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1

Quantum Mechanics + Open Systems

Quantum Mechanics + Open Systems = Thermodynamics ? Jochen Gemmer TÂ¨ubingen, 09.02.2006 #12., World Scientific) #12;Fundamental Law or Emergent Description? Quantum Mechanics i t = (- 2 2m + V or Emergent Description? Quantum Mechanics i t = (- 2 2m + V ) "Heisenberg Cut" Classical Mechanics: m d2

Steinhoff, Heinz-JÃ¼rgen

2

Control of open quantum systems

This thesis describes the development, investigation and experimental implementation via liquid state nuclear magnetic resonance techniques of new methods for controlling open quantum systems. First, methods that improve ...

Boulant, Nicolas

2005-01-01

3

Perturbative approach to Markovian open quantum systems

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

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

2014-01-01

4

Repeated interactions in open quantum systems

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.

Bruneau, Laurent, E-mail: laurent.bruneau@u-cergy.fr [Laboratoire AGM, Université de Cergy-Pontoise, Site Saint-Martin, BP 222, 95302 Cergy-Pontoise (France); Joye, Alain, E-mail: Alain.Joye@ujf-grenoble.fr [Institut Fourier, UMR 5582, CNRS-Université Grenoble I, BP 74, 38402 Saint-Martin d’Hères (France); Merkli, Marco, E-mail: merkli@mun.ca [Department of Mathematics and Statistics Memorial University of Newfoundland, St. John's, NL Canada A1C 5S7 (Canada)

2014-07-15

5

Quantum trajectories and open many-body quantum systems

The study of open quantum systems has become increasingly important in the past years, as the ability to control quantum coherence on a single particle level has been developed in a wide variety of physical systems. In quantum optics, the study of open systems goes well beyond understanding the breakdown of quantum coherence. There, the coupling to the environment is sufficiently well understood that it can be manipulated to drive the system into desired quantum states, or to project the system onto known states via feedback in quantum measurements. Many mathematical frameworks have been developed to describe such systems, which for atomic, molecular, and optical (AMO) systems generally provide a very accurate description of the open quantum system on a microscopic level. In recent years, AMO systems including cold atomic and molecular gases and trapped ions have been applied heavily to the study of many-body physics, and it has become important to extend previous understanding of open system dynamics in single- and few-body systems to this many-body context. A key formalism that has already proven very useful in this context is the quantum trajectories technique. This was developed as a numerical tool for studying dynamics in open quantum systems, and falls within a broader framework of continuous measurement theory as a way to understand the dynamics of large classes of open quantum systems. We review the progress that has been made in studying open many-body systems in the AMO context, focussing on the application of ideas from quantum optics, and on the implementation and applications of quantum trajectories methods. Control over dissipative processes promises many further tools to prepare interesting and important states in strongly interacting systems, including the realisation of parameter regimes in quantum simulators that are inaccessible via current techniques.

Andrew J. Daley

2014-05-26

6

Universal simulation of Markovian open quantum systems

We consider the problem of constructing a "universal set" of Markovian processes, such that any Markovian open quantum system, described by a one-parameter semigroup of quantum channels, can be simulated through sequential simulations of processes from the universal set. In particular, for quantum systems of dimension $d$, we explicitly construct a universal set of semigroup generators, parametrized by $d^2-3$ continuous parameters, such that in order to simulate the dynamics of an arbitrary $d$ dimensional Markovian quantum system it is necessary and sufficient to be able to implement unitary operations on the system, and quantum channels from the semigroups generated by elements of the universal set of generators. Furthermore, assuming the ability to implement operations from the universal set, we provide an explicit algorithm for the efficient simulation of Markovian open quantum systems for which the number of distinct Lindblad operators scales polynomially with respect to the number of subsystems.

Ryan Sweke; Ilya Sinayskiy; Denis Bernard; Francesco Petruccione

2015-04-07

7

Superadiabatic dynamics in open quantum systems

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

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

2014-05-08

8

Feynman's Clock for open quantum systems

We show that Feynman's Clock construction, in which the time-evolution of a closed quantum system is encoded as a ground state problem, can be extended to open quantum systems. In our formalism, the ground states of an ensemble of non-Hermitian Feynman Clock Hamiltonians yield stochastic trajectories, which unravel the evolution of a Lindblad master equation. In this way, one can use Feynman's Clock not only to simulate the evolution of a quantum system, but also it's interaction with an environment such as a heat bath or measuring apparatus. A simple numerical example of a two-level atom undergoing spontaneous emission is presented and analyzed.

David G. Tempel; Alan Aspuru-Guzik

2014-06-21

9

Open quantum systems with loss and gain

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.

Hichem Eleuch; Ingrid Rotter

2014-09-09

10

Frustration of Decoherence in Open Quantum Systems

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 analytic and numerical renormalization group methods and obtain expressions for the frequency and temperature dependence of the impurity susceptibility in different regimes.

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

2005-02-18

11

Quantum Entanglement and Quantum Discord in Gaussian Open Systems

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two noninteracting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the temperature of the thermal reservoir, an initial separable Gaussian state remains separable for all times. In the case of an entangled initial Gaussian state, entanglement suppression (entanglement sudden death) takes place for non-zero temperatures of the environment. Only for a zero temperature of the thermal bath the initial entangled state remains entangled for finite times. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that quantum discord decays asymptotically in time under the effect of the thermal bath.

Isar, Aurelian [National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, P.O. Box MG-6 (Romania)

2011-10-03

12

Open quantum systems and random matrix theory

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 ?{sub 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 ?{sub 3}(L) statistic exhibit the signatures of missed levels.

Mulhall, Declan [Department of Physics/Engineering, University of Scranton, Scranton, Pennsylvania 18510-4642 (United States)

2014-10-15

13

Open quantum systems and Random Matrix Theory

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

Declan Mulhall

2015-01-09

14

Open quantum systems and error correction

NASA Astrophysics Data System (ADS)

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

15

Periodically driven quantum open systems: Tutorial

We present a short derivation and discussion of the master equation for an open quantum system weakly coupled to a heat bath and then its generalization to the case of with periodic external driving based on the Floquet theory. Further, a single heat bath is replaced by several ones. We present also the definition of heat currents which satisfies the second law of thermodynamics and apply the general results to a simple model of periodically modulated qubit.

Robert Alicki; David Gelbwaser-Klimovsky; Gershon Kurizki

2012-05-21

16

Periodically driven quantum open systems: Tutorial

We present a short derivation and discussion of the master equation for an open quantum system weakly coupled to a heat bath and then its generalization to the case of with periodic external driving based on the Floquet theory. Further, a single heat bath is replaced by several ones. We present also the definition of heat currents which satisfies the second law of thermodynamics and apply the general results to a simple model of periodically modulated qubit.

Alicki, Robert; Kurizki, Gershon

2012-01-01

17

Complex Time Evolution of Open Quantum Systems

We combine, in a single set-up,the complex time parametrization in path integration, and the closed time formalism of non-equilibrium field theories to produce a compact representation of the time evolution of the reduced density matrix. In this framework we introduce a cluster-type expansion that facilitates perturbative and non-perturbative calculations in the realm of open quantum systems. The technical details of some very simple examples are discussed.

C. N. Gagatsos; A. I. Karanikas; G. I. Kordas

2011-04-19

18

Feshbach projection formalism for open quantum systems.

We provide a new approach to open quantum systems which is based on the Feshbach projection method. Instead of looking for a master equation for the dynamical map acting in the space of density operators we provide the corresponding equation for the evolution in the Hilbert space of the amplitude operators. Its solution enables one to construct a legitimate quantum evolution (completely positive and trace preserving). Our approach, contrary to the standard Nakajima-Zwanzig method, allows for a series of consistent approximations resulting in a legitimate quantum evolution. The new scheme is illustrated by the well-known spin-boson model beyond the rotating wave approximation. It is shown that the presence of counterrotating terms dramatically changes the asymptotic evolution of the system. PMID:23952370

Chru?ci?ski, Dariusz; Kossakowski, Andrzej

2013-08-01

19

Relativistic Quantum Metrology in Open System Dynamics

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. PMID:25609187

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

2015-01-01

20

Quantum response of dephasing open systems

NASA Astrophysics Data System (ADS)

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

Avron, J. E.; Fraas, M.; Graf, G. M.; Kenneth, O.

2011-05-01

21

Quantum and statistical mechanics in open systems: theory and examples

NASA Astrophysics Data System (ADS)

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

2009-08-01

22

Models and Feedback Stabilization of Open Quantum Systems

At the quantum level, feedback-loops have to take into account measurement back-action. We present here the structure of the Markovian models including such back-action and sketch two stabilization methods: measurement-based feedback where an open quantum system is stabilized by a classical controller; coherent or autonomous feedback where a quantum system is stabilized by a quantum controller with decoherence (reservoir engineering). We begin to explain these models and methods for the photon box experiments realized in the group of Serge Haroche (Nobel Prize 2012). We present then these models and methods for general open quantum systems.

Pierre Rouchon

2015-01-08

23

Conserved current in Markovian open-quantum systems

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

Bodor, Andras; Diosi, Lajos [Department of the Physics of Complex Systems, Eoetvoes University, H-1117 Budapest (Hungary); Research Institute for Particle and Nuclear Physics, H-1525 Budapest 114, P.O. Box 49 (Hungary)

2006-06-15

24

Continuous Measurement of a Non-Markovian Open Quantum System

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

25

Complete Positivity and Thermodynamics in a Driven Open Quantum System

NASA Astrophysics Data System (ADS)

While it is well known that complete positivity guarantees the fulfilment of the second law of thermodynamics, its possible violations have never been proposed as a check of the complete positivity of a given open quantum dynamics. We hereby consider an open quantum micro-circuit, effectively describable as a two-level open quantum system, whose asymptotic current might be experimentally accessible. This latter could indeed be used to discriminate between its possible non-completely positive Redfield dynamics and a completely positive one obtained by standard weak-coupling limit techniques, at the same time verifying the fate of the second law of thermodynamics in such a context.

Argentieri, Giuseppe; Benatti, Fabio; Floreanini, Roberto; Pezzutto, Marco

2015-02-01

26

Open quantum systems approach to atomtronics

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.

Pepino, R. A.; Cooper, J.; Meiser, D.; Anderson, D. Z.; Holland, M. J. [JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2010-07-15

27

Open systems dynamics for propagating quantum fields

NASA Astrophysics Data System (ADS)

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

28

Quantum Metrology in Open Systems: Dissipative Cramér-Rao Bound

NASA Astrophysics Data System (ADS)

Estimation of parameters is a pivotal task throughout science and technology. The quantum Cramér-Rao bound provides a fundamental limit of precision allowed to be achieved under quantum theory. For closed quantum systems, it has been shown how the estimation precision depends on the underlying dynamics. Here, we propose a general formulation for metrology scenarios in open quantum systems, aiming to relate the precision more directly to properties of the underlying dynamics. This feature may be employed to enhance an estimation precision, e.g., by quantum control techniques. Specifically, we derive a Cramér-Rao bound for a fairly large class of open system dynamics, which is governed by a (time-dependent) dynamical semigroup map. We illustrate the utility of this scenario through three examples.

Alipour, S.; Mehboudi, M.; Rezakhani, A. T.

2014-03-01

29

Quantum Metrology in Open Systems: Dissipative Cramér-Rao Bound

Estimation of parameters is a pivotal task throughout science and technology. Quantum Cram\\'{e}r-Rao bound provides a fundamental limit of precision allowed to achieve under quantum theory. For closed quantum systems, it has been shown how the estimation precision depends on the underlying dynamics. Here, we propose a general formulation for metrology scenarios in open quantum systems, aiming to relate the precision more directly to properties of the underlying dynamics. This feature may be employed to enhance an estimation precision, e.g., by quantum control techniques. Specifically, we derive a Cram\\'{e}r-Rao bound for a fairly large class of open system dynamics, which is governed by a (time-dependent) dynamical semi-group map. We illustrate the utility of this scenario through three examples.

S. Alipour; M. Mehboudi; A. T. Rezakhani

2014-03-31

30

Nonequilibrium-thermodynamics approach to open quantum systems

NASA Astrophysics Data System (ADS)

Open quantum systems are studied from the thermodynamical point of view unifying the principle of maximum informational entropy and the hypothesis of relaxation times hierarchy. The result of the unification is a non-Markovian and local-in-time master equation that provides a direct connection for dynamical and thermodynamical properties of open quantum systems. The power of the approach is illustrated by the application to the damped harmonic oscillator and the damped driven two-level system, resulting in analytical expressions for the non-Markovian and nonequilibrium entropy and inverse temperature.

Semin, Vitalii; Petruccione, Francesco

2014-11-01

31

Nonlocal Memory Effects in the Dynamics of Open Quantum Systems

NASA Astrophysics Data System (ADS)

We explore the possibility to generate nonlocal dynamical maps of an open quantum system through local system-environment interactions. Employing a generic decoherence process induced by a local interaction Hamiltonian, we show that initial correlations in a composite environment can lead to nonlocal open system dynamics which exhibit strong memory effects, although the local dynamics is Markovian. In a model of two entangled photons interacting with two dephasing environments, we find a direct connection between the degree of memory effects and the amount of correlation in the initial environmental state. The results demonstrate that, contrary to conventional wisdom, enlarging an open system can change the dynamics from Markovian to non-Markovian.

Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki; Li, Chuan-Feng; Guo, Guang-Can

2012-05-01

32

Adiabatic Charge Pumping in Open Quantum Systems JOSEPH E. AVRON

Adiabatic Charge Pumping in Open Quantum Systems JOSEPH E. AVRON Technion ALEXANDER ELGART Courant pumps con- nected to a number of external leads. It is proven that under the rather general assumption on the Hamiltonian describing the system, in the adiabatic limit, the current through the pump is given by a formula

Avron, Joseph

33

Ground-state Stabilization of Open Quantum Systems by Dissipation

Control by dissipation, or environment engineering, constitutes an important methodology within quantum coherent control which was proposed to improve the robustness and scalability of quantum control systems. The system-environment coupling, often considered to be detrimental to quantum coherence, also provides the means to steer the system to desired states. This paper aims to develop the theory for engineering of the dissipation, based on a ground-state Lyapunov stability analysis of open quantum systems via a Heisenberg-picture approach. Algebraic conditions concerning the ground-state stability and scalability of quantum systems are obtained. In particular, Lyapunov stability conditions expressed as operator inequalities allow a purely algebraic treatment of the environment engineering problem, which facilitates the integration of quantum components into a large-scale quantum system and draws an explicit connection to the classical theory of vector Lyapunov functions and decomposition-aggregation methods for control of complex systems. The implications of the results in relation to dissipative quantum computing and state engineering are also discussed in this paper.

Yu Pan; Valery Ugrinovskii; Matthew R. James

2015-02-19

34

Hidden Quantum Markov Models and Open Quantum Systems with Instantaneous Feedback

Hidden Markov Models are widely used in classical computer science to model stochastic processes with a wide range of applications. This paper concerns the quantum analogues of these machines --- so-called Hidden Quantum Markov Models (HQMMs). Using the properties of Quantum Physics, HQMMs are able to generate more complex random output sequences than their classical counterparts, even when using the same number of internal states. They are therefore expected to find applications as quantum simulators of stochastic processes. Here, we emphasise that open quantum systems with instantaneous feedback are examples of HQMMs, thereby identifying a novel application of quantum feedback control.

Lewis A. Clark; Wei Huang; Thomas M. Barlow; Almut Beige

2014-07-05

35

Control landscapes for observable preparation with open quantum systems

A quantum control landscape is defined as the observable as a function(al) of the system control variables. Such landscapes were introduced to provide a basis to understand the increasing number of successful experiments controlling quantum dynamics phenomena. This paper extends the concept to encompass the broader context of the environment having an influence. For the case that the open system dynamics are fully controllable, it is shown that the control landscape for open systems can be lifted to the analysis of an equivalent auxiliary landscape of a closed composite system that contains the environmental interactions. This inherent connection can be analyzed to provide relevant information about the topology of the original open system landscape. Application to the optimization of an observable expectation value reveals the same landscape simplicity observed in former studies on closed systems. In particular, no false suboptimal traps exist in the system control landscape when seeking to optimize an observable, even in the presence of complex environments. Moreover, a quantitative study of the control landscape of a system interacting with a thermal environment shows that the enhanced controllability attainable with open dynamics significantly broadens the range of the achievable observable values over the control landscape.

Wu Rebing; Pechen, Alexander; Rabitz, Herschel; Hsieh, Michael; Tsou, Benjamin [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

2008-02-15

36

Fluctuations of work in nearly adiabatically driven open quantum systems

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.

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

2015-03-27

37

Fluctuations of work in nearly adiabatically driven open quantum systems

NASA Astrophysics Data System (ADS)

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

38

Fluctuations of work in nearly adiabatically driven open quantum systems

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 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.

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

2014-11-18

39

A semiclassical theory of quantum noise in open chaotic systems

We consider the quantum evolution of classically chaotic systems in contact with surroundings. Based on $\\hbar$-scaling of an equation for time evolution of the Wigner's quasi-probability distribution function in presence of dissipation and thermal diffusion we derive a semiclassical equation for quantum fluctuations. This identifies an early regime of evolution dominated by fluctuations in the curvature of the potential due to classical chaos and dissipation. A stochastic treatment of this classical fluctuations leads us to a Fokker-Planck equation which is reminiscent of Kramers' equation for thermally activated processes. This reveals an interplay of three aspects of evolution of quantum noise in weakly dissipative open systems; the reversible Liouville flow, the irreversible chaotic diffusion which is characteristic of the system itself, and irreversible dissipation induced by the external reservoir. It has been demonstrated that in the dissipation-free case a competition between Liouville flow in the contracting direction of phase space and chaotic diffusion sets a critical width in the Wigner function for quantum fluctuations. We also show how the initial quantum noise gets amplified by classical chaos and ultimately equilibrated under the influence of dissipation. We establish that there exists a critical limit to the expansion of phase space. The limit is determined by chaotic diffusion and dissipation. Making use of appropriate quantum-classical correspondence we verify the semiclassical analysis by the fully quantum simulation in a chaotic quartic oscillator.

B. C. Bag; S. Chaudhuri; J. Ray Chaudhuri; D. S. Ray

1998-11-13

40

The Kitaev-Feynman clock for open quantum systems

NASA Astrophysics Data System (ADS)

We show that Kitaev's construction of Feynman's clock, in which the time-evolution of a closed quantum system is encoded as a ground state problem, can be extended to open quantum systems. In our formalism, the ground states of an ensemble of non-Hermitian Kitaev-Feynman clock Hamiltonians yield stochastic trajectories, which unravel the evolution of a Lindblad master equation. In this way, one can use the Kitaev-Feynman clock not only to simulate the evolution of a quantum system, but also its interaction with an environment such as a heat bath or measuring apparatus. A simple numerical example of a two-level atom undergoing spontaneous emission is presented and analyzed.

Tempel, David G.; Aspuru-Guzik, Alán

2014-11-01

41

Hierarchy of stochastic pure states for open quantum system dynamics.

We derive a hierarchy of stochastic evolution equations for pure states (quantum trajectories) for open quantum system dynamics with non-Markovian structured environments. This hierarchy of pure states (HOPS) is generally applicable and provides the exact reduced density operator as an ensemble average over normalized states. The corresponding nonlinear equations are presented. We demonstrate that HOPS provides an efficient theoretical tool and apply it to the spin-boson model, the calculation of absorption spectra of molecular aggregates, and energy transfer in a photosynthetic pigment-protein complex. PMID:25375694

Suess, D; Eisfeld, A; Strunz, W T

2014-10-10

42

Maps for general open quantum systems and a theory of linear quantum error correction

We show that quantum subdynamics of an open quantum system can always be described by a linear, Hermitian map irrespective of the form of the initial total system state. Since the theory of quantum error correction was developed based on the assumption of completely positive (CP) maps, we present a generalized theory of linear quantum error correction, which applies to any linear map describing the open system evolution. In the physically relevant setting of Hermitian maps, we show that the CP-map-based version of quantum error correction theory applies without modifications. However, we show that a more general scenario is also possible, where the recovery map is Hermitian but not CP. Since non-CP maps have nonpositive matrices in their range, we provide a geometric characterization of the positivity domain of general linear maps. In particular, we show that this domain is convex and that this implies a simple algorithm for finding its boundary.

Shabani, Alireza [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States); Lidar, Daniel A. [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States); Departments of Chemistry and Physics, University of Southern California, Los Angeles, California 90089 (United States)

2009-07-15

43

Resonance Width Distribution for Open Chaotic Quantum Systems

NASA Astrophysics Data System (ADS)

Recent measurements of resonance widths, ?, for low-energy neutron scattering off heavy nuclei claim significant deviations from the standard chi-square 2?1(?), or the Porter-Thomas, distribution. The unstable nucleus is an open quantum system, where the intrinsic dynamics has to be supplemented by the coupling of chaotic internal states through the continuum. We propose a new resonance width distribution based on the random matrix theory for an open quantum system. For a single open channel, the new distribution is P(?)=C2?1(?)?sinh?/? where ?=??/2D and D is the mean energy level spacing. This result naturally recovers the Porter-Thomas distribution for small ? and can be directly applied to a whole range of mesoscopic systems, and is invariant under ?->?-?, where? is the total width. The realistic situation in nuclei is not that of a single neutron channel. Many photon channels are always opened which modifies the width distribution into P(,)=C2?1(?-?)?sinh??/?? with ??=?(?-?)/2D, and the whole distribution is shifted by ?, an average radiation width.

Shchedrin, Gavriil

2012-10-01

44

Stochastic theory of non-Markovian open quantum system

NASA Astrophysics Data System (ADS)

In this thesis, a stochastic approach to solving non-Markovian open quantum system called "non-Markovian quantum state diffusion" (NMQSD) approach is discussed in details. The NMQSD approach can serve as an analytical and numerical tool to study the dynamics of the open quantum systems. We explore three main topics of the NMQSD approach. First, we extend the NMQSD approach to many-body open systems such as two-qubit system and coupled N-cavity system. Based on the exact NMQSD equations and the corresponding master equations, we investigate several interesting non-Markovian features due to the memory effect of the environment such as the entanglement generation in two-qubit system and the coherence and entanglement transfer between cavities. Second, we extend the original NMQSD approach to the case that system is coupled to a fermionic bath or a spin bath. By introducing the anti-commutative Grassmann noise and the fermionic coherent state, we derive a fermionic NMQSD equation and the corresponding master equation. The fermionic NMQSD is illustrated by several examples. In a single qubit dissipative example, we have explicitly demonstrated that the NMQSD approach and the ordinary quantum mechanics give rise to the exactly same results. We also show the difference between fermionic bath and bosonic bath. Third, we combine the bosonic and fermionic NMQSD approach to develop a unified NMQSD approach to study the case that an open system is coupled to a bosonic bath and a fermionic bath simultaneously. For all practical purposes, we develop a set of useful computer programs (NMQSD Toolbox) to implement the NMQSD equation in realistic computations. In particular, we develop an algorithm to calculate the exact O operator involved in the NMQSD equation. The NMQSD toolbox is designed to be user friendly, so it will be especially valuable for a non-expert who has interest to employ the NMQSD equation to solve a practical problem. Apart from the central topics on the NMQSD approach, we also study the environment-assisted error correction (EAEC) scheme. We have proposed two new schemes beyond the original EAEC scheme. Our schemes can be used to recover an unknown entangled initial state for a dephasing channel and recover an arbitrary unknown initial state for a dissipative channel using a generalized quantum measurement.

Zhao, Xinyu

45

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

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

X. L. Huang; S. L. Wu; L. C. Wang; X. X. Yi

2010-04-17

46

The behavior of most physical systems is affected by their natural surroundings. A quantum system with an environment is referred to as open, and its study varies according to the classical or quantum description adopted for the environment. We propose an approach to open quantum systems that allows us to follow the cross-over from quantum to classical environments; to achieve this, we devise an exact parametric representation of the principal system, based on generalized coherent states for the environment. The method is applied to the s = 1/2 Heisenberg star with frustration, where the quantum character of the environment varies with the couplings entering the Hamiltonian H. We find that when the star is in an eigenstate of H, the central spin behaves as if it were in an effective magnetic field, pointing in the direction set by the environmental coherent-state angle variables (?, ?), and broadened according to their quantum probability distribution. Such distribution is independent of ?, whereas as a function of ? is seen to get narrower as the quantum character of the environment is reduced, collapsing into a Dirac-? function in the classical limit. In such limit, because ? is left undetermined, the Von Neumann entropy of the central spin remains finite; in fact, it is equal to the entanglement of the original fully quantum model, a result that establishes a relation between this latter quantity and the Berry phase characterizing the dynamics of the central spin in the effective magnetic field. PMID:23572581

Calvani, Dario; Cuccoli, Alessandro; Gidopoulos, Nikitas I; Verrucchi, Paola

2013-04-23

47

Boundary driven open quantum many-body systems

In this lecture course I outline a simple paradigm of non-eqjuilibrium quantum statistical physics, namely we shall study quantum lattice systems with local, Hamiltonian (conservative) interactions which are coupled to the environment via incoherent processes only at the system's boundaries. This is arguably the simplest nontrivial context where one can study far from equilibrium steady states and their transport properties. We shall formulate the problem in terms of a many-body Markovian master equation (the so-called Lindblad equation, and some of its extensions, e.g. the Redfield eqaution). The lecture course consists of two main parts: Firstly, and most extensively we shall present canonical Liouville-space many-body formalism, the so-called 'third quantization' and show how it can be implemented to solve bi-linear open many-particle problems, the key peradigmatic examples being the XY spin 1/2 chains or quasi-free bosonic (or harmonic) chains. Secondly, we shall outline several recent approaches on how to approach exactly solvable open quantum interacting many-body problems, such as anisotropic Heisenberg ((XXZ) spin chain or fermionic Hubbard chain.

Prosen, Tomaž [Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana (Slovenia)

2014-01-08

48

Tensor networks and graphical calculus for open quantum systems

We present a graphical calculus for completely positive maps and in doing so cast the theory of open quantum systems into the language of tensor networks. We tailor the theory of tensor networks to pictographically represent the Liouville-superoperator, Choi-matrix, process-matrix, Kraus, and system-environment representations for the evolution of open-system states, to expose how these representations interrelate, and to concisely transform between them. Several of these transformations have succinct depictions as wire bending dualities in our graphical calculus --- reshuffling, vectorization, and the Choi-Jamiolkowski isomorphism. To further demonstrate the utility of the presented graphical calculus we include several examples where we provide constructions, and simpler proofs of several useful quantities in quantum information theory. We demonstrate the use of graphical approaches to construct superoperator representations of common matrix operations, and to deal with composing and reducing the number of quantum systems in the superoperator convention. We present a proof of a simple condition for whether an arbitrary bipartite state may be used for ancilla assisted process tomography and find that after applying reshuffling transformation to the bipartite state the resulting operator must be invertible if it is to allow for complete recovery of the unknown channel. As final examples we derive expressions for the average gate fidelity and entanglement fidelity of a channel in terms of each of the different representations of the channel. Having new tools to investigate old problems can often lead to surprising new results, and the graphical calculus presented in this paper should lead to a better understanding of the interrelation between CP-maps and quantum theory.

Christopher J. Wood; Jacob D. Biamonte; David G. Cory

2014-10-10

49

Semiclassical Mechanism for the Quantum Decay in Open Chaotic Systems

We address the decay in open chaotic quantum systems and calculate semiclassical corrections to the classical exponential decay. We confirm random matrix predictions and, going beyond, calculate Ehrenfest time effects. To support our results we perform extensive numerical simulations. Within our approach we show that certain (previously unnoticed) pairs of interfering, correlated classical trajectories are of vital importance. They also provide the dynamical mechanism for related phenomena such as photo-ionization and -dissociation, for which we compute cross section correlations. Moreover, these orbits allow us to establish a semiclassical version of the continuity equation.

Daniel Waltner; Martha Gutierrez; Arseni Goussev; Klaus Richter

2008-05-23

50

Open quantum system approaches are widely used in the description of physical, chemical and biological systems. A famous example is electronic excitation transfer in the initial stage of photosynthesis, where harvested energy is transferred with remarkably high efficiency to a reaction center. This transport is affected by the motion of a structured vibrational environment, which makes simulations on a classical computer very demanding. Here we propose an analog quantum simulator of complex open system dynamics with a precisely engineered quantum environment. Our setup is based on superconducting circuits, a well established technology. As an example, we demonstrate that it is feasible to simulate exciton transport in the Fenna-Matthews-Olson photosynthetic complex. Our approach allows for a controllable single-molecule simulation and the investigation of energy transfer pathways as well as non-Markovian noise-correlation effects.

Sarah Mostame; Patrick Rebentrost; Alexander Eisfeld; Andrew J. Kerman; Dimitris I. Tsomokos; Alán Aspuru-Guzik

2012-03-20

51

Quantum-speed-limit time for multiqubit open systems

NASA Astrophysics Data System (ADS)

Quantum-speed-limit (QSL) time captures the intrinsic minimal time interval for a quantum system evolving from an initial state to a target state. In single qubit open systems, it was found that the memory (non-Markovian) effect of environment plays an essential role in shortening QSL time or, say, increasing the capacity for potential speedup. In this paper, we investigate the QSL time for multiqubit open systems. We find that for a certain class of states the memory effect still acts as the indispensable requirement for cutting the QSL time down, while for another class of states this takes place even when the environment is of no memory. In particular, when the initial state is in product state |111 ⋯1 > , there exists a sudden transition from no capacity for potential speedup to potential speedup in a memoryless environment. In addition, we also display evidence for the subtle connection between QSL time and entanglement that weak entanglement may shorten QSL time even more.

Liu, Chen; Xu, Zhen-Yu; Zhu, Shiqun

2015-02-01

52

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

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

Huang, X. L.; Wu, S. L.; Wang, L. C.; Yi, X. X. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

2010-05-15

53

Quantum algorithm for simulating the dynamics of an open quantum system

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.

Wang Hefeng; Ashhab, S.; Nori, Franco [Advanced Science Institute, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

2011-06-15

54

Ab-Initio Coupled Cluster Theory for Open Quantum Systems

We discuss peculiarities of open-quantum systems, as compared to closed-quantum systems. We emphasize the importance of taking continuum degrees of freedom into account when dealing with systems with a tendency to decay through emission of fragments. In this context, we introduce the coupled-cluster theory and argue that this method allows for an accurate description of such systems starting from nucleon-nucleon degrees of freedom. We present ab-initio coupled-cluster calculations with singles and doubles excitations (CCSD) for the ground states of the helium isotopes {^3-10}He. The correlated many-body wave function is built from a single-particle basis which treats bound-, resonant-, and non-resonant continuum states on equal footing, which is a Berggren basis. In order to keep the basis size manageable, we use a renormalized interaction of the low-momentum type derived from the N{^3}LO nucleon-nucleon interaction. The calculated masses and decay widths are in semi-quantitative agreement with experiment. The discrepancy with experiment is suspected to be attributed to the three-nucleon force (3NF) which is not included at this point.

Hagen, Gaute [ORNL; Dean, David Jarvis [ORNL; Hjorth-Jensen, M. [University of Oslo, Norway; Papenbrock, Thomas F [ORNL

2008-01-01

55

An Open Quantum System Approach to the B-Mesons System

In this paper we consider a nonstandard evolution for the B0-\\u000a$$\\\\overline B$$\\u000a0 system, namely, an evolution in the open quantum systems framework. Such approach is justified by the very high sensitivity of experiments studying CP-violating phenomena in the B-mesons sector, very near to the one required to test some possible scenarios induced by quantum gravity at the Planck

Raffaele Romano

2003-01-01

56

A positive tensor network approach for simulating open quantum many-body systems

Open many-body quantum systems play an important role in quantum optics and condensed-matter physics, and capture phenomena like transport, interplay between Hamiltonian and incoherent dynamics, and topological order generated by dissipation. We introduce a versatile method to numerically simulate one-dimensional open quantum many-body dynamics using tensor networks representing mixed quantum states in a locally purified form. This strategy guarantees that positivity is preserved at all times, while keeping the algorithm stable and efficient, thus actually overcoming various obstacles of the known numerical open-system evolution schemes. To exemplify the functioning of the approach, we study both stationary states and transient dissipative behaviour, for various open quantum systems ranging from few to many-body physics.

A. H. Werner; D. Jaschke; P. Silvi; T. Calarco; J. Eisert; S. Montangero

2014-12-18

57

Scalable approaches to the characterization of open quantum system dynamics

One of the biggest challenges in the physical realization of quantum information processing (QIP) is the precise control of the system. In order to achieve this, we characterize the gates, errors, and noise occurring in ...

López, Cecilia Carolina

2009-01-01

58

Heat-exchange statistics in driven open quantum systems

NASA Astrophysics Data System (ADS)

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

59

Heat-exchange statistics in driven open quantum systems

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 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.

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

2014-07-29

60

Linearity versus complete positivity of the evolution of open quantum systems

NASA Astrophysics Data System (ADS)

The title may be a bit misleading. Perhaps, "On the Complete Positivity of Reduced Quantum Dynamics," would be a more fitting title. Determining whether or not completely positive (CP) maps are required to describe open system quantum dynamics is an extremely important issue concerning the fundamental mathematical foundations of QM, as well as many other areas of physics. it had been typically believed that only CP maps actually describe the dynamical evolution of open quantum systems, however there has been speculation as to whether this is a strict constraint on the mathematical and physical structure of stochastic quantum dynamical maps. The objective of this thesis is to demonstrate that given a particular unitary operator, an initial system state, a final system state, and the dimension of the environment state, there exists no CP map with a composite system-environment, product initial state that is compatible with the given constraints on the reduced quantum dynamics of the system under investigation.

Ceballos, Russell R.

61

Non-Markovian generalization of the Lindblad theory of open quantum systems

A systematic approach to the non-Markovian quantum dynamics of open systems is given by the projection operator techniques of nonequilibrium statistical mechanics. Combining these methods with concepts from quantum information theory and from the theory of positive maps, we derive a class of correlated projection superoperators that take into account in an efficient way statistical correlations between the open system and its environment. The result is used to develop a generalization of the Lindblad theory to the regime of highly non-Markovian quantum processes in structured environments.

Breuer, Heinz-Peter [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany)

2007-02-15

62

Non-Markovianity and memory effects in quantum open systems

NASA Astrophysics Data System (ADS)

Although a number of measures for quantum non-Markovianity have been proposed recently, it is still an open question whether these measures directly characterize the memory effect of the environment, i.e., the dependence of a quantum state on its past in a time evolution. In this paper, we present a criterion and propose a measure for non-Markovianity with clear physical interpretations of the memory effect. The non-Markovianity is defined by the inequality T (t2,t0) ?T (t2,t1) T (t1,t0) in terms of memoryless dynamical map T introduced in this paper. This definition is conceptually distinct from that based on divisibility used by Rivas et al. [Phys. Rev. Lett. 105, 050403 (2010), 10.1103/PhysRevLett.105.050403], whose violation is manifested by noncomplete positivity of the dynamical map. We demonstrate via a typical quantum process that without Markovian approximation, nonzero memory effects (non-Markovianity) always exist even if the non-Markovianity is zero by the other non-Markovianity measures.

Hou, S. C.; Liang, S. L.; Yi, X. X.

2015-01-01

63

Optimal control for generating quantum gates in open dissipative systems

NASA Astrophysics Data System (ADS)

Optimal control methods for implementing quantum modules with least amount of relaxative loss are devised to give best approximations to unitary gates under relaxation. The potential gain by optimal control fully exploiting known relaxation parameters against time-optimal control (the alternative for unknown relaxation parameters) is explored and exemplified in numerical and in algebraic terms: for instance, relaxation-based optimal control is the method of choice to govern quantum systems within subspaces of weak relaxation whenever the drift Hamiltonian would otherwise drive the system through fast decaying modes. In a standard model system generalizing ideal decoherence-free subspaces to more realistic scenarios, opengrape-derived controls realize a CNOT with fidelities beyond 95% instead of at most 15% for a standard Trotter expansion. As additional benefit their control fields are orders of magnitude lower in power than bang-bang decouplings.

Schulte-Herbrüggen, T.; Spörl, A.; Khaneja, N.; Glaser, S. J.

2011-08-01

64

Mappings of open quantum systems onto chain representations and Markovian embeddings

We derive a sequence of measures whose corresponding Jacobi matrices have special properties and a general mapping of an open quantum system onto 1D semi infinite chains with only nearest neighbour interactions. Then we proceed to use the sequence of measures and the properties of the Jacobi matrices to derive an expression for the spectral density describing the open quantum system when an increasing number of degrees of freedom in the environment have been embedded into the system. Finally, we derive convergence theorems for these residual spectral densities.

M. P. Woods; R. Groux; A. W. Chin; S. F. Huelga; M. B. Plenio

2012-11-04

65

White Noise and Heating of Open Quantum Field Fermi Systems

I study the time evolution of the density matrices of quantum Fermi systems interacting with classic external Fermi fields. This interaction either changes the temperature of the system or it affects the density of particles. For relativistic Dirac fermions, variations of temperature lead to creation (annihilation) of particle - antiparticle pairs. The change of the density (or of the chemical potential) indicates the existence of the incoming (outgoing) flux of fermions from (to) the bath. These changes are independent for the different modes and in order to model the thermalization one should adjust the spectrum of the noise. The linear time dependences of the densities of particles are characteristic for all the processes.

A. A. Abrikosov Jr

1993-02-09

66

Adiabatic charge pumping in open quantum systems J.E. Avron(a)

Adiabatic charge pumping in open quantum systems J.E. Avron(a) , A. Elgart(b) , G.M. Graf(c) , L for charge transport in quantum pumps connected to a number of external leads. It is proved that under rather the pump is given by a formula of BÂ¨uttiker, Pr^etre, and Thomas, relating it to the frozen S

67

Experimentally witnessing the initial correlation between an open quantum system and its environment

NASA Astrophysics Data System (ADS)

System-environment correlations, which determine the (non-)Markovian character of a dynamical process, is an area of intense interest in the study of open quantum systems. We send photons emitted from a quantum dot sample into a 15-m polarization-maintaining optical fiber to generate different system-environment correlated states and then witness the correlations by observing the growth of trace distances. This experimental scheme of correlation witnessing based on system-environment information flow can also be used for other similar systems.

Li, Chuan-Feng; Tang, Jian-Shun; Li, Yu-Long; Guo, Guang-Can

2011-06-01

68

NASA Astrophysics Data System (ADS)

System-environment correlations, which determine the (non-)Markovian character of a dynamical process, is an area of intense interest in the study of open quantum systems. We send photons emitted from a quantum dot sample into a 15-m polarization-maintaining optical fiber to generate different system-environment correlated states and then witness the correlations by observing the growth of trace distances. This experimental scheme of correlation witnessing based on system-environment information flow can also be used for other similar systems.

Li, Chuan-Feng; Tang, Jian-Shun; Li, Yu-Long; Guo, Guang-Can

2012-02-01

69

Solving non-Markovian open quantum systems with multi-channel reservoir coupling

We extend the non-Markovian quantum state diffusion (QSD) equation to open quantum systems which exhibit multi-channel coupling to a harmonic oscillator reservoir. Open quantum systems which have multi-channel reservoir coupling are those in which canonical transformation of reservoir modes cannot reduce the number of reservoir operators appearing in the interaction Hamiltonian to one. We show that the non-Markovian QSD equation for multi-channel reservoir coupling can, in some cases, lead to an exact master equation which we derive. We then derive the exact master equation for the three-level system in a vee-type configuration which has multi-channel reservoir coupling and give the analytical solution. Finally, we examine the evolution of the three-level vee-type system with generalized Ornstein-Uhlenbeck reservoir correlations numerically.

Curtis J. Broadbent; Jun Jing; Ting Yu; Joseph H. Eberly

2011-12-12

70

Real-Time Transport in Open Quantum Systems From $\\mathcal{PT}$-Symmetric Quantum Mechanics

Nanoscale electronic transport is of intense technological interest, with applications ranging from semiconducting devices and molecular junctions to charge migration in biological systems. Most explicit theoretical approaches treat transport using a combination of density functional theory (DFT) and non-equilibrium Green's functions. This is a static formalism, with dynamic response properties accommodated only through complicated extensions. To circumvent this limitation, the carrier density may be propagated using real-time time-dependent DFT (RT-TDDFT), with boundary conditions corresponding to an open quantum system. Complex absorbing potentials can emulate outgoing particles at the simulation boundary, although these do not account for introduction of charge density. It is demonstrated that the desired positive particle flux is afforded by a class of $\\mathcal{PT}$-symmetric generating potentials that are characterized by anisotropic transmission resonances. These potentials add density every time a particle traverses the cell boundary, and may be used to engineer a continuous pulse train for incident packets. This is a first step toward developing a complete transport formalism unique to RT-TDDFT.

Justin E. Elenewski; Hanning Chen

2014-08-07

71

Canonical versus noncanonical equilibration dynamics of open quantum systems.

In statistical mechanics, any quantum system in equilibrium with its weakly coupled reservoir is described by a canonical state at the same temperature as the reservoir. Here, by studying the equilibration dynamics of a harmonic oscillator interacting with a reservoir, we evaluate microscopically the condition under which the equilibration to a canonical state is valid. It is revealed that the non-Markovian effect and the availability of a stationary state of the total system play a profound role in the equilibration. In the Markovian limit, the conventional canonical state can be recovered. In the non-Markovian regime, when the stationary state is absent, the system equilibrates to a generalized canonical state at an effective temperature; whenever the stationary state is present, the equilibrium state of the system cannot be described by any canonical state anymore. Our finding of the physical condition on such noncanonical equilibration might have significant impact on statistical physics. A physical scheme based on circuit QED is proposed to test our results. PMID:25215704

Yang, Chun-Jie; An, Jun-Hong; Luo, Hong-Gang; Li, Yading; Oh, C H

2014-08-01

72

Canonical versus noncanonical equilibration dynamics of open quantum systems

In statistical mechanics, any quantum system in equilibrium with its weakly coupled reservoir is described by a canonical state at the same temperature as the reservoir. Here, by studying the equilibration dynamics of a harmonic oscillator interacting with a reservoir, we evaluate microscopically the condition under which the equilibration to a canonical state is valid. It is revealed that the non-Markovian effect and the availability of a stationary state of the total system play a profound role in the equilibration. In the Markovian limit, the conventional canonical state can be recovered. In the non-Markovian regime, when the stationary state is absent, the system equilibrates to a generalized canonical state at an effective temperature; whenever the stationary state is present, the equilibrium state of the system cannot be described by any canonical state anymore. Our finding of the physical condition on such noncanonical equilibration might have significant impact on statistical physics. A physical scheme based on circuit QED is proposed to test our results.

Chun-Jie Yang; Jun-Hong An; Hong-Gang Luo; Yading Li; C. H. Oh

2014-08-24

73

Coherent and decoherent time evolution of finite Markovian and non-Markovian open quantum systems

We examine the properties of open quantum systems with respect to their time evolution in different regimes, Markovian and non-Markovian. We analyze their behaviour with respect to their coherent or decoherent time evolution by means of different models and try to gain some insight into the possible correlations between Markovianity and coherence.

Tarek Khalil; Jean Richert

2015-03-31

74

NASA Astrophysics Data System (ADS)

Although quantum correlations in a quantum system are characterized by the evolving quantities (which are entanglement and discord usually), we reveal such basis (i.e. the set of virtual particles) for the representation of the density matrix that the entanglement and/or discord between any two virtual particles in such representation are stationary. In particular, dealing with the nearest neighbor approximation, this system of virtual particles is represented by the ? -fermions of the Jordan-Wigner transformation. Such systems are important in quantum information devices because the evolution of quantum entanglement/discord leads to the problems of realization of quantum operations. The advantage of stationary entanglement/discord is that they are completely defined by the initial density matrix and by the Hamiltonian governing the quantum dynamics in the system under consideration. Moreover, using the special initial condition together with the special system's geometry, we construct large cluster of virtual particles with the same pairwise entanglement/discord. In other words, the measure of quantum correlations is stationary in this system and correlations are uniformly "distributed" among all virtual particles. As examples, we use both homogeneous and non-homogeneous spin-1/2 open chains with XY-interaction although other types of interactions might be also of interest.

Fel'dman, E. B.; Zenchuk, A. I.

2013-09-01

75

Linear-algebraic bath transformation for simulating complex open quantum systems

In studying open quantum systems, the environment is often approximated as a collection of non-interacting harmonic oscillators, a configuration also known as the star-bath model. It is also well known that the star-bath can be transformed into a nearest-neighbor interacting chain of oscillators. The chain-bath model has been widely used in renormalization group approaches. The transformation can be obtained by recursion relations or orthogonal polynomials. Based on a simple linear algebraic approach, we propose a bath partition strategy to reduce the system-bath coupling strength. As a result, the non-interacting star-bath is transformed into a set of weakly-coupled multiple parallel chains. The transformed bath model allows complex problems to be practically implemented on quantum simulators, and it can also be employed in various numerical simulations of open quantum dynamics.

Huh, Joonsuk; Fujita, Takatoshi; Yung, Man-Hong; Aspuru-Guzik, Alán

2014-01-01

76

Linear-algebraic bath transformation for simulating complex open quantum systems

NASA Astrophysics Data System (ADS)

In studying open quantum systems, the environment is often approximated as a collection of non-interacting harmonic oscillators, a configuration also known as the star-bath model. It is also well known that the star-bath can be transformed into a nearest-neighbor interacting chain of oscillators. The chain-bath model has been widely used in renormalization group approaches. The transformation can be obtained by recursion relations or orthogonal polynomials. Based on a simple linear algebraic approach, we propose a bath partition strategy to reduce the system-bath coupling strength. As a result, the non-interacting star-bath is transformed into a set of weakly coupled multiple parallel chains. The transformed bath model allows complex problems to be practically implemented on quantum simulators, and it can also be employed in various numerical simulations of open quantum dynamics.

Huh, Joonsuk; Mostame, Sarah; Fujita, Takatoshi; Yung, Man-Hong; Aspuru-Guzik, Alán

2014-12-01

77

Open quantum system stochastic dynamics with and without the RWA

NASA Astrophysics Data System (ADS)

We study the dynamics of a two-level quantum system interacting with a single frequency electromagnetic field and a stochastic magnetic field, with and without making the rotating wave approximation (RWA). The transformation to the rotating frame does not commute with the stochastic Hamiltonian if the stochastic field has nonvanishing components in the transverse direction, hence, applying the RWA requires transformation of the stochastic terms in the Hamiltonian. For Gaussian white noise, the master equation is derived from the stochastic Schrödinger–Langevin equations, with and without the RWA. With the RWA, the master equation for the density matrix has Lindblad terms with coefficients that are time-dependent (i.e., the master equation is time-local). An approximate analytic expression for the density matrix is obtained with the RWA. For Ornstein–Uhlenbeck noise, as well as other types of colored noise, in contradistinction to the Gaussian white noise case, the non-commutation of the RWA transformation and the noise Hamiltonian can significantly affect the RWA dynamics when ? {{? }corr} 1, where ? is the electromagnetic field frequency and {{? }corr} is the stochastic magnetic field correlation time.

Band, Y. B.

2015-02-01

78

Quantum group approach to steady states of boundary-driven open quantum systems

NASA Astrophysics Data System (ADS)

We present a systematic approach for constructing steady state density operators of Markovian dissipative evolution for open quantum chain models with integrable bulk interaction and boundary incoherent driving. The construction is based on fundamental solutions of the quantum Yang-Baxter equation pertaining to quantum algebra symmetries and their quantizations (q-deformations). In particular, we facilitate a matrix-product state description, by resorting to generic spin-s infinite-dimensional solutions associated with non-compact spins, serving as ancillary degrees of freedom. After formally deriving already known steady states for the anisotropic spin-1/2 Heisenberg chain from first symmetry principles, we obtain a class of solutions belonging to interacting quantum gases with SU(N)-symmetric Hamiltonians, using a restricted set of incoherent boundary jump processes, and point out how new non-trivial generalizations emerge from twists of quantum group structures. Finally, we discuss the possibilities for the analytical calculation of observables by employing the algebraic properties of associated auxiliary vertex operators.

Ilievski, Enej; Žunkovi?, Bojan

2014-01-01

79

QuTiP: An open-source Python framework for the dynamics of open quantum systems

NASA Astrophysics Data System (ADS)

We present an object-oriented open-source framework for solving the dynamics of open quantum systems written in Python. Arbitrary Hamiltonians, including time-dependent systems, may be built up from operators and states defined by a quantum object class, and then passed on to a choice of master equation or Monte Carlo solvers. We give an overview of the basic structure for the framework before detailing the numerical simulation of open system dynamics. Several examples are given to illustrate the build up to a complete calculation. Finally, we measure the performance of our library against that of current implementations. The framework described here is particularly well suited to the fields of quantum optics, superconducting circuit devices, nanomechanics, and trapped ions, while also being ideal for use in classroom instruction. Catalogue identifier: AEMB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 16 482 No. of bytes in distributed program, including test data, etc.: 213 438 Distribution format: tar.gz Programming language: Python Computer: i386, x86-64 Operating system: Linux, Mac OSX, Windows RAM: 2+ Gigabytes Classification: 7 External routines: NumPy (http://numpy.scipy.org/), SciPy (http://www.scipy.org/), Matplotlib (http://matplotlib.sourceforge.net/) Nature of problem: Dynamics of open quantum systems. Solution method: Numerical solutions to Lindblad master equation or Monte Carlo wave function method. Restrictions: Problems must meet the criteria for using the master equation in Lindblad form. Running time: A few seconds up to several tens of minutes, depending on size of underlying Hilbert space.

Johansson, J. R.; Nation, P. D.; Nori, Franco

2012-08-01

80

Open quantum system model of the one-dimensional Burgers equation with tunable shear viscosity

Presented is an analysis of an open quantum model of the time-dependent evolution of a flow field governed by the nonlinear Burgers equation in one spatial dimension. The quantum model is a system of qubits where there exists a minimum time interval in the time-dependent dynamics. Each temporally discrete unitary quantum-mechanical evolution is followed by state reduction of the quantum state. The mesoscopic behavior of this quantum model is described by a quantum Boltzmann equation with a naturally emergent entropy function and H theorem and the model obeys the detailed balance principle. The macroscopic-scale effective field theory for the quantum model is derived using a perturbative Chapman-Enskog expansion applied to the linearized quantum Boltzmann equation. The entropy function is consistent with the quantum-mechanical collision process and a Fermi-Dirac single-particle distribution function for the occupation probabilities of the qubit's energy eigenstates. Comparisons are presented between analytical predictions and numerical predictions and the agreement is excellent, indicating that the nonlinear Burgers equation with a tunable shear viscosity is the operative macroscopic scale effective field theory.

Yepez, Jeffrey [Air Force Research Laboratory, 29 Randolph Road, Hanscom Field, Massachusetts 01731 (United States)

2006-10-15

81

Superradiance, disorder, and the non-Hermitian Hamiltonian in open quantum systems

We first briefly review the non-Hermitian effective Hamiltonian approach to open quantum systems and the associated phenomenon of superradiance. We next discuss the superradiance crossover in the presence of disorder and the relationship between superradiance and the localization transition. Finally, we investigate the regime of validity of the energy-independent effective Hamiltonian approximation and show that the results obtained by these methods are applicable to realistic physical systems.

Celardo, G. L.; Biella, A.; Giusteri, G. G.; Mattiotti, F. [Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics, Università Cattolica, via Musei 41, 25121 Brescia (Italy); Zhang, Y.; Kaplan, L. [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118 (United States)

2014-10-15

82

Absorption and injection models for open time-dependent quantum systems.

In the time-dependent simulation of pure states dealing with transport in open quantum systems, the initial state is located outside of the active region of interest. Using the superposition principle and the analytical knowledge of the free time evolution of such a state outside the active region, together with absorbing layers and remapping, a model for a very significant reduction of the computational burden associated with the numerical simulation of open time-dependent quantum systems is presented. The model is specially suited to study (many-particle and high-frequency effects) quantum transport, but it can also be applied to any other research field where the initial time-dependent pure state is located outside of the active region. From numerical simulations of open quantum systems described by the (effective mass) Schrödinger and (atomistic) tight-binding equations, a reduction of the computational burden of about two orders of magnitude for each spatial dimension of the domain with a negligible error is presented. PMID:25215848

Traversa, F L; Zhan, Z; Oriols, X

2014-08-01

83

Effect of high frequency modes of medium on an open quantum system

We present a method to calculate the real time effective propagator of a generic open quantum system, immersed in a medium using a wave function based framework. The medium is characterised by a set of harmonic oscillators having a continuous span of frequencies. This technique has been applied to the Caldeira-Leggett model showing that high frequency modes of the medium do not contribute towards decay of the population of states of the open system. In fact, they cause a Rabi type oscillation. Moreover, our wave function based approach provides an excellent alternative to conventional formalisms involving the density matrix.

Nirupam Dutta; A. K. Chaudhuri; P. K. Panigrahi

2014-09-09

84

The Open-System Dicke-Model Quantum Phase Transition with a Sub-Ohmic Bath

We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N-spin couple to independent reservoirs at zero temperature. The critical exponent, which is $1$ if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.

Nagy, D

2015-01-01

85

Solving non-Markovian open quantum systems with multi-channel reservoir coupling

We extend the non-Markovian quantum state diffusion (QSD) equation to open quantum systems which exhibit multi-channel coupling to a harmonic oscillator reservoir. Open quantum systems which have multi-channel reservoir coupling are those in which canonical transformation of reservoir modes cannot reduce the number of reservoir operators appearing in the interaction Hamiltonian to one. We show that the non-Markovian QSD equation for multi-channel reservoir coupling can, in some cases, lead to an exact master equation which we derive. We then derive the exact master equation for the three-level system in a vee-type configuration which has multi-channel reservoir coupling and give the analytical solution. Finally, we examine the evolution of the three-level vee-type system with generalized Ornstein-Uhlenbeck reservoir correlations numerically. - Highlights: Black-Right-Pointing-Pointer The concept of multi-channel vs. single-channel reservoir coupling is rigorously defined. Black-Right-Pointing-Pointer The non-Markovian quantum state diffusion equation for arbitrary multi-channel reservoir coupling is derived. Black-Right-Pointing-Pointer An exact time-local master equation is derived under certain conditions. Black-Right-Pointing-Pointer The analytical solution to the three-level system in a vee-type configuration is found. Black-Right-Pointing-Pointer The evolution of the three-level system under generalized Ornstein-Uhlenbeck noise is plotted for many parameter regimes.

Broadbent, Curtis J., E-mail: curtis.broadbent@rochester.edu [Rochester Theory Center, and Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Jing, Jun; Yu, Ting [Center for Controlled Quantum Systems, and the Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)] [Center for Controlled Quantum Systems, and the Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States); Eberly, Joseph H. [Rochester Theory Center, and Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)] [Rochester Theory Center, and Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)

2012-08-15

86

The existence and uniqueness of a steady state for nonequilibrium systems (NESS) is a fundamental subject and a main theme of research in statistical mechanics for decades. For Gaussian systems, such as a chain of harmonic oscillators connected at each end to a heat bath, and for anharmonic oscillators under specified conditions, definitive answers exist in the form of proven theorems. Answering this question for quantum many-body systems poses a challenge for the present. In this work we address this issue by deriving the stochastic equations for the reduced system with self-consistent backaction from the two baths, calculating the energy flow from one bath to the chain to the other bath, and exhibiting a power balance relation in the total (chain + baths) system which testifies to the existence of a NESS in this system at late times. Its insensitivity to the initial conditions of the chain corroborates to its uniqueness. The functional method we adopt here entails the use of the influence functional, the coarse-grained and stochastic effective actions, from which one can derive the stochastic equations and calculate the average values of physical variables in open quantum systems. This involves both taking the expectation values of quantum operators of the system and the distributional averages of stochastic variables stemming from the coarse-grained environment. This method though formal in appearance is compact and complete. It can also easily accommodate perturbative techniques and diagrammatic methods from field theory. Taken all together it provides a solid platform for carrying out systematic investigations into the nonequilibrium dynamics of open quantum systems and quantum thermodynamics.

J. -T. Hsiang; B. L. Hu

2014-06-01

87

The open quantum Brownian motions

NASA Astrophysics Data System (ADS)

Using quantum parallelism on random walks as the original seed, we introduce new quantum stochastic processes, the open quantum Brownian motions. They describe the behaviors of quantum walkers—with internal degrees of freedom which serve as random gyroscopes—interacting with a series of probes which serve as quantum coins. These processes may also be viewed as the scaling limit of open quantum random walks and we develop this approach along three different lines: the quantum trajectory, the quantum dynamical map and the quantum stochastic differential equation. We also present a study of the simplest case, with a two level system as an internal gyroscope, illustrating the interplay between the ballistic and diffusive behaviors at work in these processes. Notation H_z : orbital (walker) Hilbert space, {C}^{{Z}} in the discrete, L^2({R}) in the continuum H_c : internal spin (or gyroscope) Hilbert space H_sys=H_z\\otimesH_c : system Hilbert space H_p : probe (or quantum coin) Hilbert space, H_p={C}^2 \\rho^tot_t : density matrix for the total system (walker + internal spin + quantum coins) \\bar \\rho_t : reduced density matrix on H_sys : \\bar\\rho_t=\\int dxdy\\, \\bar\\rho_t(x,y)\\otimes | x \\rangle _z\\langle y | \\hat \\rho_t : system density matrix in a quantum trajectory: \\hat\\rho_t=\\int dxdy\\, \\hat\\rho_t(x,y)\\otimes | x \\rangle _z\\langle y | . If diagonal and localized in position: \\hat \\rho_t=\\rho_t\\otimes| X_t \\rangle _z\\langle X_t | ?t: internal density matrix in a simple quantum trajectory Xt: walker position in a simple quantum trajectory Bt: normalized Brownian motion ?t, \\xi_t^\\dagger : quantum noises

Bauer, Michel; Bernard, Denis; Tilloy, Antoine

2014-09-01

88

Problem-free time-dependent variational principle for open quantum systems

Methods of quantum nuclear wave-function dynamics have become very efficient in simulating large isolated systems using the time-dependent variational principle (TDVP). However, a straightforward extension of the TDVP to the density matrix framework gives rise to methods that do not conserve the energy in the isolated system limit and the total system population for open systems where only energy exchange with the environment is allowed. These problems arise when the system density is in a mixed state and is simulated using an incomplete basis. Thus, the basis set incompleteness, which is inevitable in practical calculations, creates artificial channels for energy and population dissipation. To overcome this unphysical behavior, we have introduced a constrained Lagrangian formulation of TDVP applied to the non-stochastic open system Schrodinger equation (NOSSE) [L. Joubert-Doriol, I. G. Ryabinkin, and A. F. Izmaylov, J. Chem. Phys. 141, 234112 (2014)]. While our formulation can be applied to any variational a...

Joubert-Doriol, Loic

2015-01-01

89

Simulating open quantum systems: from many-body interactions to stabilizer pumping

In a recent experiment, Barreiro et al. demonstrated the fundamental building blocks of an open-system quantum simulator with trapped ions [Nature 470, 486 (2011)]. Using up to five ions, single- and multi-qubit entangling gate operations were combined with optical pumping in stroboscopic sequences. This enabled the implementation of both coherent many-body dynamics as well as dissipative processes by controlling the coupling of the system to an artificial, suitably tailored environment. This engineering was illustrated by the dissipative preparation of entangled two- and four-qubit states, the simulation of coherent four-body spin interactions and the quantum non-demolition measurement of a multi-qubit stabilizer operator. In the present paper, we present the theoretical framework of this gate-based ("digital") simulation approach for open-system dynamics with trapped ions. In addition, we discuss how within this simulation approach minimal instances of spin models of interest in the context of topological quantum computing and condensed matter physics can be realized in state-of-the-art linear ion-trap quantum computing architectures. We outline concrete simulation schemes for Kitaev's toric code Hamiltonian and a recently suggested color code model. The presented simulation protocols can be adapted to scalable and two-dimensional ion-trap architectures, which are currently under development.

M. Mueller; K. Hammerer; Y. L. Zhou; C. F. Roos; P. Zoller

2011-04-13

90

We suggest a generalisation of the expression of the nonequilibrium density matrix obtained by Hershfield's method for the cases where both heat and charge steady state currents are present in a quantum open system. The finite-size quantum system, connected to two temperature and particle reservoirs, is driven out of equilibrium by the presence of both a temperature gradient and a chemical potential gradient between the two reservoirs. We show that the NE density matrix is given by a generalised Gibbs-like ensemble, and is in full agreement with the general results of the McLennan-Zubarev nonequilibrium ensembles. The extra non-equilibrium terms are related to the entropy production in the system and characterise the fluxes of heat and particle.An explicit example, for the lowest order expansion, is provide for a model system of non-interacting fermions.

H. Ness

2014-12-02

91

Quantum systems are invariably open, evolving under surrounding influences rather than in isolation. Standard open quantum system methods eliminate all information on the environmental state to yield a tractable description of the system dynamics. By incorporating a collective coordinate of the environment into the system Hamiltonian, we circumvent this limitation. Our theory provides straightforward access to important environmental properties that would otherwise be obscured, allowing us to quantify the evolving system-environment correlations. As a direct result, we show that the generation of robust system-environment correlations that persist into equilibrium (heralded also by the emergence of non-Gaussian environmental states) renders the canonical system steady-state almost always incorrect. The resulting equilibrium states deviate markedly from those predicted by standard perturbative techniques and are instead fully characterised by thermal states of the mapped system-collective coordinate Hamiltonian. We outline how noncanonical system states could be investigated experimentally to study deviations from canonical thermodynamics, with direct relevance to molecular and solid-state nanosystems.

Jake Iles-Smith; Neill Lambert; Ahsan Nazir

2014-09-25

92

Dynamical A and B maps have been employed extensively by Sudarshan and co-workers to investigate open system evolution of quantum systems. A canonical structure of the A-map is introduced here. It is shown that this canonical A-map enables us to investigate if the dynamics is completely positive (CP) or non-completely positive (NCP) in an elegant way and hence, it subsumes the basic results on open system dynamics. Identifying memory effects in open system evolution is gaining increasing importance recently and here, a criterion of non-Markovianity, based on the relative entropy of the dynamical state is proposed. The relative entropy difference of the dynamical system serves as a complementary characterization - though not related directly - to the fidelity difference criterion proposed recently. Three typical examples of open system evolution of a qubit, prepared initially in a correlated state with another qubit (environment), and evolving jointly under a specific unitary dynamics - which corresponds to a NCP dynamical map - are investigated by employing both the relative entropy difference and fidelity difference tests of non-Markovianity. The two qubit initial states are chosen to be (i) a pure entangled state, (ii) theWerner state, which exemplifies both entangled and separable states of qubits, depending on a real parameter, and (3) a separable mixed state. Both the relative entropy and fidelity criteria offer a nice display of how non-Markovianity manifests in all the three examples.

A. R. Usha Devi; A. K. Rajagopl; Sudha

2011-01-28

93

Intermittency and dynamical Lee-Yang zeros of open quantum systems

NASA Astrophysics Data System (ADS)

We use high-order cumulants to investigate the Lee-Yang zeros of generating functions of dynamical observables in open quantum systems. At long times the generating functions take on a large-deviation form with singularities of the associated cumulant generating functions—or dynamical free energies—signifying phase transitions in the ensemble of dynamical trajectories. We consider a driven three-level system as well as the dissipative Ising model. Both systems exhibit dynamical intermittency in the statistics of quantum jumps. From the short-time behavior of the dynamical Lee-Yang zeros, we identify critical values of the counting field which we attribute to the observed intermittency and dynamical phase coexistence. Furthermore, for the dissipative Ising model we construct a trajectory phase diagram and estimate the value of the transverse field where the stationary state changes from being ferromagnetic (inactive) to paramagnetic (active).

Hickey, James M.; Flindt, Christian; Garrahan, Juan P.

2014-12-01

94

Equilibrium states of open quantum systems in the strong coupling regime.

In this work we investigate the late-time steady states of open quantum systems coupled to a thermal reservoir in the strong coupling regime. In general such systems do not necessarily relax to a Boltzmann distribution if the coupling to the thermal reservoir is nonvanishing or equivalently if the relaxation time scales are finite. Using a variety of nonequilibrium formalisms valid for non-Markovian processes, we show that starting from a product state of the closed system = system+environment, with the environment in its thermal state, the open system which results from coarse graining the environment will evolve towards an equilibrium state at late times. This state can be expressed as the reduced state of the closed system thermal state at the temperature of the environment. For a linear (harmonic) system and environment, which is exactly solvable, we are able to show in a rigorous way that all multitime correlations of the open system evolve towards those of the closed system thermal state. Multitime correlations are especially relevant in the non-Markovian regime, since they cannot be generated by the dynamics of the single-time correlations. For more general systems, which cannot be exactly solved, we are able to provide a general proof that all single-time correlations of the open system evolve to those of the closed system thermal state, to first order in the relaxation rates. For the special case of a zero-temperature reservoir, we are able to explicitly construct the reduced closed system thermal state in terms of the environmental correlations. PMID:23367918

Suba??, Y; Fleming, C H; Taylor, J M; Hu, B L

2012-12-01

95

A Perturbative Method for Nonequilibrium Steady State of Open Quantum Systems

NASA Astrophysics Data System (ADS)

We develop a method of calculating the nonequilibrium steady state (NESS) of an open quantum system that is weakly coupled to reservoirs in different equilibrium states. We describe the system using a Redfield-type quantum master equation (QME). We decompose the Redfield QME into a Lindblad-type QME and the remaining part R. Regarding the steady state of the Lindblad QME as the unperturbed solution, we perform a perturbative calculation with respect to R to obtain the NESS of the Redfield QME. The NESS thus determined is exact up to the first order in the system-reservoir coupling strength (pump/loss rate), which is the same as the order of validity of the QME. An advantage of the proposed method in numerical computation is its applicability to systems larger than those in methods of directly solving the original Redfield QME. We apply the method to a noninteracting fermion system to obtain an analytical expression of the NESS density matrix. We also numerically demonstrate the method in a nonequilibrium quantum spin chain.

Yuge, Tatsuro; Sugita, Ayumu

2015-01-01

96

Creation of Two-Particle Entanglement in Open Macroscopic Quantum Systems

We consider an open quantum system of N not directly interacting spins (qubits) in contact with both local and collective thermal environments. The qubit-environment interactions are energy conserving. We trace out the variables of the thermal environments and N-2 qubits to obtain the time-dependent reduced density matrix for two arbitrary qubits. We numerically simulate the reduced dynamics and the creation of entanglement (concurrence) as a function of the parameters of the thermal environments and the number of qubits, N. Our results demonstrate that the two-qubit entanglement generally decreases as N increases. We show analytically that in the limit N tending to infinity, no entanglement can be created. This indicates that collective thermal environments cannot create two-qubit entanglement when many qubits are located within a region of the size of the environment coherence length. We discuss possible applications of our approach to the development of a new quantum characterization of noisy environments.

Merkli, M; Borgonovi, F; Tsifrinovic, V I

2011-01-01

97

Problem-free time-dependent variational principle for open quantum systems.

Methods of quantum nuclear wave-function dynamics have become very efficient in simulating large isolated systems using the time-dependent variational principle (TDVP). However, a straightforward extension of the TDVP to the density matrix framework gives rise to methods that do not conserve the energy in the isolated system limit and the total system population for open systems where only energy exchange with environment is allowed. These problems arise when the system density is in a mixed state and is simulated using an incomplete basis. Thus, the basis set incompleteness, which is inevitable in practical calculations, creates artificial channels for energy and population dissipation. To overcome this unphysical behavior, we have introduced a constrained Lagrangian formulation of TDVP applied to a non-stochastic open system Schrödinger equation [L. Joubert-Doriol, I. G. Ryabinkin, and A. F. Izmaylov, J. Chem. Phys. 141, 234112 (2014)]. While our formulation can be applied to any variational ansatz for the system density matrix, derivation of working equations and numerical assessment is done within the variational multiconfiguration Gaussian approach for a two-dimensional linear vibronic coupling model system interacting with a harmonic bath. PMID:25854228

Joubert-Doriol, Loïc; Izmaylov, Artur F

2015-04-01

98

NASA Astrophysics Data System (ADS)

We consider stochastic and open quantum systems with a finite number of states, where a stochastic transition between two specific states is monitored by a detector. The long-time counting statistics of the observed realizations of the transition, parametrized by cumulants, is the only available information about the system. We present an analytical method for reconstructing generators of the time evolution of the system compatible with the observations. The practicality of the reconstruction method is demonstrated by the examples of a laser-driven atom and the kinetics of enzyme-catalyzed reactions. Moreover, we propose cumulant-based criteria for testing the non-classicality and non-Markovianity of the time evolution, and lower bounds for the system dimension. Our analytical results rely on the close connection between the cumulants of the counting statistics and the characteristic polynomial of the generator, which takes the role of a cumulant generating function.

Bruderer, M.; Contreras-Pulido, L. D.; Thaller, M.; Sironi, L.; Obreschkow, D.; Plenio, M. B.

2014-03-01

99

Ultracold Mixtures of Rubidium and Ytterbium for Open Quantum System Engineering

NASA Astrophysics Data System (ADS)

Exquisite experimental control of quantum systems has led to sharp growth of basic quantum research in recent years. Controlling dissipation has been crucial in producing ultracold, trapped atomic samples. Recent theoretical work has suggested dissipation can be a useful tool for quantum state preparation. Controlling not only how a system interacts with a reservoir, but the ability to engineer the reservoir itself would be a powerful platform for open quantum system research. Toward this end, we have constructed an apparatus to study ultracold mixtures of rubidium (Rb) and ytterbium (Yb). We have developed a Rb-blind optical lattice at 423.018(7) nm, which will enable us to immerse a lattice of Yb atoms (the system) into a Rb BEC (superfluid reservoir). We have produced Bose-Einstein condensates of 170Yb and 174Yb, two of the five bosonic isotopes of Yb, which also has two fermionic isotopes. Flexible optical trapping of Rb and Yb was achieved with a two-color dipole trap of 532 and 1064 nm, and we observed thermalization in ultracold mixtures of Rb and Yb. Using the Rb-blind optical lattice, we measured very small light shifts of 87Rb BECs near the light shift zero-wavelengths adjacent the 6p electronic states, through a coherent series of lattice pulses. The positions of the zero-wavelengths are sensitive to the electric dipole matrix elements between the 5s and 6p states, and we made the first experimental measurement of their strength. By measuring a light shift, we were not sensitive to excited state branching ratios, and we achieved a precision better than 0.3%.

Herold, Creston David

100

Critical exponent of a quantum-noise-driven phase transition: The open-system Dicke model

The quantum phase transition of the Dicke model has been observed recently in a system formed by motional excitations of a laser-driven Bose-Einstein condensate coupled to an optical cavity [Baumann et al., Nature (London) 464, 1301 (2010)]. The cavity-based system is intrinsically open: photons leak out of the cavity where they are detected. Even at zero temperature, the continuous weak measurement of the photon number leads to an irreversible dynamics toward a steady state. In the framework of a generalized Bogoliubov theory, we show that the steady state exhibits a dynamical quantum phase transition. We find that the critical point and the mean field are only slightly modified with respect to the phase transition in the ground state. However, the critical exponents of the singular quantum correlations are significantly different in the two cases. There is also a drastic modification of the atom-field entanglement, since the divergence of the logarithmic negativity of the ground state at the critical point is suppressed and a finite entanglement is found in the steady state.

Nagy, D.; Szirmai, G.; Domokos, P. [Research Institute for Solid State Physics and Optics, P.O. Box 49, H-1525 Budapest (Hungary)

2011-10-15

101

Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

Chen, Xin, E-mail: xin.chen.nj@gmail.com [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2014-04-21

102

NASA Astrophysics Data System (ADS)

Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

Chen, Xin

2014-04-01

103

It is shown that the effective Hamiltonian representation, as it is formulated in author's papers, serves as a basis for distinguishing, in a broadband environment of an open quantum system, independent noise sources that determine, in terms of the stationary quantum Wiener and Poisson processes in the Markov approximation, the effective Hamiltonian and the equation for the evolution operator of the open system and its environment. General stochastic differential equations of generalized Langevin (non-Wiener) type for the evolution operator and the kinetic equation for the density matrix of an open system are obtained, which allow one to analyze the dynamics of a wide class of localized open systems in the Markov approximation. The main distinctive features of the dynamics of open quantum systems described in this way are the stabilization of excited states with respect to collective processes and an additional frequency shift of the spectrum of the open system. As an illustration of the general approach developed, the photon dynamics in a single-mode cavity without losses on the mirrors is considered, which contains identical intracavity atoms coupled to the external vacuum electromagnetic field. For some atomic densities, the photons of the cavity mode are 'locked' inside the cavity, thus exhibiting a new phenomenon of radiation trapping and non-Wiener dynamics.

Basharov, A. M., E-mail: basharov@gmail.com [National Research Centre 'Kurchatov Institute,' (Russian Federation)

2012-09-15

104

This paper is concerned with open quantum systems whose dynamic variables satisfy canonical commutation relations and are governed by quantum stochastic differential equations. The latter are driven by quantum Wiener processes which represent external boson fields. The system-field coupling operators are linear functions of the system variables. The Hamiltonian consists of a nominal quadratic function of the system variables and an uncertain perturbation which is represented in a Weyl quantization form. Assuming that the nominal linear quantum system is stable, we develop sufficient conditions on the perturbation of the Hamiltonian which guarantee robust mean square stability of the perturbed system. Examples are given to illustrate these results for a class of Hamiltonian perturbations in the form of trigonometric polynomials of the system variables.

Arash Kh. Sichani; Igor G. Vladimirov; Ian R. Petersen

2015-03-07

105

Tracking an open quantum system using a finite state machine: Stability analysis

A finite-dimensional Markovian open quantum system will undergo quantum jumps between pure states, if we can monitor the bath to which it is coupled with sufficient precision. In general these jumps, plus the between-jump evolution, create a trajectory which passes through infinitely many different pure states, even for ergodic systems. However, as shown recently by us [Phys. Rev. Lett. 106, 020406 (2011)], it is possible to construct adaptive monitorings which restrict the system to jumping between a finite number of states. That is, it is possible to track the system using a finite state machine as the apparatus. In this paper we consider the question of the stability of these monitoring schemes. Restricting to cyclic jumps for a qubit, we give a strong analytical argument that these schemes are always stable and supporting analytical and numerical evidence for the example of resonance fluorescence. This example also enables us to explore a range of behaviors in the evolution of individual trajectories, for several different monitoring schemes.

Karasik, R. I.; Wiseman, H. M. [Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111 (Australia)

2011-11-15

106

Quantum trajectories and superoperator algorithms implemented within the matrix product state (MPS) framework are powerful tools to simulate the real-time dynamics of open dissipative quantum systems. As for the unitary case, the reachable time-scales as well as system sizes are limited by the (possible) build-up of entanglement entropy. The aforementioned methods constitute complementary approaches how Lindblad master equations can be integrated relying either on a quasi-exact representation of the full density matrix or a stochastic unraveling of the density matrix in terms of pure states. In this work, we systematically benchmark both methods by studying the dynamics of a Bose-Hubbard chain in the presence of local as well as global dephasing. The build-up as well as system-size scaling of entanglement entropy strongly depends on the method and the parameter regime and we discuss the applicability of the methods for these cases as well as study the distribution of observables and time discretization errors that can become a limiting factor for global dissipation.

Lars Bonnes; Andreas M. Läuchli

2014-11-18

107

Real-time dynamics of open quantum spin systems driven by dissipative processes

We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY-model towards a disordered phase at late times. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.

Florian Hebenstreit; Debasish Banerjee; Manes Hornung; Fu-Jiun Jiang; Franziska Schranz; Uwe-Jens Wiese

2015-02-10

108

Real-time dynamics of open quantum spin systems driven by dissipative processes

We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY-model towards a disordered phase at late times. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.

Hebenstreit, Florian; Hornung, Manes; Jiang, Fu-Jiun; Schranz, Franziska; Wiese, Uwe-Jens

2015-01-01

109

Casimir force for absorbing media in an open quantum system framework: Scalar model

In this article we compute the Casimir force between two finite-width mirrors at finite temperature, working in a simplified model in 1+1 dimensions. The mirrors, considered as dissipative media, are modeled by a continuous set of harmonic oscillators which in turn are coupled to an external environment at thermal equilibrium. The calculation of the Casimir force is performed in the framework of the theory of open quantum systems. It is shown that the Casimir interaction has two different contributions: the usual radiation pressure from the vacuum, which is obtained for ideal mirrors without dissipation or losses, and a Langevin force associated with the noise induced by the interaction between dielectric atoms in the slabs and the thermal bath. Both contributions to the Casimir force are needed in order to reproduce the analogous Lifshitz formula in 1+1 dimensions. We also discuss the relationship between the electromagnetic properties of the mirrors and the spectral density of the environment.

Lombardo, Fernando C.; Rubio Lopez, Adrian E. [Departamento de Fisica Juan Jose Giambiagi, FCEyN UBA and IFIBA CONICET, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); Mazzitelli, Francisco D. [Departamento de Fisica Juan Jose Giambiagi, FCEyN UBA and IFIBA CONICET, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); Centro Atomico Bariloche Comision Nacional de Energia Atomica, R8402AGP Bariloche (Argentina)

2011-11-15

110

Optimal control in an open quantum system : selecting DNP pathways in an electron-nuclear system

There is much interest in improving quantum control techniques for the purposes of quantum information processing. High fidelity control is necessary for the future of quantum computing. Optimal control theory has been ...

Sheldon, Sarah (Sarah Elizabeth)

2013-01-01

111

Quantum speed limits in open systems: Non-Markovian dynamics without rotating-wave approximation

NASA Astrophysics Data System (ADS)

We derive an easily computable quantum speed limit (QSL) time bound for open systems whose initial states can be chosen as either pure or mixed states. Moreover, this QSL time is applicable to either Markovian or non-Markovian dynamics. By using of a hierarchy equation method, we numerically study the QSL time bound in a qubit system interacting with a single broadened cavity mode without rotating-wave, Born and Markovian approximation. By comparing with rotating-wave approximation (RWA) results, we show that the counter-rotating terms are helpful to increase evolution speed. The problem of non-Markovianity is also considered. We find that for non-RWA cases, increasing system-bath coupling can not always enhance the non-Markovianity, which is qualitatively different from the results with RWA. When considering the relation between QSL and non-Markovianity, we find that for small broadening widths of the cavity mode, non-Markovianity can increase the evolution speed in either RWA or non-RWA cases, while, for larger broadening widths, it is not true for non-RWA cases.

Sun, Zhe; Liu, Jing; Ma, Jian; Wang, Xiaoguang

2015-02-01

112

Time-reversal symmetric resolution of unity without background integrals in open quantum systems

We present a new complete set of states for a class of open quantum systems, to be used in expansion of the Green's function and the time-evolution operator. A remarkable feature of the complete set is that it observes time-reversal symmetry in the sense that it contains decaying states (resonant states) and growing states (anti-resonant states) parallelly. We can thereby pinpoint the occurrence of the breaking of time-reversal symmetry at the choice of whether we solve Schroedinger equation as an initial-condition problem or a terminal-condition problem. Another feature of the complete set is that in the subspace of the central scattering area of the system, it consists of contributions of all states with point spectra but does not contain any background integrals. In computing the time evolution, we can clearly see contribution of which point spectrum produces which time dependence. In the whole infinite state space, the complete set does contain an integral but it is over unperturbed eigenstates of the environmental area of the system and hence can be calculated analytically. We demonstrate the usefulness of the complete set by computing explicitly the survival probability and the escaping probability as well as the dynamics of wave packets. The origin of each term of matrix elements is clear in our formulation, particularly the exponential decays due to the resonance poles.

Naomichi Hatano; Gonzalo Ordonez

2014-05-26

113

Time-reversal symmetric resolution of unity without background integrals in open quantum systems

NASA Astrophysics Data System (ADS)

We present a new complete set of states for a class of open quantum systems, to be used in expansion of the Green's function and the time-evolution operator. A remarkable feature of the complete set is that it observes time-reversal symmetry in the sense that it contains decaying states (resonant states) and growing states (anti-resonant states) parallelly. We can thereby pinpoint the occurrence of the breaking of time-reversal symmetry at the choice of whether we solve Schrödinger equation as an initial-condition problem or a terminal-condition problem. Another feature of the complete set is that in the subspace of the central scattering area of the system, it consists of contributions of all states with point spectra but does not contain any background integrals. In computing the time evolution, we can clearly see contribution of which point spectrum produces which time dependence. In the whole infinite state space, the complete set does contain an integral but it is over unperturbed eigenstates of the environmental area of the system and hence can be calculated analytically. We demonstrate the usefulness of the complete set by computing explicitly the survival probability and the escaping probability as well as the dynamics of wave packets. The origin of each term of matrix elements is clear in our formulation, particularly, the exponential decays due to the resonance poles.

Hatano, Naomichi; Ordonez, Gonzalo

2014-12-01

114

It is shown that the exact dynamics of a composite quantum system can be represented through a pair of product states which evolve according to a Markovian random jump process. This representation is used to design a general Monte Carlo wave function method that enables the stochastic treatment of the full non-Markovian behavior of open quantum systems. Numerical simulations are carried out which demonstrate that the method is applicable to open systems strongly coupled to a bosonic reservoir, as well as to the interaction with a spin bath. Full details of the simulation algorithms are given, together with an investigation of the dynamics of fluctuations. Several potential generalizations of the method are outlined.

Heinz-Peter Breuer

2003-09-15

115

Time-reversal symmetric resolution of unity without background integrals in open quantum systems

We present a new complete set of states for a class of open quantum systems, to be used in expansion of the Green's function and the time-evolution operator. A remarkable feature of the complete set is that it observes time-reversal symmetry in the sense that it contains decaying states (resonant states) and growing states (anti-resonant states) parallelly. We can thereby pinpoint the occurrence of the breaking of time-reversal symmetry at the choice of whether we solve Schroedinger equation as an initial-condition problem or a terminal-condition problem. Another feature of the complete set is that in the subspace of the central scattering area of the system, it consists of contributions of all states with point spectra but does not contain any background integrals. In computing the time evolution, we can clearly see contribution of which point spectrum produces which time dependence. In the whole infinite state space, the complete set does contain an integral but it is over unperturbed eigenstates of the env...

Hatano, Naomichi

2014-01-01

116

NASA Astrophysics Data System (ADS)

This MATLAB program calculates the dynamics of the reduced density matrix of an open quantum system modeled either by the Feynman-Vernon model or the Caldeira-Leggett model. The user gives the program a Hamiltonian matrix that describes the open quantum system as if it were in isolation, a matrix of the same size that describes how that system couples to its environment, and a spectral distribution function and temperature describing the environment’s influence on it, in addition to the open quantum system’s initial density matrix and a grid of times. With this, the program returns the reduced density matrix of the open quantum system at all moments specified by that grid of times (or just the last moment specified by the grid of times if the user makes this choice). This overall calculation can be divided into two stages: the setup of the Feynman integral, and the actual calculation of the Feynman integral for time propagation of the density matrix. When this program calculates this propagation on a multi-core CPU, it is this propagation that is usually the rate-limiting step of the calculation, but when it is calculated on a GPU, the propagation is calculated so quickly that the setup of the Feynman integral can actually become the rate-limiting step. The overhead of transferring information from the CPU to the GPU and back seems to have a negligible effect on the overall runtime of the program. When the required information cannot fit on the GPU, the user can choose to run the entire program on a CPU. Catalogue identifier: AEPX_v1_0. Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPX_v1_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.: 703. No. of bytes in distributed program, including test data, etc.: 11026. Distribution format: tar.gz. Programming language: MATLAB R2012a. Computer: See “Operating system”. Operating system: Any operating system that can run MATLAB R2007a or above. Classification: 4.4. Nature of problem: Calculating the dynamics of the reduced density operator of an open quantum system. Solution method: Numerical Feynman integral. Running time: Depends on the input parameters. See the main text for examples.

Dattani, Nikesh S.

2013-12-01

117

Nonadiabatic dynamics in open quantum-classical systems: forward-backward trajectory solution.

A new approximate solution to the quantum-classical Liouville equation is derived starting from the formal solution of this equation in forward-backward form. The time evolution of a mixed quantum-classical system described by this equation is obtained in a coherent state basis using the mapping representation, which expresses N quantum degrees of freedom in a 2N-dimensional phase space. The solution yields a simple dynamics in which a set of N coherent state coordinates evolves in forward and backward trajectories, while the bath coordinates evolve under the influence of the mean potential that depends on these forward and backward trajectories. It is shown that the solution satisfies the differential form of the quantum-classical Liouville equation exactly. Relations to other mixed quantum-classical and semi-classical schemes are discussed. PMID:23249044

Hsieh, Chang-Yu; Kapral, Raymond

2012-12-14

118

Phase lapses in open quantum systems and the non-Hermitian Hamilton operator

We study transmission through a system with N=10 states coupled to K=2 continua of scattering wave functions in the framework of the S matrix theory by using the Feshbach projection operator formalism for open quantum systems. Due to the coupling of the system (being localized in space) to the (extended) continuum of scattering wave functions, the Hamilton operator H{sub eff} of the system is non-Hermitian. The numerical calculations are performed for different distributions of both the positions E{sub i}{sup 0} (i=1,...,N) of the states of the isolated (closed) system and the elements of the coupling vectors V{sup c} between system and continua (c=1,...,K). The overall coupling strength {alpha} simulating the degree of resonance overlapping, is used as a parameter. In all cases, the complex eigenvalues and eigenfunctions of H{sub eff} are controlled by {alpha}. In the regime of overlapping resonances, the well-known spectroscopic reordering processes (resonance trapping) take place because the phases of the eigenfunctions of H{sub eff} are not rigid in the neighborhood of singular points (being crossing points of eigenvalue trajectories). Finally, width bifurcation generates K=2 short-lived and N-K trapped long-lived states. Thus, narrow (Fano-like) resonances may appear in the transmission at high level density. They are similar to, but different from the Fano resonances in the scattering theory with K=1. Phase lapses are related to zeros in the transmission probability. Their number and position (in energy) are determined by the V{sup c} and E{sub i}{sup 0}, but not by {alpha}. However, number and position of the resonance states depend on {alpha} due to resonance trapping occurring in the regime of overlapping resonances. As a consequence, universal phase lapses between every two resonances may appear at high level density while the system will show mesoscopic features at low level density. The phase lapses are not a single phenomenon. Due to their link to singularities in the continuum, they are related also to other 'puzzling' experimental results such as dephasing at low temperature.

Mueller, Markus [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, 62210 Cuernavaca, Morelos (Mexico); Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany); Rotter, Ingrid [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany)

2009-10-15

119

NASA Astrophysics Data System (ADS)

We suggest a generalization of the expression of the nonequilibrium (NE) density matrix obtained by Hershfield's method for the cases where both heat and charge steady-state currents are present in a quantum open system. The finite-size quantum system, connected to two temperature and particle reservoirs, is driven out of equilibrium by the presence of both a temperature gradient and a chemical potential gradient between the two reservoirs. We show that the NE density matrix is given by a generalized Gibbs-like ensemble and is in full agreement with the general results of the McLennan-Zubarev nonequilibrium ensembles. The extra nonequilibrium terms are related to the entropy production in the system and characterize the fluxes of heat and particle. An explicit example, for the lowest-order expansion, is provide for a model system of noninteracting fermions.

Ness, H.

2014-12-01

120

We suggest a generalization of the expression of the nonequilibrium (NE) density matrix obtained by Hershfield's method for the cases where both heat and charge steady-state currents are present in a quantum open system. The finite-size quantum system, connected to two temperature and particle reservoirs, is driven out of equilibrium by the presence of both a temperature gradient and a chemical potential gradient between the two reservoirs. We show that the NE density matrix is given by a generalized Gibbs-like ensemble and is in full agreement with the general results of the McLennan-Zubarev nonequilibrium ensembles. The extra nonequilibrium terms are related to the entropy production in the system and characterize the fluxes of heat and particle. An explicit example, for the lowest-order expansion, is provide for a model system of noninteracting fermions. PMID:25615056

Ness, H

2014-12-01

121

We study the problem of the basis of an open quantum system, under a quantum chaotic environment, which is preferred in view of its stationary reduced density matrix (RDM), that is, the basis in which the stationary RDM is diagonal. It is shown that, under an initial condition composed of sufficiently many energy eigenstates of the total system, such a basis is given by the eigenbasis of a renormalized self-Hamiltonian of the system, in the limit of large Hilbert space of the environment. Here, the renormalized self-Hamiltonian is given by the unperturbed self-Hamiltonian plus a certain average of the interaction Hamiltonian over the environmental degrees of freedom. Numerical simulations performed in two models, both with the kicked rotor as the environment, give results consistent with the above analytical predictions. PMID:25353440

He, Lewei; Wang, Wen-Ge

2014-02-01

122

Adiabatic charge pumping in open quantum systems J.E. Avron (a) , A. Elgart (b) , G.M. Graf (c) , L for charge transport in quantum pumps connected to a number of external leads. It is proved that under rather the pump is given by a formula of Buttiker, Pr^etre, and Thomas, relating it to the frozen S

123

Adiabatic charge pumping in open quantum systems J.E. Avron (a) , A. Elgart (b) , G.M. Graf (c) , L for charge transport in quantum pumps connected to a number of external leads. It is proved that under rather the pump is given by a formula of BË?uttiker, Prâ??etre, and Thomas, relating it to the frozen S

124

Entanglement Relativity in the Foundations of The Open Quantum Systems Theory

Realistic many-particle systems dynamically exchange particles with their environments. In classical physics, small variations in the number of constituent particles are commonly considered practically irrelevant. However, in the quantum mechanical context, such and similar structural variations are generically taxed due to the so-called Entanglement Relativity. In this paper we point out difficulties in deriving master equation for a subsystem of an alternative partition of the closed quantum system. We find that the Nakajima-Zwanzig projection method cannot be straightforwardly used to solve the problem. The emerging tasks and prospects for the consistent foundations are examined.

M. Arsenijevic; J. Jeknic-Dugic; D. Todorovic; M. Dugic

2015-02-24

125

NASA Technical Reports Server (NTRS)

The harmonic oscillator with dissipation is studied within the framework of the Lindblad theory for open quantum systems. By using the Wang-Uhlenbeck method, the Fokker-Planck equation, obtained from the master equation for the density operator, is solved for the Wigner distribution function, subject to either the Gaussian type or the delta-function type of initial conditions. The obtained Wigner functions are two-dimensional Gaussians with different widths. Then a closed expression for the density operator is extracted. The entropy of the system is subsequently calculated and its temporal behavior shows that this quantity relaxes to its equilibrium value.

Isar, Aurelian

1995-01-01

126

KNIT : An open source code for quantum transport in multi-terminal systems

This paper is the documentation for a numerical code for quantum transport called KNIT. The KNIT library implements a generalization of the well known recursive Green function technique for a large class of multi-terminal mesoscopic systems with arbitrary geometries, topology and dimension. The systems are described by tight-biding Hamiltonians (with arbitrary internal degree of freedom like spin, electron/hole grading, orbitals...) and the calculation done within the non equilibrium Green function formalism (equivalent to the Landauer-Buttiker Scattering approach). KNIT can (and has) been applied to many different physical systems including quantum Hall effect, topological insulators, graphene ribbons, hybrid superconducting systems and ferromagnetic multilayers. KNIT main functionality is written in C++ and wrapped into Python, providing a simple and flexible interface for the user. Usual "input files" of numerical codes are replaced by small python scripts where the user builds the system and then computes...

Rychkova, Irina; Kazymyrenko, Kyryl; Borlenghi, Simone; Waintal, Xavier

2010-01-01

127

NASA Astrophysics Data System (ADS)

Information about the interaction of a many-electron quantum system with its environment, we show, is encoded within the one-electron density matrix (1-RDM). While the 1-RDM from an ensemble many-electron quantum system must obey the Pauli exclusion principle, the 1-RDM must obey additional constraints known as generalized Pauli conditions when it corresponds to a closed system describable by a single wave function. By examining the 1-RDM's violation of these generalized Pauli conditions, we obtain a sufficient condition at the level of a single electron for a many-electron quantum system's openness. In an application to exciton dynamics in photosynthetic light harvesting we show that the interaction of the system with the environment (quantum noise) relaxes significant constraints imposed on the exciton dynamics by the generalized Pauli conditions. This relaxation provides a geometric (kinematic) interpretation for the role of noise in enhancing exciton transport in quantum systems.

Chakraborty, Romit; Mazziotti, David A.

2015-01-01

128

Multiscale dynamics of open three-level quantum systems with two quasi-degenerate levels

We consider a three-level quantum system interacting with a bosonic thermal reservoir. Two energy levels of the system are nearly degenerate but well separated from the third one. The system-reservoir interaction constant is larger than the energy difference of the degenerate levels, but it is smaller than the separation between the latter and the remaining level. We show that the quasi-degeneracy of energy levels leads to the existence of a manifold of quasi-stationary states, and the dynamics exhibits two characteristic time scales. On the first, shorter one, initial states approach the quasi-stationary manifold. Then, on the much longer second time scale, the final unique equilibrium is reached.

Marco Merkli; Haifeng Song; Gennady Berman

2014-11-11

129

From open quantum walks to unitary quantum walks

We present an idea to convert to a unitary quantum walk any open quantum walk which is defined on lattices as well as on finite graphs. This approach generalizes to the domain of open quantum walks (or quantum Markov chains) the framework introduced by Szegedy for quantizing Markov chains. For the unitary quantum walks formulated in this article, we define the probability and the mean probability of finding the walk at a node, then derive the asymptotic mean probability.

Chaobin Liu

2015-02-05

130

Non-Markovian non-stationary completely positive open quantum system dynamics

By modeling the interaction of a system with an environment through a renewal approach, we demonstrate that completely positive non-Markovian dynamics may develop some unexplored non-standard statistical properties. The renewal approach is defined by a set of disruptive events, consisting in the action of a completely positive superoperator over the system density matrix. The random time intervals between events are described by an arbitrary waiting-time distribution. We show that, in contrast to the Markovian case, if one performs a system-preparation (measurement) at an arbitrary time, the subsequent evolution of the density matrix evolution is modified. The non-stationary character refers to the absence of an asymptotic master equation even when the preparation is performed at arbitrary long times. In spite of this property, we demonstrate that operator expectation values and operators correlations have the same dynamical structure, establishing the validity of a non-stationary quantum regression hypothesis. The non-stationary property of the dynamic is also analyzed through the response of the system to an external weak perturbation.

Adrian A. Budini Paolo Grigolini

2009-08-05

131

White noise and heating of quantum field theory in an open system

NASA Astrophysics Data System (ADS)

The time evolution of the density matrix of a relativistic quantum field theory coupled to random noise is discussed. Using path-integral techniques, we solve analytically for the density matrix of a system of free fields coupled to noise. We show that in the limit of large time the density matrix evolves to a thermal state and we compute the temperature of the state in terms of the characteristics of the noise. While the noise is coupled the temperature increases steadily in time. Also, it is necessary to choose a specific spectrum for the noise in order that all of the modes of the free field theory come to the same temperature after some given time. We then present an alternative derivation of these results using time-path techniques. In this case we consider a system where noise couples for a finite time interval and find that the propagator interpolates between finite-temperature field-theory propagators with the temperatures of the system at initial and final times. We argue that this can be used as a model of heating in an interacting field theory.

Cloutier, Jacques; Semenoff, Gordon W.

1991-11-01

132

NASA Astrophysics Data System (ADS)

The ambient concentration of nitrous oxide (N2O), the fourth most abundant greenhouse gas, is rapidly increasing with emissions from both natural and anthropogenic sources [1]. Soil and aquatic areas are important sources and sinks for N2O due to complicated biogenic processes. However, N2O emissions are poorly constrained in space and time, despite its importance to global climate change and ozone depletion. We report our recent N2O emission measurements with an open-path quantum cascade laser (QCL)-based sensor for ecological systems. The newly emergent QCLs have been used to build compact, sensitive trace gas sensors in the mid-IR spectral region. A compact open-path QCL based sensor was developed to detect atmospheric N2O and CO at ~ 4.5 ?m using wavelength modulation spectroscopy (WMS) to achieve a sensitivity of 0.26 ppbv of N2O and 0.24 ppbv of CO in 1 s with a power consumption of ~50 W [2]. This portable sensor system has been used to perform N2O emission flux measurement both with a static flux chamber and on an eddy covariance (EC) flux tower. In the flux chamber measurements, custom chambers were used to host the laser sensor, while gas samples for gas chromatograph (GC) were collected at the same time in the same chamber for validation and comparison. Different soil treatments have been applied in different chambers to study the relationship between N2O emission and the amount of fertilizer (and water) addition. Measurements from two methods agreed with each other (95% or higher confidence interval) for emission flux results, while laser sensor gave measurements with a much high temporal resolution. We have also performed the first open-path eddy covariance N2O flux measurement at Kellogg research station, Michigan State University for a month in June, 2012. Our sensor was placed on a 4-meter tower in a corn field and powered by batteries (connected with solar panels). We have observed the diurnal cycle of N2O flux. During this deployment, an inter-comparison between our sensor and a commercial gas sensor was done to check the sensor's performance. Overall, our sensor showed a good performance with both static chamber measurement and EC flux measurement of N2O. Its open-path, compact and portable design with low power consumption provides lots of advantages for N2O emission flux measurement in the ecological systems. [1] S. A. Montzka, E. J. Dlugokencky, and J. H. Butler, "Non-CO2 greenhouse gases and climate change," Nature 476, 43-50 (2011). [2] L. Tao, K, Sun, D. J. Miller, M. A. Khan and M.A. Zondlo, "Optimizations for simultaneous detection of atmospheric N2O and CO with a quantum cascade laser," CLEO, 2012

Tao, L.; Sun, K.; Cavigelli, M. A.; Gelfand, I.; Zenone, T.; Cui, M.; Miller, D. J.; Khan, M. A.; Zondlo, M. A.

2012-12-01

133

Open Quantum Walks: a short introduction

NASA Astrophysics Data System (ADS)

The concept of open quantum walks (OQW), quantum walks exclusively driven by the interaction with the external environment, is reviewed. OQWs are formulated as discrete completely positive maps on graphs. The basic properties of OQWs are summarised and new examples of OQWs on Bbb Z and their simulation by means of quantum trajectories are presented.

Sinayskiy, Ilya; Petruccione, Francesco

2013-06-01

134

A Theoretical Investigation Into Energy Transfer In Photosynthetic Open Quantum Systems

This thesis looks at the electronic energy transfer in the Fenna-Matthews-Olson complex, in which evidence of long-lived coherence has been observed in 2-dimensional infrared experiments. I use three techniques: the numerically exact Hierarchical Equations of Motion, and the perturbative Redfield and Foerster theories, the latter of which ignores quantum coherence in the transfer. Both of the approximate methods perform very well - and while oscillations in site populations (a hallmark of coherence) are present in the exact transfer dynamics and absent in the dynamics of Foerster theory, the latter gives a reasonable prediction of transfer rates and steady-state populations, despite being incoherent - suggesting that coherence is not vital for the dynamics of transfer. Since Foerster theory is very inexpensive to run and performs so well, I then apply it to calculate the effects of static disorder in bacteriochlorophyll site energies and of a more structured spectral density. Ultimately, the energy transfer i...

Wilkins, David M

2015-01-01

135

NASA Astrophysics Data System (ADS)

The Gorini-Kossakowski-Sudarshan-Lindblad equation allows us to model the process of decision making in US elections. The crucial point we attempt to make is that the voter's mental state can be represented as a superposition of two possible choices for either republicans or democrats. However, reality dictates a more complicated situation: typically a voter participates in two elections, i.e. the congress and the presidential elections. In both elections the voter has to decide between two choices. This very feature of the US election system requires that the mental state is represented by a 2-qubit state corresponding to the superposition of 4 different choices. The main issue is to describe the dynamics of the voters' mental states taking into account the mental and political environment. What is novel in this paper is that we apply the theory of open quantum systems to social science. The quantum master equation describes the resolution of uncertainty (represented in the form of superposition) to a definite choice.

Khrennikova, Polina; Haven, Emmanuel; Khrennikov, Andrei

2014-04-01

136

Control of open quantum systems: case study of the central spin model

NASA Astrophysics Data System (ADS)

We study the controllability of a central spin guided by a classical field and interacting with a spin bath and show that the central spin is fully controllable independently of the number of bath spins. Additionally we find that for unequal system-bath couplings even the bath becomes controllable by acting on the central spin alone. We then analyze numerically how the time to implement gates on the central spin scales with the number of bath spins and conjecture that for equal system-bath couplings it reaches a saturation value. We provide evidence that sometimes noise can be effectively suppressed through control.

Arenz, Christian; Gualdi, Giulia; Burgarth, Daniel

2014-06-01

137

Time-dependent approach to electron pumping in open quantum systems G. Stefanucci,1,2,* S. Kurth,1 time-dependent approach to investigate the motion of electrons in quantum pump device configurations that for pumping across a single potential barrier, electrons are transported in pockets and the transport

Gross, E.K.U.

138

Mappings of open quantum systems onto chain representations and Markovian embeddings

We study systems coupled linearly to a bath of oscillators. In an iterative process, the bath is transformed into a chain of oscillators with nearest neighbour interactions. A systematic procedure is provided to obtain the spectral density of the residual bath in each step, and it is shown that under general conditions these data converge. That is, the asymptotic part of the chain is universal, translation invariant with semicircular spectral density. The methods are based on orthogonal polynomials, in which we also solve the outstanding so-called “sequence of secondary measures problem” and give them a physical interpretation.

Woods, M. P., E-mail: mischa.woods05@imperial.ac.uk [QOLS, Blackett Laboratory, Imperial College London, London SW7 2BW (United Kingdom); Institute für Theoretische Physik, Universität Ulm, D-89069 Ulm (Germany); Groux, R. [Lycée Polyvalent Rouvière, Rue Sainte Claire Deville. BP 1205, 83070 Toulon (France)] [Lycée Polyvalent Rouvière, Rue Sainte Claire Deville. BP 1205, 83070 Toulon (France); Chin, A. W.; Huelga, S. F.; Plenio, M. B. [Institute für Theoretische Physik, Universität Ulm, D-89069 Ulm (Germany)] [Institute für Theoretische Physik, Universität Ulm, D-89069 Ulm (Germany)

2014-03-15

139

Open quantum system approach to the modeling of spin recombination reactions.

In theories of spin-dependent radical pair reactions, the time evolution of the radical pair, including the effect of the chemical kinetics, is described by a master equation in the Liouville formalism. For the description of the chemical kinetics, a number of possible reaction operators have been formulated in the literature. In this work, we present a framework that allows for a unified description of the various proposed mechanisms and the forms of reaction operators for the spin-selective recombination processes. On the basis of the concept that master equations can be derived from a microscopic description of the spin system interacting with external degrees of freedom, it is possible to gain insight into the underlying microscopic processes and develop a systematic approach toward determining the specific form of the reaction operator in concrete scenarios. PMID:22401141

Tiersch, M; Steiner, U E; Popescu, S; Briegel, H J

2012-04-26

140

NASA Astrophysics Data System (ADS)

For an open, time-dependent quantum system, Lindblad derived the most general modification of the quantum Liouville equation in the Markovian approximation that models environmental effects while preserving the non-negativity of the system's density matrix. While Lindblad's modification is correct for N-electron density matrices, solution of the Liouville equation with a Lindblad operator causes the one-electron reduced density matrix (1-RDM) to violate the Pauli exclusion principle. Consequently, after a short time, the 1-RDM is not representable by an ensemble N-electron density matrix (not ensemble N-representable). In this communication, we derive the necessary and sufficient constraints on the Lindbladian matrix within the Lindblad operator to ensure that the 1-RDM remains N-representable for all time. The theory is illustrated by considering the relaxation of an excitation in several molecules F2, N2, CO, and BeH2 subject to environmental noise.

Head-Marsden, Kade; Mazziotti, David A.

2015-02-01

141

For an open, time-dependent quantum system, Lindblad derived the most general modification of the quantum Liouville equation in the Markovian approximation that models environmental effects while preserving the non-negativity of the system's density matrix. While Lindblad's modification is correct for N-electron density matrices, solution of the Liouville equation with a Lindblad operator causes the one-electron reduced density matrix (1-RDM) to violate the Pauli exclusion principle. Consequently, after a short time, the 1-RDM is not representable by an ensemble N-electron density matrix (not ensemble N-representable). In this communication, we derive the necessary and sufficient constraints on the Lindbladian matrix within the Lindblad operator to ensure that the 1-RDM remains N-representable for all time. The theory is illustrated by considering the relaxation of an excitation in several molecules F2, N2, CO, and BeH2 subject to environmental noise. PMID:25662627

Head-Marsden, Kade; Mazziotti, David A

2015-02-01

142

Born-Oppenheimer approximation in open systems

We generalize the standard Born-Oppenheimer approximation to the case of open quantum systems. We define the zeroth order Born-Oppenheimer approximation of an open quantum system as the regime in which its effective Hamiltonian can be diagonalized with fixed slowly changing variables. We then establish validity and invalidity conditions for this approximation for two kinds of dissipations--the spin relaxation and the dissipation of center-of-mass motion. As an example, the Born-Oppenheimer approximation of a two-level open system is analyzed.

X. L. Huang; X. X. Yi

2009-09-16

143

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 sequences are ``refueled'' 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

Miloslav Dusek; Ondrej Haderka; Martin Hendrych; Robert Myska

1999-01-01

144

and Natan Andrei Center for Materials Theory, Rutgers University, Piscataway, New Jersey 08854, USA steady-state properties of quantum impurities subject to a finite bias. We show that the steady-state level model and derive exact, nonperturbative results for the steady-state properties of the system. DOI

Mehta, Pankaj

145

NASA Astrophysics Data System (ADS)

We analyze the dynamics of entanglement in a two-qubit system interacting with an initially squeezed thermal environment via a quantum nondemolition system-reservoir interaction, with the system and reservoir assumed to be initially separable. We compare and contrast the decoherence of the two-qubit system in the case where the qubits are mutually close-by (`collective regime') or distant (`localized regime') with respect to the spatial variation of the environment. Sudden death of entanglement (as quantified by concurrence) is shown to occur in the localized case rather than in the collective case, where entanglement tends to `ring down'. A consequence of the QND character of the interaction is that the time-evolved fidelity of a Bell state never falls below 1/sqrt{2}, a fact that is useful for quantum communication applications like a quantum repeater. Using a novel quantification of mixed state entanglement, we show that there are noise regimes where even though entanglement vanishes, the state is still available for applications like NMR quantum computation, because of the presence of a pseudo-pure component.

Banerjee, S.; Ravishankar, V.; Srikanth, R.

2010-01-01

146

Quantum Open-Closed Homotopy Algebra and String Field Theory

We reformulate the algebraic structure of Zwiebach's quantum open-closed string field theory in terms of homotopy algebras. We call it the quantum open-closed homotopy algebra (QOCHA) which is the generalization of the open-closed homotopy algebra (OCHA) of Kajiura and Stasheff. The homotopy formulation reveals new insights about deformations of open string field theory by closed string backgrounds. In particular, deformations by Maurer Cartan elements of the quantum closed homotopy algebra define consistent quantum open string field theories.

Korbinian Muenster; Ivo Sachs

2011-10-19

147

We analyze the dynamics of entanglement in a two-qubit system\\u000a interacting with an initially squeezed thermal environment via a\\u000a quantum nondemolition system-reservoir interaction, with the system\\u000a and reservoir assumed to be initially separable. We compare and\\u000a contrast the decoherence of the two-qubit system in the case where\\u000a the qubits are mutually close-by (`collective regime’) or distant\\u000a (`localized regime’) with respect

Subhashish Banerjee; V. Ravishankar; R. Srikanth

2010-01-01

148

A general argument leading from the formula for currents through an open noninteracting mesoscopic system given by the theory of non-equilibrium steady states (NESS) to the Landauer-Buettiker formula is pointed out. Time reversal symmetry is not assumed. As a consequence it follows that, as far as the system has a nontrivial scattering theory and the reservoirs have different temperatures and/or chemical potentials, the entropy production is strictly positive.

G. Nenciu

2006-10-26

149

This work establishes a strongly correlated system-and-bath dynamics theory, the many-dissipaton density operators formalism. It puts forward a quasi-particle picture for environmental influences. This picture unifies the physical descriptions and algebraic treatments on three distinct classes of quantum environments, electron bath, phonon bath, and two-level spin or exciton bath, as their participating in quantum dissipation processes. Dynamical variables for theoretical description are no longer just the reduced density matrix for system, but remarkably also those for quasi-particles of bath. The present theoretical formalism offers efficient and accurate means for the study of steady-state (nonequilibrium and equilibrium) and real-time dynamical properties of both systems and hybridizing environments. It further provides universal evaluations, exact in principle, on various correlation functions, including even those of environmental degrees of freedom in coupling with systems. Induced environmental dynamics could be reflected directly in experimentally measurable quantities, such as Fano resonances and quantum transport current shot noise statistics.

Yan, YiJing [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong)] [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong)

2014-02-07

150

NASA Astrophysics Data System (ADS)

This work establishes a strongly correlated system-and-bath dynamics theory, the many-dissipaton density operators formalism. It puts forward a quasi-particle picture for environmental influences. This picture unifies the physical descriptions and algebraic treatments on three distinct classes of quantum environments, electron bath, phonon bath, and two-level spin or exciton bath, as their participating in quantum dissipation processes. Dynamical variables for theoretical description are no longer just the reduced density matrix for system, but remarkably also those for quasi-particles of bath. The present theoretical formalism offers efficient and accurate means for the study of steady-state (nonequilibrium and equilibrium) and real-time dynamical properties of both systems and hybridizing environments. It further provides universal evaluations, exact in principle, on various correlation functions, including even those of environmental degrees of freedom in coupling with systems. Induced environmental dynamics could be reflected directly in experimentally measurable quantities, such as Fano resonances and quantum transport current shot noise statistics.

Yan, YiJing

2014-02-01

151

Open quantum reaction-diffusion dynamics: Absorbing states and relaxation

NASA Astrophysics Data System (ADS)

We consider an extension of classical stochastic reaction-diffusion (RD) dynamics to open quantum systems. We study a class of models of hard-core particles on a one-dimensional lattice whose dynamics is generated by a quantum master operator. Particle hopping is coherent while reactions, such as pair annihilation or pair coalescence, are dissipative. These are quantum open generalizations of the A +A ?? and A +A ?A classical RD models. We characterize the relaxation of the state towards the stationary regime via a decomposition of the system Hilbert space into transient and recurrent subspaces. We provide a complete classification of the structure of the recurrent subspace (and the nonequilibrium steady states) in terms of the dark states associated to the quantum master operator and its general spectral properties. We also show that, in one dimension, relaxation towards these absorbing dark states is slower than that predicted by a mean-field analysis due to fluctuation effects, in analogy with what occurs in classical RD systems. Numerical simulations of small systems suggest that the decay of the density in one dimension, in both the open quantum A +A ?? and A +A ?A systems, behaves asymptotically as t-b with 1 /2 **
**

van Horssen, Merlijn; Garrahan, Juan P.

2015-03-01

152

We establish the path integral approach for the time-dependent heat exchange of an externally driven quantum system coupled to a thermal reservoir. We derive the relevant influence functional and present an exact formal expression for the moment generating functional which carries all statistical properties of the heat exchange process for general linear dissipation. The general method is applied to the time-dependent average heat transfer in the dissipative two-state system. We show that the heat can be written as a convolution integral which involves the population and coherence correlation functions of the two-state system and additional correlations due to a polarization of the reservoir. The corresponding expression can be solved in the weak-damping limit both for white noise and for quantum mechanical coloured noise. The implications of pure quantum effects are discussed. Altogether a complete description of the dynamics of the average heat transfer ranging from the classical regime down to zero temperature is achieved.

M. Carrega; P. Solinas; A. Braggio; M. Sassetti; U. Weiss

2014-12-22

153

Open quantum reaction-diffusion dynamics: absorbing states and relaxation

We consider an extension of classical stochastic reaction-diffusion (RD) dynamics to open quantum systems. We study a class of models of hard core particles on a one-dimensional lattice whose dynamics is generated by a quantum master operator and where particle hopping is coherent while reactions, such as pair annihilation or pair coalescence, are dissipative. These are quantum open generalisations of the $A+A \\to \\varnothing$ and $A+A \\to A$ classical RD models. We characterise the relaxation of the state towards the stationary regime via a decomposition of the system Hilbert space into transient and recurrent subspaces. We provide a complete classification of the structure of the recurrent subspace (and the non-equilibrium steady states) in terms of the dark states associated to the quantum master operator and its general spectral properties. We also show that, in one dimension, relaxation towards these absorbing dark states is slower than that predicted by a mean-field analysis due to fluctuation effects, in analogy with what occurs in classical RD systems. Numerical simulations of small systems suggest that the decay of the density in one dimension, in both the open quantum $A+A \\to \\varnothing$ and $A+A \\to A$ cases, may go asymptotically as $t^{-b}$ with $1/2 < b < 1$.

Merlijn van Horssen; Juan P. Garrahan

2014-11-28

154

Central limit theorem for reducible and irreducible open quantum walks

In this work we aim at proving central limit theorems for open quantum walks on $\\mathbb{Z}^d$. We study the case when there are various classes of vertices in the network. Furthermore, we investigate two ways of distributing the vertex classes in the network. First we assign the classes in a regular pattern. Secondly, we assign each vertex a random class with a uniform distribution. For each way of distributing vertex classes, we obtain an appropriate central limit theorem, illustrated by numerical examples. These theorems may have application in the study of complex systems in quantum biology and dissipative quantum computation.

Przemys?aw Sadowski; ?ukasz Pawela

2014-12-16

155

Quantum Dynamics in Biological Systems

NASA Astrophysics Data System (ADS)

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

Shim, Sangwoo

156

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

Daniel Burgarth; Kazuya Yuasa

2011-04-04

157

A mesoscopic superposition of quantum states involving radiation fields with classically distinct phases was created and its progressive decoherence observed. The experiment involved Rydberg atoms interacting one at a time with a few photon coherent fields trapped in a high {ital Q} microwave cavity. The mesoscopic superposition was the equivalent of an {open_quote}{open_quote}atom+measuringapparatus{close_quote}{close_quote} system in which the {open_quote}{open_quote}meter{close_quote}{close_quote} was pointing

M. Brune; E. Hagley; J. Dreyer; X. Maitre; A. Maali; C. Wunderlich; J. M. Raimond; S. Haroche

1996-01-01

158

Entropic inequalities for noncomposite quantum systems realized by superconducting circuits

We study a class of entropic inequalities obtained for noncomposite quantum system realized by a many-level superconducting circuit. By using a mapping on bipartite quantum states, we consider possible realization schemes of various quantum logic gates for noncomposite quantum systems. In this framework, we discuss $\\log{N}$ entropic inequalities for Shannon and R\\'eniy entropies based on the quantum Fourier transform. Implementation of the quantum Fourier transform on a quantum processor based on many-level superconducting circuits opens a way for experimental verification of $\\log{N}$ entropic inequalities.

A. K. Fedorov; E. O. Kiktenko; O. V. Man'ko; V. I. Man'ko

2014-12-31

159

A degenerate dynamical system is characterized by a symplectic structure whose rank is not constant throughout phase space. Its phase space is divided into causally disconnected, nonoverlapping regions in each of which the rank of the symplectic matrix is constant, and there are no classical orbits connecting two different regions. Here the question of whether this classical disconnectedness survives quantization is addressed. Our conclusion is that in irreducible degenerate systems-in which the degeneracy cannot be eliminated by redefining variables in the action-the disconnectedness is maintained in the quantum theory: there is no quantum tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces are boundaries separating distinct physical systems, not only classically, but in the quantum realm as well. The relevance of this feature for gravitation and Chern-Simons theories in higher dimensions cannot be overstated.

Micheli, Fiorenza de [Centro de Estudios Cientificos, Arturo Prat 514, Valdivia (Chile); Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Zanelli, Jorge [Centro de Estudios Cientificos, Arturo Prat 514, Valdivia (Chile); Universidad Andres Bello, Av. Republica 440, Santiago (Chile)

2012-10-15

160

Scheme of thinking quantum systems

NASA Astrophysics Data System (ADS)

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

161

In this paper, an alternative solution to the traditional CNC machine tool controller has been introduced. Software and hardware modules have been described and their incorporation in a CNC control system has been outlined. This type of CNC machine tool controller demonstrates that technology is accessible and can be readily implemented into an open architecture machine tool controller. Benefit to the user is greater controller flexibility, while being economically achievable. PC based, motion as well as non-motion features will provide flexibility through a Windows environment. Up-grading this type of controller system through software revisions will keep the machine tool in a competitive state with minimal effort. Software and hardware modules are mass produced permitting competitive procurement and incorporation. Open architecture CNC systems provide diagnostics thus enhancing maintainability, and machine tool up-time. A major concern of traditional CNC systems has been operator training time. Training time can be greatly minimized by making use of Windows environment features.

Tal, J. [Galil Motion Control Inc., Sunnyvale, CA (United States); Lopez, A.; Edwards, J.M. [Los Alamos National Lab., NM (United States)

1995-04-01

162

We present a density matrix approach for computing global solutions of restricted open-shell Hartree-Fock theory, based on semidefinite programming (SDP), that gives upper and lower bounds on the Hartree-Fock energy of quantum systems. While wave function approaches to Hartree-Fock theory yield an upper bound to the Hartree-Fock energy, we derive a semidefinite relaxation of Hartree-Fock theory that yields a rigorous lower bound on the Hartree-Fock energy. We also develop an upper-bound algorithm in which Hartree-Fock theory is cast as a SDP with a nonconvex constraint on the rank of the matrix variable. Equality of the upper- and lower-bound energies guarantees that the computed solution is the globally optimal solution of Hartree-Fock theory. The work extends a previously presented method for closed-shell systems [S. Veeraraghavan and D. A. Mazziotti, Phys. Rev. A 89, 010502–R (2014)]. For strongly correlated systems the SDP approach provides an alternative to the locally optimized Hartree-Fock energies and densities with a certificate of global optimality. Applications are made to the potential energy curves of C{sub 2}, CN, Cr {sub 2}, and NO {sub 2}.

Veeraraghavan, Srikant; Mazziotti, David A., E-mail: damazz@uchicago.edu [Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

2014-03-28

163

Quantum Path Interference through Incoherent Motions in Multilevel Quantum Systems

Quantum path interferences or resonances in multilevel dissipative quantum systems play an important and intriguing role in the transport processes of nanoscale systems. Many previous minimalistic models used to describe the quantum path interference driven by incoherent fields are based on the approximations including the second order perturbation for the weak coupling limit, the ad-hoc choices of two-time correlation functions and $\\it{etc}$. On the other hand, the similar model to study the non-adiabatic molecular electronic excitation have been extensively developed and many efficient quantum molecular dynamics simulation schemes, such as the Ehrenfest scheme, have been proposed. In this paper, I aim to propose an unified model, extend the Ehrenfest scheme to study the interactions of system-light and system-phonon simultaneously and gain insight into and principles of the roles of quantum path interferences in the realistic molecular systems. I discuss how to derive the time-dependent stochastic Schr$\\ddot{o}$dinger equation from the Ehrenfest scheme as a foundation to discuss the detailed balance for the weak coupling limit and therefore the quantum correction in the Ehrenfest scheme. Different from the master equation technique, the Ehrenfest scheme doesn't need any specific assumptions about spectral densities and two time correlation functions. With simple open two-level and three-level quantum systems, I show the effect of the quantum path interference on the steady state populations. Currently I only focus on the role of the phonon thermal reservoir. The electromagnetic field (solar light) will be modeled as a thermal reservoir and discussed in detail in the future paper.

Xin Chen

2013-10-21

164

Efficiency of open quantum walk implementation of dissipative quantum computing algorithms

An open quantum walk formalism for dissipative quantum computing is presented. The approach is illustrated with the examples of the Toffoli gate and the Quantum Fourier Transform for 3 and 4 qubits. It is shown that the algorithms based on the open quantum walk formalism are more efficient than the canonical dissipative quantum computing approach. In particular, the open quantum walks can be designed to converge faster to the desired steady state and to increase the probability of detection of the outcome of the computation.

I. Sinayskiy; F. Petruccione

2014-01-26

165

Naval open systems architecture

NASA Astrophysics Data System (ADS)

For the past 8 years, the Navy has been working on transforming the acquisition practices of the Navy and Marine Corps toward Open Systems Architectures to open up our business, gain competitive advantage, improve warfighter performance, speed innovation to the fleet and deliver superior capability to the warfighter within a shrinking budget1. Why should Industry care? They should care because we in Government want the best Industry has to offer. Industry is in the business of pushing technology to greater and greater capabilities through innovation. Examples of innovations are on full display at this conference, such as exploring the impact of difficult environmental conditions on technical performance. Industry is creating the tools which will continue to give the Navy and Marine Corps important tactical advantages over our adversaries.

Guertin, Nick; Womble, Brian; Haskell, Virginia

2013-05-01

166

Quantum statistics of overlapping modes in open resonators Gregor Hackenbroich, Carlos Viviescas, Fritz Haake Fachbereich Physik, Universitat Duisburg-Essen, 45117 Essen, Germany (Dated: September 2 descrip- tion of the quantum statistics of overlapping modes. A few example systems were discussed [8, 9

Hackenbroich, Gregor

167

General System theory, Like-Quantum Semantics and Fuzzy Sets

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 . In conclusion we propose an example of formal quantum coherence.

Ignazio Licata

2007-03-31

168

Just as conventional institutions are organisational structures for coordinating the activities of multiple interacting individuals, electronic institutions provide a computational analogue for coordinating the activities of multiple interacting software agents. In this paper, we argue that open multi-agent systems can be effectively designed and implemented as electronic institutions, for which we provide a comprehensive computational model. More specifically, the paper provides an operational semantics for electronic institutions, specifying the essential data structures, the state representation and the key operations necessary to implement them. We specify the agent workflow structure that is the core component of such electronic institutions and particular instantiations of knowledge representation languages that support the institutional model. In so doing, we provide the first formal account of the electronic institution concept in a rigorous and unambiguous way.

Mark d& apos; Inverno; Michael Luck; Pablo Noriega; Juan Rodriguez-Aguilar; Carles Sierra

2012-01-01

169

Classical command of quantum systems.

Quantum computation and cryptography both involve scenarios in which a user interacts with an imperfectly modelled or 'untrusted' system. It is therefore of fundamental and practical interest to devise tests that reveal whether the system is behaving as instructed. In 1969, Clauser, Horne, Shimony and Holt proposed an experimental test that can be passed by a quantum-mechanical system but not by a system restricted to classical physics. Here we extend this test to enable the characterization of a large quantum system. We describe a scheme that can be used to determine the initial state and to classically command the system to evolve according to desired dynamics. The bipartite system is treated as two black boxes, with no assumptions about their inner workings except that they obey quantum physics. The scheme works even if the system is explicitly designed to undermine it; any misbehaviour is detected. Among its applications, our scheme makes it possible to test whether a claimed quantum computer is truly quantum. It also advances towards a goal of quantum cryptography: namely, the use of 'untrusted' devices to establish a shared random key, with security based on the validity of quantum physics. PMID:23619692

Reichardt, Ben W; Unger, Falk; Vazirani, Umesh

2013-04-25

170

Quantum information science as an approach to complex quantum systems

What makes quantum information science a science? These notes explore the idea that quantum information science may offer a powerful approach to the study of complex quantum systems. We discuss how to quantify complexity in quantum systems, and argue that there are two qualitatively different types of complex quantum system. We also explore ways of understanding complex quantum dynamics by quantifying the strength of a quantum dynamical operation as a physical resource. This is the text for a talk at the ``Sixth International Conference on Quantum Communication, Measurement and Computing'', held at MIT, July 2002. Viewgraphs for the talk may be found at http://www.qinfo.org/talks/.

Michael A. Nielsen

2002-08-13

171

Quantum technologies with hybrid systems.

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

172

Quantum Effects in Biological Systems

NASA Astrophysics Data System (ADS)

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

173

Multiple System-Decomposition Method for Avoiding Quantum Decoherence

NASA Astrophysics Data System (ADS)

Decomposition of a composite system C into different subsystems, A + B or D + E, may help in avoiding decoherence. For example, the environment-induced decoherence for an A+B system need not destroy entanglement present in the D + E system (A + B = C = D + E). This new approach opens some questions also in the foundations of the quantum computation theory that might eventually lead to a new model of quantum computation.

Jekni?-Dugi?, J.; Dugi?, M.

2008-02-01

174

Classical equations for quantum systems

The origin of the phenomenological deterministic laws that approximately govern the quasiclassical domain of familiar experience is considered in the context of the quantum mechanics of closed systems such as the universe as a whole. A formulation of quantum mechanics is used that predicts probabilities for the individual members of a set of alternative coarse-grained histories that decohere, which means

Murray Gell-Mann; James B. Hartle

1993-01-01

175

Decoherence in infinite quantum systems

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

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

2012-09-01

176

Quantum technologies with hybrid systems

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 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 multi-tasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and the challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.

G. Kurizki; P. Bertet; Y. Kubo; K. Mølmer; D. Petrosyan; P. Rabl; J. Schmiedmayer

2015-04-01

177

Stability of local quantum dissipative systems

Open quantum systems weakly coupled to the environment are modeled by completely positive, trace preserving semigroups of linear maps. The generators of such evolutions are called Lindbladians. For practical and theoretical reasons, it is crucial to estimate the impact that noise or errors in the generating Lindbladian can have on the evolution. In the setting of quantum many-body systems on a lattice it is natural to consider local or exponentially decaying interactions. We show that even for polynomially decaying errors in the Lindbladian, local observables and correlation functions are stable if the unperturbed Lindbladian is translationally invariant, has a unique fixed point (with no restriction on its rank) and has a mixing time which scales logarithmically with the system size. These conditions can be relaxed to the non-translationally invariant case. As a main example, we prove that classical Glauber dynamics is stable under local perturbations, including perturbations in the transition rates which may not preserve detailed balance.

Toby S. Cubitt; Angelo Lucia; Spyridon Michalakis; David Perez-Garcia

2014-09-29

178

Rapid readout of a register of qubits using open-loop quantum control

NASA Astrophysics Data System (ADS)

Measurements are a primitive for characterizing quantum systems. Reducing the time taken to perform a measurement may be beneficial in many areas of quantum information processing. We show that permuting the eigenvalues of the state matrix in the logical basis, using open-loop control, provides an O (n ) reduction in the measurement time, where n is the number of qubits in the register. This reduction is of the same order as the (previously introduced) locally optimal feedback protocol. The advantage of the open-loop protocol is that it is far less difficult experimentally. Because the control commutes with the measured observable at all times, our rapid measurement protocol could be used for characterizing a quantum system, by state or process tomography, or to implement measurement-based quantum error correction.

Combes, Joshua; Denney, Aaron; Wiseman, Howard M.

2015-02-01

179

Nonequilibrium Quantum Systems: Fluctuations and Interactions

NASA Astrophysics Data System (ADS)

We explore some aspects of nonequilibrium statistical mechanics of classical and quantum systems. Two chapters are devoted to fluctuation theorems which were originally derived for classical systems. The main challenge in formulating them in quantum mechanics is the fact that fundamental quantities of interest, like work, are defined via the classical concept of a phase space trajectory. We utilize the decoherent histories conceptual framework, in which classical trajectories emerge in quantum mechanics as a result of coarse graining, and provide a first-principles analysis of the nonequilibrium work relation of Jarzynski and Crooks's fluctuation theorem for a quantum system interacting with a general environment based on the quantum Brownian motion (QBM) model. We indicate a parameter range at low temperatures where the theorems might fail in their original form. Fluctuation theorems of Jarzynski and Crooks for systems obeying classical Hamiltonian dynamics are derived under the assumption that the initial conditions are sampled from a canonical ensemble, even though the equilibrium state of an isolated system is typically associated with the microcanonical ensemble. We address this issue through an exact analysis of the classical Brownian motion model. We argue that a stronger form of ensemble equivalence than usually discussed in equilibrium statistical mechanics is required for these theorems to hold in the infinite environment limit irrespective of the ensemble used, and proceed to prove it for this model. An exact expression for the probability distribution of work is obtained for finite environments. Intuitively one expects a system to relax to an equilibrium state when brought into contact with a thermal environment. Yet it is important to have rigorous results that provide conditions for equilibration and characterize the equilibrium state. We consider the dynamics of open quantum systems using the Langevin and master equations and rigorously show that under fairly general conditions quantum systems interacting with a heat bath relax to the equilibrium state defined as the reduced thermal state of the system plus environment, even in the strong coupling regime. Our proof is valid to second-order in interaction strength for general systems and exact for the linear QBM model, for which we also show the equivalence of multi-time correlations. In the final chapter we give a sampling of our investigations into macroscopic quantum phenomena. We work out in detail a specific example of how and under what conditions the center of mass (CoM) coordinate of a macroscopic object emerges as the relevant degree of freedom. Interaction patterns are studied in terms of the couplings they induce between the CoM and relative coordinates of two macroscopic objects. We discuss the implications of these interaction patterns on macroscopic entanglement.

Subasi, Yigit

180

Quantum measurements of coupled systems

We propose an approach to measuring coupled systems, which gives a parametrically smaller error than the conventional fast projective measurements. The measurement error is due to the excitations being not entirely localized on individual systems even where the excitation energies are different. Our approach combines spectral selectivity of the detector with temporal resolution and uses the ideas of the quantum diffusion theory. The results bear on quantum computing with perpetually coupled qubits.

Fedichkin, L.; Dykman, M. I. [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States); Shapiro, M. [Department of Mathematics, Michigan State University, East Lansing, Michigan 48824 (United States)

2009-07-15

181

Adaptive hybrid optimal quantum control for imprecisely characterized systems

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

D. J. Egger; F. K. Wilhelm

2014-06-24

182

Adiabatic theorem for bipartite quantum systems in weak coupling limit

NASA Astrophysics Data System (ADS)

We study the adiabatic approximation of the dynamics of a bipartite quantum system with respect to one of its components, when the coupling between the two components is perturbative. We show that the density matrix of the considered component is described by adiabatic transport formulae exhibiting operator-valued geometric and dynamical phases. The present results can be used to study the quantum control of the dynamics of qubits and of open quantum systems where the two components are the system and its environment. We treat two examples, the control of an atomic qubit interacting with another one and the control of a spin in the middle of a Heisenberg spin chain.

Viennot, David; Aubourg, Lucile

2015-01-01

183

Quantum proof systems and entanglement theory

Quantum complexity theory is important from the point of view of not only theory of computation but also quantum information theory. In particular, quantum multi-prover interactive proof systems are defined based on ...

Abolfathe Beikidezfuli, Salman

2009-01-01

184

Periodic scarred States in open quantum dots as evidence of quantum Darwinism.

Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism. PMID:20482124

Burke, A M; Akis, R; Day, T E; Speyer, Gil; Ferry, D K; Bennett, B R

2010-04-30

185

Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism

NASA Astrophysics Data System (ADS)

Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.

2010-04-01

186

Stabilizing Feedback Controls for Quantum Systems

No quantum measurement can give full information on the state of a quantum system; hence any quantum feedback control problem is necessarily one with partial observations and can generally be converted into a completely observed control problem for an appropriate quantum filter as in classical stochastic control theory. Here we study the properties of controlled quantum filtering equations as classical

Mazyar Mirrahimi; Ramon van Handel

2007-01-01

187

Contextual logic for quantum systems

In this work we build a quantum logic that allows us to refer to physical magnitudes pertaining to different contexts from a fixed one without the contradictions with quantum mechanics expressed in no-go theorems. This logic arises from considering a sheaf over a topological space associated to the Boolean sublattices of the ortholattice of closed subspaces of the Hilbert space of the physical system. Differently to standard quantum logics, the contextual logic maintains a distributive lattice structure and a good definition of implication as a residue of the conjunction.

Graciela Domenech; Hector Freytes

2007-02-02

188

Quantum statistics of overlapping modes in open resonators

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of optical fields in weakly confining resonators with overlapping modes. Employing a recently developed quantization scheme involving a discrete set of resonator modes and continua of external modes we derive Langevin equations and a master equation for the resonator modes. Langevin dynamics and the master equation are proved to be equivalent in the Markovian limit. Our open-resonator dynamics may be used as a starting point for a quantum theory of random lasers.

Hackenbroich, Gregor; Viviescas, Carlos; Haake, Fritz

2003-12-01

189

Applications of Feedback Control in Quantum Systems

We give an introduction to feedback control in quantum systems, as well as an overview of the variety of applications which have been explored to date. This introductory review is aimed primarily at control theorists unfamiliar with quantum mechanics, but should also be useful to quantum physicists interested in applications of feedback control. We explain how feedback in quantum systems

Kurt Jacobs

2006-01-01

190

Quantum information processing in mesoscopic systems

introduce the Quantum Dots as the solid state system that will primarily be used as the hardware of quantum computation in quantum dots is described. The principal sources of decoherence and the measurementQuantum information processing in mesoscopic systems Jose Luis Garcia Coello A dissertation

Guillas, Serge

191

Hybrid quantum systems of atoms and ions

In recent years, ultracold atoms have emerged as an exceptionally controllable experimental system to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Here we go one step further and explore how cold atoms can be combined with other quantum systems to create new quantum hybrids with tailored properties. Coupling atomic quantum many-body states to

Christoph Zipkes; Lothar Ratschbacher; Stefan Palzer; Carlo Sias; Michael Köhl

2011-01-01

192

Improving the coherence time of a quantum system via a coupling with an unstable system

Here, we propose a counter-intuitive use of a hybrid system where the coherence time of a quantum system is actually improved via a coupling with an unstable system. If we couple a two-level system with a single NV center, then a dark state of the NV center naturally forms after the hybridization. We show that this dark state becomes robust against environmental fluctuations due to the coupling even when the coherence time of the two-level system is much shorter than that of the NV center. Our proposal opens a new way to use a quantum hybrid system for the realization of robust quantum information processing

Yuichiro Matsuzaki; Xiaobo Zhu; Kosuke Kakuyanagi; Hiraku Toida; Takaaki Shimo-Oka; Norikazu Mizuochi; Kae Nemoto; Kouichi Semba; William J. Munro; Hiroshi Yamaguchi; Shiro Saito

2014-04-08

193

Hybrid quantum-classical models as constrained quantum systems

Constrained Hamiltonian description of the classical limit is utilized in order to derive consistent dynamical equations for hybrid quantum-classical systems. Starting with a compound quantum system in the Hamiltonian formulation conditions for classical behavior are imposed on one of its subsystems and the corresponding hybrid dynamical equations are derived. The presented formalism suggests that the hybrid systems have properties that are not exhausted by those of quantum and classical systems.

M. Radonjic; S. Prvanovic; N. Buric

2012-06-07

194

Exceptional points in open and PT symmetric systems

Exceptional points (EPs) determine the dynamics of open quantum systems and cause also PT symmetry breaking in PT symmetric systems. From a mathematical point of view, this is caused by the fact that the phases of the wavefunctions (eigenfunctions of a non-Hermitian Hamiltonian) relative to one another are not rigid when an EP is approached. The system is therefore able to align with the environment to which it is coupled and, consequently, rigorous changes of the system properties may occur. We compare analytically as well as numerically the eigenvalues and eigenfunctions of a $2\\times 2$ matrix that is characteristic of either open quantum systems at high level density or of PT symmetric optical lattices. In both cases, the results show clearly the influence of the environment onto the system in the neighborhood of EPs. Although the systems are very different from one another, the eigenvalues and eigenfunctions indicate the same characteristic features.

Hichem Eleuch; Ingrid Rotter

2014-04-29

195

RKKY interaction in a chirally coupled double quantum dot system

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

Heine, A. W.; Tutuc, D.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover (Germany); Zwicknagl, G. [Institut für Mathematische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig (Germany); Schuh, D. [Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätstr. 31, 93053 Regensburg (Germany); Wegscheider, W. [Laboratorium für Festkörperphysik, ETH Zürich, Schafmattstr. 16, 8093 Zürich, Switzerland and Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätstr. 31, 93053 Regens (Germany)

2013-12-04

196

Free space quantum system based on quantum secure direct communication

NASA Astrophysics Data System (ADS)

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

197

Hall conductance and topological invariant for open systems

NASA Astrophysics Data System (ADS)

The Hall conductivity given by the Kubo formula is a linear response of quantum transverse transport to a weak electric field. It has been intensively studied for quantum systems without decoherence, but it is barely explored for systems subject to decoherence. In this paper, we develop a formulism to deal with this issue for topological insulators. The Hall conductance of a topological insulator coupled to an environment is derived, the derivation is based on a linear response theory developed for open systems in this paper. As an application, the Hall conductance of a two-band topological insulator and a two-dimensional lattice is presented and discussed.

Shen, H. Z.; Wang, W.; Yi, X. X.

2014-09-01

198

Hall conductance and topological invariant for open systems

The Hall conductivity given by the Kubo formula is a linear response of quantum transverse transport to a weak electric field. It has been intensively studied for quantum systems without decoherence, but it is barely explored for systems subject to decoherence. In this paper, we develop a formulism to deal with this issue for topological insulators. The Hall conductance of a topological insulator coupled to an environment is derived, the derivation is based on a linear response theory developed for open systems in this paper. As an application, the Hall conductance of a two-band topological insulator and a two-dimensional lattice is presented and discussed. PMID:25248375

Shen, H. Z.; Wang, W.; Yi, X. X.

2014-01-01

199

Hall conductance and topological invariant for open systems.

The Hall conductivity given by the Kubo formula is a linear response of quantum transverse transport to a weak electric field. It has been intensively studied for quantum systems without decoherence, but it is barely explored for systems subject to decoherence. In this paper, we develop a formulism to deal with this issue for topological insulators. The Hall conductance of a topological insulator coupled to an environment is derived, the derivation is based on a linear response theory developed for open systems in this paper. As an application, the Hall conductance of a two-band topological insulator and a two-dimensional lattice is presented and discussed. PMID:25248375

Shen, H Z; Wang, W; Yi, X X

2014-01-01

200

Correlations in quantum systems and branch points in the complex plane

Branch points in the complex plane are responsible for avoided level crossings in closed and open quantum systems. They create not only an exchange of the wave functions but also a mixing of the states of a quantum system at high level density. The influence of branch points in the complex plane on the low-lying states of the system is small.

I. Rotter

2001-07-04

201

The quantum Hall effect in quantum dot systems

NASA Astrophysics Data System (ADS)

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

202

Open quantum random walks: bi-stability on pure states and ballistically induced diffusion

Open quantum random walks (OQRWs) deal with quantum random motions on the line for systems with internal and orbital degrees of freedom. The internal system behaves as a quantum random gyroscope coding for the direction of the orbital moves. We reveal the existence of a transition, depending on OQRW moduli, in the internal system behaviors from simple oscillations to random flips between two unstable pure states. This induces a transition in the orbital motions from usual diffusion to ballistically induced diffusion with large mean free path and large effective diffusion constant at large time. We also show that mixed states of the internal system are converted into random pure states during the process. We touch upon possible experimental realizations.

Michel Bauer; Denis Bernard; Antoine Tilloy

2014-02-12

203

Universal Braess paradox in open quantum dots

NASA Astrophysics Data System (ADS)

We present analytical and numerical results that demonstrate the presence of the Braess paradox in chaotic quantum dots. The paradox that we identify, originally perceived in classical networks, shows that the addition of more capacity to the network can suppress the current flow in the universal regime. We investigate the weak localization term, showing that it presents the paradox encoded in a saturation minimum of the conductance, under the presence of hyperflow in the external leads. In addition, we demonstrate that the weak localization suffers a transition signal depending on the overcapacity lead and presents an echo on the magnetic crossover before going to zero due to the full time-reversal symmetry breaking. We also show that the quantum interference contribution can dominate the Ohm term in the presence of constrictions and that the corresponding Fano factor engenders an anomalous behavior.

Barbosa, A. L. R.; Bazeia, D.; Ramos, J. G. G. S.

2014-10-01

204

System identification for passive linear quantum systems

System identification is a key enabling component for the implementation of quantum technologies, including quantum control. In this paper, we consider the class of passive linear input-output systems, and investigate several basic questions: (1) which parameters can be identified? (2) Given sufficient input-output data, how do we reconstruct system parameters? (3) How can we optimize the estimation precision by preparing appropriate input states and performing measurements on the output? We show that minimal systems can be identified up to a unitary transformation on the modes, and systems satisfying a Hamiltonian connectivity condition called "infecting" are completely identifiable. We propose a frequency domain design based on a Fisher information criterion, for optimizing the estimation precision for coherent input state. As a consequence of the unitarity of the transfer function, we show that the Heisenberg limit with respect to the input energy can be achieved using non-classical input states.

Madalin Guta; Naoki Yamamoto

2014-08-27

205

Universal quantum computation in integrable systems

Quantized integrable systems can be made to perform universal quantum computation by the application of a global time-varying control. The action-angle variables of the integrable system function as qubits or qudits, which can be coupled selectively by the global control to induce universal quantum logic gates. By contrast, chaotic quantum systems, even if controllable, do not generically allow quantum computation under global control.

Seth Lloyd; Simone Montangero

2014-08-03

206

Quantum Game Theory and Open Access Publishing

The digital revolution of the information age and in particular the sweeping changes of scientific communication brought about by computing and novel communication technology, potentiate global, high grade scientific information for free. The arXiv for example is the leading scientific communication platform, mainly for mathematics and physics, where everyone in the world has free access on. While in some scientific disciplines the open access way is successfully realized, other disciplines (e.g. humanities and social sciences) dwell on the traditional path, even though many scientists belonging to these communities approve the open access principle. In this paper we try to explain these different publication patterns by using a game theoretical approach. Based on the assumption, that the main goal of scientists is the maximization of their reputation, we model different possible game settings, namely a zero sum game, the prisoners' dilemma case and a version of the stag hunt game, that show the dilemma of sc...

Hanauske, M; Dugall, B; Bernius, Steffen; Dugall, Berndt; Hanauske, Matthias

2006-01-01

207

OpenRIMS: An Open Architecture Radiology Informatics Management System

The following are benefits of an integrated picture archiving and communication system\\/radiology information system archive built with open-source tools and methods: open source, inexpensive interfaces can be updated as needed, and reduced risk of redundant and inconsistent data. Also, wide adoption would promote standard data mining tools, reducing user needs to learn multiple methods to perform the same task. A

Steve G. Langer

2002-01-01

208

Non-Markovian Dynamical Maps: Numerical Processing of Open Quantum Trajectories

NASA Astrophysics Data System (ADS)

The initial stages of the evolution of an open quantum system encode the key information of its underlying dynamical correlations, which in turn can predict the trajectory at later stages. We propose a general approach based on non-Markovian dynamical maps to extract this information from the initial trajectories and compress it into non-Markovian transfer tensors. Assuming time-translational invariance, the tensors can be used to accurately and efficiently propagate the state of the system to arbitrarily long time scales. The non-Markovian transfer tensor method (TTM) demonstrates the coherent-to-incoherent transition as a function of the strength of quantum dissipation and predicts the noncanonical equilibrium distribution due to the system-bath entanglement. TTM is equivalent to solving the Nakajima-Zwanzig equation and, therefore, can be used to reconstruct the dynamical operators (the system Hamiltonian and memory kernel) from quantum trajectories obtained in simulations or experiments. The concept underlying the approach can be generalized to physical observables with the goal of learning and manipulating the trajectories of an open quantum system.

Cerrillo, Javier; Cao, Jianshu

2014-03-01

209

On adiabatic evolution for a general time-dependent quantum system

The unitary operator corresponding to the classical canonical transformation that connects a general closed system to an open system under adiabatic conditions is found. The quantum invariant operator of the adiabatic open system is derived from the unitary transformation of the quantum Hamiltonian of the closed system. On the basis of these results, we investigate the evolution of the general quantum adiabatic system and construct a revised adiabatic theorem. The adiabatic theorem developed here exactly reduces to the well-known Berry adiabatic theorem when the control parameter

Kyu Hwang Yeon; Jeong Ryeol Choi; Shou Zhang; Thomas F. George

2011-01-18

210

Waves in Open Systems via Bi-orthogonal Basis

Dissipative quantum systems are sometimes phenomenologically described in terms of a non-hermitian hamiltonian $H$, with different left and right eigenvectors forming a bi-orthogonal basis. It is shown that the dynamics of waves in open systems can be cast exactly into this form, thus providing a well-founded realization of the phenomenological description and at the same time placing these open systems into a well-known framework. The formalism leads to a generalization of norms and inner products for open systems, which in contrast to earlier works is finite without the need for regularization. The inner product allows transcription of much of the formalism for conservative systems, including perturbation theory and second-quantization.

P. T. Leung; W. -M. Suen; C. P. Sun; K. Young

1999-03-08

211

Hybrid quantum systems of atoms and ions

In recent years, ultracold atoms have emerged as an exceptionally\\u000acontrollable experimental system to investigate fundamental physics, ranging\\u000afrom quantum information science to simulations of condensed matter models.\\u000aHere we go one step further and explore how cold atoms can be combined with\\u000aother quantum systems to create new quantum hybrids with tailored properties.\\u000aCoupling atomic quantum many-body states to

Christoph Zipkes; Lothar Ratschbacher; Stefan Palzer; Carlo Sias; Michael Köhl

2010-01-01

212

Quantum Teleportation in One-Dimensional Quantum Dots System

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) entanglement and after a Bell measurement, the unknown qubit is transfered to quantum dot B. Selecting an appropriate Hamiltonian for the quantum gate allows the spin-based information to be transformed into a charge-based information. The possibility of generalizing this model to N-electrons is discussed.

Hefeng Wang; Sabre Kais

2006-05-18

213

Enhancing quantum effects via periodic modulations in optomechanical systems

NASA Astrophysics Data System (ADS)

Parametrically modulated optomechanical systems have been recently proposed as a simple and efficient setting for the quantum control of a micromechanical oscillator: relevant possibilities include the generation of squeezing in the oscillator position (or momentum) and the enhancement of entanglement between mechanical and radiation modes. In this paper we further investigate this modulation regime, considering an optomechanical system with one or more parameters being modulated over time. We first apply a sinusoidal modulation of the mechanical frequency and characterize the optimal regime in which the visibility of purely quantum effects is maximal. We then introduce a second modulation on the input laser intensity and analyze the interplay between the two. We find that an interference pattern shows up, so that different choices of the relative phase between the two modulations can either enhance or cancel the desired quantum effects, opening new possibilities for optimal quantum control strategies.

Farace, Alessandro; Giovannetti, Vittorio

2012-07-01

214

Quantum theory of a two-mode open-cavity laser

We develop the quantum theory of an open-cavity laser assuming that only two modes compete for gain. We show that the modes interact to build up a collective mode that becomes the lasing mode when pumping exceeds a threshold. This collective mode exhibits all the features of a typical laser mode, whereas its precise behavior depends explicitly on the openness of the cavity. We approach the problem by using the density-matrix formalism and derive the master equation for the light field. Our results are of particular interest in the context random laser systems.

V. Eremeev; S. E. Skipetrov; M. Orszag

2011-08-25

215

Numerical results for the energy spectra of {ital N} electrons on a spherical surface are used as input data to determine the quasiparticle energies and the pairwise {open_quote}{open_quote}Fermi liquid{close_quote}{close_quote} interactions of composite fermion (CF) excitations in fractional quantum Hall systems. The quasiparticle energies and their interactions are then used to determine the energy spectra, {ital E} vs total angular momentum

P. Sitko; S. N. Yi; K. S. Yi; J. J. Quinn

1996-01-01

216

Maxwell's demons in multipartite quantum correlated systems

NASA Astrophysics Data System (ADS)

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

217

Characterizing quantum dynamics with initial system-environment correlations

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment we tomographically reconstruct a superchannel---a generalised channel that treats preparation procedures as inputs---from measurement of the system alone, despite its coupling to the environment. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimised in regards to its environment.

Martin Ringbauer; Christopher J. Wood; Kavan Modi; Alexei Gilchrist; Andrew G. White; Alessandro Fedrizzi

2014-10-21

218

Characterizing quantum dynamics with initial system-environment correlations.

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment, we tomographically reconstruct a superchannel-a generalized channel that treats preparation procedures as inputs-from measurement of the system alone. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimized in regard to its environment. PMID:25793785

Ringbauer, M; Wood, C J; Modi, K; Gilchrist, A; White, A G; Fedrizzi, A

2015-03-01

219

Characterizing Quantum Dynamics with Initial System-Environment Correlations

NASA Astrophysics Data System (ADS)

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment, we tomographically reconstruct a superchannel—a generalized channel that treats preparation procedures as inputs—from measurement of the system alone. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimized in regard to its environment.

Ringbauer, M.; Wood, C. J.; Modi, K.; Gilchrist, A.; White, A. G.; Fedrizzi, A.

2015-03-01

220

Coherent versus Measurement Feedback: Linear Systems Theory for Quantum Information

NASA Astrophysics Data System (ADS)

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

221

Coherent versus measurement feedback: Linear systems theory for quantum information

To control a quantum system via feedback, we generally have two options in choosing 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 the 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/disadvantages, depending on the system and the control goal, hence their comparison in several situation is important. This paper considers a general open linear quantum system with the following specific control goals; back-action evasion (BAE), generation of a quantum non-demolished (QND) variable, and generation of a decoherence-free subsystem (DFS), all of which have important roles in quantum information science. Then 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 BAE, QND, and DFS in terms of controllability and observability properties or transfer functions of linear systems, which are consistent with their standard definitions.

Naoki Yamamoto

2014-10-10

222

Evolution of an open system as a continuous measurement of this system by its environment

The restricted-path-integral (RPI) description of a continuous quantum measurement is rederived starting from the description of an open system by the Feynman-Vernon influence functional. For this end the total evolution operator of the compound system consisting of the open system and its environment is decomposed into the sum of partial evolution operators. Accordingly, the influence functional of the open system is decomposed into the integral of partial influence functionals (PIF). If the partial evolution operators or PIF are chosen in such a way that they decohere (do not interfere with each other), then the formalism of RPI effectively arises. The evolution of the open system may then be interpreted as a continuous measurement of this system by its environment. This is possible if the environment is macroscopic or mesoscopic.

Mensky, M B

2003-01-01

223

Evolution of an open system as a continuous measurement of this system by its environment

The restricted-path-integral (RPI) description of a continuous quantum measurement is rederived starting from the description of an open system by the Feynman-Vernon influence functional. For this end the total evolution operator of the compound system consisting of the open system and its environment is decomposed into the sum of partial evolution operators. Accordingly, the influence functional of the open system is decomposed into the integral of partial influence functionals (PIF). If the partial evolution operators or PIF are chosen in such a way that they decohere (do not interfere with each other), then the formalism of RPI effectively arises. The evolution of the open system may then be interpreted as a continuous measurement of this system by its environment. This is possible if the environment is macroscopic or mesoscopic.

Michael B. Mensky

2002-11-19

224

The thermodynamic hamiltonian for open systems

The variational method is very important in mathematical and theoretical physics because it allows us to describe the natural systems by physical quantities independently from the frame of reference used. A global and statistical approach have been introduced starting from non-equilibrium thermodynamics, obtaining the principle of maximum entropy generation for the open systems. This principle is a consequence of the lagrangian approach to the open systems. Here it will be developed a general approach to obtain the thermodynamic hamiltonian for the dynamical study of the open systems. It follows that the irreversibility seems to be the fundamental phenomenon which drives the evolution of the states of the open systems.

Umberto Lucia

2011-01-06

225

OpenRIMS: An Open Architecture Radiology Informatics Management System

The benefits of an integrated picture archiving and communication system\\/radiology information system (PACS\\/RIS) archive built\\u000a with open source tools and methods are 2-fold. Open source permits an inexpensive development model where interfaces can be\\u000a updated as needed, and the code is peer reviewed by many eyes (analogous to the scientific model). Integration of PACS\\/RIS\\u000a functionality reduces the risk of inconsistent

Steve Langer

2002-01-01

226

NASA Astrophysics Data System (ADS)

Entanglement is known today as a key resource in many protocols from quantum computation and quantum information theory. However, despite the successful demonstration of several protocols, such as teleportation or quantum key distribution, there are still many open questions of how entanglement affects the efficiency of quantum algorithms or how it can be protected against noisy environments. The investigation of these and related questions often requires a search or optimization over the set of quantum states and, hence, a parametrization of them and various other objects. To facilitate this kind of studies in quantum information theory, here we present an extension of the FEYNMAN program that was developed during recent years as a toolbox for the simulation and analysis of quantum registers. In particular, we implement parameterizations of hermitian and unitary matrices (of arbitrary order), pure and mixed quantum states as well as separable states. In addition to being a prerequisite for the study of many optimization problems, these parameterizations also provide the necessary basis for heuristic studies which make use of random states, unitary matrices and other objects. Program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v4_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v4_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.: 24 231 No. of bytes in distributed program, including test data, etc.: 1 416 085 Distribution format: tar.gz Programming language: Maple 11 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; program has been tested under Microsoft Windows XP, Linux Classification: 4.15 Does the new version supersede the previous version?: Yes Nature of problem: During the last decades, quantum information science has contributed to our understanding of quantum mechanics and has provided also new and efficient protocols, based on the use of entangled quantum states. To determine the behavior and entanglement of n-qubit quantum registers, symbolic and numerical simulations need to be applied in order to analyze how these quantum information protocols work and which role the entanglement plays hereby. Solution method: Using the computer algebra system Maple, we have developed a set of procedures that 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 that act upon the quantum registers. With the parameterization of various frequently-applied objects, that are implemented in the present version, the program now facilitates a wider range of symbolic and numerical studies. All commands 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: In the first version of the FEYNMAN program [1], we implemented the data structures and tools that are necessary to create, manipulate and to analyze the state of quantum registers. Later [2,3], support was added to deal with quantum operations (noisy channels) as an ingredient which is essential for studying the effects of decoherence. With the present extension, we add a number of parametrizations of objects frequently utilized in decoherence and entanglement studies, such that as hermitian and unitary matrices, probability distributions, or various kinds of quantum states. This extension therefore provides the basis, for example, for the optimization of a given function over the set of pure states or the simple generation of random objects. Running time: Most commands that act upon quantum registers with five or less qubits take ?10 seconds of processor time on a Pentium 4 processor with ?2GHz or newer, and about 5-20 MB of working memory (in addition to the memory for the

Radtke, T.; Fritzsche, S.

2008-11-01

227

Concatenated quantum codes in biological systems

NASA Astrophysics Data System (ADS)

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

228

Quantum teleportation in one-dimensional quantum dots system Hefeng Wang, Sabre Kais *

Quantum teleportation in one-dimensional quantum dots system Hefeng Wang, Sabre Kais * Department 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

Kais, Sabre

229

Quantum Teleportation in Quantum Dots System Hefeng Wang and Sabre Kais

Quantum Teleportation in Quantum Dots System Hefeng Wang and Sabre Kais Department of Chemistry 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

Kais, Sabre

230

Open radio map based indoor navigation system

In this presentation, we introduce an open radio map based indoor navigation system. The system is implemented on a Google android phone and tested on 3rd floor, Main-building, KAIST Munji Campus, Korea. The open radio map for the system is constructed by partly participatory approach. That is, the radio map data for rooms and laboratories are collected by ordinary users

Dongsoo Han; Minkyu Lee; Laeyoung Chang; Hyunil Yang

2010-01-01

231

QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General

Paolo Giannozzi; Stefano Baroni; Nicola Bonini; Matteo Calandra; Roberto Car; Carlo Cavazzoni; Davide Ceresoli; Guido L. Chiarotti; Matteo Cococcioni; Ismaila Dabo; Andrea Dal Corso; Stefano de Gironcoli; Stefano Fabris; Guido Fratesi; Ralph Gebauer; Uwe Gerstmann; Christos Gougoussis; Anton Kokalj; Michele Lazzeri; Layla Martin-Samos; Nicola Marzari; Francesco Mauri; Riccardo Mazzarello; Stefano Paolini; Alfredo Pasquarello; Lorenzo Paulatto; Carlo Sbraccia; Sandro Scandolo; Gabriele Sclauzero; Ari P. Seitsonen; Alexander Smogunov; Paolo Umari; Renata M. Wentzcovitch

2009-01-01

232

Variational approach for the quantum Zakharov system

The quantum Zakharov system is described in terms of a Lagrangian formalism. A time-dependent Gaussian trial function approach for the envelope electric field and the low-frequency part of the density fluctuation leads to a coupled, nonlinear system of ordinary differential equations. In the semiclassical case, linear stability analysis of this dynamical system shows a destabilizing role played by quantum effects. Arbitrary values of the quantum effects are also considered, yielding the ultimate destruction of the localized, Gaussian trial solution. Numerical simulations are shown for both the semiclassical and the full quantum cases.

Haas, F. [Universidade do Vale do Rio dos Sinos, Unidade de Exatas e Tecnologicas, Av. Unisinos, 950, 93022-000 Sao Leopoldo, RS (Brazil)

2007-04-15

233

Quantum demolition filtering and optimal control of unstable systems.

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

Belavkin, V P

2012-11-28

234

Predictive Information for Quantum Bio-Systems

NASA Astrophysics Data System (ADS)

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

235

Energy balance for a dissipative quantum system

NASA Astrophysics Data System (ADS)

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

236

Flow of quantum correlations from a two-qubit system to its environment

NASA Astrophysics Data System (ADS)

The open-system dynamics of entanglement plays an important role in the assessment of the robustness of quantum information processes and also in the investigation of the classical limit of quantum mechanics. Here we show that, subjacent to this dynamics, there is a subtle flow of quantum correlations. We use a recently proposed optical setup, which allows joint tomography of system and environment, to show that the decay of an initial bipartite entangled state leads to the buildup of multipartite entanglement and quantum discord, the latter exhibiting a nonanalytic behavior that signals the emergence of maximal genuine quantum entanglement. The origin of this analyticity is shown to be distinct from similar behavior previously found in bipartite systems. Monogamy relations within the context of open-system dynamics explain this phenomenon.

Aguilar, G. H.; Farías, O. Jiménez; Valdés-Hernández, A.; Souto Ribeiro, P. H.; Davidovich, L.; Walborn, S. P.

2014-02-01

237

Open system geometric phase based on system-reservoir joint state evolution

The geometric phase is of fundamental interest and plays an important role in quantum information processing. However, the definition and calculation of this phase for open systems remains a problem due to the lack of agreement on generalizations of the parallel transport condition to mixed state nonunity evolutions. Here we tackle this problem by associating the open system geometric phase with the parallel transport of the joint system-reservoir state. Our approach not only provides a way around the nonunitary evolution obstacle, but also sheds light on the relation between the geometric phase and the system-reservoir entanglement, which has not been investigated. Based on this approach, we calculate the geometric phase of different quantum systems subject to energy decay, showing that it is robust against decoherence, which is in distinct contrast with previous results.

Shi-Biao Zheng

2014-05-06

238

78 FR 11988 - Open Video Systems

Federal Register 2010, 2011, 2012, 2013, 2014

...47 CFR Part 76 [CS Docket No. 96-46, FCC 96-334] Open Video Systems AGENCY: Federal Communications Commission. ACTION...The final rules modified rules and policies concerning Open Video Systems. DATES: The amendments to 47 CFR 76.1505(d)...

2013-02-21

239

Classical Equations for Quantum Systems

The origin of the phenomenological deterministic laws that approximately govern the quasiclassical domain of familiar experience is considered in the context of the quantum mechanics of closed systems such as the universe as a whole. We investigate the requirements for coarse grainings to yield decoherent sets of histories that are quasiclassical, i.e. such that the individual histories obey, with high probability, effective classical equations of motion interrupted continually by small fluctuations and occasionally by large ones. We discuss these requirements generally but study them specifically for coarse grainings of the type that follows a distinguished subset of a complete set of variables while ignoring the rest. More coarse graining is needed to achieve decoherence than would be suggested by naive arguments based on the uncertainty principle. Even coarser graining is required in the distinguished variables for them to have the necessary inertia to approach classical predictability in the presence of t...

Gell-Mann, Murray; Gell-Mann, Murray; Hartle, James B.

1993-01-01

240

Uniquely defined geometric phase of an open system

Various types of unravelings of Lindblad master equation have been used to define the geometric phase for an open quantum system. Approaches of this type were criticized for lacking in unitary symmetry of the Lindblad equation [A. Bassi and E. Ippoliti, Phys. Rev. A 73, 062104 (2006)]. We utilize quantum state diffusion (QSD) approach to demonstrate that a geometric phase invariant on the symmetries of the Lindblad equation can be defined. It is then shown that such a definition of the geometric phase could be either invariant on the decomposition of the initial mixed state or gauge invariant, but not both. This alternative is inherent to the definitions based on quantum trajectories. The QSD geometric phase is computed for a qubit in different types of environments.

Buric, Nikola; Radonjic, Milan [Institute of Physics, University of Belgrade, P.O. Box 68, 11000 Belgrade (Serbia)

2009-07-15

241

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

How Quantum Computers Fail: Quantum Codes, Correlations in Physical Systems, and Noise Accumulation for quantum evolutions when noise accumulates. 1 Introduction Quantum computers were offered by Feynman [6: The postulate of quantum computation: Computational devices based on quantum mechanics will be computationally

Kalai, Gil

242

Slightly anharmonic systems in quantum optics

NASA Technical Reports Server (NTRS)

We consider an arbitrary atomic system (n-level atom or many such atoms) interacting with a strong resonant quantum field. The approximate evolution operator for a quantum field case can be produced from the atomic evolution operator in an external classical field by a 'quantization prescription', passing the operator arguments to Wigner D-functions. Many important phenomena arising from the quantum nature of the field can be described by such a way.

Klimov, Andrey B.; Chumakov, Sergey M.

1995-01-01

243

Maximal atom-photon entanglement in a double-? quantum system

NASA Astrophysics Data System (ADS)

The atom-photon entanglement of a dressed atom and its spontaneous emission in a double-? closed-loop atomic system is studied under multi-photon resonance condition. It is shown that even in the absence of quantum interference due to the spontaneous emission, the von Neumann entropy is phase-sensitive and it can be controlled by either intensity or relative phase of the applied fields. It is demonstrated that for the special case of Rabi frequency of the applied fields, the system is maximally entangled. Moreover, an open-loop configuration is considered, and it is shown that the degree of entanglement can be controlled by intensity of the applied fields. Furthermore, in electromagnetically induced transparency condition, the system is disentangled. Such a system can be used for quantum information processing via entanglement using optical switching.

Kordi, Zeinab; Ghanbari, Saeed; Mahmoudi, Mohammad

2015-03-01

244

Alternative linear structures for classical and quantum systems

The possibility of deforming the (associative or Lie) product to obtain alternative descriptions for a given classical or quantum system has been considered in many papers. Here we discuss the possibility of obtaining some novel alternative descriptions by changing the linear structure instead. In particular we show how it is possible to construct alternative linear structures on the tangent bundle TQ of some classical configuration space Q that can be considered as "adapted" to the given dynamical system. This fact opens the possibility to use the Weyl scheme to quantize the system in different non equivalent ways, "evading", so to speak, the von Neumann uniqueness theorem.

E. Ercolessi; A. Ibort; G. Marmo; G. Morandi

2007-06-12

245

Quantum discord for a two-parameter class of states in $2 \\otimes d$ quantum systems

Quantum discord witnesses the nonclassicality of quantum states even when there is no entanglement in these quantum states. This type of quantum correlation also has some interesting and significant applications in quantum information processing. Quantum discord has been evaluated explicitly only for certain class of two-qubit states. We extend the previous studies to $2 \\otimes d$ quantum systems and derive an analytical expression for quantum discord for a two-parameter class of states for $d \\geq 3$. We compare quantum discord, classical correlation, and entanglement for qubit-qutrit systems to demonstrate that different measures of quantum correlation are not identical and conceptually different.

Mazhar Ali

2010-08-24

246

Classical and Quantum Surgery of Geometries in an Open Inflationary Universe

We study classically and quantum mechanically the Euclidean geometries compatible with an open inflationary universe of a Lorentzian geometry. The Lorentzian geometry of the open universe with an ordinary matter state matches either an open or a closed Euclidean geometry at the cosmological singularity. With an exotic matter state it matches only the open Euclidean geometry and describes a genuine instanton regular at the boundary of a finite radius. The wave functions are found that describe the quantum creation of the open inflationary universe.

Sang Pyo Kim

2000-05-09

247

Software-defined Quantum Communication Systems

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 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 an example, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We conclude that software-defined quantum communication provides a robust framework in which to explore the large design space offered by this new regime of communication.

Travis S. Humble; Ronald J. Sadlier

2014-10-20

248

Quantum contextuality in N-boson systems

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

Benatti, Fabio [Dipartimento di Fisica, Universita degli Studi di Trieste, I-34151 Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste (Italy); Floreanini, Roberto [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste (Italy); Genovese, Marco [INRIM, Strada delle Cacce 91, I-10135 Torino (Italy); Olivares, Stefano [Dipartimento di Fisica, Universita degli Studi di Trieste, I-34151 Trieste (Italy)

2011-09-15

249

Quantum simulation of tunneling in small systems.

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, 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

250

Quantum Simulation of Tunneling in Small Systems

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, 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

251

Controlling quantum critical dynamics of isolated systems

NASA Astrophysics Data System (ADS)

Controlling the non adiabatic dynamics of isolated quantum systems driven through a critical point is of interest in a variety of fields ranging from quantum simulation to finite-time thermodynamics. We briefly review the different methods for designing protocols which minimize excitation (defect) production in a closed quantum critical system driven out of equilibrium. We chart out the role of specific driving schemes for this procedure, point out their experimental relevance, and discuss their implementation in the context of ultracold atom and spin systems.

del Campo, A.; Sengupta, K.

2015-02-01

252

Engineering Democracy in Open Agent Systems

How should open agent societies be organized? Should they be democ- racies, and, if so, what types of democracy? We present three normative models of democracy from political philosophy and consider their relevance for the engi- neering of open multi-agent systems: democracy as wise rule by an elite; democ- racy as the exercise of rational consumer choices by voters; and

Peter Mcburney; Simon Parsons

2003-01-01

253

Open protocol in multi-agent systems

Protocols for intelligent agents are difficult to write. This is partially because intelligent agents accommodate their interaction to the situation that arises. As a result, the interaction among intelligent agents cannot be governed by a fixed protocol. In this paper I describe an open protocol paradigm for reasoning in a multi-agent system with decentralized control. An open protocol is a

Gerard A. W. Vreeswijk

1995-01-01

254

Bound states in the continuum in open quantum billiards with a variable shape

We show the existence of bound states in the continuum (BICs) in quantum billiards (QBs) that are opened by attaching single-channel leads to them. They may be observed by varying an external parameter continuously, e.g., the shape of the QB. At some values of the parameter, resonance states with vanishing decay width (the BICs) occur. They are localized almost completely in the interior of the closed system. The phenomenon is shown analytically to exist in the simplest case of a two level QB and is complemented by numerical calculations for a real QB.

Sadreev, Almas F.; Bulgakov, Evgeny N. [Institute of Physics, Academy of Sciences, 660036 Krasnoyarsk (Russian Federation); Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany); Rotter, Ingrid [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany)

2006-06-15

255

Quantum Metrology for Noisy Systems

NASA Astrophysics Data System (ADS)

The estimation of parameters characterizing dynamical processes is a central problem in science and technology. It concerns for instance the evaluation of the duration of some interaction, of the value of a coupling constant, or yet of a frequency in atomic spectroscopy. The estimation error changes with the number N of resources employed in the experiment (which could quantify, for instance, the number of probes or the probing energy). For independent probes, it scales as 1/sqrt{N}—the standard limit—a consequence of the central-limit theorem. Quantum strategies, involving for instance entangled or squeezed states, may improve the precision, for noiseless processes, by an extra factor 1/sqrt{N}, leading to the so-called Heisenberg limit. For noisy processes, an important question is if and when this improvement can be achieved. Here, we review and detail our recent proposal of a general framework for obtaining attainable and useful lower bounds for the ultimate limit of precision in noisy systems. We apply this bound to lossy optical interferometry and show that, independently of the initial states of the probes, it captures the main features of the transition, as N grows, from the 1/ N to the 1/sqrt{N} behavior.

Escher, B. M.; de Matos Filho, R. L.; Davidovich, L.

2011-12-01

256

Open source, open standards, and health care information systems.

Recognition of the improvements in patient safety, quality of patient care, and efficiency that health care information systems have the potential to bring has led to significant investment. Globally the sale of health care information systems now represents a multibillion dollar industry. As policy makers, health care professionals, and patients, we have a responsibility to maximize the return on this investment. To this end we analyze alternative licensing and software development models, as well as the role of standards. We describe how licensing affects development. We argue for the superiority of open source licensing to promote safer, more effective health care information systems. We claim that open source licensing in health care information systems is essential to rational procurement strategy. PMID:21447469

Reynolds, Carl J; Wyatt, Jeremy C

2011-01-01

257

Quantum entanglement in photoactive prebiotic systems.

This paper contains the review of quantum entanglement investigations in living systems, and in the quantum mechanically modelled photoactive prebiotic kernel systems. We define our modelled self-assembled supramolecular photoactive centres, composed of one or more sensitizer molecules, precursors of fatty acids and a number of water molecules, as a photoactive prebiotic kernel systems. We propose that life first emerged in the form of such minimal photoactive prebiotic kernel systems and later in the process of evolution these photoactive prebiotic kernel systems would have produced fatty acids and covered themselves with fatty acid envelopes to become the minimal cells of the Fatty Acid World. Specifically, we model self-assembling of photoactive prebiotic systems with observed quantum entanglement phenomena. We address the idea that quantum entanglement was important in the first stages of origins of life and evolution of the biospheres because simultaneously excite two prebiotic kernels in the system by appearance of two additional quantum entangled excited states, leading to faster growth and self-replication of minimal living cells. The quantum mechanically modelled possibility of synthesizing artificial self-reproducing quantum entangled prebiotic kernel systems and minimal cells also impacts the possibility of the most probable path of emergence of protocells on the Earth or elsewhere. We also examine the quantum entangled logic gates discovered in the modelled systems composed of two prebiotic kernels. Such logic gates may have application in the destruction of cancer cells or becoming building blocks of new forms of artificial cells including magnetically active ones. PMID:24799958

Tamulis, Arvydas; Grigalavicius, Mantas

2014-06-01

258

Black Holes and Nonrelativistic Quantum Systems

We describe black holes in d+3 dimensions, whose thermodynamic properties correspond to those of a scale-invariant nonrelativistic (d+1)-dimensional quantum system with a dynamical exponent z=2. The gravitational model ...

Nickel, Marcel Dominik Johannes

259

Quantum cosmology of openR×S2×S1

NASA Astrophysics Data System (ADS)

We examine the classical and quantum cosmology of a Kantowski-Sachs spacetime manifold with a topology openR×S2×S1 and a nonzero cosmological constant, within the framework of canonical quantum gravity. The classical trajectories are analyzed, and it is shown that the classical problem can be reduced to that of free particles. Both the Hartle-Hawking ``no-boundary'' proposal and the Vilenkin ``outgoing flux'' proposal are examined. First, the Hartle-Hawking proposal is generalized to canonical quantum gravity by imposing generic initial conditions on the solutions to the Wheeler-DeWitt equation at small scale factors. The resulting wave function has essentially the same leading exponential behavior as the semiclassical approximation to the ``no-boundary'' Euclidean functional integral in the nonoscillatory region. It is further shown, by calculating overlap integrals with semiclassical wave functions, that the wave function diverges too quickly in this region to be interpreted probabilistically. An analogue of the Baum-Hawking factor appears, and is interpreted as indicating that, given a small ?, the wave function is highly peaked around a class of configurations in which the S2 radius is R=[1/(2G?1/2)]. These configurations are classically unstable. Second, given a complete set of solutions to the Wheeler-DeWitt equation, the outgoing flux proposal is found to be insufficient to select a unique wave function. A source is found for the Wheeler-DeWitt current of the above solutions. No analogue of the Baum-Hawking factor appears in the outgoing flux model.

Uglum, John

1992-11-01

260

Engineering optical properties of quantum dot systems

NASA Astrophysics Data System (ADS)

Properties and functions of nanodevices are determined by quantum behavior of nanosystems which constitute the nucleus of the nanodevices. This work is devoted to investigation of the linear and nonlinear optical properties of quantum dot systems, in part the intrinsic optical bistability. The resonance effects and many-body effects in the systems as well as the self-consistent treatment of the phenomena form the framework of the consideration. Effects of the size parameters of quantum dot systems, shapes of quantum dots, and electron population of quantum dots on the optical properties are investigated. It is shown that a few Angstroms more or less and/or one electron more or less can make a dramatic difference in the nanosystem behavior. Knowledge of the maps of the allowed dipole coupled interlevel transitions in quantum dots are demonstrated to be crucially important. A special attention is paid to the vital effects of the electron-electron interaction in the quantum dot systems: static, dynamic, intradot, and iterdot.

Bondarenko, Victor

261

Software-defined Quantum Communication Systems

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

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

2013-01-01

262

Hybrid Impulsive Control for Closed Quantum Systems

The state transfer problem of a class of nonideal quantum systems is investigated. It is known that traditional Lyapunov methods may fail to guarantee convergence for the nonideal case. Hence, a hybrid impulsive control is proposed to accomplish a more accurate convergence. In particular, the largest invariant sets are explicitly characterized, and the convergence of quantum impulsive control systems is analyzed accordingly. Numerical simulation is also presented to demonstrate the improvement of the control performance. PMID:23781158

Sun, Jitao; Lin, Hai

2013-01-01

263

Quantum correlations in qutrit-qutrit systems under local quantum noise channels

Due to decoherence, realistic quantum systems inevitably interact with the environment when quantum information is processed, which causes the loss of quantum properties. As a fundamental issue of quantum properties, quantum correlations have attracted a lot of interests in recent years. In this work, we study the quantum correlations affected by the Markovian environment by considering the quantum correlations of qutrit-qutrit quantum systems measured by the local quantum uncertainty. The local noise channels covered in this work includes dephasing, trit-flip, trit-phase-flip, and depolarising channels. We have also investigated the cases where the local decoherence channels of two sides are identical and non-identical.

Nasibollah Doustimotlagh; Jin-Liang Guo; Shuhao Wang

2014-08-07

264

A General Transfer-Function Approach to Noise Filtering in Open-Loop Quantum Control

We present a general transfer-function approach to noise filtering in open-loop Hamiltonian engineering protocols for open quantum systems. We show how to identify a computationally tractable set of fundamental filter functions, out of which arbitrary transfer filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental filter-functions set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. We prove that the resulting notion of filtering order reveals conceptually distinct, albeit complementary, features of the controlled dynamics as compared to the order of error cancellation, traditionally defined in the Magnus sense. Examples and implications are discussed.

Gerardo A. Paz-Silva; Lorenza Viola

2015-02-05

265

General Transfer-Function Approach to Noise Filtering in Open-Loop Quantum Control

NASA Astrophysics Data System (ADS)

We present a general transfer-function approach to noise filtering in open-loop Hamiltonian engineering protocols for open quantum systems. We show how to identify a computationally tractable set of fundamental filter functions, out of which arbitrary transfer filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental filter-function set suffices to characterize the error suppression capabilities of the control protocol in both the time and the frequency domain. We prove that the resulting notion of filtering order reveals conceptually distinct, albeit complementary, features of the controlled dynamics as compared to the order of error cancellation, traditionally defined in the Magnus sense. Examples and implications are discussed.

Paz-Silva, Gerardo A.; Viola, Lorenza

2014-12-01

266

Software-defined Quantum Communication Systems

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

267

Dynamics of fluctuations in a quantum system

"\\textit{The noise is the signal}"[R. Landauer, Nature \\textbf{392}, 658 (1998)] emphasizes the rich information content encoded in fluctuations. This paper assesses the dynamical role of fluctuations of a quantum system driven far from equilibrium, with laser-aligned molecules as a physical realization. Time evolutions of the expectation value and the uncertainty of a standard observable are computed quantum mechanically and classically. We demonstrate the intricate dynamics of the uncertainty that are strikingly independent of those of the expectation value, and their exceptional sensitivity to quantum properties of the system. In general, detecting the time evolution of the fluctuations of a given observable provides information on the dynamics of correlations in a quantum system.

Yi-Jen Chen; Stefan Pabst; Zheng Li; Oriol Vendrell; Robin Santra

2014-05-09

268

Open quantum systems are often encountered in many different physical situations. From quantum optics to statistical mechanics, they are fundamental in the understanding of a great variety of different phenomena. Some of the most common examples are the relaxation to equilibrium, the existence of nonequilibrium stationary states, and the dynamics of atoms in interaction with electromagnetic fields. A crucial step in the analysis is to consider the quantum open system and its environment as the two mutually interacting components of a larger isolated system. Thereafter, the so-called Markov approximation is often considered, which consists on assuming that the time scales associated to the dynamics of the quantum open system are larger than those of the environment. It is the interplay of the different time scales associated with the system and the environment what determines the validity of the different approximations made. In this paper we will discuss the dynamics of a open quantum system in contact with a reservoir when the Markov approximation is not valid, and we have to include some non-Markovian or memory effects.

Alonso, Daniel [Instituto Universitario de Estudios Avanzados (IUdEA) en Fisica Atomica, Molecular y Fotonica Departamento de Fisica Fundamental y Experimental, Electronica y Sistemas. Universidad de La Laguna, La Laguna 38203, Tenerife (Spain); Vega, Ines de [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str, 1., 85748 Garching (Germany)

2010-06-15

269

Second-order superintegrable quantum systems

A classical (or quantum) superintegrable system on an n-dimensional Riemannian manifold is an integrable Hamiltonian system with potential that admits 2n - 1 functionally independent constants of the motion that are polynomial in the momenta, the maximum number possible. If these constants of the motion are all quadratic, then the system is second-order superintegrable, the most tractable case and the one we study here. Such systems have remarkable properties: multi-integrability and separability, a quadratic algebra of symmetries whose representation theory yields spectral information about the Schroedinger operator, and deep connections with expansion formulas relating classes of special functions. For n = 2 and for conformally flat spaces when n = 3, we have worked out the structure of the classical systems and shown that the quadratic algebra always closes at order 6. Here, we describe the quantum analogs of these results. We show that, for nondegenerate potentials, each classical system has a unique quantum extension.

Miller, W. [University of Minnesota, School of Mathematics (United States); Kalnins, E. G. [University of Waikato, Department of Mathematics and Statistics (New Zealand); Kress, J. M. [The University of New South Wales, School of Mathematics (Australia)], E-mail: j.kress@unsw.edu.au

2007-03-15

270

Hidden symmetries enhance quantum transport in Light Harvesting systems

For more than 50 years we have known that photosynthetic systems harvest solar energy with almost unit {\\it quantum efficiency}. However, recent experimental evidence of {\\it quantum coherence} during the excitonic energy transport in photosynthetic organisms challenges our understanding of this fundamental biological function. Currently, and despite numerous efforts, the causal connection between coherence and efficiency is still a matter of debate. We show, through the study of extensive simulations of quantum coherent transport on networks, that three dimensional structures characterized by centro-symmetric Hamiltonians are statistically more efficient than random arrangements. Moreover, we demonstrate that the experimental data available for the electronic Hamiltonians of the Fenna-Mathew-Olson (FMO) complex of sulfur bacteria and of the crypophyte PC645 complex of marine algae are consistent with this strong correlation of centro-symmetry with quantum efficiency. These results show that what appears to be geometrically disordered complexes may well exhibit a hidden symmetry which enhances the energy transport between chromophores. We are confident that our results will motivate research to explore the properties of nearly centro-symmetric Hamiltonians in more realistic environments, and to unveil the role of symmetries for quantum effects in biology. The unravelling of such symmetries may open novel perspectives and suggest new design principles in the development of artificial devices.

Tobias Zech; Roberto Mulet; Thomas Wellens; Andreas Buchleitner

2012-05-23

271

Quadratic Plus Linear Operators which Preserve Pure States of Quantum Systems: Small Dimensions

NASA Astrophysics Data System (ADS)

A mathematical formalism of quantum mechanics says that a pure state of a quantum system corresponds to a vector of norm 1 and an observable is a self-adjoint operator on the space of states. It is of interest to describe all linear or nonlinear operators which preserve the pure states of the system. In the linear case, it is nothing more than isometries of Hilbert spaces. In the nonlinear case, this problem was open. In this paper, in the small dimensional spaces, we shall describe all quadratic plus linear operators which preserve pure states of the quantum system.

Saburov, Mansoor

2014-11-01

272

A classical leash for a quantum system: Command of quantum systems via rigidity of CHSH games

Can a classical system command a general adversarial quantum system to realize arbitrary quantum dynamics? If so, then we could realize the dream of device-independent quantum cryptography: using untrusted quantum devices to establish a shared random key, with security based on the correctness of quantum mechanics. It would also allow for testing whether a claimed quantum computer is truly quantum. Here we report a technique by which a classical system can certify the joint, entangled state of a bipartite quantum system, as well as command the application of specific operators on each subsystem. This is accomplished by showing a strong converse to Tsirelson's optimality result for the Clauser-Horne-Shimony-Holt (CHSH) game: the only way to win many games is if the bipartite state is close to the tensor product of EPR states, and the measurements are the optimal CHSH measurements on successive qubits. This leads directly to a scheme for device-independent quantum key distribution. Control over the state and operators can also be leveraged to create more elaborate protocols for realizing general quantum circuits, and to establish that QMIP = MIP*.

Ben W. Reichardt; Falk Unger; Umesh Vazirani

2012-09-03

273

Rapid mixing renders quantum dissipative systems stable

The physics of many materials is modeled by quantum many-body systems with local interactions. If the model of the system is sensitive to noise from the environment, or small perturbations to the original interactions, it will not model properly the robustness of the real physical system it aims to describe, or be useful when engineering novel systems for quantum information processing. We show that local observables and correlation functions of local Liouvillians are stable to local perturbations if the dynamics is rapidly mixing and has a unique fixed point. No other condition is required.

Angelo Lucia; Toby S. Cubitt; Spyridon Michalakis; David Pérez-García

2015-03-17

274

Engineering coherent control of quantum information in spin systems

Quantum Information Processing (QIP) promises increased efficiency in computation. A key step in QIP is implementing quantum logic gates by engineering the dynamics of a quantum system. This thesis explores the requirements ...

Hodges, Jonathan Stuart

2007-01-01

275

Strong local passivity in finite quantum systems

NASA Astrophysics Data System (ADS)

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.

Frey, Michael; Funo, Ken; Hotta, Masahiro

2014-07-01

276

Strong local passivity in finite quantum systems.

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

277

Quantum Mechanics in AF C*-SYSTEMS

NASA Astrophysics Data System (ADS)

Motivated from the chemical potential theory, we study quantum statistical thermodynamics in AF C*-systems generalizing usual one-dimensional quantum lattice systems. Our systems are C*-algebras { A} which have a localization \\{{ A}{[i, j]}\\} of finite-dimensional subalgebras indexed by finite intervals of Z and an automorphism ? acting as a right shift on the localization. Model examples are supplied from derived towers (string algebras) for type II1 factor-subfactor pairs. Given a (?-invariant) interaction and a specific tracial state, we formulate the Gibbs conditions and the variational principle for (?-invariant) states on { A}, and investigate the relationship among these conditions and the KMS condition for the time evolution generated by the interaction. Special attention is paid to C*-systems of gauge invariance (typical model in the chemical potential theory) and to C*-systems considered as quantum random walks on discrete groups. The CNT-dynamical entropy for the shift automorphism ? is also discussed.

Hiai, Fumio; Petz, Dénes

278

Open quantum dynamics of single-photon optomechanical devices

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of a Michelson interferometer with Fabry-Perot cavity arms and one movable end mirror, and driven by a single photon—an optomechanical device previously studied by Marshall as a device that searches for gravity decoherence. We obtain an exact analytical solution for the system's quantum mechanical equations of motion, including details about the exchange of the single photon between the cavity mode and the external continuum. The resulting time evolution of the interferometer's fringe visibility displays interesting new features when the incoming photon's frequency uncertainty is narrower or comparable to the cavity's line width—only in the limiting case of much broader-band photon does the result return to that of Marshall , but in this case the photon is not very likely to enter the cavity and interact with the mirror, making the experiment less efficient and more susceptible to imperfections. In addition, we show that in the strong-coupling regime, by engineering the incoming photon's wave function, it is possible to prepare the movable mirror into an arbitrary quantum state of a multidimensional Hilbert space.

Hong, Ting; Yang, Huan; Miao, Haixing; Chen, Yanbei

2013-08-01

279

Levitated Quantum Nano-Magneto-Mechanical Systems

NASA Astrophysics Data System (ADS)

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

280

The Distance Between Classical and Quantum Systems

In a recent paper, a “distance” function,\\u000a\\u000a, was defined which measures the distance between pure classical and quantum systems. In this work, we present a new definition of a “distance”, D, which measures the distance between either pure or impure classical and quantum states. We also compare the new distance formula with the previous formula, when the latter is

Deanna Abernethy; John R. Klauder

2005-01-01

281

QUANTUM STOCHASTIC CALCULUS AND QUANTUM NONLINEAR FILTERING

QUANTUM STOCHASTIC CALCULUS AND QUANTUM NONLINEAR FILTERING V. P. BELAVKIN Abstract. A ?Âalgebraic inde...nite structure of quantum stochastic (QS) cal- culus is introduced and a continuity property...nitely dimensional nuclear space. The class of nondemolition output QS processes in quantum open systems

Belavkin, Viacheslav P.

282

Zero forcing, linear and quantum controllability for systems evolving on networks

We study the dynamics of systems on networks from a linear algebraic perspective. The control theoretic concept of controllability describes the set of states that can be reached for these systems. Under appropriate conditions, there is a connection between the quantum (Lie theoretic) property of controllability and the linear systems (Kalman) controllability condition. We investigate how the graph theoretic concept of a zero forcing set impacts the controllability property. In particular, we prove that if a set of vertices is a zero forcing set, the associated dynamical system is controllable. The results open up the possibility of further exploiting the analogy between networks, linear control systems theory, and quantum systems Lie algebraic theory. This study is motivated by several quantum systems currently under study, including continuous quantum walks modeling transport phenomena. Additionally, it proposes zero forcing as a new notion in the analysis of complex networks.

Daniel Burgarth; Domenico D'Alessandro; Leslie Hogben; Simone Severini; Michael Young

2011-11-07

283

Magnetoconductance in Open Stadium Billiard: Quantum Analogue of Transition from Chaos to Tori

Quantum and classical analyses are made on transport in an open Bunimovich stadium billiard in the perpendicular magnetic field B. The mild and violent undulations of quantum conductance g(B) in low- and high-field regions are due to the stability of the fully chaotic phase space in the underlying classical dynamics and to the transitional instability of the ergodic part which

Katsuhiro Nakamura; Ken Ito; Yositake Takane

1994-01-01

284

Open-PEA Space Charge Measurement System

NASA Astrophysics Data System (ADS)

The pulsed electro-acoustic (PEA) method has been widely used to observe space charge phenomena in dielectric materials. There have been awaited demands for monitoring space charge phenomena under electron beam or radioactive rays irradiations, or during plasma processing. Therefore we have developed a new PEA space charge measurement system that can observe space charge distributions under such severe conditions. This system uses an open upper electrode that can measure surface and internal space charge profiles at the same time. This paper introduces the 'Open-PEA system' with experimental results obtained during electron irradiation in vacuum.

Imai, Satoshi; Tanaka, Yasuhiro; Fukao, Tadashi; Takada, Tatsuo; Maeno, Takashi

285

Relaxation of isolated quantum systems beyond chaos

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.

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

2015-01-23

286

Relaxation of isolated quantum systems beyond chaos.

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. PMID:25679559

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

2015-01-01

287

Relaxation of isolated quantum systems beyond chaos

NASA Astrophysics Data System (ADS)

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

288

Quantum Hall systems Representation theory of vertex operator algebras Applications The end Quantum Science, CAS #12;Quantum Hall systems Representation theory of vertex operator algebras Applications quantum computation 2 Representation theory of vertex operator algebras Vetrex operator algebras, modules

Huang, Yi-Zhi

289

Open Multi-Agent Systems: Agent

that facilitate the communication process in a multi-agent system. These agents, referred to with terms like facilitators, routers, mediators, bro- kers and so on (cf. [8]) act as intermediaries between communicatingOpen Multi-Agent Systems: Agent Communication and Integration Rogier M. van Eijk, Frank S. de Boer

Utrecht, Universiteit

290

Witnessing Quantum Coherence: from solid-state to biological systems

Quantum coherence is one of the primary non-classical features of quantum systems. While protocols such as the Leggett-Garg inequality (LGI) and quantum tomography can be used to test for the existence of quantum coherence and dynamics in a given system, unambiguously detecting inherent “quantumness” still faces serious obstacles in terms of experimental feasibility and efficiency, particularly in complex systems. Here we introduce two “quantum witnesses” to efficiently verify quantum coherence and dynamics in the time domain, without the expense and burden of non-invasive measurements or full tomographic processes. Using several physical examples, including quantum transport in solid-state nanostructures and in biological organisms, we show that these quantum witnesses are robust and have a much finer resolution in their detection window than the LGI has. These robust quantum indicators may assist in reducing the experimental overhead in unambiguously verifying quantum coherence in complex systems. PMID:23185690

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

2012-01-01

291

Witnessing Quantum Coherence: from solid-state to biological systems

NASA Astrophysics Data System (ADS)

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

292

Quantum key distribution system clocked at 2 GHz

Quantum key distribution system clocked at 2 GHz Karen J. Gordon, Veronica Fernandez, Gerald S, Ireland http://www.phy.hw.ac.uk/resrev/photoncounting/index.html Abstract: An improved quantum key-based quantum key distribution test system performance in terms of transmission distance and quantum bit error

Buller, Gerald S.

293

Heisenberg picture approach to the stability of quantum Markov systems

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

294

Heisenberg picture approach to the stability of quantum Markov systems

NASA Astrophysics Data System (ADS)

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

295

Heisenberg Picture Approach to the Stability of Quantum Markov Systems

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.

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

2014-05-27

296

Synchro-thermalization of composite quantum system

We study the thermalization of a composite quantum system consisting of several subsystems, where only a small one of the subsystem contacts with a heat bath in equilibrium, while the rest of the composite system is contact free. We show that the whole composite system still can be thermalized after a relaxation time long enough, if the energy level structure of the composite system is connected, which means any two energy levels of the composite system can be connected by direct or indirect quantum transitions. With an example where an multi-level system interacts with a set of harmonic oscillators via non-demolition coupling, we find that the speed of relaxation to the global thermal state is suppressed by the multi-Franck-Condon factor due to the displacements of the Fock states when the degrees of freedom is large.

Sheng-Wen Li; D. Z. Xu; X. F. Liu; C. P. Sun

2014-03-21

297

Spectral theorem for the Lindblad equation for quadratic open fermionic systems

The spectral theorem is proven for the quantum dynamics of quadratic open systems of n fermions described by the Lindblad equation. Invariant eigenspaces of the many-body Liouvillean dynamics and their largest Jordan blocks are explicitly constructed for all eigenvalues. For eigenvalue zero we describe an algebraic procedure for constructing (possibly higher dimensional) spaces of (degenerate) non-equilibrium steady states.

Tomaz Prosen

2010-05-05

298

NASA Astrophysics Data System (ADS)

We propose a quantitative criterion to determine whether the coupled quantum systems can achieve complete synchronization or phase synchronization in the process of analyzing quantum synchronization. Adopting the criterion, we discuss the quantum synchronization effects between optomechanical systems and find that the error between the systems and the fluctuation of error is sensitive to coupling intensity by calculating the largest Lyapunov exponent of the model and quantum fluctuation, respectively. By taking the appropriate coupling intensity, we can control quantum synchronization even under different logical relationships between switches. Finally, we simulate the dynamical evolution of the system to verify the quantum synchronization criterion and to show the ability of synchronization control.

Li, Wenlin; Li, Chong; Song, Heshan

2015-02-01

299

A quantum dynamics study of the benzopyran ring opening guided by laser pulses

NASA Astrophysics Data System (ADS)

The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists to control the photoreactivity vs. photostability ratio (selectivity). In this work we present: (i) a pump-dump technique used to control the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation in the electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the first adiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics.

Saab, Mohamad; Doriol, Loïc Joubert; Lasorne, Benjamin; Guérin, Stéphane; Gatti, Fabien

2014-10-01

300

Quantum gears: a simple mechanical system in the quantum Angus MacKinnon

Quantum gears: a simple mechanical system in the quantum regime Angus MacKinnon Blackett Laboratory. The quantum mechanics of a simple mechanical system is considered. A group of gears can serve as a model molecules. An expression is derived for the quantisation of the dynamics of a 2Âgear system. The general

MacKinnon, Angus

301

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

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

302

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

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.

Edgar A. Gomez; J. D. Hernandez-Rivero; Herbert Vinck-Posada

2015-02-01

303

Open Source Course Management and Assessment System

LON-CAPA: Open Source Course Management and Assessment System Gerd Kortemeyer Michigan State, homework problems) is a lot of work Â· Doing so for use in just one course is a waste of time and effort Assembly Course Management Resource Assembly Course Management #12;Campus A Campus B Resource Assembly

304

Quantum information processing in multi-spin systems

Coherence and entanglement in multi-spin systems are valuable resources for quantum information processing. In this thesis, I explore the manipulation of quantum information in complex multi-spin systems, with particular ...

Cappellaro, Paola

2006-01-01

305

Semiclassical analysis of quantum systems with constraints

NASA Astrophysics Data System (ADS)

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

306

Photorefractive quantum wells: Materials, devices and systems

NASA Astrophysics Data System (ADS)

Photorefractive quantum wells are dynamic holographic materials that combine the advantages of large excitonic electroabsorption with large carrier mobilities to produce high-sensitivity holographic devices operable at extremely low optical intensities compatible with image processing applications. They are finding a niche as versatile optical devices in systems such as joint image correlators, femtosecond autocorrelators, laser-based ultrasound detection, and time-to-space mapping. These devices contain high defect densities which trap and store photogenerated carriers. The trapped space-charge results in a spatially varying space-charge field that matches the periodicity of the incident intensity pattern, which alters the optical properties of the device. The principal objective of the present study was to develop a new material system (low-temperature-grown AlGaAs/GaAs quantum wells) for photorefractive applications. We have achieved ultrafast electron recombination lifetimes in combination with sharp excitonic features, a goal which was considered mutually exclusive, by engineering low-temperature-grown AlAs/GaAs quantum wells. This material system was used to develop photorefractive p-i-n quantum well diodes operating in the quantum-confined Stark geometry for holographic applications. These photorefractive diodes operate with photocarrier transport perpendicular to the grating vector, unlike traditional photorefractive materials. They operate under transient electrical excitation resulting in a rich variety of spatio-temporal dynamics. We have optimized these devices to achieve record output diffraction efficiencies and shown that the design of these devices is relatively flexible as long as the principal functions of photoconductivity, electro-optics, and charge trapping are supplied by one or several functional layers. Nonreciprocal energy transfer, normally forbidden in Stark-effect devices, has been achieved using moving gratings. This led to the development of these photorefractive diodes to measure Doppler shifts by using electrically strobed gratings. Related to this work on longitudinal geometries, transverse-field photorefractive quantum wells were developed as adaptive beamsplitters to interrogate surface vibrations for laser-based ultrasound detection systems. These devices are tuned to quadrature for true linear detection by tailoring the excitonic spectral phase, a new contribution that is unique to the photorefractive quantum wells. This work has evolved from the physics of semi-insulating materials, to optimizing devices, to building complete systems using photorefractive quantum wells.

Lahiri, Indrajit

307

Quantum coherence of biophotons and living systems.

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

308

Quantum Phase Transitions in a Finite System

A general procedure for studying finite-N effects in quantum phase transitions of finite systems is presented and applied to the critical-point dynamics of nuclei undergoing a shape-phase transition of second-order (continuous), and of first-order with an arbitrary barrier.

A. Leviatan

2006-12-05

309

Simulability and regularity of complex quantum systems

We show that the transition from regular to chaotic spectral statistics in interacting many-body quantum systems has an unambiguous signature in the distribution of Schmidt coefficients dynamically generated from a generic initial state, and thus limits the efficiency of the t-DMRG algorithm.

Hannah Venzl; Andrew J. Daley; Florian Mintert; Andreas Buchleitner

2008-08-28

310

Lithography system using quantum entangled photons

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

311

Coherent control in simple quantum systems

NASA Technical Reports Server (NTRS)

Coherent dynamics of two, three, and four-level quantum systems, simultaneously driven by concurrent laser pulses of arbitrary and different forms, is treated by using a nonperturbative, group-theoretical approach. The respective evolution matrices are calculated in an explicit form. General aspects of controllability of few-level atoms by using laser fields are treated analytically.

Prants, Sergey V.

1995-01-01

312

Quantum Chaos & Quantum Computers

The standard generic quantum computer model is studied analytically and numerically and the border for emergence of quantum chaos, induced by imperfections and residual inter-qubit couplings, is determined. This phenomenon appears in an isolated quantum computer without any external decoherence. The onset of quantum chaos leads to quantum computer hardware melting, strong quantum entropy growth and destruction of computer operability. The time scales for development of quantum chaos and ergodicity are determined. In spite the fact that this phenomenon is rather dangerous for quantum computing it is shown that the quantum chaos border for inter-qubit coupling is exponentially larger than the energy level spacing between quantum computer eigenstates and drops only linearly with the number of qubits n. As a result the ideal multi-qubit structure of the computer remains rather robust against imperfections. This opens a broad parameter region for a possible realization of quantum computer. The obtained results are related to the recent studies of quantum chaos in such many-body systems as nuclei, complex atoms and molecules, finite Fermi systems and quantum spin glass shards which are also reviewed in the paper.

D. L. Shepelyansky

2000-06-15

313

Quantum correlations in different density-matrix representations of spin-1/2 open chain

NASA Astrophysics Data System (ADS)

We consider quantum correlations in a spin-1/2 open chain of N nodes with the XY Hamiltonian using different bases for the density-matrix representation and the initial state with a single polarized node. These bases of our choice are the following: (i) the basis of eigenvectors of the fermion operators which appears naturally through the Jordan-Wigner transformation (this representation of the density matrix is referred to as the ? representation); (ii) its Fourier representation (c representation of the density matrix); and (iii) the basis of eigenvectors of the operators Ijz (the z projection of the jth spin, j=1,⋯,N). Although for the short chains (a few nodes) the qualitative behavior of the entanglement and the discord are very similar (the difference is quantitative), this is not valid for longer chains (N?10). In this case, there are qualitative and quantitative distinctions between the entanglement and the discord in all three cases. We underline the three most important features: (i) the quantum discord is static in the ? representation, where the entanglement is identical to zero; (ii) in the c representation, the concurrence may be nonzero only between the nearest neighbors (with a single exception), while the discord is nonzero between any two nodes; and (iii) there is so-called “echo” in the evolution of the discord, which is not observed in the evolution of the concurrence. Using different bases, we may choose the preferable behavior of quantum correlations which allows a given quantum system to be more flexible in applications.

Fel'dman, E. B.; Zenchuk, A. I.

2012-07-01

314

Quantum dynamics of biological systems and dust plasma nanoparticles

NASA Astrophysics Data System (ADS)

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

315

Observation of dark states in a superconductor diamond quantum hybrid system

NASA Astrophysics Data System (ADS)

The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1?MHz) at 2.878?GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory.

Zhu, Xiaobo; Matsuzaki, Yuichiro; Amsüss, Robert; Kakuyanagi, Kosuke; Shimo-Oka, Takaaki; Mizuochi, Norikazu; Nemoto, Kae; Semba, Kouichi; Munro, William J.; Saito, Shiro

2014-04-01

316

Observation of dark states in a superconductor diamond quantum hybrid system

The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1?MHz) at 2.878?GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory. PMID:24709792

Zhu, Xiaobo; Matsuzaki, Yuichiro; Amsüss, Robert; Kakuyanagi, Kosuke; Shimo-Oka, Takaaki; Mizuochi, Norikazu; Nemoto, Kae; Semba, Kouichi; Munro, William J.; Saito, Shiro

2014-01-01

317

Thermodynamics of quantum systems under dynamical control

In this review the debated rapport between thermodynamics and quantum mechanics is addressed in the framework of the theory of periodically-driven/controlled quantum-thermodynamic machines. The basic model studied here is that of a two-level system (TLS), whose energy is periodically modulated while the system is coupled to thermal baths. When the modulation interval is short compared to the bath memory time, the system-bath correlations are affected, thereby causing cooling or heating of the TLS, depending on the interval. In steady state, a periodically-modulated TLS coupled to two distinct baths constitutes the simplest quantum heat machine (QHM) that may operate as either an engine or a refrigerator, depending on the modulation rate. We find their efficiency and power-output bounds and the conditions for attaining these bounds. An extension of this model to multilevel systems shows that the QHM power output can be boosted by the multilevel degeneracy. These results are used to scrutinize basic thermodynamic principles: (i) Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but when the driving is done by a quantum device ("piston"), the efficiency strongly depends on its initial quantum state. Such dependence has been unknown thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the temperature approaches absolute zero for certain quantized baths, e.g., magnons, thous challenging Nernst's unattainability principle. (iii) System-bath correlations allow more work extraction under periodic control than that expected from the Szilard-Landauer principle, provided the period is in the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from hitherto unexploited thermodynamic resources.

D. Gelbwaser-Klimovsky; Wolfgang Niedenzu; Gershon Kurizki

2015-03-04

318

Quantum cryptographic system with reduced data loss

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

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

1998-03-24

319

Chiral quantum mechanics (CQM) for antihydrogen systems

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.

G. Van Hooydonk

2005-12-03

320

Geometrical Excess Entropy Production in Nonequilibrium Quantum Systems

NASA Astrophysics Data System (ADS)

For open systems described by the quantum Markovian master equation, we study a possible extension of the Clausius equality to quasistatic operations between nonequilibrium steady states (NESSs). We investigate the excess heat divided by temperature (i.e., excess entropy production) which is transferred into the system during the operations. We derive a geometrical expression for the excess entropy production, which is analogous to the Berry phase in unitary evolution. Our result implies that in general one cannot define a scalar potential whose difference coincides with the excess entropy production in a thermodynamic process, and that a vector potential plays a crucial role in the thermodynamics for NESSs. In the weakly nonequilibrium regime, we show that the geometrical expression reduces to the extended Clausius equality derived by Saito and Tasaki (J. Stat. Phys. 145:1275, 2011). As an example, we investigate a spinless electron system in quantum dots. We find that one can define a scalar potential when the parameters of only one of the reservoirs are modified in a non-interacting system, but this is no longer the case for an interacting system.

Yuge, Tatsuro; Sagawa, Takahiro; Sugita, Ayumu; Hayakawa, Hisao

2013-11-01

321

Simulation of n-qubit quantum systems. I. Quantum registers and quantum gates

NASA Astrophysics Data System (ADS)

During recent years, quantum computations and the study of n-qubit quantum systems have attracted a lot of interest, both in theory and experiment. Apart from the promise of performing quantum computations, however, these investigations also revealed a great deal of difficulties which still need to be solved in practice. In quantum computing, unitary and non-unitary quantum operations act on a given set of qubits to form (entangled) states, in which the information is encoded by the overall system often referred to as quantum registers. To facilitate the simulation of such n-qubit quantum systems, we present the FEYNMAN program to provide all necessary tools in order to define and to deal with quantum registers and quantum operations. Although the present version of the program is restricted to unitary transformations, it equally supports—whenever possible—the representation of the quantum registers both, in terms of their state vectors and density matrices. In addition to the composition of two or more quantum registers, moreover, the program also supports their decomposition into various parts by applying the partial trace operation and the concept of the reduced density matrix. Using an interactive design within the framework of MAPLE, therefore, we expect the FEYNMAN program to be helpful not only for teaching the basic elements of quantum computing but also for studying their physical realization in the future. Program summaryTitle of program:FEYNMAN Catalogue number:ADWE Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE Program obtainable from:CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:None Computers for which the program is designed:All computers with a license of the computer algebra system MAPLE [Maple is a registered trademark of Waterlo Maple Inc.] Operating systems or monitors under which the program has been tested:Linux, MS Windows XP Programming language used:MAPLE 9.5 (but should be compatible with 9.0 and 8.0, too) Memory and time required to execute with typical data:Storage and time requirements critically depend on the number of qubits, n, in the quantum registers due to the exponential increase of the associated Hilbert space. In particular, complex algebraic operations may require large amounts of memory even for small qubit numbers. However, most of the standard commands (see Section 4 for simple examples) react promptly for up to five qubits on a normal single-processor machine ( ?1GHz with 512 MB memory) and use less than 10 MB memory. No. of lines in distributed program, including test data, etc.: 8864 No. of bytes in distributed program, including test data, etc.: 493 182 Distribution format: tar.gz Nature of the physical problem:During the last decade, quantum computing has been found to provide a revolutionary new form of computation. The algorithms by Shor [P.W. Shor, SIAM J. Sci. Statist. Comput. 26 (1997) 1484] and Grover [L.K. Grover, Phys. Rev. Lett. 79 (1997) 325. [2

Radtke, T.; Fritzsche, S.

2005-12-01

322

Uncertainty relation for non-Hamiltonian quantum systems

General forms of uncertainty relations for quantum observables of non-Hamiltonian quantum systems are considered. Special cases of uncertainty relations are discussed. The uncertainty relations for non-Hamiltonian quantum systems are considered in the Schroedinger-Robertson form since it allows us to take into account Lie-Jordan algebra of quantum observables. In uncertainty relations, the time dependence of quantum observables and the properties of this dependence are discussed. We take into account that a time evolution of observables of a non-Hamiltonian quantum system is not an endomorphism with respect to Lie, Jordan, and associative multiplications.

Tarasov, Vasily E. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)] [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)

2013-01-15

323

This paper is concerned with a stochastic dissipativity theory using quadratic-exponential storage functions for open quantum systems with canonically commuting dynamic variables governed by quantum stochastic differential equations. The system is linearly coupled to external boson fields and has a quadratic Hamiltonian which is perturbed by nonquadratic functions of linear combinations of system variables. Such perturbations are similar to those in the classical Lur'e systems and make the quantum dynamics nonlinear. We study their effect on the quantum expectation of the exponential of a positive definite quadratic form of the system variables. This allows conditions to be established for the risk-sensitive stochastic storage function of the quantum system to remain bounded, thus securing boundedness for the moments of system variables of arbitrary order. These results employ a noncommutative analogue of the Doleans-Dade exponential and a multivariate partial differential version of the Gronwall-Bellman lemma.

Igor G. Vladimirov; Ian R. Petersen

2012-05-16

324

Improving the Coherence Time of a Quantum System via a Coupling to a Short-Lived System

NASA Astrophysics Data System (ADS)

In this Letter, we propose a counterintuitive use of a hybrid system where the coherence time of a quantum system can be significantly improved by coupling it with a system of a shorter coherence time. Coupling a two-level system with a single nitrogen-vacancy (NV- ) center, a dark state of the NV- center naturally forms after the hybridization. We show that this dark state becomes robust against noise due to the coupling even when the coherence time of the two-level system is much shorter than that of the NV- center. Our proposal opens a new way to use a quantum hybrid system for the realization of robust quantum information processing.

Matsuzaki, Yuichiro; Zhu, Xiaobo; Kakuyanagi, Kosuke; Toida, Hiraku; Shimo-Oka, Takaaki; Mizuochi, Norikazu; Nemoto, Kae; Semba, Kouichi; Munro, William J.; Yamaguchi, Hiroshi; Saito, Shiro

2015-03-01

325

Observable measure of quantum coherence in finite dimensional systems.

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d2) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes. PMID:25379903

Girolami, Davide

2014-10-24

326

Observable Measure of Quantum Coherence in Finite Dimensional Systems

NASA Astrophysics Data System (ADS)

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d2) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes.

Girolami, Davide

2014-10-01

327

Open-system dynamics of entanglement:a key issues review.

One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and every constituent of quantum systems with an ever increasing number of particles. Within this endeavor, harnessing of many-body entanglement against the detrimental effects of the environment is a major pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognized as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations.In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors.In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information. PMID:25811809

Aolita, Leandro; de Melo, Fernando; Davidovich, Luiz

2015-04-01

328

Open-system dynamics of entanglement:a key issues review

NASA Astrophysics Data System (ADS)

One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and every constituent of quantum systems with an ever increasing number of particles. Within this endeavor, harnessing of many-body entanglement against the detrimental effects of the environment is a major pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognized as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations. In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors. In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information.

Aolita, Leandro; de Melo, Fernando; Davidovich, Luiz

2015-04-01

329

Shear flow pumping in open microfluidic systems

We propose to drive open microfluidic systems by shear in a covering fluid layer, e.g., oil covering water-filled chemical channels. The advantages as compared to other means of pumping are simpler forcing and prevention of evaporation of volatile components. We calculate the expected throughput for straight channels and show that devices can be built with off-the-shelf technology. Molecular dynamics simulations suggest that this concept is scalable down to the nanoscale.

Markus Rauscher; S. Dietrich; Joel Koplik

2006-10-26

330

QUBIT-RESONATOR SYSTEM AS AN APPLICATION TO QUANTUM COMPUTATION

QUBIT-RESONATOR SYSTEM AS AN APPLICATION TO QUANTUM COMPUTATION Ren-Shou Huang Submitted #12;Abstract Ren-Shou Huang Qubit-Resonator System as an Application to Quantum Computation The recent development of quantum computation has inspired lots of interesting ideas in a variety of fields

331

Non-Equilibrium Quantum Entanglement in Biological Systems

NASA Astrophysics Data System (ADS)

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

332

An open system for intravascular ultrasound imaging.

Visualization of the blood vessels can provide valuable morphological information for diagnosis and therapy strategies for cardiovascular disease. Intravascular ultrasound (IVUS) is able to delineate internal structures of vessel wall with fine spatial resolution. However, the developed IVUS is insufficient to identify the fibrous cap thickness and tissue composition of atherosclerotic lesions. Novel imaging strategies have been proposed, such as increasing the center frequency of ultrasound or using a modulated excitation technique to improve the accuracy of diagnosis. Dual-mode tomography combining IVUS with optical tomography has also been developed to determine tissue morphology and characteristics. The implementation of these new imaging methods requires an open system that allows users to customize the system for various studies. This paper presents the development of an IVUS system that has open structures to support various imaging strategies. The system design is based on electronic components and printed circuit board, and provides reconfigurable hardware implementation, programmable image processing algorithms, flexible imaging control, and raw RF data acquisition. In addition, the proposed IVUS system utilized a miniaturized ultrasound transducer constructed using PMNPT single crystal for better piezoelectric constant and electromechanical coupling coefficient than traditional lead zirconate titanate (PZT) ceramics. Testing results showed that the IVUS system could offer a minimum detectable signal of 25 ?V, allowing a 51 dB dynamic range at 47 dB gain, with a frequency range from 20 to 80 MHz. Finally, phantom imaging, in vitro IVUS vessel imaging, and multimodality imaging with photoacoustics were conducted to demonstrate the performance of the open system. PMID:23143570

Qiu, Weibao; Chen, Yan; Li, Xiang; Yu, Yanyan; Cheng, Wang Fai; Tsang, Fu Keung; Zhou, Qifa; Shung, K Kirk; Dai, Jiyan; Sun, Lei

2012-10-01

333

An Open System for Intravascular Ultrasound Imaging

Visualization of the blood vessels can provide valuable morphological information for diagnosis and therapy strategies for cardiovascular disease. Intravascular ultrasound (IVUS) is able to delineate internal structures of vessel wall with fine spatial resolution. However, the developed IVUS is insufficient to identify the fibrous cap thickness and tissue composition of atherosclerotic lesions. Novel imaging strategies have been proposed, such as increasing the center frequency of ultrasound or using a modulated excitation technique to improve the accuracy of diagnosis. Dual-mode tomography combining IVUS with optical tomography has also been developed to determine tissue morphology and characteristics. The implementation of these new imaging methods requires an open system that allows users to customize the system for various studies. This paper presents the development of an IVUS system that has open structures to support various imaging strategies. The system design is based on electronic components and printed circuit board, and provides reconfigurable hardware implementation, programmable image processing algorithms, flexible imaging control, and raw RF data acquisition. In addition, the proposed IVUS system utilized a miniaturized ultrasound transducer constructed using PMN-PT single crystal for better piezoelectric constant and electromechanical coupling coefficient than traditional lead zirconate titanate (PZT) ceramics. Testing results showed that the IVUS system could offer a minimum detectable signal of 25 ?V, allowing a 51 dB dynamic range at 47 dB gain, with a frequency range from 20 to 80 MHz. Finally, phantom imaging, in vitro IVUS vessel imaging, and multimodality imaging with photoacoustics were conducted to demonstrate the performance of the open system. PMID:23143570

Qiu, Weibao; Chen, Yan; Li, Xiang; Yu, Yanyan; Cheng, Wang Fai; Tsang, Fu Keung; Zhou, Qifa; Shung, K. Kirk; Dai, Jiyan; Sun, Lei

2013-01-01

334

NASA Astrophysics Data System (ADS)

Implementing a scalable quantum information processor using polar molecules in optical lattices requires precise control over the long-range dipole-dipole interaction between molecules in selected lattice sites. We present here a scheme using trapped open-shell ^{2}\\Sigma polar molecules that allows dipolar exchange processes between nearest and next-nearest neighbors to be controlled in order to construct a generalized transverse Ising spin Hamiltonian with tunable XX, YY and XY couplings in the rotating frame of the driving lasers. The scheme requires a moderately strong bias magnetic field together with near-infrared light to provide local tuning of the qubit energy gap, and mid-infrared pulses to perform rotational state transfer via stimulated Raman adiabatic passage. No interaction between qubits occurs in the absence of the infrared driving. We analyze the fidelity of the resulting two-qubit matchgate, and demonstrate its robustness as a function of the driving parameters. We discuss a realistic application of the system for universal matchgate quantum computing in optical lattices.

Herrera, Felipe; Cao, Yudong; Kais, Sabre; Whaley, K. Birgitta

2014-07-01

335

Quantum statistical and dynamical effects in vortex systems

We review some recent developments in the quantum statistical mechanics and in the quantum dynamics of the vortex system in high temperature- and in conventional high-resistivity thin-film superconductors.

G. Blatter; B. Ivlev; Yu. Kagan; V. Vinokur; Theoretische Physik

1994-01-01

336

Evolution of quantum correlations in a two-atom system

We discuss the evolution of quantum correlations for a system of two two-level atoms interacting with a common reservoir. The Markovian master equation is used to describe the evolution of various measures of quantum correlations.

Ryszard Tana?

2012-10-22

337

Time fractional development of quantum systems

In this study, the effect of time fractionalization on the development of quantum systems is taken under consideration by making use of fractional calculus. In this context, a Mittag-Leffler function is introduced as an important mathematical tool in the generalization of the evolution operator. In order to investigate the time fractional evolution of the quantum (nano) systems, time fractional forms of motion are obtained for a 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 {alpha}, which is a measure of the fractality of time. In the case {alpha}=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 {alpha} is relevant to time. It is understood that the fractionalization of time gives rise to energy fluctuations of the quantum (nano) systems.

Ertik, Hueseyin; Demirhan, Dogan; Sirin, Hueseyin; Bueyuekkilic, Fevzi [Department of Physics, Science Faculty, Ege University, Bornova, Izmir 35100 (Turkey)

2010-08-15

338

Phase transitions in quantum Hall multiple layer systems

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.

Pusep, Yu A.; Fernandes dos Santos, L. [Instituto de Fisica de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, SP (Brazil); Smirnov, D. [National High Magnetic Field Laboratory, Tallahassee, FL 32312 (United States); Bakarov, A. K.; Toropov, A. I. [Institute of Semiconductor Physics, Novosibirsk 630090 (Russian Federation)

2013-12-04

339

OCSEGen: Open Components and Systems Environment Generator

NASA Technical Reports Server (NTRS)

To analyze a large system, one often needs to break it into smaller components.To analyze a component or unit under analysis, one needs to model its context of execution, called environment, which represents the components with which the unit interacts. Environment generation is a challenging problem, because the environment needs to be general enough to uncover unit errors, yet precise enough to make the analysis tractable. In this paper, we present a tool for automated environment generation for open components and systems. The tool, called OCSEGen, is implemented on top of the Soot framework. We present the tool's current support and discuss its possible future extensions.

Tkachuk, Oksana

2014-01-01

340

Quantum Signatures of Solar System Dynamics

Let w(i) be a period of rotation of the i-th planet around the Sun (or w(j;i) be a period of rotation of j-th satellite around the i-th planet). From empirical observations it is known that the sum of n(i)w(i)=0 (or the sum of n(j)w(j;i)=0) for some integers n(i) (or n(j)), different for different satellite systems. These conditions, known as resonance conditions, make uses of theories such as KAM difficult to implement. The resonances in Solar System are similar to those encountered in old quantum mechanics where applications of methods of celestial mechanics to atomic and molecular physics were highly sucsessful. With such a success, the birth of new quantum mechanics is difficult to understand. In short, the rationale for its birth lies in simplicity with which the same type of calculations are done using new methods capable of taking care of resonances. The solution of quantization puzzle was found by Heisenberg. In this paper new uses of Heisenberg's ideas are found. When superimposed with the equivalence principle of general relativity, they lead to quantum mechanical tratment of observed resonances in Solar System. To test correctness of our theoretical predictions the number of allowed stable orbits for planets and for equatorial stable orbits of satellites of heavy planets is calculated resulting in good agreement with observational data. In addition, the paper briefly discusses quantum mechanical nature of rings of heavy planets and potential usefulness of the obtained results for cosmology.

Arkady L. Kholodenko

2008-10-17

341

We report a nuclear magnetic resonance experiment, which simulates the quantum transverse Ising spin system in a triangular configuration and further show that the monogamy of quantum correlations can be used to distinguish between the frustrated and non-frustrated regimes in the ground state of this system. Adiabatic state preparation methods are used to prepare the ground states of the spin system. We employ two different multipartite quantum correlation measures to analyze the experimental ground state of the system in both the frustrated and non-frustrated regimes. In particular, we use multipartite quantum correlation measures generated by monogamy considerations of negativity, a bipartite entanglement measure, and that of quantum discord, an information-theoretic quantum correlation measure. As expected from theoretical predictions, the experimental data confirm that the non-frustrated regime shows higher multipartite quantum correlations compared to the frustrated one.

K. Rama Koteswara Rao; Hemant Katiyar; T. S. Mahesh; Aditi Sen De; Ujjwal Sen; Anil Kumar

2013-08-17

342

Open-Loop Control of Quantum Particle Motion: Effective Splitting in Momentum Space

In this paper an effective quantum particle beam-splitter in the momentum space is realized in the frame of open-loop control scheme. We demonstrate for small interaction time that the splitting effect $\\pm40\\hbar k$ with summarized relative intensity in both main components is about 50 per cent from initial intensity of the atomic beam.

Babar Ahmad; Sergei Borisenok; Saifullah; Yuri Rozhdestvensky

2007-03-16

343

Chapter 5: Quantum Dynamics in Dissipative Molecular Systems

NASA Astrophysics Data System (ADS)

The following sections are included: * Introduction * HEOM versus Path Integral Formalism: Background * Generic form and terminology of HEOM * Statistical mechanics description of bath influence * Feynman-Vernon influence functional formalism * General comments * Memory-Frequency Decomposition of Bath Correlation Functions * PSD of Bose function * Brownian oscillators decomposition of bath spectral density function * Optimized HEOM Theory With Accuracy Control * Construction of HEOM via path integral formalism * Accuracy control on white-noise residue ansatz * Efficient HEOM propagator: Numerical filtering and indexing algorithm * HEOM in Quantum Mechanics for Open Systems * The HEOM space and the Schrödinger picture * HEOM in the Heisenberg picture * Mixed Heisenberg-Schrödinger block-matrix dynamics in nonlinear optical response functions * Two-Dimensional Spectroscopy: Model Calculations * Concluding Remarks * Acknowledgments * References

Zhang, Hou-Dao; Xu, J.; Xu, Rui-Xue; Yan, Y. J.

2014-04-01

344

In the paper with the above-noted title, D. T. Gillespie [Phys. Rev. A {bold 49}, 1607 (1994)] claims that the theory of Markov stochastic processes cannot provide an adequate mathematical framework for quantum mechanics. In conjunction with the specific quantum dynamics considered there, we give a general analysis of the associated dichotomic jump processes. If we assume that Gillespie{close_quote}s {open_quote}{open_quote}measurement

P. Garbaczewski; R. Olkiewicz

1996-01-01

345

The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.

Gonzalo A. Alvarez

2007-05-15

346

NASA Astrophysics Data System (ADS)

The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.

Alvarez, Gonzalo A.

2007-05-01

347

Thermalization in Quantum Systems: An Emergent Approach

The problems with an emergent approach to quantum statistical mechanics are discussed and shown to follow from some of the same sources as those of quantum measurement. A wavefunction of an N atom solid is described in the ground and excited eigenstates with explicit modifications for phonons. Using the particular subclass of wavefunctions that can correspond to classical solids we investigate the localization properties of atomic centers of mass motion and contrast it with more general linear combinations of phonon states. The effectively large mass of longer modes means that localization present in the ground state persists on excitation of the material by macroscopic coherent disturbances. The "thermalization" that arises then follows from the long term well defined motion of these localized peaks in their 3N dimensional harmonic wells in the same fashion as that of a classical solid in phase space. Thermal production of photons then create an internal radiation field and provides the first dynamical derivation of the Planck distribution from material motions. Significantly, this approach resolves a long standing paradox of thermalization of many body quantum systems from Schr\\"{o}dinger dynamics alone.

Clifford Chafin

2015-02-23

348

An Open-Source Learning Content Management and Assessment System

LON-CAPA An Open-Source Learning Content Management and Assessment System Gerd Kortemeyer-CAPA is free open-source a learning content management system an assessment system around since 1992 #12 Resource Library Â· The distributed network looks like one big file system ( Um conjunto de InstituiÃ§Ãµes

349

Partitioning technique for a discrete quantum system

We develop the partitioning technique for quantum discrete systems. The graph consists of several subgraphs: a central graph and several branch graphs, with each branch graph being rooted by an individual node on the central one. We show that the effective Hamiltonian on the central graph can be constructed by adding additional potentials on the branch-root nodes, which generates the same result as does the the original Hamiltonian on the entire graph. Exactly solvable models are presented to demonstrate the main points of this paper.

L. Jin; Z. Song

2011-05-31

350

Black holes and nonrelativistic quantum systems.

We describe black holes in d+3 dimensions, whose thermodynamic properties correspond to those of a scale-invariant nonrelativistic (d+1)-dimensional quantum system with a dynamical exponent z=2. The gravitational model involves a massive Abelian vector field and a scalar field, in addition to the metric. The energy per particle in the dual theory is |micro|d/(d+2) at any temperature (micro is the chemical potential). The ratio of shear viscosity to entropy density is variant Planck's over 2pi/4pi in any dimension d > or =2. PMID:19257179

Kovtun, Pavel; Nickel, Dominik

2009-01-01

351

Black Holes and Nonrelativistic Quantum Systems

We describe black holes in d+3 dimensions, whose thermodynamic properties correspond to those of a scale-invariant nonrelativistic (d+1)-dimensional quantum system with a dynamical exponent z=2. The gravitational model involves a massive Abelian vector field and a scalar field, in addition to the metric. The energy per particle in the dual theory is |{mu}|d/(d+2) at any temperature ({mu} is the chemical potential). The ratio of shear viscosity to entropy density is ({Dirac_h}/2{pi})/4{pi} in any dimension d{>=}2.

Kovtun, Pavel; Nickel, Dominik [Department of Physics and Astronomy, University of Victoria, Victoria BC, V8P 5C2 (Canada); Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2009-01-09

352

Equivalence of the measures of non-Markovianity for open two-level systems

Different measures have been presented to depict the deviation of quantum time evolution in open systems from Markovian processes. We demonstrate that the measure proposed by Breuer, Laine, and Piilo [Phys. Rev. Lett. 103, 210401 (2009)] and the two measures proposed by Rivas, Huelga, and Plenio [Phys. Rev. Lett. 105, 050403 (2010)] have exactly the same non-Markovian time-evolution intervals and thus are really equivalent to each other when they are applied to open two-level systems coupled to environments via the Jaynes-Cummings or dephasing models. This equivalence implies that the three measures, in different ways, capture the intrinsic character of the non-Markovianity of quantum evolutional processes. We also show that the maximization in the definition of the first measure can be actually removed for the considered models without influencing the sensibility of the measure to detect non-Markovianity.

Zeng Haosheng; Tang Ning; Zheng Yanping; Wang Guoyou [Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, and Department of Physics, Hunan Normal University, Changsha 410081 (China)

2011-09-15

353

Energy transport in closed quantum systems.

We examine energy transport in an ensemble of closed quantum systems driven by stochastic perturbations. One can show that the probability and energy fluxes can be described in terms of quantum advection modes (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

354

Spectra of nonlocally bound quantum systems

NASA Astrophysics Data System (ADS)

We discuss a class of nonlinear and nonlocal models for the dynamics of a composite quantum system. The models in question depend on the following constituents: on two subsystem Hamiltonians (denoted by H and ?), an analytic function ( f), and a real parameter ( s). As demonstrated elsewhere before, the stationary states can be described in these models fairly explicitly. In this article, we build upon that result, and discuss the topological as well as statistical characteristics of the spectra. Here, we concentrate on the special case f = log. It turns out that an energy spectrum of the nonlocally bound system substantially differs from that of its components. Indeed, we show rigorously that, if H is the harmonic oscillator and ? is completely degenerate with one energy level, then the energy spectrum of the composite system has the topology of the Cantor set (for s > 2). In addition, we show that, if H is replaced by the logarithm of the harmonic oscillator, then the spectrum consists of finitely many intervals separated by gaps (for s sufficiently large). In the last case, the key analytic object is the series ? n - s . In particular, as an interesting offshoot, this structure furnishes a nontautological immersion of fundamental number-theoretic functions into the quantum formalism.

Sowa, A.

2011-06-01

355

The Quantum H4 Integrable System

NASA Astrophysics Data System (ADS)

The quantum H4 integrable system is a 4D system with rational potential related to the non-crystallographic root system H4 with 600-cell symmetry. It is shown that the gauge-rotated H4 Hamiltonian as well as one of the integrals, when written in terms of the invariants of the Coxeter group H4, is in algebraic form: it has polynomial coefficients in front of the derivatives. Any eigenfunction is a polynomial multiplied by ground-state function (factorization property). Spectra correspond to one of the anisotropic harmonic oscillators. The Hamiltonian has infinitely-many finite-dimensional invariant subspaces in polynomials, they form the infinite flag with the characteristic vector ? = (1, 5, 8, 12).

García, Marcos A. G.; Turbiner, Alexander V.

356

Software-defined quantum communication systems

NASA Astrophysics Data System (ADS)

Quantum communication (QC) systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for QC engineering is designing and prototyping these systems to evaluate the proposed capabilities. We apply the paradigm of software-defined communication for engineering QC systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose QC terminals into functional layers defining hardware, software, and middleware concerns, and we describe how each layer behaves. Using the superdense coding protocol as an example, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We conclude that the software-defined QC provides a robust framework in which to explore the large design space offered by this new regime of communication.

Humble, Travis S.; Sadlier, Ronald J.

2014-08-01

357

Quantum chaotic system as a model of decohering environment

As a model of decohering environment, we show that quantum chaotic system behave equivalently as many-body system. An approximate formula for the time evolution of the reduced density matrix of a system interacting with a quantum chaotic environment is derived. This theoretical formulation is substantiated by the numerical study of decoherence of two qubits interacting with a quantum chaotic environment modeled by a chaotic kicked top. Like the many-body model of environment, the quantum chaotic system is efficient decoherer, and it can generate entanglement between the two qubits which have no direct interaction.

Jayendra N. Bandyopadhyay

2009-04-24

358

Statistical Mechanics of Quantum-Classical Systems with Holonomic Constraints

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

Alessandro Sergi

2005-11-15

359

Quantum Hall systems Representation theory of vertex operator algebras Applications The end Quantum;Quantum Hall systems Representation theory of vertex operator algebras Applications The end Outline 1 An approach to a fundamental conjecture #12;Quantum Hall systems Representation theory of vertex operator

Huang, Yi-Zhi

360

Characterizing and quantifying frustration in quantum many-body systems.

We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration. PMID:22243147

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

2011-12-23

361

Characterizing and Quantifying Frustration in Quantum Many-Body Systems

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

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

2012-01-05

362

A remote monitoring system for Open Ocean Aquaculture

The purpose of this project was to determine the practicality and characteristics of a remote monitoring system for an open ocean aquaculture fish cage. The Open Ocean Aquaculture program at the University of New Hampshire currently uses two fish cages to develop the technology and methodology to raise finned fish in the open ocean. The cages are located about six

A. P. M. Michel; K. L. Croff; K. W. McLetchie; J. D. Irish

2002-01-01

363

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

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

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

2011-08-15

364

Quantum Coherence Effects in Novel Quantum Optical Systems

and find interesting applications. We show that quantum coherence can lead to transient Raman lasing and lasing without inversion in short wavelength spectral regions--extreme ultraviolet and x-ray--without the requirement of incoherent pumping. For example...

Sete, Eyob Alebachew

2012-10-19

365

Open Giant Intelligent Information Systems and Its Multiagent-Oriented System Design

is actually a human-computer-cooperated intelligent information system[2,3]. As for how to build an open giant of an MAS. Among all system complexities of open giant intelligent information system, society and humanOpen Giant Intelligent Information Systems and Its Multiagent-Oriented System Design Longbing Cao

Cao, Longbing

366

On Invariant Subspace In Quantum Control Systems and Some Concepts of Integrable Quantum Systems

NASA Astrophysics Data System (ADS)

Trajectories of some dynamical systems can be analysed by algebraic methods. In this paper we discuss certain applications of the so-called Shemesh criterion and its generalisations to analysis of properties of quantum control systems. In particular, some Hamiltonians with non-degenerated spectrum are considered, and also the case of a Hamiltonian with m 1,...,m N degeneracies, where {sum }N_{i=1}mi=n, is discussed.

Jamio?kowski, Andrzej; Kamizawa, Takeo; Pastuszak, Grzegorz

2015-01-01

367

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

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.

Banchi, L. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Apollaro, T. J. G. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Cuccoli, A. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); INFN, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Vaia, R. [Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Verrucchi, P. [Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); INFN, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy)

2010-11-15

368

SHORT COMMUNICATION Open Access Testing the VEMCO Positioning System: spatial

SHORT COMMUNICATION Open Access Testing the VEMCO Positioning System: spatial distribution animals over long periods of time with regular fine-scale positions. The VEMCO Positioning System (VPS Positioning System, Probability of location, Positioning error, Spatial distribution Findings Background

369

Precisely characterizing and controlling the dynamics of realistic open quantum systems has emerged in recent years as a key challenge across contemporary quantum sciences and technologies, with implications ranging from physics, chemistry and applied mathematics to quantum information processing (QIP) and quantum engineering. Quantum control theory aims to provide both a general dynamical-system framework and a constructive toolbox to meet

Lorenza Viola; David Tannor

2011-01-01

370

Device-Independent Certification of High-Dimensional Quantum Systems

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

371

Strong field control of multilevel quantum systems

NASA Astrophysics Data System (ADS)

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

372

Optimal dynamic discrimination of similar quantum systems

NASA Astrophysics Data System (ADS)

The techniques for identifying and separating similar molecules have always been very important to chemistry and other branches of science and engineering. Similar quantum systems share comparable Hamiltonians, so their eigenenergy levels, transition dipole moments, and therefore their ordinary observable properties are alike. Traditional analytical methods have mostly been restricted by working with the subtle differences in the physical and chemical properties of the similar species. Optimal Dynamic Discrimination (ODD) aims at magnifying the dissimilarity of the agents by actively controlling their quantum evolution, drawing on the extremely rich information embedded in their dynamics. ODD is developed based on the tremendous flexibility of Optimal Control Theory (OCT) and on the practical implementation of closed-loop learning control, which has become a more and more indispensable tool for controlling quantum processes. The ODD experimental paradigm is designed to combat a number of factors that are detrimental to the discrimination of similar molecules: laser pulse noise, signal detection errors, finite time resolution in the signals, and environmental decoherence effects. It utilizes either static signals or time series signal, the latter capable of providing more information. Simulations are performed in this dissertation progressing from the wave function to the density matrix formulation, in order to study the decoherence effects. Analysis of the results reveals the roles of the adverse factors, unravels the underlying mechanisms of ODD, and provides insights on laboratory implementation. ODD emphasizes the incorporation of algorithmic development and laboratory design, and seeks to bridge the gap between theoretical/computational chemistry and experimental chemistry, with the help from applied mathematics and computer science.

Li, Baiqing

2005-07-01

373

The ring-opening reactions of the radical cations of hexamethyl Dewar benzene (1) and Dewar benzene have been studied using density functional theory (DFT) and complete active-space self-consistent field (CASSCF) calculations. Compound 1 is known to undergo photoinitiated ring opening by a radical cation chain mechanism, termed "quantum amplified isomerization" (QAI), which is due to the high quantum yield. Why QAI is efficient for 1 but not other reactions is explained computationally. Two radical cation minima of 1 and transition states located near avoided crossings are identified. The state crossings are characterized by conical intersections corresponding to degeneracy between doublet surfaces. Ring opening occurs by formation of the radical cation followed by a decrease in the flap dihedral angle. A rate-limiting Cs transition state leads to a second stable radical cation with an elongated transannular C-C bond and an increased flap dihedral. This structure proceeds through a conrotatory-like pathway of Cs symmetry to give the benzene radical cation. The role of electron transfer was investigated by evaluating oxidation of various systems using adiabatic ionization energies and electron affinities calculated from neutral and cation geometries. Electron-transfer theory was applied to 1 to investigate the limiting effects of back-electron transfer as it is related to the unusual stability of the two radical cations. Expected changes in optical properties between reactants and products of Dewar benzene compounds and other systems known to undergo QAI were characterized by computing frequency-dependent indices of refraction from isotropic polarizabilities. In particular, the reaction of 1 shows greater contrast in index of refraction than that of the Dewar benzene parent system. PMID:16771497

Norton, Joseph E; Olson, Leif P; Houk, K N

2006-06-21

374

A basic quantum-mechanical model for wave functions and current flow in open quantum dots or billiards is investigated. The model involves non-Hertmitian quantum mechanics, parity-time (PT) symmetry, and PT-symmetry breaking. Attached leads are represented by positive and negative imaginary potentials. Thus probability densities, currents flows, etc., for open quantum dots or billiards may be simulated in this way by solving the Schrödinger equation with a complex potential. Here we consider a nominally open ballistic quantum dot emulated by a planar microwave billiard. Results for probability distributions for densities, currents (Poynting vector), and stress tensor components are presented and compared with predictions based on Gaussian random wave theory. The results are also discussed in view of the corresponding measurements for the analogous microwave cavity. The model is of conceptual as well as of practical and educational interest. PMID:25019854

Wahlstrand, B; Yakimenko, I I; Berggren, K-F

2014-06-01

375

The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age

RESEARCH ARTICLE Open Access The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age Sam Adams1, Pablo de Castro2, Pablo Echenique3,4,5, Jorge Estrada3,4,6, Marcus D Hanwell7, Peter Murray-Rust1*, Paul... wildly optimistic. Therefore without seeing a working repository it is difficult to know what its value is, or the costs of sustaining it. However the Internet age shows that it is much easier, cheaper and quicker to get new applications off the ground...

Adams, Sam; de Castro, Pablo; Echenique, Pablo; Estrada, Jorge; Hanwell, Marcus D; Murray-Rust, Peter; Sherwood, Paul; Thomas, Jens; Townsend, Joe A

2011-10-14

376

Classical command of quantum systems via rigidity of CHSH games

Can a classical system command a general adversarial quantum system to realize arbitrary quantum dynamics? If so, then we could realize the dream of device-independent quantum cryptography: using untrusted quantum devices to establish a shared random key, with security based on the correctness of quantum mechanics. It would also allow for testing whether a claimed quantum computer is truly quantum. Here we report a technique by which a classical system can certify the joint, entangled state of a bipartite quantum system, as well as command the application of specific operators on each subsystem. This is accomplished by showing a strong converse to Tsirelson's optimality result for the Clauser-Horne-Shimony-Holt (CHSH) game: the only way to win many games is if the bipartite state is close to the tensor product of EPR states, and the measurements are the optimal CHSH measurements on successive qubits. This leads directly to a scheme for device-independent quantum key distribution. Control over the state and operators can also be leveraged to create more elaborate protocols for reliably realizing general quantum circuits.

Ben W. Reichardt; Falk Unger; Umesh Vazirani

2012-09-03

377

A quantum many-body spin system in an optical lattice clock.

Strongly interacting quantum many-body systems arise in many areas of physics, but their complexity generally precludes exact solutions to their dynamics. We explored a strongly interacting two-level system formed by the clock states in (87)Sr as a laboratory for the study of quantum many-body effects. Our collective spin measurements reveal signatures of the development of many-body correlations during the dynamical evolution. We derived a many-body Hamiltonian that describes the experimental observation of atomic spin coherence decay, density-dependent frequency shifts, severely distorted lineshapes, and correlated spin noise. These investigations open the door to further explorations of quantum many-body effects and entanglement through use of highly coherent and precisely controlled optical lattice clocks. PMID:23929976

Martin, M J; Bishof, M; Swallows, M D; Zhang, X; Benko, C; von-Stecher, J; Gorshkov, A V; Rey, A M; Ye, Jun

2013-08-01

378

Automated drawing system of quantum energy levels

NASA Astrophysics Data System (ADS)

The purpose of this work is to derive an automated system that provides advantageous drawings of energy spectra for quantum systems (nuclei, atoms, molecules, etc.) required in various physical sciences. The automation involves the development of appropriate computational code and graphical imaging system based on raw data insertion, theoretical calculations and experimental or bibliographic data insertion. The system determines the appropriate scale to depict graphically with the best possible way in the available space. The presently developed code operates locally and the results are displayed on the screen and can be exported to a PostScript file. We note its main features to arrange and visualize in the available space the energy levels with their identity, taking care the existence in the final diagram the least auxiliary deviations. Future improvements can be the use of Java and the availability on the Internet. The work involves the automated plotting of energy levels in molecules, atoms, nuclei and other types of quantized energy spectra. The automation involves the development of an appropriate computational code and graphical imaging system.

Stampoultzis, M.; Sinatkas, J.; Tsakstara, V.; Kosmas, T. S.

2014-03-01

379

The thesis comprises two major themes of quantum statistical dynamics. One is the development of quantum dissipation theory (QDT). It covers the establishment of some basic relations of quantum statistical dynamics, the construction of several nonequivalent complete second-order formulations, and the development of exact QDT. Another is related to the applications of quantum statistical dynamics to a variety of research

Ping Cui

2006-01-01

380

Measure synchronization in quantum many-body systems

The concept of measure synchronization between two coupled quantum many-body systems is presented. In general terms we consider two quantum many-body systems whose dynamics gets coupled through the contact particle-particle interaction. This coupling is shown to produce measure synchronization, a generalization of synchrony to a large class of systems which takes place in absence of dissipation. We find that in quantum measure synchronization, the many-body quantum properties for the two subsystems, e.g. condensed fractions and particle fluctuations, behave in a coordinated way. To illustrate the concept we consider a simple case of two species of bosons occupying two distinct quantum states. Measure synchronization can be readily explored with state-of-the-art techniques in ultracold atomic gases and, if propertly controlled, be employed to share quantum correlations between different degrees of freedom.

Haibo Qiu; Bruno Julia-Diaz; Miguel Angel Garcia-March; Artur Polls

2014-10-24

381

How open should an open system be? : essays on mobile computing

"Systems" goods-such as computers, telecom networks, and automobiles-are made up of multiple components. This dissertation comprises three essays that study the decisions of system innovators in mobile computing to "open" ...

Boudreau, Kevin J. (Kevin Joseph)

2006-01-01

382

A closed quantum system giving ergodicity J.M. Deutsch

A closed quantum system giving ergodicity J.M. Deutsch Department of Physics, University A closed quantum mechanical system does not necessarily give time averages in accor- dance the simultaneous measurement of any quantity of physical interest. His approach and a variety of related work has

Deutsch, Josh

383

Evolution of correlations of quantum many-particle systems

We consider the origin of the microscopic description of correlations in quantum systems. For correlation operators that give the alternative description of the quantum state evolution of many-particle systems, we deduce the von Neumann hierarchy of nonlinear equations and discuss the relationships of its solution both with the solution of the BBGKY hierarchy and with the s-particle correlation operators. A

V I Gerasimenko; V O Shtyk

2008-01-01

384

Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems

ERIC Educational Resources Information Center

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

385

NASA Astrophysics Data System (ADS)

We analytically derive deterministic equations of order parameters such as spontaneous magnetization in infinite-range quantum spin systems obeying quantum Monte Carlo dynamics. By means of the Trotter decomposition, we consider the transition probability of Glauber-type dynamics of microscopic states for the corresponding classical system. Under the static approximation, differential equations with respect to macroscopic order parameters are explicitly obtained from the master equation that describes the microscopic-law. We discuss several possible applications of our approach to disordered spin systems for statistical-mechanical informatics. Especially, we argue the ground state searching for infinite-range random spin systems via quantum adiabatic evolution.

Inoue, Jun-Ichi

2011-03-01

386

Detective quantum efficiency of the LODOX system

NASA Astrophysics Data System (ADS)

The Detective Quantum Efficiency (DQE) of a digital x-ray imaging system describes how much of the signal to noise ratio of the incident radiation is sustained in the resultant digital image. This measure of dose efficiency is suitable for the comparison of detectors produced by different manufacturers. The International Electrotechnical Commission (IEC) stipulates standard methods and conditions for the measurement of the DQE for single exposure imaging systems such as flat panel detectors. This paper shows how the calculation is adapted for DQE measurements of scanning systems. In this paper it is described how to measure the presampled Modulation Transfer Function (MTF) using an edge test method and how to extract the horizontal and vertical components of the Noise Power Spectrum (NPS) in a way that is insensitive to structured noise patterns often found in scanned images. The calculation of the total number of incident photons from the radiation dose measurement is explained and results are provided for the Lodox low dose full body digital x-ray scanning system which is developed in South Africa.

de Villiers, Mattieu; de Jager, Gerhard

2003-06-01

387

Phonon Overlaps in Molecular Quantum Dot Systems

NASA Astrophysics Data System (ADS)

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

388

Energy transmutation in nonequilibrium quantum systems

We investigate the particle and heat transport in quantum junctions with the geometry of star graphs. The system is in a nonequilibrium 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-Buettiker 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.

Mihail Mintchev; Luca Santoni; Paul Sorba

2014-12-19

389

Energy transmutation in nonequilibrium quantum systems

NASA Astrophysics Data System (ADS)

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

390

The study of classical dynamical systems using quantum theory

NASA Astrophysics Data System (ADS)

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

391

Skeletal anchorage system for open-bite correction

A skeletal anchorage system was developed for tooth movements. It consists of a titanium miniplate that is temporarily implanted in the maxilla or the mandible as an immobile anchorage. In this article, we introduce the skeletal anchorage system to intrude the lower molars in open-bite malocclusion and evaluate the results of treatment in two severe open-bite cases that underwent orthodontic

Mikako Umemori; Junji Sugawara; Hideo Mitani; Hiroshi Nagasaka; Hiroshi Kawamura

1999-01-01

392

Open MultiAgent Systems: Agent Communication and Integration

have been proposed that facilitate the communication process in a multiÂagent system. These agentsOpen MultiÂAgent Systems: Agent Communication and Integration Rogier M. van Eijk, Frank S. de Boer is on the issues of agent communication and integration. We define an abstract programming lanÂ guage for open

Utrecht, Universiteit

393

USER-FRIENDLY, OPEN-SYSTEM SOFTWARE FOR TEACHING PROTECTIVE

1 USER-FRIENDLY, OPEN-SYSTEM SOFTWARE FOR TEACHING PROTECTIVE RELAYING APPLICATION AND DESIGN was on implementing user-friendly and open-system solution that will allow an easy use and straight-forward future as the common framework [1]. To be efficient, such a framework needs to be user-friendly and amenable to future

394

Architecture of an Open Object-Oriented Database Management System

The architecture of the open object-oriented database (OODB) management system, its requirements, and its computational model, which builds database functionality as an extensible collection of transparent extensions to existing programming languages, are described. The way in which open OODB's system architecture is decomposed into a kernal meta-architecture and a collection of modules implementing specific behavioral extensions is discussed. The potential

David L. Wells; José A. Blakeley; Craig W. Thompson

1992-01-01

395

Recent development in open systems for EMS\\/SCADA

Based on the current situation and emerging trends of development of EMS\\/SCADA systems throughout the world, this report examines the `open system' concept from the viewpoints of users and suppliers. Current technologies for open distributed EMS\\/SCADAs and their possible future trends are described.

Yutaka Kokai; Fumio Masuda; Satoshi Horiike; Yasuji Sekine

1998-01-01

396

The ALPS project release 2.0: open source software for strongly correlated systems

NASA Astrophysics Data System (ADS)

We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. The code development is centered on common XML and HDF5 data formats, libraries to simplify and speed up code development, common evaluation and plotting tools, and simulation programs. The programs enable non-experts to start carrying out serial or parallel numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG) both in a static version and a dynamic time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for dynamical mean field theory (DMFT). The ALPS libraries provide a powerful framework for programmers to develop their own applications, which, for instance, greatly simplify the steps of porting a serial code onto a parallel, distributed memory machine. Major changes in release 2.0 include the use of HDF5 for binary data, evaluation tools in Python, support for the Windows operating system, the use of CMake as build system and binary installation packages for Mac OS X and Windows, and integration with the VisTrails workflow provenance tool. The software is available from our web server at http://alps.comp-phys.org/.

Bauer, B.; Carr, L. D.; Evertz, H. G.; Feiguin, A.; Freire, J.; Fuchs, S.; Gamper, L.; Gukelberger, J.; Gull, E.; Guertler, S.; Hehn, A.; Igarashi, R.; Isakov, S. V.; Koop, D.; Ma, P. N.; Mates, P.; Matsuo, H.; Parcollet, O.; Paw?owski, G.; Picon, J. D.; Pollet, L.; Santos, E.; Scarola, V. W.; Schollwöck, U.; Silva, C.; Surer, B.; Todo, S.; Trebst, S.; Troyer, M.; Wall, M. L.; Werner, P.; Wessel, S.

2011-05-01

397

The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age

Computational Quantum Chemistry has developed into a powerful, efficient, reliable and increasingly routine tool for exploring the structure and properties of small to medium sized molecules. Many thousands of calculations are performed every day, some offering results which approach experimental accuracy. However, in contrast to other disciplines, such as crystallography, or bioinformatics, where standard formats and well-known, unified databases exist, this QC data is generally destined to remain locally held in files which are not designed to be machine-readable. Only a very small subset of these results will become accessible to the wider community through publication. In this paper we describe how the Quixote Project is developing the infrastructure required to convert output from a number of different molecular quantum chemistry packages to a common semantically rich, machine-readable format and to build respositories of QC results. Such an infrastructure offers benefits at many levels. The standardised representation of the results will facilitate software interoperability, for example making it easier for analysis tools to take data from different QC packages, and will also help with archival and deposition of results. The repository infrastructure, which is lightweight and built using Open software components, can be implemented at individual researcher, project, organisation or community level, offering the exciting possibility that in future many of these QC results can be made publically available, to be searched and interpreted just as crystallography and bioinformatics results are today. Although we believe that quantum chemists will appreciate the contribution the Quixote infrastructure can make to the organisation and and exchange of their results, we anticipate that greater rewards will come from enabling their results to be consumed by a wider community. As the respositories grow they will become a valuable source of chemical data for use by other disciplines in both research and education. The Quixote project is unconventional in that the infrastructure is being implemented in advance of a full definition of the data model which will eventually underpin it. We believe that a working system which offers real value to researchers based on tools and shared, searchable repositories will encourage early participation from a broader community, including both producers and consumers of data. In the early stages, searching and indexing can be performed on the chemical subject of the calculations, and well defined calculation meta-data. The process of defining more specific quantum chemical definitions, adding them to dictionaries and extracting them consistently from the results of the various software packages can then proceed in an incremental manner, adding additional value at each stage. Not only will these results help to change the data management model in the field of Quantum Chemistry, but the methodology can be applied to other pressing problems related to data in computational and experimental science. PMID:21999363

2011-01-01

398

The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age.

Computational Quantum Chemistry has developed into a powerful, efficient, reliable and increasingly routine tool for exploring the structure and properties of small to medium sized molecules. Many thousands of calculations are performed every day, some offering results which approach experimental accuracy. However, in contrast to other disciplines, such as crystallography, or bioinformatics, where standard formats and well-known, unified databases exist, this QC data is generally destined to remain locally held in files which are not designed to be machine-readable. Only a very small subset of these results will become accessible to the wider community through publication.In this paper we describe how the Quixote Project is developing the infrastructure required to convert output from a number of different molecular quantum chemistry packages to a common semantically rich, machine-readable format and to build respositories of QC results. Such an infrastructure offers benefits at many levels. The standardised representation of the results will facilitate software interoperability, for example making it easier for analysis tools to take data from different QC packages, and will also help with archival and deposition of results. The repository infrastructure, which is lightweight and built using Open software components, can be implemented at individual researcher, project, organisation or community level, offering the exciting possibility that in future many of these QC results can be made publically available, to be searched and interpreted just as crystallography and bioinformatics results are today.Although we believe that quantum chemists will appreciate the contribution the Quixote infrastructure can make to the organisation and and exchange of their results, we anticipate that greater rewards will come from enabling their results to be consumed by a wider community. As the respositories grow they will become a valuable source of chemical data for use by other disciplines in both research and education.The Quixote project is unconventional in that the infrastructure is being implemented in advance of a full definition of the data model which will eventually underpin it. We believe that a working system which offers real value to researchers based on tools and shared, searchable repositories will encourage early participation from a broader community, including both producers and consumers of data. In the early stages, searching and indexing can be performed on the chemical subject of the calculations, and well defined calculation meta-data. The process of defining more specific quantum chemical definitions, adding them to dictionaries and extracting them consistently from the results of the various software packages can then proceed in an incremental manner, adding additional value at each stage.Not only will these results help to change the data management model in the field of Quantum Chemistry, but the methodology can be applied to other pressing problems related to data in computational and experimental science. PMID:21999363

Adams, Sam; de Castro, Pablo; Echenique, Pablo; Estrada, Jorge; Hanwell, Marcus D; Murray-Rust, Peter; Sherwood, Paul; Thomas, Jens; Townsend, Joe

2011-01-01

399

Empowering open systems through cross-platform interoperability

NASA Astrophysics Data System (ADS)

Most of the motivations for open systems lie in the expectation of interoperability, sometimes referred to as "plug-and-play". Nothing in the notion of "open-ness", however, guarantees this outcome, which makes the increased interest in open architecture more perplexing. In this paper, we explore certain themes of open architecture. We introduce the concept of "windows of interoperability", which can be used to align disparate portions of architecture. Such "windows of interoperability", which concentrate on a reduced set of protocol and interface features, might achieve many of the broader purposes assigned as benefits in open architecture. Since it is possible to engineer proprietary systems that interoperate effectively, this nuanced definition of interoperability may in fact be a more important concept to understand and nurture for effective systems engineering and maintenance.

Lyke, James C.

2014-06-01

400

Open and closed systems in data analysis entropy

This dissertation presents and efficient and integrated approach to data analysis. Entropy data analysis is an evolution of reconstructability analysis, which investigates the relationships between parts and wholes. The central theme of the dissertation is the development of a system to condense the information in a data set into a small number of parameters. The new system is called a k-system. k-system analysis goes beyond traditional data analysis in that it has the potentiality for changes to be made to a system; and the impact of these changes can be evaluated. k-system can be useful in designing and evaluating open and closed systems. The behavior of these systems is measured by the k(.) function. The k-system is a closed system. The concept of open comes about when the author tries to reconstruct the k-system starting with an empty system which contains no information. He adds information until he is satisfied that this constructed system adequately reproduces the k-system. The dissertation identifies and isolates the mathematics in the k-system algorithms that determine an open or closed system. It will change the algorithms to offer the option of an open or closed system, and then implement these changes in the k-system algorithms for option of an open or closed system.

Jafari, H.R.

1990-01-01

401

Strain behavior of quantum wires and quantum boxes in III-V material systems

NASA Astrophysics Data System (ADS)

Directly etched and regrown quantum wires and quantum boxes have been fabricated, characterized, and modeled in order to study the behavior of non-uniform strain in quantum heterostructures in III-V material systems. Photoluminescence data show a dramatic decrease in peak intensity as quantum wire or box width decreases, while the energy at which peak emission occurs and the width of the emission peak both increase with decreasing feature width. It is shown that strain is primarily responsible for these three effects, as each quantum heterostructure's growth-direction dilation, caused by horizontal lattice-matching to the substrate and cap layer, is opposed by growth-direction compression from lattice-matching the cladding material on the heterostructure sidewalls. Through photoluminescence data and calculations based on transmission electron microscopy measurements of spatial variation of lattice constant, the peak intensity reduction, peak energy shift, and spectral broadening are quantitatively explained by a combination of non-uniform strain behavior and purely geometric considerations. That these factors suffice to explain the observed intensity reduction also refutes the presence of strain-induced dislocations. A new theoretical analysis of strain behavior in quantum heterostructures is developed, valid for small systems whose discreteness precludes classical continuum treatment. The variation of growth-direction and in-plane lattice constants within a quantum heterostructure and the surrounding cladding is systematically derived, and novel predictions are made; the aspect ratio of the quantum wire or quantum box cross-section is found to be the principal determinant of the qualitative strain behavior. A computer simulation, executing lattice dynamics at the atomic level using the Stillinger-Weber and modified Lennard-Jones potentials, is created and is successfully used to confirm all predictions of the theoretical model. The simulation, able to model any quantum well, quantum wire, or quantum box system in III- V zincblende materials, also adds quantitative predictability to the theoretical analysis and illuminates the experimental photoluminescence and microscopy data.

Tentarelli, Eric S.

402

Supersymmetric transformations in open systems and in classical physics

NASA Astrophysics Data System (ADS)

Supersymmetry for non-relativistic quantum mechanics (SUSY QM), first formulated by Witten in 1981, relates isospectral or nearly isospectral systems. In SUSY QM, attention has historically been focused on the real normal-mode (NM) spectrum. In this work, we extend the concept to open systems and their complex quasinormal-mode (QNM) spectra, which are important for systems in which waves are not confined, but are outgoing to spatial infinity, e.g., gravitational waves from black holes. We study the second-order SUSY as well as the standard first-order SUSY. It is shown that strictly isospectral complex QNM spectra for systems defined on the full line can be obtained by both first- and second-order SUSY transformations, while only essentially isospectral spectra can be obtained for the half line. The former result generically disproves unique inversion of the potential from one complex spectrum for open systems on a full line, while the latter lends support to the conjecture of unique inversion from one spectrum for a half line. Moreover, this extension of SUSY leads to a unified picture and a better understanding of the structure of the spectrum. It is also shown that SUSY transformations preserve orthonormality under the natural bilinear map defined on QNMs, just as it preserves the inner product for NMs in conservative systems. A "mixed" SUSY transformation (where the generator is not a pure mode) naturally leads to exponential potential tails, for which many subtleties arise, e.g., the definition of QNMs, the so-called anomalous and miraculous points, and the normalization at these points. These are systematically studied with special reference to SUSY. In addition, one can formulate a classical version of SUSY (CSUSY) by applying N SUSY transformations in succession, with h ? 0, N ? infinity, hN ? ? finite. All the corresponding classical variables become functions of the continuous variable ?. This consideration leads to a class of potentials with interesting properties. It is found that time-evolution is preserved under changes in ?, the period of equal-energy orbits is independent of ?, and ?-evolution is a generalized contact transformation. Closed-form solutions for the potential include well-known examples.

Wong, Chun Wing

403

Hacking commercial quantum cryptography systems by tailored bright illumination

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

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

2010-01-01

404

Dynamical invariants for quantum control of four-level systems

NASA Astrophysics Data System (ADS)

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

405

Quantum Phase Space, Quantization Hierarchy, and Eclectic Quantum Many-Body System

An operator-valued quantum phase space formula is constructed. The phase space formula of Quantum Mechanics provides a natural link between first and second quantization, thus contributing to the understanding of quantization problem. By the combination of quantization and hamiltonization of dynamics, a quantization hierarchy is introduced, beyond the framework of first and second quantization and generalizing the standard quantum theory. We apply our quantization method to quantum many-body system and propose an eclectic model, in which the dimension of Hilbert space does not scale exponentially with the number of particles due to the locality of interaction, and the evolution is a constrained Hamiltonian dynamics.

Dong-Sheng Wang

2014-10-05

406

Terahertz spectroscopy of quantum 2D electron systems

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy permits the coherent motion of charges to be examined in a diverse range of two-dimensional semiconductor heterostructures. Studies of the THz conductivity and magnetoconductivity of two-dimensional quantum systems are reviewed, including cyclotron resonance spectroscopy and the transverse conductivity in the Hall and quantum Hall regimes. Experiments are described that demonstrate quantum phenomena at THz frequencies, principally coherent control and enhanced light–matter coupling in electromagnetic cavities.

Lloyd-Hughes, James

2014-09-01

407

Correlation approach to work extraction from finite quantum systems

NASA Astrophysics Data System (ADS)

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

408

Quantum interference in an electron-hole graphene ring system

NASA Astrophysics Data System (ADS)

Quantum interference is observed in a graphene ring system via the Aharonov Bohm effect. As graphene is a gapless semiconductor, this geometry allows to study the unique situation of quantum interference between electrons and holes in addition to the unipolar quantum interference. The period and amplitude of the observed Aharonov-Bohm oscillations are independent of the sign of the applied gate voltage showing the equivalence between unipolar and dipolar interference.

Smirnov, D.; Schmidt, H.; Haug, R. J.

2013-12-01

409

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

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

410

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

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

411

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

NASA Astrophysics Data System (ADS)

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

412

Open Source Vision Library (OpenVL) Based Local Positioning System Changsong Shen, Steve Oldridge}@ece.ubc.ca Abstract This paper presents an Open Source Vision Library (OpenVL) for hardware acceleration of video-based surveillance systems and other computer vision applications to facilitate low latency, real-time response. Our

British Columbia, University of

413

Particle escapes in an open quantum network via multiple leads

Quantum escape of a particle from an end of a one-dimensional finite region to N semi-infinite leads is discussed from a scattering theory approach. Depending on the potential barrier amplitude at the junction, the probability P(t) for a particle to remain in the finite region at time t shows two different decay behaviors at long times; one is proportional to N{sup 2}/t{sup 3} and another is proportional to 1/(N{sup 2}t). In addition, the velocity V(t) for a particle to leave the finite region, defined from a probability current of the particle position, decays asymptotically as a power of time {approx}1/t, independent of the number of leads and the initial wave function. For a finite time, the probability P(t) decays exponentially in time with a smaller decay rate for a greater number of leads, and the velocity V(t) shows a time oscillation whose amplitude is larger for a greater number of leads. Particle escapes from the both ends of a finite region to multiple leads are also discussed using a different boundary condition.

Taniguchi, Tooru; Sawada, Shin-ichi [School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda City (Japan)

2011-12-15

414

Heat flux and quantum correlations in dissipative cascaded systems

NASA Astrophysics Data System (ADS)

We study the dynamics of heat flux in the thermalization process of a pair of identical quantum systems that interact dissipatively with a reservoir in a cascaded fashion. Despite that the open dynamics of the bipartite system S is globally Lindbladian, one of the subsystems "sees" the reservoir in a state modified by the interaction with the other subsystem and hence it undergoes a non-Markovian dynamics. As a consequence, the heat flow exhibits a nonexponential time behavior which can greatly deviate from the case where each party is independently coupled to the reservoir. We investigate both thermal and correlated initial states of S and show that the presence of correlations at the beginning can considerably affect the heat-flux rate. We carry out our study in two paradigmatic cases—a pair of harmonic oscillators with a reservoir of bosonic modes and two qubits with a reservoir of fermionic modes—and compare the corresponding behaviors. In the case of qubits and for initial thermal states, we find that the trace distance discord is at any time interpretable as the correlated contribution to the total heat flux.

Lorenzo, Salvatore; Farace, Alessandro; Ciccarello, Francesco; Palma, G. Massimo; Giovannetti, Vittorio

2015-02-01

415

Quantum filter for a class of non-Markovian quantum systems

In this paper we present a Markovian representation approach to constructing quantum filters for a class of non-Markovian quantum systems disturbed by Lorenztian noise. An ancillary system is introduced to convert white noise into Lorentzian noise which is injected into a principal system via a direct interaction. The resulting dynamics of the principal system are non-Markovian, which are driven by the Lorentzian noise. By probing the principal system, a quantum filter for the augmented system can be derived from standard theory, where the conditional state of the principal system can be obtained by tracing out the ancillary system. An example is provided to illustrate the non-Markovian dynamics of the principal system.

Shibei Xue; Matthew R. James; Alireza Shabani; Valery Ugrinovskii; Ian R. Petersen

2015-04-11

416

Uhrig Dynamical Control of a Three-Level System Via Non-Markovian Quantum State Diffusion

In this paper, we use the quantum state diffusion (QSD) equation to implement the Uhrig dynamical decoupling (UDD) to a three-level quantum system coupled to a non-Markovian reservoir comprising of infinite numbers of degrees of freedom. For this purpose, we first reformulate the non-Markovian QSD to incorporate the effect of the external control fields. With this stochastic QSD approach, we demonstrate that an unknown state of the three-level quantum system can be universally protected against both colored phase and amplitude noises when the control-pulse sequences and control operators are properly designed. The advantage of using non-Markovian quantum state diffusion equations is that the control dynamics of open quantum systems can be treated exactly without using Trotter product formula and be efficiently simulated even when the environment comprise of infinite numbers of degrees of freedom. We also show how the control efficacy depends on the environment memory time and the designed time points of applied control pulses.

Wenchong Shu; Xinyu Zhao; Jun Jing; Lian-Ao Wu; Ting Yu

2014-08-09

417

Open-ended magnetic confinement systems for fusion

Magnetic confinement systems that use externally generated magnetic fields can be divided topologically into two classes: ``closed`` and `open``. The tokamak, the stellarator, and the reversed-field-pinch approaches are representatives of the first category, while mirror-based systems and their variants are of the second category. While the recent thrust of magnetic fusion research, with its emphasis on the tokamak, has been concentrated on closed geometry, there are significant reasons for the continued pursuit of research into open-ended systems. The paper discusses these reasons, reviews the history and the present status of open-ended systems, and suggests some future directions for the research.

Post, R.F.; Ryutov, D.D.

1995-05-01

418

Quantum correlation measure in arbitrary bipartite systems

NASA Astrophysics Data System (ADS)

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

419

Huge Quantum Gravity Effects in the Solar System

Normally one thinks of the motion of the planets around the Sun as a highly classical phenomenon, so that one can neglect quantum gravity in the Solar System. However, classical chaos in the planetary motion amplifies quantum uncertainties so that they become very large, giving huge quantum gravity effects. For example, evidence suggests that Uranus may eventually be ejected from the Solar System, but quantum uncertainties would make the direction at which it leaves almost entirely uncertain, and the time of its exit uncertain by about a billion billion years. For a time a billion billion years from now, there are huge quantum uncertainties whether Uranus will be within the Solar System, within the Galaxy, or even within causal contact of the Galaxy.

Don N. Page

2010-05-17

420

Recovering classical dynamics from coupled quantum systems through continuous measurement

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 back action 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 ({Dirac_h}/2{pi})

Ghose, Shohini; Alsing, Paul; Deutsch, Ivan; Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States); T-8 Theoretical Division, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2003-05-01

421

Enhanced Fault-Tolerant Quantum Computing in d -Level Systems

NASA Astrophysics Data System (ADS)

Error-correcting codes protect quantum information and form the basis of fault-tolerant quantum computing. Leading proposals for fault-tolerant quantum computation require codes with an exceedingly rare property, a transversal non-Clifford gate. Codes with the desired property are presented for d -level qudit systems with prime d . The codes use n =d -1 qudits and can detect up to ˜d /3 errors. We quantify the performance of these codes for one approach to quantum computation known as magic-state distillation. Unlike prior work, we find performance is always enhanced by increasing d .

Campbell, Earl T.

2014-12-01

422

Security proof for quantum key distribution using qudit systems

NASA Astrophysics Data System (ADS)

We provide security bounds against coherent attacks for two families of quantum key distribution protocols that use d-dimensional quantum systems. In the asymptotic regime, both the secret key rate for fixed noise and the robustness to noise increase with d. The finite key corrections are found to be almost insensitive to d?20.

Sheridan, Lana; Scarani, Valerio

2010-09-01

423

Security proof for quantum key distribution using qudit systems

We provide security bounds against coherent attacks for two families of quantum key distribution protocols that use d-dimensional quantum systems. In the asymptotic regime, both the secret key rate for fixed noise and the robustness to noise increase with d. The finite key corrections are found to be almost insensitive to d < or approx. 20.

Sheridan, Lana [Centre for Quantum Technologies, National University of Singapore (Singapore); Scarani, Valerio [Centre for Quantum Technologies, National University of Singapore (Singapore); Department of Physics, National University of Singapore (Singapore)

2010-09-15

424

Sub-ballistic behavior in quantum systems with Lévy noise

We investigate the quantum walk and the quantum kicked rotor in resonance subjected to noise with a L\\'evy waiting time distribution. We find that both systems have a sub-ballistic wave function spreading as shown by a power-law tail of the standard deviation.

A. Romanelli; R. Siri; V. Micenmacher

2007-05-02

425

Realizing the Quantum Hall System in String Theory

In a recent paper Bernevig, Brodie, Susskind and Toumbas constructed a brane realization of the Quantum Hall fluid. Since then it has been realized that the Quantum Hall system is very closely related to non--commutative Chern Simons theory and this suggests alternative brane constructions which we believe are more reliable and clear. In this paper a brane construction is given

Simeon Hellerman; Leonard Susskind

2001-01-01

426

Photon statistics: Nonlinear spectroscopy of single quantum systems Shaul Mukamel

Photon statistics: Nonlinear spectroscopy of single quantum systems Shaul Mukamel Department of their infor- mation content. A general formal expression for photon counting statistics from single quantum counting statistics which had proven to be a most valuable measure of coherence has been formulated

Mukamel, Shaul

427

Josephson inplane and tunneling currents in bilayer quantum Hall system

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.

Ezawa, Z. F. [Nishina Center, RIKEN, Saitama 351-0198 (Japan); Tsitsishvili, G. [Georgia Department of Physics, Tbilisi State University, Tbilisi 0179 (Georgia); Sawada, A. [Research Center for Low Temperature and Materials Sciences, Kyoto University, Kyoto 606-8501 (Japan)

2013-12-04

428

Testing Quantum Mechanics in the Neutral Kaon System

The neutral kaon system is a sensitive probe of quantum mechanics. We revive a parametrization of non-quantum-mechanical effects that is motivated by considerations of the nature of space-time foam, and show how it can be constrained by new measurements of $K_L \\rightarrow 2\\pi$ and $K_{L,S}$ semileptonic decays at LEAR or a $\\phi$ factory.

John Ellis; N. E. Mavromatos; D. V. Nanopoulos

1992-07-29

429

Quantum Coherence Effects in Four-level Diamond Atomic System

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

Bao-Quan Ou; Lin-Mei Liang; Cheng-Zu Li

2008-10-28

430

Separability of sequential isomorphisms on quantum effects in multipartite systems

NASA Astrophysics Data System (ADS)

In the paper, we study separability of sequential isomorphisms on quantum effects in multipartite systems. First we obtain necessary and sufficient conditions for separable sequential isomorphisms in bipartite systems. Secondly, in finite-dimensional bipartite systems, separability of sequential endomorphisms on quantum effects is discussed. Furthermore, we extend these conclusions to the multipartite case. Finally, applying our results, an equivalent characterization of local unitary operations is given.

He, Kan; Sun, Fanguo; Hou, Jinchuan

2015-02-01

431

NASA Astrophysics Data System (ADS)

The use of InGaAs quantum wells with composition graded across the intrinsic region to increase open-circuit voltage in p-i-n GaAs/InGaAs quantum well solar cells is demonstrated and analyzed. By engineering the band-edge energy profile to reduce photo-generated carrier concentration in the quantum wells at high forward bias, simultaneous increases in both open-circuit voltage and short-circuit current density are achieved, compared to those for a structure with the same average In concentration, but constant rather than graded quantum well composition across the intrinsic region. This approach is combined with light trapping to further increase short-circuit current density.

Li, Xiaohan; Dasika, Vaishno D.; Li, Ping-Chun; Ji, Li; Bank, Seth R.; Yu, Edward T.

2014-09-01

432

Experimental simulation of quantum tunneling in small systems.

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

433

Experimental simulation of quantum tunneling in small systems

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

434

47 CFR 76.1503 - Carriage of video programming providers on open video systems.

Code of Federal Regulations, 2011 CFR

...programming providers on open video systems. 76.1503 Section 76.1503...CABLE TELEVISION SERVICE Open Video Systems § 76.1503 Carriage of video programming providers on open video systems. (a) Non-discrimination...

2011-10-01

435

47 CFR 76.1504 - Rates, terms and conditions for carriage on open video systems.

Code of Federal Regulations, 2014 CFR

...conditions for carriage on open video systems. 76.1504 Section 76.1504...CABLE TELEVISION SERVICE Open Video Systems § 76.1504 Rates, terms and conditions for carriage on open video systems. (a) Reasonable rate...

2014-10-01

436

47 CFR 76.1504 - Rates, terms and conditions for carriage on open video systems.

Code of Federal Regulations, 2012 CFR

...conditions for carriage on open video systems. 76.1504 Section 76.1504...CABLE TELEVISION SERVICE Open Video Systems § 76.1504 Rates, terms and conditions for carriage on open video systems. (a) Reasonable rate...

2012-10-01

437

47 CFR 76.1504 - Rates, terms and conditions for carriage on open video systems.

Code of Federal Regulations, 2013 CFR

...conditions for carriage on open video systems. 76.1504 Section 76.1504...CABLE TELEVISION SERVICE Open Video Systems § 76.1504 Rates, terms and conditions for carriage on open video systems. (a) Reasonable rate...

2013-10-01

438

Trapping ultracold atoms in optical lattices enabled numerous breakthroughs uniting several disciplines. Although the light is a key ingredient in such systems, its quantum properties are typically neglected, reducing the role of light to a classical tool for atom manipulation. Here we show how elevating light to the quantum level leads to novel phenomena, inaccessible in setups based on classical optics. Interfacing a many-body atomic system with quantum light opens it to the environment in an essentially nonlocal way, where spatial coupling can be carefully designed. The competition between typical processes in strongly correlated systems (local tunnelling and interaction) with global measurement backaction leads to novel multimode dynamics and the appearance of long-range correlated tunnelling capable of entangling distant lattices sites, even when tunnelling between neighbouring sites is suppressed by the quantum Zeno effect. We demonstrate both the break-up and protection of strongly interacting fermion pairs by different measurements.

Gabriel Mazzucchi; Wojciech Kozlowski; Santiago F. Caballero-Benitez; Thomas J. Elliott; Igor B. Mekhov

2015-03-30

439

Trapping ultracold atoms in optical lattices enabled numerous breakthroughs uniting several disciplines. Although the light is a key ingredient in such systems, its quantum properties are typically neglected, reducing the role of light to a classical tool for atom manipulation. Here we show how elevating light to the quantum level leads to novel phenomena, inaccessible in setups based on classical optics. Interfacing a many-body atomic system with quantum light opens it to the environment in an essentially nonlocal way, where spatial coupling can be carefully designed. The competition between typical processes in strongly correlated systems (local tunnelling and interaction) with global measurement backaction leads to novel multimode dynamics and the appearance of long-range correlated tunnelling capable of entangling distant lattices sites, even when tunnelling between neighbouring sites is suppressed by the quantum Zeno effect. We demonstrate both the break-up and protection of strongly interacting fermion ...

Mazzucchi, Gabriel; Caballero-Benitez, Santiago F; Elliott, Thomas J; Mekhov, Igor B

2015-01-01

440

Geometrical and Topological Aspects of Quantum Information Systems

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

Tommaso F. Demarie

2014-07-23

441

Natural Light Harvesting Systems: Unraveling the quantum puzzles

In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies ($>$ 95\\%) at which excitation is transferred from the illuminated protein complex site to the reaction centers. The high speeds of excitation propagation within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observations of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes which occurs even in noisy environmental baths. The exact nature of the association between the high energy propagation rates and strength of quantum coherences remains largely unsolved. This review presents recent developments in quantum theories, and links information-theoretic aspects with photosynthetic light-harvesting processes in biomolecular systems. There is examination of various attempts to pinpoint the processes that underpin coherence features arising from the light harvesting activities of biomolecular systems, with particular emphasis on the effects that factors such non-Markovianity, zeno mechanisms, teleportation, quantum predictability and the role of m