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Quantum Systems (quantum + system)
Selected AbstractsPrinciples and applications of control in quantum systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2005Hideo Mabuchi Abstract We describe in this article some key themes that emerged during a Caltech/AFOSR Workshop on ,Principles and Applications of Control in Quantum Systems' (PRACQSYS), held 21,24 August 2004 at the California Institute of Technology. This workshop brought together engineers, physicists and applied mathematicians to construct an overview of new challenges that arise when applying constitutive methods of control theory to nanoscale systems whose behaviour is manifestly quantum. Its primary conclusions were that the number of experimentally accessible quantum control systems is steadily growing (with a variety of motivating applications), that appropriate formal perspectives enable straightforward application of the essential ideas of classical control to quantum systems, and that quantum control motivates extensive study of model classes that have previously received scant consideration. Copyright © 2005 John Wiley & Sons, Ltd. [source] Degeneracy in one-dimensional quantum mechanics: A case studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2010Adelio R. Matamala Abstract In this work we study the isotonic oscillator, V(x) = Ax2 + Bx,2, on the whole line ,, < x < + , as an example of a one-dimensional quantum system with energy level degeneracy. A symmetric double-well potential with a finite barrier is introduced to study the behavior of energy pattern between both limit: the harmonic oscillator (i.e., a system without degeneracy) and the isotonic oscillator (i.e., a system with degeneracy). © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Relaxation of quantum hydrodynamic modesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002Eric R. Bittner Abstract In this article, we develop a series of hierarchical mode-coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie,Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the "quantum force" in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Computer modeling of frequency-modulation spectra of coherent dark resonancesLASER PHYSICS LETTERS, Issue 9 2006J. Vladimirova Abstract Dynamics of a three-level quantum system in , -configuration driven by a resonant laser field with and without frequency modulation (FM) is studied for the first time in detail using two simulation techniques , the density matrix and quantum trajectories analysis. This analysis was applied to the Fmspectroscopy of coherent dark resonances in Cs atoms and computer simulation results for the absorption spectra are in qualitative agreement with those taken in an experiment. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Positronium interaction and its Bose-Einstein condensationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Sadhan K. Adhikari Abstract We present the actual state of affairs and future perspectives in the study of a quantum system of a collection of positronium (Ps) atoms. The interaction of a Ps atom with other atoms and molecules and specially with another Ps atom is described in some detail as Ps-Ps interaction should play a crucial role in the dynamics of an assembly of Ps atoms. Using a simple model-exchange potential, we could describe the available experimental results of Ps scattering reasonably well. The present scenario of the observation of Ps2 molecule, Ps Bose-Einstein condensate (BEC) and the annihilation laser from a Ps BEC is presented. Possibilities of a Ps BEC formation via laser cooling of Ps atoms and via Ps formation in cavities are considered and difficulties with each procedure discussed (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microscopic description of information transfer from a qudit to reservoirFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 4-5 2003telmachovi Recently Ziman et al. [3] have introduced a concept of a universal quantum homogenizer which is a quantum machine that takes as an input a system qubit initially in an arbitrary state , and a set of N reservoir qubits initially prepared in the same state ,. The homogenizer realizes, in the limit sense, the transformation such that at the output each qubit is in an arbitrarily small neighbourhood of the state , irrespective of the initial states of the system and the reservoir qubits. In this paper we generalize the concept of quantum homogenization for qudits, that is, for d -dimensional quantum systems. We prove that the partial swap operation induces a contractive map with the fixed point which is the original state of the reservoir. Finally we propose an optical realization of the quantum homogenization. [source] Principles and applications of control in quantum systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2005Hideo Mabuchi Abstract We describe in this article some key themes that emerged during a Caltech/AFOSR Workshop on ,Principles and Applications of Control in Quantum Systems' (PRACQSYS), held 21,24 August 2004 at the California Institute of Technology. This workshop brought together engineers, physicists and applied mathematicians to construct an overview of new challenges that arise when applying constitutive methods of control theory to nanoscale systems whose behaviour is manifestly quantum. Its primary conclusions were that the number of experimentally accessible quantum control systems is steadily growing (with a variety of motivating applications), that appropriate formal perspectives enable straightforward application of the essential ideas of classical control to quantum systems, and that quantum control motivates extensive study of model classes that have previously received scant consideration. Copyright © 2005 John Wiley & Sons, Ltd. [source] On quantum statistical inferenceJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 4 2003Ole E. Barndorff-Nielsen Summary. Interest in problems of statistical inference connected to measurements of quantum systems has recently increased substantially, in step with dramatic new developments in experimental techniques for studying small quantum systems. Furthermore, developments in the theory of quantum measurements have brought the basic mathematical framework for the probability calculations much closer to that of classical probability theory. The present paper reviews this field and proposes and interrelates some new concepts for an extension of classical statistical inference to the quantum context. [source] Band structure of a harmonically confined electron with an impenetrable boundaryPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2004W. Hai Abstract We study finite-size effects of the spatially bounded quantum systems exemplified by a single-electron quantum dot with a harmonic potential and an impenetrable boundary. A general solution of the corresponding Schrödinger equation is obtained and the unique special solution for any energy is derived from the normalization and boundary conditions. The classical-mechanically allowable eigenenergies form the continuous spectrum or piecewise continuous bands with the minimum value being much less than the zero point energy of a free harmonic oscillator. As the increase of the confining size, the band widths reduce and the energies finally close to the discrete level of the free oscillator. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Anderson localization of matter wavesANNALEN DER PHYSIK, Issue 12 2009P. Bouyer The transport of quantum particles in non ideal material media is strongly affected by scattering from impurities of the medium. Even for a weak disorder, semi-classical theories, such as those based on the Boltzmann equation for matter-waves scattering from the impurities, often fail to describe transport properties and full quantum approaches are necessary. The properties of the quantum systems are of fundamental interest as they show intriguing and non-intuitive phenomena that are not yet fully understood. Understanding quantum transport in amorphous solids is one of the main issues in this context, related to electric and thermal conductivities. [source] Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnetsANNALEN DER PHYSIK, Issue 10-11 2009B. Vogt Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source] Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnetsANNALEN DER PHYSIK, Issue 10-11 2009B. Vogt Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source] Scopes and limits of modality in quantum mechanicsANNALEN DER PHYSIK, Issue 12 2006G. Domenech Abstract We develop an algebraic frame for the simultaneous treatment of actual and possible properties of quantum systems. We show that, in spite of the fact that the language is enriched with the addition of a modal operator to the orthomodular structure, contextuality remains a central feature of quantum systems. [source] Adiabatic charge pumping in open quantum systemsCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 4 2004Joseph E. Avron We introduce a mathematical setup for charge transport in quantum pumps connected to a number of external leads. It is proved that under rather general assumption on the Hamiltonian describing the system, in the adiabatic limit, the current through the pump is given by a formula of Büttiker, Prêtre, and Thomas, relating it to the frozen S -matrix and its time derivative. © 2004 Wiley Periodicals, Inc. [source] | |||||||||||||||||||||||||