bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indistinguishable single photons from a quantum dot
Authors: Fattal David , Santori Charles , Vuckovic J. , Solomon G. S. , Yamamoto Yoshihisa 
Published: July 2003

AbstractWe report a set of experiments designed to test the quantum indistinguishability of single photons emitted by a resonantly pumped InAs/GaAs quantum dot, embedded in a microcavity. We first performed high resolution interferometric measurements on the source to infer its coherence time. By comparison with the exciton lifetime, obtained by time‐resolved spectroscopy, we found that some quantum dots were emitting almost transform‐limited photons. The measured ratio of the coherence time to the pulse duration gives a lower bound on the dephasing time which agrees well with previous studies. We then directly measured the mean overlap between wave packets of consecutive photons emitted 2 ns apart, through a Hong–Ou–Mandel type two‐photon interference experiment. For the best dot, an overlap as high as 0.81 was inferred. This result suggests that quantum dots could be a practical single photon source to perform quantum information processing experiments. We stress the importance of the microcavity for identical photon generation.
Large spontaneous emission enhancement in InAs quantum dots coupled to microdisk whispering gallery modes
Authors: Solomon G. S. , Xie Z. , Fang W. , Xu J. Y. , Yamilov A. , Cao H. , Ma Y. , Ho S. T. 
Published: July 2003

AbstractMeasuring the enhancement of spontaneous emission decay rates of quantum dot emission coupled to microcavity modes is typically hampered by variable coupling of the quantum dot emission. This is particularly evident in the microdisk cavity since the whispering gallery modes are localized near the disk edge, while quantum dot emitters are typically uniformily distributed throughout the disk. The distribution of spontaneous emission decay rates under these circumstances can be determined using a distribution function for the various spontaneous decay rates, and demonstrate that large decay rate enhancement are present. To remove the spatial coupling variation, quantum dots are selectively placed near the microdisk edge. Initial photoluminescence measurements indicate that recombination processes in these quantum dots are not dominated by surface recombination.
Single quantum dot pairs with controllable interdot coupling
Authors: Welsch M. K. , Bacher G. , Schömig H. , Forchel A. , Zaitsev S. , Becker C. R. , Molenkamp L. W. 
Published: July 2003

AbstractWe report on a new approach for preparing single pairs of quantum dots with controllable interdot coupling. Starting from a double quantum well heterostructure, a selective intermixing technique was applied to define pairs of vertically stacked single quantum dots. The incorporation of Mn2+ ions in only one of the dots results in strongly different effective g‐factors of the dots, enabling us to control the interdot coupling simply by applying an external magnetic field.
Exciton–phonon interaction in epitaxial CdSe/ZnSe nanostructures
Authors: Kapitonov A. M. , Woggon U. , Leonardi K. , Hommel D. , Edamatsu K. , Itoh T. 
Published: July 2003

AbstractThe low‐temperature optical properties of submonolayer CdSe/ZnSe nanostructures have been investigated with nominal layer thickness of 0.15 ML and 0.58 ML CdSe. In photoluminescence excitation spectroscopy (PLE) we observe more than 10 equidistant peaks separated by the ZnSe LO‐phonon energy even at energies high above the ZnSe‐band edge. The peak heights and line shapes are extremely sensitive to the monolayer coverage, have strongly different intensities in emission and PLE and deviate from the Poissonian intensity distribution expected within the concept of a constant, material specific Huang–Rhys parameter S. A bound polaron model is proposed to explain the optical properties of quantum structures for which the approach of a pure electronic quantum confinement is not appropriate. Intrinsic coherence of joint exciton–phonon modes is very promising, e.g. for application in quantum information processing or coherent population transfer.
Single‐photon and photon‐pair emission from CdSe/Zn(S,Se) quantum dots
Authors: S. Strauf  , Ulrich S. M. , Sebald K. , Michler P. , Passow T. , Hommel D. , Bacher G. , Forchel A. 
Published: July 2003

AbstractWe report on the generation of triggered single photons and photon pairs relying on pulsed optical excitation of epitaxially grown self‐assembled CdSe quantum dots (QDs). Single‐photon emission is studied on individual CdSe/Zn(S,Se) QDs for temperatures up to 200 K. At low temperatures nearly perfect single‐photon emission is achieved whereas at higher temperatures an increasing multi‐photon emission probability due to spectrally overlapping acoustic phonon sidebands of neighboring QDs is observed. The multi‐photon emission probability of a bare QD (background subtracted) is strongly suppressed. Furthermore, the polarization cross correlation of the biexciton–exciton cascade has been investigated in a CdSe/ZnSe QD at low temperatures. A strong polarization correlation of the emitted photon pairs of ∼74% is observed in a linear detection basis.
Simple spin textures in a quantum dot
Authors: Ciorga M. , Korkusiński M. , Pioro‐Ladriere M. , Zawadzki P. , Hawrylak P. , Sachrajda A. S. 
Published: July 2003

AbstractMeasurements and calculations previously reported for a lateral quantum dot at magnetic fields close to the transition to the maximum density droplet provided evidence that the increase of spin polarisation of a dot with magnetic field is interrupted by spin depolarization events. The loss of spin polarisation is associated with correlated states corresponding to condensation of spin excitons into spin textures. In this paper a detailed experimental and theoretical analysis is performed of the excitation spectra at the first two spin flip events in a few electron quantum dot. In this less complicated regime we are able to identify these correlated states as spin and charge excitons and bi‐excitons. In particular we focus on a dot containing eight electrons. Coulomb blockade experiments, supported by detailed calculations, confirm the presence of these correlated states at the second spin flip.
Aharonov–Bohm effect of a quantum ring in the Kondo regime
Authors: Keyser U. F. , Fühner C. , Haug R. J. , Wegscheider W. , Bichler M. , Abstreiter G. 
Published: July 2003

AbstractWe investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov–Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov–Bohm period explained by electron–electron interaction in our small quantum ring.
Spin selective tunneling and blockade in two‐electron double quantum dot
Authors: Ono K. , Austing D. G. , Tokura Y. , Tarucha S. 
Published: July 2003

AbstractWe have studied a non‐linear transport of double quantum dots in a two‐electron regime, and found a pronounced blockade region in addition to the ordinary Coulomb blockade. This extra blockade region appears only on one polarity of the source drain voltage, and is ascribed to the selection rule of two‐electron spins for an inter‐dot tunneling as well as to an irreversible tunneling from the reservoir to the dots. In this extra blockade region the two‐electron spin stays in the triplet state even in a zero magnetic field. A small leakage current indicates that the lifetime of this triplet state is about 100 ns.
Observation of in‐plane polarized intersublevel absorption in strongly coupled InGaAs/GaAs self assembled quantum dots
Authors: Adawi A. M. , Zibik E. A. , Wilson L. R. , Lemaître A. , Sheng W.D. , Cockburn J. W. , Skolnick M. S. , Leburton J. P. , Hopkinson M. , Hill G. , Liew S. L. , Cullis A. G. 
Published: July 2003

AbstractWe present a mid‐infrared absorption study of an n‐i‐n structure containing two planes of strongly coupled In0.5Ga0.5As self assembled quantum dots. We find that the dominant absorption occurs for light polarized in the growth plane (TE‐polarized), contrasting with uncoupled dots which exhibit predominantly TM‐polarized absorption in the same energy range. Our measurements suggest that uncoupled dots grown under the same conditions as the coupled dots contain one bound (s‐like) electron level. By coupling the dots the confinement length in the growth direction (z) is increased, lowering the energy of the s‐like ground state and binding additional px, y‐like excited states. A significantly increased normal incidence photocurrent sinal is measured for the sample containing coupled dots, relative to samples containing up to 30 layers of uncoupled dots, confirming the enhancement of the normal incidence absorption.
Wavelength selective data storage in InGaAs–GaAs quantum dots
Authors: Kroutvar M. , Zrenner A. , Ducommun Y. , Finley J. J. , Abstreiter G. 
Published: July 2003

AbstractWe present the first demonstration of wavelength selective charge storage (electrons or holes) in In0.5Ga0.5As self‐assembled quantum dots with optical readout. Our results demonstrate unambiguously wavelength selective charging with long (≫25 μs) data storage lifetimes and enable us to probe directly carrier excitation processes and potentially electron spin dynamics in micro‐ensembles of quantum dots.
Open issues for lasing at 1.3 μm in MOCVD‐grown quantum dots
Authors: De Giorgi M. , Passaseo A. , Maruccio G. , De Vittorio M. , Todaro M. T. , Rinaldi R. , Cingolani R. 
Published: July 2003

AbstractA study of the carrier dynamics in MOCVD‐grown InGaAs/GaAs quantum dots emitting at 1.3 μm at room temperature has been done. The PL rise time measured as a function of the temperature shows that carrier relaxation into the QD ground state occurs within a few picoseconds due to a very efficient carrier–phonon scattering process. In spite of this very efficient carrier capture in our dots and a small temperature dependence of the quantum efficiency, which are favorable for laser applications, we show that our QDs have a very strong permanent dipole moment which prevents the emission from the ground state and the lasing at 1.3 μm.
Self‐assembled quantum dots as a source of single photons and photon pairs
Authors: Shields A. J. , Stevenson R. M. , Thompson R. M. , Ward M. B. , Yuan Z. , Kardynal B. E. , See P. , Farrer I. , Lobo C. , Cooper K. , Ritchie D. A. 
Published: July 2003

AbstractWe investigate the emission from a single self‐organised InAs/GaAs quantum dots as a potential single or pair photon source. Single photon emission is stimulated by exciting the dot with ps laser pulses and collecting either the exciton or biexciton emission line. A more convenient and practical arrangement is to excite the quantum dot electrically by growing it inside a p–i–n structure. Photon pairs are generated through collecting both the exciton and biexciton emissions. We show a strong correlation in the emission times of the exciton and biexciton photon from the dot, as well as in their linear polarisations.
Overview of spin‐based quantum dot quantum computation
Authors: Hu Xuedong , Das Sarma S. 
Published: July 2003

AbstractHere we give an overview of the research on spin‐based quantum dot quantum computation. In particular, we discuss the conditions for the Heisenberg exchange Hamiltonian to be a satisfactory description of two‐electron interaction in a GaAs double dot. We also discuss theoretical issues related to spin relaxation, spin encoding, and spin measurement. A brief account is also given to spin‐based quantum computation in SiGe quantum dots and donors in Si.
Rabi‐flopping of the ground state excitonin a single self‐assembled quantum dot
Authors: Beham E. , Zrenner A. , Findeis F. , Bichler M. , Abstreiter G. 
Published: July 2003

AbstractWe report Rabi‐oscillations of the ground state exciton in a single self‐assembled quantum dot (QD). Experimentally, we apply a photocurrent (PC) technique, that enables us to monitor the occupation probability of the exciton state by measuring the dc tunneling current out of the QD. Coherent PC spectrocopy was performed by resonant ps‐excitation of the ground state exciton. Rabi‐oscillations are shown to be directly reflected in the PC. In the case of π‐pulse excitation, we receive a quantitative PC given by I = f × e, with the repetition frequency of the experiment f and the elementary charge e. In our experiment we nearly reach this maximum current showing that our experiment acts as a quantitative proof for Rabi‐flopping in a single QD. In a systematic study of field‐dependence we find Rabi‐oscillations with reduced PC amplitude.
Kinetically controlled engineering of quantum dot arrays
Authors: Dubrovskii V. G. 
Published: July 2003

AbstractA kinetic model for the formation of arrays of coherent strained islands is developed. The derived expressions provide a detailed characterization of quantum dot arrays in terms of island size and density as functions of substrate temperature, growth rate, exposition time and the amount of deposit. The obtained results give a guideline to the kinetically controlled engineering of quantum dot arrays with required structural properties.
Nonlinear optical susceptibilities of copper‐ and silver‐doped silicate glasses in the ultraviolet range
Authors: Ganeev R. A. , Ryasnyansky A. I. , Stepanov A. L. , Usmanov T. 
Published: July 2003

AbstractNonlinear optical response of copper and silver nanoparticles synthesized by ion implantation in silicate glasses was investigated in ultraviolet range (354.7 nm). The real and imaginary parts of the third‐order nonlinear susceptibility χ(3) of composite materials were measured. It was shown that Im χ(3) was connected with saturable absorption whereas Re χ(3) was due to self‐defocusing of laser radiation in materials.
Polarized electrons, trions, and nuclei in charged quantum dots
Authors: Bracker A. S. , Tischler J. G. , Korenev V. L. , Gammon D. 
Published: July 2003

AbstractSpin polarization in GaAs quantum dots has been investigated in the article [1] featured as Editor's Choice of the present issue. Electrons are polarized through relaxation processes after photoluminescence excitation and are identified by the Hanle effect. The cover figure is a schematic diagram describing the selective removal of negatively polarized excitons by optically pumped spin down electrons, which increases exciton and decreases trion PL polarization, respectively. The corresponding author, Allan Bracker, is a member of NRL's Nanostructures Section, focusing on the physics and application of electronic structures with reduced dimensionality.This paper is an invited presentation from the 2nd International Conference on Semiconductor Quantum Dots held in Tokyo, 30 September–3 October 2002. The full proceedings of this meeting, guest‐edited by Y. Arakawa and S. Tarucha, are published in physica status solidi (c) 0, No. 4 (2003).
Physicochemical and structural properties of bacteriostatic sulfonamides: Theoretical study
Authors: Soriano‐Correa Catalina , Esquivel Rodolfo O. , Sagar Robin P. 
Published: July 2003

AbstractA theoretical study at the Hartree–Fock and density functional theory levels is performed on sulfonamide‐type bacteriostatic compounds with the aim to provide an insight into their structure–activity relationship. The basicity of the p‐amino group is analyzed by means of the proton affinities and the protonation energies, showing that molecules presenting bacteriostatic activity are less basic, i.e., they are characterized by larger protonation energies and smaller proton affinities. The acidity of the amide group is analyzed through the deprotonation energy. The results reveal that the more acidic molecules present a larger bacteriostatic activity. This result is also confirmed from a study of bond orders. A bond order analysis of the amide group suggests that the electron attracting group in these molecules is responsible for the increase in acidity. The charge of the SO2 group is also shown to be affected by the presence of the electron attracting group and consequently related to the acidity of the molecules. A geometric analysis shows that structures in which the amino group is more coplanar with respect to the benzenic ring possess larger bacteriostatic activity. A conformational analysis of these molecules illustrates that active molecules have relatively larger torsion energy barriers. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 165–172, 2003
Theory of strongly correlated electron systems: Hubbard–Anderson models from an exact Hamiltonian, and perturbation theory near the atomic limit within a nonorthogonal basis set
Authors: Sandalov Igor , Johansson Börje , Eriksson Olle 
Published: July 2003

AbstractThe theory of correlated electron systems is formulated in a form that allows the use as a reference point a density functional theory in the local density approximation (LDA DFT) for solids or molecules. The theory is constructed in two steps. As a first step, the total Hamiltonian is transformed into a correlated form. To elucidate the microscopic origin of the parameters of the periodic Hubbard–Anderson model (PHAM) the terms of the full Hamiltonian that have the operator structure of PHAM are separated. It is found that the matrix element of mixing interaction includes ion configuration‐ and number of particles‐dependent contributions from the Coulomb interaction. In a second step the diagram technique (DT) is developed by means of generalization of the Baym–Kadanoff method for correlated systems. The advantages of the method are that: (1) A nonorthogonal basis can be used, in particular the one generated by LDA DFT; (2) the equations for Green's functions (GFs) for the Fermi and Bose types of quasiparticles can be formulated in the form of a closed system of functional equations. The latter allows us to avoid the question of the nonunique decoupling procedure existing in previous versions of the DT and perform the expansion in terms of dressed GFs. Although the expressions for all interactions depend on the overlap matrix, it is shown that the theory is formally equivalent to one with orthogonal states with redefined interactions. When the PHAM is treated from the atomic‐limit side the vertexes are generated by kinematic interactions. The latter arise due to nontrivial commutation relations between X‐operators and come from the mixing, hopping, and overlap of states. The equations for GFs are derived within the nonorthogonal basis set in Hubbard‐I, one‐loop and random‐phase approximations with respect to kinematic interactions. The self‐consistent equation for “Hubbard Us” is derived. The technique developed is general, in particular its “bosonic” part can be used for description of spin systems with arbitrary anisotropy, systems with orbital ordering, or ordering of multipoles. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 113–143, 2003
Chemical bonding in ternary magnesium hydrides
Authors: Orgaz Emilio , Hernández‐Trujillo Jesús 
Published: July 2003

AbstractThe electronic structure of various alkali and alkaline–earth magnesium‐based hydrides was investigated in detail. These types of crystalline compounds show MgH4or MgH6units ordered within a light‐metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state‐of the‐art density functional‐based method and the mechanism of stabilization of the MgH units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgHx,x= 4, 6, are stabilized by means of MgH closed‐shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150–164, 2003
Bond length features of linear carbon chains of finite to infinite size: Visual interpretation from Pauling bond orders
Authors: Cao Zexing , Wu Wei , Zhang Qianer 
Published: July 2003

AbstractSchemes for Kekulé structure counting of linear carbon chains are suggested. Mathematical formulas, which calculate the Pauling bond order P(k, N) of a chemical bond numbered by k, are given for the carbon chain with N carbon atoms. By use of the least‐squares fitting of a linearity, relationships between Pauling bond orders and bond lengths are obtained, and such correlation of the Pauling bond order–bond length can be qualitatively extended to the excited states. The relative magnitudes of Pauling bond orders in unsaturated carbon chains dominate C–C bond lengths a well as the bond length feature with the chain size increasing. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 144–149, 2003
Contortion and Formation Structures in the Mappings between Robotic Jointspaces and Workspaces
Authors: Rooney J. , Tanev T. K. 
Published: July 2003

AbstractThe concepts offormationin robotic workspace (WS) andcontortionin robotic jointspace (JS) are developed, based on the notions ofposeandposture,respectively. The approach focuses on the forward and reverse mappings between jointspace and workspace. It utilizes the Cartesian product spaceJS×WSto interpret these mappings, and, in particular, their singularities as determined by the Jacobians. The singularities are interpreted from the viewpoint of geometric (Clifford) algebra. Initially, systems that have 1D jointspaces and 1D workspaces are discussed before higher‐dimensional examples are examined. © 2003 Wiley Periodicals, Inc.
A Dynamic Analysis of a Spatial Manipulator to Determine Payload Weight
Authors: Crane Carl D. , Duffy Joseph 
Published: July 2003

AbstractThis paper presents a methodology whereby the payload weight of a serial manipulator can be determined from a minimum set of sensor data, i.e., joint angle and joint torque measurements. The particular manipulator geometry that is analyzed is a four degree‐of‐freedom serial chain that is commonly used in excavator systems. It was quite remarkable that a relatively simple solution was obtained for the payload weight considering that there are a total of nine unknown moments and cross moments of inertia of the payload together with the unknown location of the center of mass. Example calculations are presented. © 2003 Wiley Periodicals, Inc.
Kinematics of a Family of Translational Parallel Mechanisms with Three 4‐DOF Legs and Rotary Actuators
Authors: Carricato Marco , Parenti‐Castelli Vincenzo 
Published: July 2003

AbstractThis paper focuses on the kinematics of a family of translational parallel mechanisms equipped with three 4‐DOF legs and rotary actuators. The direct and the inverse position problems are solved in analytical form, the velocity analysis is carried out, the workspace is determined and the loci of both kinematic singularities and isotropic configurations are derived. Furthermore, the problem of singularity avoidance by means of actuator redundancy is addressed and some solutions are proposed. Two special architectures are finally considered as case studies: in the first, the three actuation axes are mutually orthogonal; in the second, two actuation axes are parallel to each other and the third is perpendicular to them. The comparison of the two architectures on the basis of kinematic considerations allows for the selection of the second one as a preferable solution. © 2003 Wiley Periodicals, Inc.