bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tunnelling of topological line defects in strongly coupled superfluids
Authors: Fischer Uwe R. 
Published: May 2022

AbstractThe geometric theory of vortex tunnelling in superfluid liquids is developed. Geometry rules the tunnelling process in the approximation of an incompressible superfluid, which yields the identity of phase and configuration space in the vortex collective co‐ordinate. To exemplify the implications of this approach to tunnelling, we solve explicitly for the two‐dimensional motion of a point vortex in the presence of an ellipse, showing that the hydrodynamic collective co‐ordinate description limits the constant energy paths allowed for the vortex in configuration space. We outline the experimental procedure used in helium II to observe tunnelling events, and compare the conclusions we draw to the experimental results obtained so far. Tunnelling in Fermi superfluids is discussed, where it is assumed that the low energy quasiparticle excitations localised in the vortex core govern the vortex dynamical equations. The tunnelling process can be dominated by Hall or dissipative terms, respectively be under the influence of both, with a possible realization of this last intermediate case in unconventional, high‐temperature superconductors.
Functional Schrödinger picture approach to a dilute bose gas and fluctuation correction to the ground state energy density
Authors: Kim Sang‐Hoon , Noh Hyun Sik , Kim Dae Kwan , Kim Chul Koo , Nahm Kyun 
Published: May 2022

AbstractA many‐body theoretical scheme based on the functional Schrödinger picture method is formulated for the study of a dilute Bose gas system. The standard ground state properties are obtained by solving the infinite dimensional Schr�dinger equation variationally with a Gaussian trial wavefunctional. It is shown that a shifted Gaussian trial functional enables us to calculate a higher order correction of order na3, which corresponds to the fluctuation constribution from the condensate.
Quantum hexaspherical observables for electrons
Authors: Jaekel Marc‐Thierry , Reynaud Serge 
Published: May 2022

AbstractA new quantum algebraic description of relativistic electrons, built on a conformal dynamical symmetry (SO(4,2 )), has recently been proposed to treat localization in space‐time. It is shown here that localization of an electron may be represented by components of a SO(4,2) vector which are quantum generalizations of the hexaspherical coordinates of classical projective geometry. The shift of this vector under transformations to uniformly accelerated frames is described by SO(4,2) rotations. Hexaspherical observables also allow one to represent the quantum law of free fall under a form explicitly compatible with the same dynamical symmetry.
Energy landscape and fluctuations in proteins
Authors: Frauenfelder H. , McMahon B.H. 
Published: May 2022

AbstractComplex systems such as biomolecules or glasses do not exist in a unique structure, but can assume a very large number of somewhat different conformations. The organization of the conformations can be described in the energy (or conformation) landscape, where individual valleys are called conformational substates. Proteins are systems where the energy landscape has been studied in some detail. Their landscape is organized in a hierarchy that contains three types of substates, taxonomic, statistical, and few‐level. Conformational substates are found in a wide variety of proteins. Some of their characteristics are described and the open experimental and theoretical problems are listed.
A renormalization approach to quantum thermal annealing
Authors: Lee Yong‐ Han , Berne B.J. 
Published: May 2022

AbstractThe details of an efficient global optimization approach, quantum thermal annealing with renormalization (QTAR) (Y. H. Lee and B. J. Berne, J. Phys. Chem. A, in press (2000)) are presented in this paper. This method is based on the application of the Migdal‐Kadanoff method for decimating Trotter time slices in the staging and primitive algorithms for sampling path integrals using Monte Carlo methods. In a nutshell, one starts in a strong quantum regime where the number of Trotter beads representing each quantum particle and the value of Planck's constant are large, thereby allowing for efficient tunneling through the barriers of a rough energy landscape typical in the folding of proteins, and anneals the system methodically to the classical limit where the values of the aforementioned quantities are 1 and 0, respectively. Global optimization of the system is achieved through the iterative use of such quantum‐to‐classical annealing cycles. The QTAR algorithm applied to a highly frustrated BLN model protein with 46 residues more efficiently locates the global energy minimum than established methods like simulated annealing.
Markov processes driven by quasi‐periodic deterministic forces
Authors: Talkner Peter 
Published: May 2022

AbstractQuasi‐periodically driven Markovian systems are rendered stationary by enlarging the state space. The eigenvalues and eigenvectors of the master operator of the enlarged process are considered for very slow driving forces in the adiabatic limit. This limit has to be performed always in the minimally enlarged state space and, for two driving frequencies in general leads to results that discontinuously depend on the frequency ratio.
Pipeline model of a Fermi‐sea electron pump
Authors: Sols Fernando , Wagner Mathias 
Published: May 2022

AbstractThe use of a band offset between the two leads of an electron pump driven by a local oscillating voltage is shown to increase the pump current dramatically. The structure of the electron transmission suggests the existence of dominant inelastic channels which we call pipelines. This permits the formulation of a simple model that gives a physical account of the numerical results for a realistic device. A spectral analysis reveals the pump current to be carried by scattering states with initial energy deep within the Fermi sea and not at its surface, thereby rendering the effect insensitive to temperature. We show this is compatible with the current flowing near the Fermi surface in the leads.
Nonlinear quantum transport and current noise
Authors: Lang Gunther , Weiss Ulrich 
Published: May 2022

AbstractWe study nonequilibrium transport and noise in a genericdissipative tightbinding model. Within a real‐time path integral approach, we derive formally exact series expressions in the number of tunneling events for the noise valid for arbitrary bias, frequency and temperature. At zero temperature, the low‐frequency noise can be summed in analytic form.The resulting Shiba‐like |ω|‐singularity is a consequence of the 1/t2 decay law for the current correlation function. At finite temperature, this singularity is smoothed out.
Quantum physics of entangled systems: Wave‐particle duality and atom‐photon molecules
Authors: Rempe G. 
Published: May 2022

AbstractOne of the cornerstones of quantum physics is the wave nature of matter. It explains experimentally observed effects like interference and diffraction, occurring when an object moves from one place to another along several indistinguishable ways simultaneously. The wave nature disappears when the individual ways are distinguishable. In this case, the particle nature of the object becomes visible. To determine the particle nature quantitatively, the way of the object has to be measured. Here, large progress has been made recently with new techniques, enabling one to investigate single moving atoms in a controlled manner. Two examples are discussed in the following two sections. The first experiment describes an atom interferometer, where the way of the atom is entangled with its internal state. This allows one to explore the origin of wave‐particle duality and perform a quantitative test of this fundamental principle. The second experiment reports on the observation of an atom‐photon molecule, a bound state between an atom and a single photon. A fascinating aspect of this system is that it makes possible to monitor the motion of a single neutral atom in real time.
Phonons: The second type of quantum excitations discovered
Authors: Cardona M. 
Published: May 2022

AbstractAfter the discovery of the quantum nature of the electromagnetic radiation by Planck in 1900, the concept of photons was introduced by Einstein in 1905. In 1907 Einstein also introduced quantified lattice vibrations (today called phonons) in order to explain the temperature dependence of the specific heat of crystals. In recent years, the availability of isotopically pure elements has facilitated the growth of crystals with variable isotopic concentration. With these crystals, several quantum effects concerning the ero‐point vibrational amplitudes of phonons have been investigated. Among them we discuss here the anharmonic renormalization of phonon lineshapes.
Heavy‐fermion systems
Authors: Fulde P. 
Published: May 2022

AbstractDifferent scenarios of heavy‐fermion behaviour are pointed out. They include Kondo lattices, the Zeeman effect and special forms of charge ordering. Specific examples for the three cases are discussed, i.e., CeRu2Si2, Nd2—xCexCuO4 and Yb4As3.
Nano‐scale studies of quantum phenomena by scanning probe spectroscopy
Authors: Wiesendanger R. 
Published: May 2022

AbstractPhenomena on the nanometer scale are dominated by quantum effects. They can be visualized in a fascinating way either by the scanning tunneling microscope (STM), which itself is based on a quantum‐mechanical effect, electron tunneling, or by related scanning probe methods. These so‐called near‐field microscopies allow the direct observation of the wave nature of electrons in solids and the determination of their effective mass as well as their spin state. Atomic resolution is obtained by STM on an energy scale which is a million times smaller than that of X‐rays. Therefore, quantum effects in solids, which usually occur on energy scales of several millielectronvolts, become accessible while operating at high spatial resolution down to the atomic level. The detailed understanding of quantum phenomena at the nanometer scale will constitute the foundations of the nanotechnology age, which will be dominated by the digital control of matter at the level of single atoms and molecules, single electrons, as well as single spins.
Relativity and quantum theory from Sommerfeld to Dirac
Authors: Kragh H. 
Published: May 2022

AbstractQuantum theory and the special theory of relativity emerged almost simultaneously. Through the formative years of quantum theory, from 1900 to about 1928, arguments based on the theory of relativity were of great importance. Starting with Sommerfeld's theory of the hydrogen atom, this paper surveys the ways in which the two fundamental theories have interacted. Relativity was of particular importance in Schrödinger's route to wave mechanics, a theory which was originally conceived as fully integrated with special relativity. The problem of uniting, or harmonising, quantum mechanics and relativity continued to occupy physicists in 1926–27. The paper ends with the solution of this problem, as it was presented in 1928 by Dirac in his seminal paper on the quantum theory of electrons. It also refers to the few attempts there were in the period to formulate a quantum theory in agreement with the general theory of relativity.
The Compton effect: Transition to quantum mechanics
Authors: Stuewer R.H. 
Published: May 2022

AbstractThe discovery of the Compton effect at the end of 1922 was a decisive event in the transition to the new quantum mechanics of 1925‐1926 because it stimulated physicists to examine anew the fundamental problem of the interaction between radiation and matter. I first discuss Albert Einstein's light‐quantum hypothesis of 1905 and why physicists greeted it with extreme skepticism, despite Robert A. Millikan's confirmation of Einstein's equation of the photoelectric effect in 1915. I then follow in some detail the experimental and theoretical research program that Arthur Holly Compton pursued between 1916 and 1922 at the University of Minnesota, the Westinghouse Lamp Company, the Cavendish Laboratory, and Washington University that culminated in his discovery of the Compton effect. Surprisingly, Compton was not influenced directly by Einstein's light‐quantum hypothesis, in contrast to Peter Debye and H.A. Kramers, who discovered the quantum theory of scattering independently. I close by discussing the most significant response to that discovery, the Bohr‐Kramers‐Slater theory of 1924, its experimental refutation, and its influence on the emerging new quantum mechanics.
Quantum entanglement and quantum teleportation
Authors: Shih Y.H. 
Published: May 2022

AbstractOne of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. The “ghost” interference and the “ghost” image experiments demonstrated the astonishing nonlocal behavior of an entangled photon pair. Even though we still have questions in regard to fundamental issues of the entangled quantum systems, quantum entanglement has started to play important roles in quantum information and quantum computation. Quantum teleportation is one of the hot topics. We have demonstrated a quantum teleportation experiment recently. The experimental results proved the working principle of irreversibly teleporting an unknown arbitrary quantum state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that the complete set of Bell states can be distinguished in the Bell state measurement. Teleportation of a quantum state can thus occur with certainty in principle.
The emergence of Quantum Schools: Munich, Göttingen and Copenhagen as new centers of atomic theory
Authors: Eckert M. 
Published: May 2022

AbstractThe institutes of Arnold Sommerfeld in Munich, Niels Bohr in Copenhagen, and Max Born in Göttingen became the leading centers for the study of quantum theory in the first decades of the twentieth century. Although founded for a broader range of theoretical physics, the quantum became the major topic of research in Munich after the Bohr‐Sommerfeld‐model of the atom (1913–16). The heyday came in the 1920s, when Bohr's and Born's institutes started operation and became further attractive centers for ambitious theorists all over the world. The discovery of quantum mechanics (1925) should be regarded not only as the achievement of a few young geniuses (in particular Werner Heisenberg and Wolfgang Pauli) but also as the result of a collaborative effort emerging in the new social and intellectual environment of their teachers' schools in Munich, Göttingen and Copenhagen.
Molecular beams entwined with quantum theory: A bouquet for Max Planck
Authors: Herschbach D. 
Published: May 2022

AbstractIn an era when the fledgling quantum theory was “uncertain and even gave contradictory answers,” Otto Stern undertook to employ molecular beams to test directly fundamental aspects of the theory. During 1921‐1935, this led to five decisive experiments reviewed here, resulting in the discovery or demonstration of space quantization, de Broglie matter waves, anomalous magnetic moments of the proton and neutron, recoil of an atom on emission of a photon, and the limitation of scattering cross‐sections for molecular collisions imposed by the uncertainty principle.
Superconductivity in ultrasmall metallic grains
Authors: von Delft Jan 
Published: May 2022

AbstractWe review recent experimental and theoretical work on superconductivity in ultrasmall metallic grains, i.e. grains sufficiently small that the conduction electron energy spectrum becomes discrete. The discrete excitation spectrum of an individual grain can be measured by the technique of single‐electron tunneling spectroscopy, and reveals parity effects indicative of pairing correlations in the grain. After introducing the discrete BCS model that has been used to model such grains, we review a phenomenological, grand‐canonical, variational BCS theory describing the paramagnetic breakdown of these pairing correlations with increasing magnetic field. We also review recent canonical theories that have been developed to describe how pairing correlations change during the crossover, with decreasing grain size, from the bulk limit to the limit of few electrons, and compare their results to those obtained using Richardson's exact solution of the discrete BCS model.
Energy momentum tensor in local causal perturbation theory
Authors: Prange Dirk 
Published: May 2022

AbstractWe study the energy momentum tensor in the Bogoliubov‐Epstein‐Glaser approach to perturbation theory. It is found to be locally conserved for a class of theories containing no derivated fields in the interaction. For the massless φ4 ‐theory we derive the trace anomaly of the improved tensor.
On the prolongation structure of the Landau‐Lifshitz equation for an anisotropic ferromagnet
Authors: Hoenselaers C. 
Published: May 2022

AbstractWe study the prolongation algebra for the Landau‐Lifshitz equation. We shall recover the known linear problems for this model. Moreover, we shall also display a 6‐dimensional linear linear problem which is linear in the spectral parameter λ.
Geometric classification of the torsion tensor of space‐time
Authors: Capozziello S. , Lambiase G. , StornaioloI C. 
Published: May 2022

AbstractTorsion appears in literature in quite different forms. Generally, spin is considered to be the source of torsion, but there are several other possibilities in which torsion emerges in different contexts. In some cases a phenomenological counterpart is absent, in some other cases torsion arises from sources without spin as a gradient of a scalar field. Accordingly, we propose two classification schemes. The firstone is based on the possibility to construct torsion tensors from the product of a covariant bivector and a vector and their respective space‐time properties. The secondone is obtained by starting from the decomposition of torsion into three irreducible pieces. Their space‐time properties again lead to a complete classification. The classifications found are given in a U 4, a four dimensional space‐time where the torsion tensors have some peculiar properties. The irreducible decomposition is useful since most of the phenomenological work done for torsion concerns four dimensional cosmological models. In the second part of the paper two applications of these classification schemes are given. The modifications of energy‐momentum tensors are considered that arise due to different sources of torsion. Furthermore, we analyze the contributions of torsion to shear, vorticity, expansion and acceleration. Finally the generalized Raychaudhuri equation is discussed.
Exact solutions for extended waves in 1d anharmonic lattices
Authors: Fischer Fred 
Published: May 2022

AbstractA cyclic chain of n equal classic particles coupled by anharmonic forces has a set of extended vibrational modes, for which exact solutions are given. This requires for the power law of the forces certain conditions to be fulfilled. Each mode is characterized by a wave number and the undulations of the particles depend on the total energy and on a new constant of motion that formally expresses a kind of angular momentum. Exact solutions for n = 7 with a twelfth power potential are discussed.
Noether Charges for self‐interacting quantum field theories in curved spacetimes with a Killing‐vector
Authors: Hollands Stefan 
Published: May 2022

AbstractWe consider a self‐interacting, perturbative Klein‐Gordon quantum field in a curved spacetime admitting a Killing vector field. We show that the action of this spacetime symmetry on interacting field operators can be implemented by a Noether charge which arises, in a certain sense, as a surface integral over the time‐component of some interacting Noether current‐density associated with the Killing field. The proof of this involves the demonstration of a corresponding set of Ward identities. Our work is based on the perturbative construction by Brunetti and Fredenhagen (Commun. Math. Phys. 208 (2000) 623—661) of self‐interacting quantum field theories in general globally hyperbolic spacetimes.
A derivation of Weyl gravity
Authors: Boulanger Nicolas , Henneaux Marc 
Published: May 2022

AbstractIn this paper, two things are done. (i) Using cohomological techniques, we explore the consistent deformations of linearized conformal gravity in 4 dimensions. We show that the only possibility involving no more than 4 derivatives of the metric (i.e., terms of the form ∂4gμν, ∂3gμν ∂gαβ, ∂2gμν ∂2gαβ, ∂2gμν ∂gαβ ∂gρσ or ∂gμν ∂gαβ ∂gρσ ∂gγδ with coefficients that involve undifferentiated metric components — or terms with less derivatives) is given by the Weyl action S ∼ ∫ d4x Wαβγδ Wαβγδ, in much the same way as the Einstein‐Hilbert action describes the only consistent manner to make a Pauli‐Fierz massless spin‐2 field self‐interact with no more than 2 derivatives. No a priori requirement of invariance under diffeomorphisms is imposed: this follows automatically from consistency. (ii) We then turn to “multi‐Weyl graviton” theories. We show the impossibility to introduce cross‐interactions between the different types of Weyl gravitons if one requests that the action reduces, in the free limit, to a sum of linearized Weyl actions. However, if different free limits are authorized, cross‐couplings become possible. An explicit example is given. We discuss also how the results extend to other spacetime dimensions.
Thermodynamics of a 4‐site Hubbard model by analytical diagonalization
Authors: Schumann R. 
Published: May 2022

AbstractBy use of the conservation laws a four‐site Hubbard model coupled to a particle bath within an external magnetic field in z‐direction was diagonalized. The analytical dependence of both the eigenvalues and the eigenstates on the interaction strength, the chemical potential and magnetic field was calculated. It is demonstrated that the low temperature behaviour is determined by a delicate interplay between many‐particle states differing in electron number and spin if the electron density is away from half‐filling. The grand partition sum is calculated and the specific heat, the susceptibility as well as various correlation functions and spectral functions are given in dependence of the interaction strength, the electron occupation and the applied magnetic field. For both the grand canonical and the canonical ensemble the high‐temperature crossing points of the specific heat are calculated. Whereas in the weak correlation regime the universal value calculated by second order perturbation theory for several Hubbard systems being in the thermodynamic limit is confirmed, these crossing points vanish for intermediate to strong correlation.
Basics of superluminal signals
Authors: Nimtz G. , Haibel A. 
Published: May 2022

AbstractThe paper elucidates the physical basis of experimental results on superluminal signal velocity. It will be made plausible that superluminal signals do not violate the principle of causality but they can shorten the vacuum time span between cause and effect. The causal behaviour is based on the property that a physical signal has a finite duration as a result of its frequency band limitation.