S_0$ transition rate. The\nexcitation fraction as a function of the magnetic field strength was deduced\naccording to the calculated results. A good agreement was found between the\nexperimental measurements and the calculations. This study should be helpful in\nevaluating the magnetic field effects on the forbidden transition rate with\nhigher accuracy. Moreover, it can help to understand the ultra-cold atomic\ninteraction in the external magnetic field.", "category": "physics_atom-ph" }, { "text": "A simple radionuclide-driven single-ion source: We describe a source capable of producing single barium ions through nuclear\nrecoils in radioactive decay. The source is fabricated by electroplating 148Gd\nonto a silicon {\\alpha}-particle detector and vapor depositing a layer of BaF2\nover it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+\nions from the BaF2 layer and emit them in the surrounding environment. The\nsimultaneous detection of an {\\alpha} particle in the substrate detector allows\nfor tagging of the nuclear decay and of the Ba+ emission. The source is simple,\ndurable, and can be manipulated and used in different environments. We discuss\nthe fabrication process, which can be easily adapted to emit most other\nchemical species, and the performance of the source.", "category": "physics_atom-ph" }, { "text": "Vibrational branching ratios and hyperfine structure of $^{11}$BH and\n its suitability for laser cooling: The simple structure of the BH molecule makes it an excellent candidate for\ndirect laser cooling. We measure the branching ratios for the decay of the\n${\\rm A}^{1}\\Pi (v'=0)$ state to vibrational levels of the ground state, ${\\rm\nX}^{1}\\Sigma^{+}$, and find that they are exceedingly favourable for laser\ncooling. We verify that the branching ratio for the spin-forbidden transition\nto the intermediate ${\\rm a}^{3}\\Pi$ state is inconsequentially small. We\nmeasure the frequency of the lowest rotational transition of the X state, and\nthe hyperfine structure in the relevant levels of both the X and A states, and\ndetermine the nuclear electric quadrupole and magnetic dipole coupling\nconstants. Our results show that, with a relatively simple laser cooling\nscheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and\ntrap BH molecules.", "category": "physics_atom-ph" }, { "text": "New form of the Boltzmann constant from search for a permanent electric\n dipole moment of K, Rb or Cs atom: Using special capacitors our experiments discovered that the ground state K,\nRb or Cs atom is polar atom with a large permanent electric dipole moment (EDM)\nof the order of eao (ao is Bohr radius) as excited state of hydrogen atom. But\nwe can not calculate the EDM of an atom using Boltzmann constant. The mechanism\nof polar atoms by which orientation polarization arises completely differs from\npolar molecules. The orientation polarization of polar molecule, such as HCl or\nH2O etc, is a molecule as a whole turned toward the direction of an external\nfield. Unlike polar molecules, the orientation polarization of polar atom, such\nas K, Rb or Cs atom, is only the valence electron in the outermost shell, along\na highly elliptical orbit, turned toward the direction of the field, but the\nrest of the atom does not move! The article derived the new form of Boltzmann\nconstant. When it was applied to orientation polarization of polar atoms, its\nvalue k is far less than 1.38*10-23 J/K(for example, k=7.14*10-29 J/K for Cs\natom) . When it was applied to any molecule, non-polar atom or translation and\nvibration of polar atom, its value k=1.38*10-23J/K. The reason is that the\nnucleus moves together with the rest of the molecule or atom. (see\narXiv:0809.4767; arXiv:0810.0770; arXiv:0810.2026)", "category": "physics_atom-ph" }, { "text": "The effect of orientation of Rydberg atoms on their collisional\n ionization cross section: Collisional ionization between two Rydberg atoms in relative motion is\nexamined. A classical trajectory Monte Carlo method is used to determine the\ncross sections associated with Penning ionization. The dependence of the\nionization cross section on the magnitude and the direction of orbital angular\nmomentum of the electrons and the direction of the Laplace-Runge-Lenz vector of\nthe electrons is studied. For a given magnitude of angular momentum, there can\nexist a difference of a factor of up to $\\sim2.5$ in the ionization cross\nsection between the orientation with the highest and the lowest ionization\ncross section. The case of exchange ionization is examined and its dependence\non the magnitude of angular momentum is studied.", "category": "physics_atom-ph" }, { "text": "Creating a self-induced dark spontaneous-force optical trap for neutral\n atoms: This communication describes the observation of a new type of dark\nspontaneous-force optical trap (dark SPOT) obtained without the use of a mask\nblocking the central part of the repumper laser beam. We observe that loading a\nmagneto-optical trap (MOT) from a continuous and intense flux of slowed atoms\nand by appropriately tuning the frequency of the repumper laser is possible to\nachieve basically the same effect of the dark SPOT, using a simpler apparatus.\nThis work characterizes the new system through measurements of absorption and\nfluorescence imaging of the atomic cloud and presents a very simple model to\nexplain the main features of our observations. We believe that this new\napproach may simplify the current experiments to produce quantum degenerated\ngases.", "category": "physics_atom-ph" }, { "text": "Regime of Validity of the Pairing Hamiltonian in the Study of Fermi\n Gases: The ground state energy and pairing gap of the interacting Fermi gases\ncalculated by the {\\it ab initio} stochastic method are compared with those\nestimated from the Bardeen-Cooper-Schrieffer pairing Hamiltonian. We discuss\nthe ingredients of this Hamiltonian in various regimes of interaction strength.\nIn the weakly interacting ($1/ak_F <<0$) regime the BCS Hamiltonian should\ndescribe Landau quasi-particle energies and interactions, on the other hand in\nthe strongly pairing regime, that is $1/ak_F \\gtrsim 0$, it becomes part of the\nbare Hamiltonian. However, the bare BCS Hamiltonian is not adequate for\ndescribing atomic gases in the regime of weak to moderate interaction strength\n$-\\infty < 1/ak_F <0$ such as $ak_F \\sim -1$.\n PACS: 05.30.Fk, 03.75.Ss, 21.65.+f", "category": "physics_atom-ph" }, { "text": "Extracting photoelectron spectra from the time-dependent wave function:\n Comparison of the projection onto continuum states and window-operator\n methods: Over the last three decades numerous numerical methods for solving the\ntime-dependent Schr\\\"{o}dinger equation within the single-active electron\napproximation have been developed for studying ionization of atomic targets\nexposed to an intense laser field. In addition, various numerical techniques\nfor extracting the photoelectron spectra from the time-dependent wave function\nhave emerged. In this paper we compare photoelectron spectra obtained by either\nprojecting the time-dependent wave function at the end of the laser pulse onto\nthe continuum state having proper incoming boundary condition or by using the\nwindow-operator method. Our results for three different atomic targets show\nthat the boundary condition imposed onto the continuum states plays a crucial\nrole for obtaining correct spectra accurate enough to resolve fine details of\nthe interference structures of the photoelectron angular distribution.", "category": "physics_atom-ph" }, { "text": "Dynamics of an unbalanced two-ion crystal in a Penning trap for\n application in optical mass spectrometry: In this article, the dynamics of an unbalanced two-ion crystal comprising the\n'target' and the 'sensor' ions confined in a Penning trap has been studied.\nFirst, the low amplitude regime is addressed. In this regime, the overall\npotential including the Coulomb repulsion between the ions can be considered\nharmonic and the axial, magnetron and reduced-cyclotron modes split up into the\nso-called 'stretch' and 'common' modes, that are generalizations of the\nwell-known 'breathing' and 'center-of-mass' motions of a balanced crystal made\nof two ions. By measuring the frequency modes of the crystal and the sensor ion\neigenfrequencies using optical detection, it will be possible to determine the\ntarget ion's free-cyclotron frequency. The measurement scheme is described and\nthe non-harmonicity of the Coulomb interaction is discussed since this might\ncause large systematic effects.", "category": "physics_atom-ph" }, { "text": "Wave-graphene: a full-auxetic carbon semiconductor with high flexibility\n and optical UV absorption: The abundant bonding possibilities of Carbon stimulate the design of numerous\ncarbon allotropes, promising the foundation for exploring\nstructure-functionality relationships. Herein, utilizing the space bending\nstrategy, we successfully engineered a two-dimensional carbon allotrope with\npure sp2 hybridization, named \"Wave-graphene\" from the unique wave-like ripple\nstructure. The novel Wave-graphene exhibits full-auxetic behavior due to\nanisotropic mechanical response, possessing both negative and zero Poisson's\nratios. The fundamental mechanism can be attributed to the fact that highly\nbuckled out-of-plane structures lead to anisotropic responses of in-plane\nnonlinear interactions, which further lead to anisotropy of lattice vibrations.\nIn addition, Wave-graphene is found having quasi-direct wide bandgap of 2.01\neV, the excellent optical transparency and the high flexibility. The successful\ndesign of Wave-graphene with excellent outstanding multifunctional properties\nshows that the utilization of space bending strategies can provide more degrees\nof freedom for designing novel materials, further enriching the carbon material\nfamily and supplementing its versatility.", "category": "physics_atom-ph" }, { "text": "The effect of dressing on high-order harmonic generation in vibrating\n H$_2$ molecules: We develop the strong-field approximation for high-order harmonic generation\nin hydrogen molecules, including the vibrational motion and the laser-induced\ncoupling of the lowest two Born-Oppenheimer states in the molecular ion that is\ncreated by the initial ionization of the molecule. We show that the field\ndressing becomes important at long laser wavelengths ($\\approx 2 \\mu$m),\nleading to an overall reduction of harmonic generation and modifying the ratio\nof harmonic signals from different isotopes.", "category": "physics_atom-ph" }, { "text": "Magnetic resonance of rubidium atoms passing through a multi-layered\n transmission magnetic grating: We measured the magnetic resonance of rubidium atoms passing through periodic\nmagnetic fields generated by two types of multilayered transmission magnetic\ngrating. One of the gratings reported here was assembled by stacking four\nlayers of magnetic films so that the direction of magnetization alternated at\neach level. The other grating was assembled so that the magnetization at each\nlevel was aligned. For both types of grating, the experimental results were in\ngood agreement with our calculations. We studied the feasibility of extending\nthe frequency band of the grating and narrowing its resonance linewidth by\nperforming calculations. For magnetic resonance precision spectroscopy, we\nconclude that the multi-layered transmission magnetic grating can generate\nperiodic fields with narrower linewidths at higher frequencies when a larger\nnumber of layers is assembled at a shorter period length. Moreover, the\nfrequency band of this type of grating can potentially achieve frequencies of\nup to hundreds of PHz.", "category": "physics_atom-ph" }, { "text": "Resonant propagation of x-rays from the linear to the nonlinear regime: We present a theoretical study of temporal, spectral, and spatial reshaping\nof intense, ultrafast x-ray pulses propagating through a resonant medium. Our\ncalculations are based on the solution of a 3D time-dependent\nSchr\\\"odinger-Maxwell equation, with the incident x-ray photon energy on\nresonance with the core-level 1s-3p transition in neon. We study the evolution\nof the combined incident and medium-generated field, including the effects of\nstimulated emission, absorption, ionization and Auger decay, as a function of\nthe input pulse energy and duration. We find that stimulated Raman scattering\nbetween core-excited states $1s^{-1}3p$ and $2p^{-1}3p$ occurs at high x-ray\nintensity, and that the emission around this frequency is strongly enhanced\nwhen also including the similar $1s^{-1}-2p^{-1}$ response of the ion. We also\nexplore the dependence of x-ray self-induced transparency (SIT) and\nself-focusing on the pulse intensity and duration, and we find that the\nstimulated Raman scattering plays an important role in both effects. Finally,\nwe discuss how these nonlinear effects may potentially be exploited as control\nparameters for pulse properties of x-ray free-electron laser sources.", "category": "physics_atom-ph" }, { "text": "Magic wavelength of the $^{138}$Ba$^+$ $6s\\;{}^2S_{1/2}-5d\\;{}^2D_{5/2}$\n clock transition: The zero crossing of the dynamic differential scalar polarizability of the\n$S_{1/2}-D_{5/2}$ clock transition in $^{138}$Ba$^+$ has been determined to be\n$459.1614(28)\\,$THz. Together with previously determined matrix elements and\nbranching ratios, this tightly constrains the dynamic differential scalar\npolarizability of the clock transition over a large wavelength range ($\\gtrsim\n700\\,$nm). In particular it allows an estimate of the blackbody radiation shift\nof the clock transition at room temperature.", "category": "physics_atom-ph" }, { "text": "2s Hyperfine Structure in Hydrogen Atom and Helium-3 Ion: The usefulness of study of hyperfine splitting in the hydrogen atom is\nlimited on a level of 10 ppm by our knowledge of the proton structure. One way\nto go beyond 10 ppm is to study a specific difference of the hyperfine\nstructure intervals 8 Delta nu_2 - Delta nu_1. Nuclear effects for are not\nimportant this difference and it is of use to study higher-order QED\ncorrections.", "category": "physics_atom-ph" }, { "text": "Pulsed Rydberg four-wave mixing with motion-induced dephasing in a\n thermal vapor: We report on time-resolved pulsed four-wave mixing (FWM) signals in a thermal\nRubidium vapor involving a Rydberg state. We observe FWM signals with dephasing\ntimes up to 7 ns, strongly dependent on the excitation bandwidth to the Rydberg\nstate. The excitation to the Rydberg state is driven by a pulsed two-photon\ntransition on ns time scales. Combined with a third cw de-excitation laser, a\nstrongly directional and collective emission is generated according to a\ncombination of the phase matching effect and averaging over Doppler classes. In\ncontrast to a previous report [1] using off-resonant FWM, at a resonant FWM\nscheme we observe additional revivals of the signal shortly after the incident\npulse has ended. We infer that this is a revival of motion-induced constructive\ninterference between the coherent emissions of the thermal atoms. The resonant\nFWM scheme reveals a richer temporal structure of the signals, compared to\nsimilar, but off-resonant excitation schemes. A simple explanation lies in the\nselectivity of Doppler classes. Our numerical simulations based on a four-level\nmodel including a whole Doppler ensemble can qualitatively describe the data.", "category": "physics_atom-ph" }, { "text": "Lifetime measurements of the 5d states of rubidium: We present lifetime measurements of the $5D_{3/2}$ and $5D_{5/2}$ states of\nrubidium using the time correlated single photon counting method. We perform\nthe experiment in a magneto-optical trap of $^{87}$Rb atoms using a two-step\nexcitation with the trap laser at 780 nm as the first step. We record the 761.9\nnm fluorescence from the decay of the $5D_{3/2}$ state to the $5P_{1/2}$ state,\nand measure the lifetime of the $5D_{3/2}$ state $\\tau=246.3(1.6)$ ns. We\nrecord the 420.2 nm fluorescence from the cascade decay of the $5D_{5/2}$ state\nto the $5S_{1/2}$ state through the $6P_{3/2}$ state, and extract the lifetime\nof the $5D_{5/2}$ state ${\\tau}=238.5(2.3)$ ns.", "category": "physics_atom-ph" }, { "text": "Optical pumping of a lithium atomic beam for atom interferometry: We apply optical pumping to prepare the lithium beam of our atom\ninterferometer in a single hyperfine-Zeeman sublevel: we use two components of\nthe D1-line for pumping the 7Li atoms in a dark state F,mF=+2 (or -2) sublevel.\nThe optical pumping efficiency has been characterized by two techniques:\nstate-selective laser atom deflection or magnetic dephasing of the atom\ninterferometer signals. The first technique has not achieved a high\nsensitivity, because of a limited signal to noise ratio, but magnetic dephasing\nsignals have shown that about 95% of the population has been transferred in the\naimed sublevel, with similar results for three mean velocities of the atomic\nbeam covering the range 744-1520m/s.", "category": "physics_atom-ph" }, { "text": "Spectroscopic Study and Lifetime Measurement of the $6d7p$ $\n ^{3}F_{2}^{o}$ state of radium: We report a method for the precision measurement of the oscillator strengths\nand the branching ratios of the decay channels of the $6d7p$ $^3F_2$ state in\n$^{226}$Ra. This method exploits a set of metastable states present in Ra,\nallowing a measurement of the oscillator strengths that does not require\nknowledge of the number of atoms in the atomic beam. We measure the oscillator\nstrengths and the branching ratios for decays to the $7s6d$ $^3D_1$, $7s6d$\n$^3D_2$, and $7s6d$ $^1D_2$ states and constrain the branching ratio to the\n$7s6d$ $^3D_3$ state to be less than 0.4$\\%$ (68$\\%$ confidence limit). The\nlifetime of the $^3F_2$ state is determined to be $15 \\pm 4$ ns.", "category": "physics_atom-ph" }, { "text": "Crossed-Beam slowing to enhance narrow-line Ytterbium Magneto-Optic\n Traps: We demonstrate a method to enhance the atom loading rate of a ytterbium (Yb)\nmagneto-optic trap (MOT) operating on the 556 nm ${^1S}_0 \\rightarrow {^3P}_1$\nintercombination transition (narrow linewidth $\\Gamma_g = 2\\pi \\times 182$\nkHz). Following traditional Zeeman slowing of an atomic beam near the 399 nm\n${^1S}_0 \\rightarrow {^1P}_1$ transition (broad linewidth $\\Gamma_p = 2\\pi\n\\times 29 $ MHz), two laser beams in a crossed-beam geometry, frequency tuned\nnear the same transition, provide additional slowing immediately prior to the\nMOT. Using this technique, we observe an improvement by a factor of 6 in the\natom loading rate of a narrow-line Yb MOT. The relative simplicity and\ngenerality of this approach make it readily adoptable to other experiments\ninvolving narrow-line MOTs. We also present a numerical simulation of this\ntwo-stage slowing process which shows good agreement with the observed\ndependence on experimental parameters, and use it to assess potential\nimprovements to the method.", "category": "physics_atom-ph" }, { "text": "Energy levels, radiative rates and electron impact excitation rates for\n transitions in He-like Kr XXXV: We report calculations of energy levels, radiative rates and electron impact\nexcitation cross sections and rates for transitions in He-like Kr XXXV. The\nGRASP (general-purpose relativistic atomic structure package) is adopted for\ncalculating energy levels and radiative rates. For determining the collision\nstrengths and subsequently the excitation rates, the Dirac Atomic R-matrix Code\n(DARC) is used. Oscillator strengths, radiative rates and line strengths are\nreported for all E1, E2, M1, and M2 transitions among the lowest 49 levels.\nAdditionally, theoretical lifetimes are listed for all 49 levels. Collision\nstrengths are averaged over a Maxwellian velocity distribution and the\neffective collision strengths obtained listed over a wide temperature range up\nto 10**8.1 K. Comparisons are made with similar data obtained with the Flexible\nAtomic Code (FAC) to assess the accuracy of the results and to highlight the\nimportance of resonances, included in calculations with DARC, in the\ndetermination of effective collision strengths. Differences between the\ncollision strengths from DARC and FAC, particularly for forbidden transitions,\nare also discussed. Finally, discrepancies between the present results of\neffective collision strengths from the {\\sc darc} code and earlier\nsemi-relativistic $R$-matrix data are noted over a wide range of electron\ntemperatures for many transitions of Kr XXXV.", "category": "physics_atom-ph" }, { "text": "Low-energy peak structure in strong-field ionization by mid-infrared\n laser-pulses: two-dimensional focusing by the atomic potential: We analyze the formation of the low-energy structure (LES) in above-threshold\nionization spectra first observed by Quan et al.\\ \\cite{quan09} and Blaga et\nal.\\ \\cite{blaga09} using both quasi-classical and quantum approaches. We show\nthis structure to be largely classical in origin resulting from a\ntwo-dimensional focusing in the energy-angular momentum plane of the\nstrong-field dynamics in the presence of the atomic potential. The peak at low\nenergy is strongly correlated with high angular momenta of the photoelectrons.\nQuantum simulations confirm this scenario. Resulting parameter dependences\nagree with experimental findings \\cite{quan09,blaga09} and, in part, with other\nsimulations \\cite{liu10,yan10,kast11}.", "category": "physics_atom-ph" }, { "text": "Energetic photoionization of neutral and ionic metal clusters: We show, with an example of Na_92, that for jellium metal clusters the\ninterference of fast electron-waves emitted from equivalent sites on the\ncluster edge produces monochromatic oscillations in all photoionization\nobservables as a function of the photoelectron momentum; the effect is\nequivalent to the usual dispersion phenomenon. In dealing with formalisms, a\nserious consequence of the inadequacy of self-interaction corrected local\ndensity-functional theory in correctly accounting for the exchange interaction\nis identified. We also briefly discuss the influence of the ionicity of the\nresidual core on photospectra by considering the neutral member with N=58 and\nand the ionic member with N=52 of the Na_58 iso-jellium series, where N is the\nnumber of valence electrons. A few final remarks on possible implications of\nthese results on other quantum systems of delocalized electrons are made.", "category": "physics_atom-ph" }, { "text": "Formation of deeply bound ultracold LiRb molecules via photoassociation\n near the Li 2S$_{1/2}$ + Rb 5P$_{3/2}$ asymptote: We present spectra of ultracold $^7$Li$^{85}$Rb molecules in their electronic\nground state formed by spontaneous decay of weakly bound photoassociated\nmolecules. Beginning with atoms in a dual species magneto-optical trap (MOT),\nweakly bound molecules are formed in the 4(1) electronic state, which\ncorresponds to the B$^1\\Pi$ state at short range. These molecules spontaneously\ndecay to the electronic ground state and we use resonantly enhanced multiphoton\nionization (REMPI) to determine the vibrational population distribution in the\nelectronic ground states after spontaneous emission. Many of the observed lines\nfrom the spectra are consistent with transitions from the X$^1\\Sigma^+$ ground\nelectronic state to either the B$^1\\Pi$ or D$^1\\Pi$ electronic states that have\nbeen previously observed, with levels possibly as low as X$^1\\Sigma^+$ $(v'' =\n2)$ being populated. We do not observe decay to weakly bound vibrational levels\nof the X$^1\\Sigma^+$ or a$^3\\Sigma^+$ electronic states in the spectra. We also\ndeduce a lower bound of 3900 cm$^{-1}$ for the dissociation energy of the\nLiRb$^+$ molecular ion.", "category": "physics_atom-ph" }, { "text": "Testing the time dependence of the fundamental constants in the spectra\n of multicharged ions: A new method for measuring a possible time dependence of the fine-structure\nconstant ($\\alpha$) is proposed. The method is based on the level-crossing in\ntwo-electron highly-charged ions facilitating resonance laser measurements of\nthe distance between the levels at the point of crossing. This provides an\nenhancement factor of about $10^{3}$ in Helium-like Europium and thus reduces\nthe requirements for the relative accuracy of resonance laser measurements at\nabout $10^{-12}$.", "category": "physics_atom-ph" }, { "text": "Static trapping of polar molecules in a traveling wave decelerator: We present experiments on decelerating and trapping ammonia molecules using a\ncombination of a Stark decelerator and a traveling wave decelerator. In the\ntraveling wave decelerator a moving potential is created by a series of\nring-shaped electrodes to which oscillating high voltages are applied. By\nlowering the frequency of the applied voltages, the molecules confined in the\nmoving trap are decelerated and brought to a standstill. As the molecules are\nconfined in a true 3D well, this new kind of deceleration has practically no\nlosses, resulting in a great improvement on the usual Stark deceleration\ntechniques. The necessary voltages are generated by amplifying the output of an\narbitrary wave generator using fast HV-amplifiers, giving us great control over\nthe trapped molecules. We illustrate this by experiments in which we\nadiabatically cool trapped NH3 and ND3 molecules and resonantly excite their\nmotion.", "category": "physics_atom-ph" }, { "text": "The library of subroutines for calculating standard quantities in atomic\n structure theory: This library (collection of subroutines) is presented for calculating\nstandard quantities in the decomposition of many-electron matrix elements in\natomic structure theory. These quantities include the coefficients of\nfractional parentage, the reduced coefficients of fractional parentage as well\nas reduced and completely reduced matrix elements for several operators. So the\nlibrary is assigned for any computational scheme. The software is an\nimplementation of a methodology based on the second quantization in coupled\ntensorial form, the angular momentum theory in 3 spaces (orbital, spin and\nquasispin), and the graphical technique of angular momentum. This\nimplementation extends applications in atomic theory capabilities to partially\nfilled f-- shells and has lead to faster execution of angular integration\ncodes.", "category": "physics_atom-ph" }, { "text": "Comment on \"Large enhancement in high-energy photoionization of Fe XVII\n and missing continuum plasma opacity\": Recent R-matrix calculations claim to produce a significant enhancement in\nthe opacity of Fe XVII due to atomic core excitations [S. N. Nahar & A.K.\nPradhan, Phys. Rev. Letters 116, 235003 (2016), arXiv:1606.02731] and assert\nthat this enhancement is consistent with recent measurements of\nhigher-than-predicted iron opacities [J. E. Bailey et al., Nature 517, 56\n(2015)]. This comment shows that the standard opacity models which have already\nbeen directly compared with experimental data produce photon absorption\ncross-sections for Fe XVII that are effectively equivalent to (and in fact\nlarger than) the new R-matrix opacities. Thus, the new R-matrix results cannot\nbe expected to significantly impact the existing discrepancies between theory\nand experiment because they produce neither a \"large enhancement\" nor account\nfor \"missing continuum plasma opacity\" relative to standard models.", "category": "physics_atom-ph" }, { "text": "The Exotic Molecular Ion H_4^{3+} in a Strong Magnetic Field: Using the variational method, a detailed study of the lowest m = 0,-1\nelectronic states of the exotic molecular ion H_4^{3+} in a strong magnetic\nfield, in the linear symmetric configuration parallel to the direction of the\nmagnetic field is carried out. A extended study of the 1\\sigma_g ground state\n(J.C. L\\'opez and A. Turbiner, Phys. Rev. A 62, 022510, 2000) was performed\nobtaining that the potential energy curve displays a sufficiently deep minimum\nfor finite internuclear distances, indicating the possible existence of the\nmolecular ion H_4^{3+}, for magnetic fields of strength B \\gtrsim 3x10^{13}G.\nIt is demonstrated that the excited state 1\\pi_u can exist for a magnetic field\nB = 4.414 x 10^{13}G corresponding to the limit of applicability of the\nnon-relativistic theory.", "category": "physics_atom-ph" }, { "text": "Static electric dipole moment of the francium atom induced by axionlike\n particle exchange: The francium atom is considered as a prospective candidate system to search\nfor the T,P-violating electron electric dipole moment [T. Aoki et al Quantum\nSci. Technol. 6, 044008 (2021)]. We demonstrate that the same experiment can be\nused for axionlike particles (ALP) search. For this, we calculate electronic\nstructure constants of ALP-mediated interaction for a wide range of ALP masses.\nUsing the recently updated constraints on the ALP-electron and ALP-nucleon\ncoupling constants, we show that the contribution of considered interactions\ncorresponding to these constraints can give significant contribution to atomic\nelectric dipole moment. Therefore, obtainment of stronger restrictions for ALP\ncharacteristics in the francium atom electric dipole moment experiment is\npossible.", "category": "physics_atom-ph" }, { "text": "Non-existence of Taylor expansion in time due to cusps: In the usual treatment of electronic structure, all matter has cusps in the\nelectronic density at nuclei. Cusps can produce non-analytic behavior in time,\neven in response to perturbations that are time-analytic. We analyze these\nnon-analyticities in a simple case from many perspectives. We describe a\nmethod, the s-expansion, that can be used in several such cases, and illustrate\nit with a variety of examples. These include both the sudden appearance of\nelectric fields and disappearance of nuclei, in both one and three dimensions.\nWhen successful, the s-expansion yields the dominant short-time behavior, no\nmatter how strong the external electric field, but agrees with linear response\ntheory in the weak limit. We discuss the relevance of these results to\ntime-dependent density functional theory.", "category": "physics_atom-ph" }, { "text": "Pulse delay and group velocity dispersion measurement in V-type\n electromagnetically induced transparency of hot $^{85}Rb$ atom: Pulse delay with the group velocity dispersion (GVD) characteristics was\nstudied in the V-type electromagnetically induced transparency in the hyperfine\nlevels of $^{85}Rb$ atoms with a closed system configuration. The phase\ncoherency between the pump and the probe laser beams was maintained. We studied\nthe pulse delay and the group velocity dispersion characteristics with the\nvariation of the pump Rabi frequency taking temperature as a parameter. We\nobserved a maximum of $268$ $ns$ pulse delay for $21.24 MHz$ pump Rabi\nfrequency at $55^0C$ temperature of the Rb vapour cell. For a better\nunderstanding of the experimental results, we have derived an analytical\nsolution for the delay characteristics considering the thermal averaging. The\nanalytical solution was derived for a three level V-type system. The\ntheoretical plots of the delay and the group velocity dispersion show the same\ncharacteristics as we observed in the experiment. This analytical approach can\nbe further generalized for the higher level schemes to calculate different\nquantities such as susceptibility, group velocity delay or group velocity\ndispersion characteristics.", "category": "physics_atom-ph" }, { "text": "Prospects for single photon sideband cooling in fermionic Lithium: We present an analytic and numerical study for realizing single photon\nsideband cooling in an ultracold sample of fermionic Lithium trapped in a\nperiodic optical potential. We develop an analytical model and obtain a master\nequation for the bound level populations. The cooling sequence is simulated\nboth with a laser at a fixed frequency and with a frequency sweep. Finally, a\nMonte Carlo simulation is performed taking into account the full hyperfine\nspectrum of $^6\\!$Li. We find that a gas of $^6\\!$Li atoms loaded from a\nMagneto-Optical trap into a deep optical lattice can be cooled down to a $99\\%$\noccupancy of the lattice ground state after a 5mm single photon sideband\ncooling using the D1 line of Li.", "category": "physics_atom-ph" }, { "text": "An R-matrix with pseudo-state (RMPS) approach to the single photon\n double ionization and excitation of the He-like Li$^{+}$ ion: The success of the R-matrix with pseudo-state (RMPS) method to model single\nphotoionization processes, benchmarked against dedicated synchrotron light\nsource measurements, is exploited and extended to investigate, single photon\ndouble ionization cross-sections for the He-like, Li$^+$ ion. We investigate\nthese processes from both the ground state and the excited $\\rm 1s2s^{1,3}S$\nmetastable levels of this He-like system. Comparisons of the results from the\nR-matrix plus pseudo-state (RMPS) method are made with other state-of-the-art\ntheoretical approaches such as time-dependent close-coupling (TDCC), B-splines\nand the convergent close-coupling (CCC). Excellent agreement with various other\ntheoretical approaches are achieved but differences occur which are\nhigh-lighted and discussed. For the ground state the peak of the cross section\nis $\\sim$ 2 kilo-barns (Kb), that for the $\\rm 1s2s^{1}S$ state is $\\sim$ 6 Kb\nand $\\sim$ 1 Kb for the corresponding $\\rm 1s2s^{3}S$ state. All the cross\nsections for single photon double ionization are extremely small, being in the\nregion of 2Kb -- 10 Kb, or less, rendering their experimental determination\nextremely challenging.", "category": "physics_atom-ph" }, { "text": "Quantum Beat Photoelectron Imaging Spectroscopy of Xe in the VUV: Time-resolved pump-probe measurements of Xe, pumped at 133~nm and probed at\n266~nm, are presented. The pump pulse prepared a long-lived hyperfine\nwavepacket, in the Xe $5p^5(^2P^{\\circ}_{1/2})6s~^2[1/2]^{\\circ}_1$ manifold\n($E=$77185 cm$^{-1}=$9.57 eV). The wavepacket was monitored via single-photon\nionization, and photoelectron images measured. The images provide angle- and\ntime-resolved data which, when obtained over a large time-window (900~ps),\nconstitute a precision quantum beat spectroscopy measurement of the hyperfine\nstate splittings. Additionally, analysis of the full photoelectron image stack\nprovides a quantum beat imaging modality, in which the Fourier components of\nthe photoelectron images correlated with specific beat components can be\nobtained. This may also permit the extraction of isotope-resolved photoelectron\nimages in the frequency domain, in cases where nuclear spins (hence beat\ncomponents) can be uniquely assigned to specific isotopes (as herein), and also\nprovides phase information. The information content of both raw, and inverted,\nimage stacks is investigated, suggesting the utility of the Fourier analysis\nmethodology in cases where images cannot be inverted.", "category": "physics_atom-ph" }, { "text": "Formation of deeply bound ultracold Sr_2 molecules by photoassociation\n near the ^1S + ^3P_1 intercombination line: We predict feasibility of the photoassociative formation of Sr_2 molecules in\narbitrary vibrational levels of the electronic ground state based on\nstate-of-the-art ab initio calculations. Key is the strong spin-orbit\ninteraction between the c^3\\Pi_u, A^1\\Sigma_u^+ and B^1\\Sigma_u^+ states. It\ncreates not only an effective dipole moment allowing free-to-bound transitions\nnear the ^1S + ^3P_1 intercombination line but also facilitates bound-to-bound\ntransitions via resonantly coupled excited state rovibrational levels to deeply\nbound rovibrational levels of the ground X^1\\Sigma_g^+ potential, with v\" as\nlow as v\"=6. The spin-orbit interaction is responsible for both optical\npathways. Therefore, those excited state levels that have the largest\nbound-to-bound transition moments to deeply bound ground state levels also\nexhibit a sufficient photoassociation probability, comparable to that of the\nlowest weakly bound excited state level previously observed by Zelevinsky et\nal. [Phys. Rev. Lett. 96, 203201 (2006)]. Our study paves the way for an\nefficient photoassociative production of Sr_2 molecules in ground state levels\nsuitable for experiments testing the electron-to-proton mass ratio.", "category": "physics_atom-ph" }, { "text": "Modulation Transfer Spectroscopy of the D1 Transition of Potassium:\n Theory and Experiment: We report on a study of modulation transfer spectroscopy of the\n$4\\textrm{S}_{1/2}\\rightarrow 4\\textrm{P}_{1/2}$ ($D_{1}$) transition of\nnaturally abundant potassium in a room-temperature vapour cell. This transition\nis critical for laser cooling and optical pumping of potassium and our study is\ntherefore motivated by the need for robust laser frequency stabilisation.\nDespite the absence of a closed transition, the small ground-state hyperfine\nsplitting in potassium results in strong crossover features in the $D_{1}$\nmodulation transfer spectrum. To emphasise this we compare the $D_{1}$ and\n$D_{2}$ spectra of potassium with those of rubidium. Further, we compare our\nexperimental results with a detailed theoretical simulation, examining\ndifferent pump-probe polarization configurations to identify the optimal\nsignals for laser frequency stabilisation. We find good agreement between the\nexperiment and the theory, especially for the $\\textrm{lin} \\parallel\n\\textrm{lin}$ polarization configuration.", "category": "physics_atom-ph" }, { "text": "A Single-Ion Trap with Minimized Ion-Environment Interactions: We present a new single-ion endcap trap for high precision spectroscopy that\nhas been designed to minimize ion-environment interactions. We describe the\ndesign in detail and then characterize the working trap using a single trapped\n171 Yb ion. Excess micromotion has been eliminated to the resolution of the\ndetection method and the trap exhibits an anomalous phonon heating rate of d\n/dt = 24 +30/-24 per second. The thermal properties of the trap structure have\nalso been measured with an effective temperature rise at the ion's position of\n0.14 +/- 0.14 K. The small perturbations to the ion caused by this trap make it\nsuitable to be used for an optical frequency standard with fractional\nuncertainties below the 10^-18 level.", "category": "physics_atom-ph" }, { "text": "Response to recent works on the discriminatory optical force for chiral\n molecules: We respond to recent works by Bradshaw and Andrews on the discriminatory\noptical force for chiral molecules, in particular to the erroneous claims made\nby them concerning our earlier work.", "category": "physics_atom-ph" }, { "text": "LCLS in - photon out: fluorescence measurement of neon using soft x-rays: We measured the fluorescence photon yield of neon upon soft x-ray ionization\n(~1200 eV) from the x-ray free electron laser at Linac Coherent Light Source,\nand demonstrated the usage of a grazing incidence spectrometer with a variable\nlinespacing grating to perform x-ray fluorescence spectroscopy on a gas phase\nsystem. Our measurements also allowed us to estimate the focal size of the beam\nfrom the theoretical description developed, in terms of the rate equation\napproximation accounting for photoionization shake-off of neutral neon and\ndouble Auger decay of single core holes.", "category": "physics_atom-ph" }, { "text": "An Adaptable Dual Species Effusive Source and Zeeman Slower Design\n Demonstrated with Rb and Li: We present a dual-species effusive source and Zeeman slower designed to\nproduce slow atomic beams of two elements with a large mass difference and with\nvery different oven temperature requirements. We demonstrate this design for\nthe case of $^6$Li and $^{85}$Rb and achieve MOT loading rates equivalent to\nthat reported in prior work on dual species (Rb+Li) Zeeman slowers operating at\nthe same oven temperatures. Key design choices, including thermally separating\nthe effusive sources and using a segmented coil design to enable computer\ncontrol of the magnetic field profile, ensure that the apparatus can be easily\nmodified to slow other atomic species. By performing the final slowing using\nthe quadruple magnetic field of the MOT, we are able to shorten our Zeeman\nslower length making for a more compact system without compromising\nperformance. We outline the construction and analyze the emission properties of\nour effusive sources. We also verify the performance of the source and slower,\nand we observe sequential loading rates of $8 \\times 10^8$ atoms/s for a Rb\noven temperature of $120\\,^{\\circ}$C and $1.5 \\times 10^8$ atoms/s for a Li\nreservoir at $450\\,^{\\circ}$C, corresponding to reservoir lifetimes for\ncontinuous operation of 10 and 4 years respectively.", "category": "physics_atom-ph" }, { "text": "Integral cross sections for electron scattering by ground state Ba atoms: We have used the convergent close-coupling method and a unitarized\nfirst-order many-body theory to calculate integral cross sections for elastic\nscattering and momentum transfer, for excitation of the 5d^2 ^1S, 6s6p^1P_1,\n6s7p^1P_1, 6s8p^1P_1, 6s5d^1D_2, 5d^2^1D_2, 6s6d^1D_2, 6p5d^1F_3, 6s4f^1F_3,\n6p5d^1D_2, 6s6p^3P_{0,1,2}, 6s5d^3D_{1,2,3}, and 6p5d^3D_2 states, for\nionization and for total scattering by electron impact on the ground state of\nbarium at incident electron energies from 1 to 1000 eV. These results and all\navailable experimental data have been combined to produce a recommended set of\nintegral cross sections.", "category": "physics_atom-ph" }, { "text": "X-ray emission measurements following charge exchange between C$^{6+}$\n and H$_2$: Lyman x-ray spectra following charge exchange between C$^{6+}$ and H$_2$ are\npresented for collision velocities between 400 and 2300 km/s (1--30 keV/amu).\nSpectra were measured by a microcalorimeter x-ray detector capable of fully\nresolving the C VI Lyman series emission lines though Lyman-$\\delta$. The\nratios of the measured emission lines are sensitive to the angular momentum\n$l$-states populated during charge exchange and are used to gauge the\neffectiveness of different $l$-distribution models in predicting Lyman emission\ndue to charge exchange. At low velocities, we observe that both single electron\ncapture and double capture autoionization contribute to Lyman emission and that\na statistical $l$-distribution best describes the measured line ratios. At\nhigher velocities single electron capture dominates with the $l$-distribution\npeaked at the maximum $l$.", "category": "physics_atom-ph" }, { "text": "Homonuclear ultracold elastic $s$-wave collisions of alkali atoms via\n multichannel quantum defect theory: Multichannel quantum defect theory (MQDT) provides a powerful toolkit for\ndescribing and understanding collisions of cold alkali atoms. Various MQDT\napproximations differ primarily in how they characterize the so-called\nshort-ranged $K$-matrix, ${\\mathbf K}_{\\text{sr}}$, which encapsulates the\nshort-ranged, high-energy physics into a handful of low-energy parameters that\nexhibit simple and smooth dependence on energy and field. Here, we compare\nthree different methods for computing ${\\mathbf K}_{\\text{sr}}$ for homonuclear\ncollisions of alkali atoms, from lithium to cesium. The MQDT calculations are\nbenchmarked against numerically converged coupled-channels calculations that\nuse a log-derivative propagator out to the asymptotic region. We study how well\nthese approximations reproduce positions of $s$-wave magnetic Feshbach\nresonances, comparing to experiment where possible, and identify the\nlimitations of various approximations.", "category": "physics_atom-ph" }, { "text": "The Levy-Perdew-Sahni equation for the density: accurate effective\n potential and self-consistent solution for two-electron atomic systems: Levy-Perdew-Sahni (LPS) provided a proof of the connection between the\ndensity and ionization potential of a many-electron system using the equation\nfor the density directly. This equation employs an effective potential which is\nderived by LPS from the many-electron wavefunction of the system. In this\npaper, we calculate this potential explicitly by employing an accurate\nwavefunction for two-electron systems. With this wavefunction connection the\nLPS equation is then solved self- consistently employing this potential and\nshown to lead to accurate densities and chemical potentials for these systems.", "category": "physics_atom-ph" }, { "text": "Motional resonances of three-dimensional dual-species Coulomb crystals: We investigate the motional resonances of dual-species Coulomb crystals\ncomprised of $^9$Be$^+$ and $^{24}$Mg$^+$ ions held in a 4-rod linear Paul\ntrap. Our experimental data and simulations show that the secular motion of\nsuch mixed crystals has rich dynamics. Their secular spectra can differ\nsignificantly from those of pure ion crystals. We propose a simple model based\non mechanical coupling with Coulomb interactions between the two different ion\nspecies that explains many features of the secular spectrum. Our findings\ncontribute to a more reliable identification of the ion species in mixed\ncrystals.", "category": "physics_atom-ph" }, { "text": "Fifteen classes of solutions of the quantum two-state problem in terms\n of the confluent Heun function: We derive 15 classes of time-dependent two-state models solvable in terms of\nthe confluent Heun functions. These classes extend over all the known families\nof three- and two-parametric models solvable in terms of the hypergeometric and\nthe confluent hypergeometric functions to more general four-parametric classes\ninvolving three-parametric detuning modulation functions. In the case of\nconstant detuning the field configurations describe excitations of two-state\nquantum systems by symmetric or asymmetric pulses of controllable width and\nedge-steepness. The classes that provide constant detuning pulses of finite\narea are identified and the factors controlling the corresponding pulse shapes\nare discussed. The positions and the heights of the peaks are mostly defined by\ntwo of the three parameters of the detuning modulation function, while the\npulse width is mainly controlled by the third one, the constant term. The\nclasses suggest numerous symmetric and asymmetric chirped pulses and a variety\nof models with two crossings of the frequency resonance. We discuss the\nexcitation of a two-level atom by a pulse of Lorentzian shape with a detuning\nproviding one or two crossings of the resonance. We derive closed form\nsolutions for particular curves in the 3D space of the involved parameters\nwhich compose the complete return spectrum of the considered two-state quantum\nsystem.", "category": "physics_atom-ph" }, { "text": "QED Calculation of E1M1 and E1E2 Transition Probabilities in\n One-Electron Ions with Arbitrary Nuclear Charge: The quantum electrodynamical theory of the two-photon transitions in\nhydrogenlike ions is presented. The emission probability for 2s1/2 -> 2E1+1s1/2\ntransitions is calculated and compared to the results of the previous\ncalculations. The emission probabilities 2p12 -> E1E2+1s1/2 and 2p1/2 ->\nE1M1+1s1/2 are also calculated for the nuclear charge Z values 1-100. This is\nthe first calculation of the two latter probabilities. The results are given in\ntwo different gauges.", "category": "physics_atom-ph" }, { "text": "Non-Equilibrium Modeling of the Fe XVII 3C/3D ratio for an Intense X-ray\n Free Electron Laser: We present a review of two methods used to model recent LCLS experimental\nresults for the 3C/3D line intensity ratio of Fe XVII (Bernitt et al. 2012),\nthe time-dependent collisional-radiative method and the density-matrix\napproach. These are described and applied to a two-level atomic system excited\nby an X-ray free electron laser. A range of pulse parameters is explored and\nthe effects on the predicted Fe XVII 3C and 3D line intensity ratio are\ncalculated. In order to investigate the behavior of the predicted line\nintensity ratio, a particular pair of A-values for the 3C and 3D transitions\nwas chosen (2.22 $\\times$ 10$^{13}$ s$^{-1}$ and 6.02 $\\times$ 10$^{12}$\ns$^{-1}$ for the 3C and 3D, respectively), but our conclusions are independent\nof the precise values. We also reaffirm the conclusions from Oreshkina et\nal.(2014, 2015): the non-linear effects in the density matrix are important and\nthe reduction in the Fe XVII 3C/3D line intensity ratio is sensitive to the\nlaser pulse parameters, namely pulse duration, pulse intensity, and laser\nbandwidth. It is also shown that for both models the lowering of the 3C/3D line\nintensity ratio below the expected time-independent oscillator strength ratio\nhas a significant contribution due to the emission from the plasma after the\nlaser pulse has left the plasma volume. Laser intensities above $\\sim 1\\times\n10^{12}$ W/cm$^{2}$ are required for a reduction in the 3C/3D line intensity\nratio below the expected time independent oscillator strength ratio.", "category": "physics_atom-ph" }, { "text": "Imprinting chirality on atoms using synthetic chiral light fields: Atoms are usually thought of as achiral objects. However, one can construct\nsuperpositions of atomic states that are chiral [1]. Here we show how to excite\nsuch superpositions with tailored light fields both in the weak-field and\nstrong-field regimes, using realistic laser parameters. First, we use\ntime-dependent Schrodinger equation (TDSE) simulations to demonstrate the\ncreation of a time-dependent bound chiral wavepacket in sodium atoms. Second,\nwe show how the time-dependent handedness of this wavepacket can be probed by\nphotoelectron circular dichroism, in spite of the central symmetry of the core\npotential. Third, we use TDSE simulations to show how chirality can be directly\nimprinted on a photoelectron wavepacket created by strong-field ionization and\nintroduce an unambigous chiral measure that allows us to characterize its\nhandedness.", "category": "physics_atom-ph" }, { "text": "Experiment and Theory in Computations of the He Atom Ground State: Extensive variational computations are reported for the ground state energy\nof the non-relativistic two-electron atom. Several different sets of basis\nfunctions were systematically explored, starting with the original scheme of\nHylleraas. The most rapid convergence is found with a combination of negative\npowers and a logarithm of the coordinate s = r_{1}+ r_{2}. At N=3091 terms we\npass the previous best calculation (Korobov's 25 decimal accuracy with N=5200\nterms) and we stop at N=10257 with E = -2.90372 43770 34119 59831 11592 45194\n40444 ...\n Previous mathematical analysis sought to link the convergence rate of such\ncalculations to specific analytic properties of the functions involved. The\napplication of that theory to this new experimental data leaves a rather\nfrustrating situation, where we seem able to do little more than invoke vague\nconcepts, such as ``flexibility.'' We conclude that theoretical understanding\nhere lags well behind the power of available computing machinery.", "category": "physics_atom-ph" }, { "text": "A Remotely Interrogated All-Optical $^{87}$Rb Magnetometer: Atomic magnetometry was performed at Earth's magnetic field over a free-space\ndistance of ten meters. Two laser beams aimed at a distant alkali-vapor cell\nexcited and detected the $^{87}$Rb magnetic resonance, allowing the magnetic\nfield within the cell to be interrogated remotely. Operated as a driven\noscillator, the magnetometer measured the geomagnetic field with\n\\lessgtrsim{\\lesssim}3.5\\,pT precision in a $\\sim$2\\,s data acquisition; this\nprecision was likely limited by ambient field fluctuations. The sensor was also\noperated in self-oscillating mode with a 5.3\\,pT/$\\sqrt{\\textrm{Hz}}$ noise\nfloor. Further optimization will yield a high-bandwidth, fully remote\nmagnetometer with sub-pT sensitivity.", "category": "physics_atom-ph" }, { "text": "A Data-Driven Machine Learning Approach for Electron-Molecule Ionization\n Cross Sections: Despite their importance in a wide variety of applications, the estimation of\nionization cross sections for large molecules continues to present challenges\nfor both experiment and theory. Machine learning algorithms have been shown to\nbe an effective mechanism for estimating cross section data for atomic targets\nand a select number of molecular targets. We present an efficient machine\nlearning model for predicting ionization cross sections for a broad array of\nmolecular targets. Our model is a 3-layer neural network that is trained using\npublished experimental datasets. There is minimal input to the network, making\nit widely applicable. We show that with training on as few as 10 molecular\ndatasets, the network is able to predict the experimental cross sections of\nadditional molecules with an accuracy similar to experimental uncertainties in\nexisting data. As the number of training molecular datasets increased, the\nnetwork's predictions became more accurate and, in the worst case, were within\n30% of accepted experimental values. In many cases, predictions were within 10%\nof accepted values. Using a network trained on datasets for 25 different\nmolecules, we present predictions for an additional 27 molecules, including\nalkanes, alkenes, molecules with ring structures, and DNA nucleotide bases.", "category": "physics_atom-ph" }, { "text": "Resonance structures in the multichannel quantum defect theory for the\n photofragmentation processes involving one closed and many open channels: The transformation introduced by Giusti-Suzor and Fano and extended by\nLecomte and Ueda for the study of resonance structures in the multichannel\nquantum defect theory (MQDT) is used to reformulate MQDT into the forms having\none-to-one correspondence with those in Fano's configuration mixing (CM) theory\nof resonance for the photofragmentation processes involving one closed and many\nopen channels. The reformulation thus allows MQDT to have the full power of the\nCM theory, still keeping its own strengths such as the fundamental description\nof resonance phenomena without an assumption of the presence of a discrete\nstate as in CM.", "category": "physics_atom-ph" }, { "text": "Modeling non local thermodynamic equilibrium plasma using the Flexible\n Atomic Code data: We present a new code, RCF(\"Radiative-Collisional code based on FAC\"), which\nis used to simulate steady-state plasmas under non local thermodynamic\nequilibrium condition, especially photoinization dominated plasmas. RCF takes\nalmost all of the radiative and collisional atomic processes into rate equation\nto interpret the plasmas systematically. The Flexible Atomic Code (FAC)\nsupplies all the atomic data\n RCF needed, which insures calculating completeness and consistency of atomic\ndata. With four input parameters relating to the radiation source and target\nplasma, RCF calculates the population of levels and charge states, as well as\npotentially emission spectrum. In preliminary application, RCF successfully\nreproduces the results of a photoionization experiment with reliable atomic\ndata. The effects of the most important atomic processes on the charge state\ndistribution are also discussed.", "category": "physics_atom-ph" }, { "text": "Direct measurement of the van der Waals interaction between two Rydberg\n atoms: We report on the direct measurement of the van der Waals interaction between\ntwo isolated, single Rydberg atoms separated by a controlled distance of a few\nmicrometers. By working in a regime where the single-atom Rabi frequency of the\nlaser used for excitation to the Rydberg state is comparable to the interaction\nenergy, we observe a \\emph{partial} Rydberg blockade, whereby the\ntime-dependent populations of the various two-atom states exhibit coherent\noscillations with several frequencies. A quantitative comparison of the data\nwith a simple model based on the optical Bloch equations allows us to extract\nthe van der Waals energy, and to observe its characteristic $C_6/R^6$\ndependence. The magnitude of the measured $C_6$ coefficient agrees well with an\n\\emph{ab-initio} theoretical calculation, and we observe its dramatic increase\nwith the principal quantum number $n$ of the Rydberg state. Our results not\nonly allow to test an important physical law, but also demonstrate a degree of\nexperimental control which opens new perspectives in quantum information\nprocessing and quantum simulation using long-range interactions between the\natoms.", "category": "physics_atom-ph" }, { "text": "Decoding electron tunnelling delay time by embracing wave-particle\n duality: Tunnelling lies at the heart of quantum mechanics and is a fundamental\nprocess in attosecond science, molecular biology, and quantum devices. Whether\ntunnelling takes time and how a microscopic particle transits through a barrier\nhave been debated since the early days of quantum mechanics. The time required\nfor an electron to tunnel through an atomic potential barrier has been measured\nwith attosecond angular streaking (attoclock), and a recent work on the\nhydrogen atom claimed that electron tunnelling is instantaneous. However, the\ntime required for Rb atoms to tunnel through an optical potential barrier has\nbeen measured to be on the order of milliseconds with a recent Larmor clock\nmeasurement. The essence of electron and atom tunnelling is identical, but the\nreason for the contradictory conclusions remains unknown. Here, we demonstrate\nthat the sub-barrier potential interaction is the root of the nonzero\ntunnelling delay time. We reveal that the wave-particle duality of a tunnelling\nelectron must be fully taken into account when decoding the tunnelling delay\ntime from the attoclock measurements. Based on energy-resolved attoclock\nmeasurements, we show that the tunnelling delay time of an electron ranges from\n24 to 58 attoseconds, and the counterintuitive result that an electron with a\nlower energy may spend less time in the barrier is consistent with the\nvelocity-dependent tunnelling time of atoms in Larmor clock measurements. Our\nresults unify the tunnelling time of microscopic particles by highlighting the\nclassically forbidden sub-barrier potential interactions of matter waves.", "category": "physics_atom-ph" }, { "text": "Site-selective preparation and multi-state readout of molecules in\n optical tweezers: Polar molecules are a quantum resource with rich internal structure that can\nbe coherently controlled. The structure, however, also makes the state\npreparation and measurement (SPAM) of molecules challenging. We advance the\nSPAM of individual molecules assembled from constituent atoms trapped in\noptical tweezer arrays. Sites without NaCs molecules are eliminated using\nhigh-fidelity Cs atom detection, increasing the peak molecule filling fraction\nof the array threefold. We site-selectively initialize the array in a\nrotational qubit subspace that is insensitive to differential AC Stark shifts\nfrom the optical tweezer. Lastly, we detect multiple rotational states per\nexperimental cycle by imaging atoms after sequential state-selective\ndissociations. These demonstrations extend the SPAM capabilities of molecules\nfor quantum information, simulation, and metrology.", "category": "physics_atom-ph" }, { "text": "Analytic, Group-Theoretic Wave Functions for Confined N-Body Quantum\n Systems: Systems involving N-identical interacting particles under quantum confinement\nappear in many areas of physics, including chemical, condensed matter, and\natomic physics. We discuss a beyondmean- field perturbation method that is\napplicable to weakly, intermediate and strongly-interacting systems. Group\ntheory is used to derive an analytic beyond-mean-field correlated wave function\nat zeroth order for a system under spherical confinement. We derive the\ncorresponding zeroth-order analytic density profile and apply it to the example\nof a Bose-Einstein condensate.", "category": "physics_atom-ph" }, { "text": "The spectral Phase-Amplitude representation of a wave function revisited: The phase and amplitude (Ph-A) of a wave function vary slowly and\nmonotonically with distance, in contrast to the wave function that can be\nhighly oscillatory. Hence an attractive feature of the Ph-A representation is\nthat it requires far fewer meshpoints than for the wave function itself. In\n1930 Milne developed an equation for the phase and the amplitude functions (W.\nE. Milne, Phys. Rev. 35, 863 (1930)), and in 1962 Seaton andPeach (M. J. Seaton\nand G. Peach, Proc. Phys. Soc. 79 1296 (1962)) developed an iterative method\nfor solving Milne's Ph-A equations. Since the zero'th order term of the\niteration is identical to the WKB approximation, there is a close relationship\nbetween the Ph-A and the WKB representations of a wave function. The objective\nof the present study is to show that a spectral Chebyshev expansion method to\nsolve Seaton and Peach's iteration scheme is feasible, and requires very few\nmeshpoints for the whole radial interval. Hence this method provides an\neconomical and accurate way to calculate wave functions out to large distances.\nIn a numerical example for which the potential decreased slowly with distance\nas 1/r^3, the whole radial range of [0-2000] covered with 301 mesh points (and\nChbyshev basis functions). The first order iteration of the Ph-A wave function\nwas found to have an accuracy better than 1%, and was always more accurate than\nthe WKB wave function.", "category": "physics_atom-ph" }, { "text": "Recombination of low energy electrons with U$^{28+}$: We performed an extensive study of configuration mixing between the doubly\nexcited (doorway) states and complex multiply excited states of U$^{28+}$ near\nits ionization threshold. The detailed investigation of complex spectrum and\nanalysis of the statistics of eigenstate components show that the dielectronic\n(doorway) states weakly mixed with each other. However, they show substantial\nmixing with the complex multiply excited states. This situation explains the\nmechanism of low energy electron recombination with U$^{28+}$. We calculated\nthe energy averaged capture cross sections as a sum over dielectronic doorway\nstates and found our present calculation interprets well the experimental\nrecombination rates in the energy range of 1 to 100 eV.", "category": "physics_atom-ph" }, { "text": "The ground-state energy and external potential as functionals of the\n electron density and their derivatives: It is shown that the ground-state energy as a functional solely of the\nelectron density is determined by the asymptotic value of the derivative of the\ndegree-one homogeneous extension of the universal density functional F[n] at\nthe given electron number. This has the consequence that its derivative cannot\nbe properly determined. Carrying out the derivative of E[n[N,v]] with respect\nto v(r) leads to a paradox, which is resolved by the non-differentiability of\nE[n] if one follows traditional wisdom regarding the non-invertibility of the\nlinear response function. However, considering the derivative of v[n[v]]\nthrough the one-electron case shows that this paradox has a more elementary\norigin, namely, an unaccounted restriction of the v(r) domain.", "category": "physics_atom-ph" }, { "text": "High-performance, additively-manufactured atomic spectroscopy apparatus\n for portable quantum technologies: We demonstrate a miniaturised and highly robust system for performing\nDoppler-free spectroscopy on thermal atomic vapour for three frequencies as\nrequired for cold atom-based quantum technologies. The application of additive\nmanufacturing techniques, together with efficient use of optical components,\nproduce a compact, stable optical system, with a volume of 0.089 L and a weight\nof 120 g. The device occupies less than a tenth of the volume of, and is\nconsiderably lower cost than, conventional spectroscopic systems, but also\noffers excellent stability against environmental disturbances. We characterise\nthe response of the system to changes in environmental temperature between 10\nand 30$^{\\circ}$C and exposure to vibrations between 0 - 2000 Hz, finding that\nthe system can reliably perform spectroscopic measurements despite substantial\nvibrational noise and temperature changes. Our results show that 3D-printed\noptical systems are an excellent solution for portable quantum technologies.", "category": "physics_atom-ph" }, { "text": "Dynamic Stark shift in a Doppler-broadened four-wave mixing: This work presents a theoretical analysis of the Autler-Townes splitting\npattern in the four-wave mixing signal generated in a three-level cascade\nDoppler-broadened system. We employ the density matrix formalism to write the\nBloch equations and solve them numerically. The solutions allow us to compare\nthe response of the upper level population and the generated signal coherence\nfor homogeneously and non-homogeneously broadened systems. Our results reveal\nan AC Stark shift in the nonlinear signal when the frequency of the strong or\nweak beam is scanned, in contrast to what is observed in the fluorescence.\nFurthermore, we present experimental data for the four-wave mixing signal in a\nhot rubidium vapor for the copropagating configuration of the exciting beams.\nThe behavior of the AC Stark displacement and signal amplitude as a function of\nlaser power indicates a good agreement between the model and the experimental\nresults.", "category": "physics_atom-ph" }, { "text": "Realizing a stable magnetic double-well potential on an atom chip: We discuss design considerations and the realization of a magnetic\ndouble-well potential on an atom chip using current-carrying wires. Stability\nrequirements for the trapping potential lead to a typical size of order microns\nfor such a device. We also present experiments using the device to manipulate\ncold, trapped atoms.", "category": "physics_atom-ph" }, { "text": "Cryogenic Penning-Trap Apparatus for Precision Experiments with\n Sympathetically Cooled (anti)protons: Current precision experiments with single (anti)protons to test CPT symmetry\nprogress at a rapid pace, but are complicated by the need to cool particles to\nsub-thermal energies. We describe a cryogenic Penning-trap setup for $^9$Be$^+$\nions designed to allow coupling of single (anti)protons to laser-cooled atomic\nions for sympathetic cooling and quantum logic spectroscopy. We report on\ntrapping and laser cooling of clouds and single $^9$Be$^+$ ions. We discuss\nprospects for a microfabricated trap to allow coupling of single (anti)protons\nto laser-cooled $^9$Be$^+$ ions for sympathetic laser cooling to sub-mK\ntemperatures on ms time scales.", "category": "physics_atom-ph" }, { "text": "High-quality level-crossing resonances under counterpropagating\n circularly polarized light waves for applications in atomic magnetometry: Level-crossing (LC) resonances in a buffer-gas-filled cesium vapor cell are\nstudied under counterpropagating pump and probe light waves with opposite\ncircular polarizations. The waves excite the D$_1$-line ground-state level\n$F_g$$=\\,$$4$, while a transverse magnetic field (${\\rm B}_x$$\\perp$${\\rm k}$)\nis scanned around zero to observe the resonance of electromagnetically induced\nabsorption (EIA). It is shown that adding the pump light wave significantly\nimproves the properties of the resonances in comparison with the commonly used\nscheme with a single light wave. As far as a small vapor cell ($\\approx\\,$0.1\ncm$^3$) at relatively low temperature ($\\approx\\,$45-60$\\,^\\circ$C) is\nutilized, the results have good prospects for developing a low-power\nminiaturized atomic magnetometer.", "category": "physics_atom-ph" }, { "text": "Benchmarking strong-field ionisation with atomic hydrogen: As the simplest atomic system, the hydrogen atom plays a key benchmarking\nrole in laser and quantum physics. Atomic hydrogen is a widely used atomic test\nsystem for theoretical calculations of strong-field ionization, since\napproximate theories can be directly compared to numerical solutions of the\ntime-dependent Schr\\\"odinger equation. However, relatively little experimental\ndata is available for comparison to these calculations, since atomic hydrogen\nsources are difficult to construct and use. We review the existing experimental\nresults on strong-field ionization of atomic hydrogen in multi-cycle and\nfew-cycle laser pulses. Quantitative agreement has been achieved between\nexperiment and theoretical predictions at the 10% uncertainty level, and has\nbeen used to develop an intensity calibration method with 1% uncertainty. Such\nquantitative agreement can be used to certify experimental techniques as being\nfree from systematic errors, guaranteeing the accuracy of data obtained on\nspecies other than H. We review the experimental and theoretical techniques\nthat enable these results.", "category": "physics_atom-ph" }, { "text": "Dispersion coefficients for the interactions of the alkali and\n alkaline-earth ions and inert gas atoms with a graphene layer: Largely motivated by a number of applications, the van der Waals dispersion\ncoefficients ($C_3$s) of the alkali ions (Li$^+$, Na$^+$, K$^+$ and Rb$^+$),\nthe alkaline-earth ions (Ca$^+$, Sr$^+$, Ba$^+$ and Ra$^+$) and the inert gas\natoms (He, Ne, Ar and Kr) with a graphene layer are determined precisely within\nthe framework of Dirac model. For these calculations, we have evaluated the\ndynamic polarizabilities of the above atomic systems very accurately by\nevaluating the transition matrix elements employing relativistic many-body\nmethods and using the experimental values of the excitation energies. The\ndispersion coefficients are, finally, given as functions of the separation\ndistance of an atomic system from the graphene layer and the ambiance\ntemperature during the interactions. For easy extraction of these coefficients,\nwe give a logistic fit to the functional forms of the dispersion coefficients\nin terms of the separation distances at the room temperature.", "category": "physics_atom-ph" }, { "text": "Demonstration of a Dual Alkali Rb/Cs Atomic Fountain Clock: We report the operation of a dual Rb/Cs atomic fountain clock. 133Cs and 87Rb\natoms are cooled, launched, and detected simultaneously in LNE-SYRTE's FO2\ndouble fountain. The dual clock operation occurs with no degradation of either\nthe stability or the accuracy. We describe the key features for achieving such\na simultaneous operation. We also report on the results of the first Rb/Cs\nfrequency measurement campaign performed with FO2 in this dual atom clock\nconfiguration, including a new determination of the absolute 87Rb hyperfine\nfrequency.", "category": "physics_atom-ph" }, { "text": "Self-Energy Correction to the Hyperfine Splitting for Excited States: The self-energy corrections to the hyperfine splitting is evaluated for\nhigher excited states in hydrogenlike ions, using an expansion in the binding\nparameter Zalpha, where Z is the nuclear charge number, and alpha is the\nfine-structure constant. We present analytic results for D, F and G states, and\nfor a number of highly excited Rydberg states with principal quantum numbers in\nthe range 13 <= n <= 16, and orbital angular momenta l = n-2 and l = n-1. A\nclosed-form, analytic expression is derived for the contribution of high-energy\nphotons, valid for any state with l <= 2$ and arbitrary n, l and total angular\nmomentum j. The low-energy contributions are written in the form of generalized\nBethe logarithms and evaluated for selected states.", "category": "physics_atom-ph" }, { "text": "Blackbody radiation shift in the Sr optical atomic clock: We evaluated the static and dynamic polarizabilities of the 5s^2 ^1S_0 and\n5s5p ^3P_0^o states of Sr using the high-precision relativistic configuration\ninteraction + all-order method. Our calculation explains the discrepancy\nbetween the recent experimental 5s^2 ^1S_0 - 5s5p ^3P_0^o dc Stark shift\nmeasurement \\Delta \\alpha = 247.374(7) a.u. [Middelmann et. al, arXiv:1208.2848\n(2012)] and the earlier theoretical result of 261(4) a.u. [Porsev and\nDerevianko, Phys. Rev. A 74, 020502R (2006)]. Our present value of 247.5 a.u.\nis in excellent agreement with the experimental result. We also evaluated the\ndynamic correction to the BBR shift with 1 % uncertainty; -0.1492(16) Hz. The\ndynamic correction to the BBR shift is unusually large in the case of Sr (7 %)\nand it enters significantly into the uncertainty budget of the Sr optical\nlattice clock. We suggest future experiments that could further reduce the\npresent uncertainties.", "category": "physics_atom-ph" }, { "text": "Bichromatic phase-control of interfering Autler-Townes spectra: We propose a new scheme to control the shape of the Autler-Townes (AT)\ndoublet in the photoelectron spectrum from atomic resonance-enhanced\nmultiphoton ionization (REMPI). The scheme is based on the interference of two\nAT doublets created by ionization of the strongly driven atom from the ground\nand the resonantly excited state using tailored bichromatic femtosecond (fs)\nlaser pulses. In this scheme, the quantum phase of the photoelectrons is\ncrucial for the manipulation of the AT doublet. The laser polarization state\nand the relative optical phase between the two colors are used to manipulate\nthe interference pattern. We develop an analytical model to describe the\nbichromatic REMPI process and provide a physical picture of the control\nmechanism. To validate the model, the results are compared to an ab initio\ncalculation based on the solution of the 2D time-dependent Schr\\\"odinger\nequation for the non-perturbative interaction of an atom with intense\npolarization-shaped bichromatic fs-laser pulses. Our results indicate that the\ncontrol mechanism is robust with respect to the laser intensity facilitating\nits experimental observation.", "category": "physics_atom-ph" }, { "text": "Coherence from multiorbital tunneling ionization of molecules: We present a simple and general coherence model for multiorbital tunnel\nionization of molecules, which we incorporate into our previously developed\ndensity matrix approach for sequential double ionization [Yuen and Lin, Phys.\nRev. A 106, 023120 (2022)]. The influence of this coherence is investigated\nthrough simulations of single ionization and sequential double ionization of\nN$_2$ and O$_2$ using few-cycle near-infrared laser pulses. In the case of\nsingle ionization, our results reveal the crucial role played by this coherence\nin generating population inversion in N$_2^+$, suggesting a potential mechanism\nfor air lasing. Regarding sequential double ionization, we observe only minor\nchanges in the kinetic energy release spectra when the coherence is included,\nwhile noticeable differences in the angle-dependent dication yield for both\nN$_2$ and O$_2$ are found. Based on these findings, we recommend the inclusion\nof multiorbital tunnel ionization coherence in models for single ionization of\ngeneral molecules, while suggesting that it can be safely neglected in the case\nof sequential double ionization.", "category": "physics_atom-ph" }, { "text": "Schlieren Imaging for the Determination of the Radius of an Excited\n Rubidium Column: AWAKE develops a new plasma wakefield accelerator using the CERN SPS proton\nbunch as a driver. The proton bunch propagates through a 10 m long rubidium\nplasma, induced by an ionizing laser pulse. The co-propagation of the laser\npulse with the proton bunch seeds the self modulation instability of the proton\nbunch that transforms the bunch to a train with hundreds of bunchlets which\ndrive the wakefields. Therefore the plasma radius must exceed the proton bunch\nradius. Schlieren imaging is proposed to determine the plasma radius on both\nends of the vapor source. We use Schlieren imaging to estimate the radius of a\ncolumn of excited rubidium atoms. A tunable, narrow bandwidth laser is split\ninto a beam for the excitation of the rubidium vapor and for the visualization\nusing Schlieren imaging. With a laser wavelength very close to the D2\ntransition line of rubidium (780 nm), it is possible to excite a column of\nrubidium atoms in a small vapor source, to record a Schlieren signal of the\nexcitation column and to estimate its radius. We describe the method and show\nthe results of the measurement.", "category": "physics_atom-ph" }, { "text": "Variation of the Fine-Structure Constant and Laser Cooling of Atomic\n Dysprosium: Radio-frequency electric-dipole transitions between nearly degenerate,\nopposite parity levels of atomic dysprosium (Dy) were monitored over an\neight-month period to search for a variation in the fine-structure constant,\n$\\alpha$. The data provide a rate of fractional temporal variation of $\\alpha$\nof $(-2.4\\pm2.3)\\times10^{-15}$ yr$^{-1}$ or a value of $(-7.8 \\pm 5.9) \\times\n10^{-6}$ for $k_\\alpha$, the variation coefficient for $\\alpha$ in a changing\ngravitational potential. All results indicate the absence of significant\nvariation at the present level of sensitivity. We also present initial results\non laser cooling of an atomic beam of dysprosium.", "category": "physics_atom-ph" }, { "text": "Alignment and orientation of an adsorbed dipole molecule: Half-cycle laser pulse is applied on an absorbed molecule to investigate its\nalignment and orientation behavior. Crossover from field-free to hindered\nrotation motion is observed by varying the angel of hindrance of potential\nwell. At small hindered angle, both alignment and orientation show\nsinusoidal-like behavior because of the suppression of higher excited states.\nHowever, mean alignment decreases monotonically as the hindered angle is\nincreased, while mean orientation displays a minimum point at certain hindered\nangle. The reason is attributed to the symmetry of wavefunction and can be\nexplained well by analyzing the coefficients of eigenstates.", "category": "physics_atom-ph" }, { "text": "Isotope shifts and hyperfine structure of the laser cooling Fe I 358-nm\n line: We report on the measurement of the isotope shifts of the $3d^74s \\,\\, a \\,\n{}^5\\!F_5 - 3d^74p \\,\\, z \\, {}^5\\!G^o_6$ Fe~I line at 358~nm between all four\nstable isotopes ${}^{54}$Fe, ${}^{56}$Fe, ${}^{57}$Fe and ${}^{58}$Fe, as well\nas the hyperfine structure of that line for ${}^{57}$Fe, the only stable\nisotope having a nonzero nuclear spin. This line is of primary importance for\nlaser cooling applications. In addition, an experimental value of the field and\nspecific mass shift coefficients of the transition is reported as well as the\nhyperfine structure magnetic dipole coupling constant $A$ of the transition\nexcited state in $^{57}$Fe, namely $A(3d^74p \\,\\, z \\, {}^5\\!G^o_6)=31.241(48)$\nMHz. The measurements were carried out by means of laser-induced fluorescence\nspectroscopy performed on an isotope-enriched iron atomic beam. All measured\nfrequency shifts are reported with uncertainties below the third percent level.", "category": "physics_atom-ph" }, { "text": "Independent Rydberg Atom Sensing using a Dual-Ladder Scheme: Rydberg atom-based electric field sensing can provide all-optical readout of\nradio frequency fields in a dielectric environment. However, because a single\nset of optical fields is typically used to prepare the Rydberg state and read\nout its response to RF fields, it is challenging to perform simultaneous and\nindependent measurements of the RF field(s). Here we show that using two\nindependent schemes to prepare and read out the same Rydberg state can be used\nto perform independent measurements in general, which we demonstrate\nspecifically by resolving the the RF polarization. We expect this work will be\nuseful for fiber-coupled sensor heads where spatial multiplexing is\nchallenging, as well as for complex multi-level sensing schemes.", "category": "physics_atom-ph" }, { "text": "{\\it Ab initio} studies of electron correlation effects in the atomic\n parity violating amplitudes in Cs and Fr: We have studied the correlation effects in Cs and Fr arising from the\ninterplay of the residual Coulomb interaction to all orders and the neutral\nweak interaction which gives rise to the parity violating electric dipole\ntransition to first order, within the framework of the relativistic\ncoupled-cluster theory which circumvents the constrain of explicitly summing\nover the intermediate states. We observe that, the contributions arising from\nthe perturbed doubly excited states are quite significant and hence, any\ncalculation should not be considered accurate unless it includes the perturbed\ndouble excitations comprehensively. In this article, we have reported a\ncomparative study of various results related to the parity violation in Cs and\nFr.", "category": "physics_atom-ph" }, { "text": "Making ultracold molecules in a two color pump-dump photoassociation\n scheme using chirped pulses: This theoretical paper investigates the formation of ground state molecules\nfrom ultracold cesium atoms in a two-color scheme. Following previous work on\nphotoassociation with chirped picosecond pulses [Luc-Koenig et al., Phys. Rev.\nA {\\bf 70}, 033414 (2004)], we investigate stabilization by a second (dump)\npulse. By appropriately choosing the dump pulse parameters and time delay with\nrespect to the photoassociation pulse, we show that a large number of deeply\nbound molecules are created in the ground triplet state. We discuss (i)\nbroad-bandwidth dump pulses which maximize the probability to form molecules\nwhile creating a broad vibrational distribution as well as (ii)\nnarrow-bandwidth pulses populating a single vibrational ground state level,\nbound by 113 cm$^{-1}$. The use of chirped pulses makes the two-color scheme\nrobust, simple and efficient.", "category": "physics_atom-ph" }, { "text": "Parametric Study for Optimal Performance of Coulomb-Coupled Quantum Dots: We study the optimal output power and efficiency of the three-terminal\nquantum heat engine with Coulomb-coupled quantum-dots (CCQD). It has been well\nknown that in the weak coupling regime, two kinds of dominant transport\nmechanisms are sequential tunneling and cotunneling processes in CCQD. What\nprocess becomes dominant, which can be controlled by several parameters such as\ntemperature difference, bias voltage, Coulomb interaction and tunneling\nparameters, is one of the key problems to determine the performance of the heat\nengine. We show the parametric dependence of the output power and coefficient\nand find the optimal performance of this CCQD heat engine through genetic\nalgorithm.", "category": "physics_atom-ph" }, { "text": "One-dimensional photonic band gaps in optical lattices: The phenomenon of photonic band gaps in one-dimensional optical lattices is\nreviewed using a microscopic approach. Formally equivalent to the transfer\nmatrix approach in the thermodynamic limit, a microscopic model is required to\nstudy finite-size effects, such as deviations from the Bragg condition.\nMicroscopic models describing both scalar and vectorial light are proposed, as\nwell as for two- and three-level atoms. Several analytical results are compared\nto experimental data, showing a good agreement.", "category": "physics_atom-ph" }, { "text": "Manifestations of dark matter and variations of fundamental constants in\n atoms and astrophysical phenomena: We present an overview of recent developments in the detection of light\nbosonic dark matter, including axion, pseudoscalar axion-like and scalar dark\nmatter, which form either a coherently oscillating classical field or\ntopological defects (solitons). We emphasise new high-precision laboratory and\nastrophysical measurements, in which the sought effects are linear in the\nunderlying interaction strength between dark matter and ordinary matter, in\ncontrast to traditional detection schemes for dark matter, where the effects\nare quadratic or higher order in the underlying interaction parameters and are\nextremely small. New terrestrial experiments include measurements with atomic\nclocks, spectroscopy, atomic and solid-state magnetometry, torsion pendula,\nultracold neutrons, and laser interferometry. New astrophysical observations\ninclude pulsar timing, cosmic radiation lensing, Big Bang nucleosynthesis and\ncosmic microwave background measurements. We also discuss various recently\nproposed mechanisms for the induction of slow `drifts', oscillating variations\nand transient-in-time variations of the fundamental constants of Nature by dark\nmatter, which offer a more natural means of producing a cosmological evolution\nof the fundamental constants compared with traditional dark energy-type\ntheories, which invoke a (nearly) massless underlying field. Thus, measurements\nof variation of the fundamental constants gives us a new tool in dark matter\nsearches.", "category": "physics_atom-ph" }, { "text": "Study of the correlation effects in Yb^+ and implications for parity\n violation: Calculation of the energies, magnetic dipole hyperfine structure constants,\nE1 transition amplitudes between the low-lying states, and nuclear\nspin-dependent parity-nonconserving amplitudes for the ^2S_{1/2} -\n^2D_{3/2,5/2} transitions in ^{171}Yb^+ ion is performed using two different\napproaches. First, we carried out many-body perturbation theory calculation\nconsidering Yb^+ as a monovalent system. Additional all-order calculations are\ncarried out for selected properties. Second, we carried out configuration\ninteraction calculation considering Yb as a 15-electron system and compared the\nresults obtained by two methods. The accuracy of different methods is\nevaluated. We find that the monovalent description is inadequate for evaluation\nof some atomic properties due to significant mixing of the one-particle and the\nhole-two-particle configurations. Performing the calculation by such different\napproaches allowed us to establish the importance of various correlation\neffects for Yb^+ atomic properties for future improvement of theoretical\nprecision in this complicated system.", "category": "physics_atom-ph" }, { "text": "Electric dipole polarizability of alkaline-Earth-metal atoms from\n perturbed relativistic coupled-cluster theory with triples: The perturbed relativistic coupled-cluster (PRCC) theory is applied to\ncalculate the electric dipole polarizabilities of alkaline Earth metal atoms.\nThe Dirac-Coulomb-Breit atomic Hamiltonian is used and we include the triple\nexcitations in the relativistic coupled-cluster (RCC) theory. The theoretical\nissues related to the triple excitation cluster operators are described in\ndetail and we also provide details on the computational implementation. The\nPRCC theory results are in good agreement with the experimental and previous\ntheoretical results. We, then, highlight the importance of considering the\nBreit interaction for alkaline Earth metal atoms.", "category": "physics_atom-ph" }, { "text": "Trapping of ultra cold atoms in a 3He/4He dilution refrigerator: We describe the preparation of ultra cold atomic clouds in a dilution\nrefrigerator. The closed cycle 3He/4He cryostat was custom made to provide\noptical access for laser cooling, optical manipulation and detection of atoms.\nWe show that the cryostat meets the requirements for cold atom experiments,\nspecifically in terms of operating a magneto-optical trap, magnetic traps and\nmagnetic transport under ultra high vacuum conditions. The presented system is\na step towards the creation of a quantum hybrid system combining ultra cold\natoms and solid state quantum devices.", "category": "physics_atom-ph" }, { "text": "High resolution calculation of low energy scattering in $e^-e^+\\bar{p}$\n and $e^+e^-\\mbox{He}^{++}$ systems via Faddeev-Merkuriev equations: The potential splitting approach incorporated into the framework of\nFaddeev-Merkuriev equations in the differential form is used for calculations\nof multichannel scattering in $e^-e^+\\bar{p}$ and $e^+e^-\\mbox{He}^{++}$\nsystems. Detailed calculations of all possible S-wave cross-sections are\nperformed %in systems $e^+e^-\\bar{p}$ and $e^+e^-\\mbox{He}^{++}$ in the\nlow-energy region which supports up to seven open channels including the\nrearrangement channels of ground and excited states of antihydrogen,\npositronium and helium ion formations. All known sharp resonances of the\nsystems obtained and approved by a number of authors are clearly reproduced in\nthe calculated cross sections. In cross sections for energies above the\nthreshold corresponding to $n=2$ state of antihydrogen the prominent\noscillations of Gailitis Damburg type have been found.", "category": "physics_atom-ph" }, { "text": "Collisional dynamics of ultracold OH molecules in an electrostatic field: Ultracold collisions of polar OH molecules are considered in the presence of\nan electrostatic field. The field exerts a strong influence on both elastic and\nstate-changing inelastic collision rate constants, leading to clear\nexperimental signatures that should help disentangle the theory of cold\nmolecule collisions. Based on the collision rates we discuss the prospects for\nevaporative cooling of electrostatically trapped OH. We also find that the\nscattering properties at ultralow temperatures prove to be remarkably\nindependent of the details of the short-range interaction, owing to avoided\ncrossings in the long-range adiabatic potential curves. The behavior of the\nscattering rate constants is qualitatively understood in terms of a novel set\nof long-range states of the [OH]$_2$ dimer.", "category": "physics_atom-ph" }, { "text": "Enhancement of the electric dipole moment of the electron in BaF\n molecule: We report results of ab initio calculation of the spin-rotational Hamiltonian\nparameters including P- and P,T-odd terms for the BaF molecule. The ground\nstate wave function of BaF molecule is found with the help of the Relativistic\nEffective Core Potential method followed by the restoration of molecular\nfour-component spinors in the core region of barium in the framework of a\nnon-variational procedure. Core polarization effects are included with the help\nof the atomic Many Body Perturbation Theory for Barium atom. For the hyperfine\nconstants the accuracy of this method is about 5-10%.", "category": "physics_atom-ph" }, { "text": "Dissociative recombination of BeH^+: The cross section for dissociative recombination of BeH^+ is calculated by\nsolution of the time-dependent Schrodinger equation in the local complex\npotential approximation. The effects of couplings between resonant states and\nthe Rydberg states converging to the ground state of the ion are studied. The\nrelevant potentials, couplings and autoionization widths are extracted using ab\ninitio electron scattering and structure calculations, followed by a\ndiabatization procedure. The calculated cross sections shows a sizable\nmagnitude at low energy, followed by a high-energy peak centered around 1 eV.\nThe electronic couplings between the neutral states induce oscillations in the\ncross section. Analytical forms for the cross sections at low collision\nenergies are given.", "category": "physics_atom-ph" }, { "text": "Candidate molecular ions for an electron electric dipole moment\n experiment: This paper is a theoretical work in support of a newly proposed experiment\n(R. Stutz and E. Cornell, Bull. Am. Soc. Phys. 89, 76 2004) that promises\ngreater sensitivity to measurements of the electron's electric dipole moment\n(EDM) based on the trapping of molecular ions. Such an experiment requires the\nchoice of a suitable molecule that is both experimentally feasible and\npossesses an expectation of a reasonable EDM signal. We find that the molecular\nions PtH+, HfH+, and HfF+ are suitable candidates in their low-lying triplet\nDelta states. In particular, we anticipate that the effective electric fields\ngenerated inside these molecules are approximately of 73 GV/cm, -17 GV/cm, and\n-18 GV/cm respectively. As a byproduct of this discussion, we also explain how\nto make estimates of the size of the effective electric field acting in a\nmolecule, using commercially available, nonrelativistic molecular structure\nsoftware.", "category": "physics_atom-ph" }, { "text": "Electron-impact fine-structure excitation of Fe II at low temperature: Fe II emission lines are observed from nearly all classes of astronomical\nobjects over a wide spectral range from the infrared to the ultraviolet. To\nmeaningfully interpret these lines, reliable atomic data are necessary. In work\npresented here we focused on low-lying fine-structure transitions, within the\nground term, due to electron impact. We provide effective collision strengths\ntogether with estimated uncertainties as functions of temperature of\nastrophysical importance ($10 - 100,000$ K). Due to the importance of\nfine-structure transitions within the ground term, the focus of this work is on\nobtaining accurate rate coefficients at the lower end of this temperature\nrange, for applications in low temperature environments such as the\ninterstellar medium. We performed three different flavours of scattering\ncalculations: i) a intermediate coupling frame transformation (ICFT) $R$-matrix\nmethod, ii) a Breit-Pauli (BP) $R$-matrix method, and iii) a Dirac $R$-matrix\nmethod. The ICFT and BP $R$-matrix calculations involved three different\nAUTOSTRUCTURE target models each. The Dirac $R$-matrix calculation was based on\na reliable 20 configuration, 6069 level atomic structure model. Good agreement\nwas found with our BP and Dirac $R$-matrix collision results compared to\nprevious $R$-matrix calculations. We present a set of recommended effective\ncollision strengths for the low-lying forbidden transitions together with\nassociated uncertainty estimates.", "category": "physics_atom-ph" }, { "text": "New constraints on axion-mediated P,T-violating interaction from\n electric dipole moments of diamagnetic atoms: The exchange of an axion-like particle between atomic electrons and the\nnucleus may induce electric dipole moments (EDMs) of atoms and molecules. This\ninteraction is described by a parity- and time-reversal-invariance-violating\npotential which depends on the product of a scalar $g^s$ and a pseudoscalar\n$g^p$ coupling constant. We consider the interaction with the specific\ncombination of these constants, $g_e^s g_N^p$, which gives significant\ncontributions to the EDMs of diamagnetic atoms. In this paper, we calculate\nthese contributions to the EDMs of $^{199}$Hg, $^{129}$Xe, $^{211}$Rn and\n$^{225}$Ra for a wide range of axion masses. Comparing these results with\nrecent experimental EDM measurements, we place new constraints on $g_e^s\ng_N^p$. The most stringent atomic EDM limits come from $^{199}$Hg and improve\non existing laboratory limits from other experiments for axion masses exceeding\n$10^{-2}$ eV.", "category": "physics_atom-ph" }, { "text": "Atomic Radiative Transitions in Thermo Field Dynamics: In this work we rederive the Lamb-Retherford energy shift for an atomic\nelectron in the presence of a thermal radiation. Using the Dalibard, Dupont-Roc\nand Cohen-Tannoudji (DDC) formalism, where physical observables are expressed\nas convolutions of suitable statistical functions, we construct the\nelectromagnetic field propagator of Thermo Field Dynamics in the Coulomb gauge\nin order to investigate finite temperature effects on the atomic energy levels.\nIn the same context, we also analyze the problem of the ground state stability.", "category": "physics_atom-ph" }, { "text": "Ramsey interferometry in three-level and five-level systems of $^{87}Rb$\n Bose-Einstein condensates: Our work here presents the analytical expressions for a typical Ramsey\ninterferometric sequence for a three- and a five-level system. The analytical\nexpressions are derived starting from the first principals of unitary time\nevolution operators. We focus on the three- and five-level systems because we\npropose a novel Ramsey interferometer created by a trapped two-state\nBose-Einstein Condensate driven by dipole oscillations and gravitational sag.\nIt involves the $^{87}Rb$ atoms in states $\\vert F=2, m_F=+2 \\rangle$ $(\\vert\n+2 \\rangle)$ and $\\vert F=2, m_F=+1 \\rangle$ $(\\vert +1 \\rangle)$ of the $5\n^2S_{\\frac{1}{2}}$ ground state. Though the interferometer focusses on the\ntwo-levels, the experimental readouts involve all the five states in $F = 2$\nhyperfine manifold. Therefore, the analytical derivation was first tested for\nthree-levels and then expanded to five-levels. We developed the expressions for\nfive-levels for greater analytical accuracy of the experimental scenario. This\nwork provides a step-by-step outline for the derivation and methodology for the\nanalytical expressions. These analytical formulae denote the population\nvariation during Rabi and Ramsey oscillations for each state as well as the\noverall average for both the three- and five-level cases. The expressions are\nderived within the rotating wave approximation (RWA) under the equal Rabi\ncondition. Further, by following the derivation methodology, these analytical\nexpressions can be easily expanded for Ramsey sequences with unequal pulses,\nand Ramsey sequences with spin echo techniques.", "category": "physics_atom-ph" }, { "text": "Permanent Electric Dipole Moment of Strontium Monofluoride as a Test of\n the Accuracy of a Relativistic Coupled Cluster Method: The permanent electric dipole moment of the X 2 {\\Sigma}+ electronic ground\nstate of the strontium monofluoride molecule is calculated using a relativistic\ncoupled cluster method. Our result is compared with those of other calculations\nand that of experiment. Individual contributions arising from different\nphysical effects are presented. The result obtained suggests that the\nrelativistic coupled cluster method used in the present work is capable of\nyielding accurate results for the permanent electric dipole moments of\nmolecules for which relativistic effects cannot be ignored.", "category": "physics_atom-ph" }, { "text": "Narrow and contrast resonance of increased absorption in Lambda-system\n observed in Rb cell with buffer gas: We report observation of a narrow (sub-natural) and high-contrast resonance\nof increased absorption (\"bright\" resonance) in Rb cell with Ne buffer gas\nunder previously unexplored experimental conditions for coupling and probe\nradiation configuration. The coupling laser stabilized frequency is detuned by\n~ 3 GHz from 5S1/2, Fg=3 --> 5P3/2, Fe=2,3,4 transitions, while the probe laser\nfrequency is scanned across these transitions. We believe the bright resonance\nformation, occurring when the probe laser frequency is blue-shifted from the\ncoupling frequency by a value of the ground state hyperfine splitting, is\ncaused predominantly by a 2-photon absorption of the probe radiation 5S1/2,\nFg=2 --> 5S1/2, Fg=3 with 5P3/2 as an intermediate state. We also report and\ninterpret splitting of the bright resonance into 6 well resolved and contrast\ncomponents in moderate magnetic fields (B ~ 10 - 250 G).", "category": "physics_atom-ph" }, { "text": "Experiment to detect dark energy forces using atom interferometry: The accelerated expansion of the universe motivates a wide class of scalar\nfield theories that modify gravity on large scales. In regions where the weak\nfield limit of General Relativity has been confirmed by experiment, such\ntheories need a screening mechanism to suppress the new force. We have measured\nthe acceleration of an atom toward a macroscopic test mass inside a high vacuum\nchamber, where the new force is unscreened in some theories. Our measurement,\nmade using atom interferometry, shows that the attraction between atoms and the\ntest mass does not differ appreciably from Newtonian gravity. This result\nplaces stringent limits on the free parameters in chameleon and symmetron\ntheories of modified gravity.", "category": "physics_atom-ph" }, { "text": "Calculation of positron binding to silver and gold atoms: Positron binding to silver and gold atoms was studied using a fully {\\it ab\ninitio} relativistic method, which combines the configuration interaction\nmethod with many-body perturbation theory. It was found that the silver atom\nforms a bound state with a positron with binding energy 123 ($\\pm$ 20%) meV,\nwhile the gold atom cannot bind a positron. Our calculations reveal the\nimportance of the relativistic effects for positron binding to heavy atoms. The\nrole of these effects was studied by varying the value of the fine structure\nconstant $\\alpha$. In the non-relativistic limit, $\\alpha = 0$, both systems\n$e^+$Ag and $e^+$Au are bound with binding energies of about 200 meV for\n$e^+$Ag and 220 meV for $e^+$Au. Relativistic corrections for a negative ion\nare essentially different from that for a positron interacting with an atom.\nTherefore, the calculation of electron affinities cannot serve as a test of the\nmethod used for positron binding in the non-relativistic case. However, it is\nstill a good test of the relativistic calculations. Our calculated electron\naffinities for silver (1.327 eV) and gold (2.307 eV) atoms are in very good\nagreement with corresponding experimental values (1.303 eV and 2.309 eV\nrespectively).", "category": "physics_atom-ph" }, { "text": "Shifts of a resonance line in a dense atomic sample: We study the collective response of a dense atomic sample to light\nessentially exactly using classical-electrodynamics simulations. In a\nhomogeneously broadened atomic sample there is no overt Lorentz-Lorenz local\nfield shift of the resonance, nor a collective Lamb shift. However, addition of\ninhomogeneous broadening restores the usual mean-field phenomenology.", "category": "physics_atom-ph" }, { "text": "Measurement of the Hyperfine Quenching Rate of the Clock Transition in\n $^{171}$Yb: We report the first experimental determination of the hyperfine quenching\nrate of the $6s^2\\ ^1\\!S_0\\ (F=1/2) - 6s6p\\ ^3\\!P_0\\ (F=1/2)$ transition in\n$^{171}$Yb with nuclear spin $I=1/2$. This rate determines the natural\nlinewidth and the Rabi frequency of the clock transition of a Yb optical\nfrequency standard. Our technique involves spectrally resolved fluorescence\ndecay measurements of the lowest lying $^3\\!P_{0,1}$ levels of neutral Yb atoms\nembedded in a solid Ne matrix. The solid Ne provides a simple way to trap a\nlarge number of atoms as well as an efficient mechanism for populating\n$^3\\!P_0$. The decay rates in solid Ne are modified by medium effects including\nthe index-of-refraction dependence. We find the $^3\\!P_0$ hyperfine quenching\nrate to be $(4.42\\pm0.35)\\times10^{-2}\\ \\mathrm{s}^{-1}$ for free $^{171}$Yb,\nwhich agrees with recent ab initio calculations.", "category": "physics_atom-ph" }, { "text": "Shuttling of Rydberg ions for fast entangling operations: We introduce a scheme to entangle Rydberg ions in a linear ion crystal, using\nthe high electric polarizability of the Rydberg electronic states in\ncombination with mutual Coulomb coupling of ions that establishes common modes\nof motion. After laser-initialization of ions to a superposition of ground- and\nRydberg-state, the entanglement operation is driven purely by applying a\nvoltage pulse that shuttles the ion crystal back and forth. This operation can\nachieve entanglement on a sub-$\\mu$s timescale, more than two orders of\nmagnitude faster than typical gate operations driven by continuous-wave lasers.\nOur analysis shows that the fidelity achieved with this protocol can exceed\n$99.9\\%$ with experimentally achievable parameters.", "category": "physics_atom-ph" }, { "text": "Partial Quantum Coherence, Ultrashort Electron Pulse Statistics, and a\n Plasmon-Enhanced Nanotip Emitter Based on Metallized Optical Fibers: The present dissertation covers two related research projects. The first\ntopic was initiated with the ultimate goal of observing quantum degeneracy in\nultrashort free electron pulses. This constitutes a thorough theoretical\nanalysis of the problem involving partial quantum coherence and spin\npolarization of the source in light of a path-integral treatment of the\nphenomenon of matter-wave diffraction-in-time. Subsequently, results of a\ntrailblazing experiment, to be superseded by a Hanbury Brown-Twiss type\nconclusive test of free fermion antibunching with electrons, is reported. In\nthis experiment, the statistical distribution of the emitted electrons is\nstudied taking advantage of a double-detector coincidence detection technique.\nThe utilized electron emitters are ultrafast photoemission tungsten nanotip\nneedle sources which are known to procure large spatial coherence lengths. The\nemission statistics is found to be sub-Poissonian. The second project involves\nintroduction and full characterization of a novel laser-driven electron nanotip\nemitter based on metallized fiber optic tapers in which the emission mechanism\nis found to be assisted by surface plasmon resonance excitation as predicted\nprior to the design of such sources. It is shown that gold-coated fiber optic\nnanotips can emit electrons using both low-power continuous wave lasers as well\nas femtosecond pulsed lasers tuned to or near the surface plasmon resonance\nexcitation wavelength of the system. The final chapter entails a proposal of a\nspin-polarized electron photoemitter based on the spin Hall effect for which\nsuch a fiber optic nanotip source is exploited.", "category": "physics_atom-ph" }, { "text": "Precision spectroscopy of the hydrogen molecular ions: present status of\n theory and experiment: We review recent experiments on HD$^+$ spectroscopy. The reduced\nproton-deuteron mass to electron mass ratio, $\\mu_{pd}/m_e$, is inferred from\nthe comparison of theory and experiment. Theoretical issues related to the\ncalculations of the spin structure, which are currently the main limiting\nfactor of theoretical accuracy, are discussed.", "category": "physics_atom-ph" }, { "text": "Isolated-core quadrupole excitation of highly excited autoionizing\n Rydberg states: The structure and photoexcitation dynamics of high lying doubly excited\nstates of the strontium atom with high angular momenta are studied in the\nvicinity of the Sr$^+(N=5)$ threshold. The spectra recorded using resonant\nmultiphoton isolated core excitation are analyzed with calculations based on\nconfiguration interaction with exterior complex scaling, which treats the\ncorrelated motion of the two valence electrons of Sr from first principles. The\nresults are rationalized with a model based on multichannel quantum-defect\ntheory and transition dipole moments calculated with a perturbative treatment\nof electron correlations. Together, both approaches reveal that most of the\nlines observed in the spectra arise from the interaction of a single optically\nactive state, coupled to the initial state by an electric-dipole transition,\nwith entire doubly-excited Rydberg series. The long-range electron correlations\nresponsible for this interaction unexpectedly vanish for identical values of\nthe initial and final principal quantum numbers, a fact related to the quasi\nhydrogenic nature of the high-$l$ Rydberg electron. This special situation, and\nin particular the vanishing interaction, leads to the surprising observation of\nan electric \\emph{quadrupole} isolated-core excitation with a similar intensity\nas the neighboring electric dipole transitions.", "category": "physics_atom-ph" }, { "text": "Supersolid Vortex Crystals in Rydberg-dressed Bose-Einstein Condensates: We study rotating quasi-two-dimensional Bose-Einstein-condensates, in which\natoms are dressed to a highly excited Rydberg state. This leads to weak\neffective interactions that induce a transition to a mesoscopic supersolid\nstate. Considering slow rotation, we determine its superfluidity using Quantum\nMonte-Carlo simulations as well as mean field calculations. For rapid rotation,\nthe latter reveal an interesting competition between the supersolid crystal\nstructure and the rotation-induced vortex lattice that gives rise to new\nphases, including arrays of mesoscopic vortex crystals.", "category": "physics_atom-ph" }, { "text": "High-resolution, vacuum-ultraviolet absorption spectrum of boron\n trifluoride: In the course of investigations of thermal neutron detection based on\nmixtures of $^{10}$BF$_3$ with other gases, knowledge was required of the\nphotoabsorption cross sections of $^{10}$BF$_3$ for wavelengths between 135 and\n205 nm. Large discrepancies in the values reported in existing literature led\nto the absolute measurements reported in this communication. The measurements\nwere made at the SURF III synchrotron radiation facility at the National\nInstitute of Standards and Technology. The measured absorption cross sections\nvary from 10$^{-20}$ cm$^2$ at 135 nm to less than 10$^{-21}$ cm$^2$ in the\nregion from 165 to 205 nm. Three previously unreported absorption features with\nresolvable structure were found in the regions 135 to 145 nm, 150 to 165 nm and\n190 to 205 nm. Quantum mechanical calculations, using the TD-B3LYP/aug-cc-pVDZ\nvariant of time-dependent density functional theory implemented in Gaussian 09,\nsuggest that the observed absorption features arise from symmetry-changing\nadiabatic transitions.", "category": "physics_atom-ph" }, { "text": "Information and backaction due to phase contrast imaging measurements of\n cold atomic gases: beyond Gaussian states: We further examine a theory of phase contrast imaging (PCI) of cold atomic\ngases, first introduced by us in Phys. Rev. Lett. {\\bf 112}, 233602 (2014). We\nmodel the PCI measurement by directly calculating the entangled state between\nthe light and the atoms due to the ac Stark shift, which induces a conditional\nphase shift on the light depending upon the atomic state. By interfering the\nlight that passes through the BEC with the original light, one can obtain\ninformation of the atomic state at a single shot level. We derive an exact\nexpression for a measurement operator that embodies the information obtained\nfrom PCI, as well as the back-action on the atomic state. By the use of exact\nexpressions for the measurement process, we go beyond the continuous variables\napproximation such that the non-Gaussian regime can be accessed for both the\nmeasured state and the post-measurement state. Features such as the photon\nprobability density, signal, signal variance, Fisher information, error of the\nmeasurement, and the backaction are calculated by applying the measurement\noperator to an atomic two spin state system. For an atomic state that is\ninitially in a spin coherent state, we obtain analytical expression for these\nquantities. There is an optimal atom-light interaction time that scales\ninversely proportional to the number of atoms, which maximizes the information\nreadout.", "category": "physics_atom-ph" }, { "text": "Solving the m-mixing problem for the three-dimensional time-dependent\n Schr\u00f6dinger equation by rotations: application to strong-field ionization\n of H2+: We present a very efficient technique for solving the three-dimensional\ntime-dependent Schrodinger equation. Our method is applicable to a wide range\nof problems where a fullly three-dimensional solution is required, i.e., to\ncases where no symmetries exist that reduce the dimensionally of the problem.\nExamples include arbitrarily oriented molecules in external fields and atoms\ninteracting with elliptically polarized light. We demonstrate that even in such\ncases, the three-dimensional problem can be decomposed exactly into two\ntwo-dimensional problems at the cost of introducing a trivial rotation\ntransformation. We supplement the theoretical framework with numerical results\non strong-field ionization of arbitrarily oriented H2+ molecules.", "category": "physics_atom-ph" }, { "text": "Limit on Lorentz and CPT Violation of the Neutron Using a Two-Species\n Noble-Gas Maser: A search for sidereal variations in the frequency difference between\nco-located 129-Xe and 3-He Zeeman masers sets the most stringent limit to date\non leading-order Lorentz and CPT violation involving the neutron, consistent\nwith no effect at the level of 10^{-31} GeV.", "category": "physics_atom-ph" }, { "text": "Storage enhanced nonlinearities in a cold atomic Rydberg ensemble: The combination of electromagnetically induced transparency (EIT) with the\nnonlinear interaction between Rydberg atoms provides an effective interaction\nbetween photons. In this paper, we investigate the storage of optical pulses as\ncollective Rydberg atomic excitations in a cold atomic ensemble. By measuring\nthe dynamics of the stored Rydberg polaritons, we experimentally demonstrate\nthat storing a probe pulse as Rydberg polaritons strongly enhances the Rydberg\nmediated interaction compared to the slow propagation case. We show that the\nprocess is characterized by two time scales. At short storage times, we observe\na strong enhancement of the interaction due to the reduction of the Rydberg\npolariton group velocity down to zero. For longer storage times, we observe a\nfurther, weaker enhancement dominated by Rydberg induced dephasing of the\nmultiparticle components of the state. In this regime, we observe a non-linear\ndependence of the Rydberg polariton coherence time with the input photon\nnumber. Our results have direct consequences in Rydberg quantum optics and\nenable the test of new theories of strongly interacting Rydberg systems.", "category": "physics_atom-ph" }, { "text": "Measurement of the Aharonov-Casher geometric phase with a separated-arm\n atom interferometer: In this letter, we report a measurement of the Aharonov-Casher (AC) geometric\nphase with our lithium atom interferometer. The AC phase appears when a\nparticle carrying a magnetic dipole propagates in a transverse electric field.\nThe first measurement of the AC phase was done with a neutron interferometer in\n1989 by A. Cimmino \\textit{et al.} (Phys. Rev. Lett. \\textbf{63}, 380, 1989)\nand all the following experiments were done with Ramsey or Ramsey-Bord\\'e\ninterferometers with molecules or atoms. In our experiment, we use lithium\natoms pumped in a single hyperfine-Zeeman sublevel and we measure the AC-phase\nby applying opposite electric fields on the two interferometer arms. Our\nmeasurements are in good agreement with the expected theoretical values and\nthey prove that this phase is independent of the atom velocity.", "category": "physics_atom-ph" }, { "text": "Addendum to \"The Dirac-Coulomb Sturmians and the series expansion of the\n Dirac-Coulomb Green function: application to the relativistic polarizability\n of the hydrogen-like atom\" [J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 825-61,\n (E) 30 (1997) 2747]: Closure relations satisfied by the radial Dirac-Coulomb Sturmians are proved\nanalytically. The Sturmian expansion of the Dirac-Coulomb Green function is\ntransformed to the form containing only series with summations running over\nnon-negative indices. The main paper was published in J. Phys. B: At. Mol. Opt.\nPhys. 30 (1997) 825-61 [Erratum: 30 (1997) 2747], see also J. Phys. A: Math.\nGen. 31 (1998) 4963--90 [Erratum: 31 (1998) 7415-6].", "category": "physics_atom-ph" }, { "text": "Topological edge states and Aharanov-Bohm caging with ultracold atoms\n carrying orbital angular momentum: We show that bosonic atoms loaded into orbital angular momentum $l=1$ states\nof a lattice in a diamond-chain geometry provides a flexible and simple\nplatform for exploring a range of topological effects. This system exhibits\nrobust edge states, and the relative phases arising naturally in the tunnelling\namplitudes lead to the appearance of Aharanov-Bohm caging in the lattice. We\ndiscuss how these properties can be realised and observed in ongoing\nexperiments.", "category": "physics_atom-ph" }, { "text": "The selection rules of high harmonic generation: the symmetries of\n molecules and laser fields: The selection rules of high harmonic generation (HHG) are investigated using\nthree-dimensional time-dependent density functional theory (TDDFT). From the\nharmonic spectra obtained with various real molecules and different forms of\nlaser fields, several factors that contribute to selection rules are revealed.\nExtending the targets to stereoscopic molecules, it is shown that the allowed\nharmonics are dependent on the symmetries of the projections of molecules. For\nlaser fields, the symmetries contributing to the selection rules are discussed\naccording to Lissajous figures and their dynamical directivities. All the\nphenomena are explained by the symmetry of the full time-dependent Hamiltonian\nunder a combined transformation. We present a systematic study on the selection\nrules and propose an intuitive method for the judgment of allowed harmonic\norders, which can be extended to more complex molecules and various forms of\nlaser pulses.", "category": "physics_atom-ph" }, { "text": "Wavelength mismatch effect in electromagnetically induced absorption: We present a theoretical investigation of the phenomenon of\nelectromagnetically induced absorption (EIA) in a 4-level system consisting of\nvee and ladder subsystems. The four levels are coupled using one weak probe\nfield, and two strong control fields. We consider an experimental realization\nusing energy levels of Rb. This necessitates dealing with different conditions\nof wavelength mismatch---near-perfect match where all three wavelengths are\napproximately equal; partial mismatch where the wavelength of one control field\nis less than the other fields; and complete mismatch where all three\nwavelengths are unequal. We present probe absorption profiles with Doppler\naveraging at room temperature to account for experiments in a room temperature\nRb vapor cell. Our analysis shows that EIA resonances can be studied using\nRydberg states excited with diode lasers.", "category": "physics_atom-ph" }, { "text": "Cavity-immune features in the spectra of superradiant crossover laser\n pulses: Lasing in the bad cavity regime has promising applications in precision\nmetrology due to the reduced sensitivity to cavity noise. Here we investigate\nthe spectral properties and phase behavior of pulsed lasing on the $^1$S$_0 -\n^3$P$_1$ line of $^{88}$Sr in a mK thermal ensemble, as first described in\narxiv:1903.12593. The system operates in a regime where the Doppler-broadened\natomic transition linewidth is several times larger than the cavity linewidth.\nWe find that by detuning the cavity resonance, the influence of the cavity\nnoise on the peak lasing frequency can be eliminated to first order despite the\nsystem not being deep in the bad cavity regime. Experimental results are\ncompared to a model based on a Tavis-Cummings Hamiltonian, which enables us to\ninvestigate the interplay between different thermal velocity classes as the\nunderlying mechanism for the reduction in cavity noise. These\nvelocity-dependent dynamics can occur in pulsed lasing and during the turn-on\nbehavior of lasers in the superradiant crossover regime.", "category": "physics_atom-ph" }, { "text": "Long-lived Bell states in an array of optical clock qubits: The generation of long-lived entanglement on an optical clock transition is a\nkey requirement to unlocking the promise of quantum metrology. Arrays of\nneutral atoms constitute a capable quantum platform for accessing such physics,\nwhere Rydberg-based interactions may generate entanglement between individually\ncontrolled and resolved atoms. To this end, we leverage the programmable state\npreparation afforded by optical tweezers along with the efficient strong\nconfinement of a 3d optical lattice to prepare an ensemble of strontium atom\npairs in their motional ground state. We engineer global single-qubit gates on\nthe optical clock transition and two-qubit entangling gates via adiabatic\nRydberg dressing, enabling the generation of Bell states, $|\\psi\\rangle =\n\\frac{1}{\\sqrt{2}}\\left(|gg\\rangle + i|ee\\rangle \\right)$, with a fidelity of\n$\\mathcal{F}= 92.8(2.0)$%. For use in quantum metrology, it is furthermore\ncritical that the resulting entanglement be long lived; we find that the\ncoherence of the Bell state has a lifetime of $\\tau_{bc} = 4.2(6)$ s via parity\ncorrelations and simultaneous comparisons between entangled and unentangled\nensembles. Such Bell states can be useful for enhancing metrological stability\nand bandwidth. Further rearrangement of hundreds of atoms into arbitrary\nconfigurations using optical tweezers will enable implementation of many-qubit\ngates and cluster state generation, as well as explorations of the transverse\nfield Ising model and Hubbard models with entangled or finite-range-interacting\ntunnellers.", "category": "physics_atom-ph" }, { "text": "Transport of launched cold atoms with a laser guide and pulsed magnetic\n fields: We propose the novel combination of a laser guide and magnetic lens to\ntransport a cold atomic cloud. We have modelled the loading and guiding of a\nlaunched cloud of cold atoms with the optical dipole force. We discuss the\noptimum strategy for loading typically 30% of the atoms from a MOT and guiding\nthem vertically through 22cm. However, although the atoms are tightly confined\ntransversely, thermal expansion in the propagation direction still results in a\ndensity loss of two orders of magnitude. By combining the laser guide with a\nsingle impulse from a magnetic lens we show one can actually increase the\ndensity of the guided atoms by a factor of 10.", "category": "physics_atom-ph" }, { "text": "Charge Qubit-Atom Hybrid: We investigate a novel hybrid system of a superconducting charge qubit\ninteracting directly with a single neutral atom via electric dipole coupling.\nInterfacing of the macroscopic superconducting circuit with the microscopic\natomic system is accomplished by varying the gate capacitance of the charge\nqubit. To achieve strong interaction, we employ two Rydberg states with an\nelectric-dipole allowed transition, which alters the polarizability of the\ndielectric medium of the gate capacitor. Sweeping the gate voltage with\ndifferent rates leads to a precise control of hybrid quantum states.\nFurthermore, we show a possible implementation of a universal two-qubit gate.", "category": "physics_atom-ph" }, { "text": "Effects of a static electric field on two-color photoassociation between\n different atoms: We study non-perturbative effects of a static electric field on two-color\nphotoassociation of different atoms. A static electric field induces anisotropy\nin scattering between two different atoms and hybridizes field-free rotational\nstates of heteronuclear dimers or polar molecules. In a previous paper [D.\nChakraborty $\\it {et.}$ $\\it {al.}$, J. Phys. B 44, 095201 (2011)], the effects\nof a static electric field on one-color photoassociation between different\natoms has been described through field-modified ground-state scattering states,\nneglecting electric field effects on heteronuclear diatomic bound states. To\nstudy the effects of a static electric field on heteronuclear bound states, and\nthe resulting influence on Raman-type two-color photoassociation between\ndifferent atoms in the presence of a static electric field, we develop a\nnon-perturbative numerical method to calculate static electric field-dressed\nheteronuclear bound states. We show that the static electric field induced\nscattering anisotropy as well as hybridization of rotational states strongly\ninfluence two-color photoassociation spectra, leading to significant\nenhancement in PA rate and large shift. In particular, for static electric\nfield strengths of a few hundred kV/cm, two-color PA rate involving high-lying\nbound states in electronic ground-state increases by several orders of\nmagnitude even in the weak photoassociative coupling regime.", "category": "physics_atom-ph" }, { "text": "Detrimental adsorbate fields in experiments with cold Rydberg gases near\n surfaces: We observe the shift of Rydberg levels of rubidium close to a copper surface\nwhen atomic clouds are repeatedly deposited on it. We measure transition\nfrequencies of rubidium to S and D Rydberg states with principal quantum\nnumbers n between 31 and 48 using the technique of electromagnetically induced\ntransparency. The spectroscopic measurement shows a strong increase of electric\nfields towards the surface that evolves with the deposition of atoms. Starting\nwith a clean surface, we measure the evolution of electrostatic fields in the\nrange between 30 and 300 \\mum from the surface. We find that after the\ndeposition of a few hundred atomic clouds, each containing ~10^6 atoms, the\nfield of adsorbates reaches 1 V/cm for a distance of 30 \\mum from the surface.\nThis evolution of the electrostatic field sets serious limitations on cavity\nQED experiments proposed for Rydberg atoms on atom chips.", "category": "physics_atom-ph" }, { "text": "Quo vadis, cold molecules? - Editorial review: We give a snapshot of the rapidly developing field of ultracold polar\nmolecules abd walk the reader through the papers appearing in this topical\nissue.", "category": "physics_atom-ph" }, { "text": "Velocity distribution measurements in atomic beams generated using laser\n induced back-ablation: We present measurements of the velocity distribution of calcium atoms in an\natomic beam generated using a dual-stage laser back-ablation apparatus.\nDistributions are measured using a velocity selective Doppler time-of-flight\ntechnique. They are Boltzmann-like with rms velocities corresponding to\ntemperatures above the melting point for calcium. Contrary to a recent report\nin the literature, this method does not generate a sub-thermal atomic beam.", "category": "physics_atom-ph" }, { "text": "Anamalous Frequency Shift in Photoassociation of a Bose-Einstein\n Condensate: We theoretically investigate the effect of anomalous quantum correlations on\nthe light-induced frequency shift in the photoassociation spectrum of a\nBose-Einstein condensate (BEC). Anomalous quantum correlations arise because,\nalthough formed from a pair of zero-momentum condensate atoms, a condensate\nmolecule need not dissociate back to the BEC, but may just as well form a\nnoncondensate atom pair with equal and opposite momentum, i.e., due to rogue\nphotodissociation. The uncorrelated frequency shift of the photoassociation\nspectrum is to the red and linearly dependent on the laser intensity. In\ncontrast, anomalous correlations due to rogue dissociation lead to a\nblueshifted photoassociation spectrum. For sufficiently low light intensities,\nthe rogue blueshift is dominant and proportional to the squareroot of\nintensity.", "category": "physics_atom-ph" }, { "text": "Quantum Three-Body Problem: An improved hyperspherical harmonic method for the quantum three-body problem\nis presented to separate three rotational degrees of freedom completely from\nthe internal ones. In this method, the Schr\\\"{o}dinger equation of three-body\nproblem is reduced to a system of linear algebraic equations in terms of the\northogonal bases of functions. As an important example in quantum mechanics,\nthe energies and the eigenfunctions of some states of the helium atom and the\nhelium-like ions are calculated.", "category": "physics_atom-ph" }, { "text": "High-Gain Harmonic Generation with temporally overlapping seed pulses\n and application to ultrafast spectroscopy: Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG)\nprocess in a free-electron laser (FEL) is a promising approach to facilitate\nvarious coherent nonlinear spectroscopy schemes in the extreme ultraviolet\n(XUV) spectral range. However, in collinear arrangements using a single\nnonlinear medium, temporally overlapping seed pulses may introduce nonlinear\nmixing signals that compromise the experiment at short time delays. Here, we\ninvestigate these effects in detail by extending the analysis described in a\nrecent publication (Wituschek et al., Nat. Commun., 11, 883, 2020). High-order\nfringe-resolved autocorrelation and wave-packet interferometry experiments at\nphoton energies > $23\\,$eV are performed, accompanied by numerical simulations.\nIt turns out that both the autocorrelation and the wave-packet interferometry\ndata are very sensitive to saturation effects and can thus be used to\ncharacterize saturation in the HGHG process. Our results further imply that\ntime-resolved spectroscopy experiments are feasible even for time delays\nsmaller than the seed pulse duration.", "category": "physics_atom-ph" }, { "text": "Spin polarized electron-positron pair production via elliptical\n polarized laser fields: We study nonperturbative multiphoton electron-positron pair creation in\nultrastrong electromagnetic fields formed by two counterpropagating pulses with\nelliptic polarization. Our numerical approach allows us to take into account\nthe temporal as well as the spatial variation of the standing electromagnetic\nfield. The spin and momentum resolved pair creation probabilities feature\ncharacteristic Rabi oscillations and resonance spectra. Therefore, each laser\nfrequency features a specific momentum distribution of the created particles.\nWe find that, depending on the relative polarization of both pulses, the\ncreated electrons may be spin polarized along the direction of field\npropagation.", "category": "physics_atom-ph" }, { "text": "Single attosecond pulse from terahertz-assisted high-order harmonic\n generation: High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas\nin the presence of a strong terahertz (THz) field is investigated numerically\nwith propagation effects taken into account. Our calculations show that the\ncombination of THz fields with up to 12 fs laser pulses can be an effective\ngating technique to generate single attosecond pulses. We show that in the\npresence of the strong THz field only a single attosecond burst can be phase\nmatched, whereas radiation emitted during other half-cycles disappears during\npropagation. The cutoff is extended and a wide supercontinuum appears in the\nnear-field spectra, extending the available spectral width for isolated\nattosecond pulse generation from 23 to 93 eV. We demonstrate that phase\nmatching effects are responsible for the generation of isolated attosecond\npulses, even in conditions when single atom response yields an attosecond pulse\ntrain.", "category": "physics_atom-ph" }, { "text": "Isotropic Light vs Six-Beam Molasses for Doppler Cooling of Atoms From\n Background Vapor - Theoretical Comparison: We present a 3D theoretical comparison between the radiation-pressure forces\nexerted on an atom in an isotropic light cooling scheme and in a six-beam\nmolasses. We demonstrate that, in the case of a background vapor where all the\nspace directions of the atomic motion have to be considered, the mean cooling\nrate is equal in both configurations. Nevertheless, we also point out what\nmainly differentiates the two cooling techniques: the force component\northogonal to the atomic motion. If this transverse force is always null in the\nisotropic light case, it can exceed the radiation-pressure-force longitudinal\ncomponent in the six-beam molasses configuration for high atomic velocities,\nhence reducing the velocity capture range.", "category": "physics_atom-ph" }, { "text": "Theoretical study on the hyperfine interaction constants and the isotope\n shift factors for the $3s^2~^1 S_{ 0} ~-~ 3s3p~^{3,1}P^o_1$ transitions in\n Al$^+$: We calculated the magnetic dipole and the electric quadrupole hyperfine\ninteraction constants of 3s3p $^{3,1}P^o_1$ states and the isotope shift,\nincluding mass and field shift, factors for transitions from these two states\nto the ground state 3s$^2~^1S_0$ in Al$^+$ ions using the multiconfiguration\nDirac-Hartree-Fock method. The effects of the electron correlations and the\nBreit interaction on these physical quantities were investigated in detail\nbased on the active space approach. It is found that the CC and the\nhigher-order correlations are considerable for evaluating the uncertainties of\nthe atomic parameters concerned. The uncertainties of the hyperfine interaction\nconstants in this work are less than 1.5\\%. Although the isotope shift factors\nare highly sensitive to the electron correlations, reasonable uncertainties\nwere obtained by exploring the effects of the electron correlations. Moreover,\nwe found that the relativistic nuclear recoil corrections to the mass shift\nfactors are very small and insensitive to the electron correlations for\nAl$^{+}$. These atomic parameters present in this work are valuable for\nextracting the nuclear electric quadrupole moments and the mean-square charge\nradii of Al isotopes.", "category": "physics_atom-ph" }, { "text": "Scattering length of the ground state Mg+Mg collision: We have constructed the X 1SIGMAg+ potential for the collision between two\nground state Mg atoms and analyzed the effect of uncertainties in the shape of\nthe potential on scattering properties at ultra-cold temperatures. This\npotential reproduces the experimental term values to 0.2 inverse cm and has a\nscattering length of +1.4(5) nm where the error is prodominantly due to the\nuncertainty in the dissociation energy and the C6 dispersion coefficient. A\npositive sign of the scattering length suggests that a Bose-Einstein condensate\nof ground state Mg atoms is stable.", "category": "physics_atom-ph" }, { "text": "Superradiance as single scattering embedded in an effective medium: We present an optical picture of linear-optics superradiance, based on a\nsingle scattering event embedded in a dispersive effective medium composed by\nthe other atoms. This linear-dispersion theory is valid at low density and in\nthe single-scattering regime, i.e., when the exciting field is largely detuned.\nThe comparison with the coupled-dipole model shows a perfect agreement for the\nsuperradiant decay rate. Then we use two advantages of this approach. First we\nmake a direct comparison with experimental data, without any free parameter,\nand show a good quantitative agreement. Second, we address the problem of\nmoving atoms, which can be efficiently simulated by adding the Doppler\nbroadening to the theory. In particular, we discuss how to recover\nsuperradiance at high temperature.", "category": "physics_atom-ph" }, { "text": "Bound-state QED solutions of the photons off-shell propagating behavior\n in atoms: We use the S-matrix formalism of bound-state QED to study the photon-atom\nscattering. We find that the internal lines in Feynman diagrams which\ndescribing the propagation of off-shell bound electrons provide the off-shell\namplitudes of photons' propagation in atoms phenomenally. Our work set up the\nconnection between the property of Feynman propagators in bound-state QED and\nthe superluminal but casual propagating behavior of light in atomic media. We\nalso studied the relation between the bound-state QED and the widely used\nlight-atom interacting model in quantum optics, and give the experimental\ncondition where only the bound-state QED is valid.", "category": "physics_atom-ph" }, { "text": "Transient absorption and reshaping of ultrafast XUV light by\n laser-dressed helium: We present a theoretical study of transient absorption and reshaping of\nextreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately\nstrong infrared (IR) laser field. We formulate the atomic response using both\nthe frequency-dependent absorption cross section and a time-frequency approach\nbased on the time-dependent dipole induced by the light fields. The latter\napproach can be used in cases when an ultrafast dressing pulse induces\ntransient effects, and/or when the atom exchanges energy with multiple\nfrequency components of the XUV field. We first characterize the dressed atom\nresponse by calculating the frequency-dependent absorption cross section for\nXUV energies between 20 and 24 eV for several dressing wavelengths between 400\nand 2000 nm and intensities up to 10^12 W/cm^2. We find that for dressing\nwavelengths near 1600 nm, there is an Autler-Townes splitting of the 1s ---> 2p\ntransition that can potentially lead to transparency for absorption of XUV\nlight tuned to this transition. We study the effect of this XUV transparency in\na macroscopic helium gas by incorporating the time-frequency approach into a\nsolution of the coupled Maxwell-Schr\\\"odinger equations. We find rich temporal\nreshaping dynamics when a 61 fs XUV pulse resonant with the 1s ---> 2p\ntransition propagates through a helium gas dressed by an 11 fs, 1600 nm laser\npulse.", "category": "physics_atom-ph" }, { "text": "Strongly resonant RABBITT on lithium: The process of reconstruction of attosecond beating by interference of\ntwo-photon transitions (RABBITT) can become resonant with a discrete atomic\nlevel either in the intermediate or the final continuous states. Experimental\nobservations of the former [Phys. Rev. Lett. 104, 103003 (2010)] or latter\n[Nat. Commun. 7, 10566 (2016)] cases revealed modification of only those parts\nof the photoelectron spectrum that overlapped directly with the resonance. In\nthe lithium atom and other members of the alkali metal family, the valence\nshell $ns\\to np$ transition to the intermediate RABBITT state affects the whole\nphotoelectron spectrum in the final state. The strong additional resonant\nchannel modifies entirely the ionization dynamics and opens direct access to\nthe resonant phase of the two-photon transitions which is common for various\nsingle and multiple electron ionization processes. Elucidation of this phase\nhas wider implications for strongly resonant laser-matter interaction.", "category": "physics_atom-ph" }, { "text": "Magnetic trapping of silver and copper, and anomolous spin relaxation in\n the Ag-He system: We have trapped large numbers of copper and silver atoms using buffer gas\ncooling. Up to 3x10^12 copper atoms and 4x10^13 silver atoms are trapped.\nLifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios\nof elastic to inelastic collision rates with He are >~ 10^6, suggesting copper\nand silver are favorable for use in ultracold applications. The temperature\ndependence of the silver-helium-3 collision rate varies as T^5.8. We find that\nthis temperature dependence is inconsistent with the behavior predicted for\nrelaxation arising from the spin-rotation interaction, and conclude that the\nsilver-helium-3 system displays anomalous collisional behavior in the\nmultiple-partial wave regime. Lifetimes of laser ablated gold in helium-3\nbuffer gas are too short to permit trapping.", "category": "physics_atom-ph" }, { "text": "Measurement of the Dynamical Structure Factor of a 1D Interacting Fermi\n Gas: We present measurements of the dynamical structure factor $S(q,\\omega)$ of an\ninteracting one-dimensional (1D) Fermi gas for small excitation energies. We\nuse the two lowest hyperfine levels of the $^6$Li atom to form a\npseudo-spin-1/2 system whose s-wave interactions are tunable via a Feshbach\nresonance. The atoms are confined to 1D by a two-dimensional optical lattice.\nBragg spectroscopy is used to measure a response of the gas to density\n(\"charge\") mode excitations at a momentum $q$ and frequency $\\omega$. The\nspectrum is obtained by varying $\\omega$, while the angle between two laser\nbeams determines $q$, which is fixed to be less than the Fermi momentum\n$k_\\textrm{F}$. The measurements agree well with Tomonaga-Luttinger theory.", "category": "physics_atom-ph" }, { "text": "Probing an excited-state atomic transition using hyperfine quantum beat\n spectroscopy: We describe a method to observe the dynamics of an excited-state transition\nin a room temperature atomic vapor using hyperfine quantum beats. Our\nexperiment using cesium atoms consists of a pulsed excitation of the D2\ntransition, and continuous-wave driving of an excited-state transition from the\n6P$_{3/2}$ state to the 7S$_{1/2}$ state. We observe quantum beats in the\nfluorescence from the 6P$_{3/2}$ state which are modified by the driving of the\nexcited-state transition. The Fourier spectrum of the beat signal yields\nevidence of Autler-Townes splitting of the 6P$_{3/2}$, F = 5 hyperfine level\nand Rabi oscillations on the excited-state transition. A detailed model\nprovides qualitative agreement with the data, giving insight to the physical\nprocesses involved.", "category": "physics_atom-ph" }, { "text": "Ergodicity breaking in rapidly rotating C60 fullerenes: Ergodicity, the central tenet of statistical mechanics, requires that an\nisolated system will explore all of its available phase space permitted by\nenergetic and symmetry constraints. Mechanisms for violating ergodicity are of\ngreat interest for probing non-equilibrium matter and for protecting quantum\ncoherence in complex systems. For decades, polyatomic molecules have served as\nan intriguing and challenging platform for probing ergodicity breaking in\nvibrational energy transport, particularly in the context of controlling\nchemical reactions. Here, we report the observation of rotational ergodicity\nbreaking in an unprecedentedly large and symmetric molecule, 12C60. This is\nfacilitated by the first ever observation of icosahedral ro-vibrational fine\nstructure in any physical system, first predicted for 12C60 in 1986. The\nergodicity breaking exhibits several surprising features: first, there are\nmultiple transitions between ergodic and non-ergodic regimes as the total\nangular momentum is increased, and second, they occur well below the\ntraditional vibrational ergodicity threshold. These peculiar dynamics result\nfrom the molecules' unique combination of symmetry, size, and rigidity,\nhighlighting the potential of fullerenes to uncover emergent phenomena in\nmesoscopic quantum systems.", "category": "physics_atom-ph" }, { "text": "Microwave spectroscopy of radio-frequency dressed $^{87}$Rb: We study the hyperfine spectrum of atoms of $^{87}$Rb dressed by a\nradio-frequency field, and present experimental results in three different\nsituations: freely falling atoms, atoms trapped in an optical dipole trap and\natoms in an adiabatic radio-frequency dressed shell trap. In all cases, we\nobserve several resonant side bands spaced (in frequency) at intervals equal to\nthe dressing frequency, corresponding to transitions enabled by the dressing\nfield. We theoretically explain the main features of the microwave spectrum,\nusing a semi-classical model in the low field limit and the Rotating Wave\nApproximation for alkali-like species in general and $^{87}$Rb atoms in\nparticular. As a proof of concept, we demonstrate how the spectral signal of a\ndressed atomic ensemble enables an accurate determination of the dressing\nconfiguration and the probing microwave field.", "category": "physics_atom-ph" }, { "text": "EUV and Visible Spectroscopy of Promethiumlike Heavy Ions: We present extreme ultraviolet and visible spectra of promethiumlike tungsten\nand gold obtained with an electron beam ion trap (EBIT). Although the\ncontributions from a few charge states are involved in the spectra, the charge\nstate of the ion assigned to the observed lines is definitely identified by the\ntime-of-flight analysis of the ions performed at the same time with the\nspectroscopic measurements. Experimental results are compared with\ncollisional-radiative model calculations as well as previous experimental and\ntheoretical studies.", "category": "physics_atom-ph" }, { "text": "Subfemtosecond glory hologrammetry for vectorial optical waveform\n reconstruction: In this paper, we propose a new method to characterize the temporal structure\nof arbitrary optical laser pulses with low pulse energies. This approach is\nbased on strong field photoelectron holography with the glory rescattering\neffect as the underlying mechanism in the near-forward direction. Utilizing the\nsubfemtosecond glory rescattering process as a fast temporal gate to sample the\nunknown light pulse, the time-dependent vectorial electric field can be\nretrieved from the streaking photoelectron momentum spectra. Our method avoids\nthe challenging task of generation or manipulation of attosecond pulses and\nsignifies important progress in arbitrary optical waveform characterization.", "category": "physics_atom-ph" }, { "text": "Millimeter Wave Detection via Autler-Townes Splitting in Rubidium\n Rydberg Atoms: In this paper we demonstrate the detection of millimeter waves via\nAutler-Townes splitting in 85Rb Rydberg atoms. This method may provide an\nindependent, atom-based, SI-traceable method for measuring mm-wave electric\nfields, which addresses a gap in current calibration techniques in the mm-wave\nregime. The electric- field amplitude within a rubidium vapor cell in the WR-10\nwaveguide band is measured for frequencies of 93 GHz, and 104 GHz. Relevant\naspects of Autler-Townes splitting originating from a four-level\nelectromagnetically induced transparency scheme are discussed. We measure the\nE-field generated by an open-ended waveguide using this technique. Experimental\nresults are compared to a full-wave finite element simulation.", "category": "physics_atom-ph" }, { "text": "All-Optical Vector Atomic Magnetometer: We demonstrate an all-optical magnetometer capable of measuring the magnitude\nand direction of a magnetic field using nonlinear magneto-optical rotation in a\ncesium vapor. Vector capability is added by effective modulation of the field\nalong orthogonal axes and subsequent demodulation of the magnetic-resonance\nfrequency. This modulation is provided by the AC Stark shift induced by\ncircularly polarized laser beams. The sensor exhibits a demonstrated rms noise\nfloor of 50 fT/Hz^(1/2) in measurement of the field magnitude and 0.5\nmrad/Hz^(1/2) in the field direction; elimination of technical noise would\nimprove these sensitivities to 12 fT/Hz^(1/2) and 5 microrad/Hz^(1/2),\nrespectively. Applications for a precise all-optical vector magnetometer would\ninclude magnetically sensitive fundamental physics experiments, such as the\nsearch for a permanent electric dipole moment of the neutron.", "category": "physics_atom-ph" }, { "text": "Low power consumption grating magneto-optical trap based on planar\n elements: The grating-based magneto-optical trap (GMOT) is a promising approach for\nminiaturizing cold-atom systems. However, the power consumption of a GMOT\nsystem dominates its feasibility in practical applications. In this study, we\ndemonstrated a GMOT system based on planar elements that can operate with low\npower consumption. A high-diffraction-efficiency grating chip was used to cool\natoms with a single incident beam. A planar coil chip was designed and\nfabricated with a low power consumption nested architecture. The grating and\ncoil chips were adapted to a passive pump vacuum chamber, and up to 106 87Rb\natoms were trapped. These elements effectively reduce the power consumption of\nthe GMOT and have great potential for applications in practical cold-atom-based\ndevices.", "category": "physics_atom-ph" }, { "text": "Characterizing Earth gravity field fluctuations with the MIGA antenna\n for future Gravitational Wave detectors: Fluctuations of the earth's gravity field are a major noise source for\nground-based experiments investigating general relativity phenomena such as\nGravitational Waves (GWs). Mass density variations caused by local seismic or\natmospheric perturbations determine spurious differential displacements of the\nfree falling test masses, what is called Gravity Gradient Noise (GGN); it\nmimics GW effects. This GGN is expected to become dominant in the infrasound\ndomain and must be tackled for the future realization of observatories\nexploring GWs at low frequency. GGN will be studied with the MIGA experiment, a\ndemonstrator for low frequency GW detection based on atom interferometry - now\nin construction at the low noise underground laboratory LSBB in France. MIGA\nwill provide precise measurements of local gravity, probed by a network of\nthree free-falling atom test masses separated up to 150~m. We model the effect\nof GGN for MIGA and use seismic and atmospheric data recorded at LSBB to\ncharacterize their impact on the future measurements. We show that the antenna\nwill be able to characterize GGN using dedicated data analysis methods.", "category": "physics_atom-ph" }, { "text": "An experimental and theoretical guide to strongly interacting Rydberg\n gases: We review experimental and theoretical tools to excite, study and understand\nstrongly interacting Rydberg gases. The focus lies on the excitation of dense\nultracold atomic samples close to, or within quantum degeneracy, to high lying\nRydberg states. The major part is dedicated to highly excited S-states of\nRubidium, which feature an isotropic van-der-Waals potential. Nevertheless, the\nsetup and the methods presented are also applicable to other atomic species\nused in the field of laser cooling and atom trapping.", "category": "physics_atom-ph" }, { "text": "QED radiative corrections to the $^2$P$_{1/2}$-$^2$P$_{3/2}$\n fine-structure in fluorinelike ions: Ab initio calculations of QED radiative corrections to the $^2P_{1/2}$ -\n$^2P_{3/2}$ fine-structure transition energy are performed for selected F-like\nions. These calculations are nonperturbative in $\\alpha Z$ and include all\nfirst-order and many-electron second-order effects in $\\alpha$. When compared\nto approximate QED computations, a notable discrepancy is found especially for\nF-like uranium for which the predicted self-energy contributions even differ in\nsign. Moreover, all deviations between theory and experiment for the\n$^2P_{1/2}$ - $^2P_{3/2}$ fine-structure energies of F-like ions, reported\nrecently by Li et al., Phys. Rev. A 98, 020502(R) (2018), are resolved if their\nhighly accurate, non-QED fine-structure values are combined with the QED\ncorrections ab initially evaluated here.", "category": "physics_atom-ph" }, { "text": "Few-body physics of ultracold atoms and molecules with long-range\n interactions: The quantum mechanical few-body problem at ultracold energies poses severe\nchallenges to theoretical techniques, particularly when long-range interactions\nare present that decay only as a power-law potential. In this paper we review\nthe techniques and progress in studies of universal few-body physics for\nultracold atoms, particularly those related to long-range interactions.", "category": "physics_atom-ph" }, { "text": "Soft x-rays induce femtosecond solid-to-solid phase transition: Soft x-rays were applied to induce graphitization of diamond through a\nnon-thermal solid-to-solid phase transition. This process was observed within\npoly-crystalline diamond with a time-resolved experiment using ultrashort soft\nx-ray pulses of duration 52.5 fs and cross correlated by an optical pulse of\nduration 32.8 fs. This scheme enabled for the first time the measurement of a\nphase transition on a timescale of ~150 fs. Excellent agreement between\nexperiment and theoretical predictions was found, using a dedicated code that\nfollowed the non-equilibrium evolution of the irradiated diamond including all\ntransient electronic and structural changes. These observations confirm that\nsoft x-rays can induce a non-thermal ultrafast solid-to-solid phase transition\non a hundred femtosecond timescale.", "category": "physics_atom-ph" }, { "text": "Autonomous frequency stabilization of two extended cavity diode lasers\n at the potassium wavelength on a sounding rocket: We have developed, assembled, and flight-proven a stable, compact, and\nautonomous extended cavity diode laser (ECDL) system designed for atomic\nphysics experiments in space. To that end, two micro-integrated ECDLs at 766.7\nnm were frequency stabilized during a sounding rocket flight by means of\nfrequency modulation spectroscopy (FMS) of 39^K and offset locking techniques\nbased on the beat note of the two ECDLs. The frequency stabilization as well as\nadditional hard- and software to test hot redundancy mechanisms were\nimplemented as part of a state-machine, which controlled the experiment\ncompletely autonomously throughout the entire flight mission.", "category": "physics_atom-ph" }, { "text": "Rotationally cold OH$^-$ ions in the cryogenic electrostatic ion-beam\n storage ring DESIREE: We apply near-threshold laser photodetachment to characterize the rotational\nquantum level distribution of OH$^-$ ions stored in the cryogenic ion-beam\nstorage ring, DESIREE, at Stockholm University. We find that the stored ions\nrelax to a rotational temperature of 13.4$\\pm$0.2 K with 94.9$\\pm$0.3 % of the\nions in the rotational ground state. This is consistent with the storage ring\ntemperature of 13.5$\\pm$0.5 K as measured with eight silicon diodes, but in\ncontrast to all earlier studies in cryogenic traps and rings where the\nrotational temperatures were always much higher than those of the storage\ndevices at their lowest temperatures. Furthermore, we actively modify the\nrotational distribution through selective photodetachment to produce an OH$^-$\nbeam where 99.1$\\pm$0.1 % of approximately one million stored ions are in the\n$J$=0 rotational ground state.", "category": "physics_atom-ph" }, { "text": "Quantum noise thermometry for bosonic Josephson junctions in the mean\n field regime: Bosonic Josephson junctions can be realized by confining ultracold gases of\nbosons in multi-well traps, and studied theoretically with the $M$-site\nBose-Hubbard model. We show that canonical equilibrium states of the $M$-site\nBose-Hubbard model may be approximated by mixtures of coherent states, provided\nthe number of atoms is large and the total energy is comparable to $k_BT$.\nUsing this approximation, we study thermal fluctuations in bosonic Josephson\njunctions in the mean field regime. Statistical estimates of the fluctuations\nof relative phase and number, obtained by averaging over many replicates of an\nexperiment, can be used to estimate the temperature and the tunneling\nparameter, or to test whether the experimental procedure is effectively\nsampling from a canonical thermal equilibrium ensemble.", "category": "physics_atom-ph" }, { "text": "High-Accuracy Determination of Paul-Trap Stability Parameters for\n Electric-Quadrupole-Shift Prediction: The motion of an ion in a radiofrequency (rf) Paul trap is described by the\nMathieu equation and the associated stability parameters that are proportional\nto the rf and dc electric field gradients. Here, a higher-order, iterative\nmethod to accurately solve the stability parameters from measured secular\nfrequencies is presented. It is then used to characterize an endcap trap by\nshowing that the trap's radial asymmetry is dominated by the dc field gradients\nand by measuring the relation between the applied voltages and the gradients.\nThe results are shown to be in good agreement with an electrostatic\nfinite-element-method simulation of the trap. Furthermore, a method to\ndetermine the direction of the radial trap axes using a 'tickler' voltage is\npresented and the temperature dependence of the rf voltage is discussed. As an\napplication for optical ion clocks, the method is used to predict and minimize\nthe electric quadrupole shift (EQS) using the applied dc voltages. Finally, a\nlower limit of 1070 for the cancellation factor of the Zeeman-averaging EQS\ncancellation method is determined in an interleaved low/high EQS clock\nmeasurement. This reduces the EQS uncertainty of our $^{88}$Sr$^+$ optical\nclock to ${\\lesssim} 1\\times 10^{-19}$ in fractional frequency units.", "category": "physics_atom-ph" }, { "text": "Systematic Shifts for Ytterbium-ion Optical Frequency Standards: The projected systematic uncertainties of single trapped Ytterbium-ion\noptical frequency standards are estimated for the quadrupole and octupole\ntransitions which are at wavelengths 435.5 nm and 467 nm, respectively. Finite\ntemperature of the ion and its interaction with the external fields introduce\ndrift in the measured frequency compared to its absolute value. Frequency\nshifts due to electric quadrupole moment, induced polarization and excess\nmicromotion of the ion depend on electric fields, which are estimated in this\narticle. Geometry of the trap electrodes also result in unwanted electric\nfields which have been considered in our calculation. Magnetic field induced\nshift and Stark shifts due to electro-magnetic radiation at a surrounding\ntemperature are also estimated. At CSIR-NPL, we are developing a frequency\nstandard based on the octupole transition for which the systematic\nuncertainties are an order of magnitude smaller than that using the quadrupole\ntransition, as described here.", "category": "physics_atom-ph" }, { "text": "Implementation of gauge-invariant time-dependent configuration\n interaction singles method for three-dimensional atoms: We present a numerical implementation of the gauge-invariant time-dependent\nconfiguration interaction singles (TDCIS) method [Appl. Sci. 8, 433 (2018)] for\nthree-dimensional atoms. In our implementation, orbital-like quantity called\nchannel orbital [Phys. Rev. A 74, 043420 (2006)] is propagated instead of\nconfiguration-interaction (CI) coefficients, which removes a computational\nbottleneck of explicitly calculating and storing numerous virtual orbitals.\nFurthermore, besides its physical consistency, the gauge-invariant formulation\nallows to take advantages of the velocity gauge treatment of the laser-electron\ninteraction over the length gauge one in the simulation of high-field\nphenomena. We apply the present implementation to high-harmonic generation from\nhelium and neon atoms, and numerically confirms the gauge invariance and\ndemonstrates the effectiveness of the rotated velocity gauge treatment.", "category": "physics_atom-ph" }, { "text": "Energy levels, radiative rates and lifetimes for transitions in Br-like\n ions with 38 $\\le$ Z $\\le$ 42: Energy levels and radiative rates for transitions in five Br-like ions (Sr\nIV, Y V, Zr VI, Nb VII and Mo VIII) are calculated with the general-purpose\nrelativistic atomic structure package ({\\sc grasp}). Extensive configuration\ninteraction has been included and results are presented among the lowest 31\nlevels of the 4s$^2$4p$^5$, 4s$^2$4p$^4$4d and 4s4p$^6$ configurations.\nLifetimes for these levels have also been determined, although unfortunately no\nmeasurements are available with which to compare. However, recently theoretical\nresults have been reported by Singh {\\em et al} [Phys. Scr. {\\bf 88} (2013)\n035301] using the same {\\sc grasp} code. But their reported data for radiative\nrates and lifetimes cannot be reproduced and show discrepancies of up to five\norders of magnitude with the present calculations.", "category": "physics_atom-ph" }, { "text": "Comparing many-body approaches against the helium atom exact solution: Over time, many different theories and approaches have been developed to\ntackle the many-body problem in quantum chemistry, condensed-matter physics,\nand nuclear physics. Here we use the helium atom, a real system rather than a\nmodel, and we use the exact solution of its Schr\\\"odinger equation as a\nbenchmark for comparison between methods. We present new results beyond the\nrandom-phase approximation (RPA) from a renormalized RPA (r-RPA) in the\nframework of the self-consistent RPA (SCRPA) originally developed in nuclear\nphysics, and compare them with various other approaches like configuration\ninteraction (CI), quantum Monte Carlo (QMC), time-dependent density-functional\ntheory (TDDFT), and the Bethe-Salpeter equation on top of the GW approximation.\nMost of the calculations are consistently done on the same footing, e.g. using\nthe same basis set, in an effort for a most faithful comparison between\nmethods.", "category": "physics_atom-ph" }, { "text": "Spin conservation in high-order-harmonic generation using bicircular\n fields: We present an alternative theoretical model for a recent experiment\n[A.Fleischer et al., Nature Photon. 8, 543 (2014)] which used bichromatic,\ncounter-rotating high intensity laser pulses to probe the conservation of spin\nangular momentum in high harmonic generation. We separate elliptical\npolarizations into independent circular fields with definite angular momentum,\ninstead of using the expectation value of spin for each photon in the\nconservation equation, and we find good agreement with the experimental\nresults. In our description the generation of each individual harmonic\nconserves spin angular momentum, in contrast to the model proposed by Fleischer\net al. Our model also correctly describes analogous processes in standard\nperturbative optics.", "category": "physics_atom-ph" }, { "text": "Precision measurement of the metastable 3P2 lifetime of neon: The lifetime of the metastable 3P2 state of neon has been determined to\n14.70(13) s (decay rate 0.06801(62) 1/s) by measuring the decay in fluorescence\nof an ensemble of Ne-20 atoms trapped in a magneto-optical trap (MOT). Due to\nlow background gas pressure p < 5 10^-11 mbar and low relative excitation to\nthe 3D3 state (0.5% excitation probability) operation only small corrections\nhave to be included in the lifetime extrapolation. Together with a careful\nanalysis of residual loss mechanisms in the MOT a lifetime determination to\nhigh precision is achieved.", "category": "physics_atom-ph" }, { "text": "Rubidium atom spectral lineshapes in high intensity electric fields near\n an optical nanofibre: The integration of cold atomic systems with optical nanofibres is an\nincreasingly important experimental platform. Here, we report on the spectra\nobserved during a strongly driven, single-frequency, two-photon excitation of\ncold rubidium atoms near an optical nanofibre. At resonance, two competitive\nprocesses, namely a higher excitation rate and stronger pushing of atoms from\nthe nanofibre due to resonance scattering, need to be considered. We discuss\nthe processes that lead to the observed two-peak profile in the fluorescence\nspectrum as the excitation laser is scanned across the resonance, noting that\nthe presence of the optical nanofibre dramatically changes the fluorescence\nsignal. These observations are useful for experiments where high electric field\nintensities near an ONF are needed, for example when driving nonlinear\nprocesses.", "category": "physics_atom-ph" }, { "text": "Coherent excitation of the highly forbidden electric octupole transition\n in ${}^{172}$Yb$^+$: We report on the first coherent excitation of the highly forbidden\n$^2S_{1/2}\\rightarrow{}^2F_{7/2}$ electric octupole (E3) transition in a single\ntrapped ${}^{172}$Yb$^+$ ion, an isotope without nuclear spin. Using the\ntransition in ${}^{171}$Yb$^+$ as a reference, we determine the transition\nfrequency to be $642\\,116\\,784\\,950\\,887.6(2.4)\\,$Hz. We map out the magnetic\nfield environment using the forbidden $^2S_{1/2} \\rightarrow{}^2D_{5/2}$\nelectric quadrupole (E2) transition and determine its frequency to be\n$729\\,476\\,867\\,027\\,206.8(4.4)\\,$Hz. Our results are a factor of $1\\times10^5$\n($3\\times10^{5}$) more accurate for the E2 (E3) transition compared to previous\nmeasurements. The results open up the way to search for new physics via precise\nisotope shift measurements and improved tests of local Lorentz invariance using\nthe metastable $^2F_{7/2}$ state of Yb$^+$.", "category": "physics_atom-ph" }, { "text": "Auger Spectra and Different Ionic Charges Following 3s, 3p and 3d\n Sub-Shells Photoionization of Kr Atoms: The decay of inner-shell vacancy in an atom through radiative and\nnon-radiative transitions leads to final charged ions. The de-excitation decay\nof 3s, 3p and 3d vacancies in Kr atoms are calculated using Monte-Carlo\nsimulation method. The vacancy cascade pathway resulted from the de-excitation\ndecay of deep core hole in 3s subshell in Kr atoms is discussed. The generation\nof spectator vacancies during the vacancy cascade development gives rise to\nAuger satellite spectra. The last transitions of the de-excitation decay of 3s,\n3p and 3d holes lead to specific charged ions. Dirac-Fock-Slater wave functions\nare adapted to calculate radiative and non-radiative transition probabilities.\nThe intensity of Kr^{4+} ions are high for 3s hole state, whereas Kr^{3+} and\nKr^{2+} ions have highest intensities for 3p and 3d hole states, respectively.\nThe present results of ion charge state distributions agree well with the\nexperimental data.", "category": "physics_atom-ph" }, { "text": "A method for accurate electron-atom resonances: The complex-scaled\n multiconfigurational spin-tensor electron propagator method for the $^2P\\,\n \\mbox{Be}^{-}$ shape resonance problem: We propose and develop the complex scaled multiconfigurational spin-tensor\nelectron propagator (CMCSTEP) technique for theoretical determination of\nresonance parameters with electron-atom/molecule systems including open-shell\nand highly correlated atoms and molecules. The multiconfigurational spin-tensor\nelectron propagator method (MCSTEP) developed and implemented by Yeager his\ncoworkers in real space gives very accurate and reliable ionization potentials\nand attachment energies. The CMCSTEP method uses a complex scaled\nmulticonfigurational self-consistent field (CMCSCF) state as an initial state\nalong with a dilated Hamiltonian where all of the electronic coordinates are\nscaled by a complex factor. CMCSCF was developed and applied successfully to\nresonance problems earlier. We apply the CMCSTEP method to get $^2\nP\\,\\mbox{Be}^{-}$ shape resonance parameters using $14s11p5d$, $14s14p2d$, and\n$14s14p5d$ basis sets with a $2s2p3d$\\,CAS. The obtained value of the resonance\nparameters are compared to previous results. This is the first time CMCSTEP has\nbeen developed and used for a resonance problem. It will be among the most\naccurate and reliable techniques. Vertical ionization potentials and attachment\nenergies in real space are typically within $\\pm 0.2\\,eV$ or better of\nexcellent experiments and full configuration interaction calculations with a\ngood basis set. We expect the same sort of agreement in complex space.", "category": "physics_atom-ph" }, { "text": "Building one molecule from a reservoir of two atoms: Chemical reactions typically proceed via stochastic encounters between\nreactants. Going beyond this paradigm, we combine exactly two atoms into a\nsingle, controlled reaction. The experimental apparatus traps two individual\nlaser-cooled atoms (one sodium and one cesium) in separate optical tweezers and\nthen merges them into one optical dipole trap. Subsequently, photoassociation\nforms an excited-state NaCs molecule. The discovery of previously unseen\nresonances near the molecular dissociation threshold and measurement of\ncollision rates are enabled by the tightly trapped ultracold sample of atoms.\nAs laser-cooling and trapping capabilities are extended to more elements, the\ntechnique will enable the study of more diverse, and eventually more complex,\nmolecules in an isolated environment, as well as synthesis of designer\nmolecules for qubits.", "category": "physics_atom-ph" }, { "text": "Establishing the Presence of Coherence in Atomic Fermi Superfluids:\n Spin-Flip and Spin-Preserving Bragg Scattering at Finite Temperatures: We show how the difference between the finite temperature T structure\nfactors, called S_-, associated with spin and density, can be used as a\nindication of superfluidity in ultracold Fermi gases. This observation can be\nexploited in two photon Bragg scattering experiments on gases which undergo\nBCS- Bose Einstein condensation crossover. Essential to our calculations is a\nproper incorporation of spin and particle number conservation laws which lead\nto compatibility at general T with two f-sum rules. Because it is applicable to\ngeneral scattering lengths, a measurement of S- can be a useful, direct\napproach for establishing where superfluidity occurs.", "category": "physics_atom-ph" }, { "text": "Doppler-free spectroscopy on Cs D$_1$ line with a dual-frequency laser: We report on Doppler-free laser spectroscopy in a Cs vapor cell using a\ndual-frequency laser system tuned on the Cs D$_1$ line. Using\ncounter-propagating beams with crossed linear polarizations, an original\nsign-reversal of the usual saturated absorption dip and large increase in\nDoppler-free atomic absorption is observed. This phenomenon is explained by\ncoherent population trapping (CPT) effects. The impact of laser intensity and\nlight polarization on absorption profiles is reported in both single-frequency\nand dual-frequency regimes. In the latter, frequency stabilization of two diode\nlasers was performed, yielding a beat-note fractional frequency stability at\nthe level of $3 \\times 10^{-12}$ at 1 s averaging time. These performances are\nabout an order of magnitude better than those obtained using a conventional\nsingle-frequency saturated absorption scheme.", "category": "physics_atom-ph" }, { "text": "Hyperfine anomalies in Fr: boundaries of the spherical single particle\n model: We have measured the hyperfine splitting of the $7P_{1/2}$ state at the 100\nppm level in Fr isotopes ($^{206g,206m, 207, 209, 213, 221}$Fr) near the closed\nneutron shell ($N$ = 126 in $^{213}$Fr). The measurements in five isotopes and\na nuclear isomeric state of francium, combined with previous determinations of\nthe $7S_{1/2}$ splittings, reveal the spatial distribution of the nuclear\nmagnetization, i.e. the Bohr-Weisskopf effect. We compare our results with a\nsimple shell model consisting of unpaired single valence nucleons orbiting a\nspherical nucleus, and find good agreement over a range of neutron-deficient\nisotopes ($^{207-213}$Fr). Also, we find near-constant proton anomalies for\nseveral even-$ N$ isotopes. This identifies a set of Fr isotopes whose nuclear\nstructure can be understood well enough for the extraction of weak interaction\nparameters from parity non-conservation studies.", "category": "physics_atom-ph" }, { "text": "Dynamical symmetries and harmonic generation: We discuss harmonic generation in the case of laser field-dressed\nHamiltonians that are invariant under so-called dynamical symmetry operations.\nExamples for such systems are molecules which exhibit a discrete rotational\nsymmetry of order\n N (e.g. benzene with N=6) interacting with a circularly polarized laser field\nand single atoms in a bichromatic field, with the two lasers having circular\npolarizations. Within a general group theory approach we study the harmonics\none obtains from the interaction of a laser pulse and a circular molecule. When\nthe system is in a pure field-dressed state the known selection rule kN \\pm 1,\nk=1,2,3, ... results. However, other lines are observed when recombinations\nwith states of a symmetry different from the initial one become important. This\nis the case for realistic laser pulses (i.e., with a finite duration). In\nparticular when the fundamental laser frequency (or one of its multiples) is\nresonant with a transition between field-dressed states. Numerical ab initio\nsimulations, confirming our analytical calculations and illustrating the power\nof the group theory approach, are presented.", "category": "physics_atom-ph" }, { "text": "Electron Correlation Effects in Hyperfine Interactions in $^{45}$Sc and\n $^{89}$Y: The relativistic coupled-cluster theory has been employed to calculate the\nmagnetic dipole and electric quadrupole hyperfine structure constants for the\nstable isotopes $^{45}$Sc and $^{89}$Y. The role of electron correlation is\nfound to be very important. The trend exhibited by these effects is rather\ndifferent from previously studied single valence atomic systems.", "category": "physics_atom-ph" }, { "text": "Robust, High-speed, All-Optical Atomic Magnetometer: A self-oscillating magnetometer based on the nonlinear magneto-optical\nrotation effect with separate modulated pump and unmodulated probe beams is\ndemonstrated. This device possesses a bandwidth exceeding $1\\khz$. Pump and\nprobe are delivered by optical fiber, facilitating miniaturization and\nmodularization. The magnetometer has been operated both with vertical-cavity\nsurface-emitting lasers (VCSELs), which are well suited to portable\napplications, and with conventional edge-emitting diode lasers. A sensitivity\nof around $3 {\\rm nG}$ is achieved for a measurement time of $1\\s$.", "category": "physics_atom-ph" }, { "text": "Chemical reactions of ultracold alkaline-earth-metal diatomic molecules: We study the energetics of chemical reactions between ultracold ground-state\nalkaline-earth-metal diatomic molecules. We show that the atom-exchange\nreactions forming homonuclear dimers are energetically allowed for all\nheteronuclear alkaline-earth-metal combinations. We perform high-level\nelectronic structure calculations on the potential energy surfaces of all\npossible homo- and heteronuclear alkaline-earth-metal trimers and show that\ntrimer formation is also energetically possible in collisions of all considered\ndimers. Interactions between alkaline-earth-metal diatomic molecules lead to\nthe formation of deeply bound reaction complexes stabilized by large\nnon-additive interactions. We check that there are no barriers to the studied\nchemical reactions. This means that all alkaline-earth-metal diatomic molecules\nare chemically unstable at ultralow temperature, and optical lattice or\nshielding schemes may be necessary to segregate the molecules and suppress\nlosses.", "category": "physics_atom-ph" }, { "text": "Highly accurate calculations of the rotationally excited bound states in\n three-body systems: An effective optimization strategy has been developed to construct highly\naccurate bound state wave functions in various three-body systems. Our\nprocedure appears to be very effective for computations of weakly bound states\nand various excited states, including rotationally excited states, i.e. states\nwith $L \\ge 1$. The efficiency of our procedure is illustrated by computations\nof the excited $P^{*}(L = 1)-$states in the $dd\\mu, dt\\mu$ and $tt\\mu$ muonic\nmolecular ions, $P(L = 1)-$states in the non-symmetric $pd\\mu, pt\\mu$ and\n$dt\\mu$ ions and $2^{1}P(L = 1)-$ and $2^{3}P(L = 1)-$states in He atom(s).", "category": "physics_atom-ph" }, { "text": "Transverse Kinematics of Ion Stored in an Electrostatic Ion Beam Trap: We present experimental results, as well as numerical simulations, for the\ntransverse velocity distribution of ions stored in an electrostatic ion beam\ntrap. The measurements indicate that the transverse velocity spread is about 1%\nof the longitudinal velocity, and that the ions fill the whole transverse\nstable phase space. We also demonstrate that ion losses from the trap due to\nmultiple scattering with molecules from the residual gas is an important factor\nlimiting the lifetime of the beam.", "category": "physics_atom-ph" }, { "text": "Shot-noise-limited spin measurements in a pulsed molecular beam: Heavy diatomic molecules have been identified as good candidates for use in\nelectron electric dipole moment (eEDM) searches. Suitable molecular species can\nbe produced in pulsed beams, but with a total flux and/or temporal evolution\nthat varies significantly from pulse to pulse. These variations can degrade the\nexperimental sensitivity to changes in spin precession phase of an electri-\ncally polarized state, which is the observable of interest for an eEDM\nmeasurement. We present two methods for measurement of the phase that provide\nimmunity to beam temporal variations, and make it possible to reach\nshot-noise-limited sensitivity. Each method employs rapid projection of the\nspin state onto both components of an orthonormal basis. We demonstrate both\nmethods using the eEDM-sensitive H state of thorium monoxide (ThO), and use one\nof them to measure the magnetic moment of this state with increased accuracy\nrelative to previous determinations.", "category": "physics_atom-ph" }, { "text": "Modified model for electron impact double ionization cross sections of\n atoms and ions: A simple modification of the semiempirical model of Shevelko et al (J. Phys.\nB: At. Mol. Opt. Phys. 38, 525 (2005)) is proposed for the calculation of\nelectron impact double ionization cross section of He^0, Li^(0,1+), B^(1+),\nC^(1+,3+), O^(0-3+), Ar^(0-7+), Fe^(1+,3+-6+), Kr^(0-4+), Xe^(0-8+),\nPr^(1+-4+), Pb^(0-9+), Bi^(1+-3+,10+), and U^(0,10+,13+) atoms and positive\nions. The contributions from the direct double ionization of outer shell and\nindirect processes of inner shells are also considered in the proposed\nmodification. Ionic correction and relativistic factor are also incorporated.\nThe results of the simplified model are compared with the experimental,\nquantum, and other semiempirical calculations where available. It is found that\nthe proposed modification provides better performance than those obtained by\nthe existing semiempirical cross sections over the range of incident energies\nand a significant number of atomic and ionic targets considered herein for the\ndescription of experimental cross sections.", "category": "physics_atom-ph" }, { "text": "Van der Waals dephasing for Dicke subradiance in cold atomic clouds: We investigate numerically the role of near-field dipole-dipole interactions\non the late emission dynamics of large disordered cold atomic samples driven by\na weak field. Previous experimental and numerical studies of subradiance in\nmacroscopic samples have focused on low-density samples of pure two-level\natoms, without internal structure, which corresponds to a scalar representation\nof the light. The cooperative nature of the late emission of light is then\ngoverned by the resonant optical depth. Here, by considering the vectorial\nnature of the light, we show the detrimental role of the near-field terms on\ncooperativity in higher-density samples. The observed reduction in the\nsubradiant lifetimes is interpreted as a signature of the inhomogeneous\nbroadening due to the near-field contributions, in analogy with the Van der\nWaals dephasing phenomenon for superradiance.", "category": "physics_atom-ph" }, { "text": "Kinetic modelling and molecular dynamics simulation of ultracold neutral\n plasmas including ionic correlations: A kinetic approach for the evolution of ultracold neutral plasmas including\ninterionic correlations and the treatment of ionization/excitation and\nrecombination/deexcitation by rate equations is described in detail. To assess\nthe reliability of the approximations inherent in the kinetic model, we have\ndeveloped a hybrid molecular dynamics method. Comparison of the results reveals\nthat the kinetic model describes the atomic and ionic observables of the\nultracold plasma surprisingly well, confirming our earlier findings concerning\nthe role of ion-ion correlations [Phys. Rev. A {\\bf 68}, 010703]. In addition,\nthe molecular dynamics approach allows one to study the relaxation of the ionic\nplasma component towards thermodynamical equilibrium.", "category": "physics_atom-ph" }, { "text": "$g$ Factor of Lithiumlike Silicon: New Challenge to Bound-State QED: The recently established agreement between experiment and theory for the $g$\nfactors of lithiumlike silicon and calcium ions manifests the most stringent\ntest of the many-electron bound-state quantum electrodynamics (QED) effects in\nthe presence of a magnetic field. In this Letter, we present a significant\nsimultaneous improvement of both theoretical $g_\\text{th} =\n2.000\\,889\\,894\\,4\\,(34)$ and experimental $g_\\text{exp} =\n2.000\\,889\\,888\\,45\\,(14)$ values of the $g$ factor of lithiumlike silicon\n$^{28}$Si$^{11+}$. The theoretical precision now is limited by the\nmany-electron two-loop contributions of the bound-state QED. The experimental\nvalue is accurate enough to test these contributions on a few percent level.", "category": "physics_atom-ph" }, { "text": "New limit on the present temporal variation of the fine structure\n constant: The comparison of different atomic transition frequencies over time can be\nused to determine the present value of the temporal derivative of the fine\nstructure constant alpha in a model-independent way without assumptions on\nconstancy or variability of other parameters. We have measured an optical\ntransition frequency at 688 THz in ^{171}Yb+ with a cesium atomic clock at two\ntimes separated by 2.8 years and find a value for the fractional variation of\nthe frequency ratio $f_{\\rm Yb}/f_{\\rm Cs}$ of $(-1.2\\pm 4.4)\\cdot 10^{-15}$\nyr$^{-1}$, consistent with zero. Combined with recently published values for\nthe constancy of other transition frequencies this measurement sets an upper\nlimit on the present variability of alpha at the level of $2.0\\cdot 10^{-15}$\nyr$^{-1}$, corresponding so far to the most stringent limit from laboratory\nexperiments.", "category": "physics_atom-ph" }, { "text": "Fractional exclusion statistics and the Random Matrix Boson Ensemble: The k-body Gaussian Embedded Ensemble of Random Matrices is considered for N\nbosons distributed on two single-particle levels. When k = N, the ensemble is\nequivalent to the Gaussian Orthogonal Ensemble (GOE), and when k = 2 it\ncorresponds to the Two-body Random Ensemble (TBRE) for bosons. It is shown that\nthe energy spectrum leads to a rank function which is of the form of a discrete\ngeneralized beta distribution. The same distribution is obtained assuming N\nnon-interacting quasiparticles that obey the fractional exclusion statistics\nintroduced by Haldane two decades ago.", "category": "physics_atom-ph" }, { "text": "Sensitivity improvement of Rydberg atom-based microwave sensing via\n electromagnetically induced transparency: A highly excited Rydberg atom via electromagnetically induced transparency\nwith two color cascading lasers has extreme sensitivity to electric fields of\nmicrowave ranging from 100 MHz to over 1 THz. It can be used as susceptible\natom-based microwave communication antennas where the carrier wave usually\nworks exactly resonant to the transition between a pair of adjacent Rydberg\nstates with large electric dipole moment. A technique of superheterodyne with a\nstrong on-resonant local microwave oscillator is employed to induce\nconsiderable Autler-Townes splitting where the antennas has a highest dynamic\nresponse to another weak target signal microwave carrier. To further improve\nthe sensitivity of atomic antenna in communication, we detune the carrier\nmicrowave frequency off resonance forming an asymmetrically optical splitting\nand fix the coupling laser frequency at the shoulder of the stronger one, and\noptimize the local field strength simultaneously. It gives a sensitivity of\n12.50(04) $\\rm{nVcm^{-1}\\cdot Hz^{-1/2}}$. Its enhancement mechanism of\nsensitivity is also proved by a theoretical simulation.", "category": "physics_atom-ph" }, { "text": "A laser-driven target of high-density nuclear polarized hydrogen gas: We report the best figure-of-merit achieved for an internal nuclear polarized\nhydrogen gas target and a Monte Carlo simulation of spin-exchange optical\npumping. The dimensions of the apparatus were optimized using the simulation\nand the experimental results were in good agreement with the simulation. The\nbest result achieved for this target was 50.5% polarization with 58.2% degree\nof dissociation of the sample beam exiting the storage cell at a hydrogen flow\nrate of $1.1\\times 10^{18}$ atoms/s.", "category": "physics_atom-ph" }, { "text": "Collision-induced stimulated photon echo at the transition 0-1: The stimulated photon echo formed by the sequence of three laser excitation\npulses in gaseous medium on the transition with the angular momentum change 0-1\nis considered with an account of elastic depolarizing collisions. The\npolarization properties of this echo may be potentially interesting for the\npurposes of data processing. It is shown, that with the polarization of the\nfirst pulse orthogonal to that of the second and third pulses the appearance of\nthe echo signal will be entirely determined by the action of collisions. The\nexistence of this echo is determined by the difference in the alignment and the\norientation relaxation rates of the excited level.", "category": "physics_atom-ph" }, { "text": "Inversion of Strong Field Photoelectron Spectra for Molecular Orbital\n Imaging: Imaging structures at the molecular level is a fast developing\ninterdisciplinary research field that spans across the boundaries of physics\nand chemistry. High spatial resolution images of molecules can be obtained with\nphotons or ultrafast electrons. In addition, images of valence molecular\norbitals can be extracted via tomographic techniques based on the coherent XUV\nradiation emitted by a molecular gas exposed to an intense ultra-short infrared\nlaser pulse. In this paper, we demonstrate that similar information can be\nobtained by inverting energy resolved photoelectron spectra using a simplified\nanalytical model.", "category": "physics_atom-ph" }, { "text": "Must Kohn-Sham Oscillator Strengths be Accurate at Threshold?: The exact ground-state Kohn-Sham(KS) potential for the helium atom is known\nfrom accurate wavefunction calculations of the ground-state density. The\nthreshold for photoabsorption from this potential matches the physical system\nexactly. By carefully studying its absorption spectrum, we show the answer to\nthe title question is no. To address this problem in detail, we generate a\nhighly accurate simple fit of a two-electron spectrum near the threshold, and\napply the method to both the experimental spectrum and that of the exact\nground-state Kohn-Sham potential.", "category": "physics_atom-ph" }, { "text": "Multichannel Quantum Defect Theory for cold molecular collisions: Multichannel Quantum Defect Theory (MQDT) is shown to be capable of producing\nquantitatively accurate results for low-energy atom-molecule scattering\ncalculations. With a suitable choice of reference potential and short-range\nmatching distance, it is possible to define a matrix that encapsulates the\nshort-range collision dynamics and is only weakly dependent on energy and\nmagnetic field. Once this has been produced, calculations at additional\nenergies and fields can be performed at a computational cost that is\nproportional to the number of channels N and not to N^3. MQDT thus provides a\npromising method for carrying out low-energy molecular scattering calculations\non systems where full exploration of the energy- and field-dependence is\ncurrently impractical.", "category": "physics_atom-ph" }, { "text": "Chaos-induced enhancement of resonant multielectron recombination in\n highly charged ions: Statistical theory: A statistical theory of resonant multielectron recombination based on\nproperties of chaotic eigenstates is developed. The level density of many-body\nstates increases exponentially with the number of excited electrons. When the\nresidual electron-electron interaction exceeds the interval between these\nlevels, the eigenstates (called compound states or compound resonances if these\nstates are in the continuum) become \"chaotic\" superpositions of large numbers\nof Hartree-Fock configurational basis states. This situation takes place in\nsome rare-earth atoms and many open-shell multiply charged ions excited in the\nprocess of electron recombination. Our theory describes resonant multielectron\nrecombination via dielectronic doorway states leading to such compound\nresonances. The result is a radiative capture cross section averaged over a\nsmall energy interval containing several compound resonances. In many cases\nindividual resonances are not resolved experimentally (since the interval\nbetween them is small, e.g., $\\le 1$ meV, possibly even smaller than their\nradiative widths), therefore, our statistical theory should correctly describe\nthe experimental data. We perform numerical calculations of the recombination\ncross sections for tungsten ions W$^{q+}$, $q=18$--25. The recombination rate\nfor W$^{20+}$ measured recently [Phys. Rev. A {\\bf 83}, 012711 (2011)] is\n$10^3$ greater than the direct radiative recombination rate at low energies,\nand our result for W$^{20+}$ agrees with the measurements.", "category": "physics_atom-ph" }, { "text": "Coherent quantum beats: spectroscopy of energy differences masked by\n inhomogeneous broadening: Precision spectroscopy of solid-state systems is challenging due to\ninhomogeneous broadening. We describe a technique -- coherent quantum beats --\nthat enables the measurement of small frequency shifts within an\ninhomogeneously broadened distribution while addressing the full ensemble. We\nshow that the technique can be used to obtain improvements in signal size and\nspectral resolution, offering advantages for precision measurements in solids.", "category": "physics_atom-ph" }, { "text": "Measurement of hyperfine structure and the Zemach radius in $\\rm^6Li^+$\n using optical Ramsey technique: We investigate the $2\\,^3\\!S_1$--$2\\,^3\\!P_J$ ($J = 0, 1, 2$) transitions in\n$\\rm^6Li^+$ using the optical Ramsey technique and achieve the most precise\nvalues of the hyperfine splittings of the $2\\,^3\\!S_1$ and $2\\,^3\\!P_J$ states,\nwith smallest uncertainty of about 10~kHz. The present results reduce the\nuncertainties of previous experiments by a factor of 5 for the $2\\,^3\\!S_1$\nstate and a factor of 50 for the $2\\,^3\\!P_J$ states, and are in better\nagreement with theoretical values. Combining our measured hyperfine intervals\nof the $2\\,^3\\!S_1$ state with the latest quantum electrodynamic (QED)\ncalculations, the improved Zemach radius of the $\\rm^6Li$ nucleus is determined\nto be 2.44(2)~fm, with the uncertainty entirely due to the uncalculated QED\neffects of order $m\\alpha^7$. The result is in sharp disagreement with the\nvalue 3.71(16) fm determined from simple models of the nuclear charge and\nmagnetization distribution. We call for a more definitive nuclear physics value\nof the $\\rm^6Li$ Zemach radius.", "category": "physics_atom-ph" }, { "text": "Description of anomalous Zeeman patterns in stellar astrophysics: The influence of a magnetic field on the broadening of spectral lines and\ntransition arrays in complex spectra is investigated. The anomalous absorption\nor emission Zeeman pattern is a superposition of many profiles with different\nrelative strengths, shifts, widths, asymmetries and sharpnesses. The \"sigma\"\nand \"pi\" profiles can be described statistically, using the moments of the\nZeeman components. We present two statistical modellings: the first one\nprovides a diagnostic of the magnetic field and the second one can be used to\ninclude the effect of a magnetic field on simulated atomic spectra in an\napproximate way.", "category": "physics_atom-ph" }, { "text": "Attosecond photoionization dynamics in neon: We study the role of electron-electron correlation in the ground-state of Ne,\nas well as in photoionization dynamics induced by an attosecond XUV pulse. For\na selection of central photon energies around 100 eV, we find that while the\nmean-field time-dependent Hartree-Fock method provides qualitatively correct\nresults for the total ionization yield, the photoionization cross section, the\nphotoelectron momentum distribution as well as for the time-delay in\nphotoionization, electron-electron correlation is important for a quantitative\ndescription of these quantities.", "category": "physics_atom-ph" }, { "text": "Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a\n Paul trap: We report on observations of thermal motion of a single, Doppler-cooled ion\nalong the axis of a linear radio-frequency quadrupole trap. We show that for a\nharmonic potential the thermal occupation of energy levels leads to Gaussian\ndistribution of the ion's axial position. The dependence of the spatial thermal\nspread on the trap potential is used for precise calibration of our imaging\nsystem's point spread function and sub-milliKelvin thermometry. We employ this\ntechnique to investigate the laser detuning dependence of the Doppler\ntemperature.", "category": "physics_atom-ph" }, { "text": "A comparison of continuous and pulsed sideband cooling on an electric\n quadrupole transition: Sideband cooling enables preparation of trapped ion motion near the ground\nstate and is essential for many scientific and technological applications of\ntrapped ion devices. Here, we study the efficiency of continuous and pulsed\nsideband cooling using both first- and second-order sidebands applied to an ion\nwhere the motion starts outside the Lamb-Dicke regime. We find that after\noptimizing these distinct cooling methods, pulsed and continuous cooling\nachieve similar results based on simulations and experiments with a\n$^{40}$Ca$^+$ ion. We consider optimization of both average phonon number\n$\\overline{n}$ and population in the ground state. We also demonstrate the\ndisparity between $\\overline{n}$ as measured by the sideband ratio method of\ntrapped ion thermometry and the $\\overline{n}$ found by averaging over the\nion's motional state distribution.", "category": "physics_atom-ph" }, { "text": "A cold-atom random laser: Conventional lasers make use of optical cavities to provide feedback to gain\nmedia. Conversely, mirrorless lasers can be built by using disordered\nstructures to induce multiple scattering, which increases the effective path\nlength in the gain medium and thus provides the necessary feedback. These\nso-called random lasers potentially offer a new and simple mean to address\napplications such as lighting. To date, they are all based on condensed-matter\nmedia. Interestingly, light or microwave amplification by stimulated emission\noccurs also naturally in stellar gases and planetary atmospheres. The\npossibility of additional scattering-induced feedback (that is, random lasing)\nhas been discussed and could explain unusual properties of some space masers.\nHere, we report the experimental observation of random lasing in a controlled,\ncold atomic vapour, taking advantage of Raman gain. By tuning the gain\nfrequency in the vicinity of a scattering resonance, we observe an enhancement\nof the light emission of the cloud due to random lasing. The unique possibility\nto both control the experimental parameters and to model the microscopic\nresponse of our system provides an ideal test bench for better understanding\nnatural lasing sources, in particular the role of resonant scattering feedback\nin astrophysical lasers.", "category": "physics_atom-ph" }, { "text": "Possibility of an ultra-precise optical clock using the $6 ^1S_0 \\to 6\n ^3P^o_0$ transition in $^{171, 173}$Yb atoms held in an optical lattice: We report calculations designed to assess the ultimate precision of an atomic\nclock based on the 578 nm $6 ^1S_0 --> 6 ^3P^o_0$ transition in Yb atoms\nconfined in an optical lattice trap. We find that this transition has a natural\nlinewidth less than 10 mHz in the odd Yb isotopes, caused by hyperfine\ncoupling. The shift in this transition due to the trapping light acting through\nthe lowest order AC polarizability is found to become zero at the magic trap\nwavelength of about 752 nm. The effects of Rayleigh scattering, higher-order\npolarizabilities, vector polarizability, and hyperfine induced electronic\nmagnetic moments can all be held below a mHz (about a part in 10^{18}), except\nin the case of the hyperpolarizability larger shifts due to nearly resonant\nterms cannot be ruled out without an accurate measurement of the magic\nwavelength.", "category": "physics_atom-ph" }, { "text": "Accumulation and thermalization of cold atoms in a finite-depth magnetic\n trap: We experimentally and theoretically study the continuous accumulation of cold\natoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in\na magnetic quadrupole trap dressed by a radiofrequency (RF) field. Chromium\natoms (52 isotope) in a MOT are continuously optically pumped by the MOT lasers\nto metastable dark states. In presence of a RF field, the temperature of the\nmetastable atoms that remain magnetically trapped can be as low as 25 microK,\nwith a density of 10^17 atoms.m-3, resulting in an increase of the phase-space\ndensity, still limited to 7.10^-6 by inelastic collisions. To investigate the\nthermalization issues in the truncated trap, we measure the free evaporation\nrate in the RF-truncated magnetic trap, and deduce the average elastic cross\nsection for atoms in the 5D4 metastable states, equal to 7.0 10^-16m2.", "category": "physics_atom-ph" }, { "text": "Higher-component quadrupole polarizabilities: Estimations for the clock\n states of the alkaline earth-metal ions: Derivations for the higher tensor components of the quadrupole\npolarizabilities are given and their values for the metastable states of the\nCa$^+$, Sr$^+$ and Ba$^+$ alkaline earth-metal ions are estimated. We also give\nthe scalar quadrupole polarizabilities of the ground and metastable states of\nthese ions to compare our results with the previously available theoretical and\nexperimental results. Reasonably good agreement between our calculations with\nthe previous values of scalar quadrupole polarizabilities demonstrate their\ncorrectness. The reported scalar and tensor quadrupole polarizabilities could\nbe very useful to estimate the uncertainties due to the gradient of the\nelectric fields in the clock frequencies of the above alkaline earth-metal ions\nwhen accuracies of these frequency measurements attain below 10$^{-19}$\nprecision level.", "category": "physics_atom-ph" }, { "text": "Inducing elliptically polarized high-order harmonics from aligned\n molecules with linearly polarized femtosecond pulses: A recent paper reported elliptically polarized high-order harmonics from\naligned N$_2$ using a linearly polarized driving field [X. Zhou \\emph{et al.},\nPhys. Rev. Lett. \\textbf{102}, 073902 (2009)]. This observation cannot be\nexplained in the standard treatment of the Lewenstein model and has been\nascribed to many-electron effects or the influence of the Coulomb force on the\ncontinuum electron. We show that non-vanishing ellipticity naturally appears\nwithin the Lewenstein model when using a multi-center stationary phase method\nfor treating the dynamics of the continuum electron. The reason for this is the\nappearance of additional contributions, that can be interpreted as quantum\norbits in which the active electron is ionized at one atomic center within the\nmolecule and recombines at another. The associated exchange harmonics are\nresponsible for the non-vanishing ellipticity and result from a correlation\nbetween the ionization site and the recombination site in high-order harmonic\ngeneration.", "category": "physics_atom-ph" }, { "text": "Phase Space Approach to Laser-driven Electronic Wavepacket Propagation: We propose a phase space method to propagate a quantum wavepacket driven by a\nstrong external field. The method employs the so-called biorthogonal von\nNeumann basis recently introduced for the calculation of the energy eigenstates\nof time-independent quantum systems [A. Shimshovitz and D.J. Tannor,\narXiv:1201.2299v1]. While the individual elements in this basis set are\ntime-independent, a small subset is chosen in a time-dependent manner to adapt\nto the evolution of the wavepacket in phase space. We demonstrate the accuracy\nand efficiency of the present propagation method by calculating the electronic\nwavepacket in a one-dimensional soft-core atom interacting with a superposition\nof an intense, few-cycle, near-infrared laser pulse and an attosecond\nextreme-ultraviolet laser pulse.", "category": "physics_atom-ph" }, { "text": "Two-way single-photon-level frequency conversion between 852nm and\n 1560nm for connecting cesium D2 line with the telecom C-band: A compact setup for two-way single-photon-level frequency conversion between\n852 nm and 1560 nm has been implemented with the same periodically-poled\nmagnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystals for connecting\ncesium D2 line (852 nm) to telecom C-band. By single-pass mixing a strong\ncontinuous-wave pump laser at 1878 nm and the single-photon-level periodical\nsignal pulses in a 50-mm-long PPMgO:LN bulk crystal, the conversion efficiency\nof ~1.7% ( ~1.9%) for 852-nm to 1560-nm down-conversion (1560-nm to 852-nm\nup-conversion) have been achieved. We analyzed noise photons induced by the\nstrong pump laser beam, including the spontaneous Raman scattering (SRS) and\nthe spontaneous parametric down-conversion (SPDC) photons, and the photons\ngenerated in the cascaded nonlinear processes. The signal-to-noise ratio (SNR)\nhas been improved remarkably by using the narrow-band filters and changing\npolarization of the noise photons in the difference frequency generation (DFG)\nprocess. With further improvement of the conversion efficiency by employing\nPPMgO:LN waveguide, instead of bulk crystal, our study may provide the basics\nfor cyclic photon conversion in quantum network.", "category": "physics_atom-ph" }, { "text": "A continuous cold rubidium atomic beam with enhanced flux and tunable\n velocity: We present a cold atomic beam source based on a two-dimensional (2D)+\nmagneto-optical trap (MOT), capable of generating a continuous cold beam of\n87Rb atoms with a flux up to 4.3*10^9 atoms/s, a mean velocity of 10.96(2.20)\nm/s, and a transverse temperature of 16.90(1.56) uK. Investigating the\ninfluence of high cooling laser intensity, we observe a significant population\nloss of atoms to hyperfine-level dark states. To account for this, we employ a\nmultiple hyperfine level model to calculate the cooling efficiency associated\nwith the population in dark states, subsequently modifying the scattering\nforce. Simulations of beam flux at different cooling and repumping laser\nintensities using the modified scattering force are in agreement with\nexperimental results. Optimizing repumping and cooling intensities enhances the\nflux by 50%. The influence of phase modulation on both the pushing and cooling\nlasers is experimentally studied, revealing that the mean velocity of cold\natoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing\nlaser. The versatility of this continuous beam source, featuring high flux,\ncontrolled velocity, and narrow transverse temperature, renders it valuable for\napplications in atom interferometers and clocks, ultimately enhancing\nbandwidth, sensitivity, and signal contrast in these devices.", "category": "physics_atom-ph" }, { "text": "Atom optical shop testing of electrostatic lenses using an atom\n interferometer: We used an atom interferometer for atom optical shop testing of lenses for\natomic de Broglie waves. We measured focal lengths and spherical aberrations of\nelectrostatic lenses in three independent ways based on contrast data, phase\ndata, or calculations of de Broglie wavefront curvature. We report focal\nlengths of -2.5 km and -21.7 km with 5% uncertainty for different lenses. All\nthree methods give consistent results. Understanding how lenses magnify and\ndistort atom interference fringes helps improve atom beam velocity measurements\nmade with phase choppers [New J. Phys. 13, 115007 (2011)], which in turn will\nimprove the accuracy of atomic polarizability measurements.", "category": "physics_atom-ph" }, { "text": "The Spectral Decomposition of the Helium atom two-electron configuration\n in terms of Hydrogenic orbitals: The two electron configuration in the Helium atom is known to very high\nprecision. Yet, we tend to refer to this configuration as a $1s\\uparrow\n1s\\downarrow$ singlet, where the designations refer to Hydrogen orbitals. The\nhigh precision calculations utilize basis sets that are suited for high\naccuracy and ease of calculation, but do not really aid in our understanding of\nthe electron configuration in terms of product states of Hydrogen orbitals.\nSince undergraduate students are generally taught to think of Helium, and\nindeed, the rest of the periodic table, in terms of Hydrogenic orbitals, we\npresent in this paper a detailed spectral decomposition of the two electron\nground state for Helium in terms of these basis states. The $1s\\uparrow\n1s\\downarrow$ singlet contributes less than 93% to the ground state\nconfiguration, with other contributions coming from both bound and continuum\nHydrogenic states.", "category": "physics_atom-ph" }, { "text": "Xe 4d photoionization in Xe@C60, Xe@C240, and Xe@C60@C240: Re-evaluated parameters for the square-well potential model for\nphotoionization of endo-fullerenes are proposed and employed to reveal the\nspectacular modifications in the Xe 4d photoionization giant resonance along\nthe path from Xe@C60 to Xe@C240 to multi-walled Xe@C60@C240.", "category": "physics_atom-ph" }, { "text": "Long-range interactions and symmetry-breaking in quantum gases through\n optical feedback: We consider a quasi two-dimensional atomic Bose Einstein condensate\ninteracting with a near-resonant laser field that is back-reflected onto the\ncondensate by a planar mirror. We show that this single-mirror optical feedback\nleads to an unusual type of effective interaction between the ultracold atoms\ngiving rise to a rich spectrum of ground states. In particular, we find that it\ncan cause the spontaneous contraction of the quasi two-dimensional condensate\nto form a self-bound one-dimensional chain of mesoscopic quantum droplets, and\ndemonstrate that the observation of this exotic effect is within reach of\ncurrent experiments.", "category": "physics_atom-ph" }, { "text": "Excitation energies, polarizabilities, multipole transition rates, and\n lifetimes in Th IV: Excitation energies of the ns_{1/2} (n=7-10), np_j (n=7-9), nd_j (n=6-8),\nnf_{j} (n=5-7), and ng_{j} (n=5-6) states in Th IV are evaluated. First-,\nsecond-, third-, and all-order Coulomb energies and first- and second-order\nCoulomb-Breit energies are calculated. Reduced matrix elements, oscillator\nstrengths, transition rates, and lifetimes are determined for the 96 possible\nnl_j-n'l'_j' electric-dipole transitions. Multipole matrix elements\n(7s_{1/2}-6d_j, 7s_{1/2}-5f_j, and 5f_{5/2}-5f_{7/2}) are evaluated to obtain\nthe lifetimes of the $5f_{7/2}$ and 7s_{1/2}$ states. Matrix elements are\ncalculated using both relativistic many-body perturbation theory, complete\nthrough third order, and a relativistic all-order method restricted to single\nand double (SD) excitations. Scalar and tensor polarizabilities for the\n5f_{5/2} ground state in Th3+ are calculated using relativistic third-order and\nall-order methods. These calculations provide a theoretical benchmark for\ncomparison with experiment and theory.", "category": "physics_atom-ph" }, { "text": "The Collective Lamb Shift of a Nanoscale Atomic Vapour Layer within a\n Sapphire Cavity: We measure the near-resonant transmission of light through a dense medium of\npotassium vapor confined in a cell with nanometer thickness in order to\ninvestigate the origin and validity of the collective Lamb-shift. A complete\nmodel including the multiple reflections in the nano-cell accurately reproduces\nthe observed strong asymmetry of the line shape and allows extraction of a\ndensity dependent shift of the atomic resonance. We observe an additional,\nunexpected dependence of this shift with the thickness of the medium. This\nextra dependence demands further experimental and theoretical investigations.", "category": "physics_atom-ph" }, { "text": "Non-adiabatic Strong Field Ionization of Atomic Hydrogen: We present experimental data on the non-adiabatic strong field ionization of\natomic hydrogen using elliptically polarized femtosecond laser pulses at a\ncentral wavelength of 390 nm. Our measured results are in very good agreement\nwith a numerical solution of the time-dependent Schr\\\"odinger equation (TDSE).\nExperiment and TDSE show four above-threshold ionization (ATI) peaks in the\nelectron's energy spectrum. The most probable emission angle (also known as\n'attoclock-offset angle' or 'streaking angle') is found to increase with\nenergy, a trend that is opposite to standard predictions based on Coulomb\ninteraction with the ion. We show that this increase of deflection-angle can be\nexplained by a model that includes non-adiabatic corrections of the initial\nmomentum distribution at the tunnel exit and non-adiabatic corrections of the\ntunnel exit position itself.", "category": "physics_atom-ph" }, { "text": "Rydberg state engineering: A comparison of tuning schemes for continuous\n frequency sensing: On-resonance Rydberg atom-based radio-frequency (RF) electric field sensing\nmethods remain limited by the narrow frequency signal detection bands available\nby resonant transitions. The use of an additional RF tuner field to dress or\nshift a target Rydberg state can be used to return a detuned signal field to\nresonance and thus dramatically extend the frequency range available for\nresonant sensing. Here we investigate three distinct tuning level schemes based\non adjacent Rydberg transitions, which are shown to have distinct\ncharacteristics and can be controlled with mechanisms based on the tuning field\nfrequency or field strength. We further show that a two-photon Raman feature\ncan be used as an effective tuning mechanism separate from conventional\nAutler-Townes splitting. We compare our tuning schemes to AC Stark effect-based\nbroadband RF field sensing and show that although the sensitivity is diminished\nas we tune away from a resonant state, it nevertheless can be used in\nconfigurations where there is a low density of Rydberg states, which would\nresult in a weak AC Stark effect.", "category": "physics_atom-ph" }, { "text": "An accurate determination of the Avogadro constant by counting the atoms\n in a 28Si crystal: The Avogadro constant links the atomic and the macroscopic properties of\nmatter. Since the molar Planck constant is well known via the measurement of\nthe Rydberg constant, it is also closely related to the Planck constant. In\naddition, its accurate determination is of paramount importance for a\ndefinition of the kilogram in terms of a fundamental constant. We describe a\nnew approach for its determination by \"counting\" the atoms in 1 kg\nsingle-crystal spheres, which are highly enriched with the 28Si isotope. It\nenabled isotope dilution mass spectroscopy to determine the molar mass of the\nsilicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18)\nx 10^23 mol^-1, is the most accurate input datum for a new definition of the\nkilogram.", "category": "physics_atom-ph" }, { "text": "Generalized perspective on chiral measurements without magnetic\n interactions: We present a unified description of several methods of chiral discrimination\nbased exclusively on electric-dipole interactions. It includes photoelectron\ncircular dichroism (PECD), enantio-sensitive microwave spectroscopy (EMWS),\nphotoexcitation circular dichroism (PXCD), and photoelectron-photoexcitation\ncircular dichroism (PXECD). We show that, in spite of the fact that the physics\nunderlying the appearance of a chiral response is very different in all these\nmethods, the enantio-sensitive and dichroic observable in all cases has a\nunique form. It is a polar vector given by the product of (i) a molecular\npseudoscalar and (ii) a field pseudovector specified by the configuration of\nthe electric fields interacting with the isotropic ensemble of chiral\nmolecules. The molecular pseudoscalar is a rotationally invariant property,\nwhich is composed from different molecule-specific vectors and in the simplest\ncase is a triple product of such vectors. The key property that enables the\nchiral response is the non-coplanarity of the vectors forming such triple\nproduct. The key property that enables chiral detection without relying on the\nchirality of the electromagnetic fields is the vectorial nature of the\nenantio-sensitive observable. Our compact and general expression for this\nobservable shows what ultimately determines the efficiency of the chiral signal\nand if, or when, it can reach 100%. We also discuss the differences between the\ntwo phenomena, which rely on the bound states, PXCD and EMWS, and the two\nphenomena using the continuum states, PECD and PXECD. Finally, we extend these\nmethods to arbitrary polarizations of the electric fields used to induce and\nprobe the chiral response.", "category": "physics_atom-ph" }, { "text": "Beam-foil Spectroscopy of the 1s2s2p23p 6L-1s2p33p 6P Transitions in O\n IV, F V and Ne VI: We present observations of VUV transitions between doubly excited sextet\nstates in O IV, F V and Ne VI. Spectra were produced by collisions of an O+,\n(FH)+ and Ne+ beam with a solid carbon target. Some observed lines are assigned\nto the 1s2s2p23p 6L-1s2p33p 6P electric-dipole transitions in O IV, F V and Ne\nVI, and are compared with results of MCHF (with QED and higher-order\ncorrections) and MCDF calculations. 31 new lines have been identified. The\nsextet systems of boronlike ions are possible candidates for x-ray and VUV\nlasers.", "category": "physics_atom-ph" }, { "text": "Hyperfine and Zeeman interactions of the $a(1)[^3\u03a3^+_1]$ state of\n PbO: The role of the interaction with the nearest electronic state\n$^3\\Sigma^+_{0^-}$ on the hyperfine structure and magnetic properties of the\n$a(1)[^3\\Sigma^+_1]$ state of PbO is assessed. The accounting for this\ncontribution leads to difference between $g$-factors of the $J=1$\n$\\Omega$-doublet levels, $ \\Delta g = 37\\times10^{-4}$, that is in a good\nagreement with the experimental datum $ \\Delta g = 30(8)\\times10^{-4}$. The\ncontribution of this interaction rapidly grows with $J$. For $J=30$ the\ndifference of $g$-factors of $\\Omega$-doublet states reaches 100%; for\nhyperfine constants it is 18%. These differences also depend on the electric\nfield and for $E=11$ V/cm for $^{207}$PbO the difference in $g$-factors turn to\nzero. The latter is important for suppressing systematic effects in the\nelectron electric dipole moment search experiment.", "category": "physics_atom-ph" }, { "text": "Application of Spin-Exchange Relaxation-Free Magnetometry to the Cosmic\n Axion Spin Precession Experiment: The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure\noscillating torques on nuclear spins caused by axion or axion-like-particle\n(ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample\nspin-polarized along a leading magnetic field experiences a resonance when the\nLarmor frequency matches the axion/ALP Compton frequency, generating precessing\ntransverse nuclear magnetization. Here we demonstrate a Spin-Exchange\nRelaxation-Free (SERF) magnetometer with sensitivity $\\approx 1~{\\rm\nfT/\\sqrt{Hz}}$ and an effective sensing volume of 0.1 $\\rm{cm^3}$ that may be\nuseful for NMR detection in CASPEr. A potential drawback of\nSERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use\nof a magnetic flux transformer to suppress the leading magnetic field is\nconsidered as a potential method to expand the SERF's dynamic range in order to\nprobe higher axion/ALP Compton frequencies.", "category": "physics_atom-ph" }, { "text": "Precision Measurements in Few-Electron Molecules: The Ionization Energy\n of Metastable $\\mathbf{^4}$He$\\mathbf{_2}$ and the First Rotational\n Interval of $\\mathbf{^4}$He$\\mathbf{{_2}^+}$: Molecular helium represents a benchmark system for testing $\\textit{ab\ninitio}$ calculations on few-electron molecules. We report on the determination\nof the adiabatic ionization energy of the $a\\,^3\\Sigma_u^+$ state of He$_2$,\ncorresponding to the energy interval between the $a\\,^3\\Sigma_u^+$ ($v''=0$,\n$N''=1$) state of He$_2$ and the $X^+\\,^2\\Sigma_u^+$ ($v^+=0$, $N^+=1$) state\nof He${_2}^+$, and of the lowest rotational interval of He${_2}^+$. These\nmeasurements rely on the excitation of metastable He$_2$ molecules to high\nRydberg states using frequency-comb-calibrated continuous-wave UV radiation in\na counter-propagating-laser-beam setup. The observed Rydberg states were\nextrapolated to their series limit using multichannel quantum-defect theory.\nThe ionization energy of He$_2$ ($a\\,^3\\Sigma_u^+$) and the lowest rotational\ninterval of He${_2}^+$ ($X^+\\,^2\\Sigma_u^+$) are 34301.207002(23)$\\pm\n0.000037_{\\mathrm{sys}}$ cm$^{-1}$ and 70.937589(23)$\\pm\n0.000060_{\\mathrm{sys}}$ cm$^{-1}$, respectively.", "category": "physics_atom-ph" }, { "text": "A cryofuge for cold-collision experiments with slow polar molecules: Ultracold molecules represent a fascinating research frontier in physics and\nchemistry, but it has proven challenging to prepare dense samples at low\nvelocities. Here we present a solution to this goal by a non-conventional\napproach dubbed cryofuge. It employs centrifugal force to bring cryogenically\ncooled molecules to kinetic energies below $1\\,$K$\\times k_B$ in the laboratory\nframe, with corresponding fluxes exceeding $10^{10}$/s at velocities below\n$20\\,$m/s. By attaining densities higher than $10^9$/cm$^3$ and interaction\ntimes longer than $25\\,$ms in samples of fluoromethane as well as deuterated\nammonia, we observe cold dipolar collisions between molecules and determine\ntheir collision cross sections.", "category": "physics_atom-ph" }, { "text": "Microwave electrometry with Rydberg atoms in a vapor cell using\n microwave amplitude modulation: We have theoretically and experimentally studied the dispersive signal of the\nRydberg atomic electromagnetically induced transparency (EIT) - Autler-Townes\n(AT) splitting spectra obtained using amplitude modulation of the microwave\n(MW) field. In addition to the two zero-crossing points, the dispersion signal\nhas two positive maxima with an interval defined as the shoulder interval of\nthe dispersion signal $\\Delta f_{\\text{sho}}$. The relationship of MW field\nstrength $E_{\\text{MW}}$ and $\\Delta f_{\\text{sho}}$ are studied at the MW\nfrequencies of 31.6 GHz, 22.1 GHz, and 9.2 GHz respectively. The results show\nthat $\\Delta f_{\\text{sho}}$ can be used to character the much weaker\n$E_{\\text{MW}}$ than the interval of two zero-crossing points $\\Delta\nf_{\\text{zeros}}$ and the traditional EIT-AT splitting interval $\\Delta\nf_{\\text{m}}$, the minimum $E_{\\text{MW}}$ measured by $\\Delta f_{\\text{sho}}$\nis about 30 times smaller than that by $\\Delta f_{\\text{m}}$. As an example,\nthe minimum $E_{\\text{MW}}$ at 9.2 GHz that can be characterized by $\\Delta\nf_{\\text{sho}}$ is 0.056 mV/cm, which is the minimum value characterized by\nfrequency interval using vapour cell without adding any auxiliary fields. The\nproposed method can improve the weak limit and sensitivity of $E_{\\text{MW}}$\nmeasured by spectral frequency interval, which is important in the direct\nmeasurement of weak $E_{\\text{MW}}$.", "category": "physics_atom-ph" }, { "text": "Explicit schemes for time propagating many-body wavefunctions: Accurate theoretical data on many time-dependent processes in atomic and\nmolecular physics and in chemistry require the direct numerical solution of the\ntime-dependent Schr\\\"odinger equation, thereby motivating the development of\nvery efficient time propagators. These usually involve the solution of very\nlarge systems of first order differential equations that are characterized by a\nhigh degree of stiffness. We analyze and compare the performance of the\nexplicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have\nexactly the same stability function, therefore sharing the same stability\nproperties that turn out to be optimum. Their respective accuracy however\ndiffers significantly and depends on the physical situation involved. In order\nto test this accuracy, we use a predictor-corrector scheme in which the\npredictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully\nimplicit four-stage Radau IIA method of order 7. We consider two physical\nprocesses. The first one is the ionization of an atomic system by a short and\nintense electromagnetic pulse; the atomic systems include a one-dimensional\nGaussian model potential as well as atomic hydrogen and helium, both in full\ndimensionality. The second process is the decoherence of two-electron quantum\nstates when a time independent perturbation is applied to a planar two-electron\nquantum dot where both electrons are confined in an anharmonic potential. Even\nthough the Hamiltonian of this system is time independent the corresponding\ndifferential equation shows a striking stiffness. For the one-dimensional\nGaussian potential we discuss in detail the possibility of monitoring the time\nstep for both explicit algorithms. In the other physical situations that are\nmuch more demanding in term of computations, we show that the accuracy of both\nalgorithms depends strongly on the degree of stiffness of the problem.", "category": "physics_atom-ph" }, { "text": "Probe light-shift elimination in Generalized Hyper-Ramsey quantum clocks: We present a new interrogation scheme for the next generation of quantum\nclocks to suppress frequency-shifts induced by laser probing fields themselves\nbased on Generalized Hyper-Ramsey resonances. Sequences of composite laser\npulses with specific selection of phases, frequency detunings and durations are\ncombined to generate a very efficient and robust frequency locking signal with\nalmost a perfect elimination of the light-shift from off resonant states and to\ndecouple the unperturbed frequency measurement from the laser's intensity. The\nfrequency lock point generated from synthesized error signals using either\n$\\pi/4$ or $3\\pi/4$ laser phase-steps during the intermediate pulse is tightly\nprotected against large laser pulse area variations and errors in potentially\napplied frequency shift compensations. Quantum clocks based on weakly allowed\nor completely forbidden optical transitions in atoms, ions, molecules and\nnuclei will benefit from these hyper-stable laser frequency stabilization\nschemes to reach relative accuracies below the 10$^{-18}$ level.", "category": "physics_atom-ph" }, { "text": "High flux cold Rubidium atomic beam for strongly coupled Cavity QED: This paper presents a setup capable of producing a high-flux continuous beam\nof cold rubidium atoms for cavity QED experiments in the regime of strong\ncoupling. A 2 $D^+$ MOT, loaded by rubidium getters in a dry film coated vapor\ncell, fed a secondary moving-molasses MOT (MM-MOT) at a rate of 1.5 x $10^{10}$\natoms/sec. The MM-MOT provided a continuous beam with tunable velocity. This\nbeam was then directed through the waist of a 280 $\\mu$m cavity resulting in a\nRabi splitting of more than +/- 10 MHz. The presence of sufficient number of\natoms in the cavity mode also enabled splitting in the polarization\nperpendicular to the input. The cavity was in the strong coupling regime, with\nparameters (g, $\\kappa$, $\\gamma$)/2$\\pi$ equal to (7, 3, 6)/ 2$\\pi$ MHz.", "category": "physics_atom-ph" }, { "text": "Atomic Interferometric Gravitational-wave Space Observatory (AIGSO): We propose a space-borne gravitational-wave detection scheme, called atom\ninterferometric gravitational-wave space observatory (AIGSO). It is motivated\nby the progress in the atomic matter-wave interferometry, which solely utilizes\nthe standing light waves to split, deflect and recombine the atomic beam. Our\nscheme consists of three drag-free satellites orbiting the Earth. The phase\nshift of AIGSO is dominated by the Sagnac effect of gravitational-waves, which\nis proportional to the area enclosed by the atom interferometer, the frequency\nand amplitude of gravitational-waves. The scheme has a strain sensitivity $<\n10^{-20}/\\sqrt{{\\rm Hz}}$ in the 100 mHz-10 Hz frequency range, which fills in\nthe detection gap between space-based and ground-based laser interferometric\ndetectors. Thus, our proposed AIGSO can be a good complementary detection\nscheme to the space-borne laser interferometric schemes, such as LISA.\nConsidering the current status of relevant technology readiness, we expect our\nAIGSO to be a promising candidate for the future space-based gravitational-wave\ndetection plan.", "category": "physics_atom-ph" }, { "text": "Dynamics of a single trapped ion immersed in a buffer gas: We provide a comprehensive theoretical framework for describing the dynamics\nof a single trapped ion interacting with a neutral buffer gas, thus extending\nour previous studies on buffer-gas cooling of ions beyond the critical mass\nratio [B. H\\\"oltkemeier et al., Phys. Rev. Lett. 116, 233003 (2016)]. By\ntransforming the collisional processes into a frame, where the ion's\nmicromotion is assigned to the buffer gas atoms, our model allows one to\ninvestigate the influence of non-homogeneous buffer gas configurations as well\nas higher multipole orders of the radio-frequency trap in great detail.\nDepending on the neutral-to-ion mass ratio, three regimes of sympathetic\ncooling are identified which are characterized by the form of the ion's energy\ndistribution in equilibrium. We provide analytic expressions and numerical\nsimulations of the ion's energy distribution, spatial profile and cooling rates\nfor these different regimes. Based on these findings, a method for actively\ndecreasing the ion's energy by reducing the spatial expansion of the buffer gas\narises (Forced Sympathetic Cooling).", "category": "physics_atom-ph" }, { "text": "Robust quantum switch with Rydberg excitations: We develop an approach to realize a quantum switch for Rydberg excitation in\natoms with $Y$-typed level configuration. We find that the steady population on\ntwo different Rydberg states can be reversibly exchanged in a controllable way\nby properly tuning the Rydberg-Rydberg interaction. Moreover, our numerical\nsimulations verify that the switching scheme is robust against spontaneous\ndecay, environmental disturbance, as well as the duration of operation on the\ninteraction, and also a high switching efficiency is quite attainable, which\nmakes it have potential applications in quantum information processing and\nother Rydberg-based quantum technologies.", "category": "physics_atom-ph" }, { "text": "Collectively enhanced resonant photoionization in a multi-atom ensemble: Photoionization of an atom via interatomic correlations to N neighboring\natoms may be strongly enhanced due to constructive interference of quantum\npathways. The ionization proceeds via resonant photoexcitation of a neighbor\natom and subsequent interatomic Coulombic decay. The enhancement can scale with\nN^2, leading to \"super-enhanced photoionization\".", "category": "physics_atom-ph" }, { "text": "An $^{115}$In$^+$-$^{172}$Yb$^+$ Coulomb crystal clock with\n $2.5\\times10^{-18}$ systematic uncertainty: We present a scalable mixed-species Coulomb crystal clock based on the\n$^1S_0$ $\\leftrightarrow$ $^3P_0$ transition in $^{115}$In$^+$. $^{172}$Yb$^+$\nions are co-trapped and used for sympathetic cooling. Reproducible\ninterrogation conditions for mixed-species Coulomb crystals are ensured by a\nconditional preparation sequence with permutation control. We demonstrate clock\noperation with a 1In$^+$-3Yb$^+$ crystal, achieving a relative systematic\nuncertainty of $2.5\\times10^{-18}$ and a relative frequency instability of\n$1.6\\times10^{-15}/\\sqrt{\\tau/1\\;s}$. We report on an absolute frequency\nmeasurement with an uncertainty of $1.3\\times10^{-16}$ and optical frequency\nratios relative to the $^{171}$Yb$^+$ (E3) and $^{87}$Sr clock transitions with\nfractional uncertainties of $4.4$ and $4.7$ parts in 10$^{18}$, respectively.\nThe latter are among the most precise measurements of frequency ratios to date\nand improve upon the previous uncertainty of the $^{115}$In$^+$/$^{87}$Sr ratio\nby two orders of magnitude. We also demonstrate operation with four\n$^{115}$In$^+$ clock ions, which reduces the instability to\n$9.2\\times10^{-16}/\\sqrt{\\tau/1\\;s}$.", "category": "physics_atom-ph" }, { "text": "Compact atom source using fiber-based pulsed laser ablation: We designed, demonstrated, and characterized an atom source based on\nfiber-based pulsed laser ablation. By using commercially available miniature\nlens system for focusing nanosecond pulsed laser of up to 225~$\\mu$J delivered\nthrough a multimode fiber of 105~$\\mu$m core, we successfully ablate a\nSrTiO$_3$ target and generate a jet of neutral strontium atoms, though our\nmethod can be applied to other transparent ablation targets containing\nmaterials under concern. Our device endures 6\\,000 cycles of pulse delivery and\nirradiation without noticeable damage on the fiber facets and lenses. The\ngenerated strontium beam is characterized with spectroscopic method and is\nrevealed to exhibit the transverse temperature of 800~K and longitudinal\nvelocity of 2\\,300~m/s, which are typical of pulsed-laser-ablation-based atom\nsource. The number of atoms generated by a single ablation pulse is estimated\nto be $2\\times 10^5$. Our device provides a compact, cryo-compatible\nfiber-pigtailed atom source with minimized device footprints and reduced\ncomplexity of vacuum systems to further promote the developments of cold-atom\nexperiments. It may also find interesting applications in atomic and molecular\nsciences.", "category": "physics_atom-ph" }, { "text": "Theoretical isotope shifts in neutral barium: The present work deals with a set of problems in isotope shifts of neutral\nbarium spectral lines. Some well known transitions\n($6s^2~^1S_0-6s6p~^{1,3}P^o_1$ and $6s^2~^1S_0-6p^2~^3P_0$) are first\ninvestigated. Values of the changes in the nuclear mean-square charge radius\nare deduced from the available experimental isotope shifts using our ab initio\nelectronic factors. The three sets $\\{ \\delta\\langle r^2\\rangle^{A,A'}\\} $\nobtained from these lines are consistent with each other. The combination of\nthe available nuclear mean-square radii with our electronic factors for the\n$6s5d~^3D_{1,2} -6s6p~^{1}P^o_1$ transitions produces isotope shift values in\nconflict with the laser spectroscopy measurements of Dammalapati et al. (Eur.\nPhys. J. D 53, 1 (2009)).", "category": "physics_atom-ph" }, { "text": "Improved isotope-shift-based bounds on bosons beyond the Standard Model\n through measurements of the $^2$D$_{3/2} - ^2$D$_{5/2}$ interval in Ca$^+$: We perform high-resolution spectroscopy of the $3$d$~^2$D$_{3/2} -\n3$d$~^2$D$_{5/2}$ interval in all stable even isotopes of $^A$Ca$^+$ (A = 40,\n42, 44, 46 and 48) with an accuracy of $\\sim$ 20 Hz using direct frequency-comb\nRaman spectroscopy. Combining these data with isotope shift measurements of the\n4s$~^2$S$_{1/2} \\leftrightarrow 3$d$~^2$D$_{5/2}$ transition, we carry out a\nKing plot analysis with unprecedented sensitivity to coupling between electrons\nand neutrons by bosons beyond the Standard Model. Furthermore, we estimate the\nsensitivity to such bosons from equivalent spectroscopy in Ba$^+$ and Yb$^+$.\nFinally, the data yield isotope shifts of the 4s$~^2$S$_{1/2} \\leftrightarrow\n3$d$~^2$D$_{3/2}$ transition at 10 part-per-billion through combination with\nrecent data of Knollmann et al (2019).", "category": "physics_atom-ph" }, { "text": "The carbon atom in intense magnetic fields: The energy levels of the first few low-lying states of carbon in intense\nmagnetic fields upwards of $\\approx 10^7$ T are calculated in this study. We\nextend our previously employed pseudospectral approach for calculating the\neigenstates of the carbon atom. We report data for the ground state and a\nlow-lying state that are in good agreement with findings elsewhere, as well as\nnew data for ten other states of the carbon atom that have not been\ninvestigated until now. It is seen that these hitherto uninvestigated states\nalso become strongly bound with increasing magnetic field strengths. The data\npresented in this study are relevant for astrophysical applications, such as\nmagnetized white dwarf and neutron star spectral analysis as well as opacity\ncalculations and absorption features, including in the context of material\naccreting onto the surfaces of these compact objects.", "category": "physics_atom-ph" }, { "text": "The Effect of Dielectric Crystals on the Electron Diffraction: A dynamic diffraction theory is developed for describing electron diffraction\nby dielectric crystals in a strong electromagnetic field. It is shown that\nadditional diffraction maxima arise in an electromagnetic field, their\nintensity appreciably depending on the field strength. In some cases the\nintensity of the diffraction maxima is modulated by the electromagnetic field\nfrequency.", "category": "physics_atom-ph" }, { "text": "Molecular vibrational cooling by Optical Pumping with shaped femtosecond\n pulses: Some of us have recently reported in Science 321 232 (2008) vibrational\ncooling of translationally cold Cs_2 molecules into the lowest vibrational\nlevel v=0 of the singlet X 1Sigma_g ground electronic state. Starting from a\nsample of cold molecules produced in a collection of vibrational levels of the\nground state, our method was based on repeated optical pumping by laser light\nwith a spectrum broad enough to excite all populated vibrational levels but\nfrequency-limited in such a way to eliminate transitions from v=0 level, in\nwhich molecules accumulate. In this paper this method is generalized to\naccumulate molecules into an arbitrary selected \"target\" vibrational level. It\nis implemented by using ultrashort pulse shaping techniques based on Liquid\nCrystal spatial light modulator. In particular a large fraction of the\ninitially present molecule is transferred into a selected vibrational level\nsuch as v=1, 2 and 7. Limitations of the method as well as the possible\nextension to rotational cooling are also discussed.", "category": "physics_atom-ph" }, { "text": "Simultaneous loss and excitation of projectile electrons in relativistic\n collisions of U$^{90+}$(1s$^2$) ions with atoms: We study relativistic collisions between helium-like uranium ions initially\nin the ground state and atoms in which, in a single collision event, one of the\nelectrons of the ion is emitted and the other is transferred into an excited\nstate of the residual hydrogen-like ion. We consider this two-electron process\nat not very high impact energies, where the action of the atom on the electrons\nof the ion can be well approximated as occurring solely due to the interaction\nwith the nucleus of the atom and, hence, the process can be regarded as a\nfour-body problem. Using the independent electron model we show that a very\nsubstantial improvement in the calculated cross sections is obtained if,\ninstead of the first order approximation, the relativistic symmetric eikonal\nand continuum-distorted-wave-eikonal-initial-state models are employed to\ndescribe the single-electron probabilities for the excitation and loss,\nrespectively.", "category": "physics_atom-ph" }, { "text": "V-type electromagnetically induced transparency and saturation effect at\n the gas-solid interface: We theoretically study electromagnetically induced transparency (EIT) in\nreflection spectra of V-type system at the gas-solid interface. In addition to\na narrow dip arising from the EIT effect, we find the other particular\nsaturation effect induced by pump field, which does not exist in $\\Lambda$ or\n$\\Xi$ -type system reflection spectra. The saturation effect only induces an\nintensity decrement in the reflection spectra, and there is no influence on the\nnarrow dip arising from the EIT effect. We detailedly calculate and analyze the\ndependence of V-type system reflection spectra on probe field intensity, pump\nfield intensity, coherent decay rate, and the initial population after the\ncollision between atoms and the interface.", "category": "physics_atom-ph" }, { "text": "High efficiency symmetric beam splitter for cold atoms with a standing\n wave light pulse sequence: In a recent experiment [1], it was observed that a sequence of two standing\nwave square pulses can split a BEC at rest into +/- 2 h_bar k diffraction\norders with almost 100% efficiency. By truncating the Raman-Nath equations to a\n2-state model, we provide an intuitive picture that explains this double square\npulse beamsplitter scheme. We further show it is possible to optimize a\nstandingwave multi square pulse sequence to efficiently diffract an atom at\nrest to symmetric superposition of +/- 2n h_bar k diffraction order with n>1.\nThe approach is considered to be qualitatively different from the traditional\nlight pulse schemes in the Bragg or the Raman-Nath region, and can be extended\nto more complex atomic optical elements that produce various tailored output\nmomentum states from a cold atom source.", "category": "physics_atom-ph" }, { "text": "Measuring magnetic field inside a microwave cavity via Rabi resonances\n in Cs atoms: We present a technique for measuring microwave (MW) field based on Rabi\nresonances induced by the interaction of atoms with a phase-modulated MW field.\nA theoretical model of field measurement is used to calculate Rabi frequency.\nSingle-peak feature of the measurement model makes the technique a valuable\ntool for simple and fast field measurement. As an example, we use the technique\nto determine the MW field strength inside a Cs vapor cell in the X-band\nrectangular cavity for applied power in the range of -21 dBm to 20 dBm. The\nresults show that this proposed technique is capable for detecting the field\nover a broad dynamical range.", "category": "physics_atom-ph" }, { "text": "Three and four identical fermions near the unitary limit: This work analyzes the three and four equal-mass fermionic systems near and\nat the $s$- and $p$-wave unitary limits using hyperspherical methods. The\nunitary regime addressed here is where the two-body dimer energy is at zero\nenergy. For fermionic systems near the $s$-wave unitary limit, the hyperradial\npotentials in the $N$-body continuum exhibit a universal long-range $R^{-3}$\nbehavior governed by the $s$-wave scattering length alone. The implications of\nthis behavior on the low energy phase shift are discussed. At the $p$-wave\nunitary limit, the four-body system is studied through a qualitative look at\nthe structure of the hyperradial potentials at unitarity for the\n$L^{\\pi}=0^{+}$ symmetry. A quantitative analysis shows that there are tetramer\nstates in the lowest hyperradial potentials for these systems. Correlations are\nmade between these tetramers and the corresponding trimers in the two-body\nfragmentation channels. Universal properties related to the four-body\nrecombination process $\\mathrm{A+A+A+A}\\leftrightarrow \\mathrm{A_3+A}$ are\ndiscussed.", "category": "physics_atom-ph" }, { "text": "Radiative rates of transitions from the 2s2p$^{3}$ $^{5}$S\u00b0$_{2}$\n level of neutral carbon: The measured radiative rates of the 2s22p2 3P1,2 - 2s2p3 5S{\\deg}2\nintercombination transitions in neutral carbon reported in the literature are\ncritically evaluated by comparing them with theoretical and semi-empirical\nresults. The experimental and theoretical values are compared for the carbon\nisoelectronic sequence from neutral carbon to nine-times ionized phosphorous.\nWe find strong support for the currently recommended theoretical data on C I\nand conclude that the published measurements for this transition in neutral\ncarbon cannot be trusted. The reasons for the discrepancies are not clear, and\nnew experiments are needed.", "category": "physics_atom-ph" }, { "text": "Metastable level properties of the excited configuration\n $4p^{6}4d^{8}4f$: Metastable levels in rhodium-like ions with the ground configuration\n$4p^{6}4d^{9}$ and the excited configurations $4p^{6}4d^{8}4f$ and\n$4p^{5}4d^{10}$ are investigated. The {\\sl ab initio} calculations of the level\nenergies, radiative multipole transition probabilities are performed in a\nquasirelativistic Hartree-Fock approximation employing an extensive\nconfiguration interaction based on quasirelativistic transformed radial\norbitals. A systematic trends in behavior of calculated radiative lifetimes of\nthe metastable levels are studied for the ions from $Z=60$ to $Z=92$. The\nsignificance of the radiative transitions of higher multipole order ($M2$ and\n$E3$) for the calculated radiative lifetimes is demonstrated and discussed.", "category": "physics_atom-ph" }, { "text": "Specular reflection of matter waves from a rough mirror: We have made a high resolution study of the specularity of the atomic\nreflection from an evanescent wave mirror using velocity selective Raman\ntransitions. We have observed a double structure in the velocity distribution\nafter reflection: a peak consistent with specular reflection and a diffuse\nreflection pedestal, whose contribution decreases rapidly with increasing\ndetuning. The diffuse reflection is due to two distinct effects: spontaneous\nemission in the evanescent wave and a roughness in the evanescent wave\npotential whose amplitude is smaller than the de Broglie wavelength of the\nreflected atoms.", "category": "physics_atom-ph" }, { "text": "Coupled atomic-molecular condensates in a double-well potential:\n decaying molecular oscillations: We present a four-mode model that describes coherent photo-association (PA)\nin a double-well Bose-Einstein condensate, focusing on the $average$ molecular\npopulations in certain parameters. Our numerical results predict an interesting\nstrong-damping effect of molecular oscillations by controlling the particle\ntunnellings and PA light strength, which may provide a promising way for\ncreating a stable molecular condensate via coherent PA in a magnetic\ndouble-well potential.", "category": "physics_atom-ph" }, { "text": "Relativistic equation-of-motion coupled-cluster theory analysis of\n black-body radiation shift in the clock transition of Zn I: We have employed equation-of-motion coupled-cluster (EOM-CC) method in the\nfour-component relativistic theory framework to understand roles of electron\ncorrelation effects in the $\\textit{ab initio}$ estimations of electric dipole\npolarizabilities ($\\alpha$) of the states engaged in the clock transition\n($^{1}$S$_{0}$$\\rightarrow$$^{3}$P$_{0}$) of the zinc atom. Roles of basis\nsize, inclusion of higher-level excitations, and higher-order relativistic\neffects in the evaluation of both excitation energies of a few low-lying\nexcited states and $\\alpha$ are analyzed systematically. Our EOM-CC values are\ncompared with the earlier reported theoretical and experimental results. This\ndemonstrates the capability of the EOM-CC method to ascertain the preciseness\nof the black-body radiation shift in a clock transition, which holds paramount\nimportance for optical clock-based experiments.", "category": "physics_atom-ph" }, { "text": "Production of cold formaldehyde molecules for study and control of\n chemical reaction dynamics with hydroxyl radicals: We propose a method for controlling a class of low temperature chemical\nreactions. Specifically, we show the hydrogen abstraction channel in the\nreaction of formaldehyde (H$_{2}$CO) and the hydroxyl radical (OH) can be\ncontrolled through either the molecular state or an external electric field. We\nalso outline experiments for investigating and demonstrating control over this\nimportant reaction. To this end, we report the first Stark deceleration of the\nH$_{2}$CO molecule. We have decelerated a molecular beam of H$_{2}$CO\nessentially to rest, producing cold molecule packets at a temperature of 100 mK\nwith a few million molecules in the packet at a density of $\\sim10^{6}$\ncm$^{-3}$.", "category": "physics_atom-ph" }, { "text": "New source for tuning the effective Rabi frequency discovered in\n multiphoton ionization: The Autler-Townes effect due to near resonance transition between 4s-4p\nstates in potassium atoms is mapped out in the photo-electron-momentum\ndistribution and manifests itself as a splitting in the photo-electron kinetic\nenergy spectra. The energy splitting fits well with the calculated Rabi\nfrequency at low laser intensities and shows clear deviation at laser\nintensities above 1.5x10^11 W/cm^2. An effective Rabi frequency formulae\nincluding the ionization process explains the observed results. Our results\nreveal the possibility to tune the effective coupling strength with the cost of\nthe number of level-populations.", "category": "physics_atom-ph" }, { "text": "Effects of the electron correlation and Breit and hyperfine interactions\n on the lifetime of the 2p$^5$3s states in neutral neon: In the framework of the multiconfiguration Dirac-Hartree-Fock method, we\ninvestigate the transition properties of four excited states in the $2p^53s$\nconfiguration of neutral neon. The electron correlation effects are taken into\naccount systematically by using the active space approach. The effect of\nhigher-order correlation on fine structures is shown. We also study the\ninfluence of the Breit interaction and find that it reduces the oscillator\nstrength of the $^3P^o_1 - ^1S_0$ transition by 17%. It turns out that the\ninclusion of the Breit interaction is essential even for such a light atomic\nsystem. Our ab initio calculated line strengths, oscillator strengths and\ntransition rates are compared with other theoretical values and experimental\nmeasurements. Good agreement is found except for the $^3P^o_2 - ^1S_0$ M2\ntransition for which discrepancies of around 15% between theories and\nexperiments remain. In addition, the impact of hyperfine interactions on the\nlifetimes of the $^3P^o_0$ and $^3P^o_2$ metastable states is investigated for\nthe $^{21}$Ne isotope (I=3/2). We find that hyperfine interactions reduce the\nlifetimes drastically. For the $^3P^o_0$ state the lifetime is decreased by a\nfactor of 630.", "category": "physics_atom-ph" }, { "text": "A Quantum Similarity Study of Atomic Density Functions: Insights from\n Information Theory and the Role of Relativistic Effects: A novel quantum similarity measure (QSM) is constructed based on concepts\nfrom information theory. In an application of QSM to atoms, the new QSM and its\ncorresponding quantum similarity index (QSI) are evaluated throughout the\nperiodic table, using the atomic electron densities and shape functions\ncalculated in the Hartree-Fock approximation. The periodicity of Mendeleev's\ntable is regained for the first time through the evaluation of a QSM.\nEvaluation of the information theory based QSI demonstrates, however, that the\npatterns of periodicity are lost due to the renormalization of the QSM,\nyielding chemically less appealing results for the QSI. A comparison of the\ninformation content of a given atom on top of a group with the information\ncontent of the elements in the subsequent rows reveals another periodicity\npattern. Relativistic effects on the electronic density functions of atoms are\ninvestigated. Their importance is quantified in a QSI study by comparing for\neach atom, the density functions evaluated in the Hartree-Fock and Dirac-Fock\napproximations. The smooth decreasing of the relevant QSI along the periodic\ntable illustrates in a quantitative way the increase of relativistic\ncorrections with the nuclear charge.", "category": "physics_atom-ph" }, { "text": "Dynamics of correlated transfer-ionization in collisions with a fast\n highly charged ion: Transfer-ionization in fast collisions between a bare ion and an atom, in\nwhich one of the atomic electrons is captured by the ion whereas another one is\nemitted, crucially depends on dynamic electron-electron correlations. We show\nthat in collisions with a highly charged ion a strong field of the ion has a\nvery profound effect on the correlated channels of transfer-ionization. In\nparticular, this field weakens electron emission into the direction opposite to\nthe motion of the ion and strongly suppresses the emission perpendicular to\nthis motion. Instead, electron emission is redirected into those parts of the\nmomentum space which are very weakly populated in fast collisions with low\ncharged ions.", "category": "physics_atom-ph" }, { "text": "A Fermi Degenerate Gas of Polar Molecules: It has long been expected that quantum degenerate gases of molecules would\nopen access to a wide range of phenomena in molecular and quantum sciences.\nHowever, the very complexity that makes ultracold molecules so enticing has\nmade reaching degeneracy an outstanding experimental challenge over the past\ndecade. We now report the production of a Fermi degenerate gas of ultracold\npolar molecules of potassium--rubidium (KRb). Through coherent adiabatic\nassociation in a deeply degenerate mixture of a rubidium Bose-Einstein\ncondensate and a potassium Fermi gas, we produce molecules at temperatures\nbelow 0.3 times the Fermi temperature. We explore the properties of this\nreactive gas and demonstrate how degeneracy suppresses chemical reactions,\nmaking a long-lived degenerate gas of polar molecules a reality.", "category": "physics_atom-ph" }, { "text": "Optical clocks based on molecular vibrations as probes of variation of\n the proton-to-electron mass ratio: Some new physics models of quantum gravity or dark matter predict drifts or\noscillations of the fundamental constants. A relatively simple model relates\nmolecular vibrations to the proton-to-electron mass ratio $\\mu$. Many\nvibrational transitions are at optical frequencies with prospects for use as\nhighly accurate optical clocks. We give a brief summary of new physics models\nthat lead to changes in $\\mu$ and the current limits on drifts and oscillation\namplitudes. After an overview of laboratory procedures, we give examples of\nmolecules with experiments currently in development or underway. These\nexperiments' projected systematic and statistical uncertainties make them\nleading candidates in next-generation searches for time-variation of $\\mu$.", "category": "physics_atom-ph" }, { "text": "Single-laser-pulse implementation of arbitrary ZYZ rotations of an\n atomic qubit: Arbitrary rotation of a qubit can be performed with a three-pulse sequence;\nfor example, ZYZ rotations. However, this requires precise control of the\nrelative phase and timing between the pulses, making it technically challenging\nin optical implementation in a short time scale. Here we show any ZYZ rotations\ncan be implemented with a single laser-pulse, that is {\\it a chirped pulse with\na temporal hole}. The hole of this shaped pulse induces a non-adiabatic\ninteraction in the middle of the adiabatic evolution of the chirped pulse,\nconverting the central part of an otherwise simple Z-rotation to a Y rotation,\nconstructing ZYZ rotations. The result of our experiment performed with shaped\nfemtosecond laser pulses and cold rubidium atoms shows strong agreement with\nthe theory.", "category": "physics_atom-ph" }, { "text": "Magic and tune-out wavelengths for atomic francium: The frequency dependent polarizabilities of the francium atom are calculated\nfrom the available data of energy levels and transition rates. Magic\nwavelengths for the state insensitive optical dipole trapping are identified\nfrom the calculated light shifts of the $7s~^2S_{1/2}$, $7p~^2P_{1/2, 3/2}$ and\n$8s~^{2}S_{1/2}$ levels of the $7s~^{2}S_{1/2}-7p~^{2}P_{1/2,3/2}$ and\n$7s~^{2}S_{1/2}-8s~^{2}S_{1/2}$ transitions, respectively. Wavelengths in the\nultraviolet, visible and near infrared region is identified that are suitable\nfor cooling and trapping. Magic wavelengths between 600-700~nm and 700-1000~nm\nregion, which are blue and red detuned with the $7s-7p$ and $7s-8s$ transitions\nare feasible to implement as lasers with sufficient power are available. In\naddition, we calculated the tune-out wavelengths where the ac polarizability of\nthe ground $7s~^{2}S_{1/2}$ state in francium is zero. These results are\nbeneficial as laser cooled and trapped francium has been in use for fundamental\nsymmetry investigations like searches for an electron permanent electric dipole\nmoment in an atom and for atomic parity non-conservation.", "category": "physics_atom-ph" }, { "text": "Atom interferometry in the presence of an external test mass: The influence of an external test mass on the phase of the signal of an atom\ninterferometer is studied theoretically. Using traditional techniques in atom\noptics based on the density matrix equations in the Wigner representation, we\nare able to extract the various contributions to the phase of the signal\nassociated with the classical motion of the atoms, the quantum correction to\nthis motion resulting from atomic recoil that is produced when the atoms\ninteract with Raman field pulses, and quantum corrections to the atomic motion\nthat occur in the time between the Raman field pulses. By increasing the\neffective wave vector associated with the Raman field pulses using modified\nfield parameters, we can increase the sensitivity of the signal to the point\nwhere the quantum corrections can be measured. The expressions that are derived\ncan be evaluated numerically to isolate the contribution to the signal from an\nexternal test mass. The regions of validity of the exact and approximate\nexpressions are determined.", "category": "physics_atom-ph" }, { "text": "Test of Einstein Equivalence Principle for 0-spin and half-integer-spin\n atoms: Search for spin-gravity coupling effects: We report on a conceptually new test of the equivalence principle performed\nby measuring the acceleration in Earth's gravity field of two isotopes of\nstrontium atoms, namely, the bosonic $^{88}$Sr isotope which has no spin vs the\nfermionic $^{87}$Sr isotope which has a half-integer spin. The effect of\ngravity upon the two atomic species has been probed by means of a precision\ndifferential measurement of the Bloch frequency for the two atomic matter waves\nin a vertical optical lattice. We obtain the values $\\eta = (0.2\\pm\n1.6)\\times10^{-7}$ for the E\\\"otv\\\"os parameter and\n$k=(0.5\\pm1.1)\\times10^{-7}$ for the coupling between nuclear spin and gravity.\nThis is the first reported experimental test of the equivalence principle for\nbosonic and fermionic particles and opens a new way to the search for the\npredicted spin-gravity coupling effects.", "category": "physics_atom-ph" }, { "text": "Ionization of oriented targets by intense circularly polarized laser\n pulses: Imprints of orbital angular nodes in the 2D momentum distribution: We solve the three-dimensional time-dependent Schr\\\"{o}dinger equation for a\nfew-cycle circularly polarized femtosecond laser pulse interacting with an\noriented target exemplified by an Argon atom, initially in a $3\\text{p}_{x}$ or\n$3\\text{p}_{y}$ state. The photoelectron momentum distributions show distinct\nsignatures of the orbital structure of the initial state as well as the\ncarrier-envelope phase of the applied pulse. Our \\textit{ab initio} results are\ncompared with results obtained using the length-gauge strong-field\napproximation, which allows for a clear interpretation of the results in terms\nof classical physics. Furthermore, we show that ionization by a circularly\npolarized pulse completely maps out the angular nodal structure of the initial\nstate, thus providing a potential tool for studying orbital symmetry in\nindividual systems or during chemical reactions.", "category": "physics_atom-ph" }, { "text": "Relativistic study of the nuclear anapole moment effects in diatomic\n molecules: Nuclear-spin-dependent (NSD) parity violating effects are studied for a\nnumber of diatomic molecules using relativistic Hartree-Fock and density\nfunctional theory and accounting for core polarization effects. Heavy diatomic\nmolecules are good candidates for the successful measurement of the nuclear\nanapole moment, which is the dominant NSD parity violation term in heavy\nelements. Improved results for the molecules studied in our previous\npublication [Borschevsky et al., Phys. Rev. A 85, 052509 (2012)] are presented\nalong with the calculations for a number of new promising candidates for the\nnuclear anapole measurements.", "category": "physics_atom-ph" }, { "text": "Ion Imaging via Long-Range Interaction with Rydberg Atoms: We demonstrate imaging of ions in an atomic gas with ion-Rydberg atom\ninteraction induced absorption. This is made possible by utilizing a\nmulti-photon electromagnetically induced transparency (EIT) scheme and the\nextremely large electric polarizability of a Rydberg state with high orbital\nangular momentum. We process the acquired images to obtain the distribution of\nion clouds and to spectroscopically investigate the effect of the ions on the\nEIT resonance. Furthermore, we show that our method can be employed to image\nthe dynamics of ions in a time resolved way. As an example, we map out the\navalanche ionization of a gas of Rydberg atoms. The minimal disruption and the\nflexibility offered by this imaging technique make it ideally suited for the\ninvestigation of cold hybrid ion-atom systems.", "category": "physics_atom-ph" }, { "text": "Finite-size effects in strongly interacting Rydberg gases: The scaling of the number of Rydberg excitations in a laser-driven cloud of\natoms with the interaction strength is found to be affected by the finite size\nof the system. The scaling predicted by a theoretical model is compared with\nresults extracted from a numerical many-body simulation. We find that the\nnumerically obtained scaling exponent in general does not agree with the\nanalytical prediction. By individually testing the assumptions leading to the\ntheoretical prediction using the results from the numerical analysis, we\nidentify the origin of the deviations, and explain it as arising from the\nfinite size of the system. Furthermore, finite-size effects in the pair\ncorrelation function $g^{(2)}$ are predicted. Finally, in larger ensembles, we\nfind that the theoretical predictions and the numerical results agree, provided\nthat the system is sufficiently homogeneous.", "category": "physics_atom-ph" }, { "text": "Enhancing frustrated double ionisation with no electronic correlation in\n triatomic molecules using counter-rotating two-color circular laser fields: We demonstrate significant enhancement of frustrated double ionization (FDI)\nin the two-electron triatomic molecule D$_{3}^{+}$ when driven by\ncounter-rotating two-color circular (CRTC) laser fields. We employ a\nthree-dimensional semiclassical model that fully accounts for electron and\nnuclear motion in strong fields. For different pairs of wavelengths, we compute\nthe probabilities of the FDI pathways as a function of the ratio of the two\nfield-strengths. We identify a pathway of frustrated double ionization that is\nnot present in strongly-driven molecules with linear fields. In this pathway\nthe first ionization step is \"frustrated\" and electronic correlation is\nessentially absent. This pathway is responsible for enhancing frustrated double\nionization with CRTC fields. We also employ a simple model that predicts many\nof the main features of the probabilities of the FDI pathways as a function of\nthe ratio of the two field-strengths.", "category": "physics_atom-ph" }, { "text": "Angular Distribution of Electrons in Photoionization of Atoms Adsorbed\n on a Graphene Sheet: Within the framework of a model representing the potential of a graphene\nsheet U(z) as an electro-neutral layer formed by smeared carbon atoms, the\neffect of this potential on spectral characteristics of atoms adsorbed on a\ngraphene sheet has been studied. Since the distance between the adsorbed atom\nnucleus and sheet surface significantly exceeds the radii of inner atomic\nshells the potential U(z) makes influence on the continuum wave functions only.\nTheir behavior in the upper semi-space (z>0) and in the lower one (z<0) where\nthe adsorbed atom is located is defined by a jump of the logarithmic derivative\nof the wave function for z=0. The photoelectron angular distributions have been\ncalculated for different mutual positions of the polarization vector e and the\naxis Z normal to the sheet surface. It has been shown that the existence of the\nelectron waves reflected from the potential U(z) leads to evident asymmetry of\nthe angular distribution relative to the plane z=0. The experimental\nobservation of this effect is of great interest for photoelectron spectroscopy\nof atoms localized on graphene structures.", "category": "physics_atom-ph" }, { "text": "Excited-Band Coherent Delocalization for Improved Optical Lattice Clock\n Performance: We implement coherent delocalization as a tool for improving the two primary\nmetrics of atomic clock performance: systematic uncertainty and instability. By\ndecreasing atomic density with coherent delocalization, we suppress\ncold-collision shifts and two-body losses. Atom loss attributed to Landau-Zener\ntunneling in the ground lattice band would compromise coherent delocalization\nat low trap depths for our $^{171}$Yb atoms; hence, we implement for the first\ntime delocalization in excited lattice bands. Doing so increases the spatial\ndistribution of atoms trapped in the vertically-oriented optical lattice by\n$\\sim7$ times. At the same time we observe a reduction of the cold-collision\nshift by 6.5(8) times, while also making inelastic two-body loss negligible.\nWith these advantages, we measure the trap-light-induced quenching rate and\nnatural lifetime of the ${}^3$P${}_0$ excited-state as $5.7(7)\\times10^{-4}$\n$E_r^{-1}s^{-1}$ and 19(2) s, respectively.", "category": "physics_atom-ph" }, { "text": "Suppression of Three-Body Loss Near a p-Wave Resonance Due to Quasi-1D\n Confinement: We investigate the three-body recombination rate of a Fermi gas of $^6$Li\natoms confined in quasi-1D near a $p$-wave Feshbach resonance. We confirm that\nthe quasi-1D loss rate constant $K_3$ follows the predicted threshold scaling\nlaw that $K_3$ is energy independent on resonance, and find consistency with\nthe scaling law $K_3 \\propto (k \\, a_{1D})^6$ far from resonance [Mehta et al.\nPhys. Rev. A 76, 022711 (2007)]. Further we develop a theory based on\nBreit-Wigner analysis that describes the loss feature for intermediate fields.\nLastly we measure how the loss rate constant scales with transverse confinement\nand find that $K_3 \\propto V_L^{-1}$, where $V_L$ is the lattice depth.\nImportantly, at our attainable transverse confinements and temperatures, we see\na 74-fold suppression of the on-resonant three-body loss rate constant in\nquasi-1D compared to 3D. With significant further enhancement of the transverse\nconfinement, this suppression may pave the way for realizing stable $p$-wave\nsuperfluids.", "category": "physics_atom-ph" }, { "text": "A Comparative Analysis of Non-relativistic and Relativistic Calculations\n of Electric Dipole Moments and Polarizabilities of Heteronuclear Alkali\n Dimers: We analyze the molecular electric dipole moments (PDMs) and static electric\ndipole polarizabilities of heteronuclear alkali dimers in their ground states\nby employing coupled-cluster theory, both in the non-relativistic and\nfour-component relativistic frameworks. The roles of electron correlations as\nwell as relativistic effects are demonstrated by studying them at different\nlevels of theory, followed by a comprehensive treatment of error estimates. We\ncompare our obtained values with the previous non-relativistic calculations,\nsome of which include lower-order relativistic corrections, as well as with the\nexperimental values, wherever available. We find that the PDMs are very\nsensitive to relativistic effects, as compared to polarizabilities; this aspect\ncan explain the long-standing question on the difference between experimental\nvalues and theoretical results for LiNa. We show that consideration of\nrelativistic values of PDMs improves significantly the isotropic Van der Waals\n$C_6$ coefficients of the investigated alkali dimers over the previously\nreported non-relativistic calculations. The dependence of dipole\npolarizabilities on molecular volume is also illustrated.", "category": "physics_atom-ph" }, { "text": "Comparison of semiclassical and quantum models of a two-level\n atom-cavity QED system in the strong coupling regime: We present a numerical study comparing semiclassical and quantum models of a\ndamped, strongly interacting cavity QED system composed of a single two-level\natom interacting with a single quantized cavity mode driven externally by a\ntunable monochromatic field. We compute the steady state transmission spectrum\nof the coupled system under each model and show that in the strong coupling\nregime, the two models yield starkly different results. The fully quantum\nmechanical model of the system correctly yields the expected multiphoton\ntransmission spectra while the semiclassical approach results in a bistable\nspectrum.", "category": "physics_atom-ph" }, { "text": "Attosecond streaking enables the measurement of quantum phase: Attosecond streaking, as a measurement technique, was originally conceived as\na means to characterize attosecond light pulses, which is a good approximation\nif the relevant transition matrix elements are approximately constant within\nthe bandwidth of the light pulse. Our analysis of attosecond streaking\nmeasurements on systems with complex response to the photoionizing pulse\nestablishes a relation between the momentum-space wave function of the outgoing\nelectron and the result of conventional retrieval algorithms. This finding\nenables the measurement of the quantum phase associated with bound-continuum\ntransition matrix elements.", "category": "physics_atom-ph" }, { "text": "Simultaneous magneto-optical trapping of lithium and ytterbium atoms\n towards production of ultracold polar molecules: We have successfully implemented the first simultaneous magneto-optical\ntrapping (MOT) of lithium ($^6$Li) and ytterbium ($^{174}$Yb) atoms, towards\nproduction of ultracold polar molecules of LiYb. For this purpose, we developed\nthe dual atomic oven which contains both atomic species as an atom source and\nsuccessfully observed the spectra of the Li and Yb atoms in the atomic beams\nfrom the dual atomic oven. We constructed the vacuum chamber including the\nglass cell with the windows made of zinc selenium (ZnSe) for the CO$_2$ lasers,\nwhich are the useful light sources of optical trapping for evaporative and\nsympathetic cooling. Typical atom numbers and temperatures in the compressed\nMOT are 7$\\times10^3$ atoms, 640 $\\mu$K for $^6$Li, 7$\\times10^4$ atoms and 60\n$\\mu$K for $^{174}$Yb, respectively.", "category": "physics_atom-ph" }, { "text": "Two-photon Annihilation of Positrons with K-shell Electrons of H-like\n ions: The two-photon annihilation of a positron with an electron bound in the 1s\nstate of a H-like ion is calculated within the fully relativistic QED\nframework. The interaction with the nucleus is treated nonperturbatively, thus\nallowing the calculations to be carried out for the annihilation with\nstrongly-bound inner shells of heavy ions. Infrared divergences, appearing when\none of the emitted photons approaches the low-frequency limit, are accurately\neliminated from final expressions. The total cross section of the two-photon\nand one-photon annihilation processes are compared for a wide range of\ncollision energies and nuclear charge numbers. It is demonstrated that the\ntwo-photon annihilation channel dominates over the one-photon channel for the\nlow and medium-Z ions, whereas for the high-Z ions the situation reverses.", "category": "physics_atom-ph" }, { "text": "New Nuclear Magnetic Moment of $^{209}$Bi - Resolving the Bismuth\n Hyperfine Puzzle: A recent measurement of the hyperfine splitting in the ground state of\nLi-like $^{209}$Bi$^{80+}$ has established a \"hyperfine puzzle\" -- the\nexperimental result exhibits a 7$\\sigma$ deviation from the theoretical\nprediction [J. Ullmann et al., Nat. Commun. 8, 15484 (2017); J. P. Karr, Nat.\nPhys. 13, 533 (2017)]. We provide evidence that the discrepancy is caused by an\ninaccurate value of the tabulated nuclear magnetic moment ($\\mu_I$) of\n$^{209}$Bi. We perform relativistic density functional theory and relativistic\ncoupled cluster calculations of the shielding constant that should be used to\nextract the value of $\\mu_I(^{209}{\\rm Bi})$ and combine it with nuclear\nmagnetic resonance measurements of Bi(NO$_3$)$_3$ in nitric acid solutions and\nof the hexafluoridobismuthate(V) BiF$_6^-$ ion in acetonitrile. The result\nclearly reveals that $\\mu_I(^{209}{\\rm Bi})$ is much smaller than the tabulated\nvalue used previously. Applying the new magnetic moment shifts the theoretical\nprediction into agreement with experiment and resolves the hyperfine puzzle.", "category": "physics_atom-ph" }, { "text": "One-electron ion in a quantizing magnetic field: A charged particle in a magnetic field possesses discrete energy levels\nassociated with particle rotation around the field lines. A bound complex of\nparticles with a nonzero net charge possesses an analogous levels associated\nwith its center-of-mass motion and, in addition, the levels associated with\ninternal degrees of freedom, that is with relative motions of its constituent\nparticles. The center-of-mass and internal motions are mutually dependent,\nwhich complicates theoretical studies of the binding energies, radiative\ntransitions and other properties of the complex ions moving in quantizing\nmagnetic fields. In this work, we present a detailed derivation of practical\nexpressions for the numerical treatment of such properties of the hydrogenlike\nions moving in strong quantizing magnetic fields, which follows and supplements\nthe previous works of Bezchastnov et al. Second, we derive asymptotic analytic\nexpressions for the binding energies, oscillator strengths, and photoionization\ncross sections of the moving hydrogenlike ions in the limit of an ultra-strong\nmagnetic field.", "category": "physics_atom-ph" }, { "text": "Collective dipole-dipole interactions in planar nanocavities: The collective response of an atomic ensemble is shaped by its macroscopic\nenvironment. We demonstrate this effect in the near-resonant transmission of\nlight through a thermal rubidium vapor confined in a planar nanocavity. Our\nmodel reveals density-dependent line shifts and broadenings beyond continuous\nelectrodynamics models that oscillate with cavity width and have been observed\nin recent experiments. We predict that the amplitudes of these oscillations can\nbe controlled by coatings that modify the cavity's Finesse.", "category": "physics_atom-ph" }, { "text": "Ultracold collision in the presence of synthetic spin-orbit coupling: We present an analytic description of ultracold collision between two\nspin-$\\frac{1}{2}$ fermions with isotropic spin-orbit coupling of the Rashba\ntype. We show that regardless of how weak the spin-orbit coupling may be, the\nultracold collision at sufficiently low energies is significantly modified,\nincluding the ubiquitous Wigner threshold behavior. We further show that the\nparticles are preferably scattered into the lower-energy helicity state due to\nthe break of parity conservation, thus establishing interaction with spin-orbit\ncoupling as one mechanism for the spontaneous emergence of handedness.", "category": "physics_atom-ph" }, { "text": "Accurate estimations of circumstellar and interstellar lines of\n quadruply ionized vanadium using the coupled cluster approach: Accurate {\\it ab initio} calculations have been carried out to study the\nvalence electron removal energies and oscillator strengths of astrophysically\nimportant electromagnetic transitions of quadruply ionized vanadium, $V^{4+}$.\nMany important electron correlations are considered to all-orders using the\nrelativistic coupled-cluster theory. Calculated ionization potentials and fine\nstructure splittings are compared with the experimental values, wherever\navailable. To our knowledge, oscillator strengths of electric dipole\ntransitions are predicted for the first time for most of the transitions. The\ntransitions span in the range of ultraviolet, visible and near infrared regions\nand are important for astrophysical observations.", "category": "physics_atom-ph" }, { "text": "Increase of barium ion-trap lifetime via photodissociation: The lifetime of Ba$^+$ ions confined in a Paul trap is found, under typical\nconditions, to be limited by chemical reactions with residual background gas.\nAn integrated ion trap and time-of-flight mass spectrometer are used to analyze\nthe reactions of the trapped Ba$^+$ ions with three common gases in an\nultrahigh vacuum system (H$_2$, CO$_2$ and H$_2$O). It is found that the\nproducts of these reactions can all be photodissociated by a single ultraviolet\nlaser at 225~nm, thereby allowing the recovery of the Ba$^+$ ions and leading\nto an increase of the effective trap lifetime. For a Coulomb crystal, the\nlifetime increased from roughly 6~hours to 2~days at room temperature. It is\nsuggested that higher enhancement factors are possible in systems with stronger\ntraps. In addition, photodissociation wavelengths for other common trapped ion\nsystems are provided.", "category": "physics_atom-ph" }, { "text": "Search for parity and time reversal violating effects in HgH:\n Relativistic coupled-cluster study: The high effective electric field ($E_\\mathrm{eff}$) experienced by the\nunpaired electron in an atom or a molecule is one of the key ingredients in the\nsuccess of electron electric dipole moment (eEDM) experiment and its precise\ncalculation require a very accurate theory. We, therefore, employed the\nZ-vector method in the relativistic coupled-cluster framework and found that\nHgH has a very large $E_\\mathrm{eff}$ value (123.2 GV/cm) which makes it a\npotential candidate for the next generation eEDM experiment. Our study also\nreveals that it has a large scalar-pseudoscalar ${\\mathcal{P,T}}$-violating\ninteraction constant, $W_\\mathrm{s}$ = 284.2 kHz. To judge the accuracy of the\nobtained results we have calculated parallel and perpendicular magnetic HFS\nconstants and compared with the available experimental values. The results of\nour calculation are found to be in nice agreement with the experimental values.\nTherefore, by looking at the HFS results we can say that both $E_\\mathrm{eff}$\nand $W_\\mathrm{s}$ values are also very accurate. Further, We have derived the\nrelationship between these quantities and the ratio which will help to get\nmodel independent value of eEDM and S-PS interaction constant.", "category": "physics_atom-ph" }, { "text": "Atomic orientation by a broadly frequency-modulated radiation: theory\n and experiment: We investigate magnetic resonances driven in thermal vapour of alkali atoms\nby laser radiation broadly modulated at a frequency resonant with the Zeeman\nsplitting. A model accounting for both hyperfine and Zeeman pumping is\ndeveloped and its results are compared with experimental measurements performed\nat relatively weak pump irradiance. The interplay between the two pumping\nprocesses generates intriguing interaction conditions, often overlooked by\nsimplified models.", "category": "physics_atom-ph" }, { "text": "Enhancement of Ultracold Molecule Formation Using Shaped Nanosecond\n Frequency Chirps: We demonstrate that judicious shaping of a nanosecond-time-scale frequency\nchirp can dramatically enhance the formation rate of ultracold $^{87}$Rb$_{2}$\nmolecules. Starting with ultracold $^{87}$Rb atoms, we apply pulses of\nfrequency-chirped light to first photoassociate the atoms into excited\nmolecules and then, later in the chirp, de-excite these molecules into a high\nvibrational level of the lowest triplet state, $a \\, ^{3}\\Sigma_{u}^{+}$. The\nenhancing chirp shape passes through the absorption and stimulated emission\ntransitions relatively slowly, thus increasing their adiabaticity, but jumps\nquickly between them to minimize the effects of spontaneous emission.\nComparisons with quantum simulations for various chirp shapes support this\nenhancement mechanism.", "category": "physics_atom-ph" }, { "text": "Revis\u00e3o da Constru\u00e7\u00e3o de Modelos Supersim\u00e9tricos: Foi com base neste estudo que fizemos a constru\\c{c}\\~ao da vers\\~ao\nsupersim\\'etrica dos modelos de simetria $SU(3)_{C} \\otimes SU(3)_{L} \\otimes\nU(1)_{N}$ \\cite{susy331}, apresentado no final da minha tese de doutorado\n\\cite{mcr1}. Bem como dos estudos fenomenol\\'ogicos subsequente \\cite{mcr}.", "category": "physics_atom-ph" }, { "text": "Laser assisted electron dynamics: We apply the convergent close-coupling (CCC) formalism to analyse the\nprocesses of laser assisted electron impact ionisation of He, and the\nattosecond time delay in the photodetachment of the H^{-} ion and the\nphotoionisation of He. Such time dependent atomic collision processes are of\nconsiderable interest as experimental measurements on the relevant timescale\n(attoseconds 10^{-18} s) are now possible utilising ultrafast and intense laser\npulses. These processes in particular are furthermore of interest as they are\nstrongly influenced by many-electron correlations. In such cases their\ntheoretical description requires a more comprehensive treatment than that\noffered by first order perturbation theory. We apply such a treatment through\nthe use of the CCC formalism which involves the complete numeric solution of\nthe integral Lippmann-Schwinger equations pertaining to a particular scattering\nevent. For laser assisted electron impact ionisation of He such a treatment is\nof a considerably greater accuracy than the majority of previous theoretical\ndescriptions applied to this problem which treat the field-free scattering\nevent within the first Born approximation. For the photodetachment of H^{-} and\nphotoionisation of He, the CCC approach allows for accurate calculation of the\nattosecond time delay and comparison with the companion processes of\nphotoelectron scattering on H and He^{+}, respectively.", "category": "physics_atom-ph" }, { "text": "Novel radio-frequency ion trap with spherical geometry: Confinement of single ions in a novel radio-frequency (RF) quadrupole ion\ntrap with spherical shape is investigated. An optimization of this spherical\nion trap (SIT) is carried out in order to suppress its nonlinearity\nsubstantially by eliminating the electric octupole moment. Hence, a trapping\npotential and consequently an electric field very similar to the ideal\nquadrupole ion trap (QIT) are obtained. Afterwards, three stability regions for\nthe optimized SIT are numerically computed. The regions coincide well with\nthose reported in the literature for the ideal QIT. The reason is attributed to\nthe zero electric octupole moment of our proposed trap. The SIT simple geometry\nand relative ease of fabrication along with its increased trapping volume\ncompared to the conventional hyperbolic quadrupole ion trap, make it an\nappropriate choice for miniaturization.", "category": "physics_atom-ph" }, { "text": "Measurement of the hyperfine coupling constants and absolute energies of\n the $12s \\ ^2S_{1/2}$, $13s \\ ^2S_{1/2}$, and $11d \\ ^2D_{J}$ levels in\n atomic cesium: We report measurements of the absolute energies of the hyperfine components\nof the $12s \\ ^2S_{1/2}$ and $13s \\ ^2S_{1/2}$ levels of atomic cesium,\n$^{133}$Cs. Using the frequency difference between these components, we\ndetermine the hyperfine coupling constants for these states, and report these\nvalues with a relative uncertainty of $\\sim$0.06 %. We also examine the\nhyperfine structure of the $11d \\ ^2D_{J}$ ($J=3/2, 5/2$) states, and resolve\nthe sign ambiguity of the hyperfine coupling constants from previous\nmeasurements of these states. We also derive new, high precision values for the\nstate energies of the $12s \\ ^2S_{1/2}$, $13s \\ ^2S_{1/2}$ and $11d \\ ^2D_{J}$\nstates of cesium.", "category": "physics_atom-ph" }, { "text": "Nonlinear optical effects in a nucleus: Intense laser technologies generate light with unprecedented and growing\nintensities. The possibility emerges that a nucleus responds nonlinearly to an\nintense light field, pointing to a yet little explored research area of nuclear\nnonlinear optics. We consider two-photon and three-photon absorption (with\nsubsequent disintegration) processes of the deuteron, the simplest and the most\nfundamental nontrivial nucleus, as prototypes of nuclear nonlinear optical\neffects. Quantitative calculations are performed on these processes and novel\nobservable effects are predicted.", "category": "physics_atom-ph" }, { "text": "Probing CP violation with the electric dipole moment of atomic mercury: The electric dipole moment of atomic $^{199}$Hg induced by the nuclear Schiff\nmoment and tensor-pseudotensor electron-nucleus interactions has been\ncalculated. For this, we have developed and employed a novel method based on\nthe relativistic coupled-cluster theory. The results of our theoretical\ncalculations combined with the latest experimental result of $^{199}$Hg\nelectric dipole moment, provide new bounds on the T reversal or CP violation\nparameters $\\theta_{\\rm QCD}$, the tensor-pseudotensor coupling constant $C_T$\nand $(\\widetilde{d}_u - \\widetilde{d}_d)$. This is the most accurate\ncalculation of these parameters to date. We highlight the the crucial role of\nelectron correlation effects in their interplay with the P,T violating\ninteractions. Our results demonstrate substantial changes in the results of\nearlier calculations of these parameters which can be attributed to the more\naccurate inclusion of important correlation effects in the present work.", "category": "physics_atom-ph" }, { "text": "Multiple scattering of light in cold atomic clouds with a magnetic field: Starting from a microscopic theory for atomic scatterers, we describe the\nscattering of light by a single atom and study the coherent propagation of\nlight in a cold atomic cloud in the presence of a magnetic field B in the\nmesoscopic regime. Non-pertubative expressions in B are given for the\nmagneto-optical effects and optical anisotropy. We then consider the multiple\nscattering regime and address the fate of the coherent backscattering (CBS)\neffect. We show that, for atoms with nonzero spin in their ground state, the\nCBS interference contrast can be increased compared to its value when B=0, a\nresult at variance with classical samples. We validate our theoretical results\nby a quantitative comparison with experimental data.", "category": "physics_atom-ph" }, { "text": "Multiphoton ionization of the calcium atom by linearly and circularly\n polarized laser fields: We theoretically study multiphoton ionization of the Ca atom irradiated by\nthe second (photon energy 3.1 eV) and third (photon energy 4.65 eV) harmonics\nof Ti:sapphire laser pulses (photon energy 1.55 eV). Because of the dense\nenergy level structure the second and third harmonics of a Ti:sapphire laser\nare nearly single-photon resonant with the ${4s4p}$ $^1P^o$ and ${4s5p}$\n$^1P^o$ states, respectively. Although two-photon ionization takes place\nthrough the near-resonant intermediate states with the same symmetry in both\ncases, it turns out that there are significant differences between them. The\nphotoelectron energy spectra exhibit the absence/presence of substructures.\nMore interestingly, the photoelectron angular distributions clearly show that\nthe main contribution to the ionization processes by the third harmonic arises\nfrom the far off-resonant ${4s4p}$ $^1P^o$ state rather than the near-resonant\n${4s5p}$ $^1P^o$ state. These findings can be attributed to the fact that the\ndipole moment for the ${4s^2}$ $^1S^e$ - ${4s5p}$ $^1P^o$ transition is much\nsmaller than that for the ${4s^2}$ $^1S^e$ - ${4s4p}$ $^1P^o$ transition.", "category": "physics_atom-ph" }, { "text": "Radiative and correlation effects on the parity-nonconserving transition\n amplitude in heavy alkaline atoms: The complete gauge-invariant set of the one-loop QED corrections to the\nparity-nonconserving (PNC) amplitude in cesium and francium is evaluated to all\norders in $\\alpha Z$ using a local form of the Dirac-Fock potential. The\ncalculations are performed in both length and velocity gauges for the absorbed\nphoton and the total binding QED correction is found to be $-$0.27(3)% for Cs\nand $-$0.28(5)% for Fr. Moreover, a high-precision calculation of the\nelectron-correlation and Breit-interaction effects on the 7$s-8s$ PNC amplitude\nin francium using a large-scale configuration-interaction Dirac-Fock method is\nperformed. The obtained results are employed to improve the theoretical\npredictions for the PNC transition amplitude in Cs and Fr. Using an average\nvalue from two most accurate measurements of the vector transition\npolarizability, the weak charge of $^{133}$Cs is derived to amount to $\nQ_W=-72.65(29)_{\\rm exp}(36)_{\\rm theor}$. This value deviates by $1.1\\sigma$\nfrom the prediction of the standard model. The values of the $7s$-$8s$ PNC\namplitude in $^{223}$Fr and $^{210}$Fr are obtained to be $-$15.49(15) and\n$-$14.16(14), respectively, in units of i$\\times 10^{-11}(-Q_W)/N$ a.u.", "category": "physics_atom-ph" }, { "text": "Effect of alpha variation on the vibrational spectrum of Sr_2: We consider the effect of $\\alpha$ variation on the vibrational spectrum of\nSr$_2$ in the context of a planned experiment to test the stability of\n$\\mu\\equiv m_e/m_p$ using optically trapped Sr$_2$ molecules [Zelevinsky et\nal., Phys. Rev. Lett. {\\bf 100}, 043201; Kotochigova et al., Phys. Rev. A {\\bf\n79}, 012504]. We find the prospective experiment to be 3 to 4 times less\nsensitive to fractional variation in $\\alpha$ as it is to fractional variation\nin $\\mu$. Depending on the precision ultimately achieved by the experiment,\nthis result may give justification for the neglect of $\\alpha$ variation or,\nalternatively, may call for its explicit consideration in the interpretation of\nexperimental results.", "category": "physics_atom-ph" }, { "text": "Direct above-threshold ionization in intense few-cycle laser pulses:\n structures in the angle-integrated energy spectra: This paper concerns the theory of non-recollisional ionization or detachment\nof atoms or ions by intense few-cycle pulses. It is shown that in certain\nconditions of pulse duration, peak intensity and carrier-envelope phase, the\nionization probability integrated over ejection angle varies almost\nperiodically with energy, with a period roughly equal to the photon energy for\nslow enough outgoing electrons. This modulation is found both in calculations\nbased on the strong field approximation (SFA) and in ab initio time-dependent\ncalculations. It is explained as resulting from the interference between the\ncontributions of different saddle times of the modified classical action.\nMethods for efficiently calculating the SFA ionization amplitude beyond the\nusual saddle point approximation are also discussed.", "category": "physics_atom-ph" }, { "text": "A traveling wave decelerator for neutral polar molecules: Recently, a decelerator for neutral polar molecules has been presented that\noperates on the basis of macroscopic, three-dimensional, traveling\nelectrostatic traps (Osterwalder et al., Phys. Rev. A 81, 051401 (2010)). In\nthe present paper, a complete description of this decelerator is given, with\nemphasis on the electronics and the mechanical design. Experimental results\nshowing the transverse velocity distributions of guided molecules are shown and\ncompared to trajectory simulations. An assessment of non-adiabatic losses is\nmade by comparing the deceleration signals from 13-CO with those from 12-CO and\nwith simulated signals.", "category": "physics_atom-ph" }, { "text": "Study of surface potentials using resonant tunneling of cold atoms in\n optical lattices: We study a feasibility of precision measurements of surface potentials at\nmicrometer distances using resonant tunneling of cold atoms trapped in vertical\noptical lattices. A modulation of an amplitude of the lattice potential induces\natomic tunneling among the lattice sites. The resonant modulation frequency\ncorresponds to a difference of potential energy between latices sites which is\ndefined by external force i.e. gravity. The vicinity of the surface alters the\nexternal potentials, and hence the resonant frequency. Application of this\nmethod allows accurate study of Casimir-type potentials and improvement of the\npresent experimental validity of the Newtonian gravitational potential at the\ndistance range of 5 - 30 micrometers.", "category": "physics_atom-ph" }, { "text": "Stable He$^-$ can exist in a strong magnetic field: The existence of bound states of the system $(\\al,e,e,e)$ in a magnetic field\n$B$ is studied using the variational method. It is shown that for $B \\gtrsim\n0.13\\,{\\rm a.u.}$ this system gets bound with total energy below the one of the\n$(\\al,e,e)$ system. It manifests the existence of the stable He$^-$ atomic ion.\nIts ground state is a spin-doublet $^2(-1)^{+}$ at $0.74\\, {\\rm a.u.} \\gtrsim B\n\\gtrsim 0.13\\, {\\rm a.u.}$ and it becomes a spin-quartet $^4(-3)^{+}$ for\nlarger magnetic fields. For $0.8\\, {\\rm a.u.} \\gtrsim B \\gtrsim 0.7\\, {\\rm\na.u.}$ the He$^-$ ion has two (stable) bound states $^2(-1)^{+}$ and\n$^4(-3)^{+}$.", "category": "physics_atom-ph" }, { "text": "Coherence and correlation properties of a one-dimensional attractive\n Fermi gas: A recently developed Quantum Monte Carlo algorithm based on the stochastic\nevolution of Hartree-Fock states has been applied to compute the static\ncorrelation functions of a one-dimensional model of attractively interacting\ntwo component fermions. The numerical results have been extensively compared to\nexisting approximate approaches. The crossover to a condensate of pairs can be\nidentified as the first-order pair coherence extending throughout the whole\nsize of the system. The possibility of revealing the onset of the transition\nwith other observables such as the density-density correlations or the\nsecond-order momentum space correlations is discussed.", "category": "physics_atom-ph" }, { "text": "Observation of electromagnetically induced transparency in evanescent\n fields: We observe and investigate, both experimentally and theoretically,\nelectromagnetically-induced transparency experienced by evanescent fields\narising due to total internal reflection from an interface of glass and hot\nrubidium vapor. This phenomenon manifests itself as a non-Lorentzian peak in\nthe reflectivity spectrum, which features a sharp cusp with a sub-natural width\nof about 1 MHz. The width of the peak is independent of the thickness of the\ninteraction region, which indicates that the main source of decoherence is\nlikely due to collisions with the cell walls rather than diffusion of atoms.\nWith the inclusion of a coherence-preserving wall coating, this system could be\nused as an ultra-compact frequency reference.", "category": "physics_atom-ph" }, { "text": "Sensitivity to alpha-variation in ultracold atomic-scattering\n experiments: We present numerical calculations for cesium and mercury to estimate the\nsensitivity of the scattering length to the variation of the fine structure\nconstant alpha. The method used follows ideas Chin and Flambaum [Phys. Rev.\nLett. 96, 230801 (2006)], where the sensitivity to the variation of the\nelectron to proton mass ratio, beta, was considered. We demonstrate that for\nheavy systems, the sensitivity to variation of alpha is of the same order of\nmagnitude as to variation of beta. Near narrow Feshbach resonances the\nenhancement of the sensitivity may exceed nine orders of magnitude.", "category": "physics_atom-ph" }, { "text": "A simplified 461-nm laser system using blue laser diodes and a hollow\n cathode lamp for laser cooling of Sr: We develop a simplified light source at 461 nm for laser cooling of Sr\nwithout frequency-doubling crystals but with blue laser diodes. An\nanti-reflection coated blue laser diode in an external cavity (Littrow)\nconfiguration provides an output power of 40 mW at 461 nm. Another blue laser\ndiode is used to amplify the laser power up to 110 mW by injection locking. For\nfrequency stabilization, we demonstrate modulation-free polarization\nspectroscopy of Sr in a hollow cathode lamp. The simplification of the laser\nsystem achieved in this work is of great importance for the construction of\ntransportable optical lattice clocks.", "category": "physics_atom-ph" }, { "text": "Black-body radiation induced photodissociation and population\n redistribution of weakly bound states in H$_2^+$: Molecular hydrogen ions in weakly bound states close to the first\ndissociation threshold are attractive quantum sensors for measuring the\nproton-to-electron mass ratio and hyperfine-induced ortho-para mixing. The\nexperimental accuracy of previous spectroscopic studies relying on fast ion\nbeams could be improved by using state-of-the-art ion trap setups. With the\nelectric dipole moment vanishing in H$_2^+$ and preventing fast spontaneous\nemission, radiative lifetimes of the order of weeks are found. We include the\neffect of black-body radiation that can lead to photodissociation and\nrovibronic state redistribution to obtain effective lifetimes for trapped ion\nexperiments. Rate coefficients for bound-bound and bound-continuum processes\nwere calculated using adiabatic nuclear wave functions and nonadiabatic\nenergies, including relativistic and radiative corrections. Effective lifetimes\nfor the weakly bound states were obtained by solving a rate equation model and\nlifetimes in the range of 4 to 523~ms and $>$215~ms were found at room\ntemperature and liquid nitrogen temperature, respectively. Black-body induced\nphotodissociation was identified as the lifetime-limiting effect, which\nguarantees the purity of state-selectively generated molecular ion ensembles.\nThe role of hyperfine-induced $g/u$-mixing, which allows pure rovibrational\ntransitions, was found to be negligible.", "category": "physics_atom-ph" }, { "text": "Energy Levels, Lifetimes and Transition rates for P-like ions from Cr X\n to Zn XVI from large-scale Relativistic Multiconfiguration Calculations: The fully relativistic multiconfiguration Dirac--Hartree--Fock method is used\nto compute excitation energies and lifetimes for the 143 lowest states of the\n$3s^23p^3$, $3s3p^4$, $3s^23p^23d$, $3s3p^33d$, $3p^5$, $3s^23p3d^2$\nconfigurations in P-like ions from Cr X to Zn XVI. Multipole (E1, M1, E2, M2)\ntransition rates, line strengths, oscillator strengths, and branching fractions\namong these states are also given. Valence-valence and core-valence electron\ncorrelation effects are systematically accounted for using large basis function\nexpansions. Computed excitation energies are compared with the NIST ASD and\nCHIANTI compiled values and previous calculations. The mean average absolute\ndifference, removing obvious outliers, between computed and observed energies\nfor the 41 lowest identified levels in Fe XII is only 0.057 \\%, implying that\nthe computed energies are accurate enough to aid identification of new emission\nlines from the sun and other astrophysical sources. The amount of energy and\ntransition data of high accuracy is significantly increased for several P-like\nions of astrophysics interest, where experimental data are still very scarce.", "category": "physics_atom-ph" }, { "text": "Excitation and emission spectra of rubidium in rare-gas thin-films: To understand the optical properties of atoms in solid state matrices, the\nabsorption, excitation and emission spectra of rubidium doped thin-films of\nargon, krypton and xenon were investigated in detail. A two-dimensional\nspectral analysis extends earlier reports on the excitation and emission\nproperties of rubidium in rare-gas hosts. We found that the doped crystals of\nkrypton and xenon exhibit a simple absorption-emission relation, whereas\nrubidium in argon showed more complicated spectral structures. Our sample\npreparation employed in the present work yielded different results for the Ar\ncrystal, but our peak positions were consistent with the prediction based on\nthe linear extrapolation of Xe and Kr data. We also observed a bleaching\nbehavior in rubidium excitation spectra, which suggests a population transfer\nfrom one to another spectral feature due to hole-burning. The observed optical\nresponse implies that rubidium in rare-gas thin-films is detectable with\nextremely high sensitivity, possibly down to a single atom level, in low\nconcentration samples.", "category": "physics_atom-ph" }, { "text": "Quantum statistical measurements of an atom laser beam: We describe a scheme, operating in a manner analogous to a reversed Raman\noutput coupler, for measuring the phase-sensitive quadrature statistics of an\natom laser beam. This scheme allows for the transferral of the atomic field\nstatistics to an optical field, for which the quantum statistics may then be\nmeasured using the well-developed technology of optical homodyne measurement.", "category": "physics_atom-ph" }, { "text": "t-SURFF: Fully Differential Two-Electron Photo-Emission Spectra: The time dependent surface flux (t-SURFF) method is extended to single and\ndouble ionization of two electron systems. Fully differential double emission\nspectra by strong pulses at extreme UV and infrared wave length are calculated\nusing simulation volumes that only accommodate the effective range of the\natomic binding potential and the quiver radius of free electrons in the\nexternal field. For a model system we find pronounced dependence of shake-up\nand non-sequential double ionization on phase and duration of the laser pulse.\nExtension to fully three-dimensional calculations is discussed.", "category": "physics_atom-ph" }, { "text": "Phase-matched coherent hard x-rays from relativistic high-order harmonic\n generation: High-order harmonic generation (HHG) with relativistically strong laser\npulses is considered employing electron ionization-recollisions from multiply\ncharged ions in counterpropagating, linearly polarized attosecond pulse trains.\nThe propagation of the harmonics through the medium and the scaling of HHG into\nthe multi-kilo-electronvolt regime are investigated. We show that the phase\nmismatch caused by the free electron background can be compensated by an\nadditional phase of the emitted harmonics specific to the considered setup\nwhich depends on the delay time between the pulse trains. This renders feasible\nthe phase-matched emission of harmonics with photon energies of several tens of\nkilo-electronvolt from an underdense plasma.", "category": "physics_atom-ph" }, { "text": "Characterization of the electronic ground state of Mg$_2^+$ by PFI-ZEKE\n photoelectron spectroscopy: The $\\mathrm{X}^+\\ ^2\\Sigma_u^+$ ground electronic state of the Mg$_2^+$ ion\nhas been studied by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE)\nphotoelectron spectroscopy. Rotationally cold Mg$_2$ molecules produced in a\nlaser-ablation supersonic-expansion source were ionized by resonant two-photon\nabsorption from the $\\mathrm{X}\\ ^1\\Sigma_g^+(v\"=0)$ ground vibronic state. The\nphotoelectron spectra of the $v^+=3-14$ vibrational levels of the\n$\\mathrm{X}^+$ state were recorded with rotational resolution and their\nanalysis led to the determination of accurate term values and rotational\nconstants for these levels. Improved values of the adiabatic ionization energy\nof $^{24}$Mg$_2$ ($51\\,503.9(4)$ cm$^{-1}$) and of the ground-state\ndissociation energy of $^{24}$Mg$_2^+$ ($10 572.3(6)$ cm$^{-1}$) were\ndetermined from experimental data.", "category": "physics_atom-ph" }, { "text": "Homogeneous linewidth of the I_11/2--I_15/2 optical transition of erbium\n in LiNbO_3:Er^3+: We work out a simple, pulsed pump-probe measurement scheme to measure the\nhomogeneous linewidth of an atomic transition in an inhomogeneously broadened\nspectral line in a solid state environment. We apply the theory to the I_11/2\n-- I_15/2 optical transition of erbium in LiNbO_3:Er^3+ crystal. Beside\nobtaining the homogeneous linewidth, we have estimated the population\nrelaxation time as well.", "category": "physics_atom-ph" }, { "text": "Infinite Order Discrete Variable Representation for Quantum Scattering: A new approach to multi-dimensional quantum scattering by the infinite order\ndiscrete variable representation is presented. Determining the expansion\ncoefficients of the wave function at the asymptotic regions by the solution of\nthe differential Schr\\\"{o}dinger equation, we reduce an infinite set of linear\nequations to a finite one. Application to the benchmark collinear $H + H_2 \\to\nH_2 + H$ reaction is shown to yield precise reaction probabilities.", "category": "physics_atom-ph" }, { "text": "Rydberg states of triatomic hydrogen and deuterium: The triatomic hydrogen ion (H$_3^+$) has spurred tremendous interest in\nastrophysics in recent decades, and Rydberg states of H$_3$ have also\nmaintained an important role for understanding H$_3^+$ experiments. In a\nprevious study [J. Chem. Phys. \\textbf{133}, 234302 (2010)], radiative\ntransitions between neutral H$_3$ Rydberg states were calculated at wavelengths\nnear 7 microns, and could be compared with mid-infrared laser lines observed in\nhydrogen/rare gas discharges. The present study extends the investigation to\nwavelengths near 10 -- 13 microns. Rydberg states of D$_3$ are also treated.", "category": "physics_atom-ph" }, { "text": "Beyond Fowler-Nordheim model: Harmonic generation from metallic\n nano-structures: Metallic structures interacting with electromagnetic fields are known to\nexhibit properties similar to those found in atoms and molecules, such as\nmulti-photon and tunnel ionization. Developing this similarity beyond the\nelectron emission current, we generalize the wellknown Fowler-Nordheim model,\nand predict heretofore unrecognized source of nonlinear optical response from\nnano-structures exposed to illumination with intense optical pulses.", "category": "physics_atom-ph" }, { "text": "Hyperfine-mediated effects in a Lu$^+$ optical clock: We consider hyperfine-mediated effects for clock transitions in\n$^{176}$Lu$^+$. Mixing of fine structure levels due to the hyperfine\ninteraction bring about modifications to Land\\'e $g$-factors and the quadrupole\nmoment for a given state. Explicit expressions are derived for both $g$-factor\nand quadrupole corrections, for which leading order terms arise from the\nnuclear magnetic dipole coupling. High accuracy measurements of the $g$-factors\nfor the $^1S_0$ and $^3D_1$ hyperfine levels are carried out, which provide an\nexperimental determination of the leading order correction terms.", "category": "physics_atom-ph" }, { "text": "Rubidium lifetime in a dark magneto-optical trap: Measurements of rubidium lifetime in a dark magneto-optical trap (DMOT) was\nperformed at various populations of the bright and dark hyperfine states of the\ntrapped atoms. The rubidium lifetime in the trap appeared to be shorter if the\natom spent more time in the bright state. A simple explanation of this effect\nis based on the increase of the cross-section of rubidium collisions with the\nsurrounding warm atoms upon rubidium electronic excitation.", "category": "physics_atom-ph" }, { "text": "Transitions in Zr, Hf, Ta, W, Re, Hg, Ac and U ions with high\n sensitivity to variation of the fine-structure constant: We study transitions between ground and low-energy excited states of heavy\nions corresponding to s-d single-electron transitions or s^2-d^2\ndouble-electron transitions. The large nuclear charge Z and significant change\nin angular momentum of electron orbitals make these transitions highly\nsensitive to a potential variation in the fine-structure constant, alpha. The\ntransitions may be considered as candidates for laboratory searches for\nspace-time variation of alpha.", "category": "physics_atom-ph" }, { "text": "Enhancement factors for positron annihilation on valence and core\n orbitals of noble-gas atoms: Annihilation momentum densities and correlation enhancement factors for\nlow-energy positron annihilation on valence and core electrons of noble-gas\natoms are calculated using many-body theory. s, p and d-wave positrons of\nmomenta up to the positronium-formation threshold of the atom are considered.\nThe enhancement factors parametrize the effects of short-range\nelectron-positron correlations which increase the annihilation probability\nbeyond the independent-particle approximation. For all positron partial waves\nand electron subshells, the enhancement factors are found to be relatively\ninsensitive to the positron momentum. The enhancement factors for the core\nelectron orbitals are also independent of the positron angular momentum. The\nlargest enhancement factor ($\\sim 15$) is found for the 5p orbital in Xe, while\nthe values for the core orbitals are typically $\\sim 1.5$.", "category": "physics_atom-ph" }, { "text": "Radio Frequency Response of the Strongly Interacting Fermi Gases at\n Finite Temperatures: The radio frequency spectrum of the fermions in the unitary limit at finite\ntemperatures is characterized by the sum rule relations. We consider a simple\npicture where the atoms are removed by radio frequency excitations from the\nstrongly interacting states into a state of negligible interaction. We\ncalculate the moments of the response function in the range of temperature\n$0.08 \\epsilon_F < T < 0.8 \\epsilon_F$ using auxiliary field Monte Carlo\ntechnique (AFMC) in which continuum auxiliary fields with a density dependent\nshift are used. We estimate the effects of superfluid pairing from the clock\nshift. We find a qualitative agreement with the pairing gap - pseudogap\ntransition behavior. We also find within the quasiparticle picture that in\norder for the gap to come into quantitative agreement with the previously known\nvalue at T=0, the effective mass has to be $m^* \\sim 1.43 m$. Finally, we\ndiscuss implications for the adiabatic sweep of the resonant magnetic field.", "category": "physics_atom-ph" }, { "text": "Renormalization group analysis of near-field induced dephasing of\n optical spin waves in an atomic medium: While typical theories of atom-light interactions treat the atomic medium as\nbeing smooth, it is well-known that microscopic optical effects driven by\natomic granularity, dipole-dipole interactions, and multiple scattering can\nlead to important effects. Recently, for example, it was experimentally\nobserved that these ingredients can lead to a fundamental, density-dependent\ndephasing of optical spin waves in a disordered atomic medium. Here, we go\nbeyond the short-time and dilute limits considered previously, to develop a\ncomprehensive theory of dephasing dynamics for arbitrary times and atomic\ndensities. In particular, we develop a novel, non-perturbative theory based on\nstrong disorder renormalization group, in order to quantitatively predict the\ndominant role that near-field optical interactions between nearby neighbors has\nin driving the dephasing process. This theory also enables one to capture the\nkey features of the many-atom dephasing dynamics in terms of an effective\nsingle-atom model. These results should shed light on the limits imposed by\nnear-field interactions on quantum optical phenomena in dense atomic media, and\nillustrate the promise of strong disorder renormalization group as a method of\ndealing with complex microscopic optical phenomena in such systems.", "category": "physics_atom-ph" }, { "text": "Performance analysis of an optically pumped magnetometer in Earth's\n magnetic field: We experimentally investigate the influence of the orientation of optically\npumped magnetometers in Earth's magnetic field. We focus our analysis to an\noperational mode that promises femtotesla field resolu-tions at such field\nstrengths. For this so-called light-shift dispersed Mz(LSD-Mz) regime, we focus\non the key parameters defining its performance. That are the reconstructed\nLarmor frequency, the transfer function between output signal and magnetic\nfield amplitude as well as the shot noise limited field resolution. We\ndemonstrate that due to the use of two well balanced laser beams for optical\npumping with different helicities the heading error as well as the field\nsensitivity of a detector both are only weakly influenced by the heading in a\nlarge orientation angle range.", "category": "physics_atom-ph" }, { "text": "Spatially-selective in situ magnetometry of ultracold atomic clouds: We demonstrate novel implementations of high-precision optical magnetometers\nwhich allow for spatially-selective and spatially-resolved in situ measurements\nusing cold atomic clouds. These are realised by using shaped dispersive probe\nbeams combined with spatially-resolved balanced homodyne detection. Two\nmagnetometer sequences are discussed: a vectorial magnetometer, which yields\nsensitivities two orders of magnitude better compared to a previous realisation\nand a Larmor magnetometer capable of measuring absolute magnetic fields. We\ncharacterise the dependence of single-shot precision on the size of the\nanalysed region for the vectorial magnetometer and provide a lower bound for\nthe measurement precision of magnetic field gradients for the Larmor\nmagnetometer. Finally, we give an outlook on how dynamic trapping potentials\ncombined with selective probing can be used to realise enhanced quantum\nsimulations in quantum gas microscopes.", "category": "physics_atom-ph" }, { "text": "Spin-Imbalance in a One-Dimensional Fermi Gas: Superconductivity and magnetism generally do not coexist. Changing the\nrelative number of up and down spin electrons disrupts the basic mechanism of\nsuperconductivity, where atoms of opposite momentum and spin form Cooper pairs.\nNearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an\nexotic pairing mechanism (FFLO) where magnetism is accommodated by formation of\npairs with finite momentum. Despite intense theoretical and experimental\nefforts, however, polarized superconductivity remains largely elusive. Here we\nreport experimental measurements of density profiles of a two spin mixture of\nultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system\nanalogous to electrons in 1D wires. At finite spin imbalance, the system phase\nseparates with an inverted phase profile in comparison to the three-dimensional\ncase. In 1D we find a partially polarized core surrounded by wings composed of\neither a completely paired BCS superfluid or a fully polarized Fermi gas,\ndepending on the degree of polarization. Our observations are in quantitative\nagreement with theoretical calculations in which the partially polarized phase\nis found to be a 1D analogue of the FFLO state. This study demonstrates how\nultracold atomic gases in 1D may be used to create non-trivial new phases of\nmatter, and also paves the way for direct observation and further study of the\nFFLO phase.", "category": "physics_atom-ph" }, { "text": "Ionization and excitation of low-lying circular states of the hydrogen\n atom in strong circularly polarized laser fields: We perform ab initio calculations for the hydrogen atom initially in one of\nthe six circular bound states with the principal quantum numbers n = 2, 3 and\n4, irradiated by a short circularly polarized laser pulse of 400 nm. The field\npropagates in the direction parallel to the z-component of the angular momentum\nof the atom. We investigate probabilities for the atom to ionize or to get on\nsome bound (excited) state or to remain in the initial state after the end of\nthe laser pulse. In most cases, we find pronounced differences in ionization\nprobabilities for atoms in states having different signs of magnetic quantum\nnumber. Usually electrons corotating (with respect to the laser field) ionize\nfaster than their counter-rotating equivalents. We have found important\ndifference in the behavior of the excitation (as a function of the peak laser\nintensity) for initial states with n = 2 and other n (3 or 4). For higher n the\nexcitation is always weaker than the ionization and starts for higher\nintensities. For n = 2 the strong excitation appears before strong ionization\ndue to large probability of one-photon absorption combined with population of\nmany bound states having principal quantum numbers n from 3 up to several\ndozen. Quite accurate analysis of the excitation process is presented.", "category": "physics_atom-ph" }, { "text": "Measurement of electric-field noise from interchangeable samples with a\n trapped-ion sensor: We demonstrate the use of a single trapped ion as a sensor to probe\nelectric-field noise from interchangeable test surfaces. As proof of principle,\nwe measure the magnitude and distance dependence of electric-field noise from\ntwo ion-trap-like samples with patterned Au electrodes. This trapped-ion sensor\ncould be combined with other surface characterization tools to help elucidate\nthe mechanisms that give rise to electric-field noise from ion-trap surfaces.\nSuch noise presents a significant hurdle for performing large-scale trapped-ion\nquantum computations.", "category": "physics_atom-ph" }, { "text": "CARIOQA: Definition of a Quantum Pathfinder Mission: A strong potential gain for space applications is expected from the\nanticipated performances of inertial sensors based on cold atom interferometry\n(CAI) that measure the acceleration of freely falling independent atoms by\nmanipulating them with laser light. In this context, CNES and its partners\ninitiated a phase 0 study, called CARIOQA, in order to develop a Quantum\nPathfinder Mission unlocking key features of atom interferometry for space and\npaving the way for future ambitious space missions utilizing this technology.\nAs a cornerstone for the implementation of quantum sensors in space, the\nCARIOQA phase 0 aimed at defining the Quantum Pathfinder Mission's scenario and\nassociated performance objectives. To comply with these objectives, the payload\narchitecture has been designed to achieve long interrogation time and active\nrotation compensation on a BEC-based atom interferometer. A study of the\nsatellite architecture, including all the subsystems, has been conducted.\nSeveral technical solutions for propulsion and attitude control have been\ninvestigated in order to guarantee optimal operating conditions (limitation of\nmicro-vibrations, maximization of measurement time). A preliminary design of\nthe satellite platform was performed.", "category": "physics_atom-ph" }, { "text": "Spin-1/2 Optical Lattice Clock: We experimentally investigate an optical clock based on $^{171}$Yb ($I=1/2$)\natoms confined in an optical lattice. We have evaluated all known frequency\nshifts to the clock transition, including a density-dependent collision shift,\nwith a fractional uncertainty of $3.4 \\times 10^{-16}$, limited principally by\nuncertainty in the blackbody radiation Stark shift. We measured the absolute\nclock transition frequency relative to the NIST-F1 Cs fountain clock and find\nthe frequency to be 518 295 836 590 865.2(0.7) Hz.", "category": "physics_atom-ph" }, { "text": "Resonant control of photoelectron directionality by interfering one- and\n two-photon pathways: Coherent control of interfering one- and two-photon processes has for decades\nbeen the subject of research to achieve the redirection of photocurrent. The\npresent study develops two-pathway coherent control of ground state helium atom\nabove-threshold photoionization for energies up to the $N=2$ threshold, based\non a multichannel quantum defect and R-matrix calculation. Three parameters are\ncontrolled in our treatment: the optical interference phase $\\Delta\\Phi$, the\nreduced electric field strength\n$\\chi=\\mathcal{E}_{\\omega}^2/{\\mathcal{E}_{2\\omega}}$, and the final state\nenergy $\\epsilon$. A small energy change near a resonance is shown to flip the\nemission direction of photoelectrons with high efficiency, through an example\nwhere $90\\%$ of photoelectrons whose energy is near the $2p^2\\ ^1S^e$ resonance\nflip their emission direction. However, the large fraction of photoelectrons\nionized at the intermediate state energy, which are not influenced by the\noptical control, make this control scheme challenging to realize\nexperimentally.", "category": "physics_atom-ph" }, { "text": "Response time of photoemission at quantum-classic boundary: The response time of the electron to light in photoemission is difficult to\ndefine and measure. Tunneling ionization of atoms, a strong-laser-induced\nphotoemission process, provides a semiclassical case for visiting the problem.\nHere, we show that the response time can be determined at the boundary between\nquantum and classic. Specifically, tunneling is instantaneous but a finite\nresponse time (about 100 attoseconds) is needed for the state of the tunneling\nelectron to evolve into the ionized state around tunnel exit. This time can be\nwell described with a compact expression related to some basic laser and atomic\nparameters. Moreover, it can be directly mapped to and easily decoded from\nphotoelectron momentum with a simple mapping, allowing an unambiguous\nmeasurement. These results shed light on definition and measurement of the\nresponse time of photoemission.", "category": "physics_atom-ph" }, { "text": "Detailed instantaneous ionization rate of H$_2^+$ in intense laser field: Component instantaneous ionization rate (IIR) is introduced and the approach\nof its calculation is formulated. The component IIR's and the overall\n(time-averaged) component ionization rates are calculated for H$_2^+$ at\ndifferent values of inter-nuclear distance in a linearly polarized laser field\nwith $1.0 \\times10^{14}$W cm$^{-2}$ intensity and $\\lambda \\sim 1064 $nm\nwavelength by direct numerical solution of the fixed-nuclei full dimensional\ntime-dependent Schr \\\"odinger equation. The exact overall component ionization\nrates calculated by time-averaging of the component IIR are compared with those\ncalculated approximately via the virtual detector method (VD). Details of the\ntime dependent behavior of the outgoing and incoming electron wavepackets of\nthe H$_2^+$ system in intense laser field at sub-femtosecond time scale are\nstudied based on the calculated component IIR. It is shown clearly that the\npositive (outgoing electron wavepacket) signals of the IIR and its z component\nare strong and sharp but the negative (returning electron wavepacket) signals\nof the IIR are smooth and weak. The structure of the $\\rho$ component of the\nIIR has smooth structure. Relation between the R-dependent ionization rate and\nduration of the ramp of the laser pulse is studied and it is explicitly shown\nthat for internuclear distance R<5.6, when the laser pulse is turned on without\na ramp, the first peak of R-dependent ionization rates moves towards the peak\nof the lower time dependent Floquet quasi-energy state (QES).", "category": "physics_atom-ph" }, { "text": "Supersymmetric Jaynes-Cummings model and its exact solutions: The super-algebraic structure of a generalized version of the Jaynes-Cummings\nmodel is investigated. We find that a Z2 graded extension of the so(2,1) Lie\nalgebra is the underlying symmetry of this model. It is isomorphic to the\nfour-dimensional super-algebra u(1/1) with two odd and two even elements.\nDifferential matrix operators are taken as realization of the elements of the\nsuperalgebra to which the model Hamiltonian belongs. Several examples with\nvarious choices of superpotentials are presented. The energy spectrum and\ncorresponding wavefunctions are obtained analytically.", "category": "physics_atom-ph" }, { "text": "Impact of the continuum Coulomb interaction in quantum-orbit-based\n treatments of high-order above-threshold ionization: We perform a systematic comparison between photoelectron momentum\ndistributions computed with the rescattered-quantum orbit strong-field\napproximation (RQSFA) and the Coulomb-quantum orbit strong-field approximation\n(CQSFA). We exclude direct, hybrid, and multiple scattered CQSFA trajectories,\nand focus on the contributions of trajectories that undergo a single act of\nrescattering. For this orbit subset, one may establish a one-to-one\ncorrespondence between the RQSFA and CQSFA contributions for backscattered and\nforward-scattered trajectory pairs. We assess the influence of the Coulomb\npotential on the ionization and rescattering times of specific trajectory\npairs, kinematic constraints determined by rescattering, and quantum\ninterference between specific pairs of trajectories. We analyze how the Coulomb\npotential alters their ionization and return times, and their interference in\nphotoelectron momentum distributions. We show that Coulomb effects are not\nsignificant for high or medium photoelectron energies and shorter orbits,\nwhile, for lower momentum ranges or longer electron excursion times in the\ncontinuum, the residual Coulomb potential is more important. We also assess the\nagreement of both theories for different field parameters, and show that it\nimproves with the increase of the wavelength.", "category": "physics_atom-ph" }, { "text": "A compact setup for loading magneto-optical trap in ultrahigh vacuum\n environment: We have developed a compact setup which enables loading a magneto-optical\ntrap (MOT) in ultra-high vacuum (UHV) environment. Nearly $1 \\times 10^{8}$\natoms of $^{87}Rb$ are trapped in the MOT at $\\sim 2 \\times 10^{-10}$ Torr base\npressure in the chamber. After the MOT loading, we have successfully\ndemonstrated working of quadrupole magnetic trap in this chamber with a\nlifetime of $\\sim 8 $ s", "category": "physics_atom-ph" }, { "text": "Observation of collisions between cold Li atoms and Yb$^+$ ions: We report on the observation of cold collisions between $^6$Li atoms and\nYb$^+$ ions. This combination of species has recently been proposed as the most\nsuitable for reaching the quantum limit in hybrid atom-ion systems, due to its\nlarge mass ratio. For atoms and ions prepared in the $^2S_{1/2}$ ground state,\nthe charge transfer and association rate is found to be at least~10$^{3}$ times\nsmaller than the Langevin collision rate. These results confirm the excellent\nprospects of $^6$Li--Yb$^+$ for sympathetic cooling and quantum information\napplications. For ions prepared in the excited electronic states $^2P_{1/2}$,\n$^2D_{3/2}$ and $^2F_{7/2}$, we find that the reaction rate is dominated by\ncharge transfer and does not depend on the ionic isotope nor the collision\nenergy in the range $\\sim$~1--120~mK. The low charge transfer rate for ground\nstate collisions is corroborated by theory, but the $4f$ shell in the Yb$^+$\nion prevents an accurate prediction for the charge transfer rate of the\n$^2P_{1/2}$, $^2D_{3/2}$ and $^2F_{7/2}$ states. Using \\textit{ab initio}\nmethods of quantum chemistry we calculate the atom-ion interaction potentials\nup to energies of 30$\\times 10^3$~cm$^{-1}$, and use these to give qualitative\nexplanations of the observed rates.", "category": "physics_atom-ph" }, { "text": "Study of the scalar-pseudoscalar interaction in the francium atom: Fr atom can be successively used to search for the atomic permanent electric\ndipole moment (EDM) [Hyperfine Interactions 236, 53 (2015); Journal of Physics:\nConference Series 691, 012017 (2016)]. It can be induced by the permanent\nelectron EDM predicted by modern extensions of the standard model to be nonzero\nat the level accessible by the new generation of EDM experiments. We consider\nanother mechanism of the atomic EDM generation in Fr. This is caused by the\nscalar-pseudoscalar nucleus-electron neutral current interaction with the\ndimensionless strength constant, $k_{T,P}$. Similar to the electron EDM this\ninteraction violates both spatial parity and time-reversal symmetries and can\nalso induce permanent atomic EDM. It was shown in [Phys. Rev. D 89, 056006\n(2014)] that the scalar-pseudoscalar contribution to the atomic EDM can\ndominate over the direct contribution from the electron EDM within the standard\nmodel. We report high-accuracy combined all-electron and two-step relativistic\ncoupled cluster treatment of the effect from the scalar-pseudoscalar\ninteraction in the Fr atom. Up to the quadruple cluster amplitudes within the\nCCSDT(Q) method were included in correlation treatment. This calculation is\nrequired for the interpretation of the experimental data in terms of $k_{T,P}$.\nThe resulted EDM of the Fr atom expressed in terms of $k_{T,P}$ is $d_{\\rm Fr}=\nk_{T,P} \\cdot 4.50\\cdot10^{-18} e\\cdot {\\rm cm}$, where $e$ is the charge of\nthe electron. The value of the ionization potential of the $^2S_{1/2}$ ground\nstate of Fr calculated within the same methods is in a very good agreement with\nthe experiment.", "category": "physics_atom-ph" }, { "text": "Third-order many-body perturbation theory calculations for the beryllium\n and magnesium isoelectronic sequences: Relativistic third-order MBPT is applied to obtain energies of ions with two\nvalence electrons in the no virtual-pair approximation (NVPA). A total of 302\nthird-order Goldstone diagrams are organized into 12 one-body and 23 two-body\nterms. Only third-order two-body terms and diagrams are presented here, owing\nto the fact that the one-body terms are identical to the previously studied\nthird-order terms in monovalent ions. Dominant classes of diagrams are\nidentified. The model potential is a Dirac-Hartree-Fock $V^{N-2}$ potential,\nand B-spline basis functions in a cavity of finite radius are employed in the\nnumerical calculations. The Breit interaction is taken into account through\nsecond order of perturbation theory and the lowest-order Lamb shift is also\nevaluated. Sample calculations are performed for berylliumlike ions with Z =\n4--7, and for the magnesiumlike ion P IV. The third-order energies are in\nexcellent agreement with measurement with an accuracy at 0.2% level for the\ncases considered. Comparisons are made with previous second-order MBPT results\nand with other calculations. The third-order energy correction is shown to be\nsignificant, improving second-order correlation energies by an order of\nmagnitude.", "category": "physics_atom-ph" }, { "text": "Hiding Single Photons With Spread Spectrum Technology: We describe a proof-of-principal experiment demonstrating the use of spread\nspectrum technology at the single photon level. We show how single photons with\na prescribed temporal shape, in the presence of interfering noise, may be\nhidden and recovered.", "category": "physics_atom-ph" }, { "text": "K-shell photoionization of Na-like to Cl-like ions of Mg, Si, S, Ar, and\n Ca: We present $R$-matrix calculations of photoabsorption and photoionization\ncross sections across the K-edge of Mg, Si, S, Ar, and Ca ions with more than\n10 electrons. The calculations include the effects of radiative and Auger\ndamping by means of an optical potential. The wave functions are constructed\nfrom single-electron orbital bases obtained using a Thomas--Fermi--Dirac\nstatistical model potential. Configuration interaction is considered among all\nstates up to $n=3$. The damping processes affect the resonances converging to\nthe K-thresholds causing them to display symmetric profiles of constant width\nthat smear the otherwise sharp edge at the photoionization threshold. These\ndata are important for modeling of features found in photoionized plasmas.", "category": "physics_atom-ph" }, { "text": "Formation of ultracold metastable RbCs molecules by short-range\n photoassociation: Ultracold metastable RbCs molecules are observed in a double species MOT\nthrough photoassociation near the Rb(5S$_{1/2}$)+Cs(6P$_{3/2}$) dissociation\nlimit followed by radiative stabilization. The molecules are formed in their\nlowest triplet electronic state and are detected by resonant enhanced\ntwo-photon ionization through the previously unobserved $(3)^{3}\\Pi \\leftarrow\na^{3}\\Sigma^{+}$ band. The large rotational structure of the observed\nphotoassociation lines is assigned to the lowest vibrational levels of the\n$0^+,0^-$ excited states correlated to the Rb(5P$_{1/2}$)+Cs(6S$_{1/2}$)\ndissociation limit. This demonstrates the possibility to induce direct\nphotoassociation in heteronuclear alkali-metal molecules at short internuclear\ndistance, as pointed out in [J. Deiglmayr \\textit{et al.}, Phys. Rev. Lett.\n\\textbf{101}, 13304 (2008)].", "category": "physics_atom-ph" }, { "text": "Further study of the Over-Barrier Model to compute charge exchange\n processes: In this paper we study theoretically the process of electron capture between\none-optical-electron atoms (e.g. hydrogenlike or alkali atoms) and ions at\nlow-to-medium impact velocities ($v/v_e \\approx 1$) working on a modification\nof an already developed classical In this work we present an improvement over\nthe Over Barrier Model (OBM) described in a recent paper [F. Sattin, Phys. Rev.\nA {\\bf 62}, 042711 (2000)]. We show that: i) one of the two free parameters\nthere introduced actually comes out consistently from the starting assumptions\nunderlying the model; ii) the modified model thus obtained is as much accurate\nas the former one. Furthermore, we show that OBMs are able to accurately\npredict some recent results of state selective electron capture, at odds with\nwhat previously supposed.", "category": "physics_atom-ph" }, { "text": "Rydberg Electrometry for Optical Lattice Clocks: Electrometry is performed using Rydberg states to evaluate the quadratic\nStark shift of the $5s^2$ $^1\\textrm{S}_0-5s5p$ $^3\\textrm{P}_0$ clock\ntransition in strontium. By measuring the Stark shift of the highly excited\n$5s75d\\;^1\\textrm{D}_2$ state using electromagnetically induced transparency,\nwe characterize the electric field with sufficient precision to provide tight\nconstraints on the systematic shift to the clock transition. Using the\ntheoretically derived, and experimentally verified, polarizability for this\nRydberg state we can measure the residual field with an uncertainty well below\n$1 \\textrm{V} \\textrm{m}^{-1}$. This resolution allows us to constrain the\nfractional frequency uncertainty of the quadratic Stark shift of the clock\ntransition to $2\\times10^{-20}$.", "category": "physics_atom-ph" }, { "text": "Trapping of ultracold polar molecules with a Thin Wire Electrostatic\n Trap: We describe the realization of a dc electric-field trap for ultracold polar\nmolecules, the thin-wire electrostatic trap (TWIST). The thin wires that form\nthe electrodes of the TWIST allow us to superimpose the trap onto a\nmagneto-optical trap (MOT). In our experiment, ultracold polar NaCs molecules\nin their electronic ground state are created in the MOT via photoassociation,\nachieving a continuous accumulation in the TWIST of molecules in low-field\nseeking states. Initial measurements show that the TWIST trap lifetime is\nlimited only by the background pressure in the chamber.", "category": "physics_atom-ph" }, { "text": "Search for the effect of massive bodies on atomic spectra and\n constraints on Yukawa-type interactions of scalar particles: We propose a new method to search for hypothetical scalar particles that have\nfeeble interactions with Standard-Model particles. In the presence of massive\nbodies, these interactions produce a non-zero Yukawa-type scalar-field\nmagnitude. Using radio-frequency spectroscopy data of atomic dysprosium, as\nwell as atomic clock spectroscopy data, we constrain the Yukawa-type\ninteractions of a scalar field with the photon, electron, and nucleons for a\nrange of scalar-particle masses corresponding to length scales $ > 10$ cm. In\nthe limit as the scalar-particle mass $m_\\phi \\to 0$, our derived limits on the\nYukawa-type interaction parameters are: $\\Lambda_\\gamma \\gtrsim 8 \\times\n10^{19}$ GeV, $\\Lambda_e \\gtrsim 1.3 \\times 10^{19}$ GeV, and $\\Lambda_N\n\\gtrsim 6 \\times 10^{20}$ GeV. Our measurements also constrain combinations of\ninteraction parameters, which cannot otherwise be probed with traditional\nanomalous-force measurements. We suggest further measurements to improve on the\ncurrent level of sensitivity.", "category": "physics_atom-ph" }, { "text": "Fragmentation of Positronium (Ps) in collision with Li ion: Fragmentation of ground state ortho Positronium (Ps) in collision with Li ion\n(Li+) is studied in the framework of post collisional Coulomb distorted eikonal\napproximation (CDEA) for the target elastic case . The present model takes\naccount of the two center effect on the ejected e which is crucial for a proper\ndescription of the projectile ionization involving an ionic target. Both the\nfully differential (TDCS) and the doubly differential (DDCS) cross sections\n(energy spectra) are investigated at intermediate and high incident energies. A\nbroad distinct Electron loss peak (ELP) centered around v_e ~ v_p is noted in\nthe e energy spectrum in contrast to the sharp ELP for a heavy projectile. Two\nsalient features are noted in the present study: i) the shift of the e DDCS\npeak (summed over e+ angles) towards higher ejection energy with respect to\nhalf the residual energy of the system, ii) comparison of the e& e+ energy\nspectra reflect a strong e - e+ asymmetry with respect to the ratio v_e/v_p =1\n>. Both these features could be attributed to the post collisional two center\neffect on the e due to its parent nucleus (e+) and the screened target ion .\nTwo different wave functions of the Li ion are chosen in order to test the\nsensitivity of the present results with respect to the choice of the wave\nfunction.", "category": "physics_atom-ph" }, { "text": "The momentum distribution of two bosons in one dimension with infinite\n contact repulsion in harmonic trap gets analytical: For a harmonically trapped system consisting of two bosons in one spatial\ndimension with infinite contact repulsion (hard core bosons), we derive an\nexpression for the one-body density matrix $\\rho_B$ in terms of centre of mass\nand relative coordinates of the particles. The deviation from $\\rho_F$, the\ndensity matrix for the two fermions case, can be clearly identified. Moreover,\nthe obtained $\\rho_B$ allows us to derive a closed form expression of the\ncorresponding momentum distribution $n_{B}(p)$. We show how the result deviates\nfrom the noninteracting fermionic case, the deviation being associated to the\nshort range character of the interaction. Mathematically, our analytical\nmomentum distribution is expressed in terms of one and two variables confluent\nhypergeometric functions. Our formula satisfies the correct normalization and\npossesses the expected behavior at zero momentum. It also exhibits the high\nmomentum $1/p^4 $ tail with the appropriate Tan's coefficient. Numerical\nresults support our findings.", "category": "physics_atom-ph" }, { "text": "Search for vector dark matter in microwave cavities with Rydberg atoms: We propose a novel experiment to search for dark matter, based on the\napplication of an electric field inside a microwave cavity and electrometry\nusing Rydberg atoms. We show that this kind of experiment could be extremely\nuseful for detecting specific dark matter candidates, namely massive vector\nfields coupled to the photon field, more commonly known as dark photons. Such a\nmassive vector field is a good candidate for dark matter. Using realistic\nexperimental parameters we show that such an experiment could improve the\ncurrent constraint on the coupling constant of the dark photons to Standard\nModel photons in the 1~$\\mu$eV to 10~$\\mu$eV mass range, with the possibility\nof tuning the maximum sensitivity via the cavity size. The main limiting\nfactors on the sensitivity of the experiment are the amplitude stability of the\napplied field and the measurement uncertainty of the electric field by the\natoms.", "category": "physics_atom-ph" }, { "text": "Enhanced $\\mathcal{P,T}$-violating nuclear magnetic quadrupole moment\n effects in laser-coolable molecules: Nuclear magnetic quadrupole moments (MQMs), like intrinsic electric dipole\nmoments of elementary particles, violate both parity and time-reversal symmetry\nand therefore probe physics beyond the Standard Model of particle physics. We\nreport on accurate relativistic coupled cluster calculations of the nuclear MQM\ninteraction constants in BaF, YbF, BaOH, and YbOH. We elaborate on estimates of\nthe uncertainty of our results. The implications of experiments searching for\nnonzero nuclear MQMs are discussed.", "category": "physics_atom-ph" }, { "text": "Hybrid quantum systems of atoms and ions: In recent years, ultracold atoms have emerged as an exceptionally\ncontrollable experimental system to investigate fundamental physics, ranging\nfrom quantum information science to simulations of condensed matter models.\nHere we go one step further and explore how cold atoms can be combined with\nother quantum systems to create new quantum hybrids with tailored properties.\nCoupling atomic quantum many-body states to an independently controllable\nsingle-particle gives access to a wealth of novel physics and to completely new\ndetection and manipulation techniques. We report on recent experiments in which\nwe have for the first time deterministically placed a single ion into an atomic\nBose Einstein condensate. A trapped ion, which currently constitutes the most\npristine single particle quantum system, can be observed and manipulated at the\nsingle particle level. In this single-particle/many-body composite quantum\nsystem we show sympathetic cooling of the ion and observe chemical reactions of\nsingle particles in situ.", "category": "physics_atom-ph" }, { "text": "The Heidelberg compact electron beam ion traps: Electron beam ion traps (EBIT) are ideal tools for both production and study\nof highly charged ions (HCI). In order to reduce their construction,\nmaintenance, and operation costs we have developed a novel, compact,\nroom-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already\ncommissioned devices operate at the strongest fields (up to 0.86 T) reported\nfor such EBITs using permanent magnets, run electron beam currents up to 80 mA\nand energies up to 10 keV. They demonstrate HCI production, trapping, and\nextraction of pulsed Ar$^{16+}$ bunches and continuous 100 pA ion beams of\nhighly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron\nbeam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon\ncount rates, e. g., in x-ray spectroscopy of dielectronic recombination in HCIs\nup to Fe$^{24+}$, achieving an electron-energy resolving power of $E/\\Delta E >\n1500$ at 5 keV. Besides traditional on-axis electron guns, we have also\nimplemented a novel off-axis gun for laser, synchrotron, and free-electron\nlaser applications, offering clear optical access along the trap axis. We\nreport on its first operation at a synchrotron radiation facility demonstrating\nresonant photoexcitation of highly charged oxygen.", "category": "physics_atom-ph" }, { "text": "Differential phase extraction in an atom gradiometer: We present here a method for the extraction of the differential phase of an\natom gradiometer that exploits the correlation of the vibration signal measured\nby an auxiliary classical sensor, such as a seismometer or an accelerometer. We\nshow that sensitivities close to the quantum projection noise limit can be\nreached, even when the vibration noise induces phase fluctuations larger than\n2$\\pi$. This method doesn't require the correlation between the atomic and\nclassical signals to be perfect and allows for an exact determination of the\ndifferential phase, with no bias. It can also be applied to other\nconfigurations of differential interferometers, such as for instance\ngyrometers, conjugate interferometers for the measurement of the fine structure\nconstant, or differential accelerometers for tests of the equivalence principle\nor detection of gravitational waves.", "category": "physics_atom-ph" }, { "text": "Finite Nuclear Size Effect to the Fine Structure of Heavy Muonic Atoms: The finite-nuclear size correction to the fine structure of muonic atoms are\nconsidered. The procedure for the analytical calculation of the energies and\nwave functions has been derived in a homogeneously charged sphere nuclear\ncharge distribution approximation. The finite-nuclear size effect was\ncalculated in a first few orders of the perturbation energy, with the accurate\nestimations of the convergence. Finally, we present energies of the low-lying\nelectronic and muonic states with the finite-nuclear size correction,\ncalculated analytically, for ${}^{185}_{75}\\text{Re}$ ion.", "category": "physics_atom-ph" }, { "text": "Three-atom scattering via the Faddeev scheme in configuration space: Faddeev equations in configuration space and integral form for three-atom\nscattering processes are formulated allowing for additive and nonadditive\nforces. The explicit partial wave decomposition is displayed. This formulation\nappears to be a valuable alternative to current approaches based on\nhyperspherical harmonic expansion methods of the Schr\\\"odinger equation.", "category": "physics_atom-ph" }, { "text": "All-optical runaway evaporation to Bose-Einstein condensation: We demonstrate runaway evaporative cooling directly with a tightly confining\noptical dipole trap and achieve fast production of condensates of 1.5x10^5 87Rb\natoms. Our scheme is characterized by an independent control of the optical\ntrap confinement and depth, permitting forced evaporative cooling without\nreducing the trap stiffness. Although our configuration is particularly well\nsuited to the case of 87Rb atoms in a 1565nm optical trap, where an efficient\ninitial loading is possible, our scheme is general and should allow all-optical\nevaporative cooling at constant stiffness for most species.", "category": "physics_atom-ph" }, { "text": "Spin-orbit coupling in the hydrogen atom, the Thomas precession, and the\n exact solution of Dirac's equation: Bohr's model of the hydrogen atom can be extended to account for the observed\nspin-orbit interaction, either with the introduction of the Thomas precession,\nor with the stipulation that, during a spin-flip transition, the orbital radius\nremains intact. In other words, if there is a desire to extend Bohr's model to\naccommodate the spin of the electron, then experimental observations mandate\nthe existence of the Thomas precession, which is a questionable hypothesis, or\nthe existence of artificially robust orbits during spin-flip transitions. This\nis tantamount to admitting that Bohr's model, which is a poor man's way of\nunderstanding the hydrogen atom, is of limited value, and that one should\nreally rely on Dirac's equation for the physical meaning of spin, for the\nmechanism that gives rise to the gyromagnetic coefficient g=2, for Zeeman\nsplitting, for relativistic corrections to Schr\\\"odinger's equation, for\nDarwin's term, and for the correct 1/2 factor in the spin-orbit coupling\nenergy.", "category": "physics_atom-ph" }, { "text": "Active stabilization of kilogauss magnetic fields to the ppm level for\n magnetoassociation on ultranarrow Feshbach resonances: Feshbach association of ultracold molecules using narrow resonances requires\nexquisite control of the applied magnetic field. Here we present a magnetic\nfield control system to deliver magnetic fields of over 1000 G with ppm-level\nprecision integrated into an ultracold-atom experimental setup. We combine a\nbattery-powered current-stabilized power supply with active feedback\nstabilization of the magnetic field using fluxgate magnetic field sensors. As a\nreal-world test we perform microwave spectroscopy of ultracold Rb atoms and\ndemonstrate an upper limit on our magnetic field stability of 2.4(3) mG at 1050\nG [2.3(3) ppm relative] as determined from the spectral feature.", "category": "physics_atom-ph" }, { "text": "Collision-induced C_60 rovibrational relaxation probed by state-resolved\n nonlinear spectroscopy: Quantum state-resolved spectroscopy was recently achieved for C60 molecules\nwhen cooled by buffer gas collisions and probed with a midinfrared frequency\ncomb. This rovibrational quantum state resolution for the largest molecule on\nrecord is facilitated by the remarkable symmetry and rigidity of C60, which\nalso present new opportunities and challenges to explore energy transfer\nbetween quantum states in this many-atom system. Here we combine state-specific\noptical pumping, buffer gas collisions, and ultrasensitive intracavity\nnonlinear spectroscopy to initiate and probe the rotation-vibration energy\ntransfer and relaxation. This approach provides the first detailed\ncharacterization of C60 collisional energy transfer for a variety of collision\npartners, and determines the rotational and vibrational inelastic collision\ncross sections. These results compare well with our theoretical modeling of the\ncollisions, and establish a route towards quantum state control of a new class\nof unprecedentedly large molecules.", "category": "physics_atom-ph" }, { "text": "Bethe logarithms for the 1 singlet S, 2 singlet S and 2 triplet S states\n of helium and helium-like ions: We have computed the Bethe logarithms for the 1 singlet S, 2 singlet S and 2\ntriplet S states of the helium atom to about seven figure-accuracy using a\ngeneralization of a method first developed by Charles Schwartz. We have also\ncalculated the Bethe logarithms for the helium-like ions of Li, Be, O and S for\nall three states to study the 1/Z behavior of the results. The Bethe logarithm\nof H minus was also calculated with somewhat less accuracy. The use of our\nBethe logarithms for the excited states of neutral helium, instead of those\nfrom Goldman and Drake's first-order 1/Z-expansion, reduces by several orders\nof magnitude the discrepancies between the theoretically calculated and\nexperimentally measured ionization potentials of these states.", "category": "physics_atom-ph" }, { "text": "Elliptically polarized laser-pumped $M_x$ magnetometer towards\n applications at room temperature: An atomic magnetometer operated with elliptically polarized light is\ninvestigated theoretically and experimentally. To explore the potential of this\nmagnetometric configuration, the analytical form of the outgoing signal is\nderived. Parameters that significantly influence the performance are optimized,\nwhich lead to a sensitivity of 300 $\\rm fT/\\sqrt{Hz}$ at 45 $^{\\circ}$C with a\n2$\\times$2$\\times2$ cm uncoated Rb vapor cell. It is remarkable that a\nsensitivity of 690 $\\rm fT/\\sqrt{Hz}$ is achieved at room temperature of 24\n$^{\\circ}$C, which is improved by an order of magnitude compared with the\nconventional $M_x$ magnetometer under its own optimized condition. The\nelliptically polarized approach offers attractive features for developing\ncompact, low-power magnetometers, which are available without heating the\nuncoated vapor cell.", "category": "physics_atom-ph" }, { "text": "Spin-motion coupling in a circular Rydberg state quantum simulator: case\n of two atoms: Rydberg atoms are remarkable tools for the quantum simulation of spin arrays.\nCircular Rydberg atoms open the way to simulations over very long time scales,\nusing a combination of laser trapping of the atoms and spontaneous-emission\ninhibition, as shown in the proposal of a XXZ spin-array simulator based on\nchains of trapped circular atoms [T.L. Nguyen $\\textit{et al.}$, Phys. Rev. X\n8, 011032 (2018)]. Such simulators could reach regimes (thermalization, glassy\ndynamics) that are out of the reach of those based on ordinary,\nlow-angular-momentum short-lived Rydberg atoms. Over the promised long time\nscales, the unavoidable coupling of the spin dynamics with the atomic motion in\nthe traps may play an important role. We study here the interplay between the\nspin exchange and motional dynamics in the simple case of two interacting\ncircular Rydberg atoms confined in harmonic traps. The time evolution is solved\nexactly when the position dependence of the dipole-dipole interaction terms can\nbe linearized over the extension of the atomic motion. We present numerical\nsimulations in more complex cases, using the realistic parameters of the\nsimulator proposal. We discuss three applications. First, we show that\nrealistic experimental parameters lead to a regime in which atomic and spin\ndynamics become fully entangled, generating interesting non-classical motional\nstates. We also show that, in other parameter regions, the spin dynamics\nnotably depends on the initial temperature of the atoms in the trap, providing\na sensitive motional thermometry method. Last, and most importantly, we discuss\nthe range of parameters in which the motion has negligible influence over the\nspin dynamics.", "category": "physics_atom-ph" }, { "text": "Radiation trapping in a dense cold Rydberg gas: Cold atomic gases resonantly excited to Rydberg states can exhibit strong\noptical nonlinearity at the single photon level. We observe that in such\nsamples radiation trapping leads to an additional mechanism for Rydberg\nexcitation. Conversely we demonstrate that Rydberg excitation provides a novel\nin situ probe of the spectral, statistical, temporal and spatial properties of\nthe trapped re-scattered light. We also show that absorption can lead to an\nexcitation saturation that mimics the Rydberg blockade effect. Collective\neffects due to multiple scattering may co-exist with co-operative effects due\nto long-range interactions between the Rydberg atoms, adding a new dimension to\nquantum optics experiments with cold Rydberg gases.", "category": "physics_atom-ph" }, { "text": "Compact structures for single-beam magneto-optical trapping of ytterbium: Today's best optical lattice clocks are based on the spectroscopy of trapped\nalkaline-earth-like atoms such as ytterbium and strontium atoms. The\ndevelopment towards mobile or even space-borne clocks necessitates concepts for\nthe compact laser-cooling and trapping of these atoms with reduced laser\nrequirements. Here we present two compact and robust achromatic mirror\nstructures for single-beam magneto-optical trapping of alkaline-earth-like\natoms using two widely separated optical cooling frequencies. We have compared\nthe trapping and cooling performance of a monolithic aluminium structure that\ngenerates a conventional trap geometry to a quasi-planar platform based on a\nperiodic mirror structure for different isotopes of Yb. Compared to prior work\nwith strontium in non-conventional traps, where only bosons were trapped on a\nnarrow line transition, we demonstrate two-stage cooling and trapping of a\nfermionic alkaline-earth-like isotope in a single-beam quasi-planar structure.", "category": "physics_atom-ph" }, { "text": "Atomic-state diagnostics and optimization in cold-atom experiments: We report on the creation, observation and optimization of superposition\nstates of cold atoms. In our experiments, rubidium atoms are prepared in a\nmagneto-optical trap and later, after switching off the trapping fields,\nFaraday rotation of a weak probe beam is used to characterize atomic states\nprepared by application of appropriate light pulses and external magnetic\nfields. We discuss the signatures of polarization and alignment of atomic spin\nstates and identify main factors responsible for deterioration of the atomic\nnumber and their coherence and present means for their optimization, like\nrelaxation in the dark with the strobe probing. These results may be used for\ncontrolled preparation of cold atom samples and in situ magnetometry of static\nand transient fields", "category": "physics_atom-ph" }, { "text": "Solving close-coupling equations in momentum space without singularities\n for charged targets: The analytical treatment of the Greens function in the convergent\nclose-coupling method [Bray et al. Comp. Phys. Comm. 203 147 (2016)] has been\nextended to charged targets. Furthermore, we show that this approach allows for\ncalculation of cross sections at zero channel energy. For neutral targets this\nmeans the electron scattering length may be obtained from a single calculation\nwith zero incident energy. For charged targets the non-zero excitation cross\nsections at thresholds can also be calculated by simply setting the incident\nenergy to the exact threshold value. These features are demonstrated by\nconsidering electron scattering on H and He+.", "category": "physics_atom-ph" }, { "text": "Cubic wavefunction deformation of compressed atoms: We hypothesize that in a non-metallic crystalline structure under extreme\npressures, atomic wavefunctions deform to adopt a reduced rotational symmetry\nconsistent with minimizing interstitial space in the crystal. We exemplify with\na simple numeric variational calculation that yields the energy cost of this\ndeformation for Helium to 25%. Balancing this with the free energy gained by\ntighter packing we obtain the pressures required to effect such deformation.\nThe consequent modification of the structure suggests a decrease in the\nresistance to tangential stress, and an associated decrease of the crystal's\nshear modulus. The atomic form factor is also modified. We also compare with\nneutron matter in the interior of compact stars.", "category": "physics_atom-ph" }, { "text": "Relativistic ionization-rescattering with tailored laser pulses: The interaction of relativistically strong tailored laser pulses with an\natomic system is considered. Due to a special tailoring of the laser pulse, the\nsuppression of the relativistic drift of the ionized electron and a dramatic\nenhancement of the rescattering probability is shown to be achievable. The high\nharmonic generation rate in the relativistic regime is calculated and shown to\nbe increased by several orders of magnitude compared to the case of\nconventional laser pulses. The energies of the revisiting electron at the\natomic core can approach the MeV domain, thus rendering hard x-ray harmonics\nand nuclear reactions with single atoms feasible.", "category": "physics_atom-ph" }, { "text": "Post-Prior discrepancies in CDW-EIS calculations for ion impact\n ionization fully differential cross sections: In this work we present fully differential cross sections (FDCSs)\ncalculations using post and prior version of CDW--EIS theory for helium single\nionization by 100 MeV C$^{6+}$ amu$^{-1}$ and 3.6 MeV amu$^{-1}$ Au$^{24+}$ and\nAu$^{53+}$ ions. We performed our calculations for different momentum transfer\nand ejected electron energies. The influence of internuclear potential on the\nejected electron spectra is taken into account in all cases. We compare our\ncalculations with absolute experimental measurements. It is shown that prior\nversion calculations give better agreement with experiments in almost all\nstudied cases.", "category": "physics_atom-ph" }, { "text": "Many-body theory of positron binding in polyatomic molecules: Positrons bind to molecules leading to vibrational excitation and\nspectacularly enhanced annihilation. Whilst positron binding energies have been\nmeasured via resonant annihilation spectra for $\\sim$90 molecules in the past\ntwo decades, an accurate \\emph{ab initio} theoretical description has remained\nelusive. Of the molecules studied experimentally, calculations exist for only\n6, and for these, standard quantum chemistry approaches have proved severely\ndeficient, agreeing with experiment to at best 25% accuracy for polar\nmolecules, and failing to predict binding in nonpolar molecules. The mechanisms\nof binding are not understood. Here, we develop a many-body theory of\npositron-molecule interactions and uncover the role of strong many-body\ncorrelations including polarization of the electron cloud, screening of the\npositron-electron Coulomb interaction by molecular electrons, and crucially,\nthe unique non-perturbative process of virtual-positronium formation (where a\nmolecular electron temporarily tunnels to the positron): they dramatically\nenhance binding in polar molecules and enable binding in nonpolars. We also\nelucidate the role of individual molecular orbitals, highlighting the\nimportance of electronic $\\pi$ bonds. Overall, we calculate binding energies in\nagreement with experiment (to within 1% in cases), and we predict binding in\nformamide and nucleobases. As well as supporting resonant annihilation\nexperiments and positron-based molecular spectroscopy, the approach can be\nextended to positron scattering and annihilation $\\gamma$ spectra in molecules\nand condensed matter, to provide fundamental insight and predictive capability\nrequired to properly interpret materials science diagnostics, develop\nantimatter-based technologies (including positron traps, beams and positron\nemission tomography), and understand positrons in the galaxy.", "category": "physics_atom-ph" }, { "text": "Attosecond Transient Absorption Spectroscopy of doubly-excited states in\n helium: Strong-field manipulation of autoionizing states is a crucial aspect of\nelectronic quantum control. Recent measurements of the attosecond transient\nabsorption spectrum of helium dressed by a few-cycle visible pulse [Ott et al.,\narXiv:1205.0519[physics.atom-ph] ] provide evidence of novel ultrafast resonant\nphenomena, namely, two-photon Rabi oscillations between doubly-excited states\nand the inversion of Fano profiles. Here we present the results of accurate\n\\emph{ab-initio} calculations that agree with these observations and in\naddition predict that (i) inversion of Fano profiles is actually periodic in\nthe coupling laser intensity and (ii) the supposedly dark $2p^2$ {$^1$S} state\nalso appears in the spectrum. Closer inspection of the experimental data\nconfirms the latter prediction.", "category": "physics_atom-ph" }, { "text": "Enabling high-precision 3D strong-field measurements - Ionization with\n low-frequency fields in the tunneling regime: Ionization of an atom or molecule presents surprising richness beyond our\ncurrent understanding: strong-field ionization with low-frequency fields\nrecently revealed unexpected kinetic energy structures (1, 2). A solid grasp on\nelectron dynamics is however pre-requisite for attosecond-resolution\nrecollision imaging (3), orbital tomography (4), for coherent sources of keV\nlight (5), or to produce zeptosecond-duration x-rays (6). We present a\nmethodology that enables scrutinizing strong-field dynamics at an unprecedented\nlevel. Our method provides high-precision measurements only 1 meV above the\nthreshold despite 5 orders higher ponderomotive energies. Such feat was\nrealized with a specifically developed ultrafast mid-IR light source in\ncombination with a reaction microscope. We observe electron dynamics in the\ntunneling regime ({\\gamma} = 0.3) and show first 3D momentum distributions\ndemonstrating surprising new observations of near-zero momentum electrons and\nlow momentum structures, below the eV, despite quiver energies of 95 eV.", "category": "physics_atom-ph" }, { "text": "Combination of the single-double coupled cluster and the configuration\n interaction methods; application to barium, lutetium and their ions: A version of the method of accurate calculations for few valence-electron\natoms which combines linearized single-double coupled cluster method with the\nconfiguration interaction technique is presented. The use of the method is\nillustrated by calculations of the energy levels for Ba, Ba$^+$, Lu, Lu$^+$ and\nLu$^{2+}$. Good agreement with experiment is demonstrated and comparison with\nprevious version of the method (Safronova {\\em et al}, PRA {\\bf 80}, 012516\n(2009)) is made.", "category": "physics_atom-ph" }, { "text": "Model for Trapped Ion interacting with Standing Wave: We treat the interaction of a trapped ion with a standing-wave light field\nrelaxing the previous condition of the trapping ion being on the node of the\nstanding wave. In addition we work to second order in the Lamb-Dicke parameter\n$\\eta$, the extension to higher orders in $\\eta$ is also indicated. Only a\nsimple transformation to the ``dressed basis'' [subject to the constraint of\nPauli algebra] is required in order to show that the ion interacting with a\nstanding light-wave may be described by the Jaynes-Cummings Hamiltonian.", "category": "physics_atom-ph" }, { "text": "Random Phase Approximation For allowed and Parity Non-conserving\n Electric Dipole Transition Amplitudes and its connection with Many-Body\n Perturbation Theory and Coupled Cluster Theory: The connections between the Random Phase Approximation (RPA) and Many-Body\nPerturbation Theory (MBPT) and its all order generalisation, the Coupled-\nCluster Theory (CCT) have been explored. Explicit expressions have been derived\nfor the electric dipole amplitudes for allowed and forbidden transitions\ninduced by the parity non-conserving neutral weak interaction. The Goldstone\ndiagrams associated with the RPA terms in both cases are shown to arise in MBPT\nand CCT and the numerical verification of this relationship is made for the\nallowed electric dipole transitions.", "category": "physics_atom-ph" }, { "text": "High-performance, compact optical standard: We describe a high-performance, compact optical frequency standard based on a\nmicrofabricated Rb vapor cell and a low-noise, external cavity diode laser\noperating on the Rb two-photon transition at 778 nm. The optical standard\nachieves an instability of 1.8x10$^{-13}$/$\\sqrt{\\tau}$ for times less than 100\ns and a flicker noise floor of 1x10$^{-14}$ out to 6000 s. At long integration\ntimes, the instability is limited by variations in optical probe power and the\nAC Stark shift. The retrace was measured to 5.7x10$^{-13}$ after 30 hours of\ndormancy. Such a simple, yet high-performance optical standard could be\nsuitable as an accurate realization of the SI meter or, if coupled with an\noptical frequency comb, as a compact atomic clock comparable to a hydrogen\nmaser.", "category": "physics_atom-ph" }, { "text": "A Feshbach resonance in d-wave collisions: We analyse a narrow Feshbach resonance with ultra-cold chromium atoms\ncolliding in d-wave. The resonance is made possible by dipole-dipole\ninteractions, which couple an incoming $l=2$ collision channel with a bound\nmolecular state with $l=0$. We find that three-body losses associated to this\nresonance increase with temperature, and that the loss feature width as a\nfunction of magnetic field also increases linearly with temperature. The\nanalysis of our experimental data shows that the Feshbach coupling is small\ncompared both to the temperature and to the density limited lifetime of the\nresonant bound molecular state. One consequence is that the three body losse\nrate is proportionnal to the square of the number of atoms, and that we can\ndirectly relate the amplitude of the losses to the Feshbach coupling parameter.\nWe compare our measurement to a calculation of the coupling between the\ncollisionnal channel and the molecular bound state by dipole-dipole\ninteractions, and find a good agreement, with no adjustable parameter. An\nanalysis of the loss lineshape is also performed, which enables to precisely\nmeasure the position of the resonance.", "category": "physics_atom-ph" }, { "text": "Imaging Cold Molecules on a Chip: We present the integrated imaging of cold molecules in a microchip\nenvironment. The on-chip de- tection is based on REMPI, which is\nquantum-state-selective and generally applicable. We demon- strate and\ncharacterize time-resolved spatial imaging and subsequently use it to analyze\nthe effect of a phase-space manipulation sequence aimed at compressing the\nvelocity distribution of a molec- ular ensemble with a view to future\nhigh-resolution spectroscopic studies. The realization of such on-chip\nmeasurements adds the final fundamental component to the molecule chip,\noffering a new and promising route for investigating cold molecules.", "category": "physics_atom-ph" }, { "text": "A surface-patterned chip as a strong source of ultra-cold atoms for\n quantum technologies: Laser cooled atoms are central to modern precision measurements. They are\nalso increasingly important as an enabling technology for experimental cavity\nquantum electrodynamics, quantum information processing and matter wave\ninterferometry. Although significant progress has been made in miniaturising\natomic metrological devices, these are limited in accuracy by their use of hot\natomic ensembles and buffer gases. Advances have also been made in producing\nportable apparatus that benefit from the advantages of atoms in the microKelvin\nregime. However, simplifying atomic cooling and loading using microfabrication\ntechnology has proved difficult. In this letter we address this problem,\nrealising an atom chip that enables the integration of laser cooling and\ntrapping into a compact apparatus. Our source delivers ten thousand times more\natoms than previous magneto-optical traps with microfabricated optics and, for\nthe first time, can reach sub-Doppler temperatures. Moreover, the same chip\ndesign offers a simple way to form stable optical lattices. These features,\ncombined with the simplicity of fabrication and the ease of operation, make\nthese new traps a key advance in the development of cold-atom technology for\nhigh-accuracy, portable measurement devices.", "category": "physics_atom-ph" }, { "text": "Enhancing sensitivity of atomic microwave receiver combining laser\n arrays: Rydberg atom,which exhibits a strong response to weak electric(E) fields,is\nregarded as a promising atomic receiver to surpass sensitivity of conventional\nreceivers. However, its sensitivity is strongly limited by the noise coming\nfrom both classical and quantum levels and how to enhance it significantly\nremains challenging. Here we experimentally prove that the sensitivity of\nRydberg atomic receiver can be increased to 23 nV/cm/Hz1/2 by combining laser\narrays. Theoretically, we demonstrate that multiple beams illuminating on a PD\nperform better than multiple PDs for laser arrays.In our experiment,10 dB SNR\nenhancement is achieved by utilizing 2 * 2 probe beam arrays, compared to the\nperformance of a laser beam,and it can be enhanced further just by adding a\nresonator. The results could offer an avenue for the design and optimization of\nultrahigh-sensitivity Rydberg atomic receivers and promote applications in\ncosmology, meteorology, communication, and microwave quantum technology.", "category": "physics_atom-ph" }, { "text": "Fourth-order perturbative extension of the singles-doubles\n coupled-cluster method: Fourth-order many-body corrections to matrix elements for atoms with one\nvalence electron are derived. The obtained diagrams are classified using\ncoupled-cluster-inspired separation into contributions from n-particle\nexcitations from the lowest-order wavefunction. The complete set of\nfourth-order diagrams involves only connected single, double, and triple\nexcitations and disconnected quadruple excitations. Approximately half of the\nfourth-order diagrams are not accounted for by the popular coupled-cluster\nmethod truncated at single and double excitations (CCSD). Explicit formulae are\ntabulated for the entire set of fourth-order diagrams missed by the CCSD method\nand its linearized version, i.e. contributions from connected triple and\ndisconnected quadruple excitations. A partial summation scheme of the derived\nfourth-order contributions to all orders of perturbation theory is proposed.", "category": "physics_atom-ph" }, { "text": "Rubidium \"whiskers\" in a vapor cell: Crystals of metallic rubidium are observed ``growing'' from paraffin coating\nof buffer-gas-free glass vapor cells. The crystals have uniform square\ncross-section, $\\approx 30 \\mu$m on the side, and reach several mm in length.", "category": "physics_atom-ph" }, { "text": "A time-dependent Schr\u00f6dinger equation for molecular core-hole dynamics: X-ray spectroscopy is an important tool for the investigation of matter. X\nrays primarily interact with inner-shell electrons creating core (inner-shell)\nholes that will decay on the time scale of attoseconds to few femtoseconds\nthrough electron relaxations involving the emission of a photon or an electron.\nThe advent of femtosecond x-ray pulses expands x-ray spectroscopy to the time\ndomain and will eventually allow the control of core-hole population on\ntimescales comparable to core-vacancy lifetimes. For both cases, a theoretical\napproach that accounts for the x-ray interaction while the electron relaxations\noccur is required. Here we describe a time-dependent framework, based on\nsolving the time-dependent Schr\\\"odinger equation, that is suitable for\ndescribing the induced electron and nuclear dynamics.", "category": "physics_atom-ph" }, { "text": "Symmetrisation effects on the correlation time delay: We analyze the electronic correlation contribution to the time delay in the\nphoto-ionization of the excited ortho- and para-Helium states. A simple\nestimation, based on the ionization probability amplitudes, shows that the\ndifferent form of anti-symmetrising both states can in principle lead to very\ndifferent values of the correlation time delay. This result illuminates the\ninterplay between electronic correlations and symmetrisation effects in the\nattosecond regime, a relation that has been studied in other contexts.\nMoreover, it suggests the potential of excited states to explore the role of\nexchange effects in that realm.", "category": "physics_atom-ph" }, { "text": "Spatial oscillations in the spontaneous emission rate of an atom inside\n a metallic wedge: A method of images is applied to study the spontaneous emission of an atom\ninside a metallic wedge with an opening angle of $\\pi/N$, where N is an\narbitrary positive integer. We show the method of images gives a rate formula\nconsistent with that from Quantum Electrodynamics. Using the method of images,\nwe show the correspondence between the oscillations in the spontaneous emission\nrate and the closed-orbits of emitted photon going away and returning to the\natom inside the wedge. The closed-orbits can be readily constructed using the\nmethod of images and they are also extracted from the spontaneous emission\nrate.", "category": "physics_atom-ph" }, { "text": "Radio-frequency-modulated Rydberg states in a vapor cell: We measure strong radio-frequency (RF) electric fields using rubidium Rydberg\natoms prepared in a room-temperature vapor cell as field sensors.\nElectromagnetically induced transparency is employed as an optical readout. We\nRF-modulate the 60$S_{1/2}$ and 58$D_{5/2}$ Rydberg states with 50~MHz and\n100~MHz fields, respectively. For weak to moderate RF fields, the Rydberg\nlevels become Stark-shifted, and sidebands appear at even multiples of the\ndriving frequency. In high fields, the adjacent hydrogenic manifold begins to\nintersect the shifted levels, providing rich spectroscopic structure suitable\nfor precision field measurements. A quantitative description of strong-field\nlevel modulation and mixing of $S$ and $D$ states with hydrogenic states is\nprovided by Floquet theory. Additionally, we estimate the shielding of DC\nelectric fields in the interior of the glass vapor cell.", "category": "physics_atom-ph" }, { "text": "Wavelength dependent ac-Stark shift of the 1S0 - 3P1 transition at 657\n nm in Ca: We have measured the ac-Stark shift of the 4s2 1S0 - 4s4p 3P1 line in 40Ca\nfor perturbing laser wavelengths between 780 nm and 1064 nm with a time domain\nRamsey-Borde atom interferometer. We found a zero crossing of the shift for the\nmS = 0 - mP = 0 transition and \\sigma polarized perturbation at 800.8(22) nm.\nThe data was analyzed by a model deriving the energy shift from known\ntransition wavelengths and strengths. To fit our data, we adjusted the Einstein\nA coefficients of the 4s3d 3D - 4s4p 3P and 4s5s 3S - 4s4p 3P fine structure\nmultiplets. With these we can predict vanishing ac-Stark shifts for the 1S0 m =\n0 - 3P1 m = 1 transition and \\sigma- light at 983(12) nm and at 735.5(20) nm\nfor the transition to the 3P0 level.", "category": "physics_atom-ph" }, { "text": "Advanced Cold Molecule Electron EDM: Measurement of a non-zero electric dipole moment (EDM) of the electron within\na few orders of magnitude of the current best limit of |d_e| < 1.05 e -27 e cm\nwould be an indication of physics beyond the Standard Model. The ACME\nCollaboration is searching for an electron EDM by performing a precision\nmeasurement of electron spin precession in the metastable H state of thorium\nmonoxide (ThO) using a slow, cryogenic beam. We discuss the current status of\nthe experiment. Based on a data set acquired from 14 hours of running time over\na period of 2 days, we have achieved a 1-sigma statistical uncertainty of 1 e\n-28 e cm/T^(1/2), where T is the running time in days.", "category": "physics_atom-ph" }, { "text": "Deflected Beam Method for Absolute Current Density Determination: We present a broadly applicable in situ method for profiling ion beams using\nelectrostatic deflectors and a Faraday cup. By deconvolving the detector\ngeometry from the resulting current profiles, spatially resolved absolute\ncurrent density profiles are obtained. We demonstrate this method's efficacy\nwith low-density highly charged ion beams (specifically, Ne$^{8+}$). Details on\nexperimental design are provided as well as the link to the deconvolution\nroutine on Github.", "category": "physics_atom-ph" }, { "text": "Introduction to attosecond time-delays in photoionization: This tutorial presents an introduction to the interaction of light and matter\non the attosecond timescale. Our aim is to detail the theoretical description\nof ultra-short time-delays, and to relate these to the phase of extreme\nultraviolet (XUV) light pulses and to the asymptotic phase-shifts of\nphotoelectron wave packets. Special emphasis is laid on time-delay experiments,\nwhere attosecond XUV pulses are used to photoionize target atoms at\nwell-defined times, followed by a probing process in real time by a\nphase-locked, infrared laser field. In this way, the laser field serves as a\n\"clock\" to monitor the ionization event, but the observable delays do not\ncorrespond directly to the delay associated with single-photon ionization.\nInstead, a significant part of the observed delay originates from a measurement\ninduced process, which obscures the single-photon ionization dynamics. This\nartifact is traced back to a phase-shift of the above-threshold ionization\ntransition matrix element, which we call the continuum-continuum phase. It\narises due to the laser-stimulated transitions between Coulomb continuum\nstates. As we shall show here, these measurement-induced effects can be\nseparated from the single-photon ionization process, using analytical\nexpressions of universal character, so that eventually the attosecond\ntime-delays in photoionization can be accessed.", "category": "physics_atom-ph" }, { "text": "Ionisation rate and Stark shift of a one-dimensional model of the\n Hydrogen molecular ion: In this paper we study the ionization rate and the Stark shift of a\none-dimensional model of the H$_{2}^{+}$ ion. The finding of these two\nquantities is reduced to the solutions of a complex eigenvalue problem. We\nsolve this problem both numerically and analytically. In the latter case we\nconsider the regime of small external electrostatic fields and small\ninternuclear distances. We find an excellent agreement between the ionization\nrate computed with the two approaches, even when the approximate result is\npushed beyond its expected validity. The ionization rate is very sensitive to\nsmall changes of the external electrostatic field, spanning many orders of\nmagnitude for small changes of the intensity of the external field. The\ndependence of the ionization on the internuclear distance is also studied, as\nthis has a direct connection with experimental methods in molecular physics. It\nis shown that for large distances the ionization rate saturates, which is a\ndirect consequence of the behavior of the energy eigenvalue with the\ninternuclear distance. The Stark shift is computed and from it we extract the\nstatic polarizability of H$_{2}^{+}$ and compare our results with those found\nby other authors using more sophisticated methods.", "category": "physics_atom-ph" }, { "text": "Precision inertial sensing with quantum gases: Quantum sensors based on light-pulse atom interferometers allow for\nhigh-precision measurements of inertial and electromagnetic forces such as the\naccurate determination of fundamental constants as the fine structure constant\nor testing foundational laws of modern physics as the equivalence principle.\nThese schemes unfold their full performance when large interrogation times\nand/or large momentum transfer can be implemented. In this article, we\ndemonstrate how precision interferometry can benefit from the use of\nBose-Einstein condensed sources when the state of the art is challenged. We\ncontrast systematic and statistical effects induced by Bose-Einstein condensed\nsources with thermal sources in three exemplary science cases of Earth- and\nspace-based sensors.", "category": "physics_atom-ph" }, { "text": "Analysis of pattern forming instabilities in an ensemble of two-level\n atoms optically excited by counter-propagating fields: We explore various models for the pattern forming instability in a\nlaser-driven cloud of cold two-level atoms with a plane feedback mirror. Focus\nis on the combined treatment of nonlinear propagation in a diffractively thick\nmedium and the boundary condition given by feedback. The combined presence of\npurely transverse transmission gratings and reflection gratings on wavelength\nscale is addressed. Different truncation levels of the Fourier expansion of the\ndielectric susceptibility in terms of these gratings are discussed and compared\nto literature. A formalism to calculate the exact solution for the homogenous\nstate in presence of absorption is presented. The relationship between the\ncounterpropagating beam instability and the feedback instability is discussed.\nFeedback reduces the threshold by a factor of two under optimal conditions.\nEnvelope curves which bound all possible threshold curves for varying mirror\ndistances are calculated. The results are comparing well to experimental\nresults regarding the observed length scales and threshold conditions. It is\nclarified where the assumption of a diffractively thin medium is justified.", "category": "physics_atom-ph" }, { "text": "Hybridizing matter-wave and classical accelerometers: We demonstrate a hybrid accelerometer that benefits from the advantages of\nboth conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and\nlong term stability. First, the use of a real time correction of the atom\ninterferometer phase by the signal from the classical accelerometer enables to\nrun it at best performances without any isolation platform. Second, a\nservo-lock of the DC component of the conventional sensor output signal by the\natomic one realizes a hybrid sensor. This method paves the way for applications\nin geophysics and in inertial navigation as it overcomes the main limitation of\natomic accelerometers, namely the dead times between consecutive measurements.", "category": "physics_atom-ph" }, { "text": "Experimental Investigation of the Hyperfine Structure of Tm I with\n Fourier Transform Spectroscopy Part B: in the NIR wavelength range from 700\n nm to 2250 nm: In this study, we investigated the hyperfine structure of 43 spectral lines\nof atomic thulium. We analyzed Fourier-transform spectra in the wavelength\nrange from 700 nm to 2250 nm, which corresponds to the wavenumber range from\n14300 cm-1 to 4440 cm-1, respectively. The excited thulium atoms were generated\nin a hollow-cathode lamp. As a result of this investigation, the\nmagnetic-dipole hyperfine constant A of 17 fine structure levels have been\ndetermined experimentally, 14 of them for the first time. The magnetic-dipole\nhyperfine constant values of the three remaining levels, reported in the\nliterature, differed significantly from the results of our determination.", "category": "physics_atom-ph" }, { "text": "High orders of the perturbation theory for hydrogen atom in magnetic\n field: The states of hydrogen atom with principal quantum number $n\\le3$ and zero\nmagnetic quantum number in constant homogeneous magnetic field ${\\cal H}$ are\nconsidered. The coefficients of energy eigenvalues expansion up to 75th order\nin powers of ${\\cal H}^2$ are obtained for these states. The series for energy\neigenvalues and wave functions are summed up to ${\\cal H}$ values of the order\nof atomic magnetic field. The calculations are based on generalization of the\nmoment method, which may be used in other cases of the hydrogen atom\nperturbation by a polynomial in coordinates potential.", "category": "physics_atom-ph" }, { "text": "Propagating two-particle reduced density matrices without wavefunctions: Describing time-dependent many-body systems where correlation effects play an\nimportant role remains a major theoretical challenge. In this paper we develop\na time-dependent many-body theory that is based on the two-particle reduced\ndensity matrix (2-RDM). We develop a closed equation of motion for the 2-RDM\nemploying a novel reconstruction functional for the three-particle reduced\ndensity matrix (3-RDM) that preserves norm, energy, and spin symmetries during\ntime propagation. We show that approximately enforcing $N$-representability\nduring time evolution is essential for achieving stable solutions. As a\nprototypical test case which features long-range Coulomb interactions we employ\nthe one-dimensional model for lithium hydride (LiH) in strong infrared laser\nfields. We probe both one-particle observables such as the time-dependent\ndipole moment and two-particle observables such as the pair density and mean\nelectron-electron interaction energy. Our results are in very good agreement\nwith numerically exact solutions for the $N$-electron wavefunction obtained\nfrom the multiconfigurational time-dependent Hartree-Fock method.", "category": "physics_atom-ph" }, { "text": "Testing non-classical theories of electromagnetism with ion\n interferometry: We discuss using a table-top ion interferometer to search for deviations from\nCoulomb's inverse-square law. Such deviations would result from non-classical\neffects such at a non-zero photon rest mass. We discuss the theory behind the\nproposed measurement, explain which fundamental, experimentally controllable\nparameters are the relevant figures of merit, and calculate the expected\nperformance of such a device in terms of these parameters. The sensitivity to\ndeviations in the exponent of the inverse-square law is predicted to be a few\ntimes $10^{-22}$, an improvement by five orders of magnitude over current\nexperiments. It could measure a non-zero photon rest mass smaller than\n$9\\times10^{-50}$ grams, nearly 100 times smaller than current laboratory\nexperiments.", "category": "physics_atom-ph" }, { "text": "Resonant and first-order dipolar interactions between ultracold\n molecules in static and microwave electric fields: We theoretically study collisions between ultracold polar molecules that are\npolarized by microwave or static electric fields. We systematically study the\ndependence on field strength, microwave polarization, and detuning from\nrotational transitions. We calculate the loss in two-body collisions that is\nobservable experimentally and compare to the results expected for purely\nfirst-order dipolar interactions. For ground state molecules polarized by a\nstatic electric field, the dynamics are accurately described by first-order\ndipolar interactions. For microwave dressing, instead, resonant dipolar\ncollisions dominate the collision process, in which molecules reorient along\nthe intermolecular axis and interact with the full strength of the transition\ndipole. For red detuning, reorientation can only be suppressed at extreme Rabi\nfrequencies. For blue detuned microwaves, resonant dipolar interactions\ndominate even for high Rabi frequencies, leading to microwave shielding for\ncircular polarization and structured losses due to resonances for linear\npolarization. The results are presented numerically for fermionic\n$^{23}$Na$^{40}$K and bosonic $^{23}$Na$^{39}$K molecules.", "category": "physics_atom-ph" }, { "text": "Combined 4-component and relativistic pseudopotential study of ThO for\n the electron electric dipole moment search: A precise theoretical study of the electronic structure of heavy atom\ndiatomic molecules is of key importance to interpret the experiments in the\nsearch for violation of time-reversal (T) and spatial-parity (P) symmetries of\nfundamental interactions it terms of the electron electric dipole moment, eEDM,\nand dimensionless constant, $k_{T,P}$, characterizing the strength of the\nT,P-odd pseudoscalar$-$scalar electron$-$nucleus neutral current interaction.\nACME collaboration has recently obtained and improved limits on these\nquantities using a beam of ThO molecules in the $H^3\\Delta_1$ state [Science\n343, 269 (2014)]. We apply the combined direct 4-component and two-step\nrelativistic pseudopotential/restoration approaches to a benchmark calculation\nof the effective electric field, Eeff, parameter of the T,P-odd\npseudoscalar$-$scalar interaction, $W_{T,P}$, and HFS constant in $^3\\Delta_1$\nstate of the ThO molecule. The first two parameters are required to interpret\nthe experimental data in terms of the eEDM and $k_{T,P}$ constant. We have\ninvestigated the electron correlation for all of the 98 electrons of ThO\nsimultaneously up to the level of the coupled cluster with single, double and\nnoniterative triple amplitudes theory. Contributions from iterative triple and\nnoniterative quadruple cluster amplitudes for the valence electrons have been\nalso treated. The obtained values are Eeff=79.9 GV/cm, $W_{T,P}$=113.1 kHz. The\ntheoretical uncertainty of these values we estimate as about two times smaller\nthan that of our previous study [JCP, 142, 024301 (2015)]. It was found that\nthe correlation of the inner- and outer- core electrons contributes 9% to the\neffective electric field. The values of the molecule frame dipole moment of the\n$^3\\Delta_1$ state and the $H^3\\Delta_1\\to X^1\\Sigma^+$ transition energy of\nThO calculated within the same methods are in a very good agreement with the\nexperiment.", "category": "physics_atom-ph" }, { "text": "Circumventing Heisenberg's uncertainty principle in atom interferometry\n tests of the equivalence principle: Atom interferometry tests of universality of free fall based on the\ndifferential measurement of two different atomic species provide a useful\ncomplement to those based on macroscopic masses. However, when striving for the\nhighest possible sensitivities, gravity gradients pose a serious challenge.\nIndeed, the relative initial position and velocity for the two species need to\nbe controlled with extremely high accuracy, which can be rather demanding in\npractice and whose verification may require rather long integration times.\nFurthermore, in highly sensitive configurations gravity gradients lead to a\ndrastic loss of contrast. These difficulties can be mitigated by employing wave\npackets with narrower position and momentum widths, but this is ultimately\nlimited by Heisenberg's uncertainty principle. We present a novel scheme that\nsimultaneously overcomes the loss of contrast and the initial co-location\nproblem. In doing so, it circumvents the fundamental limitations due to\nHeisenberg's uncertainty principle and eases the experimental realization by\nrelaxing the requirements on initial co-location by several orders of\nmagnitude.", "category": "physics_atom-ph" }, { "text": "Electron broadening operator including penetrating collisions for\n hydrogen: The expression of the electron broadening operator including the effect of\npenetrating collisions, i.e. for which the incoming electron enters the extent\nof bound-electron wavefunctions, is rather complicated, even for hydrogen. It\ninvolves integrals of special functions, which evaluation deserves scrutiny. We\npresent a simple approximate form of the electron collision operator for\nhydrogen including penetration effects, both in direct and interference terms.\nThe new expression is accurate and easy to compute. In the Penetration Standard\nTheory, the collision operator is convergent whatever the value of the maximum\nimpact parameter. However, when penetration theory is not valid anymore, it\nshould be questioned. We discuss the problem of strong collisions when\npenetration effects are taken into account.", "category": "physics_atom-ph" }, { "text": "A novel method for unambiguous ion identification in mixed ion beams\n extracted from an EBIT: A novel technique to identify small fluxes of mixed highly charged ion beams\nextracted from an Electron Beam Ion Trap (EBIT) is presented and practically\ndemonstrated. The method exploits projectile charge state dependent potential\nemission of electrons as induced by ion impact on a metal surface to separate\nions with identical or very similar mass-to-charge ratio.", "category": "physics_atom-ph" }, { "text": "Natural Resolution of the Proton Size Puzzle: We show that off-mass-shell effects arising from the internal structure of\nthe proton provide a new proton polarization mechanism in the Lamb shift,\nproportional to the lepton mass to the fourth power. This effect is capable of\nresolving the current puzzle regarding the difference in the proton radius\nextracted from muonic compared with electronic hydrogen. These off-mass-shell\neffects could be probed in several other experiments.", "category": "physics_atom-ph" }, { "text": "Carrier-envelope phase sensitive inversion in two-level systems: We theoretically study the carrier-envelope phase dependent inversion\ngenerated in a two-level system by excitation with a few-cycle pulse. Based on\nthe invariance of the inversion under time reversal of the exciting field,\nparameters are introduced to characterize the phase sensitivity of the induced\ninversion. Linear and nonlinear phase effects are numerically studied for\nrectangular and sinc-shaped pulses. Furthermore, analytical results are\nobtained in the limits of weak fields as well as strong dephasing, and by\nnearly degenerate perturbation theory for sinusoidal excitation. The results\nshow that the phase sensitive inversion in the ideal two-level system is a\npromising route for constructing carrier-envelope phase detectors.", "category": "physics_atom-ph" }, { "text": "High efficiency preparation of single trapped atoms using blue detuned\n light assisted collisions: We report on a procedure by which we obtain a 91% loading efficiency of\nsingle 85Rb atoms in an optical microtrap. This can be achieved within a total\npreparation time of 542 ms. We employ blue detuned light assisted collisions to\nrealize a process in which only one of the collision partners is lost. We\nexplain the mechanism for efficiently loading a single atom and discuss the\nfactors that limit the final efficiency.", "category": "physics_atom-ph" }, { "text": "Instability Heating of Sympathetically-Cooled Ions in a Linear Paul Trap: Sympathetic laser cooling of ions stored within a linear-geometry, radio\nfrequency, electric-quadrupole trap has been investigated using computational\nand theoretical techniques. The simulation, which allows 5 sample ions to\ninteract with 35 laser-cooled atomic ions, revealed an instability heating\nmechanism, which can prevent ions below a certain critical mass from being\nsympathetically cooled. This critical mass can however be varied by changing\nthe trapping field parameters thus allowing ions with a very large range of\nmasses to be sympathetically cooled using a single ion species. A theoretical\nexplanation of this instability heating mechanism is presented which predicts\nthat the cooling-heating boundary in trapping parameter space is a line of\nconstant $q_u$ (ion trap stability coefficient), a result supported by the\ncomputational results. The threshold value of $q_u$ depends on the masses of\nthe interacting ions. A functional form of this dependence is given.", "category": "physics_atom-ph" }, { "text": "Harmonics generation and intense terahertz radiation from polar\n molecules at multiphoton resonant excitation in laser fields: The coherent radiation spectrum of two-level polar molecules with UV\ntransition is studied at the multiphoton resonant excitation by a moderately\nstrong laser field. The spectrum corresponding to harmonic generation and\nlow-frequency radiation is investigated both analytically and numerically.\nSpecifically, a mechanism for generation of intense smoothly tunable terahertz\nradiation by two-level molecular configurations (with dynamic Stark shifts)\npossessing permanent dipole moments, is considered.", "category": "physics_atom-ph" }, { "text": "Magic wavelengths for the $6s^2\\,^1S_0-6s6p\\,^3P_1^o$ transition in\n ytterbium atom: The static and dynamic electric-dipole polarizabilities of the $6s^2\\,^1S_0$\nand $6s6p\\,^3P_1^o$ states of Yb are calculated by using the relativistic ab\ninitio method. Focusing on the red detuning region to the\n$6s^2\\,^1S_0-6s6p\\,^3P_1^o$ transition, we find two magic wavelengths at\n1035.7(2) nm and 612.9(2) nm for the $6s^2\\,^1S_0-6s6p\\,^3P_1^o, M_J=0$\ntransition and three magic wavelengthes at 1517.68(6) nm, 1036.0(3) nm and\n858(12) nm for the $6s^2\\,^1S_0-6s6p\\,^3P_1^o, M_J=\\pm1$ transitions. Such\nmagic wavelengths are of particular interest for attaining the\nstate-insensitive cooling, trapping, and quantum manipulation of neutral Yb\natom.", "category": "physics_atom-ph" }, { "text": "Long-range interactions of hydrogen atoms in excited states. I. 2S-1S\n interactions and Dirac-delta perturbations: The theory of the long-range interaction of metastable excited atomic states\nwith ground-state atoms is analyzed. We show that the long-range interaction is\nessentially modified when quasi-degenerate states are available for virtual\ntransitions. A discrepancy in the literature regarding the van der Waals\ncoefficient C_6(2S;1S) describing the interaction of metastable atomic hydrogen\n(2S state) with a ground-state hydrogen atom is resolved. In the the van der\nWaals range a_0 << R << a_0/alpha, where a_0= hbar/(alpha m c) is the Bohr\nradius and alpha is the fine structure constant, one finds the\nsymmetry-dependent result E_{2S;1S}(R) ~ (-176.75 +/- 27.98) E_h (a_0/R)^6 (E_h\ndenotes the Hartree energy). In the Casimir-Polder range a_0/alpha << R << hbar\nc/L, where L = E(2S_{1/2})-E(2P_{1/2}) is the Lamb shift energy, one finds\nE_{2S;1S}(R) ~ (-121.50 +/- 46.61) E_h (a_0/R)^6. In the the Lamb shift range R\n>> hbar c/L, we find an oscillatory tail with a negligible interaction energy\nbelow 10^(-36) Hz. Dirac-delta perturbations to the interaction are also\nevaluated and results are given for all asymptotic distance ranges; these\neffects describe the hyperfine modification of the interaction, or, expressed\ndifferently, the shift of the hydrogen 2S hyperfine frequency due to\ninteractions with neighboring 1S atoms. The 2S hyperfine frequency has recently\nbeen measured very accurately in atomic beam experiments.", "category": "physics_atom-ph" }, { "text": "Spectroscopy on the $A^1\u03a0\\leftarrow X^1\u03a3^+$ Transition of\n Buffer-Gas Cooled AlCl: Aluminum monochloride (AlCl) has been proposed as an excellent candidate for\nlaser cooling. Here we present absorption spectroscopy measurements on the\n$A^1\\Pi \\leftarrow X^1\\Sigma^+$ transition in AlCl inside a cryogenic helium\nbuffer-gas beam cell. The high resolution absorption data enables a rigorous,\nquantitative comparison with our high-level ab initio calculations of the\nelectronic and rovibronic energies, providing a comprehensive picture of the\nAlCl quantum structure. The combination of high resolution spectral data and\ntheory permits the evaluation of spectroscopic constants and associated\nproperties, like equilibrium bond length, with an order of magnitude higher\nprecision. Based on the measured molecular equilibrium constants of the\n$A^1\\Pi$ state, we estimate a Franck-Condon factor of the $A^1\\Pi \\leftarrow\nX^1\\Sigma^+$ of 99.88%, which confirms that AlCl is amenable to laser cooling.", "category": "physics_atom-ph" }, { "text": "Anomalous excitation facilitation in inhomogeneously broadened Rydberg\n gases: When atomic gases are laser driven to Rydberg states in an off resonant way,\na single Rydberg atom may enhance the excitation rate of surrounding atoms.\nThis leads to a facilitated excitation referred to as Rydberg anti-blockade. In\nthe usual facilitation scenario, the detuning of the laser from resonance\ncompensates the interaction shift. Here, we discuss a different excitation\nmechanism, which we call anomalous facilitation. This occurs on the \"wrong\nside\" of the resonance and originates from inhomogeneous broadening. The\nanomalous facilitation may be seen in experiments of attractively interacting\natoms on the blue detuned side, where facilitation is not expected to appear.", "category": "physics_atom-ph" }, { "text": "Extending Phenomenological Crystal-Field Methods to $C_1$ Point-Group\n Symmetry: Characterization of the Optically-Excited Hyperfine Structure of\n $^{167}$Er$^{3+}$:Y$_2$SiO$_5$: We show that crystal-field calculations for $C_1$ point-group symmetry are\npossible, and that such calculations can be performed with sufficient accuracy\nto have substantial utility for rare-earth based quantum information\napplications. In particular, we perform crystal-field fitting for a\nC$_1$-symmetry site in $^{167}$Er$^{3+}$:Y$_2$SiO$_5$. The calculation\nsimultaneously includes site-selective spectroscopic data up to 20,000\ncm$^{-1}$, rotational Zeeman data, and ground- and excited-state hyperfine\nstructure determined from high-resolution Raman-heterodyne spectroscopy on the\n1.5 $\\mu$m telecom transition. We achieve an agreement of better than 50 MHz\nfor assigned hyperfine transitions. The success of this analysis opens the\npossibility of systematically evaluating the coherence properties, as well as\ntransition energies and intensities, of any rare-earth ion doped into\nY$_2$SiO$_5$ .", "category": "physics_atom-ph" }, { "text": "Spin-resolved electron-impact ionization of lithium: Electron-impact ionization of lithium is studied using the convergent\nclose-coupling (CCC) method at 25.4 and 54.4 eV. Particular attention is paid\nto the spin-dependence of the ionization cross sections. Convergence is found\nto be more rapid for the spin asymmetries, which are in good agreement with\nexperiment, than for the underlying cross sections. Comparison with the recent\nmeasured and DS3C-calculated data of Streun et al (1999) is most intriguing.\nExcellent agreement is found with the measured and calculated spin asymmetries,\nyet the discrepancy between the CCC and DS3C cross sections is very large.", "category": "physics_atom-ph" }, { "text": "Non-linear frequency-sweep correction of tunable electromagnetic sources: Tunable electromagnetic sources, such as voltage controlled oscillators\n(VCO), micro electromechanical systems (MEMS) or diode lasers are often\nrequired to be linear during frequency-sweep modulation. In many cases, it\nmight also be sufficient that the degree of the non-linearity can be well\ncontrolled. Without further efforts, these conditions are rarely achieved using\nfree running sources. Based on a pre-distortion voltage ramp, we develop in\nthis letter a simple and universal method that minimizes the non-linear\nfrequency response of tunable electromagnetic sources. Using a current-driven\nQuantum Cascade Laser (QCL) as an example, we demonstrate that the\nnon-linearity can easily be reduced by a factor of ten when using a single\ndistortion parameter $\\gamma$. In the investigation of the IR absorption\nspectrum of ozone at 10\\,$\\mu$m, an even better reduction of the frequency\nscale error by two orders of magnitude is obtained by using the pre-distortion\nmethod to generate an essentially purely quadratic sweep frequency dependency\nwhich can be inverted easily to retrieve precise molecular line positions.\nAfter having tested our method on a variety of electromagnetic sources, we\nanticipate a wide range of applications in a variety of fields.", "category": "physics_atom-ph" }, { "text": "Observation of absorptive photon switching by quantum interference: We report an experimental demonstration of photon switching by quantum\ninterference in a four-level atomic system proposed by Harris and Yamamoto\n(Phys. Rev. Lett. 81, 3611 (1998)). Quantum interference inhibits single-photon\nabsorption but enhances third-order, two-photon type absorption in the\nfour-level system. We have observed greatly enhanced nonlinear absorption in\nthe four-level system realized with cold 87Rb atoms and demonstrated fast\nswitching of the nonlinear absorption with a pulsed pump laser.", "category": "physics_atom-ph" }, { "text": "Two-dimensional atomic lithography by sub-micron focusing of atomic\n beams: We analyze a method for serial writing of arbitrary two-dimensional patterns\nusing optical focusing of a collimated atomic beam. A spatial light modulator\nis used in a side illumination geometry to create a localized optical spot with\nsecondary maxima that are well separated from the central peak. Numerical\nsimulation of a lithography experiment using a magneto-optical trap as a source\nof cold Cs atoms, collimation and cooling in a magnetic guide, and optical\nfocusing predicts full width at half maximum pixel sizes of 110 x 110 nm and\nwriting times of about $20 \\rm ms$ per pixel.", "category": "physics_atom-ph" }, { "text": "The leading term of the He$-\\bar{p}\\mbox{He}^+$ long-range interaction: The long range interaction between an antiprotonic helium atom\n$\\bar{p}$He$^+$ and helium atom in its ground state is studied. We calculate\nthe dispersion coefficients $C_6$ using the Complex Coordinate Rotation (CCR)\nformalism in order to comply with the resonant nature of metastable states of\nthe antiprotonic helium. We present as well numerical data on static dipole\npolarizabilities of antiprotonic helium states. The obtained coefficients $C_6$\nmay be used to estimate the collisional shift and broadening of transition\nlines in a low density precision spectroscopy of the antiprotonic helium.", "category": "physics_atom-ph" }, { "text": "Enhancement of parity and time invariance violation in Radium atom: There are several factors which lead to a huge enhancement of parity and time\ninvariance violating effects in the Ra atom: very close electronic levels of\nopposite parity, the large nuclear charge Z and the collective nature of\nT,P-odd nuclear moments. Experiments with Radium may be used to measure it's\nnuclear anapole, magnetic quadrupole and Schiff moments. Such measurements\nprovide information about parity and time invariance violating nuclear forces\nand electron-nucleon interactions.", "category": "physics_atom-ph" }, { "text": "Theoretical model for ultracold molecule formation via adaptive feedback\n control: We investigate pump-dump photoassociation of ultracold molecules with\namplitude- and phase-modulated femtosecond laser pulses. For this purpose a\nperturbative model for the light-matter interaction is developed and combined\nwith a genetic algorithm for adaptive feedback control of the laser pulse\nshapes. The model is applied to the formation of 85Rb2 molecules in a\nmagneto-optical trap. We find for optimized pulse shapes an improvement for the\nformation of ground state molecules by more than a factor of 10 compared to\nunshaped pulses at the same pump-dump delay time, and by 40% compared to\nunshaped pulses at the respective optimal pump-dump delay time. Since our model\nyields directly the spectral amplitudes and phases of the optimized pulses, the\nresults are directly applicable in pulse shaping experiments.", "category": "physics_atom-ph" }, { "text": "Preparing pure $^{43}$Ca$^+$ samples in an ion trap with photoionization\n and parametric excitations: We present a practical scheme for the efficient preparation of laser-cooled\n$^{43}$Ca$^+$ ions in an ion trap. Our approach integrates two well-established\nmethods: isotope-selective photoionization and isotope-specific parametric\nexcitation. Drawing inspiration from the individual merits of each method, we\nhave successfully integrated these techniques to prepare extended chains of\n$^{43}$Ca$^+$ ions, overcoming the challenge posed by their low natural\nabundance of 0.135\\% in a natural source. Furthermore, we explore the\nsubtleties of our scheme, focusing on the influence of different factors on the\npurification process. Our investigation contributes to a broader understanding\nof the technique and highlights the adaptability of established methods in\naddressing specific isotopic challenges.", "category": "physics_atom-ph" }, { "text": "Long lifetime and high-fidelity quantum memory of photonic polarization\n qubit by lifting Zeeman degeneracy: Long-lived and high-fidelity memory for photonic polarization qubit (PPQ) is\ncrucial for constructing quantum networks. Here we present an EIT-based\nmillisecond storage system in which a moderate magnetic field is applied on a\ncold-atom cloud to lift Zeeman degeneracy. PPQ states are stored as two\nmagnetic-field-insensitive spin waves. Especially, the influence of\nmagnetic-field-sensitive spin waves on the storage performances is almost\ntotally avoided. The measured average fidelities of polarization states are\n98.6% at 200 us and 78.4% at 4.5 ms, respectively.", "category": "physics_atom-ph" }, { "text": "Emergence of synchronisation in a driven-dissipative hot Rydberg vapor: We observe synchronisation in a thermal (35-60 {\\deg}C) atomic (Rb) ensemble\ndriven to a highly-excited Rydberg state (principle quantum number n ranging\nfrom 43 to 79). Synchronisation in this system is unexpected due to the atomic\nmotion, however, we show theoretically that sufficiently strong interactions\nvia a global Rydberg density mean field causes frequency and phase entrainment.\nThe emergent oscillations in the vapor's bulk quantities are detected in the\ntransmission of the probe laser for a two-photon excitation scheme.", "category": "physics_atom-ph" }, { "text": "Implementation of infinite-range exterior complex scaling to the\n time-dependent complete-active-space self-consistent-field method: We present a numerical implementation of the infinite-range exterior complex\nscaling (irECS) [Phys. Rev. A 81, 053845 (2010)] as an efficient absorbing\nboundary to the time-dependent complete-active-space self-consistent field\n(TD-CASSCF) method [Phys. Rev. A 94, 023405 (2016)] for multielectron atoms\nsubject to an intense laser pulse. We introduce Gauss-Laguerre-Radau quadrature\npoints to construct discrete variable representation basis functions in the\nlast radial finite element extending to infinity. This implementation is\napplied to strong-field ionization and high-harmonic generation in He, Be, and\nNe atoms. It efficiently prevents unphysical reflection of photoelectron wave\npackets at the simulation boundary, enabling accurate simulations with\nsubstantially reduced computational cost, even under significant (~ 50%) double\nionization. For the case of a simulation of high-harmonic generation from Ne,\nfor example, 80% cost reduction is achieved, compared to a mask-function\nabsorption boundary.", "category": "physics_atom-ph" }, { "text": "Optical Stark decelerator for cw molecular beam with a quasi-cw\n semi-Gaussian laser beam: We propose a promising scheme to decelerate a cw filtering out molecular beam\nusing a red-detuned quasi-cw semi-Gaussian laser beam. By using Monte-Carlo\nsimulation method, we demonstrate this optical Stark deceleration scheme, and\nstudy its decelerated dynamic process for a cw ND3 molecular beam as well as\nthe dependence of the deceleration effect on the border width of the\nsemi-Gaussian beam. Our study shows that the proposed scheme can be used to\nefficiently slow a cw ND3 molecular beam, and obtain a relative average\nkinetic-energy loss of 9.33% by using a single semi-Gaussian beam with a well\ndepth of 7.3 mK.", "category": "physics_atom-ph" }, { "text": "Electron correlation effects on the $g$ factor of lithiumlike ions: We present the systematic QED treatment of the electron correlation effects\non the $g$ factor of lithiumlike ions for the wide range of nuclear charge\nnumber $Z= 14$ -- $82$. The one- and two-photon exchange corrections are\nevaluated rigorously within the QED formalism. The electron-correlation\ncontributions of the third and higher orders are accounted for within the Breit\napproximation employing the recursive perturbation theory. The calculations are\nperformed in the framework of the extended Furry picture, i.e., with inclusion\nof the effective local screening potential in the zeroth-order approximation.\nIn comparison to the previous theoretical calculations, the accuracy of the\ninterelectronic-interaction contributions to the bound electron $g$ factor in\nlithiumlike ions is substantially improved.", "category": "physics_atom-ph" }, { "text": "Quantum electrodynamics of heavy ions and atoms: The present status of quantum electrodynamics (QED) theory of heavy\nfew-electron ions is reviewed. The theoretical results are compared with\navailable experimental data. A special attention is focused on tests of QED at\nstrong fields and on determination of the fundamental constants. A recent\nprogress on calculations of the QED corrections to the parity nonconserving\n6s-7s transition amplitude in neutral Cs is also discussed.", "category": "physics_atom-ph" }, { "text": "Atomic many-body effects and Lamb shifts in alkali metals: We present a detailed study of the Flambaum-Ginges radiative potential method\nwhich enables the accurate inclusion of quantum electrodynamics (QED) radiative\ncorrections in a simple manner in atoms, ions, and molecules over the range\n10<=Z<=120, where Z is the nuclear charge. Calculations are performed for\nbinding energy shifts to the lowest valence s, p, and d waves over the series\nof alkali atoms Na to E119. The high accuracy of the radiative potential method\nis demonstrated by comparison with rigorous QED calculations in frozen atomic\npotentials, with deviations on the level of 1%. The many-body effects of core\nrelaxation and second- and higher-order perturbation theory on the interaction\nof the valence electron with the core are calculated. The inclusion of\nmany-body effects tends to increase the size of the shifts, with the\nenhancement particularly significant for d waves; for K to E119, the\nself-energy shifts for d waves are only an order of magnitude smaller than the\ns-wave shifts. It is shown that account of many-body effects is essential for\nan accurate description of the Lamb shift.", "category": "physics_atom-ph" }, { "text": "Magnetic trapping of ultracold molecules at high density: Trapping ultracold molecules in conservative traps is essential for\napplications -- such as quantum state-controlled chemistry, quantum\nsimulations, and quantum information processing. These applications require\nhigh densities or phase-space densities. We report magnetic trapping of NaLi\nmolecules in the triplet ground state at high density ($\\approx 10^{11} \\;\n\\rm{cm}^{-3}$) and ultralow temperature ($\\approx 1\\;{\\rm \\mu K}$). Magnetic\ntrapping at these densities allows studies on both atom-molecule and\nmolecule-molecule collisions in the ultracold regime in the absence of trapping\nlight, which has often lead to undesired photo-chemistry. We measure the\ninelastic loss rates in a single spin sample and spin-mixtures of fermionic\nNaLi as well as spin-stretched NaLi$+$Na mixtures. We demonstrate sympathetic\ncooling of NaLi molecules in the magnetic trap by radio frequency evaporation\nof co-trapped Na atoms and observe an increase in the molecules' phase-space\ndensity by a factor of $\\approx 16$.", "category": "physics_atom-ph" }, { "text": "Quantum coherence in the dynamical excitation, ionization, and decaying\n of neon gas induced by X-ray laser: We develop a large scale quantum master equation approach to describe\ndynamical processes of practical open quantum systems driven by both coherent\nand stochastic interactions by including more than one thousand true states of\nthe systems, motivated by the development of highly bright and fully coherent\nlasers in the X-ray wavelength regime. The method combines the processes of\ncoherent dynamics induced by the X-ray laser and incoherent relaxations due to\nspontaneous emissions, Auger decays, and electronic collisions. As examples,\ntheoretical investigation of {\\it real} coherent dynamics of inner-shell\nelectrons of a neon gas, irradiated by a high-intensity X-ray laser with a full\ntemporal coherence, is carried out with the approach. In contrast to the rate\nequation treatment, we find that coherence can suppress the multiphoton\nabsorptions of a neon gas in the ultra-intense X-ray pulse, due to\ncoherence-induced Rabi oscillations and power broadening effects. We study the\ninfluence of coherence on ionization processes of neon, and directly prove that\nsequential single-photon processes for both outer- and inner-shell electrons\ndominate the ionizations for the recently typical experiments with a laser\nintensity of $\\approx10^{18}$ ${\\rm W/cm^2}$. We discuss possible experimental\nimplementations such as signatures for coherent evolution of inner-shell\nelectrons via resonance fluorescence processes. The approach can also be\napplied to many different practical open quantum systems in atomic, quantum\noptical, and cold matter systems, which are treated qualitatively by a\nfew-level master equation model before.", "category": "physics_atom-ph" }, { "text": "Coherent population trapping in a Raman atom interferometer: We investigate the effect of coherent population trapping (CPT) in an atom\ninter-ferometer gravimeter based on the use of stimulated Raman transitions. We\nfind that CPT leads to significant phase shifts, of order of a few mrad, which\nmay compromise the accuracy of inertial measurements. We show that this effect\nis rejected by the k-reversal technique, which consists in averaging inertial\nmeasurements performed with two opposite orientations of the Raman wavevector\nk, provided that internal states at the input of the interferometer are kept\nidentical for both configurations.", "category": "physics_atom-ph" }, { "text": "Determination of quantum defect for the Rydberg P series of Ca II: We present an experimental investigation of the Rydberg 23 P$_{1/2}$ state of\nlaser-cooled $^{40}$Ca$^+$ ions in a radiofrequency ion trap. Using micromotion\nsideband spectroscopy on a narrow quadrupole transition, the oscillating\nelectric field at the ion position was precisely characterised, and the\nmodulation of the Rydberg transition due to this field was minimised. From a\ncorrelated fit to this P line and previously measured P and F level energies of\nCa II, we have determined the ionization energy of 95 751.916(32) $\\rm\n{cm}^{-1}$, in agreement with the accepted value, and the quantum defect for\nthe $n$ P$_{1/2}$ states.", "category": "physics_atom-ph" }, { "text": "Elastic scattering of twisted electrons by diatomic molecules: The elastic scattering of twisted electrons by diatomic molecules is studied\nwithin the framework of the non-relativistic first Born approximation. In this\nprocess, the coherent interaction of incident electrons with two molecular\ncenters may cause interference patterns in the angular distributions of\noutgoing particles. We investigate how this Young-type interference is\ninfluenced by the complex internal structure of twisted beams. In particular,\nwe show that the corkscrew-like phase front and the inhomogeneous intensity\nprofile of the incident beam can strongly modify the angular distribution of\nelectrons, scattered off a single well-localized molecule. For the collision\nwith a macroscopic target, composed of randomly distributed but aligned\nmolecules, the angular-differential cross section may reveal valuable\ninformation about the transverse and longitudinal momenta of twisted states. In\norder to illustrate the difference between the scattering of twisted and\nplane-wave beams for both, single-molecule and macroscopic-target scenarios,\ndetailed calculations have been performed for a H_2 target.", "category": "physics_atom-ph" }, { "text": "Multielectron effects in high harmonic generation in N2 and benzene:\n simulation using a non-adiabatic quantum molecular dynamics approach for\n laser-molecule interactions: A mixed quantum-classical approach is introduced which allows the dynamical\nresponse of molecules driven far from equilibrium to be modeled. This method is\napplied to the interaction of molecules with intense, short-duration laser\npulses. The electronic response of the molecule is described using\ntime-dependent density functional theory (TDDFT) and the resulting Kohn-Sham\nequations are solved numerically using finite difference techniques in\nconjunction with local and global adaptations of an underlying grid in\ncurvilinear coordinates. Using this approach, simulations can be carried out\nfor a wide range of molecules and both all-electron and pseudopotential\ncalculations are possible. The approach is applied to the study of high\nharmonic generation in N2 and benzene using linearly-polarized laser pulses\nand, to the best of our knowledge, the results for benzene represent the first\nTDDFT calculations of high harmonic generation in benzene using linearly\npolarized laser pulses. For N2 an enhancement of the cut-off harmonics is\nobserved whenever the laser polarization is aligned perpendicular to the\nmolecular axis. This enhancement is attributed to the symmetry properties of\nthe Kohn-Sham orbital that responds predominantly to the pulse. In benzene we\npredict that a suppression in the cut-off harmonics occurs whenever the laser\npolarization is aligned parallel to the molecular plane. We attribute this\nsuppression to the symmetry-induced response of the highest-occupied molecular\norbital.", "category": "physics_atom-ph" }, { "text": "Continuous loading of magneto-optical trap of Rb at narrow transition: We report continuous loading of $^{\\textrm{87}}$Rb atoms in a magneto-optical\ntrap (MOT) at narrow linewidth, 420 nm 5S$_{1/2}$, F$=2\\rightarrow$ 6P$_{3/2}$,\nF$=3$ blue transition (blue MOT). Continuous loading of the blue MOT is\nachieved by superimposing the blue laser beam, inside a hollow core of infrared\nlaser beam driving the broad 5S$_{1/2}$, F$=2\\rightarrow$ 5P$_{3/2}$, F$=3$\ntransition at 780 nm. We typically load $\\sim10^{8}$ atoms in the blue MOT in\n2.5 seconds. We characterize the continuous loading of blue MOT with various\nparameters such as magnetic field gradient, detuning, power and diameter of\nblue MOT beam and diameter of the hollow core (spot) inside the IR MOT beam. We\nobserve that the blue laser beam should overfill the spot of the IR laser beam.\nThis is because the blue laser cools the atoms to a lower temperature even in\nthe presence of the broad IR laser i.e. in the overlapped region and hence\nhelps in loading. We also present the theoretical framework for cooling atoms\nin the presence of simultaneously two transitions to support the experimental\nresult. This method of continuous loading of the blue MOT can be useful to\nproduce a continuous atomic beam of cold Rb atoms.", "category": "physics_atom-ph" }, { "text": "Muonium Lamb shift: theory update and experimental prospects: We review the theory of the Lamb shift for muonium, provide an updated\nnumerical value and present the prospects of the Mu-MASS collaboration at PSI\nto improve upon their recent measurement. Due to its smaller nuclear mass, the\ncontributions of the higher-order recoil corrections (160kHz level) and nucleus\nself-energy 40kHz level) are enhanced for muonium compared to hydrogen where\nthose are below the level of the latest measurement performed by Hessels et al.\nand thus could not be tested yet. The ongoing upgrades to the Mu-MASS setup\nwill open up the possibility to probe these contributions and improve the\nsensitivity of this measurement to searches for new physics in the muonic\nsector.", "category": "physics_atom-ph" }, { "text": "Cold inelastic collisions between lithium and cesium in a two-species\n magneto-optical trap: We investigate collisional properties of lithium and cesium which are\nsimultaneously confined in a combined magneto-optical trap. Trap-loss\ncollisions between the two species are comprehensively studied. Different\ninelastic collision channels are identified, and inter-species rate\ncoefficients as well as cross sections are determined. It is found that loss\nrates are independent of the optical excitation of Li, as a consequence of the\nrepulsive Li$^*$-Cs interaction. Li and Cs loss by inelastic inter-species\ncollisions can completely be attributed to processes involving optically\nexcited cesium (fine-structure changing collisions and radiative escape). By\nlowering the trap depth for Li, an additional loss channel of Li is observed\nwhich results from ground-state Li-Cs collisions changing the hyperfine state\nof cesium.", "category": "physics_atom-ph" }, { "text": "Decay modes of two repulsively interacting bosons: We study the decay of two repulsively interacting bosons tunneling through a\ndelta potential barrier by direct numerical solution of the time-dependent\nSchr\\\"odinger equation. The solutions are analyzed according to the regions of\nparticle presence: both particles inside the trap (in-in), one particle in and\none particle out (in-out), and both particles outside (out-out). It is shown\nthat the in-in probability is dominated by exponential decay, and its decay\nrate is predicted very well from outgoing boundary conditions.\n Up to a certain range of interaction strength the decay of in-out probability\nis dominated by the single particle decay mode.\n The decay mechanisms are adequately described by simple models.", "category": "physics_atom-ph" }, { "text": "On the Li-Rosmej analytical formula for energy level shifts in dense\n plasmas: Li and Rosmej derived analytical fits for the energy level shifts due to\nplasma screening on the basis of a free-electron potential published by Rosmej\net al. one year earlier. The derivation of the fits, which were shown by\nIglesias to be inconsistent with the fundamental premise of the ion-sphere\nmodel, was motivated by the belief that no analytical expression exists for the\nexpectation value $\\langle r^{3/2}\\rangle$, an assertion that was also\ncontradicted by Iglesias. In this short note, I point out that a simple\nexpression for the latter quantity can be obtained as a particular case of a\nformula published by Shertzer, and I provide a corresponding compact analytical\nexpression for the level shifts in the framework of Rosmej's formalism.", "category": "physics_atom-ph" }, { "text": "Two-dimensional magneto-optical trap as a source for cold strontium\n atoms: We report on the realization of a transversely loaded two-dimensional\nmagneto-optical trap serving as a source for cold strontium atoms. We analyze\nthe dependence of the source's properties on various parameters, in particular\nthe intensity of a pushing beam accelerating the atoms out of the source. An\natomic flux exceeding $10^9\\,\\mathrm{atoms/s}$ at a rather moderate oven\ntemperature of $500\\,^\\circ\\mathrm{C}$ is achieved. The longitudinal velocity\nof the atomic beam can be tuned over several tens of m/s by adjusting the power\nof the pushing laser beam. The beam divergence is around $60$ mrad, determined\nby the transverse velocity distribution of the cold atoms. The slow atom source\nis used to load a three-dimensional magneto-optical trap realizing loading\nrates up to $10^9\\,\\mathrm{atoms/s}$ without indication of saturation of the\nloading rate for increasing oven temperature. The compact setup avoids\nundesired effects found in alternative sources like, e.g., Zeeman slowers, such\nas vacuum contamination and black-body radiation due to the hot strontium oven.", "category": "physics_atom-ph" }, { "text": "Slingshot non-sequential double ionization as a gate to anti-correlated\n two electron escape: At intensities below-the-recollision threshold, we show that\nre-collision-induced excitation with one electron escaping fast after\nre-collision and the other electron escaping with a time delay via a Coulomb\nslingshot motion is one of the most important mechanisms of non-sequential\ndouble ionization, for strongly-driven He at 400 nm. Slingshot-NSDI is a\ngeneral mechanism present for a wide range of low intensities and pulse\ndurations. Anti-correlated two-electron escape is its striking hallmark. This\nmechanism offers an alternative explanation of anti-correlated two-electron\nescape obtained in previous studies.", "category": "physics_atom-ph" }, { "text": "Quantum correlations in the two-photon decay of few-electron ions: A theoretical study of the polarization entanglement of two photons emitted\nin the decay of metastable ionic states is performed within the framework of\ndensity matrix theory and second-order perturbative approach. Particular\nattention is paid to relativistic and non-dipole effects that become important\nfor medium- and high-$Z$ ions. To analyze these effects, the degree of\nentanglement is evaluated both in the dipole approximation and within the\nrigorous relativistic theory. Detailed calculations are performed for the\ntwo-photon $2s_{1/2}\\to 1s_{1/2}$ transition in hydrogen-like, as well as for\nthe $1s_{1/2}\\, 2s_{1/2} \\; {}^1S_0 \\to 1s_{1/2}^2 \\; {}^1S_0$, $1s_{1/2} \\,\n2s_{1/2} \\; {}^3S_1\\to 1s_{1/2}^2 \\; {}^1S_0$ and $1s_{1/2} \\, 2p_{1/2} \\;\n{}^3P_0\\to 1s_{1/2}^2 \\; {}^1S_0$ transitions in helium-like ions.", "category": "physics_atom-ph" }, { "text": "Preparation of Long-Lived, Non-Autoionizing Circular Rydberg States of\n Strontium: Alkaline earth Rydberg atoms are very promising tools for quantum\ntechnologies. Their highly excited outer electron provides them with the\nremarkable properties of Rydberg atoms and, notably, with a huge coupling to\nexternal fields or to other Rydberg atoms while the ionic core retains an\noptically active electron. However, low angular-momentum Rydberg states suffer\nalmost immediate autoionization when the core is excited. Here, we demonstrate\nthat strontium circular Rydberg atoms with a core excited in a $4D$ metastable\nlevel are impervious to autoionization over more than a few millisecond time\nscale. This makes it possible to trap and laser-cool Rydberg atoms. Moreover,\nwe observe singlet to triplet transitions due to the core optical\nmanipulations, opening the way to a quantum microwave to optical interface.", "category": "physics_atom-ph" }, { "text": "Chemical pathways in ultracold reactions of SrF molecules: We present a theoretical investigation of the chemical reaction SrF + SrF\n$\\rightarrow$ products, focusing on reactions at ultralow temperatures. We find\nthat bond swapping, SrF + SrF $\\rightarrow$ Sr$_2$ + F$_2$, is energetically\nforbidden at these temperatures. Rather, the only energetically allowed\nreaction is SrF + SrF $\\rightarrow$ SrF$_2$ + Sr, and even then only singlet\nstates of the SrF$_2$ trimer can form. A calculation along a reduced reaction\npath demonstrates that this abstraction reaction is barrierless, and proceeds\nby one SrF molecule \"handing off\" a fluorine atom to the other molecule.", "category": "physics_atom-ph" }, { "text": "Polyatomic Molecules as Quantum Sensors for Fundamental Physics: Precision measurements in molecules have advanced rapidly in recent years\nthrough developments in techniques to cool, trap, and control. The complexity\nof molecules makes them a challenge to study, but also offers opportunities for\nenhanced sensitivity to many interesting effects. Polyatomic molecules offer\nadditional complexity compared to diatomic molecules, yet are still \"simple\"\nenough to be laser-cooled and controlled. While laser cooling molecules is\nstill a research frontier itself, there are many proposed and ongoing\nexperiments seeking to combine the advanced control enabled by ultracold\ntemperatures with the intrinsic sensitivity of molecules. In this perspective,\nwe discuss some applications where laser-cooled polyatomic molecules may offer\nadvantages for precision measurements of fundamental physics, both within and\nbeyond the Standard Model.", "category": "physics_atom-ph" }, { "text": "Photodissociation of trapped Rb$^+_2$ : Implications for simultaneous\n trapping of atoms and molecular ions: The direct photodissociation of trapped $^{85}$Rb$_2^+$ (rubidium) molecular\nions by the cooling light for the $^{85}$Rb magneto-optical trap (MOT) is\nstudied, both experimentally and theoretically. Vibrationally excited\nRb$_{2}^{+}$ ions are created by photoionization of Rb$_{2}$ molecules formed\nphotoassociatively in the Rb MOT and are trapped in a modified spherical Paul\ntrap. The decay rate of the trapped Rb$_{2}^{+}$ ion signal in the presence of\nthe MOT cooling light is measured and agreement with our calculated rates for\nmolecular ion photodissociation is observed. The photodissociation mechanism\ndue to the MOT light is expected to be active and therefore universal for all\nhomonuclear diatomic alkali metal molecular ions.", "category": "physics_atom-ph" }, { "text": "Collision strengths and transition probabilities for Co III forbidden\n lines: In this paper we compute the collision strengths and their thermally-averaged\nMaxwellian values for electron transitions between the fifteen lowest levels of\ndoubly-ionised cobalt, Co^{2+}, which give rise to forbidden emission lines in\nthe visible and infrared region of spectrum. The calculations also include\ntransition probabilities and predicted relative line emissivities. The data are\nparticularly useful for analysing the thermodynamic conditions of supernova\nejecta.", "category": "physics_atom-ph" }, { "text": "Role of negative-energy states and Breit interaction in calculation of\n atomic parity-nonconserving amplitudes: It is demonstrated that Breit and negative-energy state contributions reduce\nthe 2.5 sigma deviation [S.C. Bennett and C.E. Wieman, Phys. Rev. Lett. 82,\n2484 (1999)] in the value of the weak charge of 133Cs from the Standard Model\nprediction to 1.7sigma. The corrections are obtained in the relativistic\nmany-body perturbation theory by combining all-order Coulomb and second-order\nBreit contributions. The corrections to parity-nonconserving amplitudes amount\nto 0.6% in 133Cs and 1.1% in 223Fr. The relevant magnetic-dipole hyperfine\nstructure constants are modified at the level of 0.3% in Cs, and 0.6% in Fr.\nElectric-dipole matrix elements are affected at 0.1% level in Cs and a few 0.1%\nin Fr.", "category": "physics_atom-ph" }, { "text": "Quantum tunneling isotope exchange reaction H2 + D- -> HD + H-: The tunneling reaction H$_2$ + D$^-$ $\\rightarrow$ HD + H$^-$ was studied in\na recent experimental work at low temperatures (10, 19, and 23~K) by Endres\n{\\it et al.}, Phys. Rev. A {\\bf 95}, 022706 (2017). An upper limit of the rate\ncoefficient was found to be about 10$^{-18}$ cm$^3$/s. In the present study,\nreaction probabilities are determined using the ABC program developed by\nSkouteris {\\it et al.}, Comput. Phys. Commun. {\\bf 133}, 128 (2000). The\nprobabilities for ortho-H$_2$ and para-H$_2$ in their ground rovibrational\nstates are obtained numerically at collision energies above 50~meV with the\ntotal angular momentum $J$ = 0 - 15 and extrapolated below 50~meV using a WKB\napproach. Thermally averaged rate coefficients for ortho- and para-H$_2$ are\nobtained; the largest one, for ortho-H$_2$ is about $3.1\\times10^{-20}$\ncm$^3$/s, which agrees with the experimental results.", "category": "physics_atom-ph" }, { "text": "Charge Migration in Heterocyclic Five-Membered Rings: This contribution presents numerical simulations of N-electron dynamics in\nheterocyclic five-membered ring molecules to shed light on the effect of\nmolecular symmetry on charge migration. Laser-driven dynamics is studied using\nthe hybrid time-dependent density functional theory/configuration methodology,\nand the ensuing field-free charge migration is investigated by means of\ntransient electronic flux density maps. Our results demonstrate that the charge\nmigration in aromatic rings is sensitive to the presence of heteroatoms such as\noxygen and nitrogen. Their presence within the ring induces significant\nmodifications of the character in the ground and low-lying electronic states,\nwhich is imprinted in the charge migration mechanism.", "category": "physics_atom-ph" }, { "text": "Broadband Rydberg Atom-Based Electric-Field Probe: From Self-Calibrated\n Measurements to Sub-Wavelength Imaging: We discuss a fundamentally new approach for the measurement of electric (E)\nfields that will lead to the development of a broadband, direct SI-traceable,\ncompact, self-calibrating E-field probe (sensor). This approach is based on the\ninteraction of radio frequency (RF) fields with alkali atoms excited to Rydberg\nstates. The RF field causes an energy splitting of the Rydberg states via the\nAutler-Townes effect and we detect the splitting via electromagnetically\ninduced transparency (EIT). In effect, alkali atoms placed in a vapor cell act\nlike an RF-to-optical transducer, converting an RF E-field strength measurement\nto an optical frequency measurement. We demonstrate the broadband nature of\nthis approach by showing that one small vapor cell can be used to measure\nE-field strengths over a wide range of frequencies: 1 GHz to 500 GHz. The\ntechnique is validated by comparing experimental data to both numerical\nsimulations and far-field calculations for various frequencies. We also discuss\nvarious applications, including: a direct traceable measurement, the ability to\nmeasure both weak and strong field strengths, compact form factors of the\nprobe, and sub-wavelength imaging and field mapping.", "category": "physics_atom-ph" }, { "text": "Excitation Suppression Due to Interactions Between Microwave-Dressed\n Rydberg Atoms: Atom-atom interactions within a small volume were investigated through the\nexcitation of ultracold Rb atoms. The application of microwaves enhances these\ninteractions, causing the suppression of Rydberg state excitation. The\nsuppression of Rydberg atom excitation was both qualitatively observed and\nquantitatively analyzed using a universal scaling law, giving a measure of the\natom-atom interaction strength in agreement with theoretical prediction.", "category": "physics_atom-ph" }, { "text": "Experimental search for the violation of Pauli Exclusion Principle: The VIolation of Pauli exclusion principle -2 experiment, or VIP-2\nexperiment, at the Laboratori Nazionali del Gran Sasso searches for x-rays from\ncopper atomic transition that are prohibited by the Pauli Exclusion Principle.\nCandidate direct violation events come from the transition of a $2p$ electron\nto the ground state that is already occupied by two electrons. From the first\ndata taking campaign in 2016 of VIP-2 experiment, we determined a best upper\nlimit of 3.4 $\\times$ 10$^{-29}$ for the probability that such a violation\nexists. Significant improvement in the control of the experimental systematics\nwas also achieved, although not explicitly reflected in the improved upper\nlimit. By introducing a simultaneous spectral fit of the signal and background\ndata in the analysis, we succeeded in taking into account systematic errors\nthat could not be evaluated previously in this type of measurements.", "category": "physics_atom-ph" }, { "text": "Ro-vibrational states of H$_2^+$. Variational calculations: The nonrelativistic variational calculation of a complete set of\nro-vibrational states in the H$_2^+$ molecular ion supported by the ground\n$1s\\sigma$ adiabatic potential is presented. It includes both bound states and\nresonances located above the $n=1$ threshold. In the latter case we also\nevaluate a predissociation width of a state wherever it is significant.\nRelativistic and radiative corrections are discussed and effective adiabatic\npotentials of these corrections are included as supplementary files.", "category": "physics_atom-ph" }, { "text": "Observation of interatomic Coulombic decay induced by double excitation\n of helium in nanodroplets: Interatomic Coulombic decay (ICD) plays a crucial role in weakly bound\ncomplexes exposed to intense or high-energy radiation. So far, neutral or ionic\natoms or molecules have been prepared in singly excited electron or hole states\nwhich can transfer energy to neighboring centers and cause ionization and\nradiation damage. Here we demonstrate that a doubly excited atom, despite its\nextremely short lifetime, can decay by ICD; evidenced by high-resolution\nphotoelectron spectra of He nanodroplets excited to the 2s2p+ state. We find\nthat ICD proceeds by relaxation into excited He$^*$He$^+$ atom-pair states, in\nagreement with calculations. The ability of inducing ICD by resonant excitation\nfar above the single-ionization threshold opens opportunities for controlling\nradiation damage to a high degree of element specificity and spectral\nselectivity.", "category": "physics_atom-ph" }, { "text": "Recollision scenario without tunneling : Role of the ionic core\n potential: The standard model of strong laser physics, the recollision scenario, omits\nthe ionic core potential after tunneling. Strikingly, although the Coulomb\ninteraction drives all stages of recollision, the maximum energy the electrons\nbring back to the core is found by ignoring it. We resolve this long-standing\nparadox by showing that this good agreement stems from a fortuitous\ncancellation at high intensities. Instead of the three step model, we find that\nthe Coulomb interaction can be fully integrated into a purely classical\nscenario that explains recollisions without invoking tunneling.", "category": "physics_atom-ph" }, { "text": "An ultracold molecular beam for testing fundamental physics: We use two-dimensional transverse laser cooling to produce an ultracold beam\nof YbF molecules. Through experiments and numerical simulations, we study how\nthe cooling is influenced by the polarization configuration, laser intensity,\nlaser detuning and applied magnetic field. The ultracold part of the beam\ncontains more than $2 \\times 10^5$ molecules per shot and has a temperature\nbelow 200 $\\mu$K, and the cooling yields a 300-fold increase in the brightness\nof the beam. The method can improve the precision of experiments that use\nmolecules to test fundamental physics. In particular, the beam is suitable for\nmeasuring the electron electric dipole moment with a statistical precision\nbetter than $10^{-30}$ e cm.", "category": "physics_atom-ph" }, { "text": "Nonlinear dynamics in an alternating gradient guide for neutral\n particles: Neutral particles can be guided and focussed using electric field gradients\nthat focus in one transverse direction and defocus in the other, alternating\nbetween the two directions. Such a guide is suitable for transporting particles\nthat are attracted to strong electric fields, which cannot be guided using\nstatic fields. Particles are only transmitted if their initial positions and\ntransverse speeds lie within the guide's phase space acceptance. Nonlinear\nforces are always present in the guide and can severely reduce this acceptance.\nWe consider the effects of the two most important nonlinear forces, a term in\nthe force that is cubic in the off-axis displacement, and a nonlinear term\nwhich couples together the two transverse motions. We use approximate\nanalytical techniques, along with numerical methods, to calculate the influence\nof these nonlinear forces on the particle trajectories and on the phase space\nacceptance. The cubic term alters the focussing and defocussing powers, leading\neither to an increase or a decrease of the acceptance depending on its sign. We\nfind an approximate analytical result for the phase space acceptance including\nthis cubic term. Using a perturbation method we show how the coupling term\nleads to slow changes in the amplitudes of the transverse oscillations. This\nterm reduces the acceptance when it reduces the focussing power, but has little\ninfluence when it increases that power. It is not possible to eliminate both\nnonlinear terms, but one can be made small at the expense of the other. We show\nhow to choose the guide parameters so that the acceptance is optimized.", "category": "physics_atom-ph" }, { "text": "Sympathetic cooling schemes for separately trapped ions coupled via\n image currents: Cooling of particles to mK-temperatures is essential for a variety of\nexperiments with trapped charged particles. However, many species of interest\nlack suitable electronic transitions for direct laser cooling. We study\ntheoretically the remote sympathetic cooling of a single proton with\nlaser-cooled $^9$Be$^+$ in a double-Penning-trap system. We investigate three\ndifferent cooling schemes and find, based on analytical calculations and\nnumerical simulations, that two of them are capable of achieving proton\ntemperatures of about 10 mK with cooling times on the order of 10 s. In\ncontrast, established methods such as feedback-enhanced resistive cooling with\nimage-current detectors are limited to about 1 K in 100 s. Since the studied\ntechniques are applicable to any trapped charged particle and allow spatial\nseparation between the target ion and the cooling species, they enable a\nvariety of precision measurements based on trapped charged particles to be\nperformed at improved sampling rates and with reduced systematic uncertainties.", "category": "physics_atom-ph" }, { "text": "Deciphering Core, Valence and Double-Core-Polarization Contributions to\n Parity Violating Amplitudes in $^{133}$Cs using Different Methods: As a prerequisite of probing physics beyond the Standard Model (BSM) of\nparticle physics, it is imperative to perform calculation of parity violating\nelectric dipole ($E1_{PV}$) amplitudes within 0.5\\% accuracy in atomic systems.\nLatest high precision calculations of $E1_{PV}$ of the $6s ~ ^2S \\rightarrow 7s\n~ ^2S $ transition in $^{133}$Cs by three different groups claim achieving its\naccuracy below 0.5\\%, but such claims contradict on the view that their final\nvalues differ by 1\\%. One of the major issues in these calculations is the\nopposite signs among the core correlation contribution from different works\nleading to 200\\% difference in its value. In a review [Rev. Mod. Phys. 90,\n025008 (2018)], a Letter [Phys. Rev. D 103, L111303 (2021)] and a Comment\n[Phys. Rev. D 105, 018301 (2022)], reliability of all these calculations are\nstrongly contended. We unearthed here the underlying reason for getting sign\ndiscrepancies in various works by investigating how different electron\ncorrelation effects are encapsulated through the undertaken methods in the\nabove works to determine $E1_{PV}$. Detailed discussions presented in this work\nwould help in guiding theoretical studies to improve accuracy of $E1_{PV}$ in\natomic systems to probe BSM physics.", "category": "physics_atom-ph" }, { "text": "Reactive Collisions of Ultracold Molecules Confined in quasi-2D Geometry: We present a formalism for rigorous calculations of cross sections for\ninelastic and reactive collisions of ultracold atoms and molecules confined by\nlaser fields in quasi-2D geometry. Our results show that the\nelastic-to-inelastic ratios of collision cross sections are enhanced in the\npresence of a laser confinement and that the threshold energy dependence of the\ncollision cross sections can be tuned by varying the confinement strength and\nexternal magnetic fields. The enhancement of the elastic-to-inelastic ratios is\ninversely proportional to $\\sqrt{\\epsilon/\\hbar \\omega_0}$, where $\\epsilon$ is\nthe kinetic energy and $\\omega_0$ is the oscillation frequency of the trapped\nparticles in the confinement potential.", "category": "physics_atom-ph" }, { "text": "Resonant-state solution of the Faddeev-Merkuriev integral equations for\n three-body systems with Coulomb-like potentials: A novel method for calculating resonances in three-body Coulombic systems is\npresented. The Faddeev-Merkuriev integral equations are solved by applying the\nCoulomb-Sturmian separable expansion method. To show the power of the method we\ncalculate resonances of the three-$\\alpha$ and the $H^-$ systems.", "category": "physics_atom-ph" }, { "text": "Adiabaticity and localization in one-dimensional incommensurate lattices: We experimentally investigate the role of localization on the adiabaticity of\nloading a Bose-Einstein condensate into a one-dimensional optical potential\ncomprised of a shallow primary lattice plus one or two perturbing lattice(s) of\nincommensurate period. We find that even a very weak perturbation causes\ndramatic changes in the momentum distribution and makes adiabatic loading of\nthe combined lattice much more difficult than for a single period lattice. We\ninterpret our results using a band structure model and the one-dimensional\nGross-Pitaevskii equation.", "category": "physics_atom-ph" }, { "text": "Coherent control with shaped femtosecond laser pulses applied to\n ultracold molecules: We report on coherent control of excitation processes of translationally\nultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond\nlaser pulses. Evolution strategies are applied in a feedback loop in order to\noptimize the photoexcitation of the Rb2 molecules, which subsequently undergo\nionization or fragmentation. A superior performance of the resulting pulses\ncompared to unshaped pulses of the same pulse energy is obtained by\ndistributing the energy among specific spectral components. The demonstration\nof coherent control to ultracold ensembles opens a path to actively influence\nfundamental photo-induced processes in molecular quantum gases.", "category": "physics_atom-ph" }, { "text": "Neon in ultrashort and intense x rays from free electron lasers: We theoretically examine neon atoms in ultrashort and intense x rays from\nfree electron lasers and compare our results with data from experiments\nconducted at the Linac Coherent Light Source (LCLS). For this purpose, we treat\nin detail the electronic structure in all possible nonrelativistic cationic\nconfigurations using a relativistic multiconfiguration approach. The\ninteraction with the x rays is described in rate-equation approximation. To\nunderstand the mechanisms of the interaction, a path analysis is devised which\nallows us to investigate what sequences of photoionization and decay processes\nlead to a specific configuration and with what probability. Thereby, we uncover\na connection to the mathematics of graph theory and formal languages. In\ndetail, we study the ion yields and find that plain rate equations do not\nprovide a satisfactory description. We need to extend the rate equations for\nneon to incorporate double Auger decay of a $K$-shell vacancy and\nphotoionization shake off for neutral neon. Shake off is included for valence\nand core ionization; the former has hitherto been overlooked but has important\nconsequences for the ion yields from an x-ray energy below the core ionization\nthreshold. Furthermore, we predict the photon yields from XUV and x-ray\nfluorescence; these allow one insights into the configurations populated by the\ninteraction with the x rays. Finally, we discover that inaccuracies in those\nAuger decay widths employed in previous studies have only a minor influence on\nion and photon yields.", "category": "physics_atom-ph" }, { "text": "On the general theory of bound state spectra in the Coulomb few- and\n many-body systems: Based on the fact that the Hamiltonians of the Coulomb many-particle systems\nare always factorized we develop the two different approaches for analytical\nsolution of the Schr\\\"{o}dinger equation written for arbitrary few- and\nmany-particle Coulomb systems. The first approach is the matrix factorization\nmethod. Another method is based on the $D^{+}-$series of representations of the\nhyper-radial O(2,1)-algebra. The both these methods allow us to obtain the\nclosed analytical formulas for the bound state energies in an arbitrary\nmany-particle Coulomb system.", "category": "physics_atom-ph" }, { "text": "Atomic Parity Violation. Early days, present results, prospects: This is a personal recollection of the time when the search for APV was\nbeginning. In spite of today's remarkable results, summarized here, there are\nstill important goals to be achieved. I indicate a possible way to tackle the\nremaining experimental challenges, by adapting methods now of frequent use in\nprecision metrology.", "category": "physics_atom-ph" }, { "text": "Scaling laws for the non-linear coupling constant of a Bose-Einstein\n condensate at the threshold of delocalization: We explore the localization of a quasi-one-, quasi-two-, and\nthree-dimensional ultra-cold gas by a finite-range defect along the\ncorresponding 'free'-direction/s. The time-independent non-linear Schroedinger\nequation that describes a Bose-Einstein condensate was used to calculate the\nmaximum non-linear coupling constant, g_max, and thus the maximum number of\natoms, N_max, that the defect potential can localize. An analytical model,\nbased on the Thomas-Fermi approximation, is introduced for the wavefunction. We\nshow that g_max becomes a function of R_0 sqrt(V_0) for various one-, two-, and\nthree-dimensional defect shapes with depths V_0 and characteristic lengths R_0.\nOur explicit calculations show surprising agreement with this crude model over\na wide range of V_0 and R_0. A scaling rule is also found for the wavefunction\nfor the ground state at the threshold at which the localized states approach\ndelocalization. The implication is that two defects with the same product R_0\nsqrt(V_0) will thus be related to each other with the same g_max and will have\nthe same (reduced) density profile in the free-direction/s.", "category": "physics_atom-ph" }, { "text": "The dual King relation: We introduce a new linear relation in the isotope shifts of atomic\nspectroscopy. While the famous King relation is the linear relation among the\ndifferent transitions, the new one is the linear relation among the different\nisotope pairs. Since we obtain this relation by exchanging the roles of the\nelectronic and the nuclear factors in the original relation, we call it the\ndual King relation. This relation shows us similar information to the original\nKing relation without including new fit parameters when we measure the isotope\nshifts of many transitions. In the dual King relation, the fit coefficients\nconsist of the nuclear factors. Then, the fit results give us constraints to\nthe ratios of the isotope dependence independent of the electron wave\nfunctions. This helps us to test the origin of unknown higher order isotope\nshifts. We show that the dual King relation can also be employed to constrain\nthe weakly interacting light new boson at the same level as the original King\nrelation.", "category": "physics_atom-ph" }, { "text": "Finite-Basis-Set Approach to the Two-Center Heteronuclear \\\\ Dirac\n Problem: The rigorous two-center approach based on the dual-kinetically balanced\nfinite-basis-set expansion is applied to one-electron, heteronuclear diatomic\nBi-Au, U-Pb, and Cf-U quasimolecules. The obtained $1\\sigma$ ground-state\nenergies are compared with previous calculations, when possible. Upon analysis\nof three different placements of the coordinate system's origin in the monopole\napproximation of the two-center potential: (1) in the middle, between the\nnuclei, (2) in the center of the heavy nucleus, and (3) in the center of the\nlight nucleus, a substantial difference between the results is found. The\nleading contributions of one-electron quantum electrodynamics (self-energy and\nvacuum polarization) are evaluated within the monopole approximation as well.", "category": "physics_atom-ph" }, { "text": "A Two-Photon E1-M1 Optical Clock: An allowed E1-M1 excitation scheme creates optical access to the ${^1S_0}\n\\rightarrow {^3P_0}$ clock transition in group II type atoms. This method does\nnot require the hyperfine mixing or application of an external magnetic field\nof other optical clock systems. The advantages of this technique include a\nDoppler-free excitation scheme and increased portability with the use of vapor\ncells. We will discuss technical mechanisms of a monochromatic excitation\nscheme for a hot E1-M1 clock and briefly discuss a bichromatic scheme to\neliminate light shifts. We determine the optimal experimental parameters for\nHg, Yb, Ra, Sr, Ba, Ca, Mg, and Be and calculate that neutral Hg has ideal\nproperties for a hot, portable frequency standard.", "category": "physics_atom-ph" }, { "text": "Borromean molecules: For some values of the constituent masses m_i, the hydrogen-like molecule\n(m_1^+,m_2^+,m_3^-,m_4^-) is stable with respect to spontaneous dissociation\ninto two neutral atoms, while none of its three-body subsystems such as\n(m_1^+,m_2^+,m_3^-) is stable. This occurs in particular in the neighbourhood\nof the (M^+,m^+,M^-,m^-) configuration with M/m=2, as for instance for the\nmolecule (p,d,\\bar{p},\\bar{d}) involving an antiproton and an antideuteron.", "category": "physics_atom-ph" }, { "text": "Einstein-Hopf drag, Doppler shift of thermal radiation and blackbody\n friction: A unifying perspective on an intriguing physical effect: The thermal friction force acting on an atom moving relative to a thermal\nphoton bath has recently been calculated on the basis of the\nfluctuation-dissipation theorem. The thermal fluctuations of the\nelectromagnetic field give rise to a drag force on an atom provided one allows\nfor dissipation of the field energy via spontaneous emission. The drag force\nexists if the atomic polarizability has a nonvanishing imaginary part. Here, we\nexplore alternative derivations. The damping of the motion of a simple harmonic\noscillator is described by radiative reaction theory (result of Einstein and\nHopf), taking into account the known stochastic fluctuations of the\nelectromagnetic field. Describing the excitations of the atom as an ensemble of\ndamped harmonic oscillators, we identify the previously found expressions as\ngeneralizations of the Einstein-Hopf result. In addition, we present a simple\nexplanation for blackbody friction in terms of a Doppler shift of the thermal\nradiation in the inertial frame of the moving atom: The atom absorbs\nblue-shifted photons from the front and radiates off energy in all directions,\nthereby losing energy. The original plus the two alternative derivations\nprovide for additional confirmation of an intriguing physical effect, and leave\nno doubt regarding its existence.", "category": "physics_atom-ph" }, { "text": "Constraints on anomalous spin-spin interactions from spin-exchange\n collisions: Measured and calculated cross sections for spin-exchange between alkali atoms\nand noble gases (specifically sodium and helium) are used to constrain\nanomalous spin-dependent forces between nuclei at the atomic scale ($\\sim\n10^{-8}~{\\rm cm}$). Combined with existing stringent limits on anomalous\nshort-range, spin-dependent couplings of the proton, the dimensionless coupling\nconstant for a heretofore undiscovered axial vector interaction of the neutron\narising from exchange of a boson of mass $\\lesssim 100~{\\rm eV}$ is constrained\nto be $g_A^n/\\sqrt{4 \\pi \\hbar c} < 2 \\times 10^{-3}$. Constraints are\nestablished for a velocity- and spin-dependent interaction $\\propto\n\\prn{\\mathbf{I} \\cdot \\mathbf{v}} \\prn{\\mathbf{K} \\cdot \\mathbf{v}}$, where\n$\\mathbf{I}$ and $\\mathbf{K}$ are the nuclear spins of He and Na, respectively,\nand $\\mathbf{v}$ is the relative velocity of the atoms. Constraints on torsion\ngravity are also considered.", "category": "physics_atom-ph" }, { "text": "High-accuracy Complete Active Space multiconfiguration\n Dirac-Hartree-Fock calculations of hyperfine structure constants of the gold\n atom: The multiconfiguration Dirac-Hartree-Fock (MCDHF) model has been employed to\ncalculate the expectation values for the hyperfine splittings of the 5d96s2\n2D3/2 and 5d96s2 2D5/2 levels of atomic gold. One-, two-, and three-body\nelectron correlation effects involving all 79 electrons have been included in a\nsystematic manner. The approximation employed in this study is equivalent to a\nComplete Active Space (CAS) approach. Calculated electric field gradients,\ntogether with experimental values of the electric quadrupole hyperfine\nstructure constants, allow us to extract a nuclear electric quadrupole moment\nQ(197Au)=521.5(5.0) mb.", "category": "physics_atom-ph" }, { "text": "Quantum interference effects in laser spectroscopy of muonic hydrogen,\n deuterium, and helium-3: Quantum interference between energetically close states is theoretically\ninvestigated, with the state structure being observed via laser spectroscopy.\nIn this work, we focus on hyperfine states of selected hydrogenic muonic\nisotopes, and on how quantum interference affects the measured Lamb shift. The\nprocess of photon excitation and subsequent photon decay is implemented within\nthe framework of nonrelativistic second-order perturbation theory. Due to its\nexperimental interest, calculations are performed for muonic hydrogen,\ndeuterium, and helium-3. We restrict our analysis to the case of photon\nscattering by incident linear polarized photons and the polarization of the\nscattered photons not being observed. We conclude that while quantum\ninterference effects can be safely neglected in muonic hydrogen and helium-3,\nin the case of muonic deuterium there are resonances with close proximity,\nwhere quantum interference effects can induce shifts up to a few percent of the\nlinewidth, assuming a pointlike detector. However, by taking into account the\ngeometry of the setup used by the CREMA collaboration, this effect is reduced\nto less than 0.2% of the linewidth in all possible cases, which makes it\nirrelevant at the present level of accuracy.", "category": "physics_atom-ph" }, { "text": "Interference-induced peak splitting in EUV superfluorescence: We investigate the laser-induced quantum interference in EUV\nsuperfluorescence occurring in a dense gas of $\\Lambda$-type helium atoms\ncoupled by a coherent laser field in the visible region. Due to the\nconstructive interatomic and intraatomic interferences, the superfluorescence\ncan split in two pulses conveniently controlled by the gas density and\nintensity of the driving field, suggesting potential applications for\npump-probe experiments.", "category": "physics_atom-ph" }, { "text": "Sensitivity test of a blue-detuned dipole trap designed for parity\n non-conservation measurements in Fr: A dynamic blue-detuned optical dipole trap with stable $^{87}Rb$ atoms\nproduces a differential ac Stark shift of 18 Hz in the ground state hyperfine\ntransition, and it preserves the ground state hyperfine superpositions for a\nlong coherence time of 180 ms. The trapped atoms undergoing microwave Rabi\noscillations are sensitive to a small signal, artificially generated with a\nsecond microwave source, phase locked to the first allow- ing a simple and\neffective method for determining signal-to-noise ratio limits through\ninterference techniques. This provides an excellent means of calibrating\nsensitivity in experiments such as our ongoing Fr parity non-conservation\nmeasurement.", "category": "physics_atom-ph" }, { "text": "High-precision calculations of In I and Sn II atomic properties: We use all-order relativistic many-body perturbation theory to study 5s^2 nl\nconfigurations of In I and Sn II. Energies, E1-amplitudes, and hyperfine\nconstants are calculated using all-order method, which accounts for single and\ndouble excitations of the Dirac-Fock wave functions.", "category": "physics_atom-ph" }, { "text": "Relativistic coupled-cluster single-double calculations of positron-atom\n bound states: Relativistic coupled-cluster single-double approximation is used to calculate\npositron-atom bound states. The method is tested on closed-shell atoms such as\nBe, Mg, Ca, Zn, Cd, and Hg where a number of accurate calculations is\navailable. It is then used to calculate positron binding energies for a range\nof open-shell transition metal atoms from Sc to Cu, from Y to Pd, and from Lu\nto Pt. These systems possess Feshbach resonances, which can be used to search\nfor positron-atom binding experimentally through resonant annihilation or\nscattering.", "category": "physics_atom-ph" }, { "text": "Collisional shift and broadening of Rydberg states in nitric oxide at\n room temperature: We report on the collisional shift and line broadening of Rydberg states in\nnitric oxide (NO) with increasing density of a background gas at room\ntemperature. As a background gas we either use NO itself or nitrogen (N$_{2}$).\nThe precision spectroscopy is performed by a sub-Doppler three-photon\nexcitation scheme with a subsequent readout of the Rydberg states realized by\nthe amplification of a current generated by free charges due to collisions. The\nshift shows a dependence on the rotational quantum state of the ionic core and\nno dependence on the principle quantum number of the orbiting Rydberg electron.\nThe experiment was performed in the context of developing a trace-gas sensor\nfor breath-gas analysis in a medical application.", "category": "physics_atom-ph" }, { "text": "Spectroscopy of a cold strontium Rydberg gas: We present a study of a cold strontium Rydberg gas. The narrowband laser\nexcitation of Rydberg states in the range n=20-80 from a 6~mK cloud of\nstrontium atoms is detected using the spontaneous ionization of the Rydberg\natoms. Using a high-resolution step-scanning technique, we perform detailed\nmeasurements of the Stark maps of selected Rydberg states. We find excellent\nagreement between the measured Stark maps and a numerical calculation based on\nan independent-electron model. Finally we show that excitation of the second\nvalence electron can be used to probe the dynamics of the Rydberg gas with\nnanosecond temporal resolution via autoionization.", "category": "physics_atom-ph" }, { "text": "Electron radiative recombination with a hydrogen-like ion: We survey the results of a long-term study of the process of radiative\nrecombination. A rigorous theory of nonrelativistic electron radiative\nrecombination with a hydrogen-like ion is used to calculate the total cross\nsection of the process, the effective radiation, the recombination rate\ncoefficient, and the emission coefficient in a plasma with a Maxwellian\nelectron distribution. The exact results are compared with the numerous known\nasymptotic and interpolation formulas. We propose interpolation formulas which\nensure a uniform approximation of all mentioned quantities in a wide range of\nplasma temperatures.", "category": "physics_atom-ph" }, { "text": "Statistical properties of levels and lines in complex spectra: We review recent developments of the statistical properties of complex atomic\nspectra, based on the pioneering work of Claire Bauche-Arnoult and Jacques\nBauche. We discuss several improvements of the statistical methods (UTA, SOSA)\nfor the modeling of the lines in a transition array: impact of high-order\nmoments, choice of the distribution (Generalized Gaussian, Normal Inverse\nGaussian) and corrections at low temperatures. The second part of the paper\nconcerns general properties of transition arrays, such as propensity rule and\ngeneralized J-file sum rule (for E1 or E2 lines), emphasizing the particular\nrole of the G1 exchange Slater integral. The statistical modeling introduced by\nJ. Bauche and C. Bauche-Arnoult for the distribution of the M values\n(projection of total angular momentum J) in an electron configuration, written\nP(M), was extended in order to account for configurations with a high-l\nspectator and a new analytical formula for the evaluation of the number of E1\nlines with a wider range of applicability was derived.", "category": "physics_atom-ph" }, { "text": "A High Temperature Calcium Vapor Cell for Spectroscopy on the 4s^2 1S0\n to 4s4p 3P1 Intercombination Line: We have demonstrated a high temperature vapor cell for absorption\nspectroscopy on the Ca intercombination line. The cell uses a dual chamber\ndesign to achieve the high temperatures necessary for an optically dense vapor\nwhile avoiding the necessity of high temperature vacuum valves and\nglass-to-metal seals. We have observed over 50 percent absorption in a single\npass through the cell. Although pressure broadening in the cell prevented us\nfrom performing saturated-absorption spectroscopy, the broadening resulted in\nhigher signal-to-noise ratios by allowing us to probe the atoms with\nintensities much greater than the 0.2 uW/cm^2 saturation intensity of the\nunbroadened transition.", "category": "physics_atom-ph" }, { "text": "Application of the Finite Field Coupled Cluster Method to Calculate\n Molecular Properties Relevant to Electron Electric Dipole Moment Searches: Heavy polar diatomic molecules are currently among the most promising probes\nof fundamental physics. Constraining the electric dipole moment of the electron\n(eEDM), in order to explore physics beyond the Standard Model, requires a\nsynergy of molecular experiment and theory. Recent advances in experiment in\nthis field have motivated us to implement a finite field coupled cluster\napproach (FFCC). This work has distinct advantages over the theoretical methods\nthat we had used earlier in the analysis of eEDM searches. We used the\nrelativistic FFCC to calculate molecular properties of interest to eEDM\nexperiments, that is, the effective electric field (Eeff), and the permanent\nelectric dipole moment (PDM). We theoretically determine these quantities for\nthe alkaline earth monofluorides (AEMs), the mercury monohalides (HgX), and\nPbF. The latter two systems, as well as BaF from the AEMs, are of interest to\neEDM searches. We also report the calculations of the properties using a\nrelativistic coupled cluster approach with single, double, and partial triples'\nexcitations, which is considered to be the gold standard of electronic\nstructure calculations. We also present a detailed error estimate, including\nerrors that stem from the choice of basis sets, and higher order correlation\neffects.", "category": "physics_atom-ph" }, { "text": "Bose-Einstein condensation by polarization gradient laser cooling: Attempts to create quantum degenerate gases without evaporative cooling have\nbeen pursued since the early days of laser cooling, with the consensus that\npolarization gradient cooling (PGC, also known as \"optical molasses\") alone\ncannot reach condensation. In the present work, we report that simple PGC can\ngenerate a small Bose-Einstein condensate (BEC) inside a corrugated\nmicrometer-sized optical dipole trap. The experimental parameters enabling BEC\ncreation were found by machine learning, which increased the atom number by a\nfactor of 5 and decreased the temperature by a factor of 2.5, corresponding to\nalmost two orders of magnitude gain in phase space density. When the trapping\nlight is slightly misaligned through a microscopic objective lens, a BEC of\n$\\sim 250$ $^{87}$Rb atoms is formed inside a local dimple within 40 ms of PGC.", "category": "physics_atom-ph" }, { "text": "High-precision measurements and theoretical calculations of indium\n excited-state polarizabilities: We report measurements of the $^{115}$In $7p_{1/2}$ and $7p_{3/2}$ scalar and\ntensor polarizabilities using two-step diode laser spectroscopy in an atomic\nbeam. The scalar polarizabilities are one to two orders of magnitude larger\nthan for lower lying indium states due to the close proximity of the $7p$ and\n$6d$ states. For the scalar polarizabilities, we find values (in atomic units)\nof $1.811(4) \\times 10^5$ $a_0^3$ and $2.876(6) \\times 10^5$ $a_0^3$ for the\n$7p_{1/2}$ and $7p_{3/2}$ states respectively. We estimate the smaller tensor\npolarizability component of the $7p_{3/2}$ state to be $-1.43(18) \\times 10^4$\n$a_0^3$. These measurements represent the first high-precision benchmarks of\ntransition properties of such high excited states of trivalent atomic systems.\nWe also present new ab initio calculations of these quantities and other In\npolarizabilities using two high-precision relativistic methods to make a global\ncomparison of the accuracies of the two approaches. The precision of the\nexperiment is sufficient to differentiate between the two theoretical methods\nas well as to allow precise determination of the indium $7p-6d$ matrix\nelements. The results obtained in this work are applicable to other heavier and\nmore complicated systems, and provide much needed guidance for the development\nof even more precise theoretical approaches.", "category": "physics_atom-ph" }, { "text": "Evaluation of accurate uncertainty of measurement in L subshell\n ionization cross-section: To have a better understanding of a physical process, a comparison of\nex-perimental data with theoretical values is mandatory. The comparison\nismeaningful if the uncertainty in the experiment is accounted well. However,it\nis seldom seen, especially for a complex phenomenon. We take a test casethrough\nL subshell ionization of atoms by particle impact. Experimentally,x-ray\nproduction cross-sections are measured, but ionization cross-sectionsare\ncalculated theoretically. Furthermore, the uncertainty of the x-ray pro-duction\ncross-section is mainly statistics and detector-efficiency driven.\nButionization cross-section involves many other factors because of the\nrelation-ship between the production and ionization cross section, having wide\nuncer-tainty spectrum. Consequently, determining the measurement uncertainty\ninL subshell ionization cross-section is always difficult. We have studied\nthisissue in the simplest way, where the rule of weighted propagation of\nrela-tive uncertainty is utilised. We notice that larger uncertainties are\ninvolvedin atomic parameters relevant to L1(2s1/2) subshell than those\nassociatedwith the other two L2(2p1/2) and L3(2p3/2) subshells. Hence,\ncomparisonbetween theory and experiment would give higher emphasis\nonL2andL3subshell ionization cross sections. We believe this work aware us that\ntheappropriate uncertainty evaluation is extremely important for providing\ntheright judgment on the data.", "category": "physics_atom-ph" }, { "text": "Development of an apparatus for cooling 6Li-87Rb Fermi-Bose mixtures in\n a light-assisted magnetic trap: We describe an experimental setup designed to produce ultracold trapped gas\nclouds of fermionic 6Li and bosonic 87Rb. This combination of alkali metals has\nthe potential to reach deeper Fermi degeneracy with respect to other mixtures\nsince it allows for improved heat capacity matching which optimizes sympathetic\ncooling efficiency. Atomic beams of the two species are independently produced\nand then decelerated by Zeeman slowers. The slowed atoms are collected into a\nmagneto-optical trap and then transferred into a quadrupole magnetic trap. An\nultracold Fermi gas with temperature in the 10^-3 T_F range should be\nattainable through selective confinement of the two species via a properly\ndetuned laser beam focused in the center of the magnetic trap.", "category": "physics_atom-ph" }, { "text": "$M_F$-dependent Hyperfine Induced Transition Rates in an External\n Magnetic Field for Be-like $^{47}$Ti$^{18+}$: Hyperfine induced $2s2p~^3P_0 \\rightarrow 2s^2~^1S_0$ transition rates in an\nexternal magnetic field for Be-like $^{47}$Ti were calculated based on the\nmulticonfiguration Dirac-Fock method. It was found that the transition\nprobability is dependent on the magnetic quantum number $M_F$ of the excited\nstate, even in the weak field. The present investigation clarified that the\ndifference of the hyperfine induced transition rate of Be-like Ti ions between\nexperiment [Schippers {\\sl et al.}, Phys Rev Lett {\\bf 98}, (2007) 033001(4)]\nand theory does not result from the influence of external magnetic field.", "category": "physics_atom-ph" }, { "text": "Twisted electron impact single ionization coincidence cross-sections for\n noble gas atoms: We present the angular profiles of the triple differential cross-section\n(TDCS) for the (e,2e) process on the noble gas atoms, namely He (1s), Ne (2s\nand 2p), and Ar (3p) for the plane wave and the twisted electron impact. We\ndevelop the theoretical formalism in the first-born approximation. The present\nstudy compares the TDCS for different values of orbital angular momentum number\n$m$ and opening angles $\\theta_p$ of the twisted electron beam with that of the\nplane wave beam. In addition, we also investigate the TDCS for macroscopic\natomic targets to explore the influence of opening angle $\\theta_p$ of the\ntwisted electron beam on the TDCS. Our results show that the peaks in binary\nand recoil region shift from the momentum transfer direction. The results also\nshow that for larger opening angles the peaks for $p$-type orbitals split into\ndouble-peak structures which are not observed in the plane wave results for the\ngiven kinematics. The angular profiles for averaged cross-section show the\ndependence of TDCS on the opening angles which are significantly different from\nthe plane wave TDCS.", "category": "physics_atom-ph" }, { "text": "Laser-induced thermal source for cold atoms: We demonstrate a simple and compact approach to laser cool and trap atoms\nbased on laser-induced thermal ablation (LITA) of a pure solid granule. A rapid\nthermalisation of the granule leads to a fast recovery of the ultra-high vacuum\ncondition required for a long trapping lifetime of the cold gas. We give a\nproof-of-concept of the technique, performing a magneto-optical trap on the 461\nnm $^1S_0\\rightarrow^1P_1$ transition of strontium. We get up to 3.5 million of\ncold strontium-88 atoms with a trapping lifetime of more than 4 s. The lifetime\nis limited by the pressure of the strontium-free residual background vapour. We\nalso implement an original configuration of permanent magnets to create the\nquadruple magnetic field of the magneto-optical trap. The LITA technique can be\ngeneralized to other atomic elements such as transition metals and lanthanide\natoms, and shows a strong potential for applications in quantum technologies\nranging from quantum computing to precision measurements such as outdoor\ninertial sensing.", "category": "physics_atom-ph" }, { "text": "Accurate Determination of Blackbody Radiation Shifts in a Strontium\n Molecular Lattice Clock: Molecular lattice clocks enable the search for new physics, such as fifth\nforces or temporal variations of fundamental constants, in a manner\ncomplementary to atomic clocks. Blackbody radiation (BBR) is a major\ncontributor to the systematic error budget of conventional atomic clocks and is\nnotoriously difficult to characterize and control. Here, we combine infrared\nStark-shift spectroscopy in a molecular lattice clock and modern quantum\nchemistry methods to characterize the polarizabilities of the Sr$_2$ molecule\nfrom dc to infrared. Using this description, we determine the static and\ndynamic blackbody radiation shifts for all possible vibrational clock\ntransitions to the $10^{-16}$ level. This constitutes an important step towards\nmHz-level molecular spectroscopy in Sr$_2$, and provides a framework for\nevaluating BBR shifts in other homonuclear molecules.", "category": "physics_atom-ph" }, { "text": "Spectroscopy and frequency measurement of the $^{87}$Sr clock transition\n by laser linewidth transfer using an optical frequency comb: We perform spectroscopic observations of the 698-nm clock transition in\n$^{87}$Sr confined in an optical lattice using a laser linewidth transfer\ntechnique. A narrow-linewidth laser interrogating the clock transition is\nprepared by transferring the linewidth of a master laser (1064 nm) to that of a\nslave laser (698 nm) with a high-speed controllable fiber-based frequency comb.\nThe Fourier-limited spectrum is observed for an 80-ms interrogating pulse. We\ndetermine that the absolute frequency of the 5s$^{2}$ $^{1}$S$_{0}$ - 5s5p\n$^{3}$P$_{0}$ clock transition in $^{87}$Sr is 429 228 004 229 872.0 (1.6) Hz\nreferenced to the SI second.", "category": "physics_atom-ph" }, { "text": "Optimized ultra-narrow atomic bandpass filters via magneto-optic\n rotation in an unconstrained geometry: Atomic bandpass filters are widely used in a variety of applications, owing\nto their high peak transmission and narrow bandwidth. Much of the previous\nliterature has used the Faraday effect to realize such filters, where an axial\nmagnetic field is applied across the atomic medium. Here we show that by using\na non-axial magnetic field, the performance of these filters can be improved in\ncomparison to the Faraday geometry. We optimize the performance of these\nfilters using a numerical model and verify their performance by direct\nquantitative comparison with experimental data. We find excellent agreement\nbetween experiment and theory. These optimized filters could find use in many\nof the areas where Faraday filters are currently used, with little modification\nto the optical setup, allowing for improved performance with relatively little\nchange.", "category": "physics_atom-ph" }, { "text": "Second-Scale $^9\\text{Be}^+$ Spin Coherence in a Compact Penning Trap: We report microwave spectroscopy of co-trapped $^9\\text{Be}^+$ and\n$^{40}\\text{Ca}^+$ within a compact permanent-magnet-based Penning ion trap.\nThe trap is constructed with a reconfigurable array of NdFeB rings providing a\n0.654 T magnetic field that is near the 0.6774-T magnetic-field-insensitive\nhyperfine transition in $^9\\text{Be}^+$. Performing Ramsey spectroscopy on this\nhyperfine transition, we demonstrate nuclear spin coherence with a contrast\ndecay time of >1 s. The $^9\\text{Be}^+$ is sympathetically cooled by a Coulomb\ncrystal of $^{40}\\text{Ca}^+$, which minimizes $^9\\text{Be}^+$ illumination and\nthus mitigates reactive loss. Introducing a unique high-magnetic-field optical\ndetection scheme for $^{40}\\text{Ca}^+$, we perform spin state readout without\na 729~nm shelving laser. We record a fractional trap magnetic field instability\nbelow 20 ppb (<13 nT) at 43 s of averaging time with no magnetic shielding and\nonly passive thermal isolation. We discuss potential applications of this\ncompact, reconfigurable Penning trap.", "category": "physics_atom-ph" }, { "text": "Nuclear magnetic shielding in heliumlike ions: Ab initio QED calculations of the nuclear magnetic shielding constant in\nhelium-like ions are presented. We combine the nonrelativistic QED approach\nbased on an expansion in powers of the fine-structure constant $\\alpha$ and the\nso-called ``all-order'' QED approach which includes all orders in the parameter\n$Z\\alpha$ but uses a perturbation expansion in the parameter $1/Z$ (where $Z$\nis the nuclear charge number). The combination of the two complementary methods\nmakes our treatment applicable both to low-$Z$ and high-$Z$ ions. Our\ncalculations confirm the presence of a rare antiscreening effect for the\nrelativistic shielding correction and demonstrate the importance of the\ninclusion of the negative-energy part of the Dirac spectrum.", "category": "physics_atom-ph" }, { "text": "Optimized pulsed sideband cooling and enhanced thermometry of trapped\n ions: Resolved sideband cooling is a standard technique for cooling trapped ions\nbelow the Doppler limit to near their motional ground state. Yet, the most\ncommon methods for sideband cooling implicitly rely on low Doppler-cooled\ntemperatures and tightly confined ions, and they cannot be optimized for\ndifferent experimental conditions. Here we introduce a framework which\ncalculates the fastest possible pulsed sideband cooling sequence for a given\nnumber of pulses and set of experimental parameters, and we verify its\nimprovement compared to traditional methods using a trapped $^{171}$Yb$^+$ ion.\nAfter extensive cooling, we find that the ion motional distribution is\ndistinctly non-thermal and thus not amenable to standard thermometry\ntechniques. We therefore develop and experimentally validate an improved method\nto measure ion temperatures after sideband cooling. These techniques will\nenable more efficient cooling and thermometry within trapped-ion systems,\nespecially those with high initial temperatures or spatially-extended ion\nwavepackets.", "category": "physics_atom-ph" }, { "text": "Non-perturbative calculation of the two-loop Lamb shift in Li-like ions: A calculation valid to all orders in the nuclear-strength parameter is\npresented for the two-loop Lamb shift, notably for the two-loop self-energy\ncorrection, to the 2p-2s transition energies in heavy Li-like ions. The\ncalculation removes the largest theoretical uncertainty for these transitions\nand yields the first experimental identification of two-loop QED effects in the\nregion of the strong binding field.", "category": "physics_atom-ph" }, { "text": "A two-dimensional, two-electron model atom in a laser pulse: exact\n treatment, single active electron-analysis, time-dependent density functional\n theory, classical calculations, and non-sequential ionization: Owing to its numerical simplicity, a two-dimensional two-electron model atom,\nwith each electron moving in one direction, is an ideal system to study\nnon-perturbatively a fully correlated atom exposed to a laser field. Frequently\nmade assumptions, such as the ``single active electron''- approach and\ncalculational approximations, e.g. time dependent density functional theory or\n(semi-) classical techniques, can be tested. In this paper we examine the\nmultiphoton short pulse-regime. We observe ``non-sequential'' ionization, i.e.\\\ndouble ionization at lower field strengths as expected from a sequential,\nsingle active electron-point of view. Since we find non-sequential ionization\nalso in purely classical simulations, we are able to clarify the mechanism\nbehind this effect in terms of single particle trajectories. PACS Number(s):\n32.80.Rm", "category": "physics_atom-ph" }, { "text": "Transition rates and radiative lifetimes of Ca I: We tabulate spontaneous emission rates for all possible 811\nelectric-dipole-allowed transitions between the 75 lowest-energy states of Ca\nI. These involve the $4sns$ ($n=4-8$), $4snp$ ($n=4-7$), $4snd$ ($n=3-6$),\n$4snf$ ($n=4-6$), $4p^2$, and $3d4p$ electronic configurations. We compile the\ntransition rates by carrying out ab initio relativistic calculations using the\ncombined method of configuration interaction and many-body perturbation theory.\nThe results are compared to the available literature values. The tabulated\nrates can be useful in various applications, such as optimizing laser cooling\nin magneto-optical traps, estimating various systematic effects in optical\nclocks and evaluating static or dynamic polarizabilities and long-range\natom-atom interaction coefficients and related atomic properties.", "category": "physics_atom-ph" }, { "text": "Resummation of the Divergent Perturbation Series for a Hydrogen Atom in\n an Electric Field: We consider the resummation of the perturbation series describing the energy\ndisplacement of a hydrogenic bound state in an electric field (known as the\nStark effect or the LoSurdo-Stark effect), which constitutes a divergent formal\npower series in the electric field strength. The perturbation series exhibits a\nrich singularity structure in the Borel plane. Resummation methods are\npresented which appear to lead to consistent results even in problematic cases\nwhere isolated singularities or branch cuts are present on the positive and\nnegative real axis in the Borel plane. Two resummation prescriptions are\ncompared: (i) a variant of the Borel-Pade resummation method, with an\nadditional improvement due to utilization of the leading renormalon poles (for\na comprehensive discussion of renormalons see [M. Beneke, Phys. Rep. vol. 317,\np. 1 (1999)]), and (ii) a contour-improved combination of the Borel method with\nan analytic continuation by conformal mapping, and Pade approximations in the\nconformal variable. The singularity structure in the case of the LoSurdo-Stark\neffect in the complex Borel plane is shown to be similar to (divergent)\nperturbative expansions in quantum chromodynamics.", "category": "physics_atom-ph" }, { "text": "Determination of principal axes orientation in an ion trap using\n matter-wave interference: We investigate the control mechanism of trap frequencies and determine the\norientation of ion trap principal axes. The application of DC voltage to the\nground electrodes, commonly employed to finely tune trap frequencies in ion\ntraps, leads to the rotation of the trap principal axes. Analyzing the ion\nmatter-wave interference signal enables us to determine the directions of the\ntrap principal axes. Both the experiments and simulations reveal an\navoided-crossing behavior resulting from the coupling between the trap radial\naxes. Additionally, simulations indicate that symmetric trap structures lack\nthis coupling, suggesting that trap structure asymmetry causes coupling between\nthe axes. The findings of this study offer valuable insights into ion traps for\ndiverse applications in quantum science and technology.", "category": "physics_atom-ph" }, { "text": "Short-length storage of intense optical pulses in solid by adiabatic\n passage: We propose a novel scheme of storage of intense pulses which allows a\nsignificant reduction of the storage length with respect to standard schemes.\nThis scheme is particularly adapted to store optical information in media with\nfast relaxations.", "category": "physics_atom-ph" }, { "text": "Feedback control of an interacting Bose-Einstein condensate using\n phase-contrast imaging: The linewidth of an atom laser is limited by density fluctuations in the\nBose-Einstein condensate (BEC) from which the atom laser beam is outcoupled. In\nthis paper we show that a stable spatial mode for an interacting BEC can be\ngenerated using a realistic control scheme that includes the effects of the\nmeasurement backaction. This model extends the feedback theory, based on a\nphase-contrast imaging setup, presented in \\cite{Szigeti:2009}. In particular,\nit is applicable to a BEC with large interatomic interactions and solves the\nproblem of inadequacy of the mean-field (coherent state) approximation by\nutilising a fixed number state approximation. Our numerical analysis shows the\ncontrol to be more effective for a condensate with a large nonlinearity.", "category": "physics_atom-ph" }, { "text": "Active optical clock based on four-level quantum system: Active optical clock, a new conception of atomic clock, has been proposed\nrecently. In this report, we propose a scheme of active optical clock based on\nfour-level quantum system. The final accuracy and stability of two-level\nquantum system are limited by second-order Doppler shift of thermal atomic\nbeam. To three-level quantum system, they are mainly limited by light shift of\npumping laser field. These limitations can be avoided effectively by applying\nthe scheme proposed here. Rubidium atom four-level quantum system, as a typical\nexample, is discussed in this paper. The population inversion between\n$6S_{1/2}$ and $5P_{3/2}$ states can be built up at a time scale of $10^{-6}$s.\nWith the mechanism of active optical clock, in which the cavity mode linewidth\nis much wider than that of the laser gain profile, it can output a laser with\nquantum-limited linewidth narrower than 1 Hz in theory. An experimental\nconfiguration is designed to realize this active optical clock.", "category": "physics_atom-ph" }, { "text": "Relations between photoionization cross sections and photon radius: The relations between photoionization cross sections and photon radius are\nobtained on basis of quantum mechanics and the particle-like properties of a\nphoton. The photoionization cross sections of H atom and H-like ions, He atom\nand He like ions, alkali metal atoms, and Rydberg atoms are calculated using\nthe relations. The calculation results are found to be good agreement with the\nknown experimental data. The results show that the photoionization cross\nsection is always smaller than the cross section of the photon to ionize the\natom or ion and can be expressed as the product of the cross section of the\nphoton and the probability that electron meets with the photon. These provide\nthe intuitive understanding for the photoionization phenomena and open a new\navenue of research on interaction between a photon and an atom or ion.", "category": "physics_atom-ph" }, { "text": "Isotope shift, non-linearity of King plots and the search for new\n particles: We derive a mean-field relativistic formula for the isotope shift of an\nelectronic energy level for arbitrary angular momentum; we then use it to\npredict the spectra of superheavy metastable neutron-rich isotopes belonging to\nthe hypothetical island of stability. Our results may be applied to the search\nfor superheavy atoms in astrophysical spectra using the known values of the\ntransition frequencies for the neutron deficient isotopes produced in the\nlaboratory. An example of a relevant astrophysical system may be the spectra of\nthe Przybylski's star where superheavy elements up to Z=99 have been possibly\nidentified. In addition, it has been recently suggested to use the measurements\nof King plot non-linearity in a search for hypothetical new light bosons. On\nthe other hand, one can find the non-linear corrections to the King-plot\narising already in the Standard Model framework. We investigate contributions\nto the non-linearity arising from relativistic effects in the isotope\nfield-shift, the nuclear polarizability and many-body effects. It is found that\nthe nuclear polarizability contribution can lead to the significant deviation\nof the King plot from linearity. Therefore, the measurements of the\nnon-linearity of King plots may be applied to obtain the nuclear polarizability\nchange between individual isotopes. We then proceed with providing a rough\nanalytical estimate of the non-linearity arising solely from the effect of a\nhypothetical scalar boson. Our predictions give theoretical limitations on the\nsensitivity of the search for new interactions and should help to identify the\nmost suitable atoms for corresponding experiments.", "category": "physics_atom-ph" }, { "text": "Hyperfine induced $1s2s ^1S_0 \\to 1s^2 ^1S_0$ M1 transition of He-like\n ions: Hyperfine induced $1s2s ^1S_0 \\to 1s^2 ^1S_0$ M1 transition probabilities of\nHe-like ions have been calculated from relativistic configuration interaction\nwavefunctions including the frequency independent Breit interaction and QED\neffects. Present results for {$^{151}$}Eu and {$^{155}$}Gd are in good\nagreement with previous calculations [Phys. Rev. A {\\bf 63}, 054105 (2001)].\nElectronic data are given in terms of a general scaling law in $Z$ that, given\nisotopic nuclear spin and magnetic moment, allows hyperfine induced decay rates\nto be estimated for any isotope. The results should be helpful for future\nexperimental investigations on QED and parity non-conservation effects.", "category": "physics_atom-ph" }, { "text": "Collisional Control of Ground State Polar Molecules and Universal\n Dipolar Scattering: We explore the impact of the short range interaction on the scattering of\nground state polar molecules, and study the transition from a weak to strong\ndipolar scattering over an experimentally reasonable range of energies and\nelectric field values. In the strong dipolar limit, the scattering scales with\nrespect to a dimensionless quantity defined by mass, induced dipole moment, and\ncollision energy. The scaling has implications for all quantum mechanical\ndipolar scattering, and therefore this universal dipolar scaling provides\nestimates of scattering cross sections for any dipolar system.", "category": "physics_atom-ph" }, { "text": "Atomic ionization by multicharged ions interpreted in terms of poles in\n the velocity complex space: We study the single ionization of hydrogen and helium by the impact of a\nhighly-charged Coulomb projectile. To interpretate the cross section we\nintroduce a diagonal Pad\\'{e} approximant. We find that the use of Pad\\'{e}%\n[4,4] describes very well the Continnum Distorted Wave Eikonal Initial State\ntheory within its range of validity. The nodes of the denominator of the Pad%\n\\'{e} approximant give rise to four poles in the velocity complex plane: two in\nthe upper plane and their conjugate in the lower plane. The dependence of these\npoles with the projectile charge can be reasonably fitted to give a closed-form\nfor the ionization cross section, resulting a scaling very near to the one of\nJanev and Presnyakov. The experiments available were described very well in its\nentire velocity range with the use of a Pad\\'{e}[8,8], having four poles in the\nupper plane and their conjugate in the lower plane. We conclude that the poles\nof the Pad\\'{e} approximant seem to have all the information of the total\nionization cross section", "category": "physics_atom-ph" }, { "text": "Fully saturated hydrocarbons as hosts of optical cycling centers: Designing closed, laser-induced optical cycling transitions in trapped atoms\nor molecules is useful for quantum information processing, precision\nmeasurement, and quantum sensing. Larger molecules that feature such closed\ntransitions are particularly desirable, as they extend the scope of\napplicability of such systems. The search for molecules with robust optically\ncycling centers has been a challenge, and requires design principles beyond\ntrial-and-error. Here, two design principles are proposed for the particular\narchitecture of M-O-R, where M is an alkaline earth metal radical, and R is a\nligand: 1) Fairly large saturated hydrocarbons can serve as ligands, R, due to\na substantial HOMO-LUMO gap that encloses the cycling transition, so long as\nthe R group is rigid. 2) Electron-withdrawing groups, via induction, can\nenhance Franck-Condon factors (FCFs) of the optical cycling transition, as long\nas they do not disturb the locally linear structure in the M-O-R motif. With\nthese tools in mind, larger molecules can be trapped and used as optical\ncycling centers, sometimes with higher FCFs than smaller molecules.", "category": "physics_atom-ph" }, { "text": "Measurement of the lowest millimetre-wave transition frequency of the CH\n radical: The CH radical offers a sensitive way to test the hypothesis that fundamental\nconstants measured on earth may differ from those observed in other parts of\nthe universe. The starting point for such a comparison is to have accurate\nlaboratory frequencies. Here we measure the frequency of the lowest\nmillimetre-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz.\nThis improves the uncertainty by roughly two orders of magnitude over previous\ndeterminations and opens the way for sensitive new tests of varying constants.", "category": "physics_atom-ph" }, { "text": "Getting a Grip on the Transverse Motion in a Zeeman Decelerator: Zeeman deceleration is an experimental technique in which inhomogeneous,\ntime-dependent magnetic fields generated inside an array of solenoid coils are\nused to manipulate the velocity of a supersonic beam. A 12-stage Zeeman\ndecelerator has been built and characterized using hydrogen atoms as a test\nsystem. The instrument has several original features including the possibility\nto replace each deceleration coil individually. In this article, we give a\ndetailed description of the experimental setup, and illustrate its performance.\nWe demonstrate that the overall acceptance in a Zeeman decelerator can be\nsignificantly increased with only minor changes to the setup itself. This is\nachieved by applying a rather low, anti-parallel magnetic field in one of the\nsolenoid coils that forms a temporally varying quadrupole field, and improves\nparticle confinement in the transverse direction. The results are reproduced by\nthree-dimensional numerical particle trajectory simulations thus allowing for a\nrigorous analysis of the experimental data. The findings suggest the use of a\nmodified coil configuration to improve transverse focusing during the\ndeceleration process.", "category": "physics_atom-ph" }, { "text": "Current progress in laser cooling of antihydrogen: We discuss laser cooling methods of (anti)hydrogen and its importance for\ncurrent and future experiments. The exploration of antimatter presents a great\ninterest for $CERN$ and $GSI$ experiments aimed at check of quantum mechanics\nlaws, fundamental symmetries of nature and gravity and investigations in atomic\nand nuclear physics. The spectral transition $1S\\rightarrow 2P$ in $\\bar{H}\n(H)$ atom is the most suitable for laser cooling due to a small lifetime of\n$2P$ state and insignificant ionization losses. However the pulsed and\ncontinuous laser sources at Lyman-$\\alpha$ wavelength do not possess enough\npower for fast and efficient cooling. The small power of laser sources at\n$\\lambda=121.6\\ \\nm$ is poor technical problem associated with a complexity of\ngeneration scheme of such radiation, which arises due to absence of nonlinear\n$BBO$ crystals at this wavelength. The advances in this area will completely\ndestine the future progress of the experiments aimed at study of antimatter.", "category": "physics_atom-ph" }, { "text": "Laser cooling with a single laser beam and a planar diffractor: A planar triplet of diffraction gratings is used to transform a single laser\nbeam into a four-beam tetrahedral magneto-optical trap. This `flat' pyramid\ndiffractor geometry is ideal for future microfabrication. We demonstrate the\ntechnique by trapping and subsequently sub-Doppler cooling 87Rb atoms to\n30microKelvin.", "category": "physics_atom-ph" }, { "text": "QED effects on the nuclear magnetic shielding of $^3$He: The leading quantum electrodynamic corrections to the nuclear magnetic\nshielding in one- and two-electron atomic systems are obtained in a complete\nform, and the shielding constants of $^1$H, $^3$He$^+$, and $^3$He are\ncalculated to be $17.735\\,436(3) \\cdot 10^{-6}$, $35.507\\,434(9)\\cdot 10^{-6}$,\nand $59.967\\,029(23)\\cdot 10^{-6}$, respectively. These results are orders of\nmagnitude more accurate than previous ones, and, with the ongoing measurement\nof the nuclear magnetic moment of $^3$He$^+$ and planned $^3$He$^{2+}$, they\nopen the window for high-precision absolute magnetometry using $^3$He NMR\nprobes. The presented theoretical approach is applicable to all other light\natomic and molecular systems, which facilitates the improved determination of\nmagnetic moments of any light nuclei.", "category": "physics_atom-ph" }, { "text": "A buffer gas beam source for short, intense and slow molecular pulses: Experiments with cold molecules usually begin with a molecular source. We\ndescribe the construction and characteristics of a cryogenic buffer gas source\nof CaF molecules. The source emits pulses with a typical duration of 240\n$\\mu$s, a mean speed of about 150 m/s, and a flux of $5\\times 10^{10}$\nmolecules per steradian per pulse in a single rotational state.", "category": "physics_atom-ph" }, { "text": "Direct evidences for inner-shell electron-excitation by laser induced\n electron recollision: Extreme ultraviolet (XUV) attosecond pulses, generated by a process known as\nlaser-induced electron recollision, are a key ingredient for attosecond\nmetrology, providing a tool to precisely initiate and probe sub-femtosecond\ndynamics in the microcosms of atoms, molecules and solids[1]. However, with the\ncurrent technology, extending attosecond metrology to scrutinize the dynamics\nof the inner-shell electrons is a challenge, that is because of the lower\nefficiency in generating the required soft x-ray \\hbar\\omega>300 eV attosecond\nbursts and the lower absorption cross-sections in this spectral range. A way\naround this problem is to use the recolliding electron to directly initiate the\ndesired inner-shell process, instead of using the currently low flux x-ray\nattosecond sources.Such an excitation process occurs in a sub-femtosecond\ntimescale, and may provide the necessary \"pump\" step in a pump-probe\nexperiment[2]. Here we used a few cycle infrared \\lambda_{0}~1800nm source[3]\nand observed direct evidences for inner-shell excitations through the\nlaser-induced electron recollision process. It is the first step toward\ntime-resolved core-hole studies in the keV energy range with sub-femtosecond\ntime resolution.", "category": "physics_atom-ph" }, { "text": "0.5 keV soft X-ray attosecond continua: Attosecond light pulses in the extreme ultraviolet have drawn a great deal of\nattention due to their ability to interrogate electronic dynamics in real time.\nNevertheless, to follow charge dynamics and excitations in materials, element\nselectivity is a prerequisite, which demands such pulses in the soft X-ray\nregion, above 200 eV, to simultaneously cover several fundamental absorption\nedges of the constituents of the materials. Here, we experimentally demonstrate\nthe exploitation of a transient phase matching regime to generate carrier\nenvelope controlled soft X-ray supercontinua with pulse energies up to 2.9 +/-\n0.1 pJ and a flux of (7.3 +/- 0.1)x10^7 photons/s across the entire water\nwindow and attosecond pulses with 13 as transform limit. Our results herald\nattosecond science at the fundamental absorption edges of matter by bridging\nthe gap between ultrafast temporal resolution and element specific probing.", "category": "physics_atom-ph" }, { "text": "Improved limits on interactions of low-mass spin-0 dark matter from\n atomic clock spectroscopy: Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently\noscillating classical field $\\phi = \\phi_0 \\cos(m_\\phi t)$, can induce\noscillating variations in the fundamental constants through their interactions\nwith the Standard Model sector. We calculate the effects of such possible\ninteractions, which may include the linear interaction of $\\phi$ with the Higgs\nboson, on atomic and molecular transitions. Using recent atomic clock\nspectroscopy measurements, we derive new limits on the linear interaction of\n$\\phi$ with the Higgs boson, as well as its quadratic interactions with the\nphoton and light quarks. For the linear interaction of $\\phi$ with the Higgs\nboson, our derived limits improve on existing constraints by up to $2-3$ orders\nof magnitude.", "category": "physics_atom-ph" }, { "text": "Non-Sequential Double Ionization by Counter Rotating Circularly\n Polarized Two-Color Laser Fields: We report on non-sequential double ionization of Ar by a laser pulse\nconsisting of two counter rotating circularly polarized fields (390 nm and 780\nnm). The double ionization probability depends strongly on the relative\nintensity of the two fields and shows a \"knee\"-like structure as function of\nintensity. We conclude that double ionization is driven by a beam of nearly\nmonoenergetic recolliding electrons, which can be controlled in intensity and\nenergy by the field parameters. The electron momentum distributions show the\nrecolliding electron as well as a second electron which escapes from an\nintermediate excited state of Ar$^+$.", "category": "physics_atom-ph" }, { "text": "Computational insight into diatomic molecules as probes to measure the\n variation of the proton-to-electron mass ratio: Astrophysical molecular spectroscopy is an important means of searching for\nnew physics through probing the variation of the proton-to-electron mass ratio,\n$\\mu$. New molecular probes could provide tighter constraints on the variation\nof $\\mu$ and better direction for theories of new physics. Here we summarise\nour previous paper \\citep{19SyMoCu.CN} for astronomers, highlighting the\nimportance of accurate estimates of peak molecular abundance and temperature as\nwell as spectral resolution and sensitivity of telescopes in different regions\nof the electromagnetic spectrum. Whilst none of the 11 astrophysical diatomic\nmolecules we investigated showed enhanced sensitive rovibronic transitions at\nobservable intensities for astrophysical environments, we have gained a better\nunderstanding of the factors that contribute to high sensitivities. From our\nresults, CN, CP, SiN and SiC have shown the most promise of all astrophysical\ndiatomic molecules for further investigation, with further work currently being\ndone on CN.", "category": "physics_atom-ph" }, { "text": "Gravito-magnetic trapping of 87Rb: Three-dimensional trapping of neutral atoms in a combined gravito-magnetic\npotential is reported. Clouds of cold rubidium atoms in different hyperfine\nstates of the ground level were trapped with a lifetime of 4.5 s. Confinement\nexclusively occurred as a combination of the static magnetic force and the\ngravitational force.", "category": "physics_atom-ph" }, { "text": "Ultralong-Range Rydberg Molecules in a Divalent-Atomic System: We report the creation of ultralong-range Sr$_2$ molecules comprising one\nground-state $5s^2$ $^1S_0$ atom and one atom in a $5sns$ $^3S_1$ Rydberg state\nfor $n$ ranging from 29 to 36. Molecules are created in a trapped ultracold\natomic gas using two-photon excitation near resonant with the $5s5p$ $^3P_1$\nintermediate state, and their formation is detected through ground-state atom\nloss from the trap. The observed molecular binding energies are fit with the\naid of first-order perturbation theory that utilizes a Fermi pseudopotential\nwith effective $s$-wave and $p$-wave scattering lengths to describe the\ninteraction between an excited Rydberg electron and a ground-state Sr atom.", "category": "physics_atom-ph" }, { "text": "Frequency shifts in NIST Cs Primary Frequency Standards due To\n Transverse RF Field Gradients: A single-particle Green's function (propagator) is introduced to study the\ndetection of laser-cooled Cesium atoms in an atomic fountain due to RF field\ngradients in the Ramsey TE011 cavity. The detection results in a\nstate-dependent loss of atoms at apertures in the physics package, resulting in\na frequency bias. A model accounting only for motion in one dimension\ntransverse to the symmetry axis of the fountain is discussed in detail and then\ngeneralized to two transverse dimensions. Results for fractional frequency\nshifts due to transverse field gradients are computed for NIST F-1 and F-2\nCesium fountains. The shifts are found to be negligible except in cases of\nhigher RF power applied to the cavities.", "category": "physics_atom-ph" }, { "text": "A Partitioned Correlation Function Interaction approach for describing\n electron correlation in atoms: Traditional multiconfiguration Hartree-Fock (MCHF) and configuration\ninteraction (CI) methods are based on a single orthonormal orbital basis (OB).\nFor atoms with complicated shell structures, a large OB is needed to saturate\nall the electron correlation effects. The large OB leads to massive\nconfiguration state function (CSF) expansions that are difficult to handle. We\nshow that it is possible to relax the orthonormality restriction on the OB and\nbreak down the originally large calculations to a set of smaller ones that can\nbe run in parallel. Each calculation determines a partitioned correlation\nfunction (PCF) that accounts for a specific correlation effect. The PCFs are\nbuilt on optimally localized orbital sets and are added to a zero-order\nmultireference (MR) function to form a total wave function. The mixing\ncoefficients of the PCFs are fixed from a small generalized eigenvalue problem.\nThe required matrices are computed using a biorthonormal transformation\ntechnique. The new method, called partitioned correlation function interaction\n(PCFI), converges rapidly and gives total energies that are lower than the\nordinary ones (MCHF and CI). Considering Li I, we show that by dedicating a PCF\nto the single excitations from the core highly improves the convergence\npatterns of the hyperfine parameters. Collecting the optimized PCFs to correct\nthe MR function, the variational degrees of freedom in the relative mixing\ncoefficients of the CSFs building the PCFs are inhibited. These constraints\nlead to small off-sets in computed properties other than total energy, with\nrespect to the correct values. By (partially) deconstraining the mixing\ncoefficients one converges to the correct limits and keeps the important\nadvantage in the convergence rates. Reducing ultimately each PCF to a single\nCSF with its own OB leads to a non-orthogonal CI approach. Various perspectives\nof the new method are given.", "category": "physics_atom-ph" }, { "text": "Nuclear size correction to the Lamb shift of one-electron atoms: The nuclear size effect on the one-loop self energy and vacuum polarization\nis evaluated for the 1s, 2s, 3s, 2p_{1/2}, and 2p_{3/2} states of hydrogen-like\nions. The calculation is performed to all orders in the binding nuclear\nstrength parameter Z\\alpha. Detailed comparison is made with previous all-order\ncalculations and calculations based on the expansion in the parameter Z\\alpha.\nExtrapolation of the all-order numerical results obtained towards Z=1 provides\nresults for the radiative nuclear size effect on the hydrogen Lamb shift.", "category": "physics_atom-ph" }, { "text": "Improving the Q factor of an optical atomic clock using quantum\n non-demolition measurement: Quantum non-demolition (QND) measurement is a remarkable tool for the\nmanipulation of quantum systems. It allows specific information to be extracted\nwhile still preserving fragile quantum observables of the system. Here we apply\ncavity-based QND measurement to an optical lattice clock---a type of atomic\nclock with unrivalled frequency precision---preserving the quantum coherence of\nthe atoms after readout with 80\\% fidelity. We apply this technique to\nstabilise the phase of an ultrastable laser to a coherent atomic state via a\nseries of repeated QND measurements. We exploit the improved phase-coherence of\nthe ultrastable laser to interrogate a separate optical lattice clock, using a\nRamsey spectroscopy time extended from 300~ms to 2~s. With this technique we\nmaintain 95\\% contrast and observe a seven-fold increase in the clock's\n\\emph{Q} factor to $1.7\\times10^{15}$.", "category": "physics_atom-ph" }, { "text": "Envelope-driven recollisions triggered by an elliptically polarized\n laser pulse: Increasing ellipticity usually suppresses the recollision probability\ndrastically. In contrast, we report on a recollision channel with large return\nenergy and a substantial probability, regardless of the ellipticity. The laser\nenvelope plays a dominant role in the energy gained by the electron, and in the\nconditions under which the electron comes back to the core. We show that this\nrecollision channel eciently triggers multiple ionization with an elliptically\npolarized pulse.", "category": "physics_atom-ph" }, { "text": "Interactions between non-resonant rf fields and atoms with strong\n spin-exchange collisions: We study the interactions between oscillating non-resonant rf fields and\natoms with strong spin-exchange collisions in the presence of a weak dc\nmagnetic field. We find that the atomic Larmor precession frequency shows a new\nfunctional form to the rf field parameters when the spin-exchange collision\nrate is tuned. In the weak rf field amplitude regime, a strong modification of\natomic Larmor frequency appears when the spin-exchange rate is comparable to\nthe rf field frequency. This new effect has been neglected before due to its\nnarrow observation window. We compare the experimental results with density\nmatrix calculations, and explain the data by an underdamped oscillator model.\nWhen the rf field amplitude is large, there is a minimum atomic gyromagnetic\nratio point due to the rf photon dressing, and we find that strong\nspin-exchange interactions modify the position of such a point.", "category": "physics_atom-ph" }, { "text": "Two-photon atomic level widths at finite temperatures: The thermal two-photon level broadening of the excited energy levels in the\nhydrogen and H-like helium is evaluated via the imaginary part of thermal\ntwo-loop self-energy correction for bound electron. All the derivations are\npresented in the framework of rigorous quantum electrodynamic theory at finite\ntemperatures and are applicable for the H-like ions. On this basis, we found a\ncontribution to the level broadening induced by the blackbody radiation which\nis fundamentally different from the usual line broadening caused by the\nstimulated two-photon decay and the Raman scattering of thermal photons.\nNumerical calculations of the two-loop thermal correction to the two-photon\nwidth for the $2s$ state in hydrogen and singly ionized helium atoms show that\nthe effect could significantly exceed the higher-order relativistic and\nradiative QED corrections commonly included in the calculations. In addition,\nthe thermal two-loop self-energy correction significantly exceeds the\n\"ordinary\" stimulated one-photon depopulation rate at the relevant laboratory\ntemperatures. In this work, detailed analysis and the corresponding comparison\nof the effect with the existing laboratory measurements in H-like ions are\ncarried out.", "category": "physics_atom-ph" }, { "text": "Electron supercontinuum in ionization by relativistically intense laser\n pulses: Ionization of hydrogen-like ions by intense, circularly polarized laser\npulses is analyzed under the scope of the relativistic strong-field\napproximation. We show that, for specific parameters of the laser field, the\nenergy spectra of photoelectrons present a broad region without interference\n(supercontinuum) which can be controlled by modifying the laser field\nintensity. The physical interpretation of the process is developed according to\nthe Keldysh theory, emphasizing the importance of the complex-time saddle point\ncontributions to the total probability of photoionization. The corresponding\npolar-angle distributions present an asymmetry attributed to radiation pressure\neffects.", "category": "physics_atom-ph" }, { "text": "Two-photon photoassociation spectroscopy of CsYb: ground-state\n interaction potential and interspecies scattering lengths: We perform two-photon photoassociation spectroscopy of the heteronuclear CsYb\nmolecule to measure the binding energies of near-threshold vibrational levels\nof the $X~^{2}\\Sigma_{1/2}^{+}$ molecular ground state. We report results for\n$^{133}$Cs$^{170}$Yb, $^{133}$Cs$^{173}$Yb and $^{133}$Cs$^{174}$Yb, in each\ncase determining the energy of several vibrational levels including the\nleast-bound state. We fit an interaction potential based on electronic\nstructure calculations to the binding energies for all three isotopologs and\nfind that the ground-state potential supports 77 vibrational levels. We use the\nfitted potential to predict the interspecies s-wave scattering lengths for all\nseven Cs+Yb isotopic mixtures.", "category": "physics_atom-ph" }, { "text": "The photon-ion merged-beams experiment PIPE at PETRAIII - The first five\n years: The Photon-Ion Spectrometer at PETRA III - in short, PIPE - is a permanently\ninstalled user facility at the \"Variable Polarization XUV Beamline\" P04 of the\nsynchrotron light source PETRA III operated by DESY in Hamburg, Germany. The\ncareful design of the PIPE ion-optics in combination with the record-high\nphoton flux at P04 has lead to a breakthrough in experimental studies of photon\ninteractions with ionized small quantum systems. This short review provides an\noverview over the published scientific results from photon-ion merged-beams\nexperiments at PIPE that were obtained since the start of P04 operations in\n2013. The topics covered comprise photoionization of ions of astrophysical\nrelevance, quantitative studies of multi-electron processes upon inner-shell\nphotoexcitation and photoionization of negative and positive atomic ions,\nprecision spectroscopy of photoionization resonances, photoionization and\nphotofragmentation of molecular ions and of endohedral fullerene ions.", "category": "physics_atom-ph" }, { "text": "Measurement of the muon transfer rate from muonic hydrogen to oxygen in\n the range 70-336 K: The first measurement of the temperature dependence of the muon transfer rate\nfrom muonic hydrogen to oxygen was performed by the FAMU collaboration in 2016.\nThe results provide evidence that the transfer rate rises with the temperature\nin the range 104-300 K. This paper presents the results of the experiment done\nin 2018 to extend the measurements towards lower (70 K) and higher (336 K)\ntemperatures. The 2018 results confirm the temperature dependence of the muon\ntransfer rate observed in 2016 and sets firm ground for comparison with the\ntheoretical predictions.", "category": "physics_atom-ph" }, { "text": "Analytic Evaluation of some 2-, 3- and 4- Electron Atomic Integrals\n Containing Exponentially Correlated Functions of $r_{ij}$: A simple method is outlined for analytic evaluation of the basic 2-electron\natomic integral with integrand containing products of atomic s-type Slater\norbitals and exponentially correlated function of the form $r_{ij}\nexp(-\\lambda_{ij}r_{ij})$, by employing the Fourier representation of\n$exp(-\\lambda_{ij}r_{ij})/r_{ij}$ without the use of either the spherical\nharmonic addition theorem or the Feynman technique. This method is applied to\nobtain closed-form expressions, in a simple manner, for certain other 2-,3- and\n4-electron atomic integrals with integrands which are products of exponentially\ncorrelated functions and atomic s-type Slater orbitals.", "category": "physics_atom-ph" }, { "text": "Atom Interferometry in a Vertical Optical Lattice: We have studied the interference of degenerate quantum gases in a vertical\noptical lattice. The coherence of the atoms leads to an interference pattern\nwhen the atoms are released from the lattice. This has been shown for a\nBose-Einstein condensate in early experiments. Here we demonstrate that also\nfor fermions an interference pattern can be observed provided that the momentum\ndistribution is smaller then the recoil momentum of the lattice. Special\nattention is given to the role of interactions which wash out the interference\npattern for a condensate but do not affect a spin polarized Fermi gas, where\ncollisions at ultra cold temperatures are forbidden. Comparing the interference\nof the two quantum gases we find a clear superiority of fermions for trapped\natom interferometry.", "category": "physics_atom-ph" }, { "text": "Anderson localization of a Rydberg electron along a classical orbit: Anderson localization is related to exponential localization of a particle in\nthe configuration space in the presence of a disorder potential. Anderson\nlocalization can be also observed in the momentum space and corresponds to\nquantum suppression of classical diffusion in systems that are classically\nchaotic. Another kind of Anderson localization has been recently proposed, i.e.\nlocalization in the time domain due to the presence of {\\it disorder} in time.\nThat is, the probability density for the detection of a system at a fixed\nposition in the configuration space is localized exponentially around a certain\nmoment of time if a system is driven by a force that fluctuates in time. We\nshow that an electron in a Rydberg atom, perturbed by a fluctuating microwave\nfield, Anderson localizes along a classical periodic orbit. In other words the\nprobability density for the detection of an electron at a fixed position on an\norbit is exponentially localized around a certain time moment. This phenomenon\ncan be experimentally observed.", "category": "physics_atom-ph" }, { "text": "Universality of the dynamic characteristic relationship of electron\n correlation in the two-photon double ionization process of a helium-like\n system: Universality of the dynamic characteristic relationship between the\ncharacteristic time $t_c$ and the two-electron Coulomb interaction energy\n$\\overline{V}_{12}$ of the ground state in the two-photon double ionization\nprocess is investigated through changing the parameters of the two-electron\natomic system and the corresponding laser conditions. The numerical results\nshow that the product $t_{c}\\overline{V}_{12}$ keeps constant around 4.1 in the\ncases of changing the nucleus charge, the electron charge, the electron mass,\nand changing simultaneously the nucleus charge and the electron charge. These\nresults demonstrate that the dynamic characteristic relationship in the\ntwo-photon double ionization process is universal. This work sheds more light\non the the dynamic characteristic relationship in ultrafast processes and may\nfind its application in the measurement of attosecond pulses.", "category": "physics_atom-ph" }, { "text": "Multi frequency evaporative cooling to BEC in a high magnetic field: We demonstrate a way to circumvent the interruption of evaporative cooling\nobserved at high bias field for $^{87}$Rb atoms trapped in the (F=2, m=+2)\nground state. Our scheme uses a 3-frequencies-RF-knife achieved by mixing two\nRF frequencies. This compensates part of the non linearity of the Zeeman\neffect, allowing us to achieve BEC where standard 1-frequency-RF-knife\nevaporation method did not work. We are able to get efficient evaporative\ncooling, provided that the residual detuning between the transition and the RF\nfrequencies in our scheme is smaller than the power broadening of the RF\ntransitions at the end of the evaporation ramp.", "category": "physics_atom-ph" }, { "text": "Precision spectroscopy of antiprotonic helium: Antiprotonic helium, a neutral exotic three-body system consisting of a\nhelium nucleus, an electron and an antiproton, is being studied at the\nAntiproton Decelerator of CERN by the ASAUCSA collaboration. Using laser\nspectroscopy of the energy levels of the antiproton in this system and\ncomparison to theory, a value of the antiproton-to-electron mass ratio with an\nerror of 3 ppb could be obtained. This result agrees with the most precise\nmeasurement of the value of the proton and allows us to extract a limit of the\nequality of the proton and antiproton charge and mass of 2 ppb. Using microwave\nspectroscopy, the hyperfine structure of antiprotonic helium has been measured\nto 30 ppm. Experimental improvements are expected to soon provide a new value\nfor the magnetic moment of the antiproton.", "category": "physics_atom-ph" }, { "text": "Electromagnetically Induced Transparency in 6Li: We report electromagnetically induced transparency for the D1 and D2 lines in\n$^{6}$Li in both a vapour cell and an atomic beam. Electromagnetically induced\ntransparency is created using co-propagating mutually coherent laser beams with\na frequency difference equal to the hyperfine ground state splitting of 228.2\nMHz. The effects of various optical polarization configurations and applied\nmagnetic fields are investigated. In addition, we apply an optical Ramsey\nspectroscopy technique which further reduces the observed resonance width.", "category": "physics_atom-ph" }, { "text": "A strontium lattice clock with $3 \\times 10^{-17}$ inaccuracy and its\n frequency: We have measured the absolute frequency of the optical lattice clock based on\n$^{87}$Sr at PTB with an uncertainty of $3.9\\times 10^{-16}$ using two caesium\nfountain clocks. This is close to the accuracy of today's best realizations of\nthe SI second. The absolute frequency of the 5s$^2$ $^1$S$_0$-5s5p $^3$P$_0$\ntransition in $^{87}$Sr is 429,228,004,229,873.13(17) Hz. Our result is in\nexcellent agreement with recent measurements performed in different\nlaboratories worldwide. We improved the total systematic uncertainty of our Sr\nfrequency standard by a factor of five and reach $3\\times 10^{-17}$, opening\nnew prospects for frequency ratio measurements between optical clocks for\nfundamental research, geodesy, or optical clock evaluation.", "category": "physics_atom-ph" }, { "text": "Optically enhanced production of metastable xenon: Metastable states of noble gas atoms are typically produced by electrical\ndischarge techniques or \"all-optical\" excitation methods. Here we combine\nelectrical discharges with optical pumping to demonstrate \"optically enhanced\"\nproduction of metastable xenon (Xe*). We experimentally measure large increases\nin Xe* density with relatively small optical control field powers. This\ntechnique may have applications in systems where large metastable state\ndensities are desirable.", "category": "physics_atom-ph" }, { "text": "Measurement of diffusion coefficients of francium and rubidium in\n yttrium based on laser spectroscopy: We report the first measurement of the diffusion coefficients of francium and\nrubidium ions implanted in a yttrium foil. We developed a methodology, based on\nlaser spectroscopy, which can be applied to radioactive and stable species, and\nallows us to directly take record of the diffusion time. Francium isotopes are\nproduced via fusion-evaporation nuclear reaction of a 100 MeV 18-O beam on a Au\ntarget at the Tandem XTU accelerator facility in Legnaro, Italy. Francium is\nionized at the gold-vacuum interface and Fr+ ions are then transported with a 3\nkeV electrostatic beamline to a cell for neutralization and capture in a\nmagneto-optical trap (MOT). A Rb+ beam is also available, which follows the\nsame path as Fr+ ions. The accelerated ions are focused and implanted in a 25\num thick yttrium foil for neutralization: after diffusion to the surface, they\nare released as neutrals, since the Y work function is lower than the alkali\nionization energies. The time evolution of the MOT and the vapor fluorescence\nsignals are used to determine diffusion times of Fr and Rb in Y as a function\nof temperature.", "category": "physics_atom-ph" }, { "text": "Two-path interference in the resonance-enhanced few-photon ionization of\n atoms: We investigate the resonance-enhanced few-photon ionization of atomic lithium\nby linearly polarized light whose frequency is tuned near the 2s-2p transition.\nConsidering the direction of light polarization orthogonal to the quantization\naxis, the process can be viewed as an atomic \"double-slit experiment\" where the\n2p states with magnetic quantum numbers m_l=+-1 act as the slits. In our\nexperiment, we can virtually close one of the two slits by preparing lithium in\none of the two circularly polarized 2p states before subjecting it to the\nionizing radiation. This allows us to extract the interference term between the\ntwo pathways and obtain complex phase information on the final state. The\nexperimental results show very good agreement with numerical solutions of the\ntime-dependent Schroedinger equation. The validity of the two-slit model is\nalso analyzed theoretically using a time-dependent perturbative approach.", "category": "physics_atom-ph" }, { "text": "Static and dynamic polarizabilities of Yb-ion]{Accurate determination of\n black-body radiation shift, magic and tune-out wavelengths for the $\\rm\n 6S_{1/2} \\rightarrow 5D_{3/2}$ clock transition in Yb$^+$: We present precise values of the dipole polarizabilities ($\\alpha$) of the\nground $\\rm [4f^{14}6s] ~ ^2S_{1/2}$ and metastable $\\rm [4f^{14} 5d] ~\n^2D_{3/2}$ states of Yb$^+$, that are %vital {\\bf important} in reducing\nsystematics in the clock frequency of the $\\rm[4f^{14}6s] ~ ^2S_{1/2}\n\\rightarrow [4f^{14}5d] ~ ^2D_{3/2}$ transition. The static values of $\\alpha$\nfor the ground and $\\rm [4f^{14} 5d] ~ ^2D_{3/2}$ states are estimated to be\n$9.8(1) \\times 10^{-40} \\,\\,\\rm Jm^2V^{-2}$ and $17.6(5) \\times 10^{-40}\\,\\,\n\\rm Jm^2V^{-2}$, respectively, while the tensor contribution to the $\\rm\n[4f^{14} 5d] ~ ^2D_{3/2}$ state as $- 12.3(3) \\times 10^{-40}\\,\\, \\rm\nJm^2V^{-2}$ compared to the experimental value $-13.6(2.2) \\times\n10^{-40}\\,\\,\\rm Jm^2V^{-2}$. This corresponds to the differential scalar\npolarizability value of the above transition as $-7.8$(5)$\\,\\times\\,\n10^{-40}\\,\\rm Jm^2 V^{-2}$ in contrast to the available experimental value\n$-6.9$(1.4)$\\,\\times\\, 10^{-40}$\\,\\, $\\rm Jm^2V^{-2}$. This results in the\nblack-body radiation (BBR) shift of the clock transition as $-0.44(3)$ Hz at\nthe room temperature, which is large as compared to the previously estimated\nvalues. Using the dynamic $\\alpha$ values, we report the tune-out and magic\nwavelengths that could be of interest to subdue %major systematics due to the\nStark shifts and for constructing lattice optical clock using Yb$^+$.", "category": "physics_atom-ph" }, { "text": "Ionization of a Model Atom: Exact Results and Connection with Experiment: We prove that a model atom having one bound state will be fully ionized by a\ntime periodic potential of arbitrary strength $r$ and frequency $\\omega$. The\nsurvival probability is for small $r$ given by $e^{-\\Gamma t}$ for times of\norder $\\Gamma^{-1} \\sim r^{-2n}$, where $n$ is the number of ``photons''\nrequired for ionization, with enhanced stability at resonances. For late times\nthe decay is like $t^{-3}$. Results are for a 1d system with a delta function\npotential of strength $-g(1 + \\eta (t))$ but comparison with experiments on the\nmicrowave ionization of excited hydrogen atoms and with recent analytical work\nindicate that many features are universal.", "category": "physics_atom-ph" }, { "text": "Comparison of collimated blue light generation in ${}^{85}$Rb atoms via\n the D${}_1$ and D${}_2$ lines: We experimentally studied the characteristics of the collimated blue light\n(CBL) produced in ${}^{85}$Rb vapor by two resonant laser fields exciting atoms\ninto the $5D_{3/2}$ state, using either the $5P_{1/2}$ or the $5P_{3/2}$\nintermediate state. We compared the CBL output at different values of frequency\ndetunings, powers, and polarizations of the pump lasers in these two cases, and\nconfirmed the observed trends using a simple theoretical model. We also\ndemonstrated that the addition of the repump laser, preventing the accumulation\nof atomic population in the uncoupled hyperfine ground state, resulted in\nnearly an order of magnitude increase in CBL power output. Overall, we found\nthat the $5S_{1/2} - 5P_{1/2} - 5D_{3/2}$ excitation pathway results in\nstronger CBL generation, as we detected up to $4.25~\\mu$W using two pumps of\nthe same linear polarization. The optimum CBL output for the $5S_{1/2} -\n5P_{3/2} - 5D_{3/2}$ excitation pathway required the two pump lasers to have\nthe same circular polarization, but resulted only in a maximum CBL power of\n$450$~nW.", "category": "physics_atom-ph" }, { "text": "A modified Michelson interferometer type Raman laser system for atom\n interferometers: We have developed a modified Michelson interferometer type Raman laser system\nto manipulate cold 87 Rb atoms to interfere. A frequency modulated continuous\nwave technique was introduced to determine the optical path difference, thus\ncompensating it to zero to minimize the effects of common mode noise. The\nlinewidth (full width at half maximum) of the beat signal at 6.834 GHz was\nmeasured to 1Hz limited by the resolution bandwidth of the spectral analyzer.\nThe measured rms phase variance of the phase noise at 166 MHz was 0.015 rad2,\nmainly restricted by our poor performance radio frequency microwave source.\nWith modest improvements, we plan to apply this laser system to form an atom\ninterferometer for acceleration and rotation measurements.", "category": "physics_atom-ph" }, { "text": "Recombination of W18+ ions with electrons: Absolute rate coefficients\n from a storage-ring experiment and from theoretical calculations: We present new experimentally measured and theoretically calculated rate\ncoefficients for the electron-ion recombination of W$^{18+}$([Kr] $4d^{10}$\n$4f^{10}$) forming W$^{17+}$. At low electron-ion collision energies, the\nmerged-beam rate coefficient is dominated by strong, mutually overlapping,\nrecombination resonances. In the temperature range where the fractional\nabundance of W$^{18+}$ is expected to peak in a fusion plasma, the\nexperimentally derived Maxwellian recombination rate coefficient is 5 to 10\ntimes larger than that which is currently recommended for plasma modeling. The\ncomplexity of the atomic structure of the open-$4f$-system under study makes\nthe theoretical calculations extremely demanding. Nevertheless, the results of\nnew Breit-Wigner partitioned dielectronic recombination calculations agree\nreasonably well with the experimental findings. This also gives confidence in\nthe ability of the theory to generate sufficiently accurate atomic data for the\nplasma modeling of other complex ions.", "category": "physics_atom-ph" }, { "text": "The Invisible Quantum Barrier: We construct the invisible quantum barrier which represents the phenomenon of\nquantum reflection using the available data. We use the Abel equation to invert\nthe data. The resulting invisible quantum barrier is double-valued in both\naxes. We study this invisible barrier in the case of atom and Bose-Einstein\nCondensate reflection from a solid silicon surface. A time-dependent,\none-spatial dimension Gross-Pitaevskii equation is solved for the BEC case. We\nfound that the BEC behaves very similarly to the single atom except for size\neffects, which manifest themselves in a maximum in the reflectivity at small\ndistances from the wall. The effect of the atom-atom interaction on the BEC\nreflection and correspondingly on the invisible barrier is found to be\nappreciable at low velocities and comparable to the finite size effect. The\ntrapping of ultracold atoms or BEC between two walls is discussed.", "category": "physics_atom-ph" }, { "text": "A general approach to state-dependent optical tweezer traps for polar\n molecules: State-dependent optical tweezers can be used to trap a pair of molecules with\na separation much smaller than the wavelength of the trapping light, greatly\nenhancing the dipole-dipole interaction between them. Here we describe a\ngeneral approach to producing these state-dependent potentials using the tensor\npart of the ac Stark shift and show how it can be used to carry out two-qubit\ngates between pairs of molecules. The method is applicable to broad classes of\nmolecules including bialkali molecules produced by atom association and those\namenable to direct laser cooling.", "category": "physics_atom-ph" }, { "text": "Observation of the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ clock\n transition at 431 nm in $^{171}$Yb: We report on the observation of the $4f^{14}6s^{2}~^1S_0-\n4f^{13}5d6s^{2}(J=2)$ transition at 431 nm in $^{171}$Yb by depleting atoms in\na magneto-optical trap formed by the $6s^{2}~^1S_0-6s6p~^3P_1$ intercombination\ntransition. The absolute frequency of the transition to the $F=3/2$ state is\ndetermined to be $695~171~054~858.1(8.2)$~kHz against physical realization of\nCoordinated Universal Time maintained by the National Metrology Institute of\nJapan with a frequency comb. The $g$ factor of the transition to the $F=3/2$\nstate and the A hyperfine constant are measured to be $g_J=1.54(13)$ and\n1123.273(13)~MHz, respectively. More precise spectroscopy of this transition\ncan lead to searches for time variation of the fine structure constant and\nsearches for new physics with isotope shift measurements.", "category": "physics_atom-ph" }, { "text": "p-Wave cold collisions in an optical lattice clock: We study ultracold collisions in fermionic ytterbium by precisely measuring\nthe energy shifts they impart on the atom's internal clock states. Exploiting\nFermi statistics, we uncover p-wave collisions, in both weakly and strongly\ninteracting regimes. With the higher density afforded by two-dimensional\nlattice confinement, we demonstrate that strong interactions can lead to a\nnovel suppression of this collision shift. In addition to reducing the\nsystematic errors of lattice clocks, this work has application to quantum\ninformation and quantum simulation with alkaline-earth atoms.", "category": "physics_atom-ph" }, { "text": "Two-photon ionization of Helium studied with the multiconfigurational\n time-dependent Hartree-Fock method: The multiconfigurational time-dependent Hartree-Fock method (MCTDHF) is\napplied for simulations of the two-photon ionization of Helium. We present\nresults for the single- and double ionization from the groundstate for photon\nenergies in the non-sequential regime, and compare them to direct solutions of\nthe Schr\\\"odinger equation using the time-dependent (full) Configuration\nInteraction method (TDCI). We find that the single-ionization is accurately\nreproduced by MCTDHF, whereas the double ionization results correctly capture\nthe main trends of TDCI.", "category": "physics_atom-ph" }, { "text": "Few-Body Bound States of Dipole-Dipole Interacting Rydberg Atoms: We show that the resonant dipole-dipole interaction can give rise to bound\nstates between two and three Rydberg atoms with non-overlapping electron\nclouds. The dimer and trimer states arise from avoided level crossings between\nstates converging to different fine structure manifolds in the limit of\nseparated atoms. We analyze the angular dependence of the potential wells,\ncharacterize the quantum dynamics in these potentials and discuss methods for\ntheir production and detection. Typical distances between the atoms are of the\norder of several micrometers which can be resolved in state-of-the-art\nexperiments. The potential depths and typical oscillation frequencies are about\none order of magnitude larger as compared to the dimer and trimer states\ninvestigated in [PRA $\\textbf{86}$ 031401(R) (2012)] and [PRL $\\textbf{111}$\n233003 (2014)], respectively. We find that the dimer and trimer molecules can\nbe aligned with respect to the axis of a weak electric field.", "category": "physics_atom-ph" }, { "text": "Continuous radio frequency electric-field detection through adjacent\n Rydberg resonance tuning: We demonstrate the use of multiple atomic-level Rydberg-atom schemes for\ncontinuous frequency detection of radio frequency (RF) fields. Resonant\ndetection of RF fields by electromagnetically-induced transparency and\nAutler-Townes (AT) in Rydberg atoms is typically limited to frequencies within\nthe narrow bandwidth of a Rydberg transition. By applying a second field\nresonant with an adjacent Rydberg transition, far-detuned fields can be\ndetected through a two-photon resonance AT splitting. This two-photon AT\nsplitting method is several orders of magnitude more sensitive than\noff-resonant detection using the Stark shift. We present the results of various\nexperimental configurations and a theoretical analysis to illustrate the\neffectiveness of this multiple level scheme. These results show that this\napproach allows for the detection of frequencies in continuous band between\nresonances with adjacent Rydberg states.", "category": "physics_atom-ph" }, { "text": "Bragg-diffraction-induced imperfections of the signal in retroreflective\n atom interferometers: We present a detailed study of the effects of imperfect atom-optical\nmanipulation in Bragg-based light-pulse atom interferometers. Off-resonant\nhigher-order diffraction leads to population loss, spurious interferometer\npaths, and diffraction phases. In a path-dependent formalism, we study\nnumerically various effects and analyze the interference signal caused by an\nexternal phase or gravity. We compare first-order single and double Bragg\ndiffraction in retroreflective setups. In double Bragg diffraction, phase\nimperfections lead to a beating due to three-path interference. Some effects of\ndiffraction phases can be avoided by adding the population of the outer exit\nports of double diffraction.", "category": "physics_atom-ph" }, { "text": "Relativistically extended Blanchard recurrence relation for hydrogenic\n matrix elements: General recurrence relations for arbitrary non-diagonal, radial hydrogenic\nmatrix elements are derived in Dirac relativistic quantum mechanics. Our\napproach is based on a generalization of the second hypervirial method\npreviously employed in the non-relativistic Schr\\\"odinger case. A relativistic\nversion of the Pasternack-Sternheimer relation is thence obtained in the\ndiagonal (i.e. total angular momentum and parity the same) case, from such\nrelation an expression for the relativistic virial theorem is deduced. To\ncontribute to the utility of the relations, explicit expressions for the radial\nmatrix elements of functions of the form $r^\\lambda$ and $\\beta r^\\lambda$\n---where $\\beta$ is a Dirac matrix--- are presented.", "category": "physics_atom-ph" }, { "text": "Tracking Berry curvature effect in molecular dynamics by ultrafast\n magnetic x-ray scattering: The spin-dependent Berry force is a genuine effect of Berry curvature in\nmolecular dynamics, which can dramatically result in spatial spin separation\nand change of reaction pathways. However, the way to probe the effect of Berry\nforce remains challenging, because the time-reversal (TR) symmetry required for\nopposite Berry forces conflicts with TR symmetry breaking spin alignment needed\nto observe the effect, and the net effect could be transient for a molecular\nwave packet. We demonstrate that in molecular photodissociation, the\ndissociation rates can be different for molecules with opposite initial spin\ndirections due to Berry force. We showcase that the spatially separated spin\ndensity, which is transiently induced by Berry force as the molecular wave\npacket passes through conical intersection, can be reconstructed from the\ncircular dichroism (CD) of ultrafast non-resonant magnetic x-ray scattering\nusing free electron lasers.", "category": "physics_atom-ph" }, { "text": "Black-body radiation shift of atomic energy-levels:The $ (Z\n \u03b1)^2\u03b1T^2/m $ correction: The next-to-leading order black-body radiation(BBR) shift to atomic\nenergy-levels, namely $ (Z\\alpha)^2\\alpha T^2/m $ correction, was studied by\nusing the nonrelativistic quantum electrodynamics(NRQED). We also estimate the\none-loop contribution of quadrupole and the two-loop contributions of BBR-shift\nof the thermal(real) photon. These corrections have not been investigated\nbefore. The order of magnitude BBR-shift indicates the one-loop contribution of\nquadrupole is stronger than the previous result. And the two-loop contribution\nof BBR-shift of the thermal(real) photon is tiny, but this next-to-leading\norder BBR-shift may be as significant as the leading order in the\nmulti-electron atoms or cold ones.", "category": "physics_atom-ph" }, { "text": "Simulation of optical lattice trap loading from a cold atomic ensemble: We model the efficiency of loading atoms of various species into a one\ndimensional optical lattice from a cold ensemble taking into account the\ninitial cloud temperature and size, the lattice laser properties affecting the\ntrapping potential, and atomic parameters. Stochastic sampling and dynamical\nevolution are used to simulate the transfer, leading to estimates of transfer\nefficiency for varying trap depth and profile. Tracing the motion of the atoms\nalso enables the evaluation of the equilibrium temperature and site occupancy\nin the lattice. The simulation compares favourably against a number of\nexperimental results, and is used to compute an optimum lattice-waist to\ncloud-radius ratio for a given optical power.", "category": "physics_atom-ph" }, { "text": "A magnetic lens for cold atoms controlled by a rf field: We report on a new type of magnetic lens that focuses atomic clouds using a\nstatic inhomogeneous magnetic field in combination with a radio-frequency\nfield. The experimental study is performed with a cloud of cold cesium atoms.\nThe rf field adiabatically deforms the magnetic potential of a coil and\ntherefore changes its focusing properties. The focal length can be tuned\nprecisely by changing the rf frequency value. Depending on the rf antenna\nposition relative to the DC magnetic profile, the focal length of the atomic\nlens can be either decreased or increased by the rf field.", "category": "physics_atom-ph" }, { "text": "High-resolution mid-infrared spectroscopy of buffer-gas-cooled\n methyltrioxorhenium molecules: We demonstrate cryogenic buffer-gas cooling of gas-phase methyltrioxorhenium\n(MTO). This molecule is closely related to chiral organometallic molecules\nwhere the parity-violating energy differences between enantiomers may be\nmeasurable. The molecules are produced with a rotational temperature of\napproximately 6~K by laser ablation of an MTO pellet inside a cryogenic helium\nbuffer gas cell. Facilitated by the low temperature, we demonstrate absorption\nspectroscopy of the 10.2~$\\mu$m antisymmetric Re=O stretching mode of MTO with\na resolution of 8~MHz and a frequency accuracy of 30~MHz. We partially resolve\nthe hyperfine structure and measure the nuclear quadrupole coupling of the\nexcited vibrational state.", "category": "physics_atom-ph" }, { "text": "Configuration Interaction Study of the $^3{\\rm P}$ Ground State of the\n Carbon Atom: Configuration Interaction (CI) calculations on the ground state of the C atom\nare carried out using a small basis set of Slater orbitals [7s6p5d4f3g]. The\nconfigurations are selected according to their contribution to the total\nenergy. One set of exponents is optimized for the whole expansion. Using some\ncomputational techniques to increase efficiency, our computer program is able\nto perform partially-parallelized runs of 1000 configuration term functions\nwithin a few minutes. With the optimized computer programme we were able to\ntest a large number of configuration types and chose the most important ones.\nThe energy of the $^3{\\rm P}$ ground state of carbon atom with a wave function\nof angular momentum L=1 and M$_{\\rm L}$=0 and spin eigenfunction with S=1 and\nM$_{\\rm S}$=0 leads to -37.83526523 h, which is millihartree accurate. We\ndiscuss the state of the art in the determination of the ground state of the\ncarbon atom and give an outlook about the complex spectra of this atom and its\nlow-lying states.", "category": "physics_atom-ph" }, { "text": "Optical Stabilization of a Microwave Oscillator for Fountain Clock\n Interrogation: We describe an optical frequency stabilization scheme of a microwave\noscillator that is used for the interrogation of primary caesium fountain\nclocks. Because of its superior phase noise properties, this scheme, which is\nbased on an ultrastable laser and a femtosecond laser frequency comb, overcomes\nthe frequency instability limitations of fountain clocks given by the\npreviously utilized quartz-oscillator-based frequency synthesis. The presented\nscheme combines the transfer of the short-term frequency instability of an\noptical cavity and the long-term frequency instability of a hydrogen maser to\nthe microwave oscillator and is designed to provide continuous long-term\noperation for extended measurement periods of several weeks. The utilization of\nthe twofold stabilization scheme on the one hand ensures the referencing of the\nfountain frequency to the hydrogen maser frequency and on the other hand\nresults in a phase noise level of the fountain interrogation signal, which\nenables fountain frequency instabilities at the $2.5 \\times 10^{-14} (\\tau\n/\\mathrm{s})^{-1/2}$ level which are quantum projection noise limited.", "category": "physics_atom-ph" }, { "text": "Josephson effects in dilute Bose-Einstein condensates: We propose an experiment that would demonstrate the ``dc'' and ``ac''\nJosephson effects in two weakly linked Bose-Einstein condensates. We consider a\ntime-dependent barrier, moving adiabatically across the trapping potential. The\nphase dynamics are governed by a ``driven-pendulum'' equation, as in\ncurrent-driven superconducting Josephson junctions. At a critical velocity of\nthe barrier (proportional to the critical tunneling current), there is a sharp\ntransition between the ``dc'' and ``ac'' regimes. The signature is a sudden\njump of a large fraction of the relative condensate population. Analytical\npredictions are compared with a full numerical solution of the time dependent\nGross-Pitaevskii equation, in an experimentally realistic situation.", "category": "physics_atom-ph" }, { "text": "Ionization potentials and electron affinities of Rg, Cn, Nh, and Fl\n superheavy elements: The successive ionization potentials (IPs) and electron affinities (EAs) for\nsuperheavy elements with $111 \\leq Z \\leq 114$, namely, Rg, Cn, Nh, and Fl are\nreexamined using the relativistic Fock-space coupled-cluster method with\nnonperturbative single (S), double (D), and triple (T) cluster amplitudes\n(FS-CCSDT). For the most of considered quantities, the triple-amplitude\ncontributions turn out to be important. The Breit and frequency-dependent Breit\ncorrections are evaluated by means of the configuration-interaction method. The\nquantum-electrodynamics corrections to the IPs and EAs are taken into account\nwithin the model-QED-operator approach. The obtained results are within 0.10 eV\nuncertainty.", "category": "physics_atom-ph" }, { "text": "Centralised Design and Production of the Ultra-High Vacuum and\n Laser-Stabilisation Systems for the AION Ultra-Cold Strontium Laboratories: This paper outlines the centralised design and production of the\nUltra-High-Vacuum sidearm and Laser-Stabilisation systems for the AION\nUltra-Cold Strontium Laboratories. Commissioning data on the residual gas and\nsteady-state pressures in the sidearm chambers, on magnetic field quality, on\nlaser stabilisation, and on the loading rate for the 3D Magneto-Optical Trap\nare presented. Streamlining the design and production of the sidearm and laser\nstabilisation systems enabled the AION Collaboration to build and equip in\nparallel five state-of-the-art Ultra-Cold Strontium Laboratories within 24\nmonths by leveraging key expertise in the collaboration. This approach could\nserve as a model for the development and construction of other cold atom\nexperiments, such as atomic clock experiments and neutral atom quantum\ncomputing systems, by establishing dedicated design and production units at\nnational laboratories.", "category": "physics_atom-ph" }, { "text": "Blue-detuned molecular magneto-optical trap schemes based on bayesian\n optimization: Direct laser cooling and trapping of molecules to temperature below Doppler\nlimit and density exceeding $10^8$ are challenging due to the sub-Doppler\nheating effects of molecular magneto-optical trap (MOT). In our previous paper\n[1], we presented a general approach to engineering the sub- Doppler force by\ntuning the AC stark shift with the addition of a blue detuned laser. Here, by\nemploying the Bayesian optimization method to optical Bloch equations, we have\nidentified multiple blue-detuned MOT schemes for the CaF molecule. From the\nthree-dimensional Monte-Carlo simulation, we obtained a MOT temperature and\ndensity of 14 $\\rm \\mu K$ and $\\rm 4.5 \\times 10^8 cm^{-3}$, respectively. Our\nfindings present a potential avenue for directly loading molecular MOTs into\nconservative traps, which can capitalize on the high density and low\ntemperature of the MOT", "category": "physics_atom-ph" }, { "text": "Analytical model for laser-assisted recombination of hydrogenic atoms: We introduce a new method that allows one to obtain an analytical cross\nsection for the laser-assisted electron-ion collision in a closed form. As an\nexample we perform a calculation for the hydrogen laser-assisted recombination.\nThe $S$-matrix element for the process is constructed from an exact electron\nCoulomb-Volkov wave function and an approximate laser modified hydrogen state.\nAn explicit expression for the field-enhancement coefficient of the process is\nexpressed in terms of the dimensionless parameter $\\kappa=\n|{e\\epsilon_{0}}/{q\\omega_{0}}|^{2}$, where $e$ and $q$ are the electron charge\nand momentum respectively, and $\\epsilon_{0}$ and $\\omega_{0}$ are the\namplitude and frequency of the laser field respectively. The simplified version\nof the cross section of the process is derived and analyzed within a soft\nphoton approximation.", "category": "physics_atom-ph" }, { "text": "Convergent variational calculation of positronium-hydrogen-atom\n scattering lengths: We present a convergent variational basis-set calculational scheme for\nelastic scattering of positronium atom by hydrogen atom in S wave. Highly\ncorrelated trial functions with appropriate symmetry are needed for achieving\nconvergence. We report convergent results for scattering lengths in atomic\nunits for both singlet ($=3.49\\pm 0.20$) and triplet ($=2.46\\pm 0.10$) states.", "category": "physics_atom-ph" }, { "text": "Testing sub-gravitational forces on atoms from a miniature, in-vacuum\n source mass: Gravity is the weakest fundamental interaction and the only one that has not\nbeen measured at the particle level. Traditional experimental methods, from\nastronomical observations to torsion balances, use macroscopic masses to both\nsource and probe gravitational fields. Matter wave interferometers have used\nneutrons, atoms and molecular clusters as microscopic test particles, but\ninitially probed the field sourced by the entire earth. Later, the\ngravitational field arising from hundreds of kilograms of artificial source\nmasses was measured with atom interferometry. Miniaturizing the source mass and\nmoving it into the vacuum chamber could improve positioning accuracy, allow the\nuse of monocrystalline source masses for improved gravitational measurements,\nand test new physics, such as beyond-standard-model (\"fifth\") forces of nature\nand non-classical effects of gravity. In this work, we detect the gravitational\nforce between freely falling cesium atoms and an in-vacuum, centimeter-sized\nsource mass using atom interferometry with state-of-the-art sensitivity. The\nability to sense gravitational-strength coupling is conjectured to access a\nnatural lower bound for fundamental forces, thereby representing an important\nmilestone in searches for physics beyond the standard model. A local, in-vacuum\nsource mass is particularly sensitive to a wide class of interactions whose\neffects would otherwise be suppressed beyond detectability in regions of high\nmatter density. For example, our measurement strengthens limits on a number of\ncosmologically-motivated scalar field models, such as chameleon and symmetron\nfields, by over two orders of magnitude and paves the way toward novel\nmeasurements of Newton's gravitational constant G and the gravitational\nAharonov-Bohm effect", "category": "physics_atom-ph" }, { "text": "Gravity gradient suppression in spaceborne atomic tests of the\n equivalence principle: The gravity gradient is one of the most serious systematic effects in atomic\ntests of the equivalence principle (EP). While differential acceleration\nmeasurements performed with different atomic species under free fall test the\nvalidity of EP, minute displacements between the test masses in a gravity\ngradient produces a false EP-violating signal that limits the precision of the\ntest. We show that gravity inversion and modulation using a gimbal mount can\nsuppress the systematics due to gravity gradients caused by both moving and\nstationary parts of the instrument as well as the environment, strongly\nreducing the need to overlap two species.", "category": "physics_atom-ph" }, { "text": "Mixed configuration-interaction and many-body perturbation theory\n calculations of energies and oscillator strengths of J=1 odd states of neon: Ab-initio theory is developed for energies of J=1 particle-hole states of\nneutral neon and for oscillator strengths of transitions from such states to\nthe J=0 ground state. Hole energies of low-Z neonlike ions are evaluated.", "category": "physics_atom-ph" }, { "text": "Test of many-electron QED effects in the hyperfine splitting of heavy\n high-Z ions: A rigorous evaluation of the two-photon exchange corrections to the hyperfine\nstructure in lithiumlike heavy ions is presented. As a result, the theoretical\naccuracy of the specific difference between the hyperfine splitting values of\nH- and Li-like Bi ions is significantly improved. This opens a possibility for\nthe stringent test of the many-electron QED effects on a few percent level in\nthe strongest electromagnetic field presently available in experiments.", "category": "physics_atom-ph" }, { "text": "Transporting cold atoms towards a GaN-on-sapphire chip via an optical\n conveyor belt: Trapped atoms on photonic structures inspire many novel quantum devices for\nquantum information processing and quantum sensing. Here, we have demonstrated\na hybrid photonic-atom chip platform based on a GaN-on-sapphire chip and the\ntransport of an ensemble of atoms from free space towards the chip with an\noptical conveyor belt. The maximum transport efficiency of atoms is about 50%\nwith a transport distance of 500 $\\mathrm{\\mu m}$. Our results open up a new\nroute toward the efficiently loading of cold atoms into the evanescent-field\ntrap formed by the photonic integrated circuits, which promises strong and\ncontrollable interactions between single atoms and single photons.", "category": "physics_atom-ph" }, { "text": "On the Stability Domain of Systems of Three Arbitrary Charges: We present results on the stability of quantum systems consisting of a\nnegative charge $-q_1$ with mass $m_{1}$ and two positive charges $q_2$ and\n$q_3$, with masses $m_{2}$ and $m_{3}$, respectively. We show that, for given\nmasses $m_{i}$, each instability domain is convex in the plane of the variables\n$(q_{1}/q_{2}, q_{1}/q_{3})$. A new proof is given of the instability of muonic\nions $(\\alpha, p, \\mu^-)$. We then study stability in some critical regimes\nwhere $q_3\\ll q_2$: stability is sometimes restricted to large values of some\nmass ratios; the behaviour of the stability frontier is established to leading\norder in $q_3/q_2$. Finally we present some conjectures about the shape of the\nstability domain, both for given masses and varying charges, and for given\ncharges and varying masses.", "category": "physics_atom-ph" }, { "text": "Oscillating nuclear electric dipole moments inside atoms: Interaction with the axion dark matter (DM) field generates an oscillating\nnuclear electric dipole moment (EDM) with a frequency corresponding to the\naxion's Compton frequency. Within an atom, an oscillating EDM can drive\nelectric dipole transitions in the electronic shell. In the absence of\nradiation, and if the axion frequency matches a dipole transition, it can\npromote the electron into the excited state. The excitation events can be\ndetected, for example, via subsequent uorescence or photoionization. Here we\ncalculate the rates of such transitions. For a single light atom and an axion\nCompton frequency resonant with a transition energy corresponding to 1 eV, the\nrate is on the order of 10^(-22) per year, so a macroscopic atomic sample would\nbe needed. A fundamental challenge is discriminating against background\nprocesses that may lead to the excitation of the same electric dipole\ntransition. The ways to enhance the signals to potentially observable levels\nexceeding backgrounds and to search for axions in an extended frequency range\nare discussed.", "category": "physics_atom-ph" }, { "text": "Measurements of the Hyperfine Structure of Atomic Energy Levels in Co II: Analysis of hyperfine structure constants of singly ionised cobalt (Co II)\nwere performed on cobalt spectra measured by Fourier transform spectrometers in\nthe region $3000-63000$ cm$^{-1}$ ($3333-159$ nm). Fits to over $700$ spectral\nlines led to measurements of $292$ magnetic dipole hyperfine interaction $A$\nconstants, with values between $-32.5$ mK and $59.5$ mK ($1$ mK $=0.001$\ncm$^{-1}$). Uncertainties of $255$ A constants were between $\\pm0.4$ mK and\n$\\pm3.0$ mK, the remaining $37$ ranged up to $\\pm7$ mK. The electric quadrupole\nhyperfine interaction $B$ constant could be estimated for only $1$ energy\nlevel. The number of Co II levels with known $A$ values has now increased\ntenfold, improving and enabling the wider, more reliable and accurate\napplication of Co II in astronomical chemical abundance analyses.", "category": "physics_atom-ph" }, { "text": "Observation and Control of Laser-Enabled Auger Decay: Single photon laser enabled Auger decay (spLEAD) has been redicted\ntheoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its\nfirst experimental observation in neon. Using coherent, bichromatic\nfree-electron laser pulses, we have detected the process and coherently\ncontrolled the angular distribution of the emitted electrons by varying the\nphase difference between the two laser fields. Since spLEAD is highly sensitive\nto electron correlation, this is a promising method for probing both\ncorrelation and ultrafast hole migration in more complex systems.", "category": "physics_atom-ph" }, { "text": "Manipulating ultracold atoms with a reconfigurable nanomagnetic system\n of domain walls: The divide between the realms of atomic-scale quantum particles and\nlithographically-defined nanostructures is rapidly being bridged. Hybrid\nquantum systems comprising ultracold gas-phase atoms and substrate-bound\ndevices already offer exciting prospects for quantum sensors, quantum\ninformation and quantum control. Ideally, such devices should be scalable,\nversatile and support quantum interactions with long coherence times.\nFulfilling these criteria is extremely challenging as it demands a stable and\ntractable interface between two disparate regimes. Here we demonstrate an\narchitecture for atomic control based on domain walls (DWs) in planar magnetic\nnanowires that provides a tunable atomic interaction, manifested experimentally\nas the reflection of ultracold atoms from a nanowire array. We exploit the\nmagnetic reconfigurability of the nanowires to quickly and remotely tune the\ninteraction with high reliability. This proof-of-principle study shows the\npracticability of more elaborate atom chips based on magnetic nanowires being\nused to perform atom optics on the nanometre scale.", "category": "physics_atom-ph" }, { "text": "Characterization of Cs vapor cell coated with octadecyltrichlorosilane\n using coherent population trapping spectroscopy: We report the realization and characterization using coherent population\ntrapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated\ncentimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape,\nwith presence of a narrow structure line at the top of a Doppler-broadened\nstructure, is clearly observed. The linewidth of the narrow resonance is\ncompared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell\nof similar size. The Cs-OTS adsorption energy is measured to be (0.42 $\\pm$\n0.03) eV, leading to a clock frequency shift rate of $2.7\\times10^{-9}/$K in\nfractional unit. A hyperfine population lifetime, $T_1$, and a microwave\ncoherence lifetime, $T_2$, of 1.6 and 0.5 ms are reported, corresponding to\nabout 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey\nnarrowing of dark resonances is observed in Cs-OTS cells by reducing the\noptical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT\ninterrogation scheme. Potential applications of the Cs-OTS cell to the\ndevelopment of a vapor cell atomic clock are discussed.", "category": "physics_atom-ph" }, { "text": "Wave-function Visualization of Core-induced Interaction of\n Non-hydrogenic Rydberg Atom in Electric Field: We have investigated the wave-function feature of Rydberg sodium in a uniform\nelectric field and found that the core-induced interaction of non-hydrogenic\natom in electric field can be directly visualized in the wave-function. As is\nwell known, the hydrogen atom in electric field can be separated in parabolic\ncoordinates (\\eta, \\xi), whose eigen-function can show a clear pattern towards\nnegative and positive directions corresponding to the so-called red and blue\nstates without ambiguity, respectively. It can be served as a complete\northogonal basis set to study the core-induced interaction of non-hydrogenic\natom in electric field. Owing to complete different patterns of the probability\ndistribution for red and blue states, the interaction can be visualized in the\nwave-function directly via superposition. Moreover, the constructive and\ndestructive interferences between red and blue states are also observed in the\nwave-function, explicitly explaining the experimental measurement for the\nspectral oscillator strength.", "category": "physics_atom-ph" }, { "text": "Decay dynamics in the coupled-dipole model: Cooperative scattering in cold atoms has gained renewed interest, in\nparticular in the context of single-photon superradiance, with the recent\nexperimental observation of super-and subradiance in dilute atomic clouds.\nNumerical simulations to support experimental signatures of cooperative\nscattering are often limited by the number of dipoles which can be treated,\nwell below the number of atoms in the experiments. In this paper, we provide\nsystematic numerical studies aimed at matching the regime of dilute atomic\nclouds. We use a scalar coupled-dipole model in the low excitation limit and an\nexclusion volume to avoid density-related effects. Scaling laws for super-and\nsubradiance are obtained and the limits of numerical studies are pointed out.\nWe also illustrate the cooperative nature of light scattering by considering an\nincident laser field, where half of the beam has a $\\pi$ phase shift. The\nenhanced subradiance obtained under such condition provides an additional\nsignature of the role of coherence in the detected signal.", "category": "physics_atom-ph" }, { "text": "Electron-impact direct double ionization: Electron-impact direct double ionization (DDI) process is studied as a\nsequence of two and three step processes. Contribution from\nionization-ionization, ionization-excitation-ionization, and\nexcitation-ionization-ionization processes is taken into account. The present\nresults help to resolve the long-standing discrepancies; in particular, a good\nagreement with experimental measurements is obtained for double ionization\ncross-sections of $O^{1+}$, $O^{2+}$, $O^{3+}$, $C^{1+}$, and $Ar^{2+}$ ions.\nWe show that distribution of the energy of scattered and ejected electrons,\nwhich participate in the next step of ionization, strongly affects DDI\ncross-sections.", "category": "physics_atom-ph" }, { "text": "Deeply bound (24$D_J$ + 5$S_{1/2}$) $^{87}$Rb and $^{85}$Rb molecules\n for eight spin couplings: We observe long-range $^{85}$Rb and $^{87}$Rb (24$D$+5$S_{1/2}$) Rydberg\nmolecules for eight different spin couplings, with binding energies up to\n440~MHz and sub-percent relative uncertainty. Isotopic effects of the molecular\nbinding energies arise from the different masses and nuclear spins. Because the\nvibrational states involve different spin configurations and cover a wide range\nof internuclear separations, the states have different dependencies on the\n$s$-wave and $p$-wave scattering phase shifts for singlet and triplet\nscattering. Fitting the spectroscopic data, we comprehensively determine all\nfour scattering length functions over the relevant energy range as well as the\nzero-energy scattering lengths of the two $s$-wave channels. Our unusually high\ntemperature and low density (180 $\\mu$K, 1 $\\times$ 10$^{11}$ cm$^{-3}$)\nsuggest that the molecule excitation occurs through photoassisted collisions.", "category": "physics_atom-ph" }, { "text": "Regge resonances in low-energy electron elastic cross sections for Ge,\n Sn and Pb atoms: manifestations of stable excited anions: Low-energy E < 2 eV electron elastic collisions with Ge, Sn and Pb atoms\nyield stable excited Ge-, Sn- and Pb- anions. The recent Regge-pole methodology\nis used with Thomas-Fermi type potential incorporating the crucial\ncore-polarization interaction to calculate elastic total and Mulholland partial\ncross sections. For excited Ge- and Sn- anions the extracted binding energies\nfrom the unique characteristic sharp Regge resonances manifesting stable\nexcited states formed during the collisions agree excellently with experimental\nvalues; for Pb- the prediction requires experimental verification. The\ncalculated differential cross sections also yield the binding energies.", "category": "physics_atom-ph" }, { "text": "Disentangling enantiosensitivity from dichroism using bichromatic fields: We discuss how tensorial observables, available in photoelectron angular\ndistributions resulting from interaction between isotropic chiral samples and\ncross polarized $\\omega$-$2\\omega$ bichromatic fields, allow for chiral\ndiscrimination without chiral light and within the electric-dipole\napproximation. We extend the concept of chiral setup [Phys. Rev. A 98, 063428\n(2018)], which explains how chiral discrimination can be achieved in the\nabsence of chiral light, to the case of tensorial observables. We derive\nselection rules for the enantiosensitivity and dichroism of the $b_{l,m}$\ncoefficients describing the photoelectron angular distribution valid for both\nweak and strong fields and for arbitrary $\\omega$-$2\\omega$ relative phase.\nExplicit expressions for simple perturbative cases are given. We find that,\nbesides the dichroic non-enantiosensitive [J. Chem. Phys. 151 074106 (2019)],\nand dichroic-and-enantiosensitive $b_{l,m}$ coefficients found recently [Phys.\nRev. A 99, 063406 (2019)], there are also enantiosensitive non-dichroic\n$b_{l,m}$ coefficients. These reveal the molecular enantiomer independently of\nthe relative phase between the two colors and are therefore observable even in\nthe absence of stabilization of the $\\omega$-$2\\omega$ relative phase.", "category": "physics_atom-ph" }, { "text": "Controlling fast transport of cold trapped ions: We realize fast transport of ions in a segmented micro-structured Paul trap.\nThe ion is shuttled over a distance of more than 10^4 times its groundstate\nwavefunction size during only 5 motional cycles of the trap (280 micro meter in\n3.6 micro seconds). Starting from a ground-state-cooled ion, we find an\noptimized transport such that the energy increase is as low as 0.10 $\\pm$ 0.01\nmotional quanta. In addition, we demonstrate that quantum information stored in\na spin-motion entangled state is preserved throughout the transport. Shuttling\noperations are concatenated, as a proof-of-principle for the shuttling-based\narchitecture to scalable ion trap quantum computing.", "category": "physics_atom-ph" }, { "text": "Numerical solution to the time-dependent Gross-Pitaevskii equation: In this work we employ the split-step technique combined with a Legendre\npseudospectral representation to solve various time-dependent Gross-Pitaevskii\nequations (GPE). Our findings based on the numerical accuracy of this approach\napplied for one-dimensional (1D) and two-dimensional (2D) problems show that it\ncan provide accurate and stable solutions. Moreover, this approach has been\napplied to study the dynamics of the Bose-Einstein condensate which is modeled\nwith the GPE. The breathing of condensate with an repulsive and attractive\ninteractions trapped in 1D and 2D harmonic potentials has been simulated as\nwell.", "category": "physics_atom-ph" }, { "text": "Magic wavelength for the hydrogen 1S-2S transition: Contribution of the\n continuum and the reduced-mass correction: Recently, we studied the magic wavelength for the atomic hydrogen 1S-2S\ntransition [A.K., Phys. Rev. A 92, 042507 (2015)]. An explicit summation over\nvirtual atomic states of the discrete part of the hydrogen spectrum was\nperformed to evaluate the atomic polarizability. In this paper, we supplement\nthe contribution of the continuum part of the spectrum and add the reduced-mass\ncorrection. The magic wavelength, at which the lowest-order ac Stark shifts of\nthe 1S and 2S states are equal, is found to be equal to 514.6 nm. The ac Stark\nshift at the magic wavelength is -221.6 Hz / (kW/cm^2), and the slope of the ac\nStark shift at the magic wavelength under a change of the driving laser\nfrequency is -0.2157 Hz/ (GHz kW/cm^2).", "category": "physics_atom-ph" }, { "text": "Polarizabilities of Rn-like Th4+ from rf spectroscopy of Th3+ Rydberg\n levels: High resolution studies of the fine structure pattern in high-L n=37 levels\nof Th3+ have been carried out using radio-frequency (rf) spectroscopy detected\nwith Resonant Excitation Stark Ionization Spectroscopy (RESIS). Intervals\nseparating L=9 to L=15 levels have been measured, and the results analyzed with\nthe long-range effective potential model. The dipole polarizability of Th4+is\ndetermined to be aD= 7.720(7) a.u.. The quadrupole polarizability is found to\nbe 21.5(3.9) a.u. Both measurements represent significant tests of a-priori\ntheoretical descriptions of this highly relativistic ion.", "category": "physics_atom-ph" }, { "text": "Lifetime of Magnetically Trapped Antihydrogen in ALPHA: How long antihydrogen atoms linger in the ALPHA magnetic trap is an important\ncharacteristic of the ALPHA apparatus. The initial trapping experiments in 2010\n[1] were conducted with 38 detected antiatoms confined for 172 ms and in 2011\n[2] with seven for 1000 s. Long confinement times are necessary to perform\ndetailed frequency scans during spectroscopic measurements. An analysis carried\nout, using machine learning methods, on more than 1000 antiatoms confined for\nseveral hours in the ALPHA-2 magnetic trap, yields a preliminary lower limit to\nthe lifetime of 66 hours. Hence this observation suggests that the measured\nconfinement time of antihydrogen is extended by more than two orders of\nmagnitude.\n [1] Andresen, G. B. et al. (ALPHA collaboration), Nature 468, 673-676 (2010)\n [2] Andresen, G. B. et al. (ALPHA collaboration), Nature Phys. 7, 558-564\n(2011)", "category": "physics_atom-ph" }, { "text": "Screening of electric field and nuclear EDM in non-stationary states of\n atoms and molecules: According to the Schiff theorem, an external electric field vanishes at\natomic nucleus in a neutral atom in a stationary state, i.e. it is completely\nshielded by electrons. This makes a nuclear electric dipole moment (EDM)\nunobservable. We show that if atom or molecule is not in a stationary state\n(e.g. in a superposition of two stationary states), electric field on the\nnucleus is not zero and interaction with nuclear EDM does not vanish. In\nmolecules this effect is enhanced by the ratio of nuclear mass to to electron\nmass, $M_n/m_e$ , since nuclei in a molecule are slow (compare to electrons)\nand do not provide efficient screening in a non-stationary environment.\nElectric field on the nucleus may also affect nuclear reactions.", "category": "physics_atom-ph" }, { "text": "Strongly aligned and oriented molecular samples at a kHz repetition rate: We demonstrate strong adiabatic laser alignment and mixed-field orientation\nat kHz repetition rates. We observe degrees of alignment as large as\ncos\\Theta=0.94 at 1 kHz operation for iodobenzene. The experimental setup\nconsist of a kHz laser system simultaneously producing pulses of 30 fs (1.3 mJ)\nand 450 ps (9 mJ). A cold 1 K state-selected molecular beam is produced at the\nsame rate by appropriate operation of an Even-Lavie valve. Quantum state\nselection has been obtained using an electrostatic deflector. A camera and data\nacquisition system records and analyzes the images on a single-shot basis. The\nsystem is capable of producing, controlling (translation and rotation) and\nanalyzing cold molecular beams at kHz repetition rates and is, therefore,\nideally suited for the recording of ultrafast dynamics in so-called \"molecular\nmovies\".", "category": "physics_atom-ph" }, { "text": "On the secondly quantized theory of many-electron atom: Traditional theory of many-electron atoms and ions is based on the\ncoefficients of fractional parentage and matrix elements of tensorial\noperators, composed of unit tensors. Then the calculation of spin-angular\ncoefficients of radial integrals appearing in the expressions of matrix\nelements of arbitrary physical operators of atomic quantities has two main\ndisadvantages: (i) The numerical codes for the calculation of spin-angular\ncoefficients are usually very time-consuming; (ii) f-shells are often omitted\nfrom programs for matrix element calculation since the tables for their\ncoefficients of fractional parentage are very extensive. The authors suppose\nthat a series of difficulties persisting in the traditional approach to the\ncalculation of spin-angular parts of matrix elements could be avoided by using\nthis secondly quantized methodology, based on angular momentum theory, on the\nconcept of the irreducible tensorial sets, on a generalized graphical method,\non quasispin and on the reduced coefficients of fractional parentage.", "category": "physics_atom-ph" }, { "text": "Controlling interactions between highly-magnetic atoms with Feshbach\n resonances: This paper reviews current experimental and theoretical progress in the study\nof dipolar quantum gases of ground and meta-stable atoms with a large magnetic\nmoment. We emphasize the anisotropic nature of Feshbach resonances due to\ncoupling to fast-rotating resonant molecular states in ultracold s-wave\ncollisions between magnetic atoms in external magnetic fields. The dramatic\ndifferences in the distribution of resonances of magnetic $^7$S$_3$ chromium\nand magnetic lanthanide atoms with a submerged 4f shell and non-zero electron\nangular momentum is analyzed. We focus on Dysprosium and Erbium as important\nexperimental advances have been recently made to cool and create\nquantum-degenerate gases for these atoms. Finally, we describe progress in\nlocating resonances in collisions of meta-stable magnetic atoms in electronic P\nstates with ground-state atoms, where an interplay between collisional\nanisotropies and spin-orbit coupling exists.", "category": "physics_atom-ph" }, { "text": "Relativistic all-order many-body calculation of energies, wavelengths,\n and $M1$ and $E2$ transition rates for the $3d^n$ configurations in tungsten\n ions: Energy levels, wavelengths, magnetic-dipole and electric-quadrupole\ntransition rates between the low-lying states are evaluated for W$^{51+}$ to\nW$^{54+}$ ions with $3d^n$ (n = 2 to 5) electronic configurations using an\napproach combining configuration interaction with linearized coupled-cluster\nsingle-double method. The QED corrections are directly incorporated into the\ncalculations and their effect is studied in detail. Uncertainties of the\ncalculations are discussed. This first study of such highly charged ions with\nthe present method opens the way for future applications allowing an accurate\nprediction of properties for a very wide range of highly charged ions aimed at\nproviding precision benchmarks for various applications.", "category": "physics_atom-ph" }, { "text": "High-order harmonic generation in Xe, Kr, and Ar driven by a 2.1-\u03bcm\n source: high-order harmonic spectroscopy under macroscopic effects: We experimentally and numerically study the atomic response and pulse\npropagation effects of high-order harmonics generated in Xe, Kr, and Ar driven\nby a 2.1-\\mu m infrared femtosecond light source. The light source is an\noptical parametric chirped-pulse amplifier, and a modified strong-field\napproximation and 3-dimensional pulse propagation code are used for the\nnumerical simulations. The extended cutoff in the long-wavelength driven\nhigh-harmonic generation has revealed the spectral shaping of high-order\nharmonics due to the atomic structure (or photo-recombination cross-section)\nand the macroscopic effects, which are the main factors of determining the\nconversion efficiency besides the driving wavelength. Using precise numerical\nsimulations to determine the macroscopic electron wavepacket, we are able to\nextract the photo-recombination cross-sections from experimental high-order\nharmonic spectra in the presence of macroscopic effects. We have experimentally\nobserved that the macroscopic effects shift the observed Cooper minimum of Kr\nfrom 80 eV to 60-70 eV and wash out the Cooper minimum of Ar. Measured\nhigh-harmonic conversion efficiencies per harmonic near the cutoff are ~10^{-9}\nfor all three gases.", "category": "physics_atom-ph" }, { "text": "Collisional trap losses of cold, magnetically-trapped Br atoms: Near-threshold photodissociation of Br$_2$ from a supersonic beam produces\nslow bromine atoms that are trapped in the magnetic field minimum formed\nbetween two opposing permanent magnets. Here, we quantify the dominant trap\nloss rate due to collisions with two sources of residual gas: the background\nlimited by the vacuum chamber base pressure, and the carrier gas during the\nsupersonic gas pulse. The loss rate due to collisions with residual Ar in the\nbackground follows pseudo first-order kinetics, and the bimolecular rate\ncoefficient for collisional loss from the trap is determined by measurement of\nthis rate as a function of the background Ar pressure. This rate coefficient is\nsmaller than the total elastic collision rate coefficient, as it only samples\nthose collisions that lead to trap loss, and is determined to be\n$\\langle\\nu\\sigma\\rangle = (1.12\\pm0.09)\\times10^{-9}\\,\\text{cm}^3\\,\n\\text{s}^{-1}$. The calculated differential cross section can be used with this\nvalue to estimate a trap depth of $293\\pm24\\,\\text{mK}$. Carrier gas collisions\noccur only during the tail of the supersonic beam pulse. Using the differential\ncross section verified by the background-gas collision measurements provides an\nestimate of the peak molecular beam density of\n$(3.0\\pm0.3)\\times10^{13}\\,\\text{cm}^{-3}$ in good agreement with the\nprediction of a simple supersonic expansion model. Finally, we estimate the\ntrap loss rate due to Majorana transitions to be negligible, owing to the\nrelatively large trapped-atom phase-space volume.", "category": "physics_atom-ph" }, { "text": "Universality and the three-body parameter of helium-4 trimers: We consider a system of three helium-4 atoms, which is so far the simplest\nrealistic three-body system exhibiting the Efimov effect, in order to analyse\ndeviations from the universal Efimov three-body spectrum. We first calculate\nthe bound states using a realistic two-body potential, and then analyse how\nthey can be reproduced by simple effective models beyond Efimov's universal\ntheory. We find that the non-universal variations of the first two states can\nbe well reproduced by models parametrized with only three quantities: the\nscattering length and effective range of the original potential, and the\nstrength of a small three-body force. Furthermore, the three-body parameter\nwhich fixes the origin of the infinite set of three-body levels is found to be\nconsistent with recent experimental observations in other atomic species.", "category": "physics_atom-ph" }, { "text": "Strong Field Non-Franck-Condon Ionization of H$_2$: A Semi-Classical\n Analysis: Single ionization of H$_2$ molecules exposed to strong and short laser pulses\nis investigated by a semi-classical method. Three laser characteristics are\nconsidered: i) The carrier-wave frequency corresponds to wavelengths covering\nand bridging the two ionization regimes: From tunnel ionization (TI) at 800 nm\nto multiphoton ionization (MPI) at 266 nm. ii) Values of the peak intensity are\nchosen within a window to eliminate competing double ionization processes. iii)\nParticular attention is paid to the polarization of the laser field, which can\nbe linearly or circularly polarized. The results and their interpretation\nconcern two observables, namely the end-of-pulse total ionization probability\nand vibrational distribution generated in the cation H$_2^+$. The most\nprominent findings are an increased ionization efficiency in circular\npolarization and a vibrational distribution of the cation that favors\nlower-lying levels than those that would be populated in a vertical\n(Franck-Condon) ionization, leading to non Franck-Condon distributions, both in\nlinear and circular polarizations.", "category": "physics_atom-ph" }, { "text": "Intensities of KCs $E(4)^1\u03a3^+\\to (a^3\u03a3^+,X^1\u03a3^+)$ band\n system up to dissociation threshold: an interplay between spin-orbit,\n hyperfine and rovibronic coupling effects: The relative intensity distribution in the rotationally resolved\nlaser-induced fluorescence spectra belonging to the $E(4)^1\\Sigma^+\\to\n(a^3\\Sigma^+_1,X^1\\Sigma^+)$ band systems of the KCs molecule was analyzed. The\nexperimental intensities in doublet $P$,$R$ progressions assigned to\nspin-allowed $E\\to X$ and spin-forbidden $E\\to a$ transitions up to their\ncommon ground dissociation limit were described in the framework of a\ncoupled-channels (CC) deperturbation model applied for the interacting \\Xstate\\\nand \\astate\\ states. The CC intensity simulation was based solely on fixed\nelectronic structure parameters as functions of the internuclear distance $R$,\nnamely: accurate empirical potential energy curves for all three states,\n\\emph{ab initio} estimates for matrix elements $A(R)$ of the hyperfine\nstructure (HFS) , and transition dipole moments $d_{EX}(R)$ and $d_{Ea}(R)$. A\ncomparison between the measured intensities and their theoretical counterparts\ndemonstrates a strong competition between different intramolecular\ninteractions. A weak spin-orbit coupling of the upper \\Estate\\ state with the\nremote $^3\\Pi$ states is responsible for appearance of the $E\\to a$ vibrational\nbands for the intermediate $v_a$-values. In turn, the HFS coupling between\n\\Xstate\\ and \\astate\\ states leads to peculiarities in $E\\to (X,a)$\nintensities, which are pronounced for high $v_{X/a}$-values in the vicinity of\nK(4$^2S$)+Cs(6$^2S$) dissociation threshold. Both adiabatic ro-vibrational and\nnon-adiabatic electronic-rotational interactions explain the abrupt deviation\nof some observed $P/R$ intensity ratios from the expected H\\\"{o}nl-London\nfactors.", "category": "physics_atom-ph" }, { "text": "A note on recursive calculations of particular 9j coefficients: The calculation of angular-momentum coupling transformation matrices can be\nvery time consuming and alternative methods, even if they apply only in special\ncases, are helpful. We present a recursion relation for the calculation of\nparticular 9j symbols used in the quantum theory of angular momentum.", "category": "physics_atom-ph" }, { "text": "Spin State Detection and Manipulation and Parity Violation in a Single\n Trapped Ion: Atomic Parity Violation provides the rare opportunity of a low energy window\ninto possible new fundamental processes at very high mass scales normally\ninvestigated at large high energy accelerators. Precise measurements on atomic\nsystems are currently the most sensitive probes of many kinds of new physics,\nand complement high energy experiments. Present atomic experiments are\nbeginning to reach their limits of precision due to either sensitivity,\nsystematics or atomic structure uncertainties. An experiment in a single\ntrapped Barium ion can improve on all of these difficulties. This experiment\nuses methods to precisely manipulate and detect the spin state of a single ion\nin order to measure a parity induced splitting of the ground state magnetic\nsublevels in externally applied laser fields. The same methods can be used to\nprovide precise measurements of more conventional atomic structure parameters.", "category": "physics_atom-ph" }, { "text": "Diffusion, thermalization and optical pumping of YbF molecules in a cold\n buffer gas cell: We produce YbF molecules with a density of 10^18 m^-3 using laser ablation\ninside a cryogenically-cooled cell filled with a helium buffer gas. Using\nabsorption imaging and absorption spectroscopy we study the formation,\ndiffusion, thermalization and optical pumping of the molecules. The absorption\nimages show an initial rapid expansion of molecules away from the ablation\ntarget followed by a much slower diffusion to the cell walls. We study how the\ntime constant for diffusion depends on the helium density and temperature, and\nobtain values for the YbF-He diffusion cross-section at two different\ntemperatures. We measure the translational and rotational temperatures of the\nmolecules as a function of time since formation, obtain the characteristic time\nconstant for the molecules to thermalize with the cell walls, and elucidate the\nprocess responsible for limiting this thermalization rate. Finally, we make a\ndetailed study of how the absorption of the probe laser saturates as its\nintensity increases, showing that the saturation intensity is proportional to\nthe helium density. We use this to estimate collision rates and the density of\nmolecules in the cell.", "category": "physics_atom-ph" }, { "text": "Deep inner-shell multiphoton ionization by intense x-ray free-electron\n laser pulses: We have investigated multiphoton multiple ionization dynamics of argon and\nxenon atoms using a new x-ray free electron laser (XFEL) facility, SPring-8\nAngstrom Compact free electron LAser (SACLA) in Japan, and identified that\nhighly charged Xe ions with the charge state up to +26 are produced\npredominantly via four-photon absorption as well as highly charged Ar ions with\nthe charge state up to +10 are produced via two-photon absorption at a photon\nenergy of 5.5 keV. The absolute fluence of the XFEL pulse, needed for\ncomparison between theory and experiment, has been determined using two-photon\nprocesses in the argon atom with the help of benchmark ab initio calculations.\nOur experimental results, in combination with a newly developed theoretical\nmodel for heavy atoms, demonstrate the occurrence of multiphoton absorption\ninvolving deep inner shells.", "category": "physics_atom-ph" }, { "text": "Effective Langevin Equation Approach to the Molecular Diffusion on\n Optical Lattices: Optical micro-manipulation techniques has evolved into powerful tools to\nefficiently steer the motion of microscopical particles on periodic and\nquasi-periodic potentials, driven by the external electromagnetic field. Here,\nthe dynamics of molecular diffusion on optical lattices is analysed within the\nframework of the theory of open systems, for polar molecules coupled to a\ntransient electromagnetic field. Using the normal mode expansion of the field,\nwe derive an effective, generalised Langevin equation which describes the\nmotion of the system along the molecular degrees of freedom. The present\napproach is universally applicable (for molecules with non-vanishing permanent\ndipole moment) and it opens a wide spectrum of applications in the control of\nthe molecular transport mechanisms on optical lattices. The numerical analysis\nof suitable model external fields demonstrates the feasibility of neglecting\nmemory terms in the resulting Langevin equation.", "category": "physics_atom-ph" }, { "text": "Time-resolved quantum beats in the fluorescence of helium resonantly\n excited by XUV radiation: We report on the observation of time-resolved quantum beats in the helium\nfluorescence from the transition 1s3p -> 1s2s, where the initial state is\nexcited by XUV free-electron laser radiation. The quantum beats originate from\nthe Zeeman splitting of the magnetic substates due to an external magnetic\nfield. We perform a systematic study of this effect and discuss the\npossibilities of studying this phenomenon in the XUV and x-ray regime.", "category": "physics_atom-ph" }, { "text": "Fast configuration-interaction calculations for nobelium and ytterbium: We calculate excitation energies for low states of nobelium, including states\nwith open $5f$ subshell. An efficient version of the many-electron\nconfiguration-interaction method for treating the atom as a sixteen external\nelectrons system has been developed and used. The method is tested on\ncalculations for ytterbium which has external electron structure similar to\nnobelium. The results for nobelium are important for prediction of its spectrum\nand for interpretation of recent measurements. Ytterbium is mostly used to\nstudy the features of the method.", "category": "physics_atom-ph" }, { "text": "Polarization gradient cooling of single atoms in optical dipole traps: We experimentally investigate $\\sigma^+$-$\\sigma^-$ polarization gradient\ncooling~(PGC) of a single $^{87}$Rb atom in a tightly focused dipole trap and\nshow that the cooling limit strongly depends on the polarization of the\ntrapping field. For optimized cooling light power, the temperature of the atom\nreaches~$10.4(6)\\,\\mu$K in a linearly polarized trap, approximately five times\nlower than in a circularly polarized trap. The inhibition of PGC is\nqualitatively explained by the fictitious magnetic fields induced by the\ntrapping field. We further demonstrate that switching the trap polarization\nfrom linear to circular after PGC induces only minor heating.", "category": "physics_atom-ph" }, { "text": "Doppler Amplification of Motion of a Trapped Three-Level Ion: The system of a trapped ion translationally excited by a blue-detuned\nnear-resonant laser, sometimes described as an instance of a phonon laser, has\nrecently received attention as interesting in its own right and for its\napplication to non-destructive readout of internal states of non-fluorescing\nions. Previous theoretical work has been limited to cases of two-level ions.\nHere, we perform simulations to study the dynamics of a phonon laser involving\nthe $\\Lambda$-type $^{138}\\mbox{Ba}^{+}$ ion, in which coherent population\ntrapping effects lead to different behavior than in the previously studied\ncases. We also explore optimization of the laser parameters to maximize\namplification gain and signal-to-noise ratio for internal state readout.", "category": "physics_atom-ph" }, { "text": "Controllable steep dispersion with gain in a four-level N-scheme with\n four-wave mixing: We present a theoretical analysis of the propagation of light pulses through\na medium of four-level atoms, with two strong pump fields and a weak signal\nfield in an N-scheme arrangement. We show that the generation of four-wave\nmixing has a profound effect on the signal field group velocity and absorption,\nallowing the signal field propagation to be tuned from superluminal to slow\nlight regimes with amplification.", "category": "physics_atom-ph" }, { "text": "Synchronization in non dissipative optical lattices: The dynamics of cold atoms in conservative optical lattices obviously depends\non the geometry of the lattice. But very similar lattices may lead to deeply\ndifferent dynamics. For example, in a 2D optical lattice with a square mesh,\nthe sign of the detuning plays a crucial role: in the blue detuned case,\ntrajectories of an atom inside a well are chaotic for high enough energies. On\nthe contrary, in the red detuned case, chaos is completely inhibited inside the\nwells. Here, we study in details the dynamical regimes of atoms inside a well\nof a red detuned lattice, with the aim to understand the dynamical mechanisms\nleading to the disappearance of chaos. We show that the motions in the two\ndirections of space are frequency locked in most of the phase space, for most\nof the parameters of the lattice and atoms. This synchronization, not as strict\nas that of a dissipative system, is nevertheless a mechanism powerful enough to\nexplain that chaos cannot appear in red detuned lattices.", "category": "physics_atom-ph" }, { "text": "Inhomogeneous broadening of optical transitions of 87Rb atoms in an\n optical nanofiber trap: We experimentally demonstrate optical trapping of 87Rb atoms using a\ntwo-color evanescent field around an optical nanofiber. In our trapping\ngeometry, a blue-detuned traveling wave whose polarization is nearly parallel\nto the polarization of a red-detuned standing wave produces significant vector\nlight shifts that lead to broadening of the absorption profile of a\nnear-resonant beam at the trapping site. A model that includes scalar, vector,\nand tensor light shifts of the probe transition $5S_{1/2}$-$5P_{3/2}$ from the\ntrapping beams, weighted by the temperature-dependent position of the atoms in\nthe trap, qualitatively describes the observed asymmetric profile and explains\ndifferences with previous experiments that used Cs atoms. The model provides a\nconsistent way to extract the number of atoms in the trap.", "category": "physics_atom-ph" }, { "text": "Random phase approximation with exchange for the photoionization of\n confined atoms: Xe in C_{60} fullerene: Photoionization of a Xe atom confined inside C$_{60}$ has been studied using\nthe random phase approximation with exchange (RPAE) method. The C$_{60}$\nfullerene has been descr ibed by an attractive short range spherical well with\npotential $V(r)$, given by $V(r)=-V_ 0$ for $r_ir_0$ have been obtained by solving the\nSchr\\\"{o}dinger equation using both regular and irregular solutions and the\ncontinuous boundary conditions at $r_i$ and $r_0$. The photoionization cross\nsections for the Xe 4d, $5s$ and $5p$ ele ctrons in the Xe@C$_{60}$ endohedral\nmolecule have been evaluated and compared with those of the photoionization for\nthe free Xe atom and other previo us calculations for the Xe@C$_{60}$\nfullerene. Our method surmounted the weaknesses of the previous model potential\ncalculation s and demonstrated significantly stronger correlated confinement\nresonances for the Xe@C$_{60}$ photoionization.", "category": "physics_atom-ph" }, { "text": "Raman sideband cooling of molecules in an optical tweezer array to the\n 3-D motional ground state: Ultracold polar molecules are promising for quantum information processing\nand searches for physics beyond the Standard Model. Laser cooling to ultracold\ntemperatures is an established technique for trapped diatomic and triatomic\nmolecules. Further cooling of the molecules to near the motional ground state\nis crucial for reducing various dephasings in quantum and precision\napplications. In this work, we demonstrate Raman sideband cooling of CaF\nmolecules in optical tweezers to near their motional ground state, with average\nmotional occupation quantum numbers of $\\bar{n}_{x}=0.16(12)$,\n$\\bar{n}_{y}=0.17(17)$ (radial directions), $\\bar{n}_{z}=0.22(16)$ (axial\ndirection) and a 3-D motional ground state probability of $54\\pm18\\%$. This\npaves the way to increase molecular coherence times in optical tweezers for\nrobust quantum computation and simulation applications.", "category": "physics_atom-ph" }, { "text": "Electron-positron pair creation in low-energy collisions of heavy bare\n nuclei: A new method for calculations of electron-positron pair-creation\nprobabilities in low-energy heavy-ion collisions is developed. The approach is\nbased on the propagation of all one-electron states via the numerical solving\nof the time-dependent Dirac equation in the monopole approximation. The\nelectron wave functions are represented as finite sums of basis functions\nconstructed from B-splines using the dual-kinetic-balance technique. The\ncalculations of the created particle numbers and the positron energy spectra\nare performed for the collisions of bare nuclei at the energies near the\nCoulomb barrier with the Rutherford trajectory and for different values of the\nnuclear charge and the impact parameter. To examine the role of the spontaneous\npair creation the collisions with a modified velocity and with a time delay are\nalso considered. The obtained results are compared with the previous\ncalculations and the possibility of observation of the spontaneous pair\ncreation is discussed.", "category": "physics_atom-ph" }, { "text": "Lifetimes of ultralong-range strontium Rydberg molecules in a dense BEC: The lifetimes and decay channels of ultralong-range Rydberg molecules created\nin a dense BEC are examined by monitoring the time evolution of the Rydberg\npopulation using field ionization. Studies of molecules with values of\nprincipal quantum number, $n$, in the range $n=49$ to $n=72$ that contain tens\nto hundreds of ground state atoms within the Rydberg electron orbit show that\ntheir presence leads to marked changes in the field ionization characteristics.\nThe Rydberg molecules have lifetimes of $\\sim1-5\\,\\mu$s, their destruction\nbeing attributed to two main processes: formation of Sr$^+_2$ ions through\nassociative ionization, and dissociation induced through $L$-changing\ncollisions. The observed loss rates are consistent with a reaction model that\nemphasizes the interaction between the Rydberg core ion and its nearest\nneighbor ground-state atom. The measured lifetimes place strict limits on the\ntime scales over which studies involving Rydberg species in cold, dense atomic\ngases can be undertaken and limit the coherence times for such measurements.", "category": "physics_atom-ph" }, { "text": "Observation of single-photon superradiance and the cooperative Lamb\n shift in an extended sample of cold atoms: We report direct, time-resolved observations of single-photon superradiance\nin a highly extended, elliptical sample of cold 87Rb atoms. The observed rapid\ndecay rate is accompanied by its counterpart, the cooperative Lamb shift. The\nrate of the strongly directional decay, and the associated shift, scale\nlinearly with the number of atoms and show a strong dependence on the sample\nshape, demonstrating the collective nature of the observed quantities.", "category": "physics_atom-ph" }, { "text": "Atom interferometry with coherent enhancement of Bragg pulse sequences: We report here on the realization of light-pulse atom interferometers with\nLarge-momentum-transfer atom optics based on a sequence of Bragg transitions.\nWe demonstrate momentum splitting up to 200 photon recoils in an ultra-cold\natom interferometer. We highlight a new mechanism of destructive interference\nof the losses leading to a sizeable efficiency enhancement of the beam\nsplitters. We perform a comprehensive study of parasitic interferometers due to\nthe inherent multi-port feature of the quasi-Bragg pulses. Finally, we\nexperimentally verify the phase shift enhancement and characterize the\ninterferometer visibility loss.", "category": "physics_atom-ph" }, { "text": "Light scattering detection of quantum phases of ultracold atoms in\n optical lattices: Ultracold atoms loaded on optical lattices can provide unprecedented\nexperimental systems for the quantum simulations and manipulations of many\nquantum phases. However, so far, how to detect these quantum phases effectively\nremains an outstanding challenge. Here, we show that the optical Bragg\nscattering of cold atoms loaded on optical lattices can be used to detect many\nquantum phases which include not only the conventional superfluid and Mott\ninsulating phases, but also other important phases such as various kinds of\ndensity waves (CDW), valence bond solids (VBS), CDW supersolids and VBS\nsupersolids.", "category": "physics_atom-ph" }, { "text": "Limits on Magnetically Induced Faraday Rotation from Polarized $^3$He\n Atoms: Faraday rotation has become a powerful tool in a large variety of physics\napplications. Most prominently, Faraday rotation can be used in precision\nmagnetometry. Here we report the first measurements of gyromagnetic Faraday\nrotation on a dense, hyperpolarized $^3$He gas target. Theoretical calculations\npredict the rotations of linearly polarized light due to the magnetization of\nspin-1/2 particles are on the scale of 10$^{-7}$ radians. To maximize the\nsignal, a $^3$He target designed to use with a multipass cavity is combined\nwith a sensitive apparatus for polarimetry that can detect optical rotations on\nthe order of 10$^{-8}$ radians. Although the expected results are well above\nthe sensitivity for the given experimental conditions, no nuclear-spin induced\nrotation was observed.", "category": "physics_atom-ph" }, { "text": "Surface analysis via fast atom diffraction: pattern visibility and\n spot-beam contribution: Grazing incidence fast atom diffraction (GIFAD or FAD) is a sensitive tool\nfor surface analysis, which strongly relies on the quantum coherence of the\nincident beam. In this article the influence of the incidence conditions and\nthe projectile mass on the visibility of the FAD patterns is addressed. Both\nparameters determine the transverse coherence length of the impinging\nparticles, which governs the general features of FAD distributions. We show\nthat by varying the impact energy, while keeping the same collimating setup and\nnormal energy, it is possible to control the interference mechanism that\nprevails in FAD patterns. Furthermore, we demonstrate that the contribution\ncoming from different positions of the focus point of the incident particles,\nwhich gives rise to the spot-beam effect, allows projectiles to explore\ndifferent zones of a single crystallographic channel when a narrow surface area\nis coherently lighted. In this case the spot-beam effect gives also rise to a\nnon-coherent background, which contributes to the gradual quantum-classical\ntransition of FAD spectra. Present results are compared with available\nexperimental data, making evident that the inclusion of focusing effects is\nnecessary for the proper theoretical description of the experimental\ndistributions.", "category": "physics_atom-ph" }, { "text": "Relativistic calculations of the energies of the low-lying $1sns$,\n $1snp$, $1snd$ states and the probabilities of the one-photon $1snl\\to\n 1sn'l'$ transitions in heliumlike uranium: For heliumlike uranium, the energies of the singly-excited $1sns$, $1snp$,\nand $1snd$ states with $n\\leq 4$ and the probabilities of the one-photon\n$1s3d\\to 1s2p$, $1s3p\\to 1s2s$, $1s3p\\to 1s2p$ and $1s4d\\to 1s2p$ transitions\nare evaluated. The calculations are performed within the Breit approximation\nusing the configuration-interaction method in the basis of the Dirac-Fock-Sturm\norbitals. The QED corrections to the energy levels are calculated employing the\nmodel-QED-operator approach. The nuclear recoil, frequency-dependent\nBreit-interaction, nuclear polarization, and nuclear deformation corrections\nare taken into account as well.", "category": "physics_atom-ph" }, { "text": "Improved frequency measurement of a one-dimensional optical lattice\n clock with a spin-polarized fermionic $^{87}$Sr isotope: We demonstrate a one-dimensional optical lattice clock with a spin-polarized\nfermionic isotope designed to realize a collision-shift-free atomic clock with\nneutral atom ensembles. To reduce systematic uncertainties, we developed both\nZeeman shift and vector light-shift cancellation techniques. By introducing\nboth an H-maser and a Global Positioning System (GPS) carrier phase link, the\nabsolute frequency of the $^1S_0(F=9/2) - {}^3P_0(F=9/2)$ clock transition of\nthe $^{87}$Sr optical lattice clock is determined as 429,228,004,229,875(4) Hz,\nwhere the uncertainty is mainly limited by that of the frequency link. The\nresult indicates that the Sr lattice clock will play an important role in the\nscope of the redefinition of the ``second'' by optical frequency standards.", "category": "physics_atom-ph" }, { "text": "Influence of the Coulomb potential on above-threshold ionization: a\n quantum-orbit analysis beyond the strong-field approximation: We perform a detailed analysis of how the interplay between the residual\nbinding potential and a strong laser field influences above-threshold\nionization (ATI), employing a semi-analytical, Coulomb-corrected strong-field\napproximation (SFA) in which the Coulomb potential is incorporated in the\nelectron propagation in the continuum. We find that the Coulomb interaction\nlifts the degeneracy of some SFA trajectories, and we identify a set of orbits\nwhich, for high enough photoelectron energies, may be associated with\nrescattering. Furthermore, by performing a direct comparison with the standard\nSFA, we show that several features in the ATI spectra can be traced back to the\ninfluence of the Coulomb potential on different electron trajectories. These\nfeatures include a decrease in the contrast, a shift towards lower energies in\nthe interference substructure, and an overall increase in the photoelectron\nyield. All features encountered exhibit a very good agreement with the \\emph{ab\ninitio} solution of the time-dependent Schr\\\"odinger equation.", "category": "physics_atom-ph" }, { "text": "Optical Production of Ultracold Polar Molecules: We demonstrate the production of ultracold polar RbCs molecules in their\nvibronic ground state, via photoassociation of laser-cooled atoms followed by a\nlaser-stimulated state transfer process. The resulting sample of $X ^1\\Sigma^+\n(v=0)$ molecules has a translational temperature of $\\sim100 \\mu$K and a narrow\ndistribution of rotational states. With the method described here it should be\npossible to produce samples even colder in all degrees of freedom, as well as\nother bi-alkali species.", "category": "physics_atom-ph" }, { "text": "Universal Four-Boson States in Ultracold Molecular Gases: Resonant\n Effects in Dimer-Dimer Collisions: We study the manifestations of universal four-body physics in ultracold\ndimer-dimer collisions.\n We show that resonant features associated with three-body Efimov physics and\ndimer-dimer scattering lengths are universally related. The emergence of\nuniversal four-boson states allows for the tunability of the dimer-dimer\ninteraction, thus enabling the future study of ultracold molecular gases with\nboth attractive and repulsive interactions. Moreover, our study of the\ninterconversion between dimers and Efimov trimers shows that $B_{2}+B_{2}\\to\nB_{3}+B$ rearrangement reactions can provide an efficient trimer formation\nmechanism. Our analysis of the temperature dependence of this reaction provides\nan interpretation of the available experimental data and sheds light on the\npossible experimental realization of rearrangement processes in ultracold\ngases.", "category": "physics_atom-ph" }, { "text": "Direct limits on the interaction of antiprotons with axion-like dark\n matter: Astrophysical observations indicate that there is roughly five times more\ndark matter in the Universe than ordinary baryonic matter, with an even larger\namount of the Universe's energy content due to dark energy. So far, the\nmicroscopic properties of these dark components have remained shrouded in\nmystery. In addition, even the five percent of ordinary matter in our Universe\nhas yet to be understood, since the Standard Model of particle physics lacks\nany consistent explanation for the predominance of matter over antimatter.\nInspired by these central problems of modern physics, we present here a direct\nsearch for interactions of antimatter with dark matter, and place direct\nconstraints on the interaction of ultra-light axion-like particles $-$ one of\nthe dark-matter candidates $-$ and antiprotons. If antiprotons exhibit a\nstronger coupling to these dark-matter particles than protons, such a CPT-odd\ncoupling could provide a link between dark matter and the baryon asymmetry in\nthe Universe. We analyse spin-flip resonance data acquired with a single\nantiproton in a Penning trap [Smorra et al., Nature 550, 371 (2017)] in the\nfrequency domain to search for spin-precession effects from ultra-light axions\nwith a characteristic frequency governed by the mass of the underlying\nparticle. Our analysis constrains the axion-antiproton interaction parameter\n$f_a/C_{\\overline{p}}$ to values greater than $0.1$ to $0.6$ GeV in the mass\nrange from $2 \\times 10^{-23}$ to $4 \\times 10^{-17}\\,$eV/$c^2$, improving over\nastrophysical antiproton bounds by up to five orders of magnitude. In addition,\nwe derive limits on six combinations of previously unconstrained\nLorentz-violating and CPT-violating terms of the non-minimal Standard Model\nExtension.", "category": "physics_atom-ph" }, { "text": "Electric dipole polarizability of group-IIIA ions using PRCC: Large\n correlation effects from nonlinear terms: We compute the ground-state electric dipole polarizability of group-IIIA ions\nusing the perturbed relativistic coupled-cluster (PRCC) theory. To account for\nthe relativistic effects and QED corrections, we use the Dirac-Coulomb-Breit\nHamiltonian with the corrections from the Uehling potential and the\nself-energy. The effects of triple excitations are considered perturbatively in\nthe PRCC. Our PRCC results for $\\alpha$ are good in agreement with the previous\ntheoretical results for all the ions. From our computations we find that the\nnonlinear terms in PRCC have significant contributions and must be included to\nobtain the accurate value of $\\alpha$ for group-IIIA ions. For the correction\nfrom the Breit interaction, we find that it is largest for Al$^+$ and decreases\nas we go towards the heavier ions. The corrections from the vacuum polarization\nand the self-energy increase from lighter to heavier ions.", "category": "physics_atom-ph" }, { "text": "Atomic structure calculations of super heavy noble element oganesson\n (Z=118): We calculate the spectrum and allowed E1 transitions of the superheavy\nelement Og (Z=118). A combination of configuration interaction (CI) and\nperturbation theory (PT) is used (Dzuba \\textit{et at.} Phys. Rev. A,\n\\textbf{95}, 012503 (2017)). The spectrum of lighter analog Rn I is also\ncalculated and compared to experiment with good agreement.", "category": "physics_atom-ph" }, { "text": "Lithium Ionization by a Strong Laser Field: We study ab initio computations of the interaction of Lithium with a strong\nlaser field. Numerical solutions of the time-dependent fully-correlated\nthree-particle Schroedinger equation restricted to the one-dimensional\nsoft-core approximation are presented. Our results show a clear transition from\nnon-sequential to sequential double ionization for increasing intensities. Non\nsequential double ionization is found to be sensitive to the spin configuration\nof the ionized pair. This asymmetry, also found in experiments of\nphotoionization of Li with synchrotron radiation, shows the evidence of the\ninfluence of the exclusion principle in the underlying rescattering mechanism.", "category": "physics_atom-ph" }, { "text": "Tri-spin dynamics in alkali metal-noble gas NMR gyroscope: Alkali metal-noble gas NMR gyroscope is widely used for precision rotation\nmeasurement in fundamental and applied physics. By numerically simulating the\nalkali-nuclear-nuclear tri-spin dynamics, we investigate the dependence of\ngyroscope response on alkali spin relaxation time and nuclear spin\nmagnetization. We found additional resonance peaks appear due to a new source\nof instability, namely the inherent multistability of tri-spin dynamics. The\nnumerical simulation results agree well with the recent experiment, enabling a\nbetter understanding and exploitation of the gyroscope signal.", "category": "physics_atom-ph" }, { "text": "Landau Damping in the Transverse Modulational Dynamics of Co-Propagating\n Light and Matter Beams: The optomechanical coupling and transverse stability of a co-propagating\nmonochromatic electromagnetic wave and mono-energetic beam of two-level atoms\nis investigated in the collisionless regime. The coupled dynamics are studied\nthrough a Landau stability analysis of the coupled gas- kinetic and paraxial\nwave equations, including the effect of the electronic nonlinearity. The\nresulting dispersion relation captures the interaction of kinetic and\nsaturation effects and shows that for blue detuning the combined nonlinear\ninteraction is unstable below a critical wavenumber which reduces to the result\nof Bespalov and Talanov in the limit of a negligible kinetic nonlinearity. For\nred detuning we find that under a saturation parameter threshold exists whereby\nthe system stabilizes unconditionally. With negligible saturation, an\noptomechanical form of Landau damping stabilizes all wavenumbers above a\ncritical wavenumber determined by the combined strength of the kinetic and\nrefractive optomechanical feedback. The damping is mediated primarily by atoms\ntraveling along the primary diagonals of the Talbot carpet.", "category": "physics_atom-ph" }, { "text": "5s correlation confinement resonances in Xe-endo-fullerenes: Spectacular trends in the modification of the Xe 5s photoionization via\ninterchannel coupling with confinement resonances emerging in the Xe 4d giant\nresonance upon photoionization of the Xe@C60, Xe@C240 and Xe@C60@C240\nendo-fullerenes are theoretically unraveled and interpreted.", "category": "physics_atom-ph" }, { "text": "Scalar Static Polarizabilities of Lanthanides and Actinides: We calculate scalar static polarizabilities for lanthanides and actinides,\nthe atoms with open $4f$ or $5f$ subshell. We show that polarizabilities of the\nlow states are approximately the same for all states of given configuration and\npresent a way of calculating them reducing valence space to just two or three\nvalence electrons occupying $6s$ and $5d$ states for lanthanides or $7s$ and\n$6d$ states for actinides while $4f$ and $5f$ states are considered to be in\nthe core. Configuration interaction technique is used to calculate\npolarizabilities of lanthanides and actinides for all states of the $4f^n6s^2$\nand $4f^{n-1}6s^25d$ configurations of lanthanides and all states of the\n$5f^{n}7s^2$ and $5f^{n-1}7s^26d$ configurations of actinides. Polarizability\nof the electron core (including f-orbitals) has been calculated in the RPA\napproximation.", "category": "physics_atom-ph" }, { "text": "Dramatic reductions in inelastic cross sections for ultracold collisions\n near Feshbach resonances: We show that low-energy inelastic cross sections can decrease as well as\nincrease in the vicinity of a zero-energy Feshbach resonance. When an external\nfield is used to tune across such a resonance, the real and imaginary parts of\nthe scattering length show asymmetric oscillations, with both peaks and\ntroughs. In favorable circumstances the inelastic collision rate can be reduced\nalmost to zero. This may be important for efforts to achieve evaporative and\nsympathetic cooling for molecules.", "category": "physics_atom-ph" }, { "text": "Fundamental transitions and ionization energies of the hydrogen\n molecular ions at the few ppt level: We calculate ionization energies and fundamental vibrational transitions for\nH$_2^+$, D$_2^+$, and HD$^+$ molecular ions. The NRQED expansion for the energy\nin terms of the fine structure constant $\\alpha$ is used. Previous calculations\nof orders $m\\alpha^6$ and $m\\alpha^7$ are improved by including second-order\ncontributions due to the vibrational motion of nuclei. Furthermore, we evaluate\nthe largest corrections at the order $m\\alpha^8$. That allows to reduce the\nfractional uncertainty to the level of $7\\cdot10^{-12}$ for fundamental\ntransitions and to $4\\cdot10^{-12}$ for the ionization energies.", "category": "physics_atom-ph" }, { "text": "Tunable disorder in a crystal of cold polar molecules: In the present work, we demonstrate the possibility of controlling by an\nexternal field the dynamics of collective excitations (excitons) of molecules\non an optical lattice. We show that a suitably chosen two-species mixture of\nultracold polar molecules loaded on an optical lattice forms a phononless\ncrystal, where exciton-impurity interactions can be controlled by applying an\nexternal electric field. This can be used for the controlled creation of\nmany-body entangled states of ultracold molecules and the time-domain quantum\nsimulation of disorder-induced localization and delocalization of quantum\nparticles.", "category": "physics_atom-ph" }, { "text": "Manipulating the motion of large neutral molecules: Large molecules have complex potential-energy surfaces with many local\nminima. They exhibit multiple stereo-isomers, even at very low temperatures. In\nthis paper we discuss the different approaches for the manipulation of the\nmotion of large and complex molecules, like amino acids or peptides, and the\nprospects of state- and conformer-selected, focused, and slow beams of such\nmolecules for studying their molecular properties and for fundamental physics\nstudies. Accepted for publication in Faraday Disc. 142 (2009), DOI:\n10.1039/b820045a", "category": "physics_atom-ph" }, { "text": "Laser-assisted electron-argon scattering at small angles: Electron-argon scattering in the presence of a linearly polarized, low\nfrequency laser field is studied theoretically. The scattering geometries of\ninterest are small angles where momentum transfer is nearly perpendicular to\nthe field, which is where the Kroll-Watson approximation has the potential to\nbreak down. The Floquet R matrix method solves the velocity gauge Schr\\\"odinger\nequation, using a larger reaction volume than previous treatments in order to\ncarefully assess the importance of the long range polarization potential to the\ncross section. A comparison of the cross sections calculated with the target\npotential fully included inside 20 and 100 a.u. shows no appreciable\ndifferences, which demonstrates that the long range interaction can not account\nfor the high cross sections measured in experiments.", "category": "physics_atom-ph" }, { "text": "Influence of coherent adiabatic excitation on femtosecond transient\n signals: The transient signals derived from femtosecond pump-probe experiments are\nanalyzed in terms of the coherent evolution of the energy levels perturbed by\nthe excitation pulse. The model system is treated as the sum of independent\ntwo-level subsystems that evolve adiabatically or are permanently excited,\ndepending on the detuning from the central wavelength of the excitation laser.\nThis approach will allow us to explain numerically and analytically the\nconvergence between the coherent and incoherent (rate equations) treatments for\ncomplex multi-level systems. It will be also shown that the parameter that\ndetermines the validity of the incoherent treatment is the distribution of\nstates outside and inside the laser bandwidth, rather than the density of\nstates as it is commonly accepted.", "category": "physics_atom-ph" }, { "text": "Raman transitions between hyperfine clock states in a magnetic trap: We present our experimental investigation of an optical Raman transition\nbetween the magnetic clock states of $^{87}$Rb in an atom chip magnetic trap.\nThe transfer of atomic population is induced by a pair of diode lasers which\ncouple the two clock states off-resonantly to an intermediate state manifold.\nThis transition is subject to destructive interference of two excitation paths,\nwhich leads to a reduction of the effective two-photon Rabi-frequency.\nFurthermore, we find that the transition frequency is highly sensitive to the\nintensity ratio of the diode lasers. Our results are well described in terms of\nlight shifts in the multi-level structure of $^{87}$Rb. The differential light\nshifts vanish at an optimal intensity ratio, which we observe as a narrowing of\nthe transition linewidth. We also observe the temporal dynamics of the\npopulation transfer and find good agreement with a model based on the system's\nmaster equation and a Gaussian laser beam profile. Finally, we identify several\nsources of decoherence in our system, and discuss possible improvements.", "category": "physics_atom-ph" }, { "text": "The structure of the atomic helium trimers: Halos and Efimov states: The Faddeev equations for the atomic helium-trimer systems are solved\nnumerically with high accuracy both for the most sophisticated realistic\npotentials available and for simple phenomenological potentials. An efficient\nnumerical procedure is described. The large-distance asymptotic behavior,\ncrucial for weakly bound three-body systems, is described almost analytically\nfor arbitrary potentials. The Efimov effect is especially considered. The\ngeometric structures of the bound states are quantitatively investigated. The\naccuracy of the schematic models and previous computations is comparable, i.e.\nwithin 20% for the spatially extended states and within 40% for the smaller\n^4He-trimer ground state.", "category": "physics_atom-ph" }, { "text": "The role of Coulomb anti-blockade in the photoassociation of long-range\n Rydberg molecules: We present a new mechanism contributing to the detection of photoassociated\nlong-range Rydberg molecules via pulsed-field ionization: ionic products,\ncreated by the decay of a long-range Rydberg molecule, modify the excitation\nspectrum of surrounding ground-state atoms and facilitate the excitation of\nfurther atoms into Rydberg states by the photoassociation light. Such an\nion-mediated excitation mechanism has been previously called \"Coulomb\nanti-blockade\". Pulsed-field ionisation typically doesn't discriminate between\nthe ionization of a long-range Rydberg molecule and an isolated Rydberg atom,\nand thus the number of atomic ions detected by this mechanism is not\nproportional to the number of long-range Rydberg molecules present in the probe\nvolume. By combining high-resolution UV and RF spectroscopy of a dense,\nultracold gas of cesium atoms, theoretical modeling of the molecular level\nstructures of long-range Rydberg molecules bound below nP_3/2 Rydberg states of\ncesium, and a rate model of the photoassociation and decay processes, we\nunambiguously identify the signatures of this detection mechanism in the\nphotoassociation of long-range Rydberg molecules bound below atomic asymptotes\nwith negative Stark shifts.", "category": "physics_atom-ph" }, { "text": "Coherent light transport in a cold Strontium cloud: We study light coherent transport in the weak localization regime using\nmagneto-optically cooled strontium atoms. The coherent backscattering cone is\nmeasured in the four polarization channels using light resonant with a J=0 to\nJ=1 transition of the Strontium atom. We find an enhancement factor close to 2\nin the helicity preserving channel, in agreement with theoretical predictions.\nThis observation confirms the effect of internal structure as the key mechanism\nfor the contrast reduction observed with an Rubidium cold cloud (see: Labeyrie\net al., PRL 83, 5266 (1999)). Experimental results are in good agreement with\nMonte-Carlo simulations taking into account geometry effects.", "category": "physics_atom-ph" }, { "text": "QED approach to valence-hole excitation in closed shell systems: An ab initio QED approach to treat a valence-hole excitation in closed shell\nsystems is developed in the framework of the two-time-Green function method.\nThe derivation considers a redefinition of the vacuum state and its excitation\nas a valence-hole pair. The proper two-time Green function, whose spectral\nrepresentation confirms the poles at valence-hole excitation energies is\nproposed. An contour integral formula which connects the energy corrections and\nthe Green function is also presented. First-order corrections to the\nvalence-hole excitation energy involving self-energy, vacuum polarization, and\none-photon-exchange terms are explicitly derived in the redefined vacuum\npicture. Reduction to the usual vacuum electron propagators is given that\nagrees in the Breit approximation with the many-body perturbation theory\nexpressions for the valence-hole excitation energy.", "category": "physics_atom-ph" }, { "text": "Radiative rates for E1, E2, M1, and M2 transitions in the Br-like ions\n Sr IV, Y V, Zr VI, Nb VII, and Mo VIII: Energies and lifetimes are reported for the lowest 375 levels of five Br-like\nions, namely Sr~IV, Y~V, Zr~VI, Nb~VII, and Mo~VIII, mostly belonging to the\n4s$^2$4p$^5$, 4s$^2$4p$^4$4$\\ell$, 4s4p$^6$, 4s$^2$4p$^4$5$\\ell$,\n4s$^2$4p$^3$4d$^2$, 4s4p$^5$4$\\ell$, and 4s4p$^5$5$\\ell$ configurations.\nExtensive configuration interaction has been included and the general-purpose\nrelativistic atomic structure package ({\\sc grasp}) has been adopted for the\ncalculations. Additionally, radiative rates are listed among these levels for\nall E1, E2, M1, and M2 transitions. From a comparison with the measurements,\nthe majority of our energy levels are assessed to be accurate to better than\n2\\%, although discrepancies between theory and experiment for a few are up to\n6\\%. An accuracy assessment of the calculated radiative rates (and lifetimes)\nis more difficult, because no prior results exist for these ions.", "category": "physics_atom-ph" }, { "text": "Electromagnetic Imaging with Atomic Magnetometers: A Novel Approach to\n Security and Surveillance: We describe our research programme on the use of atomic magnetometers to\ndetect conductive objects via electromagnetic induction. The extreme\nsensitivity of atomic magnetometers at low frequencies, up to seven orders of\nmagnitude higher than a coil-based system, permits deep penetration through\ndifferent media and barriers, and in various operative environments. This\neliminates the limitations usually associated with electromagnetic detection.", "category": "physics_atom-ph" }, { "text": "A new formulation of the relativistic many-body theory of electric\n dipole moments of closed shell atoms: The electric dipole moments of closed-shell atoms are sensitive to the parity\nand time-reversal violating phenomena in the nucleus. The nuclear Schiff moment\nis one such property, it arises from the parity and time reversal violating\nquark-quark interactions and the quark-chromo electric dipole moments. We\ncalculate the electric dipole moment of atomic $^{199}{\\rm Hg}$ arising from\nthe nuclear Schiff moment using the relativistic coupled-cluster theory. This\nis the most accurate calculation of the quantity to date. Our calculations in\ncombination with the experiment data provide important insights to the P and T\nviolating coupling constants at the elementary particle level. In addition, a\nnew limit on the tensor-pseudo tensor induced atomic EDM, calculated using the\nrelativistic coupled-cluster theory is also presented.", "category": "physics_atom-ph" }, { "text": "Suppression of reflection from the grid boundary in solving the\n time-dependent Schroedinger equation by split-step technique with fast\n Fourier transform: We present an approach to numerically solving the time-dependent Schroedinger\nequation and other parabolic equations by the split-step technique with fast\nFourier transform, which suppresses the backreflection of waves from the grid\nboundaries with any specified accuracy. Most importantly, all known methods\nwork well only for a narrow region of incident waves spectrum, and the proposed\nmethod provides absorption of any wave whose length is large enough in\ncomparison with the size of absorption region.", "category": "physics_atom-ph" }, { "text": "Relativistic corrections of order m\u03b1^6 to the two-center problem: Effective potentials of the relativistic m\\alpha^6 order correction for the\nground state of the Coulomb two-center problem are calculated. They can be used\nto evaluate the relativistic contribution of that order to the energies of\nhydrogen molecular ions or metastable states of the antiprotonic helium atom,\nwhere precision spectroscopic data are available. In our studies we use the\nvariational expansion based on randomly chosen exponents that permits to\nachieve high numerical accuracy.", "category": "physics_atom-ph" }, { "text": "Capture and isolation of highly-charged ions in a unitary Penning trap: We recently used a compact Penning trap to capture and isolate highly-charged\nions extracted from an electron beam ion trap (EBIT) at the National Institute\nof Standards and Technology (NIST). Isolated charge states of highly-stripped\nargon and neon ions with total charge $Q \\geq 10$, extracted at energies of up\nto $4\\times 10^3\\,Q$ eV, are captured in a trap with well depths of $\\,\\approx\n(4\\, {\\rm to}\\, 12)\\,Q$ eV. Here we discuss in detail the process to optimize\nvelocity-tuning, capture, and storage of highly-charged ions in a unitary\nPenning trap designed to provide easy radial access for atomic or laser beams\nin charge exchange or spectroscopic experiments, such as those of interest for\nproposed studies of one-electron ions in Rydberg states or optical transitions\nof metastable states in multiply-charged ions. Under near-optimal conditions,\nions captured and isolated in such rare-earth Penning traps can be\ncharacterized by an initial energy distribution that is $\\approx$ 60 times\nnarrower than typically found in an EBIT. This reduction in thermal energy is\nobtained passively, without the application of any active cooling scheme in the\nion-capture trap.", "category": "physics_atom-ph" }, { "text": "Formation of ultracold SrYb molecules in an optical lattice by\n photoassociation spectroscopy: theoretical prospects: State-of-the-art {\\em ab initio} techniques have been applied to compute the\npotential energy curves for the SrYb molecule in the Born-Oppenheimer\napproximation for the ground state and first fifteen excited singlet and\ntriplet states within the coupled-cluster framework. The leading long-range\ncoefficients describing the dispersion interactions at large interatomic\ndistances are also reported. The electric transition dipole moments have been\nobtained as the first residue of the polarization propagator computed with the\nlinear response coupled-cluster method restricted to single and double\nexcitations. Spin-orbit coupling matrix elements have been evaluated using the\nmultireference configuration interaction method restricted to single and double\nexcitations with a large active space. The electronic structure data was\nemployed to investigate the possibility of forming deeply bound ultracold SrYb\nmolecules in an optical lattice in a photoassociation experiment using\ncontinuous-wave lasers. Photoassociation near the intercombination line\ntransition of atomic strontium into the vibrational levels of the strongly\nspin-orbit mixed $b^3\\Sigma^+$, $a^3\\Pi$, $A^1\\Pi$, and $C^1\\Pi$ states with\nsubsequent efficient stabilization into the $v^{\\prime\\prime}=1$ vibrational\nlevel of the electronic ground state is proposed. Ground state SrYb molecules\ncan be accumulated by making use of collisional decay from $v^{\\prime\\prime}=1$\nto $v^{\\prime\\prime}=0$. Alternatively, photoassociation and stabilization to\n$v^{\\prime\\prime}=0$ can proceed via stimulated Raman adiabatic passage\nprovided that the trapping frequency of the optical lattice is large enough and\nphase coherence between the pulses can be maintained over at least tens of\nmicroseconds.", "category": "physics_atom-ph" }, { "text": "Two-Orders-of-Magnitude Improvement in the Total Spin Angular Momentum\n of 131Xe Nuclei Using Spin Exchange Optical Pumping: We report on hyperpolarization of quadrupolar (I=3/2) 131Xe via spin-exchange\noptical pumping. Observations of the 131Xe polarization dynamics show that the\neffective alkali-metal/131Xe spin-exchange cross-sections are large enough to\ncompete with 131Xe spin relaxation. 131Xe polarization up to 7.6 p/m 1.5\npercent was achieved in ca. 8.5EE20 spins--a ca. 100-fold improvement in the\ntotal spin angular momentum--enabling applications including measurement of\nspin-dependent neutron-131Xe s-wave scattering and sensitive searches for\ntime-reversal violation in neutron-131Xe interactions beyond the Standard\nModel.", "category": "physics_atom-ph" }, { "text": "Magnetic-field effect in high-order above-threshold ionization: We experimentally and theoretically investigate the influence of the magnetic\ncomponent of an electromagnetic field on high-order above-threshold ionization\nof xenon atoms driven by ultrashort femtosecond laser pulses. The nondipole\nshift of the electron momentum distribution along the light-propagation\ndirection for high energy electrons beyond the classical cutoff is found to be\nvastly different from that below the cutoff. A V-shape structure in the\nmomentum dependence of the nondipole shift above the cutoff is identified for\nthe first time. With the help of classical and quantum-orbit analysis, we show\nthat large-angle rescattering of the electrons strongly alters the partitioning\nof the photon momentum between electron and ion. The sensitivity of the\nobserved nondipole shift to the electronic structure of the target atom is\nconfirmed by three-dimensional time-dependent Schr\\\"odinger equation\nsimulations for different model potentials.", "category": "physics_atom-ph" }, { "text": "Connecting field and intensity correlations: the Siegert relation and\n how to test it: The Siegert relation relates the electric field and intensity correlations of\nlight, under given assumptions. After a brief history of intensity\ncorrelations, we give a derivation of the relation. Then we present an\nexperiment, which can be easily adapted for an undergraduate setup, and that\nallows measuring both field and intensity correlations at the same time, thus\nproviding a direct test of the Siegert relation. As a conclusion, we discuss\ntypical situations where the relation fails.", "category": "physics_atom-ph" }, { "text": "Suppression of Black-body Radiation Induced Zeeman Shifts in the Optical\n Clocks due to the Fine-structure Intramanifold Resonances: The roles of the fine-structure intramanifold resonances to the Zeeman shifts\ncaused by the blackbody radiation (BBRz shifts) in the optical clock\ntransitions are analyzed. The clock frequency measurement in the $^1S_0-^3P_0$\nclock transition of the singly charged aluminium ion (Al$^+$) has already been\nreached the $10^{-19}$ level at which the BBRz effect can be significant in\ndetermining the uncertainty. In view of this, we probe first the BBRz shift in\nthis transition rigorously and demonstrate the importance of the contributions\nfrom the intramanifold resonances explicitly. To carry out the analysis, we\ndetermine the dynamic magnetic dipole (M1) polarizabilities of the clock states\nover a wide range of angular frequencies by employing two variants of\nrelativistic many-body methods. This showed the BBRz shift is highly suppressed\ndue to blue-detuning of the BBR spectrum to the $^3P_0-^3P_1$ fine-structure\nintramanifold resonance in Al$^+$ and it fails to follow the usually assumed\nstatic M1 polarizability limit in the estimation of the BBRz shift. The\nresonance also leads to a reversal behavior of the temperature dependence and a\ncancellation in the shift. After learning this behavior, we extended our\nanalyses to other optical clocks and found that these shifts are of the order\nof micro-hertz leading to fractional shifts in the clock transitions at the\n$10^{-20}$ level or below.", "category": "physics_atom-ph" }, { "text": "Engineering atomic polarization with microwave-assisted optical pumping: Polarized atomic ensembles play a crucial role in precision measurements. We\ndemonstrate a novel method of creating atomic polarization in an alkali vapor\nin a continuous-wave regime. The method relies on a combination of optical\npumping by a laser beam and microwave transitions due to a cavity-enhanced\nmagnetic field. With this approach, atomic internal angular momentum can be\noriented along a static magnetic field at an arbitrary angle with respect to\nthe laser beam. Furthermore, the atomic polarization depends on the microwave\nparameters, which can be used for microwave-to-optical transduction and\nmicrowave-controlled nonlinear magneto-optical rotation.", "category": "physics_atom-ph" }, { "text": "Electric field dissociation of weakly bound molecular ions: We present a full quantal study on the dissociation of a weakly bound\nmolecular ion in the presence of an external time-dependent electric field. We\nfocus on the dissociation dynamics of a molecular ion in a Paul trap relevant\nfor atom-ion hybrid traps. Our results show that a weakly bound molecular ion\nsurvives in a Paul trap giving a theoretical ground to previous experimental\nfindings [A. Kr\\\"ukow et al. Phys. Rev. Lett. 116, 193201 (2016) and A.\nMohammadi et al. Phys. Rev. Research 3, 013196 (2021)]. In particular, we find\nthat weakly bound molecular ions are more likely to survive in traps with large\nRF frequency. Similarly, we show that applying an electric field ramp is an\nefficient method to state-selectively detect weakly bound molecular ions,\nanalogous to the well-known selective field ionization technique applied in\nRydberg atoms, that it may also be used to detect these species in atom-ion\nhybrid traps.", "category": "physics_atom-ph" }, { "text": "State-insensitive bichromatic optical trapping: We propose a scheme for state-insensitive trapping of neutral atoms by using\nlight with two independent wavelengths. In particular, we describe the use of\ntrapping and control lasers to minimize the variance of the potential\nexperienced by a trapped Rb atom in ground and excited states. We present\ncalculated values of wavelength pairs for which the 5s and 5p_{3/2} levels have\nthe same ac Stark shifts in the presence of two laser fields.", "category": "physics_atom-ph" }, { "text": "A marginally stable optical resonator for enhanced atom interferometry: We propose a marginally stable optical resonator suitable for atom\ninterferometry. The resonator geometry is based on two flat mirrors at the\nfocal planes of a lens that produces the large beam waist required to\ncoherently manipulate cold atomic ensembles. Optical gains of about 100 are\nachievable using optics with part-per-thousand losses. The resulting power\nbuild-up will allow for enhanced coherent manipulation of the atomic\nwavepackets such as large separation beamsplitters. We study the effect of\nlongitudinal misalignments and assess the robustness of the resonator in terms\nof intensity and phase profiles of the intra-cavity field. We also study how to\nimplement atom interferometry based on Large Momentum Transfer Bragg\ndiffraction in such a cavity.", "category": "physics_atom-ph" }, { "text": "Measurement of the scalar polarizability within the 5P1/2-6S1/2, 410 nm\n transition in atomic indium: We have completed a new measurement of the Stark shift in 115In within the\n410 nm 5P1/2- 6S1/2 transition. We measure the Stark shift constant to be kS= -\n122.92(33)kHz/(kV/cm)^2, corresponding to a difference in the 6S1/2 and 5P1/2\nstate polarizabilities, \\Delta\\alpha_0, of 1000.2 (2.7) a.u.(in atomic units).\nThis result is a factor of 30 more precise than previous measurements and is in\nexcellent agreement with a new theoretical value based on an ab initio\ncalculation of the wave functions in this three-valence-electron system. The\nmeasurement was performed in an indium atomic beam apparatus, used a GaN laser\ndiode system, and exploited an FM spectroscopy technique to extract laser\ntransmission spectra under conditions where our interaction region optical\ndepth was typically less than 10^-3.", "category": "physics_atom-ph" }, { "text": "Lattice models with long-range and number-non-conserving interactions\n with Zeeman excitations of ultracold magnetic atoms: We show that Zeeman excitations of ultracold Dy atoms trapped in an optical\nlattice can be used to engineer extended Hubbard models with tunable inter-site\nand particle number-non-conserving interactions. We show that the ratio of the\nhopping amplitude and inter-site interactions in these lattice models can be\ntuned in a wide range by transferring the atoms to different Zeeman states. We\npropose to use the resulting controllable models for the study of the effects\nof direct particle interactions and particle number-non-conserving terms on\nAnderson localization.", "category": "physics_atom-ph" }, { "text": "Adiabatic radio frequency potentials for the coherent manipulation of\n matter waves: Adiabatic dressed state potentials are created when magnetic sub-states of\ntrapped atoms are coupled by a radio frequency field. We discuss their\ntheoretical foundations and point out fundamental advantages over potentials\npurely based on static fields. The enhanced flexibility enables one to\nimplement numerous novel configurations, including double wells, Mach-Zehnder\nand Sagnac interferometers which even allows for internal state-dependent atom\nmanipulation. These can be realized using simple and highly integrated wire\ngeometries on atom chips.", "category": "physics_atom-ph" }, { "text": "Efficient algorithm for many-electron angular momentum and spin\n diagonalization on atomic subshells: We devise an efficient algorithm for the symbolic calculation of irreducible\nangular momentum and spin (LS) eigenspaces within the $n$-fold antisymmetrized\ntensor product $\\wedge^n V_u$, where $n$ is the number of electrons and $u =\n\\mathrm{s}, \\mathrm{p}, \\mathrm{d},\\dots$ denotes the atomic subshell. This is\nan essential step for dimension reduction in configuration-interaction (CI)\nmethods applied to atomic many-electron quantum systems. The algorithm relies\non the observation that each $L_z$ eigenstate with maximal eigenvalue is also\nan $\\boldsymbol{L}^2$ eigenstate (equivalently for $S_z$ and\n$\\boldsymbol{S}^2$), as well as the traversal of LS eigenstates using the\nlowering operators $L_-$ and $S_-$. Iterative application to the remaining\nstates in $\\wedge^n V_u$ leads to an implicit simultaneous diagonalization. A\ndetailed complexity analysis for fixed $n$ and increasing subshell number $u$\nyields run time $\\mathcal{O}(u^{3n-2})$. A symbolic computer algebra\nimplementation is available online.", "category": "physics_atom-ph" }, { "text": "Theoretical Atto-nano Physics: Two emerging areas of research, attosecond and nanoscale physics, have\nrecently started to merge. Attosecond physics deals with phenomena occurring\nwhen ultrashort laser pulses, with duration on the femto- and sub-femtosecond\ntime scales, interact with atoms, molecules or solids. The laser-induced\nelectron dynamics occurs natively on a timescale down to a few hundred or even\ntens of attoseconds (1 attosecond=1 as=10$^{-18}$ s), which is of the order of\nthe optical field cycle. For comparison, the revolution of an electron on a\n$1s$ orbital of a hydrogen atom is $\\sim152$ as. On the other hand, the second\ntopic involves the manipulation and engineering of mesoscopic systems, such as\nsolids, metals, and dielectrics, with nanometric precision. Although\nnano-engineering is a vast and well-established research field on its own, the\ncombination with intense laser physics is relatively recent. We present a\ncomprehensive theoretical overview of the tools to tackle and understand the\nphysics that takes place when short and intense laser pulses interact with\nnanosystems, such as metallic and dielectric nanostructures. In particular, we\nelucidate how the spatially inhomogeneous laser-induced fields at a nanometer\nscale modify the laser-driven electron dynamics. Consequently, this has an\nimportant impact on pivotal processes such as above-threshold ionization and\nhigh-order harmonic generation. The deep understanding of the coupled dynamics\nbetween these spatially inhomogeneous fields and matter configures a promising\nway to new avenues of research and applications. Thanks to the maturity that\nattosecond physics has reached, together with the tremendous advance in\nmaterial engineering and manipulation techniques, the age of atto-nano physics\nhas begun, but it is still in an incipient stage.", "category": "physics_atom-ph" }, { "text": "Detecting the Harmonic Vibrations of Micro Amplitudes and Low\n Frequencies with Atomic Mach-Zehnder Interferometer: We study the effects of atomic beams harmonic vibrations of micro amplitudes\nand low frequencies on the mean atomic numbers of the detectors in atomic\nMach-Zehnder interferometer, where the two atomic beams are in the same wave\nsurface and have the same phases. We propose a vibrant factor F to\nquantitatively describe the effects of atomic beams vibrations. It shows that:\n(i)the vibrant factor F depends on the relative vibrant displacements and the\ninitial phases rather than the absolute amplitudes, (ii)the factor F increases\nwith the increase of the initial phases, and (iii)the frequencies can be\nderived from equal time interval measurement of the mean atomic numbers. These\nresults imply that it is possible to detect the vibrations of micro amplitudes\nand low frequencies by measuring the variations of mean atomic numbers.", "category": "physics_atom-ph" }, { "text": "Generation of high-purity, low-temperature samples of $^{39}$K for\n applications in metrology: We present an all optical technique to prepare a sample of $^{39}$K in a\nmagnetically-insensitive state with 95\\% purity while maintaining a temperature\nof 6 $\\mu$K. This versatile preparation scheme is particularly well suited to\nperforming matter-wave interferometry with species exhibiting closely-separated\nhyperfine levels, such as the isotopes of lithium and potassium, and opens new\npossibilities for metrology with these atoms. We demonstrate the feasibility of\nsuch measurements by realizing an atomic gravimeter and a Ramsey-type\nspectrometer, both of which exhibit a state-of-the-art sensitivity for cold\npotassium.", "category": "physics_atom-ph" }, { "text": "Diagrammatic approach to coherent backscattering of laser light by cold\n atoms: Double scattering revisited: We present a diagrammatic derivation of the coherent backscattering spectrum\nfrom two two-level atoms using the pump-probe approach, wherein the multiple\nscattering signal is deduced from single-atom responses, and provide a physical\ninterpretation of the single-atom building blocks.", "category": "physics_atom-ph" }, { "text": "Ground state sideband cooling of an ion in a room temperature trap with\n a sub-Hertz heating rate: We demonstrate resolved sideband laser cooling of a single 40Ca+ ion in a\nmacroscopic linear radio frequency trap with a radial diagonal electrode\nspacing of 7 mm and an rf drive frequency of just 3.7 MHz. For an oscillation\nfrequency of 585 kHz along the rf-field-free axis, a ground state population of\n99+-1% has been achieved, corresponding to a temperature of only 6 microkelvin.\nFor several oscillation frequencies in the range 285 - 585 kHz, heating rates\nbelow one motional quantum per second have been measured at room temperature.\nThe lowest measured heating power is about an order of magnitude lower than\nreported previously in room temperature, as well as cryogenically cooled traps.", "category": "physics_atom-ph" }, { "text": "Attosecond electron thermalization by laser-driven electron recollision\n in atoms: Nonsequential multiple ionization of atoms in intense laser fields is\ninitiated by a recollision between an electron, freed by tunneling, and its\nparent ion. Following recollision, the initial electron shares its energy with\nseveral bound electrons. We use a classical model based on rapid electron\nthermalization to interpret recent experiments. For neon, good agreement with\nthe available data is obtained with an upper bound of 460 attoseconds for the\nthermalization time.", "category": "physics_atom-ph" }, { "text": "New standard magnetic field values determined by cancellations of\n ${}^{85}\\text{Rb}$ and ${}^{87}\\text{Rb}$ atomic vapors $5{}^2{S}_{1/2}\n \\rightarrow 6{}^2{P}_{1/2,~3/2}$ transitions: In this article, we study the theoretical behaviour of all the possible\nhyperfine transitions ($\\pi$, $\\sigma^+$ and $\\sigma^-$) between the $5S$ and\n$6P$ states of ${}^{87}\\text{Rb}$ and ${}^{85}\\text{Rb}$ atomic vapors under\nthe influence of an external magnetic field $B$. We show that, for specific\ntransitions, we obtain one or several $B$-values for which the transition\nintensity is cancelled. The precision of these values is limited to the\nuncertainty of the physical quantities that are involved in the problem, thus\nmeasuring precisely the $B$-values for the cancellations could be a way to\ndetermine these quantities more precisely. In the simplest cases involving\n$2\\times 2$ hamiltonians, we give eigenvectors, eigenvalues and analytical\nformulas to determine the transition cancellation. By checking accuracy between\nformulas and numerical simulations, we conclude that it is possible to use the\nlatter in order to determine all the cancellations even in the most complicated\ncases.", "category": "physics_atom-ph" }, { "text": "Multi-loop atomic Sagnac interferometry: The sensitivity of light and matter-wave interferometers to rotations is\nbased on the Sagnac effect and increases with the area enclosed by the\ninterferometer. In the case of light, the latter can be enlarged by forming\nmultiple fibre loops, whereas the equivalent for matter-wave interferometers\nremains an experimental challenge. We present a concept for a multi-loop atom\ninterferometer with a scalable area formed by light pulses. Our method will\noffer sensitivities as high as $2\\cdot10^{-11}$ rad/s at 1 s in combination\nwith the respective long-term stability as required for Earth rotation\nmonitoring.", "category": "physics_atom-ph" }, { "text": "Spin effects probed by Rayleigh X-ray scattering off hydrogenic ions: We study the polarization characteristics of x-ray photons scattered by\nhydrogenic atoms, based on the Dirac equation and second-order perturbation\ntheory. The relativistic states used in calculations are obtained using the\nfinite basis set method and expressed in terms of B-splines and B-polynomials.\nWe derive general analytical expressions for the polarization-dependent total\ncross sections, which are applicable to any atom and ion, and evaluate them\nseparately for linear and circular polarization of photons. In particular,\ndetailed calculations are performed for the integrated Stokes parameters of the\nscattered light for hydrogen as well as hydrogenlike neon and argon. Analyzing\nsuch integrated Stokes parameters, special attention is given to the\nelectron-photon spin-spin interaction, which mostly stems from the\nmagnetic-dipole contribution of the electron-photon interaction. Subsequently,\nwe find an energy window for the selected targets in which such spin-spin\ninteractions can be probed.", "category": "physics_atom-ph" }, { "text": "Ultracold ion-atom experiments: cooling, chemistry, and quantum effects: Experimental setups that study laser-cooled ions immersed in baths of\nultracold atoms merge the two exciting and well-established fields of quantum\ngases and trapped ions. These experiments benefit both from the exquisite\nread-out and control of the few-body ion systems as well as the many-body\naspects, tunable interactions, and ultracold temperatures of the atoms.\nHowever, combining the two leads to challenges both in the experimental design\nand the physics that can be studied. Nevertheless, these systems have provided\ninsights into ion-atom collisions, buffer gas cooling of ions and quantum\neffects in the ion-atom interaction. This makes them promising candidates for\nultracold quantum chemistry studies, creation of cold molecular ions for\nspectroscopy and precision measurements, and as test beds for quantum\nsimulation of charged impurity physics. In this review we aim to provide an\nexperimental account of recent progress and introduce the experimental setup\nand techniques that enabled the observation of quantum effects.", "category": "physics_atom-ph" }, { "text": "MCDHF-CI calculations for Hg and Cd with estimates for unknown clock\n transition frequencies: By use of the \\textsc{grasp2018} package we perform Multiconfiguration\nDirac-Hartree-Fock (MCDHF) calculations with configuration interaction (CI) for\nthe $^{1}S_{0}$ and $^{3}P_{0,1}^o$ levels in neutral cadmium and mercury. By\nsupplying the resultant atomic state functions to the \\textsc{ris4} program, we\nevaluate the mass and field shift parameters for the $^{1}S_{0}-\\,^{3}P_{0}^o$\n(clock) and $^{1}S_{0}-\\,^{3}P_{1}^o$ (intercombination) lines. We make revised\nestimates of the nuclear charge parameters $\\lambda^{A,A'}$ and differences in\nmean-square charge radii $\\delta\\langle r^2\\rangle^{A,A'}$ for both elements\nand point out a discrepancy with tabulated data for Cd. In constructing a King\nplot with the Hg lines we examine the second-order hyperfine interaction for\nthe $^{3}P_{0,1}^o$ levels. Isotope shifts for the clock transition have been\nestimated from which we predict the unknown clock line frequencies in the\nbosonic Hg isotopes and all the naturally occurring isotopes of Cd.", "category": "physics_atom-ph" }, { "text": "Exact exchange potential evaluated solely from occupied Kohn-Sham and\n Hartree-Fock solutions: The reported new algorithm determines the exact exchange potential v_x in a\niterative way using energy and orbital shifts (ES, OS) obtained - with\nfinite-difference formulas - from the solutions (occupied orbitals and their\nenergies) of the Hartree-Fock-like equation and the Kohn-Sham-like equation,\nthe former used for the initial approximation to v_x and the latter - for\nincrements of ES and OS due to subsequent changes of v_x. Thus, solution of the\ndifferential equations for OS, used by Kummel and Perdew (KP) [Phys. Rev. Lett.\n90, 043004 (2003)], is avoided. The iterated exchange potential, expressed in\nterms of ES and OS, is improved by modifying ES at odd iteration steps and OS\nat even steps. The modification formulas are related to the OEP equation\n(satisfied at convergence) written as the condition of vanishing density shift\n(DS) - they are obtained, respectively, by enforcing its satisfaction through\ncorrections to approximate OS and by determining optimal ES that minimize the\nDS norm. The proposed method, successfully tested for several closed-(sub)shell\natoms, from Be to Kr, within the DFT exchange-only approximation, proves highly\nefficient. The calculations using pseudospectral method for representing\norbitals give iterative sequences of approximate exchange potentials (starting\nwith the Krieger-Li-Iafrate approximation) that rapidly approach the exact v_x\nso that, for Ne, Ar and Zn, the corresponding DS norm becomes less than 10^{-6}\nafter 13, 13 and 9 iteration steps for a given electron density. In\nself-consistent density calculations, orbital energies of 10^{-4} Hartree\naccuracy are obtained for these atoms after, respectively, 9, 12 and 12 density\niteration steps, each involving just 2 steps of v_x iteration, while the\naccuracy limit of 10^{-6}--10^{-7} Hartree is reached after 20 density\niterations.", "category": "physics_atom-ph" }, { "text": "Improved all-order results for the one-loop QED correction to the\n hyperfine structure in light H-like atoms: A calculation of the one-loop self-energy and vacuum-polarization corrections\nto the hyperfine splitting of the 1s and 2s states in light H-like ions is\ncarried out to all orders in the parameter Z \\alpha. Using the known values for\nthe Z \\alpha-expansion coefficients, the numerical data obtained are\nextrapolated from Z=5 and higher to Z=0, 1, and 2, with the resulting accuracy\nbeing significantly better than in previous evaluations. Our calculation shifts\nthe theoretical value of the normalized difference of the 1s and 2s\nhyperfine-structure intervals in ^3He^+ by 0.056 kHz and improves its accuracy.", "category": "physics_atom-ph" }, { "text": "Evaluation of the screened vacuum-polarization corrections to the\n hyperfine splitting of Li-like bismuth: The rigorous calculation of the vacuum-polarization screening corrections to\nthe hyperfine splitting in Li-like bismuth is presented. The two-electron\ndiagrams with electric and magnetic vacuum-polarization loops are evaluated to\nall orders in alpha*Z, including the Wichmann-Kroll contributions. This\nimproves the accuracy of the theoretical prediction for the specific difference\nof the hyperfine splitting values of H- and Li-like bismuth.", "category": "physics_atom-ph" }, { "text": "Measurement of the trapping lifetime close to a cold metallic surface on\n a cryogenic atom-chip: We have measured the trapping lifetime of magnetically trapped atoms in a\ncryogenic atom-chip experiment. An ultracold atomic cloud is kept at a fixed\ndistance from a thin gold layer deposited on top of a superconducting trapping\nwire. The lifetime is studied as a function of the distances to the surface and\nto the wire. Different regimes are observed, where loss rate is determined\neither by the technical current noise in the wire or the Johnson-Nyquist noise\nin the metallic gold layer, in good agreement with theoretical predictions. Far\nfrom the surface, we observe exceptionally long trapping times for an\natom-chip, in the 10-minutes range.", "category": "physics_atom-ph" }, { "text": "Relativistic calculations of the chemical properties of the superheavy\n element with $Z=119$ and its homologues: Relativistic calculations of the electronic structure of the superheavy\nelement of the eighth period $-$ eka-francium ($Z=119$) and its homologues,\nwhich form the group of alkali metals, are performed in the framework of the\nconfiguration-interaction method and many-body perturbation theory using the\nbasis of the Dirac-Fock-Sturm orbitals (DFS). The obtained values of the\nionization potentials, electron affinities, and root-mean-square radii are\ncompared with the corresponding values calculated within the non-relativistic\napproximation. A comparison with the available experimental data and the\nresults of previous theoretical calculations is given as well. The analysis of\nthe obtained results indicates a significant influence of the relativistic\neffects for the francium and eka-francium atoms, which leads to a violation of\nthe monotonic behaviour of the listed above chemical properties as a function\nof the alkaline-element atomic number. In addition, the quantum electrodynamics\ncorrections to the ionization potentials are evaluated by employing the model\nLamb-shift operator (QEDMOD).", "category": "physics_atom-ph" }, { "text": "Narrow bandwidth interference filter-stabilized diode laser systems for\n the manipulation of neutral atoms: We present and investigate different external cavity diode laser (ECDL)\nconfigurations for the manipulation of neutrals atoms, wavelength-stabilized by\na narrow-band high transmission interference filter. A novel diode laser,\nproviding high output power of more than 1 W, with a linewidth of less than 200\nkHz, based on a self-seeded tapered amplifier chip has been developed.\nAdditionally, we compare the optical and spectral properties of two laser\nsystems based on common laser diodes, differing in their coating, as well as\none, based on a distributed-feedback (DFB) diode. The linear cavity setup in\nall these systems combines a robust and compact design with a high wavelength\ntunability and an improved stability of the optical feedback compared to diode\nlaser setups using diffraction gratings for wavelength discrimination.", "category": "physics_atom-ph" }, { "text": "Relativistic calculations of $C_6$ and $C_8$ coefficients for strontium\n dimers: The electric dipole and quadrupole polarizabilities of the $5s5p~^3\\!P_1^o$\nstate and the $C_6$ and $C_8$ coefficients for the $^1\\!S_0 +\\, ^1\\!S_0$ and\n$^1\\!S_0 +\\, ^3\\!P_1^o$ dimers of strontium are calculated using a\nhigh-precision relativistic approach that combines configuration interaction\nand linearized coupled-cluster methods. Our recommended values of the long\nrange dispersion coefficients for the $0_u$ and $1_u$ energy levels are\n$C_6(0_u)=3771(32)$ a.u. and $C_6(1_u)= 4001(33)$ a.u., respectively. They are\nin good agreement with recent results from experimental photoassociation data.\nWe also calculate $C_8$ coefficients for Sr dimers, which are needed for\nprecise determination of long-range interaction potential. We confirm the\nexperimental value for the magic wavelength, where the Stark shift on the\n$^1\\!S_0$-$^3\\!P_1^o$ transition vanishes. The accuracy of calculations is\nanalyzed and uncertainties are assigned to all quantities reported in this\nwork.", "category": "physics_atom-ph" }, { "text": "Two-Dimensional Photonic Crystals for Engineering Atom-Light\n Interactions: We present a two-dimensional (2D) photonic crystal system for interacting\nwith cold cesium (Cs) atoms. The band structures of the 2D photonic crystals\nare predicted to produce unconventional atom-light interaction behaviors,\nincluding anisotropic emission, suppressed spontaneous decay and photon\nmediated atom-atom interactions controlled by the position of the atomic array\nrelative to the photonic crystal. An optical conveyor technique is presented\nfor continuously loading atoms into the desired trapping positions with optimal\ncoupling to the photonic crystal. The device configuration also enables\napplication of optical tweezers for controlled placement of atoms. Devices can\nbe fabricated reliably from a 200nm silicon nitride device layer using a\nlithography-based process, producing predicted optical properties in\ntransmission and reflection measurements. These 2D photonic crystal devices can\nbe readily deployed to experiments for many-body physics with neutral atoms,\nand engineering of exotic quantum matter.", "category": "physics_atom-ph" }, { "text": "Impact of overlapping resonances on magnetoassociation of cold molecules\n in tight traps: Overlapping Feshbach resonances are commonly observed in experiments with\nultracold atoms and can influence the molecule production process. We derive an\neffective approach to describe magnetoassociation in an external trap in the\npresence of multiple overlapping resonances. We study how the strength and\nshape of the trap affects the energy level structure and demonstrate the\nexistence of a regime in which the conventional two-channel Landau-Zener\ndescription of the molecule production process breaks down.", "category": "physics_atom-ph" }, { "text": "Gaussian-basis many-body theory calculations of positron binding to\n negative ions and atoms: Positron binding energies in the negative ions H$^-$, F$^-$, Cl$^-$ and\nBr$^-$, and the closed-shell atoms Be, Mg, Zn and Ca, are calculated via a\nmany-body theory approach developed by the authors [J.~Hofierka \\emph{et al.}\nNature~{\\bf 608}, 688-693 (2022)]. Specifically, the Dyson equation is solved\nusing a Gaussian basis, with the positron self energy constructed from three\ninfinite classes of diagrams that account for the strong positron-atom\ncorrelations that characterise the system including the positron-induced\npolarization of the electron cloud, screening of the electron-positron Coulomb\ninteraction, virtual-positronium formation and electron-hole and positron-hole\ninteractions. For the negative ions, binding occurs at the static level of\ntheory, and the correlations are found to enhance the binding energies by\n$\\sim$25--50\\%, yielding results in good agreement with ($\\lesssim$5\\% larger\nthan) calculations from a number of distinct methods. For the atoms, for which\nbinding is enabled exclusively by correlations, most notably virtual-Ps\nformation, the binding energies are found to be of similar order to (but\n$\\sim$10--30\\% larger than) relativistic coupled-cluster calculations of [C.\nHarabati, V.~A.~Dzuba and V.~V. Flambaum, Phys.~Rev.~A {\\bf 89}, 022517\n(2014)], both of which are systematically larger than stochastic variational\ncalculations of [M.~Bromley and J.~Mitroy, Phys.~Rev.~A {\\bf 73} (2005);\nJ.~Mitroy, J.~At.~Mol.~Sci.~{\\bf 1}, 275 (2010)].", "category": "physics_atom-ph" }, { "text": "Vacuum Characterization of a Compact Room-temperature Trapped Ion System: We present the design and vacuum performance of a compact room-temperature\ntrapped ion system for quantum computing, consisting of a ultra-high vacuum\n(UHV) package, a micro-fabricated surface trap and a small form-factor ion\npump. The system is designed to maximize mechanical stability and robustness by\nminimizing the system size and weight. The internal volume of the UHV package\nis only 2 cm$^3$, a significant reduction in comparison with conventional\nvacuum chambers used in trapped ion experiments. We demonstrate trapping of\n$^{174}$Yb$^+$ ions in this system and characterize the vacuum level in the UHV\npackage by monitoring both the rates of ion hopping in a double-well potential\nand ion chain reordering events. The calculated pressure in this vacuum package\nis about 1.5e-11 Torr, which is sufficient for the majority of current trapped\nion experiments.", "category": "physics_atom-ph" }, { "text": "Many-electron character of two-photon above-threshold ionization of Ar: The absolute generalized cross sections and angular distribution parameters\nof photoelectrons for the two-photon above threshold $3p$-ionization of Ar were\ncalculated in the exciting photon energy range from 15.76 to 36 eV. The\ncorrelation function technique developed earlier was extended for the case when\nan intermediate-state function is of a continuum-type. We show that two-photon\nionization of Ar near the $3p^{4}$ threshold to a large extent is determined by\nthe $(3p\\dashrightarrow\\varepsilon d)^{2}$ two-photon absorption via the giant\nresonance. This many-electron correlation causes (i) an increase of the\nphotoionization cross sections by more than a factor of 3; (ii) the appearance\nof resonances in the exciting-photon energy range of the doubly-excited states.\nThe predictions are supported by a good agreement between length and velocity\nresults obtained after taking into account of the higher-order perturbation\ntheory corrections.", "category": "physics_atom-ph" }, { "text": "Giant dipole oscillations and ionization of heavy atoms by intense\n electromagnetic fields: Binding energy of heavy atoms is estimated by means of the Thomas-Fermi\nmodel, giant dipole oscillation are highlighted and ionization is discussed.", "category": "physics_atom-ph" }, { "text": "Pump-probe studies of resonantly saturated selective reflection from\n high-density rubidium vapor: Nonlinear selective reflection from the interface YAG window-high density\nrubidium vapor in the high-temperature cell is studied at the transition\n5S$_{1/2}$-5P$_{3/2}$. In the experiment tunable pump and probe lasers are\nused. The selective reflection spectra for the laser probe beam are\ninvestigated at four different rubidium atomic densities and five different\npump beam intensities. The estimated dipole-dipole interaction-induced line\nbroadening varies from $13.2$ to $39.6$ GHz, the measured pumped intensities\nchange from $1.2$ to $8.8$ kW$\\cdot$cm$^{-2}$. Growth of the pump intensity\ncauses reduction of the magnitude and the width of the recorded selective\nreflection resonance. We suggest developing all-optical modulators on the basis\nof nonlinear selective reflection.", "category": "physics_atom-ph" }, { "text": "Molecular spectroscopy for ground-state transfer of ultracold RbCs\n molecules: We perform one- and two-photon high resolution spectroscopy on ultracold\nsamples of RbCs Feshbach molecules with the aim to identify a suitable route\nfor efficient ground-state transfer in the quantum-gas regime to produce\nquantum gases of dipolar RbCs ground-state molecules. One-photon loss\nspectroscopy allows us to probe deeply bound rovibrational levels of the mixed\nexcited (A1{\\Sigma}+ - b3{\\Pi}0) 0+ molecular states. Two-photon dark state\nspectroscopy connects the initial Feshbach state to the rovibronic ground\nstate. We determine the binding energy of the lowest rovibrational level\n|v\"=0,J\"=0> of the X1{\\Sigma}+ ground state to be DX 0 = 3811.5755(16) 1/cm, a\n300-fold improvement in accuracy with respect to previous data. We are now in\nthe position to perform stimulated two-photon Raman transfer to the rovibronic\nground state.", "category": "physics_atom-ph" }, { "text": "Inner-shell excitation of open-shell atoms: A spin-dependent localized\n Hartree-Fock density-functional calculation: The spin-dependent localized Hartree-Fock (SLHF) density-functional approach\nis extended to the treatment of the inner-shell excited-state calculation of\nopen-shell atomic systems. In this approach, the electron spin-orbitals in an\nelectronic configuration are obtained by solving Kohn-Sham (KS) equation with\nSLHF exchange potential and the Slater's diagonal sum rule is used to evaluate\nthe multiplet energy of an inner-shell excited state from the\nsingle-Slater-determinant energies of the electronic configurations involved.\nThis approach together with the correlation potentials and energy functionals\nproposed by Perdew and Wang's (PW) or Lee, Yang, and Parr's (LYP) have been\nused to calculate the total and excitation energies of inner-shell excited\nstates of open-shell atomic systems: Li, B, Ne^+, Ne^{2+}, Ne^{3+}, and Na. The\nresults with the PW and LYP energy functionals are in overall good agreement\nwith each other and also with available experimental and other ab initio\ntheoretical data. Some new results for highly excited inner-shell states are\npresented.", "category": "physics_atom-ph" }, { "text": "Loading of a large Yb MOT on the $^1$S$_0$-$^1$P$_1$ transition: We present an experimental setup to laser cool and trap a large number of\nYtterbium atoms. Our design uses an oven with an array of microtubes for\nefficient collimation of the atomic beam and we implement a magneto-optical\ntrap of $^{174}$Yb on the $^1$S$_0$-$^1$P$_1$ transition at 399nm. Despite the\nabsence of a Zeeman slower, we are able to trap up to $N = 10^9$ atoms. We\nprecisely characterize our atomic beam, the loading rate of the magneto-optical\ntrap and several loss mechanisms relevant for trapping a large number of atoms.", "category": "physics_atom-ph" }, { "text": "Full two-electron calculations of antiproton collisions with molecular\n hydrogen: Total cross sections for single ionization and excitation of molecular\nhydrogen by antiproton impact are presented over a wide range of impact energy\nfrom 1 keV to 6.5 MeV. A nonpertubative time-dependent close-coupling method is\napplied to fully treat the correlated dynamics of the electrons. Good agreement\nis obtained between the present calculations and experimental measurements of\nsingle-ionization cross sections at high energies, whereas some discrepancies\nwith the experiment are found around the maximum. The importance of the\nmolecular geometry and a full two-electron description is demonstrated. The\npresent findings provide benchmark results which might be useful for the\ndevelopment of molecular models.", "category": "physics_atom-ph" }, { "text": "New atomic data for Ge XX: We have performed large-scale configuration interaction (CI) calculations\nusing CIV3for the lowest (in energy) 155 fine-structure levels of aluminum-like\ngermanium ion. We have calculated the energy levels, lifetimes, oscillator\nstrengths, and transition probabilities for the electric-dipole allowed and\nintercombination transitions among the levels of ground state3s23p(2P)and\nhigher energy levels of states3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2,3p3d2,\n3d3,3s2(4s, 4p, 4d, 4f) ofGe XX in the LSJ coupling scheme.The present results\ninclude relativistic effects through the Breit-Pauli operator. In order to keep\nour calculated energy splittings as close as possible to the experimental and\ntheoretical results complied by NIST, we attempt to correct the inaccuracies in\nthe CI coefficients in the wavefunctions, which would lead to inaccuracies in\ntransition probabilities, by applying a \"fine-tuning\" technique. Fine-tuning of\nthe ab initio energies was donethrough adjusting, by a small amount, some\ndiagonal elements of the Hamiltonian matrix.Comparisons are made with other\navailable experimental and theoretical results and the accuracy of the present\nresults is assessed.", "category": "physics_atom-ph" }, { "text": "Fast Ion Surface Energy Loss and Straggling in the Surface Wake Fields: We have measured the stopping powers and straggling of fast, highly ionized\natoms passing through thin bilayer targets made up of metals and insulators. We\nwere surprised to find that the energy losses as well as the straggling depend\non the ordering of the target and have small but significantly different values\non bilayer reversal. We ascribe this newly found difference in energy loss to\nthe surface energy loss field effect due to the differing surface wake fields\nas the beam exits the target in the two cases. This finding is validated with\nexperiments using several different projectiles, velocities, and bilayer\ntargets. Both partners of the diatomic molecular ions also display similar\nresults. A comparison of the energy loss results with those of previous\ntheoretical predictions for the surface wake potential for fast ions in solids\nsupports the existence of a self-wake.", "category": "physics_atom-ph" }, { "text": "Trapping ultracold gases near cryogenic materials with rapid\n reconfigurability: We demonstrate a novel atom chip trapping system that allows the placement\nand high-resolution imaging of ultracold atoms within microns from any <100\num-thin, UHV-compatible material, while also allowing sample exchange with\nminimal experimental downtime. The sample is not connected to the atom chip,\nallowing rapid exchange without perturbing the atom chip or laser cooling\napparatus. Exchange of the sample and retrapping of atoms has been performed\nwithin a week turnaround, limited only by chamber baking. Moreover, the\ndecoupling of sample and atom chip provides the ability to independently tune\nthe sample temperature and its position with respect to the trapped ultracold\ngas, which itself may remain in the focus of a high-resolution imaging system.\nAs a first demonstration of this new system, we have confined a 700-nK cloud of\n8x10^4 87Rb atoms within 100 um of a gold-mirrored 100-um-thick silicon\nsubstrate. The substrate was cooled to 35 K without use of a heat shield, while\nthe atom chip, 120 um away, remained at room temperature. Atoms may be imaged\nand retrapped every 16 s, allowing rapid data collection.", "category": "physics_atom-ph" }, { "text": "Non-dipole recollision-gated double ionization and observable effects: Using a three-dimensional semiclassical model, we study double ionization for\nstrongly-driven He fully accounting for magnetic field effects. For linearly\nand slightly elliptically polarized laser fields, we show that recollisions and\nthe magnetic field combined act as a gate. This gate favors more transverse -\nwith respect to the electric field - initial momenta of the tunneling electron\nthat are opposite to the propagation direction of the laser field. In the\nabsence of non-dipole effects, the transverse initial momentum is symmetric\nwith respect to zero. We find that this asymmetry in the transverse initial\nmomentum gives rise to an asymmetry in a double ionization observable. Finally,\nwe show that this asymmetry in the transverse initial momentum of the tunneling\nelectron accounts for a recently-reported unexpectedly large average sum of the\nelectron momenta parallel to the propagation direction of the laser field.", "category": "physics_atom-ph" }, { "text": "Experimental fingerprint of the electron's longitudinal momentum at the\n tunnel exit in strong field ionization: We present experimental data on the strong field tunnel ionization of argon\nin a counter-rotating two-color (CRTC) laser field. We find that the initial\nmomentum component along the tunneling direction changes sign comparing the\nrising and the falling edge of the CRTC field. If the initial momentum at the\ntunnel exit points in the direction of the ion at the instant of tunneling,\nthis manifests as an enhanced Coulomb interaction of the outgoing electron with\nits parent ion. Our conclusions are in accordance with predictions based on\nstrong field approximation.", "category": "physics_atom-ph" }, { "text": "High-precision calculations of van der Waals coefficients for\n heteronuclear alkali-metal dimers: Van der Waals coefficients for the heteronuclear alkali-metal dimers of Li,\nNa, K, Rb, Cs, and Fr are calculated using relativistic ab initio methods\naugmented by high-precision experimental data. We argue that the uncertainties\nin the coefficients are unlikely to exceed about 1%.", "category": "physics_atom-ph" }, { "text": "Electronic Quantum Confinement in Cylindrical Potential Well: The effects of quantum confinement on the momentum distribution of electrons\nconfined within a cylindrical potential well have been analyzed. The motivation\nis to understand specific features of the momentum distribution of electrons\nwhen the electron behavior is completely controlled by the parameters of a\nnon-isotropic potential cavity. It is shown that studying the solutions of the\nwave equation for an electron confined in a cylindrical potential well offers\nthe possibility to analyze the confinement behavior of an electron executing\none- or two-dimensional motion in the three-dimensional space within the\nframework of the same mathematical model. Some low-lying electronic states with\ndifferent symmetries have been considered and the corresponding wave functions\nhave been calculated; the behavior of their nodes and their peak positions with\nrespect to the parameters of the cylindrical well has been analyzed.\nAdditionally, the momentum distributions of electrons in these states have been\ncalculated. The limiting cases of the ratio of the cylinder length H and its\nradius R0 have been considered; when the cylinder length H significantly\nexceeds its radius R0 and when the cylinder radius is much greater than its\nlength. The cylindrical quantum confinement effects on the momentum\ndistribution of electrons in these potential wells have been analyzed. The\npossible application of the results obtained here for the description of the\ngeneral features in the behavior of electrons in nanowires with metallic type\nof conductivity (or nanotubes) and ultrathin epitaxial films (or graphene\nsheets) are discussed. Possible experiments are suggested where the quantum\nconfinement can be manifested.", "category": "physics_atom-ph" }, { "text": "Sisyphus Optical Lattice Decelerator: We experimentally demonstrate a variation on a Sisyphus cooling technique\nthat was proposed for cooling antihydrogen. In our implementation, atoms are\nselectively excited to an electronic state whose energy is spatially modulated\nby an optical lattice, and the ensuing spontaneous decay completes one Sisyphus\ncooling cycle. We characterize the cooling efficiency of this technique on a\ncontinuous beam of Sr, and compare it with radiation pressure based laser\ncooling. We demonstrate that this technique provides similar atom number for\nlower end temperatures, provides additional cooling per scattering event and is\ncompatible with other laser cooling methods. This method can be instrumental in\nbringing new exotic species and molecules to the ultracold regime.", "category": "physics_atom-ph" }, { "text": "Axion-mediated electron-electron interaction in ytterbium monohydroxide\n molecule: The YbOH triatomic molecule can be efficiently used to measure the electron\nelectric dipole moment, which violates time-reversal (T) and spatial parity (P)\nsymmetries of fundamental interactions [I. Kozyryev, N.R. Hutzler, Phys. Rev.\nLett. 119, 133002 (2017)]. We study another mechanism of the T,P-violation in\nthe YbOH molecule - the electron-electron interaction mediated by the low-mass\naxiolike particle. For this, we calculate the molecular constant that\ncharacterizes this interaction and use it to estimate the expected magnitude of\nthe effect to be measured. It is shown that this molecular constant has the\nsame order of magnitude as the corresponding molecular constant corresponding\nto the axion-mediated electron-nucleus interaction. According to our\nestimation, an experiment on YbOH will allow one to set updated laboratory\nconstraints on the CP-violating electron-axion coupling constants.", "category": "physics_atom-ph" }, { "text": "Transition Properties of Low Lying States in Atomic Indium: We present here the results of our relativistic many-body calculations of\nvarious properties of the first six low-lying excited states of indium. The\ncalculations were performed using the relativistic coupled-cluster method in\nthe framework of the singles, doubles and partial triples approximation. We\nobtain a large lifetime ~10s for the [4p^6]5s^2 5p_{3/2} state, which had not\nbeen known earlier. Our precise results could be used to shed light on the\nreliability of the lifetime measurements of the excited states of atomic indium\nthat we have considered in the present work.", "category": "physics_atom-ph" }, { "text": "Quantum sensing of microwave electric fields based on Rydberg atoms: Microwave electric field sensing is of importance for a wide range of\napplications in areas of remote sensing, radar astronomy and communications.\nOver the past decade, Rydberg atoms, owing to their exaggerated response to\nmicrowave electric fields, plentiful optional energy levels and integratable\npreparation methods, have been used in ultra-sensitive, wide broadband,\ntraceable, stealthy microwave electric field sensing. This review first\nintroduces the basic concept of quantum sensing, properties of Rydberg atoms\nand principles of quantum sensing of microwave electric fields with Rydberg\natoms. Then an overview of this very active research direction is gradually\nexpanded, covering progresses of sensitivity and bandwidth in Rydberg atoms\nbased icrowavesensing,uperheterodyne quantum sensing with microwave-dressed\nRydberg atoms, quantum-enhanced sensing of microwave electric field, recent\nadvanced quantum measurement systems and approaches to further improve the\nperformance of microwave electric field sensing. Finally, a brief outlook on\nfuture development directions is discussed.", "category": "physics_atom-ph" }, { "text": "Ground state hyperfine splitting of high Z hydrogenlike ions: The ground state hyperfine splitting values of high Z hydrogenlike ions are\ncalculated. The relativistic, nuclear and QED corrections are taken into\naccount. The nuclear magnetization distribution correction (the Bohr-Weisskopf\neffect) is evaluated within the single particle model with the g_{S}-factor\nchosen to yield the observed nuclear moment. An additional contribution caused\nby the nuclear spin-orbit interaction is included in the calculation of the\nBohr-Weisskopf effect. It is found that the theoretical value of the wavelength\nof the transition between the hyperfine splitting components in ^{165}Ho^{66+}\nis in good agreement with experiment.", "category": "physics_atom-ph" }, { "text": "Fine and hyperfine interactions in $^{171}$YbOH and $^{173}$YbOH: The odd isotopologues of ytterbium monohydroxide, $^{171,173}$YbOH, have been\nidentified as promising molecules in which to measure parity (P) and time\nreversal (T) violating physics. Here we characterize the\n$\\tilde{A}^{2}\\Pi_{1/2}(0,0,0)-\\tilde{X}^2\\Sigma^+(0,0,0)$ band near 577 nm for\nthese odd isotopologues. Both laser-induced fluorescence (LIF) excitation\nspectra of a supersonic molecular beam sample and absorption spectra of a\ncryogenic buffer-gas cooled sample were recorded. Additionally, a novel\nspectroscopic technique based on laser-enhanced chemical reactions is\ndemonstrated and utilized in the absorption measurements. This technique is\nespecially powerful for disentangling congested spectra. An effective\nHamiltonian model is used to extract the fine and hyperfine parameters for the\n$\\tilde{A}^{2}\\Pi_{1/2}(0,0,0)$ and $\\tilde{X}^2\\Sigma^+(0,0,0)$ states. A\ncomparison of the determined $\\tilde{X}^2\\Sigma^+(0,0,0)$ hyperfine parameters\nwith recently predicted values (M. Denis, et al., J. Chem. Phys. $\\bf{152}$,\n084303 (2020), K. Gaul and R. Berger, Phys. Rev. A $\\bf{101}$, 012508 (2020),\nJ. Liu et al., J. Chem. Phys. $\\bf{154}$, 064110 (2021)) is made. The measured\nhyperfine parameters provide experimental confirmation of the computational\nmethods used to compute the P,T-violating coupling constants $W_d$ and $W_M$,\nwhich correlate P,T-violating physics to P,T-violating energy shifts in the\nmolecule. The dependence of the fine and hyperfine parameters of the\n$\\tilde{A}^{2}\\Pi_{1/2}(0,0,0)$ and $\\tilde{X}^2\\Sigma^+(0,0,0)$ states for all\nisotopologues of YbOH are discussed and a comparison to isoelectronic YbF is\nmade.", "category": "physics_atom-ph" }, { "text": "Observation of positronium annihilation in the 2S state: towards a new\n measurement of the 1S-2S transition frequency: We report the first observation of the annihilation of positronium from the\n2S state. Positronium (Ps) is excited with a two-photon transition from the 1S\nto the 2S state where its lifetime is increased by a factor of eight compared\nto the ground state due to the decrease in the overlap of the positron electron\nwavefunction. The yield of delayed annihilation photons detected as a function\nof laser frequency is used as a new method of detecting laser-excited Ps in the\n2S state. This can be considered the first step towards a new high precision\nmeasurement of the 1S-2S Ps line.", "category": "physics_atom-ph" }, { "text": "Phase Synchronization between Two Superradiant Lasers: We experimentally demonstrate synchronization between two distinct ensembles\nof cold atoms undergoing steady state superradiance within a single\nlongitudinal and transverse mode of the same optical cavity. The\nsynchronization process is studied first in terms of the time dynamics of\nre-synchronization when the phase alignment of the two oscillators is abruptly\nbroken. We also observe the steady state behavior of the lasers as their\nrelative frequency is continuously varied. This system has the potential to\nrealize a non-equilibrium quantum phase transition and could inform future\nimplementations of milliHertz linewidth lasers.", "category": "physics_atom-ph" }, { "text": "The positronium hyperfine structure: Progress towards a direct\n measurement of the $\\text{2}^\\text{3}\\text{S}_\\text{1} \\rightarrow\n \\text{2}^\\text{1}\\text{S}_\\text{0}$ transition in vacuum: We present the current status for the direct measurement of the positronium\nhyperfine structure using the $\\text{2}^\\text{3}\\text{S}_\\text{1} \\rightarrow\n\\text{2}^\\text{1}\\text{S}_\\text{0}$ transition. This experiment, currently\nbeing commissioned at the slow positron beam facility at ETH Zurich, will be\nthe first measurement of this transition and the first positronium hyperfine\nsplitting experiment conducted in vacuum altogether. This experiment will be\nfree of systematic effects found in earlier experiments, namely the\ninhomogeneity in static magnetic fields and the extrapolation from dense gases\nto vacuum. The achievable precision is expected to be on the order of $10\\,\n\\mathrm{ppm}$ while the systematic uncertainty is estimated to be within a few\n$\\mathrm{ppm}$. This would allow to check recent bound state QED calculations\nand a $3$-$\\sigma$ discrepancy with earlier experiments.", "category": "physics_atom-ph" }, { "text": "Atomic spin-wave control and spin-dependent kicks with shaped\n subnanosecond pulses: The absorption of traveling photons resonant with electric dipole transitions\nof an atomic gas naturally leads to electric dipole spin wave excitations. For\na number of applications, it would be highly desirable to shape and coherently\ncontrol the spatial waveform of the spin waves before spontaneous emission can\noccur. This paper details a recently developed optical control technique to\nachieve this goal, where counter-propagating, shaped sub-nanosecond pulses\nimpart sub-wavelength geometric phases to the spin waves by cyclically driving\nan auxiliary transition. In particular, we apply this technique to reversibly\nshift the wave vector of a spin wave on the $D2$ line of laser-cooled $^{87}$Rb\natoms, by driving an auxiliary $D1$ transition with shape-optimized pulses, so\nas to shut off and recall superradiance on demand. We investigate a\nspin-dependent momentum transfer during the spin-wave control process, which\nleads to a transient optical force as large as $\\sim 1\\hbar k$/ns, and study\nthe limitations to the achieved $70\\sim 75\\%$ spin wave control efficiency by\njointly characterizing the spin-wave control and matterwave acceleration. Aided\nby numerical modeling, we project potential future improvements of the control\nfidelity to the $99\\%$ level when the atomic states are better prepared and by\nequipping a faster and more powerful pulse shaper. Our technique also enables a\nbackground-free measurement of the superradiant emission to unveil the precise\nscaling of the emission intensity and decay rate with optical depth.", "category": "physics_atom-ph" }, { "text": "Canceling spin-dependent contributions and systematic shifts in\n precision spectroscopy of the molecular hydrogen ions: We consider the application of a basic principle of quantum theory, the\ntracelessness of a certain class of hamiltonians, to the precision spectroscopy\nof the molecular hydrogen ions. We show that it is possible to obtain the\nspin-averaged transition frequencies between states from a simple weighted sum\nof experimentally accessible spin-dependent transition frequencies. We discuss\nthe cases ${\\rm H}_{2}^{+}$ and ${\\rm HD}^{+}$, which are distinct in the\nmultipole character of their rovibrational transitions. Inclusion of additional\nfrequencies permits canceling also the electric quadrupole shift, the Zeeman\nshift and partially the Stark shift. In this context, we find that measuring\nelectric quadrupole transitions in ${\\rm HD}^{+}$ is advantageous. The required\nexperimental effort appears reasonable.", "category": "physics_atom-ph" }, { "text": "Blockade-induced resonant enhancement of the optical nonlinearity in a\n Rydberg medium: We predict a resonant enhancement of the nonlinear optical response of an\ninteracting Rydberg gas under conditions of electromagnetically induced\ntransparency. The enhancement originates from a two-photon process which\nresonantly couples electronic states of a pair of atoms dressed by a strong\ncontrol field. We calculate the optical response for the three-level system by\nexplicitly including the dynamics of the intermediate state. We find an\nanalytical expression for the third order susceptibility for a weak classical\nprobe field. The nonlinear absorption displays the strongest resonant behavior\non two-photon resonance where the detuning of the probe field equals the Rabi\nfrequency of the control field. The nonlinear dispersion of the medium exhibits\nvarious spatial shapes depending on the interaction strength. Based on the\ndeveloped model, we propose a realistic experimental scenario to observe the\nresonance by performing transmission measurements.", "category": "physics_atom-ph" }, { "text": "Double photoionization of propylene oxide: a coincidence study of the\n ejection of a pair of valence-shell electrons: Propylene oxide, a favorite target of experimental and theoretical studies of\ncircular dichroism, was recently discovered in interstellar space, further\namplifying the attention to its role in the current debate on protobiological\nhomochirality. In the present work, a photoelectron-photoion-photoion\ncoincidence technique, using an ion-imaging detector and tunable synchrotron\nradiation in the 18.0-37.0 eV energy range, permits: (i)-to observe six\ndouble-ionization fragmentation channels, their relative yields being accounted\nfor about two-thirds by the couple (C2H4+, CH2O+), one-fifth by (C2H3+, CH3O+);\n(ii)-to measure thresholds for their openings as a function of photon energy;\n(iii)-to unravel a pronounced bimodality for a kinetic-energy-released\ndistribution, fingerprint of competitive non-adiabatic mechanisms.", "category": "physics_atom-ph" }, { "text": "Observation of a Cooperative Radiation Force in the Presence of Disorder: Cooperative scattering of light by an extended object such as an atomic\nensemble or a dielectric sphere is fundamentally different from scattering from\nmany point-like scatterers such as single atoms. Homogeneous distributions tend\nto scatter cooperatively, whereas fluctuations of the density distribution\nincrease the disorder and suppress cooperativity. In an atomic cloud, the\namount of disorder can be tuned via the optical thickness, and its role can be\nstudied via the radiation force exerted by the light on the atomic cloud.\nMonitoring cold $^{87}\\text{Rb}$ atoms released from a magneto-optical trap, we\npresent the first experimental signatures of radiation force reduction due to\ncooperative scattering. The results are in agreement with an analytical\nexpression interpolating between the disorder and the cooperativity-dominated\nregimes.", "category": "physics_atom-ph" }, { "text": "Multiphoton detachment from negative ions: new theory vs experiment: In this paper we compare the results of our adiabatic theory (Gribakin and\nKuchiev, Phys. Rev. A, accepted for publication) with other theoretical and\nexperimental results, mostly for halogen negative ions. The theory is based on\nthe Keldysh approach. It shows that the multiphoton detachment rates and the\ncorresponding n-photon detachment cross sections depend only on the asymptotic\nbehaviour of the bound state radial wave function. The dependence on the\nexponent is very strong. This is the main reason for the disagreement with some\nprevious calculations, which employed bound state wave functions with incorrect\nasymptotic forms. In a number of cases our theoretical results produces best\nagreement with absolute and relative experimental data.", "category": "physics_atom-ph" }, { "text": "Comment on \"Time delays in molecular photoionization\": In a recent article by P. Hockett \\textit{et al.}, time delays arising in the\ncontext of molecular single-photon ionization are investigated from a\ntheoretical point of view. We argue that one of the central equations derived\nin the paper is incorrect and present a reformulation that is consistent with\nthe established treatment of angle-dependent scattering delays.", "category": "physics_atom-ph" }, { "text": "Ion transport in macroscopic RF linear traps: Efficient transport of cold atoms or ions is a subject of increasing concern\nin many experimental applications reaching from quantum information processing\nto frequency metrology. For the scalable quantum computer architectures based\non the shuttling of individual ions, different transport schemes have been\ndeveloped, which allow to move single atoms minimizing their energy gain. In\nthis article we discuss the experimental implementation of the transport of a\nthree-dimensional ion cloud in a macroscopic linear radiofrequency (RF) trap.\nThe present work is based on numerical simulations done by molecular dynamics\ntaking into account a realistic experimental environment. The deformation of\nthe trapping potential and the spatial extension of the cloud during transport\nappears to be the major source of the ion energy gain. The efficiency of\ntransport in terms of transfer probability and ion number is also discussed.", "category": "physics_atom-ph" }, { "text": "2D electron momentum distributions for transfer ionization in fast\n proton Helium collisions: The momentum distribution of the electron in the reaction p+He $\\rightarrow$\nH + He$^{2+}$ + $e$ is measured for projectile energies $E_p$=300 and 630 keV/u\nat very small scattering angles of hydrogen. We mainly present two dimensional\ndistributions parallel $(k_{||})$ and perpendicular $(k_{\\perp})$ to the\nprojectile beam. Theoretical calculations were carried out within the Plane\nWave First Born Approximation (PWFBA), which includes both electron emission\nmechanisms, shake-off and sequential capture and ionization. It is shown that\nelectron correlations in the target wave function play the most important role\nin the explanation of experimentally observed backward emission. Second order\neffects have to be involved to correctly describe the forward emission of the\nelectron.", "category": "physics_atom-ph" }, { "text": "Frequency noise characterization of diode lasers for vapor cell clocks\n applications: The knowledge of the frequency noise spectrum of a diode laser is of interest\nin several high resolution experiments. Specifically, in laser-pumped vapor\ncell clocks, it is well established that the laser frequency noise plays a role\nin affecting the clock performances. It is then important to characterize the\nfrequency noise of a diode laser, especially since such measurements are rarely\nfound in the literature and hardly ever provided by vendors. In this paper, we\ndescribe a technique based on a frequency-to-voltage converter that transforms\nthe laser frequency fluctuations into voltage fluctuations. In this way, it is\npossible to characterize the laser frequency noise power spectral density in a\nwide range of Fourier frequencies, as required in cell clock applications.", "category": "physics_atom-ph" }, { "text": "Metrology with Atom Interferometry: Inertial Sensors from Laboratory to\n Field Applications: Developments in atom interferometry have led to atomic inertial sensors with\nextremely high sensitivity. Their performances are for the moment limited by\nthe ground vibrations, the impact of which is exacerbated by the sequential\noperation, resulting in aliasing and dead time. We discuss several experiments\nperformed at LNE-SYRTE in order to reduce these problems and achieve the\nintrinsic limit of atomic inertial sensors. These techniques have resulted in\ntransportable and high-performance instruments that participate in gravity\nmeasurements, and pave the way to applications in inertial navigation.", "category": "physics_atom-ph" }, { "text": "Difference-frequency combs in cold atom physics: Optical frequency combs provide the clockwork to relate optical frequencies\nto radio frequencies. Hence, combs allow to measure optical frequencies with\nrespect to a radio frequency where the accuracy is limited only by the\nreference signal. In order to provide a stable link between the radio and\noptical frequencies, the two parameters of the frequency comb must be fixed:\nthe carrier envelope offset frequency $f_{\\rm ceo}$ and the pulse\nrepetition-rate $f_{\\rm rep}$. We have developed the first optical frequency\ncomb based on difference frequency generation (DFG) that eliminates $f_{\\rm\nceo}$ by design - specifically tailored for applications in cold atom physics.\nAn $f_{\\rm ceo}$-free spectrum at 1550 nm is generated from a super continuum\nspanning more than an optical octave. Established amplification and frequency\nconversion techniques based on reliable telecom fiber technology allow\ngeneration of multiple wavelength outputs. In this paper we discuss the\nfrequency comb design, characterization, and optical frequency measurement of\nSr Rydberg states. The DFG technique allows for a compact and robust, passively\n$f_{\\rm ceo}$ stable frequency comb significantly improving reliability in\npractical applications.", "category": "physics_atom-ph" }, { "text": "Establishing a nearly closed cycling transition in a polyatomic molecule: We study optical cycling in the polar free radical calcium monohydroxide\n(CaOH) and establish an experimental path towards scattering $\\sim$$10^4$\nphotons. We report rovibronic branching ratio measurements with precision at\nthe $\\sim10^{-4}$ level and observe weak symmetry-forbidden decays to bending\nmodes with non-zero vibrational angular momentum. Calculations are in excellent\nagreement with these measurements and predict additional decay pathways.\nAdditionally, we perform high-resolution spectroscopy of the\n$\\widetilde{\\text{X}}\\,^2\\Sigma^+(12^00)$ and\n$\\widetilde{\\text{X}}\\,^2\\Sigma^+(12^20)$ hybrid vibrational states of CaOH.\nThese advances establish a path towards radiative slowing, 3D magneto-optical\ntrapping, and sub-Doppler cooling of CaOH.", "category": "physics_atom-ph" }, { "text": "Time-dependent second Born calculations for model atoms and molecules in\n strong laser fields: Using the finite-element discrete variable representation of the\nnonequilibrium Green's function (NEGF) we extend previous work [K.~Balzer et\nal., Phys. Rev. A \\textbf{81}, 022510 (2010)] to nonequilibrium situations and\ncompute---from the two-time Schwinger-Keldysh-Kadanoff-Baym equations---the\nresponse of the helium atom and the heteronuclear molecule lithium hydride to\nlaser fields in the uv and xuv regime. In particular, by comparing the\none-electron density and the dipole moment to time-dependent Hartree-Fock\nresults on one hand and the full solution of the time-dependent Schr\\\"odinger\nequation on the other hand, we demonstrate that the time-dependent second Born\napproximation carries valuable information about electron-electron correlation\neffects. Also, we outline an efficient distributed memory concept which enables\na parallel and well scalable algorithm for computing the NEGF in the two-time\ndomain.", "category": "physics_atom-ph" }, { "text": "Time-dependent calculations of transfer ionization by fast proton-helium\n collision in one-dimensional kinematics: We analyze a transfer ionization (TI) reaction in the fast proton-helium\ncollision $\\rm H^+ + He \\to H^0 + He^{2+} + e^-$ by solving a time-dependent\nSchr\\\"odinger equation (TDSE) under the classical projectile motion\napproximation in one-dimensional kinematics. In addition, we construct various\ntime independent analogues of our model using lowest order perturbation theory\nin the form of the Born series. By comparing various aspects of the TDSE and\nthe Born series calculations, we conclude that the recent discrepancies of\nexperimental and theoretical data may be attributed to deficiency of the Born\nmodels used by other authors. We demonstrate that the correct Born series for\nTI should include the momentum space overlap between the double ionization\namplitude and the wave function of the transferred electron.", "category": "physics_atom-ph" }, { "text": "Current-feedback-stabilized laser system for quantum simulation\n experiments using Yb clock transition at 578 nm: We developed a laser system for the spectroscopy of the clock transition in\nytterbium (Yb) atoms at 578 nm based on an interference-filter stabilized\nexternal-cavity diode laser (IFDL) emitting at 1156 nm. Owing to the improved\nfrequency-to-current response of the laser-diode chip and the less sensitivity\nof the IFDL to mechanical perturbations, we succeeded in stabilizing the\nfrequency to a high-finesse ultra-low-expansion glass cavity with a simple\ncurrent feedback system. Using this laser system, we performed high-resolution\nclock spectroscopy of Yb and found that the linewidth of the stabilized laser\nwas less than 320 Hz.", "category": "physics_atom-ph" }, { "text": "Proposal for laser-cooling of rare-earth ions: The efficiency of laser-cooling relies on the existence of an almost closed\noptical-transition cycle in the energy spectrum of the considered species. In\nthis respect rare-earth elements exhibit many transitions which are likely to\ninduce noticeable leaks from the cooling cycle. In this work, to determine\nwhether laser-cooling of singly-ionized erbium Er$^+$ is feasible, we have\nperformed accurate electronic-structure calculations of energies and\nspontaneous-emission Einstein coefficients of Er$^+$, using a combination of\n\\textit{ab initio} and least-square-fitting techniques. We identify five weak\nclosed transitions suitable for laser-cooling, the broadest of which is in the\nkilohertz range. For the strongest transitions, by simulating the cascade\ndynamics of spontaneous emission, we show that repumping is necessary, and we\ndiscuss possible repumping schemes. We expect our detailed study on Er$^+$ to\ngive a good insight into laser-cooling of neighboring ions like Dy$^+$.", "category": "physics_atom-ph" }, { "text": "Population trapping in bound states during IR-assisted ultra-fast\n photoionization of Ne$^+$: We have investigated photoionization of Ne$^+$ in the combined field of a\nshort infra-red laser pulse and a delayed ultra-short pulse of the infra-red\nlaser's 23$^r$$^d$ harmonic. We observe an ionization yield compatible with a\npicture in which one electron gets excited into Rydberg states by the harmonic\nlaser field and is subsequently removed by the infra-red laser field.\nModulations are seen in the ionization yield as a function of time delay. These\nmodulations originate from the trapping of population in low members of the\nRydberg series with different states being populated at different ranges of\ndelay times. The calculations further demonstrate that single-threshold\ncalculations cannot reproduce the Ne$^+$ photoionization yields obtained in\nmulti-threshold calculations.", "category": "physics_atom-ph" }, { "text": "Superradiant detection of microscopic optical dipolar interactions: The interaction between light and cold atoms is a complex phenomenon\npotentially featuring many-body resonant dipole interactions. A major obstacle\ntoward exploring these quantum resources of the system is macroscopic light\npropagation effects, which not only limit the available time for the\nmicroscopic correlations to locally build up, but also create a directional,\nsuperradiant emission background whose variations can overwhelm the microscopic\neffects. In this Letter, we demonstrate a method to perform ``background-free''\ndetection of the microscopic optical dynamics in a laser-cooled atomic\nensemble. This is made possible by transiently suppressing the macroscopic\noptical propagation over a substantial time, before a recall of superradiance\nthat imprints the effect of the accumulated microscopic dynamics into an\nefficiently detectable outgoing field. We apply this technique to unveil and\nprecisely characterize a density-dependent, microscopic dipolar dephasing\neffect that generally limits the lifetime of optical spin-wave order in\nensemble-based atom-light interfaces.", "category": "physics_atom-ph" }, { "text": "Three-photon coherence in a ladder-type atomic system: We present a theoretical study of three-photon electromagnetically induced\nabsorption for a ladder-type three-level atomic system. A probe beam was tuned\nto the lower line and two counter-propagating, linearly polarized coupling\nbeams were tuned to the upper line. The system can be modeled with a three- (or\nfive-) level scheme when the polarization directions of the coupling beams are\nparallel (or perpendicular). By calculating the absorption coefficients\nanalytically for the two schemes, we found that the corresponding absorption\ncoefficients were identical except for different transition strengths, and that\nthe primitive scheme embedded in those schemes was a simple four-level scheme.", "category": "physics_atom-ph" }, { "text": "Hydrogen 1s-2s transition frequency: Comparison of experiment and theory: Using the Dirac equation, radiative corrections and finite nuclear size and\nmass corrections, we calculate the $1s$-$2s$ quantum transition frequency\n$f_{1s,2s}$ of hydrogen and its uncertainty due to the uncertainties $\\delta\nm_e, \\delta m_p, \\delta \\alpha, \\delta r_p, \\delta R_{\\infty}$ of the electron\nmass $m_e$, proton mass $m_p$, fine structure constant $\\alpha$, proton root\nmean squared charge radius $r_p$, and the Rydberg constant $R_{\\infty}$. We use\nthe 2018 CODATA [E. Tiesinga, P. J. Mohr, D. B. Newell, B. N. Taylor, Rev. Mod.\nPhys. {\\bf 93}, 025010 (2021)] procedure for the calculation of $f_{1s,2s}$,\nand the fundamental constants given therein. We find that the value of the\nexperimental frequency lies outside the theoretical uncertainty (the\ndiscrepancy between the theoretical and the experimental frequency is $\\Delta\nf_{1s,2s}^{(2018)} = -23.948$~kHz). But, by fitting $r_p$ we obtain a vanishing\ndiscrepancy between the calculated and experimental frequencies and a 6.4 kHz\ntheoretical uncertainty, with $r_p = 0.830734$~fm (and a theoretical\nuncertainty of $\\delta r_p = 0.0022$ fm), consistent with a recent\nmeasurement~[W. Xiong, {\\it{et al}}., Nature (London) {\\bf 575}, 147 (2019)].", "category": "physics_atom-ph" }, { "text": "Higher-order QED corrections to the hyperfine splitting in $^3$He: We present a calculation of the hyperfine splitting of the $2^3S$ state in\nthe $^3$He atom with inclusion of all QED effects up to $\\alpha^3E_F$, where\n$E_F$ is the Fermi splitting. Using the experimental value of the $1S$\nhyperfine splitting in $^3$He$^+$, we obtain the theoretical prediction for\n$^3$He of $\\nu_\\mathrm{hfs}= -6\\,739\\,701\\,181(41)$ Hz, which is in perfect\nagreement with the experimental value $-6\\,739\\,701\\,177(16)$ Hz [S. D. Rosner\nand F. M. Pipkin, Phys. Rev. A ${\\bf 1}$, 571 (1970)]. This result constitutes\na 40-fold improvement in precision as compared to the previous value and is the\nmost accurate theoretical prediction ever obtained for a non-hydrogenic system.", "category": "physics_atom-ph" }, { "text": "Quantum Defect Theory description of weakly bound levels and Feshbach\n resonances in LiRb: The multichannel quantum defect theory (MQDT) in combination with the frame\ntransformation (FT) approach is applied to model the Fano-Feshbach resonances\nmeasured for $^{7}$Li$^{87}$Rb and $^{6}$Li$^{87}$Rb [Marzok {\\it et al.} Phys.\nRev. A {\\bf 79} 012717 (2009)]. The MQDT results show a level of accuracy\ncomparable to that of previous models based on direct, fully numerical\nsolutions of the the coupled channel Schr\\\"odinger equations (CC). Here, energy\nlevels deduced from 2-photon photoassociation spectra for $^{7}$Li$^{85}$Rb are\nassigned by applying the MQDT approach, obtaining the bound state energies for\nthe coupled channel problem. Our results confirm that MQDT yields a compact\ndescription of photoassociation observables as well as the Fano-Feshbach\nresonance positions and widths.", "category": "physics_atom-ph" }, { "text": "Comparative simulations of Fresnel holography methods for atomic\n waveguides: We have simulated the optical properties of micro-fabricated Fresnel zone\nplates (FZPs) as an alternative to spatial light modulators (SLMs) for\nproducing non-trivial light potentials to trap atoms within a lensless Fresnel\narrangement. We show that binary (1-bit) FZPs with wavelength (1 \\mu m) spatial\nresolution consistently outperform kinoforms of spatial and phase resolution\ncomparable to commercial SLMs in root mean square error comparisons, with FZP\nkinoforms demonstrating increasing improvement for complex target intensity\ndistributions. Moreover, as sub-wavelength resolution microfabrication is\npossible, FZPs provide an exciting possibility for the creation of static\ncold-atom trapping potentials useful to atomtronics, interferometry, and the\nstudy of fundamental physics.", "category": "physics_atom-ph" }, { "text": "Under-the-barrier dynamics in laser-induced relativistic tunneling: The tunneling dynamics in relativistic strong-field ionization is\ninvestigated with the aim to develop an intuitive picture for the relativistic\ntunneling regime. We demonstrate that the tunneling picture applies also in the\nrelativistic regime by introducing position dependent energy levels. The\nquantum dynamics in the classically forbidden region features two time scales,\nthe typical time that characterizes the probability density's decay of the\nionizing electron under the barrier (Keldysh time) and the time interval which\nthe electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time).\nIn the relativistic regime, an electron momentum shift as well as a spatial\nshift along the laser propagation direction arise during the under-the-barrier\nmotion which are caused by the laser magnetic field induced Lorentz force. The\nmomentum shift is proportional to the Keldysh time, while the wave-packet's\nspatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature\nof the momentum shift is shown to be present in the ionization spectrum at the\ndetector and, therefore, observable experimentally. In contrast, the signature\nof the Eisenbud-Wigner-Smith time delay disappears at far distances for pure\nquasistatic tunneling dynamics.", "category": "physics_atom-ph" }, { "text": "Interferometry with Bose-Einstein Condensates in Microgravity: Atom interferometers covering macroscopic domains of space-time are a\nspectacular manifestation of the wave nature of matter. Due to their unique\ncoherence properties, Bose-Einstein condensates are ideal sources for an atom\ninterferometer in extended free fall. In this paper we report on the\nrealization of an asymmetric Mach-Zehnder interferometer operated with a\nBose-Einstein condensate in microgravity. The resulting interference pattern is\nsimilar to the one in the far-field of a double-slit and shows a linear scaling\nwith the time the wave packets expand. We employ delta-kick cooling in order to\nenhance the signal and extend our atom interferometer. Our experiments\ndemonstrate the high potential of interferometers operated with quantum gases\nfor probing the fundamental concepts of quantum mechanics and general\nrelativity.", "category": "physics_atom-ph" }, { "text": "Comment on \"Recurrences without closed orbits\": In a recent paper Robicheaux and Shaw [Phys. Rev. A 58, 1043 (1998)]\ncalculate the recurrence spectra of atoms in electric fields with non-vanishing\nangular momentum not equal to 0. Features are observed at scaled actions\n``an order of magnitude shorter than for any classical closed orbit of this\nsystem.'' We investigate the transition from zero to nonzero angular momentum\nand demonstrate the existence of short closed orbits with L_z not equal to 0.\nThe real and complex ``ghost'' orbits are created in bifurcations of the\n``uphill'' and ``downhill'' orbit along the electric field axis, and can serve\nto interpret the observed features in the quantum recurrence spectra.", "category": "physics_atom-ph" }, { "text": "Coulomb Effects on time-trajectory-resolved high-order harmonic\n generation: We study the effect of Coulomb potential on high-order harmonic generation\n(HHG) numerically and analytically. We focus on the influence of Coulomb\npotential on emission times of HHG associated with specific electron\ntrajectories. By using a numerical procedure based on numerical solution of\ntime-dependent Schr\\\"{o}dinger equation (TDSE) in three dimensions, we extract\nthe HHG emission times both for long and short electron trajectories. We\ncompare TDSE predictions with those of a Coulomb-modified model arising from\nstrong-field approximation (SFA). We show that the Coulomb effect induces\nearlier HHG emission times than those predicted by the general SFA model\nwithout considering the Coulomb potential. In particular, this effect\ninfluences differently on long and short electron trajectories and is more\nremarkable for low-energy harmonics than high ones. It also changes the HHG\namplitudes for long and short electron trajectories. We validate our\ndiscussions with diverse laser parameters and forms of Coulomb potential. Our\nresults strongly support a four-step model of HHG.", "category": "physics_atom-ph" }, { "text": "Harmonic generation of noble-gas atoms in the Near-IR regime using\n ab-initio time-dependent R-matrix theory: We demonstrate the capability of ab-initio time-dependent R-matrix theory to\nobtain accurate harmonic generation spectra of noble-gas atoms at Near-IR\nwavelengths between 1200 and 1800 nm and peak intensities up to 1.8 X 10(14)\nW/cm(2) . To accommodate the excursion length of the ejected electron, we use\nan angular-momentum expansion up to Lmax = 279. The harmonic spectra show\nevidence of atomic structure through the presence of a Cooper minimum in\nharmonic generation for Kr, and of multielectron interaction through the giant\nresonance for Xe. The theoretical spectra agree well with those obtained\nexperimentally.", "category": "physics_atom-ph" }, { "text": "Semirelativistic $1s-2s$ excitation of atomic hydrogen by electron\n impact: In the framework of the first Born approximation, we present a\nsemirelativistic theoretical study of the inelastic excitation\n($1s_{1/2}\\longrightarrow 2s_{1/2}$) of hydrogen atom by electronic impact. The\nincident and scattered electrons are described by a free Dirac spinor and the\nhydrogen atom target is described by the Darwin wave function. Relativistic and\nspin effects are examined in the relativistic regime. A detailed study has been\ndevoted to the nonrelativistic regime as well as the moderate relativistic\nregime. Some aspects of this dependence as well as the dynamic behavior of the\nDCS in the relativistic regime have been addressed.", "category": "physics_atom-ph" }, { "text": "A dual-isotope rubidium comagnetometer to search for anomalous\n long-range spin-mass (spin-gravity) couplings of the proton: The experimental concept of a search for a long-range coupling between\nrubidium (Rb) nuclear spins and the mass of the Earth is described. The\nexperiment is based on simultaneous measurement of the spin precession\nfrequencies for overlapping ensembles of Rb-85 and Rb-87 atoms contained within\nan evacuated, antirelaxation-coated vapor cell. Rubidium atoms are\nspin-polarized in the presence of an applied magnetic field by synchronous\noptical pumping with circularly polarized laser light. Spin precession is\nprobed by measuring optical rotation of far-off-resonant, linearly polarized\nlaser light. Simultaneous measurement of Rb-85 and Rb-87 spin precession\nfrequencies enables suppression of magnetic-field-related systematic effects.\nThe nuclear structure of the Rb isotopes makes the experiment particularly\nsensitive to anomalous spin-dependent interactions of the proton. Experimental\nsensitivity and a variety of systematic effects are discussed, and initial data\nare presented.", "category": "physics_atom-ph" }, { "text": "Photodetachment study of He^- quartet resonances below the He(n=3)\n thresholds: The photodetachment cross section of He^- has been measured in the photon\nenergy range 2.9 eV to 3.3 eV in order to investigate doubly excited states.\nMeasurements were made channel specific by selectively detecting the residual\nHe atoms left in a particular excited state following detachment. Three\nFeshbach resonances were found in the He(1s2p ^3P)+e^-(epsilon p) partial cross\nsection: a ^4S resonance below the He(1s3s ^3S) threshold and two ^4P\nresonances below the He(1s3p ^3P) threshold. The measured energies of these\ndoubly excited states are 2.959260(6) eV, 3.072(7) eV and 3.26487(4) eV. The\ncorresponding widths are found to be 0.20(2) meV, 50(5) meV and 0.61(5) meV.\nThe measured energies agree well with recent theoretical predictions for the\n1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P states, respectively, but the widths\ndeviate noticeably from calculations for 1s3p^2 ^4P and 1s3p4p ^4P states.", "category": "physics_atom-ph" }, { "text": "A project based on Multi-Configuration Dirac-Fock calculations for\n plasma spectroscopy: We present a project dedicated to hot plasma spectroscopy based on a\nMulti-Configuration Dirac-Fock (MCDF) code, initially developed by J. Bruneau.\nThe code is briefly described and the use of the transition-state method for\nplasma spectroscopy is detailed. Then an opacity code for\nlocal-thermodynamic-equilibrium plasmas using MCDF data, named OPAMCDF, is\npresented. Transition arrays for which the number of lines is too large to be\nhandled in a Detailed-Line-Accounting calculation can be modeled within the\nPartially-Resolved-Transition-Array method or using the\nUnresolved-Transition-Arrays formalism in jj-coupling. An improvement of the\noriginal Partially-Resolved-Transition-Array method is presented which gives a\nbetter agreement with Detailed-Line-Accounting computations. Comparisons with\nsome absorption and emission experimental spectra are shown. Finally, the\ncapability of the MCDF code to compute atomic data required for\ncollisional-radiative modeling of plasma at non local thermodynamic equilibrium\nis illustrated. Additionally to photoexcitation, this code can be used to\ncalculate photoionization, electron impact excitation and ionization\ncross-sections as well as autoionization rates in the Distorted-Wave or Close\nCoupling approximations. Comparisons with cross-sections and rates available in\nthe literature are discussed.", "category": "physics_atom-ph" }, { "text": "The total cross-sections for the photoeffect for K-shell bound electrons\n and pair production with the created electron in the ground state for photon\n energies above 1 MeV: Considering the contributions of the main term of the relativistic Coulombian\nGreen function given by Hostler to the second order of S matrix element and\ntaking into account only the large components of the Dirac spinor of the ground\nstate we obtain the imaginary part of the Rayleigh amplitudes in terms of\nelementary functions. Thereby simple and high accurate formulae for the total\ncross-sections for photoeffect and pair production with the electron created in\nthe K-shell are obtained \\textit{via} the optical theorem.Comparing the\npredictions given by our formulae with the full relativistic numerical\ncalculations of Kissel \\textit{et al} [Phys. Rev. A 22, 1970 (1980)] and\nScofield [LLRL, Internal Report,1973], a good agreement is found for photon\nenergies above the pair production threshold up to 5 MeV for any Z elements. We\npresent our numerical results for the total photoeffect and pair production\ncross-sections, for various photon energies for the K-shell of Ag and Pb.", "category": "physics_atom-ph" }, { "text": "Rydberg Macrodimers: Diatomic molecules on the micrometer scale: Controlling molecular binding at the level of single atoms is one of the holy\ngrails of quantum chemistry. Rydberg macrodimers -- bound states between highly\nexcited Rydberg atoms -- provide a novel perspective in this direction.\nResulting from binding potentials formed by the strong, long-range interactions\nof Rydberg states, Rydberg macrodimers feature bond lengths in the micrometer\nregime, exceeding those of conventional molecules by orders of magnitude. Using\nsingle-atom control in quantum gas microscopes, the unique properties of these\nexotic states can be studied with unprecedented control, including the response\nto magnetic fields or the polarization of light in their photoassociation. The\nhigh accuracy achieved in spectroscopic studies of macrodimers makes them an\nideal testbed to benchmark Rydberg interactions, with direct relevance to\nquantum computing and information protocols where these are employed. This\nreview provides a historic overview and summarizes the recent findings in the\nfield of Rydberg macrodimers. Furthermore, it presents new data on interactions\nbetween macrodimers, leading to a phenomenon analogous to Rydberg blockade at\nthe level of molecules, opening the path towards studying many-body systems of\nultralong-range Rydberg molecules.", "category": "physics_atom-ph" }, { "text": "Interdimensional degeneracies for a quantum three-body system in D\n dimensions: A new approach is developed to derive the complete spectrum of exact\ninterdimensional degeneracies for a quantum three-body system in D-dimensions.\nThe new method gives a generalization of previous methods.", "category": "physics_atom-ph" }, { "text": "Rabi oscillations between ground and Rydberg states and van der Waals\n blockade in a mesoscopic frozen Rydberg gas: We present a detailed analysis of our recent observation of synchronous Rabi\noscillations between the electronic ground state and Rydberg states in a\nmesoscopic ensemble containing roughly 100 ultracold atoms [M. Reetz-Lamour\n\\textit{et al.}, submitted, arXiv:0711.4321]. The mesoscopic cloud is selected\nout of a sample of laser-cooled Rb atoms by optical pumping. The atoms are\ncoupled to a Rydberg state with principal quantum number around 30 by a\ntwo-photon scheme employing flat-top laser beams. The influence of residual\nspatial intensity fluctuations as well as sources of decoherence such as\nredistribution to other states, radiative lifetime, and laser bandwidth are\nanalysed. The results open up new possibilities for the investigation of\ncoherent many-body phenomena in dipolar Rydberg gases. As an example we\ndemonstrate the van der Waals blockade, a variant of the dipole blockade, for a\nmesoscopic atom sample.", "category": "physics_atom-ph" }, { "text": "Long-range interactions between polar bialkali ground-state molecules in\n arbitrary vibrational levels: We have calculated the isotropic $C\\_6$ coefficients characterizing the\nlong-range van der Waals interaction between two identical heteronuclear\nalkali-metal diatomic molecules in the same arbitrary vibrational level of\ntheir ground electronic state $X^1\\Sigma^+$. We consider the ten species made\nup of $^7$Li, $^{23}$Na, $^{39}$K, $^{87}$Rb and $^{133}$Cs. Following our\nprevious work [M.~Lepers \\textit{et.~al.}, Phys.~Rev.~A \\textbf{88}, 032709\n(2013)] we use the sum-over-state formula inherent to the second-order\nperturbation theory, composed of the contributions from the transitions within\nthe ground state levels, from the transition between ground-state and excited\nstate levels, and from a crossed term. These calculations involve a combination\nof experimental and quantum-chemical data for potential energy curves and\ntransition dipole moments. We also investigate the case where the two molecules\nare in different vibrational levels and we show that the Moelwyn-Hughes\napproximation is valid provided that it is applied for each of the three\ncontributions to the sum-over-state formula. Our results are particularly\nrelevant in the context of inelastic and reactive collisions between ultracold\nbialkali molecules, in deeply bound or in Feshbach levels.", "category": "physics_atom-ph" }, { "text": "Imaging Molecular Structure through Femtosecond Photoelectron\n Diffraction on Aligned and Oriented Gas-Phase Molecules: This paper gives an account of our progress towards performing femtosecond\ntime-resolved photoelectron diffraction on gas-phase molecules in a pump-probe\nsetup combining optical lasers and an X-ray Free-Electron Laser. We present\nresults of two experiments aimed at measuring photoelectron angular\ndistributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and\ndissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss\nthem in the larger context of photoelectron diffraction on gas-phase molecules.\nWe also show how the strong nanosecond laser pulse used for adiabatically\nlaser-aligning the molecules influences the measured electron and ion spectra\nand angular distributions, and discuss how this may affect the outcome of\nfuture time-resolved photoelectron diffraction experiments.", "category": "physics_atom-ph" }, { "text": "Breakup of rotating asymmetric quartic-quadratic trapped condensates: The threshold conditions for a rotating pancake-like asymmetric\nquartic-quadratic confined condensate to break in two localized fragments, as\nwell as to produce giant vortex at the center within the vortex-pattern\ndistributions, are investigated within the Thomas-Fermi (TF) approximation and\nexact numerical solution of the corresponding Gross-Pitaevskii (GP) formalism.\nBy comparing the TF predictions with exact GP solutions, in our investigation\nwith two different quartic-quadratic trap geometries, of particular relevance\nis to observe that the TF approach is not only very useful to display the\naveraged density distribution, but also quite realistic in establishing the\ncritical rotational conditions for the breakup occurrence and possible\ngiant-vortex formation. It provides almost exact results to define the contour\nof the condensate distribution, even for high rotating system, after the system\nsplit in two (still confined) clouds. The applicability of the Feynman rule to\nthe vortex distribution (full-numerical GP solutions) is also being confirmed\nfor these non-homogeneous asymmetric trap configurations. This study is\nexpected to be relevant for manipulating the rotation and trap parameters in\naddition to Feshbach resonance techniques. It can also be helpful to define\ninitial conditions for any further studies on dynamical evolution of vortex\npattern distributions.", "category": "physics_atom-ph" }, { "text": "Toward a quantum-enhanced strontium optical lattice clock at INRIM: The new strontium atomic clock at INRIM seeks to establish a new frontier in\nquantum measurement by joining state-of-the-art optical lattice clocks and the\nquantized electromagnetic field provided by a cavity QED setup. The goal of our\nexperiment is to apply advanced quantum techniques to state-of-the-art optical\nlattice clocks, demonstrating enhanced sensitivity while preserving long\ncoherence times and the highest accuracy. In this paper we describe the current\nstatus of the experiment and the prospected sensitivity gain for the designed\ncavity QED setup.", "category": "physics_atom-ph" }, { "text": "Absolute frequency measurement of molecular iodine hyperfine transitions\n at 554 nm and its application to stabilize a 369 nm laser for Yb+ ions\n cooling: We investigate 13 hyperfine structures of transition lines of 127I2 near 554\nnm, namely, the R(50) 22-0, P(46) 22-0, P(121) 24-0, P(69) 25-1, R(146) 25-0,\nR(147) 28-1, P(160) 26-0, P(102) 26-1, R(96) 23-0, R(49) 22-0, P(45) 22-0,\nP(92) 23-0, and R(72) 25-1 transitions, and measure their absolute frequencies\nwith an optical frequency comb. A 369 nm frequency-tripled laser is frequency\nstabilized by locking the 554 nm harmonic-frequency laser to the R(146) 25-0\na15 line of 127I2 via modulation transfer spectroscopy. A frequency stability\nof 5E-12 is observed over a 1000 s integration time. The measurement of the\nmolecular iodine spectroscopy at 554 nm enriches high-precision experimental\ndata, and also enables theoretical predictions. Meanwhile, the 369 nm\nfrequency-tripled laser stabilized by molecular iodine spectroscopy has wide\napplications in frequency metrology, and quantum information processing based\non Yb+ ions.", "category": "physics_atom-ph" }, { "text": "Characterization and limits of a cold atom Sagnac interferometer: We present the full evaluation of a cold atom gyroscope based on atom\ninterferometry. We have performed extensive studies to determine the systematic\nerrors, scale factor and sensitivity. We demonstrate that the acceleration\nnoise can be efficiently removed from the rotation signal allowing to reach the\nfundamental limit of the quantum projection noise for short term measurements.\nThe technical limits to the long term sensitivity and accuracy have been\nidentified, clearing the way for the next generations of ultra-sensitive atom\ngyroscopes.", "category": "physics_atom-ph" }, { "text": "Thomas--Reiche--Kuhn Correction for Truncated Configuration Interaction\n Spaces: Case of Laser-Assisted Dynamical Interference: The Thomas--Reiche--Kuhn sum rule is used to form an effective potential that\nis added to the time-dependent configuration interaction singles (TDCIS)\nequations of motion in velocity gauge. The purpose of the effective potential\nis to include virtual coupling from singles to doubles, which is required for\nsize-consistent velocity gauge TDCIS results. The proposed method is compared\nto length gauge TDCIS results for laser-assisted photoionization. Finally, a\nnovel dynamical interference effect controlled by two-color fields is predicted\nfor atomic targets.", "category": "physics_atom-ph" }, { "text": "Theoretical investigation of orbital alignment of x-ray-ionized atoms in\n exotic electronic configurations: We theoretically study orbital alignment in x-ray-ionized atoms and ions,\nbased on improved electronic-structure calculations starting from the\nHartree-Fock-Slater model. We employ first-order many-body perturbation theory\nto improve the Hartree-Fock-Slater calculations and show that the use of\nfirst-order-corrected energies yields significantly better transition energies\nthan originally obtained. The improved electronic-structure calculations enable\nus also to compute individual state-to-state cross sections and transition\nrates and, thus, to investigate orbital alignment induced by linearly polarized\nx rays. To explore the orbital alignment of transiently formed ions after\nphotoionization, we discuss alignment parameters and ratios of individual\nstate-resolved photoionization cross sections for initially neutral argon and\ntwo exotic electronic configurations that may be formed during x-ray\nmultiphoton ionization dynamics induced by x-ray free-electron lasers. We also\npresent how the orbital alignment is affected by Auger-Meitner decay and\ndemonstrate how it evolves during a sequence of one photoionization and one\nAuger-Meitner decay. Our present work establishes a step toward investigation\nof orbital alignment in atomic ionization driven by high-intensity x rays.", "category": "physics_atom-ph" }, { "text": "Exponential decrease of Ramsey linewidth via coherent atomic phase\n tracking: We propose an effective method to decrease the Ramsey linewidth of microwave\natomic clock by tracking the coherent atomic phase through nondestructive\nmeasurement. The free evolution time T between two Ramsey pulses is divided\ninto N subsections. In each subsection, the coherent phase of the atomic\nensemble is probed by an additional large-detuning laser. The probed phase in\nthe previous subsection is used to change the phase of the microwave pulse in\nthe following subsection. After tracking the coherent atomic phase for N-1\ntimes, the final linewidth of Ramsey fringe decreases quickly as N/(2N-1). We\nthen demonstrate this proposal in a vapor cell atomic clock. The linewidth of\nthe Ramsey fringe is decreased down to 27 Hz after 5 successive\nsub-interrogations, which is much narrower than the linewidth of 142 Hz\nobtained by normal Ramsey spectroscopy.", "category": "physics_atom-ph" }, { "text": "Sensitivity of double resonance alignment magnetometers: We present an experimental study of the intrinsic magnetometric sensitivity\nof an optical/rf-frequency double resonance magnetometer in which linearly\npolarized laser light is used in the optical pumping and detection processes.\nWe show that a semi-empirical model of the magnetometer can be used to describe\nthe magnetic resonance spectra. Then, we present an efficient method to predict\nthe optimum operating point of the magnetometer, i.e., the light power and rf\nRabi frequency providing maximum magnetometric sensitivity. Finally, we apply\nthe method to investigate the evolution of the optimum operating point with\ntemperature. The method is very efficient to determine relaxation rates and\nthus allowed us to determine the three collisional disalignment cross sections\nfor the components of the alignment tensor. Both first and second harmonic\nsignals from the magnetometer are considered and compared.", "category": "physics_atom-ph" }, { "text": "Spin-alignment noise in atomic vapor: In the conventional spin noise spectroscopy, the probe laser light monitors\nfluctuations of the spin orientation of a paramagnet revealed as fluctuations\nof its gyrotropy, i.e., circular birefringence. For spins larger than 1/2,\nthere exists spin arrangement of a higher order---the spin alignment---which\nalso exhibits spontaneous fluctuations. We show theoretically and\nexperimentally that the alignment fluctuations manifest themselves as the noise\nof the linear birefringence. In a magnetic field, the spin-alignment\nfluctuations, in contrast to those of spin orientation, show up as the noise of\nthe probe-beam ellipticity at the double Larmor frequency, with the most\nefficient geometry of its observation being the Faraday configuration with the\nlight propagating along the magnetic field. We have detected the spin-alignment\nnoise in a cesium-vapor cell probed at the wavelength of D2 line (852.35 nm).\nThe magnetic-field and polarization dependence of the ellipticity noise are in\nfull agreement with the developed theory.", "category": "physics_atom-ph" }, { "text": "Relativistic coupled-cluster theory analysis of energies, hyperfine\n structure constants, and dipole polarizabilities of Cd$^{+}$: Roles of electron correlation effects in the determination of attachment\nenergies, magnetic dipole hyperfine structure constants and electric dipole\n(E1) matrix elements of the low-lying states in the singly charged cadmium ion\n(Cd$^+$) have been analyzed. We employ the singles and doubles approximated\nrelativistic coupled-cluster (RCC) method to calculate these properties.\nIntermediate results from the Dirac-Hartree-Fock approximation, second-order\nmany-body perturbation theory and considering only the linear terms of the RCC\nmethod are given to demonstrate propagation of electron correlation effects in\nthis ion. Contributions from important RCC terms are also given to highlight\nimportance of various correlation effects in the evaluation of these\nproperties. At the end, we also determine E1 polarizabilities ($\\alpha^{E1}$)\nof the ground and $5p \\ ^2P_{1/2;3/2}$ states of Cd$^+$ in the {\\it ab initio}\napproach. We estimate them again by replacing some of the E1 matrix elements\nand energies from the measurements to reduce their uncertainties so that they\ncan be used in the high precision experiments of this ion.", "category": "physics_atom-ph" }, { "text": "Four-Wave Mixing in Ultracold Atoms using Intermediate Rydberg States: Ultracold Rb atoms were used to demonstrate non-degenerate four-wave mixing\nthrough a Rydberg state. Continuous 5S-5P-nD two-photon excitation to the\nRydberg state was combined with an nD-6P tuned laser in a phase matched\ngeometry. The angular dependence, spatial profile, and dependence on detuning\nwere investigated, showing good agreement with theory. Under optimum conditions\n50 percent of the radiation was emitted into the phase-matched direction.", "category": "physics_atom-ph" }, { "text": "A Stark decelerator on a chip: A microstructured array of 1254 electrodes on a substrate has been configured\nto generate an array of local minima of electric field strength with a\nperiodicity of 120 $\\mu$m about 25 $\\mu$m above the substrate. By applying\nsinusoidally varying potentials to the electrodes, these minima can be made to\nmove smoothly along the array. Polar molecules in low-field seeking quantum\nstates can be trapped in these traveling potential wells. Recently, we\nexperimentally demonstrated this by transporting metastable CO molecules at\nconstant velocities above the substrate [Phys. Rev. Lett. 100 (2008) 153003].\nHere, we outline and experimentally demonstrate how this microstructured array\ncan be used to decelerate polar molecules directly from a molecular beam. For\nthis, the sinusoidally varying potentials need to be switched on when the\nmolecules arrive above the chip, their frequency needs to be chirped down in\ntime, and they need to be switched off before the molecules leave the chip\nagain. Deceleration of metastable CO molecules from an initial velocity of 360\nm/s to a final velocity as low as 240 m/s is demonstrated in the 15-35 mK deep\npotential wells above the 5 cm long array of electrodes. This corresponds to a\ndeceleration of almost $10^5$ $g$, and about 85 cm$^{-1}$ of kinetic energy is\nremoved from the metastable CO molecules in this process.", "category": "physics_atom-ph" }, { "text": "Search for isotope effects in projectile and target ionization in swift\n He$^+$ on H$_2$ or D$_2$ collisions: Using the cold target recoil ion momentum spectroscopy (COLTRIMS) technique,\nwe have measured the simultaneous projectile and target ionization in\ncollisions of He$^+$ projectiles with a mixture of gaseous H$_2$ and D$_2$ for\nan incident projectile energy of 650 keV. Motivated by Cooper et al. [Phys.\nRev. Lett. 100, 043204 (2008)], we look for differences in the ionization cross\nsection of the two isotopes with the highest resolution and statistical\nsignificance. Contributions of the electron-electron and electron-nucleus\ninteractions have been clearly separated kinematically by measuring the\nlongitudinal and transverse momentum of the recoiling ion. We find no\nsignificant isotope effect in any of our momentum distributions.", "category": "physics_atom-ph" }, { "text": "The role of electronic excitation in cold atom-ion chemistry: The role of electronic excitation in charge exchange chemical reactions\nbetween ultracold Ca atoms and Ba$^+$ ions, confined in a hybrid trap, is\nstudied. This prototypical system is energetically precluded from reacting in\nits ground state, allowing a particularly simple interpretation of the\ninfluence of electronic excitation. It is found that while electronic\nexcitation of the ion can critically influence the chemical reaction rate,\nelectronic excitation of the neutral atom is less important. It is also\nexperimentally demonstrated that with the correct choice of the atom-ion pair,\nit is possible to mitigate the unwanted effects of these chemical reactions in\nultracold atom-ion environments, marking an important step towards the next\ngeneration of hybrid devices.", "category": "physics_atom-ph" }, { "text": "Optical atomic clocks with suppressed black body radiation shift: We study a wide range of neutral atoms and ions suitable for ultra-precise\natomic optical clocks with naturally suppressed black body radiation shift of\nclock transition frequency. Calculations show that scalar polarizabilities of\nclock states cancel each other for at least one order of magnitude for\nconsidered systems. Results for calculations of frequencies, quadrupole moments\nof the states, clock transition amplitudes and natural widths of upper clock\nstates are presented.", "category": "physics_atom-ph" }, { "text": "Imagining density distribution of molecular orbitals in IR+XUV\n co-rotating circular laser fields by frequency-domain theory: We have investigated the angle-resolved ATI spectrum of oriented molecules in\nthe IR+XUV co-rotating circular laser fields. According to the different roles\nof IR and XUV laser in the ionization process, we purposefully adjust the\nphoton energy of XUV and the intensity of IR laser to make the ionization\nspectrum of the molecule distributed in a suitable momentum region. Moreover,\nunder the same laser conditions, the background fringes in the ionization\nspectrum of the molecule can be removed by using the ionization spectrum of the\natom with the same ionization energy as the molecule, so that the molecular\norbital density distribution in the suitable momentum region can be obtained.\nThat is, for any unknown molecule, as long as the ionization energy of the\nmolecule can be measured, the density distribution of the molecular orbital can\nbe imaged in a definite momentum region by adjusting the laser field\nconditions, which may shed light on the experimental detection of molecular\norbitals.", "category": "physics_atom-ph" }, { "text": "Optical transmission of an atomic vapor in the mesoscopic regime: By measuring the transmission of near-resonant light through an atomic vapor\nconfined in a nano-cell we demonstrate a mesoscopic optical response arising\nfrom the non-locality induced by the motion of atoms with a phase coherence\nlength larger than the cell thickness. Whereas conventional dispersion theory\n-- where the local atomic response is simply convolved by the Maxwell-Boltzmann\nvelocity distribution -- is unable to reproduce the measured spectra, a model\nincluding a non-local, size-dependent susceptibility is found to be in\nexcellent agreement with the measurements. This result improves our\nunderstanding of light-matter interaction in the mesoscopic regime and has\nimplications for applications where mesoscopic effects may degrade or enhance\nthe performance of miniaturized atomic sensors.", "category": "physics_atom-ph" }, { "text": "Velocimetry of cold atoms by matterwave interferometry: We present an elegant application of matterwave interferometry to the\nvelocimetry of cold atoms whereby, in analogy to Fourier transform\nspectroscopy, the 1-D velocity distribution is manifest in the frequency domain\nof the interferometer output. By using stimulated Raman transitions between\nhyperfine ground states to perform a three-pulse interferometer sequence, we\nhave measured the velocity distributions of clouds of freely-expanding\n$^{85}$Rb atoms with temperatures of 33 $\\mu$K and 17 $\\mu$K. Quadrature\nmeasurement of the interferometer output as a function of the temporal\nasymmetry yields velocity distributions with excellent fidelity. Our technique,\nwhich is particularly suited to ultracold samples, compares favourably with\nconventional Doppler and time-of-flight techniques, and reveals artefacts in\nstandard Raman Doppler methods. The technique is related to, and provides a\nconceptual foundation of, interferometric matterwave accelerometry, gravimetry\nand rotation sensing.", "category": "physics_atom-ph" }, { "text": "Sympathetic cooling of OH- ions using ultracold Rb atoms in a dark SPOT: We are developing a new hybrid atom-ion trap to study the interaction of\nultracold rubidium atoms with mass-selected OH- molecules. The ions are trapped\ninside an octupole rf-trap made of thin wires instead of the commonly used\nrods. This ensures good optical access to the center of the trap where the ions\ncan be overlapped with laser cooled rubidium atoms stored in a dark spontaneous\nforce optical trap (dark SPOT). This setup provides high collision rates since\nthe density in a dark SPOT is about one order of magnitude higher than in a\nstandard magneto-optical trap. Further, inelastic collisions with excited atoms\nare suppressed since almost all atoms are in the ground state. Numerical\nsimulations of our setup using SIMION predict that cooling of the ions is\nfeasible.", "category": "physics_atom-ph" }, { "text": "Nonadiabatic effects in attosecond transient absorption spectroscopy: We study effects of nonadiabatic couplings in a model of a diatomic molecule\nin the context of attosecond transient absorption spectroscopy. By using a\nmodel system consisting of four diabatic electronic states and with a variable\nstrength of the diabatic coupling, we can explore attosecond transient\nabsorption spectra in different regimes of the vibronic couplings between the\nelectronic and nuclear dynamics, and determine when nonadiabatic couplings can\nbe ignored or when they have a substantial effect. The findings are\nrationalized in terms of a multilevel model, which captures aspects of both\nelectronic and nuclear degrees of freedom.", "category": "physics_atom-ph" }, { "text": "Interaction-induced crossover versus finite-size condensation in a\n weakly interacting trapped one-dimensional Bose gas: We discuss the transition from a fully decoherent to a (quasi-)condensate\nregime in a harmonically trapped weakly interacting 1D Bose gas. By using\nanalytic approaches and verifying them against exact numerical solutions, we\nfind a characteristic crossover temperature and crossover atom number that\ndepend on the interaction strength and the trap frequency. We then identify the\nconditions for observing either an interaction-induced crossover scenario or\nelse a finite-size Bose-Einstein condensation phenomenon characteristic of an\n\\textit{ideal} trapped 1D gas.", "category": "physics_atom-ph" }, { "text": "A general expression for the excitation cross section of polarized atoms\n by polarized electrons: The general expression for excitation cross section of polarized atoms by\npolarized electrons is derived by using the methods of the theory of an atom\nadapted for polarization. The special cases of the general expression for the\ndescription of the angular distribution and alignment of excited atoms in the\ncase of polarized and non-polarized atoms as well as the magnetic dichroism of\nthe total excitation cross section of polarized atoms are obtained. The cross\nsections and alignment parameters for the excitation of the autoionizing states\n2p$^5$3s$^2$ $^2$P$_{3/2}$ for Na and 3p$^5$4s$^2$ $^2$P$_{3/2}$ for K are\ncalculated in distorted wave with exchange approximation.", "category": "physics_atom-ph" }, { "text": "Resonant ion-pair formation in electron recombination with HF^+: The cross section for resonant ion-pair formation in the collision of\nlow-energy electrons with HF^+ is calculated by the solution of the\ntime-dependent Schrodinger equation with multiple coupled states using a wave\npacket method. A diabatization procedure is proposed to obtain the electronic\ncouplings between quasidiabatic potentials of ^1Sigma^+ symmetry for HF. By\nincluding these couplings between the neutral states, the cross section for\nion-pair formation increases with about two orders of magnitude compared with\nthe cross section for direct dissociation. Qualitative agreement with the\nmeasured cross section is obtained. The oscillations in the calculated cross\nsection are analyzed. The cross section for ion-pair formation in electron\nrecombination with DF^+ is calculated to determine the effect of isotopic\nsubstitution.", "category": "physics_atom-ph" }, { "text": "Sub-kelvin temperature management in ion traps for optical clocks: The uncertainty of the ac Stark shift due to thermal radiation represents a\nmajor contribution to the systematic uncertainty budget of state-of-the-art\noptical atomic clocks. In the case of optical clocks based on trapped ions, the\nthermal behavior of the rf-driven ion trap must be precisely known. This\ndetermination is even more difficult when scalable linear ion traps are used.\nSuch traps enable a more advanced control of multiple ions and have become a\nplatform for new applications in quantum metrology, simulation and computation.\nNevertheless, their complex structure makes it more difficult to precisely\ndetermine its temperature in operation and thus the related systematic\nuncertainty. We present here scalable linear ion traps for optical clocks,\nwhich exhibit very low temperature rise under operation. We use a\nfinite-element model refined with experimental measurements to determine the\nthermal distribution in the ion trap and the temperature at the position of the\nions. The trap temperature is investigated at different rf-drive frequencies\nand amplitudes with an infrared camera and integrated temperature sensors. We\nshow that for typical trapping parameters for $\\mathrm{In}^{+}$,\n$\\mathrm{Al}^{+}$, $\\mathrm{Lu}^{+}$, $\\mathrm{Ca}^{+}$, $\\mathrm{Sr}^{+}$ or\n$\\mathrm{Yb}^{+}$ ions, the temperature rise at the position of the ions\nresulting from rf heating of the trap stays below 700 mK and can be controlled\nwith an uncertainty on the order of a few 100 mK maximum.", "category": "physics_atom-ph" }, { "text": "Restricted Thermalization for Two Interacting Atoms in a Multimode\n Harmonic Waveguide: In this article, we study the thermalizability of a system consisting of two\natoms in a circular, transversely harmonic waveguide in the multimode regime.\nWhile showing some signatures of the quantum-chaotic behavior, the system fails\nto reach a thermal equilibrium in a relaxation from an initial state, even when\nthe interaction between the atoms is infinitely strong. We relate this\nphenomenon to the previously addressed unattainability of a complete quantum\nchaos in the Seba billiard [P. Seba, Phys. Rev. Lett., 64, 1855 (1990)], and we\nconjecture the absence of a complete thermalization to be a generic property of\nintegrable quantum systems perturbed by a non-integrable but well localized\nperturbation.", "category": "physics_atom-ph" }, { "text": "Indium tin oxide films meet circular Rydberg atoms: prospects for novel\n quantum simulation schemes: Long-lived circular Rydberg atoms are picking up increasing interest for\nboosting coherence times in Rydberg-based quantum simulation. We elaborate a\nnovel approach to stabilize circular Rydberg states against spontaneous and\nblackbody-induced decay using a suppression capacitor made from indium tin\noxide (ITO) thin films, which combine reflection of microwaves with\ntransparency in the visible spectral range. To this end, we perform detailed\ncharacterization of such films using complementary spectroscopic methods at GHz\nand THz frequencies and identify conditions that allow for reaching\ncircular-state lifetimes up to tens of milliseconds in a room-temperature\nenvironment. We discuss prospects of our findings in view of the quest for\nquantum simulations with high-$n$ circular Rydberg states at room temperature.", "category": "physics_atom-ph" }, { "text": "Observation of Photoion Backward Emission in Photoionization of He and\n N2: We experimentally investigate the effects of the linear photon momentum on\nthe momentum distributions of photoions and photoelectrons generated in\none-photon ionization in an energy range of 300 eV $\\leq~E_\\gamma~\\leq$ 40 keV.\nOur results show that for each ionization event the photon momentum is imparted\nonto the photoion, which is essentially the system's center of mass.\nNevertheless, the mean value of the ion momentum distribution along the light\npropagation direction is backward-directed by $-3/5$ times the photon momentum.\nThese results experimentally confirm a 90 year old prediction.", "category": "physics_atom-ph" }, { "text": "Optical atomic clocks: In the last ten years extraordinary results in time and frequency metrology\nhave been demonstrated. Frequency-stabilization techniques for continuous-wave\nlasers and femto-second optical frequency combs have enabled a rapid\ndevelopment of frequency standards based on optical transitions in ultra-cold\nneutral atoms and trapped ions. As a result, today's best performing atomic\nclocks tick at an optical rate and allow scientists to perform high-resolution\nmeasurements with a precision approaching a few parts in $10^{18}$. This paper\nreviews the history and the state of the art in optical-clock research and\naddresses the implementation of optical clocks in a possible future\nredefinition of the SI second as well as in tests of fundamental physics.", "category": "physics_atom-ph" }, { "text": "Observation of mixed singlet-triplet Rb$_2$ Rydberg molecules: We present high-resolution spectroscopy of Rb$_\\text{2}$ ultralong-range\nRydberg molecules bound by mixed singlet-triplet electron-neutral atom\nscattering. The mixing of the scattering channels is a consequence of the\nhyperfine interaction in the ground-state atom, as predicted recently by\nAnderson et al. \\cite{Anderson2014b}. Our experimental data enables the\ndetermination of the effective zero-energy singlet $s$-wave scattering length\nfor Rb. We show that an external magnetic field can tune the contributions of\nthe singlet and the triplet scattering channels and therefore the binding\nenergies of the observed molecules. This mixing of molecular states via the\nmagnetic field results in observed shifts of the molecular line which differ\nfrom the Zeeman shift of the asymptotic atomic states. Finally, we calculate\nmolecular potentials using a full diagonalization approach including the\n$p$-wave contribution and all orders in the relative momentum $k$, and compare\nthe obtained molecular binding energies to the experimental data.", "category": "physics_atom-ph" }, { "text": "Large Momentum Beamsplitter using Bloch Oscillations: The sensitivity of an inertial sensor based on an atomic interfermometer is\nproportional to the velocity separation of atoms in the two arms of the\ninterferometer. In this paper we describe how Bloch oscillations can be used to\nincrease this separation and to create a large momentum transfer (LMT)\nbeamsplitter. We experimentally demonstrate a separation of 10 recoil\nvelocities. Light shifts during the acceleration introduce phase fluctuations\nwhich can reduce the contrast of the interferometer. We precisely calculate\nthis effect and demonstrate that it can be significantly reduced by using a\nsuitable combination of LMT pulses. We finally show that this method seems to\nbe very promising to realize LMT beamsplitter with several 10s of recoil and a\nvery good efficiency.", "category": "physics_atom-ph" }, { "text": "Development of co-located ${}^{129}$Xe and ${}^{131}$Xe nuclear spin\n masers with external feedback scheme: We report on the operation of co-located ${}^{129}$Xe and ${}^{131}$Xe\nnuclear spin masers with an external feedback scheme, and discuss the use of\n${}^{131}$Xe as a comagnetometer in measurements of the ${}^{129}$Xe spin\nprecession frequency. By applying a correction based on the observed change in\nthe ${}^{131}$Xe frequency, the frequency instability due to magnetic field and\ncell temperature drifts are eliminated by two orders of magnitude. The\nfrequency precision of 6.2 $\\mu$Hz is obtained for a 10$^4$ s averaging time,\nsuggesting the possibility of future improvement to $\\approx$ 1 nHz by\nimproving the signal-to-noise ratio of the observation.", "category": "physics_atom-ph" }, { "text": "Ab initio MCDHF calculations of the In and Tl electron affinities and\n their isotope shifts: We report multiconfiguration Dirac-Hartree-Fock and relativistic\nconfiguration interaction calculations on the Thallium (Tl) electron affinity,\nas well as on the excited energy levels arising from the ground configuration\nof Tl$^-$. The results are compared with the available experimental values and\nfurther validated by extending the study to its homologous, lighter element,\nIndium (In), belonging to Group 13 (III.A) of the periodic table. The\ncalculated electron affinities of In and Tl, 383.4 and 322.8 meV, agree with\nthe latest measurements by within 1\\%. Three bound states $^3P_{0,1,2}$ are\nconfirmed in the $5s^25p^2$ configuration of In$^-$ while only the ground state\n$^3P_{0}$ is bound in the $6s^26p^2$ configuration of Tl$^-$. The isotope\nshifts on the In and Tl electron affinities are also estimated. The E2/M1\nintraconfiguration radiative transition rates within $5s^25p^2 \\; ^3P_{0,1,2}$\nof In$^-$ are used to calculate the radiative lifetimes of the metastable\n$^3P_{1,2}$ levels.", "category": "physics_atom-ph" }, { "text": "A Determination of the Fine Structure Constant using Precision\n Measurements of Helium Fine Structure: Spectroscopic measurements of the helium atom are performed to high precision\nusing an atomic beam apparatus and electro-optic laser techniques. These\nmeasurements, in addition to serving as a test of helium theory, also provide a\nnew determination of the fine structure constant {\\alpha}. An apparatus was\ndesigned and built to overcome limitations encountered in a previous\nexperiment. Not only did this allow an improved level of precision but also\nenabled new consistency checks, including an extremely useful measurement in\n3He. I discuss the details of the experimental setup along with the major\nchanges and improvements. A new value for the J = 0 to 2 fine structure\ninterval in the 23P state of 4He is measured to be 31 908 131.25(30) kHz. The\n300 Hz precision of this result represents an improvement over previous results\nby more than a factor of three. Combined with the latest theoretical\ncalculations, this yields a new determination of {\\alpha} with better than 5\nppb uncertainty, {\\alpha}-1 = 137.035 999 55(64).", "category": "physics_atom-ph" }, { "text": "Ion trap with integrated time-of-flight mass spectrometer: Recently, we reported an ion trap experiment with an integrated\ntime-of-flight mass spectrometer (TOFMS) [Phys. Rev. Appl. 2, 034013 (2014)]\nfocussing on the improvement of mass resolution and detection limit due to\nsample preparation at millikelvin temperatures. The system utilizes a\nradio-frequency (RF) ion trap with asymmetric drive for storing and\nmanipulating laser-cooled ions and features radial extraction into a compact\n$275$ mm long TOF drift tube. The mass resolution exceeds $m / \\Delta m = 500$,\nwhich provides isotopic resolution over the whole mass range of interest in\ncurrent experiments and constitutes an improvement of almost an order of\nmagnitude over other implementations. In this manuscript, we discuss the\nexperimental implementation in detail, which is comprised of newly developed\ndrive electronics for generating the required voltages to operate RF trap and\nTOFMS, as well as control electronics for regulating RF outputs and\nsynchronizing the TOFMS extraction.", "category": "physics_atom-ph" }, { "text": "Coulomb glory effect in collisions of antiprotons with heavy nuclei:\n relativistic theory: Collisions of antiprotons with bare uranium nuclei are studied for scattering\nangles nearby 180$^{\\circ}$ in the framework of relativistic theory. The\nCoulomb glory phenomenon is investigated at energies of the antiprotons in the\nrange 100 eV to 2.5 keV. The vacuum polarization effect and the anomalous\nmagnetic moment of the antiproton are taken into account. The estimations of\npossible influence of such effects as radiative recombination and antiproton\nannihilation are given.", "category": "physics_atom-ph" }, { "text": "Kinetic constraints, hierarchical relaxation and onset of glassiness in\n strongly interacting and dissipative Rydberg gases: We show that the dynamics of a laser driven Rydberg gas in the limit of\nstrong dephasing is described by a master equation with manifest kinetic\nconstraints. The equilibrium state of the system is uncorrelated but the\nconstraints in the dynamics lead to spatially correlated collective relaxation\nreminiscent of glasses. We study and quantify the evolution towards equilibrium\nin one and two dimensions, and analyze how the degree of glassiness and the\nrelaxation time are controlled by the interaction strength between Rydberg\natoms. We also find that spontaneous decay of Rydberg excitations leads to an\ninterruption of glassy relaxation that takes the system to a highly correlated\nnon-equilibrium stationary state. The results presented here, which are in\nprinciple also applicable other systems such as polar molecules and atoms with\nlarge magnetic dipole moments, show that the collective behavior of cold atomic\nand molecular ensembles can be similar to that found in soft condensed-matter\nsystems.", "category": "physics_atom-ph" }, { "text": "New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength\n Problem: One of the most enduring and intensively studied problems of X-ray astronomy\nis the disagreement of state-of-the art theory and observations for the\nintensity ratio of two Fe XVII transitions of crucial value for plasma\ndiagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III\nsynchrotron facility by increasing the resolving power two and a half times and\nthe signal-to-noise ratio thousand-fold compared to our previous work. The\nLorentzian wings had hitherto been indistinguishable from the background and\nwere thus not modeled, resulting in a biased line-strength estimation. The\npresent experimental oscillator-strength ratio\n$R_\\mathrm{exp}=f_{\\mathrm{3C}}/f_{\\mathrm{3D}}=3.51(2)_{\\mathrm{stat}}(7)_{\\mathrm{sys}}$\nagrees with our state-of-the-art calculation of $R_\\mathrm{th}=3.55(2)$, as\nwell as with some previous theoretical predictions. To further rule out any\nuncertainties associated with the measured ratio, we also determined the\nindividual natural linewidths and oscillator strengths of 3C and 3D\ntransitions, which also agree well with the theory. This finally resolves the\ndecades-old mystery of Fe XVII oscillator strengths.", "category": "physics_atom-ph" }, { "text": "QED theory of the nuclear recoil with finite size: We investigate the modification of the transverse electromagnetic interaction\nbetween two point-like particles when one particle acquires a finite size. It\nis shown that the correct treatment of such interaction cannot be accomplished\nwithin the Breit approximation but should be addressed within the QED. The\ncomplete QED formula is derived for the finite-size nuclear recoil, exact in\nthe coupling strength parameter $Z\\,\\alpha$. Numerical calculations are carried\nout for a wide range of $Z$ and verified against the $(Z\\,\\alpha)^5$\ncontribution. The comparison with the $Z\\,\\alpha$ expansion identifies the\ncontribution of order $(Z\\,\\alpha)^6$, which is linear in the nuclear radius\nand numerically dominates over the lower-order $(Z\\,\\alpha)^5$ term.", "category": "physics_atom-ph" }, { "text": "The proton radius puzzle: High-precision measurements of the proton radius from laser spectroscopy of\nmuonic hydrogen demonstrated up to six standard deviations smaller values than\nobtained from electron-proton scattering and hydrogen spectroscopy. The status\nof this discrepancy, which is known as the proton radius puzzle will be\ndiscussed in this paper, complemented with the new insights obtained from\nspectroscopy of muonic deuterium.", "category": "physics_atom-ph" }, { "text": "Multistage Zeeman deceleration of metastable neon: A supersonic beam of metastable neon atoms has been decelerated by exploiting\nthe interaction between the magnetic moment of the atoms and time-dependent\ninhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91\ndeceleration solenoids, the atoms were decelerated from an initial velocity of\n580m/s to final velocities as low as 105m/s, corresponding to a removal of more\nthan 95% of their initial kinetic energy. The phase-space distribution of the\ncold, decelerated atoms was characterized by time-of-flight and imaging\nmeasurements, from which a temperature of 10mK was obtained in the moving frame\nof the decelerated sample. In combination with particle-trajectory simulations,\nthese measurements allowed the phase-space acceptance of the decelerator to be\nquantified. The degree of isotope separation that can be achieved by multistage\nZeeman deceleration was also studied by performing experiments with pulse\nsequences generated for $^{20}$Ne and $^{22}$Ne.", "category": "physics_atom-ph" }, { "text": "Relativistic Fock space coupled cluster study of bismuth electronic\n structure to extract the Bi nuclear quadrupole moment: We report the value of the electric quadrupole moment of $^{209}$Bi extracted\nfrom the atomic data. For this, we performed electronic structure calculations\nfor the ground $^4S^o_{3/2}$ and excited $^2P^o_{3/2}$ states of atomic Bi\nusing the Dirac-Coulomb-Breit Hamiltonian and the Fock space coupled cluster\nmethod with single, double, and full triple amplitudes for the three-particle\nFock space sector. The value of the quadrupole moment of $^{209}$Bi,\n$Q(^{209}$Bi$)=-418(6)$~mb, derived from the resulting electric field gradient\nvalues and available atomic hyperfine splittings is in excellent agreement with\nmolecular data. Due to the availability of the hyperfine constants for unstable\nisotopes of Bi, current atomic calculation allows also to correct their\nquadrupole moments.", "category": "physics_atom-ph" }, { "text": "Comparing a mercury optical lattice clock with microwave and optical\n frequency standards: In this paper we report the evaluation of an optical lattice clock based on\nneutral mercury down to a relative uncertainty of $1.7\\times 10^{-16}$.\nComparing this characterized frequency standard to a Cs atomic fountain we\ndetermine the absolute frequency of the $^1S_0 \\rightarrow \\phantom{}^3P_0$\ntransition of $^{199}$Hg as $\\nu_{\\mathrm{Hg}} = 1\n128\\,575\\,290\\,808\\,154.62\\,$Hz $\\pm\\,0.19\\,$Hz (statistical) $\\pm\\,0.38\\,$Hz\n(systematic), limited solely by the realization of the SI second. Furthermore,\nby comparing the mercury optical lattice clock to a Rb atomic fountain, we\ndetermine for the first time to our knowledge the ratio between the $^{199}$Hg\nclock transition and the $^{87}$Rb ground state hyperfine transition. Finally\nwe present a direct optical to optical measurement of the $^{199}$Hg/$^{87}$Sr\nfrequency ratio. The obtained value of\n$\\nu_{\\mathrm{Hg}}/\\nu_{\\mathrm{Sr}}=2.629\\,314\\,209\\,898\\,909\\,15$ with a\nfractional uncertainty of $1.8\\times10^{-16}$ is in excellent agreement with\nthe same measurement obtained by Yamanaka et al. (arXiv:1503.07941). This makes\nthis frequency ratio one of the few physical quantities agreed upon by\ndifferent laboratories to this level of uncertainty. Frequency ratio\nmeasurements of the kind of those reported in this paper have a strong impact\nfor frequency metrology but also for fundamental physics as they can be used to\nmonitor putative variations of fundamental constants.", "category": "physics_atom-ph" }, { "text": "Doppler-free spectroscopy of molecular iodine using a frequency-stable\n light source at 578 nm: A stable light source obtained using sum-frequency generation (SFG) is\ndeveloped for high-resolution spectroscopy at 578 nm. Hyperfine transitions of\nmolecular iodine are observed by using the SFG light source with saturation\nspectroscopy. The light source is frequency stabilized to the observed\nhyperfine transition and achieves a stability of 2*10-12 for a 1-s averaging\ntime. The absolute frequency of the light source stabilized on the a1 component\nof the R(37)16-1 transition is determined as 518304551833 (2) kHz. This\ntransition serves as a frequency reference for the 1S0 - 3P0 optical clock\ntransition in neutral ytterbium (Yb).", "category": "physics_atom-ph" }, { "text": "2S hyperfine structure of atomic deuterium: We have measured the frequency splitting between the $(2S, F=1/2)$ and $(2S,\nF=3/2)$ hyperfine sublevels in atomic deuterium by an optical differential\nmethod based on two-photon Doppler-free spectroscopy on a cold atomic beam. The\nresult $f_{\\rm HFS}^{(D)}(2S)= 40 924 454(7)$ Hz is the most precise value for\nthis interval to date. In comparison to the previous radio-frequency\nmeasurement we have improved the accuracy by the factor of three.\n The specific combination of hyperfine frequency intervals for metastable- and\nground states in deuterium atom $D_{21}=8f_{\\rm HFS}^{(D)}(2S)-f_{\\rm\nHFS}^{(D)}(1S)$ derived from our measurement is in a good agreement with\n$D_{21}$ calculated from quantum-electrodynamics theory.", "category": "physics_atom-ph" }, { "text": "Manifestations of a spatial variation of fundamental constants on atomic\n clocks, Oklo, meteorites, and cosmological phenomena: The remarkable detection of a spatial variation in the fine-structure\nconstant, alpha, from quasar absorption systems must be independently confirmed\nby complementary searches. In this letter, we discuss how terrestrial\nmeasurements of time-variation of the fundamental constants in the laboratory,\nmeteorite data, and analysis of the Oklo nuclear reactor can be used to\ncorroborate the spatial variation seen by astronomers. Furthermore, we show\nthat spatial variation of the fundamental constants may be observable as\nspatial anisotropy in the cosmic microwave background, the accelerated\nexpansion (dark energy), and large-scale structure of the Universe.", "category": "physics_atom-ph" }, { "text": "Effects of autoionization in electron loss from helium-like highly\n charged ions in collisions with photons and fast atomic particles: We study theoretically single electron loss from helium-like highly charged\nions involving excitation and decay of autoionizing states of the ion. Electron\nloss is caused by either photo absorption or the interaction with a fast atomic\nparticle (a bare nucleus, a neutral atom, an electron). The interactions with\nthe photon field and the fast particles are taken into account in the first\norder of perturbation theory. Two initial states of the ion are considered:\n$1s^2$ and $(1s2s)_{J=0}$. We analyze in detail how the shape of the emission\npattern depends on the atomic number $Z_{I}$ of the ion discussing, in\nparticular, the inter-relation between electron loss via photo absorption and\ndue to the impact of atomic particles in collisions at modest relativistic and\nextreme relativistic energies. According to our results, in electron loss from\nthe $1s^2$ state autoionization may substantially influence the shape of the\nemission spectra only up to $Z_{I} \\approx 35-40$. A much more prominent role\nis played by autoionization in electron loss from $(1s2s)_{J=0}$ where it not\nonly strongly affect the shape of the emission pattern but also may\nsubstantially increase the total loss cross section.", "category": "physics_atom-ph" }, { "text": "Self-Energy Correction to the Two-Photon Decay Width in Hydrogenlike\n Atoms: We investigate the gauge invariance of the leading logarithmic radiative\ncorrection to the two-photon decay width in hydrogenlike atoms. It is shown\nthat an effective treatment of the correction using a Lamb-shift \"potential\"\nleads to equivalent results in both the length as well as the velocity gauges\nprovided all relevant correction terms are taken into account. Specifically,\nthe relevant radiative corrections are related to the energies that enter into\nthe propagator denominators, to the Hamiltonian, to the wave functions, and to\nthe energy conservation condition that holds between the two photons; the form\nof all of these effects is different in the two gauges, but the final result is\nshown to be gauge invariant, as it should be. Although the actual calculation\nonly involves integrations over nonrelativistic hydrogenic Green functions, the\nderivation of the leading logarithmic correction can be regarded as slightly\nmore complex than that of other typical logarithmic terms. The dominant\nradiative correction to the 2S two-photon decay width is found to be -2.020536\n(alpha/pi) (Zalpha)^2 ln[(Zalpha)^-2] in units of the leading nonrelativistic\nexpression. This result is in agreement with a length-gauge calculation [S. G.\nKarshenboim and V. G. Ivanov, e-print physics/9702027], where the coefficient\nwas given as -2.025(1).", "category": "physics_atom-ph" }, { "text": "Long-range Rydberg molecule Rb$_2$: Two-electron \\textit{R}-matrix\n calculations at intermediate internuclear distances: The adiabatic potential energy curves of Rb$_2$ in the long-range Rydberg\nelectronic states are calculated using the two-electron \\textit{R}-matrix\nmethod [M. Tarana, R. \\v{C}ur\\'{i}k, Phys. Rev. A \\textbf{93}, 012515 (2016)]\nfor the intermediate internuclear separations between 35 a.u. and 200 a.u. The\nresults are compared with the zero-range models to find a region of the\ninternuclear distances where the Fermi's pseudopotential approach provides\naccurate energies. A finite-range potential model of the atomic perturber is\nused to calculate the wave functions of the Rydberg electron and their features\nspecific for the studied range of internuclear distances are identified.", "category": "physics_atom-ph" }, { "text": "Frequency measurements of $5s5p^{3}$P$_{0}\\to5s6d^{3}$D$_{1}$ and\n observation of nonlinearities in King plot with Sr: We report the first precision measurement of the absolute frequency of\n$5s5p^{3}$P$_{0}\\to5s6d^{3}$D$_{1}$ for all four stable Sr isotopes with an\naccuracy of $\\sim$25 kHz employing repumping induced spectroscopy. By combining\nthe isotope shifts of this transition with the existing measurement data on the\nintercombination line, the King plot is established which reveals a deviation\nfrom the linearity at the 5.2$\\sigma$ level.", "category": "physics_atom-ph" }, { "text": "Convolutional neural network for retrieval of the time-dependent bond\n length in a molecule from photoelectron momentum distributions: We apply deep learning for retrieval of the time-dependent bond length in the\ndissociating two-dimensional H$_2^{+}$ molecule using photoelectron momentum\ndistributions. We consider a pump-probe scheme and calculate electron momentum\ndistributions from strong-field ionization by treating the motion of the nuclei\nclassically, semiclassically or quantum mechanically. A convolutional neural\nnetwork trained on momentum distributions obtained at fixed internuclear\ndistances retrieves the time-varying bond length with an absolute error of\n$0.2$-$0.3$ a.u.", "category": "physics_atom-ph" }, { "text": "A Wigner Function Approach to Coherence in a Talbot-Lau Interferometer: Using a thermal gas, we model the signal of a trapped interferometer. This\ninterferometer uses two short laser pulses, separated by time T, which act as a\nphase grating for the matter waves. Near time 2T, there is an echo in the\ncloud's density due to the Talbot-Lau effect. Our model uses the Wigner\nfunction approach and includes a weak residual harmonic trap. The analysis\nshows that the residual potential limits the interferometer's visibility,\nshifts the echo time of the interferometer, and alters its time dependence.\nLoss of visibility can be mitigated by optimizing the initial trap frequency\njust before the interferometer cycle begins.", "category": "physics_atom-ph" }, { "text": "High-accuracy inertial measurements with cold-atom sensors: The research on cold-atom interferometers gathers a large community of about\n50 groups worldwide both in the academic and now in the industrial sectors. The\ninterest in this sub-field of quantum sensing and metrology lies in the large\npanel of possible applications of cold-atom sensors for measuring inertial and\ngravitational signals with a high level of stability and accuracy. This review\npresents the evolution of the field over the last 30 years and focuses on the\nacceleration of the research effort in the last 10 years. The article describes\nthe physics principle of cold-atom gravito-inertial sensors as well as the main\nparts of hardware and the expertise required when starting the design of such\nsensors. It then reviews the progress in the development of instruments\nmeasuring gravitational and inertial signals, with a highlight on the\nlimitations to the performances of the sensors, on their applications, and on\nthe latest directions of research.", "category": "physics_atom-ph" }, { "text": "Prospects for the formation of ultracold polar ground state KCs\n molecules via an optical process: Heteronuclear alkali-metal dimers represent the class of molecules of choice\nfor creating samples of ultracold molecules exhibiting an intrinsic large\npermanent electric dipole moment. Among them, the KCs molecule, with a\npermanent dipole moment of 1.92~Debye still remains to be observed in ultracold\nconditions. Based on spectroscopic studies available in the literature\ncompleted by accurate quantum chemistry calculations, we propose several\noptical coherent schemes to create ultracold bosonic and fermionic KCs\nmolecules in their absolute rovibrational ground level, starting from a weakly\nbound level of their electronic ground state manifold. The processes rely on\nthe existence of convenient electronically excited states allowing an efficient\nstimulated Raman adiabatic transfer of the level population.", "category": "physics_atom-ph" }, { "text": "Nonlinear resonant X-ray Raman scattering: We report the observation of a novel nonlinear effect in the hard x-ray\nrange. Upon illuminating Fe and Cu metal foils with intense x-ray pulses tuned\nnear their respective K edges, photons at nearly twice the incoming photon\nenergy are emitted. The signal rises quadratically with the incoming intensity,\nconsistent with two-photon excitation. The spectrum of emitted high-energy\nphotons comprises multiple Raman lines that disperse with the incident photon\nenergy. Upon reaching the double K-shell ionization threshold, the signal\nstrength undergoes a marked rise. Above this threshold, the lines cease\ndispersing, turning into orescence lines with energies much greater than\nobtainable by single electron transitions, and additional Raman lines appear.\nWe attribute these processes to electron-correlation mediated multielectron\ntransitions involving double-core hole excitation and various two-electron\nde-excitation processes to a final state involving one or more L and M\ncore-holes.", "category": "physics_atom-ph" }, { "text": "Electron-ion merged-beam experiments at heavy-ion storage rings: In the past two decades, the electron-ion merged-beams technique has\nextensively been exploited at heavy-ion storage rings equipped with electron\ncoolers for spectroscopic studies of highly charged ions as well as for\nmeasuring absolute cross sections and rate coefficients for electron-ion\nrecombination and electron-impact ionization of multiply charged atoms ions.\nSome recent results are highlighted and future perspectives are pointed out, in\nparticular, in view of novel experimental possibilities at the FAIR facility in\nDarmstadt and at the Cryogenic Storage Ring at the Max-Planck-Institute for\nNuclear Physics in Heidelberg.", "category": "physics_atom-ph" }, { "text": "Characterization of fluorescence collection optics integrated with a\n micro-fabricated surface electrode ion trap: One of the outstanding challenges for ion trap quantum information processing\nis to accurately detect the states of many ions in a scalable fashion. In the\nparticular case of surface traps, geometric constraints make imaging\nperpendicular to the surface appealing for light collection at multiple\nlocations with minimal cross-talk. In this report we describe an experiment\nintegrating Diffractive Optic Elements (DOE's) with surface electrode traps,\nconnected through in-vacuum multi-mode fibers. The square DOE's reported here\nwere all designed with solid angle collection efficiencies of 3.58%; with all\nlosses included a detection efficiency of 0.388% (1.02% excluding the PMT loss)\nwas measured with a single Ca+ ion. The presence of the DOE had minimal effect\non the stability of the ion, both in temporal variation of stray electric\nfields and in motional heating rates.", "category": "physics_atom-ph" }, { "text": "Numerical Simulation of Nano Scanning in Intermittent-Contact Mode AFM\n under Q control: We investigate nano scanning in tapping mode atomic force microscopy (AFM)\nunder quality (Q) control via numerical simulations performed in SIMULINK. We\nfocus on the simulation of whole scan process rather than the simulation of\ncantilever dynamics and the force interactions between the probe tip and the\nsurface alone, as in most of the earlier numerical studies. This enables us to\nquantify the scan performance under Q control for different scan settings.\nUsing the numerical simulations, we first investigate the effect of elastic\nmodulus of sample (relative to the substrate surface) and probe stiffness on\nthe scan results. Our numerical simulations show that scanning in attractive\nregime using soft cantilevers with high Qeff results in a better image quality.\nWe, then demonstrate the trade-off in setting the effective Q factor (Qeff) of\nthe probe in Q control: low values of Qeff cause an increase in tapping forces\nwhile higher ones limit the maximum achievable scan speed due to the slow\nresponse of the cantilever to the rapid changes in surface profile. Finally, we\nshow that it is possible to achieve higher scan speeds without causing an\nincrease in the tapping forces using adaptive Q control (AQC), in which the Q\nfactor of the probe is changed instantaneously depending on the magnitude of\nthe error signal in oscillation amplitude. The scan performance of AQC is\nquantitatively compared to that of standard Q control using iso-error curves\nobtained from numerical simulations first and then the results are validated\nthrough scan experiments performed using a physical set-up.", "category": "physics_atom-ph" }, { "text": "First observation of two hyperfine transitions in antiprotonic He-3: We report on the first experimental results for microwave spectroscopy of the\nhyperfine structure of antiprotonic He-3. Due to the helium nuclear spin,\nantiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4\nwhich has already been studied before. Thus a comparison between theoretical\ncalculations and the experimental results will provide a more stringent test of\nthe three-body quantum electrodynamics (QED) theory. Two out of four\nsuper-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were\nobserved. The measured frequencies of the individual transitions are\n11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current\ntheoretical values, but still within their estimated errors. Although the\nexperimental uncertainty for the difference of these frequencies is still very\nlarge as compared to that of theory, its measured value agrees with theoretical\ncalculations. This difference is crucial to be determined because it is\nproportional to the magnetic moment of the antiproton.", "category": "physics_atom-ph" }, { "text": "An inverted crossover resonance within one Zeeman manifold: We carry out investigations of inverted crossover resonances in $\\pi$-driven\nfour-level systems where $\\Delta F$ can be zero. Through the use of sub-Doppler\nfrequency modulation spectroscopy of the $(6s^{2})$ $^{1}S_{0}$ $-$ $(6s6p)$\n$^{3}P_{1}$ transition in $^{171}$Yb the resonance becomes manifest. The\ncentre-frequency is inherently insensitive to first-order Zeeman shifts and\nequates to the two-level resonance frequency in the absence of a magnetic\nfield. A rate equation model is used to help validate the nature of the\nresonance. Optical frequency measurements of the $F'=1/2$ hyperfine line\nrecorded over two months demonstrate a statistical uncertainty of\n$2\\times10^{-11}$. The inverted crossover resonance found with the $F'=3/2$\nline is used for 556 nm laser frequency stabilization, which is an alternative\nmeans when applied to magneto-optical trapping of $^{171}$Yb.", "category": "physics_atom-ph" }, { "text": "Causality and quantum interference in time-delayed laser-induced\n nonsequential double ionization: We perform a detailed analysis of the importance of causality within the\nstrong-field approximation and the steepest descent framework for the\nrecollision-excitation with subsequent tunneling ionization (RESI) pathway in\nlaser-induced nonsequential double ionization (NSDI). In this time-delayed\npathway, an electron returns to its parent ion, and, by recolliding with the\ncore, gives part of its kinetic energy to excite a second electron at a time\n$t^{\\prime}$. The second electron then reaches the continuum at a later time\n$t$ by tunneling ionization. We show that, if $t^{\\prime}$ and $t$ are complex,\nthe condition that recollision of the first electron occurs before tunnel\nionization of the second electron translates into boundary conditions for the\nsteepest-descent contours, and thus puts constraints on the saddles to be taken\nwhen computing the RESI transition amplitudes. We also show that this\ngeneralized causality condition has a dramatic effect in the shapes of the RESI\nelectron momentum distributions for few-cycle laser pulses. Physically,\ncausality determines how the dominant sets of orbits an electron returning to\nits parent ion can be combined with the dominant orbits of a second electron\ntunneling from an excited state. All features encountered are analyzed in terms\nof such orbits, and their quantum interference.", "category": "physics_atom-ph" }, { "text": "Intercombination line photoassociation spectroscopy of\n ${}^{87}$Rb${}^{170}$Yb: We report on the first observation of photoassociation near the ${}^2 S\n_\\frac 1 2 + {}^3P_1$-asymptote in a mixture of ${}^{87}$Rb and ${}^{170}$Yb.\nIn a search spanning binding energies between 0.1 GHz and 11 GHz, a single pair\nof interspecies PA resonances is detected around 3.1 GHz. These resonances are\ncharacterized by extracting PA rates, binding energies and Zeeman shift\ncoefficients. Using one of these resonances, 2-photon-photoassociaton is\nperformed, improving on previous measurements of the binding energies of the\ntwo least bound states in the electronic ground state and demonstrating\nintercombination line photoassociation as a powerful spectroscopic tool. We\ndiscuss implications for pathways towards RbYb molecules in the absolute ground\nstate.", "category": "physics_atom-ph" }, { "text": "Frequency-Domain Coherent Control of Femtosecond Two-Photon Absorption:\n Intermediate-Field vs. Weak-Field Regime: Coherent control of femtosecond two-photon absorption in the\nintermediate-field regime is analyzed in detail in the powerful frequency\ndomain using an extended 4th-order perturbative description. The corresponding\nabsorption is coherently induced by the weak-field non-resonant two-photon\ntransitions as well as by four-photon transitions involving three absorbed\nphotons and one emitted photons. The interferences between these two groups of\ntransitions lead to a difference between the intermediate-field and weak-field\nabsorption dynamics. The corresponding interference nature (constructive or\ndestructive) strongly depends on the detuning direction of the pulse spectrum\nfrom half the two-photon transition frequency. The model system of the study is\natomic sodium, for which both experimental and theoretical results are\nobtained. The detailed understanding obtained here serves as a basis for\ncoherent control with rationally-shaped femtosecond pulses in a regime of\nsizable absorption yields.", "category": "physics_atom-ph" }, { "text": "Measurement scheme and analysis for weak ground state hyperfine\n transition moments through two-pathway coherent control: We report our detailed analysis of a table-top system for the measurement of\nthe weak-force-induced electric dipole moment of a ground state hyperfine\ntransition carried out in an atomic beam geometry. We describe an experimental\nconfiguration of conductors for application of orthogonal r.f. and static\nelectric fields, with cavity enhancement of the r.f. field amplitude, that\nallows confinement of the r.f. field to a region in which the static fields are\nuniform and well-characterized. We carry out detailed numerical simulations of\nthe field modes, and analyze the expected magnitude of statistical and\nsystematic limits to the measurement of this transition amplitude in atomic\ncesium. The combination of an atomic beam with this configuration leads to\nstrong suppression of magnetic dipole contributions to the atomic signal. The\napplication of this technique to the measurement of extremely weak transition\namplitudes in other atomic systems, especially alkali metals, seems very\nfeasible.", "category": "physics_atom-ph" }, { "text": "Pair creation in heavy ion channeling: Heavy ions channeling through crystals with multi-GeV kinetic energies can\ncreate electron-positron pairs. In the framework of the ion, the energy of\nvirtual photons arising from the periodic crystal potential may exceed the\nthreshold $2mc^2$. The repeated periodic collisions with the crystal ions yield\nhigh pair production rates. When the virtual photon frequency matches a nuclear\ntransition in the ion, the production rate can be resonantly increased. In this\ntwo-step excitation-pair conversion scheme, the excitation rates are coherently\nenhanced, and they scale approximately quadratically with the number of crystal\nsites along the channel.", "category": "physics_atom-ph" }, { "text": "The radiative potential method for calculations of QED radiative\n corrections to energy levels and electromagnetic amplitudes in many-electron\n atoms: We derive an approximate expression for a \"radiative potential\" which can be\nused to calculate QED strong Coulomb field radiative corrections to energies\nand electric dipole (E1) transition amplitudes in many-electron atoms with an\naccuracy of a few percent. The expectation value of the radiative potential\ngives radiative corrections to the energies. Radiative corrections to E1\namplitudes can be expressed in terms of the radiative potential and its energy\nderivative (the low-energy theorem): the relative magnitude of the radiative\npotential contribution is ~alpha^3 Z^2 ln(1/(alpha^2 Z^2)), while the sum of\nother QED contributions is ~alpha^3 (Z_i+1)^2, where Z_i is the ion charge;\nthat is, for neutral atoms (Z_i=0) the radiative potential contribution exceeds\nother contributions ~Z^2 times. The advantage of the radiative potential method\nis that it is very simple and can be easily incorporated into many-body theory\napproaches: relativistic Hartree-Fock, configuration interaction, many-body\nperturbation theory, etc. As an application we have calculated the radiative\ncorrections to the energy levels and E1 amplitudes as well as their\ncontributions (-0.33% and 0.42%, respectively) to the parity non-conserving\n(PNC) 6s-7s amplitude in neutral cesium (Z=55). Combining these results with\nthe QED correction to the weak matrix elements (-0.41%) we obtain the total QED\ncorrection to the PNC 6s-7s amplitude, (-0.32 +/- 0.03)%. The cesium weak\ncharge Q_W=-72.66(29)_{exp}(36)_{theor} agrees with the Standard Model value\nQ_W^{SM}=-73.19(13), the difference is 0.53(48).", "category": "physics_atom-ph" }, { "text": "Box traps on an atom chip for one-dimensional quantum gases: We present the implementation of tailored trapping potentials for ultracold\ngases on an atom chip. We realize highly elongated traps with box-like\nconfinement along the long, axial direction combined with conventional harmonic\nconfinement along the two radial directions. The design, fabrication and\ncharacterization of the atom chip and the box traps is described. We load\nultracold ($\\lesssim1 \\mu$K) clouds of $^{87}$Rb in a box trap, and demonstrate\nBose-gas focusing as a means to characterize these atomic clouds in arbitrarily\nshaped potentials. Our results show that box-like axial potentials on atom\nchips are very promising for studies of one-dimensional quantum gases.", "category": "physics_atom-ph" }, { "text": "Strong-field approximation for harmonic generation in diatomic molecules: The generation of high-order harmonics in diatomic molecules is investigated\nwithin the framework of the strong-field approximation. We show that the\nconventional saddle-point approximation is not suitable for large internuclear\ndistances. An adapted saddle-point method that takes into account the molecular\nstructure is presented. We analyze the predictions for the harmonic-generation\nspectra in both the velocity and the length gauge. At large internuclear\nseparations, we compare the resulting cutoffs with the predictions of the\nsimple-man's model. Good agreement is obtained only by using the adapted\nsaddle-point method combined with the velocity gauge.", "category": "physics_atom-ph" }, { "text": "The frequency of the ultranarrow ${^1\\text{S}_0} - {^3\\text{P}_2}$\n transition in $^{87}\\text{Sr}$: We determine the frequency of the ultranarrow $^{87}\\text{Sr}$\n${^{1}\\text{S}_{0}} - {^{3}\\text{P}_{2}}$ transition by spectroscopy of an\nultracold gas. This transition is referenced to four molecular iodine lines\nthat are observed by Doppler-free saturation spectroscopy of hot iodine vapor.\nThe frequency differences between the Sr and the I$_2$ transitions are measured\nwith an uncertainty of 250 kHz. The absolute frequency of the $^{87}\\text{Sr}$\n${^{1}\\text{S}_{0}} - {^{3}\\text{P}_{2}}$ ($\\text{F}'=7/2$) transition is\n446648775(30) MHz and limited in accuracy by the iodine reference. This work\nprepares the use of the Sr ${^{1}\\text{S}_{0}} - {^{3}\\text{P}_{2}}$ transition\nfor quantum simulation and computation.", "category": "physics_atom-ph" }, { "text": "A spaceborne gravity gradiometer concept based on cold atom\n interferometers for measuring Earth's gravity field: We propose a concept for future space gravity missions using cold atom\ninterferometers for measuring the diagonal elements of the gravity gradient\ntensor and the spacecraft angular velocity. The aim is to achieve better\nperformance than previous space gravity missions due to a very low white noise\nspectral behavior and a very high common mode rejection, with the ultimate\ngoals of determining the fine structures of the gravity field with higher\naccuracy than GOCE and detecting time-variable signals in the gravity field\nbetter than GRACE.", "category": "physics_atom-ph" }, { "text": "Progress on indium and barium single ion optical frequency standards: We report progress on 115In+ and 137Ba+ single ion optical frequency\nstandards using all solid-state sources. Both are free from quadrupole field\nshifts and together enable a search for drift in fundamental constants.", "category": "physics_atom-ph" }, { "text": "High Density Pulsed Molecular Beam for Cold Ion Chemistry: A recent expansion of cold and ultracold molecule applications has led to\nrenewed focus on molecular species preparation under ultrahigh vacuum\nconditions. Meanwhile, molecular beams have been used to study gas phase\nchemical reactions for decades. In this manuscript, we describe an apparatus\nthat uses pulsed molecular beam technology to achieve high local gas densities,\nleading to faster reaction rates with cold trapped ions. We characterize the\nbeam's spatial profile using the trapped ions themselves. This apparatus could\nbe used for preparation of molecular species by reactions requiring excitation\nof trapped ion precursors to states with short lifetimes or for obtaining a\nhigh reaction rate with minimal increase of background chamber pressure.", "category": "physics_atom-ph" }, { "text": "Revisiting Bohr's quantization hypothesis for the atomic orbitals: We deduce the quantization of the atomic orbit for the hydrogen's atom model\nproposed by Bohr without using his hypothesis of angular momentum quantization.\nWe show that his hypothesis can be deduced from and is a consequence of the\nPlanck's energy quantization.", "category": "physics_atom-ph" }, { "text": "Optical stimulated slowing of polar heavy-atom molecules with a constant\n beat phase: Polar heavy-atom molecules have been well recognized as promising candidates\nfor precision measurements and tests of fundamental physics. A much slower\nmolecular beam to increase the interaction time should lead to a more sensitive\nmeasurement. Here we theoretically demonstrate the possibility of the\nstimulated longitudinal slowing of heavy-atom molecules by the coherent optical\nbichromatic force with a constant beat phase. Taking the YbF meolecule as an\nexample, we show that a rapid and short-distance deceleration of heavy\nmolecules by a phase-compensation method is feasible with moderate conditions.\nA molecular beam of YbF with a forward velocity of 120 m/s can be decelerated\nbelow 10 m/s within a distance of 3.5 cm and with a laser irradiance for each\ntraveling wave of 107.2 W/cm$^2$. We also give a simple approach to estimate\nthe performance of the BCF on some other heavy molecules, which is helpful for\nmaking a rapid evaluation on the feasibility of the stimulated slowing\nexperiment. Our proposed slowing method could be a promising approach to break\nthrough the space constraint or the limited capture efficiency of molecules\nloadable into a MOT in traditional deceleration schemes, opening the\npossibility for a significant improvement of the precision measurement\nsensitivity.", "category": "physics_atom-ph" }, { "text": "Wave-packet propagation based calculation of above-threshold ionization\n in the x-ray regime: We investigate the multi-photon process of above-threshold ionization for the\nlight elements hydrogen, carbon, nitrogen and oxygen in the hard x-ray regime.\nNumerical challenges are discussed and by comparing Hartree-Fock-Slater\ncalculations to configuration-interaction-singles results we justify the\nmean-field potential approach in this regime. We present a theoretical\nprediction of two-photon above-threshold-ionization cross sections for the\nmentioned elements. Moreover, we study how the importance of above-threshold\nionization varies with intensity. We find that for carbon, at x-ray intensities\naround $10^{23}{\\rm Wcm}^{-2}$, two-photon above-threshold ionization of the\nK-shell electrons is as probable as one-photon ionization of the L-shell\nelectrons.", "category": "physics_atom-ph" }, { "text": "New Window Resonances in the Potassium 3s Photoabsorption Spectrum: The photoion spectrum of atomic potassium was measured over the 3s -> np\nexcitation region with the photoion time-of-flight method and monochromatized\nsynchrotron radiation. An unusual spectrum with paired windows structure was\nfound instead of a simple regular Rydberg series. Such subsidiary windows have\nnot been observed in the 3s -> np resonances of Ar, which has a closed outer\nshell. Based on Dirac-Fock calculations, the dual window structure at 36.7 eV\nand at 37.4 eV was assigned to the 3s^{-1}3p^{6}4s4p resonance. The line shape\ncan be fitted by Fano's formula and the Fano parameters were obtained.", "category": "physics_atom-ph" }, { "text": "Nonlinear effects in Anderson localization of light by two-level atoms: While Anderson is a single-particle wave effect, guaranteeing a single\nexcitation in the system can be challenging. We here tackle this limitation in\nthe context of light localization in three dimensions in disordered cold atom\nclouds, in presence of several photons. We show that the presence of these\nmultiple excitations does not affect substantially the abnormal intensity\nfluctuations which characterize the Anderson localization transition, provided\nthat the radiated light is frequency filtered. Due to their narrow linewidth,\nlong-lived modes, and particularly the localized ones, are strongly saturated\neven for a weak resonant pump, leading to a large increase of the inelastic\nscattering and to reduced fluctuations in the total radiation. Yet the atomic\ncoherences and the resulting elastic scattering remain a proper witness of the\nAnderson localization transition. Hence, frequency filtering allows one to\ninvestigate the single-excitation sector, dismissing the many-body effects\nshowing up in the fluorescence spectrum.", "category": "physics_atom-ph" }, { "text": "Ramsey interferometry with an atom laser: We present results on a free-space atom interferometer operating on the first\norder magnetically insensitive |F=1,mF=0> -> |F=2,mF=0> transition of\nBose-condensed 87Rb atoms. A pulsed atom laser is output-coupled from a\nBose-Einstein condensate and propagates through a sequence of two internal\nstate beam splitters, realized via coherent Raman transitions between the two\ninterfering states. We observe Ramsey fringes with a visibility close to 100%\nand determine the current and the potentially achievable interferometric phase\nsensitivity. This system is well suited to testing recent proposals for\ngenerating and detecting squeezed atomic states.", "category": "physics_atom-ph" }, { "text": "Rotation related systematic effects in a cold atom interferometer\n onboard a Nadir pointing satellite: We study the effects of rotations on a cold atom accelerometer onboard a\nNadir pointing satellite. A simulation of the satellite attitude combined with\na calculation of the phase of the cold atom interferometer allow us to evaluate\nthe noise and bias induced by rotations. In particular, we evaluate the effects\nassociated to the active compensation of the rotation due to Nadir pointing.\nThis study was realized in the context of the preliminary study phase of the\nCARIOQA Quantum Pathfinder Mission.", "category": "physics_atom-ph" }, { "text": "Agile low phase noise radio-frequency sine wave generator applied to\n experiments on ultracold atoms: We report on the frequency performance of a low cost (~500$) radio-frequency\nsine wave generator, using direct digital synthesis (DDS) and a\nfield-programmable gate array (FPGA). The output frequency of the device may be\nchanged dynamically to any arbitrary value ranging from DC to 10 MHz without\nany phase slip. Sampling effects are substantially reduced by a high sample\nrate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. By\nusing a low noise external oscillator to clock the DDS, we demonstrate a phase\nnoise as low as that of the master clock, that is at the level of -113\ndB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. The\ndevice is successfully used to confine an ultracold atomic cloud of rubidium 87\nin a RF-based trap, and there is no extra heating from the RF source.", "category": "physics_atom-ph" }, { "text": "Photon angular distribution and nuclear-state alignment in nuclear\n excitation by electron capture: The alignment of nuclear states resonantly formed in nuclear excitation by\nelectron capture (NEEC) is studied by means of a density matrix technique. The\nvibrational excitations of the nucleus are described by a collective model and\nthe electrons are treated in a relativistic framework. Formulas for the angular\ndistribution of photons emitted in the nuclear relaxation are derived. We\npresent numerical results for alignment parameters and photon angular\ndistributions for a number of heavy elements in the case of E2 nuclear\ntransitions. Our results are intended to help future experimental attempts to\ndiscern NEEC from radiative recombination, which is the dominant competing\nprocess.", "category": "physics_atom-ph" }, { "text": "Observation of Dynamic Stark Resonances in Strong-Field Excitation: We investigate AC Stark-shifted resonances in argon with ultrashort\nnear-infrared pulses. Using 30 fs pulses we observe periodic enhancements of\nthe excitation yield in the intensity regions corresponding to the absorption\nof 13 and 14 photons. By reducing the pulse duration to 6 fs with only a few\noptical cycles, we also demonstrate that the enhancements are significantly\nreduced beyond what is measurable in the experiment. Comparing these to\nnumerical predictions, which are in quantitative agreement with experimental\nresults, we find that even though the quantum-state distribution can be broad,\nthe enhancements are largely due to efficient population of a select few AC\nStark-shifted resonant states rather than the closing of an ionization channel.\nBecause these resonances are dependent on the frequency and intensity of the\nlaser field, the broad bandwidth of the 6 fs pulses means that the resonance\ncondition is fulfilled across a large range of intensities. This is further\nexaggerated by volume-averaging effects, resulting in excitation of the $5g$\nstate at almost all intensities and reducing the apparent magnitude of the\nenhancements. For 30 fs pulses, volume averaging also broadens the quantum\nstate distribution but the enhancements are still large enough to survive. In\nthis case, selectivity of excitation to a single state is reduced below 25% of\nthe relative population. However, an analysis of TDSE simulations indicates\nthat excitation of up to 60% into a single state is possible if volume\naveraging can be eliminated and the intensity can be precisely controlled.", "category": "physics_atom-ph" }, { "text": "Dynamically Probing Ultracold Lattice Gases via Rydberg Molecules: We show that the excitation of long-range Rydberg molecules in a\nthree-dimensional optical lattice can be used as a position- and time-sensitive\nprobe of the site occupancy in the system. To this end, we detect the ions\nwhich are continuously generated by the decay of the formed Rydberg molecules.\nWhile a superfluid gas shows molecule formation for all parameters, a Mott\ninsulator with $n=1$ filling reveals a strong suppression of the number of\nformed molecules. In the limit of weak probing, the technique can be used to\nprobe the superfluid to Mott-insulator transition in real-time. Our method can\nbe extended to higher fillings and has various applications for the real-time\ndiagnosis and manipulation of ultracold lattice gases.", "category": "physics_atom-ph" }, { "text": "Autler - Townes doublet probed by strong field: This paper deals with the Autler - Townes doublet structure. Applied driving\nand probing laser fields can have arbitrary intensities. The explanation is\ngiven of the broadening of doublet components with the growth of probing field\nintensity, which was observed in experiment. The effects of Doppler averaging\nare discussed.", "category": "physics_atom-ph" }, { "text": "Sympathetic cooling and slowing of molecules with Rydberg atoms: We propose to sympathetically slow and cool polar molecules in a cold,\nlow-density beam using laser-cooled Rydberg atoms. The elastic collision cross\nsections between molecules and Rydberg atoms are large enough to efficiently\nthermalize the molecules even in a low density environment. Molecules traveling\nat 100 m/s can be stopped in under 30 collisions with little inelastic loss.\nOur method does not require photon scattering from the molecules and can be\ngenerically applied to complex species for applications in precision\nmeasurement, quantum information science, and controlled chemistry.", "category": "physics_atom-ph" }, { "text": "Evidence for Nonlinear Isotope Shift in Yb$^+$ Search for New Boson: We measure isotope shifts for five Yb$^+$ isotopes with zero nuclear spin on\ntwo narrow optical quadrupole transitions ${}^2S_{1/2} \\rightarrow\n{}^2D_{3/2}$, ${}^2S_{1/2} \\rightarrow {}^2D_{5/2}$ with an accuracy of $\\sim\n300$ Hz. The corresponding King plot shows a $3 \\times 10^{-7}$ deviation from\nlinearity at the 3 $\\sigma$ uncertainty level. Such a nonlinearity can indicate\nphysics beyond the Standard Model (SM) in the form of a new bosonic force\ncarrier, or arise from higher-order nuclear effects within the SM. We identify\nthe quadratic field shift as a possible contributor to the nonlinearity at the\nobserved scale, and show how the nonlinearity pattern can be used in future,\nmore accurate measurements to separate a new-boson signal from nuclear effects.", "category": "physics_atom-ph" }, { "text": "Isotope shift calculations in Ti II: We present an accurate ab initio method of calculating transition energies\nand isotope shifts in the 3d-transition metals. It extends previous work that\ncombines the configuration-interaction calculation with many-body perturbation\ntheory by including the effective three-body interaction and modification of\nthe energy denominator. We show that these effects are of importance in Ti II.\nThe need to develop methods that can accurately calculate isotope shifts in\n3d-transition metals comes from studies of quasar absorption spectra that seek\nto measure possible variation of the fine-structure constant alpha over the\nlifetime of the Universe. Isotope shift can also be used to measure isotope\nabundances in gas clouds in the early Universe, which are needed in order to\ntest models of chemical evolution.", "category": "physics_atom-ph" }, { "text": "Threshold of a Random Laser with Cold Atoms: We address the problem of achieving an optical random laser with a cloud of\ncold atoms, in which gain and scattering are provided by the same atoms. The\nlasing threshold can be defined using the on-resonance optical thickness b0 as\na single critical parameter. We predict the threshold quantitatively, as well\nas power and frequency of the emitted light, using two different light\ntransport models and the atomic polarizability of a strongly-pumped two-level\natom. We find a critical b0 on the order of 300, which is within reach of\nstate-of-the-art cold-atom experiments. Interestingly, we find that random\nlasing can already occur in a regime of relatively low scattering.", "category": "physics_atom-ph" }, { "text": "Self-referenced coherent diffraction x-ray movie of Angstrom- and\n femtosecond-scale atomic motion: Time-resolved femtosecond x-ray diffraction patterns from laser-excited\nmolecular iodine are used to create a movie of intramolecular motion with time\nand space resolution of $30~$fs and $0.3$ \\AA . The high spatial fidelity is\ndue to interference between the moving excitation and the static initial charge\ndistribution. This x-ray interference has not been employed to image internal\nmotion in molecules before. The initial state is used as the local oscillator\nfor heterodyne amplification of the excited charge distribution to retrieve\nreal-space movies of atomic motion on \\AA ngstrom and femtosecond scales.\nCoherent vibrational motion and dispersion, dissociation, and rotational\ndephasing are all clearly visible in the data, thereby demonstrating the\nstunning sensitivity of heterodyne methods.", "category": "physics_atom-ph" }, { "text": "Improved detection of small atom numbers through image processing: We demonstrate improved detection of small trapped atomic ensembles through\nadvanced post-processing and optimal analysis of absorption images. A fringe\nremoval algorithm reduces imaging noise to the fundamental photon-shot-noise\nlevel and proves beneficial even in the absence of fringes. A\nmaximum-likelihood estimator is then derived for optimal atom-number estimation\nand is applied to real experimental data to measure the population differences\nand intrinsic atom shot-noise between spatially separated ensembles each\ncomprising between 10 and 2000 atoms. The combined techniques improve our\nsignal-to-noise by a factor of 3, to a minimum resolvable population difference\nof 17 atoms, close to our ultimate detection limit.", "category": "physics_atom-ph" }, { "text": "Spectral Properties and Lifetimes of Neutral Spin-1/2-Fermions in a\n Magnetic Guide: We investigate the resonant motion of neutral spin-1/2-fermions in a magnetic\nguide. A wealth of unitary and anti-unitary symmetries is revealed in\nparticular giving rise to a two-fold degeneracy of the energy levels. To\ncompute the energies and decay widths of a large number of resonances the\ncomplex scaling method is employed. We discuss the dependence of the lifetimes\non the angular momentum of the resonance states. In this context the existence\nof so-called quasi-bound states is shown. In order to approximately calculate\nthe resonance energies of such states a radial Schr\\\"odinger equation is\nderived which improves the well-known adiabatic approximation. The effects of\nan additionally applied homogeneous Ioffe field on the resonance energies and\ndecay widths are also considered. The results are applied to the case of the\n$^6\\text{Li}$ atom in the $F=1/2$ hyperfine ground state.", "category": "physics_atom-ph" }, { "text": "Inclusion of Coulomb effects in laser-atom interactions: We investigate the role of the Coulomb interaction in strong field processes.\nWe find that the Coulomb field of the ion makes its presence known even in\nhighly intense laser fields, in contrast to the assumptions of the strong field\napproximation. The dynamics of the electron after ionization is analyzed with\nfour models for an arbitrary laser polarization: the Hamiltonian model in the\ndipole approximation, the strong field approximation, the Coulomb-corrected\nstrong field approximation and the guiding center. These models illustrate\nclearly the Coulomb effects, in particular Coulomb focusing and Coulomb\nasymmetry. We show that the Coulomb-corrected strong field approximation and\nthe guiding center are complementary, in the sense that the Coulomb-corrected\nstrong field approximation describes well short time scale phenomena (shorter\nthan a laser cycle) while the guiding center is well suited for describing long\ntime scale phenomena (longer than a laser cycle) like Coulomb-driven\nrecollisions and Rydberg state creation.", "category": "physics_atom-ph" }, { "text": "Molecular Laser-Cooling in a Dynamically Tunable Repulsive Optical Trap: Recent work with laser-cooled molecules in attractive optical traps has shown\nthat the differential AC Stark shifts arising from the trap light itself can\nbecome problematic, limiting collisional shielding efficiencies, rotational\ncoherence times, and laser-cooling temperatures. In this work, we explore\ntrapping and laser-cooling of CaF molecules in a ring-shaped repulsive optical\ntrap. The observed dependences of loss rates on temperature and barrier height\nshow characteristic behavior of repulsive traps and indicate strongly\nsuppressed average AC Stark shifts. Within the trap, we find that\n$\\Lambda$-enhanced gray molasses cooling is effective, producing similar\nminimum temperatures as those obtained in free space. By combining in-trap\nlaser cooling with dynamical reshaping of the trap, we also present a method\nthat allows highly efficient and rapid transfer from molecular magneto-optical\ntraps into conventional attractive optical traps, which has been an outstanding\nchallenge for experiments to date. Notably, our method could allow nearly\nlossless transfer over millisecond timescales.", "category": "physics_atom-ph" }, { "text": "Reservoir spectroscopy of 5s5p $^3$P$_2$ - 5s$n$d $^3$D$_{1,2,3}$\n transitions in strontium: We perform spectroscopy on the optical dipole transitions 5s5p $^3$P$_2$ -\n5s$n$d $^3$D$_{1,2,3}$, $n \\in (5,6)$, for all stable isotopes of atomic\nstrontium. We develop a new spectroscopy scheme, in which atoms in the\nmetastable $^3$P$_2$ state are stored in a reservoir before being probed. The\nmethod presented here increases the attained precision and accuracy by two\norders of magnitude compared to similar experiments performed in a\nmagneto-optical trap or discharge. We show how the state distribution and\nvelocity spread of atoms in the reservoir can be tailored to increase the\nspectroscopy performance. The absolute transition frequencies are measured with\nan accuracy of 2 MHz. The isotope shifts are given to within 200 kHz. We\ncalculate the $A$ and $Q$ parameters for the hyperfine structure of the\nfermionic isotope at the MHz-level. Furthermore, we investigate the branching\nratios of the $^3$D$_{J}$ states into the $^3$P$_{J}$ states and discuss\nimmediate implications on schemes of optical pumping and fluorescence\ndetection.", "category": "physics_atom-ph" }, { "text": "Excitations of N$_{2 }$ and O$_{2}$ molecules due to helium ion impact\n and a polarization effect: We present an experimental study of the dissociative excitation in the\ncollision of helium ions with nitrogen and oxygen molecules for collision\nenergy of $0.7-10$ keV. Absolute emission cross sections are measured and\nreported for most nitrogen and oxygen atomic and ionic lines in wide, vacuum\nultraviolet ($80-130$ nm) and visible ($380-800$ nm), spectral regions.\nRemarkable similarities of the processes realized in He$^{+}+$N$_{2}$ and\nHe$^{+}+$O$_{2}$ collision systems are observed. We present polarization\nmeasurements for He$^{+}+$N$_{2}$ collision system.\n The emission of excited dissociative products was detected using an improved\nhigh-resolution optical spectroscopy method. This method incorporates the\nretarding potential method and a high resolution electrostatic energy analyzer\nto precisely measure the energy of incident particles and the energy of\ndispersion. The improvement in the optics resolution allows us to measure the\ncross section on the order of 10$^{-19}$ cm$^{2}$ or lower.", "category": "physics_atom-ph" }, { "text": "Atomic clocks highly sensitive to the variation of the fine structure\n constant based on Hf II, Hf IV, and W VI ions: We demonstrate that several metastable excited states in Hf$~$II, Hf$~$IV and\nW$~$VI ions may be good clock states since they are sufficiently long-living\nand are not sensitive to the perturbations. Cooling E1 transitions are\navailable. Energy levels, Land\\'{e} $g$-factors, transition amplitudes for\nelectric dipole (E1), electric quadrupole (E2), and magnetic dipole (M1)\ntransitions, lifetimes, and electric quadrupole moments for Hf$~$II, Hf$~$IV,\nand W$~$VI ions are investigated using a combination of several methods of\nrelativistic many-body calculations including the configuration interaction\n(CI), linearized coupled-cluster single-doubles (SD) and many-body perturbation\ntheory (CI+SD), and also the configuration interaction with perturbation theory\n(CIPT). Scalar polarizabilities of the ground states and the clock states have\nbeen calculated to determine the black body radiation (BBR) shifts. We have\nfound that the relative BBR shifts for these transitions range between\n10$^{-16}$ $-$ 10$^{-18}$. A linear combination of two clock transition\nfrequencies allows one to further suppress BBR. Several $5d$ - $6s$\nsingle-electron clock transitions ensure high sensitivity of the transition\nfrequencies to the variation of the fine structure constant $\\alpha$ and may be\nused to search for dark matter producing this variation of $\\alpha$. The\nenhancement coefficient for $\\alpha$ variation reaches $K=8.3$. Six stable\nisotopes of Hf and 5 stable isotopes in W allow one to make King plots and\nsearch for new interactions mediated by scalar particles or other mechanisms.", "category": "physics_atom-ph" }, { "text": "Subcycle resolved strong-field tunneling ionization: Identification of\n magnetic dipole and electric quadrupole effects: Interaction of a strong laser pulse with matter transfers not only energy but\nalso linear momentum of the photons. Recent experimental advances have made it\npossible to detect the small amount of linear momentum delivered to the\nphotoelectrons in strong-field ionization of atoms. Linear momentum transfer is\na unique signature of the laser-atom interaction beyond its dipolar limit.\nHere, we present a decomposition of the subcycle time-resolved linear momentum\ntransfer in term of its multipolar components. We show that the magnetic dipole\ncontribution dominates the linear momentum transfer during the dynamical\ntunneling process while the post-ionization longitudinal momentum transfer in\nthe field-driven motion of the electron in the continuum is primarily governed\nby the electric quadrupole interaction. Alternatively, exploiting the radiation\ngauge, we identify nondipole momentum transfer effects that scale either\nlinearly or quadratically with the coupling to the laser field. The present\nresults provide detailed insights into the physical mechanisms underlying the\nsubcycle linear momentum transfer induced by nondipole effects.", "category": "physics_atom-ph" }, { "text": "Avoided crossings in driven systems: We characterize the avoided crossings in a two-parameter, time-periodic\nsystem which has been the basis for a wide variety of experiments. By studying\nthese avoided crossings in the near-integrable regime, we are able to determine\nscaling laws for the dependence of their characteristic features on the\nnon-integrability parameter. As an application of these results, the influence\nof avoided crossings on dynamical tunneling is described and applied to the\nrecent realization of multiple-state tunneling in an experimental system.", "category": "physics_atom-ph" }, { "text": "QED theory of the nuclear recoil effect on the atomic g factor: The quantum electrodynamic theory of the nuclear recoil effect on the atomic\ng factor to all orders in \\alpha Z and to first order in m/M is formulated. The\ncomplete \\alpha Z-dependence formula for the recoil correction to the\nbound-electron g factor in a hydrogenlike atom is derived. This formula is used\nto calculate the recoil correction to the bound-electron g factor in the order\n(\\alpha Z)^2 m/M for an arbitrary state of a hydrogenlike atom.", "category": "physics_atom-ph" }, { "text": "High-order harmonic generation enhanced by XUV light: The combination of high-order harmonic generation (HHG) with resonant XUV\nexcitation of a core electron into the transient valence vacancy that is\ncreated in the course of the HHG process is investigated theoretically. In this\nsetup, the first electron performs a HHG three-step process whereas, the second\nelectron Rabi flops between the core and the valence vacancy. The modified HHG\nspectrum due to recombination with the valence and the core is determined and\nanalyzed for krypton on the 3d -- > 4p resonance in the ion. We assume an 800\nnm laser with an intensity of about 10^14 W/cm^2 and XUV radiation from the\nFree Electron Laser in Hamburg (FLASH) with an intensity in the range\n10^13--10^16 W/cm^2. Our prediction opens perspectives for nonlinear XUV\nphysics, attosecond x rays, and HHG-based spectroscopy involving core orbitals.", "category": "physics_atom-ph" }, { "text": "Optical coherence and energy-level properties of a Tm$^{3+}$-doped\n LiNbO$_{3}$ waveguide at sub-Kelvin temperatures: We characterize the optical coherence and energy-level properties of the 795\nnm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$\nwaveguide at temperatures as low as 0.65 K. Coherence properties are measured\nwith varied temperature, magnetic field, optical excitation power and\nwavelength, and measurement time-scale. We also investigate nuclear\nspin-induced hyperfine structure and population dynamics with varying magnetic\nfield and laser excitation power. Except for accountable differences due to\ndifference Ti$^{4+}$ and Tm$^{3+}$-doping concentrations, we find that the\nproperties of Tm$^{3+}$:Ti$^{4+}$:LiNbO$_{3}$ produced by indiffusion doping\nare consistent with those of a bulk-doped Tm$^{3+}$:LiNbO$_{3}$ crystal\nmeasured under similar conditions. Our results, which complement previous work\nin a narrower parameter space, support using rare-earth-ions for integrated\noptical and quantum signal processing.", "category": "physics_atom-ph" }, { "text": "Constraints on long-range spin-gravity and monopole-dipole couplings of\n the proton: Results of a search for a long-range monopole-dipole coupling between the\nmass of the Earth and rubidium (Rb) nuclear spins are reported. The experiment\nsimultaneously measures the spin precession frequencies of overlapping\nensembles of $^{85}$Rb and $^{87}$Rb atoms contained within an evacuated,\nantirelaxation-coated vapor cell. The nuclear structure of the Rb isotopes\nmakes the experiment particularly sensitive to spin-dependent interactions of\nthe proton. The spin-dependent component of the gravitational energy of the\nproton in the Earth's field is found to be smaller than $3 \\times 10^{-18}~{\\rm\neV}$, improving laboratory constraints on long-range monopole-dipole\ninteractions by over three orders of magnitude.", "category": "physics_atom-ph" }, { "text": "Momentum Distribution of Near-Zero-Energy Photoelectrons in the\n Strong-Field Tunneling Ionization in the Long Wavelength Limit: We investigate the ionization dynamics of Argon atoms irradiated by an\nultrashort intense laser of a wavelength up to 3100 nm, addressing the momentum\ndistribution of the photoelectrons with near-zero-energy. We find a surprising\naccumulation in the momentum distribution corresponding to meV energy and a\n\\textquotedblleft V\"-like structure at the slightly larger transverse momenta.\nSemiclassical simulations indicate the crucial role of the Coulomb attraction\nbetween the escaping electron and the remaining ion at extremely large\ndistance. Tracing back classical trajectories, we find the tunneling electrons\nborn in a certain window of the field phase and transverse velocity are\nresponsible for the striking accumulation. Our theoretical results are\nconsistent with recent meV-resolved high-precision measurements.", "category": "physics_atom-ph" }, { "text": "Relativistic calculations of the K-K charge transfer and K-vacancy\n production probabilities in low-energy ion-atom collisions: The previously developed technique for evaluation of charge-transfer and\nelectron-excitation processes in low-energy heavy-ion collisions [I.I. Tupitsyn\net al., Phys. Rev. A 82, 042701(2010)] is extended to collisions of ions with\nneutral atoms. The method employs the active electron approximation, in which\nonly the active electron participates in the charge transfer and excitation\nprocesses while the passive electrons provide the screening DFT potential. The\ntime-dependent Dirac wave function of the active electron is represented as a\nlinear combination of atomic-like Dirac-Fock-Sturm orbitals, localized at the\nions (atoms). The screening DFT potential is calculated using the overlapping\ndensities of each ions (atoms), derived from the atomic orbitals of the passive\nelectrons. The atomic orbitals are generated by solving numerically the\none-center Dirac-Fock and Dirac-Fock-Sturm equations by means of a\nfinite-difference approach with the potential taken as the sum of the exact\nreference ion (atom) Dirac-Fock potential and of the Coulomb potential from the\nother ion within the monopole approximation. The method developed is used to\ncalculate the K-K charge transfer and K-vacancy production probabilties for the\nNe$(1s^2 2s^2 2p^6)$ -- F$^{8+}(1s)$ collisions at the F$^{8+}(1s)$ projectile\nenergies 130 keV/u and 230 keV/u. The obtained results are compared with\nexperimental data and other theoretical calculations. The K-K charge transfer\nand K-vacancy production probabilities are also calculated for the Xe --\nXe$^{53+}(1s)$ collision.", "category": "physics_atom-ph" }, { "text": "Signatures of magnetic field effects in non-sequential double ionization\n manifesting as back-scattering for molecules versus forward-scattering for\n atoms: For two-electron diatomic molecules, we investigate magnetic field effects in\nnon-sequential double ionization where recollisions prevail. We do so by\nformulating a three-dimensional semi-classical model that fully accounts for\nthe Coulomb singularities and for magnetic field effects during time\npropagation. Using this model, we identify a prominent signature of non-dipole\neffects. Namely, we demonstrate that the recolliding electron back-scatters\nalong the direction of light propagation. Hence, this electron escapes opposite\nto the direction of change in momentum due to the magnetic field. This is in\nstriking contrast to strongly-driven atoms where the recolliding electron\nforward-scatters along the direction of light propagation. We attribute these\ndistinct signatures to the different gate that the magnetic field creates\njointly with a soft recollision in molecules compared to a hard recollision in\natoms. These two different gates give rise, shortly before recollision, to\ndifferent momenta and positions of the recolliding electron along the direction\nof light propagation. As a result, we show that the Coulomb forces from the\nnuclei act to back-scatter the recolliding electron in molecules and\nforward-scatter it in atoms along the direction of light propagation.", "category": "physics_atom-ph" }, { "text": "Ultraviolet laser spectroscopy of aluminum atoms in hollow-cathode lamp: We report precision measurement of aluminum atoms\n${^{2}P_{1/2}}-{^{2}S_{1/2}}$ transition at 394 nm and\n${^{2}P_{3/2}}-{^{2}S_{1/2}}$ transition at 396 nm in a hollow-cathode lamp\n(HCL). Both absorption spectroscopy and saturated absorption spectroscopy (SAS)\nare performed. From the absorption spectroscopy the Doppler linewidth is\nestimated to be 2.6 GHz. The SAS spectroscopy is analyzed based on the\nvelocity-changing-effect model. With a frequency comb calibrated wavemeter, the\nfrequencies of ${^{2}P_{1/2}},{F=3}-{^{2}S_{1/2}},{F=2}$ transition and\n${^{2}P_{3/2}},{F=4}-{^{2}S_{1/2}},{F=3}$ transition are measured to be\n759.905401(10) THz and 756.547403(10) THz, respectively. The hyperfine\nstructure constants of aluminum atoms are determined and compared with\npreviously reported measurement results and theoretical calculation. Reasonable\nagreement is found for the magnetic dipole constant (A constant), while the\nelectric quadrupole constant (B constant) has a large deviation.", "category": "physics_atom-ph" }, { "text": "Quantum optical signatures in strong-field laser physics: Infrared\n photon counting in high-order-harmonic generation: We analytically describe the strong-field light-electron interaction using a\nquantized coherent laser state with arbitrary photon number. We obtain a\nlight-electron wave function which is a closed-form solution of the\ntime-dependent Schrodinger equation (TDSE). This wave function provides\ninformation about the quantum optical features of the interaction not\naccessible by semi-classical theories. With this approach we can reveal the\nquantum optical properties of high harmonic generation (HHG) process in gases\nby measuring the photon statistics of the transmitted infrared (IR) laser\nradiation. This work can lead to novel experiments in high-resolution\nspectroscopy in extreme-ultraviolet (XUV) and attosecond science without the\nneed to measure the XUV light, while it can pave the way for the development of\nintense non-classical light sources.", "category": "physics_atom-ph" }, { "text": "Electronic correlations in double ionization of atoms in pump-probe\n experiments: The ionization dynamics of a two-electron atom in an attosecond XUV-infrared\npump-probe experiment is simulated by solving the time-dependent two-electron\nSchr\\\"odinger equation. A dramatic change of the double ionization (DI) yield\nwith variation of the pump-probe delay is reported and the governing role of\nelectron-electron correlations is shown. The results allow for a direct control\nof the DI yield and of the relative strength of double and single ionization.", "category": "physics_atom-ph" }, { "text": "Sub-Doppler laser cooling of $^{39}$K via the 4S$\\to$5P transition: We demonstrate sub-Doppler laser cooling of $ ^{39} $K using degenerate Raman\nsideband cooling via the 4S$_{1/2} \\rightarrow $5P$ _{1/2} $ transition at\n404.8 nm. By using an optical lattice in combination with a magnetic field and\noptical pumping beams, we obtain a spin-polarized sample of up to $5.6 \\times\n10^{7}$ atoms cooled down to a sub-Doppler temperature of 4 $\\mu $K, reaching a\npeak density of $3.9 \\times 10^{9}$ atoms/cm$ ^{3} $, a phase-space density\ngreater than $ 10^{-5} $, and an average vibrational level of $ \\langle \\nu\n\\rangle=0.6 $ in the lattice. This work opens up the possibility of\nimplementing a single-site imaging scheme in a far-detuned optical lattice\nutilizing shorter wavelength transitions in alkali atoms, thus allowing\nimproved spatial resolution.", "category": "physics_atom-ph" }, { "text": "RF-induced heating dynamics of non-crystallized trapped ions: We investigate the energy dynamics of non-crystallized (melted) ions,\nconfined in a Paul trap. The non-periodic Coulomb interaction experienced by\nmelted ions forms a medium for non-conservative energy transfer from the\nradio-frequency (rf) field to the ions, a process known as rf heating. We study\nrf heating by analyzing numerical simulations of non-crystallized ion motion in\nPaul trap potentials, in which the energy of the ions' secular motion changes\nat discrete intervals, corresponding to ion-ion collisions. The analysis of\nthese collisions is used as a basis to derive a simplified model of rf heating\nenergy dynamics, from which we conclude that the rf heating rate is\npredominantly dependent on the rf field strength. We confirm the predictability\nof the model experimentally: Two trapped $^{40}$Ca$^{+}$ ions are\ndeterministically driven to melt, and their fluorescence rate is used to infer\nthe ions' energy. From simulation and experimental results, we generalize which\nexperimental parameters are required for efficient recrystallization of melted\ntrapped ions.", "category": "physics_atom-ph" }, { "text": "Polarization correlations in the two--photon decay of hydrogen--like\n ions: Polarization properties of the photons emitted in the two-photon decay of\nhydrogen-like ions are studied within the framework of the density matrix and\nsecond-order perturbation theory. In particular, we derive the polarization\ncorrelation function that gives the probability of the (two-photon) coincidence\nmeasurement performed by polarization-sensitive detectors. Detailed\ncalculations of this function are performed for the $2s_{1/2} \\to 1s_{1/2}$\ntransition in neutral hydrogen as well as Xe$^{53+}$ and U$^{91+}$ ions. The\nobtained results allow us to understand the influence of relativistic and\nnon-dipole effects on the polarization correlations in the bound-bound\ntwo-photon transitions in heavy ions.", "category": "physics_atom-ph" }, { "text": "Magic wavelengths for trapping the alkali-metal atoms with circularly\n polarized light: Extending the search for the magic wavelengths using the circularly polarized\nlight in rubidium [Phys. Rev. A 86, 033416 (2012)], we pursue here to look for\nthe magic wavelengths in the $ns-np_{1/2,3/2}$ transitions of Li, Na and K\nalkali atoms. These wavelengths for all possible sub-levels are given and\ncompared with the corresponding wavelengths due to the linearly polarized\nlight. We have also mentioned explicitly the dynamic polarizabilities at few\nimportant wave lengths. The present study suggests that it is possible to carry\nout state insensitive trapping of different alkali atoms using the circularly\npolarized light.", "category": "physics_atom-ph" }, { "text": "Talbot Oscillations and Periodic Focusing in a One-Dimensional\n Condensate: An exact theory for the density of a one-dimensional Bose-Einstein condensate\nwith hard core particle interactions is developed in second quantization and\napplied to the scattering of the condensate by a spatially periodic impulse\npotential. The boson problem is mapped onto a system of free fermions obeying\nthe Pauli exclusion principle to facilitate the calculation. The density\nexhibits a spatial focusing of the probability density as well as a periodic\nself-imaging in time, or Talbot effect. Furthermore, the transition from single\nparticle to many body effects can be measured by observing the decay of the\nmodulated condensate density pattern in time. The connection of these results\nto classical and atom optical phase gratings is made explicit.", "category": "physics_atom-ph" }, { "text": "Precision Measurement of the Quadrupole Transition Matrix Element in a\n Single Trapped $^{40}$Ca$^{+}$: We report the first experimental determination of the $4s \\ ^{2}S_{1/2} $\n$\\leftrightarrow $ $3d \\ ^{2}D_{5/2}$ quadrupole transition matrix element in\n$^{40}$Ca$^+$ by measuring the branching ratio of the $3d \\ ^{2}D_{5/2} $ state\ndecaying into the ground state $4s \\ ^{2}S_{1/2} $ and the lifetime of the $3d\n\\ ^{2}D_{5/2} $ state, using a technique of highly synchronized measurement\nsequence for laser control and highly efficient quantum state detection for\nquantum jumps. The measured branching ratio and improved lifetime are,\nrespectively, 0.9992(80) and 1.1652(46) s, which yield the value of the\nquadrupole transition matrix element (in absolute value) 9.737(43)~$ea_{0}^{2}$\nwith the uncertainty at the level of 0.44\\%. The measured quadrupole transition\nmatrix element is in good agreement with the most precise many-body atomic\nstructure calculations. Our method can be universally applied to measurements\nof transition matrix elements in single ions and atoms of similar structure.", "category": "physics_atom-ph" }, { "text": "Laser Driven Fluorescence Emission in a Nitrogen Gas Jet at 100 MHz\n Repetition Rate: We report the fluorescence emission which is driven by femtosecond laser\npulses with a repetition rate of 100 MHz and a center wavelength of 1040 nm in\na nitrogen gas jet. The experiment is performed in a femtosecond enhancement\ncavity coupled with high repetition rate laser for the first time to the best\nof our knowledge. In contrast to previous observation at low repetition rate\nwith a nitrogen gas jet, where the 391 nm radiation was observed but the 337 nm\nemission was missing, the 337 nm emission is 3 times stronger than the 391 nm\nemission in our experiment. By examining the dependence of the radiation\nintensity on the flow rate of the nitrogen gas and the polarization of the pump\npulse, the formation mechanism of the N2(C3{\\Pi}u) triplet excited state, i.e.,\nthe upper state of the 337 nm emission, is investigated. We attribute the main\nexcitation process to the inelastic collision excitation process, and exclude\nthe possibility of the dissociative recombination as the dominate pathway. The\nrole of the steady state plasma that is generated under our experimental\nconditions is also discussed.", "category": "physics_atom-ph" }, { "text": "Traveling wave deceleration of heavy polar molecules in low-field\n seeking states: We demonstrate the deceleration of heavy polar molecules in low-field seeking\nstates by combining a cryogenic source and a travelling-wave Stark decelerator.\nThe cryogenic source provides a high intensity beam with low speed and\ntemperature, and the travelling-wave decelerator provides large deceleration\nforces and high phase-space acceptance. We prove these techniques using YbF\nmolecules and find the experimental data to be in excellent agreement with\nnumerical simulations. These methods extend the scope of Stark deceleration to\na very wide range of molecules.", "category": "physics_atom-ph" }, { "text": "Attosecond pulse shaping around a Cooper minimum: High harmonic generation (HHG) is used to measure the spectral phase of the\nrecombination dipole matrix element (RDM) in argon over a broad frequency range\nthat includes the 3p Cooper minimum (CM). The measured RDM phase agrees well\nwith predictions based on the scattering phases and amplitudes of the\ninterfering s- and d-channel contributions to the complementary photoionization\nprocess. The reconstructed attosecond bursts that underlie the HHG process show\nthat the derivative of the RDM spectral phase, the group delay, does not have a\nstraight-forward interpretation as an emission time, in contrast to the usual\nattochirp group delay. Instead, the rapid RDM phase variation caused by the CM\nreshapes the attosecond bursts.", "category": "physics_atom-ph" }, { "text": "Atomic population distribution in the output ports of cold-atom\n interferometers with optical splitting and recombination: Cold-atom interferometers with optical splitting and recombination use\noff-resonant laser beams to split a cloud of Bose-Einstein condensate (BEC)\ninto two clouds that travel along different paths and are then recombined again\nusing optical beams. After the recombination, the BEC in general populates both\nthe cloud at rest and the moving clouds. Measuring relative number of atoms in\neach of these clouds yields information about the relative phase shift\naccumulated by the atoms in the two moving clouds during the interferometric\ncycle. We derive the expression for the probability of finding any given number\nof atoms in each of the clouds, discuss features of the probability density\ndistribution, analyze its dependence on the relative accumulated phase shift as\na function of the strength of the interatomic interactions, and compare our\nresults with experiment.", "category": "physics_atom-ph" }, { "text": "Highly-charged ions for atomic clocks, quantum information, and search\n for $\u03b1$-variation: We propose 10 highly-charged ions as candidates for the development of next\ngeneration atomic clocks, quantum information, and search for\n$\\alpha$-variation. They have long-lived metastable states with transition\nfrequencies to the ground state between 170-3000 nm, relatively simple\nelectronic structure, stable isotopes and high sensitivity to\n$\\alpha$-variation (e.g., Sm$^{14+}$, Pr$^{10+}$, Sm$^{13+}$, Nd$^{10+}$). We\npredict their properties crucial for the experimental exploration and highlight\nparticularly attractive systems for these applications.", "category": "physics_atom-ph" }, { "text": "Effects of non-adiabatic and Coriolis couplings on the bound states of\n He(2 ^3S)+He(2 ^3P): The effects of non-adiabatic and Coriolis couplings on the bound states of\nthe He(2 ^3S_1)+He(2 ^3P_j) system, where j=0,1,2, are investigated using the\nrecently available ab initio short-range $^{1,3,5}\\Sigma^+_{g,u}$ and\n$^{1,3,5}\\Pi_{g,u}$ potentials computed by Deguilhem et al. (J. Phys. B: At.\nMol. Opt. Phys. 42 (2009) 015102). Three sets of calculations have been\nundertaken: single-channel, multichannel without Coriolis couplings and full\nmultichannel with Coriolis couplings. We find that non-adiabatic effects are\nnegligible for $0^-_u,0^{\\pm}_g,1_u,2_g,2_u,3_g$ Hund case (c) sets of levels\nin the j=2 asymptote but can be up to 15% for some of the $0^+_u$ and $1_g$\nsets of levels where near degeneracies are present in the single-channel\ndiagonalized potentials. Coriolis couplings are most significant for weakly\nbound levels, ranging from 1-5% for total angular momenta J=1,2 and up to 10%\nfor J=3. Levels near the j=1 and j=0 asymptotes agree closely with previous\nmultichannel calculations based upon long-range potentials constructed from\nretarded resonance dipole and dispersion interactions. Assignment of\ntheoretical levels to experimental observations using criteria based upon the\nshort-range character of each level and their coupling to metastable ground\nstates produces well matched assignments for the majority of observations.\nAfter a 1% increase in the slope of the $^5\\Sigma^+_{g,u}$ and $^5\\Pi_{g,u}$\ninput potentials near the classical turning point is applied, improved matching\nof previous assignments is obtained and further assignments can be made,\nreproducing very closely the number of experimental observations.", "category": "physics_atom-ph" }, { "text": "Mass-selective removal of ions from Paul traps using parametric\n excitation: We study a method for mass-selective removal of ions from a Paul trap by\nparametric excitation. This can be achieved by applying an oscillating electric\nquadrupole field at twice the secular frequency $\\omega_{\\text{sec}}$ using\npairs of opposing electrodes. While excitation near the resonance with the\nfrequency $\\omega_{\\text{sec}}$ only leads to a linear increase of the\namplitude with excitation duration, parametric excitation near $2\\,\n\\omega_{\\text{sec}}$ results in an exponential increase of the amplitude. This\nenables efficient removal of ions from the trap with modest excitation voltages\nand narrow bandwidth, therefore substantially reducing the disturbance of ions\nwith other charge-to-mass ratios. We numerically study and compare the mass\nselectivity of the two methods. In addition, we experimentally show that the\nbarium isotopes with 136 and 137 nucleons can be removed from small ion\ncrystals and ejected out of the trap while keeping $^{138}\\text{Ba}^{+}$ ions\nDoppler cooled, corresponding to a mass selectivity of better than $\\Delta m /\nm = 1/138$. This method can be widely applied to ion trapping experiments\nwithout major modifications, since it only requires modulating the potential of\nthe ion trap.", "category": "physics_atom-ph" }, { "text": "Ab initio calculations of permanent dipole moments and dipole\n polarizabilities of alkaline-earth monofluorides: The ground-state permanent dipole moments (PDMs) and molecular dipole\npolarizabilities (DPs) of open-shell alkaline-earth monofluorides, and atomic\nDPs of alkaline-earth- and fluorine atoms are reported at the\nKramers-restricted configuration interaction level of theory limited to single-\nand double excitations (KRCISD), using the finite-field approach. Sufficiently\nlarge basis sets such as quadruple-zeta (QZ) and augmented-QZ basis sets\ntogether with the generalized active space technique is employed to carry out\nthe field dependent energy calculations at the KRCISD level. The PDMs and the\ncomponents of DPs are extracted from the linear- and quadratic fit of energies\nagainst perturbative electric field, respectively. Accuracy of the present\ncalculations for the electronic properties is examined by comparison with the\nmeasurements and calculations where ever available.", "category": "physics_atom-ph" }, { "text": "Laser stabilization to an atomic transition using an optically generated\n dispersive lineshape: We report on a simple and robust technique to generate a dispersive signal\nwhich serves as an error signal to electronically stabilize a monomode cw laser\nemitting around an atomic resonance. We explore nonlinear effects in the laser\nbeam propagation through a resonant vapor by way of spatial filtering. The\nperformance of this technique is validated by locking semiconductor lasers to\nthe cesium and rubidiumD2 line and observing long-term reduction of the\nemission frequency drifts, making the laser well adapted for many atomic\nphysics applications.", "category": "physics_atom-ph" }, { "text": "Photoionization of the valence shells of the neutral tungsten atom: Results from large-scale theoretical cross section calculations for the total\nphotoionization of the 4f, 5s, 5p and 6s orbitals of the neutral tungsten atom\nusing the Dirac Coulomb R-matrix approximation (DARC: Dirac-Atomic R-matrix\ncodes) are presented. Comparisons are made with previous theoretical methods\nand prior experimental measurements. In previous experiments a time-resolved\ndual laser approach was employed for the photo-absorption of metal vapours and\nphoto-absorption measurements on tungsten in a solid, using synchrotron\nradiation.\n The lowest ground state level of neutral tungsten is $\\rm 5p^6 5d^4 6s^2 \\;\n{^5}D_{\\it J}$, with $\\it J$=0, and requires only a single dipole matrix for\nphotoionization. To make a meaningful comparison with existing experimental\nmeasurements, we statistically average the large-scale theoretical PI cross\nsections from the levels associated with the ground state $\\rm 5p^6 5d^4 6s^2\n\\; {^5}D_{\\it J}[{\\it J}=0,1,2,3,4]$ levels and the $\\rm 5d^56s \\; ^7S_3$\nexcited metastable level. As the experiments have a self-evident metastable\ncomponent in their ground state measurement, averaging over the initial levels\nallows for a more consistent and realistic comparison to be made.\n In the wider context, the absence of many detailed electron-impact excitation\n(EIE) experiments for tungsten and its multi-charged ion stages allows current\nphotoionization measurements and theory to provide a road-map for future\nelectron-impact excitation, ionization and di-electronic cross section\ncalculations by identifying the dominant resonance structure and features\nacross an energy range of hundreds of eV.", "category": "physics_atom-ph" }, { "text": "Optical Spectroscopy of Tungsten Carbide for Uncertainty Analysis in\n Electron Electric Dipole Moment Search: We perform laser induced fluorescence(LIF) spectroscopy on a pulsed\nsupersonic beam of tungsten carbide(WC) molecules, which has been proposed as a\ncandidate molecular system for a permanent Electric Dipole Moment(EDM) search\nof the electron in its rovibrational ground state of the X3Delta1 state. In\nparticular, [20.6]Omega=2, v'=4 <- X3Delta1,v\"=0 transition at 485nm was used\nfor the detection. The hyperfine structure and the Omega-doublet of the\ntransition are measured, which are essential for estimating the size of the\npotential systematic uncertainties for electron EDM measurement. For further\nsuppression of the systematic uncertainty, an alternative electron EDM\nmeasurement scheme utilizing the g factor crossing point of the Omega-doublet\nlevels is discussed. On the other hand, flux and internal temperature of the\nmolecular beam are characterized, which sets the limit on the statistical\nuncertainty of the electron EDM experiment. With the given results, the\nprospect of electron EDM experiment with the X3Delta1 state of WC molecule is\ndiscussed.", "category": "physics_atom-ph" }, { "text": "The helium atom in a strong magnetic field: We investigate the electronic structure of the helium atom in a magnetic\nfield b etween B=0 and B=100a.u. The atom is treated as a nonrelativistic\nsystem with two interactin g electrons and a fixed nucleus. Scaling laws are\nprovided connecting the fixed-nucleus Hamiltonia n to the one for the case of\nfinite nuclear mass. Respecting the symmetries of the electronic Ham iltonian\nin the presence of a magnetic field, we represent this Hamiltonian as a matrix\nwith res pect to a two-particle basis composed of one-particle states of a\nGaussian basis set. The corresponding generalized eigenvalue problem is solved\nnumerically, providing in the present paper results for vanish ing magnetic\nquantum number M=0 and even or odd z-parity, each for both singlet and triplet\nspin symmetry. Total electronic energies of the ground state and the first few\nexcitations in each su bspace as well as their one-electron ionization energies\nare presented as a function of the magnetic fie ld, and their behaviour is\ndiscussed. Energy values for electromagnetic transitions within the M=0 sub\nspace are shown, and a complete table of wavelengths at all the detected\nstationary points with respect to their field dependence is given, thereby\nproviding a basis for a comparison with observed ab sorption spectra of\nmagnetic white dwarfs.", "category": "physics_atom-ph" }, { "text": "Slow ground state molecules from matrix isolation sublimation: We describe the generation and properties of a cryogenic beam of $^7$Li$_2$\ndimers from sublimation of a neon matrix where lithium atoms have been\nimplanted via laser ablation of solid precursors of metallic lithium or lithium\nhydride (LiH). Different sublimation regimes lead to pulsed molecular beams\nwith different temperatures, densities and forward velocities. With laser\nabsorption spectroscopy these parameters were measured using the molecular\n$^7$Li$_2$ (R) transitions A$^1\\Sigma_u^+(v'=4,J'=J''+1)\\leftarrow\n$X$^1\\Sigma_g^+ (v''=0,J''=0,1,3)$. In a typical regime, sublimating a matrix\nat 16 K, translational temperatures of 6--8 K with a drift velocity of 130\nm$\\,$s$^{-1}$ in a free expanding pulsed beam with molecular density of 10$^9$\ncm$^{-3}$, averaged along the laser axis, were observed. Rotational\ntemperatures around 5--7 K were obtained. In recent experiments we were able to\nmonitor the atomic Li signal -- in the D2 line -- concomitantly with the\nmolecular signal in order to compare them as a function of the number of\nablation pulses. Based on the data and a simple model, we discuss the\npossibility that a fraction of these molecules are being formed in the matrix,\nby mating atoms from different ablation pulses, which would open up the way to\nformation of other more interesting and difficult molecules to be studied at\nlow temperatures. Such a source of cryogenic molecules have possible\napplications encompassing fundamental physics tests, quantum information\nstudies, cold collisions, chemistry, and trapping.", "category": "physics_atom-ph" }, { "text": "Search for correlation effects in linear chains of trapped ions: We report a precise search for correlation effects in linear chains of 2 and\n3 trapped Ca+ ions. Unexplained correlations in photon emission times within a\nlinear chain of trapped ions have been reported, which, if genuine, cast doubt\non the potential of an ion trap to realize quantum information processing. We\nobserve quantum jumps from the metastable 3d 2D_{5/2} level for several hours,\nsearching for correlations between the decay times of the different ions. We\nfind no evidence for correlations: the number of quantum jumps with separations\nof less than 10 ms is consistent with statistics to within errors of 0.05%; the\nlifetime of the metastable level derived from the data is consistent with that\nderived from independent single-ion data at the level of the experimental\nerrors 1%; and no rank correlations between the decay times were found with\nsensitivity to rank correlation coefficients at the level of |R| = 0.024.", "category": "physics_atom-ph" }, { "text": "Collisional excitation transfer and quenching in Rb(5P)-methane mixtures: We have examined fine-structure mixing between the rubidium $5^{2}P_{3/2}$\nand $5^{2}P_{1/2}$ states along with quenching of these states due to\ncollisions with methane gas. Measurements are carried out using ultrafast laser\npulse excitation to populate one of the Rb $5^{2}P$ states, with the\nfluorescence produced through collisional excitation transfer observed using\ntime-correlated single-photon counting. Fine-structure mixing rates and\nquenching rates are determined by the time dependence of this fluorescence. As\nRb($5^{2}P$) collisional excitation transfer is relatively fast in methane gas,\nmeasurements were performed at methane pressures of $2.5 - 25$ Torr, resulting\nin a collisional transfer cross section ($5^{2}P_{3/2} \\rightarrow\n5^{2}P_{1/2}$) of $(4.23 \\pm 0.13) \\times 10^{-15}$ cm$^{2}$. Quenching rates\nwere found to be much slower and were performed over methane pressures of $50 -\n4000$ Torr, resulting in a quenching cross section of $(7.52 \\pm 0.10) \\times\n10^{-19}$ cm$^{2}$. These results represent a significant increase in precision\ncompared to previous work, and also resolve a discrepancy in previous quenching\nmeasurements.", "category": "physics_atom-ph" }, { "text": "A novel absorption resonance for all-optical atomic clocks: We report an experimental study of an all-optical three-photon-absorption\nresonance (known as a \"N-resonance\") and discuss its potential application as\nan alternative to atomic clocks based on coherent population trapping (CPT). We\npresent measurements of the N-resonance contrast, width and light-shift for the\nD1 line of 87Rb with varying buffer gases, and find good agreement with an\nanalytical model of this novel resonance. The results suggest that N-resonances\nare promising for atomic clock applications.", "category": "physics_atom-ph" }, { "text": "Harmonic generation in ring-shaped molecules: We study numerically the interaction between an intense circularly polarized\nlaser field and an electron moving in a potential which has a discrete\ncylindrical symmetry with respect to the laser pulse propagation direction.\nThis setup serves as a simple model, e.g., for benzene and other aromatic\ncompounds. From general symmetry considerations, within a Floquet approach,\nselection rules for the harmonic generation [O. Alon Phys. Rev. Lett. 80 3743\n(1998)] have been derived recently. Instead, the results we present in this\npaper have been obtained solving the time-dependent Schroedinger equation ab\ninitio for realistic pulse shapes. We find a rich structure which is not always\ndominated by the laser harmonics.", "category": "physics_atom-ph" }, { "text": "The Spectrum of Quasistable States in a Strong Microwave Field: When atoms are exposed to intense laser or microwave pulses ~10% of the atoms\nare found in Rydberg states subsequent to the pulse, even if it is far more\nintense than required for static field ionization. The optical spectra of the\nsurviving Li atoms in the presence of a 38 GHz microwave field suggest how\natoms survive an intense pulse. The spectra exhibit a periodic train of peaks\n38 GHz apart. One peak is just below the limit, and with a 90 V/cm field\namplitude the train extends from 300 GHz above the limit to 3000 GHz below it.\nThe spectra and quantum mechanical calculations imply that the atoms survive in\nquasi stable states in which the Rydberg electron is in a weakly bound orbit\ninfrequently returning to the ionic core during the intense pulse.", "category": "physics_atom-ph" }, { "text": "Precise and accurate measurements of strong-field photoionisation and a\n transferrable laser intensity calibration standard: Ionization of atoms and molecules in strong laser fields is a fundamental\nprocess in many fields of research, especially in the emerging field of\nattosecond science. So far, demonstrably accurate data have only been acquired\nfor atomic hydrogen (H), a species that is accessible to few investigators.\nHere we present measurements of the ionization yield for argon, krypton, and\nxenon with percentlevel accuracy, calibrated using H, in a laser regime widely\nused in attosecond science. We derive a transferrable calibration standard for\nlaser peak intensity, accurate to 1.3%, that is based on a simple reference\ncurve. In addition, our measurements provide a much-needed benchmark for\ntesting models of ionisation in noble-gas atoms, such as the widely employed\nsingle-active electron approximation.", "category": "physics_atom-ph" }, { "text": "Precision Spectroscopy of Polarized Molecules in an Ion Trap: Polar molecules are desirable systems for quantum simulations and cold\nchemistry. Molecular ions are easily trapped, but a bias electric field applied\nto polarize them tends to accelerate them out of the trap. We present a general\nsolution to this issue by rotating the bias field slowly enough for the\nmolecular polarization axis to follow but rapidly enough for the ions to stay\ntrapped. We demonstrate Ramsey spectroscopy between Stark-Zeeman sublevels in\n180Hf19F+ with a coherence time of 100 ms. Frequency shifts arising from\nwell-controlled topological (Berry) phases are used to determine magnetic\ng-factors. The rotating-bias-field technique may enable using trapped polar\nmolecules for precision measurement and quantum information science, including\nthe search for an electron electric dipole moment.", "category": "physics_atom-ph" }, { "text": "Resonant electronic-bridge excitation of the U-235 nuclear transition in\n ions with chaotic spectra: Electronic bridge excitation of the 76 eV nuclear isomeric state in $^{235}$U\nis shown to be strongly enhanced in the U$^{7+}$ ion, potentially enabling\nlaser excitation of this nucleus. This is because the electronic spectrum has a\nvery high level density near the nuclear transition energy that ensures the\nresonance condition is fulfilled. We present a quantum statistical theory based\non many-body quantum chaos to demonstrate that typical values for the\nelectronic factor increase the probability of electronic bridge in\n$^{235}$U$^{7+}$ by many orders of magnitude. We also extract the nuclear\nmatrix element by considering internal conversion from neutral uranium. The\nfinal electronic bridge rate is comparable to the rate of the Yb$^+$ octupole\ntransition currently used in precision spectroscopy.", "category": "physics_atom-ph" }, { "text": "Properties of metastable alkaline-earth-metal atoms calculated using an\n accurate effective core potential: The first three electronically excited states in the alkaline-earth-metal\natoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J\n(J=0,1,2) fine-structure manifold. All three states are metastable and are of\ninterest for optical atomic clocks as well as for cold-collision physics. An\nefficient technique--based on a physically motivated potential that models the\npresence of the ionic core--is employed to solve the Schroedinger equation for\nthe two-electron valence shell. In this way, radiative lifetimes, laser-induced\nclock shifts, and long-range interaction parameters are calculated for\nmetastable Mg, Ca, and Sr.", "category": "physics_atom-ph" }, { "text": "Excitation of the $^{229}$Th nucleus by the hole in the inner electronic\n shells: The $^{229}$Th nucleus has a long-lived isomeric state $A^*$ at 8.338(24) eV\n[Kraemer et al, Nature, \\textbf{617}, 706 (2023)]. This state is connected to\nthe ground state by an M1 transition. For a hydrogenlike Th ion in the $1s$\nstate the hyperfine structure splitting is about 0.7 eV. This means that the\nhyperfine interaction can mix the nuclear ground state with the isomeric state\nwith a mixing coefficient $\\beta$ about 0.03. If the electron is suddenly\nremoved from this system, the nucleus will be left in the mixed state. The\nprobability to find the nucleus in the isomeric state $A^*$ is equal to\n$\\beta^2\\sim 10^{-3}$. For the $2s$ state the effect is roughly two orders of\nmagnitude smaller. An atom with a hole in the $1s$ or $2s$ shell is similar to\nthe hydrogenlike atom, only the hole has a short lifetime $\\tau$. After the\nhole is filled, there is a non-zero probability to find the nucleus in the\n$A^*$ state. Estimates of this probability are presented along with a\ndiscussion of possible experiments on Th-doped xenotime-type orthophosphate\ncrystals and other broad band gap materials.", "category": "physics_atom-ph" }, { "text": "Application of the Complex Kohn Variational Method to Attosecond\n Spectroscopy: The complex Kohn variational method is extended to compute light-driven\nelectronic transitions between continuum wavefunctions in atomic and molecular\nsystems. This development enables the study of multiphoton processes in the\nperturbative regime for arbitrary light polarization. As a proof of principle,\nwe apply the method to compute the photoelectron spectrum arising from the\npump-probe two-photon ionization of helium induced by a sequence of extreme\nultraviolet and infrared-light pulses. We compare several two-photon ionization\npump-probe spectra, resonant with the (2s2p)1P1o Feshbach resonance, with\nindependent simulations based on the atomic B-spline close- coupling STOCK\ncode, and find good agreement between the two approaches. This new finite-pulse\nperturbative approach is a step towards the ab initio study of weak-field\nattosecond processes in poly-electronic molecules.", "category": "physics_atom-ph" }, { "text": "Hole burning and higher order photon effects in attosecond light-atom\n interaction: We have performed calculations of attosecond laser-atom interactions for\nlaser intensities where interesting two and three photon effects become\nrelevant. In particular, we examine the case of \"hole burning\" in the initial\norbital. Hole burning is present when the laser pulse duration is shorter than\nthe classical radial period because the electron preferentially absorbs the\nphoton near the nucleus. We also examine how 3 photon Raman process can lead to\na time delay in the outgoing electron for the energy near one photon\nabsorption. For excitation out of the hydrogen $2s$ state, an intensity of\n$2.2\\times 10^{16}$ W/cm$^2$ leads to a 6 attosecond delay of the outgoing\nelectron. We argue that this delay is due to the hole burning in the initial\nstate.", "category": "physics_atom-ph" }, { "text": "Quasi-three body systems - properties and scattering: We investigate systems of three mutually interacting particles with masses of\nwhich the inner is much bigger than the intermediate and the latter is much\nbigger than the outer. Then the three-body problem reduces to the two-body\nscattering or structure of the light one in the field of the pseudo-nucleus\nformed by two others. We calculate analytically the properties of considered\nsystems, such as the scattering cross-sections, hyperfine splitting, Auger\ndecay of exited states and Lamb shits, presenting them as expansions in powers\nof the ratio of light to intermediate particle masses. This ratio is the small\nparameter of the studied problems.", "category": "physics_atom-ph" }, { "text": "Non-adiabatic Coulomb effects in strong field ionisation in circularly\n polarised laser fields: We develop the recently proposed analytical R-matrix (ARM) method to\nencompass strong field ionisation by circularly polarised fields, for atoms\nwith arbitrary binding potentials. Through ARM, the effect of the potential can\nnow be included consistently both during and after ionisation, providing a\ncomplete picture for the effects of the long-range potential. We find that the\nCoulomb effects modify the ionisation dynamics in several ways, including\nmodification of (i) the ionisation (exit) times, (ii) the initial conditions\nfor the electron continuum dynamics, (iii) the \"tunnelling angle\", at which the\nelectron \"enters\" the barrier, and (iv) the electron drift momentum. We derive\nanalytical expressions for the Coulomb-corrected ionisation times, initial\nvelocities, momentum shifts and ionisation rates in circularly polarised\nfields, for arbitrary angular momentum of the initial state. We also analyse\nhow the non-adiabatic Coulomb effects modify (i) the calibration of the\nattoclock in the angular streaking method, and (ii) the ratio of ionisation\nrates from $p^{-}$ and $p^{+}$ orbitals.", "category": "physics_atom-ph" }, { "text": "Experimental Realization of Quantum-Resonance Ratchets: Quantum-resonance ratchets associated with the periodically kicked particle\nare experimentally realized for the first time. This is achieved by using a\nBose-Einstein condensate exposed to a pulsed standing light wave and prepared\nin an initial state differing from the usual plane wave. Both the standing-wave\npotential and the initial state have a point symmetry around some center and\nthe ratchet arises from the non-coincidence of the two centers. The dependence\nof the directed quantum transport on the quasimomentum is studied. A detailed\ntheoretical analysis is used to explain the experimental results.", "category": "physics_atom-ph" }, { "text": "Constraints on exotic dipole-dipole couplings between electrons at the\n micrometer scale: New constraints on exotic dipole-dipole interactions between electrons at the\nmicrometer scale are established, based on a recent measurement of the magnetic\ninteraction between two trapped $^{88}$Sr$^+$ ions. For light bosons (mass\n$\\le$ 0.1 eV) we obtain a $90\\%$ confidence interval on axial-vector mediated\ninteraction strength of $\\left|g_A^eg_A^e/4\\pi\\hbar c\\right|\\le 1.2\\times\n10^{-17}$. Assuming CPT invariance, this constraint is compared to that on\nanomalous electron-positron interactions, derived from positronium hyperfine\nspectroscopy. We find that the electron-electron constraint is six orders of\nmagnitude more stringent than the electron-positron counterpart. Bounds on\npseudo-scalar mediated interaction as well as on torsion gravity are also\nderived and compared with previous work performed at different length scales.\nOur constraints benefit from the high controllability of the experimental\nsystem which contained only two trapped particles. It therefore suggests a\nuseful new platform for exotic particle searches, complementing other\nexperimental efforts.", "category": "physics_atom-ph" }, { "text": "Isotope shift in the Sulfur electron affinity: observation and theory: The electron affinities eA(S) are measured for the two isotopes 32S and 34S\n(16752.9753(41) and 16752.9776(85) cm-1, respectively). The isotope shift in\nthe electron affinity is found to be positive, eA(34S)-eA(32S) = +0.0023(70)\ncm-1, but the uncertainty allows for the possibility that it may be either\n\"normal\" (eA(34S) > eA(32S)) or \"anomalous\" (eA(34S) < eA(32S)). The isotope\nshift is estimated theoretically using elaborate correlation models, monitoring\nthe electron affinity and the mass polarization term expectation value. The\ntheoretical analysis predicts a very large specific mass shift that\ncounterbalances the normal mass shift and produces an anomalous isotope shift,\neA(34S)-eA(32S) = - 0.0053(24) cm-1. The observed and theoretical residual\nisotope shifts agree with each other within the estimated uncertainties.", "category": "physics_atom-ph" }, { "text": "Cross-dimensional relaxation of $^7$Li-$^{87}$Rb atomic gas mixtures in\n a spherical-quadrupole magnetic trap: We measure the interspecies interaction strength between $^7$Li and $^{87}$Rb\natoms through cross-dimensional relaxation of two-element gas mixtures trapped\nin a spherical quadrupole magnetic trap. We record the relaxation of an initial\nmomentum-space anisotropy in a lithium gas when co-trapped with rubidium atoms,\nwith both species in the $|F=1, m_F = -1\\rangle$ hyperfine state. Our\nmeasurements are calibrated by observing cross-dimensional relaxation of a\n$^{87}$Rb-only trapped gas. Through Monte Carlo simulations, we compare the\nobserved relaxation to that expected given the theoretically predicted\nenergy-dependent differential cross section for $^7$Li-$^{87}$Rb collisions.\nThe experimentally observed relaxation occurs significantly faster than\npredicted theoretically, a deviation that appears incompatible with other\nexperimental data characterising the $^7$Li-$^{87}$Rb molecular potential.", "category": "physics_atom-ph" }, { "text": "Imperfect Recollisions in High-Harmonic Generation in Solids: We theoretically investigate high-harmonic generation in hexagonal boron\nnitride with linearly polarized laser pulses. We show that imperfect\nrecollisions between electron-hole pairs in the crystal give rise to an\nelectron-hole-pair polarization energy that leads to a double-peak structure in\nthe subcycle emission profiles. An extended recollision model (ERM) is\ndeveloped that allows for such imperfect recollisions, as well as effects\nrelated to Berry connections, Berry curvatures, and transition-dipole phases.\nThe ERM illuminates the distinct spectrotemporal characteristics of harmonics\nemitted parallel and perpendicularly to the laser polarization direction.\nImperfect recollisions are a general phenomenon and a manifestation of the\nspatially delocalized nature of the real-space wave packet, they arise\nnaturally in systems with large Berry curvatures, or in any system driven by\nelliptically polarized light.", "category": "physics_atom-ph" }, { "text": "Photon Berry phases, Instantons, Schrodinger Cats with oscillating\n parities and crossover from $ U(1) $ to $ Z_2 $ limit in cavity QED systems: In this work, we study the $ U(1)/Z_2 $ Dicke model at a finite $ N $ by\nusing the $ 1/J $ expansion and exact diagonization. This model includes the\nfour standard quantum optics model as its various special limits. The $ 1/J $\nexpansions is complementary to the strong coupling expansion used by the\nauthors in arXiv:1512.08581 to study the same model in its dual $ Z_2/U(1) $\nrepresentation. We identify 3 regimes of the system's energy levels: the\nnormal, $ U(1) $ and quantum tunneling (QT) regime. The system's energy levels\nare grouped into doublets which consist of scattering states and Schrodinger\nCats with even ( e ) and odd ( o ) parities in the $ U(1) $ and quantum\ntunneling (QT) regime respectively. In the QT regime, by the WKB method, we\nfind the emergencies of bound states one by one as the interaction strength\nincreases, then investigate a new class of quantum tunneling processes through\nthe instantons between the two bound states in the compact photon phase. It is\nthe Berry phase interference effects in the instanton tunneling event which\nleads to Schrodinger Cats oscillating with even and odd parities in both ground\nand higher energy bound states. We map out the energy level evolution from the\n$ U(1) $ to the QT regime and also discuss some duality relations between the\nenergy levels in the two regimes. We also compute the photon correlation\nfunctions, squeezing spectrum, number correlation functions in both regimes\nwhich can be measured by various experimental techniques. The combinations of\nthe results achieved here by $ 1/J $ expansion and those in arXiv:1512.08581 by\nstrong coupling method lead to rather complete understandings of the $ U(1)/Z_2\n$ Dicke model at a finite $ N $ and any anisotropy parameter $ \\beta $.", "category": "physics_atom-ph" }, { "text": "Mott Scattering of polarized electrons in a circularly polarized laser\n field: We present a study of Mott scattering of polarized electrons in the presence\nof a laser field with circular polarization using the helicity formalism and\nthe introduction of the well known concept of non flip differential cross\nsection as well as that of flip differential cross section. The results we have\nobtained in the presence of a laser field are coherent with those obtained in\nthe absence of a laser field. We have studied the relativistic regime as well\nas the non relativistic regime that are precisely defined in the text. Two\nimportant consistency checks have been carried out successfully. The first one\nis that the sum of both differential cross sections (one with spin up, the\nother with spin down) always gives the unpolarized differential cross section.\nThe second one is that the relativistic unpolarized differential cross section\nconverges to the non relativistic differential cross section in the limit of\nsmall velocities. Moreover, the results obtained using the sofware Reduce\n\\cite{8} gave rise to non contracted coefficients that have been dealt with\nusing the geometry chosen.", "category": "physics_atom-ph" }, { "text": "Atomic magnetic resonance induced by amplitude-, frequency-, or\n polarization-modulated light: In recent years diode laser sources have become widespread and reliable tools\nin magneto-optical spectroscopy. In particular, laser-driven atomic\nmagnetometers have found a wide range of practical applications. More recently,\nso-called magnetically silent variants of atomic magnetometers have been\ndeveloped. While in conventional magnetometers the magnetic resonance\ntransitions between atomic sublevels are phase-coherently driven by a weak\noscillating magnetic field, silent magnetometers use schemes in which either\nthe frequency (FM) or the amplitude (AM) of the light beam is modulated. Here\nwe present a theoretical model that yields algebraic expressions for the\nparameters of the multiple resonances that occur when either amplitude-,\nfrequency- or polarization-modulated light of circular polarization is used to\ndrive the magnetic resonance transition in a transverse magnetic field. The\nrelative magnitudes of the resonances that are observed in the transmitted\nlight intensity at harmonic m of the Larmor frequency \\omega_L (either by DC or\nphase sensitive detection at harmonics q of the modulation frequency\n\\omega_mod) of the transmitted light are expressed in terms of the Fourier\ncoefficients of the modulation function. Our approach is based on an atomic\nmultipole moment representation that is valid for spin-oriented atomic states\nwith arbitrary angular momentum F in the low light power limit. We find\nexcellent quantitative agreement with an experimental case study using\n(square-wave) amplitude-modulated (AM) light.", "category": "physics_atom-ph" }, { "text": "A novel antiproton radial diagnostic based on octupole induced ballistic\n loss: We report results from a novel diagnostic that probes the outer radial\nprofile of trapped antiproton clouds. The diagnostic allows us to determine the\nprofile by monitoring the time-history of antiproton losses that occur as an\noctupole field in the antiproton confinement region is increased. We show\nseveral examples of how this diagnostic helps us to understand the radial\ndynamics of antiprotons in normal and nested Penning-Malmberg traps. Better\nunderstanding of these dynamics may aid current attempts to trap antihydrogen\natoms.", "category": "physics_atom-ph" }, { "text": "Ion Current as a Precise Measure of the Loading Rate of a\n Magneto-Optical Trap: We have demonstrated that the ion current resulting from collisions between\nmetastable krypton atoms in a magneto-optical trap can be used to precisely\nmeasure the trap loading rate. We measured both the ion current of the abundant\nisotope Kr-83 (isotopic abundance = 11%) and the single-atom counting rate of\nthe rare isotope Kr-85 (isotopic abundance ~ 1x10^-11), and found the two\nquantities to be proportional at a precision level of 0.9%. This work results\nin a significant improvement in using the magneto-optical trap as an analytical\ntool for noble-gas isotope ratio measurements, and will benefit both atomic\nphysics studies and applications in the earth sciences.", "category": "physics_atom-ph" }, { "text": "Sensitive gravity-gradiometry with atom interferometry: progress towards\n an improved determination of the gravitational constant: We here present a high sensitivity gravity-gradiometer based on atom\ninterferometry. In our apparatus, two clouds of laser-cooled rubidium atoms are\nlaunched in fountain configuration and interrogated by a Raman interferometry\nsequence to probe the gradient of gravity field. We recently implemented a\nhigh-flux atomic source and a newly designed Raman lasers system in the\ninstrument set-up. We discuss the applications towards a precise determination\nof the Newtonian gravitational constant G. The long-term stability of the\ninstrument and the signal-to-noise ratio demonstrated here open interesting\nperspectives for pushing the measurement precision below the 100 ppm level.", "category": "physics_atom-ph" }, { "text": "Solution of the two identical ion Penning trap final state: We have derived a closed form analytic expression for the asymptotic motion\nof a pair of identical ions in a high precision Penning trap. The analytic\nsolution includes the effects of special relativity and the Coulomb interaction\nbetween the ions. The existence and physical relevance of such a final state is\nsupported by a confluence of theoretical, experimental and numerical evidence.", "category": "physics_atom-ph" }, { "text": "Streaking single-electron ionization in open-shell molecules driven by\n X-ray pulses: We obtain continuum molecular wavefunctions for open-shell molecules in the\nHartree-Fock framework. We do so while accounting for the singlet or triplet\ntotal spin symmetry of the molecular ion, that is, of the open-shell orbital\nand the initial orbital where the electron ionizes from. Using these continuum\nwavefunctions, we obtain the dipole matrix elements for a core electron that\nionizes due to single-photon absorption by a linearly polarized X-ray pulse.\nAfter ionization from the X-ray pulse, we control or streak the electron\ndynamics using a circularly polarized infrared (IR) pulse. For a high intensity\nIR pulse and photon energies of the X-ray pulse close to the ionization\nthreshold of the $1{\\sigma}$ or $2{\\sigma}$ orbitals, we achieve control of the\nangle of escape of the ionizing electron by varying the phase delay between the\nX-ray and IR pulses. For a low intensity IR pulse, we obtain final electron\nmomenta distributions on the plane of the IR pulse and we find that many\nfeatures of these distributions correspond to the angular patterns of electron\nescape solely due to the X-ray pulse.", "category": "physics_atom-ph" }, { "text": "Ultra high densities of cold atoms in a holographically controlled dark\n SPOT trap: We demonstrate an atom trap geometry for 87Rb which is capable of producing\nultra high atom densities. Reradiation forces, which usually limit high\ndensities, can be avoided in dark spontaneous-force optical traps (dark SPOTs)\nby sheltering atoms from intense trapping light. Here we demonstrate a dynamic\nimplementation of a dark SPOT, resulting in an increase in atom density by\nalmost two orders of magnitude up to 1.3x10^12cm-3. Holographic control of the\ntrapping beams and dynamic switching between MOT and dark SPOT configuration\nallows us to optimise the trapping geometry. We have identified the ideal size\nof the dark core to be six times larger than the MOT. Our method also avoids\nunwanted heating so that we reach a record phase-space density for a MOT.", "category": "physics_atom-ph" }, { "text": "Demonstration and frequency noise characterization of a 17 $\u03bc$m\n quantum cascade laser: We describe the properties of a continuous-wave room-temperature quantum\ncascade laser operating at the long wavelength of 17 $\\mu$m. Long wavelength\nmid-infrared quantum cascade lasers offer new opportunities for chemical\ndetection, vibrational spectroscopy and metrological measurements using\nmolecular species. In particular, probing low energy vibrational transitions\nwould be beneficial to the spectroscopy of large and complex molecules,\nreducing intramolecular vibrational energy redistribution which acts as a\ndecoherence channel. By performing linear absorption spectroscopy of the v2\nfundamental vibrational mode of N2O molecules, we have demonstrated the\nspectral range and spectroscopic potential of this laser, and characterized its\nfree-running frequency noise properties. Finally, we also discuss the potential\napplication of this specific laser in an experiment to test fundamental physics\nwith ultra-cold molecules.", "category": "physics_atom-ph" }, { "text": "Multi-electron transitions induced by neutron impact on helium: We explore excitation and ionization by neutron impact as a novel tool for\nthe investigation of electron-electron correlations in helium. We present\nsingle and double ionization spectra calculated in accurate numerical ab-initio\nsimulations for incoming neutrons with kinetic energies of up to 150 keV. The\nresulting electron spectra are found to be fundamentally different from\nphotoioniza- tion or charged particle impact due to the intrinsic many-body\ncharacter of the interaction. In particular, doubly excited resonances that are\nstrongly suppressed in electron or photon impact become prominent. The ratio of\ndouble to single ionization is found to differ significantly from those of\nphoton and charged particle impact.", "category": "physics_atom-ph" }, { "text": "Coherent control for qubit state readout: Short pulses from mode-locked lasers can produce background-free atomic\nfluorescence by allowing temporal separation of the prompt incidental scatter\nfrom the subsequent atomic emission. We use this to improve quantum state\ndetection of optical-frequency and electron-shelved trapped ion qubits by more\nthan 2 orders of magnitude. For direct detection of qubits defined on atomic\nhyperfine structure, however, the large bandwidth of short pulses is greater\nthan the hyperfine splitting, and repeated excitation is not qubit state\nselective. Here, we show that the state resolution needed for projective\nquantum measurement of hyperfine qubits can be recovered by applying techniques\nfrom coherent control to the orbiting valence electron of the queried ion. We\ndemonstrate electron wavepacket interference to allow readout of the original\nqubit state using broadband pulses, even in the presence of large amounts of\nbackground laser scatter.", "category": "physics_atom-ph" }, { "text": "Calculations of the Relativistic Effects in Many-Electron Atoms and\n Space-Time Variation of Fundamental Constants: Theories unifying gravity and other interactions suggest the possibility of\nspatial and temporal variation of physical ``constants'' in the Universe.\nDetection of high-redshift absorption systems intersecting the sight lines\ntowards distant quasars provide a powerful tool for measuring these variations.\nWe have previously demonstrated that high sensitivity to the variation of the\nfine structure constant $\\alpha$ can be obtained by comparing spectra of heavy\nand light atoms (or molecules). Here we describe new calculations for a range\nof atoms and ions, most of which are commonly detected in quasar spectra: Fe\nII, Mg II, Mg I, C II, C IV, N~V, O I, Al III, Si II, Si IV, Ca I, Ca II, Cr\nII, Mn II, Zn II, Ge II (see the results in Table 3). The combination of Fe II\nand Mg II, for which accurate laboratory frequencies exist, have already been\nused to constrain $\\alpha$ variations. To use other atoms and ions, accurate\nlaboratory values of frequencies of the strong E1-transitions from the ground\nstates are required. We wish to draw the attention of atomic experimentalists\nto this important problem.\n We also discuss a mechanism which can lead to a greatly enhanced sensitivity\nfor placing constraints on variation on fundamental constants. Calculations\nhave been performed for Hg II, Yb II, Ca I and Sr II where there are optical\ntransitions with the very small natural widths, and for hyperfine transition in\nCs I and Hg II.", "category": "physics_atom-ph" }, { "text": "Strong-field approximation for Coulomb explosion of H_2^+ by short\n intense laser pulses: We present a simple quantum mechanical model to describe Coulomb explosion of\nH$_2^+$ by short, intense, infrared laser pulses. The model is based on the\nlength gauge version of the molecular strong-field approximation and is valid\nfor pulses shorter than 50 fs where the process of dissociation prior to\nionization is negligible. The results are compared with recent experimental\nresults for the proton energy spectrum [I. Ben-Itzhak et al., Phys. Rev. Lett.\n95, 073002 (2005), B. D. Esry et al., Phys. Rev. Lett. 97, 013003 (2006)]. The\npredictions of the model reproduce the profile of the spectrum although the\npeak energy is slightly lower than the observations. For comparison, we also\npresent results obtained by two different tunneling models for this process.", "category": "physics_atom-ph" }, { "text": "Angular distribution studies on the two-photon ionization of\n hydrogen-like ions: Relativistic description: The angular distribution of the emitted electrons, following the two-photon\nionization of the hydrogen-like ions, is studied within the framework of second\norder perturbation theory and the Dirac equation. Using a density matrix\napproach, we have investigated the effects which arise from the polarization of\nthe incoming light as well as from the higher multipoles in the expansion of\nthe electron--photon interaction. For medium- and high-Z ions, in particular,\nthe non-dipole contributions give rise to a significant change in the angular\ndistribution of the emitted electrons, if compared with the electric-dipole\napproximation. This includes a strong forward emission while, in dipole\napproxmation, the electron emission always occurs symmetric with respect to the\nplane which is perpendicular to the photon beam. Detailed computations for the\ndependence of the photoelectron angular distributions on the polarization of\nthe incident light are carried out for the ionization of H, Xe$^{53+}$, and\nU$^{91+}$ (hydrogen-like) ions.", "category": "physics_atom-ph" }, { "text": "Enhancing dipolar interactions between molecules using state-dependent\n optical tweezer traps: We show how state-dependent optical potentials can be used to trap a pair of\nmolecules in different internal states at a separation much smaller than the\nwavelength of the trapping light. This close spacing greatly enhances the\ndipole-dipole interaction and we show how it can be used to implement two-qubit\ngates between molecules that are 100 times faster than existing protocols and\nthan rotational coherence times already demonstrated. We analyze complications\ndue to hyperfine structure, tensor light shifts, photon scattering and\ncollisional loss, and conclude that none is a barrier to implementing the\nscheme.", "category": "physics_atom-ph" }, { "text": "Magneto optical trapping of Barium: First laser cooling and trapping of the heavy alkaline earth element barium\nhas been achieved based on the strong 6s$^2$ $^1$S$_0$ - 6s6p $^1$P$_1$\ntransition for the main cooling. Due to the large branching into metastable\nD-states several additional laser driven transitions are required to provide a\nclosed cooling cycle. A total efficiency of $0.4(1) \\cdot 10^{-2}$ for slowing\na thermal atomic beam and capturing atoms into a magneto optical trap was\nobtained. Trapping lifetimes of more than 1.5 s were observed. This lifetime is\nshortened at high laser intensities by photo ionization losses. The developed\ntechniques will allow to extend significantly the number of elements that can\nbe optically cooled and trapped.", "category": "physics_atom-ph" }, { "text": "Polarization effects in the total rate of biharmonic $\u03c9+ 3\u03c9$\n ionization of atoms: The total ionization rate of biharmonic ($\\omega + 3\\omega$) ionization is\nstudied within the independent particle approximation and the third order\nperturbation theory. Particular attention is paid to how the polarization of\nthe biharmonic light field affects the total rate. The ratios of the biharmonic\nionization rates for linearly and circularly polarized beams as well as for\ncorotating and counterrotating elliptically polarized beams are analyzed, and\nhow they depend on the beam parameters, such as photon frequency or phase\nbetween $\\omega$ and $3\\omega$ light beams. We show that the interference of\nthe biharmonic ionization amplitudes determines the dominance of a particular\nbeam polarization over another and that it can be controlled by an appropriate\nchoice of beam parameters. Furthermore, we demonstrate our findings for the\nionization of neon $L$ shell electrons.", "category": "physics_atom-ph" }, { "text": "Electric Rydberg-atom interferometery: An electric analogue of the longitudinal Stern-Gerlach matter-wave\ninterferometer has been realized for atoms in Rydberg states with high\nprincipal quantum number, $n$. The experiments were performed with He atoms\nprepared in coherent superpositions of the $n=55$ and $n=56$ circular Rydberg\nstates in zero electric field by a $\\pi/2$ pulse of resonant microwave\nradiation. These atoms were subjected to a pulsed inhomogeneous electric field\nto generate a superposition of momentum states before a $\\pi$ pulse was applied\nto invert the internal states. The same pulsed inhomogeneous electric field was\nthen reapplied for a second time to transform the motional states to have equal\nmomenta before a further $\\pi/2$ pulse was employed to interrogate the final\nRydberg state populations. This Hahn-echo microwave pulse sequence,\ninterspersed with a pair of equivalent inhomogeneous electric field pulses,\nyielded two spatially separated matter waves. Interferences between these\nmatter waves were observed as oscillations in the final Rydberg state\npopulations as the amplitude of the pulsed electric field gradients was\nadjusted.", "category": "physics_atom-ph" }, { "text": "Imaging an aligned polyatomic molecule with laser-induced electron\n diffraction: Laser-induced electron diffraction is an evolving tabletop method, which aims\nto image ultrafast structural changes in gas-phase polyatomic molecules with\nsub-{\\AA}ngstr\\\"om spatial and femtosecond temporal resolution. Here, we\nprovide the general foundation for the retrieval of multiple bond lengths from\na polyatomic molecule by simultaneously measuring the C-C and C-H bond lengths\nin aligned acetylene. Our approach takes the method beyond the hitherto\nachieved imaging of simple diatomic molecules and is based upon the combination\nof a 160 kHz mid-IR few-cycle laser source with full three-dimensional\nelectron-ion coincidence detection. Our technique provides an accessible and\nrobust route towards imaging ultrafast processes in complex gas phase molecules\nwith atto- to femto-second temporal resolution.", "category": "physics_atom-ph" }, { "text": "A cold-atom Ramsey clock with a low volume physics package: We demonstrate a Ramsey-type microwave clock interrogating the 6.835~GHz\nground-state transition in cold \\textsuperscript{87}Rb atoms loaded from a\ngrating magneto-optical trap (GMOT) enclosed in an additively manufactured\nloop-gap resonator microwave cavity. A short-term stability of $1.5\n\\times10^{-11} $~$\\tau^{-1/2}$ is demonstrated, in reasonable agreement with\npredictions from the signal-to-noise ratio of the measured Ramsey fringes. The\ncavity-grating package has a volume of $\\approx$67~cm\\textsuperscript{3},\nensuring an inherently compact system while the use of a GMOT drastically\nsimplifies the optical requirements for laser cooled atoms. This work is\nanother step towards the realisation of highly compact portable cold-atom\nfrequency standards.", "category": "physics_atom-ph" }, { "text": "Progress in Atomic Fountains at LNE-SYRTE: We give an overview of the work done with the Laboratoire National de\nM\\'etrologie et d'Essais-Syst\\`emes de R\\'ef\\'erence Temps-Espace (LNE-SYRTE)\nfountain ensemble during the last five years. After a description of the clock\nensemble, comprising three fountains, FO1, FO2, and FOM, and the newest\ndevelopments, we review recent studies of several systematic frequency shifts.\nThis includes the distributed cavity phase shift, which we evaluate for the FO1\nand FOM fountains, applying the techniques of our recent work on FO2. We also\nreport calculations of the microwave lensing frequency shift for the three\nfountains, review the status of the blackbody radiation shift, and summarize\nrecent experimental work to control microwave leakage and spurious phase\nperturbations. We give current accuracy budgets. We also describe several\napplications in time and frequency metrology: fountain comparisons,\ncalibrations of the international atomic time, secondary representation of the\nSI second based on the 87Rb hyperfine frequency, absolute measurements of\noptical frequencies, tests of the T2L2 satellite laser link, and review\nfundamental physics applications of the LNE-SYRTE fountain ensemble. Finally,\nwe give a summary of the tests of the PHARAO cold atom space clock performed\nusing the FOM transportable fountain.", "category": "physics_atom-ph" }, { "text": "Squeezed state metrology with Bragg interferometers operating in a\n cavity: Bragg interferometers, operating using pseudospin-1/2 systems composed of two\nmomentum states, have become a mature technology for precision measurements.\nState-of-the-art Bragg interferometers are rapidly surpassing technical\nlimitations and are soon expected to operate near the projection noise limit\nset by uncorrelated atoms. Despite the use of large numbers of atoms, their\noperation is governed by single-atom physics. Motivated by recent proposals and\ndemonstrations of Raman gravimeters in cavities, we propose a scheme to squeeze\ndirectly on momentum states for surpassing the projection noise limit in Bragg\ninterferometers. In our modeling, we consider the unique issues that arise when\na spin squeezing protocol is applied to momentum pseudospins. Specifically, we\nstudy the effects of the momentum width of the atomic cloud and the coupling to\nmomentum states outside the pseudospin manifold, as these atoms interact via a\nmode of the cavity. We show that appreciable levels of spin squeezing can be\ndemonstrated in suitable parameter regimes in spite of these complications.\nUsing this setting, we show how beyond mean-field techniques developed for spin\nsystems can be adapted to study the dynamics of momentum states of interacting\natoms. Our scheme promises to be feasible using current technology and is\nexperimentally attractive because it requires no additional setup beyond what\nwill be required to operate Bragg interferometers in cavities.", "category": "physics_atom-ph" }, { "text": "Quantum Test of the Universality of Free Fall: We simultaneously measure the gravitationally-induced phase shift in two\nRaman-type matter-wave interferometers operated with laser-cooled ensembles of\n$^{87}$Rb and $^{39}$K atoms. Our measurement yields an E\\\"otv\\\"os ratio of\n$\\eta_{\\text{Rb,K}}=(0.3\\pm 5.4)\\times 10^{-7}$. We briefly estimate possible\nbias effects and present strategies for future improvements.", "category": "physics_atom-ph" }, { "text": "Efficient sideband cooling protocol for long trapped-ion chains: Trapped ions are a promising candidate for large scale quantum computation.\nSeveral systems have been built in both academic and industrial settings to\nimplement modestly-sized quantum algorithms. Efficient cooling of the motional\ndegrees of freedom is a key requirement for high-fidelity quantum operations\nusing trapped ions. Here, we present a technique whereby individual ions are\nused to cool individual motional modes in parallel, reducing the time required\nto bring an ion chain to its motional ground state. We demonstrate this\ntechnique experimentally and develop a model to understand the efficiency of\nour parallel sideband cooling technique compared to more traditional methods.\nThis technique is applicable to any system using resolved sideband cooling of\nco-trapped atomic species and only requires individual addressing of the\ntrapped particles.", "category": "physics_atom-ph" }, { "text": "Spin-axis relaxation in spin-exchange collisions of alkali atoms: We present calculations of spin-relaxation rates of alkali-metal atoms due to\nthe spin-axis interaction acting in binary collisions between the atoms. We\nshow that for the high-temperature conditions of interest here, the spin\nrelaxation rates calculated with classical-path trajectories are nearly the\nsame as those calculated with the distorted-wave Born approximation. We compare\nthese calculations to recent experiments that used magnetic decoupling to\nisolate spin relaxation due to binary collisions from that due to the formation\nof triplet van-der-Waals molecules. The values of the spin-axis coupling\ncoefficients deduced from measurements of binary collision rates are consistent\nwith those deduced from molecular decoupling experiments. All the experimental\ndata is consistent with a simple and physically plausible scaling law for the\nspin-axis coupling coefficients.", "category": "physics_atom-ph" }, { "text": "Electron Drift Directions in Strong-Field Double Ionization of Atoms: Longitudinal momentum spectra and electron drift directions are considered\nfor several laser wavelengths in Non-Sequential Double Ionization of helium\nusing three dimensional classical ensembles. In this model, the familiar\ndoublet for wavelength 800 nm and intensities of order 0.5 PW/cm^2, becomes a\ntriplet for wavelength 1314 nm, then a doublet with plateau for 2017 nm. The\nresults are explained based on whether the post-ionization impulse from the\nlaser results in backward drift for one or both electrons.", "category": "physics_atom-ph" }, { "text": "New classes of systematic effects in gas spin co-magnetometers: Atomic co-magnetometers are widely used in precision measurements searching\nfor spin interactions beyond the Standard Model. We describe a new\n$^3$He-$^{129}$Xe co-magnetometer probed by Rb atoms and use it to identify two\ngeneral classes of systematic effects in gas co-magnetometers, one associated\nwith diffusion in second-order magnetic field gradients and another due to\ntemperature gradients. We also develop a general and practical approach for\ncalculating spin relaxation and frequency shifts due to arbitrary magnetic\nfield gradients and confirm it experimentally.", "category": "physics_atom-ph" }, { "text": "Studying and applying magnetic dressing with a Bell and Bloom\n magnetometer: The magnetic dressing phenomenon occurs when spins precessing in a static\nfield (holding field) are subject to an additional, strong, alternating field.\nIt is usually studied when such extra field is homogeneous and oscillates in\none direction.\n We study the dynamics of spins under dressing condition in two unusual\nconfigurations. In the first instance, an inhomogeneous dressing field produces\nspace dependent dressing phenomenon, which helps to operate the magnetometer in\nstrongly inhomogeneous static field.\n In the second instance, beside the usual configuration with static and the\nstrong orthogonal oscillating magnetic fields, we add a secondary oscillating\nfield, which is perpendicular to both. The system shows novel and interesting\nfeatures that are accurately explained and modelled theoretically. Possible\napplications of these novel features are briefly discussed.", "category": "physics_atom-ph" }, { "text": "Precision measurements and test of molecular theory in highly-excited\n vibrational states of H$_2$ $(v=11)$: Accurate $EF{}^1\\Sigma^+_g-X{}^1\\Sigma^+_g$ transition energies in molecular\nhydrogen were determined for transitions originating from levels with\nhighly-excited vibrational quantum number, $v=11$, in the ground electronic\nstate. Doppler-free two-photon spectroscopy was applied on vibrationally\nexcited H$_2^*$, produced via the photodissociation of H$_2$S, yielding\ntransition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An\nimportant improvement is the enhanced detection efficiency by resonant\nexcitation to autoionizing $7p\\pi$ electronic Rydberg states, resulting in\nnarrow transitions due to reduced ac-Stark effects. Using known $EF$ level\nenergies, the level energies of $X(v=11, J=1,3-5)$ states are derived with\naccuracies of typically 0.002 cm$^{-1}$. These experimental values are in\nexcellent agreement with, and are more accurate than the results obtained from\nthe most advanced ab initio molecular theory calculations including\nrelativistic and QED contributions.", "category": "physics_atom-ph" }, { "text": "Multichannel $e^{\\pm}$ scattering on excited Ps states: Scattering and reaction cross sections of $e^{\\pm}-Ps$ system are calculated\nfor total angular momentum L=0, 1 and 2 and energies between the\nPs(n=2)-Ps(n=3) threshold. We solved a set of Faddeev-Merkuriev and\nLippmann-Schwinger integral equations by applying the Coulomb-Sturmian\nseparable expansion technique. We found that the excited positronium states\nplay dominating roles in scattering processes.", "category": "physics_atom-ph" }, { "text": "Optogalvanic Spectroscopy of Metastable States in Yb^{+}: The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest\nfor applications in metrology and quantum information and also act as dark\nstates in laser cooling. These metastable states are commonly repumped to the\nground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm\n^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic\nspectroscopy of these transitions in Yb^{+} ions generated in a discharge. We\nmeasure the pressure broadening coefficient for the 638.6 nm transition to be\n70 \\pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the\n638.6 nm isotope splitting and show that our observations are consistent with\ntheory for the hyperfine splitting. Our measurements of the 935.2 nm transition\nextend those made by Sugiyama et al, showing well-resolved isotope and\nhyperfine splitting. We obtain high signal to noise, sufficient for laser\nstabilisation applications.", "category": "physics_atom-ph" }, { "text": "Electric quadrupole moment of the $4d ^{2}D_{5/2}$ state in\n $^{88}Sr^{+}$ and its role in an optical frequency standard: The electric quadrupole moment for the $4d ^2D_{5/2}$ state of\n$\\mathrm{^{88}Sr^+}$, one of the most important candidates for an optical\nclock, has been calculated using the relativistic coupled-cluster theory. The\nresult of the calculation is presented and the important many-body\ncontributions are highlighted. The calculated electric quadrupole moment is\n$(2.94\\pm0.07)ea_{0}^{2}$, where $a_{0}$ is the Bohr radius and $e$ the\nelectronic charge while the measured value is $(2.6\\pm0.3)ea_{0}^{2}$. This is\nso far the most accurate determination of the electric quadrupole moment for\nthe above mentioned state.", "category": "physics_atom-ph" }, { "text": "Diffusion of muonic hydrogen in hydrogen gas and the measurement of the\n 1$s$ hyperfine splitting of muonic hydrogen: The CREMA collaboration is pursuing a measurement of the ground-state\nhyperfine splitting (HFS) in muonic hydrogen ($\\mu$p) with 1 ppm accuracy by\nmeans of pulsed laser spectroscopy. In the proposed experiment, the $\\mu$p atom\nis excited by a laser pulse from the singlet to the triplet hyperfine\nsub-levels, and is quenched back to the singlet state by an inelastic collision\nwith a H$_2$ molecule. The resulting increase of kinetic energy after this\ncycle modifies the $\\mu$p atom diffusion in the hydrogen gas and the arrival\ntime of the $\\mu$p atoms at the target walls. This laser-induced modification\nof the arrival times is used to expose the atomic transition. In this paper we\npresent the simulation of the $\\mu$p diffusion in the H$_2$ gas which is at the\ncore of the experimental scheme. These simulations have been implemented with\nthe Geant4 framework by introducing various low-energy processes including the\nmotion of the H$_2$ molecules, i.e. the effects related with the hydrogen\ntarget temperature. The simulations have been used to optimize the hydrogen\ntarget parameters (pressure, temperatures and thickness) and to estimate signal\nand background rates. These rates allow to estimate the maximum time needed to\nfind the resonance and the statistical accuracy of the spectroscopy experiment.", "category": "physics_atom-ph" }, { "text": "Excitation of $^{87}$Rb Rydberg atoms to nS and nD states (n$\\leq$68)\n via an optical nanofiber: Cold Rydberg atoms are a promising platform for quantum technologies and\ncombining them with optical waveguides has the potential to create robust\nquantum information devices. Here, we experimentally observe the excitation of\ncold rubidium atoms to a large range of Rydberg S and D states through\ninteraction with the evanescent field of an optical nanofiber. We develop a\ntheoretical model to account for experimental phenomena present such as the AC\nStark shifts and the Casimir-Polder interaction. This work strengthens the\nknowledge of Rydberg atom interactions with optical nanofibers and is a\ncritical step toward the implementation of all-fiber quantum networks and\nwaveguide QED systems using highly excited atoms.", "category": "physics_atom-ph" }, { "text": "Self-sustained oscillations in a Large Magneto-Optical Trap: We have observed self-sustained radial oscillations in a large\nmagneto-optical trap (MOT), containing up to $10^{10}$ Rb$^{85}$ atoms. This\ninstability is due to the competition between the confining force of the MOT\nand the repulsive interaction associated with multiple scattering of light\ninside the cold atomic cloud. A simple analytical model allows us to formulate\na criterion for the instability threshold, in fair agreement with our\nobservations. This criterion shows that large numbers of trapped atoms $N>10^9$\nare required to observe this unstable behavior.", "category": "physics_atom-ph" }, { "text": "Delayed double ionization as a signature of Hamiltonian chaos: We analyze the dynamical processes behind delayed double ionization of atoms\nsubjected to strong laser pulses. Using reduced models, we show that these\nprocesses are a signature of Hamiltonian chaos which results from the\ncompetition between the laser field and the Coulomb attraction to the nucleus.\nIn particular, we exhibit the paramount role of the unstable manifold of\nselected periodic orbits which lead to a delay in these double ionizations.\nAmong delayed double ionizations, we consider the case of \"Recollision\nExcitation with Subsequent Ionization\" (RESI) and, as a hallmark of this\nmechanism, we predict oscillations in the ratio of RESI to double ionization\nyields versus laser intensity. We discuss the significance of the\ndimensionality of the reduced models for the analysis of the dynamical\nprocesses behind delayed double ionization.", "category": "physics_atom-ph" }, { "text": "Implementation strategies for multiband quantum simulators of real\n materials: The majority of quantum simulators treat simplified one-band strongly\ncorrelated models, whereas multiple bands are needed to describe materials with\nintermediate correlation. We investigate the sensitivity of multiband quantum\nsimulators to: (1) the form of optical lattices (2) the interactions between\nelectron analogues. Since the kinetic energy terms of electron analogues in a\nquantum simulator and electrons in a solid are identical, by examining both\nperiodic potential and interaction we explore the full problem of many-band\nquantum simulators within the Born-Oppenheimer approximation. Density\nfunctional calculations show that bandstructure is highly sensitive to the form\nof optical lattice, and it is necessary to go beyond sinusoidal potentials to\nensure that the bands closest to the Fermi surface are similar to those in real\nmaterials. Analysis of several electron analogue types finds that dressed\nRydberg atoms (DRAs) have promising interactions for multi band quantum\nsimulation. DRA properties can be chosen so that interaction matrices\napproximate those in real systems and decoherence effects are controlled,\nalbeit with parameters at the edge of currently available technology. We\nconclude that multiband quantum simulators implemented using the principles\nestablished here could provide insight into the complex processes in real\nmaterials.", "category": "physics_atom-ph" }, { "text": "Generating 500 mW for laser cooling of strontium atoms by injection\n locking a high power laser diode: We report on the generation of 500 mW of spectrally pure laser light at the\n460.86 nm transition used for laser cooling of strontium atoms. To this end we\ninject a high power single mode laser diode with light from a stabilized\nextended cavity diode laser. To optimize and monitor the injection status and\nthe spectral purity of the slave diode we developed a novel technique that uses\na single passive optical element. A narrow band interference filter generates a\nsuitable monitoring signal without any additional electronics for post\nprocessing of the data. Our method greatly simplifies the daily operation of\ninjection locked laser diodes and can be easily adapted to other wavelengths of\ninterest.", "category": "physics_atom-ph" }, { "text": "Holographic detection of parity in atomic and molecular orbitals: We introduce a novel and concise methodology to detect the parity of atomic\nand molecular orbitals based on photoelectron holography, which is more general\nthan the existing schemes. It fully accounts for the Coulomb distortions of\nelectron trajectories, does not require sculpted fields to retrieve phase\ninformation and, in principle, is applicable to a broad range of electron\nmomenta. By comparatively measuring the differential photoelectron spectra from\nstrong-field ionization of N$_{2}$ molecules and their companion atoms of Ar,\nsome photoelectron holography patterns are found to be dephased for both\ntargets. This is well reproduced by the full-dimensional time-dependent\nSchr\\\"{o}dinger equation and the Coulomb quantum-orbit strong-field\napproximation (CQSFA) simulation. Using the CQSFA, we trace back our\nobservations to different parities of the 3$p$ orbital of Ar and the\nhighest-occupied molecular orbital of N$_{2}$ via interfering Coulomb-distorted\nquantum orbits carrying different initial phases. This method could in\nprinciple be used to extract bound-state phases from any holographic structure,\nwith a wide range of potential applications in recollision physics and\nspectroscopy.", "category": "physics_atom-ph" }, { "text": "Precise determination of the isotope shift of ${}^{88}$Sr - ${}^{87}$Sr\n optical lattice clock by sharing perturbations: We report on the isotope shift between ${}^{88}$Sr and ${}^{87}$Sr on the\n${}^1S_0 - {}^3P_0$ clock transitions. The interleaved operation of an optical\nlattice clock with two isotopes allows the canceling out of common\nperturbations, such as the quadratic Zeeman shift, the clock-light shift, and\nthe blackbody radiation shift. The isotope shift is determined to be 62 188\n134.004(10) Hz, where the major uncertainty is introduced by the collisional\nshift that is distinct for each isotope. Our result allows us to determine the\nfrequency of $^{88}$Sr-$^{87}$Sr optical lattice clocks with a fractional\nuncertainty of $2\\times 10^{-17}$. The scheme is generally applicable for\nmeasuring the isotope shift with significantly reduced uncertainty.", "category": "physics_atom-ph" }, { "text": "Nonrelativistic double photoeffect on lithiumlike ions at high energies: The total cross section for double ionization of lithiumlike ions by a\nhigh-energy photon is calculated in leading order of the nonrelativistic\nperturbation theory. The partial contributions due to simultaneous and\nsequential emissions of two electrons are taken into account. The cross section\nunder consideration is shown to be related to those for double photoeffect on\nthe ground and excited 2^{1,3}S states of heliumlike ions. The double-to-single\nionization ratio is equal to R = 0.288/Z^2 for lithiumlike ions with moderate\nnuclear charge numbers Z. However, even for the lightest three-electron targets\nsuch as Li and Be^+, analytical predictions are found to be in good agreement\nwith the numerical calculations performed within the framework of different\nrather involved approaches.", "category": "physics_atom-ph" }, { "text": "Extended coherently delocalized states in a frozen Rydberg gas: The long-range dipole-dipole interaction can create delocalized states due to\nthe exchange of excitation between Rydberg atoms. We show that even in a random\ngas many of the single-exciton eigenstates are surprisingly delocalized,\ncomposed of roughly one quarter of the participating atoms. We identify two\ndifferent types of eigenstates: one which stems from strongly-interacting\nclusters, resulting in localized states, and one which extends over large\ndelocalized networks of atoms. These two types of states can be excited and\ndistinguished by appropriately tuned microwave pulses, and their relative\ncontributions can be modified by the Rydberg blockade and the choice of\nmicrowave parameters.", "category": "physics_atom-ph" }, { "text": "Millisecond-lived circular Rydberg atoms in a room-temperature\n experiment: Circular Rydberg states are ideal tools for quantum technologies, with huge\nmutual interactions and extremely long lifetimes in the tens of milliseconds\nrange, two orders of magnitude larger than those of laser-accessible Rydberg\nstates. However, such lifetimes are observed only at zero temperature. At room\ntemperature, blackbody-radiation-induced transfers annihilate this essential\nasset of circular states, which have thus been used mostly so far in specific,\ncomplex cryogenic experiments. We demonstrate here, on a laser-cooled atomic\nsample, a circular state lifetime of more than one millisecond at room\ntemperature for a principal quantum number 60. The inhibition structure is a\nsimple plane-parallel capacitor that efficiently inhibits the\nblackbody-radiation-induced transfers. One of the capacitor electrodes is fully\ntransparent and provides complete optical access to the atoms, an essential\nfeature for applications. This experiment paves the way to a wide use of\ncircular Rydberg atoms for quantum metrology and quantum simulation.", "category": "physics_atom-ph" }, { "text": "Velocity tuning of friction with two trapped atoms: Friction is the basic, ubiquitous mechanical interaction between two surfaces\nthat results in resistance to motion and energy dissipation. In spite of its\ntechnological and economic significance, our ability to control friction\nremains modest, and our understanding of the microscopic processes incomplete.\nAt the atomic scale, mismatch between the two contacting crystal lattices can\nlead to a reduction of stick-slip friction (structural lubricity), while\nthermally activated atomic motion can give rise to a complex velocity\ndependence, and nearly vanishing friction at sufficiently low velocities\n(thermal lubricity). Atomic force microscopy has provided a wealth of\nexperimental results, but limitations in the dynamic range, time resolution,\nand control at the single-atom level have hampered a full quantitative\ndescription from first principles. Here, using an ion-crystal friction emulator\nwith single-atom, single substrate-site spatial resolution and single-slip\ntemporal resolution, we measure the friction force over nearly five orders of\nmagnitude in velocity, and contiguously observe four distinct regimes, while\ncontrolling temperature and dissipation. We elucidate the interplay between\nthermal and structural lubricity in a system of two coupled atoms, and provide\na simple explanation in terms of the Peierls-Nabarro potential. This extensive\ncontrol at the atomic scale paves the way for fundamental studies of the\ninteraction of many-atom surfaces, as for example in the Frenkel-Kontorova\nmodel, and possibly into the quantum regime.", "category": "physics_atom-ph" }, { "text": "Four-Color Stimulated Optical Forces for Atomic and Molecular Slowing: Stimulated optical forces offer a simple and efficient method for providing\noptical forces far in excess of the saturated radiative force. The bichromatic\nforce, using a counterpropagating pair of two-color beams, has so far been the\nmost effective of these stimulated forces for deflecting and slowing atomic\nbeams. We have numerically studied the evolution of a two-level system under\nseveral different bichromatic and polychromatic light fields, while retaining\nthe overall geometry of the bichromatic force. New insights are gained by\nstudying the time-dependent trajectory of the Bloch vector, including a better\nunderstanding of the remarkable robustness of bi- and polychromatic forces with\nimbalanced beam intensities. We show that a four-color polychromatic force\nexhibits great promise. By adding new frequency components at the third\nharmonic of the original bichromatic detuning, the force is increased by nearly\n50% and its velocity range is extended by a factor of three, while the required\nlaser power is increased by only 33%. The excited-state fraction, crucial to\npossible application to molecules, is reduced from 41% to 24%. We also discuss\nsome important differences between polychromatic forces and pulse trains from a\nhigh-repetition-rate laser.", "category": "physics_atom-ph" }, { "text": "Electric-field-induced change of alkali-metal vapor density in\n paraffin-coated cells: Alkali vapor cells with antirelaxation coating (especially paraffin-coated\ncells) have been a central tool in optical pumping and atomic spectroscopy\nexperiments for 50 years. We have discovered a dramatic change of the alkali\nvapor density in a paraffin-coated cell upon application of an electric field\nto the cell. A systematic experimental characterization of the phenomenon is\ncarried out for electric fields ranging in strength from 0-8 kV/cm for\nparaffin-coated cells containing rubidium and cells containing cesium. The\ntypical response of the vapor density to a rapid (duration < 100 ms) change in\nelectric field of sufficient magnitude includes (a) a rapid (duration of < 100\nms) and significant increase in alkali vapor density followed by (b) a less\nrapid (duration of ~ 1 s) and significant decrease in vapor density (below the\nequilibrium vapor density), and then (c) a slow (duration of ~ 100 s) recovery\nof the vapor density to its equilibrium value. Measurements conducted after the\nalkali vapor density has returned to its equilibrium value indicate minimal\nchange (at the level of < 10%) in the relaxation rate of atomic polarization.\nExperiments suggest that the phenomenon is related to an electric-field-induced\nmodification of the paraffin coating.", "category": "physics_atom-ph" }, { "text": "Spin effects in laser-assisted semirelativistic excitation of atomic\n hydrogen by electronic impact: New insights into our understanding of the semirelativistic excitation of\natomic hydrogen by electronic impact have been made possible by combining the\nuse of polarized electron beams and intense laser field. The paper reviews\nrelativistic theoretical treatment in laser-assisted electron scattering with\nparticular emphasis upon spin effects. Different spin configurations for\ninelastic electron-atom collisions is also discussed. The role of laser field\nin such collision is of major importance and reveals new information on the\ndynamics of the collision process. The examined modern theoretical\ninvestigations of such relativistic laser-assisted collisions have shown that\nthe need for experimental data is of a paramount importance in order to asses\nthe accuracy of our calculations.", "category": "physics_atom-ph" }, { "text": "Beyond the Dicke Quantum Phase Transition with a Bose-Einstein\n Condensate in an Optical Ring Resonator: We experimentally investigate the dynamical instability of a Bose Einstein\ncondensate in an optical ring resonator for various cavity detuning and pump\npowers. The resulting phase diagram is asymmetric with respect to the cavity\ndetuning and can be described by the coupling of two atomic modes with one\noptical mode. We compare the experimental data to a numerical simulation and to\nan analytic expression of the phase boundary. For positive and negative pump\ncavity detuning different coupling mechanisms are identified explaining the\nasymmetry of the phase diagram. We present a physical interpretation and\ndiscuss the connection to the Dicke quantum phase transition.", "category": "physics_atom-ph" }, { "text": "Extreme UV generation from molecules in intense Ti:Sapphire light: We simulate the dynamics of H2+ and HD+ by direct solution of the\ntime-dependent Schroedinger equation for the electronic and nuclear motion for\nthe interaction of intense femtosecond pulses. On these timescales the\nrotational motion, even for such light molecules, is frozen. Therefore it is a\nreasonable assumption that the nuclear alignment is fixed during the pulse\ninteraction and that rotation can be neglected. In terms of vibrational\nrelaxation, and since the nuclei are light, vibration will be important over\nfemtosecond timescales. Although homonuclear diatomics are IR-inactive, in an\nintense field one can create vibrational excitation through continuum coupling.\nTo show the effect of vibration, consider a first approximation in which the\nnuclei are infinitely massive so they maintain their positions at a fixed bond\nlength of R=2 a.u., throughout the process.", "category": "physics_atom-ph" }, { "text": "Spontaneous and parametric processes in warm rubidium vapours: Warm rubidium vapours are known to be a versatile medium for a variety of\nexperiments in atomic physics and quantum optics. Here we present experimental\nresults on producing the frequency converted light for quantum applications\nbased on spontaneous and stimulated processes in rubidium vapours. In\nparticular, we study the efficiency of spontaneously initiated stimulated Raman\nscattering in the {\\Lambda}-level configuration and conditions of generating\nthe coherent blue light assisted by multi-photon transitions in the\ndiamond-level configuration. Our results will be helpful in search for new\ntypes of interfaces between light and atomic quantum memories.", "category": "physics_atom-ph" }, { "text": "Dynamic formation of Rydberg aggregates at off-resonant excitation: The dynamics of a cloud of ultra-cold two-level atoms is studied at\noff-resonant laser driving to a Rydberg state. We find that resonant excitation\nchannels lead to strongly peaked spatial correlations associated with the\nbuildup of asymmetric excitation structures. These aggregates can extend over\nthe entire ensemble volume, but are in general not localized relative to the\nsystem boundaries. The characteristic distances between neighboring excitations\ndepend on the laser detuning and on the interaction potential. These properties\nlead to characteristic features in the spatial excitation density, the Mandel\n$Q$ parameter, and the total number of excitations. As an application an\nimplementation of the three-atom CSWAP or Fredkin gate with Rydberg atoms is\ndiscussed. The gate not only exploits the Rydberg blockade, but also utilizes\nthe special features of an asymmetric geometric arrangement of the three atoms.\nWe show that continuous-wave off-resonant laser driving is sufficient to create\nthe required spatial arrangement of atoms out of a homogeneous cloud.", "category": "physics_atom-ph" }, { "text": "MIGA: Combining laser and matter wave interferometry for mass\n distribution monitoring and advanced geodesy: The Matter-Wave laser Interferometer Gravitation Antenna, MIGA, will be a\nhybrid instrument composed of a network of atom interferometers horizontally\naligned and interrogated by the resonant field of an optical cavity. This\ndetector will provide measurements of sub Hertz variations of the gravitational\nstrain tensor. MIGA will bring new methods for geophysics for the\ncharacterization of spatial and temporal variations of the local gravity field\nand will also be a demonstrator for future low frequency Gravitational Wave\n(GW) detections. MIGA will enable a better understanding of the coupling at low\nfrequency between these different signals. The detector will be installed\nunderground in Rustrel (FR), at the \"Laboratoire Souterrain Bas Bruit\" (LSBB),\na facility with exceptionally low environmental noise and located far away from\nmajor sources of anthropogenic disturbances. We give in this paper an overview\nof the operating mode and status of the instrument before detailing simulations\nof the gravitational background noise at the MIGA installation site.", "category": "physics_atom-ph" }, { "text": "Lifetime Measurements of the $A^2\u03a0_{1/2}$ and $A^2\u03a0_{3/2}$ States in\n BaF: Time resolved detection of laser induced fluorescence from pulsed excitation\nof electronic states in barium monofluoride (BaF) molecules has been performed\nin order to determine the lifetimes of the $A^2\\Pi_{1/2}$ and $A^2\\Pi_{3/2}$\nstates. The method permits control over experimental parameters such that\nsystematic biases in the interpretation of the data can be controlled to below\n$10^{-3}$ relative accuracy. The statistically limited values for the lifetimes\nof the $A^2\\Pi_{1/2}(\\nu=0)$ and $A^2\\Pi_{3/2}(\\nu=0)$ states are 57.1(3) ns\nand 47.9(7)~ns, respectively. The ratio of these values is in good agreement\nwith scaling for the different excitation energies. The investigated molecular\nstates are of relevance for an experimental search for a permanent electric\ndipole moment (EDM) of the electron in BaF.", "category": "physics_atom-ph" }, { "text": "Quantum beats in the polarization response of a dielectric to intense\n few-cycle laser pulses: We have investigated the polarization response of a dielectric to intense\nfew-cycle laser pulses with a focus on interband tunnelling. Once charge\ncarriers are created in an initially empty conduction band, they make a\nsignificant contribution to the polarization response. In particular, the\ncoherent superposition of conduction- and valence-band states results in\nquantum beats. This quantum-beat part of the polarization response is affected\nby the excitation dynamics and attosecond-scale motion of charge carriers in an\nintense laser field. Our analysis shows that, with the onset of Bloch\noscillations or tunnelling, the nonlinear polarization response becomes\nsensitive to the carrier-envelope phase of the laser pulse.", "category": "physics_atom-ph" }, { "text": "Azimuthal modulation of electromagnetically induced transparency using\n structured light: Recently a scheme has been proposed for detection of the structured light by\nmeasuring the transmission of a vortex beam through a cloud of cold rubidium\natoms with energy levels of the $\\Lambda$-type configuration {[}N. Radwell et\nal., Phys. Rev. Lett. 114, 123603 (2015){]}. This enables observation of\nregions of spatially dependent electromagnetically induced transparency (EIT).\nHere we suggest another scenario for detection of the structured light by\nmeasuring the absorption profile of a weak nonvortex probe beam in a highly\nresonant five-level combined tripod and $\\Lambda$ (CTL) atom-light coupling\nsetup. We demonstrate that due to the closed-loop structure of CTL scheme, the\nabsorption of the probe beam depends on the azimuthal angle and orbital angular\nmomentum (OAM) of the control vortex beams. This feature is missing in simple\n$\\Lambda$ or tripod schemes, as there is no loop in such atom-light couplings.\nOne can identify different regions of spatially structured transparency through\nmeasuring the absorption of probe field under different configurations of\nstructured control light.", "category": "physics_atom-ph" }, { "text": "Peculiarities of Wigner times delay in slow elastic electron scattering\n by potential well with arising discrete levels: We generalize here the one-level consideration in our recent paper\narXiv:1901.00411 [1] to the case when an electron collides with a potential\nthat have any number of s bound states. We investigate peculiarities in the\nWigner time delay behavior for slow electron elastic s-scattering by\nspherically symmetric square-potential well. We have considered potential\nwells, the variation of parameters of which (potential depth U and its radius\nR) lead to arising arbitrary number of s bound states. We demonstrate that\nwhile the time delay for potential wells with no discrete s-levels always has a\npositive value for small electron energies, it changes sign after level\narising. We found that at the moments of arising in the well not only of the\nfirst but also following s-levels as well, the time delay as a function of U\nexperiences instant jumps from a positive value to a negative one. The\namplitudes of these jumps increases with decrease of the electron wave vector\nk. The times delay for potential well, the variation of the radius of which R\nleads to the appearance of discrete levels, also change sign at these critical\nradii.", "category": "physics_atom-ph" }, { "text": "Anisotropic long-range interaction investigated with cold atoms: In two dimensions, a system of self-gravitating particles collapses and forms\na singularity in finite time below a critical temperature $T_c$. We investigate\nexperimentally a quasi two-dimensional cloud of cold neutral atoms in\ninteraction with two pairs of perpendicular counter-propagating quasi-resonant\nlaser beams, in order to look for a signature of this ideal phase transition:\nindeed, the radiation pressure forces exerted by the laser beams can be viewed\nas an anisotropic, and non-potential, generalization of two-dimensional\nself-gravity. We first show that our experiment operates in a parameter range\nwhich should be suitable to observe the collapse transition. However, the\nexperiment unveils only a moderate compression instead of a phase transition\nbetween the two phases. A three-dimensional numerical simulation shows that\nboth the finite small thickness of the cloud, which induces a competition\nbetween the effective gravity force and the repulsive force due to multiple\nscattering, and the atomic losses due to heating in the third dimension,\ncontribute to smearing the transition.", "category": "physics_atom-ph" }, { "text": "Nuclear fission in intense laser fields: Rapid-advancing intense laser technologies enable the possibility of a direct\nlaser-nucleus coupling. In this paper the effect of intense laser fields on a\nseries of nuclear fission processes, including proton decay, alpha decay, and\ncluster decay, is theoretically studied with the help of nuclear double folding\npotentials. The results show that the half-lives of these decay processes can\nbe modified by non-negligible amounts, for example on the order of 0.01 or 0.1\npercents in intense laser fields available in the forthcoming years. In\naddition to numerical results, an approximate analytical formula is derived to\nconnect the laser-induced modification to the decay half-life and the decay\nenergy.", "category": "physics_atom-ph" }, { "text": "Rubidium Spectroscopy at 778-780 nm with a Distributed Feedback Laser\n Diode: We have performed high resolution spectroscopy of rubidium with a single mode\ncontinuous wave distributed feedback (DFB) laser diode. The saturation spectrum\nof the D_2-line of 85Rb and 87Rb was recorded with a resolution close to the\nnatural line width. The emission frequency was actively stabilized to\nDoppler-free transitions with a relative accuracy of better than 7 parts in\n10^9 using commercially available servo devices only. An output power of 80 mW\nwas sufficient to allow for two-photon spectroscopy of the 5S-5D-transition of\n87Rb. Further, we report on the spectral properties of the DFB diode, its\ntuning range and its frequency modulation properties. The line width of the\ndiode laser, determined with high resolution Doppler free two photon\nspectroscopy, was 4 MHz without applying any active stabilization techniques.\nFor time scales below 5 us the line width drops below 2 MHz.", "category": "physics_atom-ph" } ]