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1

Reducing dephasing in coupled quantum dot-cavity systems by engineering the carrier wavefunctions

DEFF Research Database (Denmark)

We demonstrate theoretically how photon-assisted dephasing by the electron-phonon interaction in a coupled cavity-quantum dot system can be significantly reduced for specific QD-cavity detunings. Our starting point is a recently published theory,1 which considers longitudinal acoustic phonons, described by a non-Markovian model, interacting with a coupled quantum dot-cavity system. The reduction of phonon-induced dephasing is obtained by placing the cavity-quantum dot system inside an infinite slab, assuming spherical electronic wavefunctions. Based on our calculations, we expect this to have important implications in single-photon sources, allowing the indistinguishability of the photons to be improved.

Nysteen, Anders; Nielsen, Per KÃ¦r

2012-01-01

2

Exciton-polariton dynamics in quantum dot-cavity system

International Nuclear Information System (INIS)

Full text: One of the basic requirement for quantum information processing systems is the ability to completely control the state of a single qubit. This imply in know all sources of decoherence and elaborate ways to avoid them. In recent work, A. Laucht et al. [1] presented detailed theoretical and experimental investigations of electrically tunable single quantum dot (QD) - photonic crystal (PhC) nanocavity systems operating in the strong coupling regime of the light matter interaction. Unlike previous studies, where the exciton-cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, they employ the quantum confined Stark-effect to electro-optically control the exciton-cavity detuning. The new built device enabled them to systematically probe the emission spectrum of the strongly coupled system as a function of external control parameters, as for example the incoherent excitation power density or the lattice temperature. Those studies reveal for the first time insights in dephasing mechanisms of 0D exciton polaritons [1]. In another study [2], using a similar device, they investigate the coupling between two different QDs with a single cavity mode. In both works, incoherent pumping was used, but for quantum information, coherent and controlled excitations are necessary. Here, we theoretically investigate the dynamics a single quantum dot inside a cavity under coherent pulse excitation and explore a wide range of parameters, as for example, the exciton-cavity detunings, the excitation power, the spontaneous decay, and pure dephasing. We use density matrix formalism in the Lindblad form, and we solve it numerically. Our results show that coherent excitation can be used to probe strong coupling between exciton and cavity mode by monitoring the exciton Rabi oscillation as function of the cavity detuning. This can give new insights for future experimental measurement focusing on quantum information processing. 1] A. Laucht et all. Phys. Rev. Lett. 103, 087405 (2009); [2] A. Laucht et all Phys. Rev. B 82, 075305 (2010). (author)

2012-05-14

3

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the influence of electron-phonon interactions on the dynamical properties of a quantum-dot-cavity QED system. We show that non-Markovian effects in the phonon reservoir lead to strong changes in the dynamics, arising from photon-assisted dephasing processes, not present in Markovian treatments. A pronounced consequence is the emergence of a phonon induced spectral asymmetry when detuning the cavity from the quantum-dot resonance. The asymmetry can only be explained when conside...

2010-01-01

4

Lasing properties of non-resonant single quantum dot-cavity system under incoherent excitation.

Single quantum dot laser has earned extensive interest due to its peculiar properties, however, most of works are focused on the resonant case. In this paper, the lasing oscillation based on off-resonant quantum dot (QD)-cavity system is investigated detailedly through two-electrons QD model. By gradually increasing the pump rate, the typical lasing signatures are shown with and without detuning, include the spectral transition from multiple peaks to single peak, and antibunching to Poissonian distribution. It is also demonstrated how detuning factor strongly influence photon statistics and emission properties, specially, the side peak of spectra induced by the exchange energy (named "sub-peak") will go across the main peak from left to right when the detuning is gradually increased, and, furthermore, we find the "sub-peak cross of spectra" will facilitate the lasing oscillation because of the existence of exchange energy. PMID:23263079

Guan, Huan; Yao, Peijun; Yu, Wenhai; Wang, Pei; Ming, Hai

2012-12-17

5

Quantum Dot Cavity-QED in the Presence of Strong Electron-Phonon Interactions

A quantum dot strongly coupled to a single high finesse optical microcavity mode constitutes a new fundamental system for quantum optics. Here, the effect of exciton-phonon interactions on reversible quantum-dot cavity coupling is analysed without making Born-Markov approximation. The analysis is based on techniques that have been used to study the ``spin boson'' Hamiltonian. Observability of vacuum-Rabi splitting depends on the strength and the frequency dependence of the spectral density function characterizing the interactions with phonons, both of which can be influenced by phonon confinement.

Wilson-Rae, I

2001-01-01

6

Rabi oscillations in a quantum dot-cavity system coupled to a non-zero temperature phonon bath

We study a quantum dot strongly coupled to a single high-finesse optical microcavity mode. We use a rotating wave approximation method, commonly used in ion-laser interactions, to obtain an analytic solution of this problem beyond the Born-Markov approximation. The decay of Rabi oscillations because of the electron-phonon coupling are studied at arbitrary temperature and analytical expressions for the collapse and revival times are presented. Analysis without the rotating wave approximation are presented and new structures and phenomena of the Rabi oscillations occur in this regime either due to level crossings of the energy eigenvalues or because of equidistant eigenenergies.

Larson, J; Larson, Jonas; Moya-Cessa, Hector

2007-01-01

7

Quantum Dot Cavity Spin Entanglement at a Distance - A Theoretical Analysis

International Nuclear Information System (INIS)

Full text: Measurement of conditional Faraday rotation has recently been proposed for entanglement generation at a distance. In this talk we present a theoretical analysis of entanglement formation at a distance between two electron spins, each sitting in one of two 'distant' quantum dot cavities. Entanglement is induced by measuring the conditional Faraday rotation of a non-resonant laser pulse which has propagated through the two cavities. The basis for this scheme are two 'identical' scatterers, such as an atom or a quantum dot, where each has two initial states, whereby only one of them is optically active, for example, by dipole selection rules. Here we investigate one-sided cavities which avoid unintentional measurement in the reflected beam. Frequency 'sweet-spots' are identified for which, in spite of dissipative action, good fidelity entanglement generation should be possible. We also predict that monitoring of the Faraday rotation allows the detection of single spin flips, similar to single non-demolition photo-emission monitoring in atom quantum cavity systems. The possibility of studying entanglement death and revival in this system is discussed. (author)

2012-09-18

8

High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom band are challenges facing the development of fibre-based long-haul quantum communication networks. Here we report a very fast single photon source in the 1,550-nm telecom band, which is achieved by a large Purcell enhancement that results from the coupling of a single InAs quantum dot and an InP photonic crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550 nm. We also demonstrate that this emission exhibits an enhanced anti-bunching dip. This is the first realization of nanocavity-enhanced single photon emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system in the telecom band thus provides a bright high-bit-rate non-classical single photon source that offers appealing novel opportunities for the development of a long-haul quantum telecommunication system via optical fibres.

Birowosuto, M D; Matsuo, S; Taniyama, H; van Veldhoven, P J; Nötzel, R; Notomi, M; 10.1038/srep00321

2012-01-01

9

Digital Repository Infrastructure Vision for European Research (DRIVER)

Advances in semiconductor technology constitute a new physical system to investigate quantum optics in a solid state environment: a quantum dot strongly coupled to a single cavity mode. In the strong coupling regime, the electron-photon coupling dominates over dissipation processes and Rabi oscillations occur. This thesis focuses on the theoretical investigation of the strong coupling regime in the single-photon limit, in which few photons interact with a single quantum dot and the combined e...

Carmele, Alexander

2011-01-01

10

Probing the ladder of dressed states and nonclassical light generation in quantum dot-cavity QED

We investigate the photon induced tunneling phenomena in a photonic crystal cavity containing a strongly coupled quantum dot and describe how this tunneling can be used to generate photon states consisting mainly of a particular Fock state. Additionally, we study experimentally the photon-induced tunneling as a function of excitation laser power and frequency and show the signature of second rung of the Jaynes-Cummings Hamiltonian in the observed photon-statistics.

Majumdar, Arka; Vuckovic, Jelena

2011-01-01

11

Optical manipulation of quantum dot excitons strongly coupled to photonic crystal cavities

In this paper, we review some recent cavity quantum electrodynamic (CQED) experiments with single quantum dot exciton coupled to photonic crystal cavities, performed in our group. We show how the coupled quantum-dot/ cavity system can be used to modulate light with at a very fundamental level with very low power and discuss some applications of these low power modulators.

Majumdar, Arka; Faraon, Andrei; Englund, Dirk; Manquest, Nicolas; Kim, Hyochul; Petroff, Pierre; Vuckovic, Jelena

2010-02-01

12

Fundamental properties of devices for quantum information technology

DEFF Research Database (Denmark)

This thesis reports a theoretical investigation of the influence of the electronphonon interaction on semiconductor cavity quantum electrodynamical systems, specifically a quantum dot coupled to an optical microcavity. We develop a theoretical description of the decay dynamics of the quantum dot interacting with the cavity and the phonons. It is shown that the presence of the phonon interaction, fundamentally changes the spontaneous emission decay behavior of the quantum dot. Especially in the regime where the quantum dotcavity spectral detuning is significantly larger than any linewidth of the system, the effect of the phonon interaction is very pronounced. A simple approximate analytical expression for the quantum dot decay rate is derived, which predicts a strong asymmetry with respect to the quantum dot-cavity detuning at low temperatures, and allows for a clear interpretation of the physics. Furthermore, a study of the indistinguishability of single photons emitted from the coupled quantum dot-cavity system is performed, with special emphasis on non-Markovian decoherence due to the phonon interaction. We show that common theoretical approaches fail to predict the degree of indistinguishability, on both a qualitative and quantitative level, for experimentally relevant parameters regimes. The important role of non-Markovian effects in the shorttime regime, where virtual processes dominate the decoherence of the quantum dot-cavity system, is emphasized. Importantly, our investigations lead to a maximum achievable degree of indistinguishability, a prediction which eludes common approaches.

Nielsen, Per KÃ¦r

2012-01-01

13

The input/output characteristics of coherent photon transport through a semiconductor cavity system containing a single quantum dot is presented. The nonlinear quantum optics formalism uses a master equation approach and focuses on a waveguide-cavity system containing a semiconductor quantum dot; our general technique also applies to studying coherent reflection from a micropillar cavity. We investigate the effects of light propagation and show the need for quantized multiphoton effects for various dot-cavity systems, including weakly-coupled, intermediately-coupled, and strongly-coupled regimes. We demonstrate that for mean photon numbers much less than 0.1, the commonly adopted weak excitation (single quantum) approximation breaks down---even in the weak coupling regime. As a measure of the photon correlations, we compute the Fano factor and the error associated with making a semiclassical approximation. We also investigate the role of electron--acoustic-phonon scattering and show that phonon-mediated scatt...

Hughes, S

2011-01-01

14

DEFF Research Database (Denmark)

We study the fundamental limit on single-photon indistinguishability imposed by decoherence due to phonon interactions in semiconductor quantum dot-cavity quantum electrodynamics systems. Employing an exact diagonalization approach we find large differences compared to standard methods. An important finding is that short-time non-Markovian effects limit the maximal attainable indistinguishability. The results are explained using a polariton picture that yields valuable insight into the phonon-induced dephasing dynamics.

Nielsen, Per KÃ¦r; Lodahl, Peter

2013-01-01

15

Controlled Quantum Open Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

The theory of controlled quantum open systems describes quantum systems interacting with quantum environments and influenced by external forces varying according to given algorithms. It is aimed, for instance, to model quantum devices which can find applications in the future technology based on quantum information processing. One of the main problems making difficult the practical implementations of quantum information theory is the fragility of quantum states under externa...

Alicki, Robert

2003-01-01

16

Quantum discord in open quantum systems

Open quantum systems have attracted great attentions for the inevitable interaction between quantum systems and their environment would largely affect the features of interest in the systems. Quantum discord, as a measure of the total nonclassical correlation in a quantum system, includes but not only the distinct property of quantum entanglement. Quantum discord can exist in separated quantum states and it has been shown to play important roles in many fundamental physical problems and practical quantum information tasks. There have been plentiful investigations on the quantum discord and its counterpart classical correlation in open quantum systems. In this short review, we would focus on the recent development and applications of distinctive properties of quantum discord and classical correlation in open quantum systems. Several related experimental works are included.

Xu, Jin-Shi

2012-01-01

17

Quantum Games and Programmable Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Attention to the very physical aspects of information characterizes the current research in quantum computation, quantum cryptography and quantum communication. In most of the cases quantum description of the system provides advantages over the classical approach. Game theory, the study of decision making in conflict situation has already been extended to the quantum domain. We would like to review the latest development in quantum game theory that is relevant to information...

Piotrowski, Edward W.; Sladkowski, Jan

2005-01-01

18

So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the new notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a stochastic neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is an information theory of reality in which space and quantum phenomena are emergent, and so indicates the deep origins of quantum phenomena. Analogous complex stochastic dynamical systems have recently been proposed within neurobiology to deal with the emergent complexity of biosystems, particularly the biodynamics of higher brain function. The reasons for analogous discoveries in fundamental physics and neurobiology are discussed.

Cahill, R T

2002-01-01

19

Energy Technology Data Exchange (ETDEWEB)

A dispersive quantum system is a quantum system which is both isolated and non-time reversal invariant. This article presents precise definitions for those concepts and also a characterization of dispersive quantum systems within the class of completely positive Markovian quantum systems in finite dimension (through a homogeneous linear equation for the non Hamiltonian part of the system's Liouvillian). To set the framework, the basic features of quantum mechanics are reviewed focusing on time evolution and also on the theory of completely positive Markovian quantum systems, including Kossakowski-Lindblad's standard form for Liouvillians. After those general considerations, a simple two-dimensional example is presented and then applied to describe the neutrino oscillation, with the introduction of a new-dispersive parameter. (author)

Fassarella, Lucio, E-mail: lucio.fassarella@ufes.br [Universidade Federal do Espirito Santo, CEUNES, Sao Mateus, ES (Brazil)

2012-04-15

20

Digital Repository Infrastructure Vision for European Research (DRIVER)

An introduction to some basic ideas of the author's "quantum cybernetics" is given, which depicts waves and "particles" as mutually dependent system components, thus defining "organizationally closed systems" characterized by a fundamental circular causality. According to this, a new derivation of quantum theory's most fundamental equation, the Schroedinger equation, is presented. Finally, it is shown that quantum systems can be described by what Heinz von Foerster has calle...

Groessing, Gerhard

2004-01-01

21

Digital Repository Infrastructure Vision for European Research (DRIVER)

Models of PT symmetric quantum mechanics provide examples of biorthogonal quantum systems. The latter incorporporate all the structure of PT symmetric models, and allow for generalizations, especially in situations where the PT construction of the dual space fails. The formalism is illustrated by a few exact results for models of the form H=(p+\

Curtright, Thomas; Mezincescu, Luca

2005-01-01

22

The aim of quantum system identification is to estimate the ingredients inside a black box, in which some quantum-mechanical unitary process takes place, by just looking at its input-output behavior. Here we establish a basic and general framework for quantum system identification, that allows us to classify how much knowledge about the quantum system is attainable, in principle, from a given experimental setup. Prior knowledge on some elements of the black box helps the system identification. We present an example in which a Bell measurement is more efficient to identify the system. When the topology of the system is known, the framework enables us to establish a general criterion for the estimability of the coupling constants in its Hamiltonian.

Burgarth, Daniel

2011-01-01

23

A secure quantum identification system combining a classical identification procedure and quantum key distribution is proposed. Each identification sequence is always used just once and new sequences are ``refuelled'' from a shared provably secret key transferred through the quantum channel. Two identification protocols are devised. The first protocol can be applied when legitimate users have an unjammable public channel at their disposal. The deception probability is derived for the case of a noisy quantum channel. The second protocol employs unconditionally secure authentication of information sent over the public channel, and thus it can be applied even in the case when an adversary is allowed to modify public communications. An experimental realization of a quantum identification system is described.

Dusek, M; Hendrych, M; Myska, R; Dusek, Miloslav; Haderka, Ondrej; Hendrych, Martin; Myska, Robert

1999-01-01

24

This book deals with the statistical mechanics and dynamics of open quantum systems moving irreversibly under the influence of a dissipative environment. The basic concepts and methods are described on the basis of a microscopic description with emphasis on the functional integral approach. The general theory for the time evolution of the density matrix of the damped system is developed. Many of the sophisticated ideas in the field are explained with simple models. The discussion includes, among others, the interplay between thermal and quantum fluctuations, quantum statistical decay, macrosco

Weiss, Ulrich

1993-01-01

25

Energy Technology Data Exchange (ETDEWEB)

The book is based on the lectures given at the CIME school ''Quantum many body systems'' held in the summer of 2010. It provides a tutorial introduction to recent advances in the mathematics of interacting systems, written by four leading experts in the field: V. Rivasseau illustrates the applications of constructive Quantum Field Theory to 2D interacting electrons and their relation to quantum gravity; R. Seiringer describes a proof of Bose-Einstein condensation in the Gross-Pitaevski limit and explains the effects of rotating traps and the emergence of lattices of quantized vortices; J.-P. Solovej gives an introduction to the theory of quantum Coulomb systems and to the functional analytic methods used to prove their thermodynamic stability; finally, T. Spencer explains the supersymmetric approach to Anderson localization and its relation to the theory of random matrices. All the lectures are characterized by their mathematical rigor combined with physical insights.

Rivasseau, Vincent [Paris-Sud Univ. Orsay (France). Laboratoire de Physique Theorique; Seiringer, Robert [McGill Univ., Montreal, QC (Canada). Dept. of Mathematics and Statistics; Solovej, Jan Philip [Copenhagen Univ. (Denmark). Dept. of Mathematics; Spencer, Thomas [Institute for Advanced Study, Princeton, NJ (United States). School of Mathematics

2012-11-01

26

International Nuclear Information System (INIS)

We generalize the classical notion of a K-system to a non-commutative dynamical system by requiring that an invariantly defined memory loss be 100%. We give some examples of quantum K-systems and show that they cannot contain any quasi-periodic subsystem. 13 refs. (Author)

1988-01-01

27

Scheme of thinking quantum systems

A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans. The algebra of probability operators, associated with the possible options available to the decision maker, plays the role of the algebra of observables in quantum theory of measurements. A scheme is advanced for a practical realization of decision procedures by thinking quantum systems. Such thinking quantum systems can be realized by using spin lattices, systems of magnetic molecules, cold atoms trapped in optical lattices, ensembles of quantum dots, or multilevel atomic systems interacting with electromagnetic field.

Yukalov, V I

2009-01-01

28

Scheme of thinking quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans...

Yukalov, V. I.; Sornette, D.

2009-01-01

29

Starting from first principles, this book introduces the fundamental concepts and methods of dissipative quantum mechanics and explores related phenomena in condensed matter systems. Major experimental achievements in cooperation with theoretical advances have brightened the field and brought it to the attention of the general community in natural sciences. Nowadays, working knowledge of dissipative quantum mechanics is an essential tool for many physicists. This book - originally published in 1990 and republished in 1999 and and 2008 as enlarged second and third editions - delves significantl

Weiss, Ulrich

2012-01-01

30

Recent advances in the quantum theory of macroscopic systems have brightened up the field and brought it into the focus of a general community in natural sciences. The fundamental concepts, methods and applications including the most recent developments, previously covered for the most part only in the original literature, are presented here in a comprehensive treatment to an audience who is reasonably familiar with quantum-statistical mechanics and has had rudimentary contacts with the path integral formulation.This book deals with the phenomena and theory of decoherence and dissipation in qu

Weiss, U

1999-01-01

31

Transitionless quantum driving in open quantum systems

We extend the concept of superadiabatic dynamics, or transitionless quantum driving, to quantum open systems whose evolution is governed by a master equation in the Lindblad form. We provide the general framework needed to determine the control strategy required to achieve superadiabaticity. We apply our formalism to two examples consisting of a two-level system coupled to environments with time-dependent bath operators.

Vacanti, G.; Fazio, R.; Montangero, S.; Palma, G. M.; Paternostro, M.; Vedral, V.

2014-05-01

32

Quantum Cybernetics and Complex Quantum Systems Science - A Quantum Connectionist Exploration

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum cybernetics and its connections to complex quantum systems science is addressed from the perspective of complex quantum computing systems. In this way, the notion of an autonomous quantum computing system is introduced in regards to quantum artificial intelligence, and applied to quantum artificial neural networks, considered as autonomous quantum computing systems, which leads to a quantum connectionist framework within quantum cybernetics for complex quantum comput...

Gonc?alves, Carlos Pedro

2014-01-01

33

We present a semiconductor master equation technique to study the input/output characteristics of coherent photon transport in a semiconductor waveguide-cavity system containing a single quantum dot. We use this approach to investigate the effects of photon propagation and anharmonic cavity-QED for various dot-cavity interaction strengths, including weakly-coupled, intermediately-coupled, and strongly-coupled regimes. We demonstrate that for mean photon numbers much less than 0.1, the commonly adopted weak excitation (single quantum) approximation breaks down, even in the weak coupling regime. As a measure of the multiphoton correlations, we compute the Fano factor and the correlation error associated with making a semiclassical approximation. We also explore the role of electron-acoustic-phonon scattering and find that phonon-mediated scattering plays a qualitatively important role on the light propagation characteristics. As an application of the theory, we simulate a conditional phase gate at a phonon bath temperature of 20 K in the strong coupling regime.

Hughes, S.; Roy, C.

2012-01-01

34

Quasiperiodically kicked quantum systems

Energy Technology Data Exchange (ETDEWEB)

We consider a two-state system kicked quasiperiodically by an external force. When the two kicking frequencies assumed for the force are incommensurate, there can be quantum chaos in the sense that (a) the autocorrelation function of the state vector decays, (b) the power spectrum of the state vector is broadband, and (c) the motion on the Bloch sphere is ergodic. The time evolution of the state vector is nevertheless dynamically stable in the sense that memory of the initial state is retained. We also consider briefly the kicked quantum rotator and find, in agreement with Shepelyansky (Physica 8D, 208 (1983)), that the quantum localization effect is greatly weakened by the presence of two incommensurate driving frequencies.

Milonni, P.W.; Ackerhalt, J.R.; Goggin, M.E.

1987-02-15

35

Quasiperiodically kicked quantum systems

International Nuclear Information System (INIS)

We consider a two-state system kicked quasiperiodically by an external force. When the two kicking frequencies assumed for the force are incommensurate, there can be quantum chaos in the sense that (a) the autocorrelation function of the state vector decays, (b) the power spectrum of the state vector is broadband, and (c) the motion on the Bloch sphere is ergodic. The time evolution of the state vector is nevertheless dynamically stable in the sense that memory of the initial state is retained. We also consider briefly the kicked quantum rotator and find, in agreement with Shepelyansky [Physica 8D, 208 (1983)], that the quantum localization effect is greatly weakened by the presence of two incommensurate driving frequencies

1987-02-15

36

International Nuclear Information System (INIS)

We demonstrate non-perturbative coupling between a single self-assembled InGaAs quantum dot and an external fiber-mirror-based microcavity. Our results extend the previous realizations of tunable microcavities while ensuring spatial and spectral overlap between the cavity mode and the emitter by simultaneously allowing for deterministic charge control of the quantum dots. Using resonant spectroscopy, we show that the coupled quantum dot cavity system is at the onset of strong coupling, with a cooperativity parameter of C ? 2.0 ± 1.3. Our results constitute a milestone in the progress toward the realization of a high-efficiency solid-state spin–photon interface. (paper)

2013-04-01

37

Decoherence in open quantum systems

International Nuclear Information System (INIS)

In the framework of the theory of open quantum systems based on completely positive quantum dynamical semigroups we study the transition from quantum to classical behaviour of the system of a harmonic oscillator interacting with an environment (in particular with a thermal bath) by discussing the evolution of the density matrix and Wigner function of the system. The two necessary conditions for a system to become classical - quantum decoherence and classical correlations - are discussed and the degree of quantum decoherence and the degree of classical correlations are estimated in order to analyze the classicality of the considered system. (author)

2004-08-26

38

Quantum critical points in quantum impurity systems

International Nuclear Information System (INIS)

The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the soft-gap Anderson model, where an impurity couples to a non-trivial fermionic bath. In this case, zero-temperature phase transitions occur between two different phases whose fixed points can be built up of non-interacting single-particle states. However, the quantum critical point cannot be described by non-interacting fermionic or bosonic excitations

2005-04-30

39

Equilibration of quantum chaotic systems

The quantum ergordic theorem for a large class of quantum systems was proved by von Neumann [Z. Phys. 57, 30 (1929), 10.1007/BF01339852] and again by Reimann [Phys. Rev. Lett. 101, 190403 (2008), 10.1103/PhysRevLett.101.190403] in a more practical and well-defined form. However, it is not clear whether the theorem applies to quantum chaotic systems. With a rigorous proof still elusive, we illustrate and verify this theorem for quantum chaotic systems with examples. Our numerical results show that a quantum chaotic system with an initial low-entropy state will dynamically relax to a high-entropy state and reach equilibrium. The quantum equilibrium state reached after dynamical relaxation bears a remarkable resemblance to the classical microcanonical ensemble. However, the fluctuations around equilibrium are distinct: The quantum fluctuations are exponential while the classical fluctuations are Gaussian.

Zhuang, Quntao; Wu, Biao

2013-12-01

40

DEFF Research Database (Denmark)

Differences in the confinement of electrons and holes in quantum dots are shown to profoundly impact the magnitude of scattering with acoustic phonons. Using an extensive model that includes the non-Markovian nature of the phonon reservoir, we show how the effect may be addressed by photoluminescence excitation spectroscopy of a single quantum dot. We also investigate the implications for cavity QED, i.e., a coupled quantum dot-cavity system, and demonstrate that the phonon scattering may be strongly quenched. The quenching is explained by a balancing between the deformation potential interaction strengths and the carrier confinement and depends on the quantum dot shape. Numerical examples suggest a route towards engineering the phonon scattering.

Nysteen, Anders; Nielsen, Per KÃ¦r

2013-01-01

41

Asymptotically open quantum systems

International Nuclear Information System (INIS)

In the present thesis we investigate the structure of time-dependent equations of motion in quantum mechanics.We start from two coupled systems with an autonomous equation of motion. A limit, in which the dynamics of one of the two systems has a decoupled evolution and imposes a non-autonomous evolution for the second system is identified. A result due to K. Hepp that provides a classical limit for dynamics turns out to be part and parcel for this limit and is generalized in our work. The method introduced by J.S. Howland for the solution of the time-dependent Schroedinger equation is interpreted as such a limit. Moreover, we associate our limit with the modern theory of quantization. (orig.)

2008-01-01

42

Controlling cavity reflectivity with a single quantum dot.

Solid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices. In particular, systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed the observation of weak and strong coupling regimes of interaction between the photonic crystal cavity and a single quantum dot in photoluminescence. In the weak coupling regime, the quantum dot radiative lifetime is modified; in the strong coupling regime, the coupled quantum dot also modifies the cavity spectrum. Several proposals for scalable quantum information networks and quantum computation rely on direct probing of the cavity-quantum dot coupling, by means of resonant light scattering from strongly or weakly coupled quantum dots. Such experiments have recently been performed in atomic systems and superconducting circuit QED systems, but not in solid-state quantum dot-cavity QED systems. Here we present experimental evidence that this interaction can be probed in solid-state systems, and show that, as expected from theory, the quantum dot strongly modifies the cavity transmission and reflection spectra. We show that when the quantum dot is coupled to the cavity, photons that are resonant with its transition are prohibited from entering the cavity. We observe this effect as the quantum dot is tuned through the cavity and the coupling strength between them changes. At high intensity of the probe beam, we observe rapid saturation of the transmission dip. These measurements provide both a method for probing the cavity-quantum dot system and a step towards the realization of quantum devices based on coherent light scattering and large optical nonlinearities from quantum dots in photonic crystal cavities. PMID:18064008

Englund, Dirk; Faraon, Andrei; Fushman, Ilya; Stoltz, Nick; Petroff, Pierre; Vuckovi?, Jelena

2007-12-01

43

Open quantum systems recent developments

Understanding dissipative dynamics of open quantum systems remains a challenge in mathematical physics. This problem is relevant in various areas of fundamental and applied physics. From a mathematical point of view, it involves a large body of knowledge. Significant progress in the understanding of such systems has been made during the last decade. These books present in a self-contained way the mathematical theories involved in the modeling of such phenomena. They describe physically relevant models, develop their mathematical analysis and derive their physical implications. In Volume I the Hamiltonian description of quantum open systems is discussed. This includes an introduction to quantum statistical mechanics and its operator algebraic formulation, modular theory, spectral analysis and their applications to quantum dynamical systems. Volume II is dedicated to the Markovian formalism of classical and quantum open systems. A complete exposition of noise theory, Markov processes and stochastic differential...

Joye, Alain; Pillet, Claude-Alain

2006-01-01

44

Decoherence in infinite quantum systems

Energy Technology Data Exchange (ETDEWEB)

We review and discuss a notion of decoherence formulated in the algebraic framework of quantum physics. Besides presenting some sufficient conditions for the appearance of decoherence in the case of Markovian time evolutions we provide an overview over possible decoherence scenarios. The framework for decoherence we establish is sufficiently general to accommodate quantum systems with infinitely many degrees of freedom.

Blanchard, Philippe; Hellmich, Mario [Faculty of Physics, University of Bielefeld, Universitaetsstr. 25, 33615 Bielefeld (Germany); Bundesamt fuer Strahlenschutz (Federal Office for Radiation Protection), Willy-Brandt-Strasse 5, 38226 Salzgitter (Germany)

2012-09-01

45

International Nuclear Information System (INIS)

The overview of recent developments in the theory of quantum chaos is presented with the special emphasis on a number of unsolved problems and current apparent contradictions. The relation between dynamical quantum chaos and statistical random matrix theory is discussed. 97 refs

1991-01-01

46

A prototype quantum cryptography system

International Nuclear Information System (INIS)

In this work we have constructed a new secure quantum key distribution system based on the BB84 protocol. Many current state-of-the-art quantum cryptography systems encounter major problems concerning low bit rate, synchronization, and stabilization. Our quantum cryptography system utilizes only laser diodes and standard passive optical components, to enhance the stability and also to decrease the space requirements. The development of this demonstration for a practical quantum key distribution system is a consequence of our previous work on the quantum cryptographic system using optical fiber components for the transmitter and receiver. There we found that the optical fiber couplers should not be used due to the problems with space, stability and alignment. The goal of the synchronization is to use as little transmission capacities as possible. The experimental results of our quantum key distribution system show the feasibility of getting more than 90 % transmission capacities with the approaches developed in this work. Therefore it becomes feasible to securely establish a random key sequence at a rate of 1 to ? 5K bit/s by using our stable, compact, cheap, and user-friendly modules for quantum cryptography. (author)

1998-01-01

47

Three Terminal Quantum Dot System

Directory of Open Access Journals (Sweden)

Full Text Available In this study, the transmission rate for the three terminal quantum dot system is determined using Keldysh nonequilibrium Green’s function technique for interacting and non-interacting cases. The three terminal quantum dot systems consist of three leads and three quantum dots that are arranged in a triangular form. Each led is coupled with each dot. The lesser and retarded Green’s functions are used for the calculations of transmission rates and how the transmission rates vary for interacting and non-interacting system are studied is investigated.

N. Chandrasekar

2012-01-01

48

Quantum Relativity: Physical Laws Must be Invariant Over Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Decoherence may not solve all of the measurement problems of quantum mechanics. It is proposed that a solution to these problems may be to allow that superpositions describe physically real systems in the following sense. Each quantum system "carries" around a local spacetime in whose terms other quantum systems may take on nonlocal states. Each quantum system forms a physically valid coordinate frame. The laws of physics should be formulated to be invariant under the group ...

Merriam, Paul

2005-01-01

49

Quantum contextuality in complex systems

We show that, for a system of several qubits, there is an inequality for the correlations between three compatible dichotomic measurements which must be satisfied by any noncontextual theory, but is violated by any quantum state. Remarkably, the violation grows exponentially with the number of qubits, and the tolerated error per correlation also increases with the number of qubits, showing that state-independent quantum contextuality is experimentally observable in complex systems.

Cabello, Adan

2010-01-01

50

Introduction to quantum spin systems

Directory of Open Access Journals (Sweden)

Full Text Available This manuscript is the collection of lectures given in the summer school on strongly correlated electron systems held at Isfahan university of technology, June 2007. A short overview on quantum magnetism and spin systems is presented. The numerical exact diagonalization (Lanczos alghorithm is explained in a pedagogical ground. This is a method to get some ground state properties on finite cluster of lattice models. Two extensions of Lanczos method to get the excited states and also finite temperature properties of quantum models are also explained. The basic notions of quantum phase transition is discussed in term of Ising model in transverse field. Its phase diagram and critical properties are explained using the quantum renormalization group approach. Most of the topics are in tutorial level with hints to recent research activities.

A. Langari

2008-06-01

51

Quantum Dot Systems: a versatile platform for quantum simulations

Energy Technology Data Exchange (ETDEWEB)

Quantum mechanics often results in extremely complex phenomena, especially when the quantum system under consideration is composed of many interacting particles. The states of these many-body systems live in a space so large that classical numerical calculations cannot compute them. Quantum simulations can be used to overcome this problem: complex quantum problems can be solved by studying experimentally an artificial quantum system operated to simulate the desired hamiltonian. Quantum dot systems have shown to be widely tunable quantum systems, that can be efficiently controlled electrically. This tunability and the versatility of their design makes them very promising quantum simulators. This paper reviews the progress towards digital quantum simulations with individually controlled quantum dots, as well as the analog quantum simulations that have been performed with these systems. The possibility to use large arrays of quantum dots to simulate the low-temperature Hubbard model is also discussed. The main issues along that path are presented and new ideas to overcome them are proposed. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Barthelemy, Pierre; Vandersypen, Lieven M.K. [Kavli Institute of Nanoscience, TU Delft, 2600 GA Delft (Netherlands)

2013-11-15

52

Quantum Dot Systems: a versatile platform for quantum simulations

International Nuclear Information System (INIS)

Quantum mechanics often results in extremely complex phenomena, especially when the quantum system under consideration is composed of many interacting particles. The states of these many-body systems live in a space so large that classical numerical calculations cannot compute them. Quantum simulations can be used to overcome this problem: complex quantum problems can be solved by studying experimentally an artificial quantum system operated to simulate the desired hamiltonian. Quantum dot systems have shown to be widely tunable quantum systems, that can be efficiently controlled electrically. This tunability and the versatility of their design makes them very promising quantum simulators. This paper reviews the progress towards digital quantum simulations with individually controlled quantum dots, as well as the analog quantum simulations that have been performed with these systems. The possibility to use large arrays of quantum dots to simulate the low-temperature Hubbard model is also discussed. The main issues along that path are presented and new ideas to overcome them are proposed. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

2013-11-01

53

The scalable quantum computation based on quantum dot systems

We propose a scheme for realizing the scalable quantum computation based on the system of quantum dots trapped in a single-mode waveguide. In this system, the quantum dots simultaneously interact with a large detuned waveguide and classical light fields. During the process, neither the waveguide mode nor the quantum dots are excited, so the decoherence can be suppressed, while the system can acquire phases conditional upon the states of any two quantum dots. Therefore, it can be used to realize graph states, one qubit controlling multi-qubit phase $\\pi $ gate, and cluster states.

Zhang, Jian-Qi; Feng, Xun-Li; Zhang, Zhi-Ming

2011-01-01

54

Geometrical structures of multipartite quantum systems

In this paper I will investigate geometrical structures of multipartite quantum systems based on complex projective varieties. These varieties are important in characterization of quantum entangled states. In particular I will establish relation between multi-projective Segre varieties and multip-qubit quantum states. I also will discuss other geometrical approaches such as toric varieties to visualize complex multipartite quantum systems.

Heydari, Hoshang

2011-01-01

55

Geometrical structures of multipartite quantum systems

International Nuclear Information System (INIS)

In this paper I will investigate geometrical structures of multipartite quantum systems based on complex projective varieties. These varieties are important in characterization of quantum entangled states. In particular I will establish relation between multi-projective Segre varieties and multip-qubit quantum states. I also will discuss other geometrical approaches such as toric varieties to visualize complex multipartite quantum systems.

2012-02-08

56

From EPR to quantum computing: experiments on entangled quantum systems

International Nuclear Information System (INIS)

Einstein, together with Podolski and Rosen (EPR), tried to point out inconsistencies of standard quantum mechanics using an effect which is now called entanglement. The experiments testing EPR's hypothesis laid the basis for the new field of quantum information processing, which in turn gave rise to impressive progress in methods to observe and to analyse the phenomenon of entanglement. Here we give an overview of the various systems useful for the novel applications of quantum communication and quantum computation

2005-05-14

57

Computation in Sofic Quantum Dynamical Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze how measured quantum dynamical systems store and process information, introducing sofic quantum dynamical systems. Using recently introduced information-theoretic measures for quantum processes, we quantify their information storage and processing in terms of entropy rate and excess entropy, giving closed-form expressions where possible. To illustrate the impact of measurement on information storage in quantum processes, we analyze two spin-1 sofic quantum systems...

Wiesner, Karoline; Crutchfield, James P.

2007-01-01

58

Computation in Sofic Quantum Dynamical Systems

We analyze how measured quantum dynamical systems store and process information, introducing sofic quantum dynamical systems. Using recently introduced information-theoretic measures for quantum processes, we quantify their information storage and processing in terms of entropy rate and excess entropy, giving closed-form expressions where possible. To illustrate the impact of measurement on information storage in quantum processes, we analyze two spin-1 sofic quantum systems that differ only in how they are measured.

Wiesner, Karoline

2007-01-01

59

Open Quantum Systems An Introduction

In this volume the fundamental theory of open quantum systems is revised in the light of modern developments in the field. A unified approach to the quantum evolution of open systems is presented by merging concepts and methods traditionally employed by different communities, such as quantum optics, condensed matter, chemical physics and mathematical physics. The mathematical structure and the general properties of the dynamical maps underlying open system dynamics are explained in detail. The microscopic derivation of dynamical equations, including both Markovian and non-Markovian evolutions, is also discussed. Because of the step-by-step explanations, this work is a useful reference to novices in this field. However, experienced researches can also benefit from the presentation of recent results.

Rivas, ´Angel

2012-01-01

60

DEFF Research Database (Denmark)

We show that Auger processes involving wetting layer transitions mediate emission from a cavity that is detuned from a quantum dot by even tens of meV. The wetting layer thus acts as a reservoir, which by Coulomb scattering can supply or absorb the energy difference between emitter and cavity. We perform microscopic calculations of the effect treating the wetting layer as a non-Markovian reservoir interacting with the coupled quantum dot-cavity system through Coulomb interactions. Experimentally, cavity feeding has been observed in the asymmetric detuning range of -10 to +45 meV. We show that this asymmetry arises naturally from the quasiequilibrium properties of the wetting layer reservoir. Furthermore, we present numerical calculations of both photoluminescence spectra and photon correlations, demonstrating good qualitative agreement with experiments.

Settnes, Mikkel; Nielsen, Per KÃ¦r

2013-01-01

61

Quantum Dynamics in Biological Systems

In the first part of this dissertation, recent efforts to understand quantum mechanical effects in biological systems are discussed. Especially, long-lived quantum coherences observed during the electronic energy transfer process in the Fenna-Matthews-Olson complex at physiological condition are studied extensively using theories of open quantum systems. In addition to the usual master equation based approaches, the effect of the protein structure is investigated in atomistic detail through the combined application of quantum chemistry and molecular dynamics simulations. To evaluate the thermalized reduced density matrix, a path-integral Monte Carlo method with a novel importance sampling approach is developed for excitons coupled to an arbitrary phonon bath at a finite temperature. In the second part of the thesis, simulations of molecular systems and applications to vibrational spectra are discussed. First, the quantum dynamics of a molecule is simulated by combining semiclassical initial value representation and density funcitonal theory with analytic derivatives. A computationally-tractable approximation to the sum-of-states formalism of Raman spectra is subsequently discussed.

Shim, Sangwoo

62

Quantum Annealing and Quantum Fluctuation Effect in Frustrated Ising Systems

Quantum annealing method has been widely attracted attention in statistical physics and information science since it is expected to be a powerful method to obtain the best solution of optimization problem as well as simulated annealing. The quantum annealing method was incubated in quantum statistical physics. This is an alternative method of the simulated annealing which is well-adopted for many optimization problems. In the simulated annealing, we obtain a solution of optimization problem by decreasing temperature (thermal fluctuation) gradually. In the quantum annealing, in contrast, we decrease quantum field (quantum fluctuation) gradually and obtain a solution. In this paper we review how to implement quantum annealing and show some quantum fluctuation effects in frustrated Ising spin systems.

Tanaka, Shu

2012-01-01

63

Quantum Annealing and Quantum Fluctuation Effect in Frustrated Ising Systems

Quantum annealing method has been widely attracted attention in statistical physics and information science since it is expected to be a powerful method to obtain the best solution of optimization problem as well as simulated annealing. The quantum annealing method was incubated in quantum statistical physics. This is an alternative method of the simulated annealing which is well-adopted for many optimization problems. In the simulated annealing, we obtain a solution of optimization problem by decreasing temperature (thermal fluctuation) gradually. In the quantum annealing, in contrast, we decrease quantum field (quantum fluctuation) gradually and obtain a solution. In this paper we review how to implement quantum annealing and show some quantum fluctuation effects in frustrated Ising spin systems.

Tanaka, Shu; Tamura, Ryo

2013-09-01

64

Quantum mappings and the problem of stochasticity in quantum systems

International Nuclear Information System (INIS)

Discrete mappings for a dynamical quantum system possessing in the classical limit (h = 0) the property of stochasticity are analysed. The quasiclassical approximation is shown to be valid for the limited time and the asymptotic behaviour of the system for large times is to be determined by the quantum effects essentially. Contrary to the classical case when the correlation function decreases exponentially, the correlations decay with a powerlaw in the quantum case. This results in zero entropy of the quantum dynamical system while the entropy is nonzero in the classical limit case. It is shown that there is a quasiclassical region in which the quantum system dynamics is close to the stochastic dynamics of the corresponding classical system for a finite time. The parameter separating this quasiclassical region from the region of essentially quantum dynamics is obtained. (orig.)

1982-01-01

65

Quantum chaos in nanoelectromechanical systems

We present a theoretical study of the electron-phonon coupling in suspended nanoelectromechanical systems (NEMS) and investigate the resulting quantum chaotic behavior. The phonons are associated with the vibrational modes of a suspended rectangular dielectric plate, with free or clamped boundary conditions, whereas the electrons are confined to a large quantum dot (QD) on the plate's surface. The deformation potential and piezoelectric interactions are considered. By performing standard energy-level statistics we demonstrate that the spectral fluctuations exhibit the same distributions as those of the Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE), therefore evidencing the emergence of quantum chaos. That is verified for a large range of material and geometry parameters. In particular, the GUE statistics occurs only in the case of a circular QD. It represents an anomalous phenomenon, previously reported for just a small number of systems, since the problem is time-reversal invarian...

Gusso, A; Rego, L G C; Gusso, Andre; Rego, Luis G. C.

2005-01-01

66

Entangled systems. New directions in quantum physics

International Nuclear Information System (INIS)

Entangled Systems is an introductory textbook for advanced students of physics, chemistry and computer science which covers an area of physics that has lately witnessed rapid expansion. The topics treated here include foundations of quantum theory, quantum information, quantum communication, quantum computing, quantum teleportation and hidden variables, thus providing not only a solid basis for the study of quantum theory as such, but also a profound foundation of knowledge from which readers can follow the rapid development of the topic or start out into a more specialized branch of research. Commented recommendations for further reading as well as end-of-chapter problems help the reader to access quickly the basic theoretical concepts of future key technologies. Only a basic prior knowledge of quantum theory and the necessary mathematical foundations is assumed, as introductory chapters are provided to present these to the readers. Thus, 'Entangled Systems' can be used both as a course book and for self-study purposes. From the contents: - The Mathematical Framework - Basic Concepts of Quantum Theory - The Simplest Quantum Systems: Qubits - Mixed State and Density Operator - Shannon's Entropy and Classical Information - The von Neumann Entropy and Quantum Information - Composite Systems - Entanglement - Correlations and Non-Local Measurements - There is no (Local-Realistic) Alternative to the Quantum Theory - Working with Entanglement - The Quantum Computer - General Measurements, POVM - The General Evolution of an Open Quantum System and Special Quantum Channels - Decoherence and Approaches to the Description of the Quantum Measurement Process - Two Implementations of Quantum Operations. (orig.)

2007-01-01

67

On quantum mechanics for macroscopic systems

International Nuclear Information System (INIS)

The parable of Schroedinger's cat may lead to several up-to date questions: how to treat open systems in quantum theory, how to treat thermodynamically irreversible processes in the quantum mechanics framework, how to explain, following the quantum theory, the existence, phenomenologically evident, of classical observables, what implies the predicted existence by the quantum theory of non localized macroscopic material object ?

1992-01-01

68

Quantum gate entangler for general multipartite systems

We construct quantum gate entangler for general multipartite states based on topological unitary operators. We show that these operators can entangle quantum states if they satisfy the separability condition that is given by the complex multi-projective Segre variety. We also in detail discuss the construction of quantum gate entangler for higher dimensional bipartite and three-partite quantum systems.

Heydari, H

2007-01-01

69

Quantum Bi-Hamiltonian Systems

We define quantum bi-Hamiltonian systems, by analogy with the classical case, as derivations in operator algebras which are inner derivations with respect to two compatible associative structures. We find such structures by means of the associative version of Nijenhuis tensors. Explicit examples, e.g. for the harmonic oscillator, are given.

Cariñena, J F; Marmo, G; Cari\\~nena, Jos\\'e F.; Grabowski, Janusz; Marmo, Giuseppe

2000-01-01

70

Hamiltonian systems on quantum spaces

In this paper we consider Hamiltonian systems on the quantum plane and we show that the set of Q-meromorphic Hamiltonians is a Virasoro algebra with central charge zero and the set of Hamiltonian derivations of the algebra of Q-analytic functions {\\cal A}_q with values in the algebra of Q-meromorphic functions {\\cal M}_q is the Lie algebra sl(2,A_1(q)). Moreover we will show that any motion on a quantum space is associated with a quadratic Hamiltonian.

Abad, D

1995-01-01

71

Structure of propagators for quantum nondemolition systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the scheme of a quantum nondemolition (QND) measurement, an observable is measured without perturbing its evolution. In the context of studies of decoherence in quantum computing, we examine the `open' quantum system of a two-level atom, or equivalently, a spin-1/2 system, in interaction with quantum reservoirs of either oscillators or spins, under the QND condition of the Hamiltonian of the system commuting with the system-reservoir interaction. The propagators for these...

Banerjee, Subhashish; Ghosh, R.

2006-01-01

72

Polygamy of Entanglement in Multipartite Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that bipartite entanglement distribution (or entanglement of assistance) in multipartite quantum systems is by nature polygamous. We first provide an analytic upper bound for the concurrence of assistance in bipartite quantum systems, and derive a polygamy inequality of multipartite entanglement in arbitrary dimensional quantum systems.

Kim, Jeong San

2009-01-01

73

Eigenfunctions in chaotic quantum systems

Energy Technology Data Exchange (ETDEWEB)

The structure of wavefunctions of quantum systems strongly depends on the underlying classical dynamics. In this text a selection of articles on eigenfunctions in systems with fully chaotic dynamics and systems with a mixed phase space is summarized. Of particular interest are statistical properties like amplitude distribution and spatial autocorrelation function and the implication of eigenfunction structures on transport properties. For systems with a mixed phase space the separation into regular and chaotic states does not always hold away from the semiclassical limit, such that chaotic states may completely penetrate into the region of the regular island. The consequences of this flooding are discussed and universal aspects highlighted. (orig.)

Baecker, Arnd

2007-07-01

74

Eigenfunctions in chaotic quantum systems

International Nuclear Information System (INIS)

The structure of wavefunctions of quantum systems strongly depends on the underlying classical dynamics. In this text a selection of articles on eigenfunctions in systems with fully chaotic dynamics and systems with a mixed phase space is summarized. Of particular interest are statistical properties like amplitude distribution and spatial autocorrelation function and the implication of eigenfunction structures on transport properties. For systems with a mixed phase space the separation into regular and chaotic states does not always hold away from the semiclassical limit, such that chaotic states may completely penetrate into the region of the regular island. The consequences of this flooding are discussed and universal aspects highlighted. (orig.)

2007-01-01

75

Perturbative approach to Markovian open quantum systems

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical.

Li, Andy C. Y.; Petruccione, F.; Koch, Jens

2014-01-01

76

Perturbative approach to Markovian open quantum systems.

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical. PMID:24811607

Li, Andy C Y; Petruccione, F; Koch, Jens

2014-01-01

77

Perturbative approach to Markovian open quantum systems

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical.

Li, Andy C. Y.; Petruccione, F.; Koch, Jens

2014-05-01

78

Classical and quantum correlative capacities of quantum systems

International Nuclear Information System (INIS)

How strongly can one system be correlated with another? In the classical world, this basic question concerning correlative capacity has a very satisfying answer: The ''effective size'' of the marginal system, as quantified by the Shannon entropy, sets a tight upper bound to the correlations, as quantified by the mutual information. Although in the quantum world bipartite correlations, like their classical counterparts, are also well quantified by mutual information, the similarity ends here: The correlations in a bipartite quantum system can be twice as large as the marginal entropy. In the paradigm of quantum discord, the correlations are split into classical and quantum components, and it was conjectured that both the classical and quantum correlations are (like the classical mutual information) bounded above by each subsystem's entropy. In this work, by exploiting the interplay between entanglement of formation, mutual information, and quantum discord, we disprove that conjecture. We further indicate a scheme to restore harmony between quantum and classical correlative capacities. The results illustrate dramatically the asymmetric nature of quantum discord and highlight some subtle and unusual features of quantum correlations.

2011-10-01

79

Quantum systems, channels, information. A mathematical introduction

Energy Technology Data Exchange (ETDEWEB)

The subject of this book is theory of quantum system presented from information science perspective. The central role is played by the concept of quantum channel and its entropic and information characteristics. Quantum information theory gives a key to understanding elusive phenomena of quantum world and provides a background for development of experimental techniques that enable measuring and manipulation of individual quantum systems. This is important for the new efficient applications such as quantum computing, communication and cryptography. Research in the field of quantum informatics, including quantum information theory, is in progress in leading scientific centers throughout the world. This book gives an accessible, albeit mathematically rigorous and self-contained introduction to quantum information theory, starting from primary structures and leading to fundamental results and to exiting open problems.

Holevo, Alexander S.

2012-07-01

80

Quantum mechanics of damped systems

We show that the quantization of a simple damped system leads to a self-adjoint Hamiltonian with a family of complex generalized eigenvalues. It turns out that they correspond to the poles of energy eigenvectors when continued to the complex energy plane. Therefore, the corresponding generalized eigenvectors may be interpreted as resonant states. We show that resonant states are responsible for the irreversible quantum dynamics of our simple model.

Chruscinski, D

2003-01-01

81

Quantum chaotic attractor in a dissipative system

A dissipative quantum system is treated here by coupling it with a heat bath of harmonic oscillators. Through quantum Langevin equations and Ehrenfest's theorem, we establish explicitly the quantum Duffing equations with a double-well potential chosen. A quantum noise term appears the only driving force in dynamics. Numerical studies show that the chaotic attractor exists in this system while chaos is certainly forbidden in the classical counterpart.

Liu, W V; Schieve, William C.

1997-01-01

82

Enhanced autocompensating quantum cryptography system.

We have improved the hardware and software of our autocompensating system for quantum key distribution by replacing bulk optical components at the end stations with fiber-optic equivalents and implementing software that synchronizes end-station activities, communicates basis choices, corrects errors, and performs privacy amplification over a local area network. The all-fiber-optic arrangement provides stable, efficient, and high-contrast routing of the photons. The low-bit error rate leads to high error-correction efficiency and minimizes data sacrifice during privacy amplification. Characterization measurements made on a number of commercial avalanche photodiodes are presented that highlight the need for improved devices tailored specifically for quantum information applications. A scheme for frequency shifting the photons returning from Alice's station to allow them to be distinguished from backscattered noise photons is also described. PMID:11921790

Bethune, Donald S; Navarro, Martha; Risk, William P

2002-03-20

83

Quantum Friction: Cooling Quantum Systems with Unitary Time Evolution

We introduce a type of quantum dissipation -- local quantum friction -- by adding to the Hamiltonian a local potential that breaks time-reversal invariance so as to cool the system. Unlike the Kossakowski-Lindblad master equation, local quantum friction directly effects unitary evolution of the wavefunctions rather than the density matrix: it may thus be used to cool fermionic many-body systems with thousands of wavefunctions that must remain orthogonal. In addition to providing an efficient way to simulate quantum dissipation and non-equilibrium dynamics, local quantum friction coupled with adiabatic state preparation significantly speeds up many-body simulations, making the solution of the time-dependent Schr\\"odinger equation significantly simpler than the solution of its stationary counterpart.

Bulgac, Aurel; Roche, Kenneth J; Wlaz?owski, Gabriel

2013-01-01

84

Simulation of n-qubit quantum systems. V. Quantum measurements

The FEYNMAN program has been developed during the last years to support case studies on the dynamics and entanglement of n-qubit quantum registers. Apart from basic transformations and (gate) operations, it currently supports a good number of separability criteria and entanglement measures, quantum channels as well as the parametrizations of various frequently applied objects in quantum information theory, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions. With the present update of the FEYNMAN program, we provide a simple access to (the simulation of) quantum measurements. This includes not only the widely-applied projective measurements upon the eigenspaces of some given operator but also single-qubit measurements in various pre- and user-defined bases as well as the support for two-qubit Bell measurements. In addition, we help perform generalized and POVM measurements. Knowing the importance of measurements for many quantum information protocols, e.g., one-way computing, we hope that this update makes the FEYNMAN code an attractive and versatile tool for both, research and education. New version program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 210 No. of bytes in distributed program, including test data, etc.: 1 960 471 Distribution format: tar.gz Programming language: Maple 12 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; the program has been tested under Microsoft Windows XP and Linux Classification: 4.15 Catalogue identifier of previous version: ADWE_v4_0 Journal reference of previous version: Comput. Phys. Commun. 179 (2008) 647 Does the new version supersede the previous version?: Yes Nature of problem: During the last decade, the field of quantum information science has largely contributed to our understanding of quantum mechanics, and has provided also new and efficient protocols that are used on quantum entanglement. To further analyze the amount and transfer of entanglement in n-qubit quantum protocols, symbolic and numerical simulations need to be handled efficiently. Solution method: Using the computer algebra system Maple, we developed a set of procedures in order to support the definition, manipulation and analysis of n-qubit quantum registers. These procedures also help to deal with (unitary) logic gates and (nonunitary) quantum operations and measurements that act upon the quantum registers. All commands are organized in a hierarchical order and can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems, both in ideal and noisy quantum circuits. Reasons for new version: Until the present, the FEYNMAN program supported the basic data structures and operations of n-qubit quantum registers [1], a good number of separability and entanglement measures [2], quantum operations (noisy channels) [3] as well as the parametrizations of various frequently applied objects, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions [4]. With the current extension, we here add all necessary features to simulate quantum measurements, including the projective measurements in various single-qubit and the two-qubit Bell basis, and POVM measurements. Together with the previously implemented functionality, this greatly enhances the possibilities of analyzing quantum information protocols in which measurements play a central role, e.g., one-way computation. Running time: Most commands require ?10 seconds of processor time on a Pentium 4 processor with ?2 GHz RAM or newer, if they work with quantum registers with five or less qubits. Moreover, about 5-20 MB of working memory is typically n

Radtke, T.; Fritzsche, S.

2010-02-01

85

Classical and quantum dissipative systems

This book discusses issues associated with the quantum mechanical formulation of dissipative systems. It begins with an introductory review of phenomenological damping forces, and the construction of the Lagrangian and Hamiltonian for the damped motion. It is shown, in addition to these methods, that classical dissipative forces can also be derived from solvable many-body problems. A detailed discussion of these derived forces and their dependence on dynamical variables is also presented. The second part of this book investigates the use of classical formulation in the quantization of dynamica

Razavy, Mohsen

2006-01-01

86

Quantum Stochastic Processes, Quantum Iterated Function Systems and Entropy

We describe some basic results for Quantum Stochastic Processes and present some new results about a certain class of processes which are associated to Quantum Iterated Function Systems (QIFS). We discuss questions related to the Markov property and we present a definition of entropy which is induced by a QIFS. This definition is a natural generalization of the Shannon-Kolmogorov entropy from Ergodic Theory. This definition is different from the one in the paper "A Thermodynamic Formalism for density matrices in Quantum Information" by the same authors.

Baraviera, A; Lopes, A O; Cunha, M Terra

2009-01-01

87

Thermal quantum Fisher information in quantum dot system

Using the quantum Fisher information (QFI), we investigate the problem of the parameter estimation in quantum system dot (QDS) including the effects of different parameters. We find that the QFI is affected by the strength temperature and might be finite even for higher temperatures in the asymptotic limit. Furthermore, we show that there is an optimal value of temperature such that the precision of the parameter estimation is maximal and that revivals and retardation of information loss may occur by adjusting the initial conditions. Finally, we show that this quantity may be proposed to detect the amount of the total quantum information that a QDS state contains with respect to projective measurements.

Berrada, K.

2014-04-01

88

Past Quantum States of a Monitored System

DEFF Research Database (Denmark)

A density matrix Ï(t) yields probabilistic information about the outcome of measurements on a quantum system. We introduce here the past quantum state, which, at time T, accounts for the state of a quantum system at earlier times t

Gammelmark, SÃ¸ren; Julsgaard, Brian

2013-01-01

89

Thermalization of isolated quantum systems

Understanding the evolution towards thermal equilibrium of an isolated quantum system is at the foundation of statistical mechanics and a subject of interest in such diverse areas as cold atom physics or the quantum mechanics of black hole formation. Since a pure state can never evolve into a thermal density matrix, the Eigenstate Thermalization Hypothesis (ETH) has been put forward by Deutsch and Srednicki as a way to explain this apparent thermalization, similarly to what the ergodic theorem does in classical mechanics. In this paper this hypothesis is tested numerically. First, it is observed that thermalization happens in a subspace of states (the Krylov subspace) with dimension much smaller than that of the total Hilbert space. We check numerically the validity of ETH in such a subspace, for a system of hard core bosons on a two-dimensional lattice. We then discuss how well the eigenstates of the Hamiltonian projected on the Krylov subspace represent the true eigenstates. This discussion is aided by brin...

Khlebnikov, Sergei

2013-01-01

90

Hybrid quantum systems of atoms and ions

In recent years, ultracold atoms have emerged as an exceptionally controllable experimental system to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Here we go one step further and explore how cold atoms can be combined with other quantum systems to create new quantum hybrids with tailored properties. Coupling atomic quantum many-body states to an independently controllable single-particle gives access to a wealth of novel physics and to completely new detection and manipulation techniques. We report on recent experiments in which we have for the first time deterministically placed a single ion into an atomic Bose Einstein condensate. A trapped ion, which currently constitutes the most pristine single particle quantum system, can be observed and manipulated at the single particle level. In this single-particle/many-body composite quantum system we show sympathetic cooling of the ion and observe chemical reactions of single particles in situ...

Zipkes, Christoph; Palzer, Stefan; Sias, Carlo; Köhl, Michael

2010-01-01

91

Statistical Thermodynamics of Polymer Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Polymer quantum systems are mechanical models quantized similarly as loop quantum gravity. It is actually in quantizing gravity that the polymer term holds proper as the quantum geometry excitations yield a reminiscent of a polymer material. In such an approach both non-singular cosmological models and a microscopic basis for the entropy of some black holes have arisen. Also important physical questions for these systems involve thermodynamics. With this motivation, in this work, we study the...

2011-01-01

92

Stochastic processes associated with quantum systems

Energy Technology Data Exchange (ETDEWEB)

Stochastic processes have been useful in constructing and studying states in Quantum Field Theory. By analytically continuing into imaginary time, we may in certain cases replace the non-commutative algebra of observables of the quantum system by a commutative algebra consisting of funcions of a stochastic process. In this article we are going to discuss an appropriate mathematical framework for this connection between quantum systems and stochastic processes.

Klein, A. (California Univ., Irvine (USA). Dept. of Mathematics)

1981-11-01

93

Repeated interactions in open quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Analyzing the dynamics of open quantum systems has a long history in mathematics and physics. Depending on the system at hand, basic physical phenomena that one would like to explain are, for example, convergence to equilibrium, the dynamics of quantum coherences (decoherence) and quantum correlations (entanglement), or the emergence of heat and particle fluxes in non-equilibrium situations. From the mathematical physics perspective, one of the main challenges is to derive t...

Bruneau, Laurent; Joye, Alain; Merkli, Marco

2013-01-01

94

Manipulating Quantum Coherence in Solid State Systems

The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems", in Cluj-Napoca, Romania, August 29-September 9, 2005, presented a fundamental introduction to solid-state approaches to achieving quantum computation. This proceedings volume describes the properties of quantum coherence in semiconductor spin-based systems and the behavior of quantum coherence in superconducting systems. Semiconductor spin-based approaches to quantum computation have made tremendous advances in the past several years. Coherent populations of spins can be oriented, manipulated and detected experimentally. Rapid progress has been made towards performing the same tasks on individual spins (nuclear, ionic, or electronic) with all-electrical means. Superconducting approaches to quantum computation have demonstrated single qubits based on charge eigenstates as well as flux eigenstates. These topics have been presented in a pedagogical fashion by leading researchers in the fields of semiconductor-spin-based qu...

Flatté, Michael E

2007-01-01

95

Geometric Phase in Open Quantum Systems

Geometric phase of an open two-level quantum system with a squeezed, thermal environment is studied for various types of system-environment interactions, both non-dissipative and dissipative. In the former type, we consider quantum non-demolition interaction with a bath of harmonic oscillators as well as of that of two-level systems. In the latter type, we consider the system interacting with a bath of harmonic oscillators in the weak Born-Markov approximation, and further, a simplified Jaynes-Cummings model in a vacuum bath. Our results extend features of geometric phase in open systems reported in the literature to include effects due to squeezing. The Kraus operator representation is employed to connect the open-system effects to quantum noise processes familiar from quantum information theory. This study has some implications for a practical implementation of geometric quantum computation.

Banerjee, S; Banerjee, Subhashish

2006-01-01

96

Quantum information theory with Gaussian systems

International Nuclear Information System (INIS)

This thesis applies ideas and concepts from quantum information theory to systems of continuous-variables such as the quantum harmonic oscillator. The focus is on three topics: the cloning of coherent states, Gaussian quantum cellular automata and Gaussian private channels. Cloning was investigated both for finite-dimensional and for continuous-variable systems. We construct a private quantum channel for the sequential encryption of coherent states with a classical key, where the key elements have finite precision. For the case of independent one-mode input states, we explicitly estimate this precision, i.e. the number of key bits needed per input state, in terms of these parameters. (orig.)

2006-01-01

97

Robust Stability of Uncertain Quantum Systems

This paper considers the problem of robust stability for a class of uncertain quantum systems subject to unknown perturbations in the system Hamiltonian. Some general stability results are given for different classes of perturbations to the system Hamiltonian. Then, the special case of a nominal linear quantum system is considered with either quadratic or non-quadratic perturbations to the system Hamiltonian. In this case, robust stability conditions are given in terms of strict bounded real conditions.

Petersen, Ian R; James, Matthew R

2012-01-01

98

Understanding electronic systems in semiconductor quantum dots

International Nuclear Information System (INIS)

Systems of confined electrons are found everywhere in nature in the form of atoms where the orbiting electrons are confined by the Coulomb attraction of the nucleus. Advancement of nanotechnology has, however, provided us with an alternative way to confine electrons by using artificial confining potentials. A typical structure of this nature is the quantum dot, a nanoscale system which consists of few confined electrons. There are many types of quantum dots ranging from self-assembled to miniaturized semiconductor quantum dots. In this work we are interested in electrostatically confined semiconductor quantum dot systems where the electrostatic confining potential that traps the electrons is generated by external electrodes, doping, strain or other factors. A large number of semiconductor quantum dots of this type are fabricated by applying lithographically patterned gate electrodes or by etching on two-dimensional electron gases in semiconductor heterostructures. Because of this, the whole structure can be treated as a confined two-dimensional electron system. Quantum confinement profoundly affects the way in which electrons interact with each other, and external parameters such as a magnetic field. Since a magnetic field affects both the orbital and the spin motion of the electrons, the interplay between quantum confinement, electron–electron correlation effects and the magnetic field gives rise to very interesting physical phenomena. Thus, confined systems of electrons in a semiconductor quantum dot represent a unique opportunity to study fundamental quantum theories in a controllable atomic-like setup. In this work, we describe some common theoretical models which are used to study confined systems of electrons in a two-dimensional semiconductor quantum dot. The main emphasis of the work is to draw attention to important physical phenomena that arise in confined two-dimensional electron systems under various quantum regimes. (comment)

2013-11-01

99

Hartman effect and dissipative quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dwell time for dissipative quantum system is shown to increase with barrier width. It clearly precludes Hartman effect for dissipative systems. Here calculation has been done for inverted parabolic potential barrier.

Bhattacharya, Samyadeb; Roy, Sisir

2012-01-01

100

Mixing and entropy increase in quantum systems

International Nuclear Information System (INIS)

This paper attempts to explain the key feature of deterministic chaotic classical systems and how they can be translated to quantum systems. To do so we develop the appropriate algebraic language for the non-specialist. 22 refs. (Author)

1989-01-01

101

Classical approaches to quantum dynamical systems

International Nuclear Information System (INIS)

Quantum dynamical systems are often investigated by classical or semi-classical approaches. Classical methods are applied when a full quantum mechanical treatment is not feasible. They allow to work in the framework of familiar classical concepts and to investigate the quantum-to-classical transition However, the limits of classical approaches to quantum dynamical systems are often not very well understood. In our contribution, we investigate the validity and the limits of the classical trajectory Monte Carlo method by comparing the dynamics of non-interacting classical particles under the evolution of the Liouville equation with the quantum dynamics in phase space under the quantum Liouville equation. Our results allow us to estimate in which setups quantum effects become non-negligible. We show that a modified classical trajectory Monte Carlo method becomes equivalent to the actual quantum dynamics in the limit that all forces are harmonic. This method allows us to study time-dependent processes in driven many particle quantum systems with harmonic interactions.

2011-03-13

102

Nonequilibrium Quantum Evolution of Open Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We apply the Liouville-von Neumann (LvN) approach to open systems to describe the nonequilibrium quantum evolution. The Liouville-von Neumann approach is a unified method that can be applied to both time-independent (closed) and time-dependent (open) systems and to both equilibrium and nonequilibrium systems. We study the nonequilibrium quantum evolution of oscillator models for open boson and fermion systems

Kim, Sang Pyo

1999-01-01

103

Quantum Walk of Two Quantum Particles on One Dimensional System

Directory of Open Access Journals (Sweden)

Full Text Available We study two particle quantum walks on one dimensional chain. Probability distribution of two particle quantum walks is dependent on the initial state, and symmetric quantum walk or asymmetric quantum walk is analogous to that of one particle quantum walk. The quantum correlation probability is much different from classical coincidence probability. The difference reflects quantum interference between two particles.

Yongmei Zhang

2013-11-01

104

Entanglement properties of composite quantum systems

We present here an overview of our work concerning entanglement properties of composite quantum systems. The characterization of entanglement, i.e. the possibility to assert if a given quantum state is entangled with others and how much entangled it is, remains one of the most fundamental open questions in quantum information theory. We discuss our recent results related to the problem of separability and distillability for distinguishable particles, employing the tool of witness operators. Finally, we also state our results concerning quantum correlations for indistinguishable particles.

Eckert, K; Hulpke, F; Hyllus, P; Korbicz, J; Mompart, J; Bruss, D; Lewenstein, M; Sanpera, A

2002-01-01

105

Is the Universe a Quantum System?

In order to relate the probabilistic predictions of quantum theory uniquely to measurement results, one has to conceive of an ensemble of identically prepared copies of the quantum system under study. Since the universe is the total domain of physical experience, it cannot be copied, not even in a thought experiment. Therefore, a quantum state of the whole universe can never be made accessible to empirical test. Hence the existence of such a state is only a metaphysical idea. Despite prominent claims to the contrary, recent developments in the quantum-interpretation debate do not invalidate this conclusion.

Fink, H; Fink, Helmut; Leschke, Hajo

2000-01-01

106

Entanglement in quantum dissipative Ising spin systems

International Nuclear Information System (INIS)

We study the behavior of entanglement estimators on chains of few quantum Ising spins coupled to an environment by means of Monte Carlo simulations. We analyze the ground state value of the von Neumann entropy and the concurrence of our spins system for different couplings with the quantum bath

2007-09-01

107

Storing Images in Entangled Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce a new method of storing visual information in Quantum Mechanical systems which has certain advantages over more restricted classical memory devices. To do this we employ uniquely Quantum Mechanical properties such as Entanglement in order to store information concerning the position and shape of simple objects.

Venegas-andraca, S. E.; Ball, J. L.

2004-01-01

108

Quantum Dynamical Entropy of Spin Systems

We investigate a quantum dynamical entropy of one-dimesional quantum spin systems. We show that the dynamical entropy is bounded from above by a quantity which is related with group velocity determined by the interaction and mean entropy of the state.

Miyadera, T; Miyadera, Takayuki; Ohya, Masanori

2003-01-01

109

From open quantum systems to open quantum maps

For a class of quantized open chaotic systems satisfying a natural dynamical assumption, we show that the study of the resolvent, and hence of scattering and resonances, can be reduced to the study of a family of open quantum maps, that is of finite dimensional operators obtained by quantizing the Poincar\\'e map associated with the flow near the set of trapped trajectories.

Nonnenmacher, Stéphane; Zworski, Maciej

2010-01-01

110

Quantum Markov Semigroups (Product Systems and Subordination)

We show that if a product system comes from a quantum Markov semigroup, then it carries a natural Borel structure with respect to which the semigroup may be realized in terms of a measurable representation. We show, too, that the dual product system of a Borel product system also carries a natural Borel structure. We apply our analysis to study the order interval consisting of all quantum Markov semigroups that are subordinate to a given one.

Muhly, P S; Muhly, Paul S.; Solel, Baruch

2005-01-01

111

Nonequilibrium Dynamics of Strongly Correlated Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis, strongly correlated quantum many-body systems in equilibrium and in out-of-equilibrium situations are investigated. This is done by applying and developing well established numerical methods. The focus of the thesis lies in the development and application of the density matrix renormalization group method (DMRG) to quantum many-body systems out of equilbrium. In this thesis, in addition to the DMRG, methods for the exact diagonalization of the Hamiltonian of the system, like t...

Manmana, Salvatore Rosario

2006-01-01

112

Galilei invariant technique for quantum system description

Problems with quantum systems models, violating Galilei invariance are examined. The method for arbitrary non-relativistic quantum system Galilei invariant wave function construction, applying a modified basis where center-of-mass excitations have been removed before Hamiltonian matrix diagonalization, is developed. For identical fermion system, the Galilei invariant wave function can be obtained while applying conventional antisymmetrization methods of wave functions, dependent on single particle spatial variables.

Kamuntavi?ius, Gintautas P.

2014-04-01

113

Quantum discord from system–environment correlations

In an initially uncorrelated mixed separable bi-partite system, quantum correlations can emerge under the action of a local measurement or local noise [1]. We analyse this counter-intuitive phenomenon using quantum discord as a quantifier. We then relate changes in quantum discord to system–environment correlations between the system in a mixed state and some purifying environmental mode using the Koashi–Winter inequality. On this basis, we suggest an interpretation of discord as a byproduct of transferring entanglement and correlations around the different subsystems of a global pure state.

Tatham, R.; Korolkova, N.

2014-04-01

114

Optimal control of open quantum systems

International Nuclear Information System (INIS)

The present work deals with the application of Optimal Control Theory (OCT) to open quantum systems with a particular focus on solid-state quantum information processing devices. The latter are typically nanoscale structures that have to be manufactured, prepared, controlled and measured with an extraordinary degree of precision so that their quantum properties can be harnessed. Because array scalability is one of the main advantages of solid-state qubit realizations, they distinguish themselves as promising candidates for the implementation of efficient quantum information processors. However, these devices usually interact with a solid-state environment that may lead to adverse effects regarding their performance. Therefore, isolation of the nanostructure from its environment poses an important problem. This corresponds to a somewhat contradictory requirement since unwanted interactions can affect the quantum system by the same channels that are used to control the qubit. Closing these channels would lead to a reduction in the sensitivity with respect to environmental interacti

2010-01-01

115

Classical and Quantum Discrete Dynamical Systems

We study deterministic and quantum dynamics from a constructive "finite" point of view, since the introduction of a continuum, or other actual infinities in physics poses serious conceptual and technical difficulties, without any need for these concepts to physics as an empirical science. For a consistent description of the symmetries of dynamical systems at different times and the symmetries of the various parts of such systems, we introduce discrete analogs of the gauge connections. Gauge structures are particularly important to describe the quantum behavior. We show that quantum behavior is the result of a fundamental inability to trace the identity of indistinguishable objects in the process of evolution. Information is available only on invariant statements and values, relating to such objects. Using mathematical arguments of a general nature we can show that any quantum dynamics can be reduced to a sequence of permutations. Quantum interferences occur in the invariant subspaces of permutation representa...

Kornyak, Vladimir V

2013-01-01

116

Quantum dynamics of large systems

Using Feynman’s path integral representation of quantum mechanics, ensemble-averaged quantities (e.g. correlation functions or the reduced density matrix) are expressed in terms of a reduced dimension path integral, where the effects of the environment on the degrees of freedom of interest enter via an influence functional. We have introduced efficient semiclassical methods based on forward-backward propagation that can be used to evaluate influence functionals from anharmonic media. By combining the forward and backward time evolution operators into a single semiclassical propagation one avoids large action integrals. As a consequence, the semiclassical integrand is smooth and thus amenable to Monte Carlo methods. Due to dephasing effects, the nonlocality of the influence functional has a finite span. Exploiting this fact leads to an iterative procedure for evaluating the path integral on a systems-specific DVR grid. This scheme circumvents the sign problem, allowing accurate calculation of the dynamics over long time intervals. Fully semiclassical forward-backward treatment of all degrees of freedom, where combined forward-backward propagation is employed to eliminate the rapid oscillations of the integrand, are also described.

Makri, Nancy

2000-03-01

117

Software-defined Quantum Communication Systems

Energy Technology Data Exchange (ETDEWEB)

We show how to extend the paradigm of software-defined communication to include quantum communication systems. We introduce the decomposition of a quantum communication terminal into layers separating the concerns of the hardware, software, and middleware. We provide detailed descriptions of how each component operates and we include results of an implementation of the super-dense coding protocol. We argue that the versatility of software-defined quantum communication test beds can be useful for exploring new regimes in communication and rapidly prototyping new systems.

Humble, Travis S [ORNL; Sadlier, Ronald J [ORNL

2013-01-01

118

Quantum correlations in the collective spin systems

Quantum and classical pairwise correlations in two typical collective spin systems, i.e. the Dicke model and the Lipkin-Meshkov-Glick model are discussed. In the thermodynamical limit, analytical expressions of these correlations are derived. Within the effective technique proposed previously, theses correlations for finite size system can be also obtained numerically up to very large size. The scaling behavior for the quantum discord and its first derivative are analyzed. The comparison of the quantum discord and the concurrence are performed and essentially different behaviors are observed.

Wang, Chen; Chen, Qing-Hu

2012-01-01

119

Transmission and System Control in Quantum Cryptography

Directory of Open Access Journals (Sweden)

Full Text Available Quantum cryptography provides security using thelaws of quantum mechanics. Currently, several typesof protocols of quantum key distribution (QKD havebeen established. Some QKD protocols have beencertified by proofs of unconditional security. QKDprotocols have been confirmed to be resistant to anypossible attack. Along with the progress in keytransmission and post processing, the system controlneeds to be integrated with some steps for the QKD.No future technology can break such security. There isa sequence of process for implementing a QKDprotocol. Starting from clock synchronization function,real-time frame synchronization, transmission, postprocessingprotocols to system control and security. Inthis paper we are considering only transmission andsystem control for QKD.

Anand Sharma

2011-05-01

120

Extended objects in quantum systems

International Nuclear Information System (INIS)

A quantum field theoretical study of the properties of extended objects appearing in the quantum ordered state is carried out in the framework of boson theory. First the process of creation of the ordered state is studied, and then the creation of extended objects in quantum ordered states. It is found that the spontaneous creation of an ordered state is always caused by a symmetry rearrangement when the symmetry of the Heisenberg fields is global, and that in quantum electrodynamics the dynamic rearrangement of symmetry takes place even when no ordered state is created. The c-number field phi sup(f)(chi) constructed by the boson method becomes the soliton solution of the Euler equations when the Planck constant is ignored, implying that the soliton solution can be regarded as an extended object with quantum origin. Finally the relations between the basic symmetry of the theory and topological charge is analyzed. Although basic symmetry does not restrict the shape of extended objects appearing in the ordered state, it influences which object can be classified by topological quantum number. The condition for topological quantization of an extended object is expressed in terms of the asymptotic behaviour of the boson function

1979-01-01

121

Quantum Statistics of Interacting Dimer Spin Systems

The compound TlCuCl3 represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Wuertz [Phys. Rev. B 50, 13515 (1994)] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important.

Rüegg, C; Matsumoto, M; Niedermayer, C; Furrer, A; Krämer, K W; G"udel, H U; Bourges, P; Sidis, Y; Mutka, H; R\\"uegg, Ch.; Niedermayer, Ch.; Bourges, Ph.

2005-01-01

122

International Nuclear Information System (INIS)

We investigate the influence of environmental decoherence on the dynamics of a coupled qubit system and quantum correlation. We analyse the relationship between concurrence and the degree of initial entanglement or the purity of initial quantum state, and also their relationship with quantum discord. The results show that the decrease of the purity of an initial quantum state can induce the attenuation of concurrence or quantum discord, but the attenuation of quantum discord is obviously slower than the concurrence's, correspondingly the survival time of quantum discord is longer. Further investigation reveals that the robustness of quantum discord and concurrence relies on the entanglement degree of the initial quantum state. The higher the degree of entanglement, the more robust the quantum discord is than concurrence. And the reverse is equally true. Birth and death happen to quantum discord periodically and a newborn quantum discord comes into being under a certain condition, so does the concurrence

2012-11-01

123

Carrier Spin Polarization in Quantum Confined System

In this dissertation, systematic studies of magneto-photoluminescence of manganese-doped lead salt (Mn doped lead sulfide and lead selenide) quantum dots and core/shell quantum dots will be presented. It was observed that large carrier spin polarization can be obtained in manganese doped IV-VI lead salt quantum dots upon excitation by circularly polarized light; and a clear dependence of spin polarization on the sizes of quantum dots and thickness of core/shell quantum dots was observed as well. The quantum dots in this study were synthesized by solution-phase chemical method. The sizes of the quantum dots could be controlled by the growth temperature (50 to 150) and growth time (1min to 24hr). The doping concentrations in the compounds Pb1-xMn xS (or Pb1-xMnxSe) ranging from x = 0 to 8% can be adjusted by varying synthesis conditions as well. Studies on size dependence (from 3 to 10 nm), temperature dependence (from 7K to 50K), magnetic field dependence (from 0 to 7T), and laser power dependence (from 1mW to 20mW) of photoluminescence intensities and peak positions were systematically carried out. The spin-polarization, which was directly calculated from magneto-luminescence measurements, was studied as a function of quantum dot sizes, temperatures and magnetic fields. It was observed that, depending on the sizes and growth conditions (growth temperature and time), the spin polarization, as large as 40% at 7K in a 7T magnetic field, could be tuned in magnitude. Core/shell structured quantum dots with Mn2+ ions doped in the inner core or outer shell were also studied. The spin polarization was observed in core/shell system to decrease as thickness of the shell increases. We believe the wave function overlap between carriers and dopants can be tuned by quantum confinement and therefore the magnitude of exchange interactions can be tuned via varying the sizes of quantum dots or the shell thickness of core/shell quantum dots. There are a couple of measurements that showed inversion of spin polarization but the reproducibility is low. Further studies are needed to verify the possibility of reversing the sign of spin polarization through quantum confinement, i.e., varying the sizes of quantum dots or the shell thickness of core/shell quantum dots.

Long, Gen

124

CIME School on Quantum Many Body Systems

The book is based on the lectures given at the CIME school "Quantum many body systems" held in the summer of 2010. It provides a tutorial introduction to recent advances in the mathematics of interacting systems, written by four leading experts in the field: V. Rivasseau illustrates the applications of constructive Quantum Field Theory to 2D interacting electrons and their relation to quantum gravity; R. Seiringer describes a proof of Bose-Einstein condensation in the Gross-Pitaevski limit and explains the effects of rotating traps and the emergence of lattices of quantized vortices; J.-P. Solovej gives an introduction to the theory of quantum Coulomb systems and to the functional analytic methods used to prove their thermodynamic stability; finally, T. Spencer explains the supersymmetric approach to Anderson localization and its relation to the theory of random matrices. All the lectures are characterized by their mathematical rigor combined with physical insights.

Rivasseau, Vincent; Solovej, Jan Philip; Spencer, Thomas

2012-01-01

125

Dynamical effects of Stark-shifted quantum dots strongly coupled to photonic crystal cavities

Single semiconductor quantum-dots (QDs) strongly coupled to photonic crystal cavities are a strong candidate for single photon generation, ultra-fast all optical switching and quantum information processing. Recent experiments on coupled-cavity quantum dot systems show possible manipulation of emission wavelength of the dot through optical Stark effect. Interesting dynamical features arise when the Stark pulse duration is comparable to QD-cavity interaction time. Here, we present a theoretical treatment of these dynamical effects and investigate dynamical emission spectrum, energy transfer and single photon generation. We study these effects through numerical solution of the full master equation. We demonstrate that dynamic Stark effects can be used to generate ultra-fast indistinguishable single photons using rapid Stark tuning of the quantum dot. The theoretical limit for the speed is shown to be faster than adiabatic rapid passage technique used for microwave photon generation in circuit QED. A systematic study of role of device parameters such as pulse-shape, dot-cavity coupling and incoherent losses on the efficiency and speed of single photon generation is also presented for possible experimental realization.

Choudhury, Kaushik Roy; Bose, Ranojoy; Waks, Edo

2013-03-01

126

Conductance in double quantum well systems

International Nuclear Information System (INIS)

The object of this paper is to review the electronic conductance in double quantum well systems. These are quantum well structures in which electrons are confined in the z direction by large band gap material barrier layers, yet form a free two-dimensional Fermi gas within the sandwiched low band gap material layers in the x-y plane. Aspects related to the conductance in addition to the research progress made since the inception of such systems are included. While the review focuses on the tunnelling conductance properties of double quantum well devices, the longitudinal conductance is also discussed. Double quantum well systems are a more recent generation of structures whose precursors are the well known double-barrier resonant tunnelling systems. Thus, they have electronic signatures such as negative differential resistance, in addition to resonant tunnelling, whose behaviours depend on the wavefunction coupling between the quantum wells. As such, the barrier which separates the quantum wells can be tailored in order to provide better control of the device's electronic properties over their single well ancestors. (topical review)

2003-02-05

127

Computational Studies of Quantum Spin Systems

These lecture notes introduce quantum spin systems and several computational methods for studying their ground-state and finite-temperature properties. Symmetry-breaking and critical phenomena are first discussed in the simpler setting of Monte Carlo studies of classical spin systems, to illustrate finite-size scaling at continuous and first-order phase transitions. Exact diagonalization and quantum Monte Carlo (stochastic series expansion) algorithms and their computer implementations are then discussed in detail. Applications of the methods are illustrated by results for some of the most essential models in quantum magnetism, such as the S=1/2 Heisenberg antiferromagnet in one and two dimensions, as well as extended models useful for studying quantum phase transitions between antiferromagnetic and magnetically disordered states.

Sandvik, Anders W

2011-01-01

128

Quantum information processing in nanostructures

International Nuclear Information System (INIS)

Since information has been regarded os a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, 'nanostructures', through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results of quantum information theory and quantum computation are briefly reviewed. Next, the state-of-the-art of quantum dots technology is described. In so doing, the theoretical background and the practicalities required for this thesis are introduced. A discussion of the current quantum hardware used for quantum information processing is given. In particular, the solid-state proposals to date are emphasised. A detailed prescription is given, using an optically-driven coupled quantum dot system, to reliably prepare and manipulate exciton maximally entangled Bell and Greenberger-Horne-Zeilinger (GHZ) states. Manipulation of the strength and duration of selective light-pulses needed for producing these highly entangled states provides us with crucial elements for the processing of solid-state based quantum information. The all-optical generation of states of the so-called Bell basis for a system of two quantum dots (QDs) is exploited for performing the quantum teleportation of the excitonic state of a dot in an array of three coupled QDs. Theoretical predictions suggest that several hundred single quantum bit rotations and controlled-NOT gates could be performed before decoherence of the excitonic states takes place. In addition, the exciton coherent dynamics of a coupled QD system confined within a semiconductor single mode microcavity is reported. It is shown that this system enables the control of exciton entanglement by varying the coupling strength between the optically-driven dot system and the microcavity. The exciton entanglement shows collapses and revivals for suitable amplitudes of the incident radiation field and dot-cavity coupling strengths. The results given here could offer a new approach for the control of decoherence mechanisms arising from entangled 'artificial molecules'. In addition to these ultrafast coherent optical control proposals, an approach for reliable implementation of quantum logic gates and long decoherence times in a QD system based on nuclear magnetic resonance (NMR) is given, where the nuclear resonance is controlled by the ground state 'magic number' transitions of few-electron QDs in an external magnetic field. The dynamical evolution of quantum registers of arbitrary length in the presence of environmentally-induced decoherence effects is studied in detail. The cases of quantum bits (qubits) coupling individually to different environments ('independent decoherence'), and qubits interacting collectively with the same reservoir ('collective decoherence') are analysed in order to find explicit decoherence functions for any number of qubits. The decay of the coherences of the register is shown to strongly depend on the input states: this sensitivity is a characteristic of both types of coupling (collective and independent) and not only of the collective coupling, as has been reported previously. A non-trivial behaviour--'recoherence'-- is found in the decay of the off-diagonal elements of the reduced density matrix in the specific situation of independent decoherence. The results lead to the identification of decoherence-free states in the collective decoherence limit. These states belong to s

2002-01-01

129

Weakly-coupled systems in quantum control

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper provides rigorous definitions and analysis of the dynamics of weakly-coupled systems and gives sufficient conditions for an infinite dimensional quantum control system to be weakly-coupled. As an illustration we provide examples chosen among common physical systems.

2013-01-01

130

Bogolyubov kinetic equation for quantum dynamic systems

International Nuclear Information System (INIS)

The Weil representation of quantum-mechanic dynamic variables of the system is considered. At the very first stage of the problem solution the authors pass on to Weil symbols of the corresponding variables in the von Neuman equation. This gives the possibility of deriving opportune for investigation concrete systems of kinetic equations and permits to develop a consecutive approach to plotting of a closed kinetic equation for a case of a weak interaction of classical dynamic systems for a quantum case separating to the possible extent variables of the great and small systems in the equation

1985-01-01

131

Pairing in the quantum Hall system

Digital Repository Infrastructure Vision for European Research (DRIVER)

We find an analogy between the single skyrmion state in the quantum Hall system and the BCS superconducting state and address that the quantum mechanical origin of the skyrmion is electronic pairing. The skyrmion phase is found to be unstable for magnetic fields above the critical field $B_{c}(T)$ at temperature $T$, which is well represented by the relation $B_c(T)/B_{c}(0) \\approx {[1-(T/T_c)^3]}^{1/2}$.

Ahn, Kang-hun; Chang, K. J.

1997-01-01

132

Mathematical Modeling of Finite Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider the problem of quantum behavior in the finite background. Introduction of continuum or other infinities into physics leads only to technical complications without any need for them in description of empirical observations. The finite approach makes the problem constructive and more tractable. We argue that quantum behavior is a natural consequence of symmetries of dynamical systems. It is a result of fundamental impossibility to trace identity of indistinguishabl...

Kornyak, Vladimir V.

2011-01-01

133

Quantum contextuality in N-boson systems

Quantum contextuality in systems of identical bosonic particles is explicitly exhibited via the maximum violation of a suitable inequality of Clauser-Horne-Shimony-Holt type. Unlike the approaches considered so far, which make use of single-particle observables, our analysis involves collective observables constructed using multi-boson operators. An exemplifying scheme to test this violation with a quantum optical setup is also discussed.

Benatti, F; Genovese, M; Olivares, S

2011-01-01

134

Open quantum systems far from equilibrium

This monograph provides graduate students and also professional researchers aiming to understand the dynamics of open quantum systems with a valuable and self-contained toolbox. Special focus is laid on the link between microscopic models and the resulting open-system dynamics. This includes how to derive the celebrated Lindblad master equation without applying the rotating wave approximation. As typical representatives for non-equilibrium configurations it treats systems coupled to multiple reservoirs (including the description of quantum transport), driven systems, and feedback-controlled quantum systems. Each method is illustrated with easy-to-follow examples from recent research. Exercises and short summaries at the end of every chapter enable the reader to approach the frontiers of current research quickly and make the book useful for quick reference.

Schaller, Gernot

2014-01-01

135

Complex quantum systems analysis of large Coulomb systems

This volume is based on lectures given during the program Complex Quantum Systems held at the National University of Singapore's Institute for Mathematical Sciences from 17 February to 27 March 2010. It guides the reader through two introductory expositions on large Coulomb systems to five of the most important developments in the field: derivation of mean field equations, derivation of effective Hamiltonians, alternative high precision methods in quantum chemistry, modern many body methods originating from quantum information, and - the most complex - semirelativistic quantum electrodynamics.

Siedentop, Heinz

2013-01-01

136

Witnessing Quantum Coherence: from solid-state to biological systems

Quantum coherence is one of the primary non-classical features of quantum systems. While protocols such as the Leggett-Garg inequality (LGI) and quantum tomography can be used to test for the existence of quantum coherence and dynamics in a given system, unambiguously detecting inherent "quantumness" still faces serious obstacles in terms of experimental feasibility and efficiency, particularly in complex systems. Here we introduce two "quantum witnesses" to efficiently verify quantum coherence and dynamics in the time domain, without the expense and burden of non-invasive measurements or full tomographic processes. Using several physical examples, including quantum transport in solid-state nanostructures and in biological organisms, we show that these quantum witnesses are robust and have a much finer resolution in their detection window than the LGI has. These robust quantum indicators may assist in reducing the experimental overhead in unambiguously verifying quantum coherence in complex systems.

Li, Che-Ming; Chen, Yueh-Nan; Chen, Guang-Yin; Nori, Franco; 10.1038/srep00885

2012-01-01

137

Quantum scaling in many-body systems

This book on quantum phase transitions has been written by one of the pioneers in the application of scaling ideas to many-body systems - a new and exciting subject that has relevance to many areas of condensed matter and theoretical physics. One of the few books on the subject, it emphasizes strongly correlated electronic systems. Although dealing with complex problems in statistical mechanics, it does not lose sight of the experiments and the actual physical systems which motivate the theoretical work. The book starts by presenting the scaling theory of quantum critical phenomena. Critical e

Continentino, Mucio A

2001-01-01

138

Quantum Hall spherical systems: The filling fraction

International Nuclear Information System (INIS)

Within the recently formulated composite fermion hierarchy the filling fraction of a spherical quantum Hall system is obtained when it can be expressed as an odd or even denominator fraction. A plot of ?(2S/N-1) as a function of 2S for a constant number of particles (up to N=10001) exhibits a structure of the fractional quantum Hall effect. It is confirmed that ?e+?h=1 for all particle-hole conjugate systems, except systems with Ne=Nh and Ne=Nh±1. copyright 1997 The American Physical Society

1997-08-01

139

Superconducting Quantum Arrays for Broadband RF Systems

Superconducting Quantum Arrays (SQAs), homogenous arrays of Superconducting Quantum Cells, are developed for implementation of broadband radio frequency (RF) systems capable of providing highly linear magnetic signal to voltage transfer with high dynamic range, including active electrically small antennas (ESAs). Among the proposed quantum cells which are bi-SQUID and Differential Quantum Cell (DQC), the latter delivered better performance for SQAs. A prototype of the transformer-less active ESA based on a 2D SQA with nonsuperconducting electric connection of the DQCs was fabricated using HYPRES niobium process with critical current density 4.5 kA/cm2. The measured voltage response is characterized by a peak-to-peak swing of ~100 mV and steepness of ~6500 ?V/?T.

Kornev, V.; Sharafiev, A.; Soloviev, I.; Kolotinskiy, N.; Mukhanov, O.

2014-05-01

140

Quantum Simulation of Tunneling in Small Systems

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution. We show that physically interesting simulations of tunneling using 2 qubits (i.e. on 4 lattice point grids) may be performed with 40 single and two-qubit gates. Approximately 70 to 140 gates are needed to see interesting tunneling dynamics in three-qubit (8 lattice point) simulations.

Sornborger, Andrew T

2012-01-01

141

Statistical thermodynamics of polymer quantum systems

Polymer quantum systems are mechanical models quantized similarly as loop quantum gravity. It is actually in quantizing gravity that the polymer term holds proper as the quantum geometry excitations yield a reminiscent of a polymer material. In such an approach both non-singular cosmological models and a microscopic basis for the entropy of some black holes have arisen. Also important physical questions for these systems involve thermodynamics. With this motivation, in this work, we study the statistical thermodynamics of two one dimensional {\\em polymer} quantum systems: an ensemble of oscillators that describe a solid and a bunch of non-interacting particles in a box, which thus form an ideal gas. We first study the spectra of these polymer systems. It turns out useful for the analysis to consider the length scale required by the quantization and which we shall refer to as polymer length. The dynamics of the polymer oscillator can be given the form of that for the standard quantum pendulum. Depending on the...

Chacón-Acosta, Guillermo; Dagdug, Leonardo; Morales-Técotl, Hugo A

2011-01-01

142

Recent advances in quantum integrable systems

Energy Technology Data Exchange (ETDEWEB)

This meeting was dedicated to different aspects of the theory of quantum integrable systems. The organizers have intended to concentrate on topics related to the study of correlation functions, to systems with boundaries and to models at roots of unity. This document gathers the abstracts of 32 contributions, most of the contributions are accompanied by the set of transparencies.

Amico, L.; Belavin, A.; Buffenoir, E.; Castro Alvaredo, A.; Caudrelier, V.; Chakrabarti, A.; Corrig, E.; Crampe, N.; Deguchi, T.; Dobrev, V.K.; Doikou, A.; Doyon, B.; Feher, L.; Fioravanti, D.; Gohmann, F.; Hallnas, M.; Jimbo, M.; Konno, N.C.H.; Korchemsky, G.; Kulish, P.; Lassalle, M.; Maillet, J.M.; McCoy, B.; Mintchev, M.; Pakuliak, S.; Quano, F.Y.Z.; Ragnisco, R.; Ravanini, F.; Rittenberg, V.; Rivasseau, V.; Rossi, M.; Satta, G.; Sedrakyan, T.; Shiraishi, J.; Suzuki, N.C.J.; Yamada, Y.; Zamolodchikov, A.; Ishimoto, Y.; Nagy, Z.; Posta, S.; Sedra, M.B.; Zuevskiy, A.; Gohmann, F

2005-07-01

143

Recent advances in quantum integrable systems

International Nuclear Information System (INIS)

This meeting was dedicated to different aspects of the theory of quantum integrable systems. The organizers have intended to concentrate on topics related to the study of correlation functions, to systems with boundaries and to models at roots of unity. This document gathers the abstracts of 32 contributions, most of the contributions are accompanied by the set of transparencies

2005-09-06

144

Smooth Boundary Conditions For Quantum Lattice Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce a new type of boundary conditions, {\\it smooth boundary conditions}, for numerical studies of quantum lattice systems. In a number of circumstances, these boundary conditions have substantially smaller finite-size effects than periodic or open boundary conditions. They can be applied to nearly any short-ranged Hamiltonian system in any dimensionality and within almost any type of numerical approach.

Vekic, M.; White, S. R.

1993-01-01

145

Probability Distributions and Hilbert Spaces Quantum and Classical Systems

We use the fact that some linear Hamiltonian systems can be considered as ``finite level'' quantum systems, and the description of quantum mechanics in terms of probabilities, to associate probability distributions with this particular class of linear Hamiltonian systems.

Man'ko, V I

1999-01-01

146

Thermodynamics of quantum informational systems - Hamiltonian description

It is often claimed, that from a quantum system of d levels, and entropy S and heat bath of temperature T one can draw kT(ln d -S) amount of work. However, the usual arguments based on Szilard engine are not fully rigorous. Here we prove the formula within Hamiltonian description of drawing work from a quantum system and a heat bath, at a cost of entropy of the system. We base on the derivation of thermodynamical laws and quantities in [R. Alicki, J. Phys. A, 12, L103 (1979)] within a weak coupling limit. Our result provides fully physical scenario for extracting thermodynamical work from quantum correlations [J. Oppenheim et al. Phys. Rev. Lett. 89, 180402 (2002)]. We also derive Landauer principle as a consquence of second law within the considered model.

Alicki, R; Horodecki, P; Horodecki, R; Alicki, Robert; Horodecki, Michal; Horodecki, Pawel; Horodecki, Ryszard

2004-01-01

147

Geometric magnetism in open quantum systems

An isolated classical chaotic system, when driven by the slow change of several parameters, responds with two reaction forces: geometric friction and geometric magnetism. By using the theory of quantum fluctuation relations we show that this holds true also for open quantum systems, and provide explicit expressions for those forces in this case. This extends the concept of Berry curvature to the realm of open quantum systems. We illustrate our findings by calculating the geometric magnetism of a charged harmonic oscillator transported along a path in physical space in presence of a magnetic field and a thermal environment. We find that in this case the geometric magnetism is unaffected by the presence of the heat bath.

Campisi, Michele; Hänggi, Peter

2012-01-01

148

Entanglement in Many Body Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

THESIS SUMMARYTEXT:This thesis is made of two parts. In the first one, the issue of entanglement in many body systems is addressed. The concept of entanglement and some of the recent progress on the study of entropy of entanglement in many body quantum systems are reviewed. Emphasis is placed on the scaling properties of entropy for one-dimensional models at quantum phase transitions. Then, we focus on the area-law scaling of the entanglement entropy. An explicit computation in arbitrary dime...

Riera Graells, Arnau

2010-01-01

149

Entanglement in Many Body Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

[eng] THESIS SUMMARY TEXT: This thesis is made of two parts. In the first one, the issue of entanglement in many body systems is addressed. The concept of entanglement and some of the recent progress on the study of entropy of entanglement in many body quantum systems are reviewed. Emphasis is placed on the scaling properties of entropy for one-dimensional models at quantum phase transitions. Then, we focus on the area-law scaling of the entanglement entropy. An explicit computation in arbitr...

Riera Graells, Arnau

2010-01-01

150

Constraint algebra for interacting quantum systems

We consider relativistic constrained systems interacting with external fields. We provide physical arguments to support the idea that the quantum constraint algebra should be the same as in the free quantum case. For systems with ordering ambiguities this principle is essential to obtain a unique quantization. This is shown explicitly in the case of a relativistic spinning particle, where our assumption about the constraint algebra plus invariance under general coordinate transformations leads to a unique S-matrix. On leave from Dipartimento di Fisica Nucleare e Teorica, Università di Pavia and INFN, I-27100 Pavia, Italy.

Fubini, S.; Roncadelli, M.

1988-04-01

151

Effective resonance transitions in quantum systems

International Nuclear Information System (INIS)

Full text: (author)It is shown that quantum optical systems preserving the total number of excitations admit a simple classification of possible resonant transitions (including effective), which can be classified by analyzing the free Hamiltonian and the corresponding integrals of motion. Quantum systems not preserving the total number of excitations do not admit such a simple classification, so that an explicit form of the effective Hamiltonian is needed to specify the allowed resonances. The structure of the resonant transitions essentially depends on the algebraic properties of interacting subsystems

2006-07-03

152

Current in open quantum systems

We show that a dissipative current component is present in the dynamics generated by a Liouville-master equation, in addition to the usual component associated with Hamiltonian evolution. The dissipative component originates from coarse graining in time, implicit in a master equation, and needs to be included to preserve current continuity. We derive an explicit expression for the dissipative current in the context of the Markov approximation. Finally, we illustrate our approach with a simple numerical example, in which a quantum particle is coupled to a harmonic phonon bath and dissipation is described by the Pauli master equation.

Gebauer, R; Gebauer, Ralph; Car, Roberto

2004-01-01

153

Fluctuations of Quantum Statistical Two-Dimensional Systems of Electrons

The random matrix ensembles (RME) of quantum statistical Hamiltonian operators, {\\em e.g.} Gaussian random matrix ensembles (GRME) and Ginibre random matrix ensembles (Ginibre RME), are applied to following quantum statistical systems: nuclear systems, molecular systems, and two-dimensional electron systems (Wigner-Dyson electrostatic analogy). Measures of quantum chaos and quantum integrability with respect to eigenergies of quantum systems are defined and calculated. Quantum statistical information functional is defined as negentropy (either opposite of entropy or minus entropy). The distribution function for the random matrix ensembles is derived from the maximum entropy principle.

Duras, M M

2005-01-01

154

The thesis comprises two major themes of quantum statistical dynamics. One is the development of quantum dissipation theory (QDT). It covers the establishment of some basic relations of quantum statistical dynamics, the construction of several nonequivalent complete second-order formulations, and the development of exact QDT. Another is related to the applications of quantum statistical dynamics to a variety of research fields. In particular, unconventional but novel theories of the electron transfer in Debye solvents, quantum transport, and quantum measurement are developed on the basis of QDT formulations. The thesis is organized as follows. In Chapter 1, we present some background knowledge in relation to the aforementioned two themes of this thesis. The key quantity in QDT is the reduced density operator rho(t) ? trBrho T(t); i.e., the partial trace of the total system and bath composite rhoT(t) over the bath degrees of freedom. QDT governs the evolution of reduced density operator, where the effects of bath are treated in a quantum statistical manner. In principle, the reduced density operator contains all dynamics information of interest. However, the conventional quantum transport theory is formulated in terms of nonequilibrium Green's function. The newly emerging field of quantum measurement in relation to quantum information and quantum computing does exploit a sort of QDT formalism. Besides the background of the relevant theoretical development, some representative experiments on molecular nanojunctions are also briefly discussed. In chapter 2, we outline some basic (including new) relations that highlight several important issues on QDT. The content includes the background of nonequilibrium quantum statistical mechanics, the general description of the total composite Hamiltonian with stochastic system-bath interaction, a novel parameterization scheme for bath correlation functions, a newly developed exact theory of driven Brownian oscillator (DBO) systems, and its closely related solvation mode transformation of system-bath coupling Hamiltonian in general. The exact QDT of DBO systems is also used to clarify the validity of conventional QDT formulations that involve Markovian approximation. In Chapter 3, we develop three nonequivalent but all complete second-order QDT (CS-QDT) formulations. Two of them are of the conventional prescriptions in terms of time-local dissipation and memory kernel, respectively. The third one is called the correlated driving-dissipation equations of motion (CODDE). This novel CS-QDT combines the merits of the former two for its advantages in both the application and numerical implementation aspects. Also highlighted is the importance of correlated driving-dissipation effects on the dynamics of the reduced system. In Chapter 4, we construct an exact QDT formalism via the calculus on path integrals. The new theory aims at the efficient evaluation of non-Markovian dissipation beyond the weak system-bath interaction regime in the presence of time-dependent external field. By adopting exponential-like expansions for bath correlation function, hierarchical equations of motion formalism and continued fraction Liouville-space Green's function formalism are established. The latter will soon be used together with the Dyson equation technique for an efficient evaluation of non-perturbative reduced density matrix dynamics. The interplay between system-bath interaction strength, non-Markovian property, and the required level of hierarchy is also studied with the aid of simple spin-boson systems, together with the three proposed schemes to truncate the infinite hierarchy. In Chapter 5, we develop a nonperturbative theory of electron transfer (ET) in Debye solvents. The resulting exact and analytical rate expression is constructed on the basis of the aforementioned continued fraction Liouville-space Green's function formalism, together with the Dyson equation technique. Not only does it recover the celebrated Marcus' inversion and Kramers' turnover behaviors, the new theory also shows some disti

Cui, Ping

155

Long-range quantum discord in critical spin systems

International Nuclear Information System (INIS)

We show that quantum correlations as quantified by quantum discord can characterize quantum phase transitions by exhibiting nontrivial long-range decay as a function of distance in spin systems. This is rather different from the behavior of pairwise entanglement, which is typically short-ranged even in critical systems. In particular, we find a clear change in the decay rate of quantum discord as the system crosses a quantum critical point. We illustrate this phenomenon for first-order, second-order, and infinite-order quantum phase transitions, indicating that pairwise quantum discord is an appealing quantum correlation function for condensed matter systems. -- Highlights: ? Quantum discord may exhibit long-range decay in spin systems. ? Long-range behavior of discord occurs as the system crosses a critical point. ? Long-range behavior of discord is found for phase transitions of different orders. ? Discussion of discord as a function of distance is shown for several spin chains.

2012-04-02

156

Quantum temporal probabilities in tunneling systems

International Nuclear Information System (INIS)

We study the temporal aspects of quantum tunneling as manifested in time-of-arrival experiments in which the detected particle tunnels through a potential barrier. In particular, we present a general method for constructing temporal probabilities in tunneling systems that (i) defines ‘classical’ time observables for quantum systems and (ii) applies to relativistic particles interacting through quantum fields. We show that the relevant probabilities are defined in terms of specific correlation functions of the quantum field associated with tunneling particles. We construct a probability distribution with respect to the time of particle detection that contains all information about the temporal aspects of the tunneling process. In specific cases, this probability distribution leads to the definition of a delay time that, for parity-symmetric potentials, reduces to the phase time of Bohm and Wigner. We apply our results to piecewise constant potentials, by deriving the appropriate junction conditions on the points of discontinuity. For the double square potential, in particular, we demonstrate the existence of (at least) two physically relevant time parameters, the delay time and a decay rate that describes the escape of particles trapped in the inter-barrier region. Finally, we propose a resolution to the paradox of apparent superluminal velocities for tunneling particles. We demonstrate that the idea of faster-than-light speeds in tunneling follows from an inadmissible use of classical reasoning in the description of quantum systems. -- Highlights: •Present a general methodology for deriving temporal probabilities in tunneling systems. •Treatment applies to relativistic particles interacting through quantum fields. •Derive a new expression for tunneling time. •Identify new time parameters relevant to tunneling. •Propose a resolution of the superluminality paradox in tunneling

2013-09-01

157

Quantum temporal probabilities in tunneling systems

Energy Technology Data Exchange (ETDEWEB)

We study the temporal aspects of quantum tunneling as manifested in time-of-arrival experiments in which the detected particle tunnels through a potential barrier. In particular, we present a general method for constructing temporal probabilities in tunneling systems that (i) defines ‘classical’ time observables for quantum systems and (ii) applies to relativistic particles interacting through quantum fields. We show that the relevant probabilities are defined in terms of specific correlation functions of the quantum field associated with tunneling particles. We construct a probability distribution with respect to the time of particle detection that contains all information about the temporal aspects of the tunneling process. In specific cases, this probability distribution leads to the definition of a delay time that, for parity-symmetric potentials, reduces to the phase time of Bohm and Wigner. We apply our results to piecewise constant potentials, by deriving the appropriate junction conditions on the points of discontinuity. For the double square potential, in particular, we demonstrate the existence of (at least) two physically relevant time parameters, the delay time and a decay rate that describes the escape of particles trapped in the inter-barrier region. Finally, we propose a resolution to the paradox of apparent superluminal velocities for tunneling particles. We demonstrate that the idea of faster-than-light speeds in tunneling follows from an inadmissible use of classical reasoning in the description of quantum systems. -- Highlights: •Present a general methodology for deriving temporal probabilities in tunneling systems. •Treatment applies to relativistic particles interacting through quantum fields. •Derive a new expression for tunneling time. •Identify new time parameters relevant to tunneling. •Propose a resolution of the superluminality paradox in tunneling.

Anastopoulos, Charis, E-mail: anastop@physics.upatras.gr; Savvidou, Ntina, E-mail: ksavvidou@physics.upatras.gr

2013-09-15

158

Quantum frustrated and correlated electron systems

Directory of Open Access Journals (Sweden)

Full Text Available Quantum phases and fluctuations in correlated electron systems with frustration and competing interactions are reviewed. In the localized moment case the S=1/2 J1 - J2 - model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signature in magnetocaloric quantities and the high field magnetization are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides. In itinerant electron systems frustration is an emergent property caused by electron correlations. It leads to enhanced spin fluctuations in a very large region of momentum space and therefore may cause heavy fermion type low temperature anomalies as in the 3d spinel compound LiV2O4 . Competing on-site and inter-site electronic interactions in Kondo compounds are responsible for the quantum phase transition between nonmagnetic Kondo singlet phase and magnetic phase such as observed in many 4f compounds. They may be described by Kondo lattice and simplified Kondo necklace type models. Their quantum phase transitions are investigated by numerical exact diagonalization and analytical bond operator methods respectively.

P Thalmeier

2008-06-01

159

Unstable particles as open quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the probability preserving description of the decaying particle within the framework of quantum mechanics of open systems taking into account the superselection rule prohibiting the superposition of the particle and vacuum. In our approach the evolution of the system is given by a family of completely positive trace preserving maps forming one-parameter dynamical semigroup. We give the Kraus representation for the general evolution of such systems which allows one...

Caban, P.; Rembielinski, J.; Smolinski, K. A.; Walczak, Z.

2005-01-01

160

Relaxation phenomena in classical and quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Relaxation phenomena in three different classical and quantum systems are investigated. First, the role of multiplicative and additive noise in a classical metastable system is analyzed. The mean lifetime of the metastable state shows a nonmonotonic behavior with a maximum as a function of both the additive and multiplicative noise intensities. In the second system, the simultaneous action of thermal and non-Gaussian noise on the dynamics of an overdamped point Josephson junction is studied. ...

Spagnolo, Bernardo; Fiasconaro, Alessandro

2012-01-01

161

Quantum-mechanical aspects of classically chaotic driven systems

International Nuclear Information System (INIS)

This paper treats atoms and molecules in laser fields as periodically driven quantum systems. The paper concludes by determining that stochastic excitation is possible in quantum systems with quasiperiodic driving. 17 refs

1987-07-13

162

Effective Hamiltonian approach to periodically perturbed quantum optical systems

International Nuclear Information System (INIS)

We apply the method of Lie-type transformations to Floquet Hamiltonians for periodically perturbed quantum systems. Some typical examples of driven quantum systems are considered in the framework of this approach and corresponding effective time dependent Hamiltonians are found

2006-02-20

163

Lithography system using quantum entangled photons

A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.

Williams, Colin (Inventor); Dowling, Jonathan (Inventor); della Rossa, Giovanni (Inventor)

2002-01-01

164

Wigner quantum systems (Lie superalgebraic approach)

We present three groups of examples of Wigner Quantum Systems related to the Lie superalgebras $osp(1/6n)$, $sl(1/3n)$ and $sl(n/3)$ and discuss shortly their physical features. In the case of $sl(1/3n)$ we indicate that the underlying geometry is noncommutative.

Palev, T D

2002-01-01

165

Local unitary invariants for multipartite quantum systems

Energy Technology Data Exchange (ETDEWEB)

A method is presented to obtain local unitary invariants for multipartite quantum systems consisting of fermions or distinguishable particles. The invariants are organized into infinite families, in particular, the generalization to higher dimensional single-particle Hilbert spaces is straightforward. Many well-known invariants and their generalizations are also included.

Vrana, Peter, E-mail: vranap@math.bme.hu [Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics, H-1111 Budapest (Hungary)

2011-03-18

166

Statistics of skyrmions in Quantum Hall systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze statistical interactions of skyrmions in the quantum Hall system near a critical filling fraction in the framework of the Ginzburg-Landau model. The phase picked up by the wave-function during an exchange of two skyrmions close to $\

Dziarmaga, Jacek

1995-01-01

167

Quantum dissipation of a simple conservative system

International Nuclear Information System (INIS)

A model of quantum dissipative system is presented. Here dissipation of energy is demonstrated as based on the coupling of a free translational motion of a centre of mass to a harmonic oscillator. The two-dimensional arrangement of two coupled particles of different masses is considered.

2013-03-25

168

Hidden supersymmetry in quantum bosonic systems

International Nuclear Information System (INIS)

We show that some simple well-studied quantum mechanical systems without fermion (spin) degrees of freedom display, surprisingly, a hidden supersymmetry. The list includes the bound state Aharonov-Bohm, the Dirac delta and the Poeschl-Teller potential problems, in which the unbroken and broken N = 2 supersymmetry of linear and nonlinear (polynomial) forms is revealed

2007-10-01

169

We study how to protect quantum information in quantum systems subjected to local dissipation. We show that combining the use of three-level systems, environment monitoring, and local feedback can fully and deterministically protect any available quantum information, including entanglement initially shared by different parties. These results can represent a gain in resources and/or distances in quantum communication protocols such as quantum repeaters and teleportation as well as time for quantum memories. Finally, we show that monitoring local environments physically implements the optimum singlet conversion protocol, essential for classical entanglement percolation.

Mascarenhas, E; Cavalcanti, D; Cunha, M Terra; Santos, M França

2010-01-01

170

QUANTUM THEOREM OF CORRESPONDING STATES AND SPIN-POLARIZED QUANTUM SYSTEM

Digital Repository Infrastructure Vision for European Research (DRIVER)

A review of the thermodynamic properties of macroscopic quantum systems is given from the unified point of view provided by the Quantum Theorem of Corresponding States. These results are used to predict and discuss the thermodynamic properties of spin-polarized quantum systems.

Nosanow, L.

1980-01-01

171

Functional integral treatment of some quantum nondemolition systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the scheme of a quantum nondemolition (QND) measurement, an observable is measured without perturbing its evolution. In the context of studies of decoherence in quantum computing, we examine the `open' quantum system of a two-level atom, or equivalently, a spin-1/2 system, in interaction with quantum reservoirs of either oscillators or spins, under the QND condition of the Hamiltonian of the system commuting with the system-reservoir interaction. For completeness, we also...

Banerjee, Subhashish; Ghosh, R.

2006-01-01

172

An Operator-Based Exact Treatment of Open Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

"Quantum mechanics must be regarded as open systems. On one hand, this is due to the fact that, like in classical physics, any realistic system is subjected to a coupling to an uncontrollable environment which influences it in a non-negligible way. The theory of open quantum systems thus plays a major role in many applications of quantum physics since perfect isolation of quantum system is not possible and since a complete microscopic description or control of the environmen...

Nicolosi, S.

2005-01-01

173

Perfect eavesdropping on a quantum cryptography system

The stated goal of quantum key distribution (QKD) is to grow a secret key securely between two parties with a minimum of additional assumptions. The number of assumptions has been continuously reduced, from requiring the validity of quantum mechanics in early QKD, to more general constraints on the laws of physics in device-independent QKD. Despite steady theoretical progress in dealing with known limitations of current technology, in practice the security of QKD relies not only on the quantum protocol but on the physical implementation. A variety of attacks have been conceived to exploit weaknesses of current systems. Here we demonstrate the first full field implementation of an eavesdropper attacking an established QKD connection. The eavesdropper obtains the complete 'secret' key, while none of the results measured by the legitimate parties indicate a breach in security. This confirms that non-idealities in physical implementations of QKD can be fully exploitable.

Gerhardt, Ilja; Lamas-Linares, Antia; Skaar, Johannes; Kurtsiefer, Christian; Makarov, Vadim

2010-01-01

174

Quantum cryptographic system with reduced data loss

Energy Technology Data Exchange (ETDEWEB)

A secure method for distributing a random cryptographic key with reduced data loss is disclosed. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically. 23 figs.

Lo, H.K.; Chau, H.F.

1998-03-24

175

Quantum cryptographic system with reduced data loss

Energy Technology Data Exchange (ETDEWEB)

A secure method for distributing a random cryptographic key with reduced data loss. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically.

Lo, Hoi-Kwong (1309, Low Block, Lei Moon House Ap Lei Chau Estate, Hong Kong, HK); Chau, Hoi Fung (Flat C, 42nd Floor, Tower 1, University Heights 23 Pokfield Road, Pokfulam, Hong Kong, HK)

1998-01-01

176

Symmetry and stability of open quantum systems

International Nuclear Information System (INIS)

The presentation of the thesis involves an introduction and six chapters. Chapter 1 presents notions and results used in the other chpaters. Chapters 2-6 present our results which are focused on two notions: generalized observable and dynamic semigroup. These notions characterize a specific research domain (set up during the last 10 years) which is currently called quantum mechanics of open systems. The two notions (generalized observable and dynamic semigroup) are mathematically correlated. They belong to the set of completely positive linear applications among observable algebras. This fact, associated with that formulation of quantum mechanics according to which it is a special case of quantum mechanics namely, that for which the observable algebra is commutative, help to understand the similar essence of the results presented in chapter 2-6. Thus, the natural mathematical background has been achieved for our results; it is represented by that category whose objects are the observable algebras and whose morphisms are completely positive linear contractions generating unity within unity. These ideas are extensively presented in the introduction. The fact that the relations between classical mechanics and quantum mechanics can be rigorously treated as positive linear applications between classical observable algebras commutative and quantum observable algebras non-commutative, which are automatically fully positive, has been initially shown in our paper. (author)

1979-01-01

177

From quantum correlations in dissipative quantum walk to two-qubit systems

A dissipative quantum walk (according to the semigroup approach) has been used as the starting point from which to study quantum correlations in an open system. This system is a fruitful model that allows the definition of several bipartite systems (sets of qubits). Thus the quantum correlations and the decoherence properties induced by a phonon bath can be investigated analytically using tools from quantum information. In particular we have studied the negativity, concurrence and quantum discord for different bipartitions in our dissipative system, and we have found analytical expression for these measures, using a local initial condition for the density matrix of the walker. In general quantum correlations are affected by dissipation in a complex non-monotonic way, showing at long time an expected asymptotic decrease with the increase of the dissipation. In addition, our results for the quantum correlations can be used as an indicator of the transition from the quantum to the classical regimen, as has recently been shown experimentally.

Nizama, Marco; Cáceres, Manuel O.

2014-04-01

178

International Nuclear Information System (INIS)

Quantum-cryptography key distribution (QCKD) experiments have been recently reported using polarization-entangled photons. However, in any practical realization, quantum systems suffer from either unwanted or induced interactions with the environment and the quantum measurement system, showing up as quantum and, ultimately, statistical noise. In this paper, we investigate how an ideal polarization entanglement in spontaneous parametric down-conversion (SPDC) suffers quantum noise in its practical implementation as a secure quantum system, yielding errors in the transmitted bit sequence. Since all SPDC-based QCKD schemes rely on the measurement of coincidence to assert the bit transmission between the two parties, we bundle up the overall quantum and statistical noise in an exhaustive model to calculate the accidental coincidences. This model predicts the quantum-bit error rate and the sifted key and allows comparisons between different security criteria of the hitherto proposed QCKD protocols, resulting in an objective assessment of performances and advantages of different systems

2003-02-01

179

Periodic thermodynamics of isolated quantum systems.

The nature of the behavior of an isolated many-body quantum system periodically driven in time has been an open question since the beginning of quantum mechanics. After an initial transient period, such a system is known to synchronize with the driving; in contrast to the nondriven case, no fundamental principle has been proposed for constructing the resulting nonequilibrium state. Here, we analytically show that, for a class of integrable systems, the relevant ensemble is constructed by maximizing an appropriately defined entropy subject to constraints, which we explicitly identify. This result constitutes a generalization of the concepts of equilibrium statistical mechanics to a class of far-from-equilibrium systems, up to now mainly accessible using ad hoc methods. PMID:24785013

Lazarides, Achilleas; Das, Arnab; Moessner, Roderich

2014-04-18

180

Compact quantum systems and the Pauli data problem

Energy Technology Data Exchange (ETDEWEB)

Compact quantum systems have underlying compact kinematical Lie algebras, in contrast to familiar noncompact quantum systems built on the Weyl-Heisenberg algebra. Pauli asked in the latter case: to what extent does knowledge of the probability distributions in coordinate and momentum space determine the state vector The analogous questions for compact quantum system is raised, and some preliminary results are obtained.

Bracken, A.J. (Univ. of Queensland, Brisbane (Australia)); Fawcett, R.J.B. (Queensland Univ. of Technology, Brisbane (Australia))

1993-02-01

181

Quantum tunneling in multidimensional systems

Energy Technology Data Exchange (ETDEWEB)

The effects of coupling to a harmonic oscillator on the quantum tunneling of a macroscopic motion are studied through the influence functional formalism of Feynman's path integral method for the general coupling form factor. As an example, we consider the model in which the potential barrier is parabolic and the coupling Hamiltonian is linear in both coordinates of the macroscopic motion and of the intrinsic harmonic oscillator. The results are then compared with the exact solution obtained through the canonical transformation into normal coordinates in the limiting cases when the normal coordinates reduce to the original coordinates. We found that: (1) In the adiabatic case, i.e., when the recurrence time ..pi../..omega.. of the oscillator is much shorter than the transmission time through the macroscopic potential barrier, the effect of oscillator coupling can be well represented by an effective potential. The coupling enhances the tunneling probability on the whole. (2) There exists a critical energy, above which the tunneling probability is reduced because of the linear oscillator coupling. In the weak coupling limit and when ..omega -->..0, the critical energy becomes -infinity, so that the coupling to the oscillator always reduces the tunneling probability.

Lee, S.Y.; Takigawa, N.

1983-09-01

182

Thermo field dynamics of quantum spin systems

International Nuclear Information System (INIS)

Thermo field dynamics of quantum spin systems is formulated to give a new variational principle at finite temperatures. The KMS relation is reformulated as identities among thermal vacuum states. Path integral formulations of the thermal vacuum state are given which yield a new ''thermo field Monte Carlo method.'' Thermo field dynamics of finite-spin systems are studied in detail as simple examples of the present method. Perturbation expansion methods of the thermal state and time-dependent state are also given

1986-01-01

183

Nonequilibrium representative ensembles for isolated quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

An isolated quantum system is considered, prepared in a nonequilibrium initial state. In order to uniquely define the system dynamics, one has to construct a representative statistical ensemble. From the principle of least action it follows that the role of the evolution generator is played by a grand Hamiltonian, but not merely by its energy part. A theorem is proved expressing the commutators of field operators with operator products through variational derivatives of thes...

Yukalov, V. I.

2012-01-01

184

Entanglement entropy of a simple quantum system

We propose a simple approach to the calculation of the entanglement entropy of a spherically symmetric quantum system composed of two separate regions. We consider bound states of the system described by a wave function that is scale invariant and vanishes exponentially at infinity. Our result is in accordance with the holographic bound on entropy and shows that entanglement entropy scales with the area of the boundary.

Melis, Maurizio

2009-01-01

185

Towards the theory of control in observable quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

An operational description of the controlled Markov dynamics of quantum-mechanical system is introduced. The feedback control strategies with regard to the dynamical reduction of quantum states in the course of quantum real-time measurements are discribed in terms of quantum filtering of these states. The concept of sufficient coordinates for the description of the a posteriori quantum states from a given class is introduced, and it is proved that they form a classical Marko...

Belavkin, V. P.

2004-01-01

186

Quantum information processing based on cavity QED with mesoscopic systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Introduction: Recent developments in quantum communication and computing [1-3] stimulated an intensive search for physical systems that can be used for coherent processing of quantum information. It is generally believed that quantum entanglement of distinguishable quantum bits (qubits) is at the heart of quantum information processing. Significant efforts have been directed towards the design of elementary logic gates, which perform certain unitary processes on pairs of qubits. These gates m...

Lukin, Mikhail; Fleischhauer, Michael; Imamoglu, Atac

2000-01-01

187

Directory of Open Access Journals (Sweden)

Full Text Available In this article we give a generalization of Hartley's model for the measure of information. We propose a rate of emergence, which is applicable to systems obeying classical or quantum statistics. Quantum sys-tems that obey Fermi-Dirac statistics and Bose-Einstein condensate, as well as classical systems obey-ing the Maxwell-Boltzmann statistics have been con-sidered. We found that the emergence parameter of quantum and classical systems differ as well as the emergence parameter of quantum systems of fermions and bosons. Consequently, the emergence parameter might be used to distinguish the classical system and quantum system, as well as quantum system of fermions and the quantum system of bosons

Lutsenko Y. V.

2013-06-01

188

Macroscopic Interpretability of Quantum Component Systems

Preliminary accounts on three subjects are produced in Secs. 1, 2, 3. The guiding idea is Universality of Physics, by which we mean that the boundary between the system {S} that is selected, and which is described by Quantum Theory, and the macroscopic environment {A} where the single physical events as well as the events of ordinary life occur, which is described within a Boolean structure, may always be shifted by constructing a Quantum Model also of the environment {A} (to be selected from the "further environment"), as it is set forth in Sec. 1. This introduces the subject of Sec. 2, which examines what should be understood when saying that the quantum component system {A} may be macroscopically or at least "semimacroscopically" interpreted. In its turn this introduces Sec. 3, reporting two still unpublished theorems produced at Camerino 1988, which very closely connect the above requirements on the Quantum Model of {A} with some properties of the operations that the "instrument" {A} performs on {S}, with the result that the macroscopicity conditions of Sec. 2 turn out to be widely model-independent ("environmental").

Ascoli, R.

2006-06-01

189

Irreversible processes in quantum mechanical systems

International Nuclear Information System (INIS)

Although the information provided by the evolution of the density matrix of a quantum system is equivalent with the knowledge of all observables at a given time, it turns out ot be insufficient to answer certain questions in quantum optics or linear response theory where the commutator of certain observables at different space-time points is needed. In this doctoral thesis we prove the existence of density matrices for common probabilities at multiple times and discuss their properties and their characterization independent of a special representation. We start with a compilation of definitions and properties of classical common probabilities and correlation functions. In the second chapter we give the definition of a quantum mechanical Markov process and derive the properties of propagators, generators and conditional probabilities as well as their mutual relations. The third chapter is devoted to a treatment of quantum mechanical systems in thermal equilibrium for which the principle of detailed balance holds as a consequence of microreversibility. We work out the symmetry properties of the two-sided correlation functions which turn out to be analogous to those in classical processes. In the final chapter we use the Gaussian behavior of the stationary correlation function of an oscillator and determine a class of Markov processes which are characterized by dissipative Lionville operators. We succeed in obtaining the canonical representation in a purely algebraic way by means of similarity transformations. Starting from this representation it is particularly easy to calculate the propagator and the correlation function. (HJ) 891 HJ/HJ 892 MKO

1979-01-01

190

Simulating quantum systems on classical computers with matrix product states

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis, the numerical simulation of strongly-interacting many-body quantum-mechanical systems using matrix product states (MPS) is considered. Compared to classical systems, quantum many-body systems possess an exponentially enlarged number of degrees of freedom, significantly complicating a simulation on a classical computer. Matrix-Product-States are a novel representation of arbitrary quantum many-body states. Using quantum information theory, it is possible to show that Matrix-Pro...

Kleine, Adrian

2010-01-01

191

Quantum mechanics in general quantum systems (I): Exact solution

After proving and using a mathematical identity we deduce an expansion formula of operator binomials power. Then, in the unperturbed Hamiltonian representation, we find an explicit and general form of time evolution operator that is a $c$-number function and a power series of perturbation including all order approximations. Based on it, we obtain an exact solution of the Schr\\"{o}dinger equation in general quantum systems independent of time. Comparison of our exact solution with the existed perturbation theory makes some features and significance of our exact solution clear. The conclusions expressly indicate that our exact solution is obviously consistent with the usual time-independent perturbation theory at any order approximation, it explicitly calculates out the expanding coefficients of the unperturbed state in the non-perturbation method, and it fully solves the recurrence equation of the expansion coefficients of final state in the unperturbed Hamiltonian representation from a view of time-dependent ...

Wang, A M

2006-01-01

192

Mathematical Structure in Quantum Systems and applications

International Nuclear Information System (INIS)

This volume contains most of the contributions presented at the Conference 'Mathematical Structures in Quantum Systems and applications', held at the Centro de Ciencias de Benasque 'Pedro Pascual', Benasque (Spain) from 8-14 July 2012. The aim of the Conference was to bring together physicists working on different applications of mathematical methods to quantum systems in order to enable the different communities to become acquainted with other approaches and techniques that could be used in their own fields of expertise. We concentrated on three main subjects: – the geometrical description of Quantum Mechanics; – the Casimir effect and its mathematical implications; – the Quantum Zeno Effect and Open system dynamics. Each of these topics had a set of general lectures, aimed at presenting a global view on the subject, and other more technical seminars. We would like to thank all participants for their contribution to creating a wonderful scientific atmosphere during the Conference. We would especially like to thank the speakers and the authors of the papers contained in this volume, the members of the Scientific Committee for their guidance and support and, of course, the referees for their generous work. Special thanks are also due to the staff of the Centro de Ciencias de Benasque 'Pedro Pascual' who made this successful meeting possible. On behalf of the organising committee and the authors we would also like to acknowledge the partial support provided by the ESF-CASIMIR network ('New Trends and Applications of the Casimir Effect'), the QUITEMAD research Project (“Quantum technologies at Madrid”, Ref. Comunidad de Madrid P2009/ESP-1594), the MICINN Project (MTM2011-16027-E) and the Government from Arag´on (DGA) (DGA, Department of Industry and Innovation and the European Social Fund, DGA-Grant 24/1) who made the Conference and this Proceedings volume possible.

2013-01-01

193

Thermalization of field driven quantum systems.

There is much interest in how quantum systems thermalize after a sudden change, because unitary evolution should preclude thermalization. The eigenstate thermalization hypothesis resolves this because all observables for quantum states in a small energy window have essentially the same value; it is violated for integrable systems due to the infinite number of conserved quantities. Here, we show that when a system is driven by a DC electric field there are five generic behaviors: (i) monotonic or (ii) oscillatory approach to an infinite-temperature steady state; (iii) monotonic or (iv) oscillatory approach to a nonthermal steady state; or (v) evolution to an oscillatory state. Examining the Hubbard model (which thermalizes under a quench) and the Falicov-Kimball model (which does not), we find both exhibit scenarios (i-iv), while only Hubbard shows scenario (v). This shows richer behavior than in interaction quenches and integrability in the absence of a field plays no role. PMID:24736404

Fotso, H; Mikelsons, K; Freericks, J K

2014-01-01

194

Quantum phase transitions in finite systems

The aim of this work is to develop a technique for identifying quantum phase transitions which does not rely on the existence of a thermodynamic limit, for studies in finite systems. The approach we adopt exploits an exact mapping of the spectrum of a many-body integrable system, which admits an exact Bethe ansatz solution, into the quasi-exactly solvable spectrum of a one-particle Schrodinger operator. Bifurcations of the minima for the potential of the Schrodinger operator determine critical ground-state couplings. By considering the behaviour of certain ground-state correlation functions, these may be identified as quantum phase transitions in the many-body integrable system with finite particle number. We study two particular examples of bosonic Hamiltonians which admit second-order transitions, and discuss further applications.

Dunning, C; Links, J; Dunning, Clare; Hibberd, Katrina E.; Links, Jon

2006-01-01

195

Aberration-corrected quantum temporal imaging system

We describe the design of a temporal imaging system that simultaneously reshapes the temporal profile and converts the frequency of a photonic wavepacket, while preserving its quantum state. A field lens, which imparts a temporal quadratic phase modulation, is used to correct for the residual phase caused by field curvature in the image, thus enabling temporal imaging for phase-sensitive quantum applications. We show how this system can be used for temporal imaging of time-bin entangled photonic wavepackets and compare the field lens correction technique to systems based on a temporal telescope and far-field imaging. The field-lens approach removes the residual phase using four dispersive elements. The group delay dispersion (GDD) $D$ is constrained by the available bandwidth $\\Delta\

Zhu, Yunhui; Gauthier, Daniel J

2013-01-01

196

Distillability of inseparable quantum systems

We apply the inseparability criterion for 2 \\times 2 systems, local filtering and Bennett et al. purification protocol [Phys. Rev. Lett. {\\bf 76}, 722 (1996), quant-ph/9511027] to show how to distill {\\it any} inseparable 2\\times 2 system. The extended protocol is illustrated geometrically by means of the state parameters in the Hilbert-Schmidt space.

Horodecki, M; Horodecki, R; Horodecki, Michal; Horodecki, Pawel; Horodecki, Ryszars

1996-01-01

197

Geometric measure of quantum discord for an arbitrary state of a bipartite quantum system

Quantum discord, as introduced by Olliver and Zurek [Phys. Rev. Lett. \\textbf{88}, 017901 (2001)], is a measure of the discrepancy between quantum versions of two classically equivalent expressions for mutual information. Dakic, Vedral, and Brukner [arXiv:1004.0190 (2010)] introduced a geometric measure of quantum discord and derived an explicit formula for any two-qubit state. Luo and Fu [Phys. Rev. A \\textbf{82}, 034302 (2010)] introduced another form for geometric measure of quantum discord. We find an exact formula for the geometric measure of quantum discord for an arbitrary state of a $m\\times n$ bipartite quantum system.

Hassan, Ali Saif M; Joag, Pramod S

2010-01-01

198

Quantum computation in a quantum-dot-Majorana-fermion hybrid system

We propose a scheme to implement universal quantum computation in a quantum-dot-Majorana-fermion hybrid system. Quantum information is encoded on pairs of Majorana fermions, which live on the the interface between topologically trivial and nontrivial sections of a quantum nanowire deposited on an s-wave superconductor. Universal single-qubit gates on topological qubit can be achieved. A measurement-based two-qubit Controlled-Not gate is produced with the help of parity measurements assisted by the quantum-dot and followed by prescribed single-qubit gates. The parity measurement, on the quantum-dot and a topological qubit, is achieved by the Aharonov- Casher effect.

Xue, Zheng-Yuan

2012-01-01

199

Intertwining Symmetry Algebras of Quantum Superintegrable Systems

Directory of Open Access Journals (Sweden)

Full Text Available We present an algebraic study of a kind of quantum systems belonging to a family of superintegrable Hamiltonian systems in terms of shape-invariant intertwinig operators, that span pairs of Lie algebras like (su(n,so(2n or (su(p,q,so(2p,2q. The eigenstates of the associated Hamiltonian hierarchies belong to unitary representations of these algebras. It is shown that these intertwining operators, related with separable coordinates for the system, are very useful to determine eigenvalues and eigenfunctions of the Hamiltonians in the hierarchy. An study of the corresponding superintegrable classical systems is also included for the sake of completness.

Juan A. Calzada

2009-04-01

200

Isochronous classical systems and quantum systems with equally spaced spectra

Energy Technology Data Exchange (ETDEWEB)

We study isoperiodic classical systems, what allows us to find the classical isochronous systems, i.e. having a period independent of the energy. The corresponding quantum analog, systems with an equally spaced spectrum are analysed by looking for possible creation-like differential operators. The harmonic oscillator and the isotonic oscillator are the two main essentially unique examples of such situation.

Carinena, J F; Perelomov, A M; Ranada, M F [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza (Spain)

2007-11-15

201

Quantum response of dephasing open systems

Energy Technology Data Exchange (ETDEWEB)

We develop a theory of adiabatic response for open systems governed by Lindblad evolutions. The theory determines the dependence of the response coefficients on the dephasing rates and allows for residual dissipation even when the ground state is protected by a spectral gap. We give the quantum response a geometric interpretation in terms of Hilbert space projections: for a two-level system and, more generally, for systems with a suitable functional form of the dephasing, the dissipative and non-dissipative parts of the response are linked to a metric and to a symplectic form. The metric is the Fubini-Study metric and the symplectic form is the adiabatic curvature. When the metric and symplectic structures are compatible, the non-dissipative part of the inverse matrix of response coefficients turns out to be immune to dephasing. We give three examples of physical systems whose quantum states induce compatible metric and symplectic structures on control space: qubit, coherent states and a model of the integer quantum Hall effect.

Avron, J E; Fraas, M; Kenneth, O [Department of Physics, Technion, 32000 Haifa (Israel); Graf, G M, E-mail: martin.fraas@gmail.com [Theoretische Physik, ETH Zurich, CH-8093 Zuerich (Switzerland)

2011-05-15

202

Non-Equilibrium Quantum Entanglement in Biological Systems

International Nuclear Information System (INIS)

A non-equilibrium model of a classically driven quantum harmonic oscillator is proposed to explain persistent quantum entanglement in biological systems at ambient temperature. The conditions for periodic entanglement generation are derived. Our results support the evidence that biological systems may have quantum entanglement at biological temperatures. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2012-04-01

203

Non-Reversible Evolution of Quantum Chaotic System. Kinetic Description

Time dependent dynamics of the chaotic quantum-mechanical system has been studied. Irreversibility of the dynamics is shown. It is shown, that being in the initial moment in pure quantum-mechanical state, system makes irreversible transition into mixed state. Original mechanism of mixed state formation is offered. Quantum kinetic equation is obtained. Growth of the entropy during the evolution process is estimated.

Chotorlishvili, L

2006-01-01

204

Controllability of multi-partite quantum systems and selective excitation of quantum dots

International Nuclear Information System (INIS)

We consider the degrees of controllability of multi-partite quantum systems, as well as necessary and sufficient criteria for each case. The results are applied to the problem of simultaneous control of an ensemble of quantum dots with a single laser pulse. Finally, we apply optimal control techniques to demonstrate selective excitation of individual dots for a simultaneously controllable ensemble of quantum dots

2005-10-01

205

Quantum phases and dynamics of geometric phase in a quantum spin chain system under linear quench

We study the quantum phases of anisotropic XY spin chain system in presence and absence of adiabatic quench. A connection between geometric phase and criticality is established from the dynamical behaviour of the geometric phase for a quench induced quantum phase transition in a quantum spin chain. We predict XX criticality associated with a sequence of non-contractible geometric phases.

Sarkar, Sujit

2011-01-01

206

Network Synthesis of Linear Dynamical Quantum Stochastic Systems

The purpose of this paper is to develop a synthesis theory for linear dynamical quantum stochastic systems that are encountered in linear quantum optics and in phenomenological models of linear quantum circuits. In particular, such a theory will enable the systematic realization of coherent/fully quantum linear stochastic controllers for quantum control, amongst other potential applications. We show how general linear dynamical quantum stochastic systems can be constructed by assembling an appropriate interconnection of one degree of freedom open quantum harmonic oscillators and, in the quantum optics setting, discuss how such a network of oscillators can be approximately synthesized or implemented in a systematic way from some linear and non-linear quantum optical elements. An example is also provided to illustrate the theory.

Nurdin, H I; Doherty, A C

2008-01-01

207

Resonance width distribution for open quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent measurements of resonance widths for low-energy neutron scattering off heavy nuclei show large deviations from the standard Porter-Thomas distribution. We propose a new resonance width distribution based on the random matrix theory for an open quantum system. Two methods of derivation lead to a single analytical expression; in the limit of vanishing continuum coupling, we recover the Porter-Thomas distribution. The result depends on the ratio of typical widths $\\Gamma...

Shchedrin, Gavriil; Zelevinsky, Vladimir

2011-01-01

208

Bipartite entanglement of large quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis we study the behavior of bipartite entanglement of a large quantum system, by analyzing the distribution of the Schmidt coefficients of the reduced density matrix. Applying the general methods of classical statistical mechanics, we develop a canonical approach for the study of the distribution of these coefficients for a fixed value of the average entanglement. We introduce a partition function depending on a fictitious temperature, which localizes the measure...

Pasquale, Antonella

2012-01-01

209

Dynamical systems and quantum bicrossproduct algebras

Energy Technology Data Exchange (ETDEWEB)

We present a unified study of some aspects of quantum bicrossproduct algebras of inhomogeneous Lie algebras, such as Poincare, Galilei and Euclidean in N dimensions. The action associated with the bicrossproduct structure allows us to obtain a nonlinear action over a new group linked to the translations. This new nonlinear action associates a dynamical system with each generator which is the object of our study. (author)

Arratia, Oscar [Departamento de Matematica Aplicada a la Ingenieria, Universidad de Valladolid, Valladolid (Spain)]. E-mail: oscarr@wmatem.eis.uva.es; Olmo, Mariano A. del [Departamento de Fisica Teorica, Universidad de Valladolid, Valladolid (Spain)]. E-mail: olmo@fta.uva.es

2002-06-28

210

Planar lightwave circuits for quantum cryptographic systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a quantum cryptographic system based on a planar lightwave circuit (PLC) and report on optical interference experiments using PLC-based unbalanced Mach-Zehnder interferometers (MZIs). The interferometers exhibited high-visibility (>0.98) interference even when the polarisation in the optical fibre connecting the two MZIs was randomly modulated. The results demonstrate that a PLC-based setup is suitable for achieving a polarisation-insensitive phase-coding cryptogr...

Nambu, Yoshihiro; Hatanaka, Takaaki; Nakamura, Kazuo

2003-01-01

211

Anomalous quantum response of driven chaotic systems

Chaotic systems that have small Lyapunov exponent, do not obey the common random matrix theory predictions within a wide "weak quantum chaos" regime. This leads to a novel prediction for the rate of heating for cold atoms in optical billiards with vibrating walls. The Hamiltonian matrix of the driven system does not look like taken from a Gaussian ensemble, but rather it is very sparse. This sparsity can be characterized by parameters $s$ and $g$ that reflect the percentage of large elements, and their connectivity respectively. For $g$ we use a resistor network calculation that has direct relation to the semi-linear response characteristics of the system.

Stotaland, Alexander; Cohen, Doron

2010-01-01

212

Multiphoton spectroscopy of a hybrid quantum system

We report on experimental multiphoton spectroscopy of a hybrid quantum system consisting of a superconducting phase qubit coherently coupled to an intrinsic two-level system (TLS). We directly probe hybridized states of the combined qubit-TLS system in the strongly interacting regime, where both the qubit-TLS coupling and the driving cannot be considered as weak perturbations. This regime is described by a theoretical model which incorporates anharmonic corrections, multiphoton processes and decoherence. We present a detailed comparison between experiment and theory and find excellent agreement over a wide range of parameters.

Bushev, P.; Müller, C.; Lisenfeld, J.; Cole, J. H.; Lukashenko, A.; Shnirman, A.; Ustinov, A. V.

2010-10-01

213

Open quantum systems and Random Matrix Theory

A simple model for open quantum systems is analyzed with Random Matrix Theory. The system is coupled to the continuum in a minimal way. In this paper we see the effect of opening the system on the level statistics, in particular the $\\Delta_3(L)$ statistic, width distribution and level spacing are examined as a function of the strength of this coupling. A super-radiant transition is observed, and it is seen that as it is formed, the level spacing and $\\Delta_3(L)$ statistic exhibit the signatures of missed levels.

Mulhall, Declan

2014-01-01

214

Polyadic systems, representations and quantum groups

Polyadic systems and their representations are reviewed and a classification of general polyadic systems is presented. A new multiplace generalization of associativity preserving homomorphisms, a 'heteromorphism' which connects polyadic systems having unequal arities, is introduced via an explicit formula, together with related definitions for multiplace representations and multiactions. Concrete examples of matrix representations for some ternary groups are then reviewed. Ternary algebras and Hopf algebras are defined, and their properties are studied. At the end some ternary generalizations of quantum groups and the Yang-Baxter equation are presented.

Duplij, Steven

2013-01-01

215

The quantum $H_3$ integrable system

Digital Repository Infrastructure Vision for European Research (DRIVER)

The quantum $H_3$ integrable system is a 3D system with rational potential related to the non-crystallographic root system $H_3$. It is shown that the gauge-rotated $H_3$ Hamiltonian as well as one of the integrals, when written in terms of the invariants of the Coxeter group $H_3$, is in algebraic form: it has polynomial coefficients in front of derivatives. The Hamiltonian has infinitely-many finite-dimensional invariant subspaces in polynomials, they form the infinite fla...

Garci?a, Marcos A. G.; Turbiner, Alexander V.

2010-01-01

216

Cavity-Assisted Monitoring of Dynamics for Complex Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cavity and circuit quantum electrodynamics (CQED) technologies have progressed significantly during recent years, enabling real-time monitoring and control of quantum systems, yet their potential for quantum tomography or spectroscopy is largely unexplored. We develop here a CQED formalism for monitoring the dynamics of a complex quantum system, deriving a set of Stochastic Hierarchy Equations of Motion to describe continuous measurement in presence of non-perturbative and n...

Shabani, A.; Roden, J.; Whaley, K. B.

2013-01-01

217

Time fractional development of quantum systems

In this study, the effect of time fractionalization on the development of quantum systems is taken under consideration by making use of fractional calculus. In this context, a Mittag-Leffler function is introduced as an important mathematical tool in the generalization of the evolution operator. In order to investigate the time fractional evolution of the quantum (nano) systems, time fractional forms of motion are obtained for a Schrödinger equation and a Heisenberg equation. As an application of the concomitant formalism, the wave functions, energy eigenvalues, and probability densities of the potential well and harmonic oscillator are time fractionally obtained via the fractional derivative order ?, which is a measure of the fractality of time. In the case ?=1, where time becomes homogenous and continuous, traditional physical conclusions are recovered. Since energy and time are conjugate to each other, the fractional derivative order ? is relevant to time. It is understood that the fractionalization of time gives rise to energy fluctuations of the quantum (nano) systems.

Ertik, Hüseyin; Demirhan, Do?an; ?irin, Hüseyin; Büyükk?l?ç, Fevzi

2010-08-01

218

Time fractional development of quantum systems

International Nuclear Information System (INIS)

In this study, the effect of time fractionalization on the development of quantum systems is taken under consideration by making use of fractional calculus. In this context, a Mittag-Leffler function is introduced as an important mathematical tool in the generalization of the evolution operator. In order to investigate the time fractional evolution of the quantum (nano) systems, time fractional forms of motion are obtained for a Schroedinger equation and a Heisenberg equation. As an application of the concomitant formalism, the wave functions, energy eigenvalues, and probability densities of the potential well and harmonic oscillator are time fractionally obtained via the fractional derivative order ?, which is a measure of the fractality of time. In the case ?=1, where time becomes homogenous and continuous, traditional physical conclusions are recovered. Since energy and time are conjugate to each other, the fractional derivative order ? is relevant to time. It is understood that the fractionalization of time gives rise to energy fluctuations of the quantum (nano) systems.

2010-08-01

219

Quantum statistics of charged particle systems

International Nuclear Information System (INIS)

This book presents information on the following topics: basic concepts for Coulomb systems; quantum statistics of many-particle systems; the method of Green's functions in quantum statistics; the binary collision approximation; application of the Green's function technique to Coulomb systems; many-particle complexes and T-matrices; cluster formation and the chemical picture; single particle excitations; equilibrium properties in classical and quasiclassical approximation; the one-component plasma model; the pair distribution function; quantum-statistical calculations of equilibrium properties; the mass action law; electron-hole plasmas; Pade approximations; hydrogen plasmas; the two-fluid model; transport properties; linear response theory; evaluation of collision integrals using Green's functions; results for a hydrogen plasma; self-energy and Debye-Onsager relaxation effects; hopping conductivity; Green's function approach to optical properties; many-body theory of absorption spectra; Doppler broadening; explicit expressions for shift and broadening; shift of spectral lines in dense hydrogen plasmas; and estimation of the shift and broadening of spectral lines for an argon plasma

1986-01-01

220

International Nuclear Information System (INIS)

We present a method for probabilistic quantum entanglement swapping between high-dimensional pure entangled systems by introducing only one auxiliary two-level particle. The probability of successful entanglement swapping is just the entanglement of the quantum channel. It can be used for practical long-distance quantum communication efficiently. We present a quantum secret sharing scheme based on quantum entanglement swapping with high-dimensional pure entangled systems. It has the advantage of having high intrinsic qubit efficiency and high capacity. Moreover, it greatly reduces the classical information exchanged for creating the private key.

2009-03-01

221

Many electronic systems exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are empirical suggestions of particular increasing length scales that accompany such transitions, this identification is not universal. To better understand such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic, or supersymmetric, quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general non-equilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods (or holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our exact result is that a Wick rotation relates (i) dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this cor...

Nussinov, Zohar; Graf, Matthias J; Balatsky, Alexander V

2013-01-01

222

Continuous measurement of a non-Markovian open quantum system.

Continuous quantum measurement is the backbone of various methods in quantum control, quantum metrology, and quantum information. Here, we present a generalized formulation of dispersive measurement of a complex quantum systems. We describe the complex system as an open quantum system that is strongly coupled to a non-Markovian environment, enabling the treatment of a broad variety of natural or engineered complex systems. The system is monitored via a probe resonator coupled to a broadband (Markovian) reservoir. Based on this model, we derive a formalism of stochastic hierarchy equations of motion describing the decoherence dynamics of the system conditioned on the measurement record. Furthermore, we demonstrate a spectroscopy method based on weak quantum measurement to reveal the non-Markovian nature of the environment, which we term weak spectroscopy. PMID:24702367

Shabani, A; Roden, J; Whaley, K B

2014-03-21

223

Quantum Computing in Condensed Matter Systems.

Specific theoretical calculations of Hamiltonians corresponding to several quantum logic gates, including the NOT gate, quantum signal splitting, and quantum copying, were obtained and prepared for publication. Directions for future work have been identif...

V. Privman

1997-01-01

224

Statistical Thermodynamics of Polymer Quantum Systems

Directory of Open Access Journals (Sweden)

Full Text Available Polymer quantum systems are mechanical models quantized similarly as loop quantum gravity. It is actually in quantizing gravity that the polymer term holds proper as the quantum geometry excitations yield a reminiscent of a polymer material. In such an approach both non-singular cosmological models and a microscopic basis for the entropy of some black holes have arisen. Also important physical questions for these systems involve thermodynamics. With this motivation, in this work, we study the statistical thermodynamics of two one dimensional polymer quantum systems: an ensemble of oscillators that describe a solid and a bunch of non-interacting particles in a box, which thus form an ideal gas. We first study the spectra of these polymer systems. It turns out useful for the analysis to consider the length scale required by the quantization and which we shall refer to as polymer length. The dynamics of the polymer oscillator can be given the form of that for the standard quantum pendulum. Depending on the dominance of the polymer length we can distinguish two regimes: vibrational and rotational. The first occur for small polymer length and here the standard oscillator in Schrödinger quantization is recovered at leading order. The second one, for large polymer length, features dominant polymer effects. In the case of the polymer particles in the box, a bounded and oscillating spectrum that presents a band structure and a Brillouin zone is found. The thermodynamical quantities calculated with these spectra have corrections with respect to standard ones and they depend on the polymer length. When the polymer length is small such corrections resemble those coming from the phenomenological generalized uncertainty relation approach based on the idea of the existence of a minimal length. For generic polymer length, thermodynamics of both systems present an anomalous peak in their heat capacity C_V. In the case of the polymer oscillators this peak separates the vibrational and rotational regimes, while in the ideal polymer gas it reflects the band structure which allows the existence of negative temperatures.

Guillermo Chacón-Acosta

2011-12-01

225

Extending scientific computing system with structural quantum programming capabilities

We present a basic high-level structures used for developing quantum programming languages. The presented structures are commonly used in many existing quantum programming languages and we use quantum pseudo-code based on QCL quantum programming language to describe them. We also present the implementation of introduced structures in GNU Octave language for scientific computing. Procedures used in the implementation are available as a package quantum-octave, providing a library of functions, which facilitates the simulation of quantum computing. This package allows also to incorporate high-level programming concepts into the simulation in GNU Octave and Matlab. As such it connects features unique for high-level quantum programming languages, with the full palette of efficient computational routines commonly available in modern scientific computing systems. To present the major features of the described package we provide the implementation of selected quantum algorithms. We also show how quantum errors can be...

Gawron, P; Miszczak, J A; Winiarczyk, R

2010-01-01

226

Using a quantum dot system to realize perfect state transfer

International Nuclear Information System (INIS)

There are some disadvantages to Nikolopoulos et al.'s protocol [Nikolopoulos G M, Petrosyan D and Lambropoulos P 2004 Europhys. Lett. 65 297] where a quantum dot system is used to realize quantum communication. To overcome these disadvantages, we propose a protocol that uses a quantum dot array to construct a four-qubit spin chain to realize perfect quantum state transfer (PQST). First, we calculate the interaction relation for PQST in the spin chain. Second, we review the interaction between the quantum dots in the Heitler—London approach. Third, we present a detailed program for designing the proper parameters of a quantum dot array to realize PQST. (general)

2011-10-01

227

Using a quantum dot system to realize perfect state transfer

There are some disadvantages to Nikolopoulos et al.'s protocol [Nikolopoulos G M, Petrosyan D and Lambropoulos P 2004 Europhys. Lett. 65 297] where a quantum dot system is used to realize quantum communication. To overcome these disadvantages, we propose a protocol that uses a quantum dot array to construct a four-qubit spin chain to realize perfect quantum state transfer (PQST). First, we calculate the interaction relation for PQST in the spin chain. Second, we review the interaction between the quantum dots in the Heitler—London approach. Third, we present a detailed program for designing the proper parameters of a quantum dot array to realize PQST.

Li, Ji; Wu, Shi-Hai; Zhang, Wen-Wen; Xi, Xiao-Qiang

2011-10-01

228

Algebraic Approach to Interacting Quantum Systems

We present an algebraic framework for interacting extended quantum systems that enable us to study complex phenomena characterized by the coexistence and competition of various broken symmetry states. We show how to connect different (spin-particle-gauge) {\\it languages} by means of exact mappings (isomorphisms) that we name {\\it dictionaries}, and prove a fundamental theorem that establishes when two arbitrary languages can be connected. These mappings serve to unravel symmetries which are hidden in one representation and are manifest in another. In addition, we show that by changing the language of a given model, it is possible to link seemingly unrelated physical phenomena, leading to a notion of {\\it universality} or equivalence. By introducing the concept of {\\it hierarchical languages}, we determine the quantum phase diagram of lattice models (previously unsolved), and unveil hidden order parameters to explore new states of matter. Hierarchical languages constitute also an essential tool to provide a un...

Batista, C D

2002-01-01

229

Quantum Spin Systems after DLS1978

In their 1978 paper, Dyson, Lieb, and Simon (DLS) proved the existence of Ne'el order at positive temperature for the spin-S Heisenberg antiferromagnet on the d-dimensional hypercubic lattice when either S >= 1 and d >= 3 or S=1/2 and d is sufficiently large. This was the first proof of spontaneous breaking of a continuous symmetry in a quantum model at finite temperature. Since then the ideas of DLS have been extended and adapted to a variety of other problems. In this paper will present an overview of the most important developments in the study of the Heisenberg model and related quantum lattice systems since 1978, including but not restricted to those directly related to the paper by DLS.

Nachtergaele, B

2006-01-01

230

Defense frontier analysis of quantum cryptographic systems.

When a quantum cryptographic system operates in the presence of background noise, security of the key can be recovered by a procedure called key distillation. A key-distillation scheme effective against so-called individual (bitwise-independent) eavesdropping attacks involves sacrifice of some of the data through privacy amplification. We derive the amount of data sacrifice sufficient to defend against individual eavesdropping attacks in both BB84 and B92 protocols and show in what sense the communication becomes secure as a result. We also compare the secrecy capacity of various quantum cryptosystems, taking into account data sacrifice during key distillation, and conclude that the BB84 protocol may offer better performance characteristics than the B92. PMID:18273233

Slutsky, B; Rao, R; Sun, P C; Tancevski, L; Fainman, S

1998-05-10

231

Effective operator formalism for open quantum systems

DEFF Research Database (Denmark)

We present an effective operator formalism for open quantum systems. Employing perturbation theory and adiabatic elimination of excited states for a weakly driven system, we derive an effective master equation which reduces the evolution to the ground-state dynamics. The effective evolution involves a single effective Hamiltonian and one effective Lindblad operator for each naturally occurring decay process. Simple expressions are derived for the effective operators which can be directly applied to reach effective equations of motion for the ground states. We compare our method with the hitherto existing concepts for effective interactions and present physical examples for the application of our formalism, including dissipative state preparation by engineered decay processes.

Reiter, Florentin; SÃ¸rensen, Anders SÃ¸ndberg

2012-01-01

232

A kicked quantum system including the continuum

International Nuclear Information System (INIS)

The behaviour of a quantum particle in a separable one-term potential with three-dimensional form factor is investigated under the influence of an external force which alters the potential strength periodically or quasiperiodically. The unperturbed system possesses one bound state and a continuum of scattering states which has treated almost analytically. First numerical results, fully including the emission channel, indicate, for certain parameter combinations with commensurate or incommensurate frequency ratios, either a regular or an irregular dynamical behaviour of the system. 17 refs.; 3 figs

1988-01-01

233

Dynamical Localization in Disordered Quantum Spin Systems

We say that a quantum spin system is dynamically localized if the time-evolution of local observables satisfies a zero-velocity Lieb-Robinson bound. In terms of this definition we have the following main results: First, for general systems with short range interactions, dynamical localization implies exponential decay of ground state correlations, up to an explicit correction. Second, the dynamical localization of random xy spin chains can be reduced to dynamical localization of an effective one-particle Hamiltonian. In particular, the isotropic xy chain in random exterior magnetic field is dynamically localized.

Hamza, Eman; Stolz, Günter

2011-01-01

234

Polynomial conservation laws of quantum systems

International Nuclear Information System (INIS)

The systems with the freedom degrees finite number, the potential energy whereof constitutes the exponents sum with purely imaginable or material indices, are considered. The problem on describing all the quantum conservation laws, presented in the form of the differential operators, polynomial relative to the differentiations and commutating with the Hamilton operator is also considered. It is proved in the common situation (without the assumption on the spectrum symmetry) that the complete integrability of the corresponding classic system follows from availability of the complete set of the independent conservation laws

2004-09-01

235

QUANTUM TUNNELLING AND MAGNETIZATION DYNAMICS IN LOW DIMENSIONAL SYSTEMS

Directory of Open Access Journals (Sweden)

Full Text Available Quantum mechanics allows a system to overcome a classically-unsurmountable energy barrier through a mechanism called Quantum Tunnelling (QT. Although pertaining to the quantum domain, QT is the cause of important physical phenomena that can be detected at the macroscopic scale. Some of them have led to breakthrough applications in electronics (tunnel junctions and imaging (scanning tunnelling microscope.

ANDREA CORNIA

2011-12-01

236

Superconvergent perturbation method for weak nonintegrable quantum systems

International Nuclear Information System (INIS)

Quantum canonical transformation is defined in comparison with classical case. The superconvergent perturbation method in quantum systems established by Scherer is briefly introduced in contrast with classical KAM theorem, and the relationship between this method and quantum canonical transformation is discussed. The physical implication of success and failure of this perturbation is studied with a simple example as an illustration

1997-06-01

237

Quantum fluid dynamics of classical nonlinear dynamical systems

International Nuclear Information System (INIS)

Hydrodynamic versions of several classical nonlinear equations of motion governing important physico-chemical phenomena have been obtained. This approach would provide insight into the corresponding systems in quantum domain which may eventually lead to a method for analyzing quantum chaos. As a test case, a quantum Henon-Heiles oscillator has been studied numerically. (author). 32 refs., 2 figs

1994-02-01

238

Conditional density matrix: systems and subsystems in quantum mechanics

International Nuclear Information System (INIS)

A new quantum mechanical notion - Conditional Density Matrix - is discussed and is applied to describe some physical processes. This notion is a natural generalization of von Neumann density matrix for such processes as divisions of quantum systems into subsystems and reunifications of subsystems into new joint systems. Conditional Density Matrix assigns a quantum state to a subsystem of a composite system on condition that another part of the composite system is in some pure state

2002-05-16

239

Measurement, Filtering and Control in Quantum Open Dynamical Systems

A Markovian model for a quantum automata, i.e. an open quantum dynamical discrete-time system with input and output channels and a feedback, is described. A dynamical theory of quantum discrete-time adaptive measurements and multi-stage quantum statistical decisions is developed and applied to the optimal feedback control problem for the quantum dynamical objects. Quantum analogies of Stratonovich non-stationary filtering, and Bellman quantum dynamical programming in the discrete time are derived. A Gaussian Langevin model of the quantum one-dimensional linear Markovian dynamical system matched with a quantum linear transmission line as an input-output quantum noisy channel is studied. The optimal quantum multi-stage decision rule consisting of a classical linear optimal control strategy and the quantum optimal filtering of the noise is found. The latter contains the optimal quantum coherent measurement on the output of the line and the recursive processing by the Kalman filter. A time-continuous limit of the...

Belavkin, V P

1999-01-01

240

A neural-network-like quantum information processing system

The Hopfield neural networks and the holographic neural networks are models which were successfully simulated on conventional computers. Starting with these models, an analogous fundamental quantum information processing system is developed in this article. Neuro-quantum interaction can regulate the "collapse"-readout of quantum computation results. This paper is a comprehensive introduction into associative processing and memory-storage in quantum-physical framework.

Perus, M; Perus, Mitja; Bischof, Horst

2003-01-01

241

Controlled Population Transfer in a Double Quantum Dot System

International Nuclear Information System (INIS)

We study the potential for controlled population transfer between the ground states of two anharmonic coupled quantum dots. We propose a method based on the interaction of the quantum dot structure with external electromagnetic fields. The interaction of the quantum dot system with the electromagnetic fields is studied with the use of the time-dependent Schroedinger equation. We present numerical results for an asymmetric quantum dot structure

2007-12-26

242

Quantum arrival time for open systems

International Nuclear Information System (INIS)

We extend previous work on the arrival time problem in quantum mechanics, in the framework of decoherent histories, to the case of a particle coupled to an environment. The usual arrival time probabilities are related to the probability current, so we explore the properties of the current for general open systems that can be written in terms of a master equation of the Lindblad form. We specialize to the case of quantum Brownian motion, and show that after a time of order the localization time of the current becomes positive. We show that the arrival time probabilities can then be written in terms of a positive operator-valued measure (POVM), which we compute. We perform a decoherent histories analysis including the effects of the environment and show that time-of-arrival probabilities are decoherent for a generic state after a time much greater than the localization time, but that there is a fundamental limitation on the accuracy ?t, with which they can be specified which obeys E?t>>(?/2?). We confirm that the arrival time probabilities computed in this way agree with those computed via the current, provided there is decoherence. We thus find that the decoherent histories formulation of quantum mechanics provides a consistent explanation for the emergence of the probability current as the classical arrival time distribution, and a systematic rule for deciding when probabilities may be assigned.

2010-07-01

243

MURI Center for Photonic Quantum Information Systems.

We have continued the development of several photonic quantum technologies: single-photon and entangled-photon sources from quantum dots and parametric down-conversion; solid-state quantum gates based on quantum dots in semiconductors and on NV centers in...

J. Vuckovic P. Kwiat

2009-01-01

244

Linear quantum state diffusion for non-Markovian open quantum systems

We demonstrate the relevance of complex Gaussian stochastic processes to the stochastic state vector description of non-Markovian open quantum systems. These processes express the general Feynman-Vernon path integral propagator for open quantum systems as the classical ensemble average over stochastic pure state propagators in a natural way. They are the coloured generalization of complex Wiener processes in quantum state diffusion stochastic Schrodinger equations.

Strunz, W T

1996-01-01

245

Control of non-controllable quantum systems: a quantum control algorithm based on Grover iteration

International Nuclear Information System (INIS)

A new notion of controllability, eigenstate controllability, is defined for finite-dimensional bilinear quantum mechanical systems which are neither strongly completely controllable nor completely controllable. Moreover, a quantum control algorithm based on Grover iteration is designed to perform a quantum control task of steering a system, which is eigenstate controllable but may not be (strongly) completely controllable, from an arbitrary state to a target state

2005-10-01

246

On the notion of a macroscopic quantum system

We analyse the notion of macroscopic quantum system from the point of view of the statistical structure of quantum theory. We come to conclusion that the presence of interference of probabilities should be used the main characteristic of quantumness (in the opposition to N. Bohr who permanently emphasized the crucial role of quantum action). In the light of recent experiments with statistical ensembles of people who produced interference of probabilities for special pairs of questions (which can be considered as measurements on people) human being should be considered as a macroscopic quantum system. There is also discussed relation with experiments of A. Zeilinger on interference of probabilities for macromoleculas.

Khrenikov, A Yu

2004-01-01

247

Quantum MIMO n-Systems and Conditions for Stability

In this paper we present some conditions for the (strong) stabilizability of an n-D Quantum MIMO system P(X). It contains two parts. The first part is to introduce the n-D Quantum MIMO systems where the coefficients vary in the algebra of Q-meromorphic functions. Then we introduce some conditions for the stabilizability of these systems. The second part is to show that this Quantum system has the n-D system as its quantum limit and the results for the SISO,SIMO,MISO,MIMO are obtained again as special cases.

Mansourbeigi, Seyed M H

2009-01-01

248

Propagation of decoherence in distributed quantum systems

We study the decohering influence of measurement performed locally on some region of a distributed quantum system. We demonstrate that the local decohering perturbation exerted on the measured region can propagate over the system in the form of decoherence wave. This process refers to the local properties at different points inside the system, and is fundamentally different from such processes as the wave function collapse, which concern the properties of the system as a whole. As an example, we consider the gas of bosons forming Bose-Einstein condensate. We show that the decoherence propagation in ideal Bose-gas is a diffusion process, while in the gas of weakly interacting bosons it is a wave traveling with the sound velocity. The results obtained can be checked in real experiments using, e.g. the Bose-gas of supercooled trapped ions.

Katsnelson, M I; Harmon, B N

2000-01-01

249

Unstable particles as open quantum systems

We present the probability preserving description of the decaying particle within the framework of quantum mechanics of open systems taking into account the superselection rule prohibiting the superposition of the particle and vacuum. In our approach the evolution of the system is given by a family of completely positive trace preserving maps forming one-parameter dynamical semigroup. We give the Kraus representation for the general evolution of such systems which allows one to write the evolution for systems with two or more particles. Moreover, we show that the decay of the particle can be regarded as a Markov process by finding explicitly the master equation in the Lindblad form. We also show that there are remarkable restrictions on the possible strength of decoherence.

Caban, P; Smolinski, K A; Walczak, Z

2005-01-01

250

Unstable particles as open quantum systems

International Nuclear Information System (INIS)

We present the probability-preserving description of the decaying particle within the framework of quantum mechanics of open systems, taking into account the superselection rule prohibiting the superposition of the particle and vacuum. In our approach the evolution of the system is given by a family of completely positive trace-preserving maps forming a one-parameter dynamical semigroup. We give the Kraus representation for the general evolution of such systems, which allows one to write the evolution for systems with two or more particles. Moreover, we show that the decay of the particle can be regarded as a Markov process by finding explicitly the master equation in the Lindblad form. We also show that there are remarkable restrictions on the possible strength of decoherence

2005-09-01

251

Towards the theory of control in observable quantum systems

An operational description of the controlled Markov dynamics of quantum-mechanical system is introduced. The feedback control strategies with regard to the dynamical reduction of quantum states in the course of quantum real-time measurements are described in terms of quantum filtering of these states. The concept of sufficient coordinates for the description of the a posteriori quantum states from a given class is introduced, and it is proved that they form a classical Markov process with values in either state operators or state vector space. The general problem of optimal control of a quantum-mechanical system is discussed and the corresponding Bellman equation in the space of sufficient coordinates is derived. The results are illustrated in the example of control of the semigroup dynamics of a quantum system that is instantaneously observed at discrete times and evolves between measurement times according to the Schroedinger equation.

Belavkin, V P

1983-01-01

252

Sampling the time evolution of mixed quantum-classical systems

Directory of Open Access Journals (Sweden)

Full Text Available Quantum mechanics is not logically closed with respect to the classical world. Its formalism unfolds as the quantization of a sub-set of classical Hamiltonians. The interpretation of quantum theory in terms of the measurement process inevitably requires to deal with systems composed by a mixture of both classical and quantum degrees of freedom. Moreover, when energy can flow between the quantum and classical degrees of freedom (i.e., in the case of nonadiabatic dynamics, there are more theoretical difficulties in order to obtain a fully consistent quantum-classical formalism. In order to perform calculations, one can renounce to the usual Lie algebraic structure of well-established physical theories, adopt non-Hamiltonian brackets, and obtain a formalism for the dynamics and statistics of quantum-classical systems that has an affordable computational complexity. Recent progress in the algorithms for the sampling of nonadiabatic dynamics of quantum-classical systems at long time is reviewed here.

Alessandro Sergi

2011-05-01

253

Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum systems

International Nuclear Information System (INIS)

The capability of faithfully transmit quantum states and entanglement through quantum channels is one of the key requirements for the development of quantum devices. Different solutions have been proposed to accomplish such a challenging task, which, however, require either an ad hoc engineering of the internal interactions of the physical system acting as the channel or specific initialization procedures. Here we show that optimal dynamics for efficient quantum-state and entanglement transfer can be attained in generic quantum systems with homogeneous interactions by tuning the coupling between the system and the two attached qubits. We devise a general procedure to determine the optimal coupling, and we explicitly implement it in the case of a channel consisting of a spin-(1/2)XY chain. The quality of quantum-state and entanglement transfer is found to be very good and, remarkably, almost independent of the channel length.

2010-11-01

254

Entanglement in fermion systems and quantum metrology

Entanglement in fermion many-body systems is studied using a generalized definition of separability based on partitions of the set of observables, rather than on particle tensor products. In this way, the characterizing properties of non-separable fermion states can be explicitly analyzed, allowing a precise description of the geometric structure of the corresponding state space. These results have direct applications in fermion quantum metrology: sub-shot noise accuracy in parameter estimation can be obtained without the need of a preliminary state entangling operation.

Benatti, F; Marzolino, U

2014-01-01

255

Quantum Field Induced Orderings in Fully Frustrated Ising Spin Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study ordering mechanisms which are induced by the quantum fluctuation in fully frustrated Ising spin systems. Since there are many degenerated states in frustrated systems, "order by thermal disorder" often takes place due to a kind of entropy effect. To consider "order by quantum disorder" in fully frustrated Ising spin systems, we apply transverse field as quantum fluctuation. There exists a ferromagnetic correlation in each sublattice. The sublattice correlation at ze...

Tanaka, Shu; Hirano, Masaki; Miyashita, Seiji

2010-01-01

256

Co-existence of states in quantum systems

Co-existence of different states is a profound concept, which possibly underlies the phase transition and the symmetry breaking. Because of a property inherent to quantum mechanics (cf. uncertainty), the co-existence is expected to appear more naturally in quantum-microscopic systems than in macroscopic systems. In this paper a mathematical theory describing co-existence of states in quantum systems is presented, and the co-existence is classified into 9 types.

Iwata, Yoritaka

2014-01-01

257

On quantum chaos, stochastic webs and localization in a quantum mechanical kick system

Energy Technology Data Exchange (ETDEWEB)

In this study quantum chaos is discussed using the kicked harmonic oscillator as a model system. The kicked harmonic oscillator is characterized by an exceptional scenario of weak chaos: In the case of resonance between the frequency of the harmonic oscillator and the frequency of the periodic forcing, stochastic webs in phase space are generated by the classical dynamics. For the quantum dynamics of this system it is shown that the resulting Husimi distributions in quantum phase space exhibit the same web-like structures as the classical webs. The quantum dynamics is characterized by diffusive energy growth - just as the classical dynamics in the channels of the webs. In the case of nonresonance, the classically diffusive dynamics is found to be quantum mechanically suppressed. This bounded energy growth, which corresponds to localization in quantum phase space, is explained analytically by mapping the system onto the Anderson model. In this way, within the context of quantum chaos, the kicked harmonic oscillator is characterized by exhibiting its noteworthy geometrical and dynamical properties both classically and quantum mechanically, while at the same time there are also very distinct quantum deviations from classical properties, the most prominent example being quantum localization. (orig.)

Engel, U.M.

2007-07-01

258

Characterizing and Quantifying Frustration in Quantum Many-Body Systems

We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration.

Giampaolo, S. M.; Gualdi, G.; Monras, A.; Illuminati, F.

2011-12-01

259

Statistical mechanics of quantum-classical systems with holonomic constraints.

The statistical mechanics of quantum-classical systems with holonomic constraints is formulated rigorously by unifying the classical Dirac bracket and the quantum-classical bracket in matrix form. The resulting Dirac quantum-classical theory, which conserves the holonomic constraints exactly, is then used to formulate time evolution and statistical mechanics. The correct momentum-jump approximation for constrained systems arises naturally from this formalism. Finally, in analogy with what was found in the classical case, it is shown that the rigorous linear-response function of constrained quantum-classical systems contains nontrivial additional terms which are absent in the response of unconstrained systems. PMID:16422574

Sergi, Alessandro

2006-01-14

260

The quantum $H_4$ integrable system

The quantum $H_4$ integrable system is a $4D$ system with rational potential related to the non-crystallographic root system $H_4$ with 600-cell symmetry. It is shown that the gauge-rotated $H_4$ Hamiltonian as well as one of the integrals, when written in terms of the invariants of the Coxeter group $H_4$, is in algebraic form: it has polynomial coefficients in front of derivatives. Any eigenfunctions is a polynomial multiplied by ground-state function (factorization property). Spectra corresponds to one of the anisotropic harmonic oscillator. The Hamiltonian has infinitely-many finite-dimensional invariant subspaces in polynomials, they form the infinite flag with the characteristic vector $\\vec \\al\\ =\\ (1,5,8,12)$.

García, Marcos A G

2010-01-01

261

Asymptotically open quantum systems; Asymptotisch offene Quantensysteme

Energy Technology Data Exchange (ETDEWEB)

In the present thesis we investigate the structure of time-dependent equations of motion in quantum mechanics.We start from two coupled systems with an autonomous equation of motion. A limit, in which the dynamics of one of the two systems has a decoupled evolution and imposes a non-autonomous evolution for the second system is identified. A result due to K. Hepp that provides a classical limit for dynamics turns out to be part and parcel for this limit and is generalized in our work. The method introduced by J.S. Howland for the solution of the time-dependent Schroedinger equation is interpreted as such a limit. Moreover, we associate our limit with the modern theory of quantization. (orig.)

Westrich, M.

2008-04-15

262

Exploiting Quantum Parallelism To Simulate Quantum Random Many-Body Systems

We present an algorithm that exploits quantum parallelism to simulate randomness in a quantum system. In our scheme, all possible realizations of the random parameters are encoded quantum mechanically in a superposition state of an auxiliary system. We show how our algorithm allows for the efficient simulation of dynamics of quantum random spin chains with known numerical methods. We also propose an experimental realization based on atoms in optical lattices in which disorder could be simulated in parallel and in a controlled way through the interaction with another atomic species.

Paredes, B; Cirac, J I

2005-01-01

263

Coherent-Classical Estimation for Quantum Linear Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper introduces a problem of coherent-classical estimation for a class of linear quantum systems. In this problem, the estimator is a mixed quantum-classical system which produces a classical estimate of a system variable. The coherent-classical estimator may also involve coherent feedback. An example involving optical squeezers is given to illustrate the efficacy of this idea.

Petersen, Ian R.

2013-01-01

264

Sistemas cuánticos individuales / Individual Quantum Systems

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: Spanish Abstract in spanish El Premio Nobel de Física 2012 fue otorgado a Serge Haroche y David J.Wineland por métodos experimentales innovadores que permiten la medición y manipulación de sistemas cuánticos individuales. La primera estudia fotones midiéndolos con átomos, y la segunda estudia iones que manipula con fotones. La [...] s aplicaciones tanto potenciales como ya materializadas para el manejo de sistemas cuánticos están en la vía de revolucionar no solamente la tecnología sino la forma en la que comprendemos el mundo microscópico. Abstract in english The Nobel Prize in Physics for 2012 was awarded to Serge Haroche and David J. Wineland "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems". The former deals with photons and measures them with atoms and the latter deals with ions and manipu [...] lates them with photons. The potential and actual applications of handling quantum systems are on their way to revolutionize not only technology but the way we understand the microscopic world.

Jorge A., Campos.

265

Energy Transport in Closed Quantum Systems

We examine energy transport in an ensemble of closed quantum systems driven by stochastic perturbations. One can show that the probability and energy fluxes can be described in terms of quantum advection modes (QAM) associated with the off-diagonal elements of the density matrix. These QAM play the role of Landauer channels in a system with discrete energy spectrum and the eigenfunctions that cannot be described as plane waves. In order to determine the type of correlations that exist between the direction and magnitudes of each QAM and the average direction of energy and probability fluxes we have numerically solved the time-dependent Schr\\"{o}dinger equation describing a single particle trapped in a parabolic potential well which is perturbed by stochastic 'ripples'. The ripples serve as a localized energy source and are offset to one side of the potential well. As the result a non-zero net energy flux flows from one part of the potential well to another across the symmetry center of the potential. We find ...

Levin, G A; Walczak, K; Yerkes, K L

2012-01-01

266

Deformed oscillator algebras for two dimensional quantum superintegrable systems

Quantum superintegrable systems in two dimensions are obtained from their classical counterparts, the quantum integrals of motion being obtained from the corresponding classical integrals by a symmetrization procedure. For each quantum superintegrable systema deformed oscillator algebra, characterized by a structure function specific for each system, is constructed, the generators of the algebra being functions of the quantum integrals of motion. The energy eigenvalues corresponding to a state with finite dimensional degeneracy can then be obtained in an economical way from solving a system of two equations satisfied by the structure function, the results being in agreement to the ones obtained from the solution of the relevant Schrodinger equation. The method shows how quantum algebraic techniques can simplify the study of quantum superintegrable systems, especially in two dimensions.

Bonatsos, Dennis; Kokkotas, K D; Bonatsos, Dennis

1994-01-01

267

Quantum-assisted and Quantum-based Solutions in Wireless Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In wireless systems there is always a trade-off between reducing the transmit power and mitigating the resultant signal-degradation imposed by the transmit-power reduction with the aid of sophisticated receiver algorithms, when considering the total energy consumption. Quantum-assisted wireless communications exploits the extra computing power offered by quantum mechanics based architectures. This paper summarizes some recent results in quantum computing and the correspondin...

Imre, Sandor; Gyongyosi, Laszlo

2012-01-01

268

On microstates counting in many body polymer quantum systems

International Nuclear Information System (INIS)

Polymer quantum systems are mechanical models quantized in a similar way as loop quantum gravity but in which loops/graphs resembling polymers are replaced by discrete sets of points. Such systems have allowed to study in a simpler context some novel aspects of loop quantum gravity. Although thermal aspects play a crucial role in cosmology and black hole physics little attention has been given to the thermostatistics of many body polymer quantum systems. In this work we explore how the features of a one-dimensional effective polymer gas, affect its microstate counting and hence the corresponding thermodynamical quantities.

2011-10-14

269

Device-Independent Certification of High-Dimensional Quantum Systems

An important problem in quantum information processing is the certification of the dimension of quantum systems without making assumptions about the devices used to prepare and measure them, that is, in a device-independent manner. A crucial question is whether such certification is experimentally feasible for high-dimensional quantum systems. Here we experimentally witness in a device-independent manner the generation of six-dimensional quantum systems encoded in the orbital angular momentum of single photons and show that the same method can be scaled, at least, up to dimension 13.

D'Ambrosio, Vincenzo; Bisesto, Fabrizio; Sciarrino, Fabio; Barra, Johanna F.; Lima, Gustavo; Cabello, Adán

2014-04-01

270

On microstates counting in many body polymer quantum systems

Polymer quantum systems are mechanical models quantized in a similar way as loop quantum gravity but in which loops/graphs resembling polymers are replaced by discrete sets of points. Such systems have allowed to study in a simpler context some novel aspects of loop quantum gravity. Although thermal aspects play a crucial role in cosmology and black hole physics little attention has been given to the thermostatistics of many body polymer quantum systems. In this work we explore how the features of a one-dimensional effective polymer gas, affect its microstate counting and hence the corresponding thermodynamical quantities.

Chacón-Acosta, Guillermo; Dagdug, Leonardo; Morales-Técotl, Hugo A.

2011-10-01

271

Uncertainty relations, quantum and thermal fluctuations in Lindblad theory of open quantum systems

In the framework of the Lindblad theory for open quantum systems we derive closed analytical expressions of the uncertainty relation for a particle moving in a harmonic oscillator potential. The particle is in arbitrarily squeezed initial state and interacts with an environment at finite temperature. We examine how the quantum and thermal fluctuations of the environment contribute to the uncertainty in the canonical variables of the systems and study their relative importance in the evolution of the system towards equilibrium with be aim of clarifying the meaning of quantum, classical and thermal dissipation of energy. We show that upon contact with the bath the system evolves from a quantum-dominated state to a thermal-dominated state in a time which is of the same order as the decoherence time calculated before in similar models in the context of a transition from quantum mechanics to classical mechanics. (authors)

Isar, A

2002-01-01

272

Quantum dynamical echo in two-level systems

Evolution of quantum fidelity for two-level systems is studied in the context of periodic echo. From a general treatment for time independent case, we obtain a simple condition on the governing Hamiltonians under which the systems display periodic quantum echo. For a specific time dependent problem the quantum fidelity is shown to exhibit Rabi oscillation. This may be considered as a simple mechanism to generate periodic echo, except for a specific initial superpositional state in which case the fidelity remains invariant.

Sankaranarayanan, R; Lakshmanan, M; Sheeba, Jane H.

2005-01-01

273

Oscillatory tunneling between quantum Hall systems

Electron tunneling between quantum Hall systems on the same two dimensional plane separated by a narrow barrier is studied. We show that in the limit where inelastic scattering time is much longer than the tunneling time, which can be achieved in practice, electrons can tunnel back and forth through the barrier continously, leading to an oscillating current in the absence of external drives. The oscillatory behavior is dictated by a tunneling gap in the energy spectrum. We shall discuss ways to generate oscillating currents and the phenomenon of natural ``dephasing" between the tunneling currents of edge states. The noise spectra of these junctions are also studied. They contain singularites reflecting the existence of tunneling gaps as well as the inherent oscillation in the system. (Figures will be given upon requests).

Ho, T

1994-01-01

274

On the kinetic theory of quantum systems

International Nuclear Information System (INIS)

The contents of this thesis which deals with transport phenomena of specific gases, plasmas and fluids, can be separated into two distinct parts. In the first part a statistical way is suggested to estimate the neutrino mass. Herefore use is made of the fact that massive neutrinos possess a non-zero volume viscosity in contrast with massless neutrinos. The second part deals with kinetic theory of strongly condensed quantum systems of which examples in nature are: liquid Helium, heavy nuclei, electrons in a metal and the interior of stars. In degenerate systems fermions in general interact strongly so that ordinary kinetic theory is not directly applicable. For such cases Landau-Fermi-liquid theory, in which the strongly interacting particles are replaced by much weaker interacting quasiparticles, proved to be very useful. A method is developed in this theory to calculate transport coefficients. Applications of this method on liquid 3Helium yield surprisingly good agreement with experimental results for thermal conductivities. (Auth.)

1986-01-01

275

System of classical nonlinear oscillators as a coarse-grained quantum system

Energy Technology Data Exchange (ETDEWEB)

Constrained Hamiltonian dynamics of a quantum system of nonlinear oscillators is used to provide the mathematical formulation of a coarse-grained description of the quantum system. It is seen that the evolution of the coarse-grained system preserves constant and minimal quantum fluctuations of the fundamental observables. This leads to the emergence of the corresponding classical system on a sufficiently large scale.

Radonjc, Milan; Prvanovic, Slobodan; Buric, Nikola [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia)

2011-08-15

276

Towards the experimental realization of hybrid quantum systems

International Nuclear Information System (INIS)

One of the main interests of quantum physics in this new millennium is the exploitation of quantum mechanical principles in technical applications. One approach here is to use entanglement and superpositions of states to realize powerful algorithms capable of solving challenging computational tasks on a much faster time scale than a classical computer ever could. To find the quantum analogue of a classical bit one needs a quantum mechanical two level system that can be used to store and process quantum information. Most of the current approaches to find such a 'qubit' have the intention to find a single system that is able to fulfill all desirable tasks. But actually most quantum systems are only favorable for very specific tasks (e.g storage, processing, data exchange,..), similar as it is in classical computing. For some qubits the main disadvantages is that their quantum state is very fragile. Those systems loose their 'quantum information' (that is the possibility to store superpositions of their states coherently) easily. They 'decohere' on a timescale that is much shorter then any more involving algorithm. Other systems can keep those superposition states for quite a while, but are so difficult to address that the number of operations that can be made is very limited. The task of a so called hybrid quantum system is now to combine the strengths of these different systems, using e.g. one for manipulation and an other system for storage. Similar to a processor/memory architecture in conventional computers these systems could use a kind of bus system to couple between them. The main task of this thesis was to make steps towards the realization of such a system using two different combinations of quantum systems. Both are planned to use superconducting qubits (transmons) as processor qubit and either atoms (ultra cold rubidium 87 ensembles) or solid state spin systems (Nitrogen Vacancies in diamonds - NV centers) as memory. (author)

2012-01-01

277

Mechanical Systems that are both Classical and Quantum

Quantum dynamics can be regarded as a generalization of classical finite-state dynamics. This is a familiar viewpoint for workers in quantum computation, which encompasses classical computation as a special case. Here this viewpoint is extended to mechanics, where classical dynamics has traditionally been viewed as a macroscopic approximation of quantum behavior, not as a special case. When a classical dynamics is recast as a special case of quantum dynamics, the quantum description can be interpreted classically. For example, sometimes extra information is added to the classical state in order to construct the quantum description. This extra information is then eliminated by representing it in a superposition as if it were unknown information about a classical statistical ensemble. This usage of superposition leads to the appearance of Fermions in the quantum description of classical lattice-gas dynamics and turns continuous-space descriptions of finite-state systems into illustrations of classical sampling ...

Margolus, Norman

2008-01-01

278

Quantum Oscillator in the Thermostat as a Model in the Thermodynamics of Open Quantum Systems

The quantum oscillator in the thermostat is considered as the model of an open quantum system. Our analysis will be heavily founded on the use of the Schroedinger generalized uncertainties relations (SUR). Our first aim is to demonstrate that for the quantum oscillator the state of thermal equilibrium belongs to the correlated coherent states (CCS), which imply the saturation of SUR at any temperature. The obtained results open the perspective for the search of some statistical theory, which unifies the elements of quantum mechanics and GDT; this in turn will give the foundation for the modification of the standard thermodynamics.

Sukhanov, A

2005-01-01

279

Correlation Functions in Open Quantum-Classical Systems

Directory of Open Access Journals (Sweden)

Full Text Available Quantum time correlation functions are often the principal objects of interest in experimental investigations of the dynamics of quantum systems. For instance, transport properties, such as diffusion and reaction rate coefficients, can be obtained by integrating these functions. The evaluation of such correlation functions entails sampling from quantum equilibrium density operators and quantum time evolution of operators. For condensed phase and complex systems, where quantum dynamics is difficult to carry out, approximations must often be made to compute these functions. We present a general scheme for the computation of correlation functions, which preserves the full quantum equilibrium structure of the system and approximates the time evolution with quantum-classical Liouville dynamics. Several aspects of the scheme are discussed, including a practical and general approach to sample the quantum equilibrium density, the properties of the quantum-classical Liouville equation in the context of correlation function computations, simulation schemes for the approximate dynamics and their interpretation and connections to other approximate quantum dynamical methods.

Chang-Yu Hsieh

2013-12-01

280

Efficient Quantum Signature and Its Application in On-line Quantum Payment System

Two arbitrated quantum signature schemes, one with message recovery and the other with appendix, are proposed. The most significant property of the proposed schemes is that both the signatory and the receiver can share and use a long-term secret key with the arbitrator by utilizing the key together with a random number. While in previous quantum signature schemes, the shared key could be used only once, and thus each time when a signatory needs to sign, the signatory and the receiver have to obtain a new key shared with the arbitrator through quantum key distribution protocol. Results show that the presented schemes could be provably secure under the Unbiased-Chosen Basis (UCB) assumption. Moreover, we applies the quantum signature to quantum payment and propose an on-line quantum payment system.

Li, Qin; Wang, Chang-ji

2008-01-01

281

Generalized conditional entropy in bipartite quantum systems

We analyze, for a general concave entropic form, the associated conditional entropy of a quantum system A + B, obtained as a result of a local measurement on one of the systems (B). This quantity is a measure of the average mixedness of A after such measurement, and its minimum over all local measurements is shown to be the associated entanglement of formation between A and a purifying third system C. In the case of the von Neumann entropy, this minimum determines also the quantum discord. For classically correlated states and mixtures of a pure state with the maximally mixed state, we show that the minimizing measurement can be determined analytically and is universal, i.e., the same for all concave forms. While these properties no longer hold for general states, we also show that in the special case of the linear entropy, an explicit expression for the associated conditional entropy can be obtained, whose minimum among projective measurements in a general qudit-qubit state can be determined analytically, in terms of the largest eigenvalue of a simple 3 × 3 correlation matrix. Such minimum determines the maximum conditional purity of A, and the associated minimizing measurement is shown to be also universal in the vicinity of maximal mixedness. Results for X states, including typical reduced states of spin pairs in XY chains at weak and strong transverse fields, are also provided and indicate that the measurements minimizing the von Neumann and linear conditional entropies are typically coincident in these states, being determined essentially by the main correlation. They can differ, however, substantially from that minimizing the geometric discord.

Gigena, N.; Rossignoli, R.

2014-01-01

282

Quantum Heat Engines; Multiple-State 1D Box System

Directory of Open Access Journals (Sweden)

Full Text Available We evaluate quantum Otto, Diesel and Brayton cycles employing multiple-state 1D box system instead of ideal gas filled cylinder. The work and heat are extracted using the change in the expectation of Hamiltonian of the system which leads to the first law of thermodynamics to quantum system. The first law makes available to redefine the force which is in fact not well defined in a quantum mechanical system and then it is applied to define the quantum version of thermodynamic processes, i.e. isobaric, isovolume and adiabatic. As the results, the efficiency of quantum Otto engine depends only on the compression ratio and will be higher than the efficiency of quantum Diesel which can decrease by the widening of expansion under isobaric process. The efficiency of quantum Brayton engine may reach maximum on certain combination between the wide of box under isobaric expansion and compression, under certain conditions. The amount of levels participated in the quantum heat engine system will potentially reduce the performance of the quantum heat cycles consisting isobaric process, but it can be resisted using isobaric process controller.

Eny Latifah

2013-08-01

283

Analog control of open quantum systems under arbitrary decoherence

We derive and investigate a general non-Markovian equation for the time-dependence of a Hamiltonian that maximizes the fidelity of a desired quantum gate on any finite-dimensional quantum system in the presence of arbitrary bath and noise sources. The method is illustrated for a single-qubit gate implemented on a three-level system.

Clausen, Jens; Kurizki, Gershon

2009-01-01

284

Strongly correlated electronic systems and quantum critical phenomena

International Nuclear Information System (INIS)

The activities of the first seminar The strongly correlated electronic systems and quantum critical phenomena (QCP) (town of Troitsk, 11 April, 2003) are described. The following problems: the quantum phase transmissions, QCP under high pressures, the superconductivity near QC point, strongly correlated and heavy-fermion systems and Bose condensation are described

2004-04-01

285

Duality and Non-linear Response for Quantum Hall Systems

We derive the implications of particle-vortex duality for the electromagnetic response of Quantum Hall systems beyond the linear-response regime. This provides a first theoretical explanation of the remarkable duality which has been observed in the nonlinear regime for the electromagnetic response of Quantum Hall systems.

Dolan, B P

2002-01-01

286

Gazeau-Klauder squeezed states associated with solvable quantum systems

Energy Technology Data Exchange (ETDEWEB)

A formalism for the construction of some classes of Gazeau-Klauder squeezed states, corresponding to arbitrary solvable quantum systems with a known discrete spectrum, are introduced. As some physical applications, the proposed structure is applied to a few known quantum systems and then statistical properties as well as squeezing of the obtained squeezed states are studied. Finally, numerical results are presented.

Tavassoly, M K [Department of Physics, University of Yazd, Yazd (Iran, Islamic Republic of)

2006-09-15

287

Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems

This thesis is devoted to the investigation of the quantum liquid crystal phases in strongly correlated electronic systems. Such phases are characterized by their partially broken spatial symmetries and are observed in various strongly correlated systems as being summarized in Chapter 1. Although quantum liquid crystal phases often involve…

Sun, Kai

2009-01-01

288

Symmetry of Quantum Phase Space in a Degenerate Hamiltonian System

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using Husimi function approach, we study the ``quantum phase space'' of a harmonic oscillator interacting with a plane monochromatic wave. We show that in the regime of weak chaos, the quantum system has the same symmetry as the classical system. Analytical results agree with the results of numerical calculations.

Berman, G. P.; Demikhovskii, V. Ya; Kamenev, D. I.

1999-01-01

289

We show that the quantum de Finetti theorem holds for states on infinite-dimensional systems, provided they satisfy certain experimentally verifiable conditions. This result can be applied to prove the security of quantum key distribution based on weak coherent states or other continuous variable states against general attacks. PMID:19392183

Renner, R; Cirac, J I

2009-03-20

290

Dilution Effects in Two-Dimensional Quantum Orbital Systems

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger than that in spin models, but it is also much weaker than that of the classical model. The difference between the classical and the quantum-orbital systems arises from the enhancement of the effective dimensionality due to quantum fluctuations.

Tanaka, Takayoshi; Ishihara, Sumio

2007-06-01

291

In this work, we study the effect of environment on quantum systems relevant for quantum information processing. We begin with the analysis of noise-distorted evolution (decoherence) for a single qubit (two-state quantum system) subject to time-dependent control (quantum gates). We develop two unitarity-preserving approximation schemes for the reduced density matrix and quantify decoherence at shortto-intermediate times. It is demonstrated that the structure of a time-dependent external control can suppress as well as enhance decoherence, and therefore should be taken into consideration while constructing quantum-computing schemes. For more complex quantum-computing systems, it turns out that in certain cases some decoherence can be beneficial. We present an analytical treatment of quantum walks on cycles and hyper-cycles and investigate a realistic physical model based on semiconductor heterostructure with the graph represented by coupled quantum dots formed using a split-gate technique. The decoherence is induced by continuous monitoring of each quantum dot by a nearby quantum point contact. We derive expressions for the probability distribution and calculate bounds for the mixing time. We show that mixing time can be minimized for some rates of decoherence. Apart from coherence, a crucial property of a multi-quoit system affected by environment is its ability to develop and maintain entanglement. It is anticipated that quantum noise destroys fragile entanglement between qubits, making dynamics rather classical. It is also expected that common environment can quantum correlate qubits. The interplay of these two phenomena is analyzed on the example of two spin systems emersed in a bosonic bath. We identify the time scales for which the spins develop entanglement for various spatial separations. Estimates for the interaction and the level of quantum noise for localized impurity electron spins in Si-Ge are given. Properties of entanglement are further investigated for larger qubit systems. An idling multi-qubit system interacting with a common bosonic field experiences quantum phase transition as one alters the coupling to the bath. We derive an exact solution in the limit of a large number of qubits and analyze critical behavior of pairwise entanglement.

Solenov, Dmitry

292

An Open-System Quantum Simulator with Trapped Ions

The control of quantum systems is of fundamental scientific interest and promises powerful applications and technologies. Impressive progress has been achieved in isolating the systems from the environment and coherently controlling their dynamics, as demonstrated by the creation and manipulation of entanglement in various physical systems. However, for open quantum systems, engineering the dynamics of many particles by a controlled coupling to an environment remains largely unexplored. Here we report the first realization of a toolbox for simulating an open quantum system with up to five qubits. Using a quantum computing architecture with trapped ions, we combine multi-qubit gates with optical pumping to implement coherent operations and dissipative processes. We illustrate this engineering by the dissipative preparation of entangled states, the simulation of coherent many-body spin interactions and the quantum non-demolition measurement of multi-qubit observables. By adding controlled dissipation to coheren...

Barreiro, Julio T; Schindler, Philipp; Nigg, Daniel; Monz, Thomas; Chwalla, Michael; Hennrich, Markus; Roos, Christian F; Zoller, Peter; Blatt, Rainer; 10.1038/nature09801

2011-01-01

293

An open-system quantum simulator with trapped ions.

The control of quantum systems is of fundamental scientific interest and promises powerful applications and technologies. Impressive progress has been achieved in isolating quantum systems from the environment and coherently controlling their dynamics, as demonstrated by the creation and manipulation of entanglement in various physical systems. However, for open quantum systems, engineering the dynamics of many particles by a controlled coupling to an environment remains largely unexplored. Here we realize an experimental toolbox for simulating an open quantum system with up to five quantum bits (qubits). Using a quantum computing architecture with trapped ions, we combine multi-qubit gates with optical pumping to implement coherent operations and dissipative processes. We illustrate our ability to engineer the open-system dynamics through the dissipative preparation of entangled states, the simulation of coherent many-body spin interactions, and the quantum non-demolition measurement of multi-qubit observables. By adding controlled dissipation to coherent operations, this work offers novel prospects for open-system quantum simulation and computation. PMID:21350481

Barreiro, Julio T; Müller, Markus; Schindler, Philipp; Nigg, Daniel; Monz, Thomas; Chwalla, Michael; Hennrich, Markus; Roos, Christian F; Zoller, Peter; Blatt, Rainer

2011-02-24

294

Multiple-scale analysis of quantum systems

International Nuclear Information System (INIS)

Conventional weak-coupling Rayleigh-Schroedinger perturbation theory suffers from problems that arise from resonant coupling of successive orders in the perturbation series. Multiple-scale analysis, a powerful and sophisticated perturbative method that quantitatively analyzes characteristic physical behaviors occurring on various length or time scales, avoids such problems by implicitly performing an infinite resummation of the conventional perturbation series. Multiple-scale perturbation theory provides a good description of the classical anharmonic oscillator. Here, it is extended to study (1) the Heisenberg operator equations of motion and (2) the Schroedinger equation for the quantum anharmonic oscillator. In the former case, it leads to a system of coupled operator differential equations, which is solved exactly. The solution provides an operator mass renormalization of the theory. In the latter case, multiple-scale analysis elucidates the connection between weak-coupling perturbative and semiclassical nonperturbative aspects of the wave function. copyright 1996 The American Physical Society

1996-12-01

295

Multiple-scale analysis of quantum systems

Conventional weak-coupling Rayleigh-Schr\\"odinger perturbation theory suffers from problems that arise from resonant coupling of successive orders in the perturbation series. Multiple-scale analysis, a powerful and sophisticated perturbative method that quantitatively analyzes characteristic physical behaviors occurring on various length or time scales, avoids such problems by implicitly performing an infinite resummation of the conventional perturbation series. Multiple-scale perturbation theory provides a good description of the classical anharmonic oscillator. Here, it is extended to study (1) the Heisenberg operator equations of motion and (2) the Schr\\"odinger equation for the quantum anharmonic oscillator. In the former case, it leads to a system of coupled operator differential equations, which is solved exactly. The solution provides an operator mass renormalization of the theory. In the latter case, multiple-scale analysis elucidates the connection between weak-coupling perturbative and semiclassical...

Bender, C M; Bender, Carl M; Bettencourt, Luis M A

1996-01-01

296

Anions, quantum particles in planar systems

International Nuclear Information System (INIS)

Our purpose here is to present a general review of the non-relativistic quantum-mechanical description of excitations that do not obey neither the Fermi-Dirac nor the Bose-Einstein statistics; they rather fulfill an intermediate statistics, the we called 'any-statistics'. As we shall see, this is a peculiarity of (1+1) and (1+2) dimensions, due to the fact that, in two space dimensions, the spin is not quantised, once the rotation group is Abelian. The relevance of studying theories in (1+2) dimensions is justified by the evidence that, in condensed matter physics, there are examples of planar systems, for which everything goes as if the third spatial dimension is frozen. (author)

2000-01-01

297

Experimental feedback control of quantum systems using weak measurements

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario--the stabilization of non-orthogonal states of a qubit against dephasing--we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.

Gillett, G G; Lanyon, B P; Almeida, M P; Barbieri, M; Pryde, G J; O'Brien, J L; Resch, K J; Bartlett, S D; White, A G

2009-01-01

298

Quantum Computing Using an Open System and Projected Subspace

Using the subdynamical kinetic equation for an open quantum system, a formulation is presented for performing decoherence-free (DF) quantum computing in Rigged Liouville Space (RLS). Three types of interactions were considered, and in each case, stationary and evolutionary states were evaluated for DF behavior in both the total space and the projected subspace. Projected subspaces were found using the subdynamics kinetic equation. It was shown that although the total space may be decoherent, the subspace can be DF. In the projected subspace, the evolution of the density operator may be time asymmetric. Hence, a formulation for performing quantum computing in RLS or rigged Hilbert space (RHS) was proposed, and a quantum Controlled-Not Logical gate with corresponding operations in RLS (RHS) was constructed. A generalized quantum Turing machine in RHS was also discussed. Key Words: Quantum Computing, Subdynamics, Rigged Liouvile Space, Decoherence, Open System PACS: 05.30.-d+85.30+82.20.Db+84.35.+i

Qiao, B; Zhen, X H; Qiao, Bi; Ruda, Harry. E.

2001-01-01

299

Representation of quantum dynamics of interacting systems through classical trajectories

We formulate representation of quantum dynamics of many-particle interacting systems through classical trajectories as a perturbative expansion in quantum fluctuations around the classical limit. We explicitly consider three different classical limits in the coordinate-momentum representation (corpuscular classical limit), coherent state representation (wave classical limit), and the classical limit for spin systems. We describe how one recovers truncated Wigner approximation (TWA) in the leading order in quantum fluctuations around each of these limits. Further quantum corrections can be found either in the form of non-linear response of observables to infinitesimal quantum jumps or equivalently in terms of stochastic quantum jumps with non-positive weight. We discuss how one can find both equal and non-equal time correlation functions within this approach and which correlation functions have casual representation. Our approach is closely related to phase space methods based on Weyl quantization, coherent st...

Polkovnikov, Anatoli

2009-01-01

300

Hacking commercial quantum cryptography systems by tailored bright illumination

The peculiar properties of quantum mechanics allow two remote parties to grow a private, secret key, even if the eavesdropper can do anything permitted by the laws of nature. In quantum key distribution (QKD) the parties exchange non-orthogonal or entangled quantum states to generate quantum correlated classical data. Consequently, QKD implementations always rely on detectors to measure the relevant quantum property of the signal states. However, practical detectors are not only sensitive to quantum states. Here we show how an eavesdropper can exploit such deviations from the ideal behaviour: We demonstrate experimentally how the detectors in two commercially available QKD systems can be fully remote controlled using specially tailored bright illumination. This makes it possible to acquire the full secret key without leaving any trace; we propose an eavesdropping apparatus built of off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photo diodes (APDs) to detect ...

Lydersen, Lars; Wittmann, Christoffer; Elser, Dominique; Skaar, Johannes; Makarov, Vadim; 10.1038/NPHOTON.2010.214

2010-01-01

301

Quantum Non-Demolition Detection of Strongly Correlated Systems

Preparation, manipulation, and detection of strongly correlated states of quantum many body systems are among the most important goals and challenges of modern physics. Ultracold atoms offer an unprecedented playground for realization of these goals. Here we show how strongly correlated states of ultracold atoms can be detected in a quantum non-demolition scheme, that is, in the fundamentally least destructive way permitted by quantum mechanics. In our method, spatially resolved components of atomic spins couple to quantum polarization degrees of freedom of light. In this way quantum correlations of matter are faithfully mapped on those of light; the latter can then be efficiently measured using homodyne detection. We illustrate the power of such spatially resolved quantum noise limited polarization measurement by applying it to detect various standard and "exotic" types of antiferromagnetic order in lattice systems and by indicating the feasibility of detection of superfluid order in Fermi liquids.

Eckert, Kai; Rodriguez, Mirta; Lewenstein, Maciej; Polzik, Eugene S; Sanpera, Anna

2008-01-01

302

Non-reversible evolution of quantum chaotic system. Kinetic description

International Nuclear Information System (INIS)

It is well known that the appearance of non-reversibility in classical chaotic systems is connected with a local instability of phase trajectories relatively to a small change of initial conditions and parameters of the system. Classical chaotic systems reveal an exponential sensitivity to these changes. This leads to an exponential growth of initial error with time, and as the result after the statistical averaging over this error, the dynamics of the system becomes non-reversible. In spite of this, the question about the origin of non-reversibility in quantum case remains actual. The point is that the classical notion of instability of phase trajectories loses its sense during quantum consideration. The current work is dedicated to the clarification of the origin of non-reversibility in quantum chaotic systems. For this purpose we study a non-stationary dynamics of the chaotic quantum system. By analogy with classical chaos, we consider an influence of a small unavoidable error of the parameter of the system on the non-reversibility of the dynamics. It is shown in the Letter that due to the peculiarity of chaotic quantum systems, the statistical averaging over the small unavoidable error leads to the non-reversible transition from the pure state into the mixed one. The second part of the Letter is dedicated to the kinematic description of the chaotic quantum-mechanical system. Using the formalism of superoperators, a muster kinematic equation for chaotic quantum system was obtained from Liouville equation under a strict mathematical consideration

2008-02-04

303

Quantum-based electronic devices and systems selected topics in electronics and systems, v.14

This volume includes highlights of the theories and experimental findings that underlie essential phenomena occurring in quantum-based devices and systems as well as the principles of operation of selected novel quantum-based electronic devices and systems. A number of the emerging approaches to creating new types of quantum-based electronic devices and systems are also discussed.

Dutta, Mitra

1998-01-01

304

Many electronic systems (e.g., the cuprate superconductors and heavy fermions) exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are some empirical suggestions of particular increasing length scales that accompany such transitions in some cases, this identification is not universal and in numerous instances no large correlation length is evident. To better understand, as a matter of principle, such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic or supersymmetric quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general nonequilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods in field theories (as well as more recent holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our very broad and rigorous result is that a Wick rotation exactly relates (i) the dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this correspondence, we illustrate that, even in the absence of imposed disorder, many continuum quantum fluid systems (and possible lattice counterparts) may exhibit a zero-point “quantum dynamical heterogeneity” wherein the dynamics, at a given instant, is spatially nonuniform. While the static length scales accompanying this phenomenon do not seem to exhibit a clear divergence in standard correlation functions, the length scale of the dynamical heterogeneities can increase dramatically. We further study “quantum jamming” and illustrate how a hard-core bosonic system can undergo a zero temperature quantum critical metal-to-insulator-type transition with an extremely large effective dynamical exponent z>4 that is consistent with length scales that increase far more slowly than the relaxation time as a putative critical transition is approached. Similar results may hold for spin-liquid-type as well as interacting electronic systems. We suggest ways to analyze experimental data in order to adduce such phenomena. Our approach may be used to analyze other quenched quantum systems.

Nussinov, Zohar; Johnson, Patrick; Graf, Matthias J.; Balatsky, Alexander V.

2013-05-01

305

Hacking commercial quantum cryptography systems by tailored bright illumination

Digital Repository Infrastructure Vision for European Research (DRIVER)

The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumina...

Lydersen, Lars; Wiechers, Carlos; Wittmann, Christoffer; Elser, Dominique; Skaar, Johannes; Makarov, Vadim

2010-01-01

306

Dynamics of open bosonic quantum systems in coherent state representation

International Nuclear Information System (INIS)

We consider the problem of decoherence and relaxation of open bosonic quantum systems from a perspective alternative to the standard master equation or quantum trajectories approaches. Our method is based on the dynamics of expectation values of observables evaluated in a coherent state representation. We examine a model of a quantum nonlinear oscillator with a density-density interaction with a collection of environmental oscillators at finite temperature. We derive the exact solution for dynamics of observables and demonstrate a consistent perturbation approach

2006-01-01

307

Quantum Cost Efficient Reversible BCD Adder for Nanotechnology Based Systems

Reversible logic allows low power dissipating circuit design and founds its application in cryptography, digital signal processing, quantum and optical information processing. This paper presents a novel quantum cost efficient reversible BCD adder for nanotechnology based systems using PFAG gate. It has been demonstrated that the proposed design offers less hardware complexity and requires minimum number of garbage outputs than the existing counterparts. The remarkable property of the proposed designs is that its quantum realization is given in NMR technology.

Islam, Md Saiful; Begum, Zerina

2011-01-01

308

Classical and quantum simulations of many-body systems

Energy Technology Data Exchange (ETDEWEB)

This thesis is devoted to recent developments in the fields of classical and quantum simulations of many-body systems. We describe new classical algorithms that overcome problems apparent in conventional renormalization group and Monte Carlo methods. These algorithms make possible the detailed study of finite temperature properties of 2-D classical and 1-D quantum systems, the investigation of ground states of 2-D frustrated or fermionic systems and the analysis of time evolutions of 2-D quantum systems. Furthermore, we propose new 'analog' quantum simulators that are able to realize interesting models such as a Tonks-Girardeau gas or a frustrated spin-1/2 XY model on a trigonal lattice. These quantum simulators make use of optical lattices and trapped ions and are technically feasible. In fact, the Tonks-Girardeau gas has been realized experimentally and we provide a detailed comparison between the experimental data and the theoretical predictions. (orig.)

Murg, Valentin

2008-04-07

309

Periodic orbits of nonscaling Hamiltonian systems from quantum mechanics

International Nuclear Information System (INIS)

Quantal (E,?) plots are constructed from the eigenvalues of the quantum system. We demonstrate that these representations display the periodic orbits of the classical system, including bifurcations and the transition from stable to unstable

1995-03-01

310

The Geometric Phase in Quantum Systems

International Nuclear Information System (INIS)

The discovery of the geometric phase is one of the most interesting and intriguing findings of the last few decades. It led to a deeper understanding of the concept of phase in quantum mechanics and motivated a surge of interest in fundamental quantum mechanical issues, disclosing unexpected applications in very diverse fields of physics. Although the key ideas underlying the existence of a purely geometrical phase had already been proposed in 1956 by Pancharatnam, it was Michael Berry who revived this issue 30 years later. The clarity of Berry's seminal paper, in 1984, was extraordinary. Research on the topic flourished at such a pace that it became difficult for non-experts to follow the many different theoretical ideas and experimental proposals which ensued. Diverse concepts in independent areas of mathematics, physics and chemistry were being applied, for what was (and can still be considered) a nascent arena for theory, experiments and technology. Although collections of papers by different authors appeared in the literature, sometimes with ample introductions, surprisingly, to the best of my knowledge, no specific and exhaustive book has ever been written on this subject. The Geometric Phase in Quantum Systems is the first thorough book on geometric phases and fills an important gap in the physical literature. Other books on the subject will undoubtedly follow. But it will take a fairly long time before other authors can cover that same variety of concepts in such a comprehensive manner. The book is enjoyable. The choice of topics presented is well balanced and appropriate. The appendices are well written, understandable and exhaustive - three rare qualities. I also find it praiseworthy that the authors decided to explicitly carry out most of the calculations, avoiding, as much as possible, the use of the joke 'after a straightforward calculation, one finds...' This was one of the sentences I used to dislike most during my undergraduate studies. A student is inexperienced in such matters and needs to look at details. This book is addressed to graduate physics and chemistry students and was written thinking of students. However, I would recommend it also to young and mature physicists, even those who are already 'into' the subject. It is a comprehensive work, jointly written by five researchers. After a simple introduction to the subject, the book gradually provides deeper concepts, more advanced theory and finally an interesting introduction and explanation of recent experiments. For its multidisciplinary features, this work could not have been written by one single author. The collaborative effort is undoubtedly one of its most interesting qualities. I would definitely recommend it to anyone who wants to learn more on the geometric phase, a topic that is both beautiful and intriguing. (book review)

2003-12-12

311

Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by Lithographic Techniques: III-V Semiconductors and Carbon: 15. Electrically controlling single spin coherence in semiconductor nanostructures Y. Dovzhenko, K. Wang, M. D. Schroer and J. R. Petta; 16. Theory of electron and nuclear spins in III-V semiconductor and carbon-based dots H. Ribeiro and G. Burkard; 17. Graphene quantum dots: transport experiments and local imaging S. Schnez, J. Guettinger, F. Molitor, C. Stampfer, M. Huefner, T. Ihn and K. Ensslin; Part VI. Single Dots for Future Telecommunications Applications: 18. Electrically operated entangled light sources based on quantum dots R. M. Stevenson, A. J. Bennett and A. J. Shields; 19. Deterministic single quantum dot cavities at telecommunication wavelengths D. Dalacu, K. Mnaymneh, J. Lapointe, G. C. Aers, P. J. Poole, R. L. Williams and S. Hughes; Index.

Tartakovskii, Alexander

2012-07-01

312

Nonequilibrium phenomena in many-body quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis contributes to the field of nonequilibrium phenomena in many-body quantum systems. The properties of systems driven out of equilibrium are studied from three different perspectives: dynamics, thermodynamics, and dynamical phase transitions. The real-time dynamics of quenched quantum systems is studied on the basis of explicit examples of strongly-correlated many-body systems such as the Kondo model, the Luttinger liquid, and the anisotropic Heisenberg chain. The thermodynamic poin...

Heyl, Markus Philip Ludwig

2012-01-01

313

The quantum $H_3$ integrable system

The quantum $H_3$ integrable system is a $3D$ system with rational potential related to the non-crystallographic root system $H_3$. It is shown that the gauge-rotated $H_3$ Hamiltonian as well as one of the integrals, when written in terms of the invariants of the Coxeter group $H_3$, is in algebraic form: it has polynomial coefficients in front of derivatives. The Hamiltonian has infinitely-many finite-dimensional invariant subspaces in polynomials, they form the infinite flag with the characteristic vector $\\vec \\al\\ =\\ (1,2,3)$. One among possible integrals is found (of the second order) as well as its algebraic form. A hidden algebra of the $H_3$ Hamiltonian is determined. It is an infinite-dimensional, finitely-generated algebra of differential operators possessing finite-dimensional representations characterized by a generalized Gauss decomposition property. A quasi-exactly-solvable integrable generalization of the model is obtained. A discrete integrable model on the uniform lattice in a space of $H_3$...

García, Marcos A G

2010-01-01

314

Quantum groups, orthogonal polynomials and applications to some dynamical systems

International Nuclear Information System (INIS)

The first part is concerned with the introduction of quantum groups as an extension of Lie groups. In particular, we study the case of unitary enveloping algebras in dimension 2. We then connect the quantum group formalism to the construction of g CGC recurrent relations. In addition, we construct g-deformed Krawtchouck and Meixner orthogonal polynomials and list their respective main characteristics. The second part deals with some dynamical systems from a classical, a quantum and a gp-analogue point of view. We investigate the Coulomb Kepler system by using the canonical namical systems which contain as special cases some interesting systems for nuclear of atomic physics and for quantum chemistry, such as the Hartmann system, the ring-shaped oscillator, the Smarodinsky-Winternitz system, the Aharonov-Bohen system and the dyania of Dirac and Schroedinger. (author)

1993-01-01

315

Adaptive Hybrid Optimal Quantum Control for Imprecisely Characterized Systems

Optimal quantum control theory carries a huge promise for quantum technology. Its experimental application, however, is often hindered by imprecise knowledge of the input variables, the quantum system's parameters. We show how to overcome this by adaptive hybrid optimal control, using a protocol named Ad-HOC. This protocol combines open- and closed-loop optimal control by first performing a gradient search towards a near-optimal control pulse and then an experimental fidelity estimation with a gradient-free method. For typical settings in solid-state quantum information processing, adaptive hybrid optimal control enhances gate fidelities by an order of magnitude, making optimal control theory applicable and useful.

Egger, D. J.; Wilhelm, F. K.

2014-06-01

316

Quantum simulation of a frustrated Heisenberg spin system

Quantum simulators are capable of calculating properties of quantum systems unfeasible for classical computers. Here we report the analog quantum simulation of arbitrary Heisenberg-type interactions among four spin-1/2 particles. This spin-1/2 tetramer is the two-dimensional archetype system whose ground state belongs to the class of valence-bond states. Depending on the interaction strength, frustration within the system emerges such that the ground state evolves from a localized to a resonating valence-bond state. This spin-1/2 tetramer is created using the polarization states of four photons. We utilize the particular advantages of the precise single-particle addressability and a tunable measurement-induced interaction to obtain fundamental insights into entanglement dynamics among individual particles. We also directly extract ground-state energies and pair-wise quantum correlations, which enable our quantum simulator to investigate the frustration of entanglement. Remarkably, the pair-wise correlations a...

Ma, Xiao-song; Naylor, William; Zeilinger, Anton; Walther, Philip

2010-01-01

317

Quantum Liouville-space trajectories for dissipative systems

In this paper we present a new quantum-trajectory based treatment of quantum dynamics suitable for dissipative systems. Starting from a de Broglie/Bohm-like representation of the quantum density matrix, we derive and define quantum equations-of-motion for Liouville-space trajectories for a generalized system coupled to a dissipative environment. Our theory includes a vector potential which mixes forward and backwards propagating components and non-local quantum potential which continuously produces coherences in the system. These trajectories are then used to propagate an adaptive Lagrangian grid which carries the density matrix, $\\rho(x,y)$, and the action, $A(x,y)$, thereby providing a complete hydrodynamic-like description of the dynamics.

Maddox, J B; Maddox, Jeremy B.; Bittner, Eric R.

2001-01-01

318

Quantum Monte Carlo simulations of bosonic systems

International Nuclear Information System (INIS)

In this thesis several strongly correlated bosonic systems are studied by means of Quantum Monte Carlo (QMC). The QMC method is introduced and first applied to cold atoms in optical lattices as well as a to a recently proposed system of coupled light modes in cavities. The Bose Hubbard model is studied in one and two dimensions with and without a parabolic confining potential. The cavities are described by the so called Jaynes-Cummings Hubbard model which is studied in one dimension. Although these two models describe completely different systems, the physics is similar in many respects even in their dynamical properties. The focus lies on the calculation of excitation spectra such as the dynamical structure factor and one particle spectral functions. These quantities are accessible experimentally by means of spectroscopy, which has recently been applied to cold atomic systems. A comparison to approximate methods is made. This is important since most of the experimental data is compared to such calculations, like mean field or Bogoliubov approaches. It is shown, in which regions of the phase diagram of the Bose-Hubbard model such approaches give reasonable results when dynamical properties are investigated and more importantly, where more involved calculations should be used. Furthermore, the Holstein model which is a model of spinless fermions that couple to phononic degrees of freedom is investigated. To this end an extension to an existing method is introduced. This method was developed for spin-Peierls systems in which the phonon degrees of freedom are sampled in Fourier space for each electron configuration in the Monte Carlo. Here a variant of the algorithm is presented, that uses a path integral representation of the electronic part of the partition sum instead of the stochastic series expansion (SSE) representation. Again the main interest is in dynamical properties such as the dynamical structure factor or the phonon spectral function. (author)

2010-01-01

319

Quantum Percolation and the Anderson Transition in Dilute Systems.

Computer simulation results are presented for quantum systems with discrete off-diagonal disorder in square and cubic lattices. For the quantum percolation model with bonds present or absent at random, the density of states shows a dip at the band center ...

S. N. Evangelou

1983-01-01

320

Phase-modulation transmission system for quantum cryptography.

We describe a new method for quantum key distribution that utilizes phase modulation of sidebands of modulation by use of integrated electro-optic modulators at the transmitting and receiving modules. The system is shown to produce constructive or destructive interference with unity visibility, which should allow quantum cryptography to be carried out with high flexibility by use of conventional devices. PMID:18071422

Mérolla, J M; Mazurenko, Y; Goedgebuer, J P; Porte, H; Rhodes, W T

1999-01-15

321

Notes on Coherent Feedback Control for Linear Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper considers some formulations and possible approaches to the coherent LQG and $H^\\infty$ quantum control problems. Some new results for these problems are presented in the case of annihilation operator only quantum systems showing that in this case, the optimal controllers are trivial controllers.

Petersen, Ian R.

2013-01-01

322

Quantum cryptography with 3-state systems.

We consider quantum cryptographic schemes where the carriers of information are 3-state particles. One protocol uses four mutually unbiased bases and appears to provide better security than obtainable with 2-state carriers. Another possible method allows quantum states to belong to more than one basis. Security is not better, but many curious features arise. PMID:11019329

Bechmann-Pasquinucci, H; Peres, A

2000-10-01

323

Quantum Hall effect-insulator transition in InAs/GaAs quantum dots system

International Nuclear Information System (INIS)

The InAs/GaAs structures with the quantum dots layers, which demonstrate the electron properties of the two-dimensional systems, are studied. The jump-type conductivity with the variable jump length is observed by the current carriers low concentration at low temperatures. The localization length corresponds to the characteristic dimensions of the quantum dots clusters, obtained through the atomic power microscope. The quantum Hall effect-insulator transition, induced by the magnetic field, is observed in the quantum dots layers with the InAs/GaAs metallic conductivity. The values of the specific resistance by the transition exceed the values obtained for the electrons in the heterostructures and quantum holes, which may be explained by presence of the large-scale potential fluctuations and correspondingly the electron density

2003-04-01

324

Attosecond neutron scattering from open quantum systems

Energy Technology Data Exchange (ETDEWEB)

Neutron Compton scattering (NCS) from single nuclei of atoms in molecules, e.g. H{sub 2} (and/or single atoms, e.g. He) is effectuated in the attosecond timescale. The related scattering time is considered in detail, in relation with the Uncertainty Relations. It is shown that the entity scattering time gives a statistical measure of the length of the time interval during which an elementary neutron-nucleus collision may occur, in the same way that the spatial extent of a particle wavefunction (or wavepacket) gives a statistical measure of the extent of the region in which the particle may be found. Consequently, the elementary neutron-nucleus scattering process represents a time-interference phenomenon over the sub-femtosecond ''scattering time'' window. Moreover, the very short-range strong interaction of the neutron-nucleus collision implies that the scattering system (e.g. a proton partically dressed'' with electrons) must be considered as an open quantum system. Experimental results from H{sub 2}, D{sub 2} and HD are mentioned and their anomalous scattering property in the attosecond timescale is qualitatively discussed, also in connection with the Schulman-Gaveau effect.

Dreismann, C.; Aris, C. [Institute of Chemistry, Technical University of Berlin (Germany)

2010-07-01

325

Floquet states of many-body quantum systems

Energy Technology Data Exchange (ETDEWEB)

Periodic driving of a quantum many-body system could provide an access to a multitude of new-non-equilibrium states, essentially different from those a system exhibits at equilibrium. However, the field of ac-driven many-body quantum systems is a little-explored area, mainly for two reasons. First, until recently there were enough exciting problems to study at the equilibrium corner. Second, even under equilibrium conditions, a typical many-body system is a hard nut to crack due to the exponential growth of the number of system states with the number of quantum entities it contains. We discuss the possible directions to take in order to get insight into the evolution of ac-driven many-body quantum systems, outline the obstacles and possible means to overcome them. Our approach is based on the Floquet operator formalism and density-matrix renormalization group (DMRG) methods.

Denisov, Sergey; Seibert, Armin; Ponomarev, Alexey Vladimir; Haenggi, Peter [Institut fuer Physik, Universitaet Augsburg, Universitaetsstr. 1, D-86135 Augsburg (Germany)

2012-07-01

326

Simulations of fluctuations of quantum statistical systems of electrons

The random matrix ensembles (RMT) of quantum statistical Hamiltonian operators, e.g.Gaussian random matrix ensembles (GRME) and Ginibre random matrix ensembles (Ginibre RME), are applied to following quantum statistical systems: nuclear systems, molecular systems, and two-dimensional electron systems (Wigner-Dyson's electrostatic analogy). The Ginibre ensemble of nonhermitean random Hamiltonian matrices $K$ is considered. Each quantum system described by $K$ is a dissipative system and the eigenenergies $Z_{i}$ of the Hamiltonian are complex-valued random variables. The second difference of complex eigenenergies is viewed as discrete analog of Hessian with respect to labelling index. The results are considered in view of Wigner and Dyson's electrostatic analogy. An extension of space of dynamics of random magnitudes is performed by introduction of discrete space of labeling indices. The comparison with the Gaussian ensembles of random hermitean Hamiltonian matrices $H$ is performed. Measures of quantum chaos ...

Duras, M M

2005-01-01

327

Quantum Markov processes and applications in many-body systems

International Nuclear Information System (INIS)

This thesis is concerned with the investigation of quantum as well as classical Markov processes and their application in the field of strongly correlated many-body systems. A Markov process is a special kind of stochastic process, which is determined by an evolution that is independent of its history and only depends on the current state of the system. The application of Markov processes has a long history in the field of statistical mechanics and classical many-body theory. Not only are Markov processes used to describe the dynamics of stochastic systems, but they predominantly also serve as a practical method that allows for the computation of fundamental properties of complex many-body systems by means of probabilistic algorithms. The aim of this thesis is to investigate the properties of quantum Markov processes, i.e. Markov processes taking place in a quantum mechanical state space, and to gain a better insight into complex many-body systems by means thereof. Moreover, we formulate a novel quantum algorithm which allows for the computation of the thermal and ground states of quantum many-body systems. After a brief introduction to quantum Markov processes we turn to an investigation of their convergence properties. We find bounds on the convergence rate of the quantum process by generalizing geometric bounds found for classical processes. We generalize a distance measure that serves as the basis for our investigations, the chi-square divergence, to non-commuting probability spaces. This divergence allows for a convenient generalization of the detailed balance condition to quantum processes. We then devise the quantum algorithm that can be seen as the natural generalization of the ubiquitous Metropolis algorithm to simulate quantum many-body Hamiltonians. By this we intend to provide further evidence, that a quantum computer can serve as a fully-fledged quantum simulator, which is not only capable of describing the dynamical evolution of quantum systems, but also gives access to the computation of their static properties. After this, we turn to an investigation of classical non-equilibrium steady states with methods derived from quantum information theory. We construct a special class of matrix product states that exhibit correlations which can best be understood in terms of classical Markov processes. Finally, we investigate the transport properties of non-equilibrium steady states. The dynamical equations are constructed in such a manner that they allow for both stochastic as well as coherent transport in the same formal framework. It is therefore possible to compare different forms of transport within the same model. (author)

2010-01-01

328

International Nuclear Information System (INIS)

In this paper, within a parasupersymmetric and quantum deformed formalism, we introduce a class of bound-state problems which represents the coupling of a three-level atom with a two-dimensional potential system. We consider second-order parasupersymmetric quantum-mechanical models and a nonlinear deformed algebraic formulation for shape-invariant potential systems to study the quantum dynamics of physical observable, such as atomic level occupation, level transition probabilities, entropy and entanglement, in terms of time and deformation intensity. An application is given for a couple of shape-invariant potentials widely used to model quantum confined systems in several fields of physics, assuming a simple exponential form for the nonlinear deformation function. (paper)

2013-02-08

329

Quantum Coherence Effects in Four-level Diamond Atomic System

A symmetric four-level closed-loop $\\diamondsuit$ type (the diamond structure) atomic system driven by four coherent optical fields is investigated. The system shows rich quantum interference and coherence features. When symmetry of the system is broken, interesting phenomena such as single and double dark resonances appear. As a result, the double electromagnetically induced transparency effect is generated, which will facilitate the implementation of quantum phase gate operation.

Ou, Bao-Quan; Li, Cheng-Zu

2008-01-01

330

Hybrid entanglement concentration using quantum dot and microcavity coupled system

We present two hybrid entanglement concentration protocols based on quantum dots (QDs) and optical microcavity coupled systems. The system is theoretically analyzed and used for photon and electron hybrid entanglement generation. Also, the proposed system can be further used for parity check that allows a quantum nondemolition measurement on the spin parity. By performing parity check process on electron spins, the entangled state can be concentrated into maximally entangled state efficiently.

Wang, Chuan; Cao, Cong; He, Ling-yan; Zhang, Chuan-lin

2014-04-01

331

Perfect Entanglement Transport in Quantum Spin Chain Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a mechanism for perfect entanglement transport in anti-ferromagnetic (AFM) quantum spin chain systems with modulated exchange coupling and also for the modulation of on-site magnetic field. We use the principle of adiabatic quantum pumping process for entanglement transfer in the spin chain systems. We achieve the perfect entanglement transfer over an arbitrarily long distance and a better entanglement transport for longer AFM spin chain system than for the ferromagnetic one. We ex...

Sujit Sarkar

2011-01-01

332

Electron transport in the multi-terminal quantum dot system

Directory of Open Access Journals (Sweden)

Full Text Available The time-dependent electron transport through a multi-terminal quantum dot system is studied. External microwave fields with arbitrary amplitudes, phases and frequencies are applied to different parts of the system considered. The dependence of the average current and average differential conductance on different parameters of the external microwave fields is analyzed. Special attention is paid to the photon–electron pump effect observed for some values of the quantum dot system parameters.

Malgorzata WIERTEL

2005-01-01

333

Strongly correlated electron systems and quantum critical phenomena

International Nuclear Information System (INIS)

Paper is devoted to the 2-nd Workshop on the Strongly Correlated Electron Systems and the Quantum Critical Phenomena. 43 reports were discussed in the course of the Workshop work in the following committees: the Strongly Correlated Electrons and Superconductivity, the Quantum Critical Phenomena (QCP) and Magnetic Features, the Strongly Correlated Systems of Various Nature and the Laboratory Bench Base Reports describing mainly the experiments dealing with the QCP and the correlated systems

2005-10-01

334

Reduced dynamics and the master equation of open quantum systems

Energy Technology Data Exchange (ETDEWEB)

An exact reduced density operator of a quantum system interacting with a bosonic thermal reservoir is derived by means of the simple algebraic method. The necessary and sufficient condition is found that the time-convolutionless master equation becomes exact up to the second order with respect to the system-reservoir interaction. The result is examined by means of the boson-detector model. The reduced dynamics of a quantum system interacting with a classical reservoir is also discussed.

Ban, Masashi, E-mail: ban.masashi@ocha.ac.j [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Kitajima, Sachiko [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Shibata, Fumiaki [Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan)] [International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585 (Japan)

2010-05-10

335

Geometrical and Topological Aspects of Quantum Information Systems

In this Thesis we examine the interplay between the encoding of information in quantum systems and their geometrical and topological properties. We first study photonic qubit probes of space-time curvature, showing how gauge-independent trajectories of photons can help to perform quantum information tasks in space. Then we introduce the first example of topologically ordered systems constructed using interacting light modes on a two-dimensional lattice, which paves the way for feasible observations of topological order in bosonic systems. To conclude, motivated by a theory of quantum gravity we analyze the convergence of entropy in unitarily inequivalent quantization schemes.

Demarie, Tommaso F

2014-01-01

336

Time delays and advances in classical and quantum systems

The paper reviews positive and negative time delays in various processes of classical and quantum physics. In the beginning, we demonstrate how a time-shifted response of a system to an external perturbation appears in classical mechanics and classical electrodynamics. Then we quantify durations of various quantum mechanical processes. The duration of the quantum tunneling is studied. An interpretation of the Hartman paradox is suggested. Time delays and advances appearing in the three-dimensional scattering problem on a central potential are considered. Then we discuss delays and advances appearing in quantum field theory and after that we focus on the issue of time delays and advancements in quantum kinetics. We discuss problems of the application of generalized kinetic equations in simulations of the system relaxation towards equilibrium and analyze the kinetic entropy flow. Possible measurements of time delays and advancements in experiments similar to the recent OPERA neutrino experiment are also discuss...

Kolomeitsev, E E

2013-01-01

337

A robust, scanning quantum system for nanoscale sensing and imaging

Controllable atomic-scale quantum systems hold great potential as sensitive tools for nanoscale imaging and metrology. Possible applications range from nanoscale electric and magnetic field sensing to single photon microscopy, quantum information processing, and bioimaging. At the heart of such schemes is the ability to scan and accurately position a robust sensor within a few nanometers of a sample of interest, while preserving the sensor's quantum coherence and readout fidelity. These combined requirements remain a challenge for all existing approaches that rely on direct grafting of individual solid state quantum systems or single molecules onto scanning-probe tips. Here, we demonstrate the fabrication and room temperature operation of a robust and isolated atomic-scale quantum sensor for scanning probe microscopy. Specifically, we employ a high-purity, single-crystalline diamond nanopillar probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the versatility and performance of our sc...

Maletinsky, P; Grinolds, M S; Hausmann, B; Lukin, M D; Walsworth, R -L; Loncar, M; Yacoby, A

2011-01-01

338

Time delays and advances in classical and quantum systems

This article reviews positive and negative time delays in various processes of classical and quantum physics. In the beginning, we demonstrate how a time-shifted response of a system to an external perturbation appears in classical mechanics and classical electrodynamics. Then we quantify durations of various quantum mechanical processes. The duration of the quantum tunneling is studied, and an interpretation of the Hartmann paradox is suggested. Time delays and advances appearing in the three-dimensional scattering problem on a central potential are considered. We then discuss delays and advances appearing in quantum field theory and after that we focus on the issue of time delays and advancements in quantum kinetics. We discuss problems of the application of generalized kinetic equations in simulations of the system relaxation toward equilibrium and analyze the kinetic entropy flow. Possible measurements of time delays and advancements in experiments similar to the recent OPERA neutrino experiment are also discussed.

Kolomeitsev, E. E.; Voskresensky, D. N.

2013-11-01

339

Classical Processing Requirements for a Topological Quantum Computing System

Dedicated research into the design and construction of a large scale Quantum Information Processing (QIP) system is a complicated task. The design of an experientially feasible quantum processor must draw upon results in multiple fields; from experimental efforts in system control and fabrication through to far more abstract areas such as quantum algorithms and error correction. Recently, the adaptation of topological coding models to physical systems in optics has illustrated a possible long term pathway to truly large scale QIP. As the topological model has well defined protocols for Quantum Error Correction (QEC) built in as part of its construction, a more grounded analysis of the classical processing requirements is possible. In this paper we analyze the requirements for a classical processing system, designed specifically for the topological cluster state model. We demonstrate that via extensive parallelization, the construction of a classical "front-end" system capable of processing error correction da...

Devitt, Simon J; Tilma, Todd; Munro, William J; Nemoto, Kae

2009-01-01

340

Open quantum spin systems in semiconductor quantum dots and atoms in optical lattices

Energy Technology Data Exchange (ETDEWEB)

In this Thesis, we study open quantum spin systems from different perspectives. The first part is motivated by technological challenges of quantum computation. An important building block for quantum computation and quantum communication networks is an interface between material qubits for storage and data processing and travelling photonic qubits for communication. We propose the realisation of a quantum interface between a travelling-wave light field and the nuclear spins in a quantum dot strongly coupled to a cavity. Our scheme is robust against cavity decay as it uses the decay of the cavity to achieve the coupling between nuclear spins and the travelling-wave light fields. A prerequiste for such a quantum interface is a highly polarized ensemble of nuclear spins. High polarization of the nuclear spin ensemble is moreover highly desirable as it protects the potential electron spin qubit from decoherence. Here we present the theoretical description of an experiment in which highly asymmetric dynamic nuclear spin pumping is observed in a single self-assembled InGaAs quantum dot. The second part of this Thesis is devoted to fundamental studies of dissipative spin systems. We study general one-dimensional spin chains under dissipation and propose a scheme to realize a quantum spin system using ultracold atoms in an optical lattice in which both coherent interaction and dissipation can be engineered and controlled. This system enables the study of non-equilibrium and steady state physics of open and driven spin systems. We find, that the steady state expectation values of different spin models exhibit discontinuous behaviour at degeneracy points of the Hamiltonian in the limit of weak dissipation. This effect can be used to dissipatively probe the spectrum of the Hamiltonian. We moreover study spin models under the aspect of state preparation and show that dissipation drives certain spin models into highly entangled state. Finally, we study a spin chain with subwavelength interatomic distances that exhibits long rage interactions. What lies at the heart of all these approaches is the endeavour to include the coupling to the environment into the description of the physical system with the aim of harnessing dissipative processes. While decoherence masks or destroys quantum effects and is considered as the main adversary of any quantum information application, we turn the existence of the dissipative coupling of spin systems to the environment into a fruitful resource.

Schwager, Heike

2012-07-04

341

Quantum Chaos and Entanglement in Atomic Spin Systems

Chaotic behavior is widespread in nature and plays a role in many scientific disciplines. In classical physics, chaos is characterized by hypersensitivity of the evolution to initial conditions (the ``butterfly effect''). Remarkably, this definition is fundamentally at odds with quantum mechanics, in part due to the uncertainty principle and in part due to the Schrödinger equation which preserves the overlap between quantum states. This disconnect has motivated a longstanding search for quantum signatures of chaos, including dynamical signatures such as the generation of entropy and entanglement. I will discuss an experiment [1] in which we realize a common paradigm for quantum chaos - the quantum kicked top - and observe its behavior directly in quantum phase space. Our system is based on the combined electronic and nuclear spin of a single Cs atom and is therefore deep in the quantum regime. We nevertheless find good correspondence between the quantum dynamics and classical phase space structures, and obtain the first experimental evidence for dynamical entanglement as a signature of chaos.[4pt] [1] ``Quantum signatures of chaos in a kicked top'', S. Chaudhury et al., Nature Vol. 461, 768 (2009).

Jessen, Poul

2010-03-01

342

Effects of spacetime fluctuations on quantum systems

Energy Technology Data Exchange (ETDEWEB)

Spacetime can be understood as some kind of spacetime foam of fluctuating bubbles or loops which is expected to be an outcome of a theory of quantum gravity. This should lead to a fluctuating spacetime. In our approach we assume that spacetime fluctuations manifest as classical stochastic fluctuations of the metric. It will be shown how quantum dynamics is affected and we discuss the following effects: (i) an apparent violation of the weak equivalence principle, (ii) a modification of the spreading of wavepackets, and (iii) a loss of quantum coherence.

Goeklue, Ertan; Laemmerzahl, Claus [ZARM - Universitaet Bremen (Germany)

2010-07-01

343

How Quantum Computers Fail: Quantum Codes, Correlations in Physical Systems, and Noise Accumulation

The feasibility of computationally superior quantum computers is one of the most exciting and clear-cut scientific questions of our time. The question touches on fundamental issues regarding probability, physics, and computability, as well as on exciting problems in experimental physics, engineering, computer science, and mathematics. We propose three related directions towards a negative answer. The first is a conjecture about physical realizations of quantum codes, the second has to do with correlations in stochastic physical systems, and the third proposes a model for quantum evolutions when noise accumulates. The paper is dedicated to the memory of Itamar Pitowsky.

Kalai, Gil

2011-01-01

344

Correlation after reflection in a quantum system

Reflection of a microscopic non-zero rest mass particle from a macroscopic mirror generates two-particle interference from the incident and reflected particle substates and the associated mirror substates. This amplifies effects such as fringe spacing since they are essentially determined not by the mass of the macroscopic mirror but rather by the much smaller mass of the microscopic particle. Coherence can be transferred during reflection from the initial particle substate to the mirror substate. Interference of multiple such two-particle states is discussed. These effects could lead to extending measurements of the quantum-classical boundary to larger masses. The possibility of non-simultaneous measurement of the positions of the particle and the mirror is also discussed. The joint probability density, which is a function both of the different positions and different times at which the particle and mirror are measured, is derived assuming that no interaction occurs between the measurement times. An analog of the Doppler shift for this correlated system is discussed along with interference of multiple such two-particle states.

Browne, Ryan S.

345

Dynamical Phase Transitions in Quantum Systems

Directory of Open Access Journals (Sweden)

Full Text Available Many years ago Bohr characterized the fundamental differences between the two extreme cases of quantum mechanical many-body problems known at that time: between the compound states in nuclei at extremely high level density and the shell-model states in atoms at low level density. It is shown in the present paper that the compound nucleus states at high level density are the result of a dynamical phase transition due to which they have lost any spectroscopic relation to the individual states of the nucleus. The last ones are shell-model states which are of the same type as the shell-model states in atoms. Mathematically, dynamical phase transitions are caused by singular (exceptional points at which the trajectories of the eigenvalues of the non-Hermitian Hamilton operator cross. In the neighborhood of these singular points, the phases of the eigenfunctions are not rigid. It is possible therefore that some eigenfunctions of the system align to the scattering wavefunctions of the environment by decoupling (trapping the remaining ones from the environment. In the Schrödinger equation, nonlinear terms appear in the neighborhood of the singular points.

Ingrid Rotter

2010-11-01

346

Closed-loop and robust control of quantum systems.

For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control) have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA), and reinforcement learning (RL) methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H(?) control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention. PMID:23997680

Chen, Chunlin; Wang, Lin-Cheng; Wang, Yuanlong

2013-01-01

347

Relativistic quantum dynamics of many-body systems.

Relativistic quantum dynamics requires a unitary representation of the Poincare group on the Hilbert space of states. The Dynamics of many-body systems must satisfy cluster separability requirements. In this paper we formulate an abstract framework of fou...

F. Coester W. N. Polyzou

2000-01-01

348

Conserved current in Markovian open-quantum systems

International Nuclear Information System (INIS)

We reexamine the Markovian approximation of local current in open quantum systems, discussed recently by Gebauer and Car. Our derivation is more transparent; the proof of the current conservation becomes explicit and easy

2006-06-01

349

Superconducting Quantum Interference based Electromechanical Systems:

Digital Repository Infrastructure Vision for European Research (DRIVER)

Mechanical sensors are essential tools for the detection of small forces. This thesis presents the dc SQUID as a detector for the displacement of embedded micromechanical resonators. The device geometry and basic operating principle are described. The SQUID displacement detector reaches an excellent resolution, a factor of 1.5 below the standard quantum limit: It can detect one-third of a single vibrational quantum in a 129 kHz resonator. We use the high displacement sensitivity to perform fe...

2012-01-01

350

Entanglement Generation in Spatially Separated Systems Using Quantum Walk

Directory of Open Access Journals (Sweden)

Full Text Available We present a scheme for generating entanglement between two spatially separated systems from the spatial entanglement generated by the interference effect during the evolution of a single-particle quantum walk. Any two systems which can interact with the spatial modes entangled during the walk evolution can be entangled using this scheme. A notable feature is the ability to control the quantum walk dynamics and its localization at desired pair lattice sites irrespective of separation distance resulting in a substantial control and improvement in the entanglement output. Implementation schemes to entangle spatially separated atoms using quantum walk on a single atom is also presented.

Sandeep K. Goyal

2012-06-01

351

Relativistic Quantum Dynamics of Many-Body Systems

Relativistic quantum dynamics requires a unitary representation of the Poincare group on the Hilbert space of states. The dynamics of many-body systems must satisfy cluster separability requirements. In this paper we formulate an abstract framework of four dimensional Euclidean Green functions that can be used to construct relativistic quantum dynamics of N-particle systems consistent with these requirements. This approach should be useful in bridging the gap between few-body dynamics based on phenomenological mass operators and on quantum field theory.

Coester, F

2001-01-01

352

Asymptotically Optimal Quantum Circuits for d-level Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

As a qubit is a two-level quantum system whose state space is spanned by |0>, |1>, so a qudit is a d-level quantum system whose state space is spanned by |0>,...,|d-1>. Quantum computation has stimulated much recent interest in algorithms factoring unitary evolutions of an n-qubit state space into component two-particle unitary evolutions. In the absence of symmetry, Shende, Markov and Bullock use Sard's theorem to prove that at least C 4^n two-qubit unitary evolutions are r...

Bullock, Stephen S.; O Leary, Dianne P.; Brennen, Gavin K.

2004-01-01

353

Quantum Monte Carlo methods for rovibrational states of molecular systems

International Nuclear Information System (INIS)

We present applications to molecular problems of a recently developed quantum Monte Carlo algorithm [Phys. Rev. E 55, 3664 (1997)] for the calculation of excited state energies of multi?dimensional quantum systems, employing a projection operator imaginary time spectral evolution (POITSE). The extraction of vibrational energies is demonstrated on a double well potential and on two coupled harmonic oscillators, and on excited rotational states of a rotating harmonic oscillator. All energies extracted by the quantum Monte Carlo algorithm are in good agreement with exact results, showing that the new method is very promising for the calculation of tunneling splittings, and of vibrational and rotational excitations in real multi?dimensional molecular systems

1997-12-01

354

Quantum dynamics applications in biological and material systems

Even though time-dependent spectroscopic techniques continue to push the frontier of chemical physics, they receive scant mention in introductory courses and are poorly covered in standard texts. Quantum Dynamics: Applications in Biological and Materials Systems bridges the gap between what is traditionally taught in a one-semester quantum chemistry course and the modern field of chemical dynamics, presenting the quantum theory of charge and energy transport in biological systems and optical-electronic materials from a dynamic perspective.Reviews the basicsTaking a pedagogical approach, the bo

Bittner, Eric R

2010-01-01

355

Entanglement and correlation in anisotropic quantum spin systems

Analytical expressions for the entanglement measures concurrence, i-concurrence and 3-tangle in terms of spin correlation functions are derived using general symmetries of the quantum spin system. These relations are exploited for the one-dimensional XXZ-model, in particular the concurrence and the critical temperature for disentanglement are calculated for finite systems with up to six qubits. A recent NMR quantum error correction experiment is analyzed within the framework of the proposed theoretical approach.

Glaser, U; Fehske, H; Glaser, Ulrich; Buettner, Helmut; Fehske, Holger

2003-01-01

356

Quantum Dynamics of Molecular Systems and Guided Matter Waves

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum dynamics is the study of time-dependent phenomena in fundamental processes of atomic and molecular systems. This thesis focuses on systems where nature reveals its quantum aspect; e.g. in vibrational resonance structures, in wave packet revivals and in matter wave interferometry. Grid based numerical methods for solving the time-dependent Schrödinger equation are implemented for simulating time resolved molecular vibrations and to compute photo-electron spectra, without the necessity...

2001-01-01

357

Density matrices and Wigner functions of quasiclassical quantum systems

International Nuclear Information System (INIS)

A wide variety of problems of quantum mechanics, which are most easily solved with the use of the Wigner function is considered. It primarily comprises the problem of quantum description of open (dissipative) systems with the relevant linear equations of motion (in the general case, non-Hamiltonian). Possibilities of describing such systems within the frames of the Fokker-Planck equation for the Wigner function, satisfying conditions of preservation of normality, hermiticity and positive definiteness of the density matrix, are studied

1986-01-01

358

Plausibility of Quantum Coherent States in Biological Systems

In this paper we briefly discuss the necessity of using quantum mechanics as a fundamental theory applicable to some key functional aspects of biological systems. This is especially relevant to three important parts of a neuron in the human brain, namely the cell membrane, microtubules (MT) and ion channels. We argue that the recently published papers criticizing the use of quantum theory in these systems are not convincing.

Salari, V; Rahnama, M; Bernroider, G

2010-01-01

359

Electron-vibron effects in interacting quantum dot systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis we consider the vibrational effects on the electric transport properties of a quantum dot system. We thereby address three different problems. In the first part, we develope a theoretical model of a single level quantum dot system which is coupled to many vibronic modes. According to this model, many vibronic degenerate state can contribute to transport at finite bias. However, the coherences between the degenerate states do not play any significant role. In the differentia...

Yar, Abdullah

2012-01-01

360

Lepton and quark families as quantum-dynamical systems

International Nuclear Information System (INIS)

We conjecture that the observed four lepton and quark families (#betta#sub(N)), (esub(N)) and (usub(N)), (dsub(N)), if considered in the space of generations N = 1,2,3..., are quantum-dynamical systems, much like particles of the first quantization are quantum-dynamical systems in the position space. We call this far-going conjecture the ''zeroth quantization'' and discuss its consequences for lepton and quark mass spectra. (author)

1980-01-01

361

On the response of quantum linear systems to single photon input fields

Digital Repository Infrastructure Vision for European Research (DRIVER)

The purpose of this paper is to extend linear systems and signals theory to include single photon quantum signals. We provide detailed results describing how quantum linear systems respond to multichannel single photon quantum signals. In particular, we characterize the class of states (which we call {\\em photon-Gaussian} states) that result when multichannel photons are input to a quantum linear system. We show that this class of quantum states is preserved by quantum linea...

Zhang, Guofeng; James, Matthew R.

2012-01-01

362

Mixed quantum-classical description of spectroscopy of dissipative systems.

Mixed quantum-classical statistical mechanics is employed to calculate dipole moment correlation function and linear absorption spectra. A quantum two-level subsystem interacting with quantum vibrations (primary oscillators) which in turn are coupled to a classical bath composed of infinite set of harmonic oscillators is used as a dissipative system. Starting with mixed quantum-classical Liouville equation for the evaluation of the mixed quantum-classical dipole moment correlation function and using coherent states and the inverse of Baker-Campbell-Hausdorf formula to evaluate the trace over the primary oscillators, whereby, a closed analytical expression for the electronic dipole moment correlation function is obtained. Illustrations of several absorption spectra at different temperatures are provided. An approximate optical four-point correlation is obtained in the high temperature limit. A strategy for deriving an exact optical four-point correlation is suggested. PMID:17129136

Toutounji, Mohamad

2006-11-21

363

International Nuclear Information System (INIS)

Full text: (author)The developed approach allows one to construct a more realistic nonrelativistic quantum theory which includes 'fundamental environment' (FE) (physical vacuum's fluctuations) as a constituent part of a quantum system (QS). As a result of this, the problems of spontaneous transitions (including decay of the ground state) between energy levels of quantum system, the Lamb shift of energy levels, erp paradox and many other difficulties of standard quantum theory are solved more naturally. In this approach, we find a new feature of quantum systems. Unlike de-Broglie wave this peculiarity does not disappear with increase in mass of the system. In other words, a macroscopic system which till now has been considered exclusively classical has some quantum-field properties which at definite conditions can be quite observable and measurable. Moreover, it is proved that after the disintegration of macrosystem into parts its fragments are in the entanglement states, which is specified by nonpotential interaction and all this takes place due to fundamental environment. It especially concerns nonstationary systems, for example, biological systems in which elementary atom-molecular processes proceed continuously. Note that such conclusion becomes even more obvious, if to take into account the well known work of [1], where the idea of universal description for unified dynamics of micro and macroscopic systems in the form of the Fokker-Planck equation was for the first time suggested. Finally, in the limits of the developed approach the closed system 'QS + FE' in equilibrium is being described on extended space R3 x En , where En is compactified subspace

2011-07-12

364

Manipulating quantum information on the controllable systems or subspaces

In this paper, we explore how to constructively manipulate quantum information on the controllable systems or subspaces. It is revealed that one can make full use of distinguished properties of Pauli operators to design control Hamiltonian based on the geometric parametrization of quantum states. It is demonstrated in this research that Bang-Bang controls, triangle-function controls and square-function control can be utilized to manipulate controllable qubits or encoded qubits on controllable subspace for both open quantum dynamical systems and uncontrollable closed quantum dynamical systems. Furthermore, we propose a new kind of time-energy performance index to trade-off time and energy resource cost, and comprehensively discuss how to design control magnitude to minimize a kind of time-energy performance. A comparison has been made among these three kind of optimal control. It is underlined in this research that the optimal time performance can be always expressed as J^{*} =\\lamda{\\cdot}t^{*}_{f} +E^{*} for...

Zhang, Ming

2010-01-01

365

Perfect Entanglement Transport in Quantum Spin Chain Systems

Directory of Open Access Journals (Sweden)

Full Text Available We propose a mechanism for perfect entanglement transport in anti-ferromagnetic (AFM quantum spin chain systems with modulated exchange coupling and also for the modulation of on-site magnetic field. We use the principle of adiabatic quantum pumping process for entanglement transfer in the spin chain systems. We achieve the perfect entanglement transfer over an arbitrarily long distance and a better entanglement transport for longer AFM spin chain system than for the ferromagnetic one. We explain analytically and physically—why the entanglement hops in alternate sites. We find the condition for blocking of entanglement transport even in the perfect pumping situation. Our analytical solution interconnects quantum many body physics and quantum information science.

Sujit Sarkar

2011-12-01

366

Applying quantum mechanics to macroscopic and mesoscopic systems

There exists a paradigm in which Quantum Mechanics is an exclusively developed theory to explain phenomena on a microscopic scale. As the Planck's constant is extremely small, $h\\sim10^{-34}{J.s}$, and as in the relation of de Broglie the wavelength is inversely proportional to the momentum; for a mesoscopic or macroscopic object the Broglie wavelength is very small, and consequently the undulatory behavior of this object is undetectable. In this paper we show that with a particle oscillating around its classical trajectory, the action is an integer multiple of a quantum of action, $S = nh_{o}$. The quantum of action, $h_{o}$, which plays a role equivalent to Planck's constant, is a free parameter that must be determined and depends on the physical system considered. For a mesoscopic and macroscopic system: $h_{o}\\gg h$, this allows us to describe these systems with the formalism of quantum mechanics.

T., N Poveda

2012-01-01

367

The entropy power inequality for quantum systems

When two independent analog signals, X and Y are added together giving Z=X+Y, the entropy of Z, H(Z), is not a simple function of the entropies H(X) and H(Y), but rather depends on the details of X and Y's distributions. Nevertheless, the entropy power inequality (EPI), which states that exp [2H(Z)] \\geq exp[2H(X) + exp[2H(Y)], gives a very tight restriction on the entropy of Z. This inequality has found many applications in information theory and statistics. The quantum analogue of adding two random variables is the combination of two independent bosonic modes at a beam splitter. The purpose of this work is to give a detailed outline of the proof of two separate generalizations of the entropy power inequality to the quantum regime. Our proofs are similar in spirit to standard classical proofs of the EPI, but some new quantities and ideas are needed in the quantum setting. Specifically, we find a new quantum de Bruijin identity relating entropy production under diffusion to a divergence-based quantum Fisher i...

Koenig, Robert

2012-01-01

368

Tampering detection system using quantum-mechanical systems

The use of quantum-mechanically entangled photons for monitoring the integrity of a physical border or a communication link is described. The no-cloning principle of quantum information science is used as protection against an intruder's ability to spoof a sensor receiver using a `classical` intercept-resend attack. Correlated measurement outcomes from polarization-entangled photons are used to protect against quantum intercept-resend attacks, i.e., attacks using quantum teleportation.

Humble, Travis S. (Knoxville, TN); Bennink, Ryan S. (Knoxville, TN); Grice, Warren P. (Oak Ridge, TN)

2011-12-13

369

Tampering detection system using quantum-mechanical systems

Energy Technology Data Exchange (ETDEWEB)

The use of quantum-mechanically entangled photons for monitoring the integrity of a physical border or a communication link is described. The no-cloning principle of quantum information science is used as protection against an intruder's ability to spoof a sensor receiver using a `classical` intercept-resend attack. Correlated measurement outcomes from polarization-entangled photons are used to protect against quantum intercept-resend attacks, i.e., attacks using quantum teleportation.

Humble, Travis S. (Knoxville, TN); Bennink, Ryan S. (Knoxville, TN); Grice, Warren P. (Oak Ridge, TN)

2011-12-13

370

Scavenging quantum information: Multiple observations of quantum systems

Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system `collapses' into a post-measurement state from which the {\\em{same}} observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity, when one or several qudits are available to carry information about the single-qudit state, and study the `classical' limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In add...

Rapcan, Peter; Munoz-Tapia, Ramon; Bagan, Emilio; Buzek, Vladimir

2011-01-01

371

Scavenging quantum information: Multiple observations of quantum systems

Energy Technology Data Exchange (ETDEWEB)

Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system collapses into a postmeasurement state from which the same observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or can scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity when one or several qudits are available to carry information about the single-qudit state, and we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In addition to the case where all observers perform most informative measurements, we study the scenario where a finite number of observers estimates the state with equal fidelity, regardless of their position in the measurement sequence and the scenario where all observers use identical measurement apparatuses (up to a mutually unknown orientation) chosen so that a particular observer's estimation fidelity is maximized.

Rapcan, P. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Calsamiglia, J.; Munoz-Tapia, R. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Bagan, E. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Department of Physics, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10021 (United States); Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Buzek, V. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Faculty of Informatics, Masaryk University, Botanicka 68a, CZ-602 00 Brno (Czech Republic)

2011-09-15

372

Scavenging quantum information: Multiple observations of quantum systems

International Nuclear Information System (INIS)

Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system collapses into a postmeasurement state from which the same observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or can scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity when one or several qudits are available to carry information about the single-qudit state, and we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In addition to the case where all observers perform most informative measurements, we study the scenario where a finite number of observers estimates the state with equal fidelity, regardless of their position in the measurement sequence and the scenario where all observers use identical measurement apparatuses (up to a mutually unknown orientation) chosen so that a particular observer's estimation fidelity is maximized.

2011-09-01

373

Faraday-Michelson system for quantum cryptography.

Quantum key distribution provides unconditional security for communication. Unfortunately, current experimental schemes are not suitable for long-distance fiber transmission because of phase drift or Rayleigh backscattering. In this Letter we present a unidirectional intrinsically stable scheme that is based on Michelson-Faraday interferometers, in which ordinary mirrors are replaced with 90 degree Faraday mirrors. With the scheme, a demonstration setup was built and excellent stability of interference fringe visibility was achieved over a fiber length of 175 km. Through a 125 km long commercial communication fiber cable between Beijing and Tianjin, the key exchange was performed with a quantum bit-error rate of less than 6%, which is to our knowledge the longest reported quantum key distribution experiment under field conditions. PMID:16208923

Mo, Xiao-Fan; Zhu, Bing; Han, Zheng-Fu; Gui, You-Zhen; Guo, Guang-Can

2005-10-01

374

Symmetry in quantum system theory: Rules for quantum architecture design

International Nuclear Information System (INIS)

We investigate universality in the sense of controllability and observability, of multi-qubit systems in architectures of various symmetries of coupling type and topology. By determining the respective dynamic system Lie algebras, explicit reachability sets under symmetry constraints are provided. Thus for a given (possibly symmetric) experimental coupling architecture several decision problems can be solved in a unified way: (i) can a target Hamiltonian be simulated? (ii) can a target gate be synthesised? (iii) to which extent is the system observable by a given set of detection operators? and, as a special case of the latter, (iv) can an underlying system Hamiltonian be identified with a given set of detection operators? Finally, in turn, the absence of symmetry provides a convenient necessary condition for full controllability. Though often easier to assess than the well-established Lie-algebra rank condition, this is not sufficient unless the candidate dynamic simple Lie algebra can be pre-identified uniquely. Thus for architectures with various Ising and Heisenberg coupling types we give design rules sufficient to ensure full controllability. In view of follow-up studies, we relate the unification of necessary and sufficient conditions for universality to filtering simple Lie subalgebras of su(N) comprising classical and exceptional types.

2010-03-08

375

Decoherence Control in Open Quantum System via Classical Feedback

In this work we propose a novel strategy using techniques from systems theory to completely eliminate decoherence and also provide conditions under which it can be done so. A novel construction employing an auxiliary system, the bait, which is instrumental to decoupling the system from the environment is presented. Our approach to decoherence control in contrast to other approaches in the literature involves the bilinear input affine model of quantum control system which lends itself to various techniques from classical control theory, but with non-trivial modifications to the quantum regime. The elegance of this approach yields interesting results on open loop decouplability and Decoherence Free Subspaces(DFS). Additionally, the feedback control of decoherence may be related to disturbance decoupling for classical input affine systems, which entails careful application of the methods by avoiding all the quantum mechanical pitfalls. In the process of calculating a suitable feedback the system has to be restru...

Ganesan, N; Ganesan, Narayan; Tarn, Tzyh Jong

2006-01-01

376

Towards polymer quantum mechanics for fermionic systems

Polymer quantum mechanics is based on models that mimic the loop quantization of gravity. It coincides with the results of the standard quantum mechanical treatment for such models when a certain length scale parameter is considered to be small. In this work we present some steps in the construction of the polymer representation of a Fermi oscillator, the fermonic counterpart of the harmonic oscillator. It is suggested that the non regular character of the bosonic polymer representation has as a counterpart the non superanalytic character of the fermonic polymer case. We propose a candidate Hamiltonian operator and investigate and contrast its energy spectrum with the standard one.

García-Chung, Angel A.; Morales-Técotl, Hugo A.; Reyes, Juan D.

2013-07-01

377

Quantum information transfer between topological and spin qubit systems

We propose a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. Our suggestion uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, we show how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.

Leijnse, Martin

2011-01-01

378

Quantum information transfer between topological and spin qubit systems

International Nuclear Information System (INIS)

In this talk I introduce a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. The transfer method uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, I discuss how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.

2012-03-25

379

Evaluation of Abbott Quantum II yeast identification system.

Digital Repository Infrastructure Vision for European Research (DRIVER)

The identity of each of 239 yeasts, encompassing 9 genera and 30 species, was determined with the Quantum II and API 20C identification systems. With API 20C results accepted as being correct, Quantum II proved to be 92% accurate in identification of common isolates, e.g., Candida albicans and Torulopsis glabrata, but only 73% effective with less frequently encountered yeasts, e.g., Trichosporon beigelii and Rhodotorula glutinis. Overall, Quantum II was 86% as accurate as API 20C for the yeas...

Salkin, I. F.; Schadow, K. H.; Bankaitis, L. A.; Mcginnis, M. R.; Kemna, M. E.

1985-01-01

380

International Nuclear Information System (INIS)

The manifestation of measurements, randomly distributed in time, on the evolution of quantum systems are analyzed in detail. The set of randomly distributed measurements (RDM) is modeled within the renewal theory, in which the distribution is characterized by the probability density function (PDF) W(t) of times t between successive events (measurements). The evolution of the quantum system affected by the RDM is shown to be described by the density matrix satisfying the stochastic Liouville equation. This equation is applied to the analysis of the RDM effect on the evolution of a two-level system for different types of RDM statistics, corresponding to different PDFs W(t). Obtained general results are illustrated as applied to the cases of the Poissonian (W(t)? e-wrt) and anomalous (W(t) ? 1/t1+?, ? ? 1) RDM statistics. In particular, specific features of the quantum and inverse Zeno effects, resulting from the RDM, are thoroughly discussed.

2011-02-04

381

The manifestation of measurements, randomly distributed in time, on the evolution of quantum systems are analyzed in detail. The set of randomly distributed measurements (RDM) is modeled within the renewal theory, in which the distribution is characterized by the probability density function (PDF) W(t) of times t between successive events (measurements). The evolution of the quantum system affected by the RDM is shown to be described by the density matrix satisfying the stochastic Liouville equation. This equation is applied to the analysis of the RDM effect on the evolution of a two-level system for different types of RDM statistics, corresponding to different PDFs W(t). Obtained general results are illustrated as applied to the cases of the Poissonian (W(t) \\sim \\,e^{-w_r t}) and anomalous (W(t) ~ 1/t1 + ?, ? RDM statistics. In particular, specific features of the quantum and inverse Zeno effects, resulting from the RDM, are thoroughly discussed.

Shushin, A. I.

2011-02-01

382

Quantum cavity modes in spatially extended Josephson systems

We report a theoretical study of the macroscopic quantum dynamics in spatially extended Josephson systems. We focus on a Josephson tunnel junction of finite length placed in an externally applied magnetic field. In such a system, electromagnetic waves in the junction are excited in the form of cavity modes manifested by Fiske resonances, which are easily observed experimentally. We show that in the quantum regime various characteristics of the junction as its critical current $I_c$, width of the critical current distribution $\\sigma$, escape rate $\\Gamma$ from the superconducting state to a resistive one, and the time-dependent probability $P(t)$ of the escape are influenced by the number of photons excited in the junction cavity. Therefore, these characteristics can be used as a tool to measure the quantum states of photons in the junction, e.g. quantum fluctuations, coherent and squeezed states, entangled Fock states, etc.

Fistul, M V

2006-01-01

383

We employ the theoretical framework of positive operator valued measures, to study Markovian open quantum systems. In particular, we discuss how a quantum system influences its environment. Using the theory of indirect measurements, we then draw conclusions about the information we could hypothetically obtain about the system by observing the environment. Although the environment is not actually observed, we can use these results to describe the change of the quantum system due to its interaction with the environment. We apply this technique to two different problems. In the first part, we study the coherently driven dynamics of a particle on a rail of quantum dots. This tunnelling between adjacent quantum dots can be controlled externally. We employ an adiabatic scheme similar to stimulated Raman adiabatic passage, to transfer the particle between different quantum dots. We compare two fundamentally different sources of decoherence. In the second part, we study the dynamics of a free quantum particle, which ...

Kamleitner, Ingo

2010-01-01

384

Implementation of Grover's quantum search algorithm in a scalable system

International Nuclear Information System (INIS)

We report the implementation of Grover's quantum search algorithm in the scalable system of trapped atomic ion quantum bits. Any one of four possible states of a two-qubit memory is marked, and following a single query of the search space, the marked element is successfully recovered with an average probability of 60(2)%. This exceeds the performance of any possible classical search algorithm, which can only succeed with a maximum average probability of 50%

2005-11-01

385

Far from equilibrium energy flow in quantum critical systems

We investigate far from equilibrium energy transport in strongly coupled quantum critical systems. Combining results from gauge-gravity duality, relativistic hydrodynamics, and quantum field theory, we argue that long-time energy transport occurs via a universal steady-state for any spatial dimensionality. This is described by a boosted thermal state. We determine the transport properties of this emergent steady state, including the average energy flow and its long-time fluctuations.

Bhaseen, M J; Lucas, Andrew; Schalm, Koenraad

2013-01-01

386

The Signals and Systems Approach to Quantum Computation

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this note we point out the fact that the proper conceptual setting of quantum computation is the theory of Linear Time Invariant systems. To convince readers of the utility of the approach, we introduce a new model of computation based on the orthogonal group. This makes the link to traditional electronics engineering clear. We conjecture that the speed up achieved in quantum computation is at the cost of increased circuit complexity.

Gadiyar, H. Gopalkrishna; Maini, K. M. Sangeeta; Padma, R.; Sharatchandra, H. S.

2003-01-01

387

Computer simulation of mixed classical-quantum systems

Energy Technology Data Exchange (ETDEWEB)

We briefly review three important methods that are currently used in the simulation of mixed systems. Two of these techniques, path integral Monte Carlo or molecular dynamics and dynamical simulated annealing, have the limitation that they can only describe the structural properties in the ground state. The third so-called quantum molecular dynamics (QMD) method can provide not only the static properties but also the real-time dynamics of a quantum particle at finite temperatures. 10 refs.

Kalia, R.K.; Vashishta, P.

1988-11-01

388

Implementation of Grover's Quantum Search Algorithm in a Scalable System

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the implementation of Grover's quantum search algorithm in the scalable system of trapped atomic ion quantum bits. Any one of four possible states of a two-qubit memory is marked, and following a single query of the search space, the marked element is successfully recovered with an average probability of 60(2)%. This exceeds the performance of any possible classical search algorithm, which can only succeed with a maximum average probability of 50%.

Brickman, K. -a; Haljan, P. C.; Lee, P. J.; Acton, M.; Deslauriers, L.; Monroe, C.

2005-01-01

389

Projected wave functions for fractionalized phases of quantum spin systems

Gutzwiller projection allows a construction of an assortment of variational wave functions for strongly correlated systems. For quantum spin S=1/2 models, Gutzwiller-projected wave functions have resonating-valence-bond structure and may represent states with fractional quantum numbers for the excitations. Using insights obtained from field-theoretical descriptions of fractionalization in two dimensions, we construct candidate wave functions of fractionalized states by projecting specific superconducting states. We explicitly demonstrate the presence of topological order in these states.

Ivanov, D A

2002-01-01

390

Multipartite quantum systems and symplectic toric manifolds

In this paper we study the geometrical structures of multi-qubit states based on symplectic toric manifolds. After a short review of symplectic toric manifolds, we discuss the space of a single quantum state in terms of these manifolds. We also investigate entangled multipartite states based on moment map and Delzant's construction of toric manifolds and algebraic toric varieties.

Heydari, Hoshang

2010-01-01

391

Coherent control of open quantum dynamical systems

International Nuclear Information System (INIS)

A systematic analysis of the behavior of the quantum Markovian master equation driven by coherent control fields is proposed. Its irreversible character is formalized using control-theoretic notions and the sets of states that can be reached via coherent controls are described. The analysis suggests to what extent (and how) it is possible to counteract the effect of dissipation

2004-12-01

392

Effects of symmetry breaking in finite quantum systems

The review considers the peculiarities of symmetry breaking and symmetry transformations and the related physical effects in finite quantum systems. Some types of symmetry in finite systems can be broken only asymptotically. However, with a sufficiently large number of particles, crossover transitions become sharp, so that symmetry breaking happens similarly to that in macroscopic systems. This concerns, in particular, global gauge symmetry breaking, related to Bose-Einstein condensation and superconductivity, or isotropy breaking, related to the generation of quantum vortices, and the stratification in multicomponent mixtures. A special type of symmetry transformation, characteristic only for finite systems, is the change of shape symmetry. These phenomena are illustrated by the examples of several typical mesoscopic systems, such as trapped atoms, quantum dots, atomic nuclei, and metallic grains. The specific features of the review are: (i) the emphasis on the peculiarities of the symmetry breaking in finit...

Birman, J L; Yukalov, V I

2013-01-01

393

Deconstructing non-Dirac-Hermitian supersymmetric quantum systems

Energy Technology Data Exchange (ETDEWEB)

A method to construct a non-Dirac-Hermitian supersymmetric quantum system that is isospectral with a Dirac-Hermitian Hamiltonian is presented. The general technique involves a realization of the basic canonical (anti-)commutation relations involving both bosonic and fermionic degrees of freedom in terms of non-Dirac-Hermitian operators which are Hermitian in a Hilbert space that is endowed with a pre-determined positive-definite metric. A pseudo-Hermitian realization of the Clifford algebra for a pre-determined positive-definite metric is used to construct supersymmetric systems with one or many degrees of freedom. It is shown that exactly solvable non-Dirac-Hermitian supersymmetric quantum systems can be constructed corresponding to each exactly solvable Dirac-Hermitian system. Examples of non-Dirac-Hermitian (i) non-relativistic Pauli Hamiltonian, (ii) super-conformal quantum system, and (iii) supersymmetric Calogero-type models admitting entirely real spectra are presented.

Ghosh, Pijush K, E-mail: pijushkanti.ghosh@visva-bharati.ac.in [Department of Physics, Siksha-Bhavana, Visva-Bharati University, Santiniketan 731 235, West Bengal (India)

2011-05-27

394

Deconstructing non-Dirac-Hermitian supersymmetric quantum systems

A method to construct a non-Dirac-Hermitian supersymmetric quantum system that is isospectral with a Dirac-Hermitian Hamiltonian is presented. The general technique involves a realization of the basic canonical (anti-)commutation relations involving both bosonic and fermionic degrees of freedom in terms of non-Dirac-Hermitian operators which are Hermitian in a Hilbert space that is endowed with a pre-determined positive-definite metric. A pseudo-Hermitian realization of the Clifford algebra for a pre-determined positive-definite metric is used to construct supersymmetric systems with one or many degrees of freedom. It is shown that exactly solvable non-Dirac-Hermitian supersymmetric quantum systems can be constructed corresponding to each exactly solvable Dirac-Hermitian system. Examples of non-Dirac-Hermitian (i) non-relativistic Pauli Hamiltonian, (ii) super-conformal quantum system, and (iii) supersymmetric Calogero-type models admitting entirely real spectra are presented.

Ghosh, Pijush K.

2011-05-01

395

The solution of the quantum $A_1$ T-system for arbitrary boundary

We solve the quantum version of the $A_1$ $T$-system by use of quantum networks. The system is interpreted as a particular set of mutations of a suitable (infinite-rank) quantum cluster algebra, and Laurent positivity follows from our solution. As an application we re-derive the corresponding quantum network solution to the quantum $A_1$ $Q$-system and generalize it to the fully non-commutative case. We give the relation between the quantum $T$-system and the quantum lattice Liouville equation, which is the quantized $Y$-system.

Di Francesco, Philippe

2011-01-01

396

Quantum demolition filtering and optimal control of unstable systems.

A brief account of the quantum information dynamics and dynamical programming methods for optimal control of quantum unstable systems is given to both open loop and feedback control schemes corresponding respectively to deterministic and stochastic semi-Markov dynamics of stable or unstable systems. For the quantum feedback control scheme, we exploit the separation theorem of filtering and control aspects as in the usual case of quantum stable systems with non-demolition observation. This allows us to start with the Belavkin quantum filtering equation generalized to demolition observations and derive the generalized Hamilton-Jacobi-Bellman equation using standard arguments of classical control theory. This is equivalent to a Hamilton-Jacobi equation with an extra linear dissipative term if the control is restricted to Hamiltonian terms in the filtering equation. An unstable controlled qubit is considered as an example throughout the development of the formalism. Finally, we discuss optimum observation strategies to obtain a pure quantum qubit state from a mixed one. PMID:23091216

Belavkin, V P

2012-11-28

397

Modeling a quantum Hall system via elliptic equations

Quantum Hall systems are a suitable theme for a case study in the general area of nanotechnology. In particular, it is a good framework for considering such general problems as nanosystem modeling, and nanosystem-specific signal processing. It has been demonstrated in my recent work--A. Sowa, Fractional quantization of Hall resistance as a consequence of mesoscopic feedback, Russ. J. Math. Phys., Vol. 15, No.1 (2008), 122-127--how to construct a simple model of a quantum Hall system. Briefly speaking, this is achieved by complementing the Schroedinger dynamics with a special type of nonlinear feedback loop. This result stems from a novel systematic approach to describing quantum Hall systems. In particular, our analysis of such systems implicitly involves the notion of quantum entanglement. In this article we undertake to modify the original model of a quantum Hall system by substituting the dynamics based on the Dirac operator. This leads to a model that consists of a system of three nonlinearly coupled firs...

Sowa, Artur

2008-01-01

398

According to the quantum de Finetti theorem, if the state of an N-partite system is invariant under permutations of the subsystems then it can be approximated by a state where almost all subsystems are identical copies of each other, provided N is sufficiently large compared to the dimension of the subsystems. The de Finetti theorem has various applications in physics and information theory, where it is for instance used to prove the security of quantum cryptographic schemes. Here, we extend de Finetti's theorem, showing that the approximation also holds for infinite dimensional systems, as long as the state satisfies certain experimentally verifiable conditions. This is relevant for applications such as quantum key distribution (QKD), where it is often hard - or even impossible - to bound the dimension of the information carriers (which may be corrupted by an adversary). In particular, our result can be applied to prove the security of QKD based on weak coherent states or Gaussian states against general atta...

Renner, Renato

2008-01-01

399

Born-Oppenheimer approximation for open quantum systems within the quantum trajectory approach

International Nuclear Information System (INIS)

Using the quantum trajectory approach, we extend the Born-Oppenheimer (BO) approximation from closed to open quantum systems, where the open quantum system is described by a master equation in Lindblad form. The BO approximation is defined and the validity condition is derived. We find that the dissipation in fast variables improves the BO approximation, unlike the dissipation in slow variables. A detailed comparison is presented between this extension and our previous approximation based on the effective Hamiltonian approach [X. L. Huang and X. X. Yi, Phys. Rev. A 80, 032108 (2009)]. Several additional features and advantages are analyzed, which show that the two approximations are complementary to each other. Two examples are described to illustrate our method.

2010-05-01

400

Numerical approaches to complex quantum, semiclassical and classical systems

International Nuclear Information System (INIS)

In this work we analyse the capabilities of several numerical techniques for the description of different physical systems. Thereby, the considered systems range from quantum over semiclassical to classical and from few- to many-particle systems. In chapter 1 we investigate the behaviour of a single quantum particle in the presence of an external disordered background (static potentials). Starting from the quantum percolation problem, we address the fundamental question of a disorder induced (Anderson-) transition from extended to localised single-particle eigenstates. Distinguishing isolating from conducting states by applying a local distribution approach for the local density of states (LDOS), we detect the quantum percolation threshold in two- and three-dimensions. Extending the quantum percolation model to a quantum random resistor model, we comment on the possible relevance of our results to the influence of disorder on the conductivity in graphene sheets. For the calculation of the LDOS as well as for the Chebyshev expansion of the time evolution operator, the kernel polynomial method (KPM) is the key numerical technique. In chapter 2 we examine how a single quantum particle is influenced by retarded bosonic fields that are inherent to the system. Within the Holstein model, these bosonic degrees of freedom (phonons) give rise to an infinite dimensional Hilbert space, posing a true many-particle problem. Constituting a minimal model for polaron formation, the Holstein model allows us to study the optical absorption and activated transport in polaronic systems. Using a two-dimensional variant of the KPM, we calculate for the first time quasi-exactly the optical absorption and dc-conductivity as a function of temperature. In chapter 3 we come back to the time evolution of a quantum particle in an external, static potential and investigate the capability of semiclassical approximations to it. We address basic quantum effects as tunneling, interference and anharmonicity. To this end we consider the linearised semiclassical propagator method, the Wigner-Moyal approach and the recently proposed quantum tomography. Finally, in chapter 4 we calculate the dynamics of a classical many-particle system under the influence of external fields. Considering a low-temperature rf-plasma, we investigate the interplay of the plasma dynamics and the motion of dust particles, immersed into the plasma for diagnostic reasons. (orig.)

2008-01-01

401

A quantum information perspective of fermionic quantum many-body systems

International Nuclear Information System (INIS)

In this Thesis fermionic quantum many-body system are theoretically investigated from a quantum information perspective. Quantum correlations in fermionic many-body systems, though central to many of the most fascinating effects of condensed matter physics, are poorly understood from a theoretical perspective. Even the notion of ''paired'' fermions which is widely used in the theory of superconductivity and has a clear physical meaning there, is not a concept of a systematic and mathematical theory so far. Applying concepts and tools from entanglement theory, we close this gap, developing a pairing theory allowing to unambiguously characterize paired states. We develop methods for the detection and quantification of pairing according to our definition which are applicable to current experimental setups. Pairing is shown to be a quantum correlation distinct from any notion of entanglement proposed for fermionic systems, giving further understanding of the structure of highly correlated quantum states. In addition, we show the resource character of paired states for precision metrology, proving that BCS-states allow phase measurements at the Heisenberg limit. Next, the power of fermionic systems is considered in the context of quantum simulations, where we study the possibility to simulate Hamiltonian time evolutions on a cubic lattice under the constraint of translational invariance. Given a set of translationally invariant local Hamiltonians and short range interactions we determine time evolutions which can and those which can not be simulated. Bosonic and finite-dimensional quantum systems (''spins'') are included in our investigations. Furthermore, we develop new techniques for the classical simulation of fermionic many-body systems. First, we introduce a new family of states, the fermionic Projected Entangled Pair States (fPEPS) on lattices in arbitrary spatial dimension. These are the natural generalization of the PEPS known for spin systems, and they approximate efficiently ground and thermal states of systems with short-range interaction. We give an explicit mapping between fPEPS and PEPS, allowing to extend previous simulation methods to fermions. In addition, we show that fPEPS naturally arise as exact ground states of certain fermionic Hamiltonians, and give an example that exhibits criticality while fulfilling the area law. Finally, we derive methods for the determination of ground and thermal states, as well as the time evolution, of interacting fermionic systems using generalized Hartree-Fock theory (gHFT). With the computational complexity scaling polynomially with the number of particles, this method can deal with large systems. As a benchmark we apply our methods to the translationally invariant Hubbard model with attractive interaction and find excellent agreement with known results. (orig.)

2009-01-01

402

A quantum information perspective of fermionic quantum many-body systems

Energy Technology Data Exchange (ETDEWEB)

In this Thesis fermionic quantum many-body system are theoretically investigated from a quantum information perspective. Quantum correlations in fermionic many-body systems, though central to many of the most fascinating effects of condensed matter physics, are poorly understood from a theoretical perspective. Even the notion of ''paired'' fermions which is widely used in the theory of superconductivity and has a clear physical meaning there, is not a concept of a systematic and mathematical theory so far. Applying concepts and tools from entanglement theory, we close this gap, developing a pairing theory allowing to unambiguously characterize paired states. We develop methods for the detection and quantification of pairing according to our definition which are applicable to current experimental setups. Pairing is shown to be a quantum correlation distinct from any notion of entanglement proposed for fermionic systems, giving further understanding of the structure of highly correlated quantum states. In addition, we show the resource character of paired states for precision metrology, proving that BCS-states allow phase measurements at the Heisenberg limit. Next, the power of fermionic systems is considered in the context of quantum simulations, where we study the possibility to simulate Hamiltonian time evolutions on a cubic lattice under the constraint of translational invariance. Given a set of translationally invariant local Hamiltonians and short range interactions we determine time evolutions which can and those which can not be simulated. Bosonic and finite-dimensional quantum systems (''spins'') are included in our investigations. Furthermore, we develop new techniques for the classical simulation of fermionic many-body systems. First, we introduce a new family of states, the fermionic Projected Entangled Pair States (fPEPS) on lattices in arbitrary spatial dimension. These are the natural generalization of the PEPS known for spin systems, and they approximate efficiently ground and thermal states of systems with short-range interaction. We give an explicit mapping between fPEPS and PEPS, allowing to extend previous simulation methods to fermions. In addition, we show that fPEPS naturally arise as exact ground states of certain fermionic Hamiltonians, and give an example that exhibits criticality while fulfilling the area law. Finally, we derive methods for the determination of ground and thermal states, as well as the time evolution, of interacting fermionic systems using generalized Hartree-Fock theory (gHFT). With the computational complexity scaling polynomially with the number of particles, this method can deal with large systems. As a benchmark we apply our methods to the translationally invariant Hubbard model with attractive interaction and find excellent agreement with known results. (orig.)

Kraus, Christina V.

2009-11-02

403

Experimental detection of quantum information sharing and its quantification in quantum spin systems

International Nuclear Information System (INIS)

We study the macroscopic entanglement properties of a low-dimensional quantum spin system by investigating its magnetic properties at low temperatures and high magnetic fields. The spin system chosen for this is copper nitrate (Cu(NO3)2 × 2.5H2O), which is a spin chain that exhibits dimerization. The temperature and magnetic field dependence of entanglement from the susceptibility and magnetization data are given, by comparing the experimental results with the theoretical estimates. Extraction of entanglement has been made possible through the macroscopic witness operator, magnetic susceptibility. An explicit comparison of the experimental extraction of entanglement with theoretical estimates is provided. It was found that theory and experiments match over a wide range of temperatures and fields. The spin system studied exhibits quantum phase transition (QPT) at low temperatures when the magnetic field is swept through a critical value. We show explicitly for the first time, using tools used in quantum information processing, that QPT can be captured experimentally using quantum complementary observables, which clearly delineate entangled states from separable ones across the QPT. We have also estimated the partial information sharing in this system from our magnetization and susceptibility data. The complementarity relation has been experimentally verified to hold in this system. (paper)

2013-01-01

404

Shot noise in chaotic systems "classical" to quantum crossover

This paper is devoted to study of the classical-to-quantum crossover of the shot noise value in chaotic systems. This crossover is determined by the ratio of the particle dwell time in the system, $\\tau_d$, to the characteristic time for diffraction $t_E \\simeq \\lambda^{-1} |\\ln \\hbar|$, where $\\lambda$ is the Lyapunov exponent. The shot noise vanishes in the limit $t_E \\gg \\tau_d $, while reaches its universal quantum value in the opposite limit. Thus, the Lyapunov exponent of chaotic mesoscopic systems may be found by the shot noise measurements.

Agam, O; Larkin, A; Agam, Oded; Aleiner, Igor; Larkin, Anatoly

1999-01-01

405

Equivalence of the Symbol Grounding and Quantum System Identification Problems

Directory of Open Access Journals (Sweden)

Full Text Available The symbol grounding problem is the problem of specifying a semantics for the representations employed by a physical symbol system in a way that is neither circular nor regressive. The quantum system identification problem is the problem of relating observational outcomes to specific collections of physical degrees of freedom, i.e., to specific Hilbert spaces. It is shown that with reasonable physical assumptions these problems are equivalent. As the quantum system identification problem is demonstrably unsolvable by finite means, the symbol grounding problem is similarly unsolvable.

Chris Fields

2014-02-01

406

Alternative routes to equivalent classical models of a quantum system

International Nuclear Information System (INIS)

Coarse-graining of some sort is a fundamental and unavoidable step in any attempt to derive the classical mechanical behavior from the quantum formalism. We utilize the two-mode Bose—Hubbard model to illustrate how different coarse-grained systems can be naturally associated with a fixed quantum system if it is compatible with different dynamical algebras. Alternative coarse-grained systems generate different evolutions of the same physical quantities, and the difference becomes negligible only in the appropriate macro-limit. (general)

2012-12-01

407

Nonlinear dynamics and quantum entanglement in optomechanical systems.

To search for and exploit quantum manifestations of classical nonlinear dynamics is one of the most fundamental problems in physics. Using optomechanical systems as a paradigm, we address this problem from the perspective of quantum entanglement. We uncover strong fingerprints in the quantum entanglement of two common types of classical nonlinear dynamical behaviors: periodic oscillations and quasiperiodic motion. There is a transition from the former to the latter as an experimentally adjustable parameter is changed through a critical value. Accompanying this process, except for a small region about the critical value, the degree of quantum entanglement shows a trend of continuous increase. The time evolution of the entanglement measure, e.g., logarithmic negativity, exhibits a strong dependence on the nature of classical nonlinear dynamics, constituting its signature. PMID:24702337

Wang, Guanglei; Huang, Liang; Lai, Ying-Cheng; Grebogi, Celso

2014-03-21

408

Thermodynamics of quantum dissipative many-body systems

We consider quantum nonlinear many-body systems with dissipation described within the Caldeira-Leggett model, i.e., by a nonlocal action in the path integral for the density matrix. Approximate classical-like formulas for thermodynamic quantities are derived for the case of many degrees of freedom, with general kinetic and dissipative quadratic forms. The underlying scheme is the pure-quantum self-consistent harmonic approximation (PQSCHA), equivalent to the variational approach by the Feynman-Jensen inequality with a suitable quadratic nonlocal trial action. A low-coupling approximation permits to get manageable PQSCHA expressions for quantum thermal averages with a classical Boltzmann factor involving an effective potential and an inner Gaussian average that describes the fluctuations originating from the interplay of quanticity and dissipation. The application of the PQSCHA to a quantum phi4-chain with Drude-like dissipation shows nontrivial effects of dissipation, depending upon its strength and bandwidth...

Cuccoli, A; Tognetti, V; Vaia, R

1999-01-01

409

Quantum maximum entropy principle for a system of identical particles

International Nuclear Information System (INIS)

By introducing a functional of the reduced density matrix, we generalize the definition of a quantum entropy which incorporates the indistinguishability principle of a system of identical particles. With the present definition, the principle of quantum maximum entropy permits us to solve the closure problem for a quantum hydrodynamic set of balance equations corresponding to an arbitrary number of moments in the framework of extended thermodynamics. The determination of the reduced Wigner function for equilibrium and nonequilibrium conditions is found to become possible only by assuming that the Lagrange multipliers can be expanded in powers of (?/2?)2. Quantum contributions are expressed in powers of (?/2?)2 while classical results are recovered in the limit (?/2?)?0.

2010-02-01

410

RKKY interaction in a chirally coupled double quantum dot system

The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is investigated in a double quantum dots system, coupled via a central open conducting region. A perpendicular magnetic field induces the formation of Landau Levels which in turn give rise to the so-called Kondo chessboard pattern in the transport through the quantum dots. The two quantum dots become therefore chirally coupled via the edge channels formed in the open conducting area. In regions where both quantum dots exhibit Kondo transport the presence of the RKKY exchange interaction is probed by an analysis of the temperature dependence. The thus obtained Kondo temperature of one dot shows an abrupt increase at the onset of Kondo transport in the other, independent of the magnetic field polarity, i.e. edge state chirality in the central region.

Heine, A. W.; Tutuc, D.; Zwicknagl, G.; Schuh, D.; Wegscheider, W.; Haug, R. J.

2013-12-01

411

Quantum corrections to fidelity decay in chaotic systems

By considering correlations between classical orbits we derive semiclassical expressions for the decay of the quantum fidelity amplitude for classically chaotic quantum systems, as well as for its squared modulus, the fidelity or Loschmidt echo. Our semiclassical results for the fidelity amplitude agree with random matrix theory (RMT) and supersymmetry predictions in the universal Fermi-golden rule regime. The calculated quantum corrections can be viewed as arising from a static random perturbation acting on nearly self-retracing interfering paths, and hence will be suppressed for time-varying perturbations. Moreover, using trajectory-based methods we show a relation, recently obtained in RMT, between the fidelity amplitude and the cross-form factor for parametric level correlations. Beyond RMT, we compute Ehrenfest-time effects on the fidelity amplitude. Furthermore our semiclassical approach allows for a unified treatment of the fidelity, both in the Fermi-golden rule and Lyapunov regimes, demonstrating that quantum corrections are suppressed in the latter.

Gutkin, Boris; Waltner, Daniel; Gutiérrez, Martha; Kuipers, Jack; Richter, Klaus

2010-03-01

412

Complex Critical Exponents in Diluted Systems of Quantum Rotors

In this work, we investigate the effects of the Berry phase 2 ?? on the critical properties of XY quantum-rotors that undergo a percolation transition. This model describes a variety of randomly-diluted quantum systems, such as interacting bosons coupled to a particle reservoir, quantum planar antiferromagnets under a perpendicular magnetic field, and Josephson-junction arrays with an external bias-voltage. Focusing on the quantum critical point at the percolation threshold, we find that, for rational ?, one recovers the power-law behavior with the same critical exponents as in the case with no Berry phase. However, for irrational ?, the low-energy excitations change completely and are given by emergent spinless fermions with fractal spectrum. As a result, critical properties that cannot be described by the usual Ginzburg-Landau-Wilson theory of phase transitions emerge, such as complex critical exponents, log-periodic oscillations, and dynamically-broken scale invariance.

Fernandes, Rafael; Schmalian, Jörg

2011-03-01

413

Scattering Theory for Open Quantum Systems with Finite Rank Coupling

International Nuclear Information System (INIS)

Quantum systems which interact with their environment are often modeled by maximal dissipative operators or so-called Pseudo-Hamiltonians. In this paper the scattering theory for such open systems is considered. First it is assumed that a single maximal dissipative operator AD in a Hilbert space is used to describe an open quantum system. In this case the minimal self-adjoint dilation of AD can be regarded as the Hamiltonian of a closed system which contains the open system, but since K-tilde is necessarily not semibounded from below, this model is difficult to interpret from a physical point of view. In the second part of the paper an open quantum system is modeled with a family {A(?)} of maximal dissipative operators depending on energy ?, and it is shown that the open system can be embedded into a closed system where the Hamiltonian is semibounded. Surprisingly it turns out that the corresponding scattering matrix can be completely recovered from scattering matrices of single pseudo-Hamiltonians as in the first part of the paper. The general results are applied to a class of Sturm-Liouville operators arising in dissipative and quantum transmitting Schroedinger-Poisson systems

2007-11-01

414

Hydrogen atom as a quantum-classical hybrid system

International Nuclear Information System (INIS)

Hydrogen atom is studied as a quantum-classical hybrid system, where the proton is treated as a classical object while the electron is regarded as a quantum object. We use a well known mean-field approach to describe this hybrid hydrogen atom; the resulting dynamics for the electron and the proton is compared to their full quantum dynamics. The electron dynamics in the hybrid description is found to be only marginally different from its full quantum counterpart. The situation is very different for the proton: in the hybrid description, the proton behaves like a free particle; in the fully quantum description, the wave packet center of the proton orbits around the center of mass. Furthermore, we find that the failure to describe the proton dynamics properly can be regarded as a manifestation of the fact that there is no conservation of momentum in the mean-field hybrid approach. We expect that such a failure is a common feature for all existing approaches for quantum-classical hybrid systems of Born-Oppenheimer type.

2013-06-10

415

Quantum Processes and Dynamic Networks in Physical and Biological Systems.

Quantum theory since its earliest formulations in the Copenhagen Interpretation has been difficult to integrate with general relativity and with classical Newtonian physics. There has been traditionally a regard for quantum phenomena as being a limiting case for a natural order that is fundamentally classical except for microscopic extrema where quantum mechanics must be applied, more as a mathematical reconciliation rather than as a description and explanation. Macroscopic sciences including the study of biological neural networks, cellular energy transports and the broad field of non-linear and chaotic systems point to a quantum dimension extending across all scales of measurement and encompassing all of Nature as a fundamentally quantum universe. Theory and observation lead to a number of hypotheses all of which point to dynamic, evolving networks of fundamental or elementary processes as the underlying logico-physical structure (manifestation) in Nature and a strongly quantized dimension to macroscalar processes such as are found in biological, ecological and social systems. The fundamental thesis advanced and presented herein is that quantum phenomena may be the direct consequence of a universe built not from objects and substance but from interacting, interdependent processes collectively operating as sets and networks, giving rise to systems that on microcosmic or macroscopic scales function wholistically and organically, exhibiting non-locality and other non -classical phenomena. The argument is made that such effects as non-locality are not aberrations or departures from the norm but ordinary consequences of the process-network dynamics of Nature. Quantum processes are taken to be the fundamental action-events within Nature; rather than being the exception quantum theory is the rule. The argument is also presented that the study of quantum physics could benefit from the study of selective higher-scale complex systems, such as neural processes in the brain, by virtue of mathematical and computational models that may be transferred from the macroscopic domain to the microscopic. A consequence of this multi-faceted thesis is that there may be mature analytical tools and techniques that have heretofore not been adequately recognized for their value to quantum physics. These may include adaptations of neural networks, cellular automata, chaotic attractors, and parallel processing systems. Conceptual and practical architectures are presented for the development of software and hardware environments to employ massively parallel computing for the modeling of large populations of dynamic processes.

Dudziak, Martin Joseph

416

Signature of squeezing in controlled quantum systems

International Nuclear Information System (INIS)

We report on specific signatures of one-mode squeezing due to multipulse control over quantum dynamics. As an important example, we discuss generation of squeezed bright light beams in optical parametric oscillator subjected to a periodic sequence of laser pulses. We show that the synchronized pulse control essentially improves the degree of integral squeezing, making it below the standard limit established for a stationary cw regime

2005-07-03

417

On Entropies of Quantum Dynamical Systems

Classical dynamical entropy is an important tool to discuss coding theorems in classical information theory. Quantum dynamical entropy was first studied by Connes, Størmer and Emch. Thereafter, there have been many researches to construct or calculate the dynamical entropies for several models. In this paper, we briefly review two formulations due to (i) Ohya and (ii) Kossakowski, Ohya and Watanabe. Some numerical computations of these entropies are carried for several states.

Watanabe, Noboru

2010-01-01

418

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum key distribution (QKD) systems can send signals over more than 100 km standard optical fiber and are widely believed to be secure. Here, we show experimentally for the first time a technologically feasible attack, namely the time-shift attack, against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability (~4%) to break the security of the system. Eve's success is due to the well-known detect...

Zhao, Yi; Fung, Chi-hang Fred; Qi, Bing; Chen, Christine; Lo, Hoi-kwong

2007-01-01

419

Efficient simulation of stochastically-driven quantum systems

The simulation of noisy quantum systems is critical for accurate modeling of many experiments, including those implementing quantum information tasks. The expansion of a stochastic equation for the coupled evolution of a quantum system and an Ornstein-Uhlenbeck process into a hierarchy of coupled differential equations is a useful technique that simplifies the simulation of stochastically-driven quantum systems. We expand the applicability of this technique by completely characterizing the class of diffusive Markov processes for which a useful hierarchy of equations can be derived. The expansion of this technique enables the examination of quantum systems driven by non-Gaussian stochastic processes with bounded range. We present an application of this extended technique by simulating Stark-tuned Forster resonance transfer in Rydberg atoms with non-perturbative position fluctuations. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Sarovar, Mohan; Grace, Matthew

2013-03-01

420

Hidden symmetry of the quantum Calogero-Moser system.

DEFF Research Database (Denmark)

The hidden symmetry of the quantum Calogero-Moser system with an inverse-square potential is algebraically demonstrated making use of Dunkl's operators. We find the underlying algebra explaining the super-integrability phenomenon for this system. Applications to related multi-variable Bessel functions are also discussed.

Kuzentsov, Vadim b

1996-01-01

421

Stochastic pure state representation for open quantum systems

International Nuclear Information System (INIS)

It is shown that the usual master equation formalism of Markovian open quantum systems is completely equivalent to a certain state vector formalism. The state vector of the system satisfies a given frictional Schroedinger equation except for random instant transitions of discrete nature. Hasse's frictional Hamiltonian is recovered for the damped harmonic oscillator. (author)

1985-01-01

422

Dissipation and entropy production in open quantum systems

Energy Technology Data Exchange (ETDEWEB)

A microscopic description of an open system is generally expressed by the Hamiltonian of the form: H{sub tot} = H{sub sys} + H{sub environ} + H{sub sys-environ}. We developed a microscopic theory of entropy and derived a general formula, so-called 'entropy-Hamiltonian relation' (EHR), that connects the entropy of the system to the interaction Hamiltonian represented by H{sub sys-environ} for a nonequilibrium open quantum system. To derive the EHR formula, we mapped the open quantum system to the representation space of the Liouville-space formulation or thermo field dynamics (TFD), and thus worked on the representation space L := H x H-tilde, where H denotes the ordinary Hilbert space while H-tilde the tilde Hilbert space conjugates to H. We show that the natural transformation (mapping) of nonequilibrium open quantum systems is accomplished within the theoretical structure of TFD. By using the obtained EHR formula, we also derived the equation of motion for the distribution function of the system. We demonstrated that by knowing the microscopic description of the interaction, namely, the specific form of H{sub sys-environ} on the representation space L, the EHR formulas enable us to evaluate the entropy of the system and to gain some information about entropy for nonequilibrium open quantum systems.

Majima, H; Suzuki, A, E-mail: majima@rs.kagu.tus.ac.j, E-mail: asuzuki@rs.kagu.tus.ac.j [Department of Physics, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601 Japan (Japan)

2010-11-01

423

Parafermions and superoperator-mediated quantum system reduction

International Nuclear Information System (INIS)

In this paper the authors present a nonlinear version of the superoperator formalism and show that it takes an active part in the reduction of quantum-mechanical systems of a given size to other, in a specifiable sense, smaller ones. The class of systems considered is the supersymmetric one

1990-12-10

424

Quantum transport through the system of parallel quantum dots with Majorana bound states

We study the tunneling transport properties through a system of parallel quantum dots which are coupled to Majorana bound states (MBSs). The conductance and spectral function are computed using the retarded Green's function method based on the equation of motion. The conductance of the system is 2e2/h at zero Fermi energy and is robust against the coupling between the MBSs and the quantum dots. The dependence of the Fermi energy on the spectral function is different for the first dot (dot1) than for the second dot (dot2) with fixed dot2-MBSs coupling. The influence of the Majorana bound states on the spectral function was studied for the series and parallel configurations of the system. It was found that when the configuration is in series, the Majorana bound states play an important role, resulting in a spectral function with three peaks. However, the spectral function shows two peaks when the system is in a parallel configuration. The zero Fermi energy spectral function is always 1/2 not only in series but also in the parallel configuration and robust against the coupling between the MBSs and the quantum dots. The phase diagram of the Fermi energy versus the quantum dot energy levels was also investigated.

Wang, Ning; Lv, Shuhui; Li, Yuxian

2014-02-01

425

Energy Technology Data Exchange (ETDEWEB)

Simulations are performed of a small quantum system interacting with a quantum environment. The system consists of various initial states of two harmonic oscillators coupled to give normal modes. The environment is “designed” by its level pattern to have a thermodynamic temperature. A random coupling causes the system and environment to become entangled in the course of time evolution. The approach to a Boltzmann distribution is observed, and effective fitted temperatures close to the designed temperature are obtained. All initial pure states of the system are driven to equilibrium at very similar rates, with quick loss of memory of the initial state. The time evolution of the von Neumann entropy is calculated as a measure of equilibration and of quantum coherence. It is pointed out using spatial density distribution plots that quantum interference is eliminated only with maximal entropy, which corresponds thermally to infinite temperature. Implications of our results for the notion of “classicalizing” behavior in the approach to thermal equilibrium are briefly considered.

Barnes, George L. [Department of Chemistry and Biochemistry, Siena College, Loudonville, New York 12211 (United States); Kellman, Michael E. [Department of Chemistry and Institute of Theoretical Science, University of Oregon, Eugene, Oregon 97403 (United States)

2013-12-07

426

International Nuclear Information System (INIS)

Simulations are performed of a small quantum system interacting with a quantum environment. The system consists of various initial states of two harmonic oscillators coupled to give normal modes. The environment is “designed” by its level pattern to have a thermodynamic temperature. A random coupling causes the system and environment to become entangled in the course of time evolution. The approach to a Boltzmann distribution is observed, and effective fitted temperatures close to the designed temperature are obtained. All initial pure states of the system are driven to equilibrium at very similar rates, with quick loss of memory of the initial state. The time evolution of the von Neumann entropy is calculated as a measure of equilibration and of quantum coherence. It is pointed out using spatial density distribution plots that quantum interference is eliminated only with maximal entropy, which corresponds thermally to infinite temperature. Implications of our results for the notion of “classicalizing” behavior in the approach to thermal equilibrium are briefly considered

2013-12-07

427

An order parameter for impurity systems at quantum criticality

A quantum phase transition may occur in the ground state of a system at zero temperature when a controlling field or interaction is varied. The resulting quantum fluctuations which trigger the transition produce scaling behaviour of various observables, governed by universal critical exponents. A particularly interesting class of such transitions appear in systems with quantum impurities where a non-extensive term in the free energy becomes singular at the critical point. Curiously, the notion of a conventional order parameter that exhibits scaling at the critical point is generically missing in these systems. Here we explore the possibility to use the Schmidt gap, which is an observable obtained from the entanglement spectrum, as an order parameter. A case study of the two-impurity Kondo model confirms that the Schmidt gap faithfully captures the scaling behaviour by correctly predicting the critical exponent of the dynamically generated length scale at the critical point.

Bayat, Abolfazl; Johannesson, Henrik; Bose, Sougato; Sodano, Pasquale

2014-01-01

428

An order parameter for impurity systems at quantum criticality

A quantum phase transition may occur in the ground state of a system at zero temperature when a controlling field or interaction is varied. The resulting quantum fluctuations which trigger the transition produce scaling behaviour of various observables, governed by universal critical exponents. A particularly interesting class of such transitions appear in systems with quantum impurities where a non-extensive term in the free energy becomes singular at the critical point. Curiously, the notion of a conventional order parameter that exhibits scaling at the critical point is generically missing in these systems. Here we explore the possibility to use the Schmidt gap, which is an observable obtained from the entanglement spectrum, as an order parameter. A case study of the two-impurity Kondo model confirms that the Schmidt gap faithfully captures the scaling behaviour by correctly predicting the critical exponent of the dynamically generated length scale at the critical point.

Bayat, Abolfazl; Johannesson, Henrik; Bose, Sougato; Sodano, Pasquale

2014-05-01

429

Superintegrability and higher order constants for classical and quantum systems

We extend recent work by Tremblay, Turbiner, and Winternitz which analyzes an infinite family of solvable and integrable quantum systems in the plane, indexed by the positive parameter k. Key components of their analysis were to demonstrate that there are closed orbits in the corresponding classical system if k is rational, and for a number of examples there are generating quantum symmetries that are higher order differential operators than two. Indeed they conjectured that for a general class of potentials of this type, quantum constants of higher order should exist. We give credence to this conjecture by showing that for an even more general class of potentials in classical mechanics, there are higher order constants of the motion as polynomials in the momenta. Thus these systems are all superintegrable.

Kalnins, E G; Pogosyan, G S

2009-01-01