WorldWideScience
1

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

Science.gov (United States)

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, A.; Kaer, P.; Mørk, J.

2012-03-01

2

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 Kær

2012-01-01

3

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)

4

Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System  

Science.gov (United States)

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing.

Tang, Jing; Geng, Weidong; Xu, Xiulai

2015-03-01

5

Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System  

Science.gov (United States)

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing. PMID:25783560

Tang, Jing; Geng, Weidong; Xu, Xiulai

2015-01-01

6

Quantum interference induced photon blockade in a coupled single quantum dot-cavity system.  

Science.gov (United States)

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g((2))(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing. PMID:25783560

Tang, Jing; Geng, Weidong; Xu, Xiulai

2015-01-01

7

Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System  

CERN Document Server

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay $g^{(2)}(0)$ in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum in...

Tang, Jing; Xu, Xiulai

2015-01-01

8

Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system  

CERN Document Server

We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems. In particular, we investigate the potential of this theoretical approach by its application to compute the emission spectrum of a dissipative system composed by a single quantum dot inside of a semiconductor cavity. We also describe a simple algorithm based on the Green's functions technique for calculating the emission spectrum of the quantum dot as well as of the cavity which can easily be implemented in any numerical linear algebra package. We find that the Green's functions technique demonstrates a better accuracy and efficiency in the calculation of the emission spectrum and it allows to overcome the inherent theoretical difficulties associated to the direct application of the quantum regression theorem approach.

Gomez, Edgar A; Vinck-Posada, Herbert

2015-01-01

9

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

International Nuclear Information System (INIS)

We study a quantum dot strongly coupled to a single high-finesse optical microcavity mode. We use a rotating wave approximation (RWA) method, commonly used in ion-laser interactions, together with the Lamb-Dicke approximation to obtain an analytic solution of this problem. The decay of Rabi oscillations because of the electron-phonon coupling is studied at arbitrary temperature and analytical expressions for the collapse and revival times are presented. Analyses without the RWA are presented as means of investigating the energy spectrum

10

Influence of electron-acoustic phonon scattering on intensity power broadening in a coherently driven quantum-dot cavity system  

CERN Document Server

We present a quantum optics formalism to study intensity power broadening of a semiconductor quantum dot interacting with an acoustic phonon bath and a high $Q$ microcavity. Power broadening is investigated using a time-convolutionless master equation in the polaron frame which allows for a nonperturbative treatment of the interaction of the quantum dot with the phonon reservoir. We calculate the full non-Lorentzian photoluminescence (PL) lineshapes and numerically extract the intensity linewidths of the quantum dot exciton and the cavity mode as a function of pump rate and temperature. For increasing field strengths, multiphonon and multiphoton effects are found to be important, even for phonon bath temperatures as low as 4 K. We show that the interaction of the quantum dot with the phonon reservoir introduces pronounced features in the power broadened PL lineshape, enabling one to observe clear signatures of electron-phonon scattering. The PL lineshapes from cavity pumping and exciton pumping are found to b...

Roy, Chiranjeeb

2011-01-01

11

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 Kær

2012-01-01

12

Microscopic theory of indistinguishable single-photon emission from a quantum dot coupled to a cavity: The role of non-Markovian phonon-induced decoherence  

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 Kær; Lodahl, Peter

2013-01-01

13

Two-photon interference from a quantum dot-microcavity: Persistent pure-dephasing and suppression of time-jitter  

DEFF Research Database (Denmark)

We demonstrate the emission of highly indistinguishable photons from a quasi-resonantly pumped coupledquantum dot–microcavity system operating in the regime of cavity quantum electrodynamics. Changing thesample temperature allows us to vary the quantum dot–cavity detuning and, on spectral resonance, we observea threefold improvement in the Hong-Ou-Mandel interference visibility, reaching values in excess of 80%. Ourmeasurements off-resonance allow us to investigate varying Purcell enhancements, and to probe the dephasingenvironment at different temperatures and energy scales. By comparison with our microscopic model, we areable to identify pure dephasing and not time jitter as the dominating source of imperfections in our system.

Unsleber, Sebastian; McCutcheon, Dara

2015-01-01

14

Controlled Quantum Open Systems  

OpenAIRE

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

15

Synthetic Quantum Systems  

OpenAIRE

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 qu...

Cahill, Reginald T.

2002-01-01

16

Giant Rabi splitting in a metallic cluster–cavity system  

International Nuclear Information System (INIS)

We theoretically investigate the photoabsorption cross-section of a cluster of alkali atoms embedded in a single-mode quantum microcavity. We show that if the energy of the giant plasmonic resonance lies close to the energy of the cavity mode, the strong coupling between the plasmon and cavity photon can occur which is characterized by mode anticrossing and observation of the doublet structure in the photoabsorption spectrum. The characteristic values of the Rabi splitting are expected to be several orders of magnitude larger than those observed in single quantum dot–cavity systems. (paper)

17

Quantum system identification  

OpenAIRE

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 sys...

Raginsky, Maxim

2003-01-01

18

Quantum electromechanical systems  

International Nuclear Information System (INIS)

Quantum electromechanical systems are nano-to-micrometer (micron) scale mechanical resonators coupled to electronic devices of comparable dimensions, such that the mechanical resonator behaves in a manifestly quantum manner. We review progress towards realising quantum electromechanical systems, beginning with the phononic quantum of thermal conductance for suspended dielectric wires. We then describe efforts to reach the quantum zero-point displacement uncertainty detection limit for (sub)micron-scale mechanical resonators using the single electron transistor as displacement transducer. A scheme employing the Cooper-pair box as coherent control device to generate and detect quantum superpositions of distinct position states is then described. Finally, we outline several possible schemes to demonstrate various other quantum effects in (sub)micron mechanical resonators, including single phonon detection, quantum squeezed states and quantum tunnelling of mechanical degrees of freedom

19

Synthetic Quantum Systems  

CERN Document Server

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

20

Observing Quantum Systems  

OpenAIRE

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

Quantum Systems Exactly  

OpenAIRE

Contents: 1 Frustrated quantum spin systems 1.1 The Pyrochlore checkerboard 1.2 Singlets in reflection symmetric spin systems 2 Wehrl entropy of Bloch coherent states 2.1 Conjectures of Wehrl and Lieb 2.2 Proof of Lieb's conjecture for low spin 3 Symmetries of the Hubbard model 4 Quantum integrable systems 4.1 Twisted quantum Lax equations 4.2 Face algebras and Ruijsenaars models 5 Noncommutative gauge theory 5.1 Gauge theory on nonc...

Schupp, Peter

2002-01-01

22

Quantum Games and Programmable Quantum Systems  

OpenAIRE

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

23

Quantum identification system  

OpenAIRE

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 derive...

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

1998-01-01

24

On Quantum Integrable Systems  

CERN Document Server

Many quantum integrable systems are obtained using an accelerator physics technique known as Ermakov (or normalized variables) transformation. This technique was used to create classical nonlinear integrable lattices for accelerators and nonlinear integrable plasma traps. Now, all classical results are carried over to a nonrelativistic quantum case.

Danilov, Viatcheslav

2011-01-01

25

Quantum dissipative systems  

CERN Document Server

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

26

Quantum Dissipative Systems  

CERN Document Server

Major advances in the quantum theory of macroscopic systems, in combination with stunning experimental achievements, have brightened the field and brought it to the attention of the general community in natural sciences. Today, working knowledge of dissipative quantum mechanics is an essential tool for many physicists. This book - originally published in 1990 and republished in 1999 as an enlarged second edition - delves much deeper than ever before into the fundamental concepts, methods, and applications of quantum dissipative systems, including the most recent developments. In this third edi

Weiss, Ulrich

2008-01-01

27

Quantum many body systems  

International Nuclear Information System (INIS)

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.

28

Magmatic "Quantum-Like" Systems  

CERN Document Server

Quantum computation has suggested, among others, the consideration of "non-quantum" systems which in certain respects may behave "quantum-like". Here, what algebraically appears to be the most general possible known setup, namely, of {\\it magmas} is used in order to construct "quantum-like" systems. The resulting magmatic composition of systems has as a well known particular case the tensor products.

Rosinger, Elemer E

2008-01-01

29

Proposed Quenching of Phonon-Induced Processes in Photoexcited Quantum Dots due to Electron-Hole Asymmetries  

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 Kær

2013-01-01

30

Two-photon interference from a quantum dot microcavity: Persistent pure dephasing and suppression of time jitter  

Science.gov (United States)

We demonstrate the emission of highly indistinguishable photons from a quasi-resonantly pumped coupled quantum dot-microcavity system operating in the regime of cavity quantum electrodynamics. Changing the sample temperature allows us to vary the quantum dot-cavity detuning and, on spectral resonance, we observe a threefold improvement in the Hong-Ou-Mandel interference visibility, reaching values in excess of 80%. Our measurements off-resonance allow us to investigate varying Purcell enhancements, and to probe the dephasing environment at different temperatures and energy scales. By comparison with our microscopic model, we are able to identify pure dephasing and not time jitter as the dominating source of imperfections in our system.

Unsleber, Sebastian; McCutcheon, Dara P. S.; Dambach, Michael; Lermer, Matthias; Gregersen, Niels; Höfling, Sven; Mørk, Jesper; Schneider, Christian; Kamp, Martin

2015-02-01

31

Scheme of thinking quantum systems  

International Nuclear Information System (INIS)

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

32

Scheme of thinking quantum systems  

Science.gov (United States)

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.; Sornette, D.

2009-11-01

33

Scheme of thinking quantum systems  

OpenAIRE

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

34

Integrable quantum Stäckel systems  

International Nuclear Information System (INIS)

The Stäckel separability of a Hamiltonian system is well known to ensure existence of a complete set of Poisson commuting integrals of motion quadratic in the momenta. We consider a class of Stäckel separable systems where the entries of the Stäckel matrix are monomials in the separation variables. We show that the only systems in this class for which the integrals of motion arising from the Stäckel construction keep commuting after quantization are, up to natural equivalence transformations, the so-called Benenti systems. Moreover, it turns out that the latter are the only quantum separable systems in the class under study.

35

Integrable quantum Stäckel systems  

Energy Technology Data Exchange (ETDEWEB)

The Stäckel separability of a Hamiltonian system is well known to ensure existence of a complete set of Poisson commuting integrals of motion quadratic in the momenta. We consider a class of Stäckel separable systems where the entries of the Stäckel matrix are monomials in the separation variables. We show that the only systems in this class for which the integrals of motion arising from the Stäckel construction keep commuting after quantization are, up to natural equivalence transformations, the so-called Benenti systems. Moreover, it turns out that the latter are the only quantum separable systems in the class under study.

B?aszak, Maciej, E-mail: blaszakm@amu.edu.pl [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Pozna? (Poland); Doma?ski, Ziemowit, E-mail: ziemowit@amu.edu.pl [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Pozna? (Poland); Sergyeyev, Artur, E-mail: Artur.Sergyeyev@math.slu.cz [Mathematical Institute, Silesian University in Opava, Na Rybní?ku 1, 746 01 Opava (Czech Republic); Szablikowski, B?a?ej M., E-mail: bszablik@amu.edu.pl [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Pozna? (Poland)

2013-11-15

36

Quantum dissipative systems  

CERN Document Server

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

37

Quantum Dissipative Systems  

CERN Document Server

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

38

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)

39

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

OpenAIRE

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

40

Quantum Positioning System  

OpenAIRE

A quantum positioning system (QPS) is proposed that can provide a user with all four of his space-time coordinates. The user must carry a corner cube reflector, a good clock, and have a two-way classical channel of communication with the origin of the reference frame. Four pairs of entangled photons (biphotons) are sent through four interferometers: three interferometers are used to determine the user's spatial position, and an additional interferometer is used to synchroniz...

Bahder, Thomas B.

2004-01-01

41

Quantum algorithm in quantum network systems  

International Nuclear Information System (INIS)

Recently, the quantum computer (QC) using the nano-devices have significantly attracted attention, because a large-scale extention of the qubits could be easily realized in the nano-devices. However, some problems for the realization of the QC with nano-devices arise from the short decoherence time and the interaction of qubits only between nearest-neighbor qubits. Therefore, we try to design the optimal quantum circuit of the quantum Fourier transform in various network system by means of the genetic algorithm (GA)

42

Quantum Critical Points in Quantum Impurity Systems  

CERN Document Server

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.

Lee, H J

2004-01-01

43

Darwinism in Quantum Systems?  

CERN Document Server

We find quantum mechanics playing a role in evolutionary dynamics described by the notion of an Evolutionary Stable Strategy (ESS). An ESS being a refinement of Nash equilibrium concept is a stable strategy in an evolutionary game with replicator dynamic as the underlying process. We investigate ESSs in two and three player symmetric quantum games played by the proposed scheme of applying $^{\\prime}$identity$^{\\prime}$ and $^{\\prime}$Pauli spin-flip$^{\\prime}$ operators on an initial state with classical probabilities. The mixed Nash equilibrium (NE) we search for is not affected by a switchover between two forms of the game, one quantized and other classical, however it is an ESS when the game is played classically.We show no such mixed NE exists for two player games but there is a class of three player games where they do exist.Our results imply that an evolutionary approach originating with Darwin's idea of natural selection can be used even for quantum systems. It also indicates the possibility of genetic...

Iqbal, A

2002-01-01

44

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.)

45

Auger Processes Mediating the Nonresonant Optical Emission from a Semiconductor Quantum Dot Embedded Inside an Optical Cavity  

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 Kær

2013-01-01

46

Quantum Positioning System  

CERN Document Server

A quantum positioning system (QPS) is proposed that can provide a user with all four of his space-time coordinates. The user must carry a corner cube reflector, a good clock, and have a two-way classical channel of communication with the origin of the reference frame. Four pairs of entangled photons (biphotons) are sent through four interferometers: three interferometers are used to determine the user's spatial position, and an additional interferometer is used to synchronize the user's clock to coordinate time in the reference frame. The spatial positioning part of the QPS is similar to a classical time-of-arrival (TOA) system, however, a classical TOA system (such as GPS) must have synchronized clocks that keep coordinate time and therefore the clocks must have long-term stability, whereas in the QPS only a photon coincidence counter is needed and the clocks need only have short-term stability. Several scenarios are considered for a QPS: one is a terrestrial system and another is a space-based-system compos...

Bahder, T B

2004-01-01

47

Quantum technologies with hybrid systems.  

Science.gov (United States)

An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field. PMID:25737558

Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; Mølmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, Jörg

2015-03-31

48

Quantum Effects in Biological Systems  

Science.gov (United States)

The debates about the trivial and non-trivial effects in biological systems have drawn much attention during the last decade or so. What might these non-trivial sorts of quantum effects be? There is no consensus so far among the physicists and biologists regarding the meaning of "non-trivial quantum effects". However, there is no doubt about the implications of the challenging research into quantum effects relevant to biology such as coherent excitations of biomolecules and photosynthesis, quantum tunneling of protons, van der Waals forces, ultrafast dynamics through conical intersections, and phonon-assisted electron tunneling as the basis for our sense of smell, environment assisted transport of ions and entanglement in ion channels, role of quantum vacuum in consciousness. Several authors have discussed the non-trivial quantum effects and classified them into four broad categories: (a) Quantum life principle; (b) Quantum computing in the brain; (c) Quantum computing in genetics; and (d) Quantum consciousness. First, I will review the above developments. I will then discuss in detail the ion transport in the ion channel and the relevance of quantum theory in brain function. The ion transport in the ion channel plays a key role in information processing by the brain.

Roy, Sisir

2014-07-01

49

Interaction of "rigid" quantum systems  

OpenAIRE

We introduce the notion of a "rigid" quantum system as a system with constant relative positions of its nuclei and constant relative distribution of the electrons with respect to the nuclei. In accordance with this definition, a molecule which does not interact with other objects, is a "rigid" quantum system. Molecule is also "rigid" if it interacts with other objects, but the interaction does not change the intrinsic structure of the molecule (or this change can be neglec...

Kolpakov, A. A.; Kolpakov, A. G.

2012-01-01

50

Chaotic quantum systems  

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

51

Dissipation in quantum systems  

Energy Technology Data Exchange (ETDEWEB)

The quantum dynamics of a mechanical subsystem interacting with a thermal bath is studied. A new approach to dissipated quantum mechanics is proposed which is based on the thermodynamic treatment of the energy balance. Simple application of the theory to ideal gases is considered and equations for the evolution of the main average quantities are derived. (author)

Tsekov, R. [Dept. of Phys. Chem., Sofia Univ. (Bulgaria)

1995-11-07

52

Dissipation in quantum systems  

International Nuclear Information System (INIS)

The quantum dynamics of a mechanical subsystem interacting with a thermal bath is studied. A new approach to dissipated quantum mechanics is proposed which is based on the thermodynamic treatment of the energy balance. Simple application of the theory to ideal gases is considered and equations for the evolution of the main average quantities are derived. (author)

53

Manipulation of single quantum systems  

International Nuclear Information System (INIS)

Full text: The founders of quantum theory assumed in thought experiments that they were manipulating isolated quantum systems obeying the counterintuitive laws which they had just discovered. Technological advances have recently turned these virtual experiments into real ones by making possible the actual control of isolated quantum particles. Many laboratories are realizing such experiments, in a research field at the frontier between physics and information science. Fundamentally, these studies explore the transition between the microscopic world ruled by quantum laws and our macroscopic environment which appears classical. Practically, physicists hope that these experiments will result in new technologies exploiting the strange quantum logic to compute, communicate or measure physical quantities better than was previously conceivable. In Paris, we perform such experiments by juggling with photons trapped between superconducting mirrors. I will give a simple description of these studies, compare them to similar ones performed on other systems and guess about possible applications. (author)

54

Geometry of dynamical quantum systems  

International Nuclear Information System (INIS)

We relate the geometry of dynamical quantum systems to the broader context of classifying Lie algebras. We give an explicit description of all possible geometries and their inclusion relations relying on results of Dynkin and complementing the work of McKay and Patera. Building on previous work, we use the description of all possible geometries to present readily applicable conditions for the controllability of quantum systems. We compare our approach with the standard method of deciding controllability by computing the Lie closure. We emphasize the importance of our methods for the universality of quantum computers and consider partial universality with respect to subsystems. We discuss computer implementations and present concrete examples.

55

Quantum Geometry and Quantum Mechanics of Integrable Systems  

OpenAIRE

Quantum integrable systems and their classical counterparts are considered. We show that the symplectic structure and invariant tori of the classical system can be deformed by a quantization parameter $\\hbar$ to produce a new (classical) integrable system. The new tori selected by the $\\hbar$-equidistance rule represent the spectrum of the quantum system up to $O(\\hbar^\\infty)$ and are invariant under quantum dynamics in the long-time range $O(\\hbar^{-\\infty})$. The quantum ...

Karasev, M. V.

2009-01-01

56

Smart Nanostructures and Synthetic Quantum Systems  

OpenAIRE

So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is a semantic information theory of reality in which space and quantum p...

Cahill, Reginald T.

2001-01-01

57

Quantum systems and symmetric spaces  

International Nuclear Information System (INIS)

Certain class of quantum systems with Hamiltonians related to invariant operators on symmetric spaces has been investigated. A number of physical facts have been derived as a consequence. In the classical limit completely integrable systems related to root systems are obtained

58

Software-defined Quantum Communication Systems  

OpenAIRE

Quantum communication systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for quantum communication engineering is designing and prototyping these systems to evaluate proposed capabilities. We apply the paradigm of software-defined communication for engineering quantum communication systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose quantum communica...

Humble, Travis S.; Sadlier, Ronald J.

2014-01-01

59

Thermalization of isolated quantum systems  

OpenAIRE

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 holes. 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 ergod...

Khlebnikov, Sergei; Kruczenski, Martin

2013-01-01

60

Quantum Teleportation in One-Dimensional Quantum Dots System  

OpenAIRE

We present a model of quantum teleportation protocol based on one-dimensional quantum dots system. Three quantum dots with three electrons are used to perform teleportation, the unknown qubit is encoded using one electron spin on quantum dot A, the other two dots B and C are coupled to form a mixed space-spin entangled state. By choosing the Hamiltonian for the mixed space-spin entangled system, we can filter the space (spin) entanglement to obtain pure spin (space) entangle...

Wang, Hefeng; Kais, Sabre

2006-01-01

61

Hypothesis Testing with Open Quantum Systems  

Science.gov (United States)

Using a quantum circuit model we derive the maximal ability to distinguish which of several candidate Hamiltonians describe an open quantum system. This theory, in particular, provides the maximum information retrievable from continuous quantum measurement records, available when a quantum system is perturbatively coupled to a broadband quantized environment.

Mølmer, Klaus

2015-01-01

62

Hypothesis testing with open quantum systems.  

Science.gov (United States)

Using a quantum circuit model we derive the maximal ability to distinguish which of several candidate Hamiltonians describe an open quantum system. This theory, in particular, provides the maximum information retrievable from continuous quantum measurement records, available when a quantum system is perturbatively coupled to a broadband quantized environment. PMID:25679881

Mølmer, Klaus

2015-01-30

63

Hypothesis testing with open quantum systems  

OpenAIRE

Using a quantum circuit model we derive the maximal ability to distinguish which of several candidate Hamiltonians describe an open quantum system. This theory, in particular, provides the maximum information retrievable from continuous quantum measurement records, available when a smaller open quantum system is perturbatively coupled to a broadband quantized environment.

Molmer, Klaus

2014-01-01

64

Lyapunov Control of Quantum Systems with Applications to Quantum Computing  

OpenAIRE

In the design of complex quantum systems like ion traps for quantum computing, it is usually desired to stabilize a particular system state or make the system state track a desired trajectory. Several control theoretical approaches based on feedback seem attractive to solve such problems. But the uncertain dynamics introduced by measurement on quantum systems makes the synthesis of feedback control laws very complicated. Although we have not explicitly modeled the change in ...

Nagarjun, K. P.; Sivaranjani, S.; Koshy, George

2012-01-01

65

Quantum dynamics in open quantum-classical systems.  

Science.gov (United States)

Often quantum systems are not isolated and interactions with their environments must be taken into account. In such open quantum systems these environmental interactions can lead to decoherence and dissipation, which have a marked influence on the properties of the quantum system. In many instances the environment is well-approximated by classical mechanics, so that one is led to consider the dynamics of open quantum-classical systems. Since a full quantum dynamical description of large many-body systems is not currently feasible, mixed quantum-classical methods can provide accurate and computationally tractable ways to follow the dynamics of both the system and its environment. This review focuses on quantum-classical Liouville dynamics, one of several quantum-classical descriptions, and discusses the problems that arise when one attempts to combine quantum and classical mechanics, coherence and decoherence in quantum-classical systems, nonadiabatic dynamics, surface-hopping and mean-field theories and their relation to quantum-classical Liouville dynamics, as well as methods for simulating the dynamics. PMID:25634784

Kapral, Raymond

2015-02-25

66

Quantum dynamics in open quantum-classical systems  

Science.gov (United States)

Often quantum systems are not isolated and interactions with their environments must be taken into account. In such open quantum systems these environmental interactions can lead to decoherence and dissipation, which have a marked influence on the properties of the quantum system. In many instances the environment is well-approximated by classical mechanics, so that one is led to consider the dynamics of open quantum-classical systems. Since a full quantum dynamical description of large many-body systems is not currently feasible, mixed quantum-classical methods can provide accurate and computationally tractable ways to follow the dynamics of both the system and its environment. This review focuses on quantum-classical Liouville dynamics, one of several quantum-classical descriptions, and discusses the problems that arise when one attempts to combine quantum and classical mechanics, coherence and decoherence in quantum-classical systems, nonadiabatic dynamics, surface-hopping and mean-field theories and their relation to quantum-classical Liouville dynamics, as well as methods for simulating the dynamics.

Kapral, Raymond

2015-02-01

67

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 - Generatanglement - 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.)

68

Design of coherent quantum observers for linear quantum systems  

Science.gov (United States)

Quantum versions of control problems are often more difficult than their classical counterparts because of the additional constraints imposed by quantum dynamics. For example, the quantum LQG and quantum {{H}? } optimal control problems remain open. To make further progress, new, systematic and tractable methods need to be developed. This paper gives three algorithms for designing coherent quantum observers, i.e., quantum systems that are connected to a quantum plant and their outputs provide information about the internal state of the plant. Importantly, coherent quantum observers avoid measurements of the plant outputs. We compare our coherent quantum observers with a classical (measurement-based) observer by way of an example involving an optical cavity with thermal and vacuum noises as inputs.

Vuglar, Shanon L.; Amini, Hadis

2014-12-01

69

Dynamics of complex quantum systems  

CERN Document Server

This book gathers together a range of similar problems that can be encountered in different fields of modern quantum physics and that have common features with regard to multilevel quantum systems. The main motivation was to examine from a uniform standpoint various models and approaches that have been developed in atomic, molecular, condensed matter, chemical, laser and nuclear physics in various contexts. The book should help senior-level undergraduate, graduate students and researchers putting particular problems in these fields into a broader scientific context and thereby taking advantage of well-established techniques used in adjacent fields. This second edition has been expanded to include substantial new material (e.g. new sections on Dynamic Localization and on Euclidean Random Matrices and new chapters on Entanglement, Open Quantum Systems, and Coherence Protection). It is based on the author’s lectures at the Moscow Institute of Physics and Technology, at the CNRS Aimé Cotton Laboratory, and on ...

Akulin, Vladimir M

2014-01-01

70

Quantum Relativity: Physical Laws Must be Invariant Over Quantum Systems  

CERN Document Server

Decoherence may not solve all of the measurement problems of quantum mechanics. A solution to these problems is 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 unsharp values. Each quantum system forms a physically valid coordinate frame. The laws of physics should be formulated to be invariant under the group of allowed transformations among such frames. A transformation of relatively superposed spatial coordinates that allows an electron system to preserve the de Broglie Relation in describing a doubleslit laboratory system in analogy to a Minkowskian Transformation is given. In general, quantum relativity says h cross equals 1 is invariant over transformations among quantum reference frames. It is argued this impacts gravity and gauge invariance.

Merriam, P

2005-01-01

71

Quantum Heat Engine With Multi-Level Quantum Systems  

OpenAIRE

By reformulating the first law of thermodynamics in the fashion of quantum-mechanical operators on the parameter manifold, we propose a universal class of quantum heat engines (QHE) using the multi-level quantum system as the working substance. We obtain a general expression of work for the thermodynamic cycle with two thermodynamic adiabatic processes, which are microscopically quantum adiabatic processes. We also classify the conditions for a 3-level QHE to extract positiv...

Quan, H. T.; Zhang, P.; Sun, C. P.

2005-01-01

72

Entanglement within the Quantum Trajectory Description of Open Quantum Systems  

CERN Document Server

The degree of entanglement in an open quantum system varies according to how information in the environment is read. A measure of this contextual entanglement is introduced based on quantum trajectory unravellings of the open system dynamics. It is used to characterize the entanglement in a driven quantum system of dimension $2\\times\\infty$ where the entanglement is induced by the environmental interaction. A detailed mechanism for the environment-induced entanglement is given.

Nha, H; Nha, Hyunchul

2004-01-01

73

On Quantum Iterated Function Systems  

OpenAIRE

Quantum Iterated Function System on a complex projective space is defined by a family of linear operators on a complex Hilbert space. The operators define both the maps and their probabilities by one algebraic formula. Examples with conformal maps (relativistic boosts) on the Bloch sphere are discussed.

Jadczyk, Arkadiusz

2003-01-01

74

Quantum gravity and spin systems  

International Nuclear Information System (INIS)

A new method for nonperturbative investigations of quantum gravity is presented in which the simplicial path integral is approximated by the partition function of a spin system. This facilitates analytical and numerical computations considerably. In two dimensions equivalence to an Ising model with ternary couplings is recovered. First simulations in four dimensions indicate strong similarities to the phase structure of original Regge theory. ((orig.))

75

Free space quantum system based on quantum secure direct communication  

Science.gov (United States)

A new practical free space quantum communication system is proposed, it is based on the principle of quantum secure direct communication. Quantum cryptography is a practical method to realize free space optical communication. Different from the existing free space quantum key distribution communication system, the free space quantum secure direct communication is deterministic and the system is more simple. In this paper, a new structure of four transmitting channels is prensented, this structure could increase the security and capacity of system. The setup of transmitter and receiver of each transmitting channel is discussed in detail, and the communication process is analyzed. The result shows that this free space quantum system could be realized and can work over long distance.

Ge, Hua; Liu, Wenyu

2007-11-01

76

The quantum Hall effect in quantum dot systems  

Science.gov (United States)

It is proposed to use quantum dots in order to increase the temperatures suitable for observation of the integer quantum Hall effect. A simple estimation using Fock-Darwin spectrum of a quantum dot shows that good part of carriers localized in quantum dots generate the intervals of plateaus robust against elevated temperatures. Numerical calculations employing local trigonometric basis and highly efficient kernel polynomial method adopted for computing the Hall conductivity reveal that quantum dots may enhance peak temperature for the effect by an order of magnitude, possibly above 77 K. Requirements to potentials, quality and arrangement of the quantum dots essential for practical realization of such enhancement are indicated. Comparison of our theoretical results with the quantum Hall measurements in InAs quantum dot systems from two experimental groups is also given.

Beltukov, Y. M.; Greshnov, A. A.

2014-12-01

77

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.)

78

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

79

Quantum Computing in Solid State Systems  

CERN Document Server

The aim of Quantum Computation in Solid State Systems is to report on recent theoretical and experimental results on the macroscopic quantum coherence of mesoscopic systems, as well as on solid state realization of qubits and quantum gates. Particular attention has been given to coherence effects in Josephson devices. Other solid state systems, including quantum dots, optical, ion, and spin devices which exhibit macroscopic quantum coherence are also discussed. Quantum Computation in Solid State Systems discusses experimental implementation of quantum computing and information processing devices, and in particular observations of quantum behavior in several solid state systems. On the theoretical side, the complementary expertise of the contributors provides models of the various structures in connection with the problem of minimizing decoherence.

Ruggiero, B; Granata, C

2006-01-01

80

Quantum mechanics of damped systems  

International Nuclear Information System (INIS)

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

81

Recurrences in driven quantum systems  

CERN Document Server

We consider an initially bound quantum particle subject to an external time-dependent field. When the external field is large, the particle shows a tendency to repeatedly return to its initial state, irrespective of whether the frequency of the field is sufficient for escape from the well. These recurrences, which are absent in a classical calculation, arise from the system evolving primarily like a free particle in the external field.

Poduri, V; Patil, U; Poduri, V; Browne, D A; Patil, U

1994-01-01

82

Repeated interactions in open quantum systems  

International Nuclear Information System (INIS)

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 the irreversible dynamics of the open system, starting from a unitary dynamics of the system and its environment. The repeated interactions systems considered in these notes are models of non-equilibrium quantum statistical mechanics. They are relevant in quantum optics, and more generally, serve as a relatively well treatable approximation of a more difficult quantum dynamics. In particular, the repeated interaction models allow to determine the large time (stationary) asymptotics of quantum systems out of equilibrium

83

Relation between classical and quantum particle systems  

International Nuclear Information System (INIS)

An exact correspondence is established between a N-body classical interacting system and a (N-1)-body quantum system with respect to the partition function. The resulting Hermitian quantum potential is a (N-1)-body one. Inversely the Kelbg potential is reproduced which describes quantum systems at a quasi-classical level. The correspondence found between classical and quantum systems allows also to approximate dense classical many-body systems by lower order quantum perturbation theory, replacing Planck's constant properly by temperature and density dependent expressions. As an example, the dynamical behavior of a one-component plasma is well reproduced concerning the formation of correlation energy after a disturbance, utilizing solely the analytical quantum-Born result for dense degenerated Fermi systems. As a practical guide, the quantum-Bruckner parameter rs has been replaced by the classical plasma parameter ? as rs?0.3?3/2

84

The Quantum Mechanics of Closed Systems  

OpenAIRE

A pedagogical introduction is given to the quantum mechanics of closed systems, most generally the universe as a whole. Quantum mechanics aims at predicting the probabilities of alternative coarse-grained time histories of a closed system. Not every set of alternative coarse-grained histories that can be described may be consistently assigned probabilities because of quantum mechanical interference between individual histories of the set. In the quantum mechanics of closed s...

Hartle, James B.

1992-01-01

85

Maxwell's demons in multipartite quantum correlated systems  

Science.gov (United States)

We investigate the extraction of thermodynamic work by a Maxwell's demon in a multipartite quantum correlated system. We begin by adopting the standard model of a Maxwell's demon as a Turing machine, either in a classical or quantum setup depending on its ability to implement classical or quantum conditional dynamics. Then, for an n -partite system (A1,A2,⋯,An) , we introduce a protocol of work extraction that bounds the advantage of the quantum demon over its classical counterpart through the amount of multipartite quantum correlation present in the system, as measured by a thermal version of the global quantum discord. This result is illustrated for an arbitrary n -partite pure state of qubits with Schmidt decomposition, where it is shown that the thermal global quantum discord exactly quantifies the quantum advantage. Moreover, we also consider the work extraction via mixed multipartite states, where examples of tight upper bounds can be obtained.

Braga, Helena C.; Rulli, Clodoaldo C.; de Oliveira, Thiago R.; Sarandy, Marcelo S.

2014-10-01

86

Modeling of quantum electromechanical systems  

CERN Document Server

We discuss methods for numerically solving the generalized Master equation GME which governs the time-evolution of the reduced density matrix of a mechanically movable mesoscopic device in a dissipative environment. As a specific example, we consider the quantum shuttle -- a generic quantum nanoelectromechanical system (NEMS). When expressed in the oscillator basis, the static limit of the GME becomes a large linear non-sparse matrix problem (characteristic size larger than 10^4 by 10^4) which however, as we show, can be treated using the Arnoldi iteration scheme. The numerical results are interpreted with the help of Wigner functions, and we compute the current and the noise in a few representative cases.

Jauho, A P; Donarini, A; Flindt, C; Jauho, Antti-Pekka; Novotny, Tomas; Donarini, Andrea; Flindt, Christian

2004-01-01

87

Could nanostructure be unspeakable quantum system?  

CERN Document Server

Heisenberg, Bohr and others were forced to renounce on the description of the objective reality as the aim of physics because of the paradoxical quantum phenomena observed on the atomic level. The contemporary quantum mechanics created on the base of their positivism point of view must divide the world into speakable apparatus which amplifies microscopic events to macroscopic consequences and unspeakable quantum system. Examination of the quantum phenomena corroborates the confidence expressed by creators of quantum theory that the renunciation of realism should not apply on our everyday macroscopic world. Nanostructures may be considered for the present as a boundary of realistic description for all phenomena including the quantum one.

Aristov, V V

2010-01-01

88

Quantum Friction: Cooling Quantum Systems with Unitary Time Evolution  

CERN Document Server

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

89

On Realization Theory of Quantum Linear Systems  

OpenAIRE

The purpose of this paper is to study the realization theory of quantum linear systems. It is shown that for a general quantum linear system its controllability and observability are equivalent and they can be checked by means of a simple matrix rank condition. Based on controllability and observability a specific realization is proposed for general quantum linear systems in which an uncontrollable and unobservable subspace is identified. When restricted to the passive case,...

Gough, John E.; Zhang, Guofeng

2013-01-01

90

Quantum discord from system-environment correlations  

OpenAIRE

In an initially uncorrelated mixed separable bi-partite system, quantum correlations can emerge under the action of a local measurement or local noise [A. Streltsov, H. Kampermann, and D. Bru\\ss{}, Phys. Rev. Lett. 107, 170502 (2011)]. We analyze 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 th...

Tatham, Richard; Korolkova, Natalia

2013-01-01

91

Simulation of n-qubit quantum systems. III. Quantum operations  

Science.gov (United States)

During the last decade, several quantum information protocols, such as quantum key distribution, teleportation or quantum computation, have attracted a lot of interest. Despite the recent success and research efforts in quantum information processing, however, we are just at the beginning of understanding the role of entanglement and the behavior of quantum systems in noisy environments, i.e. for nonideal implementations. Therefore, in order to facilitate the investigation of entanglement and decoherence in n-qubit quantum registers, here we present a revised version of the FEYNMAN program for working with quantum operations and their associated (Jamio?kowski) dual states. Based on the implementation of several popular decoherence models, we provide tools especially for the quantitative analysis of quantum operations. Apart from the implementation of different noise models, the current program extension may help investigate the fragility of many quantum states, one of the main obstacles in realizing quantum information protocols today. Program summaryTitle of program: Feynman Catalogue identifier: ADWE_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v3_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Operating systems: Any system that supports MAPLE; tested under Microsoft Windows XP, SuSe Linux 10 Program language used:MAPLE 10 Typical time and memory requirements: Most commands that act upon quantum registers with five or less qubits take ?10 seconds of processor time (on a Pentium 4 processor with ?2 GHz or equivalent) and 5-20 MB of memory. Especially when working with symbolic expressions, however, the memory and time requirements critically depend on the number of qubits in the quantum registers, owing to the exponential dimension growth of the associated Hilbert space. For example, complex (symbolic) noise models (with several Kraus operators) for multi-qubit systems often result in very large symbolic expressions that dramatically slow down the evaluation of measures or other quantities. In these cases, MAPLE's assume facility sometimes helps to reduce the complexity of symbolic expressions, but often only numerical evaluation is possible. Since the complexity of the FEYNMAN commands is very different, no general scaling law for the CPU time and memory usage can be given. No. of bytes in distributed program including test data, etc.: 799 265 No. of lines in distributed program including test data, etc.: 18 589 Distribution format: tar.gz Reasons for new version: While the previous program versions were designed mainly to create and manipulate the state of quantum registers, the present extension aims to support quantum operations as the essential ingredient for studying the effects of noisy environments. Does this version supersede the previous version: Yes Nature of the physical problem: Today, entanglement is identified as the essential resource in virtually all aspects of quantum information theory. In most practical implementations of quantum information protocols, however, decoherence typically limits the lifetime of entanglement. It is therefore necessary and highly desirable to understand the evolution of entanglement in noisy environments. Method of solution: Using the computer algebra system MAPLE, we have developed a set of procedures that support the definition and manipulation of n-qubit quantum registers as well as (unitary) logic gates and (nonunitary) quantum operations that act on the quantum registers. The provided hierarchy of commands can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems in ideal and nonideal quantum circuits.

Radtke, T.; Fritzsche, S.

2007-05-01

92

Distinctive signature of indium gallium nitride quantum dot lasing in microdisk cavities.  

Science.gov (United States)

Low-threshold lasers realized within compact, high-quality optical cavities enable a variety of nanophotonics applications. Gallium nitride materials containing indium gallium nitride (InGaN) quantum dots and quantum wells offer an outstanding platform to study light-matter interactions and realize practical devices such as efficient light-emitting diodes and nanolasers. Despite progress in the growth and characterization of InGaN quantum dots, their advantages as the gain medium in low-threshold lasers have not been clearly demonstrated. This work seeks to better understand the reasons for these limitations by focusing on the simpler, limited-mode microdisk cavities, and by carrying out comparisons of lasing dynamics in those cavities using varying gain media including InGaN quantum wells, fragmented quantum wells, and a combination of fragmented quantum wells with quantum dots. For each gain medium, we use the distinctive, high-quality (Q ? 5,500) modes of the cavities, and the change in the highest-intensity mode as a function of pump power to better understand the dominant radiative processes. The variations of threshold power and lasing wavelength as a function of gain medium help us identify the possible limitations to lower-threshold lasing with quantum dot active medium. In addition, we have identified a distinctive lasing signature for quantum dot materials, which consistently lase at wavelengths shorter than the peak of the room temperature gain emission. These findings not only provide better understanding of lasing in nitride-based quantum dot cavity systems but also shed insight into the more fundamental issues of light-matter coupling in such systems. PMID:25197073

Woolf, Alexander; Puchtler, Tim; Aharonovich, Igor; Zhu, Tongtong; Niu, Nan; Wang, Danqing; Oliver, Rachel; Hu, Evelyn L

2014-09-30

93

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

Science.gov (United States)

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

94

Concatenated quantum codes in biological systems  

Science.gov (United States)

This talk investigates how biological systems such as photosynthetic bacteria use quantum coding techniques such as decoherent subspaces, noiseless subsystems, and concatenated quantum codes to engineer long exitonic lifetimes and rapid energy transport. The existence of hierarchical structures in photosynthetic complexes is associated with concatenated quantum codes. A concatenated code is one that combines two or more codes to construct a hierarchical code that possesses features of all its constituent codes. In photosynthetic complexes, structures at the smallest level use quantum coding techniques to enhance exciton lifetimes, and structures at higher scales possess symmetries that enhance exciton hopping rates. The result is a concatenated quantum code that simultaneously protects excitons and enhances their transport rate. All known quantum codes can be described within the framework of group representation theory. This talk reviews the relationship between symmetry and quantum codes, and shows how photosynthetic bacteria and plants put quantum coding techniques to use to improve the efficiency of photosynthetic transport.

Lloyd, Seth

2011-03-01

95

Thermalization of isolated quantum systems  

CERN Document Server

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

96

Zeno dynamics for open quantum systems  

Science.gov (United States)

In this paper, we formulate limit Zeno dynamics of general open systems as the adiabatic elimination of fast components. We are able to exploit previous work on adiabatic elimination of quantum stochastic models to give explicitly the conditions under which open Zeno dynamics will exist. The open systems formulation is further developed as a framework for Zeno master equations, and Zeno filtering (that is, quantum trajectories based on a limit Zeno dynamical model). We discuss several models from the point of view of quantum control. For the case of linear quantum stochastic systems, we present a condition for stability of the asymptotic Zeno dynamics.

Gough, J.

2014-07-01

97

Entangled quantum systems in number theory  

Energy Technology Data Exchange (ETDEWEB)

There is an evident connection between quantum mechanics and number theory. Simply think of Shor's algorithm or quantum billards. In important function in number theory is the {zeta}-function of Riemann and a fundamental concept of quantum theory are entangled systems. We bring these two elements together and depict analytic continuation in mathematics in terms of a physical system. We present a method to evaluate the {zeta}-function by preparing an appropriate quantum system. We emphasize the point where entanglement comes to play a role.

Mack, Ruediger; Schleich, Wolfgang P. [Institute for Quantum Physics, Ulm University (Germany)

2009-07-01

98

Frustration of Decoherence in Open Quantum Systems  

OpenAIRE

We study a model of frustration of decoherence in an open quantum system. Contrary to other dissipative ohmic impurity models, such as the Kondo model or the dissipative two-level system, the impurity model discussed here never presents overdamped dynamics even for strong coupling to the environment. We show that this unusual effect has its origins in the quantum mechanical nature of the coupling between the quantum impurity and the environment. We study the problem using an...

Novais, E.; Neto, A. H. Castro; Borda, L.; Affleck, I.; Zarand, G.

2005-01-01

99

Predictive Information for Quantum Bio-Systems  

Science.gov (United States)

We consider the evolution of a quantum bio-system that interacts with an external environment in a stochastic manner. We ask an important question: when can a bio-system be more predictive to a changing environment? We prove that the non-predictive information for a driven quantum bio-system is lower bounded by the change in the quantum correlation and upper bounded by the entropy production in the system and the environment. We argue that for a system to have more predictive information, it must retain the quantum correlation. This shows that at a fundamental level if a biological system has to be energetically efficient, it must minimize the loss of quantum correlation.

Pati, Arun Kumar

2014-07-01

100

Energy balance for a dissipative quantum system  

Science.gov (United States)

The role of random force in maintaining equilibrium in a dissipative quantum system is studied here. We compute the instantaneous power supplied by the fluctuating (random) force, which provides information about the work done by the random force on the quantum subsystem of interest. The quantum Langevin equation formalism is used here to verify that, at equilibrium, the work done by the fluctuating force balances the energy lost by the quantum subsystem to the heat bath. The quantum subsystem we choose to couple to the heat bath is the charged oscillator in a magnetic field. We perform the calculations using the Drude regularized spectral density of bath oscillators instead of using a strict ohmic spectral density that gives memoryless damping. We also discuss the energy balance for our dissipative quantum system and in this regard it is to be understood that the physical system is the charged magneto-oscillator coupled to the heat bath, not the uncoupled charged magneto-oscillator.

Kumar, Jishad

2014-09-01

101

Dynamical entropy for infinite quantum systems  

International Nuclear Information System (INIS)

We review the recent physical application of the so-called Connes-Narnhofer-Thirring entropy, which is the successful quantum mechanical generalization of the classical Kolmogorov-Sinai entropy and, by its very conception, is a dynamical entropy for infinite quantum systems. We thus comparingly review also the physical applications of the classical dynamical entropy for infinite classical systems. 41 refs. (Author)

102

Quantum chaos in open systems a quantum state diffusion analysis  

CERN Document Server

Except for the universe, all quantum systems are open, and according to quantum state diffusion theory, many systems localize to wave packets in the neighborhood of phase space points. This is due to decoherence from the interaction with the environment, and makes the quasiclassical limit of such systems both more realistic and simpler in many respects than the more familiar quasiclassical limit for closed systems. A linearized version of this theory leads to the correct classical dynamics in the macroscopic limit, even for nonlinear and chaotic systems. We apply the theory to the forced, damped Duffing oscillator, comparing the numerical results of the full and linearized equations, and argue that this can be used to make explicit calculations in the decoherent histories formalism of quantum mechanics.

Brun, T A; Schack, R; Brun, Todd A; Percival, Ian C; Schack, Rudiger

1995-01-01

103

Symplectic transformations and quantum tomography in finite quantum systems  

International Nuclear Information System (INIS)

Quantum systems where the position and momentum are in the ring Zd (d is an odd integer) are considered. Symplectic transformations are studied, and the order of Sp(2,Zd) is calculated. Quantum tomography is also discussed. It is shown that measurements (used in the inverse Radon transform) need to be made on J2(d) lines (where J2(d) is the Jordan totient function). (fast track communication)

104

Quantum information theory with Gaussian systems  

Energy Technology Data Exchange (ETDEWEB)

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.)

Krueger, O.

2006-04-06

105

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.)

106

Observation of quantum stochastic synchronization in a dissipative quantum system  

Science.gov (United States)

We report the observation of quantum stochastic synchronization (QSS) in a dissipative quantum system—a moderately damped current-biased Josephson junction. We show that when the junction is biased subcritically by a combination of a constant current and a small sinusoidal modulation signal, forced phase synchronization between the otherwise random, incoherent quantum tunneling and the signal may arise as a consequence of the interplay between quantum fluctuation and the weak periodic drive. It is found that optimal synchronization occurs at a signal frequency fQSS that is comparable to the quantum tunneling rate. We also find a phenomenon called "modulation induced suppression of quantum noise": for signal frequency well below fQSS, the power spectral density of escape time distribution of the junction could be reduced substantially from the floor level of the unmodulated system. Furthermore, we demonstrate that the application of a small signal with proper phase can suppress the average tunneling rate and enhance the stability of the metastable system. Our experimental results agree well with the numerical calculations without the use of adjustable parameters.

Xue, G. M.; Gong, Ming; Xu, H. K.; Liu, W. Y.; Deng, H.; Tian, Ye; Yu, H. F.; Yu, Yang; Zheng, D. N.; Zhao, S. P.; Han, Siyuan

2014-12-01

107

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)

108

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)

109

Quantum master equation approach to quantum transport through mesoscopic systems  

CERN Document Server

For quantum transport through mesoscopic system, a unified quantum master equation approach is developed in terms of compact expressions for the transport current and the reduced density matrix of the mesoscopic system. The established formalism is applicable for a wide range of conditions such as in the presence of many-body interaction, at finite temperatures and under arbitrary voltages. Moreover, the formalism is free from state representation and specific system Hamiltonian, which therefore holds the merit of generality and convenience for practical applications.

Li, X Q; Luo, J; Cui, P; Yan, Y J; Li, Xin-Qi; Yang, Yong-Gang; Luo, Junyan; Cui, Ping; Yan, YiJing

2004-01-01

110

Random dynamical systems of integrable quantum mechanics  

International Nuclear Information System (INIS)

We discuss the quantum mechanics of completely integrable classical systems in a probabilistic formulation. We derive a stochastic analogue of a constant of motion. We discuss stochastic differential equations defining the time evolution of classical action-angle variables. We derive a random series expansion around the invariant tori. We relate periodic solutions of deterministic systems to periodic solutions of random systems and to the discrete spectrum of the corresponding quantum systems. ((orig.))

111

Interaction between classical and quantum systems  

International Nuclear Information System (INIS)

An unconventional approach to the measurement problem in quantum mechanics is considered--the apparatus is treated as a classical system, belonging to the macro-world. In order to have a measurement the apparatus must interact with the quantum system. As a first step, the classical apparatus is embedded into a large quantum mechanical structure, making use of a superselection principle. The apparatus and system are coupled such that the apparatus remains classical (principle of integrity), and unambiguous information of the values of a quantum observable are transferred to the variables of the apparatus. Further measurement of the classical apparatus can be done, causing no problems of principle. Thus interactions causing pointers to move (which are not treated) can be added. The restrictions placed by the principle of integrity on the form of the interaction between classical and quantum systems are examined and illustration is given by means of a simple example in which one sees the principle of integrity at work

112

Non-perturbative description of quantum systems  

CERN Document Server

This book introduces systematically the operator method for the solution of the Schrödinger equation. This method permits to describe the states of quantum systems in the entire range of parameters of Hamiltonian with a predefined accuracy. The operator method is unique compared with other non-perturbative methods due to its ability to deliver in zeroth approximation the uniformly suitable estimate for both ground and excited states of quantum system. The method has been generalized for the application to quantum statistics and quantum field theory.  In this book, the numerous applications of operator method for various physical systems are demonstrated. Simple models are used to illustrate the basic principles of the method which are further used for the solution of complex problems of quantum theory for many-particle systems. The results obtained are supplemented by numerical calculations, presented as tables and figures.

Feranchuk, Ilya; Le, Van-Hoang; Ulyanenkov, Alexander

2015-01-01

113

Quantum chaos in generic systems  

International Nuclear Information System (INIS)

First I briefly review the basic elements of the stationary quantum chaos in Hamiltonian systems, the universality classes of energy spectra and eigenfunctions. Then I consider the problem of the generic systems whose classical dynamics and the phase portrait is of the mixed type, i.e. regular for certain initial conditions and irregular (chaotic) for other initial conditions. I present the Berry-Robnik picture, the Principle of Uniform Semiclassical Condensation (of the Wigner functions of the eigenstates), and the statistical description of the energy spectra in terms of E(k,L) statistics, which is shown to be valid in the semiclassical limit of sufficiently small effective Planck constant and is numerically firmly confirmed. Then I consider the spectral autocorrelation function and the form factor (its Fourier transform) in the same limit, and show its agreement with the numerical investigations in the regular and fully chaotic cases. I show the numerical evidence for the deviations from that prediction in mixed type systems at low energies, due to localization and tunneling effects. Here are also the important open theoretical questions that I address. (author)

114

Sliding mode control of quantum systems  

International Nuclear Information System (INIS)

This paper proposes a new robust control method for quantum systems with uncertainties involving sliding mode control (SMC). SMC is a widely used approach in classical control theory and industrial applications. We show that SMC is also a useful method for robust control of quantum systems. In this paper, we define two specific classes of sliding modes (i.e. eigenstates and state subspaces) and propose two novel methods combining unitary control and periodic projective measurements for the design of quantum SMC systems. Two examples including a two-level system and a three-level system are presented to demonstrate the proposed SMC method. One of the main features of the proposed method is that the designed control laws can guarantee the desired control performance in the presence of uncertainties in the system Hamiltonian. This SMC approach provides a useful control theoretic tool for robust quantum information processing with uncertainties.

115

Sliding mode control of quantum systems  

Energy Technology Data Exchange (ETDEWEB)

This paper proposes a new robust control method for quantum systems with uncertainties involving sliding mode control (SMC). SMC is a widely used approach in classical control theory and industrial applications. We show that SMC is also a useful method for robust control of quantum systems. In this paper, we define two specific classes of sliding modes (i.e. eigenstates and state subspaces) and propose two novel methods combining unitary control and periodic projective measurements for the design of quantum SMC systems. Two examples including a two-level system and a three-level system are presented to demonstrate the proposed SMC method. One of the main features of the proposed method is that the designed control laws can guarantee the desired control performance in the presence of uncertainties in the system Hamiltonian. This SMC approach provides a useful control theoretic tool for robust quantum information processing with uncertainties.

Dong Daoyi; Petersen, Ian R [School of Information Technology and Electrical Engineering, University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600 (Australia)], E-mail: daoyidong@gmail.com, E-mail: i.r.petersen@gmail.com

2009-10-15

116

Control of open quantum systems dynamics  

OpenAIRE

We investigate the control resources needed to effect arbitrary quantum dynamics. We show that the ability to perform measurements on a quantum system, combined with the ability to feed back the measurement results via coherent control, allows one to control the system to follow any desired open-system evolution. Such universal control can be achieved, in principle, through the repeated application of only two coherent control operations and a simple ``Yes-No'' measurement.

Lloyd, Seth; Viola, Lorenza

2000-01-01

117

Strong Local Passivity in Finite Quantum Systems  

OpenAIRE

Passive states of quantum systems are states from which no system energy can be extracted by any cyclic (unitary) process. Gibbs states of all temperatures are passive. Strong local (SL) passive states are defined to allow any general quantum operation, but the operation is required to be local, being applied only to a specific subsystem. Any mixture of eigenstates in a system-dependent neighborhood of a nondegenerate, entangled ground state is found to be SL passive. In par...

Frey, Michael; Funo, Ken; Hotta, Masahiro

2014-01-01

118

Impedance measurement technique for quantum systems  

OpenAIRE

The impedance measurement technique consists in that the phase-dependent (parametric) inductance of the system is probed by the classical tank circuit via measuring the voltage. The notion of the parametric inductance for the impedance measurement technique is revisited for the case when a quantum system is probed. Measurement of the quantum state of the system of superconducting circuits (qubits) is studied theoretically. It is shown that the result of the measurement is de...

Shevchenko, S. N.

2007-01-01

119

Quantum simulation of tunneling in small systems.  

Science.gov (United States)

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, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures. PMID:22916333

Sornborger, Andrew T

2012-01-01

120

Macroscopic quantum tunneling in nanoelectromechanical systems  

CERN Document Server

The experimental observation of quantum phenomena in mechanical degrees of freedom is difficult, as the systems become linear towards low energies and the quantum limit, and thus reside in the correspondence limit. Here we investigate how to access quantum phenomena in flexural nanomechanical systems which are strongly deflected by a voltage. Near a metastable point, one can achieve a significant nonlinearity in the electromechanical potential at the scale of zero point energy. The system could then escape from the metastable state via macroscopic quantum tunneling (MQT). We consider two model systems suspended atop a voltage gate, namely, a graphene sheet, and a carbon nanotube. We find that the experimental demonstration of the phenomenon is currently possible but demanding, since the MQT crossover temperatures fall in the milli-Kelvin range. A carbon nanotube is suggested as the most promising system.

Sillanpaa, Mika A; Heikkila, Tero T; Hakonen, Pertti J

2011-01-01

121

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

122

Stabilization of classic and quantum systems  

International Nuclear Information System (INIS)

It is shown that the mechanism of quantum whirligig can be successfully used for stabilization of classical systems. In particular, the conditions for stabilization of charged particles and radiation fluxes in plasma are found.

123

Quantum Phenomena in Low-Dimensional Systems  

OpenAIRE

A brief summary of the physics of low-dimensional quantum systems is given. The material should be accessible to advanced physics undergraduate students. References to recent review articles and books are provided when possible.

Geller, Michael R.

2001-01-01

124

Zeno Dynamics for Open Quantum Systems  

OpenAIRE

In this paper we formulate limit Zeno dynamics of general open systems as the adiabatic elimination of fast components. We are able to exploit previous work on adiabatic elimination of quantum stochastic models to give explicitly the conditions under which open Zeno dynamics will exist. The open systems formulation is further developed as a framework for Zeno master equations, and Zeno filtering (that is, quantum trajectories based on a limit Zeno dynamical model). We discus...

Gough, J. E.

2014-01-01

125

Sliding mode control of quantum systems  

OpenAIRE

This paper proposes a new robust control method for quantum systems with uncertainties involving sliding mode control (SMC). Sliding mode control is a widely used approach in classical control theory and industrial applications. We show that SMC is also a useful method for robust control of quantum systems. In this paper, we define two specific classes of sliding modes (i.e., eigenstates and state subspaces) and propose two novel methods combining unitary control and periodi...

Dong, Daoyi; Petersen, Ian R.

2009-01-01

126

Fluctuation Relations for Quantum Markovian Dynamical System  

OpenAIRE

We derive a general set of fluctuation relations for a nonequilibrium open quantum system described by a Lindblad master equation. In the special case of conservative Hamiltonian dynamics, these identities allow us to retrieve quantum versions of Jarzynski and Crooks relations. In the linear response regime, these fluctuation relations yield a fluctuation-dissipation theorem (FDT) valid for a stationary state arbitrarily far from equilibrium. For a closed system, this FDT re...

Chetrite, Raphael; Mallick, Kirone

2010-01-01

127

Isoperiodic classical systems and their quantum counterparts  

CERN Document Server

One-dimensional isoperiodic classical systems have been first analyzed by Abel. Abel's characterization can be extended for singular potentials and potentials which are not defined on the whole real line. The standard shear equivalence of isoperiodic potentials can also be extended by using reflection and inversion transformations. We provide a full characterization of isoperiodic rational potentials showing that they are connected by translations, reflections or Joukowski transformations. Upon quantization many of these isoperiodic systems fail to exhibit identical quantum energy spectra. This anomaly occurs at order O(h^2) because semiclassical corrections of energy levels of order O(h) are identical for all isoperiodic systems. We analyze families of systems where this quantum anomaly occurs and some special systems where the spectral identity is preserved by quantization. Conversely, we point out the existence of isospectral quantum systems which do not correspond to isoperiodic classical systems.

Asorey, M; Marmo, G; Perelomov, A

2007-01-01

128

Quantum electro-mechanical system (QEMS)  

International Nuclear Information System (INIS)

Full text: Recent development in Nano Electro-Mechanical Systems (NEMS) has yield oscillators with resonant frequencies above Giga Hertz with quality factors above 100,000. At this scale a NEMS oscillator becomes a quantum device capable of operating at the atomic level with extraordinary sensitivity to small forces or molecular masses. With this motivation, we study the phonon-electron interaction in several quantum electromechanical systems (QEMS). First, a system comprising a single quantum dot harmonically bound between two electrodes which facilitates a tunneling current between them and secondly the electron shuttle system firstly introduced by Gorelik. We describe the system via quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise. This dynamical description is related to observable features of the system including the stationary current as a function of bias voltage. A number of possible applications are explored for feasibility including molecular QEMS devices as quantum limited nanoscale detectors and as elements in quantum computer architectures. Copyright (2005) Australian Institute of Physicsf Physics

129

The classical capacity of a quantum dense coding system  

International Nuclear Information System (INIS)

Quantum dense coding transmits classical information by sending a quantum system with the assistance of quantum entanglement. The classical information capacity of a quantum dense coding system is obtained, where a sender and receiver share a completely entangled state and a quantum system encoded by applying unitary operators is sent through an arbitrary quantum channel. The result is compared with that obtained in another setting. (letter to the editor)

130

Open quantum systems and error correction  

Science.gov (United States)

Quantum effects can be harnessed to manipulate information in a desired way. Quantum systems which are designed for this purpose are suffering from harming interaction with their surrounding environment or inaccuracy in control forces. Engineering different methods to combat errors in quantum devices are highly demanding. In this thesis, I focus on realistic formulations of quantum error correction methods. A realistic formulation is the one that incorporates experimental challenges. This thesis is presented in two sections of open quantum system and quantum error correction. Chapters 2 and 3 cover the material on open quantum system theory. It is essential to first study a noise process then to contemplate methods to cancel its effect. In the second chapter, I present the non-completely positive formulation of quantum maps. Most of these results are published in [Shabani and Lidar, 2009b,a], except a subsection on geometric characterization of positivity domain of a quantum map. The real-time formulation of the dynamics is the topic of the third chapter. After introducing the concept of Markovian regime, A new post-Markovian quantum master equation is derived, published in [Shabani and Lidar, 2005a]. The section of quantum error correction is presented in three chapters of 4, 5, 6 and 7. In chapter 4, we introduce a generalized theory of decoherence-free subspaces and subsystems (DFSs), which do not require accurate initialization (published in [Shabani and Lidar, 2005b]). In Chapter 5, we present a semidefinite program optimization approach to quantum error correction that yields codes and recovery procedures that are robust against significant variations in the noise channel. Our approach allows us to optimize the encoding, recovery, or both, and is amenable to approximations that significantly improve computational cost while retaining fidelity (see [Kosut et al., 2008] for a published version). Chapter 6 is devoted to a theory of quantum error correction (QEC) that applies to any linear map, in particular maps that are not completely positive (CP). This is a complementary to the second chapter which is published in [Shabani and Lidar, 2007]. In the last chapter 7 before the conclusion, a formulation for evaluating the performance of quantum error correcting codes for a general error model is presented, also published in [Shabani, 2005]. In this formulation, the correlation between errors is quantified by a Hamiltonian description of the noise process. In particular, we consider Calderbank-Shor-Steane codes and observe a better performance in the presence of correlated errors depending on the timing of the error recovery.

Shabani Barzegar, Alireza

131

T-systems and Y-systems for quantum affinizations of quantum Kac-Moody algebras  

OpenAIRE

The T-systems and Y-systems are classes of algebraic relations originally associated with quantum affine algebras and Yangians. Recently the T-systems were generalized to quantum affinizations of a wide class of quantum Kac-Moody algebras by Hernandez. In this note we introduce the corresponding Y-systems and establish a relation between T and Y-systems. We also introduce the T and Y-systems associated with a class of cluster algebras, which include the former T and Y-system...

Tomoki Nakanishi; Junji Suzuki(Department of Physics, Shizuoka University, Shizuoka 422-8529, Japan); Atsuo Kuniba

2009-01-01

132

Noise in quantum systems: facts and fantasies  

International Nuclear Information System (INIS)

Full text: We present a critical review of recent developments on quantum noise in a variety of mesoscopic conductors including ballistic, diffusive and tunnelling systems. We begin with a microscopic approach that describes quantum transport and fluctuations for correlated electrons at high external field taking the system beyond the linear response regime. We discuss two commonly believed results that (a) shot noise in diffusive systems is suppressed by '1/3' universally and (b) there is a 'crossover' of shot noise to thermal noise at finite temperature and applied field. Our analysis reveals contradictions based on fundamental physics and its logical implications. We examine another issue of measuring fractional charges in fractional quantum Hall effect (FQHE) experiments. It is believed that shot noise spectral density reveals the charge quantum of the current carriers as a Schottky phenomenon. Here again we analyse a number of unverified assumptions beyond the myth

133

Software-defined Quantum Communication Systems  

Energy Technology Data Exchange (ETDEWEB)

Quantum communication systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for quantum communication engineering is designing and prototyping these systems to prototype proposed capabilities. We apply the paradigm of software-defined communica- tion for engineering quantum communication systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose quantum communication terminals into functional layers defining hardware, software, and middleware concerns, and we describe how each layer behaves. Using the super-dense coding protocol as a test case, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We find that while the theoretical benefits of super dense coding are maintained, there is a classical overhead associated with the full implementation.

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

2014-01-01

134

CIME School on Quantum Many Body Systems  

CERN Document Server

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

135

Quantum weak chaos in a degenerate system  

CERN Document Server

Quantum weak chaos is studied in a perturbed degenerate system --- a charged particle interacting with a monochromatic wave in a transverse magnetic field. The evolution operator for an arbitrary number of periods of the external field is built and its structure is explored in terms of the QE (quasienergy eigenstates) under resonance condition (wave frequency $=$ cyclotron frequency) in the regime of weak classical chaos. The new phenomenon of diffusion via the quantum separatrices and the influence of chaos on diffusion are investigated and, in the quasi classical limit, compared with its classical dynamics. We determine the crossover from purely quantum diffusion to a diffusion which is the quantum manifestation of classical diffusion along the stochastic web. This crossover results from the non-monotonic dependence of the characteristic localization length of the QE states on the wave amplitude. The width of the quantum separatrices was computed and compared with the width of the classical stochastic web. ...

Demikhovskii, V Y; Luna-Acosta, G A

1998-01-01

136

Dynamical programming of continuously observed quantum systems  

CERN Document Server

We develop dynamical programming methods for the purpose of optimal control of quantum states with convex constraints and concave cost and target functions of the quantum state. Consideration is given to both open loop and feedback control schemes corresponding respectively to deterministic and stochastic Master Equation dynamics. For the quantum feedback control scheme with continuous nondemolition observations we exploit the separation theorem of filtering and control aspects for quantum stochastic micro-dynamics of the total system. This allows to start with the Belavkin quantum filtering equation and derive the generalised 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 only Hamiltonian terms in the filtering equation. We consider also the case when control is restricted to only observation. A controlled qubit is considered as an example throughout t...

Belavkin, Viacheslav P; Molmer, Klaus

2008-01-01

137

Relativistic Quantum Metrology in Open System Dynamics  

CERN Document Server

Quantum metrology studies the ultimate limit of precision in estimating a physical quantity if quantum strategies are exploited. Here we investigate the evolution of a two-level atom as a detector which interacts with a massless scalar field using the master equation approach for open quantum system. We employ local quantum estimation theory to estimate the Unruh temperature when probed by a uniformly accelerated detector in the Minkowski vacuum. In particular, we evaluate the Fisher information (FI) for population measurement, maximize its value over all possible detector preparations and evolution times, and compare its behavior with that of the quantum Fisher information (QFI). We find that the optimal precision of estimation is achieved when the detector evolves for a long enough time. Furthermore, we find that in this case the FI for population measurement is independent of initial preparations of the detector and is exactly equal to the QFI, which means that population measurement is optimal. This resul...

Tian, Zehua; Fan, Heng; Jing, Jiliang

2015-01-01

138

Entanglement in quantum critical spin systems  

CERN Document Server

We study the field dependence of the entanglement of formation in anisotropic S=1/2 antiferromagnetic chains and two-leg ladders displaying a T=0 field-driven quantum phase transition. The analysis is carried out via Quantum Monte Carlo simulations. At zero temperature the entanglement estimators show abrupt changes at and around criticality, vanishing below the critical field, in correspondence with an exactly factorized state, and then immediately recovering a finite value upon passing through the quantum phase transition. At the quantum critical point, a deep minimum in the pairwise-to-global entanglement ratio shows that multi-spin entanglement is strongly enhanced; moreover this signature represents a novel way of detecting the quantum phase transition of the system, relying entirely on entanglement estimators.

Roscilde, T; Fubini, A; Haas, S; Tognetti, V; Roscilde, Tommaso; Verrucchi, Paola; Fubini, Andrea; Haas, Stephan; Tognetti, Valerio

2004-01-01

139

Open Quantum Systems with Loss and Gain  

Science.gov (United States)

We consider different properties of small open quantum systems coupled to an environment and described by a non-Hermitian Hamilton operator. Of special interest is the non-analytical behavior of the eigenvalues in the vicinity of singular points, the so-called exceptional points (EPs), at which the eigenvalues of two states coalesce and the corresponding eigenfunctions are linearly dependent from one another. The phases of the eigenfunctions are not rigid in approaching an EP and providing therewith the possibility to put information from the environment into the system. All characteristic properties of non-Hermitian quantum systems hold true not only for natural open quantum systems that suffer loss due to their embedding into the continuum of scattering wavefunctions. They appear also in systems coupled to different layers some of which provide gain to the system.Thereby gain and loss, respectively, may be fixed inside every layer, i.e. characteristic of it.

Eleuch, Hichem; Rotter, Ingrid

2014-10-01

140

Complex quantum systems analysis of large Coulomb systems  

CERN Document Server

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

141

Measurement, Filtering and Control in Quantum Open Dynamical Systems  

OpenAIRE

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 dis...

Belavkin, V. P.

2002-01-01

142

Transitivity and ergodicity of quantum systems  

International Nuclear Information System (INIS)

First we try to generalize the notion of a topological transitive or a topologically mixing system for quantum mechanical systems in a consistent way. Furthermore we compare these ergodic properties with the classical results. Finaly we deal with some aspects of nearly abelian systems and investigate some relations between these notions. 11 refs. (Author)

143

Isospectrality for quantum toric integrable systems  

CERN Document Server

We settle affirmatively the isospectral problem for quantum toric integrable systems: the semiclassical joint spectrum of such a system, given by a sequence of commuting Toeplitz operators on a sequence of Hilbert spaces, determines the classical integrable system given by the symplectic manifold and Poisson commuting functions, up to symplectomorphisms. We also give a full description of the semiclassical spectral theory of quantum toric integrable systems. This type of problem belongs to the realm of classical questions in spectral theory going back to pioneer works of Colin de Verdiere, Guillemin, Sternberg and others in the 1970s and 1980s.

Charles, Laurent; Ngoc, San Vu

2011-01-01

144

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

145

Strong local passivity in finite quantum systems.  

Science.gov (United States)

Passive states of quantum systems are states from which no system energy can be extracted by any cyclic (unitary) process. Gibbs states of all temperatures are passive. Strong local (SL) passive states are defined to allow any general quantum operation, but the operation is required to be local, being applied only to a specific subsystem. Any mixture of eigenstates in a system-dependent neighborhood of a nondegenerate entangled ground state is found to be SL passive. In particular, Gibbs states are SL passive with respect to a subsystem only at or below a critical system-dependent temperature. SL passivity is associated in many-body systems with the presence of ground state entanglement in a way suggestive of collective quantum phenomena such as quantum phase transitions, superconductivity, and the quantum Hall effect. The presence of SL passivity is detailed for some simple spin systems where it is found that SL passivity is neither confined to systems of only a few particles nor limited to the near vicinity of the ground state. PMID:25122271

Frey, Michael; Funo, Ken; Hotta, Masahiro

2014-07-01

146

Quantum system lifetimes and measurement perturbations  

International Nuclear Information System (INIS)

The recently proposed description of quantum system decay in terms of repeated measurement perturbations is modified. The possibility of retarded reductions to a unique quantum state, due to ineffective localization of the decay products at initial time measurements, is simply taken into account. The exponential decay law is verified again. A modified equation giving the observed lifetime in terms of unperturbed quantum decay law, measurement frequency and reduction law is derived. It predicts deviations of the observed lifetime from the umperturbed one, together with a dependence on experimental procedures. The influence of different model unperturbed decay laws and reduction laws on this effect is studied

147

Levitated Quantum Nano-Magneto-Mechanical Systems  

Science.gov (United States)

Quantum nanomechanical sysems have attracted much attention as they provide new macroscopic platforms for the study of quantum mechanics but may also have applications in ultra-sensitive sensing, high precision measurements and in quantum computing. In this work we study the control and cooling of a quantum nanomechanical system which is magnetically levitated via the Meissner effect. Supercurrents in nano-sized superconducting loops give rise to a motional restoring force (trap), when placed in an highly inhomogenous magnetic field and can yield complete trapping of all translational and rotational motions of the levitated nano-object with motional oscillation frequencies ?˜10-100MHz. As the supercurrents experience little damping this system will possess unprecendented motional quality factors, with Qmotion˜10^9-10^13, and motional superposition states may remain coherent for days. We describe how to execute sideband cooling through inductive coupling to a nearby flux qubit, cooling the mechanical motion close to the ground state.

Cirio, Mauro; Twamley, Jason; Brennen, Gavin K.; Milburn, Gerard J.

2011-03-01

148

Approximation, Proof Systems, and Correlations in a Quantum World  

OpenAIRE

This thesis studies three topics in quantum computation and information: The approximability of quantum problems, quantum proof systems, and non-classical correlations in quantum systems. In the first area, we demonstrate a polynomial-time (classical) approximation algorithm for dense instances of the canonical QMA-complete quantum constraint satisfaction problem, the local Hamiltonian problem. In the opposite direction, we next introduce a quantum generalization of the po...

Gharibian, Sevag

2013-01-01

149

Overlapping Resonances in Open Quantum Systems  

OpenAIRE

An $N$-level quantum system is coupled to a bosonic heat reservoir at positive temperature. We analyze the system-reservoir dynamics in the following regime: The strength $\\lambda$ of the system-reservoir coupling is fixed and small, but larger than the spacing $\\sigma$ of system energy levels. For vanishing $\\sigma$ there is a manifold of invariant system-reservoir states and for $\\sigma>0$ the only invariant state is the joint equilibrium. The manifold is invariant for $\\s...

Merkli, Marco; Song, Haifeng

2014-01-01

150

Open quantum systems approach to atomtronics  

OpenAIRE

We derive a quantum master equation to treat quantum systems interacting with multiple reservoirs. The formalism is used to investigate atomic transport across a variety of lattice configurations. We demonstrate how the behavior of an electronic diode, a field-effect transistor, and a bipolar junction transistor can be realized with neutral, ultracold atoms trapped in optical lattices. An analysis of the current fluctuations is provided for the case of the atomtronic diode. ...

Pepino, R. A.; Cooper, J.; Meiser, D.; Anderson, D. Z.; Holland, M. J.

2010-01-01

151

Quantum mechanics in general quantum systems (II): Perturbation theory  

OpenAIRE

We propose an improved scheme of perturbation theory based on our exact solution [An Min Wang, quant-ph/0611216] in general quantum systems independent of time. Our elementary start-point is to introduce the perturbing parameter as late as possible. Our main skills are Hamiltonian redivision so as to overcome a flaw of the usual perturbation theory, and the perturbing Hamiltonian matrix product decomposition in order to separate the contraction and anti-contraction terms. Ou...

Wang, An Min

2006-01-01

152

Scattering theory for open quantum systems  

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 H is used to describe an open quantum system. In this case the minimal self-adjoint dilation K of AD can be regarded as the Hamiltonian of a closed system which contains the open system {AD,h}, but since K 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. (orig.)

153

Scattering theory for open quantum systems  

Energy Technology Data Exchange (ETDEWEB)

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 A{sub D} in a Hilbert space H is used to describe an open quantum system. In this case the minimal self-adjoint dilation K of A{sub D} can be regarded as the Hamiltonian of a closed system which contains the open system {l_brace}A{sub D},h{r_brace}, but since K 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 {l_brace}A({mu}){r_brace} of maximal dissipative operators depending on energy {mu}, 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. (orig.)

Behrndt, Jussi [Technische Univ. Berlin (Germany). Inst. fuer Mathematik; Malamud, Mark M. [Donetsk National University (Ukraine). Dept. of Mathematics; Neidhardt, Hagen [Weierstrass-Institut fuer Angewandte Analysis und Stochastik (WIAS) im Forschungsverbund Berlin e.V. (Germany)

2006-07-01

154

Relaxation of isolated quantum systems beyond chaos  

Science.gov (United States)

In classical statistical mechanics there is a clear correlation between relaxation to equilibrium and chaos. In contrast, for isolated quantum systems this relation is—to say the least—fuzzy. In this work we try to unveil the intricate relation between the relaxation process and the transition from integrability to chaos. We study the approach to equilibrium in two different many-body quantum systems that can be parametrically tuned from regular to chaotic. We show that a universal relation between relaxation and delocalization of the initial state in the perturbed basis can be established regardless of the chaotic nature of system.

García-Mata, Ignacio; Roncaglia, Augusto J.; Wisniacki, Diego A.

2015-01-01

155

Quantum scaling in many-body systems  

CERN Document Server

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

156

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

157

Witnessing Quantum Coherence: from solid-state to biological systems  

CERN Document Server

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

158

Witnessing Quantum Coherence: from solid-state to biological systems  

Science.gov (United States)

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; Lambert, Neill; Chen, Yueh-Nan; Chen, Guang-Yin; Nori, Franco

2012-11-01

159

Majorization Relation in Quantum Critical Systems  

Science.gov (United States)

The most basic local conversion is local operations and classical communications (LOCC), which is also the most natural restriction in quantum information processing. We investigate the conversions between the ground states in quantum critical systems via LOCC and propose a novel method to reveal the different convertibilities via majorization relation when a quantum phase transition occurs. The ground-state local convertibility in the one-dimensional transverse field Ising model is studied. It is shown that the LOCC convertibility changes nearly at the phase transition point. The relation between the order of quantum phase transitions and the LOCC convertibility is discussed. Our results are compared with the corresponding results by using the Rényi entropy and the LOCC convertibility with assisted entanglement.

Huai, Lin-Ping; Zhang, Yu-Ran; Liu, Si-Yuan; Yang, Wen-Li; Qu, Shi-Xian; Fan, Heng

2014-07-01

160

Quantum Dynamics of Nonlinear Cavity Systems  

CERN Document Server

We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal and noise response where it is found that a soft-spring Duffing self-interaction enables a closer approach to the displacement detection standard quantum limit, as well as cooling closer to the ground state. Next, we make use of a superconducting transmission line formed from an array of dc-SQUIDs for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. This setup allows for quan...

Nation, Paul D

2010-01-01

161

Quantum games in open systems using biophysical Hamiltonians  

International Nuclear Information System (INIS)

We analyze the necessary physical conditions to model an open quantum system as a quantum game. By applying the formalism of quantum operations on a particular system, we use Kraus operators as quantum strategies. The physical interpretation is a conflict among different configurations of the environment. The resolution of the conflict displays regimes of minimum loss of information

162

Quantum Games in Open Systems using Biophysic Hamiltonians  

OpenAIRE

We analyze the necessary physical conditions to model an open quantum system as a quantum game. By applying the formalism of Quantum Operations on a particular system, we use Kraus operators as quantum strategies. The physical interpretation is a conflict among different configurations of the environment. The resolution of the conflict displays regimes of minimum loss of information.

Faber, Jean; Portugal, Renato; Rosa, Luiz Pinguelli

2006-01-01

163

Thermodynamics of quantum informational systems - Hamiltonian description  

CERN Document Server

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

164

Heisenberg picture approach to the stability of quantum Markov systems  

International Nuclear Information System (INIS)

Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks

165

Heisenberg picture approach to the stability of quantum Markov systems  

Energy Technology Data Exchange (ETDEWEB)

Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks.

Pan, Yu, E-mail: yu.pan@anu.edu.au, E-mail: zibo.miao@anu.edu.au; Miao, Zibo, E-mail: yu.pan@anu.edu.au, E-mail: zibo.miao@anu.edu.au [Research School of Engineering, Australian National University, Canberra, ACT 0200 (Australia); Amini, Hadis, E-mail: nhamini@stanford.edu [Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States); Gough, John, E-mail: jug@aber.ac.uk [Institute of Mathematics and Physics, Aberystwyth University, SY23 3BZ Wales (United Kingdom); Ugrinovskii, Valery, E-mail: v.ugrinovskii@gmail.com [School of Engineering and Information Technology, University of New South Wales at ADFA, Canberra, ACT 2600 (Australia); James, Matthew R., E-mail: matthew.james@anu.edu.au [ARC Centre for Quantum Computation and Communication Technology, Research School of Engineering, Australian National University, Canberra, ACT 0200 (Australia)

2014-06-15

166

Heisenberg picture approach to the stability of quantum Markov systems  

Science.gov (United States)

Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks.

Pan, Yu; Amini, Hadis; Miao, Zibo; Gough, John; Ugrinovskii, Valery; James, Matthew R.

2014-06-01

167

Tunneling with dissipation in open quantum systems  

International Nuclear Information System (INIS)

Based on the general form of the master equation for open quantum systems the tunneling is considered. Using the path integral technique a simple closed form expression for the tunneling rate through a parabolic barrier is obtained. The tunneling in the open quantum systems strongly depends on the coupling with environment. We found the cases when the dissipation prohibits tunneling through the barrier but decreases the crossing of the barrier for the energies above the barrier. As a particular application, the case of decay from the metastable state is considered

168

Josephson tunneling in bilayer quantum Hall system  

International Nuclear Information System (INIS)

A Bose–Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (?e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ?=1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless. Our results explain recent experiments due to [L. Tiemann, Y. Yoon, W. Dietsche, K. von Klitzing, W. Wegscheider, Phys. Rev. B 80 (2009) 165120] and due to [Y. Yoon, L. Tiemann, S. Schmult, W. Dietsche, K. von Klitzing, Phys. Rev. Lett. 104 (2010) 116802]. We predict also how the critical current changes as the sample is tilted in the magnetic field. -- Highlights: ? Composite bosons undergo Bose–Einstein condensation to form the bilayer quantum Hall state. ? A composite boson is a single electron bound to a flux quantum and carries one unit charge. ? Quantum coherence develops due to the condensation. ? Quantum coherence drives the supercurrent in each layer and the tunneling current. ? There exists the critical input current so that the tunneling current is coherent and dissipationless.

169

Relativistic Quantum Metrology in Open System Dynamics  

Science.gov (United States)

Quantum metrology studies the ultimate limit of precision in estimating a physical quantity if quantum strategies are exploited. Here we investigate the evolution of a two-level atom as a detector which interacts with a massless scalar field using the master equation approach for open quantum system. We employ local quantum estimation theory to estimate the Unruh temperature when probed by a uniformly accelerated detector in the Minkowski vacuum. In particular, we evaluate the Fisher information (FI) for population measurement, maximize its value over all possible detector preparations and evolution times, and compare its behavior with that of the quantum Fisher information (QFI). We find that the optimal precision of estimation is achieved when the detector evolves for a long enough time. Furthermore, we find that in this case the FI for population measurement is independent of initial preparations of the detector and is exactly equal to the QFI, which means that population measurement is optimal. This result demonstrates that the achievement of the ultimate bound of precision imposed by quantum mechanics is possible. Finally, we note that the same configuration is also available to the maximum of the QFI itself.

Tian, Zehua; Wang, Jieci; Fan, Heng; Jing, Jiliang

2015-01-01

170

Stripes in Quantum Hall Double Layer Systems  

OpenAIRE

We present results of a study of double layer quantum Hall systems in which each layer has a high-index Landau level that is half-filled. Hartree-Fock calculations indicate that, above a critical layer separation, the system becomes unstable to the formation of a unidirectional coherent charge density wave (UCCDW), which is related to stripe states in single layer systems. The UCCDW state supports a quantized Hall effect when there is tunneling between layers, and is {\\it al...

Brey, L.; Fertig, H. A.

2000-01-01

171

Quantum information and continuous variable systems  

International Nuclear Information System (INIS)

This thesis treats several questions concerning quantum information theory of infinite dimensional continuous variable (CV) systems. We investigate the separability properties of Gaussian states of such systems. Both the separability and the distillability problem for bipartite Gaussian states are solved by deriving operational criteria for these properties. We consider multipartite Gaussian states and obtain a necessary and sufficient condition that allows the complete classification of three-mode tripartite states according to their separability properties. Moreover we study entanglement distillation protocols. We show that the standard protocols for qubits are robust against imperfect implementation of the required quantum operations. For bipartite Gaussian states we find a universal scheme to distill all distillable states and propose a concrete quantum optical realization. (author)

172

Stochastic resonance in a fundamental quantum system  

International Nuclear Information System (INIS)

We provide a detailed description of the response of an experimentally accessible, open, driven quantum system in its stationary state to a weak periodic signal. The system, a single mode of the quantized radiation field in coherent interaction with a sequence of two-level atoms and coupled to an environment of temperature T, is shown to exhibit stochastic resonance on output, under changes of T. Furthermore, at vanishing temperature, the transition rates between the metastable states of the radiation field remain finite and are set by the quantum noise level at T = O K. Consequently, signal enhancement and synchronization can be achieved even in this very quantum limit, for a properly tuned signal frequency. (author)

173

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.

174

Connectivity analysis of controlled quantum systems  

International Nuclear Information System (INIS)

A connectivity analysis of controlled quantum systems assesses the feasibility of a field existing that can transfer at least some amplitude between any specified pair of states. Although Hamiltonians with special structure or symmetry may not produce full connectivity, it is argued and demonstrated that virtually any Hamiltonian is expected to be connected. The connectivity of any particular system is generally revealed in the quantum evolution over a single or at most a few time steps. A connectivity analysis is inexpensive to perform and it can also identify statistically significant intermediate states linking a specified initial and final state. These points are illustrated with several simple systems. The likelihood of an arbitrary system being connected implies that at least some product yield can be expected in the laboratory for virtually all systems subjected to a suitable control

175

Environment-assisted quantum transport in ordered systems  

OpenAIRE

Noise-assisted transport in quantum systems occurs when quantum time-evolution and decoherence conspire to produce a transport efficiency that is higher than what would be seen in either the purely quantum or purely classical cases. In disordered systems, it has been understood as the suppression of coherent quantum localisation through noise, which brings detuned quantum levels into resonance and thus facilitates transport. We report several new mechanisms of environment-as...

Kassal, Ivan; Aspuru-guzik, Alan

2012-01-01

176

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

177

Semiclassical analysis of quantum systems with constraints  

Science.gov (United States)

This dissertation addresses the problem of constructing true degrees of freedom in quantum mechanical systems with constraints. The method developed relies on assuming the behavior of the system of interest is "nearly classical", or semiclassical, in a precise quantitative sense. The approximation is formulated as a perturbative hierarchy of the expectation values of quantum observables and their non-linear combinations, such as spreads and correlations. We formulate the constraint conditions and additional quantum gauge transformations that arise directly on the aforementioned quantities. We specialize this framework to several situations of particular interest. The first situation considered is the case of a constraint that commutes with all quantum observables, which is appropriate for quantization of a Lie algebra with a single Casimir polynomial. Through explicit order-by order counting argue that the true degrees of freedom are captured correctly at each order of the approximation. The rest of the models considered are motivated by the canonical approach to quantizing general relativity. The homogeneous sector of general relativity splits into classes of models, according to topology, which are described by a finite number of degrees of freedom and can therefore be quantized as quantum mechanical systems, making our construction directly applicable. In the Hamiltonian formulation the dynamics of these systems is governed by the Hamiltonian constraint, which, in the quantum theory, gives rise to several conceptual and technical issues collectively known as the Problem of Time. One of the aspects of this problem that does not possess a general solution is the dynamical interpretation of the theory. We use our construction, truncated at the leading order in quantum corrections, together with the intuition gained from dealing with constrained systems in classical mechanics, to define local notion of dynamics relative to a chosen configuration clock variable. We consider a class of models, where the chosen clock in not globally valid, eventually leading to singular dynamics. Within these models we construct an explicit transformation between dynamical evolution relative to two distinct clocks, thus providing a consistent local dynamical interpretation of the true degrees of freedom of the quantum theory.

Tsobanjan, Artur

178

Optical investigations of multicomponent quantum Hall systems  

Science.gov (United States)

Absorption, photoluminescence, and photoluminescence excitation spectroscopy have been used to investigate the nature of the ground-state and fundamental excitations of the small odd-integer quantum Hall states in single-layer and double-layer two-dimensional electron systems residing in GaAs quantum wells. In the single-layer system at filling factor /nu =1, electron-electron interactions are shown to stabilize the formation of multiparticle spin excitations called skyrmions. The presence of skyrmions is manifest in the rapid loss of spin polarization for small excursions from /nu =1 as measured by absorption spectroscopy. Further experimental evidence for the highly correlated nature of the /nu =1 state in the single-layer system is given by a study of temperature dependence of the spin- polarization exactly at /nu =1. The spin-polarization as a function of temperature exactly at /nu =1 is found to evolve in accord with the thermodynamics of a continuum quantum ferromagnetic model of the /nu =1 state. Photoluminescence studies of /nu =3 and /nu =5 in the single-layer system are shown to be sensitive to the presence of an Anderson-Fano-like resonance in the final state of the two-dimensional electron system. The many- body origin of this effect is evident in the complicated filling factor and temperature dependence of the optical anomalies. Finally we present the first absorption studies of the double-layer two-dimensional electron system in the quantum Hall regime. Around total filling /nu =1, absorption spectra have revealed the complex interplay between single-particle gaps and many-body effects for stabilizing this quantum Hall state. Our measurements are shown to provide the first direct experimental evidence for a not fully pseudospin-polarized ground-state at /nu =1.

Manfra, Michael J.

1999-02-01

179

Quantum coherence of biophotons and living systems.  

Science.gov (United States)

Coherence is a property of the description of the system in the classical framework in which the subunits of a system act in a cooperative manner. Coherence becomes classical if the agent causing cooperation is discernible otherwise it is quantum coherence. Both stimulated and spontaneous biophoton signals show properties that can be attributed to the cooperative actions of many photon-emitting units. But the agents responsible for the cooperative actions of units have not been discovered so far. The stimulated signal decays with non-exponential character. It is system and situation specific and sensitive to many physiological and environmental factors. Its measurable holistic parameters are strength, shape, relative strengths of spectral components, and excitation curve. The spontaneous signal is non-decaying with the probabilities of detecting various number of photons to be neither normal nor Poisson. The detected probabilities in a signal of Parmelia tinctorum match with probabilities expected in a squeezed state of photons. It is speculated that an in vivo nucleic acid molecule is an assembly of intermittent quantum patches that emit biophoton in quantum transitions. The distributions of quantum patches and their lifetimes determine the holistic features of biophoton signals, so that the coherence of biophotons is merely a manifestation of the coherence of living systems. PMID:15244274

Bajpai, R P

2003-05-01

180

The quantum effects in quadratically damped systems  

International Nuclear Information System (INIS)

A dynamical system with a damping that is quadratic in velocity is converted into the Hamiltonian format using a nonlinear transformation. Its quantum mechanical behaviour is then analysed by invoking the Gaussian effective potential technique. The method is worked out explicitly for the Duffing oscillator potential. ((orig.))

181

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

182

Quantum field theory and multiparticle systems  

International Nuclear Information System (INIS)

The use of quantum field theory methods for the investigation of the physical characteristics of the MANY-BODY SYSTEMS is discussed. Mainly discussed is the method of second quantization and the method of the Green functions. Briefly discussed is the method of calculating the Green functions at finite temperatures. (Z.J.)

183

Quantum electrodynamics of weakly bound systems  

International Nuclear Information System (INIS)

An overview of quantum electrodynamic effects in two-body systems is presented. Recent advances in the calculation of the hydrogen Lamb shift, muonium hyperfine structure, and positronium energy levels are described in detail. The comparison of experimental results to current theoretical predictions gives agreement in most cases. However, a few significant discrepancies remain, which indicates the necessity for further refined calculations and measurements

184

Quantum distribution function of nonequilibrium system  

International Nuclear Information System (INIS)

A path integral representation is derived for the Wigner distribution function of a nonequilibrium system coupled with heat bath. Under appropriate conditions, the Wigner distribution function approaches an equilibrium distribution, which manifests shifting and broadening of spectral lines due to the interaction with heat bath. It is shown that the equilibrium distribution becomes the quantum canonical distribution in the vanishing coupling constant limit. (author)

185

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.

186

Quantum dynamics of biological systems and dust plasma nanoparticles  

Science.gov (United States)

A quantum solution of the Fisher-Kolmogorov-Petrovskii-Piskunov equation with convection and linear diffusion is obtained which can provide the basis for the quantum biology and quantum microphysics equation. On this basis, quantum emission of biological systems, separate microorganisms (cells or bacteria), and dust plasma particles is investigated.

Lasukov, V. V.; Lasukova, T. V.; Lasukova, O. V.

2012-12-01

187

Open quantum systems approach to atomtronics  

International Nuclear Information System (INIS)

We derive a quantum master equation to treat quantum systems interacting with multiple reservoirs. The formalism is used to investigate the atomic transport of bosons across a variety of lattice configurations. We demonstrate how the behavior of an electronic diode, a field-effect transistor, and a bipolar junction transistor can be realized with neutral, ultracold atoms trapped in optical lattices. An analysis of the current fluctuations is provided for the case of the atomtronic diode. Finally, we show that it is possible to demonstrate and logic gate behavior in an optical lattice.

188

Open quantum systems approach to atomtronics  

CERN Document Server

We derive a quantum master equation to treat quantum systems interacting with multiple reservoirs. The formalism is used to investigate atomic transport across a variety of lattice configurations. We demonstrate how the behavior of an electronic diode, a field-effect transistor, and a bipolar junction transistor can be realized with neutral, ultracold atoms trapped in optical lattices. An analysis of the current fluctuations is provided for the case of the atomtronic diode. Finally, we show that it is possible to demonstrate AND logic gate behavior in an optical lattice.

Pepino, R A; Meiser, D; Anderson, D Z; Holland, M J

2010-01-01

189

Exotic phases in multicomponent quantum Hall systems  

Science.gov (United States)

This talk will review novel phases that can be stabilized in multicomponent quantum Hall systems at integer filling factors in the presence of Coulomb interaction. Hartree-Fock calculations for the phase diagram of bilayer quantum Hall systems at ?=4n+1 in a tilted magnetic field will be presented. An effective low energy theory for the stripe phases which may be present in such systems will be derived and analyzed. The possibility of stripe formation in wide well systems in a tilted magnetic field will be discussed and it will be suggested that the resistance anisotropy, observed recently by W. Pan et.al. (cond-mat/0101416), may be due to the existence of a skyrmion stripe phase.

Demler, Eugene

2002-03-01

190

Dissipative effects on quantum glassy systems  

International Nuclear Information System (INIS)

We discuss the behavior of a quantum glassy system coupled to a bath of quantum oscillators. We show that the system localizes in the absence of interactions when coupled to a subOhmic bath. When interactions are switched on localization disappears and the system undergoes a phase transition towards a glassy phase. We show that the position of the critical line separating the disordered and the ordered phases strongly depends on the coupling to the bath. For a given type of bath, the ordered glassy phase is favored by a stronger coupling. Ohmic, subOhmic and superOhmic baths lead to different transition lines. We draw our conclusions from the analysis of the partition function using the replicated imaginary-time formalism and from the study of the real-time dynamics of the coupled system using the Schwinger-Keldysh closed time-path formalism. (author)

191

Open systems dynamics for propagating quantum fields  

Science.gov (United States)

In this dissertation, I explore interactions between matter and propagating light. The electromagnetic field is modeled as a Markovian reservoir of quantum harmonic oscillators successively streaming past a quantum system. Each weak and fleeting interaction entangles the light and the system, and the light continues its course. In the context of quantum tomography or metrology one attempts, using measure- ments of the light, to extract information about the quantum state of the system. An inevitable consequence of these measurements is a disturbance of the system's quantum state. These ideas focus on the system and regard the light as ancillary. It serves its purpose as a probe or as a mechanism to generate interesting dynamics or system states but is eventually traced out, leaving the reduced quantum state of the system as the primary mathematical subject. What, then, when the state of light itself harbors intrinsic self-entanglement? One such set of states, those where a traveling wave packet is prepared with a defi- nite number of photons, is a focal point of this dissertation. These N-photon states are ideal candidates as couriers in quantum information processing device. In con- trast to quasi-classical states, such as coherent or thermal fields, N-photon states possess temporal mode entanglement, and local interactions in time have nonlocal consequences. The reduced state of a system probed by an N-photon state evolves in a non-Markovian way, and to describe its dynamics one is obliged to keep track of the field's evolution. I present a method to do this for an arbitrary quantum system using a set of coupled master equations. Many models set aside spatial degrees of freedom as an unnecessary complicating factor. By doing so the precision of predictions is limited. Consider a ensemble of cold, trapped atomic spins dispersively probed by a paraxial laser beam. Atom-light coupling across the ensemble is spatially inhomogeneous as is the radiation pattern of scattered light. To achieve strong entanglement between the atoms and photons, one must match the spatial mode of the collective radiation from the ensemble to the mode of the laser beam while minimizing the effects of decoherence due to optical pumping. In this dissertation, I present a three-dimensional model for a quantum light-matter interface for propagating quantum fields specifically equipped to address these issues. The reduced collective atomic state is described by a stochastic master equation that includes coherent collective scattering into paraxial modes, decoher- ence by local inhomogeneous diffuse scattering, and measurement backaction due to continuous observation of the light. As the light is measured, backaction transmutes atom-light entanglement into entanglement between the atoms of the ensemble. This formalism is used to study the impact of spatial modes in the squeezing of a collec- tive atomic spin wave via continuous measurement. The largest squeezing occurs precisely in parameter regimes with significant spatial inhomogeneities, far from the limit in which the interface is well approximated by a one-dimensional, homogeneous model.

Baragiola, Ben Quinn

192

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

193

Perfect eavesdropping on a quantum cryptography system  

CERN Document Server

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

194

Ion-cavity system for quantum networks  

International Nuclear Information System (INIS)

Full text: A single atom interacting with a single mode of a cavity allows us to probe the quantum interaction between light and matter. In the context of quantum networks, such a system can provide an interface between stationary and flying qubits, making it possible for single photons to transport quantum information between the network nodes. We study a single 40Ca+ ion trapped inside a high-finesse optical resonator. First, we demonstrate and characterize a single-photon source, in which a vacuum-stimulated Raman process transfers atomic population between two Zeeman states of the ion, creating a single photon in the cavity. We evaluate the photon statistics by measuring the second-order correlation function. Moreover, we obtain the photon temporal profile and investigate the dynamics of the process. Secondly, we perform Raman spectroscopy using the cavity. Residual motion of the ion introduces motional sidebands in the Raman spectrum and thus offers prospects for cavity-assisted cooling. (author)

195

Chiral quantum mechanics (CQM) for antihydrogen systems  

OpenAIRE

A first deception of QM on antiH already appears in one-center integrals for two-center systems (G. Van Hooydonk, physics/0511115). In reality, full QM is a theory for chiral systems but the QM establishment was wrong footed with a permutation of reference frames. With chiral quantum mechanics (CQM), the theoretical ban on natural antiH must be lifted as soon as possible.

Hooydonk, G.

2005-01-01

196

Quantum cosmology theory of general system, 3  

CERN Document Server

The concepts of the perfect system and degeneracy are introduced. A special symmetry is found which is related to the entropy invariant. The inversion relation of system is obtained which is used to give the oppsite direction of time to classical sencond law of thermodanymics. The nature of time is discussed together with causality relation. A new understanding of quantum mechanics is put forward which describes a new picture of the world.

Zhen, W

1996-01-01

197

Planar lightwave circuits for quantum cryptographic systems  

CERN Document Server

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 cryptographic system.

Nambu, Y; Nakamura, K; Nambu, Yoshihiro; Hatanaka, Takaaki; Nakamura, Kazuo

2003-01-01

198

Thermoelectric phenomena in disordered open quantum systems  

OpenAIRE

Using a stochastic quantum approach, we study thermoelectric transport phenomena at low temperatures in disordered electrical systems connected to external baths. We discuss three different models of one-dimensional disordered electrons, namely the Anderson model of random on-site energies, the random-dimer model and the random-hopping model - also relevant for random-spin models. We find that although the asymptotic behavior of transport in open systems is closely related t...

Roy, Dibyendu; Di Ventra, Massimiliano

2009-01-01

199

Control landscapes for open system quantum operations  

International Nuclear Information System (INIS)

The reliable realization of control operations is a key component of quantum information applications. In practice, meeting this goal is very demanding for open quantum systems. This paper investigates the landscape defined as the fidelity J between the desired and achieved quantum operations with an open system. The goal is to maximize J as a functional of the control variables. We specify the complete set of critical points of the landscape function in the so-called kinematic picture. An associated Hessian analysis of the landscape reveals that, upon the satisfaction of a particular controllability criterion, the critical topology is dependent on the particular environment, but no false traps (i.e. suboptimal solutions) exist. Thus, a gradient-type search algorithm should not be hindered in searching for the ultimate optimal solution with such controllable systems. Moreover, the maximal fidelity is proven to coincide with Uhlmann’s fidelity between the environmental initial states associated with the achieved and desired quantum operations, which provides a generalization of Uhlmann’s theorem in terms of Kraus maps. (paper)

200

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)

201

EMERGENCE PARAMETER OF CLASSICAL AND QUANTUM STATISTICAL SYSTEMS ??????????? ?????????????? ???????????? ? ????????? ?????????????? ??????  

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

202

Classical representation of quantum systems at equilibrium  

Science.gov (United States)

A quantum system at equilibrium is represented by an effective classical system, chosen to reproduce thermodynamic and structural properties. The motivation is to allow application of classical strong coupling theories and classical simulations like molecular dynamics and Monte Carlo to quantum systems at strong coupling. The correspondence is made at the level of the grand canonical ensembles for the two systems. The effective classical system is defined in terms of an effective temperature, local chemical potential, and pair potential. These are determined formally by requiring the equivalence of the grand potentials and their functional derivatives of the quantum and representative classical systems. The mapping is inverted using the classical density functional theory to solve for these three parameters. Practical forms of these formal solutions are obtained using the classical liquid state theories like hypernetted chain approximation (HNC). The mapping is applied to the ideal Fermi gas is demonstrated and the details of the thermodynamics of the effective system is derived explicitly. As the next application we consider the uniform electron gas and an explicit form for the effective interaction potential is obtained in the weak coupling limit. The pair correlation functions are calculated using the HNC equations and compared with path integral Monte Carlo data and other theoretical models like Perrot Dharma-wardana. Excellent agreement is obtained over a wide range of temperatures and densities. The last application is to the shell structure of harmonically bound charges. We show that in the mean field limit, the quantum effects of degeneracy and diffraction produce shells at very low temperatures.

Dutta, Sandipan

203

Equilibration of quasi-isolated quantum systems  

International Nuclear Information System (INIS)

The evolution of a quasi-isolated finite quantum system from a nonequilibrium initial state is considered. The condition of quasi-isolation allows for the description of the system dynamics on the general basis, without specifying the system details and for arbitrary initial conditions. The influence of surrounding results in (at least partial) equilibration and decoherence. The resulting equilibrium state bears information on initial conditions and is characterized by a representative ensemble. It is shown that the system average information with time does not increase. The partial equilibration and non-increase of average information explain the irreversibility of time.

204

Mechanical systems in the quantum regime  

CERN Document Server

Mechanical systems are ideal candidates for studying quantumbehavior of macroscopic objects. To this end, a mechanical resonator has to be cooled to its ground state and its position has to be measured with great accuracy. Currently, various routes to reach these goals are being explored. In this review, we discuss different techniques for sensitive position detection and we give an overview of the cooling techniques that are being employed. These include sideband cooling and active feedback cooling. The basic concepts that are importantwhen measuring on mechanical systems with high accuracy and/or at very low temperatures, such as thermal and quantum noise, linear response theory and backaction, are explained. From this, the quantum limit on linear position detection is obtained and the sensitivities that have been achieved in recent experiments are compared to this limit. The mechanical resonators that are used in the experiments range from metersized gravitational wave detectors to nanomechanical systems t...

Poot, Menno

2011-01-01

205

General System theory, Like-Quantum Semantics and Fuzzy Sets  

OpenAIRE

It is outlined the possibility to extend the quantum formalism in relation to the requirements of the general systems theory. It can be done by using a quantum semantics arising from the deep logical structure of quantum theory. It is so possible taking into account the logical openness relationship between observer and system. We are going to show how considering the truth-values of quantum propositions within the context of the fuzzy sets is here more useful for systemics ...

Licata, Ignazio

2007-01-01

206

Quantum decoherence in the theory of open systems  

OpenAIRE

In the framework of the Lindblad theory for open quantum systems, we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. It is found that the system manifests a quantum decoherence which is more and more significant in time. We calculate also the decoherence time scale and analyze the transition from quantum to classical behaviour of the considered system.

Isar, A.

2007-01-01

207

Temporal behavior of quantum mechanical systems  

CERN Document Server

The temporal behavior of quantum mechanical systems is reviewed. We study the so-called quantum Zeno effect, that arises from the quadratic short-time behavior, and the analytic properties of the ``survival" amplitude. It is shown that the exponential behavior is due to the presence of a simple pole in the second Riemannian sheet, while the contribution of the branch point yields a power behavior for the amplitude. The exponential decay form is cancelled at short times and dominated at very long times by the branch-point contributions, which give a Gaussian behavior for the former and a power behavior for the latter. In order to realize the exponential law in quantum theory, it is essential to take into account a certain kind of macroscopic nature of the total system. Some attempts at extracting the exponential decay law from quantum theory, aiming at the master equation, are briefly reviewed, including van Hove's pioneering work and his well-known ``\\lambda^2T" limit. We clarify these general arguments by in...

Nakazato, H; Pascazio, S; Nakazato, Hiromichi; Namiki, Mikio; Pascazio, Saverio

1995-01-01

208

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

209

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.

210

Separability of Tripartite Quantum Systems  

CERN Document Server

We investigate the separability of arbitrary dimensional tripartite sys- tems. By introducing a new operator related to transformations on the subsystems a necessary condition for the separability of tripartite systems is presented.

Li, Ming; Wang, Zhi-Xi

2008-01-01

211

Experimental simulation of quantum tunneling in small systems  

OpenAIRE

It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a b...

Feng, Guan-ru; Lu, Yao; Hao, Liang; Zhang, Fei-hao; Long, Gui-lu

2012-01-01

212

Quantum information processing based on cavity QED with mesoscopic systems  

OpenAIRE

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

213

Topological Excitations in Double-Layer Quantum Hall systems  

OpenAIRE

Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel manybody quantum Hall effect due to the strong interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness $\\rho_s$ due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topol...

Moon, Kyungsun

1996-01-01

214

Topological Excitations in Double-Layer Quantum Hall systems  

CERN Document Server

Double layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel manybody quantum Hall effect due to interlayer coherence. When layer separation becomes large and close to the critical one, quantum fluctuations destroy interlayer coherence and accordingly quantum Hall effect collapses. We calculate the renormalized isospin stiffness $\\rho_s^R$ due to quantum fluctuations within Hartree-Fock-RPA formalism. The activation energy of the topological excitations thus obtained demonstrates a nice qualitative agreement with recent experiment.

Moon, K

1997-01-01

215

Geometric phase of a quantum dot system in nonunitary evolution  

OpenAIRE

Practical implementations of quantum computing are always done in the presence of decoherence. Geometric phase is useful in the context of quantum computing as a tool to achieve fault tolerance. Recent experimental progresses on coherent control of single electron have suggested that electron in quantum dot systems is a promising candidate of qubit in future quantum information processing devices. In this paper, by considering a feasible quantum dot model, we calculate the g...

Yin, Sun; Tong, D. M.

2009-01-01

216

Theory of classical and quantum frustration in quantum many-body systems  

CERN Document Server

We present a general scheme for the study of frustration in quantum systems. After introducing a universal measure of frustration for arbitrary quantum systems, we derive for it an exact inequality in terms of a class of entanglement monotones. We then state sufficient conditions for the ground states of quantum spin systems to saturate the inequality 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 and establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration.

Giampaolo, S M; Monras, A; Illuminati, F

2011-01-01

217

Electron Dynamics in Finite Quantum Systems  

Science.gov (United States)

The multiconfiguration time-dependent Hartree-Fock (MCTDHF) and multiconfiguration time-dependent Hartree (MCTDH) methods are employed to investigate nonperturbative multielectron dynamics in finite quantum systems. MCTDHF is a powerful tool that allows for the investigation of multielectron dynamics in strongly perturbed quantum systems. We have developed an MCTDHF code that is capable of treating problems involving three dimensional (3D) atoms and molecules exposed to strong laser fields. This code will allow for the theoretical treatment of multielectron phenomena in attosecond science that were previously inaccessible. These problems include complex ionization processes in pump-probe experiments on noble gas atoms, the nonlinear effects that have been observed in Ne atoms in the presence of an x-ray free-electron laser (XFEL) and the molecular rearrangement of cations after ionization. An implementation of MCTDH that is optimized for two electrons, each moving in two dimensions (2D), is also presented. This implementation of MCTDH allows for the efficient treatment of 2D spin-free systems involving two electrons; however, it does not scale well to 3D or to systems containing more that two electrons. Both MCTDHF and MCTDH were used to treat 2D problems in nanophysics and attosecond science. MCTDHF is used to investigate plasmon dynamics and the quantum breathing mode for several electrons in finite lateral quantum dots. MCTDHF is also used to study the effects of manipulating the potential of a double lateral quantum dot containing two electrons; applications to quantum computing are discussed. MCTDH is used to examine a diatomic model molecular system exposed to a strong laser field; nonsequential double ionization and high harmonic generation are studied and new processes identified and explained. An implementation of MCTDHF is developed for nonuniform tensor product grids; this will allow for the full 3D implementation of MCTDHF and will provide a means to investigate a wide variety of problems that cannot be currently treated by any other method. Finally, the time it takes for an electron to tunnel from a bound state is investigated; a definition of the tunnel time is established and the Keldysh time is connected to the wavefunction dynamics.

McDonald, Christopher R.

218

Orbits of hybrid systems as qualitative indicators of quantum dynamics  

International Nuclear Information System (INIS)

Hamiltonian theory of hybrid quantum–classical systems is used to study dynamics of the classical subsystem coupled to different types of quantum systems. It is shown that the qualitative properties of orbits of the classical subsystem clearly indicate if the quantum subsystem does or does not have additional conserved observables.

219

Non-Equilibrium Quantum Entanglement in Biological Systems  

Science.gov (United States)

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.

Li, Hong-Rong; Zhang, Pei; Gao, Hong; Bi, Wen-Ting; Alamri, M. D.; Li, Fu-Li

2012-04-01

220

Open quantum systems and random matrix theory  

International Nuclear Information System (INIS)

A simple model for open quantum systems is analyzed with RMT. 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 level spacing, width distribution and ?3(L) statistic are examined as a function of the strength of this coupling. The usual super-radiant state is observed, and it is seen that as it is formed, the level spacing and ?3(L) statistic exhibit the signatures of missed levels

221

Open quantum systems and Random Matrix Theory  

OpenAIRE

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 ...

Mulhall, Declan

2014-01-01

222

Open quantum systems and random matrix theory  

Science.gov (United States)

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 the effect on the level statistics of opening the system is seen. In particular the ?3(L ) statistic, the width distribution and the level spacing are examined as a function of the strength of this coupling. The emergence of a super-radiant transition is observed. The level spacing and ?3(L ) statistics exhibit the signatures of missed levels or intruder levels as the super-radiant state is formed.

Mulhall, Declan

2015-01-01

223

Quantum integrable systems. Quantitative methods in biology  

OpenAIRE

Quantum integrable systems have very strong mathematical properties that allow an exact description of their energetic spectrum. From the Bethe equations, I formulate the Baxter "T-Q" relation, that is the starting point of two complementary approaches based on nonlinear integral equations. The first one is known as thermodynamic Bethe ansatz, the second one as Kl\\"umper-Batchelor-Pearce-Destri- de Vega. I show the steps toward the derivation of the equations for some of the...

Feverati, Giovanni

2011-01-01

224

Fractionalization in spontaneous integer quantum Hall systems  

CERN Document Server

Using Kondo lattice model as an example, we show that systems that exhibit spontaneous integer quantum Hall effect can have fractionalized electronic excitations with anyonic exchange statistics. The fractionalized excitations are bound to the cores of topologically stable vortices in the magnetic order parameter. For highly symmetric states, the vortex charge is half-odd integer, although other, generally irrational, charges are possible for less symmetric states.

Muniz, Rodrigo A; Martin, Ivar

2011-01-01

225

Noise cancellation effect in quantum systems  

OpenAIRE

We consider the time evolution of simple quantum systems under the influence of random fluctuations of the control parameters. We show that when the parameters fluctuate sufficiently fast, there is a cancellation effect of the noise. We propose that such an effect could be experimentally observed by performing a simple experiment with trapped ions. As a byproduct of our analysis, we provide an explanation of the robustness against random perturbations of adiabatic population...

Solinas, Paolo; Zanghi, Nino

2004-01-01

226

Quantum chromodynamic evolution of multiquark systems  

International Nuclear Information System (INIS)

We present a new technique which extends the quantum chromodynamic evolution formalism in order to predict the short distance behavior of multiquark wavefunctions. In particular, predictions are given for the deuteron reduced form factor in the high momentum transfer region, and rigorous constraints on the short distance effective force between two baryons are predicted. These new techniques can be generalized in order to analyze the short distance behavior of multibaryon systems

227

Quantum-size colloid metal systems  

International Nuclear Information System (INIS)

Methods for the preparation of nano-sized metal particles are considered. Theoretical approaches to the analysis of electron behaviour in systems with quantum-size effects are outlined. The results of experimental investigations of the thermodynamic and optical characteristics of small metal particles and thin films are presented. The data of experiments on the electron dynamics in single nanoparticles and nanoparticle ensembles are described. The self-assembly of nanoparticles to form supported ordered structures is considered. The bibliography includes 343 references.

228

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

229

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.

230

Coherent and collective quantum optical effects in mesoscopic systems  

International Nuclear Information System (INIS)

A review of coherent and collective quantum optical effects like superradiance and coherent population trapping in mesoscopic systems is presented. Various new physical realizations of these phenomena are discussed, with a focus on their role for electronic transport and quantum dissipation in coupled nano-scale systems like quantum dots. A number of theoretical tools such as Master equations, polaron transformations, correlation functions, or level statistics are used to describe recent work on dissipative charge qubits (double quantum dots), the Dicke effect, phonon cavities, single oscillators, dark states and adiabatic control in quantum transport, and large spin-boson models. The review attempts to establish connections between concepts from Mesoscopics (quantum transport, coherent scattering, quantum chaos), Quantum Optics (such as superradiance, dark states, boson cavities), and (in its last part) Quantum Information Theory

231

On a correspondence between classical and quantum particle systems  

CERN Document Server

An exact correspondence is established between a $N$-body classical interacting system and a $N-1$-body quantum system with respect to the partition function. The resulting quantum-potential is a $N-1$-body one. Inversely the Kelbg potential is reproduced which describes quantum systems at a quasi-classical level. The found correspondence between classical and quantum systems allows also to approximate dense classical many body systems by lower order quantum perturbation theory replacing Planck's constant properly by temperature and density dependent expressions. As an example the dynamical behaviour of an one - component plasma is well reproduced concerning the formation of correlation energy after a disturbance utilising solely the analytical quantum - Born result for dense degenerated Fermi systems. As a practical guide the quantum - Bruckner parameter $r_s$ has been replaced by the classical plasma parameter $\\Gamma$ as $r_s\\approx0.3 \\Gamma^{3/2}$

Morawetz, K

2000-01-01

232

Quantum Dissipative Systems and Feedback Control Design by Interconnection  

OpenAIRE

The purpose of this paper is to extend J.C. Willems' theory of dissipative systems to the quantum domain. This general theory, which combines perspectives from the quantum physics and control engineering communities, provides useful methods for analysis and design of dissipative quantum systems. We describe the interaction of the plant and a class of exosystems in general quantum feedback network terms. Our results include an infinitesimal characterization of the dissipation...

James, Matthew R.; Gough, John

2007-01-01

233

Phase transitions in quantum Hall multiple layer systems  

International Nuclear Information System (INIS)

Polarized photoluminescence from multiple well electron systems was studied in the regime of the integer quantum Hall effect. Two quantum Hall ferromagnetic ground states assigned to the uncorrelated miniband quantum Hall state and to the spontaneous interwell phase coherent dimer quantum Hall state were observed. The photoluminescence associated with these states exhibits features caused by finite-size skyrmions. The depolarization of the ferromagnetic ground state was observed in bilayer system

234

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

CERN Document Server

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

235

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

236

Formulation and Application of Quantum Monte Carlo Method to Fractional Quantum Hall Systems  

CERN Document Server

Quantum Monte Carlo method is applied to fractional quantum Hall systems. The use of the linear programming method enables us to avoid the negative-sign problem in the Quantum Monte Carlo calculations. The formulation of this method and the technique for avoiding the sign problem are described. Some numerical results on static physical quantities are also reported.

Suzuki, S; Suzuki, Sei; Nakajima, Tatsuya

2003-01-01

237

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

238

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; SØrensen, Anders SØndberg

2012-01-01

239

Twisted CFT and bilayer Quantum Hall systems  

CERN Document Server

We identify the impurity interactions of the recently proposed CFT description of a bilayer Quantum Hall system at filling nu =m/(pm+2) in Mod. Phys. Lett. A 15 (2000) 1679. Such a CFT is obtained by m-reduction on the one layer system, with a resulting pairing symmetry and presence of quasi-holes. For the m=2 case boundary terms are shown to describe an impurity interaction which allows for a localized tunnel of the Kondo problem type. The presence of an anomalous fixed point is evidenced at finite coupling which is unstable with respect to unbalance and flows to a vacuum state with no quasi-holes.

Cristofano, G; Naddeo, A

2003-01-01

240

Dynamical Localization in Disordered Quantum Spin Systems  

CERN Document Server

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

241

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

242

Teaching the environment to control quantum systems  

International Nuclear Information System (INIS)

A nonequilibrium, generally time-dependent, environment whose form is deduced by optimal learning control is shown to provide a means for incoherent manipulation of quantum systems. Incoherent control by the environment (ICE) can serve to steer a system from an initial state to a target state, either mixed or in some cases pure, by exploiting dissipative dynamics. Implementing ICE with either incoherent radiation or a gas as the control is explicitly considered, and the environmental control is characterized by its distribution function. Simulated learning control experiments are performed with simple illustrations to find the shape of the optimal nonequilibrium distribution function that best affects the posed dynamical objectives

243

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

244

EDITORIAL: CAMOP: Quantum Non-Stationary Systems CAMOP: Quantum Non-Stationary Systems  

Science.gov (United States)

Although time-dependent quantum systems have been studied since the very beginning of quantum mechanics, they continue to attract the attention of many researchers, and almost every decade new important discoveries or new fields of application are made. Among the impressive results or by-products of these studies, one should note the discovery of the path integral method in the 1940s, coherent and squeezed states in the 1960-70s, quantum tunneling in Josephson contacts and SQUIDs in the 1960s, the theory of time-dependent quantum invariants in the 1960-70s, different forms of quantum master equations in the 1960-70s, the Zeno effect in the 1970s, the concept of geometric phase in the 1980s, decoherence of macroscopic superpositions in the 1980s, quantum non-demolition measurements in the 1980s, dynamics of particles in quantum traps and cavity QED in the 1980-90s, and time-dependent processes in mesoscopic quantum devices in the 1990s. All these topics continue to be the subject of many publications. Now we are witnessing a new wave of interest in quantum non-stationary systems in different areas, from cosmology (the very first moments of the Universe) and quantum field theory (particle pair creation in ultra-strong fields) to elementary particle physics (neutrino oscillations). A rapid increase in the number of theoretical and experimental works on time-dependent phenomena is also observed in quantum optics, quantum information theory and condensed matter physics. Time-dependent tunneling and time-dependent transport in nano-structures are examples of such phenomena. Another emerging direction of study, stimulated by impressive progress in experimental techniques, is related to attempts to observe the quantum behavior of macroscopic objects, such as mirrors interacting with quantum fields in nano-resonators. Quantum effects manifest themselves in the dynamics of nano-electromechanical systems; they are dominant in the quite new and very promising field of circuit QED. Another rapidly growing research field (although its origin can be traced to the beginning of the 1980s) is the quantum control of evolution at the microscopic level. These examples show that quantum non-stationary systems continue to be a living and very interesting part of quantum physics, uniting researchers from many different areas. Thus it is no mere chance that several special scientific meetings devoted to these topics have been organized recently. One was the international seminar 'Time-Dependent Phenomena in Quantum Mechanics' organized by Manfred Kleber and Tobias Kramer in 2007 at Blaubeuren, Germany. The proceedings of that event were published in 2008 as volume 99 of Journal of Physics: Conference Series. Another recent meeting was the International Workshop on Quantum Non-Stationary Systems, held on 19-23 October 2009 at the International Center for Condensed Matter Physics (ICCMP) in Brasilia, Brazil. It was organized and directed by Victor Dodonov (Institute of Physics, University of Brasilia, Brazil), Vladimir Man'ko (P N Lebedev Physical Institute, Moscow, Russia) and Salomon Mizrahi (Physics Department, Federal University of Sao Carlos, Brazil). This event was accompanied by a satellite workshop 'Quantum Dynamics in Optics and Matter', organized by Salomon Mizrahi and Victor Dodonov on 25-26 October 2009 at the Physics Department of the Federal University of Sao Carlos, Brazil. These two workshops, supported by the Brazilian federal agencies CAPES and CNPq and the local agencies FAP-DF and FAPESP, were attended by more than 120 participants from 16 countries. Almost 50 invited talks and 20 poster presentations covered a wide area of research in quantum mechanics, quantum optics and quantum information. This special issue of CAMOP/Physica Scripta contains contributions presented by some invited speakers and participants of the workshop in Brasilia. Although they do not cover all of the wide spectrum of problems related to quantum non-stationary systems, they nonetheless show some general trends. However, readers should remember that thes

Dodonov, Victor V.; Man'ko, Margarita A.

2010-09-01

245

Decoherence, delocalization and irreversibility in quantum chaotic systems  

CERN Document Server

Decoherence in quantum systems which are classically chaotic is studied. The Arnold cat map and the quantum kicked rotor are chosen as examples of linear and nonlinear chaotic systems. The Feynman-Vernon influence functional formalism is used to study the effect of the environment on the system. It is well-known that quantum coherence can obliterate many chaotic behavior in the corresponding classical system. But interaction with an environment can under general circumstances quickly diminish quantum coherence and reenact many classical chaotic behavior. How effective decoherence works to sustain chaos, and how the resultant behavior qualitatively differs from the quantum picture depend on the coupling of the system with the environment and the spectral density and temperature of the environment. We show how recurrence in the quantum cat map is lost and classical ergodicity is recovered due to the effect of the environment. Quantum coherence and diffusion suppression are instrumental to dynamical localization...

Shiokawa, K; Shiokawa, K; Hu, B L

1995-01-01

246

Moyal Semiclassical Quantum Dynamics for Atomic Systems  

Science.gov (United States)

The Moyal formalism utilizes the Wigner transform and associated Weyl calculus to define a phase space representation of quantum mechanics. In this context, the Weyl symbol image of the Heisenberg evolution operator admits a generic semiclassical expansion that is based on classical transport and related O(hbar^2) quantum corrections. For two atom systems with a mutual pair interaction described by a spherically symmetric potential, the predictive power and convergence properties of this semiclassical expansion are investigated via numerical calculation. The rotational invariance and tensor structure present are used to simplify the semiclassical dynamics to the point where numerical computation in the six dimensional phase space is feasible. For a variety of initial Gaussian wave functions and a selection of different observables, the O(hbar^0) and O(hbar^2) approximations for time dependent expectation values are determined. The interactions used are the Lennard-Jones potentials, which model helium, neon and argon. The numerical results obtained provide a first demonstration of the practicality and usefulness of Moyal quantum mechanics in the analysis of realistic atomic systems.

Tabisz, G. C.; McQuarrie, B. R.; Osborn, T. A.

1998-05-01

247

Semiclassical Moyal quantum mechanics for atomic systems  

Science.gov (United States)

The Moyal formalism utilizes the Wigner transform and associated Weyl calculus to define a phase-space representation of quantum mechanics. In this context, the Weyl symbol image of the Heisenberg evolution operator admits a generic semiclassical expansion that is based on classical transport and related O(?2) quantum corrections. For two atom systems with a mutual pair interaction described by a spherically symmetric potential, the predictive power and convergence properties of this semiclassical expansion are investigated via numerical calculation. The rotational invariance and tensor structure present are used to simplify the semiclassical dynamics to the point where numerical computation in the six-dimensional phase space is feasible. For a variety of initial Gaussian wave functions and a selection of different observables, the O(?0) and O(?2) approximations for time dependent expectation values are determined. The interactions used are the Lennard-Jones potentials, which model helium, neon, and argon. The numerical results obtained provide a first demonstration of the practicality and usefulness of Moyal quantum mechanics in the analysis of realistic atomic systems.

McQuarrie, B. R.; Osborn, T. A.; Tabisz, G. C.

1998-10-01

248

Algebraic Approach to Interacting Quantum Systems  

CERN Document Server

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

249

Topics in quantum information and the theory of open quantum systems  

OpenAIRE

This thesis examines seven topics in the areas of deterministic open-quantum-system dynamics, quantum measurements, and quantum error correction (QEC). The first topic concerns weak measurements and their universality as a means of generating quantum operations. It is shown that every generalized measurement can be implemented as a sequence of weak (infinitesimal) measurements. The second topic is an application of this result to the theory of entanglement. Necessary and suf...

Oreshkov, Ognyan

2008-01-01

250

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

251

Description of an open quantum mechanical system  

International Nuclear Information System (INIS)

A model for the description of an open quantum mechanical many-particle system is formulated. It starts from the shell model and treats the continuous states by a coupled channels method. The mixing of the discrete shell model states via the continuum of decay channels results in the genuine decaying states of the system. These states are eigenstates of a non-Hermitean Hamilton operator the eigenvalues of which give both the energies and the widths of the states. All correlations between two particles which are caused by the two-particle residual interaction, are taken into account including those via the continuum. In the formalism describing the open quantum mechanical system, the coupling between the system and its environment appears nonlinearly. If the resonance states start to overlap, a redistribution of the spectroscopic values ('trapping effect') takes place. As a result, the complexity of the system is reduced at high level density, structures in space and time are formed. This redistribution describes, on the one hand, the transition from the well-known nuclear properties at low level density to those at high level density and fits, on the other hand, into the concept of selforganization. (orig.)

252

A dynamical relation between dual finite temperature classical and zero temperature quantum systems: quantum critical jamming and quantum dynamical heterogeneities  

CERN Document Server

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

253

Probabilistic quantum entanglement swapping and quantum secret sharing with high-dimensional pure entangled systems  

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.

254

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)

255

The transition to chaos conservative classical systems and quantum manifestations  

CERN Document Server

This book provides a thorough and comprehensive discussion of classical and quantum chaos theory for bounded systems and for scattering processes Specific discussions include • Noether’s theorem, integrability, KAM theory, and a definition of chaotic behavior • Area-preserving maps, quantum billiards, semiclassical quantization, chaotic scattering, scaling in classical and quantum dynamics, dynamic localization, dynamic tunneling, effects of chaos in periodically driven systems and stochastic systems • Random matrix theory and supersymmetry The book is divided into several parts Chapters 2 through 4 deal with the dynamics of nonlinear conservative classical systems Chapter 5 and several appendices give a thorough grounding in random matrix theory and supersymmetry techniques Chapters 6 and 7 discuss the manifestations of chaos in bounded quantum systems and open quantum systems respectively Chapter 8 focuses on the semiclassical description of quantum systems with underlying classical chaos, and Chapt...

Reichl, Linda E

2004-01-01

256

Extending scientific computing system with structural quantum programming capabilities  

CERN Document Server

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

257

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

258

A toy model of a macroscopic quantum coherent system  

International Nuclear Information System (INIS)

This paper deals with macroscopic quantum coherence while using only basic quantum mechanics. A square double well is used to illustrate Leggett–Caldeira oscillations. The effect of thermal radiation on two-level systems is discussed. The concept of decoherence is introduced at an elementary level. Reference values are deduced for the energy, temperature and time scales involved in macroscopic quantum coherence. (paper)

259

Quantum MIMO n-Systems and Conditions for Stability  

CERN Document Server

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

260

Quantum MIMO n-Systems and Conditions for Stability  

OpenAIRE

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...

Mansourbeigi, Seyed M. H.; Milani, Vida

2009-01-01

261

Cluster state quantum computation for many-level systems  

OpenAIRE

The cluster state model for quantum computation [Phys. Rev. Lett. 86, 5188] outlines a scheme that allows one to use measurement on a large set of entangled quantum systems in what is known as a cluster state to undertake quantum computations. The model itself and many works dedicated to it involve using entangled qubits. In this paper we consider the issue of using entangled qudits instead. We present a complete framework for cluster state quantum computation using qudits, ...

Hall, William

2005-01-01

262

A neural-network-like quantum information processing system  

OpenAIRE

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, Mitja; Bischof, Horst

2003-01-01

263

Classical and quantum kinetics of the Zakharov system  

OpenAIRE

A kinetic theory for quantum Langmuir waves interacting nonlinearly with quantum ion-acoustic waves is derived. The formulation allows for a statistical analysis of the quantum correction to the Zakharov system. The influence of a background random phase on the modulational instability is given. In the coherent case, the effect of the quantum correction is to reduce the growth rate. Moreover, in the classical limit, a bifurcation develops in the dispersion curves due to the ...

Marklund, M.

2005-01-01

264

Ultracold Quantum Gases and Lattice Systems: Quantum Simulation of Lattice Gauge Theories  

CERN Document Server

Abelian and non-Abelian gauge theories are of central importance in many areas of physics. In condensed matter physics, Abelian U(1) lattice gauge theories arise in the description of certain quantum spin liquids. In quantum information theory, Kitaev's toric code is a Z(2) lattice gauge theory. In particle physics, Quantum Chromodynamics (QCD), the non-Abelian SU(3) gauge theory of the strong interactions between quarks and gluons, is non-perturbatively regularized on a lattice. Quantum link models extend the concept of lattice gauge theories beyond the Wilson formulation, and are well suited for both digital and analog quantum simulation using ultracold atomic gases in optical lattices. Since quantum simulators do not suffer from the notorious sign problem, they open the door to studies of the real-time evolution of strongly coupled quantum systems, which are impossible with classical simulation methods. A plethora of interesting lattice gauge theories suggests itself for quantum simulation, which should al...

Wiese, U -J

2013-01-01

265

Measurement, Filtering and Control in Quantum Open Dynamical Systems  

CERN Document Server

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

266

Scattering properties of an open quantum system  

International Nuclear Information System (INIS)

We study the scattering properties of an open quantum system, in terms of the complex poles of the analytically continued energy Green's function. We use a model for which many dynamical properties can be expressed analytically. We first study particle wave scattering and compute the Wigner delay times. Then, using perturbation theory, we compute the photodetachment rate due to a weak time-periodic electric field. In addition, we show that the model we use qualitatively reproduces several features of the experimentally obtained photodetachment cross section of H- ions and gives interesting insight into the mechanism underlying the photodetachment of H- ions. (c) 2000 The American Physical Society

267

Energy transport in closed quantum systems.  

Science.gov (United States)

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 (QAMs) associated with the off-diagonal elements of the density matrix. These QAMs 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 Schrödinger 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 nonzero net energy flux flows from one part of the potential well to another across the symmetry center of the potential. We find that some modes exhibit positive correlation with the direction of the energy flow. Other modes, that carry a smaller energy per unit of the probability flux, anticorrelate with the energy flow and thus provide a backflow of the probability. The overall picture of energy transport that emerges from our results is very different from the conventional one based on a system with continuous energy spectrum. PMID:22587040

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

2012-03-01

268

Coherent Nonlinear Feedback of Quantum Systems with Applications to Quantum Optics on Chip  

CERN Document Server

In the control of classical mechanical systems, the feedback has been successfully applied to the production of the desired nonlinear dynamics. However, how much this can be done is still an open problem in quantum mechanical systems. This paper proposes a scheme of generating strong nonlinear quantum effects via the recently developed coherent feedback techniques, which can be shown to outperform the measurement-based quantum feedback scheme that can only generate pseudo-nonlinear quantum effects. Such advancement is demonstrated by two application examples in quantum optics on chip. In the first example, we show that the nonlinear Kerr effect can be generated and amplified to be comparable with the linear effect in a transmission line resonator (TLR). In the second example, we show that by tuning the gains of the quantum amplifiers in a TLR coherent feedback network, non-Gaussian "light" (microwave field) can be generated and manipulated via the nonlinear effects which exhibits fully quantum sub-Poisson pho...

Zhang, Jing; Liu, Yu-xi; Li, Chun-Wen; Tarn, Tzyh-Jong

2011-01-01

269

Dynamical systems on quantum tori Lie algebras  

International Nuclear Information System (INIS)

We use quantum tori Lie algebras (QTLA), which are a one-parameter family of sub-algebras of gl?, to describel local and non-local versions of the Toda systems. It turns out that the central charge of QTLA is responsible for the non-locality. There are two regimes in the local systems - conformal for irrational values of the parameter and non-conformal and integrable for its radional values. We also consider infinite-dimensional analogs of rigid toops. Some of these systems give rise to ''quantized'' (magneto-)hydrodynamic equations of an ideal fluid on a torus. We also consider infinite dimensional versions of the integrable Euler and Clebsch cases. (orig.)

270

Schroedinger-cat states and decoherence in quantum electromechanical systems  

International Nuclear Information System (INIS)

Quantum-electromechanical systems are nanoscale mechanical resonators whose high-frequency oscillations are detected by an electronic transducer. Despite their macroscopic size and mechanical, ordinary-matter nature, these resonators can exhibit distinct quantum behavior that is of great interest and promise to an experimental exploration of questions in the foundations of quantum mechanics. After a brief introduction to quantum-electromechanical systems, I will sketch the feasibility and features of superposition states of macroscopically distinct positions in such systems. I will also show how these systems give rise to a new and hitherto hardly explored decoherence model and present some first results for this model

271

Schroedinger-cat states and decoherence in quantum electromechanical systems  

Energy Technology Data Exchange (ETDEWEB)

Quantum-electromechanical systems are nanoscale mechanical resonators whose high-frequency oscillations are detected by an electronic transducer. Despite their macroscopic size and mechanical, ordinary-matter nature, these resonators can exhibit distinct quantum behavior that is of great interest and promise to an experimental exploration of questions in the foundations of quantum mechanics. After a brief introduction to quantum-electromechanical systems, I will sketch the feasibility and features of superposition states of macroscopically distinct positions in such systems. I will also show how these systems give rise to a new and hitherto hardly explored decoherence model and present some first results for this model.

Schlosshauer, Maximilian [Department of Physics, University of Melbourne, Victoria, 3010 (Australia)

2007-05-15

272

Characterizing and quantifying frustration in quantum many-body systems.  

Science.gov (United States)

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. PMID:22243147

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

2011-12-23

273

Quantum Clocks and the Origin of Time in Complex Systems  

CERN Document Server

The origin and nature of time in complex systems is explored using Quantum or Feynman clocks and the signals produced by them. Networks of these clocks provide the basis for the evolution of complex systems. The arrow of time is defined for complex systems. Applications in quantum cosmology are indicated.

Hitchcock, S M

1999-01-01

274

Quantum and statistical mechanics in open systems: theory and examples  

OpenAIRE

Using the system-bath model Hamiltonian this thesis covers the equilibrium and out of equilibrium properties of quantum open systems. Topics included are the calculation of thermodynamical quantities of open systems, derivation of quantum master equations, phase space and numerical methods and Linear and non Linear Response Theory. Applications are the transport in periodic potentials and the dynamics of spins.

Zueco, David

2009-01-01

275

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.

2013-01-01

276

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.

277

Electrical control of spontaneous emission and strong coupling for a single quantum dot  

DEFF Research Database (Denmark)

We report the design, fabrication and optical investigation of electrically tunable single quantum dots—photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light–matter interaction. Unlike previous studies where the dot–cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, we demonstrate that the quantum-confined Stark effect can be employed to quickly and reversibly switch the dot–cavity coupling simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by4 meV relative to the nanocavity mode before the emission quenches due to carrier tunneling escape. This range is much larger than the typical linewidth of the high-Q cavity modes (100?eV) allowing us to explore and contrast regimes where the dots couple to the cavity or decay by spontaneous emission into the two-dimensional photonic bandgap. In the weak-coupling regime, we show that the dot spontaneous emission rate can be tuned using a gate voltage, with Purcell factors>7. New information is obtained on the nature of the dot–cavity coupling in the weak coupling regime, and electrical control of zerodimensional polaritons is demonstrated for the highest-Q cavities (Q > 12 000). Vacuum Rabi splittings up to 120?eV are observed, larger than the linewidths of either the decoupled exciton ( 6 40?eV) or cavity mode. These observations represent a voltage switchable optical nonlinearity at the single photon level, paving the way towards on-chip dot-based nano-photonic devices that can be integrated with passive optical components.

Laucht, A.; Hofbauer, F.

2009-01-01

278

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.)

279

Excitonic complexes in quantum Hall systems  

CERN Document Server

The formation and various possible decay processes of neutral and charged excitonic complexes in electronic integral and fractional quantum Hall systems are discussed. The excitonic complexes are bound states of a small number of the relevant negatively and positively charged quasiparticles (e.g., conduction electrons and valence holes, reversed-spin electrons and spin holes, Laughlin quasielectrons and quasiholes, composite fermions) that occur in an electron system under specific conditions (e.g., electron density, well width, electric and magnetic fields, or hydrostatic pressure). The examples of such bound states are interband neutral and charged excitons, fractionally charged "anyon excitons", spin waves, skyrmions, or "skyrmion excitons". Their possible decay processes include radiative recombination, experimentally observed in photoluminescence or far infrared emission, or spin transitions, important in the context of nuclear spin relaxation.

Wójs, A; Wojs, Arkadiusz; Quinn, John J

2003-01-01

280

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

International Nuclear Information System (INIS)

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.)

281

Strong field control of multilevel quantum systems  

Science.gov (United States)

In this thesis, we present work on coherent control of multilevel quantum systems in the strong field limit using shaped ultrafast laser pulses. In recent years there have been numerous multiphoton absorption experiments in two, three, and four-level atomic/molecular systems and many are performed in the limit of weak fields where perturbation theory is valid. Here, we describe a series of experiments aimed at exploring and understanding multiphoton transitions when the exciting field is strong and perturbation theory breaks down. Our approach to strong field control utilizes both parameterized scans of various pulse shapes and closed-loop learning control to identify a pulse shape that is optimal for populating a target quantum state. With this we will highlight the difference between sequential population transfer and adiabatic rapid passage in multilevel systems with multiphoton coupling between levels. Additionally, we examine strong field control of a four-level atomic interferometer and show how interference in a target state changes from resonant pathways in the frequency domain to time-domain interference via a singe path. Further, we use shaped femtosecond pulses to demonstrate a phenomenon in which a three-level atom becomes a modulator of an ultrafast pulse. The results are based on a pump-probe scheme that is very similar to Electromagnetically Induced Transparency (EIT). Important dynamics associated with a time-dependent coupling field are examined. Lastly, we extend previous work on two-photon driven superfluorescence from a shaped ultrafast drive laser and show how stimulated emission near threshold can turn modest coherent control yields into essentially perfect discrimination between systems where a control factor of about 104 is achieved between atomic and molecular species.

Clow, Stephen Daniel

282

Fourier Synthesis Methods for Control of Inhomogeneous Quantum Systems  

OpenAIRE

Finding control laws (pulse sequences) that can compensate for dispersions in parameters which govern the evolution of a quantum system is an important problem in the fields of coherent spectroscopy, imaging, and quantum information processing. The use of composite pulse techniques for such tasks has a long and widely known history. In this paper, we introduce the method of Fourier synthesis control law design for compensating dispersions in quantum system dynamics. We focus...

Pryor, Brent; Khaneja, Navin

2007-01-01

283

Quantum dynamical echo in two-level systems  

CERN Document Server

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

284

Quantum dynamics of bio-molecular systems in noisy environments  

OpenAIRE

We discuss three different aspects of the quantum dynamics of bio-molecular systems and more generally complex networks in the presence of strongly coupled environments. Firstly, we make a case for the systematic study of fundamental structural elements underlying the quantum dynamics of these systems, identify such elements and explore the resulting interplay of quantum dynamics and environmental decoherence. Secondly, we critically examine some existing approaches to the n...

Plenio, M. B.; Huelga, S. F.

2012-01-01

285

Emergent Quantum Jumps in a Nano-Electro-Mechanical System  

OpenAIRE

We describe a nano-electromechnical system that exhibits the "retroactive" quantum jumps discovered by Mabuchi and Wiseman [Phys. Rev. Lett. 81, 4620 (1998)]. This system consists of a Cooper-pair box coupled to a nano-mechanical resonator, in which the latter is continuously monitored by a single-electron transistor or quantum point-contact. Further, we show that these kinds of jumps, and the jumps that emerge in a continuous quantum non-demolition measurement are one and t...

Jacobs, Kurt; Lougovski, Pavel

2006-01-01

286

A tunable macroscopic quantum system based on two fractional vortices  

OpenAIRE

We propose a tunable macroscopic quantum system based on two fractional vortices. Our analysis shows that two coupled fractional vortices pinned at two artificially created \\kappa\\ discontinuities of the Josephson phase in a long Josephson junction can reach the quantum regime where coherent quantum oscillations arise. For this purpose we map the dynamics of this system to that of a single particle in a double-well potential. By tuning the \\kappa\\ discontinuities with inject...

Heim, D. M.; Vogel, K.; Schleich, W. P.; Koelle, D.; Kleiner, R.; Goldobin, E.

2012-01-01

287

Topological Excitations in Double-Layer Quantum Hall Systems  

Science.gov (United States)

Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel many body quantum Hall effect due to the strong interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness ?s due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topological excitations thus obtained demonstrates a nice qualitative agreement with recent experiment.

Moon, Kyungsun

1997-05-01

288

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

CERN Document Server

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

289

Quantum projection method and completely integrable systems  

International Nuclear Information System (INIS)

The projection method is a constructive proof of complete integrability of classical many body systems. Roughly, this method consists of establishing a correspondence between a system of n particles interacting via two body forces and free or harmonic motion in a space with many more dimensions. The integration of the equations of motion of the interacting system occurs naturally in the space of higher dimension. We extend the projection method to the quantum case. We consider four different n body systems where the potential is a sum of two body potentials. The two body potentials are of the form: (1) V(Q) = Q-2, (II) V(Q) = (2sinQ/2)-2, (III) V(Q) = (2sinhQ/2)-2, and (IV) V(Q) = Q-2 + omega2 Q2. The wave functions and propagators of these systems are given in the form of integrals involving the wave functions and propagators of free or harmonic motion in spaces of n2 and n(n + 1)/2 dimensions. Quantization of angular momentum in the large space yields solutions for discrete values of the coupling constant

290

Generalized conditional entropy in bipartite quantum systems  

International Nuclear Information System (INIS)

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. (paper)

291

Quantum key distribution system clocked at 2 GHz  

CERN Document Server

An improved quantum key distribution test system operating at clock rates of up to 2GHz using a specially adapted commercially available silicon single photon avalanche diode is presented. The use of improved detectors has improved the fibre-based test system performance in terms of transmission distance and quantum bit error rate.

Gordon, K J; Buller, G S; Rech, I; Cova, S D; Townsend, P D

2005-01-01

292

Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems  

Science.gov (United States)

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

293

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

294

Quantum computing through electron propagation in the edge states of quantum spin Hall systems  

OpenAIRE

We propose to implement quantum computing based on electronic spin qubits by controlling the propagation of the electron wave packets through the helical edge states of quantum spin Hall systems (QSHs). Specfically, two non-commutative single-qubit gates, which rotate a qubit around z and y axes, can be realized by utilizing gate voltages either on a single QSH edge channel or on a quantum point contact structure. The more challenging two-qubit controlled phase gate can be i...

Chen, Wei; Xue, Zheng-yuan; Wang, Z. D.; Shen, R.; Xing, D. Y.

2013-01-01

295

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

OpenAIRE

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 statisti...

Sukhanov, Aleksander

2005-01-01

296

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

297

Effects of symmetry breaking in finite quantum systems  

Energy Technology Data Exchange (ETDEWEB)

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 finite mesoscopic systems; (ii) the analysis of common properties of physically different finite quantum systems; (iii) the manifestations of symmetry breaking in the spectra of collective excitations in finite quantum systems. The analysis of these features allows for the better understanding of the intimate relation between the type of symmetry and other physical properties of quantum systems. This also makes it possible to predict new effects by employing the analogies between finite quantum systems of different physical nature.

Birman, J.L. [Department of Physics, City College, City University of New York, New York, NY 10031 (United States); Nazmitdinov, R.G. [Departament de Fisica, Universitat de les Illes Balears, Palma de Mallorca 07122 (Spain); Bogolubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Yukalov, V.I., E-mail: yukalov@theor.jinr.ru [Bogolubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation)

2013-05-15

298

Quantum integrable systems. Quantitative methods in biology  

CERN Document Server

Quantum integrable systems have very strong mathematical properties that allow an exact description of their energetic spectrum. From the Bethe equations, I formulate the Baxter "T-Q" relation, that is the starting point of two complementary approaches based on nonlinear integral equations. The first one is known as thermodynamic Bethe ansatz, the second one as Kl\\"umper-Batchelor-Pearce-Destri- de Vega. I show the steps toward the derivation of the equations for some of the models concerned. I study the infrared and ultraviolet limits and discuss the numerical approach. Higher rank integrals of motion can be obtained, so gaining some control on the eigenvectors. After, I discuss the Hubbard model in relation to the N = 4 supersymmetric gauge theory. The Hubbard model describes hopping electrons on a lattice. In the second part, I present an evolutionary model based on Turing machines. The goal is to describe aspects of the real biological evolution, or Darwinism, by letting evolve populations of algorithms. ...

Feverati, Giovanni

2011-01-01

299

Dynamics of initially entangled open quantum systems  

International Nuclear Information System (INIS)

Linear maps of matrices describing the evolution of density matrices for a quantum system initially entangled with another are identified and found to be not always completely positive. They can even map a positive matrix to a matrix that is not positive, unless we restrict the domain on which the map acts. Nevertheless, their form is similar to that of completely positive maps. Only some minus signs are inserted in the operator-sum representation. Each map is the difference of two completely positive maps. The maps are first obtained as maps of mean values and then as maps of basis matrices. These forms also prove to be useful. An example for two entangled qubits is worked out in detail. The relation to earlier work is discussed

300

Energy transmutation in nonequilibrium quantum systems  

Science.gov (United States)

We investigate particle and heat transport in quantum junctions with the geometry of star graphs. The system is in a non-equilibrium steady state, characterized by the different temperatures and chemical potentials of the heat reservoirs connected to the edges of the graph. We explore the Landauer–Büttiker state and its orbit under parity and time reversal transformations. Both particle number and total energy are conserved in these states. However, the heat and chemical potential energy are in general not separately conserved, which gives origin to a basic process of energy transmutation among them. We study both directions of this process in detail, introducing appropriate efficiency coefficients. For scale invariant interactions in the junction our results are exact and explicit. They cover the whole parameter space and take into account all nonlinear effects. The energy transmutation depends on the particle statistics.

Mintchev, Mihail; Santoni, Luca; Sorba, Paul

2015-02-01

301

Schmidt information and entanglement in quantum systems  

CERN Document Server

The purpose of this paper is to study entanglement of quantum states by means of Schmidt decomposition. The notion of Schmidt information which characterizes the non-randomness of correlations between two observers that conduct measurements of EPR-states is proposed. In two important particular cases - a finite number of Schmidt modes with equal probabilities and Gaussian correlations- Schmidt information is equal to Shannon information. A universal measure of a dependence of two variables is proposed. It is based on Schmidt number and it generalizes the classical Pearson correlation coefficient. It is demonstrated that the analytical model obtained can be applied to testing the numerical algorithm of Schmidt modes extraction. A thermodynamic interpretation of Schmidt information is given. It describes the level of entanglement and correlations of micro-system with its environment

Bogdanov, A Y; Valiev, K A; Bogdanov, Yu.I.

2005-01-01

302

Quantum chromodynamics in few-nucleon systems  

International Nuclear Information System (INIS)

One of the most important implications of quantum chromodynamics (QCD) is that nuclear systems and forces can be described at a fundamental level. The theory provides natural explanations for the basic features of hadronic physics: the meson and baryon spectra, quark statistics, the structure of the weak and electromagnetic currents of hadrons, the scale-invariance of hadronic interactions at short distances, and evidently, color (i.e., quark and gluon) confinement at large distances. Many different and diverse tests have confirmed the basic predictions of QCD; however, since tests of quark and gluon interactions must be done within the confines of hadrons there have been few truly quantitative checks. Nevertheless, it appears likely that QCD is the fundamental theory of hadronic and nuclear interactions in the same sense that QED gives a precise description of electrodynamic interctions. Topics discussed include exclusive processes in QCD, the deuteron in QCD, reduced nuclear amplitudes, and limitations of traditional nuclear physics. 32 references

303

Composite fermions in quantum Hall systems  

CERN Document Server

The occurrence of incompressible quantum fluid states of a two dimensional system is a result of electron--electron interactions in a highly degenerate fractionally filled Landau level. Novel quasiparticles (QP's) called composite Fermions (CF's) have allowed a simple single particle description of the most prominent incompressible states. Residual interactions among these QP's are investigated. These interactions determine the type of "daughter states" that can occur at the next generation. We demonstrate that at certain values of the QP filling factor nu_QP, Laughlin correlations among the QP's give rise to states of the standard CF hierarchy. At other values of nu_QP pairing of QP's is found leading to a novel hierarchy of incompressible states.

Quinn, J J; Yi, K S; Quinn, J J; Quinn, John J.; Wojs, Arkadiusz; Yi, Kyung-Soo; Quinn, Jennifer J.

2003-01-01

304

Phonon Overlaps in Molecular Quantum Dot Systems  

Science.gov (United States)

We model the amplitudes and frequencies of the vibrational sidebands for the new molecular quantum dot systems. We calculate the Franck-Condon phonon overlaps in the 3N-dimensional configuration sapce. We solve the general case where the vibrational frequencies and eigenmodes change during the transition. We perform PM3 and DFT calculations for the case of the dumb bell-shaped C140 molecule. We find that the strongest amplitudes are associated with the 11 meV stretch mode, in agreement with experiment. The experimental amplitudes vary from molecule to molecule; indicating that the molecular overlaps are environment dependent. We explore overlaps in the presence of external electric fields from image charges and counter ions.

Chang, Connie; Sethna, James

2004-03-01

305

The study of classical dynamical systems using quantum theory  

Science.gov (United States)

We have developed a method for complementing an arbitrary classical dynamical system to a quantum system using the Lorenz and Rössler systems as examples. The Schrödinger equation for the corresponding quantum statistical ensemble is described in terms of the Hamilton-Jacobi formalism. We consider both the original dynamical system in the coordinate space and the conjugate dynamical system corresponding to the momentum space. Such simultaneous consideration of mutually complementary coordinate and momentum frameworks provides a deeper understanding of the nature of chaotic behavior in dynamical systems. We have shown that the new formalism provides a significant simplification of the Lyapunov exponents calculations. From the point of view of quantum optics, the Lorenz and Rössler systems correspond to three modes of a quantized electromagnetic field in a medium with cubic nonlinearity. From the computational point of view, the new formalism provides a basis for the analysis of complex dynamical systems using quantum computers.

Bogdanov, Yu. I.; Bogdanova, N. A.

2014-12-01

306

3.3 Gigahertz Clocked Quantum Key Distribution System  

CERN Document Server

A fibre-based quantum key distribution system operating up to a clock frequency of 3.3GHz is presented. The system demonstrates significantly increased key exchange rate potential and operates at a wavelength of 850nm.

Gordon, K J; Collins, R J; Rech, I; Cova, S D; Townsend, P D; Buller, G S; Gordon, Karen J.; Fernandez, Veronica; Collins, Robert J.; Rech, Ivan; Cova, Sergio D.; Townsend, Paul D.; Buller, Gerald S.

2006-01-01

307

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

308

Density matrix of strongly coupled quantum dot - microcavity system  

International Nuclear Information System (INIS)

Any two-level quantum system can be used as a quantum bit (qubit) - the basic element of all devices and systems for quantum information and quantum computation. Recently it was proposed to study the strongly coupled system consisting of a two-level quantum dot and a monoenergetic photon gas in a microcavity-the strongly coupled quantum dot-microcavity (QD-MC) system for short, with the Jaynes-Cumming total Hamiltonian, for the application in the quantum information processing. Different approximations were applied in the theoretical study of this system. In this work, on the basis of the exact solution of the Schrodinger equation for this system without dissipation we derive the exact formulae for its density matrix. The realization of a qubit in this system is discussed. The solution of the system of rate equation for the strongly coupled QD-MC system in the presence of the interaction with the environment was also established in the first order approximation with respect to this interaction.

309

Hacking commercial quantum cryptography systems by tailored bright illumination  

CERN Document Server

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

310

Experimental feedback control of quantum systems using weak measurements  

CERN Document Server

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

311

Experimental feedback control of quantum systems using weak measurements.  

Science.gov (United States)

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 nonorthogonal 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. PMID:20366921

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

2010-02-26

312

Sliding Mode Control of Two-Level Quantum Systems  

OpenAIRE

This paper proposes a robust control method based on sliding mode design for two-level quantum systems with bounded uncertainties. An eigenstate of the two-level quantum system is identified as a sliding mode. The objective is to design a control law to steer the system's state into the sliding mode domain and then maintain it in that domain when bounded uncertainties exist in the system Hamiltonian. We propose a controller design method using the Lyapunov methodology and pe...

Dong, Daoyi; Petersen, Ian R.

2010-01-01

313

Dynamical invariants for quantum control of four-level systems  

Science.gov (United States)

We present a Lie-algebraic classification and detailed construction of the dynamical invariants, also known as Lewis-Riesenfeld invariants, of the four-level systems including two-qubit systems which are most relevant and sufficiently general for quantum control and computation. These invariants not only solve the time-dependent Schrödinger equation of four-level systems exactly but also enable the control, and hence quantum computation based on which, of four-level systems fast and beyond adiabatic regimes.

Güngördü, Utkan; Wan, Yidun; Fasihi, Mohammad Ali; Nakahara, Mikio

2012-12-01

314

Classical and quantum simulations of many-body systems  

International Nuclear Information System (INIS)

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.)

315

Environment-assisted quantum transport in ordered systems  

International Nuclear Information System (INIS)

Noise-assisted transport in quantum systems occurs when quantum time evolution and decoherence conspire to produce a transport efficiency that is higher than what would be seen in either the purely quantum or purely classical cases. In disordered systems, it has been understood as the suppression of coherent quantum localization through noise, which brings detuned quantum levels into resonance and thus facilitates transport. We report several new mechanisms of environment-assisted transport in ordered systems, in which there is no localization to overcome and where one would naively expect that coherent transport is the fastest possible. Although we are particularly motivated by the need to understand excitonic energy transfer in photosynthetic light-harvesting complexes, our model is general—transport in a tight-binding system with dephasing, a source and a trap—and can be expected to have wider application. (paper)

316

Realization of quantum state privacy amplification in a nuclear magnetic resonance quantum system  

Energy Technology Data Exchange (ETDEWEB)

Quantum state privacy amplification (QSPA) is the quantum analogue of classical privacy amplification. If the state information of a series of single-particle states has some leakage, QSPA reduces this leakage by condensing the state information of two particles into the state of one particle. Recursive applications of the operations will eliminate the quantum state information leakage to a required minimum level. In this paper, we report the experimental implementation of a quantum state privacy amplification protocol in a nuclear magnetic resonance system. The density matrices of the states are constructed in the experiment, and the experimental results agree well with theory.

Hao, Liang; Wang, Chuan; Long, Gui Lu, E-mail: gllong@tsinghua.edu.c [Key Laboratory for Atomic and Molecular NanoSciences and Department of Physics, Tsinghua University, Beijing 100084 (China)

2010-06-28

317

Correlation approach to work extraction from finite quantum systems  

Science.gov (United States)

Reversible work extraction from identical quantum systems via collective operations was shown to be possible even without producing entanglement among the sub-parts. Here, we show that implementing such global operations necessarily imply the creation of quantum correlations, as measured by quantum discord. We also reanalyze the conditions under which global transformations outperform local gates as far as maximal work extraction is considered by deriving a necessary and sufficient condition that is based on classical correlations.

Giorgi, Gian Luca; Campbell, Steve

2015-02-01

318

Correlation approach to work extraction from finite quantum systems  

International Nuclear Information System (INIS)

Reversible work extraction from identical quantum systems via collective operations was shown to be possible even without producing entanglement among the sub-parts. Here, we show that implementing such global operations necessarily imply the creation of quantum correlations, as measured by quantum discord. We also reanalyze the conditions under which global transformations outperform local gates as far as maximal work extraction is considered by deriving a necessary and sufficient condition that is based on classical correlations. (paper)

319

Asymptotic Stochastic Transformations for Nonlinear Quantum Dynamical Systems  

OpenAIRE

The Ito and Stratonovich approaches are carried over to quantum stochastic systems. Here the white noise representation is shown to be the most appropriate as here the two approaches appear as Wick and Weyl orderings, respectively. This introduces for the first time the Stratonovich form for SDEs driven by Poisson processes or quantum SDEs including the conservation process. The relation of the nonlinear Heisenberg ODES to asymptotic quantum SDEs is established extending pre...

Gough, John

2012-01-01

320

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

321

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)

322

Universal level-spacing distribution in quantum systems  

CERN Document Server

Classical counterparts of a great variety of quantum systems, from atomic physics to quantum wells and quantum dots, to optical, microwave, and acoustic resonators exhibit partially chaotic dynamics. Since it is often impossible to measure the temporal dynamics in qunatum systems, the main and probably the most dramatic manifestation of classical chaos in their phase space is seen in the distribution of spacing between the neighboring energy levels. While the mechanism leading to the onset of chaotic dynamics is different in every system, the level spacing distribution obeys the universal law, changing from Poissonian in the completely integrable systems to Wigner in completely chaotic ones.

Podolskiy, V A; Podolskiy, Viktor A.; Narimanov, Evgenii E.

2003-01-01

323

Interaction between classical and quantum systems; a new approach to quantum measurement. II. Theoretical considerations  

International Nuclear Information System (INIS)

A new approach to the quantum measurement process is developed further. In this approach, the apparatus is treated as a classical system; however, the classical apparatus is directly coupled to the quantum system. A principle of integrity, which requires that the observables of the classical apparatus retain their classical integrity, is introduced. The constraints that this Principle places upon the coupling between the apparatus and the quantum system are examined. A model loosely based on the Stern--Gerlach experiment is used to illustrate the approach. A coupling which satisfies the Principle of Integrity is exhibited for this model

324

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. Thin 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)

325

Quantum effects in a macroscopic system  

International Nuclear Information System (INIS)

The quantum energy eigenvalues near the separatrix energy are found by combination of previous analysis of the quantum states near a barrier top with recent results for the behavior of the classical action near a separatrix. It is found that the minimum energy separation vanishes only logarithmically with Planck's constant. As a result, quantum aspects of the states of a Penning trap should be observable

326

Quantum dynamics in electron-nuclei coupled spin system in quantum dots: Bunching, revival, and quantum correlation in electron-spin measurements  

OpenAIRE

We investigate quantum dynamics in the electron-nuclei coupled spin system in quantum dots and clarify the fundamental features of quantum correlation induced via successive electron spin measurements. This quantum correlation leads to interesting phenomena such as the bunching of outcomes in the electron spin measurements and the revival of an arbitrary initial electron spin state. The nuclear spin system is also affected by the quantum correlation and is in fact squeezed v...

Cakir, Ozgur; Takagahara, Toshihide

2008-01-01

327

Quantum correlation measure in arbitrary bipartite systems  

Science.gov (United States)

Quantum correlation with a novel definition is presented for an arbitrary bipartite quantum state in terms of the skew information of the complete set of rank-one orthogonal projectors. This definition not only inherits the good properties of skew information including the contractivity, but also shows a powerful analytic computability for a large range of states. In addition, the measure for a general state can be easily numerically obtained by the well-developed technique of the approximate joint diagonalization. As a comparison, we give both the analytic and the numerical quantum correlation for many high-dimensional states. The relation between our measure and quantum metrology is also analyzed.

Yu, Chang-shui; Wu, Shao-xiong; Wang, Xiaoguang; Yi, X. X.; Song, He-shan

2014-07-01

328

Quantum Liouville-space trajectories for dissipative systems  

CERN Document Server

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

329

Recovering classical dynamics from coupled quantum systems through continuous measurement  

CERN Document Server

We study the role of continuous measurement in the quantum to classical transition for a system with coupled internal (spin) and external (motional) degrees of freedom. Even when the measured motional degree of freedom can be treated classically, entanglement between spin and motion causes strong measurement backaction on the quantum spin subsystem so that classical trajectories are not recovered in this mixed quantum-classical regime. The measurement can extract localized quantum trajectories that behave classically only when the internal action also becomes large relative to h-bar.

Ghose, S; Deutsch, I H; Bhattacharya, T; Habib, S; Jacobs, K; Ghose, Shohini; Alsing, Paul M.; Deutsch, Ivan H.; Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt

2003-01-01

330

Quantum mechanics of higher derivative systems and total derivative terms  

OpenAIRE

A general theory is presented of quantum mechanics of singular, non-autonomous, higher derivative systems. Within that general theory, $n$-th order and $m$-th order Lagrangians are shown to be quantum mechanically equivalent if their difference is a total derivative.

Kaminaga, Yasuhito

1995-01-01

331

A quantum-like description of the planetary systems  

International Nuclear Information System (INIS)

The Titius-Bode law for planetary distances is reviewed. A model describing the basic features of this law in the 'quantum-like' language of a wave equation is proposed. Some considerations about the 't Hooft idea on the quantum behaviour of deterministic systems with dissipation are discussed

332

A quantum-like description of the planetary systems  

Energy Technology Data Exchange (ETDEWEB)

The Titius-Bode law for planetary distances is reviewed. A model describing the basic features of this law in the 'quantum-like' language of a wave equation is proposed. Some considerations about the 't Hooft idea on the quantum behaviour of deterministic systems with dissipation are discussed.

Scardigli, Fabio [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

2007-05-15

333

Josephson inplane and tunneling currents in bilayer quantum Hall system  

International Nuclear Information System (INIS)

A Bose-Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (–e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ? = 1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless in tunneling experiments with various geometries

334

Progress in the mathematical theory of quantum disordered systems  

OpenAIRE

We review recent progress in the mathematical theory of quantum disordered systems: the Anderson transition, including some joint work with Domingos Marchetti, the (quantum and classical) Edwards-Anderson (EA) spin-glass model and return to equilibrium for a class of spin-glass models, which includes the EA model initially in a very large transverse field.

Wreszinski, Walter F.

2012-01-01

335

Two-dimensional Gauge Theories and Quantum Integrable Systems  

CERN Document Server

In this paper the relation between 2d topological gauge theories and Bethe Ansatz equations is reviewed. In addition we present some new results and clarifications. We hope the relations discussed here are particular examples of more general relations between quantum topological fields theories in dimensions $d\\leq 4$ and quantum integrable systems.

Gerasimov, Anton A

2007-01-01

336

Decoherence as irreversible dynamical process in open quantum systems  

International Nuclear Information System (INIS)

Full text: A framework for a general discussion in Heisenberg's representation of environmentally induced decoherence will be proposed. Example showing that classical properties do not have to be postulated as an independent ingredient will be given. It will be also shown that infinite open quantum systems in some case after decoherence behave like - simple classical dynamical systems; simples quantum mechanical systems representing one particle. (author)

337

Reduced dynamics and the master equation of open quantum systems  

International Nuclear Information System (INIS)

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.

338

Dynamics of a Simple Quantum System in a Complex Environment  

OpenAIRE

We present a theory for the dynamical evolution of a quantum system coupled to a complex many-body intrinsic system/environment. By modelling the intrinsic many-body system with parametric random matrices, we study the types of effective stochastic models which emerge from random matrix theory. Using the Feynman-Vernon path integral formalism, we derive the influence functional and obtain either analytical or numerical solutions for the time evolution of the entire quantum s...

Bulgac, Aurel; Dodang, Gui; Kusnezov, Dimitri

1997-01-01

339

Hamiltonian identification for quantum systems : well posedness and numerical approaches  

OpenAIRE

This paper considers the inversion problem related to the manipulation of quantum systems using laser-matter interactions. The focus is on the identification of the field free Hamiltonian and/or the dipole moment of a quantum system. The evolution of the system is given by the Schrödinger equation. The available data are observations as a function of time corresponding to dynamics generated by electric fields. The well-posedness of the problem is proved, mainly focusing on the uniqueness of ...

Le Bris, Claude; Mirrahimi, Mazyar; Rabitz, Herschel; Turinici, Gabriel

2007-01-01

340

Quantum materials, lateral semiconductor nanostructures, hybrid systems and nanocrystals  

CERN Document Server

Semiconductor nanostructures are ideal systems to tailor the physical properties via quantum effects, utilizing special growth techniques, self-assembling, wet chemical processes or lithographic tools in combination with tuneable external electric and magnetic fields. Such systems are called 'Quantum Materials'. The electronic, photonic, and phononic properties of these systems are governed by size quantization and discrete energy levels. The charging is controlled by the Coulomb blockade. The spin can be manipulated by the geometrical structure, external gates and by integrating hybrid ferrom

Heitmann, Detlef

2010-01-01

341

Experimental simulation of quantum tunneling in small systems  

Science.gov (United States)

It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a barrier, together with the oscillation of the state in potential wells, are clearly observed through the experimental results. This experiment has clearly demonstrated the possibility to observe and study profound physical phenomena within even the reach of small quantum computers. PMID:23958996

Feng, Guan-Ru; Lu, Yao; Hao, Liang; Zhang, Fei-Hao; Long, Gui-Lu

2013-01-01

342

Experimental simulation of quantum tunneling in small systems.  

Science.gov (United States)

It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a barrier, together with the oscillation of the state in potential wells, are clearly observed through the experimental results. This experiment has clearly demonstrated the possibility to observe and study profound physical phenomena within even the reach of small quantum computers. PMID:23958996

Feng, Guan-Ru; Lu, Yao; Hao, Liang; Zhang, Fei-Hao; Long, Gui-Lu

2013-01-01

343

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-commutinghe 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)

344

Asymptotically Optimal Quantum Circuits for d-Level Systems  

International Nuclear Information System (INIS)

Scalability of a quantum computation requires that the information be processed on multiple subsystems. However, it is unclear how the complexity of a quantum algorithm, quantified by the number of entangling gates, depends on the subsystem size. We examine the quantum circuit complexity for exactly universal computation on many d-level systems (qudits). Both a lower bound and a constructive upper bound on the number of two-qudit gates result, proving a sharp asymptotic of ?(d2n) gates. This closes the complexity question for all d-level systems (d finite). The optimal asymptotic applies to systems with locality constraints, e.g., nearest neighbor interactions

345

Quantum statistical Monte Carlo methods and applications to spin systems  

International Nuclear Information System (INIS)

A short review is given concerning the quantum statistical Monte Carlo method based on the equivalence theorem that d-dimensional quantum systems are mapped onto (d+1)-dimensional classical systems. The convergence property of this approximate tansformation is discussed in detail. Some applications of this general appoach to quantum spin systems are reviewed. A new Monte Carlo method, ''thermo field Monte Carlo method,'' is presented, which is an extension of the projection Monte Carlo method at zero temperature to that at finite temperatures

346

Time Dependent Quantum Thermodynamics of a Coupled Quantum Oscillator System in a Small Thermal Environment  

CERN Document Server

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 argued, contrary to common understanding, that quantum interference and coherence are eliminated only with maximal entropy, which corresponds thermally to infinite temperature. Implications of our results for the notion of "classicalizing" be...

Barnes, George L

2013-01-01

347

Controlled multiqubit entangled states and quantum transmission in quantum molecule-spin systems  

CERN Document Server

he multiqubit entangled states are coherently controlled in the quantum spin systems composed of $N+1$ interacting antiferromagnetic molecular rings. The tunable intermolecular couplings arise from the local exchange interactions between electron spins of $N$ circumjacent magnets and those of one central molecular ring. The quantum dynamics of such system is analytically deduced by the effective spin hamiltonian with anisotropic Heisenberg couplings. It is found that entangled $W$ states can be generated with a high precision under the circumstance of quantum fluctuations. The multiqubit entangled state is also transferred from some molecular rings to others by the selection of intermolecular couplings.

Hao, Xiang; Zang, Taocheng; Zhu, Shiqun

2009-01-01

348

Dynamics of Quantum Dissipative Systems: The Example of Quantum Brownian Motors  

CERN Document Server

Brownian motors, i.e. devices able to produce useful work out of thermal forces with the help of other unbiased forces, provide an ideal benchmark for the investigation of quantum dissipative systems, for two reasons. First, the interaction with a dissipative environment plays an essential role in the performance of Brownian motors. Second, dissipative tunneling enriches the dynamics of quantum Brownian motors with respect to their classical counterpart, inducing features such as current reversals as a function of temperature. Here we report on our work on quantum Brownian motors and discuss the load characteristic of such a system.

Peguiron, J

2006-01-01

349

Synthetic Topological Qubits in Conventional Bilayer Quantum Hall Systems  

Science.gov (United States)

The idea of topological quantum computation is to build powerful and robust quantum computers with certain macroscopic quantum states of matter called topologically ordered states. These systems have degenerate ground states that can be used as robust "topological qubits" to store and process quantum information. In this paper, we propose a new experimental setup that can realize topological qubits in a simple bilayer fractional quantum Hall system with proper electric gate configurations. Our proposal is accessible with current experimental techniques, involves well-established topological states, and, moreover, can realize a large class of topological qubits, generalizing the Majorana zero modes studied in recent literature to more computationally powerful possibilities. We propose three tunneling and interferometry experiments to detect the existence and nonlocal topological properties of the topological qubits.

Barkeshli, Maissam; Qi, Xiao-Liang

2014-10-01

350

A robust, scanning quantum system for nanoscale sensing and imaging  

CERN Document Server

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

351

Quantum Effects In Low Temperature Bosonic Systems  

CERN Document Server

In the first part, we investigate the effect of long range particle exchange in ideal bosonic chains. We establish that by using the Heisenberg formalism along with matrix product state representation we can study the evolution as well as the ground state of bosonic arrangements while including terms beyond next-neighbour hopping. The method is then applied to analyse the quench dynamics of condensates in a trapping potential and also to study the emergence of entanglement as a result of collision in boson chains. In the second part, we study the ground state as well as the dynamics of 1D boson arrangements with local repulsive interactions and nearest-neighbour exchange using numerical techniques based on time evolving block decimation (TEBD). We focus on the development of quantum correlations between the terminal places of these arrangements. We find that long-range entanglement in the ground state arises as a result of intense boson tunnelling taking place across the whole chain in systems with appropriat...

Reslen, Jose

2010-01-01

352

The Dalton quantum chemistry program system.  

Science.gov (United States)

Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, Møller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms. PMID:25309629

Aidas, Kestutis; Angeli, Celestino; Bak, Keld L; Bakken, Vebjørn; Bast, Radovan; Boman, Linus; Christiansen, Ove; Cimiraglia, Renzo; Coriani, Sonia; Dahle, Pål; Dalskov, Erik K; Ekström, Ulf; Enevoldsen, Thomas; Eriksen, Janus J; Ettenhuber, Patrick; Fernández, Berta; Ferrighi, Lara; Fliegl, Heike; Frediani, Luca; Hald, Kasper; Halkier, Asger; Hättig, Christof; Heiberg, Hanne; Helgaker, Trygve; Hennum, Alf Christian; Hettema, Hinne; Hjertenæs, Eirik; Høst, Stinne; Høyvik, Ida-Marie; Iozzi, Maria Francesca; Jansík, Branislav; Jensen, Hans Jørgen Aa; Jonsson, Dan; Jørgensen, Poul; Kauczor, Joanna; Kirpekar, Sheela; Kjærgaard, Thomas; Klopper, Wim; Knecht, Stefan; Kobayashi, Rika; Koch, Henrik; Kongsted, Jacob; Krapp, Andreas; Kristensen, Kasper; Ligabue, Andrea; Lutnæs, Ola B; Melo, Juan I; Mikkelsen, Kurt V; Myhre, Rolf H; Neiss, Christian; Nielsen, Christian B; Norman, Patrick; Olsen, Jeppe; Olsen, Jógvan Magnus H; Osted, Anders; Packer, Martin J; Pawlowski, Filip; Pedersen, Thomas B; Provasi, Patricio F; Reine, Simen; Rinkevicius, Zilvinas; Ruden, Torgeir A; Ruud, Kenneth; Rybkin, Vladimir V; Sa?ek, Pawel; Samson, Claire C M; de Merás, Alfredo Sánchez; Saue, Trond; Sauer, Stephan P A; Schimmelpfennig, Bernd; Sneskov, Kristian; Steindal, Arnfinn H; Sylvester-Hvid, Kristian O; Taylor, Peter R; Teale, Andrew M; Tellgren, Erik I; Tew, David P; Thorvaldsen, Andreas J; Thøgersen, Lea; Vahtras, Olav; Watson, Mark A; Wilson, David J D; Ziolkowski, Marcin; Agren, Hans

2014-05-01

353

The Dalton quantum chemistry program system  

DEFF Research Database (Denmark)

Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree–Fock, Kohn–Sham, multiconfigurational self-consistent-field, Møller–Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, while magnetic resonance and optical activity can be studied in a gauge-origininvariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms.

Aidas, Kestutis; Angeli, Celestino

2014-01-01

354

Initialization of a nuclear spin system over the quantum Hall regime for quantum information processing  

CERN Document Server

The application of the quantum mechanical properties of physical systems to realize novel computational schemes and innovative device functions have been topics of recent interest. Proposals for associated devices are to be found in diverse branches of physics. Here, we are concerned with the experimental realization of some elements needed for quantum information processing using nuclear spin immersed in a confined electronic system in the quantum Hall regime. Thus, we follow a spin-handling approach that (a) uses the Overhauser effect in the quantum Hall regime to realize a large nuclear polarization at relatively high temperatures, (b) detects the nuclear spin state by measuring the influence of the associated magnetic field on Electron Spin Resonance, and (c) seeks to apply the electronic spin exciton as the spin transfer mechanism. Some measurements examining the viability of this approach are shown, and the utility of the approach for initializing a nuclear spin system at a relatively high temperature i...

Mani, R G; Narayanamurti, V

2003-01-01

355

Quantum driving of a two level system: quantum speed limit and superadiabatic protocols – an experimental investigation  

International Nuclear Information System (INIS)

A fundamental requirement in quantum information processing and in many other areas of science is the capability of precisely controlling a quantum system by preparing a quantum state with the highest fidelity and/or in the fastest possible way. Here we present an experimental investigation of a two level system, characterized by a time-dependent Landau-Zener Hamiltonian, aiming to test general and optimal high-fidelity control protocols. The experiment is based on a Bose-Einstein condensate (BEC) loaded into an optical lattice, then accelerated, which provides a high degree of control over the experimental parameters. We implement generalized Landau-Zener sweeps, comparing them with the well-known linear Landau-Zener sweep. We drive the system from an initial state to a final state with fidelity close to unity in the shortest possible time (quantum brachistochrone), thus reaching the ultimate speed limit imposed by quantum mechanics. On the opposite extreme of the quantum control spectrum, the aim is not to minimize the total transition time but to maximize the adiabaticity during the time-evolution, the system being constrained to the adiabatic ground state at any time. We implement such transitionless superadiabatic protocols by an appropriate transformation of the Hamiltonian parameters. This transformation is general and independent of the physical system.

356

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 sn 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)

357

Quantum dynamics applications in biological and material systems  

CERN Document Server

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

358

Fidelity and entanglement fidelity for infinite-dimensional quantum systems  

Science.gov (United States)

Instead of unitary freedom for finite-dimensional cases, bi-contractive freedom in the operator-sum representation for quantum channels of infinite-dimensional systems is established. Specifically, if the channel sends every pure state to a finite rank state, then the isometric freedom feature holds. Then, a method of computing entanglement fidelity and a relation between quantum fidelity and entanglement fidelity for infinite-dimensional systems are obtained. In addition, upper and lower bounds of the quantum fidelity, and their connection to the trace distance, are also provided.

Wang, Li; Hou, Jinchuan; Qi, Xiaofei

2014-08-01

359

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

360

Fractional quantum Hall states in charge-imbalanced bilayer systems  

International Nuclear Information System (INIS)

We study the fractional quantum Hall effect in a bilayer with charge-distribution imbalance induced, for instance, by a bias gate voltage. The bilayer can either be intrinsic or it can be formed spontaneously in wide quantum wells, due to the Coulomb repulsion between electrons. We focus on fractional quantum Hall effect in asymmetric bilayer systems at filling factor ? = 4/11 and show that an asymmetric Halperin-like trial wavefunction gives a valid description of the ground state of the system

361

Switching off the reservoir through nonstationary quantum systems  

CERN Document Server

In this paper we demonstrate that the inevitable action of the environment can be substantially weakened when considering appropriate nonstationary quantum systems. Beyond protecting quantum states against decoherence, an oscillating frequency can be engineered to make the system-reservoir coupling almost negligible. Therefore, differently from previously-reported protecting schemes, our technique does not require a previous knowledge of the state to be protected. We show, in the domain of cavity quantum electrodynamics, how to engineer such a nonstationary cavity mode through its dispersive interaction with a driven two-level atom.

C'eleri, L C; Moussa, M H Y; Villas-Bôas, C J

2006-01-01

362

Emergent quantum jumps in a nano-electro-mechanical system  

International Nuclear Information System (INIS)

We describe a nano-electro-mechanical system that exhibits the 'retroactive' quantum jumps discovered by Mabuchi and Wiseman (1998 Phys. Rev. Lett. 81 4620). This system consists of a Cooper-pair box coupled to a nano-mechanical resonator, in which the latter is continuously monitored by a single-electron transistor or quantum point contact. Further, we show that these kinds of jumps, and the jumps that emerge in a continuous quantum non-demolition measurement, are one and the same phenomena. We also consider manipulating the jumps by applying feedback control to the Cooper-pair box. (fast track communication)

363

Quantum revivals and carpets in some exactly solvable systems  

CERN Document Server

We consider the revival properties of quantum systems with an eigenspectrum E_{n} ~ n^{2}, and compare them with the simplest member of this class - the infinite square well. In addition to having perfect revivals at integer multiples of the revival time t_{R}, these systems all enjoy perfect fractional revivals at quarterly intervals of t_{R}. A closer examination of the quantum evolution is performed for the Scarf potentials, and comparison is made with the infinite square well using quantum carpets.

Loinaz, W; Loinaz, Will

1999-01-01

364

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)

365

Plausibility of quantum coherent states in biological systems  

Energy Technology Data Exchange (ETDEWEB)

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 [Institut de Mineralogie et de Physique des Milieux Condenses, Universite Pierre et Marie Curie-Paris 6, CNRS UMR7590 (France); Tuszynski, J [Department of Experimental Oncology, Cross Cancer Institute, 11560 University Avenue Edmonton, AB T6G 1Z2 (Canada); Rahnama, M [Department of Physics, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Bernroider, G, E-mail: vahid.salari@impmc.upmc.fr [Department of Organismic Biology, University of Salzburg, Hellbrunnerstrasse 34, Salzburg (Austria)

2011-07-08

366

Invisibility of quantum systems to tunneling of matter waves  

CERN Document Server

We show that an appropriate choice of the potential parameters in one-dimensional quantum systems allows for unity transmission of the tunneling particle at all incident tunneling energies, except at controllable exceedingly small incident energies. The corresponding dwell time and the transmission amplitude are indistinguishable from those of a free particle in the unity-transmission regime. This implies the possibility of designing quantum systems that are invisible to tunneling by a passing wave packet.

Cordero, Sergio

2009-01-01

367

Invisibility of quantum systems to tunneling of matter waves  

International Nuclear Information System (INIS)

We show that an appropriate choice of the potential parameters in one-dimensional quantum systems allows for unity transmission of the tunneling particle at all incident tunneling energies, except at controllable exceedingly small incident energies. The corresponding dwell time and the transmission amplitude are indistinguishable from those of a free particle in the unity-transmission regime. This implies the possibility of designing quantum systems that are invisible to tunneling by a passing wave packet.

368

QUANTUM ESTIMATION DISCRIMINATION IN CONTINUOUS VARIABLE AND FERMIONIC SYSTEMS  

OpenAIRE

In this PhD thesis we address the problem of characterizing quantum states and parameters of systems that are of particular interest for quantum technologies. In the first part we consider continuous variable systems and in particular Gaussian states; we address the estimation of quantities characterizing single-mode Gaussian states as the displacement and squeezing parameter and we study the improvement in the parameter estimation by introducing a Kerr nonlinearity. Moreover, we address the ...

Invernizzi, Carmen

2011-01-01

369

Plausibility of quantum coherent states in biological systems  

Science.gov (United States)

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.; Tuszynski, J.; Rahnama, M.; Bernroider, G.

2011-07-01

370

Plausibility of quantum coherent states in biological systems  

International Nuclear Information System (INIS)

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.

371

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

International Nuclear Information System (INIS)

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.

372

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

373

Quantum Geometric Tensor (Fubini-Study Metric) in Simple Quantum System: A pedagogical Introduction  

CERN Document Server

Geometric Quantum Mechanics is a novel and prospecting approach motivated by the belief that our world is ultimately geometrical. At the heart of that is a quantity called Quantum Geometric Tensor (or Fubini-Study metric), which is a complex tensor with the real part serving as the Riemannian metric that measures the `quantum distance', and the imaginary part being the Berry curvature. Following a physical introduction of the basic formalism, we illustrate its physical significance in both the adiabatic and non-adiabatic systems.

Cheng, Ran

2010-01-01

374

Spin-Excitation-Instability-Induced Quantum Phase Transitions in Double-Layer Quantum Hall Systems  

Science.gov (United States)

We study intersubband spin density collective modes in double-layer quantum Hall systems at ? = 2 within the time-dependent Hartree-Fock approximation. We find that these intersubband spin density excitations may soften under experimentally accessible conditions, signaling a phase transition to a new quantum Hall state with interlayer inplane antiferromagnetic spin correlations. We show that this novel canted antiferromagnetic phase is energetically stable and that the phase transition is continuous.

Zheng, Lian; Radtke, R. J.; Das Sarma, S.

1997-03-01

375

Theory and simulation of cavity quantum electro-dynamics in multi-partite quantum complex systems  

International Nuclear Information System (INIS)

The cavity quantum electrodynamics of various complex systems is here analyzed using a general versatile code developed in this research. Such quantum multi-partite systems normally consist of an arbitrary number of quantum dots in interaction with an arbitrary number of cavity modes. As an example, a nine-partition system is simulated under different coupling regimes, consisting of eight emitters interacting with one cavity mode. Two-level emitters (e.g. quantum dots) are assumed to have an arrangement in the form of a linear chain, defining the mutual dipole-dipole interactions. It was observed that plotting the system trajectory in the phase space reveals a chaotic behavior in the so-called ultrastrong-coupling regime. This result is mathematically confirmed by detailed calculation of the Kolmogorov entropy, as a measure of chaotic behavior. In order to study the computational complexity of our code, various multi-partite systems consisting of one to eight quantum dots in interaction with one cavity mode were solved individually. Computation run times and the allocated memory for each system were measured. (orig.)

376

Coherent versus Measurement Feedback: Linear Systems Theory for Quantum Information  

Science.gov (United States)

To control a quantum system via feedback, we generally have two options in choosing a control scheme. One is the coherent feedback, which feeds the output field of the system, through a fully quantum device, back to manipulate the system without involving any measurement process. The other one is measurement-based feedback, which measures the output field and performs a real-time manipulation on the system based on the measurement results. Both schemes have advantages and disadvantages, depending on the system and the control goal; hence, their comparison in several situations is important. This paper considers a general open linear quantum system with the following specific control goals: backaction evasion, generation of a quantum nondemolished variable, and generation of a decoherence-free subsystem, all of which have important roles in quantum information science. Some no-go theorems are proven, clarifying that those goals cannot be achieved by any measurement-based feedback control. On the other hand, it is shown that, for each control goal there exists a coherent feedback controller accomplishing the task. The key idea to obtain all the results is system theoretic characterizations of the above three notions in terms of controllability and observability properties or transfer functions of linear systems, which are consistent with their standard definitions.

Yamamoto, Naoki

2014-10-01

377

Open quantum system of two coupled harmonic oscillators  

International Nuclear Information System (INIS)

On the basis of the Lindblad theory for open quantum systems master equations for a system consisting of two harmonic oscillators are derived. The time dependence of expectation values, Wigner function and Weyl operator are obtained and discussed. The chosen system can be applied for the description of the charge and mass asymmetry degrees of freedom in deep inelastic collisions in nuclear physics

378

A new perspectives in nonrelativistic quantum mechanics. Quantum-field properties of many-partic systems  

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 firshe 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

379

The entropy power inequality for quantum systems  

CERN Document Server

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

380

Quantum algorithm for simulating the dynamics of an open quantum system  

International Nuclear Information System (INIS)

In the study of open quantum systems, one typically obtains the decoherence dynamics by solving a master equation. The master equation is derived using knowledge of some basic properties of the system, the environment, and their interaction: One basically needs to know the operators through which the system couples to the environment and the spectral density of the environment. For a large system, it could become prohibitively difficult to even write down the appropriate master equation, let alone solve it on a classical computer. In this paper, we present a quantum algorithm for simulating the dynamics of an open quantum system. On a quantum computer, the environment can be simulated using ancilla qubits with properly chosen single-qubit frequencies and with properly designed coupling to the system qubits. The parameters used in the simulation are easily derived from the parameters of the system + environment Hamiltonian. The algorithm is designed to simulate Markovian dynamics, but it can also be used to simulate non-Markovian dynamics provided that this dynamics can be obtained by embedding the system of interest into a larger system that obeys Markovian dynamics. We estimate the resource requirements for the algorithm. In particular, we show that for sufficiently slow decoherence a single ancilla qubit could be sufficient to represent the entire environment, in principle.

381

Atomic quantum systems in optical micro-structures  

International Nuclear Information System (INIS)

Full text: We combine state-of-the-art technology in micro-optics with the quantum optical techniques of laser cooling, laser trapping, and quantum control to open a new gateway for quantum information processing and matter wave optics with atomic systems. We use micro-fabricated optical systems to create light fields that allow us to trap and guide neutral atoms as a result of the optical dipole force experienced by the atoms. The realization of arrays of laser traps that can serve as registers for atomic quantum bits and as integrated waveguide structures for atom optics and atom interferometry has been achieved. This approach opens the possibility to scale, parallelize, and miniaturize systems for quantum information processing and atom optics. Currently we investigate the production of quantum-degenerate systems in pure optical trapping geometries and the coherent manipulation (1-qubit rotations, Ramsey-oscillations, spin-echo experiments) of internal qubit states for atoms trapped in arrays of dipole traps (author)

382

Quantum Magnets and Matrix Lorenz Systems  

Science.gov (United States)

The Landau-Lifshitz-Gilbert equations for the evolution of the magnetization, in presence of an external torque, can be cast in the form of the Lorenz equations and, thus, can describe chaotic fluctuations. To study quantum effects, we describe the magnetization by matrices, that take values in a Lie algebra. The finite dimensionality of the representation encodes the quantum fluctuations, while the non-linear nature of the equations can describe chaotic fluctuations. We identify a criterion, for the appearance of such non-linear terms. This depends on whether an invariant, symmetric tensor of the algebra can vanish or not. This proposal is studied in detail for the fundamental representation of u(2) = u(1) × su(2). We find a knotted structure for the attractor, a bimodal distribution for the largest Lyapunov exponent and that the dynamics takes place within the Cartan subalgebra, that does not contain only the identity matrix, thereby can describe the quantum fluctuations.

Tranchida, J.; Thibaudeau, P.; Nicolis, S.

2015-01-01

383

Deterministic constant-temperature dynamics for dissipative quantum systems  

CERN Document Server

A novel method is introduced in order to treat the dissipative dynamics of quantum systems interacting with a bath of classical degrees of freedom. The method is based upon an extension of the Nos\\`e-Hoover chain (constant temperature) dynamics to quantum-classical systems. Both adiabatic and nonadiabatic numerical calculations on the relaxation dynamics of the spin-boson model show that the quantum-classical Nos\\`e-Hoover chain dynamics represents the thermal noise of the bath in an accurate and simple way. Numerical comparisons, both with the ``exact'' constant energy calculation and with the quantum-classical Brownian motion treatment of the bath, show that the quantum-classical Nos\\`e-Hoover Chain dynamics can be used to introduce dissipation in the evolution of a quantum subsystem even with just one degree of freedom for the bath. The algorithm can be computationally advantageous in modeling, within computer simulation, the dynamics of a quantum subsystem interacting with complex molecular environments.

Sergi, A

2007-01-01

384

Effects of symmetry breaking in finite quantum systems  

CERN Document Server

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

385

Theoretical modelling of quantum circuit systems Superconductivity; Superconductors  

CERN Document Server

The work in this thesis concentrates on the interactions between circuit systems operating in the quantum regime. The main thrust of this work involves the use of a new model for investigating the way in which different components in such systems behave when coupled together. This is achieved by utilising the matrix representation of quantum mechanics, in conjunction with a number of other theoretical techniques (such as Wigner functions and entanglement entropies). With these tools in place it then becomes possible to investigate and review different quantum circuit systems. These investigations cover systems ranging from simple electromagnetic (cm) field oscillators in isolation to coupled SQUID rings in more sophisticated multi-component arrangements. Primarily, we look at the way SQUID rings couple to em fields, and how the ring-field interaction can be mediated by the choice of external flux, PHI sub x , applied to the SQUID ring. A lot of interest is focused on the transfer of energy between the system ...

Stiffell, P B

2002-01-01

386

Heat-exchange statistics in driven open quantum systems  

Science.gov (United States)

As the dimensions of physical systems approach the nanoscale, the laws of thermodynamics must be reconsidered due to the increased importance of fluctuations and quantum effects. While the statistical mechanics of small classical systems is relatively well understood, the quantum case still poses challenges. Here, we set up a formalism that allows us to calculate the full probability distribution of energy exchanges between a periodically driven quantum system and a thermalized heat reservoir. The formalism combines Floquet theory with a generalized master equation approach. For a driven two-level system and in the long-time limit, we obtain a universal expression for the distribution, providing clear physical insight into the exchanged energy quanta. We illustrate our approach in two analytically solvable cases and discuss the differences in the corresponding distributions. Our predictions could be directly tested in a variety of systems, including optical cavities and solid-state devices.

Gasparinetti, S.; Solinas, P.; Braggio, A.; Sassetti, M.

2014-11-01

387

Deconstructing non-Dirac-Hermitian supersymmetric quantum systems  

International Nuclear Information System (INIS)

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.

388

Evaluation of Abbott Quantum II yeast identification system.  

OpenAIRE

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

389

Quantum information transfer between topological and spin qubit systems  

Energy Technology Data Exchange (ETDEWEB)

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.

Leijnse, Martin; Flensberg, Karsten [Nano-Science Center and Niels Bohr Institute, University of Copenhagen (Denmark)

2012-07-01

390

Quantum information transfer between topological and spin qubit systems  

CERN Document Server

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

391

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.

392

Time-resolved electron transport in quantum-dot systems  

International Nuclear Information System (INIS)

In this thesis the time-resolved electron transport in quantum dot systems was studied. For this two different formalisms were presented: The nonequilibrium Green functions and the generalized quantum master equations. For both formalisms a propagation method for the numerical calculation of time-resolved expectation values, like the occupation and the electron current, was developed. For the demonstration of the propagation method two different question formulations were considered. On the one hand the stochastically driven resonant-level model was studied. On the other hand the pulse-induced transport through a double quantum dot was considered.

393

Experimental quantum computing to solve systems of linear equations.  

Science.gov (United States)

Solving linear systems of equations is ubiquitous in all areas of science and engineering. With rapidly growing data sets, such a task can be intractable for classical computers, as the best known classical algorithms require a time proportional to the number of variables N. A recently proposed quantum algorithm shows that quantum computers could solve linear systems in a time scale of order log(N), giving an exponential speedup over classical computers. Here we realize the simplest instance of this algorithm, solving 2×2 linear equations for various input vectors on a quantum computer. We use four quantum bits and four controlled logic gates to implement every subroutine required, demonstrating the working principle of this algorithm. PMID:25167475

Cai, X-D; Weedbrook, C; Su, Z-E; Chen, M-C; Gu, Mile; Zhu, M-J; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

2013-06-01

394

Emulating a mesoscopic system using superconducting quantum circuits  

Science.gov (United States)

We demonstrate an emulation of a mesoscopic system using superconducting quantum circuits. Taking advantage of our ReZQu-architectured quantum processor, we controllably splitted a microwave photon and manipulated the splitted photons before they recombined for detection. In this way, we were able to simulate the weak localization effect in mesoscopic systems - a coherent backscattering process due to quantum interference. The influence of the phase coherence was investigated by tuning the coherence time of the quantum circuit, which in turn mimics the temperature effect on the weak localization process. At the end, we demonstrated an effect resembling universal conductance fluctuations, which arises from the frequency beating between different coherent backscattering processes. The universality of the observed fluctuation was shown as the independence of the fluctuation amplitude on detailed experimental conditions.

Chen, Yu; Barends, R.; Bochmann, J.; Campbell, B.; Chiaro, B.; Jeffrey, E.; Kelly, J.; Mariantoni, M.; Megrant, A.; Mutus, J.; Neill, C.; O'Malley, P.; Ohya, S.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Cleland, A. N.; Martinis, J. M.

2013-03-01

395

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.

396

Quantum coherence and entanglement control for atom-cavity systems  

Science.gov (United States)

Coherence and entanglement play a significant role in the quantum theory. Ideal quantum systems, "closed" to the outside world, remain quantum forever and thus manage to retain coherence and entanglement. Real quantum systems, however, are open to the environment and are therefore susceptible to the phenomenon of decoherence and disentanglement which are major hindrances to the effectiveness of quantum information processing tasks. In this thesis we have theoretically studied the evolution of coherence and entanglement in quantum systems coupled to various environments. We have also studied ways and means of controlling the decay of coherence and entanglement. We have studied the exact qubit entanglement dynamics of some interesting initial states coupled to a high-Q cavity containing zero photon, one photon, two photons and many photons respectively. We have found that an initially correlated environmental state can serve as an enhancer for entanglement decay or generation processes. More precisely, we have demonstrated that the degree of entanglement, including its collapse as well as its revival times, can be significantly modified by the correlated structure of the environmental modes. We have also studied dynamical decoupling (DD) technique --- a prominent strategy of controlling decoherence and preserving entanglement in open quantum systems. We have analyzed several DD control methods applied to qubit systems that can eliminate the system-environment coupling and prolong the quantum coherence time. Particularly, we have proposed a new DD sequence consisting a set of designed control operators that can universally protected an unknown qutrit state against colored phase and amplitude environment noises. In addition, in a non-Markovian regime, we have reformulated the quantum state diffusion (QSD) equation to incorporate the effect of the external control fields. Without any assumptions on the system-environment coupling and the size of environment, we have consistently solved the control dynamics of open quantum systems using this stochastic QSD approach. By implementing the QSD equation, our numerical results have revealed that how the control efficacy depends on the designed time points and shapes of the applied control pulses, and the environment memory time scale.

Shu, Wenchong

397

Kepler-16 Circumbinary System Validates Quantum Celestial Mechanics  

Directory of Open Access Journals (Sweden)

Full Text Available We report the application of quantum celestial mechanics (QCM to the Kepler-16 circumbinary system which has a single planet orbiting binary stars with the important system parameters known to within one percent. Other gravitationally bound systems such as the Solar System of planets and the Jovian satellite systems have large uncertainties in their total angular momentum. Therefore, Kepler-16 allows us for the ?rst time to determine whether the QCM predicted angular momentum per mass quantization isvalid.

Potter F.

2012-01-01

398

Quantum discord in spin systems with dipole-dipole interaction  

OpenAIRE

The behavior of total purely quantum correlation (discord) in dimers consisting of dipolar-coupled spins 1/2 is studied. We found that the discord Q=0 at the absolute zero temperature. With increasing the temperature $T$, at first the quantum correlations in the system increase, smoothly reach the maximum, and then turn again into zero according to the asymptotic law $T^{-2}$. It is also shown that in absence of external magnetic field $B$, the classical correlation $C$ at $...

Kuznetsova, E. I.; Yurishchev, M. A.

2013-01-01

399

Nuclear magnetometry studies of spin dynamics in quantum Hall systems  

Science.gov (United States)

We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of ?tot=2 . We found not only a rapid nuclear relaxation but also a sudden change in the nuclear-spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear-spin ensemble triggered by hyperfine interaction in quantum Hall system.

Fauzi, M. H.; Watanabe, S.; Hirayama, Y.

2014-12-01

400

Quantum information transfer between topological and spin qubit systems  

OpenAIRE

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 vic...

Leijnse, Martin; Flensberg, Karsten

2011-01-01

401

GRAVITATIONAL WAVES AND STATIONARY STATES OF QUANTUM AND CLASSICAL SYSTEMS  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, we consider gravitation theory in multidimensional space. The model of the metric satisfying the basic requirements of quantum theory is proposed. It is shown that gravitational waves are described by the Liouville equation and the Schrodinger equation as well. The solutions of the Einstein equations describing the stationary states of arbitrary quantum and classical systems with central symmetry have been obtained. Thus, it is proved that atoms and atomic nuclei can be represented as standing gravitational waves

Trunev A. P.

2014-03-01

402

Conductance distributions in disordered quantum spin-Hall systems  

OpenAIRE

We study numerically the charge conductance distributions of disordered quantum spin-Hall (QSH) systems using a quantum network model. We have found that the conductance distribution at the metal-QSH insulator transition is clearly different from that at the metal-ordinary insulator transition. Thus the critical conductance distribution is sensitive not only to the boundary condition but also to the presence of edge states in the adjacent insulating phase. We have also calcu...

Kobayashi, K.; Ohtsuki, T.; Obuse, H.; Slevin, K.

2010-01-01

403

Dynamics of complex quantum systems with energy dissipation  

OpenAIRE

A complex quantum system with energy dissipation is considered. The quantum Hamiltonians $H$ belong the complex Ginibre ensemble. The complex-valued eigenenergies $Z_{i}$ are random variables. The second differences $\\Delta^{1} Z_{i}$ are also complex-valued random variables. The second differences have their real and imaginary parts and also radii (moduli) and main arguments (angles). For $N$=3 dimensional Ginibre ensemble the distributions of above random variables are pro...

Duras, Maciej M.

2003-01-01

404

Hall Drag in Correlated Double Layer Quantum Hall Systems  

OpenAIRE

We show that in the limit of zero temperature, double layer quantum Hall systems exhibit a novel phenomena called Hall drag, namely a current driven in one layer induces a voltage drop in the other layer, in the direction perpendicular to the driving current. The two-by-two Hall resistivity tensor is quantized and proportional to the ${\\bf K}$ matrix that describes the topological order of the quantum Hall state, even when the ${\\bf K}$ matrix contains a zero eigenvalue, in ...

Yang, Kun

1998-01-01

405

Interaction of quantum Hall systems with waveguide elastic modes  

OpenAIRE

An interaction of non-uniform plane elastic modes of the waveguide type with monolayer and double-layer quantum Hall systems is considered. It is shown, that unlike the case of the surface acoustic wave propagation, the restriction on maximal values of the wave vectors for which the velocity shift can be observed experimentally does not take place for the waveguide modes. In case of study of incompressible fractional quantum Hall states the effect can be used for measuring a...

Fil, D. V.

1998-01-01

406

Improving quantum phase estimation via power-law potential systems  

Science.gov (United States)

Using the quantum Fisher information (QFI), we present an improved phase estimation scheme employing power-law potential (PLP) systems in comparison to NOON states under perfect and lossy conditions for a fixed mean photon number. The study is devoted to the phase estimation of the quantum states resulting from tightly binding, harmonic and loosely binding potentials for modest particle numbers. Finally, we discuss the saturation of the optimal phase uncertainty of this interferometric setting with parity detection.

Berrada, K.

2014-06-01

407

The Signals and Systems Approach to Quantum Computation  

CERN Document Server

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 G; Padma, R; Sharatchandra, H S

2003-01-01

408

Anti-holomorphic scaling in the quantum Hall system  

International Nuclear Information System (INIS)

We point out that scaling data strongly suggest that the zeros of the beta-function for the quantum Hall system are effectively anti-holomorphic. All scaling data, both experimental and numerical, are accounted for if the quantum Hall conductivities scale as the unique anti-holomorphic function automorphic under the complexified duality group ?0(2). The RG-potential (C-function) near criticality is then known, and this universal scaling form has a simple geometrical interpretation

409

Anti-holomorphic scaling in the quantum Hall system  

Energy Technology Data Exchange (ETDEWEB)

We point out that scaling data strongly suggest that the zeros of the beta-function for the quantum Hall system are effectively anti-holomorphic. All scaling data, both experimental and numerical, are accounted for if the quantum Hall conductivities scale as the unique anti-holomorphic function automorphic under the complexified duality group {gamma}{sub 0}(2). The RG-potential (C-function) near criticality is then known, and this universal scaling form has a simple geometrical interpretation.

Luetken, C.A. [Rudolf Peierls Centre for Theoretical Physics, Department of Physics, University of Oxford (United Kingdom) and Jesus College, Oxford (United Kingdom)]. E-mail: lutken@fys.uio.no; Ross, G.G. [Rudolf Peierls Centre for Theoretical Physics, Department of Physics, University of Oxford (United Kingdom)

2006-08-14

410

Thermodynamics of dissipative quantum systems by effective potential  

OpenAIRE

Classical-like formulas are given in order to evaluate thermal averages of observables belonging to a quantum nonlinear system with dissipation described by the Caldeira-Leggett model [Phys. Rev. Lett. 46, 211 (1981); Ann. Phys. (N.Y.) 149, 374 (1983)]. The underlying scheme is the pure-quantum self-consistent harmonic approximation, which leads to expressions with a Boltzmann factor involving an effective potential and with a Gaussian average. The latter describes the effec...

Cuccoli, Alessandro; Rossi, Andrea; Tognetti, Valerio; Vaia, Ruggero

1997-01-01

411

Quantum bio-nanosensors based on quantum dot-metallic nanoparticle systems  

Science.gov (United States)

When metallic nanoparticles are put in the vicinity of semiconductor quantum dots and driven by a coherent light source, their intrinsic plasmonic fields can be replaced with a new type of fields (coherent-plasmonic fields). These fields are generated via coherent coupling of excitons in quantum dots and localized surface plasmon resonances (LSPRs). We show the coherent-plasmonic field of a metallic nanoparticle can lead to a significantly larger field enhancement than that caused by its LSPR. Utilizing this, we investigate how such a coherent field enhancement can improve the sensitivities plasmonic nanosensors for detection single biological molecules. The results demonstrate application of quantum coherence in quantum dot-metallic nanoparticle systems for chemical and biological sensing applications.

Sadeghi, S. M.

2013-03-01

412

Computational studies of quantum spin systems  

Science.gov (United States)

Quantum spin models are important for studying the magnetic behavior of strongly correlated electronic insulators. Specifically, the 2D S = 1/2 Heisenberg model closely captures the antiferromagnetic state of CuO2 layers of the high-Tc superconductor parent compounds at half band filling. Introducing competing interactions or disorder can drive quantum phase transitions to other new states. I use the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method and finite-size scaling to study the quantum critical points of two Heisenberg bilayers, each with intra- and inter-plane couplings J and J?. Tuning the inter- to intra-layer coupling constant ratio g = J? /J drives a quantum phase transition between the Neel ordered state and a quantum disordered state. I discuss the ground-state finite-size scaling properties of three different quantities and extract the critical value of the coupling ratio gc. The results improve gc by more than an order of magnitude over the previous best estimates. Upon doping with static non-magnetic impurities, (e.g., substituting Cu with Zn), the cuprate layer is driven through a percolation phase transition. While the static properties are described by 2D classical percolation, the dynamical properties are quantum mechanical. I use exact diagonalization to calculate the lowest excitation gap Delta and use SSE to study an upper bound for Delta obtained from sum rules. Scaling the gap distribution with the cluster length L, a dynamic exponent z ? 2Df is obtained, where Df is the fractal dimensionality of the percolating cluster. I present several arguments showing that the low-energy excitations are due to weakly coupled effective moments formed owing to local imbalance in sublattice occupation. Many interesting quantum spin models lead to negative signs in the importance weight used in QMC sampling, and thus this method cannot be used. Matrix product states (MPSs) and tensor product states (TPSs) have recently been proposed as good variational ansatze to circumvent the sign problem. I study the frustrated J1 -- J2 Heisenberg chain with periodic boundary conditions using variational QMC simulations based on MPSs. It is shown that the matrices can be optimized not just for the ground state, but also, simultaneously, for the lowest states in several different lattice and spin symmetry sectors. This is useful in, e.g., studies of quantum phase transitions associated with crossings of energy levels. In 2D, I present a method for contracting a square-lattice tensor network based on auxiliary tensors accomplishing successive truncations (renormalization) of 8-index tensors for 2 x 2 plaquettes into 4-index tensors. The scheme is variational, and thus the tensors can be optimized by minimizing the energy. Test results for the quantum phase transition of the transverse-field Ising model confirm that even the smallest possible tensors produce much better results than the simple product (mean-field) state.

Wang, Ling

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

414

Work extraction and thermodynamics for individual quantum systems  

Science.gov (United States)

Thermodynamics is traditionally concerned with systems comprised of a large number of particles. Here we present a framework for extending thermodynamics to individual quantum systems, including explicitly a thermal bath and work-storage device (essentially a ‘weight’ that can be raised or lowered). We prove that the second law of thermodynamics holds in our framework, and gives a simple protocol to extract the optimal amount of work from the system, equal to its change in free energy. Our results apply to any quantum system in an arbitrary initial state, in particular including non-equilibrium situations. The optimal protocol is essentially reversible, similar to classical Carnot cycles, and indeed, we show that it can be used to construct a quantum Carnot engine.

Skrzypczyk, Paul; Short, Anthony J.; Popescu, Sandu

2014-06-01

415

Quantum dynamics of bio-molecular systems in noisy environments  

CERN Document Server

We discuss three different aspects of the quantum dynamics of bio-molecular systems and more generally complex networks in the presence of strongly coupled environments. Firstly, we make a case for the systematic study of fundamental structural elements underlying the quantum dynamics of these systems, identify such elements and explore the resulting interplay of quantum dynamics and environmental decoherence. Secondly, we critically examine some existing approaches to the numerical description of system-environment interaction in the non-perturbative regime and present a promising new method that can overcome some limitations of existing methods. Thirdly, we present an approach towards deciding and quantifying the non-classicality of the action of the environment and the observed system-dynamics. We stress the relevance of these tools for strengthening the interplay between theoretical and experimental research in this field.

Plenio, M B

2012-01-01

416

Fluctuations of work in nearly adiabatically driven open quantum systems  

Science.gov (United States)

We extend the quantum jump method to nearly adiabatically driven open quantum systems in a way that allows for an accurate account of the external driving in the system-environment interaction. Using this framework, we construct the corresponding trajectory-dependent work performed on the system and derive the integral fluctuation theorem and the Jarzynski equality for nearly adiabatic driving. We show that such identities hold as long as the stochastic dynamics and work variable are consistently defined. We numerically study the emerging work statistics for a two-level quantum system and find that the conventional diabatic approximation is unable to capture some prominent features arising from driving, such as the continuity of the probability density of work. Our results reveal the necessity of using accurate expressions for the drive-dressed heat exchange in future experiments probing jump time distributions.

Suomela, S.; Salmilehto, J.; Savenko, I. G.; Ala-Nissila, T.; Möttönen, M.

2015-02-01

417

Theory and simulation of strong correlations in quantum Coulomb systems  

CERN Document Server

Strong correlations in quantum Coulomb systems (QCS) are attracting increasing interest in many fields ranging from dense plasmas and semiconductors to metal clusters and ultracold trapped ions. Examples are bound states in dense plasmas (atoms, molecules, clusters) and semiconductors (excitons, trions, biexcitons) or Coulomb crystals. We present first-principle simulation results of these systems including path integral Monte Carlo simulations of the equilibrium behaviour of dense hydrogen and electron-hole plasmas and molecular dynamics and quantum kinetic theory simulations of the nonequilibrium properties of QCS. Finally, we critically assess potential and limitations of the various methods in their application to Coulomb systems.

Bonitz, M; Filinov, A V; Golubnychiy, V O; Kremp, D; Gericke, D O; Murillo, M S; Filinov, V S; Fortov, V; Hoyer, W; Koch, S W

2003-01-01

418

An Online Banking System Based on Quantum Cryptography Communication  

Science.gov (United States)

In this paper, an online banking system has been built. Based on quantum cryptography communication, this system is proved unconditional secure. Two sets of GHZ states are applied, which can ensure the safety of purchase and payment, respectively. In another word, three trading participants in each triplet state group form an interdependent and interactive relationship. In the meantime, trading authorization and blind signature is introduced by means of controllable quantum teleportation. Thus, an effective monitor is practiced on the premise that the privacy of trading partners is guaranteed. If there is a dispute or deceptive behavior, the system will find out the deceiver immediately according to the relationship mentioned above.

Zhou, Ri-gui; Li, Wei; Huan, Tian-tian; Shen, Chen-yi; Li, Hai-sheng

2014-07-01

419

Numerical approaches to complex quantum, semiclassical and classical systems  

Energy Technology Data Exchange (ETDEWEB)

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.)

Schubert, Gerald

2008-11-03

420

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.)

421

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

CERN Document Server

Based on the quantum trajectory approach, we extend the Born-Oppenheimer (BO) approximation to open quantum systems where dissipation is in the Lindblad form. The BO approximation is applied in the non-jump trajectory and the validity condition is given. Compared with our previous study, the advantage of this extension is that we need not to extend the Hilbert space and in each trajectory, the system is a pure state if the initial state is pure. Two examples are taken to illustrate our method.

Huang, X L; Wang, L C; Yi, X X

2010-01-01

422

Josephson phenomena and quantum ferromagnetism in double-layer quantum Hall systems  

International Nuclear Information System (INIS)

We analyze an effective theory for double-layer quantum Hall systems whose effective Hamiltonian consists of a kinetic energy term for the Goldstone mode and a tunneling term for electrons. This system corresponds to the quantum ferromagnet theory recently proposed. It is shown that Josephson phenomena occur except for the Meissner effect. A detailed physical picture of the commensurate-incommensurate phase transition in the magnetic order is described on the analogy of superconductor Josephson junction. Plasmon excitations are analyzed in each phase

423

Josephson phenomena and quantum ferromagnetism in double-layer quantum Hall systems  

Science.gov (United States)

We analyze an effective theory for double-layer quantum Hall systems whose effective Hamiltonian consists of a kinetic energy term for the Goldstone mode and a tunneling term for electrons. This system corresponds to the quantum ferromagnet theory recently proposed. It is shown that Josephson phenomena occur except for the Meissner effect. A detailed physical picture of the commensurate-incommensurate phase transition in the magnetic order is described on the analogy of superconductor Josephson junction. Plasmon excitations are analyzed in each phase.

Ezawa, Z. F.

1995-04-01

424

Quantum state tomography and quantum logical operations in a three qubits NMR quadrupolar system  

CERN Document Server

In this work, we present an implementation of quantum logic gates and algorithms in a three effective qubits system, represented by a (I = 7/2) NMR quadrupolar nuclei. To implement these protocols we have used the strong modulating pulses (SMP). The various stages of each implementation were verified by quantum state tomography (QST). It is presented here the results for the computational base states, Toffolli logic gates, and Deutsch-Jozsa and Grover algorithms. Also, we discuss the di?culties and advantages of implementing such protocols using the SMP technique in quadrupolar systems.

Araujo-Ferreira, A G; Soares-Pinto, D O; deAzevedo, E R; Bonagamba, T J; Teles, J

2011-01-01

425

Shell phenomena in mesoscopic systems: from nuclei to quantum dots  

International Nuclear Information System (INIS)

The evolution of shape parameters and giant dipole and octupole resonances in rotating nuclei, the role of main classical orbits for deformed systems with octupole and hexadecapole deformations, the occurrence of magic numbers under a perpendicular magnetic field in small quantum dots are discussed from the point of view of the manifestation of shell effects in a finite Fermi system. (author)

426

GRAVITATIONAL WAVES AND EMERGENCE PARAMETER OF CLASSICAL AND QUANTUM SYSTEMS  

Directory of Open Access Journals (Sweden)

Full Text Available It was established that the Fermi-Dirac statistics, Bose-Einstein and Maxwell-Boltzmann distribution can be described by a single equation, which follows from Einstein's equations for systems with central symmetry. Emergence parameter of classical and quantum systems composed by the rays of gravitational waves interacting with gravitational field of the universe has been computed

Trunev A. P.

2014-03-01

427

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)

428

Dissipation and entropy production in open quantum systems  

International Nuclear Information System (INIS)

A microscopic description of an open system is generally expressed by the Hamiltonian of the form: Htot = Hsys + Henviron + Hsys-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 Hsys-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 Hsys-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.

429

Coherent states of non-Hermitian quantum systems  

International Nuclear Information System (INIS)

We use the Gazeau-Klauder formalism to construct coherent states of non-Hermitian quantum systems. In particular we use this formalism to construct coherent state of a PT symmetric system. We also describe the construction of coherent states following Klauder's minimal prescription

430

Stochastic resonance in a double quantum dot system.  

Science.gov (United States)

Stochastic resonance (SR) is theoretically investigated for a double quantum dot system represented by two discrete levels in respective wells. The system is driven by a periodic signal and a white noise source with variable amplitude, and thus displays an improved output signal-to-noise ratio, a characteristic signature of SR. PMID:18351970

Joshi, Amitabh

2008-02-01

431

The intensity correlation function of "blinking" quantum systems  

OpenAIRE

Explicit expressions are determined for the photon correlation function of ``blinking'' quantum systems, i.e. systems with different types of fluorescent periods. These expressions can be used for a fit to experimental data and for obtaining system parameters therefrom. For two dipole-dipole interacting $V$ systems the dependence on the dipole coupling constant is explicitly given and shown to be particularly pronounced if the strong driving is reduced. We propose to use thi...

Hegerfeldt, Gerhard C.; Seidel, Dirk

2002-01-01

432

Analysis of Lyapunov Control for Hamiltonian Quantum Systems  

OpenAIRE

We present detailed analysis of the convergence properties and effectiveness of Lyapunov control design for bilinear Hamiltonian quantum systems based on the application of LaSalle's invariance principle and stability analysis from dynamical systems and control theory. For a certain class of Hamiltonians, strong convergence results can be obtained for both pure and mixed state systems. The control Hamiltonians for realistic physical systems, however, generally do not fall in...

Wang, Xiaoting; Schirmer, Sonia

2008-01-01

433

The power of quantum systems on a line  

CERN Document Server

We study the computational strength of quantum particles (each of finite dimensionality) arranged on a line. First, we prove that it is possible to perform universal adiabatic quantum computation using a one-dimensional quantum system (with 9 states per particle). This might have practical implications for experimentalists interested in constructing an adiabatic quantum computer. Building on the same construction, but with some additional technical effort and 12 states per particle, we show that the problem of approximating the ground state energy of a system composed of a line of quantum particles is QMA-complete; QMA is a quantum analogue of NP. This is in striking contrast to the fact that the analogous classical problem, namely, one dimensional MAX-2-SAT with nearest neighbor constraints, is in P. The proof of the QMA-completeness result requires an additional idea beyond the usual techniques in the area: Not all illegal configurations can be ruled out by local checks, so instead we rule out such illegal ...

Aharonov, Dorit; Kempe, Julia

2007-01-01

434

Quantum chaos and dissipation in nuclear systems  

International Nuclear Information System (INIS)

The order-to-chaos transition is studied within a schematic model which is defined by the sum of a regular hamiltonian HO and a random part ?V with strength ? and V a member of the gaussian othogonal ensemble. In the non-chaotic regime (strength ? ? = ?/?? (spreading width ?? = 2??2/D) until equilibrium is reached, (2) the absence of recurrence for physically relevant times, and hence the occurence of true dissipation also in large-amplitude collective motion and (3) the extreme sensitivity of the time evolution on small changes of HO. All these characteristics of quantum chaos are determined by the condition ?> or approx.2D or equivalently by ??/D> or approx.25. It is suggested to consider ??/? as the crucial parameter which determines quantum chaos in the same way as the Lyapunov exponent does for classical chaos. (orig.)

435

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.

436

Quantum computing with collective ensembles of multilevel systems.  

Science.gov (United States)

We propose a new physical approach for encoding and processing of quantum information in ensembles of multilevel quantum systems, where the different bits are not carried by individual particles but associated with the collective population of different internal levels. One- and two-bit gates are implemented by collective internal state transitions taking place in the presence of an excitation blockade mechanism, which restricts the population of each internal state to the values zero and unity. Quantum computers with 10-20 bits can be built via this scheme in single trapped clouds of ground state atoms subject to the Rydberg excitation blockade mechanism, and the linear dependence between register size and the number of internal quantum states in atoms offers realistic means to reach larger registers. PMID:18233562

Brion, E; Mølmer, K; Saffman, M

2007-12-31

437

Nonlinear dynamics and quantum entanglement in optomechanical systems.  

Science.gov (United States)

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

438

Communication theory of quantum systems. Ph.D. Thesis, 1970  

Science.gov (United States)

Communication theory problems incorporating quantum effects for optical-frequency applications are discussed. Under suitable conditions, a unique quantum channel model corresponding to a given classical space-time varying linear random channel is established. A procedure is described by which a proper density-operator representation applicable to any receiver configuration can be constructed directly from the channel output field. Some examples illustrating the application of our methods to the development of optical quantum channel representations are given. Optimizations of communication system performance under different criteria are considered. In particular, certain necessary and sufficient conditions on the optimal detector in M-ary quantum signal detection are derived. Some examples are presented. Parameter estimation and channel capacity are discussed briefly.

Yuen, H. P. H.

1971-01-01

439

Canted Antiferromagnetic Phase in Double-Layer Quantum Hall Systems  

Science.gov (United States)

We present a theoretical study on double-layer quantum Hall systems at ?=2 and show that, in addition to the usual spin-polarized state and the symmetric state quantum Hall phases, there exists a new quantum Hall phase with a canted antiferromagnetic spin correlation between the layers. The phase transition between the different quantum Hall states is continuous and is signaled by the softening of the collective intersubband spin-density-excitation. Because of the broken symmetry, the canted antiferromagnetic phase possesses a Goldstone mode in its excitation spectrum and has qualitatively different thermodynamic properties, including a finite temperature Kosterlitz-Thouless transition. Our predictions agree well with recent experiments. preprint1 preprint2

Zheng, Lian

1997-03-01

440

Bipartite quantum systems: on the realignment criterion and beyond  

International Nuclear Information System (INIS)

Inspired by the 'computable cross norm' or 'realignment' criterion, we propose a new point of view about the characterization of the states of bipartite quantum systems. We consider a Schmidt decomposition of a bipartite density operator. The corresponding Schmidt coefficients, or the associated symmetric polynomials, are regarded as quantities that can be used to characterize bipartite quantum states. In particular, starting from the realignment criterion, a family of necessary conditions for the separability of bipartite quantum states are derived. We conjecture that these conditions, which are weaker than the parent criterion, can be strengthened in such a way to obtain a new family of criteria that are independent of the original one. This conjecture is supported by numerical examples for the low dimensional cases. These ideas can be applied to the study of quantum channels, leading to a relation between the rate of contraction of a map and its ability to preserve entanglement

441

Bipartite quantum systems: on the realignment criterion and beyond  

CERN Document Server

Inspired by the computable cross norm, or realignment criterion, we present a new point of view about the characterization of the states of bipartite quantum systems. We consider the Schmidt decomposition of a bipartite density operator with respect of the Hilbert-Schmidt product. The corresponding Schmidt coefficients, or the associated symmetric polynomials, are discussed as functions that can be used to characterize bipartite quantum states. In particular, starting from the realignment criterion, a family of necessary conditions for the separability of bipartite quantum states is derived. We conjecture that these conditions, which are weaker than the parent criterion, can be extended to a new family of criteria which are independent of the original one. This is confirmed by numerical examples for the low dimensional cases. These ideas can as well be applied to the study of quantum channels, leading to a relation between the rate of contraction of a map and its ability to preserve entanglement.

Lupo, Cosmo; Scardicchio, Antonello

2008-01-01

442

RKKY interaction in a chirally coupled double quantum dot system  

International Nuclear Information System (INIS)

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

443

Ultraviolet analysis of one dimensional quantum systems  

OpenAIRE

Starting from the study of one-dimensional potentials in quantum mechanics having a small distance behavior described by a harmonic oscillator, we extend this way of analysis to models where such a behavior is not generally expected. In order to obtain significant results we approach the problem by a renormalization group method that can give a fixed point Hamiltonian that has the shape of a harmonic oscillator. In this way, good approximations are obtained for the ground st...

Frasca, Marco

2002-01-01

444

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.)

445

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

446

Efficient simulation of stochastically-driven quantum systems  

Science.gov (United States)

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

447

Adiabatic passage and ensemble control of quantum systems  

International Nuclear Information System (INIS)

This paper considers population transfer between eigenstates of a finite quantum ladder controlled by a classical electric field. Using an appropriate change of variables, we show that this setting can be set in the framework of adiabatic passage, which is known to facilitate ensemble control of quantum systems. Building on this insight, we present a mathematical proof of robustness for a control protocol-chirped pulse-practised by experimentalists to drive an ensemble of quantum systems from the ground state to the most excited state. We then propose new adiabatic control protocols using a single chirped and amplitude-shaped pulse, to robustly perform any permutation of eigenstate populations, on an ensemble of systems with unknown coupling strengths. These adiabatic control protocols are illustrated by simulations on a four-level ladder.

448

Controllable quantum information network with a superconducting system  

International Nuclear Information System (INIS)

We propose a controllable and scalable architecture for quantum information processing using a superconducting system network, which is composed of current-biased Josephson junctions (CBJJs) as tunable couplers between the two superconducting transmission line resonators (TLRs), each coupling to multiple superconducting qubits (SQs). We explicitly demonstrate that the entangled state, the phase gate, and the information transfer between any two selected SQs can be implemented, respectively. Lastly, numerical simulation shows that our scheme is robust against the decoherence of the system. -- Highlights: •An architecture for quantum information processing is proposed. •The quantum information transfer between any two selected SQs is implemented. •This proposal is robust against the decoherence of the system. •This architecture can be fabricated on a chip down to the micrometer scale

449

Engineered Open Systems and Quantum Simulations with Atoms and Ions  

CERN Document Server

The enormous experimental progress in atomic, molecular and optical (AMO) physics during the last decades allows us nowadays to isolate single, a few or even many-body ensembles of microscopic particles, and to manipulate their quantum properties at a level of precision, which still seemed unthinkable some years ago. This versatile set of tools has enabled the development of the well-established concept of engineering of many-body Hamiltonians in various physical platforms. These available tools, however, can also be harnessed to extend the scenario of Hamiltonian engineering to a more general Liouvillian setting, which in addition to coherent dynamics also includes controlled dissipation in many-body quantum systems. Here, we review recent theoretical and experimental progress in different directions along these lines, with a particular focus on physical realizations with systems of atoms and ions. This comprises digital quantum simulations in a general open system setting, as well as engineering and underst...

Müller, M; Pupillo, G; Zoller, P

2012-01-01

450

Controllable quantum information network with a superconducting system  

Energy Technology Data Exchange (ETDEWEB)

We propose a controllable and scalable architecture for quantum information processing using a superconducting system network, which is composed of current-biased Josephson junctions (CBJJs) as tunable couplers between the two superconducting transmission line resonators (TLRs), each coupling to multiple superconducting qubits (SQs). We explicitly demonstrate that the entangled state, the phase gate, and the information transfer between any two selected SQs can be implemented, respectively. Lastly, numerical simulation shows that our scheme is robust against the decoherence of the system. -- Highlights: •An architecture for quantum information processing is proposed. •The quantum information transfer between any two selected SQs is implemented. •This proposal is robust against the decoherence of the system. •This architecture can be fabricated on a chip down to the micrometer scale.

Zhang, Feng-yang, E-mail: zhangfy@mail.dlut.edu.cn [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Liu, Bao [Beijing Computational Science Research Center (CSRC), Beijing 100084 (China); Chen, Zi-hong [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Wu, Song-lin [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Song, He-shan [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

2014-07-15

451

Composite Quantum Systems and Environment-Induced Heating  

Science.gov (United States)

In recent years, much attention has been paid to the development of techniques which transfer trapped particles to very low temperatures. Here we focus our attention on a heating mechanism which contributes to the finite temperature limit in laser sideband cooling experiments with trapped ions. It is emphasized that similar heating processes might be present in a variety of composite quantum systems whose components couple individually to different environments. For example, quantum optical heating effects might contribute significantly to the very high temperatures which occur during the collapse phase in sonoluminescence experiments. It might even be possible to design composite quantum systems, like atom-cavity systems, such that they continuously emit photons even in the absence of external driving.

Beige, Almut; Kurcz, Andreas; Stokes, Adam

2011-09-01

452

Composite quantum systems and environment-induced heating  

CERN Document Server

In recent years, much attention has been paid to the development of techniques which transfer trapped particles to very low temperatures. Here we focus our attention on a heating mechanism which contributes to the finite temperature limit in laser sideband cooling experiments with trapped ions. It is emphasized that similar heating processes might be present in a variety of composite quantum systems whose components couple individually to different environments. For example, quantum optical heating effects might contribute significantly to the very high temperatures which occur during the collapse phase in sonoluminescence experiments. It might even be possible to design composite quantum systems, like atom-cavity systems, such that they continuously emit photons even in the absence of external driving.

Beige, Almut; Stokes, Adam

2011-01-01

453

Composite Quantum Systems and Environment-Induced Heating  

International Nuclear Information System (INIS)

In recent years, much attention has been paid to the development of techniques which transfer trapped particles to very low temperatures. Here we focus our attention on a heating mechanism which contributes to the finite temperature limit in laser sideband cooling experiments with trapped ions. It is emphasized that similar heating processes might be present in a variety of composite quantum systems whose components couple individually to different environments. For example, quantum optical heating effects might contribute significantly to the very high temperatures which occur during the collapse phase in sonoluminescence experiments. It might even be possible to design composite quantum systems, like atom-cavity systems, such that they continuously emit photons even in the absence of external driving.

454

Input-output Analysis of Quantum Finite-level Systems in Response to Single Photon States  

OpenAIRE

Single photon states, which carry quantum information and coherently interact with quantum systems, are vital to the realization of all-optical quantum networks and quantum memory. In this paper we derive the conditions that enable an exact analysis of the response of passive quantum finite-level systems under the weak driving of single photon input. We show that when a class of finite level systems is driven by single photon inputs, expressions for the output states may be ...

Pan, Yu; Zhang, Guofeng; James, Matthew R.

2014-01-01

455

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)

456

Correlations of neutral kaons - an open quantum system approach  

International Nuclear Information System (INIS)

Full text: I will present the quantum mechanical model of decaying particles based on the open quantum system approach. I will discuss the decay of a single neutral kaon. In our model the time evolution of the density matrix describing such a kaon is given by the appropriate Lindblad equation. The corresponding Lindblad operators are constructed explicitly in two cases - when we assume CP-invariance and without this assumption. The complete positivity of the time evolution is proved by the explicit construction of the corresponding Krauss operators. We use this results to calculate the correlation function in neutral kaon system. (author)

457

On the Supersymmetric Spectra of two Planar Integrable Quantum Systems  

CERN Document Server

Two planar supersymmetric quantum mechanical systems built around the quantum integrable Kepler/Coulomb and Euler/Coulomb problems are analyzed in depth. The supersymmetric spectra of both systems are unveiled, profiting from symmetry operators not related to invariance with respect to rotations. It is shown analytically how the first problem arises at the limit of zero distance between the centers of the second problem. It appears that the supersymmetric modified Euler/Coulomb problem is a quasi-isospectral deformation of the supersymmetric Kepler/Coulomb problem.

Leon, M A Gonzalez; Guilarte, J Mateos; Senosiain, M J

2011-01-01

458

CP_N Solitons in Quantum Hall Systems  

OpenAIRE

We will present here an elementary pedagogical introduction to $CP_N$ solitons in quantum Hall systems. We begin with a brief introduction to both $CP_N$ models and to quantum Hall (QH) physics. Then we focus on spin and layer-spin degrees of freedom in QH systems and point out that these are in fact $CP_N$ fields for N=1 and N=3. Excitations in these degrees of freedom will be shown to be topologically non-trivial soliton solutions of the corresponding $CP_N$ field equation...

Rajaraman, R.

2001-01-01

459

Semiclassical analysis of tunnelling splittings in periodically driven quantum systems  

International Nuclear Information System (INIS)

For periodically driven systems, quantum tunnelling between classical resonant stability islands in phase space separated by invariant KAM curves or chaotic regions manifests itself by oscillatory motion of wavepackets centred on such an island, by mulitplet splittings of the quasienergy spectrum, and by phase space localization of the quasienergy states on symmetry-related flux tubes. Qualitatively different types of classical resonant island formation - due to discrete symmetries of the system - and their quantum implications are analysed by a (uniform) semiclassical theory. The results are illustrated by a numerical study of a driven non-harmonic oscillator. (author)

460

Interaction of quantum Hall systems with waveguide elastic modes  

CERN Document Server

An interaction of non-uniform plane elastic modes of the waveguide type with monolayer and double-layer quantum Hall systems is considered. It is shown, that unlike the case of the surface acoustic wave propagation, the restriction on maximal values of the wave vectors for which the velocity shift can be observed experimentally does not take place for the waveguide modes. In case of study of incompressible fractional quantum Hall states the effect can be used for measuring a dependence of the effective magnetic length on the filling factor and for observing phase transitions in double-layer system under the interlayer distance variation

Fil, D V

1999-01-01