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1

The damping of the harmonic oscillator is studied in the framework of the\\u000aLindblad theory for open quantum systems. A generalization of the fundamental\\u000aconstraints on quantum mechanical diffusion coefficients which appear in the\\u000amaster equation for the damped quantum oscillator is presented; the\\u000aSchr\\\\\\

A. Isar; A. Sandulescu; H. Scutaru; E. Stefanescu; W. Scheid

2004-01-01

2

Quantum dynamics and open quantum systems

NASA Astrophysics Data System (ADS)

The thesis deals with the quantum mechanical description of dynamical properties of open systems, and, in particular, with studying the temporal evolution of quantum systems interacting with their environments. In this thesis we apply a microscopic approach to study such systems thus explicitly considering the hamiltonian of the environment and its interaction with the quantum system under consideration. We also consider how the microscopic hamiltonians can be used in order to produce several logical operations as a result of the temporal dynamics of the systems governed by such hamiltonians. In the introductory chapter we start by discussing the physical motivation for studying open quantum systems and describe the most significant phenomena that result due to such interactions. We also briefly outline the experimental realizations in which the type of systems studied in the dissertation can arise. Then, in chapter 1, we consider a model of a quantum spin interacting with free electron gas. It is shown that this model can be mapped onto the spin-boson model with an Ohmic spectral function. The criterion for the localization of the spin is explicitly derived in terms of the parameters of the original fermionic model. In chapter 2, we study a general quantum system interacting with an environment modeled by the bosonic heat bath of the Caldeira and Leggett type. We argue that this model provides an appropriate description of adiabatic quantum decoherence, i.e. loss of entanglement on time scales short compared to those of thermal relaxation processes associated with energy exchange with the bath. Calculation of the elements of the reduced density matrix of the system is carried out exactly, and time-dependent decoherence is identified, similar to recent results for related models. Our key finding is that the decoherence process is controlled by the spectral properties of the interaction rather than by the system's hamiltonian. In chapter 3, a model of a quantum spin interacting with a spin environment is considered. The interaction is chosen to be such that the state of the environment is conserved. The reduced density matrix of the spin is calculated exactly for arbitrary coupling strength. The density matrix reaches its stationary state at t = /infty, which can be explicitly expressed in terms of elementary functions. It turns out that this state is quite different from the canonical distribution thus pointing out that the Markovian assumption is playing an essential role quantum mechanical description of a heat bath. Chapter 4 deals with quantum computing. We propose to design multi-spin quantum gates in which the input and output two-state systems (spins) are not necessarily identical. We outline the design criteria for such devices and then review recent results for single-unit Hamiltonians that accomplish the NOT and XOR functions. Chapter 5 is devoted to the problem of quantum copying. We consider a quantum evolution in which the basis states of I at time t are duplicated in at least two of the systems I, C, D, at time t + /Delta t. In essence, the restriction on the initial target states is exchanged for uncertainty as to which two of the three qubits retain copies of the initial source state. Finally, in chapter 6, we summarize and discuss the results obtained in the thesis and also describe directions for future research.

Mozyrsky, Dima

1999-02-01

3

Quasiequilibria in open quantum systems

In this work, the steady-state or quasiequilibrium resulting from periodically modulating the Liouvillian of an open quantum system, L-circumflex-circumflex(t), is investigated. It is shown that differences between the quasiequilibrium and the instantaneous equilibrium occur due to nonadiabatic contributions from the gauge field connecting the instantaneous eigenstates of L-circumflex-circumflex(t) to a fixed basis. These nonadiabatic contributions are shown to result in an additional rotation and/or depolarization for a single spin-1/2 in a time-dependent magnetic field and to affect the thermal mixing of two coupled spins interacting with a time-dependent magnetic field.

Walls, Jamie D. [Department of Chemistry, University of Miami, Coral Gables, Florida 33124 (United States)

2010-03-15

4

Dynamical Decoupling of Open Quantum Systems

We propose a novel dynamical method for beating decoherence and dissipation in open quantum systems. We demonstrate the possibility of filtering out the effects of unwanted (not necessarily known) system-environment interactions and show that the noise-suppression procedure can be combined with the capability of retaining control over the effective dynamical evolution of the open quantum system. Implications for quantum information processing are discussed. {copyright} {ital 1999} {ital The American Physical Society}

Viola, L.; Lloyd, S. [d`Arbeloff Laboratory for Information Systems and Technology, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Knill, E. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1999-03-01

5

Controlling open quantum systems using fast transitions

NASA Astrophysics Data System (ADS)

Unitary control and decoherence appear to be irreconcilable in quantum mechanics. When a quantum system interacts with an environment, control strategies usually fail due to decoherence. In this article we implement a time-optimal unitary control protocol suitable for quantum open systems. The method is based on successive diabatic and sudden switch transitions in the avoided crossings of the energy spectra of closed systems. We show that the speed of this control protocol meets the fundamental bounds imposed by the quantum speed limit, thus making this scheme ideal for application where decoherence needs to be avoided. We show that this method can achieve complex control strategies with high accuracy in quantum open systems.

Poggi, Pablo M.; Lombardo, Fernando C.; Wisniacki, Diego A.

2013-02-01

6

Quantum Simulation for Open-System Dynamics

NASA Astrophysics Data System (ADS)

Simulations are essential for predicting and explaining properties of physical and mathematical systems yet so far have been restricted to classical and closed quantum systems [1,2]. Although forays have been made into open-system quantum simulation [3], the strict algorithmic aspect has not been explored yet is necessary to account fully for resource consumption to deliver bounded-error answers to computational questions. An open-system quantum simulator would encompass classical and closed-system simulation and also solve outstanding problems concerning, e.g. dynamical phase transitions in non-equilibrium systems, establishing long-range order via dissipation, verifying the simulatability of open-system dynamics on a quantum Turing machine. We construct an efficient autonomous algorithm for designing an efficient quantum circuit to simulate many-body open-system dynamics described by a local Hamiltonian plus decoherence due to separate baths for each particle. The execution time and number of gates for the quantum simulator both scale polynomially with the system size.[4pt] [1] S. Lloyd, Science 273, 1073 (1996).[0pt] [2] D. W. Berry et al, Comm. Math. Phys. 270, 359 (2007).[0pt] [3] M. Kliesch et al, Phys. Rev. Lett. 107, 120501 (2011).

Wang, Dong-Sheng; de Oliveira, Marcos Cesar; Berry, Dominic; Sanders, Barry

2013-03-01

7

Quantum Speed Limits in Open System Dynamics

NASA Astrophysics Data System (ADS)

Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise.

del Campo, A.; Egusquiza, I. L.; Plenio, M. B.; Huelga, S. F.

2013-02-01

8

Quantum speed limits in open system dynamics.

Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise. PMID:23414008

del Campo, A; Egusquiza, I L; Plenio, M B; Huelga, S F

2013-01-30

9

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

10

Geometric magnetism in open quantum systems

NASA Astrophysics Data System (ADS)

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

Campisi, Michele; Denisov, Sergey; Hänggi, Peter

2012-09-01

11

Quantum correlations in two-mode Gaussian open quantum systems

NASA Astrophysics Data System (ADS)

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of continuous variable quantum entanglement and quantum discord for a system consisting of two non-interacting non-resonant bosonic modes embedded in a thermal environment. We study the time evolution of logarithmic negativity, which characterizes the degree of entanglement, and show that in the case of an entangled initial squeezed thermal state, entanglement suppression takes place for all temperatures of the environment, including zero temperature. 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 discord decays asymptotically in time under the effect of the thermal bath. We describe also the time evolution of classical correlations.

Isar, Aurelian

2013-06-01

12

Quantum localization in open chaotic systems.

We study a quasibound state of a delta -kicked rotor with absorbing boundaries focusing on the nature of the dynamical localization in open quantum systems. The localization lengths xi of lossy quasibound states located near the absorbing boundaries decrease as they approach the boundary while the corresponding decay rates Gamma are dramatically enhanced. We find the relation xi approximately Gamma(-1/2) and explain it based upon the finite time diffusion, which can also be applied to a random unitary operator model. We conjecture that this idea is valid for the system exhibiting both the diffusion in classical dynamics and the exponential localization in quantum mechanics. PMID:18851192

Ryu, Jung-Wan; Hur, G; Kim, Sang Wook

2008-09-03

13

Quantum localization in open chaotic systems

NASA Astrophysics Data System (ADS)

We study a quasibound state of a ? -kicked rotor with absorbing boundaries focusing on the nature of the dynamical localization in open quantum systems. The localization lengths ? of lossy quasibound states located near the absorbing boundaries decrease as they approach the boundary while the corresponding decay rates ? are dramatically enhanced. We find the relation ?˜?-1/2 and explain it based upon the finite time diffusion, which can also be applied to a random unitary operator model. We conjecture that this idea is valid for the system exhibiting both the diffusion in classical dynamics and the exponential localization in quantum mechanics.

Ryu, Jung-Wan; Hur, G.; Kim, Sang Wook

2008-09-01

14

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

2013-07-30

15

Evolution of Quantum Entanglement in 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 entanglement for a system consisting of two uncoupled harmonic oscillators interacting with a thermal environment. Using Peres-Simon necessary sufficient criterion for separability of two-mode Gaussian states, we show that for some values of diffusion coefficient, dissipation constant and temperature of the environment, the state keeps for all times its initial type: separable or entangled. In other cases, entanglement generation, entanglement sudden death or a periodic collapse revival of entanglement take place.

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

2010-08-04

16

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

17

Specific heat anomalies of open quantum systems.

The evaluation of the specific heat of an open damped quantum system is a subtle issue. One possible route is based on the thermodynamic partition function which is the ratio of the partition functions of system plus bath and of the bath alone. For the free damped particle it has been shown, however, that the ensuing specific heat may become negative for appropriately chosen environments. Being an open system this quantity then naturally must be interpreted as the change in the specific heat obtained as the difference between the specific heat of the heat bath coupled to the system degrees of freedom and the specific heat of the bath alone. While this difference may become negative, the involved specific heats themselves are always positive; thus, the known thermodynamic stability criteria are perfectly guaranteed. For a damped quantum harmonic oscillator, instead of negative values, under appropriate conditions one can observe a dip in the difference of specific heats as a function of temperature. Stylized minimal models containing a single oscillator heat bath are employed to elucidate the occurrence of the anomalous temperature dependence of the corresponding specific heat values. Moreover, we comment on the consequences for the interpretation of the density of states based on the thermal partition function. PMID:19658471

Ingold, Gert-Ludwig; Hänggi, Peter; Talkner, Peter

2009-06-09

18

Specific heat anomalies of open quantum systems

NASA Astrophysics Data System (ADS)

The evaluation of the specific heat of an open damped quantum system is a subtle issue. One possible route is based on the thermodynamic partition function which is the ratio of the partition functions of system plus bath and of the bath alone. For the free damped particle it has been shown, however, that the ensuing specific heat may become negative for appropriately chosen environments. Being an open system this quantity then naturally must be interpreted as the change in the specific heat obtained as the difference between the specific heat of the heat bath coupled to the system degrees of freedom and the specific heat of the bath alone. While this difference may become negative, the involved specific heats themselves are always positive; thus, the known thermodynamic stability criteria are perfectly guaranteed. For a damped quantum harmonic oscillator, instead of negative values, under appropriate conditions one can observe a dip in the difference of specific heats as a function of temperature. Stylized minimal models containing a single oscillator heat bath are employed to elucidate the occurrence of the anomalous temperature dependence of the corresponding specific heat values. Moreover, we comment on the consequences for the interpretation of the density of states based on the thermal partition function.

Ingold, Gert-Ludwig; Hänggi, Peter; Talkner, Peter

2009-06-01

19

Topics on the stochastical treatement of an open quantum system

The paper shortly presents the role of Stochastic Processes Theory in the present day Quantum Theory, and the relation to Operational Quantum Physics. The dynamics of an open quantum system is studied on a usual example from Quantum Optics, suggesting the definition of a Neumark-type dilation for the non-thermal states.

Ioan Sturzu

2002-01-01

20

Quantum arrival time for open systems

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

Yearsley, J. M. [Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom)

2010-07-15

21

Resonance width distribution for open quantum systems

NASA Astrophysics Data System (ADS)

Recent measurements of resonance widths for low-energy neutron scattering off heavy nuclei show large deviations from the Porter-Thomas distribution. We propose a “standard” width distribution based on the random matrix theory for a chaotic quantum system with a single open decay channel. Two methods of derivation lead to a single analytical expression that recovers, in the limit of very weak continuum coupling, the Porter-Thomas distribution. The parameter defining the result is the ratio of typical widths ? to the energy level spacing D. Compared to the Porter-Thomas distribution, the new distribution suppresses small widths and increases the probabilities of larger widths. We show also that it is necessary to take into account the ? channels.

Shchedrin, Gavriil; Zelevinsky, Vladimir

2012-10-01

22

Spectroscopic studies in open quantum systems

The Hamiltonian H of an open quantum system is non-Hermitian. Its complex eigenvalues E(R) are the poles of the S matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboring resonance states. Level repulsion may occur along the real or imaginary axis (the latter is called resonance trapping). In any case, the eigenvalues of the two states avoid crossing in the complex plane. We then calculate the poles of the S matrix and the corresponding wave functions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a waveguide. The calculations are performed by using the method of exterior complex scaling. Re(H) and Im(H) cause changes in the structure of the wave functions which are permanent, as a rule. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory (random matrix theory). PMID:11088480

Rotter; Persson; Pichugin; Seba

2000-07-01

23

Open Quantum Systems Coupled to Time-Dependent Classical Environments

NASA Astrophysics Data System (ADS)

We investigate the behavior of open quantum systems interacting with classical time-dependent environments. As a simple example, we employ a two-level quantum system, and a thermodynamic oscillator serves as an environment. We analyze how the relationship between parameters of the classical environment and the quantum subsystem changes the evolution. Using the nonlinear thermodynamic master equation, we demonstrate how the energy of the quantum system evolves in time and how feedback effects from a quantum to a classical system influences the dynamics.

Osmanov, Maksym; Öttinger, Hans Christian

2013-07-01

24

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

25

Non-Markovian quantum state diffusion for an open quantum system in fermionic environments

NASA Astrophysics Data System (ADS)

Non-Markovian quantum state diffusion (NMQSD) provides a powerful approach to the dynamics of an open quantum system in bosonic environments. Here we develop a NMQSD method to study the open quantum system in fermionic environments. This problem involves anticommutative noise functions (i.e., Grassmann variables) that are intrinsically different from the noise functions of bosonic baths. We obtain the NMQSD equation for quantum states of the system and the non-Markovian master equation. Moreover, we apply this NMQSD method to single- and double-quantum-dot systems.

Chen, Mi; You, J. Q.

2013-05-01

26

Driven harmonic oscillator as a quantum simulator for open systems

We show theoretically how a driven harmonic oscillator can be used as a quantum simulator for the non-Markovian damped harmonic oscillator. In the general framework, our results demonstrate the possibility to use a closed system as a simulator for open quantum systems. The quantum simulator is based on sets of controlled drives of the closed harmonic oscillator with appropriately tailored electric field pulses. The non-Markovian dynamics of the damped harmonic oscillator is obtained by using the information about the spectral density of the open system when averaging over the drives of the closed oscillator. We consider single trapped ions as a specific physical implementation of the simulator, and we show how the simulator approach reveals physical insight into the open system dynamics, e.g., the characteristic quantum mechanical non-Markovian oscillatory behavior of the energy of the damped oscillator, usually obtained by the non-Lindblad-type master equation, can have a simple semiclassical interpretation.

Piilo, Jyrki; Maniscalco, Sabrina [Department of Physics, University of Turku, FI-20014 Turun yliopisto (Finland)

2006-09-15

27

Entanglement generation and evolution in open quantum systems

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we study the continuous variable entanglement for a system consisting of two independent harmonic oscillators interacting with a general environment. We solve the Kossakowski-Lindblad master equation for the time evolution of the considered system and describe the entanglement in terms of the covariance matrix

Aurelian Isar

2009-01-01

28

Non-Hermitian Tunneling of Open Quantum Systems

We discuss some aspects of the time picture of tunneling for open quantum systems described by non-Hermitian (NH) Hamiltonians. The concept of sojourn time for such systems is introduced in the framework of the biorthonormal formalism. Due to the various definitions of probability density in the non-Hermitian case, we get three different sojourn times, two real and one complex. We

P. Angelopoulou; S. Baskoutas; A. Jannussis; R. Mignani; V. Papatheou

1995-01-01

29

Reduced order models for open quantum systems

NASA Astrophysics Data System (ADS)

Many quantum mechanical systems require large (potentially infinite) numbers of variables to exactly describe their state. In this thesis, I examine two approaches to develop simple, approximate models for such systems, which capture their essential dynamics. I use two bistable regimes of the Jaynes-Cummings model of cavity quantum electrodynamics as example systems to evaluate the effectiveness of each approach. In the phase bistable regime (which occurs with large driving field, and which I study in an on-resonance "bad cavity" regime to make numerical simulations tractable), the cavity field switches between two states with identical amplitude but opposite phase. In the absorptive bistable regime (which I study with small driving field in an on-resonance "good cavity"'), two stable regions of state space differ in cavity field amplitude as well as their shape and qualitative behavior. After introducing these two regimes and their dynamics, I give a short introduction to projecting dynamical equations onto linear subspaces. Proper Orthogonal Decomposition (POD) allows the algorithmic construction of subspaces onto which the dynamics may be projected. I demonstrate that the application of POD to phase bistability results in effective approximate filters, while the asymmetry of the absorptive bistable case requires extensions to POD, developed in this thesis, to create a functional filter. Local Tangent Space Alignment is one of a class of unsupervised manifold learning algorithms which use the local geometry of high-dimensional data, such as quantum trajectories, to calculate the coordinates of that data on a low-dimensional manifold. I show how this algorithm functions, and characterize the manifolds that result from phase and absorptive bistability. I fit the 3-dimensional phase bistable manifold with a small set of system observables, and create a three-dimensional set of equations (similar to the semi-classical Maxwell-Bloch equations) which perform very well as a filter. Absorptive bistability again proves to be more complicated, but I am able to show that the underlying manifold is small, and make some progress on characterizing its relations with system observables.

Hopkins, Asa Sies

30

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

31

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 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.

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

2013-01-01

32

Asymptotically noise decoupling for Markovian open quantum systems

The noise decoupling problem is investigated for general N-level Markovian open quantum systems. First, the concept of Cartan decomposition of the Lie algebra su(N) is introduced as a tool of designing control Hamiltonians. Next, under certain assumptions, it is shown that a part of variables of the coherence vector of the system density matrix can be asymptotically decoupled from the environmental noises. The resulting noise decoupling scheme is applied to one-qubit, qutrit, and two-qubit quantum systems, by which the coherence evolution of the one-qubit and qutrit systems can always be asymptotically preserved, while, for two-qubit systems, our findings indicate that evolution of some variables can be preserved only for some initial states.

Zhang, Jing; Li, Chun-Wen; Wu, Jian-Wu [Department of Automation, Tsinghua University, Beijing 100084 (China); Wu, Re-Bing [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Tarn, Tzyh-Jong [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States)

2007-02-15

33

Dynamical stabilization and time in open quantum systems

NASA Astrophysics Data System (ADS)

The meaning of time in an open quantum system is considered under the assumption that both, system and environment, are quantum mechanical objects. The Hamilton operator of the system is non-Hermitian. Its imaginary part is the time operator. As a rule, time and energy vary continuously when controlled by a parameter. At high level density, where many states avoid crossing, a dynamical phase transition takes place in the system under the influence of the environment. It causes a dynamical stabilization of the system what can be seen in many different experimental data. Due to this effect, time is bounded from below: the decay widths (inverse proportional to the lifetimes of the states) do not increase limitless. The dynamical stabilization is an irreversible process.

Rotter, I.

2013-02-01

34

Boundary Conditions for Open Rotating Quantum Systems

NASA Astrophysics Data System (ADS)

The customary boundary conditions for a 1 D rotational system (e.g. a rigid rotor on a surface) are continuity of the complex wave function and its gradient. These four boundary conditions are sufficient if the potential energy satisfies rotational symmetry, but fail for non-rotational potentials. However, classical systems with a rotational coordinate and non- rotational potential are easily solved if the gradient of the potential, the force, is rotational. A solution is thus needed for Schroedinger's equation with a rotational coordinate and force, but non- rotational potential. Such solutions emerge if the boundary conditions are modified, allowing a discontinuous phase in the wave function related to the discontinuous potential energy. It will be shown that the modified boundary conditions are continuity of three real quantities: the probability density, the gradient of the probability density, and the probability current density. Moreover, with these boundary conditions and non-rotational potential, energy can flow both ways between the system and its environment. The discontinuous wave functions obey the new boundary conditions, but nonetheless are not generally superposable. A subset of the discontinuous wave functions can be superposed, however, yielding the usual result for angular momentum states. The non-superposable wave functions offer an alternate interpretation of the Schroedinger's cat paradox.

Davidson, Arthur

2008-03-01

35

In the initial stage of photosynthesis, light-harvested energy is transferred with remarkably high efficiency to a reaction center, with the vibrational environment assisting the transport mechanism. It is of great interest to mimic this process with present-day technologies. Here we propose an analog quantum simulator of open system dynamics, where noise engineering of the environment has a central role. In

Sarah Mostame; Patrick Rebentrost; Dimitris I. Tsomokos; Alán Aspuru-Guzik

2011-01-01

36

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

37

Task-optimized control of open quantum systems

NASA Astrophysics Data System (ADS)

We develop a general optimization strategy for performing a chosen unitary or nonunitary task on an open quantum system. The goal is to design a controlled time-dependent system Hamiltonian by variationally minimizing or maximizing a chosen function of the system state, which quantifies the task success (score), such as fidelity, purity, or entanglement. If the time dependence of the system Hamiltonian is fast enough to be comparable to or shorter than the response time of the bath, then the resulting non-Markovian dynamics is shown to optimize the chosen task score to second order in the coupling to the bath. This strategy can protect a desired unitary system evolution from bath-induced decoherence, but can also take advantage of the system-bath coupling so as to realize a desired nonunitary effect on the system.

Clausen, Jens; Bensky, Guy; Kurizki, Gershon

2012-05-01

38

Nontrivial Eigenvalues of the Liouvillian of an Open Quantum System

NASA Astrophysics Data System (ADS)

We present methods of finding complex eigenvalues of the Liouvillian of an open quantum system. The goal is to find eigenvalues that cannot be predicted from the eigenvalues of the corresponding Hamiltonian. Our model is a T-type quantum dot with an infinitely long lead. We suggest the existence of the non-trivial eigenvalues of the Liouvillian in two ways: one way is to show that the original problem reduces to the problem of a two-particle Hamiltonian with a two-body interaction and the other way is to show that diagram expansion of the Green's function has correlation between the bra state and the ket state. We also introduce the integral equations equivalent to the original eigenvalue problem.

Nakano, Ruri; Hatano, Naomichi; Petrosky, Tomio

2011-04-01

39

Thermodynamics of quadrature trajectories in open quantum systems

NASA Astrophysics Data System (ADS)

We apply a large-deviation method to study the diffusive trajectories of the quadratures of light emitted from open quantum systems. We formulate the study of quadrature trajectories in terms of characteristic operators and show that, in the long-time limit, the statistics of such trajectories obey a large-deviation principle. We take our motivation from homodyne detection schemes which allow the statistics of light quadratures to be measured. We illustrate our approach with four examples of increasing complexity: a driven two-level system, a “blinking” three-level system, a pair of weakly coupled two-level driven systems, and the micromaser. We discuss how quadrature operators can serve as alternative order parameters for the classification of dynamical phases, which is particularly useful in cases where the statistics of quantum jumps cannot distinguish such phases. The formalism we introduce also allows us to analyze the properties of the light emitted in quantum-jump trajectories which deviate far from the typical dynamics.

Hickey, James M.; Genway, Sam; Lesanovsky, Igor; Garrahan, Juan P.

2012-12-01

40

TOPICS ON THE STOCHASTIC TREATMENT OF THE EVOLUTION OF AN OPEN QUANTUM SYSTEM

The paper shortly presents the role of Stochastic Processes Theory in the present day Quantum Theory, and the relation to Operational Quantum Physics. The dynamics of an open quantum system is studied on a usual example from Quantum Optics, suggesting the definition of a Neumark-type dilation for the non-thermal states.

Ioan Sturzu

41

Time-Dependent Density Functional Theory for Open Quantum Systems and Quantum Computation

NASA Astrophysics Data System (ADS)

First-principles electronic structure theory explains properties of atoms, molecules and solids from underlying physical principles without input from empirical parameters. Time-dependent density functional theory (TDDFT) has emerged as arguably the most widely used first-principles method for describing the time-dependent quantum mechanics of many-electron systems. In this thesis, we will show how the fundamental principles of TDDFT can be extended and applied in two novel directions: The theory of open quantum systems (OQS) and quantum computation (QC). In the first part of this thesis, we prove theorems that establish the foundations of TDDFT for open quantum systems (OQS-TDDFT). OQS-TDDFT allows for a first-principles description of non-equilibrium systems, in which the electronic degrees of freedom undergo relaxation and decoherence due to coupling with a thermal environment, such as a vibrational or photon bath. We then discuss properties of functionals in OQS-TDDFT and investigate how these differ from functionals in conventional TDDFT using an exactly solvable model system. Next, we formulate OQS-TDDFT in the linear-response regime, which gives access to environmentally broadened excitation spectra. Lastly, we present a hybrid approach in which TDDFT can be used to construct master equations from first-principles for describing energy transfer in condensed phase systems. In the second part of this thesis, we prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. TDDFT applied to universal Hamiltonians implies that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. This offers the possibility of simplifying computations by using the principles of TDDFT similar to how it is applied in electronic structure theory. Lastly, we discuss a related result; the computational complexity of TDDFT.

Tempel, David Gabriel

42

Computational issues of configuration interaction frameworks describing open quantum systems

NASA Astrophysics Data System (ADS)

Open quantum systems (OQS), extended in space (halo nuclei) or even unbound, differ from closed quantum systems (CQS), for which the methods of standard shell model (SM) [1] can be utilized in order to expand their wave function in a configuration interaction framework. Configuration interaction methods based on the use of Berggren bases [2], comprising bound, resonant and scattering states, which have the ability to generate the very long range asymptotic behavior of OQSs, are used instead for that matter. This demands the introduction of new computational techniques, including the optimization and discretization of the Berggren basis [3], the development of an algorithm to efficiently calculate their two-body matrix elements [4], and an overall optimization of memory storage absent from SM, where, for instance, all data related to proton and neutron spaces only can be precalculated and stored [1]. In order to diagonalize the very large induced matrices, the Density Matrix Renormalization Group (DMRG) method [5] extended to OQSs has been developed [6, 7]. A renormalization procedure which generates more and more correlated many-body basis states iteratively is used therein, so that the Hamiltonian matrix to diagonalize is very small compared to that occurring with a many-body basis of independent particles [6, 7]. Parallelization of presented methods will also be discussed.

Michel, Nicolas

2013-08-01

43

Generalized coherent states as preferred states of open quantum systems

We investigate the connection between quasi-classical (pointer) states and generalized coherent states (GCSs) within an algebraic approach to Markovian quantum systems (including bosons, spins, and fermions). We establish conditions for the GCS set to become most robust by relating the rate of purity loss to an invariant measure of uncertainty derived from quantum Fisher information. We find that, for damped

Sergio Boixo; Lorenza Viola; Gerardo Ortiz

2007-01-01

44

Width bifurcation and dynamical phase transitions in open quantum systems

NASA Astrophysics Data System (ADS)

The states of an open quantum system are coupled via the environment of scattering wave functions. The complex coupling coefficients ? between system and environment arise from the principal value integral and the residuum. At high-level density where the resonance states overlap, the dynamics of the system is determined by exceptional points. At these points, the eigenvalues of two states are equal and the corresponding eigenfunctions are linearly dependent. It is shown in the present paper that Im(?) and Re(?) influence the system properties differently in the surrounding of exceptional points. Controlling the system by a parameter, the eigenvalues avoid crossing in energy near an exceptional point under the influence of Re(?) in a similar manner as it is well known from discrete states. Im(?), however, leads to width bifurcation and finally (when the system is coupled to one channel, i.e., to one common continuum of scattering wave functions), to a splitting of the system into two parts with different characteristic time scales. The role of observer states is discussed. Physically, the system is stabilized by this splitting since the lifetimes of some states are longer than before, while that of one state is shorter. In the cross section the short-lived state appears as a background term in high-resolution experiments. The wave functions of the long-lived states are mixed in those of the original ones in a comparably large parameter range. Numerical results for the eigenvalues and eigenfunctions are shown for N=2,4, and 10 states coupled mostly to one channel.

Eleuch, Hichem; Rotter, Ingrid

2013-05-01

45

Survival of coherence for open quantum systems in thermal baths

NASA Astrophysics Data System (ADS)

The loss of coherence in a general open quantum system interacting with a bosonic environment is analyzed. The reservoir is initially in a thermal state. The reduced dynamics is described by a non-Markovian time-local master equation. We consider spectral densities that are sub- or super-Ohmic at low frequencies and arbitrarily shaped at high frequencies. In the super-Ohmic regime, for noninteger frequency powers larger than 2, long time survival of coherence appears. In the latter regime, at vanishing temperature, the asymptotic amount of surviving coherence is stabilized to its initial value, up to a phase factor, by properly increasing the bandwidth and decreasing the low-frequency profile of the spectral density. For noninteger positive frequency powers less than 2, stretched exponential-like decoherence is found over long times. The relaxations to the asymptotic configurations become arbitrarily slow by approaching the frequency power 2 of the super-Ohmic regime. The same dependence on temperature, spectral density, and scale frequency appears for purity and concurrence of two qubits and coherence of a qubit.

Giraldi, Filippo; Petruccione, Francesco

2013-10-01

46

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

47

Quantum Fisher information flow and non-Markovian processes of open systems

We establish an information-theoretic approach for quantitatively characterizing the non-Markovianity of open quantum processes. Here, the quantum Fisher information (QFI) flow provides a measure to statistically distinguish Markovian and non-Markovian processes. A basic relation between the QFI flow and non-Markovianity is unveiled for quantum dynamics of open systems. For a class of time-local master equations, the exactly analytic solution shows that for each fixed time the QFI flow is decomposed into additive subflows according to different dissipative channels.

Lu Xiaoming; Wang Xiaoguang [Zhejiang Institute of Modern Physics, Department of Physics, Zhejiang University, Hangzhou 310027 (China); Sun, C. P. [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2010-10-15

48

Rise and fall of quantum and classical correlations in open-system dynamics

Interacting quantum systems evolving from an uncorrelated composite initial state generically develop quantum correlations--entanglement. As a consequence, a local description of interacting quantum systems is impossible as a rule. A unitarily evolving (isolated) quantum system generically develops extensive entanglement: the magnitude of the generated entanglement will increase without bounds with the effective Hilbert space dimension of the system. It is conceivable that coupling of the interacting subsystems to local dephasing environments will restrict the generation of entanglement to such extent that the evolving composite system may be considered as approximately disentangled. This conjecture is addressed in the context of some common models of a bipartite system with linear and nonlinear interactions and local coupling to dephasing environments. Analytical and numerical results obtained imply that the conjecture is generally false. Open dynamics of the quantum correlations is compared to the corresponding evolution of the classical correlations and a qualitative difference is found.

Khasin, Michael; Kosloff, Ronnie [Fritz Haber Research Center for Molecular Dynamics, Hebrew University of Jerusalem, Jerusalem 91904 (Israel)

2007-07-15

49

Geometrical effects on energy transfer in disordered open quantum systems

NASA Astrophysics Data System (ADS)

We explore various design principles for efficient excitation energy transport in complex quantum systems. We investigate energy transfer efficiency in randomly disordered geometries consisting of up to 20 chromophores to explore spatial and spectral properties of small natural/artificial Light-Harvesting Complexes (LHC). We find significant statistical correlations among highly efficient random structures with respect to ground state properties, excitonic energy gaps, multichromophoric spatial connectivity, and path strengths. These correlations can even exist beyond the optimal regime of environment-assisted quantum transport. For random configurations embedded in spatial dimensions of 30 A? or 50 A?, we observe that the transport efficiency saturates to its maximum value if the systems contain around 7 or 14 chromophores, respectively. Remarkably, these optimum values coincide with the number of chlorophylls in the Fenna-Matthews-Olson protein complex and LHC II monomers, respectively, suggesting a potential natural optimization with respect to chromophoric density.

Mohseni, M.; Shabani, A.; Lloyd, S.; Omar, Y.; Rabitz, H.

2013-05-01

50

Geometrical effects on energy transfer in disordered open quantum systems.

We explore various design principles for efficient excitation energy transport in complex quantum systems. We investigate energy transfer efficiency in randomly disordered geometries consisting of up to 20 chromophores to explore spatial and spectral properties of small natural/artificial Light-Harvesting Complexes (LHC). We find significant statistical correlations among highly efficient random structures with respect to ground state properties, excitonic energy gaps, multichromophoric spatial connectivity, and path strengths. These correlations can even exist beyond the optimal regime of environment-assisted quantum transport. For random configurations embedded in spatial dimensions of 30 A? or 50 A?, we observe that the transport efficiency saturates to its maximum value if the systems contain around 7 or 14 chromophores, respectively. Remarkably, these optimum values coincide with the number of chlorophylls in the Fenna-Matthews-Olson protein complex and LHC II monomers, respectively, suggesting a potential natural optimization with respect to chromophoric density. PMID:23742477

Mohseni, M; Shabani, A; Lloyd, S; Omar, Y; Rabitz, H

2013-05-28

51

Geometric phase for an adiabatically evolving open quantum system

We derive a solution for a two-level system evolving adiabatically under the influence of a driving field, which includes open system effects. This solution, which is obtained by working in the representation corresponding to the eigenstates of the time-dependent Hermitian Hamiltonian, enables the dynamic and geometric phases of the evolving density matrix to be separated. The dynamic phase can be canceled in the limit of weak coupling to the environment, thereby allowing the geometric phase to be readily extracted both mathematically and operationally.

Kamleitner, Ingo [Australian Centre of Excellence for Quantum Computer Technology, Macquarie University, Sydney, New South Wales 2109 (Australia); Cresser, James D. [Australian Centre of Excellence for Quantum Computer Technology, Macquarie University, Sydney, New South Wales 2109 (Australia); Department of Physics, Macquarie University, Sydney, New South Wales 2109 (Australia); Sanders, Barry C. [Australian Centre of Excellence for Quantum Computer Technology, Macquarie University, Sydney, New South Wales 2109 (Australia); Institute for Quantum Information Science, University of Calgary, Alberta, T2N 1N4 (Canada)

2004-10-01

52

Quantum and classical fluctuation theorems from a decoherent histories, open-system analysis.

In this paper we present a first-principles analysis of the nonequilibrium work distribution and the free energy difference of a quantum system interacting with a general environment (with arbitrary spectral density and for all temperatures) based on a well-understood microphysics (quantum Brownian motion) model under the conditions stipulated by the Jarzynski equality [Jarzynski, Phys. Rev. Lett. 78, 2690 (1997)] and Crooks' fluctuation theorem [Crooks, Phys. Rev. E 60, 2721 (1999)] (in short, fluctuation theorems, FTs). We use the decoherent histories conceptual framework to explain how the notion of trajectories in a quantum system can be made viable and use the environment-induced decoherence scheme to assess the strength of noise that could provide sufficient decoherence to warrant the use of trajectories to define work in open quantum systems. From the solutions to the Langevin equation governing the stochastic dynamics of such systems we were able to produce formal expressions for these quantities entering in the FTs and from them prove explicitly the validity of the FTs at the high temperature limit. At low temperatures our general results would enable one to identify the range of parameters where FTs may not hold or need be expressed differently. We explain the relation between classical and quantum FTs and the advantage of this microphysics open-system approach over the phenomenological modeling and energy-level calculations for substitute closed quantum systems. PMID:22400517

Suba??, Y; Hu, B L

2012-01-06

53

We develop a general approach for monitoring and controlling evolution of open quantum systems. In contrast to the master equations describing time evolution of density operators, here, we formulate a dynamical equation for the evolution of the process matrix acting on a system. This equation is applicable to non-Markovian and/or strong-coupling regimes. We propose two distinct applications for this dynamical equation. We first demonstrate identification of quantum Hamiltonians generating dynamics of closed or open systems via performing process tomography. In particular, we argue how one can efficiently estimate certain classes of sparse Hamiltonians by performing partial tomography schemes. In addition, we introduce an optimal control theoretic setting for manipulating quantum dynamics of Hamiltonian systems, specifically for the task of decoherence suppression.

Mohseni, M. [Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Rezakhani, A. T. [Department of Chemistry and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States)

2009-07-15

54

Optimal control of open quantum systems: cooperative effects of driving and dissipation.

We investigate the optimal control of open quantum systems, in particular, the mutual influence of driving and dissipation. A stochastic approach to open-system control is developed, using a generalized version of Krotov's iterative algorithm, with no need for Markovian or rotating-wave approximations. The application to a harmonic degree of freedom reveals cooperative effects of driving and dissipation that a standard Markovian treatment cannot capture. Remarkably, control can modify the open-system dynamics to the point where the entropy change turns negative, thus achieving cooling of translational motion without any reliance on internal degrees of freedom. PMID:22026832

Schmidt, R; Negretti, A; Ankerhold, J; Calarco, T; Stockburger, J T

2011-09-21

55

Optimal Control of Open Quantum Systems: Cooperative Effects of Driving and Dissipation

NASA Astrophysics Data System (ADS)

We investigate the optimal control of open quantum systems, in particular, the mutual influence of driving and dissipation. A stochastic approach to open-system control is developed, using a generalized version of Krotov’s iterative algorithm, with no need for Markovian or rotating-wave approximations. The application to a harmonic degree of freedom reveals cooperative effects of driving and dissipation that a standard Markovian treatment cannot capture. Remarkably, control can modify the open-system dynamics to the point where the entropy change turns negative, thus achieving cooling of translational motion without any reliance on internal degrees of freedom.

Schmidt, R.; Negretti, A.; Ankerhold, J.; Calarco, T.; Stockburger, J. T.

2011-09-01

56

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

57

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

58

Measurement-based direct quantum feedback control in an open quantum system

NASA Astrophysics Data System (ADS)

We consider a general quantum system interacting with a bath and derive a master equation in the Lindblad form describing the evolution of the whole quantum system subjected to a measurement-based direct quantum feedback control (MDFC). As an example, we consider a qubit coupled with a dephasing environment under the MDFC. We show that for any given pure target state we can always find the corresponding MDFC scheme, which can effectively drive any initial state into this target state. By using an appropriate MDFC scheme with weak measurement we can stabilize a single qubit initially prepared in one of two nonorthogonal states against dephasing noise. Furthermore, we can effectively protect a kind of known mixed states composed of two nonorthogonal states by using the corresponding MDFC scheme.

Yan, Yan; Zou, Jian; Xu, Bao-Ming; Li, Jun-Gang; Shao, Bin

2013-09-01

59

Quantum chaos of a mixed open system of kicked cold atoms

The quantum and classical dynamics of particles kicked by a Gaussian attractive potential are studied. Classically, it is an open mixed system (the motion in some parts of the phase space is chaotic, and in some parts it is regular). The fidelity (Loschmidt echo) is found to exhibit oscillations that can be determined from classical considerations but are sensitive to phase space structures that are smaller than Planck's constant. Families of quasienergies are determined from classical phase space structures. Substantial differences between the classical and quantum dynamics are found for time-dependent scattering. It is argued that the system can be experimentally realized by cold atoms kicked by a Gaussian light beam.

Krivolapov, Yevgeny; Fishman, Shmuel; Ott, Edward; Antonsen, Thomas M. [Physics Department, Technion-Israel Institute of Technology, Haifa 32000 (Israel); University of Maryland, College Park, Maryland 20742 (United States)

2011-01-15

60

Resonant gain suppression and quantum destructive interference in a three-level open V system

We investigate the steady optical properties of a three-level open V system (i.e. a four-level closed atomic system) through both analytical and numerical calculations. Our results show that the resonant probe gain can be greatly suppressed to generate a narrow and deep transparency window associated with very steep abnormal dispersion. The underlying physics is identified as the perfect quantum destructive

Cui-Li Cui; Ji-Kui Jia; Yan Zhang; Yan Xue; Huai-Liang Xu; Jin-Hui Wu

2011-01-01

61

Statistical mechanical expression of entropy production for an open quantum system

NASA Astrophysics Data System (ADS)

A quantum statistical expression for the entropy of a nonequilibrium system is defined so as to be consistent with Gibbs' relation, and is shown to corresponds to dynamical variable by introducing analogous to the Heisenberg picture in quantum mechanics. The general relation between system-reservoir interactions and an entropy change operator in an open quantum system, relying just on the framework of statistical mechanics and the definition of von Neumann entropy. By using this formula, we can obtain the correct entropy production in the linear response framework. The present derivation of entropy production is directly based on the first principle of microscopic time-evolution, while the previous standard argument is due to the thermodynamic energy balance.

Majima, Hiroki; Suzuki, Akira

2013-02-01

62

NASA Astrophysics Data System (ADS)

We obtain exact analytic expressions for a class of functions expressed as integrals over the Haar measure of the unitary group in d dimensions. Based on these general mathematical results, we investigate generic dynamical properties of complex open quantum systems, employing arguments from ensemble theory. We further generalize these results to arbitrary eigenvalue distributions, allowing a detailed comparison of typical regular and chaotic systems with the help of concepts from random matrix theory. To illustrate the physical relevance and the general applicability of our results we present a series of examples related to the fields of open quantum systems and nonequilibrium quantum thermodynamics. These include the effect of initial correlations, the average quantum dynamical maps, the generic dynamics of system-environment pure state entanglement and, finally, the equilibration of generic open and closed quantum systems.

Gessner, Manuel; Breuer, Heinz-Peter

2013-04-01

63

Coherent control of quantum tunneling in an open double-well system

NASA Astrophysics Data System (ADS)

We investigate how to apply a high-frequency driving field to the quantum control of a single particle in an open double-well system. The linear stability analysis points out that the stability depends on the external-field parameters and the loss (or gain) coefficients of the system, and the instability leads to a transition of the Floquet quasienergy from real to complex values and results in decaying probabilities for the particle to be in the double well. By combining analytical solutions in the high-frequency approximation with numerical calculations based on an accurate model, we exhibit quantum-dynamical behavior of the particle such as Floquet oscillation, coherent destruction of tunneling, quasi-NOON-state population, partial one-particle tunneling, and the decay of the probabilities of occupation, which are due to the competition and balance between the quantum coherence and the loss (or gain) effect. The results suggest an experimental method for testing quantum motion in an open system by adjusting the driving field.

Xiao, Kewen; Hai, Wenhua; Liu, Juan

2012-01-01

64

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

NASA Astrophysics Data System (ADS)

In a recent experiment, Barreiro et al (2011 Nature 470 486) demonstrated the fundamental building blocks of an open-system quantum simulator with trapped ions. Using up to five ions, dynamics were realized by sequences that combined single- and multi-qubit entangling gate operations with optical pumping. This enabled the implementation of both coherent many-body dynamics and 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 this 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.

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

2011-08-01

65

Time-Dependent Density Functional Theory for Open Quantum Systems with Unitary Propagation

NASA Astrophysics Data System (ADS)

We extend the Runge-Gross theorem for a very general class of open quantum systems under weak assumptions about the nature of the bath and its coupling to the system. We show that for Kohn-Sham (KS) time-dependent density functional theory, it is possible to rigorously include the effects of the environment within a bath functional in the KS potential. A Markovian bath functional inspired by the theory of nonlinear Schrödinger equations is suggested, which can be readily implemented in currently existing real-time codes. Finally, calculations on a helium model system are presented.

Yuen-Zhou, Joel; Tempel, David G.; Rodríguez-Rosario, César A.; Aspuru-Guzik, Alán

2010-01-01

66

Time-dependent density functional theory for open quantum systems with unitary propagation.

We extend the Runge-Gross theorem for a very general class of open quantum systems under weak assumptions about the nature of the bath and its coupling to the system. We show that for Kohn-Sham (KS) time-dependent density functional theory, it is possible to rigorously include the effects of the environment within a bath functional in the KS potential. A Markovian bath functional inspired by the theory of nonlinear Schrödinger equations is suggested, which can be readily implemented in currently existing real-time codes. Finally, calculations on a helium model system are presented. PMID:20366703

Yuen-Zhou, Joel; Tempel, David G; Rodríguez-Rosario, César A; Aspuru-Guzik, Alán

2010-01-25

67

Electronic-vibrational dynamics in molecular systems that interact with an environment involve a large number of degrees of freedom and are therefore often described by means of open quantum system approaches. A popular approach is to include only the electronic degrees of freedom into the system part and to couple these to a non-Markovian bath of harmonic vibrational modes that is characterized by a spectral density. Since this bath represents both intra-molecular and external vibrations, it is important to understand how to construct a spectral density that accounts for intra-molecular vibrational modes that couple further to other modes. Here, we address this problem by explicitly incorporating an intra-molecular vibrational mode together with the electronic degrees of freedom into the system part and using the Fano theory for a resonance coupled to a continuum to derive an "effective" bath spectral density, which describes the contribution of intra-molecular modes. We compare this effective model for the intra-molecular mode with the method of pseudomodes, a widely used approach in simulation of non-Markovian dynamics. We clarify the difference between these two approaches and demonstrate that the respective resulting dynamics and optical spectra can be very different. PMID:23205984

Roden, Jan; Strunz, Walter T; Whaley, K Birgitta; Eisfeld, Alexander

2012-11-28

68

Avoiding dark states in open quantum systems by tailored initializations.

We study the transport of excitations on a network of three coupled two-level systems that are subjected to an environment that induces incoherent hopping between the nodes. The two end nodes are coupled to a source while the central node is coupled to a drain. A common feature of these networks is the existence of a dark state that blocks the transport to the drain. Here we propose a means to avoid this state by a suitable initialization of the system, induced by a source that is common to both coupled nodes. PMID:23005149

Schijven, P; Mülken, O

2012-06-25

69

Renormalization approach to non-Markovian open-quantum-system dynamics

NASA Astrophysics Data System (ADS)

We show that time induces a dynamical renormalization of the system-environment coupling in open-quantum-system dynamics. The renormalizability condition, of the interactions being either local, or, alternatively, defined on a finite continuum support, is generally fulfilled for both discrete and continuous environments. As a consequence, we find a generalized Lieb-Robinson bound to hold for local and, surprisingly, also for nonlocal interactions. This unified picture allows us to devise a controllable approximation for arbitrary non-Markovian dynamics with an a priori estimate of the worst-case computational cost.

Gualdi, Giulia; Koch, Christiane P.

2013-08-01

70

Attaining persistent field-free control of open and closed quantum systems.

Persistent quantum control (PQC) aims to maintain an observable objective value over a period of time following the action of an applied field. This paper assesses the feasibility of achieving PQC for arbitrary finite-level systems and observables. The analysis is carried out independent of the particular method used for state preparation. The PQC behavior is optimized over the set of physically accessible prepared states for both open and closed systems. The quality of observable value persistence in the postcontrol period was found to vary with the required duration of persistence, the system temperature, the chosen observable operator, and the energy levels of the system. The alignment of a rigid diatomic rotor is studied as a model system. The theoretical estimates of PQC behavior are encouraging and suggest feasible exploration in the laboratory using currently available technology. PMID:21456648

Anson, Erik; Beltrani, Vincent; Rabitz, Herschel

2011-03-28

71

Attaining persistent field-free control of open and closed quantum systems

NASA Astrophysics Data System (ADS)

Persistent quantum control (PQC) aims to maintain an observable objective value over a period of time following the action of an applied field. This paper assesses the feasibility of achieving PQC for arbitrary finite-level systems and observables. The analysis is carried out independent of the particular method used for state preparation. The PQC behavior is optimized over the set of physically accessible prepared states for both open and closed systems. The quality of observable value persistence in the postcontrol period was found to vary with the required duration of persistence, the system temperature, the chosen observable operator, and the energy levels of the system. The alignment of a rigid diatomic rotor is studied as a model system. The theoretical estimates of PQC behavior are encouraging and suggest feasible exploration in the laboratory using currently available technology.

Anson, Erik; Beltrani, Vincent; Rabitz, Herschel

2011-03-01

72

Open Source and Open Access Resources for Quantum Physics Education

Quantum mechanics is both a topic of great importance to modern science, engineering, and technology, and a topic with many inherent barriers to learning and understanding. Computational resources are vital tools for developing deep conceptual understanding of quantum systems for students new to the subject. This article outlines two projects that are taking an open source\\/open access approach to create

Mario Belloni; Wolfgang Christian; Bruce Mason

2009-01-01

73

Time-dependent density functional theory for open quantum systems using unitary dynamics

NASA Astrophysics Data System (ADS)

We extend the Runge-Gross theorem for a very general class of Markovian and non-Markovian open quantum systems under weak assumptions about the nature of the bath and its coupling to the system. We show that for Kohn-Sham (KS) Time-Dependent Density Functional Theory, it is possible to rigorously include the effects of the environment within a bath functional in the KS potential, thus placing the interactions between the particles of the system and the coupling to the environment on the same footing. A Markovian bath functional inspired by the theory of nonlinear Schrodinger equations is suggested, which can be readily implemented in currently existing real-time codes. Finally, calculations on a helium model system are presented.

Aspuru-Guzik, Alan

2010-03-01

74

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

NASA Astrophysics Data System (ADS)

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 , Nature (London)NATUAS0028-083610.1038/nature09009 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.

2011-10-01

75

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

76

Dephasing and decoherence in open quantum systems: A Dyson's equation approach

NASA Astrophysics Data System (ADS)

In this work, the Dyson's equation formalism is outlined and applied to several open quantum systems. These systems are composed of a core, quantum-mechanical set of discrete states and several continua, representing macroscopic systems. The macroscopic systems introduce decoherence, as well as allowing the total particle number in the system to change. Dyson's equation, an expansion in terms of proper self-energy terms, is derived. The hybridization of two quantum levels is reproduced in this formalism, and it is shown that decoherence follows naturally when one of the levels is replaced by a continuum. The work considers three physical systems in detail. The first, quantum dots coupled in series with two leads, is presented in a realistic two-level model. Dyson's equation is used to account for the leads exactly to all orders in perturbation theory, and the time dynamics of a single electron in the dots is calculated. It is shown that decoherence from the leads damps the coherent Rabi oscillations of the electron. Several regimes of physical interest are considered, and it is shown that the difference in couplings of the two leads plays a central role in the decoherence processes. The second system relates to the decay-out of superdeformed nuclei. In this case, decoherence is provided by coupling to the electromagnetic field. Two, three, and infinite-level models are considered within the discrete system. It is shown that the two-level model is usually sufficient to describe decay-out for the classic regions of nuclear superdeformation. Furthermore, a statistical model for the normal-deformed states allows extraction of parameters of interest to nuclear structure from the two-level model. An explanation for the universality of decay profiles is also given in that model. The final system is a proposed small molecular transistor. The Quantum Interference Effect Transistor is based on a single monocyclic aromatic annulene molecule, with two leads arranged in the meta configuration. This device is shown to be completely opaque to charge carriers, due to destructive interference. This coherence effect can be tunably broken by introducing new paths with a real or imaginary self-energy, and an excellent molecular transistor is the result.

Cardamone, David Michael

77

In this paper, control of open quantum systems with emphasis on the control of surface photochemical reactions is presented. A quantum system in a condensed phase undergoes strong dissipative processes. From a theoretical viewpoint, it is important to model such processes in a rigorous way. In this work, the description of open quantum systems is realized within the surrogate hamiltonian approach [R. Baer and R. Kosloff, J. Chem. Phys. 106, 8862 (1997)]. An efficient and accurate method to find control fields is optimal control theory (OCT) [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998); Y. Ohtsuki, G. Turinici, and H. Rabitz, J. Chem. Phys. 120, 5509 (2004)]. To gain control of open quantum systems, the surrogate hamiltonian approach and OCT, with time-dependent targets, are combined. Three open quantum systems are investigated by the combined method, a harmonic oscillator immersed in an ohmic bath, CO adsorbed on a platinum surface, and NO adsorbed on a nickel oxide surface. Throughout this paper, atomic units, i.e., ? = m(e) = e = a(0) = 1, have been used unless otherwise stated. PMID:22462846

Asplund, Erik; Klüner, Thorsten

2012-03-28

78

In this paper, control of open quantum systems with emphasis on the control of surface photochemical reactions is presented. A quantum system in a condensed phase undergoes strong dissipative processes. From a theoretical viewpoint, it is important to model such processes in a rigorous way. In this work, the description of open quantum systems is realized within the surrogate Hamiltonian approach [R. Baer and R. Kosloff, J. Chem. Phys. 106, 8862 (1997)]. An efficient and accurate method to find control fields is optimal control theory (OCT) [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998); Y. Ohtsuki, G. Turinici, and H. Rabitz, J. Chem. Phys. 120, 5509 (2004)]. To gain control of open quantum systems, the surrogate Hamiltonian approach and OCT, with time-dependent targets, are combined. Three open quantum systems are investigated by the combined method, a harmonic oscillator immersed in an ohmic bath, CO adsorbed on a platinum surface, and NO adsorbed on a nickel oxide surface. Throughout this paper, atomic units, i.e., ({Dirac_h}/2{pi})=m{sub e}=e=a{sub 0}= 1, have been used unless otherwise stated.

Asplund, Erik; Kluener, Thorsten [Institut fuer Reine und Angewandte Chemie, Carl von Ossietzky Universitaet Oldenburg, Postfach 2503, D-26111 Oldenburg (Germany)

2012-03-28

79

Quantum cascade laser open-path system for remote sensing of trace gases in Beijing, China

NASA Astrophysics Data System (ADS)

Exploiting several key characteristics of quantum cascade (QC) lasers, including wide tunability and room-temperature operation, the Quantum Cascade Laser Open-Path System (QCLOPS) was designed for the detection of a range of trace gases and for field deployment in urban environments. Tunability over a wavelength range from 9.3 to 9.8 ?m potentially provides the capability for monitoring ozone, ammonia, and carbon dioxide, a suite of trace gases important for air quality and regional climate applications in urban environments. The 2008 Olympic Games in Beijing, China drew attention to air quality problems in urban environments. Prior to and during the Olympic games, regional air quality modifications through factory shutdowns, car restrictions, and construction halts in Beijing and its surrounding areas created a unique test bed for new sensor technologies such as the QCLOPS sensor. We report the design of this novel, open-path air quality sensor and the results of both laboratory tests and field trials during the 2008 Olympic Games in Beijing, China.

Michel, Anna P. M.; Liu, Peter Q.; Yeung, June K.; Corrigan, Paul; Baeck, Mary Lynn; Wang, Zifa; Day, Timothy; Smith, James A.

2010-11-01

80

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

81

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

82

Quantum circuits for strongly correlated quantum systems

NASA Astrophysics Data System (ADS)

We present an approach to gain detailed control on the quantum simulation of strongly correlated quantum many-body systems by constructing the explicit finite quantum circuits that diagonalize their dynamics. As a particularly simple instance, the full dynamics of a one-dimensional Quantum Ising model in a transverse field with four spins is shown to be reproduced using a quantum circuit of only six local gates. This opens up the possibility of experimentally producing strongly correlated states, their time evolution at zero time, and even thermal superpositions at zero temperature. Our method also allows one to uncover the exact circuits corresponding to models that exhibit topological order and to stabilizer states.

Verstraete, Frank; Cirac, J. Ignacio; Latorre, José I.

2009-03-01

83

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

84

Open quantum dots: II. Probing the classical to quantum transition

NASA Astrophysics Data System (ADS)

Open quantum dots provide a natural system in which to study both classical and quantum features of transport. From the classical point of view these dots possess a mixed phase space which yields families of closed, regular orbits as well as an expansive sea of chaos. An important question concerns the manner in which these classical states evolve into the set of quantum states that populate the dot in the quantum limit. In the reverse direction, the manner in which the quantum states evolve to the classical world is governed strongly by Zurek’s decoherence theory. This was discussed from the quantum perspective in an earlier review (Ferry et al 2011 Semicond. Sci. Technol. 26 043001). Here, we discuss the nature of the various classical states, how they are formed, how they progress to the quantum world, and the signatures that they create in magnetotransport and general conductance studies of these dots.

Brunner, R.; Ferry, D. K.; Akis, R.; Meisels, R.; Kuchar, F.; Burke, A. M.; Bird, J. P.

2012-08-01

85

Remarks on time-dependent [current]-density functional theory for open quantum systems.

Time-dependent [current]-density functional theory for open quantum systems (OQS) has emerged as a formalism that can incorporate dissipative effects in the dynamics of many-body quantum systems. Here, we review and clarify some formal aspects of these theories that have been recently questioned in the literature. In particular, we provide theoretical support for the following conclusions: (1) contrary to what we and others had stated before, within the master equation framework, there is in fact a one-to-one mapping between vector potentials and current densities for fixed initial state, particle-particle interaction, and memory kernel; (2) regardless of the first conclusion, all of our recently suggested Kohn-Sham (KS) schemes to reproduce the current and particle densities of the original OQS, and in particular, the use of a KS closed driven system, remains formally valid; (3) the Lindblad master equation maintains the positivity of the density matrix regardless of the time-dependence of the Hamiltonian or the dissipation operators; (4) within the stochastic Schrödinger equation picture, a one-to-one mapping from stochastic vector potential to stochastic current density for individual trajectories has not been proven so far, except in the case where the vector potential is the same for every member of the ensemble, in which case, it reduces to the Lindblad master equation picture; (5) master equations may violate certain desired properties of the density matrix, such as positivity, but they remain as one of the most useful constructs to study OQS when the environment is not easily incorporated explicitly in the calculation. The conclusions support our previous work as formally rigorous, offer new insights into it, and provide a common ground to discuss related theories. PMID:23787804

Yuen-Zhou, Joel; Aspuru-Guzik, Alán

2013-08-14

86

Pade spectrum decomposition is an optimal sum-over-poles expansion scheme of Fermi function and Bose function [J. Hu, R. X. Xu, and Y. J. Yan, J. Chem. Phys. 133, 101106 (2010)]. In this work, we report two additional members to this family, from which the best among all sum-over-poles methods could be chosen for different cases of application. Methods are developed for determining these three Pade spectrum decomposition expansions at machine precision via simple algorithms. We exemplify the applications of present development with optimal construction of hierarchical equations-of-motion formulations for nonperturbative quantum dissipation and quantum transport dynamics. Numerical demonstrations are given for two systems. One is the transient transport current to an interacting quantum-dots system, together with the involved high-order co-tunneling dynamics. Another is the non-Markovian dynamics of a spin-boson system.

Hu Jie; Luo Meng; Jiang Feng [Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong); Xu Ruixue [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Yan Yijing [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)

2011-06-28

87

Controlling the dynamics of an open many-body quantum system with localized dissipation.

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Because of the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems. PMID:23373931

Barontini, G; Labouvie, R; Stubenrauch, F; Vogler, A; Guarrera, V; Ott, H

2013-01-15

88

Controlling the Dynamics of an Open Many-Body Quantum System with Localized Dissipation

NASA Astrophysics Data System (ADS)

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Because of the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems.

Barontini, G.; Labouvie, R.; Stubenrauch, F.; Vogler, A.; Guarrera, V.; Ott, H.

2013-01-01

89

Optical Microcavities as Quantum-Chaotic Model Systems: Openness Makes the Difference!

NASA Astrophysics Data System (ADS)

Optical microcavities are open billiards for light in which electromagnetic waves can, however, be confined by total internal reflection at dielectric boundaries. These resonators enrich the class of model systems in the field of quantum chaos and are an ideal testing ground for the correspondence of ray and wave dynamics that, typically, is taken for granted. Using phase-space methods we show that this assumption has to be corrected towards the long-wavelength limit.We first Generalizing the concept of Husimi functions to dielectric interfaces, where both the wave function and its derivative are non-zero. We then we find that curved interfaces require a semiclassical correction of Fresnel's law due to an interference effect called Goos-Hänchen shift. It is accompanied by the so-called Fresnel filtering which, in turn, corrects Snell's law. These two contributions are especially important near the critical angle. They are of similar magnitude and correspond to ray displacements in independent phase-space directions that can be incorporated in an adjusted reflection law. Implementing both effects into the ray model improves the agreement with wave optics by about one order of magnitude. We show that deviations from ray-wave correspondence can be straightforwardly understood with the resulting adjusted reflection law and discuss its consequences for the phase-space dynamics in optical billiards.

Hentschel, Martina

90

NASA Astrophysics Data System (ADS)

An experimental study of NMR spin decoherence in nematic liquid crystals is presented. Decoherence dynamics can be put in evidence by means of refocusing experiments of the dipolar interactions. The experimental technique used in this work is based on the MREV8 pulse sequence. The aim of the work is to detect the main features of the irreversible quantum decoherence in liquid crystals, on the basis of the theory presented by the authors recently. The focus is laid on experimentally probing the eigen-selection process in the intermediate time scale, between quantum interference of a closed system and thermalization, as a signature of the quantum spin decoherence of the open quantum system, as well as on quantifying the effects of non-idealities as possible sources of signal decays which could mask the intrinsic decoherence. In order to contrast experiment and theory, the theory was adapted to obtain the decoherence function corresponding to the MREV8 reversion experiments. Non-idealities of the experimental setting, like external field inhomogeneity, pulse misadjustments, and the presence of non-reverted spin interaction terms are analysed in detail within this framework, and their effects on the observed signal decay are numerically estimated. It is found that though all these non-idealities could in principle affect the evolution of the spin dynamics, their influence can be mitigated and they do not present the characteristic behaviour of the irreversible spin decoherence. As unique characteristic of decoherence, the experimental results clearly show the occurrence of eigen-selectivity in the intermediate timescale, in complete agreement with the theoretical predictions. We conclude that the eigen-selection effect is the fingerprint of decoherence associated with a quantum open spin system in liquid crystals. Besides, these features of the results account for the quasi-equilibrium states of the spin system, which were observed previously in these mesophases, and lead to conclude that the quasi-equilibrium is a definite stage of the spin dynamics during its evolution towards equilibrium.

Segnorile, H. H.; Zamar, R. C.

2013-10-01

91

Explanation of decoherence and quasi-equilibrium in systems with few degrees of freedom demands a deep theoretical analysis that considers the observed system as an open quantum system. In this work, we study the problem of decoherence of an observed system of quantum interacting particles, coupled to a quantum lattice. Our strategy is based on treating the environment and the system-environment Hamiltonians fully quantum mechanically, which yields a representation of the time evolution operator useful for disentangling the different time scales underlying in the observed system dynamics. To describe the possible different stages of the dynamics of the observed system, we introduce quantum mechanical definitions of essentially isolated, essentially adiabatic, and thermal-contact system-environment interactions. This general approach is then applied to the study of decoherence and quasi-equilibrium in proton nuclear magnetic resonance ((1)H NMR) of nematic liquid crystals. A summary of the original results of this work is as follows. We calculate the decoherence function and apply it to describe the evolution of a coherent spin state, induced by the coupling with the molecular environment, in absence of spin-lattice relaxation. By assuming quantum energy conserving or non-demolition interactions, we identify an intermediate time scale, between those controlled by self-interactions and thermalization, where coherence decays irreversibly. This treatment is also adequate for explaining the buildup of quasi-equilibrium of the proton spin system, via the process we called eigen-selectivity. By analyzing a hypothetical time reversal experiment, we identify two sources of coherence loss which are of a very different nature and give rise to distinct time scales of the spin dynamics: (a) reversible or adiabatic quantum decoherence and (b) irreversible or essentially adiabatic quantum decoherence. Local irreversibility arises as a consequence of the uncertainty introduced by the coupling with an infinite quantum environment. The reversible part can be represented by a semiclassical model, similar to standard line-shape adiabatic models. By exploiting the separation existing between the time scales of the spin coherences and the irreversible decoherence, we present a novel technique to obtain the orientational molecular distribution function for a nematic liquid crystal. The procedure is based on the comparison of the observed coherence time evolution and numerical calculation under the adiabatic quantum decoherence approach. As an example, it is used the experimental free induction decay from a nematic PAA(d6) sample to extract such an orientational distribution. This is the first theoretical description of the experimental liquid crystal NMR signal in the time domain. On the contrary, the irreversible decoherence is intrinsically full-quantum mechanical, as it is governed by the commutation properties of the environment and the spin-lattice Hamiltonians. Consistently, it depends on the molecular correlation in a decisive way, since it vanishes under a mean-field model for the molecular dynamics. The results of this work can contribute to the understanding of the open question of the applicability of the spin-temperature concept in spin systems with few degrees of freedom. PMID:22225171

Segnorile, Héctor H; Zamar, Ricardo C

2011-12-28

92

Decoherence in Composite Quantum Open Systems:. the Effectiveness of Unstable Degrees of Freedom

The effect induced by an environment on a composite quantum system is studied. The model considers the composite system as comprised by a subsystem A coupled to a subsystem B which is also coupled to an external environment. We studied all possible four combinations of subsystems A and B made up with a harmonic oscillator and an upside down oscillator.

Fernando C. Lombardo; Paula I. Villar

2006-01-01

93

Non-Markovian dynamics of an open quantum system with nonstationary coupling

The spectral, dissipative, and statistical properties of the damped quantum oscillator are studied in the case of non-Markovian and nonstationary system-heat bath coupling. The dissipation of collective energy is shown to be slowed down, and the decoherence rate and entropy grow with modulation frequency.

Kalandarov, S. A.; Adamian, G. G. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Institute of Nuclear Physics, 702132 Tashkent (Uzbekistan); Kanokov, Z. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); National University, 700174 Tashkent (Uzbekistan); Antonenko, N. V. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Scheid, W. [Institut fuer Theoretische Physik der Justus-Liebig-Universitaet, D-35392 Giessen (Germany)

2011-04-15

94

Hierarchical equations of motion: A fundamental theory for quantum open systems

NASA Astrophysics Data System (ADS)

As a powerful alternative to the influence functional path integral formalism, HEOM has been exploited in the study of various systems. In this talk, I will present some recent advancement on the HEOM-based nonlinear/nonequilibrium response theory and efficient implementation methods. Numerical demonstrations include coherent two-dimensional spectroscopy signals of light-harvesting model systems, and transport current noise spectrums through Anderson model quantum dots, operated in high-order co-tunneling regime.

Yan, Yijing

2012-02-01

95

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...)

Irina Rychkova; Valentin Rychkov; Kyryl Kazymyrenko; Simone Borlenghi; Xavier Waintal

2010-01-01

96

Demonstration of Jarzynski's equality in open quantum systems using a stepwise pulling protocol

NASA Astrophysics Data System (ADS)

We present a generalization of Jarzynski's equality, applicable to quantum systems, that is related to discretized mechanical work and free-energy changes. The theory is based on a stepwise pulling protocol. We find that work distribution functions can be constructed from fluctuations of a reaction coordinate along a reaction pathway in the stepwise pulling protocol. We also propose two sets of equations to determine the two possible optimal pathways that provide the most significant contributions to free-energy changes. We find that the transitions along these most optimal pathways, satisfying both sets of equations, follow the principle of detailed balance. We then test the theory by explicitly computing the free-energy changes for a one-dimensional quantum harmonic oscillator. This approach suggests a feasible way of measuring the fluctuations to experimentally test Jarzynski's equality in many-body systems, such as Bose-Einstein condensates.

Ngo, Van A.; Haas, Stephan

2012-09-01

97

Demonstration of Jarzynski's equality in open quantum systems using a stepwise pulling protocol.

We present a generalization of Jarzynski's equality, applicable to quantum systems, that is related to discretized mechanical work and free-energy changes. The theory is based on a stepwise pulling protocol. We find that work distribution functions can be constructed from fluctuations of a reaction coordinate along a reaction pathway in the stepwise pulling protocol. We also propose two sets of equations to determine the two possible optimal pathways that provide the most significant contributions to free-energy changes. We find that the transitions along these most optimal pathways, satisfying both sets of equations, follow the principle of detailed balance. We then test the theory by explicitly computing the free-energy changes for a one-dimensional quantum harmonic oscillator. This approach suggests a feasible way of measuring the fluctuations to experimentally test Jarzynski's equality in many-body systems, such as Bose-Einstein condensates. PMID:23030886

Ngo, Van A; Haas, Stephan

2012-09-20

98

An experimental study of NMR spin decoherence in nematic liquid crystals is presented. Decoherence dynamics can be put in evidence by means of refocusing experiments of the dipolar interactions. The experimental technique used in this work is based on the MREV8 pulse sequence. The aim of the work is to detect the main features of the irreversible quantum decoherence in liquid crystals, on the basis of the theory presented by the authors recently. The focus is laid on experimentally probing the eigen-selection process in the intermediate time scale, between quantum interference of a closed system and thermalization, as a signature of the quantum spin decoherence of the open quantum system, as well as on quantifying the effects of non-idealities as possible sources of signal decays which could mask the intrinsic decoherence. In order to contrast experiment and theory, the theory was adapted to obtain the decoherence function corresponding to the MREV8 reversion experiments. Non-idealities of the experimental setting, like external field inhomogeneity, pulse misadjustments, and the presence of non-reverted spin interaction terms are analysed in detail within this framework, and their effects on the observed signal decay are numerically estimated. It is found that though all these non-idealities could in principle affect the evolution of the spin dynamics, their influence can be mitigated and they do not present the characteristic behaviour of the irreversible spin decoherence. As unique characteristic of decoherence, the experimental results clearly show the occurrence of eigen-selectivity in the intermediate timescale, in complete agreement with the theoretical predictions. We conclude that the eigen-selection effect is the fingerprint of decoherence associated with a quantum open spin system in liquid crystals. Besides, these features of the results account for the quasi-equilibrium states of the spin system, which were observed previously in these mesophases, and lead to conclude that the quasi-equilibrium is a definite stage of the spin dynamics during its evolution towards equilibrium. PMID:24160540

Segnorile, H H; Zamar, R C

2013-10-21

99

Communication: Conditions for one-photon coherent phase control in isolated and open quantum systems

Coherent control of observables using the phase properties of weak light that induces one-photon transitions is considered. Measurable properties are shown to be categorizable as either class A, where control is not possible, or class B, where control is possible. Using formal arguments, we show that phase control in open systems can be environmentally assisted.

Spanner, Michael; Arango, Carlos A.; Brumer, Paul [Department of Chemistry, Chemical Physics Theory Group, and Center for Quantum Information and Quantum Control, University of Toronto, Toronto M5S 3H6 (Canada)

2010-10-21

100

Stimulated Raman adiabatic passage in an open quantum system: Master equation approach

A master equation approach to the study of environmental effects in the adiabatic population transfer in three-state systems is presented. A systematic comparison with the non-Hermitian Hamiltonian approach [Vitanov and Stenholm, Phys. Rev. A 56, 1463 (1997)] shows that, in the weak-coupling limit, the two treatments lead to essentially the same results. In contrast, in the strong-damping limit the predictions are quite different: In particular, the counterintuitive sequences in the STIRAP scheme turn out to be much more efficient than expected before. This point is explained in terms of quantum Zeno dynamics.

Scala, M.; Militello, B.; Messina, A. [Dipartimento di Scienze Fisiche ed Astronomiche dell'Universita di Palermo, Via Archirafi 36, I-90123 Palermo (Italy); Vitanov, N. V. [Department of Physics, Sofia University, James Bourchier 5 boulevard, 1164 Sofia (Bulgaria); Institute of Solid State Physics, Bulgarian Academy of Sciences, Tsarigradsko chaussee 72, 1784 Sofia (Bulgaria)

2010-05-15

101

Quantum electromechanical systems

Quantum electromechanical systems are nano-to-micrometer (micron) scale mechanical resonators coupled to electronic devices of comparable dimensions, such that the mechanical resonator behaves in a manifestly quantum manner. We review progress towards realising quantum electromechanical systems, beginning with the phononic quantum of thermal conductance for suspended dielectric wires. We then describe efforts to reach the quantum zero-point displacement uncertainty detection limit

Miles Blencowe

2004-01-01

102

Quantum dissipation in unbounded systems.

In recent years trajectory based methodologies have become increasingly popular for evaluating the time evolution of quantum systems. A revival of the de Broglie--Bohm interpretation of quantum mechanics has spawned several such techniques for examining quantum dynamics from a hydrodynamic perspective. Using techniques similar to those found in computational fluid dynamics one can construct the wave function of a quantum system at any time from the trajectories of a discrete ensemble of hydrodynamic fluid elements (Bohm particles) which evolve according to nonclassical equations of motion. Until very recently these schemes have been limited to conservative systems. In this paper, we present our methodology for including the effects of a thermal environment into the hydrodynamic formulation of quantum dynamics. We derive hydrodynamic equations of motion from the Caldeira-Leggett master equation for the reduced density matrix and give a brief overview of our computational scheme that incorporates an adaptive Lagrangian mesh. Our applications focus upon the dissipative dynamics of open unbounded quantum systems. Using both the Wigner phase space representation and the linear entropy, we probe the breakdown of the Markov approximation of the bath dynamics at low temperatures. We suggest a criteria for rationalizing the validity of the Markov approximation in open unbound systems and discuss decoherence, energy relaxation, and quantum/classical correspondence in the context of the Bohmian paths. PMID:11863623

Maddox, Jeremy B; Bittner, Eric R

2002-01-25

103

Quantum Games and Programmable Quantum Systems

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

Edward W. Piotrowski; Jan Sladkowski

2005-01-01

104

Detecting quantum and classical correlations using quantum dot system

NASA Astrophysics Data System (ADS)

We investigate the thermal classical and quantum correlations in an isolated quantum dot system (QDS) including the effects of different parameters. The thermal density operator is generated by simplifying the Hamiltonian of the quantum dot to the nature Hamiltonian by integrating and finding the unitary matrix. We find that the quantum discord (QD) is more resistant against temperature effect and might be finite even for higher temperatures in the asymptotic limit. Furthermore, we show that there is an optimal value of temperature such that the different kinds of correlations are maximal. Our results show that QDS is a useful resource and may open new perspectives in different quantum information tasks.

Berrada, K.

2013-12-01

105

NASA Astrophysics Data System (ADS)

We propose an analysis technique for the exceptional points (EPs) occurring in the discrete spectrum of open quantum systems (OQS), using a semi-infinite chain coupled to an endpoint impurity as a prototype. We outline our method to locate the EPs in OQS, further obtaining an eigenvalue expansion in the vicinity of the EPs that gives rise to characteristic exponents. We also report the precise number of EPs occurring in an OQS with a continuum described by a quadratic dispersion curve. In particular, the number of EPs occurring in a bare discrete Hamiltonian of dimension n D is given by n D( n D-1); if this discrete Hamiltonian is then coupled to continuum (or continua) to form an OQS, the interaction with the continuum generally produces an enlarged discrete solution space that includes a greater number of EPs, specifically 2^{nC} (nC + nD ) [ 2^{nC} (nC + nD ) - 1] , in which n C is the number of (non-degenerate) continua to which the discrete sector is attached. Finally, we offer a heuristic quantum phase transition analogy for the emergence of the resonance (giving rise to irreversibility via exponential decay) in which the decay width plays the role of the order parameter; the associated critical exponent is then determined by the above eigenvalue expansion.

Garmon, Savannah; Rotter, Ingrid; Hatano, Naomichi; Segal, Dvira

2012-11-01

106

Robust quantum gates for open systems via optimal control: Markovian versus non-Markovian dynamics

NASA Astrophysics Data System (ADS)

We study the implementation of one-, two- and three-qubit quantum gates for interacting qubits using optimal control. Markovian and non-Markovian environments are compared and efficient optimization algorithms utilizing analytic gradient expressions and quasi-Newton updates are given for both cases. The performance of the algorithms is analysed for a large set of problems in terms of the fidelities attained and the observed convergence behaviour. New notions of success rate and success speed are introduced and density plots are utilized to study the effects of key parameters, such as gate operation times, and random variables such as the initial fields required to start the iterative algorithm. Core characteristics of the optimal fields are analysed statistically. Substantial differences between Markovian and non-Markovian environments in terms of the possibilities for control and the control mechanisms are uncovered. In the non-Markovian case, gate fidelities improve substantially when the details of the system bath coupling are taken into account, although imperfections such as field leakage can be a significant problem. In the Markovian case, computation time is saved if the fields are pre-optimized neglecting the environment, while including the latter generally does not significantly improve gate fidelities.

Floether, Frederik F.; de Fouquieres, Pierre; Schirmer, Sophie G.

2012-07-01

107

General open-system quantum evolution in terms of affine maps of the polarization vector

The operator-sum decomposition of a map from one density matrix to another has many applications in quantum information science. To this mapping there corresponds an affine map which provides a geometric description of the map of the density matrix in terms of the polarization vector representation. This has been thoroughly explored for qubits since the components of the polarization vector are measurable quantities (corresponding to expectation values of Hermitian operators) and also because it enables the description of map domains geometrically. Here we extend the operator-sum-affine-map correspondence to qudits, briefly discuss general properties of the map and the form for some particular cases, and provide several explicit results for qutrit maps. We use the affine map and a singular-value-like decomposition to find positivity constraints that provide a symmetry for small polarization vector magnitudes (states which are closer to the maximally mixed state), which is broken as the polarization vector increases in magnitude (a state becomes more pure). The dependence of this symmetry on the magnitude of the polarization vector implies the polar decomposition of the map cannot be used as it can for the qubit case. However, it still leads us to a connection between positivity and purity for general d-state systems.

Byrd, Mark S. [Physics Department, Southern Illinois University, Carbondale, Illinois 62901 (United States); Computer Science Department, Southern Illinois University, Carbondale, Illinois 62901 (United States); Bishop, C. Allen; Ou, Yong-Cheng [Physics Department, Southern Illinois University, Carbondale, Illinois 62901 (United States)

2011-01-15

108

NASA Astrophysics Data System (ADS)

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

Cahill, Reginald T.

2002-10-01

109

Spectral problems in open quantum chaos

NASA Astrophysics Data System (ADS)

We present an overview of mathematical results and methods relevant for the spectral study of semiclassical Schrödinger (or wave) operators of scattering systems, in cases where the corresponding classical dynamics is chaotic; more precisely, we assume that in some energy range, the classical Hamiltonian flow admits a fractal set of trapped trajectories, which hosts chaotic (hyperbolic) dynamics. The aim is then to connect the information on this trapped set with the distribution of quantum resonances in the semiclassical limit. Our study encompasses several models sharing these dynamical characteristics: free motion outside a union of convex hard obstacles, scattering by certain families of compactly supported potentials, geometric scattering on manifolds with (constant or variable) negative curvature. We also consider the toy model of open quantum maps, and sketch the construction of quantum monodromy operators associated with a Poincaré section for a scattering flow. The semiclassical density of long-living resonances exhibits a fractal Weyl law, related to the fact that the corresponding metastable states are 'supported' by the fractal trapped set (and its outgoing tail). We also describe a classical condition for the presence of a gap in the resonance spectrum, equivalently a uniform lower bound on the quantum decay rates, and present a proof of this gap in a rather general situation, using quantum monodromy operators.

Nonnenmacher, Stéphane

2011-12-01

110

Excitation transfer through open quantum networks: a few basic mechanisms

A variety of open quantum networks are currently under intense examination to model energy transport in photosynthetic systems. Here we study the coherent transfer of a quantum excitation over a network incoherently coupled with a structured and small environment that effectively models the photosynthetic reaction center. Our goal is to distill a few basic, possibly universal, mechanisms or \\

Lorenzo Campos Venuti; Paolo Zanardi

2011-01-01

111

In this paper, the exact non-Markovian dynamics of open quantum systems in the presence of initial system-reservoir correlations is investigated for a photonic cavity system coupled to a general non-Markovian reservoir. The exact time-convolutionless master equation incorporating with initial system-reservoir correlations is obtained. The non-Markovian dynamics of the reservoir and the effects of the initial correlations are embedded into the time-dependent coefficients in the master equation. We show that the effects induced by the initial correlations play an important role in the non-Markovian dynamics of the cavity but they are washed out in the steady-state limit in the Markovian regime. Moreover, the initial two-photon correlation between the cavity and the reservoir can induce nontrivial squeezing dynamics to the cavity field.

Tan, Hua-Tang [Department of Physics and Center for Quantum information Science, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Physics, Huazhong Normal University, Wuhan 430079 (China); Zhang, Wei-Min [Department of Physics and Center for Quantum information Science, National Cheng Kung University, Tainan 70101, Taiwan (China)

2011-03-15

112

{open_quotes}Plug and play{close_quotes} systems for quantum cryptography

We present a time-multiplexed interferometer based on Faraday mirrors, and apply it to quantum key distribution. The interfering pulses follow exactly the same spatial path, ensuring very high stability and self balancing. The use of Faraday mirrors compensates automatically any birefringence effects and polarization dependent losses in the transmitting fiber. First experimental results show a fringe visibility of 0.9984 for a 23-km-long interferometer, based on installed telecom fibers. {copyright} {ital 1997 American Institute of Physics.}

Muller, A.; Herzog, T.; Huttner, B.; Tittel, W.; Zbinden, H.; Gisin, N. [Group of Applied Physics, University of Geneva, CH 1211 Geneva 4 (Switzerland)

1997-02-01

113

Conductance Peaks in Open Quantum Dots

NASA Astrophysics Data System (ADS)

We present a simple measure of the conductance fluctuations in open ballistic chaotic quantum dots, extending the number of maxima method originally proposed for the statistical analysis of compound nuclear reactions. The average number of extreme points (maxima and minima) in the dimensionless conductance T as a function of an arbitrary external parameter Z is directly related to the autocorrelation function of T(Z). The parameter Z can be associated with an applied gate voltage causing shape deformation in quantum dot, an external magnetic field, the Fermi energy, etc. The average density of maxima is found to be ??Z?=?Z/Zc, where ?Z is a universal constant and Zc is the conductance autocorrelation length, which is system specific. The analysis of ??Z? does not require large statistic samples, providing a quite amenable way to access information about parametric correlations, such as Zc.

Ramos, J. G. G. S.; Bazeia, D.; Hussein, M. S.; Lewenkopf, C. H.

2011-10-01

114

Bispectrality for the quantum open Toda chain

NASA Astrophysics Data System (ADS)

An alternative to Babelon (2003 Lett. Math. Phys. 65 229) construction of dual variables for the quantum open Toda chain is proposed that is based on the 2 × 2 Lax matrix and the corresponding quadratic R-matrix algebra.

Sklyanin, Evgeny

2013-09-01

115

QuTiP 2: A Python framework for the dynamics of open quantum systems

NASA Astrophysics Data System (ADS)

We present version 2 of QuTiP, the Quantum Toolbox in Python. Compared to the preceding version [J.R. Johansson, P.D. Nation, F. Nori, Comput. Phys. Commun. 183 (2012) 1760.], we have introduced numerous new features, enhanced performance, and made changes in the Application Programming Interface (API) for improved functionality and consistency within the package, as well as increased compatibility with existing conventions used in other scientific software packages for Python. The most significant new features include efficient solvers for arbitrary time-dependent Hamiltonians and collapse operators, support for the Floquet formalism, and new solvers for Bloch–Redfield and Floquet–Markov master equations. Here we introduce these new features, demonstrate their use, and give a summary of the important backward-incompatible API changes introduced in this version.

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

2013-04-01

116

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

117

Time-dependent approach to electron pumping in open quantum systems

NASA Astrophysics Data System (ADS)

We use a recently proposed time-dependent approach to investigate the motion of electrons in quantum pump device configurations. The occupied one-particle states are propagated in real time and employed to calculate the local electron density and current. The approach can also be embedded in the framework of time-dependent density functional theory to include electron-electron interactions. An advantage of the present computational scheme is that the same computational effort is required to simulate monochromatic, polychromatic, and nonperiodic drivings. Furthermore, initial-state dependence and history effects are naturally accounted for. We present results for one-dimensional devices exposed to a traveling potential wave. (i) We show that for pumping across a single potential barrier, electrons are transported in pockets and the transport mechanism resembles pumping of water with the Archimedean screw; (ii) we propose a simple model to study pumping through semiconductor nanostructures and we address the phenomenon of the current flowing in the opposite direction to the field propagation; (iii) we present the first numerical evidence of long-lived superimposed oscillations as induced by the presence of bound states and discuss the dependence of their lifetime on the frequency and amplitude of the driving field. By combining Floquet theory with nonequilibrium Green’s functions, we also obtain a general expression for the pumped current in terms of inelastic transmission probabilities. This latter result is used for benchmarking our propagation scheme in the long-time limit. Finally, we discuss the limitations of Floquet-based algorithms and suggest our approach as a possible way to go beyond them.

Stefanucci, G.; Kurth, S.; Rubio, A.; Gross, E. K. U.

2008-02-01

118

NASA Astrophysics Data System (ADS)

We consider the security of practical continuous-variable quantum-key-distribution implementation with the local oscillator (LO) fluctuating in time, which opens a loophole for Eve to intercept the secret key. We show that Eve can simulate this fluctuation to hide her Gaussian collective attack by reducing the intensity of the LO. Numerical simulations demonstrate that if Bob does not monitor the LO intensity and does not scale his measurements with the instantaneous intensity values of LO, the secret key rate will be compromised severely.

Ma, Xiang-Chun; Sun, Shi-Hai; Jiang, Mu-Sheng; Liang, Lin-Mei

2013-08-01

119

Many quantum integrable systems are obtained using an accelerator physics technique known as Ermakov (or normalized variables) transformation. This technique was used to create classical nonlinear integrable lattices for accelerators and nonlinear integrable plasma traps. Now, all classical results are carried over to a nonrelativistic quantum case. In this paper we have described an extension of the Ermakov-like transformation to the Schroedinger and Pauli equations. It is shown that these newly found transformations create a vast variety of time dependent quantum equations that can be solved in analytic functions, or, at least, can be reduced to time-independent ones.

Danilov, Viatcheslav; /Oak Ridge; Nagaitsev, Sergei; /Fermilab

2011-11-01

120

Creation of electrons or excitons by external fields in a system with initially statistically independent unrelaxed vibrational modes leads to an initial condition term. The contribution of this term in the time convolution generalized master-equation approach is studied in the second order of the perturbation theory in path-integral formalism. The developed approach, applied for the analysis of dynamics in the photosynthetic reaction center, exhibits the key role of the initial condition terms at the primary stage of electron transfer. PMID:22181449

Pudlak, M; Pichugin, K N; Nazmitdinov, R G; Pincak, R

2011-11-18

121

NASA Astrophysics Data System (ADS)

Practical recipes are presented for simulating high-temperature and nonequilibrium quantum spin systems that are continuously measured and controlled. The notion of a spin system is broadly conceived, in order to encompass macroscopic test masses as the limiting case of large-j spins. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into an equivalent continuous measurement and control process, and finally, projection of the trajectory onto state-space manifolds having reduced dimensionality and possessing a Kähler potential of multilinear algebraic form. These state-spaces can be regarded as ruled algebraic varieties upon which a projective quantum model order reduction (MOR) is performed. The Riemannian sectional curvature of ruled Kählerian varieties is analyzed, and proved to be non-positive upon all sections that contain a rule. These manifolds are shown to contain Slater determinants as a special case and their identity with Grassmannian varieties is demonstrated. The resulting simulation formalism is used to construct a positive P-representation for the thermal density matrix. Single-spin detection by magnetic resonance force microscopy (MRFM) is simulated, and the data statistics are shown to be those of a random telegraph signal with additive white noise. Larger-scale spin-dust models are simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low dimensionality Kähler state-space manifolds is demonstrated. The reconstruction of quantum trajectories from sparse random projections is demonstrated, the onset of Donoho-Stodden breakdown at the Candès-Tao sparsity limit is observed, a deterministic construction for sampling matrices is given and methods for quantum state optimization by Dantzig selection are given.

Sidles, John A.; Garbini, Joseph L.; Harrell, Lee E.; Hero, Alfred O.; Jacky, Jonathan P.; Malcomb, Joseph R.; Norman, Anthony G.; Williamson, Austin M.

2009-06-01

122

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

123

NASA Astrophysics Data System (ADS)

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.

de Micheli, Fiorenza; Zanelli, Jorge

2012-10-01

124

Quantum Electromechanical Systems

NASA Astrophysics Data System (ADS)

Quantum electromechanical systems are nano-to-micron scale mechanical resonators coupled to electronic devices of comparable dimensions, such that the mechanical resonator behaves in a manifestly quantum manner. Dramatic progress towards realising such systems has been made with the recent demonstration of a GHz mechanical resonator [1], and demonstrated displacement detection close to the quantum limit based on the single electron transistor [2-4]. The latter system, comprising a single electron transistor and micron-scale mechanical resonator electrostatically-coupled to the transistor island, is predicted to exhibit surprisingly rich dynamical behavior [5]. The unprecedented displacement sensitivity of the SET transducer may also enable the observation of quantum 'jumps' in the motion of nanomechanical resonators at milliKelvin temperatures, due to the strain-mediated coupling between the flexing motion and tunneling defects of the resonator [6]. Such investigations are contributing towards a deeper understanding of the transition between quantum and classical dynamics. [1] X. Huang, C. Zorman, M. Mehregany, M. Roukes, Nature 421 (2003) 496; [2] M. Blencowe, M. Wybourne, Appl. Phys. Lett. 77 (2000) 3845; [3] R. Knobel, A. Cleland, Nature 424 (2003), 291; [4] M. LaHaye, O. Buu, B. Camarota, K. Schwab (unpublished); [5] A. Armour, M. Blencowe, Y. Zhang, cond-mat/0307528 (Phys. Rev. B to appear); [6] Y. Tanaka, M. Blencowe (unpublished).

Blencowe, Miles

2004-03-01

125

Informationally coherent quantum systems

An information-theoretic approach to correlated quantum systems is developed. The precise definitions of the informationally coherent N-component system are presented in terms of the state (observable) dependent index of correlation. The informational coherence of the N-particle GHZ system in an entangled pure state is analysed and it is found that the observable-dependent index of correlation is less than or equal

Ryszard Horodecki

1994-01-01

126

Models of PT symmetric quantum mechanics provide examples of biorthogonal quantum systems. The latter incorporate all the structure of PT symmetric models, and allow for generalizations, especially in situations where the PT construction of the dual space fails. The formalism is illustrated by a few exact results for models of the form H=(p+{nu}){sup 2}+{sigma}{sub k>0}{mu}{sub k} exp(ikx). In some nontrivial cases, equivalent Hermitian theories are obtained and shown to be very simple: They are just free (chiral) particles. Field theory extensions are briefly considered.

Curtright, Thomas; Mezincescu, Luca [Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States) and School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States)

2007-09-15

127

Integrable quantum Stäckel systems

NASA Astrophysics Data System (ADS)

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

B?aszak, Maciej; Doma?ski, Ziemowit; Sergyeyev, Artur; Szablikowski, B?a?ej M.

2013-11-01

128

Quantum algorithm in quantum network systems

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

Sakamoto, I.; Yamaguchi, T.; Nagao, H.; Nishikawa, K. [Department of Computational Science, Faculty of Science, Kanazawa University, Kakuma, Kanazawa, 920-1192 (Japan)

2004-04-30

129

Intrinsic Properties of Quantum Systems

NASA Astrophysics Data System (ADS)

A new realist interpretation of quantum mechanics is introduced. Quantum systems are shown to have two kinds of properties: the usual ones described by values of quantum observables, which are called extrinsic, and those that can be attributed to individual quantum systems without violating standard quantum mechanics, which are called intrinsic. The intrinsic properties are classified into structural and conditional. A systematic and self-consistent account is given. Much more statements become meaningful than any version of Copenhagen interpretation would allow. A new approach to classical properties and measurement problem is suggested. A quantum definition of classical states is proposed.

Hájí?ek, P.; Tolar, J.

2009-05-01

130

Coulomb Oscillations in Partially Open Quantum Dots

NASA Astrophysics Data System (ADS)

Coulomb blockade conductance oscillations in quantum dots are ordinarily observed with weak dot-to-lead tunneling. Recent theoryfootnote A. Furusaki and K.A. Matveev, Phys. Rev. Lett. 75 (1995), 709. examines the effect of strong tunneling on Coulomb oscillations. We have measured the zero magnetic field conductance through a 500 × 800 nm^2 quantum dot connected to leads through tunable tunnel barriers, defined in a high mobility near-surface two-dimensional electron gas by four independently tunable split gates on a GaAs/AlGaAs heterostructure. We set the conductance of one barrier much less than e^2/h and vary the conductance of the other (G_open) between e^2/h and 6e^2/h. We observe well-defined Coulomb oscillations at 50 mK for the entire range of G_open, except when G_open ? 2e^2/h, where the oscillations are suppressed. The temperature at which the oscillations disappear decreases with increasing G_open; for G_ open>2e^2/h, the oscillations are suppressed at temperatures above the single-particle level spacing.

Crouch, C. H.; Livermore, C.; Westervelt, R. M.; Campman, K. L.; Gossard, A. C.

1996-03-01

131

Electron properties of open semiconductor quantum dots

The energy spectrum and lifetimes of electron states in an open semiconductor quantum dot (QD) have been studied using the\\u000a scattering S-matrix method. It is established that the lifetime of electron states in the QD is highly sensitive to changes in the QD\\u000a radius and the thickness of an external coating layer. As the coating layer thickness increases from one

N. V. Tkach; Yu. A. Seti; G. G. Zegrya

2007-01-01

132

Open quantum dots—probing the quantum to classical transition

NASA Astrophysics Data System (ADS)

Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

Ferry, D. K.; Burke, A. M.; Akis, R.; Brunner, R.; Day, T. E.; Meisels, R.; Kuchar, F.; Bird, J. P.; Bennett, B. R.

2011-04-01

133

Nature computes: information processing in quantum dynamical systems.

Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantum computer. To corroborate this idea we require tools to quantify the information processing. Here we review a theoretical framework for quantifying information processing in a quantum dynamical system. So-called intrinsic quantum computation combines tools from dynamical systems theory, information theory, quantum mechanics, and computation theory. We will review how far the framework has been developed and what some of the main open questions are. On the basis of this framework we discuss upper and lower bounds for intrinsic information storage in a quantum dynamical system. PMID:20887080

Wiesner, Karoline

2010-09-01

134

Review on System-Spin Environment Dynamics of Quantum Discord

NASA Astrophysics Data System (ADS)

Recent work has relatively comprehensively studied the quantum discord, which is supposed to account for all the nonclassical correlations present in a bipartite state (including entanglement), and provide computational speedup and quantum enhancement even in separable states. Firstly, we introduce several different indicators of nonclassical correlations, including their definitions and interpretations, mathematical properties, and the relationship between them. Secondly, we review two major topics of quantum discord. One is the remarkable behavior at quantum phase transitions. The pairwise quantum discord for nearest neighbors as well as distant spin pairs can perfectly signal the critical behavior of many physical models, even at finite temperatures. The other is quantum discord dynamics in open systems, especially for "system-spin environment" models. Quantum discord is more robust than entanglement against external perturbations. It can be created, greatly amplified or protected under certain conditions, and presents promising applications in quantum technologies such as quantum computers.

Liu, Ben-Qiong; Shao, Bin; Li, Jun-Gang; Zou, Jian

2013-01-01

135

NASA Astrophysics Data System (ADS)

The hierarchical equations of motion technique has found widespread success as a tool to generate the numerically exact dynamics of non-Markovian open quantum systems. However, its application to low temperature environments remains a serious challenge due to the need for a deep hierarchy that arises from the Matsubara expansion of the bath correlation function. Here we present a hybrid stochastic hierarchical equation of motion (sHEOM) approach that alleviates this bottleneck and leads to a numerical cost that is nearly independent of temperature. Additionally, the sHEOM method generally converges with fewer hierarchy tiers allowing for the treatment of larger systems. Benchmark calculations are presented on the dynamics of two level systems at both high and low temperatures to demonstrate the efficacy of the approach. Then the hybrid method is used to generate the exact dynamics of systems that are nearly impossible to treat by the standard hierarchy. First, exact energy transfer rates are calculated across a broad range of temperatures revealing the deviations from the Förster rates. This is followed by computations of the entanglement dynamics in a system of two qubits at low temperature spanning the weak to strong system-bath coupling regimes.

Moix, Jeremy M.; Cao, Jianshu

2013-10-01

136

The hierarchical equations of motion technique has found widespread success as a tool to generate the numerically exact dynamics of non-Markovian open quantum systems. However, its application to low temperature environments remains a serious challenge due to the need for a deep hierarchy that arises from the Matsubara expansion of the bath correlation function. Here we present a hybrid stochastic hierarchical equation of motion (sHEOM) approach that alleviates this bottleneck and leads to a numerical cost that is nearly independent of temperature. Additionally, the sHEOM method generally converges with fewer hierarchy tiers allowing for the treatment of larger systems. Benchmark calculations are presented on the dynamics of two level systems at both high and low temperatures to demonstrate the efficacy of the approach. Then the hybrid method is used to generate the exact dynamics of systems that are nearly impossible to treat by the standard hierarchy. First, exact energy transfer rates are calculated across a broad range of temperatures revealing the deviations from the Fo?rster rates. This is followed by computations of the entanglement dynamics in a system of two qubits at low temperature spanning the weak to strong system-bath coupling regimes. PMID:24116551

Moix, Jeremy M; Cao, Jianshu

2013-10-01

137

Determinism Beneath Composite Quantum Systems

NASA Astrophysics Data System (ADS)

This paper aims at the development of 't Hooft's quantization proposal to describe composite quantum mechanical systems. In particular, we show how 't Hooft's method can be utilized to obtain from two classical Bateman oscillators a composite quantum system corresponding to a quantum isotonic oscillator. For a suitable range of parameters, the composite system can be also interpreted as a particle in an effective magnetic field interacting through a spin-orbital interaction term. In the limit of a large separation from the interaction region we can identify the irreducible subsystems with two independent quantum oscillators.

Blasone, Massimo; Vitiello, Giuseppe; Jizba, Petr; Scardigli, Fabio

138

Local controllability of quantum systems

NASA Astrophysics Data System (ADS)

We give a criterion that is sufficient for controllability of multipartite quantum systems. We generalize the graph infection criterion to the quantum systems that cannot be described with the use of a graph theory. We introduce the notation of hypergraphs and reformulate the infection property in this setting. The introduced criterion has a topological nature and therefore it is not connected to any particular experimental realization of quantum information processing.

Pucha?a, Zbigniew

2013-01-01

139

NASA Astrophysics Data System (ADS)

We investigate the role of quantum mechanical effects in the central stability concept of evolutionary game theory, i.e., an evolutionarily stable strategy (ESS). Using two and three-player symmetric quantum games we show how the presence of quantum phenomenon of entanglement can be crucial to decide the course of evolutionary dynamics in a population of interacting individuals.

Iqbal, A.; Toor, A. H.

2002-03-01

140

Separability of Multipartite Quantum Systems

NASA Astrophysics Data System (ADS)

A necessary condition for separability of multipartite quantum systems is given. It is shown that for 2 × 2 × \\ctdot × 2 × quantum systems the condition of separability is equivalent to the criterion of positive partial transposition. We also define an entanglement measurement based on this separability condition which can be considered as a kind of generalization of negativity.

Li, Ming; Jing, Wang

2012-02-01

141

Classical and quantum massive cosmology for the open FRW universe

NASA Astrophysics Data System (ADS)

In an open Friedmann-Robertson-Walker (FRW) space background, we study the classical and quantum cosmological models in the framework of the recently proposed nonlinear massive gravity theory. Although the constraints which are present in this theory prevent it from admitting the flat and closed FRW models as its cosmological solutions, for the open FRW universe it is not the case. We have shown that, either in the absence of matter or in the presence of a perfect fluid, the classical field equations of such a theory adopt physical solutions for the open FRW model, in which the mass term shows itself as a cosmological constant. These classical solutions consist of two distinguishable branches: One is a contacting universe which tends to a future singularity with zero size, while another is an expanding universe having a past singularity from which it begins its evolution. A classically forbidden region separates these two branches from each other. We then employ the familiar canonical quantization procedure in the given cosmological setting to find the cosmological wave functions. We use the resulting wave function to investigate the possibility of the avoidance of classical singularities due to quantum effects. It is shown that the quantum expectation values of the scale factor, although they have either contracting or expanding phases like their classical counterparts, are not disconnected from each other. Indeed, the classically forbidden region may be replaced by a bouncing period in which the scale factor bounces from the contraction to its expansion eras. Using the Bohmian approach of quantum mechanics, we also compute the Bohmian trajectory and the quantum potential related to the system, which their analysis shows are the direct effects of the mass term on the dynamics of the universe.

Vakili, Babak; Khosravi, Nima

2012-04-01

142

Cooling of quantum systems through optimal control and dissipation

NASA Astrophysics Data System (ADS)

Based on an exact non-Markovian open systems quantum dynamics, we demonstrate how to reduce the entropy of an open system through a cooperative effect of driving and dissipation. We illustrate the controlled dynamics in phase space in terms of Wigner functions and discuss the applicability of approximate approaches using master equations.

Schmidt, Rebecca; Rohrer, Selina; Ankerhold, Joachim; Stockburger, Jürgen T.

2012-11-01

143

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

144

ERIC Educational Resources Information Center

The purpose of this paper is focused toward a systems understanding of the contemporary university, the American University being the data base. A general systems conceptualization called the open systems university is presented. Comprehensive and generic in character, it is hoped that the theory of the open university will be viable enough to…

Counelis, James Steve

145

NASA Astrophysics Data System (ADS)

The recently proposed coupled channel density matrix (CCDM) method for nondissipative dynamics [L. Pesce and P. Saalfrank, Chem. Phys. 219, 43 (1997)], is extended to open quantum systems. This method, which is the density matrix analogue of the coupled channel wave packet (CCWP) method in Schrödinger wave mechanics, allows for the solution of nuclear Liouville-von Neumann equations in more than one dimension including unbound modes. A semiphenomenological, Markovian, and trace-conserving dissipative model within the dynamical semigroup approach is suggested, and efficient numerical schemes for its implementation are presented. Using a two-mode model, we apply the dissipative CCDM method to the problem of vibrationally excited gas-phase hydrogen molecules, relaxing during the scattering from a cold, metallic, and nondissociative surface. The significance of a relaxation mechanism based on electron-hole pair creation in a metallic substrate is addressed. The dependence of the survival probability of the vibrationally excited molecules on the dissipative model parameters, on their initial translational energy, and on isotopic substitution is examined and rationalized on the basis of a simple classical kinetic model.

Pesce, Lorenzo; Saalfrank, Peter

1998-02-01

146

Quantum Phase Transitions in Random Spin Systems

We report a systematic numerical study of quantum critical phenomena in random spin systems. At zero temperature, quantum phase transitions in these systems are caused by the interplay of quantum fluctuations and ordering interactions with built-in quenched randomness. As demonstrated in the one dimensional case, random quantum spin systems show unusual critical behavior as compared to classical systems. In this

Muyu Guo

1995-01-01

147

Macroscopic quantum effects in Josephson systems

Macroscopic quantum effects in Josephson systems have attracted great interest in the scientific community both for the physics involved and in view of applications. We present data on macroscopic quantum tunneling on Josephson junctions. Actually the most fascinating topic is the observation of macroscopic quantum coherence in rf-SQUID. This effect also has implications for quantum computing, because a quantum two-state

Valentina Corato; Emanuela Esposito; Carmine Granata; Antonia Monaco; Berardo Ruggiero; Maurizio Russo; Leo Stodolsky; Paolo Silvestrini

2001-01-01

148

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

149

Quantum Physical Symbol Systems

Today's theories of computing and machine learning developed within a nineteenth-century mechanistic mindset. Although digital computers would be impossible without quantum physics, their physical and logical architecture is based on the view of a computer as an automaton executing pre-programmed sequences of operations exactly as instructed. Recent innovations in representations and algorithms suggest that a shift in viewpoint may be

Kathryn Blackmond Laskey

2006-01-01

150

Classical and quantum discrete time integrable systems

NASA Astrophysics Data System (ADS)

The standard objects of quantum integrable systems are identified with elements of classical nonlinear integrable difference equations. Functional relation for commuting quantum transfer matrices of quantum integrable models is shown to coincide with classical Hirota's bilinear difference equation. This equation is equivalent to the completely discretized classical 2D Toda lattice with open boundaries. Elliptic solutions of Hirota's equation give complete set of eigenvalues of the quantum transfer matrices. Eigenvalues of Baxter's Q-operator are solutions to the auxiliary linear problems for classical Hirota's equation. The elliptic solutions relevant to Bethe ansatz are studied. The nested Bethe ansatz equations for Ak-1-type models appear as discrete time equations of motions for zeros of classical ?- functions and Baker-Akhiezer functions. Determinant representations of the general solution to bilinear discrete Hirota's equation are analysed and a new determinant formula for eigenvalues of the quantum transfer matrices is obtained. Difference equations for eigenvalues of the Q-operators which generalize Baxter's three-term T-Q-relation are derived.

Lipan, Ovidiu-Zeno

151

On the resistance of relativistic quantum cryptography in open space at finite resources

NASA Astrophysics Data System (ADS)

The security of keys for the basic nonrelativistic BB84 protocol has been examined for more than 15 years. A simple proof of security for the case of a single-photon source of quantum states and finite sequences has been only recently obtained using entropy uncertainty relations. However, the existing sources of states are not strictly single-photon. Since sources are not single-photon and losses in a quantum channel—open space—are not a priori known and vary, nonrelativistic quantum cryptographic systems in open space cannot guarantee the unconditional security of keys. Recently proposed relativistic quantum cryptography removes fundamental constraints associated with non-single-photon sources and losses in open space. The resistance of a fundamentally new family of protocols for relativistic quantum key distribution through open space has been analyzed for the real situation with finite lengths of transmitted sequences of quantum states. This system is stable with real sources of non-single-photon states (weakened laser radiation) and arbitrary losses in open space.

Molotkov, S. N.

2012-11-01

152

Open Source Physics Curricular Material for Quantum Mechanics

NSDL National Science Digital Library

The Open Source Physics Curricular Material paper describes the interactive curricular material created as part of the Open Source Physics project for the teaching and learning of quantum mechanics. Here we focus on the measurement and time evolution of two-state superpositions in the context of bound states and spin.

Belloni, Mario; Christian, Wolfgang; Brown, Douglas

2008-05-30

153

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

154

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

2010-04-27

155

NASA Astrophysics Data System (ADS)

The primary focus of this work is the development of a mid-infrared pulse shaping system. The primary motivation for this system is for two-dimensional infrared (2DIR) spectroscopy, however, the mid-infrared pulse shaper also allows for more sophisticated spectroscopic experiments not previously attempted in the mid-infrared. Moreover, many can be implemented without changes or realignment of the optical setup. Example spectra are presented along with a discussion of capabilities and diagnostics. A second major project presented is 2DIR spectroscopy of iron pentacarbonyl, Fe(CO)5, a small metal carbonyl. This molecule undergoes Berry pseudorotation, a form of fluxtionality. This fast exchange of ligands mixes axial and equatorial modes and occurs on a timescale of picoseconds, too fast for NMR and other methods of measuring chemical structure and isomerization. Ultrafast chemical exchange spectroscopy, a measurement within 2DIR spectroscopy, is capable of resolving the time scales of this motion. We found that this process is affected by the solvent environment, specifically the solvent viscosity in alkanes and hydrogen bonding environments in alcohols. Lastly, a study is presented in which a series of synthetic metalloenzymes with a metal active site are studied by 2DIR spectroscopy. In this case a carbonyl is ligated to a copper-I atom in the active site, which then serves as our spectroscopic probe. We find, unexpectedly, that the shape of the carbonyl vibrational potential, as measured by the anharmonicity, is

Ross, Matthew R.

156

The decay of coherence when a quantum system interacts with a much larger environment is usually described by a master equation for the system reduced density matrix and emphasizes the evolution of an entire ensemble. We consider two methods that have been developed recently to simulate the evolution of single realizations. Quantum-state diffusion involves both diffusion, where the individual quantum

B. M. Garraway; P. L. Knight

1994-01-01

157

Open quantum dots in graphene: Scaling relativistic pointer states

NASA Astrophysics Data System (ADS)

Open quantum dots provide a window into the connection between quantum and classical physics, particularly through the decoherence theory, in which an important set of quantum states are not "washed out" through interaction with the environment-the pointer states provide connection to trapped classical orbits which remain stable in the dots. Graphene is a recently discovered material with highly unusual properties. This single layer, one atom thick, sheet of carbon has a unique bandstructure, governed by the Dirac equation, in which charge carriers imitate relativistic particles with zero rest mass. Here, an atomic orbital-based recursive Green's function method is used for studying the quantum transport. We study quantum fluctuations in graphene and bilayer graphene quantum dots with this recursive Green's function method. Finally, we examine the scaling of the domiant fluctuation frequency with dot size.

Ferry, D. K.; Huang, L.; Yang, R.; Lai, Y.-C.; Akis, R.

2010-04-01

158

Microwave quantum optics with an artificial atom in one-dimensional open space

NASA Astrophysics Data System (ADS)

We address recent advances in microwave quantum optics with artificial atoms in one-dimensional (1D) open space. This field relies on the fact that the coupling between a superconducting artificial atom and propagating microwave photons in a 1D open transmission line can be made strong enough to observe quantum coherent effects, without using any cavity to confine the microwave photons. We investigate the scattering properties in such a system with resonant coherent microwaves. We observe the strong nonlinearity of the artificial atom and under strong driving we observe the Mollow triplet. By applying two resonant tones, we also observe the Autler-Townes splitting. Exploiting these effects, we demonstrate two quantum devices at the single-photon level in the microwave regime: the single-photon router and the photon-number filter. These devices provide important steps toward the realization of an on-chip quantum network.

Hoi, Io-Chun; Wilson, C. M.; Johansson, Göran; Lindkvist, Joel; Peropadre, Borja; Palomaki, Tauno; Delsing, Per

2013-02-01

159

This paper is part of a series of papers invited by the IEEE POWER CONTROL CENTER WORKING GROUP concerning the changing designs of modern control centers. Papers invited by the Working Group discuss the following issues: Benefits of Openness, Criteria for Evaluating Open EMS Systems, Hardware Design, Configuration Management, Security, Project Management, Databases, SCADA, Inter- and Intra-System Communications and Man-Machine Interfaces,'' The goal of this paper is to provide an introduction to the issues pertaining to Open Systems and Databases.'' The intent is to assist understanding of some of the underlying factors that effect choices that must be made when selecting a database system for use in a control room environment. This paper describes and compares the major database information models which are in common use for database systems and provides an overview of SQL. A case for the control center community to follow the workings of the non-formal standards bodies is presented along with possible uses and the benefits of commercially available databases within the control center. The reasons behind the emergence of industry supported standards organizations such as the Open Software Foundation (OSF) and SQL Access are presented.

Martire, G.S. (ECC, Inc., Fairfax, VA (United States)); Nuttall, D.J.H. (Unified Information, Inc., Kirkland, WA (United States))

1993-05-01

160

Classical and quantum correlative capacities of quantum systems

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

Li Nan; Luo Shunlong [Academy of Mathematics and Systems Science, Chinese Academy of Sciences, 100190 Beijing (China)

2011-10-15

161

Feedback control of linear quantum optical systems

This paper studies feedback quantum control of a class of linear quantum optical systems by means of squeezing and phase modulation. A new quadrature representation of such systems is introduced, which includes explicitly phase modulation of light fields involved. Some fundamental relations are derived in terms of the new quadrature representation. The coherent quantum LQG control studied in (17) is

Hu Zhang; Guofeng Zhang; Daoyi Dong; Bo Huang; H. W. J. Lee

2011-01-01

162

Adiabatic approximation for weakly open systems

We generalize the adiabatic approximation to the case of open quantum systems, in the joint limit of slow change and weak open system disturbances. We show that the approximation is 'physically reasonable' as under wide conditions it leads to a completely positive evolution, if the original master equation can be written on a time-dependent Lindblad form. We demonstrate the approximation for a non-Abelian holonomic implementation of the Hadamard gate, disturbed by a decoherence process. We compare the resulting approximate evolution with numerical simulations of the exact equation.

Thunstroem, Patrik; Aaberg, Johan; Sjoeqvist, Erik [Department of Quantum Chemistry, Uppsala University, Box 518, SE-751 20 Uppsala (Sweden)

2005-08-15

163

Critical Stability in Quantum Systems

In the frame of non-relativistic quantum mechanics we discuss the systems of N particles, whose energy is close to that of the dissociation threshold. We show that in systems, where a long-range repulsion acts between the dissociation fragments, there is a super-size blocking, i.e. the halo structures in these systems do not appear. We discuss the connection between bound states at the threshold and spreading and derive the conditions on pair potentials, which guarantee the super-size blocking. Under minor assumptions we prove that negative atomic ions have a bound state at the threshold when the charge of the nucleus is critical.

Gridnev, Dmitry K. [Kassel University, Institut fuer Theoretische Physik, 34132 Kassel (Germany)

2008-04-03

164

Supersymmetric biorthogonal quantum systems

We discuss supersymmetric biorthogonal systems, with emphasis given to the periodic solutions that occur at spectral singularities of PT symmetric models. For these periodic solutions, the dual functions are associated polynomials that obey inhomogeneous equations. We construct in detail some explicit examples for the supersymmetric pairs of potentials V{sub {+-}}(z)=-U(z){sup 2}{+-}z(d/dz)U(z) where U(z){identical_to}{sigma}{sub k>0}{upsilon}{sub k}z{sup k}. In particular, we consider the cases generated by U(z)=z and z/(1-z). We also briefly consider the effects of magnetic vector potentials on the partition functions of these systems.

Curtright, Thomas; Mezincescu, Luca; Schuster, David [Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States) and School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States)

2007-09-15

165

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

NASA Astrophysics Data System (ADS)

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

Radtke, T.; Fritzsche, S.

2007-05-01

166

Global quantum discord in multipartite systems

We propose a global measure for quantum correlations in multipartite systems, which is obtained by suitably recasting the quantum discord in terms of relative entropy and local von Neumann measurements. The measure is symmetric with respect to subsystem exchange and is shown to be nonnegative for an arbitrary state. As an illustration, we consider tripartite correlations in the Werner-GHZ (Greenberger-Horne-Zeilinger) state and multipartite correlations at quantum criticality. In particular, in contrast with the pairwise quantum discord, we show that the global quantum discord is able to characterize the infinite-order quantum phase transition in the Ashkin-Teller spin chain.

Rulli, C. C.; Sarandy, M. S. [Instituto de Fisica, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, Gragoata, 24210-346 Niteroi, RJ (Brazil)

2011-10-15

167

Non-Markovian fermionic stochastic Schrödinger equation for open system dynamics

NASA Astrophysics Data System (ADS)

This paper presents an exact Grassmann stochastic Schrödinger equation for the dynamics of an open fermionic quantum system coupled to a reservoir consisting of a finite or infinite number of fermions. We use this stochastic Schrödinger equation as a generic open system tool to derive the exact master equation for an electronic system strongly coupled to fermionic reservoirs. The generality and applicability of this Grassmann stochastic approach are justified and exemplified by several quantum fermionic system problems concerning quantum coherence coupled to vacuum or finite-temperature fermionic reservoirs. Our studies show that the quantum coherence property of a quantum dot system can be profoundly modified by the environmental memory.

Shi, Wufu; Zhao, Xinyu; Yu, Ting

2013-05-01

168

Theory of dephasing by external perturbation in open quantum dots

We propose a random matrix theory describing the influence of a time\\u000adependent external field on the average magnetoresistance of open quantum dots.\\u000aThe effect is taken into account in all orders of perturbation theory, and the\\u000aresult is applicable to both weak and strong external fields.

Maxim G. Vavilova; Igor L. Aleiner

1999-01-01

169

Open Source Physics Curricular Material for Quantum Mechanics

Much of the difficulty in learning advanced concepts in quantum mechanics comes from trying to visualize abstract problems. This article addresses the situation with interactive curricular material created as part of the open source physics project. In particular, the authors focus on the measurement and time evolution of two-state superpositions in the context of bound states and spin.

Mario Belloni; Wolfgang Christian; Douglas Brown

2007-01-01

170

Bethe Ansatz and open spin-½ XXZ quantum spin chain

The open spin-½ XXZ quantum spin chain with general integrable boundary terms is a fundamental integrable model. Finding a Bethe Ansatz solution for this model has been a subject of intensive research for many years. Such solutions for other simpler spin chain models have been shown to be essential for calculating various physical quantities, e.g., spectrum, scattering amplitudes, finite size

Rajan Murgan

2008-01-01

171

Opening up three quantum boxes causes classically undetectable wavefunction collapse

One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained as the back-action required by quantum mechanics adding quantum noise to a classical signal. Here, we implement the “three-box” quantum game [Aharonov Y, et al. (1991) J Phys A Math Gen 24(10):2315–2328] by using state-of-the-art control and measurement of the nitrogen vacancy center in diamond. In this protocol, the back-action of quantum measurements adds no detectable disturbance to the classical description of the game. Quantum and classical mechanics then make contradictory predictions for the same experimental procedure; however, classical observers are unable to invoke measurement-induced disturbance to explain the discrepancy. We quantify the residual disturbance of our measurements and obtain data that rule out any classical model by ?7.8 standard deviations, allowing us to exclude the property of macroscopic state definiteness from our system. Our experiment is then equivalent to the test of quantum noncontextuality [Kochen S, Specker E (1967) J Math Mech 17(1):59–87] that successfully addresses the measurement detectability loophole.

George, Richard E.; Robledo, Lucio M.; Maroney, Owen J. E.; Blok, Machiel S.; Bernien, Hannes; Markham, Matthew L.; Twitchen, Daniel J.; Morton, John J. L.; Briggs, G. Andrew D.; Hanson, Ronald

2013-01-01

172

Forecasting of open system behaviour

Two dynamic models of the forecasted behaviour of an open thermodynamic system under given expected variations in the open system behaviour have been obtained. The two dynamic models have been presented as two machines. Each machine is made up of a closed system, which is obtained from the open one by isolation, and an environment. The first machine is driven

S. Z. Stefanov

1997-01-01

173

Measures of macroscopicity for quantum spin systems

NASA Astrophysics Data System (ADS)

We investigate the notion of ‘macroscopicity’ in the case of quantum spin systems and provide two main results. Firstly, we motivate the quantum Fisher information as a measure of the macroscopicity of quantum states. Secondly, we make a comparison with the existing literature on this topic. We report on a hierarchy among the measures and we conclude that one should carefully distinguish between ‘macroscopic quantum states’ and ‘macroscopic superpositions’, which is a strict subclass of the former.

Fröwis, Florian; Dür, Wolfgang

2012-09-01

174

Antiadiabatic control of Many Body Quantum Systems

Classical control theory has played a major role in the development of\\u000apresent-day technologies. Likewise, recently developed quantum optimal control\\u000amethods can be applied to emerging quantum technologies, e.g. quantum\\u000ainformation processing -- until now, at the level of a few qubits. However,\\u000asuch methods encounter severe limits when applied to many-body quantum systems:\\u000adue to the complexity of simulating

Patrick Doria; Tommaso Calarco; Simone Montangero

2010-01-01

175

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 [ital decohere], which means that there is negligible quantum interference between the individual histories in the set. 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 the noise consisting of the fluctuations that typical mechanisms of decoherence produce. We describe the derivation of phenomenological equations of motion explicitly for a particular class of models.

Gell-Mann, M. (Theoretical Astrophysics Group (T-6), Los Alamos National Laboratory, Los Alamos, New Mexico 87545) (United States) (Santa Fe Institute, 1660 Old Pecos Trail, Santa Fe, New Mexico 87501); Hartle, J.B. (Department of Physics, University of California enSanta Barbara, Santa Barbara, (California) 93106)

1993-04-15

176

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

177

Relativistic quantum Darwinism in Dirac fermion and graphene systems

NASA Astrophysics Data System (ADS)

We solve the Dirac equation in two spatial dimensions in the setting of resonant tunneling, where the system consists of two symmetric cavities connected by a finite potential barrier. The shape of the cavities can be chosen to yield both regular and chaotic dynamics in the classical limit. We find that certain pointer states about classical periodic orbits can exist, which are signatures of relativistic quantum Darwinism (RQD). These localized states suppress quantum tunneling, and the effect becomes less severe as the underlying classical dynamics in the cavity is chaotic, leading to regularization of quantum tunneling. Qualitatively similar phenomena have been observed in graphene. A physical theory is developed to explain relativistic quantum Darwinism and its effects based on the spectrum of complex eigenenergies of the non-Hermitian Hamiltonian describing the open cavity system.

Ni, Xuan; Huang, Liang; Lai, Ying-Cheng; Pecora, Louis

2012-02-01

178

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. 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 Maple environment). Especially

Radtke, T.; Fritzsche, S.

2008-11-01

179

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

180

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

181

Past Quantum States of a Monitored System

NASA Astrophysics Data System (ADS)

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

Gammelmark, Søren; Julsgaard, Brian; Mølmer, Klaus

2013-10-01

182

Hybrid quantum systems of atoms and ions

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

183

Communication Theory of Quantum Systems.

National Technical Information Service (NTIS)

The primary concern in this research is with communication theory problems incorporating quantum effects for optical-frequency applications. Under suitable conditions, a unique quantum channel model corresponding to a given calssical space-time varying li...

H. P. H. Yuen

1971-01-01

184

Open Systems Approach to Supportability.

National Technical Information Service (NTIS)

The open systems approach is both a technical approach to weapons systems engineering and a preferred business strategy that is becoming widely applied by manufacturers of large complex systems. Today, legacy systems continue to be developed with their ow...

A. G. Larson C. K. Banning J. F. Leonard

2002-01-01

185

National Technical Information Service (NTIS)

An open system is a system whose behavior is jointly determined by its internal structure and by the input it receives from the environment. To solve control and verification problem open systems have often been modeled as games between the System and the...

L. de Alfaro

2006-01-01

186

Control of Linear Quantum Stochastic Systems

The purpose of this paper is to formulate and solve a H infin controller synthesis problem for a class of noncommutative linear stochastic systems which includes many examples of interest in quantum technology. The paper includes results on the class of such systems for which the quantum commutation relations are preserved (such a requirement must be satisfied in a physical

Matthew R. James; Hendra I. Nurdin; Ian R. Petersen

2008-01-01

187

H ? Control of Linear Quantum Stochastic Systems

The purpose of this paper is to formulate and solve a H1 controller synthesis problem for a class of non-commutative linear stochastic systems which includes many examples of interest in quantum technology. The paper includes results on the class of such systems for which the quantum commutation relations are preserved (such a requirement must be satisfied in a physica l

Matthew R. James; Hendra I. Nurdin; Ian R. Petersen

188

Controlling the Shannon Entropy of Quantum Systems

This paper proposes a new quantum control method which controls the Shannon entropy of quantum systems. For both discrete and continuous entropies, controller design methods are proposed based on probability density function control, which can drive the quantum state to any target state. To drive the entropy to any target at any prespecified time, another discretization method is proposed for the discrete entropy case, and the conditions under which the entropy can be increased or decreased are discussed. Simulations are done on both two- and three-dimensional quantum systems, where division and prediction are used to achieve more accurate tracking.

Xing, Yifan; Wu, Jun

2013-01-01

189

Charge pumping and photovoltaic effect in open quantum dots

We propose a random matrix theory to describe the influence of a\\u000atime-dependent external field on electron transport through open quantum dots.\\u000aWe describe the generation of the current by an oscillating field for the dot,\\u000aconnected to two leads with equal chemical potentials. For low frequency fields\\u000aour results correspond to adiabatic charge pumping. Finite current can be\\u000aproduced

Maxim G. Vavilov; Vinay Ambegaokar; Igor L. Aleiner

2001-01-01

190

Quantum phenomena in condensed phase systems

NASA Astrophysics Data System (ADS)

This thesis develops mixed quantum-classical methods to model dynamical nonequilibrium quantum phenomena in condensed phase systems, and also explores properties of 2-d systems near a quantum critical point using field theoretic techniques and purely classical simulation. Mixed quantum-classical methods involve dividing the system into a quantum sub-system coupled to a classical bath, which is useful for examining the dynamics of systems in the condensed phase since the full quantum treatment of a large number of degrees of freedom is often computationally infeasible. Although the bath is treated classically, its coupling to the quantum system precludes a Newtonian description. We implement an approach that uses the quantum-classical Liouville equation to propagate the quantum subsystem density matrix, which results in an ensemble of surface-hopping trajectories. We test this method on model systems and compare with a linearized path-integral approach. We also develop a novel approach to propagating the reduced density matrix that incorporates ideas from both methods while maintaining the ease of implementation of linearized methods. We study the 2-d spin gap antiferromagnet, piperanzium hexachlorodicuprate (PHCC) near a quantum critical point, where the spin gap is closed by an applied magnetic field, and excitations behave like Sz = 1 bosons. Using field theoretic techniques, we find that the temperature dependence of the propagating mode energy is successfully described by a self-consistent Hartree-Fock theory of spin excitations. We also investigate the thermally excited 2-d dilute Bose gas near a quantum critical point, which can be used to obtain the dynamic spectrum of PHCC and other 2-d antiferromagnets. While the pairwise interactions between bosons are weak, we find that the collective properties pose a strong coupling problem (in contrast to the 3-d case). We describe these interactions effectively with a classical model.

Dunkel, Emily Rebecca

191

Optimized control of multistate quantum systems by composite pulse sequences

We introduce a technique for derivation of high-fidelity composite pulse sequences for two types of multistate quantum systems: systems with the SU(2) and Morris-Shore dynamic symmetries. For the former type, we use the Majorana decomposition to reduce the dynamics to an effective two-state system, which allows us to find the propagator analytically and use the pool of available composite pulses for two-state systems. For the latter type of multistate systems, we use the Morris-Shore decomposition, which reduces the multistate dynamics to a set of two-state systems. We present examples which demonstrate that the multistate composite sequences open a variety of possibilities for coherent control of quantum systems with multiple states.

Genov, G. T.; Vitanov, N. V. [Department of Physics, Sofia University, James Bourchier 5 Boulevard, BG-1164 Sofia (Bulgaria); Torosov, B. T. [Department of Physics, Sofia University, James Bourchier 5 Boulevard, BG-1164 Sofia (Bulgaria); Institute of Solid State Physics, Bulgarian Academy of Sciences, Tsarigradsko chaussee 72, BG-1784 Sofia (Bulgaria)

2011-12-15

192

The SU(2) Semi Quantum Systems Dynamics and Thermodynamics

NASA Astrophysics Data System (ADS)

The dynamical description of a semi quantum nonlinear systems whose classical limit is not chaotic is still an open question. These systems are characterized by mixing a classical system with a quantum-mechanical one. As some of them lead to an irregular dynamics, the name "semi quantum chaos" arises. In this contribution we study two different Hamiltonians through the Maximum Entropy Principle Approach (MEP). Taking advantage of the MEP formalism, it can be clearly established that the Hamiltonians belonging to the SU(2) Lie algebra have common properties and a common treatment can be developed for them. These Hamiltonians resemble a quantum spin system coupled to a classical cavity. In the present contribution, we show that all of them share the generalized uncertainty principle as an invariant of the motion and other invariants as well. Two different classical potentials V(q) have been studied. Their specific heat are evaluated in terms of the extensive (mean values) and the intensive (Lagrange multipliers) variables. The main result of the present contribution is to show that the specific heat of these systems can be fixed independently of the temperature by setting only the initial conditions on the extensive or intensive variables, as well as the value of the quantum-classical coupling parameter. It could be possible to infer that this result can be extended to generalized forms for the V(q) classical potential.

Sarris, C. M.; Proto, A. N.

2011-03-01

193

The SU(2) Semi Quantum Systems Dynamics and Thermodynamics

NASA Astrophysics Data System (ADS)

The dynamical description of a semi quantum nonlinear systems whose classical limit is not chaotic is still an open question. These systems are characterized by mixing a classical system with a quantum-mechanical one. As some of them lead to an irregular dynamics, the name "semi quantum chaos" arises. In this contribution we study two different Hamiltonians through the Maximum Entropy Principle Approach (MEP). Taking advantage of the MEP formalism, it can be clearly established that the Hamiltonians belonging to the SU(2) Lie algebra have common properties and a common treatment can be developed for them. These Hamiltonians resemble a quantum spin system coupled to a classical cavity. In the present contribution, we show that all of them share the generalized uncertainty principle as an invariant of the motion and other invariants as well. Two different classical potentials V(q) have been studied. Their specific heat are evaluated in terms of the extensive (mean values) and the intensive (Lagrange multipliers) variables. The main result of the present contribution is to show that the specific heat of these systems can be fixed independently of the temperature by setting only the initial conditions on the extensive or intensive variables, as well as the value of the quantum-classical coupling parameter. It could be possible to infer that this result can be extended to generalized forms for the V(q) classical potential.

Sarris, C. M.; Proto, A. N.

194

Accidental degeneracies in nonlinear quantum deformed systems

NASA Astrophysics Data System (ADS)

We construct a multi-parameter nonlinear deformed algebra for quantum confined systems that includes many other deformed models as particular cases. We demonstrate that such systems exhibit the property of accidental pairwise energy level degeneracies. We also study, as a special case of our multi-parameter deformation formalism, the extension of the Tamm-Dancoff cutoff deformed oscillator and the occurrence of accidental pairwise degeneracy in the energy levels of the deformed system. As an application, we discuss the case of a trigonometric Rosen-Morse potential, which is successfully used in models for quantum confined systems, ranging from electrons in quantum dots to quarks in hadrons.

Aleixo, A. N. F.; Balantekin, A. B.

2011-09-01

195

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

2012-08-22

196

Escape of quantum particles from an open cavity

A negative ion irradiated by a laser provides a coherent source of electrons propagating out from the location of the negative ion. The total escape rates of the electrons when the negative ion is placed inside an open cavity in the shape of a wedge are studied. It is shown that the wedge induces significant oscillations in the total escape rates because of quantum interference effects. In particular, it is shown that, for a wedge with an opening angle of {pi}/N, where N is an arbitrary positive integer, there are (2N-1) induced oscillations in the rates. As a demonstration, the case for a wedge with an opening angle {pi}/5 is calculated and analyzed in detail.

Zhao, H. J. [School of Physics and Information Science, Shanxi Normal University, Linfen 041004 (China); Du, M. L. [Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100080 (China)

2011-07-15

197

Quantum Backaction Noise Cancellation for Linear Systems

NASA Astrophysics Data System (ADS)

We show that it is always possible to convert a dissipationless linear sensor system under quantum nondemolition measurements into a backaction-evading one using the technique of quantum noise cancellation. This result generalizes our earlier work on optomechanical sensors [Tsang and Caves, Phys. Rev. Lett. 105, 123601 (2010)].

Tsang, Mankei

2011-10-01

198

The classical limit of quantum spin systems

We derive a classical integral representation for the partition function,ZQ, of a quantum spin system. With it we can obtain upper and lower bounds to the quantum free energy (or ground state energy) in terms of two classical free energies (or ground state energies). These bounds permit us to prove that when the spin angular momentumJ ? 8 (but after

Elliott H. Lieb

1973-01-01

199

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

200

Quantum effects in optomechanical systems

The search for experimental demonstrations of the quantum behavior of macroscopic mechanical resonators is a fastly growing field of investigation and recent results suggest that the generation of quantum states of resonators with a mass at the microgram scale is within reach. In this chapter we give an overview of two important topics within this research field: cooling to the

C. Genes; A. Mari; D. Vitali; P. Tombesi

2009-01-01

201

Quantum Optics of Linear Systems

The classical Jones calculus for optical networks is utilized to formulate a general theory of transfer of quantum fields through a linear quantum optics device. For input fields having Gaussian quasi-distribution functions, the output distributions can be calculated explicitly. The formalism is applied to the simple beam splitter as an illustration.

Stig Stenholm

1994-01-01

202

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

203

Quantum teleportation and entanglement swapping for systems of arbitrary spin

Summary form only given. We consider quantum teleportation and entanglement swapping for systems of arbitrary spin j ? 1\\/2. Spin quantum teleportation and entanglement swapping enable quantum state transfer between distant material systems, as well as being important for quantum network operations built on qubit elements. We identify an appropriate entangled resource state for high-fidelity spin quantum teleportation, and, in

D. W. Berry; B. C. Sanders

2002-01-01

204

Quantum correlations in a clusterlike system

We discuss a clusterlike one-dimensional system with triplet interaction. We study the topological properties of this system. We find that the degeneracy depends on the topology of the system and is well protected against external local perturbations. All these facts show that the system is topologically ordered. We also find a string order parameter to characterize the quantum phase transition. Besides, we investigate two-site correlations including entanglement, quantum discord, and mutual information. We study the different divergence behaviors of the correlations. The quantum correlation decays exponentially in both topological and magnetic phases, and diverges in reversed power law at the critical point. And we find that in topological order systems, the global difference of topology induced by dimension can be reflected in local quantum correlations.

Chen Yixin; Li Shengwen [Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China); Yin Zhi [Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China); College of Science, Ningbo University of Technology, Ningbo 315000 (China)

2010-11-15

205

Novel systems and methods for quantum communication, quantum computation, and quantum simulation

NASA Astrophysics Data System (ADS)

Precise control over quantum systems can enable the realization of fascinating applications such as powerful computers, secure communication devices, and simulators that can elucidate the physics of complex condensed matter systems. However, the fragility of quantum effects makes it very difficult to harness the power of quantum mechanics. In this thesis, we present novel systems and tools for gaining fundamental insights into the complex quantum world and for bringing practical applications of quantum mechanics closer to reality. We first optimize and show equivalence between a wide range of techniques for storage of photons in atomic ensembles. We describe experiments demonstrating the potential of our optimization algorithms for quantum communication and computation applications. Next, we combine the technique of photon storage with strong atom-atom interactions to propose a robust protocol for implementing the two-qubit photonic phase gate, which is an important ingredient in many quantum computation and communication tasks. In contrast to photon storage, many quantum computation and simulation applications require individual addressing of closely-spaced atoms, ions, quantum dots, or solid state defects. To meet this requirement, we propose a method for coherent optical far-field manipulation of quantum systems with a resolution that is not limited by the wavelength of radiation. While alkali atoms are currently the system of choice for photon storage and many other applications, we develop new methods for quantum information processing and quantum simulation with ultracold alkaline-earth atoms in optical lattices. We show how multiple qubits can be encoded in individual alkaline-earth atoms and harnessed for quantum computing and precision measurements applications. We also demonstrate that alkaline-earth atoms can be used to simulate highly symmetric systems exhibiting spin-orbital interactions and capable of providing valuable insights into strongly correlated physics of transition metal oxides, heavy fermion materials, and spin liquid phases. While ultracold atoms typically exhibit only short-range interactions, numerous exotic phenomena and practical applications require long-range interactions, which can be achieved with ultracold polar molecules. We demonstrate the possibility to engineer a repulsive interaction between polar molecules, which allows for the suppression of inelastic collisions, efficient evaporative cooling, and the creation of novel phases of polar molecules.

Gorshkov, Alexey Vyacheslavovich

206

Skyrmions in Quantum Hall Systems

NASA Astrophysics Data System (ADS)

We discuss the finite density properties of baby- and Quantum-Hall Skyrmions, using a thermodynamic approach, and a related simulated annealing technique. We show how we can find similar behaviour in both models, and also discuss possible extensions.

Walet, Niels R.; Schwindt, Oliver; Weidig, Tom

2002-12-01

207

Ergodic properties of quantum conservative systems

In this paper we discuss the ergodic properties of quantum conservative systems by analyzing the behavior of two different models. Despite their intrinsic differencies they both show localization effects in analogy to the dynamical localization found in Kicked Rotator.

Fausto Borgonovi; Giulio Casati

1997-01-01

208

Effective constraints for relativistic quantum systems

NASA Astrophysics Data System (ADS)

Determining the physical Hilbert space is often considered the most difficult but crucial part of completing the quantization of a constrained system. In such a situation it can be more economical to use effective constraint methods, which are extended here to relativistic systems as they arise for instance in quantum cosmology. By sidestepping explicit constructions of states, such tools allow one to arrive much more feasibly at results for physical observables at least in semiclassical regimes. Several questions discussed recently regarding effective equations and state properties in quantum cosmology, including the spreading of states and quantum backreaction, are addressed by the examples studied here.

Bojowald, Martin; Tsobanjan, Artur

2009-12-01

209

Effective constraints for relativistic quantum systems

Determining the physical Hilbert space is often considered the most difficult but crucial part of completing the quantization of a constrained system. In such a situation it can be more economical to use effective constraint methods, which are extended here to relativistic systems as they arise for instance in quantum cosmology. By sidestepping explicit constructions of states, such tools allow one to arrive much more feasibly at results for physical observables at least in semiclassical regimes. Several questions discussed recently regarding effective equations and state properties in quantum cosmology, including the spreading of states and quantum backreaction, are addressed by the examples studied here.

Bojowald, Martin; Tsobanjan, Artur [Institute for Gravitation and the Cosmos, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States)

2009-12-15

210

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.

Sun, Jitao; Lin, Hai

2013-01-01

211

Entanglement and dephasing of quantum dissipative systems

The von Neumann entropy of various quantum dissipative models is calculated in order to discuss the entanglement properties of these systems. First, integrable quantum dissipative models are discussed, i.e., the quantum Brownian motion and the quantum harmonic oscillator. In the case of the free particle, the related entanglement of formation shows no nonanalyticity. In the case of the dissipative harmonic oscillator, there is a nonanalyticity at the transition of underdamped to overdamped oscillations. We argue that this might be a general property of dissipative systems. We show that similar features arise in the dissipative two-level system and study different regimes using sub-Ohmic, Ohmic, and super-Ohmic baths, within a scaling approach.

Stauber, T.; Guinea, F. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain)

2006-04-15

212

Isoperiodic classical systems and their quantum counterparts

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

Asorey, M. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza (Spain)]. E-mail: asorey@unizar.es; Carinena, J.F. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza (Spain); Marmo, G. [Dipartimento di Scienze Fisiche, Universita Federico II di Napoli, Via Cintia, 80125 Napoli (Italy); INFN, Sezione di Napoli, Complesso Univ. di Monte Sant'Angelo, Via Cintia, 80125 Naples (Italy); Perelomov, A. [Institute for Theoretical and Experimental Physics, 117259 Moscow (Russian Federation)

2007-06-15

213

Experimental quantum teleportation of a two-qubit composite system

Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication

Qiang Zhang; Alexander Goebel; Claudia Wagenknecht; Yu-Ao Chen; Bo Zhao; Tao Yang; Alois Mair; Jörg Schmiedmayer; Jian-Wei Pan

2006-01-01

214

Robust observer for uncertain linear quantum systems

In the theory of quantum dynamical filtering, one of the biggest issues is that the underlying system dynamics represented by a quantum stochastic differential equation must be known exactly in order that the corresponding filter provides an optimal performance; however, this assumption is generally unrealistic. Therefore, in this paper, we consider a class of linear quantum systems subjected to time-varying norm-bounded parametric uncertainties and then propose a robust observer such that the variance of the estimation error is guaranteed to be within a certain bound. Although in the linear case much of classical control theory can be applied to quantum systems, the quantum robust observer obtained in this paper does not have a classical analog due to the system's specific structure with respect to the uncertainties. Moreover, by considering a typical quantum control problem, we show that the proposed robust observer is fairly robust against a parametric uncertainty of the system even when the other estimators--the optimal Kalman filter and risk-sensitive observer--fail in the estimation.

Yamamoto, Naoki [Physical Measurement and Control 266-33, California Institute of Technology, Pasadena, California 91125 (United States)

2006-09-15

215

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

216

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

217

NASA Astrophysics Data System (ADS)

A heuristic model for particle states and current flow in open ballistic two-dimensional (2D) quantum dots/wave billiards is proposed. The model makes use of complex potentials first introduced in phenomenological nuclear inelastic scattering theory (the optical model). Here we assume that external input and output leads connecting the system to the source and the drain regions may be represented by complex potentials. In this way, a current may be set up between the two 'pseudo-leads'. Probability densities and current flows for an open quantum dot are analyzed here numerically and the results are compared with the microwave measurements used to emulate the system. The model is of conceptual as well as practical interest. In addition to quantum billiards, it may be used as a tool per se to analyze transport in classical wave analogues, such as microwave resonators, acoustic resonators, effects of leakage on such systems, etc.

Berggren, Karl-Fredrik; Yakimenko, Irina I.; Hakanen, Jani

2010-07-01

218

Counterfactual Assessment of Decoherence in Quantum Systems

NASA Astrophysics Data System (ADS)

Quantum Zeno effect occurs when the system is observed for unusually short observation times, t, where the probability of the transition between different quantum states is known to be proportional to t^2. This results in a decrease in the probability of transitions between states and the consequent decrease in decoherence. We consider the conditions in which these observations are made counterfactual to assess whether this results in a significant change in decoherence.

Russo, Onofrio; Jiang, Liang

2013-03-01

219

Transitionless quantum driving for spin systems.

We apply the method of transitionless quantum driving for time-dependent quantum systems to spin systems. For a given Hamiltonian, the driving Hamiltonian is constructed so that the adiabatic states of the original system obey the Schrödinger equation. For several typical systems such as the XY spin chain and the Lipkin-Meshkov-Glick model, the driving Hamiltonian is constructed explicitly. We discuss possible interesting situations when the driving Hamiltonian becomes time independent and when the driving Hamiltonian is equivalent to the original one. For many-body systems, a crucial problem occurs at the quantum phase transition point where the energy gap between the ground and first excited states becomes zero. We discuss how the defect can be circumvented in the present method. PMID:23848637

Takahashi, Kazutaka

2013-06-12

220

Quantum discord in matrix product systems

We consider a class of quantum systems with spin-flip symmetry and derive the quantum correlation measured by the quantum discord (QD). As an illustration, we investigate the QD in a three-body interaction model and an XYZ interaction model, whose ground states can be expressed as matrix product states, and the QD is exactly soluble. We show that the QD behaves differently than the quantum entanglement (QE) in many ways; for example, they may show opposite monotonicity and completely different finite-size effects. Furthermore, we compare the capability of the QD and the QE to detect quantum phase transitions (QPTs) and find that the QD is more reliable than the QE for signaling QPTs in these models: In the three-body interaction model, the QE is singular at the quantum critical point, however, it exhibits an additional singularity in the noncritical region, while the analyticity of the QD can be used to identify the quantum critical point perfectly; and in the XYZ interaction model, the QE vanishes in the thermodynamic limit, thus losing its ability to detect QPTs, while the QD still functions very well.

Sun Zhaoyu; Li Liang; Du Guihuan [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Yao Kailun; Liu Jiwei; Luo Bo; Li Neng; Li Haina [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2010-09-15

221

Incoherent control of locally controllable quantum systems

An incoherent control scheme for state control of locally controllable quantum systems is proposed. This scheme includes three steps: (1) amplitude amplification of the initial state by a suitable unitary transformation, (2) projective measurement of the amplified state, and (3) final optimization by a unitary controlled transformation. The first step increases the amplitudes of some desired eigenstates and the corresponding probability of observing these eigenstates, the second step projects, with high probability, the amplified state into a desired eigenstate, and the last step steers this eigenstate into the target state. Within this scheme, two control algorithms are presented for two classes of quantum systems. As an example, the incoherent control scheme is applied to the control of a hydrogen atom by an external field. The results support the suggestion that projective measurements can serve as an effective control and local controllability information can be used to design control laws for quantum systems. Thus, this scheme establishes a subtle connection between control design and controllability analysis of quantum systems and provides an effective engineering approach in controlling quantum systems with partial controllability information.

Dong Daoyi [Institute of Cyber-Systems and Control, National Laboratory of Industrial Control Technology, Zhejiang University, Hangzhou 310027, People's Republic of China and Institute of Systems Science, AMSS, Chinese Academy of Sciences, Beijing 100190 (China); Zhang Chenbin [Department of Automation, University of Science and Technology of China, Hefei 230027 (China); Rabitz, Herschel; Pechen, Alexander [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Tarn, T.-J. [Department of Electrical and Systems Engineering, Washington University in St. Louis, St. Louis, Missouri 63130 (United States)

2008-10-21

222

Incoherent control of locally controllable quantum systems.

An incoherent control scheme for state control of locally controllable quantum systems is proposed. This scheme includes three steps: (1) amplitude amplification of the initial state by a suitable unitary transformation, (2) projective measurement of the amplified state, and (3) final optimization by a unitary controlled transformation. The first step increases the amplitudes of some desired eigenstates and the corresponding probability of observing these eigenstates, the second step projects, with high probability, the amplified state into a desired eigenstate, and the last step steers this eigenstate into the target state. Within this scheme, two control algorithms are presented for two classes of quantum systems. As an example, the incoherent control scheme is applied to the control of a hydrogen atom by an external field. The results support the suggestion that projective measurements can serve as an effective control and local controllability information can be used to design control laws for quantum systems. Thus, this scheme establishes a subtle connection between control design and controllability analysis of quantum systems and provides an effective engineering approach in controlling quantum systems with partial controllability information. PMID:19045172

Dong, Daoyi; Zhang, Chenbin; Rabitz, Herschel; Pechen, Alexander; Tarn, Tzyh-Jong

2008-10-21

223

Effective noise channels for encoded quantum systems

NASA Astrophysics Data System (ADS)

We investigate effective noise channels for encoded quantum systems with and without active error correction. Noise acting on physical qubits forming a logical qubit is thereby described as a logical noise channel acting on the logical qubits, which leads to a significant decrease of the effective system dimension. This provides us with a powerful tool to study entanglement features of encoded quantum systems. We demonstrate this framework by calculating lower bounds on the lifetime of distillable entanglement and the negativity for encoded multipartite qubit states with different encodings. At the same time, this approach leads to a simple understanding of the functioning of (concatenated) error correction codes.

Kesting, Frederik; Fröwis, Florian; Dür, Wolfgang

2013-10-01

224

Open Forum: The Future of Library Systems

Moderated by Maria Collins of North Carolina State University, discussion at this open forum on the future of library systems touched on open-source library systems, cloud computing, new initiatives by the Open Library Environment (OLE) Project and OCLC, and desired characteristics of future integrated library systems. Most participants had limited experience with next-generation library systems and attended the open forum

Maria Collins; Andrée J. Rathemacher

2010-01-01

225

NASA Astrophysics Data System (ADS)

In contrast to the local perturbation between the Rydberg series with different ionization thresholds, the perturbation between the Rydberg series with the same ionization threshold is not local in energy and acts uniformly throughout the entire series. This study examined whether imposed constancy on the quantum defect parameters by uniform perturbation leads to the isolation of overlapping resonances in the photoionization spectra. Isolation of the resonance eigenchannels by the mathematical technique of condiagonalization was obtained. Diagonalization of a complex non-normal matrix by the biorthogonal sets used by Feshbach and Shore was unsuitable for multichannel quantum defect theory. Using this method, the isolated resonances were found to comprise most of the overlapping resonances in the 2p53s(1P1) ns and 2p53s(1P1) nd autoionization series of sodium attached to the 2p53s(1P1) limit and the 5d96s2(2D5/2)np, nf (J = 1) series of mercury attached to the 5d5/2 limit. However, in the latter case, the cross terms besides the incoherent sum of Beutler-Fano terms contribute significantly to the photoionization cross section. Even the non-isolated resonance part was found to contribute appreciably in the autoionizing series of silver attached to the 4d95s(3D1, 2, 3) limit.

Lee, Chun-Woo

2010-09-01

226

Phase diffusion in quantum dissipative systems

We study the dynamics of the quantum phase distribution associated with the reduced density matrix of a system for a number of situations of practical importance, as the system evolves under the influence of its environment, interacting via a quantum nondemolition type of coupling, such that there is decoherence without dissipation, as well as when it interacts via a dissipative interaction, resulting in decoherence as well as dissipation. The system is taken to be either a two-level atom (or, equivalently, a spin-1/2 system) or a harmonic oscillator, and the environment is modeled as a bath of harmonic oscillators, starting out in a squeezed thermal state. The impact of the different environmental parameters on the dynamics of the quantum phase distribution for the system starting out in various initial states is explicitly brought out. An interesting feature that emerges from our work is that the relationship between squeezing and temperature effects depends on the type of system-bath interaction. In the case of a quantum nondemolition type of interaction, squeezing and temperature work in tandem, producing a diffusive effect on the phase distribution. In contrast, in the case of a dissipative interaction, the influence of temperature can be counteracted by squeezing, which manifests as a resistance to randomization of phase. We make use of the phase distributions to bring out a notion of complementarity in atomic systems. We also study the variance of the phase using phase distributions conditioned on particular initial states of the system.

Banerjee, Subhashish; Srikanth, R. [Raman Research Institute, Sadashiva Nagar, Bangalore 560 080 (India)]|[Poornaprajna Institute of Scientific Research, Devanahalli, Bangalore 562 110 (India)]|[Raman Research Institute, Sadashiva Nagar, Bangalore 560 080 (India)

2007-12-15

227

Multiparameter deformation theory for quantum confined systems

We introduce a generalized multiparameter deformation theory applicable to all supersymmetric and shape-invariant systems. Taking particular choices for the deformation factors used in the construction of the deformed ladder operators, we show that we can generalize the one-parameter quantum-deformed harmonic oscillator models and build alternative multiparameter deformed models that are also shape invariant like the primary undeformed system.

Aleixo, A. N. F. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro 25725232 (Brazil); Balantekin, A. B. [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2009-11-15

228

Large deviations for ideal quantum systems

We consider a general d-dimensional quantum system of non-interacting particles in a very large (formally infinite) container. We prove that, in equilibrium, the fluctuations in the density of particles in a subdomain Lambda of the container are described by a large deviation function related to the pressure of the system. That is, untypical densities occur with a probability exponentially small

Joel L. Lebowitz; Marco Lenci; Herbert Spohn

2000-01-01

229

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. 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. ], for example, gave a first impression how one could solve problems in the future, that are intractable otherwise with all classical computers. Broadly speaking, quantum computing applies quantum logic gates (unitary transformations) on a given set of qubits, often referred to a quantum registers. Although, the theoretical foundation of quantum computing is now well understood, there are still many practical difficulties to be overcome for which (classical) simulations on n-qubit systems may help understand how quantum algorithms work in detail and what kind of physical systems and environments are most suitable for their realization. Method of solution:Using the computer algebra system MAPLE, a set of procedures has been developed to define and to deal with n-qubit quantum registers and quantum logic gates. It provides a hierarchy of commands which can be applied interactively and which is flexible enough to incorporate non-unitary quantum operations and quantum error corrections models in the future. Restrictions on the complexity of the problem:The present version of the program facilitates the set-up and

Radtke, T.; Fritzsche, S.

2005-12-01

230

Consciousness, Causality, and Quantum Physics

Quantum theory is open to different interpretations, and this paper reviews some of the points of contention. The standard interpretation of quantum physics assumes that the quantum world is characterized by ab- solute indeterminism and that quantum systems exist objectively only when they are being measured or observed. David Bohm's ontological interpreta- tion of quantum theory rejects both these assumptions.

DAVID PRATT

1997-01-01

231

Entanglement entropy in quantum impurity systems and systems with boundaries

We review research on a number of situations where a quantum impurity or a physical boundary has an interesting effect on entanglement entropy. Our focus is mainly on impurity entanglement as it occurs in one-dimensional systems with a single impurity or a boundary, in particular quantum spin models, but generalizations to higher dimensions are also reviewed. Recent advances in the

Ian Affleck; Nicolas Laflorencie; Erik S. Sørensen

2009-01-01

232

Quantum temporal probabilities in tunneling systems

NASA Astrophysics Data System (ADS)

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

Anastopoulos, Charis; Savvidou, Ntina

2013-09-01

233

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

234

Open-system electronic dynamics and thermalized electronic structure

NASA Astrophysics Data System (ADS)

We propose and implement a novel computational method for simulating open-system electronic dynamics and obtaining thermalized electronic structures within an open quantum system framework. The system-bath interaction equation of motion is derived and modeled from the local harmonic oscillator description for electronic density change. The nonequilibrium electronic dynamics in a thermal bath is simulated using first-order kinetics. The resultant electronic densities are temperature-dependent and can take characteristics of the ground and excited states. We present results of calculations performed on H2 and 1,3-butadiene performed at the Hartree-Fock level of theory using a minimal Slater-type orbital basis set.

Chapman, Craig T.; Liang, Wenkel; Li, Xiaosong

2011-01-01

235

Energy–time uncertainty relation for driven quantum systems

NASA Astrophysics Data System (ADS)

We derive generalizations of the energy–time uncertainty relation for driven quantum systems. Using a geometric approach based on the Bures length between mixed quantum states, we obtain explicit expressions for the quantum speed limit time, valid for arbitrary initial and final quantum states and arbitrary unitary driving protocols. Our results establish the fundamental limit on the rate of evolution of closed quantum systems.

Deffner, Sebastian; Lutz, Eric

2013-08-01

236

Lyapunov control of quantum systems with impulsive control fields.

We investigate the Lyapunov control of finite-dimensional quantum systems with impulsive control fields, where the studied quantum systems are governed by the Schrödinger equation. By three different Lyapunov functions and the invariant principle of impulsive systems, we study the convergence of quantum systems with impulsive control fields and propose new results for the mentioned quantum systems in the form of sufficient conditions. Two numerical simulations are presented to illustrate the effectiveness of the proposed control method. PMID:23766712

Yang, Wei; Sun, Jitao

2013-05-21

237

Relative-state formulation of quantum systems

NASA Astrophysics Data System (ADS)

A relative-state formulation of quantum systems is presented in terms of relative-coordinate states, relative-number states, and relative-energy states. The relative-coordinate states are used to describe quantum systems in position and momentum representations. The probability distribution is calculated in terms of the relative-coordinate states and is shown to be equivalent to the functional definition of the quantum probability in phase space. It is shown that a quantum-mechanical phase operator can be constructed in terms of the relative-number states without the well-known difficulties. The results are compared with those obtained by the Pegg-Barnett phase-operator formalism and the relations to various other phase-operator methods are also discussed. The energy-measurement and energy-probability distributions are discussed in terms of the relative-energy states. Furthermore, a relative-state formulation is developed in the Liouville space. A phase representation in the Liouville space is introduced to investigate the time evolution of quantum coherence. In the Liouville space a time operator is defined as a canonical conjugate of the time-evolution generator, but not the Hamiltonian energy operator. The relation to the internal time presented by Prigogine and Misra is discussed.

Ban, Masashi

1993-11-01

238

Quantum Optics with Single Atoms and Photons.

National Technical Information Service (NTIS)

This research program investigated the dynamics of open quantum systems in manifestly quantum or nonclassical domains. The research program exploited recently discovered possibilities in the microscopic realm of quantum mechanics to accomplish tasks that ...

H. J. Kimble

2005-01-01

239

Could a Classical Probability Theory Describe Quantum Systems?

Quantum Mechanics (QM) is a quantum probability theory based on the density matrix. The possibility of applying classical probability theory, which is based on the probability distribution function(PDF), to describe quantum systems is investigated in this work. In a sense this is also the question about the possibility of a Hidden Variable Theory (HVT) of Quantum Mechanics. Unlike Bell's inequality,

Jinshan Wu; Shouyong Pei

2005-01-01

240

Classical system boundaries cannot be determined within quantum Darwinism

NASA Astrophysics Data System (ADS)

Multiple observers who interact with environmental encodings of the states of a macroscopic quantum system S as required by quantum Darwinism cannot demonstrate that they are jointly observing S without a joint a priori assumption of a classical boundary separating S from its environment E. Quantum Darwinism cannot, therefore, be regarded as providing a purely quantum-mechanical explanation of the "emergence" of classicality.

Fields, Chris

241

Classical and quantum discrete dynamical systems

NASA Astrophysics Data System (ADS)

We study deterministic and quantum dynamics from a constructive "finite" point of view, since the introduction of the continuum or other actual infinities in physics poses severe conceptual and technical difficulties, and while all of these concepts are not really needed in physics, which is in fact an empirical science. Particular attention is paid to the symmetry properties of discrete systems. For a consistent description of the symmetries of dynamical systems at different time instants and the symmetries of various parts of such systems, we introduce discrete analogs of gauge connections. These gauge structures are particularly important to describe the quantum behavior. The symmetries govern the fundamental properties of the behavior of dynamical systems. In particular, we can show that the moving soliton-like structures are inevitable in a deterministic (classical) dynamical system, whose symmetry group breaks the set of states into a finite number of orbits of the group. We demonstrate that the quantum behavior is a natural consequence of symmetries of dynamical systems. This behavior is a result of the fundamental inability to trace the identity of indistinguish-able objects during their evolution. Information is only available on invariant statements and values related with such objects. Using general mathematical arguments, any quantum dynamics can be shown to reduce to a sequence of permutations. The quantum interferences occur in the invariant subspaces of permutation representations of the symmetry groups of dynamical systems. The observables can be expressed in terms of permutation invariants. We also show that in order to describe quantum phenomena it is sufficient to use cyclotomic fields—the minimal extensions of natural numbers suitable for quantum mechanics, instead of a non-constructive number system—the field of complex numbers. The finite groups of symmetries play the central role in this review. In physics there is an additional reason for such groups to be of interest. Numerous experiments and observations in particle physics point to the importance of finite groups of relatively low orders in a number of fundamental processes. The origin of these groups has no explanation within presently recognized theories, such as the Standard Model.

Kornyak, V. V.

2013-01-01

242

Local unitary invariants for multipartite quantum systems

NASA Astrophysics Data System (ADS)

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

Vrana, Péter

2011-03-01

243

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

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

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

2011-01-01

244

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

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

A. Feiguin; S. Fuchs; L. Gamper; R. Igarashi; L. Pollet; U. Schollwock; S. Todo; S. Trebst; M. Troyer; P. Werner; S. Wessel; M. L. Wall; Bela Bauer; Hans Gerd Evertz; Juliana Freire; Jan Gukelberger; Emanuel Gull; Siegfried Guertler; Sergei V. Isakov; David Koop; Brigitte Surer; Claudio T. Silva; Emanuele Santos; Jean-David Picon; Grzegorz Paw?owski; Olivier Parcollet; Ping Nang Ma; Haruhiko Matsuo

2011-01-01

245

Connectivity analysis of controlled quantum systems

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

Wu Rong; Rabitz, Herschel; Turinici, Gabriel; Sola, Ignacio [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); INRIA Rocquencourt, Domaine de Voluceau, Rocquencourt B.P. 105, 78153 Le Chesnay Cedex (France); Departamento de Quimica Fisica I, Universidad Complutense, 28040 Madrid (Spain)

2004-11-01

246

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

247

Bethe Ansatz and open spin-½ XXZ quantum spin chain

NASA Astrophysics Data System (ADS)

The open spin-½ XXZ quantum spin chain with general integrable boundary terms is a fundamental integrable model. Finding a Bethe Ansatz solution for this model has been a subject of intensive research for many years. Such solutions for other simpler spin chain models have been shown to be essential for calculating various physical quantities, e.g., spectrum, scattering amplitudes, finite size corrections, anomalous dimensions of certain field operators in gauge field theories, etc. The first part of this dissertation focuses on Bethe Ansatz solutions for open spin chains with nondiagonal boundary terms. We present such solutions for some special cases where the Hamiltonians contain two free boundary parameters. The functional relation approach is utilized to solve the models at roots of unity, i.e., for bulk anisotropy values h=ipp+1 where p is a positive integer. This approach is then used to solve open spin chain with the most general integrable boundary terms with six boundary parameters, also at roots of unity, with no constraint among the boundary parameters. The second part of the dissertation is entirely on applications of the newly obtained Bethe Ansatz solutions. We first analyze the ground state and compute the boundary energy (order 1 correction) for all the cases mentioned above. We extend the analysis to study certain excited states for the two-parameter case. We investigate low-lying excited states with one hole and compute the corresponding Casimir energy (order 1N correction) and conformal dimensions for these states. These results are later generalized to many-hole states. Finally, we compute the boundary S-matrix for one-hole excitations and show that the scattering amplitudes found correspond to the well known results of Ghoshal and Zamolodchikov for the boundary sine-Gordon model provided certain identifications between the lattice parameters (from the spin chain Hamiltonian) and infrared (IR) parameters (from the boundary sine-Gordon S-matrix) are made.

Murgan, Rajan

248

Quantum systems with finite Hilbert space

Quantum systems with finite Hilbert space are considered, and phase-space methods like the Heisenberg-Weyl group, symplectic transformations and Wigner and Weyl functions are discussed. A factorization of such systems in terms of smaller subsystems, based on the Chinese remainder theorem, is studied. The general formalism is applied to the case of angular momentum. In this context, SU(2) coherent states are

A. Vourdas

2004-01-01

249

An E-payment system based on quantum group signature

NASA Astrophysics Data System (ADS)

Security and anonymity are essential to E-payment systems. However, existing E-payment systems will easily be broken into soon with the emergence of quantum computers. In this paper, we propose an E-payment system based on quantum group signature. In contrast to classical E-payment systems, our quantum E-payment system can protect not only the users' anonymity but also the inner structure of customer groups. Because of adopting the two techniques of quantum key distribution, a one-time pad and quantum group signature, unconditional security of our E-payment system is guaranteed.

Xiaojun, Wen

2010-12-01

250

Entropy production along nonequilibrium quantum jump trajectories

NASA Astrophysics Data System (ADS)

For classical nonequilibrium systems, the separation of the total entropy production into the adiabatic and nonadiabatic contributions is useful for understanding irreversibility in nonequilibrium thermodynamics. In this paper, we formulate quantum analogues for driven open quantum systems describable by quantum jump trajectories by applying a quantum stochastic thermodynamics. Our main conclusions are based on a quantum formulation of the local detailed balance condition.

Horowitz, Jordan M.; Parrondo, Juan M. R.

2013-08-01

251

The concentrations of wave functions about classical periodic orbits, or quantum scars, are a fundamental phenomenon in physics. An open question is whether scarring can occur in relativistic quantum systems. To address this question, we investigate confinements made of graphene whose classical dynamics are chaotic and find unequivocal evidence of relativistic quantum scars. The scarred states can lead to strong conductance fluctuations in the corresponding open quantum dots via the mechanism of resonant transmission.

Huang, Liang [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Lai Yingcheng [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Ferry, David K.; Goodnick, Stephen M. [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Center for Solid State Electronics Research, Arizona State University, Tempe, Arizona 85287 (United States); Akis, Richard [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Center for Solid State Electronics Research, Arizona State University, Tempe, Arizona 85287 (United States)

2009-07-31

252

Coherent and collective quantum optical effects in mesoscopic systems

A review of coherent and collective quantum optical effects like superradiance and coherent population trapping in mesoscopic systems is presented. Various new physical realizations of these phenomena are discussed, with a focus on their role for electronic transport and quantum dissipation in coupled nano-scale systems like quantum dots. A number of theoretical tools such as Master equations, polaron transformations, correlation

Tobias Brandes

2005-01-01

253

Quantum cryptography for optical networks: a systems perspective

In this paper, we demonstrate for the first time, the coexistence architectures which enable quantum cryptographic systems to use the emerging optical network infrastructure. A vision of a future network that combines classical optical communications with ultra-low power quantum signals over a shared, reconfigurable fiber infrastructure is illustrated. We have used a fiber quantum key distribution (QKD) system to experimentally

M. S. Goodman; P. Toliver; R. J. Runserl; T. E. Chapuran; J. Jackel; R. J. Hughes; C. G. Peterson; K. McCabe; J. E. Nordholt; K. Tyagi; P. Hiskett; S. McNown; N. Nweke; J. T. Blake; L. Mercer; H. Dardy

2003-01-01

254

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

Although time-dependent quantum systems have been studied since the very beginning of quantum mechanics, they continue to attract the attention of many researchers, and almost every decade new important discoveries or new fields of application are made. Among the impressive results or by-products of these studies, one should note the discovery of the path integral method in the 1940s, coherent

Victor V. Dodonov; Margarita A. Man'ko

2010-01-01

255

Path integrals for dimerized quantum spin systems

NASA Astrophysics Data System (ADS)

Dimerized quantum spin systems may appear under several circumstances, e.g. by a modulation of the antiferromagnetic exchange coupling in space, or in frustrated quantum antiferromagnets. In general, such systems display a quantum phase transition to a Néel state as a function of a suitable coupling constant. We present here two path-integral formulations appropriate for spin S=1/2 dimerized systems. The first one deals with a description of the dimers degrees of freedom in an SO(4) manifold, while the second one provides a path-integral for the bond-operators introduced by Sachdev and Bhatt. The path-integral quantization is performed using the Faddeev-Jackiw symplectic formalism for constrained systems, such that the measures and constraints that result from the algebra of the operators is provided in both cases. As an example we consider a spin-Peierls chain, and show how to arrive at the corresponding field-theory, starting with both an SO(4) formulation and bond-operators.

Foussats, Adriana; Greco, Andrés; Muramatsu, Alejandro

2011-01-01

256

Quantum Mechanics of Computing in Condensed Matter Systems.

National Technical Information Service (NTIS)

New conceptual models for solid state fermionic interactions have been investigated for quantum computational atomic-level systems. The effects of decoherence in general as well as adiabatic decoherence upon coherent states of quantum computational elemen...

V. Privman L. S. Schulman

1998-01-01

257

On Mathematical Modeling Of Quantum Systems

The world of physical systems at the most fundamental levels is replete with efficient, interesting models possessing sufficient ability to represent the reality to a considerable extent. So far, quantum mechanics (QM) forming the basis of almost all natural phenomena, has found beyond doubt its intrinsic ingenuity, capacity and robustness to stand the rigorous tests of validity from and through appropriate calculations and experiments. No serious failures of quantum mechanical predictions have been reported, yet. However, Albert Einstein, the greatest theoretical physicist of the twentieth century and some other eminent men of science have stated firmly and categorically that QM, though successful by and large, is incomplete. There are classical and quantum reality models including those based on consciousness. Relativistic quantum theoretical approaches to clearly understand the ultimate nature of matter as well as radiation have still much to accomplish in order to qualify for a final theory of everything (TOE). Mathematical models of better, suitable character as also strength are needed to achieve satisfactory explanation of natural processes and phenomena. We, in this paper, discuss some of these matters with certain apt illustrations as well.

Achuthan, P. [Department of Mathematics, Amrita Vishwa Vidyapeetham, Coimbatore, 641 105 (India); Dept. of Mathematics, Indian Institute of Technology, Madras, 600 036 (India); Narayanankutty, Karuppath [Dept. of Physics, Amrita Vishwa Vidyapeetham, Coimbatore, 641 105 (India)

2009-07-02

258

From 1994 to 2008, the University of Idaho Library published the Electronic Green Journal, a peer-reviewed, cross-disciplinary, open-access journal on environmental issues. In 2007 the editorial board decided to transition the journal into the Open Journal Systems open-source journal-management system. The new system had to be customized, back issues had to be imported, and the editorial board had to be

Ben Hunter

2010-01-01

259

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,

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

2013-11-01

260

Autonomous modular quantum systems: Contextual Jarzynski relations

NASA Astrophysics Data System (ADS)

For autonomous quantum systems with modular structure we demonstrate that the Jarzynski relation can be reinterpreted to apply even locally: For this purpose certain contexts have to be introduced by selecting the system of interest versus its environment. The respective energy exchange is then divided into heat and work based on a generalized definition of these notions. In this way we are able to identify functional parts of the environment as either heat or work sources, respectively. We investigate different combinations of these functional parts with respect to contextual Jarzynski relations. Our analytical results are confirmed by numerical investigations on small multipartite systems.

Teifel, Jens; Mahler, Günter

2011-04-01

261

Orbifold duality symmetries and quantum Hall systems

NASA Astrophysics Data System (ADS)

We consider the possible role that chiral orbifold conformal field theories may play in describing the edge state theories of quantum Hall systems. This is a generalization of work that already exists in the literature, where it has been shown that 1+1 chiral bosons living on a n-dimensional torus, and which couple to a U1 gauge field, give rise to anomalous electric currents, the anomaly being related to the Hall conductivity. The well known O(n,nZ) duality group associated with such toroidal conformal field theories transforms the edge states and Hall conductivities in a way which makes interesting connections between different theories, e.g. between systems exhibiting the integer and fractional quantum Hall effect. In this paper we try to explore the extension of these constructions to the case where such bosons live on a n-dimensional orbifold. We give a general formalism for discussing the relevant quantities like the Hall conductance and their transformation under the duality groups present in orbifold compactifications. We illustrate these ideas by presenting a detailed analysis of a toy model based on the two-dimensional Z3 orbifold. In this model we obtain new classes of filling fractions, which generally correspond to fermionic edge states carrying fractional electric charge. We also consider the relation between orbifold edge theories and Luttinger liquids (LL's), which in the past have provided important insights into the physics of quantum Hall systems.

Skoulakis, Spyros; Thomas, Steven

1999-01-01

262

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

263

Time fractional development of quantum systems

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

264

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

265

Multipartite quantum correlations reveal frustration in a quantum Ising spin system

NASA Astrophysics Data System (ADS)

We report a nuclear magnetic resonance experiment, which simulates the quantum transverse Ising spin system in a triangular configuration, and further demonstrate that multipartite quantum correlations can be used to distinguish between the frustrated and the nonfrustrated 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 the nonfrustrated regimes. As expected from theoretical predictions, the experimental data confirm that the nonfrustrated regime shows higher multipartite quantum correlations compared to the frustrated one.

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

2013-08-01

266

Statistical Mechanics of Quantum Integrable Systems

NASA Astrophysics Data System (ADS)

Recent developments in statistical mechanics of quantum integrable systems are reviewed. Those studies are fundamental and have a renewed interest related to newly developing fields such as atomic Bose-Einstein condensations, photonic crystals and quantum computations. After a brief summary of the basic concepts and methods, the following three topics are discussed. First, by the thermal Bethe ansatz (TBA), a hard-core Bose gas is exactly solved. The model includes fully the effect of excluded volume and is identified to be a c=1 conformal field theory. Second, the cluster expansion method based on the periodic boundary condition for the Bethe wave function, which we call the Bethe ansatz cluster expansion (BACE) method, is developed for a ?-function gas and the XXX Heisenberg chain. This directly proves the TBA and reveals intrinsic properties of quantum integrable systems. Third, for a ?-function gas, the integral equations for the distribution functions of the quasi-momentum and the quasi-particle energy are solved in the form of power series. In the weak coupling case, the results reproduce those of Bogoliubov theory.

Wadati, Miki; Kato, Go; Iida, Toshiaki

267

Josephson tunneling in bilayer quantum Hall system

NASA Astrophysics Data System (ADS)

A Bose-Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (-e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ?=1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless. Our results explain recent experiments due to [L. Tiemann, Y. Yoon, W. Dietsche, K. von Klitzing, W. Wegscheider, Phys. Rev. B 80 (2009) 165120] and due to [Y. Yoon, L. Tiemann, S. Schmult, W. Dietsche, K. von Klitzing, Phys. Rev. Lett. 104 (2010) 116802]. We predict also how the critical current changes as the sample is tilted in the magnetic field.

Ezawa, Z. F.; Tsitsishvili, G.; Sawada, A.

2012-07-01

268

Seniority in quantum many-body systems

The use of the seniority quantum number in many-body systems is reviewed. A brief summary is given of its introduction by Racah in the context of atomic spectroscopy. Several extensions of Racah's original idea are discussed: seniority for identical nucleons in a single-j shell, its extension to the case of many, non-degenerate j shells and to systems with neutrons and protons. To illustrate its usefulness to this day, a recent application of seniority is presented in Bose-Einstein condensates of atoms with spin.

Van Isacker, P. [Grand Accelerateur National d'Ions Lourds, CEA/DSM-CNRS/IN2P3 BP 55027, F-14076 Caen Cedex 5 (France)

2010-12-23

269

Wigner Distribution Function for Open Quantum Systems

Using the modified biorthonormal Heisenberg equations of motion for non-Hermitian (NH) Hamilton operators, in order to imply a consistent Lie-algebraic structure and also the equivalence between the Heisenberg and Schrödinger pictures, we have obtained the analytical form of the Wigner distribution function which is unavoidable complex. Its imaginary part accounts for the influence of additional degrees of freedom, which are

S. Baskoutas

1997-01-01

270

The Power of Quantum Systems on a Line

We study the computational strength of quantum particles (each of finite dimensionality) arranged on a line. First, we prove that it is possible to perform universal adiabatic quantum computation using a one-dimensional quantum system (with 9 states per particle). Building on the same construction, but with some additional technical effort and 12 states per particle, we show that the problem

Dorit Aharonov; D. Gottesman; S. Irani; J. Kempe

2007-01-01

271

Experimental quantum teleportation of a two-qubit composite system

NASA Astrophysics Data System (ADS)

Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols.

Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei

2006-10-01

272

Quantum Coherence in Laser and Micromaser Systems

NASA Astrophysics Data System (ADS)

Quantum coherence effects in lasers and micromasers are studied theoretically. First, we investigate the laser operation when coherences between various levels of the pumping three-level atoms are introduced by some external means. We find that, in the case of closely spaced lower levels (Lambda-configuration), zero -threshold lasing without inversion can be achieved with quantum noise reduced to the level of that of an ideal coherent state. Multistable regimes, phase locking, and controlled competition between the modes are found when the, thus far, single-mode operation is extended to a two -mode one. In the second line of research, we consider two micromasers coupled in series by sharing a common pumping atomic beam. Significant modifications in the behavior of the second field are found due to the atomic coherence prepared in the first cavity, together with the build-up of correlation and phase locking between the two fields. We also study the evolution of the quantum state of the nonlocal two-field system in the two schemes where the final states of the atoms are measured conditionally or nonselectively. It is found that arbitrary steady state entanglement of the two nonlocal fields can be engineered in the form of entangled trapping states. These quantum states are experimentally feasible in the short-time transient regime when dissipation does not exceed a certain threshold. We also show that the correlation between the nonlocal fields can be translated into a correlation between spatially separated atomic beams. These entangled atoms can have several applications such as studying the effect of interatomic correlations in lasers and micromasers, quantum computing, teleportation, or tests of the local realistic theories. However, we specifically discuss here their use in experimentally feasible tests of complementarity applying Ramsey's atomic interferometry. We find that the correlation between the atoms provides us with "Welcher Weg" information resulting in a destruction of the interference fringes without leading to Heisenberg's uncertainty principle. Manipulation of information results in a generalized version of the "quantum eraser.".

Bogar, Pal

1995-01-01

273

Dissipation and decoherence in open nonequilibrium electronic systems

NASA Astrophysics Data System (ADS)

We theoretically study steady-state nonequilibrium properties of various open electronic systems subject to time-independent external bias. A charge current is established across each system by its coupling to two external particle reservoirs maintained at different chemical potentials. We discuss the impact of intra-reservoir electron correlations on transport, and examine how reservoir-generated dissipation and nonequilibrium-induced decoherence influence these systems. The effect of intra-lead electron interactions on transport is investigated in the context of a phonon-coupled single molecule transistor driven by Luttinger-liquid source and drain leads. The semi-classical master equation approach is used to compute current and noise characteristics of the device for various interaction strengths in the leads. The results suggest the possibility of tuning the Fano factor of the device using intra-lead electron interactions. The Keldysh path integral formalism is used to theoretically formulate models that describe the remaining open nonequilibrium systems. We consider voltage-induced electron-phonon scattering and electron mass enhancement due to phonons in a model metallic system. The possibility of adjusting the acoustic phonon velocity and the Thomas-Fermi screening length with external voltage is discussed. The effects of dissipation is investigated in an open BCS superconducting graphene, where the dissipation-induced rearrangement of its ground state from the BCS superconductor to the Fermi liquid is examined. The results theoretically infer prospects for a voltage-tuned metal-to-BCS quantum phase transition in graphene. Lastly, we develop a theory of nonequilibrium quantum criticality in open itinerant Ising and Heisenberg magnets. Both departures from equilibrium at conventional quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are analyzed.

Takei, So

274

Quantum degeneracy in an attractive Bosonic system

NASA Astrophysics Data System (ADS)

To achieve Bose-Einstein condensate (BEC) state, one major approach is to use an efficient magnetic trap for evaporative cooling, which is one of the key steps. In our experiment, we designed and implemented a millimeter-scale Ioffe-Pritchard trap, Mini-Trap. This is not only a new instrument to achieve BEC but a novel concept. It is well known that 7Li is hard to approach BEC state. We were able to realize quantum degeneracy for Lithium. In this thesis we also present a simple double well implementation and collisional dynamics in such a trap. The capability demonstrated by Mini-Trap for Lithium scales well for other alkalic particles. Our versatile design and compact setup proved to be a good choice as a platform for a portable interference measurement system. Lithium's unique feature of negative scattering length also makes a candidate for Schrodinger cat state. Atomic Schrodinger cat could be more interesting for research study and future applications because of the easy quantum control and extremely long coherence time. The research explores the characteristics for 7 Li atoms in quantum degeneracy regime. And the study of the atomic Schrodinger Cat state is also another main subject for this thesis.

Liu, Mingchang

275

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

276

Decoherence and quantum interference in a four-site model system: mechanisms and turnovers.

We study quantum interference effects in a four-level system which can be used as a minimal model to understand such behavior in systems from synthetic molecular structures to the photosystem-1 reaction center. The effects of environmental decoherence and relaxation on the electron transfer rate are investigated for several types of decoherence processes. The rate as a function of decoherence amplitude shows Kramers turnover, as expected. However, various decoherence processes affect the quantum interference differently. It is shown that when the bridge sites are not dephased the superexchange transfer is enhanced by constructive quantum interference. Dephasing on bridge sites opens a (classical) diffusive channel for fast electron transfer, which can dominate the superexchange current and reduce the constructive quantum interference. PMID:23286386

Zarea, Mahdi; Powell, Daniel; Renaud, Nicolas; Wasielewski, Michael R; Ratner, Mark A

2013-01-15

277

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

278

The possibility of detecting correlations between two quantum-mechanical systems from only the information of a subsystem is investigated. For generic cases, we prove that there exist correlations between two quantum systems if the time derivative of the reduced purity is not zero. Therefore, an experimentalist can conclude that correlations between the system and some environment are nonzero if the time derivative of the reduced purity is found not to be zero. A quantitative estimation of the time derivative of the reduced purity with respect to correlations is also given. This clarifies the role of correlations in the mechanism of decoherence in open quantum systems.

Kimura, Gen [Graduate School of Information Sciences, Tohoku University, Aoba-ku, Sendai 980-8579 (Japan); Ohno, Hiromichi [Graduate School of Mathematics, Kyushu University, 1-10-6 Hakozaki, Fukuoka 812-8581 (Japan); Hayashi, Hiroyuki [Department of Physics, Waseda University, Tokyo 169-8555 (Japan)

2007-10-15

279

Open path atmospheric spectroscopy using room temperature operated pulsed quantum cascade laser.

We report the application of a distributed feedback quantum cascade laser for 5.8 km long open path spectroscopic monitoring of ozone, water vapor and CO(2). The thermal chirp during a 140 or 200 ns long excitation pulse is used for fast wavelength scanning. The fast wavelength scanning has the advantage of the measured spectra not being affected by atmospheric turbulence, which is essential for long open path measurements. An almost linear tuning of about 0.6 and 1.2 cm(-1) is achieved, respectively. Lines from the nu(3) vibrational band of the ozone spectra centered at 1,031 and 1,049 cm(-1) is used for ozone detection by differential absorption. The lowest column densities (LCD) for ozone of the order of 0.3 ppmm retrieved from the absorption spectra for averaging times less than 20s are better then the LCD value of 2 ppmm measured with UV DOAS systems. The intrinsic haze immunity of mid-IR laser sources is an additional important advantage of mid-IR open path spectroscopy, compared with standard UV-vis DOAS. The third major advantage of the method is the possibility to measure more inorganic and organic atmospheric species compared to the UV-vis DOAS. PMID:16503192

Taslakov, M; Simeonov, V; van den Bergh, H

2006-02-24

280

On quantum Lie algebras and quantum root systems

NASA Astrophysics Data System (ADS)

As a natural generalization of ordinary Lie algebras we introduce the concept of quantum Lie algebras 0305-4470/29/8/018/img1. We define these in terms of certain adjoint submodules of quantized enveloping algebras 0305-4470/29/8/018/img2 endowed with a quantum Lie bracket given by the quantum adjoint action. The structure constants of these algebras depend on the quantum deformation parameter q and they go over into the usual Lie algebras when q = 1. The notions of q-conjugation and q-linearity are introduced. q-linear analogues of the classical antipode and Cartan involution are defined and a generalized Killing form, q-linear in the first entry and linear in the second, is obtained. These structures allow the derivation of symmetries between the structure constants of quantum Lie algebras. The explicitly worked out examples of 0305-4470/29/8/018/img3 and 0305-4470/29/8/018/img4 illustrate the results.

Delius, Gustav W.; Hüffmann, Andreas

1996-04-01

281

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

2009-01-09

282

Partitioning technique for discrete quantum systems

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.

Jin, L.; Song, Z. [School of Physics, Nankai University, Tianjin 300071 (China)

2011-06-15

283

Spin instability of integer quantum Hall systems

We investigate possible spin instabilities of integer quantum Hall systems as a function of the density within the framework of the self-consistent Hartree-Fock theory. We have found a spin density wave (SDW) state that is lower in energy than the paramagnetic and ferromagnetic states for the filling factor {nu}=2 in the density region 2.01

Yoshizawa, Kanako; Takayanagi, Kazuo [Department of Physics, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102 (Japan)

2007-10-15

284

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

2012-03-09

285

Energy transport in closed quantum systems

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

286

Schrödinger-cat states and decoherence in quantum electromechanical systems

NASA Astrophysics Data System (ADS)

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

Schlosshauer, Maximilian

2007-05-01

287

Absorption of light by a quantum chaos system

NASA Astrophysics Data System (ADS)

A simple quantum chaos system is examined as a model with which a realistic process of light absorption can be simulated. A typical quantum chaos system composed of two degrees of freedom does not absorb light stationarily, that is, at a constant rate. However, when it is coupled with only one or two other degrees of freedom, the results of simulation strongly suggest that the chaotic system absorbs light stationarily even though the coupling strength is quite weak. This fact provides a direct evidence that quantum chaos may be an origin of dissipation in quantum systems with a few degrees of freedom.

Ikeda, K.; Adachi, S.; Toda, M.

1990-07-01

288

Quantum physics: Watching the wavefunction collapse

NASA Astrophysics Data System (ADS)

The continuous random path of a superconducting system's quantum state has been tracked as the state changes during measurement. The results open the possibility of steering quantum systems into a desired state. See Letter p.211

Jordan, Andrew N.

2013-10-01

289

Tuning of coupling modes in laterally parallel double open quantum dots

NASA Astrophysics Data System (ADS)

We consider electronic transport through laterally parallel double open quantum dots embedded in a quantum wire in a perpendicular magnetic field. The coupling modes of the dots are tunable by adjusting the strength of a central barrier and the applied magnetic field. Probability density and electron current density are calculated to demonstrate transport effects including magnetic blocking, magnetic turbulence, and a holelike quasibound state feature. Fano to dip line-shape crossover in the conductance is found by varying the magnetic field.

Tang, Chi-Shung; Yu, Wing Wa; Gudmundsson, Vidar

2005-11-01

290

NASA Astrophysics Data System (ADS)

Quantum simulators are controllable quantum systems that can be used to mimic other quantum systems. They have the potential to enable the tackling of problems that are intractable on conventional computers. The photonic quantum technology available today is reaching the stage where significant advantages arise for the simulation of interesting problems in quantum chemistry, quantum biology and solid-state physics. In addition, photonic quantum systems also offer the unique benefit of being mobile over free space and in waveguide structures, which opens new perspectives to the field by enabling the natural investigation of quantum transport phenomena. Here, we review recent progress in the field of photonic quantum simulation, which should break the ground towards the realization of versatile quantum simulators.

Aspuru-Guzik, Alán; Walther, Philip

2012-04-01

291

Impossibility of measuring the wave function of a single quantum system

The general impossibility of determining the state of a single quantum system is proved for arbitrary measuring schemes, including a succession of measurements. Some recently proposed methods are critically examined. A scheme for tomographic measurements on a single copy of a radiation field is devised, showing that the system state is perturbed however weak the system-apparatus interaction is, due to the need of preparing the apparatus in a highly {open_quote}{open_quote}squeezed{close_quote}{close_quote} state. {copyright} {ital 1996 The American Physical Society.}

DAriano, G.M.; Yuen, H.P. [Department of Electrical Engineering and Computer Science, Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208 (United States)

1996-04-01

292

Topics in biophysics and disordered quantum systems

NASA Astrophysics Data System (ADS)

We present a collection of problems applying the tools of statistical physics to biology. We also present work on the effects of disorder on quantum systems. First, we derive a mean-field phase diagram for the folding of a generic RNA molecule, focusing on the conditions under which a stable ribozyme may fold. Then, we study the statistical mechanics of nucleosorne positioning and trans-membrane protein alpha-helix prediction, applying related techniques. We compare the physical outcomes of each model, finding nucleosomes suffer from ubiquitous metastability while transmembrane proteins are designed to avoid this problem. Next we study the dynamical properties of a collection of neurons, believed to generate the spontaneous breathing rhythms of mammals, focusing on its ability to produce stable oscillations of activity. Next we address the competition between disorder and strong interaction in 2 D fermionic systems, finding that the Mott gap is completely washed out, leading to a glassy state. Finally, we study the rounding by disorder of first, order quantum phase transitions, both through a general heuristic argument and an in-depth study of a particular model.

Schwab, David Jason

293

Evaluation of the Quantum II yeast identification system.

We compared three methods for identifying clinical yeast isolates: Abbott Quantum II, API 20C, and a modified BBL Minitek system. The API 20C and modified Minitek systems agreed on the identification of 243 of 245 yeasts (99.2%). The Quantum II system correctly identified 197 (80.4%), incorrectly identified 19 (7.8%), and did not identify 29 (11.8%) of the yeasts. Most of the misidentifications with the Quantum II occurred because assimilation or biochemical results were false-positive. Sixteen different species of yeasts and 16 different Quantum II substrates contributed to the discrepancies. On retesting with the Quantum II, 31% of the discrepant strains were correctly identified, while the remaining 69% were incorrectly identified or were not identified. Erroneous biochemical and assimilation results were also noted with yeasts that were correctly identified by the Quantum II system.

Kiehn, T E; Edwards, F F; Tom, D; Lieberman, G; Bernard, E M; Armstrong, D

1985-01-01

294

Topological photonic systems: from integer to fractional quantum Hall states

NASA Astrophysics Data System (ADS)

Topological properties of systems lead to remarkable robustness against disorder. The hallmark of such behavior is the quantized quantum Hall effect, where the electronic transport in two-dimensional systems is protected against scattering from impurities and the quantized Hall conductance is the manifestation of a topological invariance. Here we suggest an analogous approach to quantum Hall physics to create robust photonic devices. Specifically, we show how quantum Hall and quantum spin Hall Hamiltonians can be implemented with linear optics using coupled resonator optical waveguides (CROW) in two dimensions. Key features of quantum Hall systems could be observed via reflection spectroscopy, including the characteristic Hofstadter "butterfly" and edge state transport. Furthermore, the addition of an optical non- linearity to our proposed system leads to the possibility of implementing a fractional quantum Hall state of photons, where phenomenon such as non-abelian statistics may be observable.

Hafezi, Mohammad; Lukin, Mikhail; Demler, Eugene; Taylor, Jacob

2011-03-01

295

Quantum field theory in stationary coordinate systems

Quantum field theory is examined in stationary coordinate systems in Minkowski space. Preliminary to quantization of the scalar field, all of the possible stationary coordinate systems in flat spacetime are classified and explicitly constructed. Six distinct classes of such systems are found. Of these six, three have (identical) event horizons associated with them and five have Killing horizons. Two classes have distinct Killing and event horizons, with an intervening region analogous to the ergosphere in rotating black holes. Particular representatives of each class are selected for subsequent use in the quantum field theory. The scalar field is canonically quantized and a vacuum defined in each of the particular coordinate systems chosen. The vacuum states can be regarded as adapted to the six classes of stationary motions. There are only two vacuum states found, the Minkowski vacuum in those coordinate systems without event horizons and the Fulling vacuum in those with event horizons. The responses of monopole detectors traveling along stationary world lines are calculated in both the Minkowski and Fulling vacuums. The responses for each class of motions are distinct from those for every other class. A vacuum defined by the response of a detector must therefore not be equivalent in general to a vacuum defined by canonical quantization. Quantization of the scalar field within a rotating wedge is examined. It has not been possible to construct mode functions satisfying appropriate boundary conditions on the surface of the wedge. The asymptotic form of the renormalized stress tensor near the surfaces had been calculated and is found to include momentum terms which represent a circulation of energy within the wedge.

Pfautsch, J.D.

1981-01-01

296

On microstates counting in many body polymer quantum systems

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

Chacon-Acosta, Guillermo; Morales-Tecotl, Hugo A. [Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, Mexico D. F. 09340 (Mexico); Dagdug, Leonardo [Mathematical and Statistical Computing Laboratory, Division of Computational Bioscience, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20892 (United States); Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, Mexico D. F. 09340 (Mexico)

2011-10-14

297

Analytic Approach for Controlling Realistic Quantum Chaotic Systems

NASA Astrophysics Data System (ADS)

An analytic approach for controlling quantum states, which was originally applied to fully random matrix systems [T. Takami and H. Fujisaki, Phys. Rev. E 75, 036219 (2007)], is extended to deal with more realistic quantum systems with a banded random matrix (BRM). The validity of the new analytic field is confirmed by directly solving the Schrödinger equation with a BRM interaction. We find a threshold of the width of the BRM for the quantum control to be successful.

Takami, Toshiya; Fujisaki, Hiroshi

2007-12-01

298

Simulation of n-qubit quantum systems. II. Separability and entanglement

NASA Astrophysics Data System (ADS)

Studies on the entanglement of n-qubit quantum systems have attracted a lot of interest during recent years. Despite the central role of entanglement in quantum information theory, however, there are still a number of open problems in the theoretical characterization of entangled systems that make symbolic and numerical simulation on n-qubit quantum registers indispensable for present-day research. To facilitate the investigation of the separability and entanglement properties of n-qubit quantum registers, here we present a revised version of the FEYNMAN program in the framework of the computer algebra system MAPLE. In addition to all previous capabilities of this MAPLE code for defining and manipulating quantum registers, the program now provides various tools which are necessary for the qualitative and quantitative analysis of entanglement in n-qubit quantum registers. A simple access, in particular, is given to several algebraic separability criteria as well as a number of entanglement measures and related quantities. As in the previous version, symbolic and numeric computations are equally supported. Catalogue identifier:ADWE_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v2_0 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 Waterloo Maple Inc.] Operating systems under which the program has been tested: Linux, MS Windows XP Programming language used:MAPLE 10 Typical time and memory requirements:Most commands acting on quantum registers with five or less qubits take ?10 seconds of processor time (on a Pentium 4 with ?2 GHz or equivalent) and 5 20 MB of memory. However, 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. No. of lines in distributed program, including test data, etc.:3107 No. of bytes in distributed program, including test data, etc.:13?859 Distribution format:tar.gz Reasons for new version:The first program version established the data structures and commands which are needed to build and manipulate quantum registers. Since the (evolution of) entanglement is a central aspect in quantum information processing the current version adds the capability to analyze separability and entanglement of quantum registers by implementing algebraic separability criteria and entanglement measures and related quantities. Does this version supersede the previous version: Yes Nature of the physical problem: Entanglement has been identified as an essential resource in virtually all aspects of quantum information theory. Therefore, the detection and quantification of entanglement is a necessary prerequisite for many applications, such as quantum computation, communications or quantum cryptography. Up to the present, however, the multipartite entanglement of n-qubit systems has remained largely unexplored owing to the exponential growth of complexity with the number of qubits involved. Method of solution: Using the computer algebra system MAPLE, a set of procedures has been developed which supports the definition and manipulation of n-qubit quantum registers and quantum logic gates [T. Radtke, S. Fritzsche, Comput. Phys. Comm. 173 (2005) 91]. The provided hierarchy of commands can be used interactively in order to simulate the behavior of n-qubit quantum systems (by applying a number of unitary or non-unitary operations) and to analyze their separability and entanglement properties. Restrictions onto the complexity of the problem: The present version of the program facilitates the setup and the manipulation of quantum registers by means of (predefined) quantum logic gates; it now also provides the tools for performing a symbolic and/or numeric analysis of the entanglement for the quantum states of such registers. Owing to the rapid increase in the computational complexity of multi-

Radtke, T.; Fritzsche, S.

2006-07-01

299

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

300

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

301

Distance growth of quantum states due to initial system-environment correlations

Intriguing features of the distance between two arbitrary states of an open quantum system are identified that are induced by initial system-environment correlations. As an example, we analyze a qubit dephasingly coupled to a bosonic environment. Within tailored parameter regimes, initial correlations are shown to substantially increase the distance between two qubit states evolving to long-time-limit states according to exact non-Markovian dynamics. It exemplifies the breakdown of the distance contractivity of the reduced dynamics.

Dajka, J.; Luczka, J. [Institute of Physics, University of Silesia, PL-40-007 Katowice (Poland)

2010-07-15

302

Approximate Stabilization of AN Infinite Dimensional Quantum Stochastic System

NASA Astrophysics Data System (ADS)

We study the state feedback stabilization of a quantum harmonic oscillator near a pre-specified Fock state (photon number state). Such a state feedback controller has been recently implemented on a quantized electromagnetic field in an almost lossless cavity. Such open quantum systems are governed by a controlled discrete-time Markov chain in the unit ball of an infinite dimensional Hilbert space. The control design is based on an unbounded Lyapunov function that is minimized at each time-step by feedback. This ensures (weak-*) convergence of probability measures to a final measure concentrated on the target Fock state with a pre-specified probability. This probability may be made arbitrarily close to 1 by choosing the feedback parameters and the Lyapunov function. They are chosen so that the stochastic flow that describes the Markov process may be shown to be tight (concentrated on a compact set with probability arbitrarily close to 1). Convergence proof uses Prohorov's theorem and specific properties of this Lyapunov function.

Somaraju, Ram; Mirrahimi, Mazyar; Rouchon, Pierre

2013-02-01

303

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

304

Quantum Computing in Fock Space Systems

NASA Astrophysics Data System (ADS)

Fock space system (FSS) has unfixed number (N) of particles and/or degrees of freedom. In quantum computing (QC) main requirement is sustainability of coherent Q-superpositions. This normally favoured by low noise environment. High excitation/high temperature (T) limit is hence discarded as unfeasible for QC. Conversely, if N is itself a quantized variable, the dimensionality of Hilbert basis for qubits may increase faster (say, N-exponentially) than thermal noise (likely, in powers of N and T). Hence coherency may win over T-randomization. For this type of QC speed (S) of factorization of long integers (with D digits) may increase with D (for 'ordinary' QC speed polynomially decreases with D). This (apparent) paradox rests on non-monotonic bijectivity (cf. Georg Cantor's diagonal counting of rational numbers). This brings entire aleph-null structurality ("Babylonian Library" of infinite informational content of integer field) to superposition determining state of quantum analogue of Turing machine head. Structure of integer infinititude (e.g. distribution of primes) results in direct "Platonic pressure" resembling semi-virtual Casimir efect (presure of cut-off vibrational modes). This "effect", the embodiment of Pythagorean "Number is everything", renders Godelian barrier arbitrary thin and hence FSS-based QC can in principle be unlimitedly efficient (e.g. D/S may tend to zero when D tends to infinity).

Berezin, Alexander A.

1997-04-01

305

The von Neumann entropy production for a quantum mechanical kicked rotor coupled to a thermal environment is calculated. This rate of entropy increase is shown to be a good criterion to distinguish between quantum mechanical counterparts of chaotic and regular classical motion. We show that for high temperatures the entropy production rate increases linearly with the Kolmogorov-Sinai entropy of the

Paul A. Miller; Sarben Sarkar

1998-01-01

306

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

In this work, we present an implementation of quantum logic gates and algorithms in a three effective qubits system, represented by a (I = 7\\/2) NMR quadrupolar nuclei. To implement these protocols we have used the strong modulating pulses (SMP). The various stages of each implementation were verified by quantum state tomography (QST). It is presented here the results for

A. G. Araujo-Ferreira; Carlos Alexandre Brasil; D. O. Soares-Pinto; E. R. deAzevedo; T. J. Bonagamba; J. Teles

2011-01-01

307

Transition of d -level quantum systems through quantum channels with correlated noise

Entanglement and entanglement assisted are useful resources to enhance the mutual information of the Pauli channels, when the noise on consecutive uses of the channel has some partial correlations. In this paper, we study quantum-communication channels in d -dimensional systems and derive the mutual information of the quantum channels for maximally entangled states and product states coding with correlated noise.

A. Fahmi; M. Golshani

2007-01-01

308

Quantum nonexpander problem is quantum-Merlin-Arthur-complete

NASA Astrophysics Data System (ADS)

A quantum expander is a unital quantum channel that is rapidly mixing, has only a few Kraus operators, and can be implemented efficiently on a quantum computer. We consider the problem of estimating the mixing time (i.e., the spectral gap) of a quantum expander. We show that the problem of deciding whether a quantum channel is not rapidly mixing is a complete problem for the quantum Merlin-Arthur complexity class. This has applications to testing randomized constructions of quantum expanders and studying thermalization of open quantum systems.

Bookatz, Adam D.; Jordan, Stephen P.; Liu, Yi-Kai; Wocjan, Pawel

2013-04-01

309

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

310

Topological photonic systems: from integer to fractional quantum Hall states

Topological properties of systems lead to remarkable robustness against disorder. The hallmark of such behavior is the quantized quantum Hall effect, where the electronic transport in two-dimensional systems is protected against scattering from impurities and the quantized Hall conductance is the manifestation of a topological invariance. Here we suggest an analogous approach to quantum Hall physics to create robust photonic

Mohammad Hafezi; Mikhail Lukin; Eugene Demler; Jacob Taylor

2011-01-01

311

Bilayer 3He: A Simple Two-Dimensional Heavy-Fermion System with Quantum Criticality

NASA Astrophysics Data System (ADS)

Two-dimensional helium-3 (3He) provides a simple model for the experimental investigation of the emergence of quantum complexity in a strongly correlated Fermi system. We have observed two-dimensional, two-band heavy-fermion behavior in bilayer films of 3He atoms when adsorbed on the surface of graphite preplated by a solid bilayer of 4He. Thermodynamic measurements on this system showed that the relevant control parameter is the total density of the 3He film. The 3He bilayer system can be driven toward a quantum critical point at which the effective mass appears to diverge, interband coupling vanishes, and a local-moment state appears. It opens a new testing ground for theories of quantum criticality in heavy-fermion materials.

Neumann, Michael; Nyéki, Ján; Cowan, Brian; Saunders, John

2007-09-01

312

Bilayer 3He: a simple two-dimensional heavy-fermion system with quantum criticality.

Two-dimensional helium-3 (3He) provides a simple model for the experimental investigation of the emergence of quantum complexity in a strongly correlated Fermi system. We have observed two-dimensional, two-band heavy-fermion behavior in bilayer films of 3He atoms when adsorbed on the surface of graphite preplated by a solid bilayer of 4He. Thermodynamic measurements on this system showed that the relevant control parameter is the total density of the 3He film. The 3He bilayer system can be driven toward a quantum critical point at which the effective mass appears to diverge, interband coupling vanishes, and a local-moment state appears. It opens a new testing ground for theories of quantum criticality in heavy-fermion materials. PMID:17656686

Neumann, Michael; Nyéki, Ján; Cowan, Brian; Saunders, John

2007-07-26

313

Measures of Quantum Synchronization in Continuous Variable Systems

NASA Astrophysics Data System (ADS)

We introduce and characterize two different measures which quantify the level of synchronization of coupled continuous variable quantum systems. The two measures allow us to extend to the quantum domain the notions of complete and phase synchronization. The Heisenberg principle sets a universal bound to complete synchronization. The measure of phase synchronization is, in principle, unbounded; however, in the absence of quantum resources (e.g., squeezing) the synchronization level is bounded below a certain threshold. We elucidate some interesting connections between entanglement and synchronization and, finally, discuss an application based on quantum optomechanical systems.

Mari, A.; Farace, A.; Didier, N.; Giovannetti, V.; Fazio, R.

2013-09-01

314

Experimental feedback control of quantum systems using weak measurements.

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems. PMID:20366921

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

2010-02-26

315

Dimensions, lengths, and separability in finite-dimensional quantum systems

NASA Astrophysics Data System (ADS)

Many important sets of normalized states in a multipartite quantum system of finite dimension d, such as the set of all separable states, are real semialgebraic sets. We compute dimensions of many such sets in several low-dimensional systems. By using dimension arguments, we show that there exist separable states which are not convex combinations of d or less pure product states. For instance, such states exist in bipartite M?N systems when (M - 2)(N - 2) > 1. This solves an open problem proposed by DiVincenzo, Terhal and Thapliyal about 12 years ago. We prove that there exist a separable state ? and a pure product state, whose mixture has smaller length than that of ?. We show that any real ??, which is invariant under all partial transpose operations, is a convex sum of real pure product states. In the case of the 2?N system, the number r of product states can be taken to be r=rank?. We also show that the general multipartite separability problem can be reduced to the case of real states. Regarding the separability problem, we propose two conjectures describing as a semialgebraic set, which may eventually lead to an analytic solution in some low-dimensional systems such as 2?4, 3?3, and 2?2?2.

Chen, Lin; ðokovi?, Dragomir Ž.

2013-02-01

316

Quantum chromodynamics in few-nucleon systems

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

Brodsky, S.J.

1983-10-01

317

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

318

Effects of symmetry breaking in finite quantum systems

NASA Astrophysics Data System (ADS)

The review considers the peculiarities of symmetry breaking and symmetry transformations and the related physical effects in finite quantum systems. Some types of symmetry in finite systems can be broken only asymptotically. However, with a sufficiently large number of particles, crossover transitions become sharp, so that symmetry breaking happens similarly to that in macroscopic systems. This concerns, in particular, global gauge symmetry breaking, related to Bose-Einstein condensation and superconductivity, or isotropy breaking, related to the generation of quantum vortices, and the stratification in multicomponent mixtures. A special type of symmetry transformation, characteristic only for finite systems, is the change of shape symmetry. These phenomena are illustrated by the examples of several typical mesoscopic systems, such as trapped atoms, quantum dots, atomic nuclei, and metallic grains. The specific features of the review are: (i) the emphasis on the peculiarities of the symmetry breaking in finite mesoscopic systems; (ii) the analysis of common properties of physically different finite quantum systems; (iii) the manifestations of symmetry breaking in the spectra of collective excitations in finite quantum systems. The analysis of these features allows for the better understanding of the intimate relation between the type of symmetry and other physical properties of quantum systems. This also makes it possible to predict new effects by employing the analogies between finite quantum systems of different physical nature.

Birman, J. L.; Nazmitdinov, R. G.; Yukalov, V. I.

2013-05-01

319

Approach to Equilibrium for Quantum Systems with Continuous Spectrum

NASA Astrophysics Data System (ADS)

Considering quantum states as functionals acting on observables to give their mean values, it is possible to deal with quantum systems with continuous spectrum, generalizing the concept of trace. Generalized observables and states are defined for a quantum oscillator linearly coupled to a scalar field, and the analytic expression for time evolution is obtained. The "final" state (t ? ?) is presented as a weak limit. Finite and infinite number of exited modes of the field are considered.

Laura, Roberto

320

In the effective mass approximation in the model of rectangular potentials, the scattering cross section of electrons in an open spherical quantum dot is calculated for the first time. It is shown that, for such a nanosystem with a barrier of several monolayers, the experimental measurements of the scattering cross section allow adequate identification of the resonance energies and the widths of resonance states in the low-energy region of the quasi-stationary electron spectrum. It is also shown that, for an open spherical quantum dot with a low-strength potential barrier, the adequate spectral parameters of the quasi-stationary spectrum are the generalized resonance energies and widths determined via the probability of an electron being inside the quantum dot.

Tkach, N. V., E-mail: ktf@chnu.edu.ua; Seti, Ju. [Chernovtsy National University (Ukraine)

2009-03-15

321

Open problems in the theory of nuclear open quantum systems

Is there a connection between the branch point singularity at the particle emission threshold and the appearance of cluster states which reveal the structure of a corresponding reaction channel? Which nuclear states are most impacted by the coupling to the scattering continuum? What should be the most important steps in developing the theory that will truly unify nuclear structure and

N. Michel; Witold Nazarewicz; J. Okolowicz; M. Ploszajczak

2010-01-01

322

Open problems in theory of nuclear open quantum systems

Is there a connection between the branch point singularity at the particle\\u000aemission threshold and the appearance of cluster states which reveal the\\u000astructure of a corresponding reaction channel? Which nuclear states are most\\u000aimpacted by the coupling to the scattering continuum? What should be the most\\u000aimportant steps in developing the theory that will truly unify nuclear\\u000astructure and

N. Michel; W. Nazarewicz; J. Okolowicz; M. Ploszajczak

2010-01-01

323

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

324

Inequalities detecting quantum entanglement for 2?d systems

NASA Astrophysics Data System (ADS)

We present a set of inequalities for detecting quantum entanglement of 2?d quantum states. For 2?2 and 2?3 systems, the inequalities give rise to sufficient and necessary separability conditions for both pure and mixed states. For the case of d>3, these inequalities are necessary conditions for separability, which detect all entangled states that are not positive under partial transposition and even some entangled states with positive partial transposition. These inequalities are given by mean values of local observables and present an experimental way of detecting the quantum entanglement of 2?d quantum states and even multiqubit pure states.

Zhao, Ming-Jing; Ma, Teng; Fei, Shao-Ming; Wang, Zhi-Xi

2011-05-01

325

Quantum Arnol'd diffusion in a simple nonlinear system.

We study the fingerprint of the Arnol'd diffusion in a quantum system of two coupled nonlinear oscillators with a two-frequency external force. In the classical description, this peculiar diffusion is due to the onset of a weak chaos in a narrow stochastic layer near the separatrix of the coupling resonance. We have found that global dependence of the quantum diffusion coefficient on model parameters mimics, to some extent, the classical data. However, the quantum diffusion happens to be slower than the classical one. Another result is the dynamical localization that leads to a saturation of the diffusion after some characteristic time. We show that this effect has the same nature as for the studied earlier dynamical localization in the presence of global chaos. The quantum Arnol'd diffusion represents a new type of quantum dynamics and can be observed, for example, in two-dimensional semiconductor structures (quantum billiards) perturbed by time-periodic external fields. PMID:12366228

Demikhovskii, V Ya; Izrailev, F M; Malyshev, A I

2002-09-20

326

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

2013-08-20

327

Optimal correlations in many-body quantum systems.

Information and correlations in a quantum system are closely related through the process of measurement. We explore such relation in a many-body quantum setting, effectively bridging between quantum metrology and condensed matter physics. To this aim we adopt the information-theory view of correlations and study the amount of correlations after certain classes of positive-operator-valued measurements are locally performed. As many-body systems, we consider a one-dimensional array of interacting two-level systems (a spin chain) at zero temperature, where quantum effects are most pronounced. We demonstrate how the optimal strategy to extract the correlations depends on the quantum phase through a subtle interplay between local interactions and coherence. PMID:23004247

Amico, L; Rossini, D; Hamma, A; Korepin, V E

2012-06-15

328

Vortices in quantum droplets: Analogies between boson and fermion systems

The main theme of this review is the many-body physics of vortices in quantum droplets of bosons or fermions in the limit of small particle numbers. Systems of interest include cold atoms in traps as well as electrons confined in quantum dots. When set to rotate, these in principle different quantum systems show remarkable analogies. The topics reviewed include the structure of the finite rotating many-body state, universality of vortex formation and localization of vortices in both bosonic and fermionic systems, and the emergence of particle-vortex composites in the quantum Hall regime. An overview of the computational many-body techniques sets focus on the configuration-interaction and density-functional methods. Studies of quantum droplets with one or several particle components, where vortices as well as coreless vortices may occur, are reviewed, and theoretical as well as experimental challenges are discussed.

Saarikoski, H.; Reimann, S. M.; Harju, A.; Manninen, M. [Mathematical Physics, LTH, Lund University, SE-22100 Lund (Sweden); Department of Applied Physics and Helsinki Institute of Physics, Aalto University, FI-02150 Espoo (Finland); Nanoscience Center, Department of Physics, University of Jyvaeskylae, FI-40014 Jyvaeskylae (Finland)

2010-07-15

329

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

330

A Quantum-Like Description of the Planetary Systems

NASA Astrophysics Data System (ADS)

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

Scardigli, Fabio

2007-08-01

331

A quantum-like description of the planetary systems

NASA Astrophysics Data System (ADS)

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

Scardigli, Fabio

2007-05-01

332

Dissipation in systems of linear and nonlinear quantum scissors

We analyse the truncation of coherent states up to a single-photon Fock state by applying linear quantum scissors, utilizing the projection synthesis in a linear optical system, and nonlinear quantum scissors, implemented by periodically driven cavity with a Kerr medium. Dissipation effects on optical truncation are studied in the Langevin and master equation approaches. Formulae for the fidelity of lossy

Adam Miranowicz; Wieslaw Leonski

2004-01-01

333

Quantum phase transitions in two-fluid systems

Quantum phase transitions in two-fluid bosonic systems are discussed. An introduction to quantum phase transitions in one-fluid algebraic models is given, using the interacting boson model (IBM) for nuclei as the primary source of examples. The phase structure of a two-fluid algebraic model, the proton-neutron interacting boson model (IBM-2), is then investigated.

Caprio, M.A. [Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520-8120 (United States)

2005-07-08

334

Chapter 2 Quantum Effects in Optomechanical Systems

The search for experimental demonstration of the quantum behavior of macroscopic mechanical resonators is a fast growing field of investigation and recent results suggest that the generation of quantum states of resonators with a mass at the microgram scale is within reach. In this chapter we give an overview of two important topics within this research field: cooling to the

C. Genes; A. Mari; D. Vitali; P. Tombesi

2009-01-01

335

Alternative Hamiltonian description for quantum systems

The existence of time-invariant Kahler structures is analyzed in both Classical and Quantum Mechanics. In Quantum Mechanics, a family of such Kahler structures is found, in the finite-dimensional case it is proven that this family is complete.

Dubrovin, B.A. (Dept. Mech.Math., Moscow State Univ., Leninskiye Gory 119899, Moscow (SU)); Marno, G.; Simoni, A. (Dipartimento di Scienze Fisiche and INFN Naples Section, Mostra d'Oltremare pad.19, 80125 Napoli (IT))

1990-06-20

336

Path Integrals and Their Application to Dissipative Quantum Systems

NASA Astrophysics Data System (ADS)

The coupling of a system to its environment is a recurrent subject in this collection of lecture notes. The consequences of such a coupling are threefold. First of all, energy may irreversibly be transferred from the system to the environment thereby giving rise to the phenomenon of dissipation. In addition, the fluctuating force exerted by the environment on the system causes fluctuations of the system degree of freedom which manifest itself for example as Brownian motion. While these two effects occur both for classical as well as quantum systems, there exists a third phenomenon which is specific to the quantum world. As a consequence of the entanglement between system and environmental degrees of freedom a coherent superposition of quantum states may be destroyed in a process referred to as decoherence. This effect is of major concern if one wants to implement a quantum computer. Therefore, decoherence is discussed in detail in Chap. 5.

Ingold, Gert-Ludwig

337

Magnon decay in gapped quantum spin systems

NASA Astrophysics Data System (ADS)

In the O(3) ?-model description of gapped spin systems, S=1 magnons can only decay into three/ lower energy magnons. We argue that the symmetry of the quantum spin Hamiltonian often allows decay into two/ magnons, and compute this decay rate in model systems. For a realistic model describing two-dimensional spin dimer material (C4H12N2)Cu2Cl6 (known as PHCC), we compare our results for the momentum-dependent magnon linewidth with recent measurements by Stone et al. (e-print cond-mat/0511266) and extract new information on the exchange coupling pattern in this material. For S=1 Haldane chains, we show that two-magnon decay is allowed in the full lattice description, even though it cannot be induced by any allowed term written in powers and gradients of the ?-model field. We present estimates for the behavior of the magnon linewidth in Haldane gap chains and discuss relation to the recent experimental work.

Kolezhuk, Alexei; Sachdev, Subir

2006-03-01

338

NASA Astrophysics Data System (ADS)

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

Malossi, N.; Bason, M. G.; Viteau, M.; Arimondo, E.; Ciampini, D.; Mannella, R.; Morsch, O.

2013-06-01

339

Asymptotically Optimal Quantum Circuits for d-Level Systems

Scalability of a quantum computation requires that the information be processed on multiple subsystems. However, it is unclear how the complexity of a quantum algorithm, quantified by the number of entangling gates, depends on the subsystem size. We examine the quantum circuit complexity for exactly universal computation on many d-level systems (qudits). Both a lower bound and a constructive upper bound on the number of two-qudit gates result, proving a sharp asymptotic of {theta}(d{sup 2n}) gates. This closes the complexity question for all d-level systems (d finite). The optimal asymptotic applies to systems with locality constraints, e.g., nearest neighbor interactions.

Bullock, Stephen S. [Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8910 (United States); O'Leary, Dianne P. [Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8910 (United States); Department of Computer Science and UMIACS, University of Maryland, College Park, Maryland 20742 (United States); Brennen, Gavin K. [Atomic Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8420 (United States)

2005-06-17

340

Quantum discord amplification of fermionic systems in an accelerated frame

NASA Astrophysics Data System (ADS)

Quantum discord of fermionic systems in the relativistic regime, that is, beyond the single-mode approximation (SMA) is investigated. It is shown that quantum discord is amplified for the fermionic system in non-inertial frames irrespective of the choice of state, region and level of mixedness. This ensures that the phenomenon of amplification can actually happen in the relativistic regime. It is seen that quantum discord converges at infinite acceleration limit, which means that it becomes independent of qR (Unruh modes) beyond SMA. This implies that most of the tensor product structures already used in the literature to compute quantum field correlations in relativistic quantum information cannot give rise to physical results. The dynamics of quantum discord is investigated under amplitude damping, depolarizing and flipping channels. The vanishing behavior of quantum discord is seen for higher level of decoherence in the infinite acceleration limit. The depolarizing channel dominantly affects the fermionic quantum discord as compared to the amplitude damping channel. It means that the depolarizing channel has most destructive influence on the discord of the fermionic systems. Moreover, the effect of environment on the discord is much stronger than that of the acceleration of non-inertial frames.

Ramzan, M.

2013-10-01

341

Time delays and advances in classical and quantum systems

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

342

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

Mascarenhas, E.; Marques, B.; Santos, M. Franca [Departamento de Fisica, Universidade Federal de Minas Gerais, Caixa Postal 702, 30123-970 Belo Horizonte, MG (Brazil); Cavalcanti, D. [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona) (Spain); Cunha, M. Terra [Departamento de Matematica, Universidade Federal de Minas Gerais, Caixa Postal 702, 30123-970 Belo Horizonte, MG (Brazil)

2010-03-15

343

NASA Astrophysics Data System (ADS)

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

Mascarenhas, E.; Marques, B.; Cavalcanti, D.; Cunha, M. Terra; Santos, M. França

2010-03-01

344

Binary systems from quantum cluster equilibrium theory

NASA Astrophysics Data System (ADS)

An extension of the quantum cluster equilibrium theory to treat binary mixtures is introduced in this work. The necessary equations are derived and a possible implementation is presented. In addition an alternative sampling procedure using widely available experimental data for the quantum cluster equilibrium approach is suggested and tested. An illustrative example, namely, the binary mixture of water and dimethyl sulfoxide, is given to demonstrate the new approach. A basic cluster set is introduced containing the relevant cluster motifs. The populations computed by the quantum cluster equilibrium approach are compared to the experimental data. Furthermore, the excess Gibbs free energy is computed and compared to experiments as well.

Brüssel, Marc; Perlt, Eva; Lehmann, Sebastian B. C.; von Domaros, Michael; Kirchner, Barbara

2011-11-01

345

Multiple-scale analysis of quantum systems

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

Bender, C.M.; Bettencourt, L.M. [Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom)

1996-12-01

346

Quantum Harmonic Oscillator Systems with Disorder

NASA Astrophysics Data System (ADS)

We study many-body properties of quantum harmonic oscillator lattices with disorder. A sufficient condition for dynamical localization, expressed as a zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the eigenfunction correlators for an effective one-particle Hamiltonian. We show how state-of-the-art techniques for proving Anderson localization can be used to prove that these properties hold in a number of standard models. We also derive bounds on the static and dynamic correlation functions at both zero and positive temperature in terms of one-particle eigenfunction correlators. In particular, we show that static correlations decay exponentially fast if the corresponding effective one-particle Hamiltonian exhibits localization at low energies, regardless of whether there is a gap in the spectrum above the ground state or not. Our results apply to finite as well as to infinite oscillator systems. The eigenfunction correlators that appear are more general than those previously studied in the literature. In particular, we must allow for functions of the Hamiltonian that have a singularity at the bottom of the spectrum. We prove exponential bounds for such correlators for some of the standard models.

Nachtergaele, Bruno; Sims, Robert; Stolz, Günter

2012-12-01

347

Using Local Perturbations To Manipulate and Control Pointer States in Quantum Dot Systems

NASA Astrophysics Data System (ADS)

Recently, scanning gate microscopy (SGM) was used to image scarred wave functions in an open InAs quantum dot[1]. The SGM tip provides a local potential perturbation and imaging is performed by measuring changes in conductance. Scarred wave functions, long associated with quantum chaos, have been shown in open dots to correspond to pointer states[2], eigenstates that survive the decoherence process that occurs via coupling to the environment. Pointer states modulate the conductance, yielding periodic fluctuations and the scars, normally thought unstable, are stabilized by quantum Darwinism [3]. We shall show that, beyond probing, pointer states can be manipulated by local perturbations. Particularly interesting effects occur in coupled quantum dot arrays, where a pointer state localized in one dot can be shifted over into another with a perturbation in a completely different part of the system. These nonlocal effects may perhaps be exploited to give such systems an exotic functionality. [1] A. M. Burke, R. Akis, T. E. Day, Gil Speyer, D. K. Ferry, and B. R. Bennett, Phys. Rev. Lett. 104, 176801 (2010). [2] D. K. Ferry, R. Akis, and J. P. Bird, Phys. Rev. Lett. 104, 176801 (2004). [3] R. Brunner, R. Akis,D. K. Ferry, F. Kuchar,and R. Meisels, Phys. Rev. Lett. 101, 024102 (2008).

Akis, Richard; Speyer, Gil; Ferry, David; Brunner, Roland

2012-02-01

348

Trust Management in Open Systems (TMOS).

National Technical Information Service (NTIS)

Distributed software subjects face the problem of determining one another's trustworthiness. The problem considered in the Trust Management in Open Systems (TMOS) project is management of the exchange of sensitive credentials between strangers for the pur...

V. E. Jones W. H. Winsborough K. Seamons

2002-01-01

349

Quantum Spin Hall Effect in a Triple-Well Quantum Dot System

A scheme for generating a quantum spin Hall effect for an ensemble of electrons trapped in a triple-well quantum dot system\\u000a is proposed. Light-induced effective spin-dependent gauge potential and gauge filed are both given in a real Gaussian pulses\\u000a space. In our scheme, the spin Hall effect can be demonstrated by electronic population without spin-orbit coupled interaction\\u000a in the absence

Ping Dong; Zhuo-Liang Cao

2011-01-01

350

Closed-loop and robust control of quantum systems.

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

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

2013-08-07

351

Closed-Loop and Robust Control of Quantum Systems

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

Wang, Lin-Cheng

2013-01-01

352

Architectures and Applications for Scalable Quantum Information Systems.

National Technical Information Service (NTIS)

The goal of this project was to understand what key interchangeable elements form a scalable, fault-tolerant quantum information systems architecture. The effort was a collaboration between computer science and physical sciences involving four groups: MIT...

I. Chuang

2007-01-01

353

Quantum feedback in a weakly driven cavity QED system

Quantum feedback in strongly coupled systems can probe a regime where one quantum of excitation is a large fluctuation. We present theoretical and experimental studies of quantum feedback in an optical cavity QED system. The time evolution of the conditional state, following a photodetection, can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured in a new steady state and then released. The feedback protocol requires resonance operation, and proper amplitude and delay for the change in the drive. We demonstrate the successful use of feedback in the suppression of the vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return to steady state. The feedback works only because we have an entangled quantum system, rather than an analogous correlated classical system.

Reiner, J.E.; Smith, W.P. [Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3800 (United States); Orozco, L.A. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3800 (United States); Wiseman, H.M. [Centre for Quantum Computer Technology, Centre for Quantum Dynamics, School of Science, Griffith University, Brisbane 4111 (Australia); Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3800 (United States); Gambetta, Jay [Centre for Quantum Computer Technology, Centre for Quantum Dynamics, School of Science, Griffith University, Brisbane 4111 (Australia)

2004-08-01

354

Relativistic quantum dynamics of many-body systems.

National Technical Information Service (NTIS)

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

F. Coester W. N. Polyzou

2000-01-01

355

Emergent thermodynamics in a quenched quantum many-body system.

We study the statistics of the work done, fluctuation relations, and irreversible entropy production in a quantum many-body system subject to the sudden quench of a control parameter. By treating the quench as a thermodynamic transformation we show that the emergence of irreversibility in the nonequilibrium dynamics of closed many-body quantum systems can be accurately characterized. We demonstrate our ideas by considering a transverse quantum Ising model that is taken out of equilibrium by an instantaneous change of the transverse field. PMID:23215064

Dorner, R; Goold, J; Cormick, C; Paternostro, M; Vedral, V

2012-10-18

356

Quantum teleportation of composite systems via mixed entangled states

We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.

Bandyopadhyay, Somshubhro [Institute for Quantum Information Science, University of Calgary, Alberta, T2N 1N4 (Canada); Sanders, Barry C. [Institute for Quantum Information Science, University of Calgary, Alberta, T2N 1N4 (Canada); Centre of Excellence for Quantum Computer Technology, Macquarie University, Sydney, New South Wales 2109 (Australia)

2006-09-15

357

Phases and phase transitions in disordered quantum systems

NASA Astrophysics Data System (ADS)

These lecture notes give a pedagogical introduction to phase transitions in disordered quantum systems and to the exotic Griffiths phases induced in their vicinity. We first review some fundamental concepts in the physics of phase transitions. We then derive criteria governing under what conditions spatial disorder or randomness can change the properties of a phase transition. After introducing the strong-disorder renormalization group method, we discuss in detail some of the exotic phenomena arising at phase transitions in disordered quantum systems. These include infinite-randomness criticality, rare regions and quantum Griffiths singularities, as well as the smearing of phase transitions. We also present a number of experimental examples.

Vojta, Thomas

2013-08-01

358

Relativistic Quantum Dynamics of Many-Body Systems

NASA Astrophysics Data System (ADS)

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

Coester, F.; Polyzou, W. N.

2001-09-01

359

Photonic reagent control of dynamically homologous quantum systems

The general objective of quantum control is the manipulation of atomic scale physical and chemical phenomena through the application of external control fields. These tailored fields, or photonic reagents, exhibit systematic properties analogous to those of ordinary laboratory reagents. This analogous behavior is explored further here by considering the controlled response of a family of homologous quantum systems to a single common photonic reagent. A level set of dynamically homologous quantum systems is defined as the family that produces the same value(s) for a target physical observable(s) when controlled by a common photonic reagent. This paper investigates the scope of homologous quantum system control using the level set exploration technique (L-SET). L-SET enables the identification of continuous families of dynamically homologous quantum systems. Each quantum system is specified by a point in a hypercube whose edges are labeled by Hamiltonian matrix elements. Numerical examples are presented with simple finite level systems to illustrate the L-SET concepts. Both connected and disconnected families of dynamically homologous systems are shown to exist.

Beltrani, Vincent; Dominy, Jason; Ho, Tak-San; Rabitz, Herschel [Department of Chemistry, Frick Laboratory, Princeton University, Princeton, New Jersey 08544 (United States); Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Department of Chemistry, Frick Laboratory, Princeton University, Princeton, New Jersey 08544 (United States)

2007-03-07

360

Quantum Brayton cycle with coupled systems as working substance

NASA Astrophysics Data System (ADS)

We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by Fx) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by Fy). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by Fx), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by Fy). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by Fy, the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.

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

2013-01-01

361

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

NASA Astrophysics Data System (ADS)

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

Alidoosty Shahraki, Moslem; Khorasani, Sina; Aram, Mohammad Hasan

2013-10-01

362

Invisibility of quantum systems to tunneling of matter waves

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

Cordero, Sergio; Garcia-Calderon, Gaston [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20 364, 01000 Mexico, Distrito Federal (Mexico)

2009-05-15

363

Quantum nonintegrability and the classical limit for usp(4) systems

NASA Astrophysics Data System (ADS)

We investigate the transition from integrability to chaos in a system built of usp(4) elements, both in the quantum case and in its classical limit, obtained using coherent states. This algebraic Hamiltonian consists in an integrable term plus a nonlinear perturbation, and we see that the level spacing distribution for the quantum system is well approximated by the Berry-Robnik-Brody distribution, and accordingly the classical limit displays mixed dynamics.

Novaes, Marcel; Hornos, José Eduardo M.

2005-02-01

364

Information Theory of Quantum Systems with some hydrogenic applications

The information-theoretic representation of quantum systems, which complements the familiar energy description of the density-functional and wave-function-based theories, is here discussed. According to it, the internal disorder of the quantum-mechanical non-relativistic systems can be quantified by various single (Fisher information, Shannon entropy) and composite (e.g. Cramer-Rao, LMC shape and Fisher-Shannon complexity) functionals of the Schrodinger probability density rho(r???). First, we

J. S. Dehesa; D. Manzano; P. Sánchez-Moreno; R. J. Yáñez

2011-01-01

365

Information Theory of Quantum Systems with some hydrogenic applications

The information-theoretic representation of quantum systems, which complements the familiar energy description of the density-functional and wave-function-based theories, is here discussed. According to it, the internal disorder of the quantum-mechanical non-relativistic systems can be quantified by various single (Fisher information, Shannon entropy) and composite (e.g. Cramer-Rao, LMC shape and Fisher-Shannon complexity) functionals of the Schrodinger probability density &rgr;(r???). First, we

J. S. Dehesa; D. Manzano; P. Sa´nchez-Moreno

2011-01-01

366

Entanglement and correlation in anisotropic quantum spin systems

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

Glaser, Ulrich; Buettner, Helmut; Fehske, Holger [Integrated Systems Laboratory, ETH Zuerich, CH-8092 Zuerich, (Switzerland); CL DAT LIB IO, Infineon Technologies, D-81541 Muenchen, (Germany); Theoretische Physik I, Universitaet Bayreuth, D-95440 Bayreuth, (Germany); Institut fuer Physik, Theoretische Physik II, Universitaet Greifswald, D-17487 Greifswald, (Germany)

2003-09-01

367

Entanglement and Quantum Superposition of a Macroscopic-Macroscopic system

NASA Astrophysics Data System (ADS)

Two quantum Macro-states and their Macroscopic Quantum Superpositions (MQS) localized in two far apart, space-like separated sites can be non-locally correlated by any entangled couple of single-particles having interacted in the past. This novel "Macro-Macro" paradigm is investigated on the basis of a recent study on an entangled Micro-Macro system involving N?105 particles. Crucial experimental issues as the violation of Bell's inequalities by the Macro-Macro system are considered.

De Martini, Francesco

2011-03-01

368

Fault-Tolerant Quantum Computation with Higher-Dimensional Systems

Instead of a quantum computer where the fundamental units are 2-dimensional qubits, we can consider a quantum computer made up of d-dimensional systems. There is a straightforward generalization of the class of stabilizer codes to d-dimensional systems, and I will discuss the theory of fault-tolerant computation using such codes. I prove that uni- versal fault-tolerant computation is possible with any

Daniel Gottesman

1998-01-01

369

Decoherence and localization in quantum two-level systems

NASA Astrophysics Data System (ADS)

We study and compare the decoherent histories approach, the environment-induced decoherence and the localization properties of the solutions to the stochastic Schrödinger equation in quantum-jump simulation and quantum-state diffusion approaches, for a quantum two-level system model. We show, in particular, that there is a close connection between the decoherent histories and the quantum-jump simulation, complementing a connection with the quantum-state diffusion approach noted earlier by Diósi, Gisin, Halliwell and Percival. In the case of the decoherent histories analysis, the degree of approximate decoherence is discussed in detail. In addition, the various time scales regarding the decoherence and localization are discussed. By using the von Neumann entropy, we also discuss the predictability and its relation to the upper bounds of degree of decoherence.

Ting, Yu

1998-02-01

370

The Foundations of Quantum Mechanics: Historical Analysis and Open Questions -- Cesena, 2004

NASA Astrophysics Data System (ADS)

Introduction / C. Garola, A. Rossi and S. Sozzo -- If Bertlmann had three feet / A. Afriat -- Macroscopic interpretability of quantum component systems / R. Ascoli -- Premeasurement versus measurement: a basic form of complementarity / G. Auletta and G. Tarozzi -- Remarks on conditioning / E. G. Beltrametti -- Entangled state preparation in experiments on quantum non-locality / V. Berardi and A. Garuccio -- The first steps of quantum electrodynamics: what is it that's being quantized? / S. Bergia -- On the meaning of element in the science of italic tradition, the question of physical objectivity (and/or physical meaning) and quantum mechanics / G. Boscarino -- Mathematics and epistemology in Planck's theoretical work (1898-1915) / P. Campogalliani -- On the free motion with noise / B. Carazza and R. Tedeschi -- Field quantization and wave/particle duality / M. Cini -- Parastatistics in econophysics? / D. Costantini and U. Garibaldi -- Theory-laden instruments and quantum mechanics / S. D'Agostino -- Quantum non-locality and the mathematical representation of experience / V. Fano -- On the notion of proposition in classical and quantum mechanics / C. Garola and S. Sozzo -- The electromagnetic conception of nature and the origins of quantum physics / E. A. Giannetto -- What we talk about when we talk about universe computability / S. Guccione -- Bohm and Bohmian mechanics / G. Introzzi and M. Rossetti -- An objective background for quantum theory relying on thermodynamic concepts / L. Lanz and B. Vacchini -- The entrance of quantum mechanics in Italy: from Garbasso to Fermi / M. Leone and N. Robotti -- The measure of momentum in quantum mechanics / F. Logiurato and C. Tarsitani -- On the two-slit interference experiment: a statistical discussion / M. Minozzo -- Why the reactivity of the elements is a relational property, and why it matters / V. Mosini -- Detecting non compatible properties in double-slit experiment without erasure / G. Nisticò -- If you can manipulate them, must they be real? The epistemological role of instruments in nanotechnological research / A. Rebaglia -- Mathematical models and physical reality from classical to quantum physics / A. Rossi -- Complex entanglement and quaternionic separability / G. Scolarici and L. Solombrino -- Mach-Zehnder interferometer and quantitative complementarity / C. Tarsitani and F. Logiurato -- Antonio Gramsci's reflection on quantum mechanics / I. Tassani -- The role of logic and mathematics in the Heisenberg formulation of quantum mechanics / A. Venezia -- Space-time at the Planck scale: the quantum computer view / P. A. Zizzi -- Three-dimensional wave behaviour of light / F. Logiurato ... [et al.].

Garola, Claudio; Rossi, Arcangelo; Sozzo, Sandro

371

Geometric phases in open tripod systems

We first consider stimulated Raman adiabatic passages in a closed four-level tripod system. In this case, the adiabatic eigenstates of the system acquire real geometric phases. When the system is open and subject to decoherence they acquire complex geometric phases that we determine by a Monte Carlo wave function approach. We calculate the geometric phases and the state evolution in the closed as well as in the open system cases and describe the deviation between these in terms of the phases acquired. When the system is closed, the adiabatic evolution implements a Hadamard gate. The open system implements an imperfect gate and hence has a fidelity below unity. We express this fidelity in terms of the acquired geometric phases.

Moeller, Ditte; Madsen, Lars Bojer; Moelmer, Klaus [Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 (Denmark)

2008-02-15

372

Securing the banking ecosystem: A quantum leap? Italian open panel

Ernesto Damiani (Professor of Service Security at the Dept. of Information Technology, University of Milan) and Claudio Santacesaria (Rototype) have promoted a non-profit initiative to deal with technical aspects of the banking ecosystem security. The kick off takes place at Campione d???Italia in the location of 2012 IEEE DEST-CEE Conference on the afternoon of June 18th with an open panel.

Ernesto Damiani; Claudio Santacesaria; Raoul Chiesa; Giorgio Fedon; Marco Tempra; Mario Monitillo

2012-01-01

373

NASA Astrophysics Data System (ADS)

The dynamical behavior of many-body systems is often richer than what can be anticipated from their static properties. Here we show that in closed quantum systems this becomes evident by considering the statistics of time-integrated observables. In particular, the analytic properties of their generating functions, as estimated by full counting statistics (FCS), allow one to identify FCS phases, i.e., phases with specific fluctuation properties of time-integrated observables, and to locate transitions between these phases. We discuss in detail the case of the quantum Ising chain in a transverse field. We show that this model displays a continuum of full counting statistics transitions, of which the static transition is just an end point. These singularities are not a consequence of particular choices of initial conditions or other external nonequilibrium protocols such as quenches in coupling constants. They can be probed generically through quantum jump statistics of an associated open problem, and for the case of the quantum Ising chain we outline a possible experimental realization of this scheme by digital quantum simulation with cold ions.

Hickey, James M.; Genway, Sam; Lesanovsky, Igor; Garrahan, Juan P.

2013-05-01

374

Local emergence of thermal correlations in an isolated quantum many-body system

NASA Astrophysics Data System (ADS)

Understanding the dynamics of isolated quantum many-body systems is a central open problem at the intersection between statistical physics and quantum physics. Despite important theoretical effort, no generic framework exists yet to understand when and how an isolated quantum system relaxes to a steady state. Regarding the question of how, it has been conjectured that equilibration must occur on a local scale in systems where correlations between distant points can establish only at a finite speed. Here, we provide the first experimental observation of this local equilibration hypothesis. In our experiment, we quench a one-dimensional Bose gas by coherently splitting it into two parts. By monitoring the phase coherence between the two parts we observe that the thermal correlations of a prethermalized state emerge locally in their final form and propagate through the system in a light-cone-like evolution. Our results underline the close link between the propagation of correlations and relaxation processes in quantum many-body systems.

Langen, T.; Geiger, R.; Kuhnert, M.; Rauer, B.; Schmiedmayer, J.

2013-10-01

375

A tunable macroscopic quantum system based on two fractional vortices

NASA Astrophysics Data System (ADS)

We propose a tunable macroscopic quantum system based on two fractional vortices. Our analysis shows that two coupled fractional vortices pinned at two artificially created ? discontinuities of the Josephson phase in a long Josephson junction can reach the quantum regime where coherent quantum oscillations arise. For this purpose we map the dynamics of this system to that of a single particle in a double-well potential. By tuning the ? discontinuities with injector currents, we are able to control the parameters of the effective double-well potential as well as to prepare a desired state of the fractional vortex molecule. The values of the parameters derived from this model suggest that an experimental realization of this tunable macroscopic quantum system is possible with today's technology.

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

2013-05-01

376

Quantum Discord in Nuclear Magnetic Resonance Systems at Room Temperature

NASA Astrophysics Data System (ADS)

We review the theoretical and the experimental researches aimed at quantifying or identifying quantum correlations in liquid-state nuclear magnetic resonance (NMR) systems at room temperature. We first overview, at the formal level, a method to determine the quantum discord and its classical counterpart in systems described by a deviation matrix. Next, we describe an experimental implementation of that method. Previous theoretical analysis of quantum discord decoherence had predicted the time dependence of the discord to change suddenly under the influence of phase noise. The experiment attests to the robustness of the effect, sufficient to confirm the theoretical prediction even under the additional influence of a thermal environment. Finally, we discuss an observable witness for the quantumness of correlations in two-qubit systems and its first NMR implementation. Should the nature, not the amount, of the correlation be under scrutiny, the witness offers the most attractive alternative.

Maziero, J.; Auccaise, R.; Céleri, L. C.; Soares-Pinto, D. O.; deAzevedo, E. R.; Bonagamba, T. J.; Sarthour, R. S.; Oliveira, I. S.; Serra, R. M.

2013-04-01

377

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

2011-10-14

378

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 model has been constructed capable of accepting orders, performing exam resource scheduling, providing Digital communications in Medicine (DICOM) work list information to modalities, archiving studies, and supporting DICOM query/retrieve from third-party viewing software. The multitiered architecture uses a single database communicating via an open database connectivity bridge to a Linux server with Health Level 7 (HL7), DICOM, and HTTP connections. Human interaction is supported via a browser, whereas other informatics systems communicate over the HL7 and DICOM links. The system is still under development, but the primary database schema is complete, as are key pieces of the Web user interface. Additional work is needed on the DICOM/HL7 interface broker and completion of the base DICOM service classes. PMID:12105742

Langer, Steve G

2002-03-21

379

Non-Adiabatic Holonomic Quantum Gates in an atomic system

NASA Astrophysics Data System (ADS)

Quantum computation is essentially the implementation of a universal set of quantum gate operations on a set of qubits, which is reliable in the presence of noise. We propose a scheme to perform robust gates in an atomic four-level system using the idea of non-adiabatic holonomic quantum computation proposed in [1]. The gates are realized by applying sequences of short laser pulses that drive transitions between the four energy levels in such a way that the dynamical phases vanish. [4pt] [1] E. Sjoqvist, D.M. Tong, B. Hessmo, M. Johansson, K. Singh, arXiv:1107.5127v2 [quant-ph

Azimi Mousolou, Vahid; Canali, Carlo M.; Sjoqvist, Erik

2012-02-01

380

Schroedinger-equation formalism for a dissipative quantum system

We consider a model dissipative quantum-mechanical system realized by coupling a quantum oscillator to a semi-infinite classical string which serves as a means of energy transfer from the oscillator to the infinity and thus plays the role of a dissipative element. The coupling between the two--quantum and classical--parts of the compound system is treated in the spirit of the mean-field approximation and justification of the validity of such an approach is given. The equations of motion of the classical subsystem are solved explicitly and an effective dissipative Schroedinger equation for the quantum subsystem is obtained. The proposed formalism is illustrated by its application to two basic problems: the decay of the quasistationary state and the calculation of the nonlinear resonance line shape.

Anisimovas, E.; Matulis, A. [Department of Theoretical Physics, Vilnius University, Sauletekio al. 9, LT-10222 Vilnius (Lithuania); Semiconductor Physics Institute, Gostauto 11, LT-01108 Vilnius (Lithuania)

2007-02-15

381

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

382

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

383

Relativistic dynamics of resonantly driven classical and quantum systems

We compare the impact of the nonlinearity associated with the relativistic motion for two different classical and quantum mechanical systems. The first one is the resonantly driven simple harmonic oscillator system and the second is a hydrogen atom subjected to intense laser and strong static magnetic fields. In both systems the nonlinearity leads to a shifted resonance condition. The time-dependent

P. Peverly; R. Wagner; Q. Su; R. Grobe

2001-01-01

384

Defect formation preempts dynamical symmetry breaking in closed quantum systems

The theory of spontaneous symmetry breaking---one of the cornerstones of modern condensed-matter physics---underlies the connection between a classically ordered object in the thermodynamic limit and its microscopic quantum-mechanical constituents. However, a large, but not infinitely large, system requires a finite symmetry-breaking perturbation to stabilize a symmetry-broken state over the exact quantum-mechanical ground state, respecting the symmetry. Here, we use the

Carmine Ortix; Jorrit Rijnbeek; Jeroen van den Brink

2011-01-01

385

Scalable quantum mechanical simulation of large polymer systems

We describe a program for quantum mechanical calculations of very large hydrocarbon polymer systems. It is based on a new algorithmic approach to the quantum mechanical tight binding equations that naturally leads to a very efficient parallel implementation and that scales linearly with respect to the number of atoms. We get both very high single node performance as well as a significant parallel speedup on the SGI Origin 2000 parallel computer.

Goedecker, S. [Max-Planck Institute for Solid State Research, Stuttgart (Germany); Hoisie, A.; Kress, J.; Lubeck, O.; Wasserman, H. [Los Alamos National Lab., NM (United States)

1997-08-01

386

Modulated reflectance lineshapes for quantum well systems

We derive analytical formulae for the modulated reflectance lineshapes of both single (SQQ) and multiple (MQW) quantum well structures, by considering optical interference between the different reflected rays. The SQW lineshape is shown to be extremely sensitive to the optical phase delay between the rays reflected from the well and the front surface. Consequently, each well in a MQW makes

A. J. Shields; P. C. Klipstein

1990-01-01

387

Quantum interference in single molecule electronic systems

NASA Astrophysics Data System (ADS)

We present a general analytical formula and an ab initio study of quantum interference in multibranch molecules. Ab initio calculations are used to investigate quantum interference in a benzene-1,2-dithiolate (BDT) molecule sandwiched between gold electrodes and through oligoynes of various lengths. We show that when a point charge is located in the plane of a BDT molecule and its position varied, the electrical conductance exhibits a clear interference effect, whereas when the charge approaches a BDT molecule along a line normal to the plane of the molecule and passing through the center of the phenyl ring, interference effects are negligible. In the case of oligoynes, quantum interference leads to the appearance of a critical energy Ec at which the electron transmission coefficient T(E) of chains with even or odd numbers of atoms is independent of length. To illustrate the underlying physics, we derive a general analytical formula for electron transport through multibranch structures and demonstrate the versatility of the formula by comparing it with the above ab initio simulations. We also employ the analytical formula to investigate the current inside the molecule and demonstrate that large countercurrents can occur within a ringlike molecule such as BDT, when the point charge is located in the plane of the molecule. The formula can be used to describe quantum interference and Fano resonances in structures with branches containing arbitrary elastic scattering regions connecting nodal sites.

Sparks, R. E.; García-Suárez, V. M.; Manrique, D. Zs.; Lambert, C. J.

2011-02-01

388

Formal test specifications in open systems

The development of formal test specifications for an open system standard is described. The effort is being conducted within the environment provided by the Clemson Automated Testing System (CATS). CATS features the ability to automatically translate formal test specifications into executable tests. The formal test specifications are written in accordance with a specification language designed in support of this effort.

J. F. Leathrum; K. A. Liburdy

1995-01-01

389

Test data visualization for open system standards

This paper describes a data visualization tool developed to support prototype development and testing of software standard interfaces in the open systems environment. The visualization capability is an extension of the Clemson Automated Testing System (CATS). CATS is a research facility which has proven valuable in exposing and addressing critical issues in emerging areas such as the IEEE POSIX real-time

D. Crane; J. F. Leathrum; Kathleen A. Liburdy

1994-01-01

390

Thermodynamics: Energy of closed and open systems

Summary The definition of energy, in thermodynamics, is deepened by stating operative definitions of the basic concepts of physics\\u000a on which it rests, such as those of isolated system, ambient of a system, separable system and set of separable states. Then\\u000a the definition of energy is rigorously extended to open systems. The extension gives a clear physical meaning to the concept

E. Zanchini

1988-01-01

391

We consider integrable open-boundary conditions for the supersymmetric t-J model commuting with the number operator n and Sz. Four families, each one depending on two arbitrary parameters, are found. We find the relation between Sklyanin's method of constructing open boundary conditions and the one for the quantum group invariant case based on Markov traces. The eigenvalue problem is solved for

A. Gonzalez-Ruiz

392

Uhrig dynamical control of a three-level system via non-Markovian quantum state diffusion

NASA Astrophysics Data System (ADS)

In this paper, we use the quantum state diffusion (QSD) equation to implement the Uhrig dynamical decoupling 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 coloured phase and amplitude noises when the control-pulse sequences and control operators are properly designed. The advantage of using non-Markovian QSD 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 is comprised 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.

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

2013-09-01

393

We describe Microsoft's Next Generation Secure Computing Base (NGSCB). The system provides high assurance computing in a manner consistent with the commercial requirements of mass market systems. This poses a number of challenges and we describe the system architecture we have used to overcome them. We pay particular attention to reducing the trusted computing base to a small and manageable

Marcus Peinado; Yuqun Chen; Paul England; John Manferdelli

2004-01-01

394

Quantifying quantum correlations in fermionic systems using witness operators

NASA Astrophysics Data System (ADS)

We present a method to quantify quantum correlations in arbitrary systems of indistinguishable fermions using witness operators. The method associates the problem of finding the optimal entanglement witness of a state with a class of problems known as semidefinite programs, which can be solved efficiently with arbitrary accuracy. Based on these optimal witnesses, we introduce a measure of quantum correlations which has an interpretation analogous to the Generalized Robustness of entanglement. We also extend the notion of quantum discord to the case of indistinguishable fermions, and propose a geometric quantifier, which is compared to our entanglement measure. Our numerical results show a remarkable equivalence between the proposed Generalized Robustness and the Schliemann concurrence, which are equal for pure states. For mixed states, the Schliemann concurrence presents itself as an upper bound for the Generalized Robustness. The quantum discord is also found to be an upper bound for the entanglement.

Iemini, Fernando; Maciel, Thiago O.; Debarba, Tiago; Vianna, Reinaldo O.

2013-02-01

395

Quantum maximum entropy principle for a system of identical particles

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

Trovato, M. [Dipartimento di Matematica, Universita di Catania, Viale A. Doria, 95125 Catania (Italy); Reggiani, L. [Dipartimento di Ingegneria dell' Innovazione and CNISM, Universita del Salento, Via Arnesano s/n, 73100 Lecce (Italy)

2010-02-15

396

Propagation of quantum information through a spin system

It has been recently suggested that the dynamics of a quantum spin system may provide a natural mechanism for transporting quantum information. We show that one-dimensional rings of qubits with fixed (time-independent) interactions, constant around the ring, allow high-fidelity communication of quantum states. We show that the problem of maximizing the fidelity of the quantum communication is related to a classical problem in Fourier wave analysis. By making use of this observation we find that if both communicating parties have access to limited numbers of qubits in the ring (a fraction that vanishes in the limit of large rings) it is possible to make the communication arbitrarily good.

Osborne, Tobias J.; Linden, Noah [Department of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW (United Kingdom)

2004-05-01

397

Preparing thermal states of quantum systems by dimension reduction.

We present an algorithm that prepares thermal Gibbs states of one dimensional quantum systems on a quantum computer without any memory overhead, and in a time significantly shorter than other known alternatives. Specifically, the time complexity is dominated by the quantity N(?h?/T), where N is the size of the system, ?h? is a bound on the operator norm of the local terms of the Hamiltonian (coupling energy), and T is the temperature. Given other results on the complexity of thermalization, this overall scaling is likely optimal. For higher dimensions, our algorithm lowers the known scaling of the time complexity with the dimension of the system by one. PMID:21231028

Bilgin, Ersen; Boixo, Sergio

2010-10-22

398

Preparing Thermal States of Quantum Systems by Dimension Reduction

We present an algorithm that prepares thermal Gibbs states of one dimensional quantum systems on a quantum computer without any memory overhead, and in a time significantly shorter than other known alternatives. Specifically, the time complexity is dominated by the quantity N{sup ||h||}/{sup T}, where N is the size of the system, || h || is a bound on the operator norm of the local terms of the Hamiltonian (coupling energy), and T is the temperature. Given other results on the complexity of thermalization, this overall scaling is likely optimal. For higher dimensions, our algorithm lowers the known scaling of the time complexity with the dimension of the system by one.

Bilgin, Ersen; Boixo, Sergio [Institute of Quantum Information, California Institute of Technology, Pasadena, California, 91125 (United States)

2010-10-22

399

Quantum Processes and Dynamic Networks in Physical and Biological Systems.

NASA Astrophysics Data System (ADS)

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

Dudziak, Martin Joseph

400

Bohmian Mechanics In A Macroscopic Quantum System

NASA Astrophysics Data System (ADS)

In the so called `causal' interpretation of quantum mechanics, an electron is considered as a particle and such particle is influenced not only by a classical but also by a so called quantum potential. This idea was developed by Professor Bohm in an important paper. In this paper we use some of the basics of this interpretation in a financial option pricing environment. The causal interpretation allows for trajectories. Path breaking work by Professors Bohm and Hiley and Khrennikov and Choustova have made that the causal interpretation is a step closer to potential applications in social science. In this paper we consider the wave function as a wave of information. We consider the gradient of the phase of this wave function and show how the option price could be influenced by this gradient.

Haven, Emmanuel

2006-01-01

401

Energy-time representation for quantum systems

We introduce a picture of quantum dynamics in which the representation basis vectors are the quantities that evolve, instead of state vectors or operators. These vectors allow us to pick the parts of a probability density that correspond to some values of energy or time, providing us with energy and time representations. The properties of these representations are analyzed and an application to the free particle is presented.

Torres-Vega, Gabino [Physics Department, Cinvestav, Apartado postal 14-740, 07000 Mexico, Distrito Federal (Mexico)

2007-03-15

402

An Architecture for Open Learning Management Systems

There exists an urgent demand on defining architectures for Learning Management Systems, so that high-level frameworks for understanding these systems can be discovered, and quality attributes like portability, interoperability, reusability and modifiability can be achieved. In this paper we propose a prototype architecture aimed to engineer Open Learning Management Systems, that professes state-of-the-art software engineering techniques such as layered structure

Simos Retalis; Manolis Skordalakis

2003-01-01

403

An Architecture for Open Learning Management Systems

There exists an urgent demand on defining architectures for Learning Management Systems, so that high-level frameworks for\\u000a understanding these systems can be discovered, and quality attributes like portability, interoperability, reusability and\\u000a modifiability can be achieved. In this paper we propose a prototype architecture aimed to engineer Open Learning Management\\u000a Systems, that professes state-of-the-art software engineering techniques such as layered structure

Symeon Retalis; Manolis Skordalakis

2001-01-01

404

Global well-posedness and the classical limit of the solution for the quantum Zakharov system

NASA Astrophysics Data System (ADS)

In this paper, we study the quantum Zakharov system, which describes the nonlinear interaction between the quantum Langmuir and quantum ion-acoustic waves. The global well-posedness result of this system in the energy and above energy spaces is obtained in the case d = 1, 2, 3. Moreover, the classical limit behavior of the quantum Zakharov system is also investigated as the quantum parameter tends to zero.

Guo, Yanfeng; Zhang, Jingjun; Guo, Boling

2013-02-01

405

NASA Astrophysics Data System (ADS)

This dissertation discusses the properties of two open quantum systems with a general class of irreversible quantum dynamics. First we study Lieb-Robinson bounds in a quantum lattice systems. This bound gives an estimate for the speed of growth of the support of an evolved local observable up to an exponentially small error. In a second model we study the properties of a leaking cavity pumped by a random atomic beam. We begin by describing quantum systems on an infinite lattice with associated finite or infinite dimensional Hilbert space. The generator of the dynamics of this system is of the Lindblad-Kossakowski type and consists of two parts: the Hamiltonian interactions and the dissipative terms. We allow both of them to be time-dependent. This generator satisfies some suitable decay condition in space. We show that the dynamics with a such generator on a finite system is a well-defined quantum dynamics in a sense of a norm-continuous cocycle of unit preserving completely positive maps. Lieb-Robinson bounds for irreversible dynamics were first considered in the classical context and in for a class of quantum lattice systems with finite-range interactions. We extend those results by proving a Lieb-Robinson bound for lattice models with a more general class of quantum dynamics. Then we use Lieb-Robinson bounds for a finite lattice systems to prove the existence of the thermodynamic limit of the dynamics. We show that in a strong limit there exits a strongly continuous cocycle of unit preserving completely positive maps. Which means that the dynamics exists in an infinite system, where Lieb-Robinson bounds also holds. In the second part of the dissertation we consider a system that consists of a beam of two-level atoms that pass one by one through the microwave cavity. The atoms are randomly excited and there is exactly one atom present in the cavity at any given moment. We consider both the ideal and leaky cavity and study the time asymptotic behavior of the state of the cavity. We show that the number of photons increases indefinitely in the case of the ideal cavity. In the case of the leaking cavity the limiting state is independent of the initial state, it is not quasi-free and it is a non-equilibrium steady state. We also compute the associated energy flow.

Vershynina, Anna

406

Reconfigurable quantum metamaterials.

By coupling controllable quantum systems into larger structures we introduce the concept of a quantum metamaterial. Conventional meta-materials represent one of the most important frontiers in optical design, with applications in diverse fields ranging from medicine to aerospace. Up until now however, metamaterials have themselves been classical structures and interact only with the classical properties of light. Here we describe a class of dynamic metamaterials, based on the quantum properties of coupled atom-cavity arrays, which are intrinsically lossless, reconfigurable, and operate fundamentally at the quantum level. We show how this new class of metamaterial could be used to create a reconfigurable quantum superlens possessing a negative index gradient for single photon imaging. With the inherent features of quantum superposition and entanglement of metamaterial properties, this new class of dynamic quantum metamaterial, opens a new vista for quantum science and technology. PMID:21716331

Quach, James Q; Su, Chun-Hsu; Martin, Andrew M; Greentree, Andrew D; Hollenberg, Lloyd C L

2011-06-01

407

Parafermions and superoperator-mediated quantum system reduction

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

Merkel, U. (Inst. fuer Informatik, Univ. Stuttgart, D-7000 Stuttgart 1, Azenbergstr. 12 (DE))

1990-12-10

408

Fermi-Bose Systems, Macroscopic Quantum Superposition States and Entanglement

We study the entanglement of states of a simple Fermi-Bose system. The Hilbert space is C2 ? l2 (N). An explicit expression is given for the entanglement. We consider number states, coherent states and macroscopic quantum superposition states in the product system. Explicit formulas for the entanglement are also given in each of these cases.

Yorick Hardy; Willi-Hans Steeb

2004-01-01

409

Quantum dynamic behaviour in a coupled cavities system

NASA Astrophysics Data System (ADS)

The dynamic behaviour of the two-site coupled cavities model which is doped with ta wo-level system is investigated. The exact dynamic solutions in the general condition are obtained via Laplace transform. The simple analytical solutions are obtained in several particular cases, which demonstrate the clear and simple physical picture for the quantum state transition of the system. In the large detuning or hoppling case, the quantum states transferring between qubits follow a slow periodic oscillation induced by the very weak excitation of the cavity mode. In the large coupling case, the system can be interpreted as two Jaynes-Cummings model subsystems which interact through photon hop between the two cavities. In the case of ? ? ? ? g, the quantum states transition of qubits is accompanied by the excitation of the cavity, and the cavity modes have the same dynamic behaviours and the amplitude of probability is equal to 0.25 which does not change with the variation of parameter.

Peng, Jun; Wu, Yun-Wen; Li, Xiao-Juan

2012-06-01

410

Quadratic algebra approach to relativistic quantum Smorodinsky-Winternitz systems

There exists a relation between the Klein-Gordon and the Dirac equations with scalar and vector potentials of equal magnitude and the Schroedinger equation. We obtain the relativistic energy spectrum for the four relativistic quantum Smorodinsky-Winternitz systems from their quasi-Hamiltonian and the quadratic algebras studied by Daskaloyannis in the nonrelativistic context. We also apply the quadratic algebra approach directly to the initial Dirac equation for these four systems and show that the quadratic algebras obtained are the same than those obtained from the quasi-Hamiltonians. We point out how results obtained in context of quantum superintegrable systems and their polynomial algebras can be applied to the quantum relativistic case.

Marquette, Ian [Department of Mathematics, University of York, Heslington, York YO10 5DD (United Kingdom)

2011-04-15

411

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 with open source tools and methods are 2-fold. Open source permits an inexpensive development model where interfaces can be updated as needed, and the code is peer reviewed by many eyes (analogous to the scientific model). Integration of PACS/RIS functionality reduces the risk of inconsistent data by reducing interfaces among databases that contain largely redundant information. Also, wide adoption would promote standard data mining tools--reducing user needs to learn multiple methods to perform the same task. A model has been constructed capable of accepting HL7 orders, performing examination and resource scheduling, providing digital imaging and communications in medicine (DICOM) worklist information to modalities, archiving studies, and supporting DICOM query/retrieve from third party viewing software. The multitiered architecture uses a single database communicating via an ODBC bridge to a Linux server with HL7, DICOM, and HTTP connections. Human interaction is supported via a web browser, whereas automated informatics services communicate over the HL7 and DICOM links. The system is still under development, but the primary database schema is complete as well as key pieces of the web user interface. Additional work is needed on the DICOM/HL7 interface broker and completion of the base DICOM service classes. PMID:12297975

Langer, Steve

2002-09-26

412

Nucleus as an Open System: New Effects and Theoretical Challenges

NASA Astrophysics Data System (ADS)

As nuclear science moves in the direction of nuclei far from stability, the studies of nuclear structure and nuclear reactions become more and more interrelated. The main theoretical challenge is to find a consistent description of the nucleus as an open mesoscopic system coupled with continuum through real decay channels and through virtual excitations. The method using the effective non-Hermitian Hamiltonian [see review article: N. Auerbach and V. Zelevinsky, Rep. Prog. Phys. 74, 106301 (2011)] is one of the most promising theoretical approaches; it can be strictly derived from quantum many-body theory, it allows for calculating bound states, resonances and reaction cross sections in the unified framework, and it is quite flexible in practical applications. After explaining the main features of this theory, I will show the method at work (continuum shell model with predictions recently confirmed by the experiments with exotic oxygen isotopes, phenomenon of super-radiance, relation to the idea of doorway states, quantum signal transmission through mesoscopic systems) and discuss new theoretical challenges.

Zelevinsky, Vladimir

2012-10-01

413

Extremely high-intensity laser interactions with fundamental quantum systems

NASA Astrophysics Data System (ADS)

The field of laser-matter interaction traditionally deals with the response of atoms, molecules, and plasmas to an external light wave. However, the recent sustained technological progress is opening up the possibility of employing intense laser radiation to trigger or substantially influence physical processes beyond atomic-physics energy scales. Available optical laser intensities exceeding 1022W/cm2 can push the fundamental light-electron interaction to the extreme limit where radiation-reaction effects dominate the electron dynamics, can shed light on the structure of the quantum vacuum, and can trigger the creation of particles such as electrons, muons, and pions and their corresponding antiparticles. Also, novel sources of intense coherent high-energy photons and laser-based particle colliders can pave the way to nuclear quantum optics and may even allow for the potential discovery of new particles beyond the standard model. These are the main topics of this article, which is devoted to a review of recent investigations on high-energy processes within the realm of relativistic quantum dynamics, quantum electrodynamics, and nuclear and particle physics, occurring in extremely intense laser fields.

Di Piazza, A.; Müller, C.; Hatsagortsyan, K. Z.; Keitel, C. H.

2012-07-01

414

Maps and inverse maps in open quantum dynamics

Two kinds of maps that describe evolution of states of a subsystem coming from dynamics described by a unitary operator for a larger system, maps defined for fixed mean values and maps defined for fixed correlations, are found to be quite different for the same unitary dynamics in the same situation in the larger system. An affine form is used for both kinds of maps to find necessary and sufficient conditions for inverse maps. All the different maps with the same homogeneous part in their affine forms have inverses if and only if the homogeneous part does. Some of these maps are completely positive; others are not, but the homogeneous part is always completely positive. The conditions for an inverse are the same for maps that are not completely positive as for maps that are. For maps defined for fixed mean values, the homogeneous part depends only on the unitary operator for the dynamics of the larger system, not on any state or mean values or correlations. Necessary and sufficient conditions for an inverse are stated several different ways: in terms of the maps of matrices, basis matrices, density matrices, or mean values. The inverse maps are generally not tied to the dynamics the way the maps forward are. A trace-preserving completely positive map that is unital cannot have an inverse that is obtained from any dynamics described by any unitary operator for any states of a larger system.

Jordan, Thomas F., E-mail: tjordan@d.umn.ed [Physics Department, University of Minnesota, Duluth, MN 55812 (United States)

2010-10-15

415

Toward engineered quantum many-body phonon systems

NASA Astrophysics Data System (ADS)

Arrays of coupled phonon cavities each including an impurity qubit in silicon are considered. We study experimentally feasible architectures that can exhibit quantum many-body phase transitions of phonons, e.g., Mott insulator and superfluid states, due to a strong phonon-phonon interaction (which is mediated by the impurity qubit-cavity phonon coupling). We investigate closed equilibrium systems as well as driven dissipative nonequilibrium systems at zero and nonzero temperatures. Our results indicate that quantum many-body phonon systems are achievable both in on-chip nanomechanical systems in silicon and distributed Bragg reflector phonon cavity heterostructures in silicon-germanium. Temperature and driving field are shown to play a critical role in achieving these phonon superfluid and insulator states, results that are also applicable to polariton systems. Experimental procedures to detect these states are also given. Cavity-phoniton systems enable strong phonon-phonon interactions as well as offering long wavelengths for forming extended quantum states; they may have some advantage in forming truly quantum many-body mechanical states as compared to other optomechanical systems.

Soykal, Ö. O.; Tahan, Charles

2013-10-01

416

Super-radiant dynamics, doorways and resonances in nuclei and other open mesoscopic systems

NASA Astrophysics Data System (ADS)

The phenomenon of super-radiance (Dicke effect, coherent spontaneous radiation by a gas of atoms coupled through a common radiation field) is well known in quantum optics. This review discusses similar physics that emerges in open and marginally stable quantum many-body systems. In the presence of open decay channels, the intrinsic states are coupled through the continuum. At sufficiently strong continuum coupling, the spectrum of resonances undergoes restructuring with segregation of very broad super-radiant states and trapping of remaining long-lived compound states. The appropriate formalism describing this phenomenon is based on the Feshbach projection method and effective non-Hermitian Hamiltonian. A broader generalization is related to the idea of doorway states connecting quantum states of different structures. The method is explained in detail and examples of applications are given to nuclear, atomic and particle physics. The interrelation of the collective dynamics through continuum and possible intrinsic many-body chaos is studied, including universal mesoscopic conductance fluctuations. The theory serves as a natural framework for the general description of quantum signal transmission through an open mesoscopic system.

Auerbach, Naftali; Zelevinsky, Vladimir

2011-10-01

417

Thermodynamic length for far-from-equilibrium quantum systems.

We consider a closed quantum system initially at thermal equilibrium and driven by arbitrary external parameters. We derive a lower bound on the entropy production which we express in terms of the Bures angle between the nonequilibrium and the corresponding equilibrium state of the system. The Bures angle is an angle between mixed quantum states and defines a thermodynamic length valid arbitrarily far from equilibrium. As an illustration, we treat the case of a time-dependent harmonic oscillator for which we obtain analytic expressions for generic driving protocols. PMID:23496495

Deffner, Sebastian; Lutz, Eric

2013-02-28

418

Dynamic Stabilization of a Quantum Many-Body Spin System

NASA Astrophysics Data System (ADS)

We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.

Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

2013-08-01

419

Quantum features in statistical observations of ``timeless'' classical systems

NASA Astrophysics Data System (ADS)

We pursue the view that quantum theory may be an emergent structure at large space-time scales. We consider classical Hamiltonian systems in which the intrinsic proper time evolution parameter is related through a probability distribution to the discrete physical time. This is motivated by studies of ``timeless'' reparametrization invariant models, where discrete physical time has recently been constructed based on coarse-graining local observables. Describing such deterministic classical systems with the help of path-integrals, primordial states can naturally be introduced which follow unitary quantum mechanical evolution in suitable limits.

Elze, H.-T.

2004-12-01

420

Optimized pulse sequences for suppressing unwanted transitions in quantum systems

We investigate the nature of the pulse sequence so that unwanted transitions in quantum systems can be inhibited optimally. For this purpose we show that the sequence of pulses proposed by Uhrig [Phys. Rev. Lett. 98, 100504 (2007)] in the context of inhibition of environmental dephasing effects is optimal. We derive exact results for inhibiting the transitions and confirm the results numerically. We posit a very significant improvement by usage of the Uhrig sequence over an equidistant sequence in decoupling a quantum system from unwanted transitions. The physics of inhibition is the destructive interference between transition amplitudes before and after each pulse.

Schroeder, C. A.; Agarwal, G. S. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St. Norman, Oklahoma 73019 (United States); Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)

2011-01-15