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1

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

DEFF Research Database (Denmark)

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

Nysteen, Anders; Nielsen, Per Kær

2012-01-01

2

Exciton-polariton dynamics in quantum dot-cavity system

Energy Technology Data Exchange (ETDEWEB)

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

Neto, Antonio F.; Lima, William J.; Villas-Boas, Jose M. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica

2012-07-01

3

Influence of a phonon bath in a quantum dot cavity QED system: Dependence of the shape

We present a systematic analysis on the role of the quantum dot (QD) shape in the influence of the phonon bath on the dynamics of a QD cavity QED system. The spectral functions of the phonon bath in three representative QD shapes: spherical, ellipsoidal, and disk, are calculated from the carrier wave functions subjected to the confinement potential provided by the corresponding shape. The obtained spectral functions are used to calculate three main effects brought by the phonon bath, i.e., the coupling renormalization, the off-resonance assisted feeding rate and the pure dephasing rate. It is found that the spectral function of a disk QD has the widest distribution, hence the phonon bath in a disk QD can lead to the smallest renormalization factor, the largest dephasing rate in the short time domains(<= 2 ps), and the off-resonance assisted feeding can support the widest detuning. Except for the pure dephasing rate in the long time domains, all the influences brought by the phonon bath show serious shape dependence.

Wang, Wei-Sheng; Zhang, Ming-Liang; Chen, Zhi-De

2014-09-01

4

Bright single photon source based on self-aligned quantum dot-cavity systems.

We report on a quasi-planar quantum-dot-based single-photon source that shows an unprecedented high extraction efficiency of 42% without complex photonic resonator geometries or post-growth nanofabrication. This very high efficiency originates from the coupling of the photons emitted by a quantum dot to a Gaussian shaped nanohill defect that naturally arises during epitaxial growth in a self-aligned manner. We investigate the morphology of these defects and characterize the photonic operation mechanism. Our results show that these naturally arising coupled quantum dot-defects provide a new avenue for efficient (up to 42% demonstrated) and pure (g(2)(0) value of 0.023) single-photon emission. PMID:24718190

Maier, Sebastian; Gold, Peter; Forchel, Alfred; Gregersen, Niels; Mørk, Jesper; Höfling, Sven; Schneider, Christian; Kamp, Martin

2014-04-01

5

Bright single photon source based on self-aligned quantum dot–cavity systems

DEFF Research Database (Denmark)

We report on a quasi-planar quantum-dot-based single-photon source that shows an unprecedented high extraction efficiency of 42% without complex photonic resonator geometries or post-growth nanofabrication. This very high efficiency originates from the coupling of the photons emitted by a quantum dot to a Gaussian shaped nanohill defect that naturally arises during epitaxial growth in a self-aligned manner. We investigate the morphology of these defects and characterize the photonic operation mechanism. Our results show that these naturally arising coupled quantum dot-defects provide a new avenue for efficient (up to 42% demonstrated) and pure (g2(0) value of 0.023) single-photon emission.

Gregersen, Niels; MØrk, Jesper

2014-01-01

6

Recently, experiments showed that the spatial-mode states of entangled photons are more robust than their polarization-mode states in quantum communications. Here, we construct a complete and deterministic protocol for analyzing the spatial Bell states using the interaction between a photon and an electron spin in a charged quantum dot inside a one-side micropillar microcavity. A quantum nondemolition detector (QND) for checking the parity of a two-photon system can be constructed with the giant optical Faraday rotation in this solid state system. With this parity-check QND, we present a complete and deterministic proposal for the analysis of the four spatial-mode Bell states. Moreover, we present a robust two-step quantum secure direct communication protocol based on the spatial-mode Bell states and the photonic spatial Bell-state analysis. Our analysis shows that our BSA proposal works in both the strong and the weak coupling regimes if the side leakage and cavity loss rate is small.

Ren, Bao-Cang; Wei, Hai-Rui; Hua, Ming; Li, Tao; Deng, Fu-Guo

2013-02-01

7

Competition between pure dephasing and photon losses in the dynamics of a dot-cavity system

We demonstrate that in quantum-dot cavity systems, the interplay between acoustic phonons and photon losses introduces novel features and characteristic dependencies in the system dynamics. In particular, the combined action of both dephasing mechanisms strongly affects the transition from the weak- to the strong-coupling regime as well as the shape of the spectral triplet that represents the quantum-dot occupation in Fourier space. The width of the central peak in the triplet is expected to decrease with rising temperature, while the widths and heights of the side peaks depend nonmonotonically on the dot-cavity coupling.

Vagov, A.; Glässl, M.; Croitoru, M. D.; Axt, V. M.; Kuhn, T.

2014-08-01

8

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

International Nuclear Information System (INIS)

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

9

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

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

2012-01-01

10

Fast Two-Qubit Gates in Semiconductor Quantum Dots using a Photonic Microcavity

Digital Repository Infrastructure Vision for European Research (DRIVER)

Implementations for quantum computing require fast single- and multi-qubit quantum gate operations. In the case of optically controlled quantum dot qubits theoretical designs for long-range two- or multi-qubit operations satisfying all the requirements in quantum computing are not yet available. We have developed a design for a fast, long-range two-qubit gate mediated by a photonic microcavity mode using excited states of the quantum dot-cavity system that addresses these ne...

Solenov, Dmitry; Economou, Sophia E.; Reinecke, T. L.

2012-01-01

11

We demonstrate non-perturbative coupling between a single self-assembled InGaAs quantum dot and an external fiber-mirror based microcavity. Our results extend the previous realizations of tunable microcavities while ensuring spatial and spectral overlap between the cavity-mode and the emitter by simultaneously allowing for deterministic charge control of the quantum dots. Using resonant spectroscopy, we show that the coupled quantum dot cavity system is at the onset of strong coupling, with a cooperativity parameter of 2. Our results constitute a milestone towards the realization of a high efficiency solid-state spin-photon interface.

Miguel-Sanchez, J; Togan, E; Volz, T; Imamoglu, A; Besga, B; Reichel, J; Esteve, J

2012-01-01

12

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Cahill, Reginald T.

2002-01-01

13

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

Cahill, R T

2002-01-01

14

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

Weiss, Ulrich

2008-01-01

15

The damping of the harmonic oscillator is studied in the framework of the Lindblad theory for open quantum systems. A generalization of the fundamental constraints on quantum mechanical diffusion coefficients which appear in the master equation for the damped quantum oscillator is presented; the Schr\\"odinger, Heisenberg and Weyl-Wigner-Moyal representations of the Lindblad equation are given explicitly. On the basis of these representations it is shown that various master equations for the damped quantum oscillator used in the literature are particular cases of the Lindblad equation and that not all of these equations are satisfying the constraints on quantum mechanical diffusion coefficients. The master equation is transformed into Fokker-Planck equations for quasiprobability distributions and a comparative study is made for the Glauber $P$ representation, the antinormal ordering $Q$ representation and the Wigner $W$ representation. The density matrix is represented via a generating function, which is obtai...

Isar, A; Scutaru, H; Stefanescu, E; Scheid, W

1994-01-01

16

International Nuclear Information System (INIS)

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

17

Energy Technology Data Exchange (ETDEWEB)

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

18

Engineering quantum communication systems

Quantum communications can provide almost perfect security through the use of quantum laws to detect any possible leak of information. We discuss critical issues in the implementation of quantum communication systems over installed optical fibers. We use stimulated four-wave mixing to generate single photons inside optical fibers, and by tuning the separation between the pump and the signal we adjust the average number of photons per pulse. We report measurements of the source statistics and show that it goes from a thermal to Poisson distribution with the increase of the pump power. We generate entangled photons pairs through spontaneous four-wave mixing. We report results for different type of fibers to approach the maximum value of the Bell inequality. We model the impact of polarization rotation, attenuation and Raman scattering and present optimum configurations to increase the degree of entanglement. We encode information in the photons polarization and assess the use of wavelength and time division multiplexing based control systems to compensate for the random rotation of the polarization during transmission. We show that time division multiplexing systems provide a more robust solution considering the values of PMD of nowadays installed fibers. We evaluate the impact on the quantum channel of co-propagating classical channels, and present guidelines for adding quantum channels to installed WDM optical communication systems without strongly penalizing the performance of the quantum channel. We discuss the process of retrieving information from the photons polarization. We identify the major impairments that limit the speed and distance of the quantum channel. Finally, we model theoretically the QBER and present results of an experimental performance assessment of the system quality through QBER measurements.

Pinto, Armando N.; Almeida, Álvaro J.; Silva, Nuno A.; Muga, Nelson J.; Martins, Luis M.

2012-06-01

19

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

Weiss, Ulrich

2012-01-01

20

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Gonc?alves, Carlos Pedro

2014-01-01

21

Quasiperiodically kicked quantum systems

International Nuclear Information System (INIS)

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

22

International Nuclear Information System (INIS)

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

23

Stationary States of Dissipative Quantum Systems

In this Letter we consider stationary states of dissipative quantum systems. We discuss stationary states of dissipative quantum systems, which coincide with stationary states of Hamiltonian quantum systems. Dissipative quantum systems with pure stationary states of linear harmonic oscillator are suggested. We discuss bifurcations of stationary states for dissipative quantum systems which are quantum analogs of classical dynamical bifurcations.

Tarasov, Vasily E

2011-01-01

24

Decoherence in open quantum systems

International Nuclear Information System (INIS)

In the framework of the Lindblad theory for open quantum systems we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. In the present paper we have studied QD with the Markovian equation of Lindblad in order to understand the quantum to classical transition for a system consisting of an one-dimensional harmonic oscillator in interaction with a thermal bath in the framework of the theory of open quantum systems based on quantum dynamical semigroups. The role of QD became relevant in many interesting physical problems from field theory, atomic physics, quantum optics and quantum information processing, to which we can add material science, heavy ion collisions, quantum gravity and cosmology, condensed matter physics. Just to mention only a few of them: to understand the way in which QD enhances the quantum to classical transition of density fluctuations; to study systems of trapped and cold atoms (or ions) which may offer the possibility of engineering the environment, like trapped atoms inside cavities, relation between decoherence and other cavity QED effects (such as Casimir effect); on mesoscopic scale, decoherence in the context of Bose-Einstein condensation. In many cases physicists are interested in understanding the specific causes of QD just because they want to prevent decoherence from damaging quantum states and to protect the information stored in quantum states from the degrading effect of the interaction w the degrading effect of the interaction with the environment. Thus, decoherence is responsible for washing out the quantum interference effects which are desirable to be seen as signals in some experiments. QD has a negative influence on many areas relying upon quantum coherence effects, such as quantum computation and quantum control of atomic and molecular processes. The physics of information and computation is such a case, where decoherence is an obvious major obstacle in the implementation of information-processing hardware that takes advantage of the superposition principle. The study of classicality using QD leads to a deeper understanding of the quantum origins of the classical world. Much work has still to be done even to settle the interpretational questions, not to speak about answering them. Nevertheless, as a result of the progress made in the last two decades, the quantum to classical transition has become a subject of experimental investigations, while previously it was mostly a domain of philosophy. The issue of quantum to classical transition points to the necessity of a better understanding of open quantum systems. The Lindblad theory provides a selfconsistent treatment of damping as a general extension of quantum mechanics

25

Theories for quantum liquid systems

International Nuclear Information System (INIS)

Several interesting quantum liquid systems are studied theoretically. The method to approach each system is chosen by considering the special properties of that system. First principles variational theory is developed to study the properties of the ground state of many-electron atomic systems. The inhomogeneity and strong Coulomb interaction are taken into account directly. The correlation energies calculated are in good agreement with experimental data. Particle-field interactions reveal another aspect of quantum liquids. The system with positive ions embedded in superfluid 4He is used as an example to study particle-field interactions in quantum liquids. A quantum model is proposed and solved by a variational method. The quantum Hall effect is one of the most important discoveries in condensed matter systems. From a quantum scattering theory, the quantum Hall effect in quasi-three-dimensional systems observed in semiconductor superlattices is explained and general criteria for the quantum Hall effect in such systems are given. Superconducting-insulating phase transition in ultrathin films realizes many aspects of the theory of localization and quantum fluctuation. A simple analysis for the superconducting-insulating phase transition in ultrathin films indicates the phase transition is a combined effect of pairing and localization

26

Classical command of quantum systems.

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

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

2013-04-25

27

Applications of quantum integrable systems

We present two applications of quantum integrable systems. First, we predict that it is possible to generate high harmonics from solid state devices by demostrating that the emission spectrum for a minimally coupled laser field of frequency $\\omega$ to an impurity system of a quantum wire, contains multiples of the incoming frequency. Second, evaluating expressions for the conductance in the high temperature regime we show that the caracteristic filling fractions of the Jain sequence, which occur in the fractional quantum Hall effect, can be obtained from quantum wires which are described by minimal affine Toda field theories.

Castro-Alvaredo, O A; Castro-Alvaredo, Olalla A.; Fring, Andreas

2003-01-01

28

Quantum Effects in Biological Systems

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

Roy, Sisir

2014-07-01

29

Open quantum systems recent developments

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

Joye, Alain; Pillet, Claude-Alain

2006-01-01

30

Decoherence in infinite quantum systems

International Nuclear Information System (INIS)

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.

31

Decoherence in infinite quantum systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-01

32

International Nuclear Information System (INIS)

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

33

A prototype quantum cryptography system

International Nuclear Information System (INIS)

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

34

Three Terminal Quantum Dot System

Directory of Open Access Journals (Sweden)

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

N. Chandrasekar

2012-01-01

35

Geometry of dynamical quantum systems

International Nuclear Information System (INIS)

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

36

Quantum retrodiction in open systems

International Nuclear Information System (INIS)

Quantum retrodiction involves finding the probabilities for various preparation events given a measurement event. This theory has been studied for some time but mainly as an interesting concept associated with time asymmetry in quantum mechanics. Recent interest in quantum communications and cryptography, however, has provided retrodiction with a potential practical application. For this purpose quantum retrodiction in open systems should be more relevant than in closed systems isolated from the environment. In this paper we study retrodiction in open systems and develop a general master equation for the backward time evolution of the measured state, which can be used for calculating preparation probabilities. We solve the master equation, by way of example, for the driven two-level atom coupled to the electromagnetic field

37

Software-defined Quantum Communication Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Humble, Travis S.; Sadlier, Ronald J.

2014-01-01

38

Quantum systems and symmetric spaces

International Nuclear Information System (INIS)

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

39

Wilson's approach to quantum systems

International Nuclear Information System (INIS)

We discuss the relevance that the Wilson Renormalization Group approach to Bose systems has for quantum systems for which a functional Bosonization exists. The role of Matsubara frequencies as concerning the phenomenon of dimensional crossover is pointed out. Furthermore we find that the unusual critical behaviour of Bose system at T=0 can be included to first order in epsilon = 2-d, in the Wilson universality class with n = -2, with n the number of order parameter components. Finally, some consierations about other quantum systems are made. (author)

40

Quantum Dot Systems: a versatile platform for quantum simulations

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-15

41

DEFF Research Database (Denmark)

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

Settnes, Mikkel; Nielsen, Per Kær

2013-01-01

42

Quantum energy teleportation in a quantum Hall system

Energy Technology Data Exchange (ETDEWEB)

We propose an experimental method for a quantum protocol termed quantum energy teleportation (QET), which allows energy transportation to a remote location without physical carriers. Using a quantum Hall system as a realistic model, we discuss the physical significance of QET and estimate the order of energy gain using reasonable experimental parameters.

Yusa, Go; Izumida, Wataru; Hotta, Masahiro [Department of Physics, Tohoku University, Sendai 980-8578 (Japan)

2011-09-15

43

Lyapunov Control of Quantum Systems with Applications to Quantum Computing

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2012-01-01

44

Quantum simulation of QFTs with discrete quantum systems

Energy Technology Data Exchange (ETDEWEB)

Classical simulation of quantum many-body systems is usually very inefficient with long running times and with high needs for memory (e.g., it is not even possible to store classically the arbitrary state of 50 qubits). One might overcome these difficulties by using other quantum systems, similar to the one we want to study, as quantum simulators. Most of the efforts in this direction has been concentrated on simulating discrete quantum systems (e.g. spin chains) with other discrete quantum systems that are relatively easy to prepare in labs (ion traps, atoms in optical lattices, etc.). In this talk I will treat a different problem: How can we simulate a continuous quantum system (e.g. a QFT) with a discrete one? I will in particular show how (and in which sense) one can use the Holstein-Primakoff transformation to store continuous quantum information in a discrete quantum system, and after the storage how one can model the time-evolution of the continuous quantum system with a quantum cellular automata action on the discrete system.

Zimboras, Zoltan; Keyl, Michael; Schlingemann, Dirk-Michael [Quantum Information Group, ISI, Torino (Italy)

2010-07-01

45

Quantum Annealing and Quantum Fluctuation Effect in Frustrated Ising Systems

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

Tanaka, Shu

2012-01-01

46

Quantum chaos in nanoelectromechanical systems

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

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

2005-01-01

47

Dynamics of complex quantum systems

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

Akulin, Vladimir M

2014-01-01

48

Control of the quantum open system via quantum generalized measurement

International Nuclear Information System (INIS)

For any specified pure state of quantum open system, we can construct a kind of quantum generalized measurement (QGM) that the state of the system after measurement will be deterministically collapsed into the specified pure state from any initial state. In other words, any pure state of quantum open system is reachable by QGM. Subsequently, whether the qubit is density matrix controllable is discussed in the case of pure dephasing. Our results reveal that combining QGM with coherent control will enhance the ability of controlling the quantum open system. Furthermore, it is found that the ability to perform QGM on the quantum open system, combined with the ability of coherence control and conditions of decoherence-free subspace, allows us to suppress quantum decoherence

49

Nonequilibrium work equalities in isolated quantum systems

We briefly introduce the quantum Jarzynski and Bochkov—Kuzovlev equalities in isolated quantum Hamiltonian systems, including their origin, their derivations using a quantum Feynman—Kac formula, the quantum Crooks equality, the evolution equations governing the characteristic functions of the probability density functions for the quantum work, and recent experimental verifications. Some results are given here for the first time. We particularly emphasize the formally structural consistence between these quantum equalities and their classical counterparts, which are useful for understanding the existing equalities and pursuing new fluctuation relations in other complex quantum systems.

Liu, Fei; Ouyang, Zhong-Can

2014-07-01

50

Quantum gravity and spin systems

International Nuclear Information System (INIS)

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

51

Quantum tomography and classical propagator for quadratic quantum systems

International Nuclear Information System (INIS)

The classical propagator for tomographic probability (which describes the quantum state instead of wave function or density matrix) is presented for quadratic quantum systems and its relation to the quantum propagator is considered. The new formalism of quantum mechanics, based on the probability representation of the state, is applied to particular quadratic systems - the harmonic oscillator, particle's free motion, problems of an ion in a Paul trap and in asymmetric Penning trap, and to the process of stimulated Raman scattering. The classical propagator for these systems is written in an explicit form. (author)

52

Quantum computing and information extraction for a dynamical quantum system

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the simulation of a complex dynamical system, the so-called quantum sawtooth map model, on a quantum computer. We show that a quantum computer can be used to efficiently extract relevant physical information for this model. It is possible to simulate the dynamical localization of classical chaos and extract the localization length of the system with quadratic speed up with respect to any known classical computation. We can also compute with algebraic speed up the ...

Benenti, Giuliano; Casati, Giulio; Montangero, Simone

2004-01-01

53

Polygamy of Entanglement in Multipartite Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Kim, Jeong San

2009-01-01

54

Dispersive Quantum Systems: a class of isolated non-time reversal quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

A "dispersive quantum system" is a quantum system which is both isolated and non-time reversal invariant. This article presents precise definitions for those concepts and also a characterization of dispersive quantum systems within the class of completely positive Markovian quantum systems in finite dimension (through a homogeneous linear equation for the non-Hamiltonian part of the system's Liouvillian). To set the framework, the basic features of quantum mechanics are revi...

Fassarella, Lu?cio

2011-01-01

55

Quantum Information Processing in Disordered and Complex Quantum Systems

We investigate quantum information processing and manipulations in disordered systems of ultracold atoms and trapped ions. First, we demonstrate generation of entanglement and local realization of quantum gates in a quantum spin glass system. Entanglement in such systems attains significantly high values, after quenched averaging, and has a stable positive value for arbitrary times. Complex systems with long range interactions, such as ion chains or dipolar atomic gases, can be modeled by neural network Hamiltonians. In such systems, we find the characteristic time of persistence of quenched averaged entanglement, and also find the time of its revival.

De, A S; Ahufinger, V; Briegel, H J; Sanpera, A; Lewenstein, M; De, Aditi Sen; Sen, Ujjwal; Ahufinger, Veronica; Briegel, Hans J.; Sanpera, Anna; Lewenstein, Maciej

2005-01-01

56

Quantum Computing in Solid State Systems

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

Ruggiero, B; Granata, C

2006-01-01

57

Eigenfunctions in chaotic quantum systems

Energy Technology Data Exchange (ETDEWEB)

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

Baecker, Arnd

2007-07-01

58

Classical and quantum correlative capacities of quantum systems

International Nuclear Information System (INIS)

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

59

Quantum systems, channels, information. A mathematical introduction

International Nuclear Information System (INIS)

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

60

Quantum systems, channels, information. A mathematical introduction

Energy Technology Data Exchange (ETDEWEB)

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

Holevo, Alexander S.

2012-07-01

61

Entanglement in many-body quantum systems

Short review on entanglement, as seen from a quantum information perspective, and some simple applications to many-body quantum systems. Special emphasis in area laws, cold atoms, and efficient descriptions using tensor network states.

Cirac, J Ignacio

2012-01-01

62

Dissipation in composite quantum systems

Dissipation in the form of spontaneous emission of photons from an optical cavity and from individually trapped atoms has been studied extensively in the framework of quantum optics. Up to now, theoretical predictions based on the dipole and the rotating wave approximation (RWA) are in very good agreement with experimental findings. However, current experiments aim at combining better and better cavities with relatively large numbers of tightly confined atoms within the same setup. Here we point out that the result might be a behaviour which is profoundly different from the behaviour of individual quantum systems and which cannot be described using the RWA. To show this, we predict a non-zero stationary-state cavity photon emission rate even in the absence of external driving. This rate and its dependence on the system parameters could be verified experimentally.

Kurcz, Andreas; Beige, Almut; Del Giudice, Emilio; Vitiello, Giuseppe

2009-01-01

63

Numerical study of vortex system quantum melting

We report a numerical study of the vortex system in the two dimensional II-type superconductors. We have proposed a phenomenological model that takes into account quantum fluctuations of Abrikosov's vortices. The results of the quantum Monte-Carlo simulations by the SSE algorithm show that the thermal fluctuations are dominated by quantum fluctuations at low temperatures. In particular, we demonstrate the possibility of the quantum melting transition for vortex system in the temperature region where thermal melting transition is improbable.

Zyubin, M V; Kashurnikov, V A

2004-01-01

64

Numerical study of vortex system quantum melting

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a numerical study of the vortex system in the two dimensional II-type superconductors. We have proposed a phenomenological model that takes into account quantum fluctuations of Abrikosov's vortices. The results of the quantum Monte-Carlo simulations by the SSE algorithm show that the thermal fluctuations are dominated by quantum fluctuations at low temperatures. In particular, we demonstrate the possibility of the quantum melting transition for vortex system in the...

Zyubin, M. V.; Rudnev, I. A.; Kashurnikov, V. A.

2004-01-01

65

The Quantum Mechanics of Closed Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Hartle, James B.

1992-01-01

66

Quantum-information processing in disordered and complex quantum systems

International Nuclear Information System (INIS)

We study quantum information processing in complex disordered many body systems that can be implemented by using lattices of ultracold atomic gases and trapped ions. We demonstrate, first in the short range case, the generation of entanglement and the local realization of quantum gates in a disordered magnetic model describing a quantum spin glass. We show that in this case it is possible to achieve fidelities of quantum gates higher than in the classical case. Complex systems with long range interactions, such as ions chains or dipolar atomic gases, can be used to model neural network Hamiltonians. For such systems, where both long range interactions and disorder appear, it is possible to generate long range bipartite entanglement. We provide an efficient analytical method to calculate the time evolution of a given initial state, which in turn allows us to calculate its quantum correlations

67

Repeated interactions in open quantum systems

Analyzing the dynamics of open quantum systems has a long history in mathematics and physics. Depending on the system at hand, basic physical phenomena that one would like to explain are, for example, convergence to equilibrium, the dynamics of quantum coherences (decoherence) and quantum correlations (entanglement), or the emergence of heat and particle fluxes in non-equilibrium situations. From the mathematical physics perspective, one of the main challenges is to derive the irreversible dynamics of the open system, starting from a unitary dynamics of the system and its environment. The repeated interactions systems considered in these notes are models of non-equilibrium quantum statistical mechanics. They are relevant in quantum optics, and more generally, serve as a relatively well treatable approximation of a more difficult quantum dynamics. In particular, the repeated interaction models allow to determine the large time (stationary) asymptotics of quantum systems out of equilibrium.

Bruneau, Laurent; Joye, Alain; Merkli, Marco

2014-07-01

68

Could nanostructure be unspeakable quantum system?

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

Aristov, V V

2010-01-01

69

Modeling of quantum electromechanical systems

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

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

2004-01-01

70

Quantum Mechanics of Disordered Systems

We investigated quantum transport properties of substitutionally disordered lattices interacting with a classically fluctuating bath and explore the effects of dephasing on Anderson localization. Two different systems with site disorder were studied, one with scalar near neighbor coupling terms and the other with tensor dipolar coupling terms. We generally observed the behavior predicted from approximate theories--the existence of a Mooij like correlation in both systems corresponding to weakly delocalized states. Also noted were the absence of strict localization in the dipolar case and the existence of a mobility edge in the near neighbor case.

Evensky, David Alan

71

Transport properties of quantum-classical systems

International Nuclear Information System (INIS)

Correlation function expressions for calculating transport coefficients for quantum-classical systems are derived. The results are obtained by starting with quantum transport coefficient expressions and replacing the quantum time evolution with quantum-classical Liouville evolution, while retaining the full quantum equilibrium structure through the spectral density function. The method provides a variety of routes for simulating transport coefficients of mixed quantum-classical systems, composed of a quantum subsystem and a classical bath, by selecting different but equivalent time evolution schemes of any operator or the spectral density. The structure of the spectral density is examined for a single harmonic oscillator where exact analytical results can be obtained. The utility of the formulation is illustrated by considering the rate constant of an activated quantum transfer process that can be described by a many-body bath reaction coordinate

72

Transport properties of quantum-classical systems.

Correlation function expressions for calculating transport coefficients for quantum-classical systems are derived. The results are obtained by starting with quantum transport coefficient expressions and replacing the quantum time evolution with quantum-classical Liouville evolution, while retaining the full quantum equilibrium structure through the spectral density function. The method provides a variety of routes for simulating transport coefficients of mixed quantum-classical systems, composed of a quantum subsystem and a classical bath, by selecting different but equivalent time evolution schemes of any operator or the spectral density. The structure of the spectral density is examined for a single harmonic oscillator where exact analytical results can be obtained. The utility of the formulation is illustrated by considering the rate constant of an activated quantum transfer process that can be described by a many-body bath reaction coordinate. PMID:15974726

Kim, Hyojoon; Kapral, Raymond

2005-06-01

73

Optimal Lyapunov-based quantum control for quantum systems

Quantum Lyapunov control was developed in order to transform a quantum system from arbitrary initial states to a target state. The idea is to find control fields that steer the Lyapunov function to zero as $t\\rightarrow \\infty$, meanwhile the quantum system is driven to the target state. In order to shorten the time required to reach the target state, we propose two designs to optimize Lyapunov control in this paper. The first design makes the Lyapunov function decrease as fast as possible with a constraint on the total power of control fields, and the second design has the same purpose but with a constraint on each control field. Examples of a three-level system demonstrate that the evolution time for Lyapunov control can be significantly shortened, especially when high control fidelity is required. Besides, this optimal Lyapunov-based quantum control is robust against uncertainties in the free Hamiltonian and decoherence in the system compared to conventional Lyapunov control.

Hou, S C; Dong, Daoyi; Petersen, Ian R; Yi, X X

2012-01-01

74

Classical and quantum dissipative systems

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

Razavy, Mohsen

2006-01-01

75

Thermalization of isolated quantum systems

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

Khlebnikov, Sergei

2013-01-01

76

A study of Quantum Correlations in Open Quantum Systems

In this work, we study quantum correlations in mixed states. The states studied are modelled by a two-qubit system interacting with its environment via a quantum nondemolition (purely dephasing) as well as dissipative type of interaction. The entanglement dynamics of this two qubit system is analyzed and the existence of entangled states which do not violate Bell's inequality, but can still be useful as a potential resource for teleportation are reported. In addition, a comparative study of various measures of quantum correlations, like Concurrence, Bell's inequality, Discord and Teleportation fidelity, is made on these states, generated by the above evolutions. Interestingly, examples are found, of states, where entanglement is vanishing, but discord is non-vanishing, bringing out the fact that entanglement is a subset of quantum correlations.

Chakrabarty, Indranil; Siddharth, Nana

2010-01-01

77

Hybrid quantum systems of atoms and ions

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

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

2010-01-01

78

Symplectic transformations and quantum tomography in finite quantum systems

International Nuclear Information System (INIS)

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

79

Controllable Subspaces of Open Quantum Dynamical Systems

International Nuclear Information System (INIS)

This paper discusses the concept of controllable subspace for open quantum dynamical systems. It is constructively demonstrated that combining structural features of decoherence-free subspaces with the ability to perform open-loop coherent control on open quantum systems will allow decoherence-free subspaces to be controllable. This is in contrast to the observation that open quantum dynamical systems are not open-loop controllable. To a certain extent, this paper gives an alternative control theoretical interpretation on why decoherence-free subspaces can be useful for quantum computation.

80

Quantum temporal probabilities in tunneling systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 sp...

Anastopoulos, Charis; Savvidou, Ntina

2012-01-01

81

Adiabatic approximation in open quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We generalize the standard quantum adiabatic approximation to the case of open quantum systems. We define the adiabatic limit of an open quantum system as the regime in which its dynamical superoperator can be decomposed in terms of independently evolving Jordan blocks. We then establish validity and invalidity conditions for this approximation and discuss their applicability to superoperators changing slowly in time. As an example, the adiabatic evolution of a two-level ope...

Sarandy, M. S.; Lidar, D. A.

2004-01-01

82

Quantum field theory of relic nonequilibrium systems

In terms of the de Broglie-Bohm pilot-wave formulation of quantum theory, we develop field-theoretical models of quantum nonequilibrium systems which could exist today as relics from the very early universe. We consider relic excited states generated by inflaton decay, as well as relic vacuum modes, for particle species that decoupled close to the Planck temperature. Simple estimates suggest that, at least in principle, quantum nonequilibrium could survive to the present day for some relic systems. The main focus of this paper is to describe the behaviour of such systems in terms of field theory, with the aim of understanding how relic quantum nonequilibrium might manifest experimentally. We show by explicit calculation that simple perturbative couplings will transfer quantum nonequilibrium from one field to another (for example from the inflaton field to its decay products). We also show that fields in a state of quantum nonequilibrium will generate anomalous spectra for standard energy measurements. Possibl...

Underwood, Nicolas G

2014-01-01

83

Predictive Information for Quantum Bio-Systems

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

Pati, Arun Kumar

2014-07-01

84

Dynamical entropy for infinite quantum systems

International Nuclear Information System (INIS)

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

85

Nonequilibrium quantum criticality in open electronic systems

A theory is presented of nonequilibrium quantum criticality in open (coupled to reservoirs) electronic systems. Results are given for itinerant Ising and Heisenberg magnets with nonequilibrium provided by current flow across the system. Both departures from equilibrium at conventional (equilibrium) quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are treated.

Mitra, A; Kim, Y B; Millis, A J; Mitra, Aditi; Takei, So; Kim, Yong Baek

2006-01-01

86

Quantum information theory with Gaussian systems

Energy Technology Data Exchange (ETDEWEB)

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

Krueger, O.

2006-04-06

87

Quantum information theory with Gaussian systems

International Nuclear Information System (INIS)

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

88

Dynamical systems where time is a quantum group and quantum ergodicity

Digital Repository Infrastructure Vision for European Research (DRIVER)

We define dynamical systems where time is a quantum group. We give the definition of quantum ergodicity for the introduced dynamical system with noncommutative (or quantum) time, and discuss the examples.

Kozyrev, S. V.

2003-01-01

89

Coherent Dynamics of Complex Quantum Systems

A large number of modern problems in physics, chemistry, and quantum electronics require a consideration of population dynamics in complex multilevel quantum systems. The purpose of this book is to provide a systematic treatment of these questions and to present a number of exactly solvable problems. It considers the different dynamical problems frequently encountered in different areas of physics from the same perspective, based mainly on the fundamental ideas of group theory and on the idea of ensemble average. Also treated are concepts of complete quantum control and correction of decoherence induced errors that are complementary to the idea of ensemble average. "Coherent Dynamics of Complex Quantum Systems" is aimed at senior-level undergraduate students in the areas of Atomic, Molecular, and Laser Physics, Physical Chemistry, Quantum Optics and Quantum Informatics. It should help them put particular problems in these fields into a broader scientific context and thereby take advantage of the well-elabora...

Akulin, Vladimir M

2006-01-01

90

Quantum phase transitions in electronic systems

Quantum phase transitions occur at zero temperature when some non-thermal control-parameter like pressure or chemical composition is changed. They are driven by quantum rather than thermal fluctuations. In this review we first give a pedagogical introduction to quantum phase transitions and quantum critical behavior emphasizing similarities with and differences to classical thermal phase transitions. We then illustrate the general concepts by discussing a few examples of quantum phase transitions occurring in electronic systems. The ferromagnetic transition of itinerant electrons shows a very rich behavior since the magnetization couples to additional electronic soft modes which generates an effective long-range interaction between the spin fluctuations. We then consider the influence of rare regions on quantum phase transitions in systems with quenched disorder, taking the antiferromagnetic transitions of itinerant electrons as a primary example. Finally we discuss some aspects of the metal-insulator transit...

Vojta, T

1999-01-01

91

Understanding electronic systems in semiconductor quantum dots

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

Ciftja, Orion

2013-11-01

92

Dissipations in coupled quantum systems

International Nuclear Information System (INIS)

We investigate the dynamics of a composite quantum system, comprised of coupled subsystems, of which only one is significantly interacting with the environment. The validity of the conventional ad hoc approach--assuming that relaxation terms can be extracted directly from the master equation of the subsystem interacting with the reservoir--was examined. We derived the equation of motion for the composite system's reduced density matrix--applying only the factorization approximation, but not the conventional sequence of Markoff, coarse grain, and secular approximations. From our analysis, we concluded that the conventional ad hoc approach is applicable to zero-temperature reservoir, but fails for finite temperatures. It is further shown that at finite temperatures, the standard procedure does not even yield a master equation for the composite system, and its dynamics has to be studied by the equations of motion which are developed here. For demonstration we considered a system of a three-level atom, the two excited states are coupled to each other, and only one of them communicates with the ground state via a radiation reservoir

93

Intrinsic and extrinsic properties of quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper attempts to convince that the orthodox interpretation of quantum mechanics does not contradict philosophical realism by throwing light onto certain properties of quantum systems that seem to have escaped attention as yet. The exposition starts with the philosophical notions of realism. Then, the quantum mechanics as it is usually taught is demoted to a mere part of the theory called phenomenology of observations, and the common impression about its contradiction to...

Hajicek, P.; Tolar, J.

2008-01-01

94

Simulating quantum systems using real Hilbert spaces

We develop a means of simulating the evolution and measurement of a multipartite quantum state under discrete or continuous evolution using another quantum system with states and operators lying in a real Hilbert space. This extends previous results which were unable to simulate local evolution and measurements with local operators and was limited to discrete evolution. We also detail applications to Bell inequalities and self-testing of quantum apparatus.

McKague, Matthew; Gisin, Nicolas

2008-01-01

95

Slightly anharmonic systems in quantum optics

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

Klimov, Andrey B.; Chumakov, Sergey M.

1995-01-01

96

Interaction between classical and quantum systems

International Nuclear Information System (INIS)

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

97

Quantum equilibria for macroscopic systems

International Nuclear Information System (INIS)

Nash equilibria are found for some quantum games with particles with spin-1/2 for which two spin projections on different directions in space are measured. Examples of macroscopic games with the same equilibria are given. Mixed strategies for participants of these games are calculated using probability amplitudes according to the rules of quantum mechanics in spite of the macroscopic nature of the game and absence of Planck's constant. A possible role of quantum logical lattices for the existence of macroscopic quantum equilibria is discussed. Some examples for spin-1 cases are also considered

98

Electromagnetically induced transparency in quantum dot systems

Energy Technology Data Exchange (ETDEWEB)

Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton-phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems.

Jiang Yiwen [Department of Physics, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240 (China); Zhu Kadi [Department of Physics, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240 (China); Wu Zhuojie [Department of Physics, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240 (China); Yuan Xiaozhong [Department of Physics, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240 (China); Yao Ming [Department of Physics, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240 (China)

2006-06-28

99

Electromagnetically induced transparency in quantum dot systems

International Nuclear Information System (INIS)

Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton-phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems

100

Dynamical Hysteresis in Bistable Quantum Systems

International Nuclear Information System (INIS)

We are studying bistable quantum systems coupled to a thermal environment in the presence of an external controlling force. The impact of thermal and quantum effects on the switching hysteresis is studied by evaluating a time-dependent real-time double path integral with the recently developed iterative tensor multiplication scheme for the quasiadiabatic path integral propagator method for temperatures ranging from well above to well below quantum-classical crossover temperature. The switching dynamics and its intimate connection to quantum stochastic resonance is studied here for the first time without limitation to a two-state description and/or small external forces. copyright 1997 The American Physical Society

101

Quantum simulation of tunneling in small systems.

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures. PMID:22916333

Sornborger, Andrew T

2012-01-01

102

Optimal Lyapunov-based quantum control for quantum systems

Quantum Lyapunov control was developed in order to transform a quantum system from arbitrary initial states to a target state. The idea is to find control fields that steer the Lyapunov function to zero as t??, meanwhile the quantum system is driven to the target state. In order to shorten the time required to reach the target state, we propose two designs to optimize Lyapunov control in this paper. The first design makes the Lyapunov function decrease as fast as possible with a constraint on the total power of control fields, and the second design has the same purpose but with a constraint on each control field. Examples of a three-level system demonstrate that the evolution time for Lyapunov control can be significantly shortened, especially when high control fidelity is required. Besides, this optimal Lyapunov-based quantum control is robust against uncertainties in the free Hamiltonian and decoherence in the system compared to conventional Lyapunov control. We apply our optimal design to cool a nanomechanical resonator where a shorter cooling time is found with respect to the cooling time by the conventional Lyapunov design.

Hou, S. C.; Khan, M. A.; Yi, X. X.; Dong, Daoyi; Petersen, Ian R.

2012-08-01

103

Avoiding irreversible dynamics in quantum systems

Devices that exploit laws of quantum physics offer revolutionary advances in computation and communication. However, building such devices presents an enormous challenge, since it would require technologies that go far beyond current capabilities. One of the main obstacles to building a quantum computer and devices needed for quantum communication is decoherence or noise that originates from the interaction between a quantum system and its environment, and which leads to the destruction of the fragile quantum information. Encoding into decoherence-free subspaces (DFS) provides an important strategy for combating decoherence effects in quantum systems and constitutes the focus of my dissertation. The theory of DFS relies on the existence of certain symmetries in the decoherence process, which allow some states of a quantum system to be completely decoupled from the environment and thus to experience no decoherence. In this thesis I describe various approaches to DFS that are developed in the current literature. Although the general idea behind various approaches to DFS is the same, I show that different mathematical definitions of DFS actually have different physical meaning. I provide a rigorous definition of DFS for every approach, explaining its physical meaning and relation to other definitions. I also examine the theory of DFS for Markovian systems. These are systems for which the environment has no memory, i.e., any change in the environment affects the quantum system instantaneously. Examples of such systems include many systems in quantum optics that have been proposed for implementation of a quantum computer, such as atomic and molecular gases, trapped ions, and quantum dots. Here I develop a rigorous theory that provides necessary and sufficient conditions for the existence of DFS. This theory allows us to identify a special new class of DFS that was not known before. Under particular circumstances, dynamics of a quantum system can connive together with the interactions between the system and its environment in a special way to reduce decoherence. This property is used to discover new DFS that rely on rather counterintuitive phenomenon, which I call an "incoherent generation of coherences." I also provide examples of physical systems that support such states. These DFS can be used to suppress & coherence, but may not be sufficient for performing full quantum computation. I also explore the possibility of physically generating the DFS that are useful for quantum computation. For quantum computation we need to preserve at least two quantum states to encode the quantum analogue of classical bits. Here I aim to generate DFS in a system composed from a large collection of atoms or molecules and I need to determine how one should position atoms or molecules in 3D space so that the overall system possesses a DFS with at least two states (i.e., non-trivial DFS). I show that for many Markovian systems, non-trivial DFS can exist only when particles are located in exactly the same position in space. This, of course, is not possible in the real world. For these systems, I also show that states in DFS are states with infinite lifetime. However, for all practical applications we just need long-lived states. Thus in reality, we do just need to bring quantum particles close together to generate an imperfect DFS, i.e. a collection of long-lived states. This can be achieved, for example, for atoms within a single molecule.

Karasik, Raisa Iosifovna

104

Galilei invariant technique for quantum system description

Energy Technology Data Exchange (ETDEWEB)

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

Kamuntavi?ius, Gintautas P. [Department of Physics, Vytautas Magnus University, Vileikos 8, Kaunas 44404 (Lithuania)

2014-04-15

105

Strong decoherence in quantum systems undergoing collisions

International Nuclear Information System (INIS)

The decoherence problem in systems with continuous variables is discussed. It is shown that in quantum systems with momentum transfers in the Markovian approximation all pure states strongly decohere making quantum information processing much more complex than in the qubit case. The time scale of the effect is calculated. -- Highlights: ? Master equation in the Markovian limit for an environment representing dust particles is discussed. ? It is shown that such a dynamics leads to the strong decoherence in the system. ? Exact solutions for the free Hamiltonian and quantum harmonic oscillator are provided. ? Time scale of the decoherence phenomenon is calculated in both cases.

106

Equilibration and thermalization in finite quantum systems

Experiments with trapped atomic gases have opened novel possibilities for studying the evolution of nonequilibrium finite quantum systems, which revived the necessity of reconsidering and developing the theory of such processes. This review analyzes the basic approaches to describing the phenomena of equilibration, thermalization, and decoherence in finite quantum systems. Isolated, nonisolated, and quasi-isolated quantum systems are considered. The relations between equilibration, decoherence, and the existence of time arrow are emphasized. The possibility for the occurrence of rare events, preventing complete equilibration, are mentioned.

Yukalov, V I

2012-01-01

107

Thermalization in closed quantum systems: Semiclassical approach

Thermalization in closed quantum systems can be understood either by means of the eigenstate thermalization hypothesis or the concept of canonical typicality. Both concepts are based on quantum-mechanical formalism, such as spectral properties of the eigenstates or entanglement between subsystems, respectively. Here we study instead the onset of thermalization of Bose particles in a two-band double-well potential using the truncated Wigner approximation. This allows us to use the familiar classical formalism to understand quantum thermalization in this system. In particular, we demonstrate that sampling of an initial quantum state mimics a statistical mechanical ensemble, while subsequent chaotic classical evolution turns the initial quantum state into the thermal state.

Cosme, J. G.; Fialko, O.

2014-11-01

108

Intrinsic and extrinsic properties of quantum systems

The paper attempts to convince that the orthodox interpretation of quantum mechanics does not contradict philosophical realism by throwing light onto certain properties of quantum systems that seem to have escaped attention as yet. The exposition starts with the philosophical notions of realism. Then, the quantum mechanics as it is usually taught is demoted to a mere part of the theory called phenomenology of observations, and the common impression about its contradiction to realism is explained. The main idea of the paper, the physical notion of intrinsic properties, is introduced and many examples thereof are given. It replaces the irritating dichotomy of quantum and classical worlds by a much softer difference between intrinsic and extrinsic properties, which concern equally microscopic and macroscopic systems. Finally, the classicality and the quantum measurement are analyzed and found to present some still unsolved problems. A possible way of dealing with the Schr\\"{o}dinger cat is suggested that is base...

Hajicek, P

2008-01-01

109

Quantum Computing in Solid State, and Coherent Behavior of Open Quantum Systems.

We have developed and investigated models of realization of quantum computing in solid-state semiconductor heterostructures, and explored decoherence properties of relevance in evaluation of quantum-computing systems. Quantum bits (qubits) are nuclear or ...

V. Privman

2003-01-01

110

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

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

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

2014-09-30

111

Generalized Entropy and Global Quantum Discord in Multi-party Quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using Tsallis-q entropy, we introduce the generalized concept of global quantum discord, namely the q-global quantum discord, and provide its analytic evaluation for two classes of multi-qubit states. We also provide a sufficient condition, for which the pairwise quantum correlations in terms of q-global quantum discord is monogamous in multi-party quantum systems.

Chi, Dong Pyo; Kim, Jeong San; Lee, Kyungjin

2013-01-01

112

Decoherence and Measurement in Open Quantum Systems

We review results of a recently developed model of a microscopic quantum system interacting with the macroscopic world components which are modeled by collections of bosonic modes. The interaction is via a general operator $\\Lambda$ of the system, coupled to the creation and annihilation operators of the environment modes. We assume that in the process of a nearly instantaneous quantum measurement, the function of the environment involves two distinct parts: the pointer and the bath. Interaction of the system with the bath leads to decoherence such that the system and the pointer both evolve into a statistical mixture state described by the density matrix such that the system is in one of the eigenstates of $\\Lambda$ with the correct quantum mechanical probability, whereas the expectation values of pointer operators retain amplified information on that eigenstate. We argue that this process represents the initial step of a quantum measurement. Calculation of the elements of the reduced density matrix of the s...

Privman, V; Privman, Vladimir; Mozyrsky, Dima

2000-01-01

113

Quantum entanglement in photoactive prebiotic systems.

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

Tamulis, Arvydas; Grigalavicius, Mantas

2014-06-01

114

Transmission and System Control in Quantum Cryptography

Directory of Open Access Journals (Sweden)

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

Anand Sharma

2011-05-01

115

Hybrid impulsive control for closed quantum systems.

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

Zhao, Shouwei; Sun, Jitao; Lin, Hai

2013-01-01

116

Electrons at the surface of quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrons can be trapped at the surfaces and interfaces of the condensed phases of quantum matter (in particular hydrogen and helium), where they form classical two-dimensional Coulomb systems. Apart from studying the intrinsic properties of these nearly ideal systems, like the transition from an electron gas to a Wigner solid, one can use the electrons also as a sensitive probe to investigate the surface of quantum liquids and solids. The examples presented here include the surface of solid ...

Leiderer, Paul

1992-01-01

117

Open quantum systems and error correction

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

Shabani Barzegar, Alireza

118

Integral formulas for quantum isomonodromic systems

We conisder time-dependent Schr\\"odinger systems, which are quantizations of the Hamiltonian systems obtained from a similarity reduction of the Drinfeld-Sokolov hierarchy by K. Fuji and T. Suzuki, and a similarity reduction of the UC hierarchy by T.Tsuda, independently. These Hamiltonian systems describe isomonodromic deformations for certain Fuchsian systems. Thus, our Schr\\"odinger systems can be regarded as quantum isomonodromic systems. Y. Yamada conjectured that our quantum isomonodromic systems determine instanton partition functions in N=2 SU(L) gauge theory. The main purpose of this paper is to present integral formulas as particular solutions to our quantum isomonodromic systems. These integral formulas are generalizations of the generalized hypergeometric function.

Nagoya, Hajime

2012-01-01

119

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

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

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

2013-03-01

120

International Nuclear Information System (INIS)

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

121

Quantum electro-mechanical system (QEMS)

International Nuclear Information System (INIS)

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

122

Noise in quantum systems: facts and fantasies

International Nuclear Information System (INIS)

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

123

Software-defined Quantum Communication Systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-01

124

Quantum electro-mechanical systems (QEMS)

We give a quantum description of a Quantum Electro-Mechanical System (QEMS) comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunnelling current between them. An example of such a system is a fullerene molecule between two metal electrodes. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise, and give a semiclassical description of the dynamics under a variety of bias conditions. This dynamical description is related to observable features of the system including the stationary conductance as a function of bias voltage.

Utami, Dian W.; Goan, Hsi-Sheng; Milburn, Gerard J.

2004-04-01

125

Fluctuations of Quantum Statistical Two-Dimensional Systems of Electrons

Digital Repository Infrastructure Vision for European Research (DRIVER)

The random matrix ensembles (RME) of quantum statistical Hamiltonian operators, {\\em e.g.} Gaussian random matrix ensembles (GRME) and Ginibre random matrix ensembles (Ginibre RME), are applied to following quantum statistical systems: nuclear systems, molecular systems, and two-dimensional electron systems (Wigner-Dyson electrostatic analogy). Measures of quantum chaos and quantum integrability with respect to eigenergies of quantum systems are defined and calculated. Quant...

Duras, Maciej M.

2005-01-01

126

Quantum phase transitions in the systems of parallel quantum dots

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the low-temperature transport properties of the systems of parallel quantum dots described by the N-impurity Anderson model. We calculate the quasiparticle scattering phase shifts, spectral functions and correlations as a function of the gate voltage for N up to 5. For any N, the conductance at the particle-hole symmetric point is unitary. For N >= 2, a transition from ferromagnetic to antiferromagnetic impurity spin correlations occurs at some gate voltage. For N >...

Zitko, Rok; Bonca, Janez

2007-01-01

127

How localized is an extended quantum system?

We elaborate on a geometric characterization of the electromagnetic properties of matter. A fundamental complex quantity, z_{L}, is introduced to study the localization properties of extended quantum systems. z_L, which allows us to discriminate between conducting and non-conducting thermodynamic phases, has an illuminating physical (and geometric) interpretation. Its phase can be related to the expectation value of the position operator (and a Berry phase), while its modulus is associated with quantum electric dipole fluctuations (and a quantum metric). We also study the scaling behavior of z_L in the one-dimensional repulsive Hubbard model.

Ortiz, G

1999-01-01

128

Quantum system lifetimes and measurement perturbations

International Nuclear Information System (INIS)

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

129

Quantum information processing in nanostructures

International Nuclear Information System (INIS)

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

130

Levitated Quantum Nano-Magneto-Mechanical Systems

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

131

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 in general unrealistic. Therefore, in this paper we consider a class of linear quantum systems subject to time-varying norm-bounded parametric uncertainty and then propose a robust observer such that the variance of the estimation error is guaranteed to be within a certain bound. Although the proposed observer is different from the optimal filter in the sense of the least mean square error, it is demonstrated in a typical quantum control problem that the observer is fairly robust against a parametric uncertainty even when the other estimators, the optimal Kalman filter and the risk-sensitive observer, fail in the estimation due to the uncertain perturbation.

Yamamoto, N

2006-01-01

132

Mathematical Modeling of Finite Quantum Systems

We consider the problem of quantum behavior in the finite background. Introduction of continuum or other infinities into physics leads only to technical complications without any need for them in description of empirical observations. The finite approach makes the problem constructive and more tractable. We argue that quantum behavior is a natural consequence of symmetries of dynamical systems. It is a result of fundamental impossibility to trace identity of indistinguishable objects in their evolution - only information about invariant combinations of such objects is available. We demonstrate that any quantum dynamics can be embedded into a simple permutation dynamics. Quantum phenomena, such as interferences, arise in invariant subspaces of permutation representations of the symmetry group of a system. Observable quantities can be expressed in terms of the permutation invariants.

Kornyak, Vladimir V

2011-01-01

133

Strong local passivity in finite quantum systems.

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

Frey, Michael; Funo, Ken; Hotta, Masahiro

2014-07-01

134

Transitivity and ergodicity of quantum systems

International Nuclear Information System (INIS)

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

135

Isospectrality for quantum toric integrable systems

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

Charles, Laurent; Ngoc, San Vu

2011-01-01

136

Quantum discord in matrix product systems

International Nuclear Information System (INIS)

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.

137

Stochastic description for open quantum systems

A linear quantum Brownian motion model with a general spectral density function is considered. In the framework of the influence functional formalism, a Langevin equation can be introduced to describe the system's fully quantum properties even beyond the semiclassical regime. In particular, we show that the reduced Wigner function for the system can be formally written as a double average over both the initial conditions and the stochastic source of the Langevin equation. This is exploited to provide a derivation of the master equation for the reduced density matrix alternative to those existing in the literature. Furthermore, we prove that all the correlation functions obtained in the context of the stochastic description associated to the Langevin equation actually correspond to quantum correlation functions for system observables. In doing so, we also compute the closed time path generating functional of the open system.

Calzetta, Esteban; Roura, Albert; Verdaguer, Enric

2003-03-01

138

Incoherent control of locally controllable quantum systems

International Nuclear Information System (INIS)

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.

139

Quantum scaling in many-body systems

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

Continentino, Mucio A

2001-01-01

140

Dynamical Hysteresis in Bistable Quantum Systems

Energy Technology Data Exchange (ETDEWEB)

We are studying bistable quantum systems coupled to a thermal environment in the presence of an external controlling force. The impact of thermal and quantum effects on the switching hysteresis is studied by evaluating a time-dependent real-time double path integral with the recently developed iterative tensor multiplication scheme for the {ital quasiadiabatic path integral propagator method} for temperatures ranging from well above to well below quantum-classical crossover temperature. The switching dynamics and its intimate connection to quantum stochastic resonance is studied here for the first time {ital without} limitation to a two-state description and/or small external forces. {copyright} {ital 1997} {ital The American Physical Society}

Thorwart, M.; Jung, P. [Department of Physics and Center for Complex Systems Research, University of Illinois, Urbana, Illinois 61801 (United States)

1997-03-01

141

Majorization Relation in Quantum Critical Systems

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

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

2014-07-01

142

Quantum Simulation of Tunneling in Small Systems

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

Sornborger, Andrew T

2012-01-01

143

Quantum Dynamics of Nonlinear Cavity Systems

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

Nation, Paul D

2010-01-01

144

Scattering theory for open quantum systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-07-01

145

Chaos in many body quantum systems

International Nuclear Information System (INIS)

A many body quantum system undergoing multiple resonant tunneling in a double barrier heterostructure is studied within a mean field approximation. The resulting nonlinear Schroedinger equation shows genuine chaos with a positive maximum Lyapunov exponent. A simplified model of the same system suggests that chaos develops only if the interaction among the particles is nonuniform in space. (author)

146

Recent advances in quantum integrable systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2005-07-01

147

Geometric magnetism in open quantum systems

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

Campisi, Michele; Hänggi, Peter

2012-01-01

148

Charge Transport in a Quantum Electromechanical System

We describe a quantum electromechanical system(QEMS) comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunneling current between them. An example of such a system is a fullerene molecule between two metal electrodes [Park et al., Nature, 407, 57 (2000)]. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise. This dynamical description is related to observable features of the system including the stationary current as a function of bias voltage.

Utami, D W; Milburn, G J; Goan, Hsi-Sheng

2004-01-01

149

Charge transport in a quantum electromechanical system

We describe a quantum electromechanical system comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunneling current between them. An example of such a system is a fullerene molecule between two metal electrodes [Park , Nature 407, 57 (2000)]. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise. This dynamical description is related to observable features of the system including the stationary current as a function of bias voltage.

Utami, D. Wahyu; Goan, Hsi-Sheng; Milburn, G. J.

2004-08-01

150

Heisenberg picture approach to the stability of quantum Markov systems

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

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

2014-06-01

151

Josephson tunneling in bilayer quantum Hall system

International Nuclear Information System (INIS)

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

152

Thermodynamic modelling of finite quantum systems

Maximum entropy has long been established as a foundational principle of statistical mechanics. Recently this maximum entropy rationale has been extended to the description of small quantum systems, for example in quantum-state reconstruction from incomplete data, even though for such systems it is no longer justified to assume the thermodynamic limit, and it is not clear a priori which observables span the proper level of description. I show how in this situation the finiteness of the sample must be accounted for; how, in particular, prior knowledge continues to exert an influence on the state estimate; and how the proper level of description becomes itself a subject of statistical inference.

Rau, Jochen

2010-01-01

153

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

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

Radtke, T.; Fritzsche, S.

2005-12-01

154

Long-range quantum discord in critical spin systems

International Nuclear Information System (INIS)

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

155

Environment-assisted quantum transport in ordered systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Kassal, Ivan; Aspuru-guzik, Alan

2012-01-01

156

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

Cui, Ping

157

Quantum temporal probabilities in tunneling systems

International Nuclear Information System (INIS)

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

158

Gain reduction in semiconductor quantum dot systems

Energy Technology Data Exchange (ETDEWEB)

For practical application of quantum dots (QDs) in light emitters as well as for fundamental studies of their emission properties, dephasing processes due to carrier-carrier and carrier-phonon interaction play a critical role. They determine the homogeneous linewidth of the QD resonances, limit the coherence properties of QD lasers and their ultrafast emission dynamics, and have a strong influence on coherent optical nonlinearities. A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line-shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes which includes non-Markovian effects. Our quantum kinetic theory predicts a new effect, not found in other gain materials. For large carrier densities, the maximum gain can decrease with increasing carrier density. This behavior arises from a interplay of state filling and dephasing, so that a appropriate treatment of the carrier density dependence of dephasing is necessary. Results for the {alpha}-factor for QD systems and a comparison of the peak gain between QDs and quantum wells are will be shown. The presented theory will also be used to determine gain spectra in nitride material systems.

Lorke, Michael; Seebeck, Jan; Gartner, Paul; Jahnke, Frank [Institute for Theoretical Physics, University of Bremen (Germany); Chow, Weng [Sandia National Laboratories, Albuquerque, New Mexico (United States)

2008-07-01

159

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that quantum subdynamics of an open quantum system can always be described by a 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...

Shabani, A.; Lidar, D. A.

2009-01-01

160

Quantum & Classical Eigenfunctions in Calogero & Sutherland Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

An interesting observation was reported by Corrigan-Sasaki that all the frequencies of small oscillations around equilibrium are " quantised" for Calogero and Sutherland (C-S) systems, typical integrable multi-particle dynamics. We present an analytic proof by applying recent results of Loris-Sasaki. Explicit forms of `classical' and quantum eigenfunctions are presented for C-S systems based on any root systems.

Loris, I.; Sasaki, R.

2003-01-01

161

Adiabatic Quantum Computation in Open Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the performance of adiabatic quantum computation (AQC) under the effect of decoherence. To this end, we introduce an inherently open-systems approach, based on a recent generalization of the adiabatic approximation. In contrast to closed systems, we show that a system may initially be in an adiabatic regime, but then undergo a transition to a regime where adiabaticity breaks down. As a consequence, the success of AQC depends sensitively on the competition between ...

Sarandy, M. S.; Lidar, D. A.

2005-01-01

162

Quantum dynamics of biological systems and dust plasma nanoparticles

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

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

2012-12-01

163

Quantum-mechanical aspects of classically chaotic driven systems

International Nuclear Information System (INIS)

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

164

Effective Hamiltonian approach to periodically perturbed quantum optical systems

International Nuclear Information System (INIS)

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

165

Quantum dissipation of a simple conservative system

International Nuclear Information System (INIS)

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

166

Lithography system using quantum entangled photons

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

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

2002-01-01

167

Dephasing maps for quantum stochastic systems

International Nuclear Information System (INIS)

Stochastic time evolution in a nonseparable and nonintegrable quantum system is manifested by rapid dephasing of guassian wavepackets, whose topological distribution in the coordinate-momentum space defines its irregular regions, while wavepackets initiated in regular regions exhibit quasiperiodic evolution. A gradual transition from quasiperiodic to chaotic dynamics with increasing energy is observed. (orig.)

168

Economical ontological models for discrete quantum systems

I use the recently proposed framework of ontological models [arXiv:0709.1149v2] to obtain economical ontological models for results of tomographically complete sets of measurements on finite-dimensional quantum systems. I describe how to obtain models with small numbers of ontic states, and present an explicit model with just 34 ontic states for a qutrit.

Galvao, Ernesto F

2009-01-01

169

Quantum field theory and multiparticle systems

International Nuclear Information System (INIS)

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

170

An Operator-Based Exact Treatment of Open Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Nicolosi, S.

2005-01-01

171

Quantum cryptographic system with reduced data loss

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

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

1998-01-01

172

Ion-cavity system for quantum networks

International Nuclear Information System (INIS)

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

173

Symmetry and stability of open quantum systems

International Nuclear Information System (INIS)

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

174

Constrained quantum systems as an adiabatic problem

We derive the effective Hamiltonian for a quantum system constrained to a submanifold (the constraint manifold) of configuration space (the ambient space) in the asymptotic limit, where the restoring forces tend to infinity. In contrast to earlier works, we consider, at the same time, the effects of variations in the constraining potential and the effects of interior and exterior geometry, which appear at different energy scales and, thus, provide a complete picture, which ranges over all interesting energy scales. We show that the leading order contribution to the effective Hamiltonian is the adiabatic potential given by an eigenvalue of the confining potential well known in the context of adiabatic quantum waveguides. At next to leading order, we see effects from the variation of the normal eigenfunctions in the form of a Berry connection. We apply our results to quantum waveguides and provide an example for the occurrence of a topological phase due to the geometry of a quantum wave circuit (i.e., a closed quantum waveguide).

Wachsmuth, Jakob; Teufel, Stefan

2010-08-01

175

An impurity-induced gap system as a quantum data bus for quantum state transfer

We introduce a tight-binding chain with a single impurity to act as a quantum data bus for perfect quantum state transfer. Our proposal is based on the weak coupling limit of the two outermost quantum dots to the data bus, which is a gapped system induced by the impurity. By connecting two quantum dots to two sites of the data bus, the system can accomplish a high-fidelity and long-distance quantum state transfer. Numerical simulations for finite system show that the numerical and analytical results of the effective coupling strength agree well with each other. Moreover, we study the robustness of this quantum communication protocol in the presence of disorder in the couplings between the nearest-neighbor quantum dots. We find that the gap of the system plays an important role in robust quantum state transfer.

Chen, Bing; Li, Yong; Song, Z.; Sun, C.-P.

2014-09-01

176

Control landscapes for open system quantum operations

International Nuclear Information System (INIS)

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

177

Control landscapes for open system quantum operations

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

Wu, Re-Bing; Rabitz, Herschel

2012-12-01

178

Hybrid quantum systems of ions and atoms

In this chapter we review the progress in experiments with hybrid systems of trapped ions and ultracold neutral atoms. We give a theoretical overview over the atom-ion interactions in the cold regime and give a summary of the most important experimental results. We conclude with an overview of remaining open challenges and possible applications in hybrid quantum systems of ions and neutral atoms.

Sias, Carlo

2014-01-01

179

Planar lightwave circuits for quantum cryptographic systems

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

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

2003-01-01

180

Irreversible processes in quantum mechanical systems

International Nuclear Information System (INIS)

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

181

Observable measure of quantum coherence in finite dimensional systems.

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d^{2}) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes. PMID:25379903

Girolami, Davide

2014-10-24

182

Observable Measure of Quantum Coherence in Finite Dimensional Systems

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

Girolami, Davide

2014-10-01

183

Multiple-state quantum Otto engine, 1D box system

Energy Technology Data Exchange (ETDEWEB)

Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.

Latifah, E., E-mail: enylatifah@um.ac.id [Laboratory of Theoretical Physics and Natural Philosophy, Physics Department, Institut Teknologi Sepuluh Nopember, ITS, Surabaya, Indonesia and Physics Department, Malang State University (Indonesia); Purwanto, A. [Laboratory of Theoretical Physics and Natural Philosophy, Physics Department, Institut Teknologi Sepuluh Nopember, ITS, Surabaya (Indonesia)

2014-03-24

184

Multiple-state quantum Otto engine, 1D box system

International Nuclear Information System (INIS)

Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes

185

Mathematical Structure in Quantum Systems and applications

International Nuclear Information System (INIS)

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

186

Topics in Quantum Chaos of Generic Systems

We review the main ideas and results in the stationary problems of quantum chaos in generic (mixed) systems, whose classical dynamics has regular (invariant tori) and chaotic regions coexisting in the phase space. First we discuss the universality classes of spectral fluctuations (GOE/GUE for ergodic systems, and Poissonian for integrable systems). We explain the problems in the calculation of the invariant (Liouville) measure of classically chaotic components, which has recently been studied by Robnik et al (1997) and by Prosen and Robnik (1998). Then we describe the Berry-Robnik (1984) picture, which is claimed to become exact in the strict semiclassical limit $\\hbar\\to 0$. However, at not sufficiently small values of $\\hbar$ we see a crossover regime due to the localization properties of stationary quantum states where Brody-like behaviour with the fractional power law level repulsion is observed in the corresponding quantal energy spectra.

Robnik, M

1999-01-01

187

Aberration-corrected quantum temporal imaging system

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

Zhu, Yunhui; Gauthier, Daniel J

2013-01-01

188

Nematic valley ordering in quantum Hall systems

The interplay between quantum Hall ordering and spontaneously broken “internal” symmetries in two-dimensional electron systems with spin or pseudospin degrees of freedom gives rise to a variety of interesting phenomena, including novel phases, phase transitions, and topological excitations. Here we develop a theory of broken-symmetry quantum Hall states, applicable to a class of multivalley systems, where the symmetry at issue is a point-group element that combines a spatial rotation with a permutation of valley indices. The anisotropy of the dispersion relation, generally present in such systems, favors states where all electrons reside in one of the valleys. In a clean system, the valley “pseudospin” ordering occurs via a finite-temperature transition accompanied by a nematic pattern of spatial symmetry breaking. In weakly disordered systems, domains of pseudospin polarization are formed, which prevents macroscopic valley and nematic ordering; however, the resulting state still asymptotically exhibits the quantum Hall effect. We discuss the transport properties in the ordered and disordered regimes, and the relation of our results to recent experiments in AlAs.

Abanin, D. A.; Parameswaran, S. A.; Kivelson, S. A.; Sondhi, S. L.

2010-07-01

189

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

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

Hassan, Ali Saif M; Joag, Pramod S

2010-01-01

190

Intertwining Symmetry Algebras of Quantum Superintegrable Systems

Directory of Open Access Journals (Sweden)

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

Juan A. Calzada

2009-04-01

191

Intertwining Symmetry Algebras of Quantum Superintegrable Systems

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

Calzada, Juan A; del Olmo, Mariano A; 10.3842/SIGMA.2009.039

2009-01-01

192

Intertwining Symmetry Algebras of Quantum Superintegrable Systems

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

Calzada, Juan A.; Negro, Javier; Del Olmo, Mariano A.

2009-04-01

193

Isochronous classical systems and quantum systems with equally spaced spectra

International Nuclear Information System (INIS)

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

194

Quantum response of dephasing open systems

International Nuclear Information System (INIS)

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.

195

Quantum response of dephasing open systems

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

196

Non-Equilibrium Quantum Entanglement in Biological Systems

International Nuclear Information System (INIS)

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

197

On Mathematical Modeling Of Quantum Systems

International Nuclear Information System (INIS)

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.

198

Constrained Quantum Systems as an Adiabatic Problem

We derive the effective Hamiltonian for a quantum system constrained to a submanifold (the constraint manifold) of configuration space (the ambient space) in the asymptotic limit where the restoring forces tend to infinity. In contrast to earlier works we consider at the same time the effects of variations in the constraining potential and the effects of interior and exterior geometry which appear at different energy scales and thus provide, for the first time, a complete picture ranging over all interesting energy scales. We show that the leading order contribution to the effective Hamiltonian is the adiabatic potential given by an eigenvalue of the confining potential well-known in the context of adiabatic quantum wave guides. At next to leading order we see effects from the variation of the normal eigenfunctions in form of a Berry connection. We apply our results to quantum wave guides and provide an example for the occurrence of a topological phase due to the geometry of a quantum wave circuit, i.e. a clo...

Wachsmuth, Jakob

2010-01-01

199

Network Synthesis of Linear Dynamical Quantum Stochastic Systems

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

Nurdin, H I; Doherty, A C

2008-01-01

200

Quantum System Engineering (QSE) Frequently Asked Questions (FAQ)

This web-page contains an FAQ offered by the quantum systems engineering group at the University of Washington. The FAQ provides some general information about the utility of quantum microscopy as well as magnetic resonance force microscopy (MRFM).

2005-11-21

201

Quantum Systems based upon Galois Fields: from Sub-quantum to Super-quantum Correlations

In this talk we describe our recent work on discrete quantum theory based on Galois fields. In particular, we discuss how discrete quantum theory sheds new light on the foundations of quantum theory and we review an explicit model of super-quantum correlations we have constructed in this context. We also discuss the larger questions of the origins and foundations of quantum theory, as well as the relevance of super-quantum theory for the quantum theory of gravity.

Chang, Lay Nam; Minic, Djordje; Takeuchi, Tatsu

2014-01-01

202

Decoherence in infinite quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Die Quantenmechanik gilt heute als unsere grundlegendste physikalische Theorie. Als solche beschränkt sie sich nicht nur auf ihre ursprünglichen Anwendungsbereiche wie die Atomphysik, Elementarteilchenphysik und die Quantenfeldtheorie, sondern ihr Gegenstandsbereich sollte auch makroskopische Systeme einschließen, die den Gesetzen der klassischen Physik gehorchen. Hier stößt man jedoch auf ein fundamentales Problem: Wendet man die Gesetze der Quantenmechanik direkt auf die Objekte unsere...

Hellmich, Mario

2009-01-01

203

Dynamical Systems and Quantum Bicrossproduct Algebras

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

Arratia, O; Arratia, Oscar; Olmo, Mariano A. del

2002-01-01

204

Dynamical systems and quantum bicrossproduct algebras

Energy Technology Data Exchange (ETDEWEB)

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

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

2002-06-28

205

Dynamical systems and quantum bicrossproduct algebras

International Nuclear Information System (INIS)

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

206

Economical ontological models for discrete quantum systems

I use the recently proposed framework of ontological models (N. Harrigan, T. Rudolph, and S. Aaronson, e-print arXiv:0709.1149) to obtain economical models for the results of tomographically complete sets of measurements on finite-dimensional quantum systems. I describe a procedure that simplifies the models by decreasing the number of necessary ontic states and present an explicit model with just 33 ontic states for a qutrit.

Galvão, Ernesto F.

2009-08-01

207

Open quantum systems and random matrix theory

A simple model for open quantum systems is analyzed with RMT. The system is coupled to the continuum in a minimal way. In this paper we see the effect of opening the system on the level statistics, in particular the level spacing, width distribution and ?3(L) statistic are examined as a function of the strength of this coupling. The usual super-radiant state is observed, and it is seen that as it is formed, the level spacing and ?3(L) statistic exhibit the signatures of missed levels.

Mulhall, Declan

2014-10-01

208

Multiphoton spectroscopy of a hybrid quantum system

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

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

2010-10-01

209

Adiabatic quantum computation in open systems

We analyze the performance of the adiabatic quantum computation (AQC) paradigm under the effect of decoherence. To this end, we introduce an inherently open-systems approach, based on a recent generalization of the adiabatic approximation. In contrast to the analysis based on the adiabatic theorem for closed systems, we show that a system may initially be in an adiabatic regime, but then transition to a regime where adiabaticity breaks down. As a consequence, the success of AQC depends sensitively on the competition between various pertinent rates, giving rise to optimality criteria. As an illustrative example, we analyze the adiabatic implementation of the Deutsch-Jozsa algorithm under dephasing.

Sarandy, M S

2005-01-01

210

Nonlocal realistic theories and continuous quantum systems

Energy Technology Data Exchange (ETDEWEB)

Recently, a certain class of non-local, realistic theories (NLRT) has been formulated for two-particle systems with dichotomic observables and has been shown to be incompatible with quantum mechanics and with experimental data. The proof us es inequalities for correlation functions, as in the original Bell case. We study how to expand the formulation to systems with continuous variables and demonst rate how such systems can violate the predictions of the NLRT. Moreover, we analyze how violations of the NLRT-inequalities are related to violations of Bell-type inequalities.

Hauber, Anna; Freyberger, Matthias [Institut fuer Quantenphysik, Universitaet Ulm, D-89069 Ulm (Germany)

2009-07-01

211

Quantum to classical limit of open systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a complete review of the quantum-to-classical limit of open systems by means of the theory of decoherence and the use of the Weyl- Wigner-Moyal (WWM) transformation. We show that the analytical ex- tension of the Hamiltonian provides a set of poles that can be used to (a) explain the non-unitary evolution of the relevant system and (b) com- pletely de?ne the set of preferred states that constitute the mixture into which the system decoheres: the Moving Preferred B...

Bellomo, Guido; Castagnino, Mario; Fortin, Sebastian

2012-01-01

212

Phase transitions in quantum Hall multiple layer systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-04

213

Time fractional development of quantum systems

International Nuclear Information System (INIS)

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

214

International Nuclear Information System (INIS)

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

215

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

Zhou, Ping; Deng, Fu-Guo; Zhou, Hong-Yu

2009-03-01

216

Energy Technology Data Exchange (ETDEWEB)

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

Zhou Ping; Deng Fuguo; Zhou Hongyu [The Key Laboratory of Beam Technology and Material Modification of Ministry of Education, and Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875 (China)], E-mail: fgdeng@bnu.edu.cn

2009-03-15

217

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

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

2013-01-01

218

Continuous measurement of a non-Markovian open quantum system.

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

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

2014-03-21

219

Simulations of fluctuations of quantum statistical systems of electrons

Digital Repository Infrastructure Vision for European Research (DRIVER)

The random matrix ensembles (RMT) of quantum statistical Hamiltonian operators, e.g.Gaussian random matrix ensembles (GRME) and Ginibre random matrix ensembles (Ginibre RME), are applied to following quantum statistical systems: nuclear systems, molecular systems, and two-dimensional electron systems (Wigner-Dyson's electrostatic analogy). The Ginibre ensemble of nonhermitean random Hamiltonian matrices $K$ is considered. Each quantum system described by $K$ is a dissipative...

Duras, Maciej M.

2005-01-01

220

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 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

221

Statistical Thermodynamics of Polymer Quantum Systems

Directory of Open Access Journals (Sweden)

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

Guillermo Chacón-Acosta

2011-12-01

222

Decoherence, delocalization and irreversibility in quantum chaotic systems

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

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

1995-01-01

223

Quantum Trajectory in Multi-Dimensional Non-Linear System

We discuss quantum dynamics in multi-dimensional non-linear systems. It is well-known that wave function is localized in a single kicked rotor. However, coupling with other degrees of freedom breaks the localization. In order to clarify the difference in the quantum dynamics, we use rigid quantum trajectories, which is accompanied with the de Broglie-Bohm interpretation of the quantum mechanics. The bundle of quantum trajectories are repulsive by the quantum potential and flow never to go across each other. We shows that, depending on the degrees of freedom, this same property appears differently.

Kubotani, H

1999-01-01

224

Energy concentration in composite quantum systems

International Nuclear Information System (INIS)

The spontaneous emission of photons from optical cavities and from trapped atoms has been studied extensively in the framework of quantum optics. Theoretical predictions based on the rotating wave approximation (RWA) are, in general, in very good agreement with experimental findings. However, current experiments aim at combining better and better cavities with large numbers of tightly confined atoms. Here we predict an energy concentrating mechanism in the behavior of such a composite quantum system which cannot be described by the RWA. Its result is the continuous leakage of photons through the cavity mirrors, even in the absence of external driving. We conclude with a discussion of the predicted phenomenon in the context of thermodynamics.

225

Effective operator formalism for open quantum systems

DEFF Research Database (Denmark)

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

Reiter, Florentin; SØrensen, Anders SØndberg

2012-01-01

226

Teaching the environment to control quantum systems

International Nuclear Information System (INIS)

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

227

Maximal work extraction from finite quantum systems

Thermodynamics teaches that if a system initially off-equilibrium is coupled to work sources, the maximum work that it may yield is governed by its energy and entropy. For finite systems this bound is usually not reachable. The maximum extractable work compatible with quantum mechanics ("ergotropy") is derived and expressed in terms of the density matrix and the Hamiltonian. It is related to the property of majorization: more major states can provide more work. Scenarios of work extraction that contrast the thermodynamic intuition are discussed, e.g. a state with larger entropy than another may produce more work, while correlations may increase or reduce the ergotropy.

Allahverdyan, A. E.; Balian, R.; Nieuwenhuizen, Th. M.

2004-08-01

228

Geometric phases in adiabatic open quantum systems

We introduce a framework to analyze Abelian and non-Abelian geometric phases associated with open quantum systems undergoing cyclic adiabatic evolution. An expression for geometric phases is derived within an inherently open-systems approach, based on an adiabatic approximation developed for general convolutionless master equations. There is then a finite time interval for the observation of geometric phases. The formalism is illustrated via the example of a spin-1/2 particle in a time-dependent magnetic field. Remarkably, the geometric phase in this example is totally robust against dephasing and spontaneous emission in the Hamiltonian eigenstate basis.

Sarandy, M S

2005-01-01

229

Equilibration of isolated macroscopic quantum systems

International Nuclear Information System (INIS)

We investigate the equilibration of an isolated macroscopic quantum system in the sense that deviations from a steady state become unmeasurably small for the overwhelming majority of times within any sufficiently large time interval. The main requirements are that the initial state, possibly far from equilibrium, exhibits a macroscopic population of at most one energy level and that degeneracies of energy eigenvalues and of energy gaps (differences of energy eigenvalues) are not of exceedingly large multiplicities. Our approach closely follows and extends recent works by Short and Farrelly (2012 New. J. Phys. 14 013063), in particular going beyond the realm of finite-dimensional systems and large effective dimensions. (paper)

230

Equilibration of isolated macroscopic quantum systems

We investigate the equilibration of an isolated macroscopic quantum system in the sense that deviations from a steady state become unmeasurably small for the overwhelming majority of times within any sufficiently large time interval. The main requirements are that the initial state, possibly far from equilibrium, exhibits a macroscopic population of at most one energy level and that degeneracies of energy eigenvalues and of energy gaps (differences of energy eigenvalues) are not of exceedingly large multiplicities. Our approach closely follows and extends recent works by Short and Farrelly, in particular going beyond the realm of finite-dimensional systems and large effective dimensions.

Reimann, Peter

2012-01-01

231

A toy model of a macroscopic quantum coherent system

International Nuclear Information System (INIS)

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

232

The transition to chaos conservative classical systems and quantum manifestations

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

Reichl, Linda E

2004-01-01

233

Imaging a Coupled Quantum Dot - Quantum Point Contact System

We performed measurements on a quantum dot and a capacitively coupled quantum point contact by using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate. The quantum point contact served as a detector for charges on the dot or nearby. It allowed us to distinguish single electron charging events in several charge traps from charging events on the dot. We analyzed the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.

Gildemeister, A E; Schleser, R; Ensslin, K; Driscoll, D C; Gossard, A C

2007-01-01

234

Coherent oscillations in a superconducting multi-level quantum system

We have observed coherent time evolution of states in a multi-level quantum system, formed by a current-biased dc SQUID. The manipulation of the quantum states is achieved by resonant microwave pulses of flux. The number of quantum states participating in the coherent oscillations increases with increasing microwave power. Quantum measurement is performed by a nanosecond flux pulse which projects the final state onto one of two different voltage states of the dc SQUID, which can be read out.

Claudon, J; Hekking, F W J; Buisson, O

2004-01-01

235

Non-Hermitian Quantum Systems and Time-Optimal Quantum Evolution

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recently, Bender et al. have considered the quantum brachistochrone problem for the non-Hermitian PT-symmetric quantum system and have shown that the optimal time evolution required to transform a given initial state |?_i> into a specific final state |?_f> can be made arbitrarily small. Additionally, it has been shown that finding the shortest possible time requires only the solution of the two-dimensional problem for the quantum system governed by the effective Hamiltonian acting in the su...

Nesterov, Alexander I.

2009-01-01

236

On the notion of a macroscopic quantum system

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

Khrenikov, A Yu

2004-01-01

237

Quantum MIMO n-Systems and Conditions for Stability

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

Mansourbeigi, Seyed M H

2009-01-01

238

Towards the theory of control in observable quantum systems

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

Belavkin, V P

1983-01-01

239

Sampling the time evolution of mixed quantum-classical systems

Directory of Open Access Journals (Sweden)

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

Alessandro Sergi

2011-05-01

240

Quantum simulation. Coherent imaging spectroscopy of a quantum many-body spin system.

Quantum simulators, in which well-controlled quantum systems are used to reproduce the dynamics of less understood ones, have the potential to explore physics inaccessible to modeling with classical computers. However, checking the results of such simulations also becomes classically intractable as system sizes increase. Here, we introduce and implement a coherent imaging spectroscopic technique, akin to magnetic resonance imaging, to validate a quantum simulation. We use this method to determine the energy levels and interaction strengths of a fully connected quantum many-body system. Additionally, we directly measure the critical energy gap near a quantum phase transition. We expect this general technique to become a verification tool for quantum simulators once experiments advance beyond proof-of-principle demonstrations and exceed the resources of conventional computers. PMID:25061207

Senko, C; Smith, J; Richerme, P; Lee, A; Campbell, W C; Monroe, C

2014-07-25

241

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

International Nuclear Information System (INIS)

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

242

Quantum Monte Carlo Study on periodic systems

Quantum Monte Carlo (QMC) calculations, using the variational (VMC) and diffusion (DMC) methods is performed on periodic systems. We report calculations of the cohesive energy, the occupied bandwidth and the pair correlation functions (PCFs)on the body-centered cubic solid sodium. DMC calculations including the core polarization potential (CPP) give an excellent value for the cohesive energy of the solid. The calculated bandwidth 3.7 eV is significantly larger than the experimental value of 2.6 eV, but is in good agreement with a recent many body caluculation with a sophisticated approximation. We also report very recent results on NiO.

Maezono, Ryo; Towler, Mike; Needs, Richard

2004-03-01

243

Entanglement in fermion systems and quantum metrology

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

Benatti, F; Marzolino, U

2014-01-01

244

Co-existence of states in quantum systems

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

Iwata, Yoritaka

2014-01-01

245

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

International Nuclear Information System (INIS)

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

246

Quantum discord for qubit-qudit systems

We present two formulae to calculate quantum discord, a kind of quantum correlation, between a qubit and a second party of arbitrary dimension d. The first formula is the original entropic definition and the second is a recently proposed geometric distance measure which leads to an analytical formulation. The tracing over the qubit in the entropic calculation is reduced to a very simple prescription. And, when the d-dimensional system is a so-calledX-state, the density matrix having non-zero elements only along the diagonal and anti-diagonal, the entropic calculation can also be carried out analytically. Such states of the full bipartite qubit-qudit system may be named ‘extended X-states’, whose density matrix is built of four block matrices, each visually appearing as an X. The optimization involved in the entropic calculation is generally over two parameters, reducing to one for many cases, and avoided altogether for an overwhelmingly large set of density matrices as our numerical investigations demonstrate. In the case of N = 2, extended X-states encompass the entire 15-dimensional parameter space, that is, they represent the full qubit-qubit system.

Vinjanampathy, Sai; Rau, A. R. P.

2012-03-01

247

Statistical Mechanics of Quantum-Classical Systems with Holonomic Constraints

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

Sergi, A

2005-01-01

248

Schroedinger-cat states and decoherence in quantum electromechanical systems

International Nuclear Information System (INIS)

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

249

Asymptotically open quantum systems; Asymptotisch offene Quantensysteme

Energy Technology Data Exchange (ETDEWEB)

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

Westrich, M.

2008-04-15

250

Properties of adsorbates as open quantum systems

We have recently developed a novel cluster-model approach to investigate adsorbate-surface systems. In our approach, a physically relevant subsystem is described as an open quantum system by considering a model cluster subject to the outgoing-wave boundary condition (OBC) at the edge of the cluster. We refer to this model as an open-boundary cluster model (OCM). Many known disadvantages of the conventional cluster-model approach, in which a model cluster is treated as an isolated system, have been remedied by introducing the OBC, whereas the local picture inherent in cluster models still remains valid. In our present research, the adsorption energy and the electron-transfer rate from adsorbates to surfaces are calculated with the OCM. Their dependences on the adsorption-distance and the Fermi energy are reasonably explained by analyzing the quasi-diabatic energy levels based on the local picture of adsorption.

Yasuike, Tomokazu; Nobusada, Katsuyuki

2008-10-01

251

On a non-unitary evolution of quantum systems

International Nuclear Information System (INIS)

A notion of deterministic evolution of quantum systems is discussed within the axiomatic framework of the propositional system formalism. It is shown that in general, the deterministic evolution of a quantum system does not need to preserve the orthogonality of states. An example of non-linear Schroedinger-like equation governing such an evolution is indicated. (Auth.)

252

Algebras and universal quantum computations with higher dimensional systems

Here is discussed application of the Weyl pair to construction of universal set of quantum gates for high-dimensional quantum system. An application of Lie algebras (Hamiltonians) for construction of universal gates is revisited first. It is shown next, how for quantum computation with qubits can be used two-dimensional analog of this Cayley-Weyl matrix algebras, i.e. Clifford algebras, and discussed well known applications to product operator formalism in NMR, Jordan-Wigner construction in fermionic quantum computations. It is introduced universal set of quantum gates for higher dimensional system (``qudit''), as some generalization of these models. Finally it is briefly mentioned possible application of such algebraic methods to design of quantum processors (programmable gates arrays) and discussed generalization to quantum computation with continuous variables.

Vlasov, A Yu

2002-01-01

253

Quantum to classical transition in the theory of open systems

International Nuclear Information System (INIS)

Classicality is an emergent property of open quantum systems, since both main features of this process - quantum decoherence (QD) and classical correlations (CC) - strongly depend on the interaction between the system and its environment. In the framework of the Lindblad theory for open quantum systems, based on quantum dynamical semigroups, we determine the degree of QD and the degree of CC and analyze the possibility of simultaneous realization of QD and CC for a system consisting of a harmonic oscillator in a thermal bath. To this end, we find the evolution of the density matrix and Wigner function of the considered system and then apply the criterion of QD and CC. We find that the system manifests a QD which is more and more significant in time, whereas CC are less and less strong as the system evolves in time, and we describe the transition of the system from quantum to classical behavior. (author)

254

Sistemas cuánticos individuales / Individual Quantum Systems

Scientific Electronic Library Online (English)

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

Jorge A., Campos.

2013-01-01

255

Combinatorial approach to multipartite quantum systems:basic formulation

In this paper we give a method to associate a graph with an arbitrary density matrix, refered to a standard orthonormal basis in the Hilbert space of a finite dimensional quantum system.We study the related issues like classification of pure and mixed states, Von Neumann entropy,separability of multipartite quantum states and quantum operations in terms of the graphs associated with quantum states.In particular,we give a necessary and sufficiant criterion for a m-partite quantum state to be separable.

Hassan, A S; Hassan, Ali Saif M.; Joag, Pramod

2006-01-01

256

Deformed oscillator algebras for two dimensional quantum superintegrable systems

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

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

1994-01-01

257

Factorization of Dephasing Process in Quantum Open System

The fluctuation-dissipation relation is well known for the quantum open system with energy dissipation. In this paper a similar underlying relation is found between the bath fluctuation and the dephasing of the quantum open system, of which energy is conserved, but the information is leaking into the bath. Through a universal dephasing model with quantum non-demolition interaction between the bath and the open system, we show that a dephasing process can be factorized into two parts relevant to two different physical sources, the vacuum part due to the quantum fluctuation of the bath and the thermal part due to the bath excitation by the initial state of finite temperature.

Gao, Y B

2007-01-01

258

Factorization of the dephasing process in a quantum open system

International Nuclear Information System (INIS)

The fluctuation-dissipation relation is well known for a quantum open system with energy dissipation. In this paper a similar underlying relation is found between the bath fluctuation and the dephasing of the quantum open system, for which energy is conserved, but the information is leaking into the bath. To obtain this relation we revisit the universal, but simple dephasing model with a quantum nondemolition interaction between the bath and the open system. Then we show that the decoherence factor describing the dephasing process is factorized into two parts, to indicate the two sources of dephasing, the vacuum quantum fluctuation, and the thermal excitations defined in the initial state of finite temperature

259

Graphene as a system near quantum criticality

Motivated by the physics of graphene, we consider a model of N species of 2+1 dimensional four-component massless Dirac fermions interacting through a 3D instantaneous Coulomb interaction. We show that in the limit of infinitely strong Coulomb interaction the system approaches a quantum critical point, at least for sufficiently large fermion degeneracy. In this regime the system exhibits invariance under scale transformations in which time and space scale by different factors. The elementary excitations are fermions with dispersion relation omega ~ p^z, where the dynamic critical exponent z depends on N. In the limit of large N we find z=1-4/(\\pi^2 N). We argue that due to the numerically large Coulomb coupling, graphene (freely suspended) in vacuum stays near the scale-invariant regime in a large momentum window, before eventually flowing to the trivial fixed point at very low momentum scales.

Son, D T

2007-01-01

260

On the kinetic theory of quantum systems

International Nuclear Information System (INIS)

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

261

Capacities of linear quantum optical systems

A wide variety of communication channels employ the quantized electromagnetic field to convey information. Their communication capacity crucially depends on losses associated to spatial characteristics of the channel such as diffraction and antenna design. Here we focus on the communication via a finite pupil, showing that diffraction is formally described as a memory channel. By exploiting this equivalence we then compute the communication capacity of an optical refocusing system, modeled as a converging lens. Even though loss of information originates from the finite pupil of the lens, we show that the presence of the refocusing system can substantially enhance the communication capacity. We mainly concentrate on communication of classical information, the extension to quantum information being straightforward.

Lupo, Cosmo; Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth

2012-01-01

262

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

International Nuclear Information System (INIS)

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

263

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

International Nuclear Information System (INIS)

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.

264

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 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 non-positive 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, A

2009-01-01

265

Quantum Discrete Fourier Transform in an Ion Trap System

International Nuclear Information System (INIS)

We propose two schemes for the implementation of quantum discrete Fourier transform in the ion trap system. In each scheme we design a tunable two-qubit phase gate as the main ingredient. The experimental implementation of the schemes would be an important step toward complex quantum computation in the ion trap system.

266

Propagator of Quantum Systems in the Probability Representation

The evolution equation for the propagator of the quantum system in the optical probability representation (optical propagator) is obtained. The relations between the optical and quantum propagators for the Schr\\"odinger equation and the optical propagator of an arbitrary quadratic system are found explicitly.

Korennoy, Yakov A

2011-01-01

267

Quantum reference systems: a new framework for quantum mechanics

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new interpretation of nonrelativistic quantum mechanics is presented. It explains the violation of Bell's inequality by maintaining realism and the principle of locality. Schrodinger's cat paradox and the Einstein-Podolsky-Rosen paradox are solved, too. The new approach assumes the universal validity of the Schrodinger equation, while von Neumann's postulates about the measurement process are replaced with a new, consistent set of postulates. The underlying idea is that qu...

Bene, Gyula

1997-01-01

268

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

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

2013-04-23

269

Automated drawing system of quantum energy levels

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

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

2014-03-01

270

Quantum to classical transition in the theory of open systems

International Nuclear Information System (INIS)

In the framework of the Lindblad theory for open quantum systems we determine the degree of quantum decoherence and classical correlations of a harmonic oscillator interacting with a thermal bath. The transition from quantum to classical behaviour of the considered system is analyzed and it is shown that the classicality takes place during a finite interval of time. We calculate also the decoherence time and show that it has the same scale as the time after which thermal fluctuations become comparable with quantum fluctuations. (authors)

271

Experimental quantum simulation of entanglement in many-body systems.

We employ a nuclear magnetic resonance (NMR) quantum information processor to simulate the ground state of an XXZ spin chain and measure its NMR analog of entanglement, or pseudoentanglement. The observed pseudoentanglement for a small-size system already displays a singularity, a signature which is qualitatively similar to that in the thermodynamical limit across quantum phase transitions, including an infinite-order critical point. The experimental results illustrate a successful approach to investigate quantum correlations in many-body systems using quantum simulators. PMID:21797528

Zhang, Jingfu; Wei, Tzu-Chieh; Laflamme, Raymond

2011-07-01

272

Experimental Quantum Simulation of Entanglement in Many-body Systems

We employ a nuclear magnetic resonance (NMR) quantum information processor to simulate the ground state of an XXZ spin chain and measure its NMR analog of entanglement, or pseudo-entanglement. The observed pseudo-entanglement for a small system size already displays singularity, a signature which is qualitatively similar to that in thermodynamical limit across quantum phase transitions, including an infinite-order critical point. The experimental results illustrate a successful approach to investigate quantum correlations in many-body systems using quantum simulators.

Zhang, Jingfu; Laflamme, Raymond

2011-01-01

273

Decoherence-free quantum information in Markovian systems

Decoherence in Markovian systems can result indirectly from the action of a system Hamiltonian which is usually fixed and unavoidable. Here, we show that in general in Markovian systems, because of the system Hamiltonian, quantum information decoheres. We give conditions for the system Hamiltonian that must be satisfied if coherence is to be preserved. Finally, we show how to construct robust subspaces for quantum information processing.

Patra, Manas K

2008-01-01

274

Quantum chromodynamics in few-nucleon systems

International Nuclear Information System (INIS)

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

275

Quantum integrable systems. Quantitative methods in biology

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

Feverati, Giovanni

2011-01-01

276

Hacking commercial quantum cryptography systems by tailored bright illumination

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

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

2010-01-01

277

Phase Transition in Disordered Quantum Systems: Transverse Ising Models

We introduce the transverse Ising model as a prototype for discussing quantum phase transition. Mean field theory, application to superconductivity by BCS and real space renormalization group technique (in one dimension) are discussed. Next we introduce Suzuki-Trotter formalism to show the correspondence between $d$-dimensional quantum system with a $(d+1)$-dimensional classical system. We then discuss transverse Ising spin glass models, namely S-K model, E-A model, and the $\\pm J$ model with Ising spin in transverse field. We briefly discuss the mean field, exact diagonalization, and quantum Monte Carlo results for their phase diagrams. Next we discuss the question of replica symmetry restoration in quantum spin glasses (due to tunnelling possibility through the barriers). Then we discuss the quantum annealing technique and indicate its relationship with replica symmetry restoration in quantum spin glasses.

Chakrabarti, Bikas K; Chakrabarti, Bikas K.; Das, Arnab

2003-01-01

278

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

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

Dutta, Mitra

1998-01-01

279

Hacking commercial quantum cryptography systems by tailored bright illumination

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2010-01-01

280

Quantum Cost Efficient Reversible BCD Adder for Nanotechnology Based Systems

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

Islam, Md Saiful; Begum, Zerina

2011-01-01

281

Quantum interference in an electron-hole graphene ring system

International Nuclear Information System (INIS)

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

282

Quantum interference in an electron-hole graphene ring system

Energy Technology Data Exchange (ETDEWEB)

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

Smirnov, D.; Schmidt, H.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2 30167 Hannover (Germany)

2013-12-04

283

Classical and quantum simulations of many-body systems

Energy Technology Data Exchange (ETDEWEB)

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

Murg, Valentin

2008-04-07

284

Adaptive quantum estimation of continuous systems

International Nuclear Information System (INIS)

We propose an adaptive scheme to reconstruct unknown quantum states of light via quantum comparison with certain classes of reference or ruler states. This comparison is realized by joint measurements of EPR variables on both states. The arising probability distribution contains the complete information of the unknown quantum state. Different ruler states allow us to estimate different representations of the unknown state. As an example, we have developed an adaptive algorithm to determine the quadrature representation using Gaussian states as ruler states

285

The Geometric Phase in Quantum Systems

International Nuclear Information System (INIS)

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

286

Entangled Systems New Directions in Quantum Physics

An introductory textbook for advanced students of physics, chemistry and computer science, covering an area of physics that has lately witnessed rapid expansion. The topics treated here include quantum information, quantum communication, quantum computing, teleportation and hidden parameters, thus imparting not only a well-founded understanding of quantum theory as such, but also a solid basis of knowledge from which readers can follow the rapid development of the topic or delve deeper into a more specialized branch of research. Commented recommendations for further reading as well as end-of-chapter problems help the reader to quickly access the theoretical basics of future key technologies

Audretsch, Jürgen

2007-01-01

287

Generalized entropy production fluctuation theorems for quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on trajectory dependent path probability formalism in state space, we derive generalized entropy production fluctuation relations for a quantum system in the presence of measurement and feedback. We have obtained these results for three different cases: (i) the system is evolving in isolation from its surroundings; (ii) the system being weakly coupled to a heat bath; and (iii) system in contact with reservoir using quantum Crooks fluctuation theorem. In case (iii), we ...

Rana, Shubhashis; Lahiri, Sourabh; Jayannavar, A. M.

2012-01-01

288

Dynamical stabilization and time in open quantum systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 caus...

Rotter, Ingrid

2012-01-01

289

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 ?(r???). First, we examine these concepts and its application to quantum systems with central potentials. Then, we calculate these measures for hydrogenic systems, emphasizing their predictive power for various physical phenomena. Finally, some recent open problems are pointed out.

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

2011-03-01

290

Quantum correlations in B and K meson systems

We study quantum correlations in meson-antimeson systems, as provided for example in meson factories used mainly to probe physics beyond the Standard Model of particle physics. We use a semigroup formalism to compute a trace-preserving density matrix for these systems, in spite of the fact that the particles are unstable. This is used to compute the time evolution of several measures of quantum correlations for three meson systems (KKbar, BdBdbar and BsBsbar). We find that the quantum correlations for these systems can be non-trivially different from their stable counterparts.

Banerjee, Subhashish; MacKenzie, Richard

2014-01-01

291

Quantum groups, orthogonal polynomials and applications to some dynamical systems

International Nuclear Information System (INIS)

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

292

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

Barnes, George L

2013-01-01

293

Image storage, retrieval, compression and segmentation in a quantum system

A set of quantum states for M colors and another set of quantum states for N coordinates are proposed in this paper to represent M colors and coordinates of the N pixels in an image respectively. We design an algorithm by which an image of N pixels and m different colors is stored in a quantum system just using 2N+m qubits. An algorithm for quantum image compression is proposed. Simulation result on the Lena image shows that compression ratio of lossless is 2.058. Moreover, an image segmentation algorithm based on quantum search quantum search which can find all solutions in the expected times in O(tsqrt{N} ) is proposed, where N is the number of pixels and t is the number of targets to be segmented.

Li, Hai-Sheng; Qingxin, Zhu; Lan, Song; Shen, Chen-Yi; Zhou, Rigui; Mo, Jia

2013-06-01

294

Generalized P-distributions for open quantum systems

International Nuclear Information System (INIS)

The master equation for the damped quantum harmonic oscillator within the Lindblad theory for open quantum systems is transformed into Fokker-Planck equations for generalized P-distributions. These equations are solved in the study state and the stationary covariance matrix is obtained. (Author)

295

Josephson inplane and tunneling currents in bilayer quantum Hall system

International Nuclear Information System (INIS)

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

296

Adiabatic Response of Quantum Systems Pinching a Gap Closure

A vanishing cause can lead to a large response in quantum systems which undergo cyclic deformations that pinch a point of level crossing. We call such behavior homeopathic. We illustrate this behavior by studying charge circulation in quantum models of necklaces of atoms driven by a running wave of small amplitude.

Avron, J E

1998-01-01

297

Security proof for quantum key distribution using qudit systems

International Nuclear Information System (INIS)

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.

298

Energy-time uncertainty for driven quantum systems

International Nuclear Information System (INIS)

We derive a generalization of the energy-time uncertainty relation for driven quantum systems based on the Bures geometric distance in Hilbert space and the concept of quantum speed limit. This relation is valid for arbitrary driving protocol and arbitrary distance between initial and final state.

299

Recycling of quantum information: Multiple observations of quantum systems

Given a finite number of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? We give a positive answer to this question and quantify the information obtainable by a given observer as a function of the number of copies in the ensemble, and of the number of independent observers that, one after the other, have independently measured the same ensemble of qubits before him. The optimality of the protocol is proven and extensions to other states and encodings are also studied. According to the general lore, the state after a measurement has no information about the state before the measurement. Our results manifestly show that this statement has to be taken with a grain of salt, specially in situations where the quantum states encode confidential information.

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

2007-01-01

300

Quantum Signatures of Solar System Dynamics

Let w(i) be a period of rotation of the i-th planet around the Sun (or w(j;i) be a period of rotation of j-th satellite around the i-th planet). From empirical observations it is known that the sum of n(i)w(i)=0 (or the sum of n(j)w(j;i)=0) for some integers n(i)(or n(j)) (some of which allowed to be zero), different for different satellite systems. These conditions, known as ressonance conditions, make uses of theories such as KAM difficult to implement. To a high degree of accuracy these periods can be described in terms of the power law dependencies of the type w(i)=Ac^i (or w(j;i)= A(i)m^i) with A,c (respectively, A(i),m) being some known empirical constants. Such power law dependencies are known in literature as the Titius-Bode law of planetary/satellite motion. The resonances in Solar system are similar to those encountered in old quantum mechanics. Although not widely known nowadays, applications of methods of celestial mechanics to atomic physics were, in fact, highly successful. With such a success, ...

Kholodenko, Arkady L

2007-01-01

301

Quantum Discord Under System-Environment Coupling: the Two-Qubit Case

Open quantum systems have attracted great attention, since inevitable coupling between quantum systems and their environment greatly affects the features of interest of these systems. Quantum discord, is a measure of the total nonclassical correlation in a quantum system that includes, but is not exclusive to, the distinct property of quantum entanglement. Quantum discord can exist in separated quantum states and plays an important role in many fundamental physics problems and practical quantum information tasks. There have been numerous investigations on quantum discord and its counterpart classical correlation. This short review focuses on highlighting the system-environment dynamics of two-qubit quantum discord and the influence of initial system-environment correlations on the dynamics of open quantum systems. The external control effect on the dynamics of open quantum systems are involved. Several related experimental works are discussed.

Xu, Jin-Shi; Li, Chuan-Feng

2013-01-01

302

Multiple System-Decomposition Method for Avoiding Quantum Decoherence

International Nuclear Information System (INIS)

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

303

Quantum materials, lateral semiconductor nanostructures, hybrid systems and nanocrystals

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

Heitmann, Detlef

2010-01-01

304

Multi-particle correlations in quaternionic quantum systems

International Nuclear Information System (INIS)

The authors investigated the outcomes of measurements on correlated, few-body quantum systems described by a quaternionic quantum mechanics that allows for regions of quaternionic curvature. It was found that a multi particles interferometry experiment using a correlated system of four nonrelativistic, spin-half particles has the potential to detect the presence of quaternionic curvature. Two-body systems, however, are shown to give predictions identical to those of standard quantum mechanics when relative angles are used in the construction of the operators corresponding to measurements of particle spin components. 15 refs

305

Quantum statistical Monte Carlo methods and applications to spin systems

International Nuclear Information System (INIS)

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

306

Decoherence control in open quantum systems via classical feedback

International Nuclear Information System (INIS)

In this work we propose a strategy using techniques from systems theory to completely eliminate decoherence and also provide conditions under which it can be done. A construction employing an auxiliary system, the bait, which is instrumental to decoupling the system from the environment is presented. Our approach to decoherence control in contrast to other approaches in the literature involves the bilinear input affine model of quantum control system which lends itself to various techniques from classical control theory, but with nontrivial modifications to the quantum regime. The elegance of this approach yields interesting results on open loop decouplability and decoherence free subspaces. Additionally, the feedback control of decoherence may be related to disturbance decoupling for classical input affine systems, which entails careful application of the methods by avoiding all the quantum mechanical pitfalls. In the process of calculating a suitable feedback the system must be restructured due to its tensorial nature of interaction with the environment, which is unique to quantum systems. In the subsequent section we discuss a general information extraction scheme to gain knowledge of the state and the amount of decoherence based on indirect continuous measurement. The analysis of continuous measurement on a decohering quantum system has not been extensively studied before. Finally, a methodology to synthesize feedback parameters itself is given, that technology permitting, could be implemented for practical 2-qubit systems to perform decoherence free quantum computing. The results obtained are qualitatively different and superior to the ones obtained via master equations

307

A robust, scanning quantum system for nanoscale sensing and imaging

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

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

2011-01-01

308

Time delays and advances in classical and quantum systems

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

Kolomeitsev, E E

2013-01-01

309

Time delays and advances in classical and quantum systems

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

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

2013-11-01

310

Does an onlooker stop an evolving quantum system?

International Nuclear Information System (INIS)

The evolution of quantum mechanics has followed the critical analysis of 'gedanken' experiments. Many of these concrete speculations can become implemented today in the laboratory - thanks to now available techniques. A key experiment is concerned with the time evolution of a quantum system under repeated or continuing observation. Here, three problems overlap: 1. The microphysical measurement by a macroscopic device, 2. the system's temporal evolution, and 3. the emergence of macroscopic reality out of the microcosmos. A well-known calculation shows the evolution of a quantum system being slowed down, or even obstructed, when the system is merely observed.An experiment designed to demonstrate this 'quantum Zeno effect' and performed in the late eighties on an ensemble of identical atomic ions confirmed its quantum description, but turned out inconclusive with respect to the very origin of the impediment of evolution. During the past years, experiments on individualelectrodynamically stored and laser-cooled ions have been performed that unequivocally demonstrate the observed system's quantum evolution being impeded. Strategy and results exclude any physical reaction on the measured object, but reveal the effect of the gain of information as put forward by the particular correlation of the ion state with the detected signal. They shed light on the process of measurement as well as on the quantum evolution and allow an epistemological interpretation

311

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

Energy Technology Data Exchange (ETDEWEB)

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

Schwager, Heike

2012-07-04

312

Fractional quantum Hall systems from Toda theories

We analyse the expression for the conductance of a quantum wire which is decribed by an integrable quantum field theory. In the high temperature regime we derive a simple formula for the filling fraction. This expression involves only the inverse of a matrix which contains the information of the asymptotic phases of the scattering matrix and the solutions of the constant thermodynamic Bethe ansatz equations. Evaluating these expressions for minimal affine Toda field theory we recover several subsequences of the famous Jain sequence for the filling fraction occurring in the context of the fractional quantum Hall effect. For instance we obtain $\

Castro-Alvaredo, O A; Castro-Alvaredo, Olalla A.; Fring, Andreas

2003-01-01

313

The Dalton quantum chemistry program system

DEFF Research Database (Denmark)

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

Aidas, Kestutis; Angeli, Celestino

2014-01-01

314

The DALTON quantum chemistry program system

DEFF Research Database (Denmark)

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

Aidas, Kestutis; Angeli, Celestino

2014-01-01

315

Dressed excitonic states and quantum interference in a three-level quantum dot ladder system

Energy Technology Data Exchange (ETDEWEB)

We observe dressed states and quantum interference effects in a strongly driven three-level quantum dot ladder system. The effect of a strong coupling field on one dipole transition is measured by a weak probe field on the second dipole transition using differential reflection. When the coupling energy is much larger than both the homogeneous and inhomogeneous linewidths an Autler-Townes splitting is observed. Significant differences are observed when the transitions resonant with the strong and weak fields are swapped, particularly when the coupling energy is nearly equal to the measured linewidth. This result is attributed to quantum interference: destructive or constructive interference with modest visibility is observed depending on the pump/probe geometry. The data demonstrate that coherence of both the bi-exciton and the exciton is maintained in this solid-state system, even under intense illumination, which is crucial for prospects in quantum information processing and nonlinear optical devices.

Gerardot, B D; Brunner, D; Dalgarno, P A; Warburton, R J [School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Karrai, K [Center for NanoScience and Department fuer Physik der LMU, Geschwister-Scholl-Platz 1, 80539 Munich (Germany); Badolato, A [Institute of Quantum Electronics, ETH Zurich, 8093 Zurich (Switzerland); Petroff, P M [Materials Department, University of California, Santa Barbara, CA 93106 (United States)], E-mail: b.d.gerardot@hw.ac.uk

2009-01-15

316

Dressed excitonic states and quantum interference in a three-level quantum dot ladder system

We observe dressed states and quantum interference effects in a strongly driven three-level quantum dot ladder system. The effect of a strong coupling field on one dipole transition is measured by a weak probe field on the second dipole transition using differential reflection. When the coupling energy is much larger than both the homogeneous and inhomogeneous linewidths an Autler-Townes splitting is observed. Significant differences are observed when the transitions resonant with the strong and weak fields are swapped, particularly when the coupling energy is nearly equal to the measured linewidth. This result is attributed to quantum interference: destructive or constructive interference with modest visibility is observed depending on the pump/probe geometry. The data demonstrate that coherence of both the bi-exciton and the exciton is maintained in this solid-state system, even under intense illumination, which is crucial for prospects in quantum information processing and nonlinear optical devices.

Gerardot, B. D.; Brunner, D.; Dalgarno, P. A.; Karrai, K.; Badolato, A.; Petroff, P. M.; Warburton, R. J.

2009-01-01

317

Driven harmonic oscillator as a quantum simulator for open systems

International Nuclear Information System (INIS)

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

318

A quantum key distribution system operating at gigahertz clock rates

Digital Repository Infrastructure Vision for European Research (DRIVER)

A fiber-optic based quantum key distribution system, operating at a wavelength of 850 nm, has been developed capable of operating up to a clock frequency of 1 GHz, creating significantly increased key exchange rates.

Gordon, Karen J.; Ferna?ndez Ma?rmol, Vero?nica; Buller, Gerald S.; Townsend, Paul D.; Cova, Segio D.; Tisa, Simone

2004-01-01

319

Quantum Brayton cycle with coupled systems as working substance

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

320

Entanglement Generation in Spatially Separated Systems Using Quantum Walk

Directory of Open Access Journals (Sweden)

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

Sandeep K. Goyal

2012-06-01

321

Statistical measure of complexity for quantum systems with continuous variables

The Fisher-Shannon statistical measure of complexity is analyzed for a continuous manifold of quantum observables. It is probed then than calculating it only in the configuration and momentum spaces will not give a complete description for certain systems. Then a more general measure for the complexity of a quantum system by the integration of the usual Fisher-Shannon measure over all the parameter space is proposed.

Manzano, D

2011-01-01

322

Modeling and Control of Quantum Systems: An Introduction

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scope of this work is to provide a self-contained introduction to a selection of basic theoretical aspects in the modeling and control of quantum mechanical systems, as well as a brief survey on the main approaches to control synthesis. While part of the existing theory, especially in the open-loop setting, stems directly from classical control theory (most notably geometric control and optimal control), a number of tools specifically tailored for quantum systems have be...

Altafini, Claudio; Ticozzi, Francesco

2012-01-01

323

Emergent Geometry Fluctuation in Quantum Confined Electron Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

The intrinsic geometric degree of freedom that was proposed to determine the optimal correlation energy of the fractional quantum Hall states, is analyzed for quantum confined planar electron systems. One major advantage in this case is that the role of various unimodular metrics resulting from the absence of rotational symmetry can be investigated independently or concurrently. For interacting electrons in our system, the confinement metric due to the anisotropy shifts the ...

Ghazaryan, Areg; Chakraborty, Tapash

2014-01-01

324

Integrable and superintegrable quantum systems in a magnetic field

Integrable quantum mechanical systems with magnetic fields are constructed in two-dimensional Euclidean space. The integral of motion is assumed to be a first or second order Hermitian operator. Contrary to the case of purely scalar potentials, quadratic integrability does not imply separation of variables in the Schroedinger equation. Moreover, quantum and classical integrable systems do not necessarily coincide: the Hamiltonian can depend on the Planck constant in a nontrivial manner.

Berube, J; Berube, Josee; Winternitz, Pavel

2004-01-01

325

Plausibility of quantum coherent states in biological systems

International Nuclear Information System (INIS)

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

326

Plausibility of quantum coherent states in biological systems

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

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

2011-07-01

327

Plausibility of Quantum Coherent States in Biological Systems

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

Salari, V; Rahnama, M; Bernroider, G

2010-01-01

328

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

International Nuclear Information System (INIS)

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

329

Quantum discord in a spin system with symmetry breaking

We analyze the quantum discord Q throughout the low-temperature phase diagram of the quantum XY model in transverse field. We first focus on the T=0 order-disorder quantum phase transition both in the symmetric ground state and in the symmetry broken one. Besides it, we highlight how Q displays clear anomalies also at a non critical value of the control parameter inside the ordered phase, where the ground state is completely factorized. We evidence how the phenomenon is in fact of collective nature and displays universal features. We also study Q at finite temperature. We show that, close to the quantum phase transition, Q exhibits quantum-classical crossover of the system with universal scaling behavior. We evidence a non trivial pattern of thermal correlations resulting from the factorization phenomenon.

Tomasello, Bruno; Hamma, Alioscia; Amico, Luigi

2011-01-01

330

Quantum encodings in spin systems and harmonic oscillators

International Nuclear Information System (INIS)

We show that higher-dimensional versions of qubits, or qudits, can be encoded into spin systems and into harmonic oscillators, yielding important advantages for quantum computation. Whereas qubit-based quantum computation is adequate for analyses of quantum vs classical computation, in practice qubits are often realized in higher-dimensional systems by truncating all but two levels, thereby reducing the size of the precious Hilbert space. We develop natural qudit gates for universal quantum computation, and exploit the entire accessible Hilbert space. Mathematically, we give representations of the generalized Pauli group for qudits in coupled spin systems and harmonic oscillators, and include analyses of the qubit and the infinite-dimensional limits

331

Applying quantum mechanics to macroscopic and mesoscopic systems

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

T., N Poveda

2012-01-01

332

The entropy power inequality for quantum systems

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

Koenig, Robert

2012-01-01

333

We develop a semiclassical method for the determination of the nonlinear dynamics of dissipative quantum optical systems in the limit of large number of photons N, based on the 1/N-expansion and the quantum-classical correspondence. The method has been used to tackle two problems: to study the dynamics of nonclassical state generation in higher-order anharmonic dissipative oscillators and to establish the difference between the quantum and classical dynamics of the second-harmonic generation in a self-pulsing regime. In addressing the first problem, we have obtained an explicit time dependence of the squeezing and the Fano factor for an arbitrary degree of anharmonism in the short-time approximation. For the second problem, we have established analytically a characteristic time scale when the quantum dynamics differs insignificantly from the classical one.

Alekseev, K N; Perina, J; Alekseev, Kirill N.; Alekseeva, Natasha V.; Perina, Jan

1999-01-01

334

Tampering detection system using quantum-mechanical systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-12-13

335

Quantum state reconstruction from dynamical systems theory

When an informationally incomplete set of observables is considered there are several solutions to the quantum state reconstruction problem using von Neumann measurements. The set of solutions are known as Pauli partners, which are not easy to find even numerically. We present, in a self-contained paper, a new way to find this solutions using the physical imposition operator. We show that every Pauli partner is an attractive fixed point of this operator, which means that we can find complete sets of Pauli partners very efficiently. As a particular case, we found numerically 24 mutually unbiased bases in dimension N=23 in less than 30 seconds in a standard PC. We hope that the algorithm presented can be adapted to construct MU Constellations, SIC-POVMs, Equiangular Tight Frames and Quantum t-Designs, which could open new possibilities to find numerical solutions to these open problems related with quantum information theory.

Goyeneche, D

2011-01-01

336

Decohering histories and open quantum systems

Energy Technology Data Exchange (ETDEWEB)

I briefly review the 'decohering histories' or 'consistent histories' formulation of quantum theory, due to Griffiths, Omnes, and Gell-Mann and Hartle (and the subject of my graduate work with George Sudarshan). I also sift through the many meanings that have been attached to decohering histories, with an emphasis on the most basic one: Decoherence of appropriate histories is needed to establish that quantum mechanics has the correct classical limit. Then I will describe efforts to find physical mechanisms that do this. Since most work has focused on density matrix versions of decoherence, I'll consider the relation between the two formulations, which historically has not been straightforward. Finally, I'll suggest a line of research that would use recent results by Sudarshan to illuminate this aspect of the classical limit of quantum theory.

Chisolm, Eric D, E-mail: echisolm@lanl.go [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2009-11-01

337

Deterministic constant-temperature dynamics for dissipative quantum systems

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

Sergi, A

2007-01-01

338

Decoherence Control in Open Quantum System via Classical Feedback

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

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

2006-01-01

339

Symmetry in quantum system theory: Rules for quantum architecture design

International Nuclear Information System (INIS)

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

340

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

DEFF Research Database (Denmark)

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

Stobbe, SØren; Lodahl, Peter

2009-01-01

341

Towards polymer quantum mechanics for fermionic systems

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

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

2013-07-01

342

Scalable quantum field simulations of conditioned systems

International Nuclear Information System (INIS)

We demonstrate a technique for performing stochastic simulations of conditional master equations. The method is scalable for many quantum-field problems and therefore allows first-principles simulations of multimode bosonic fields undergoing continuous measurement, such as those controlled by measurement-based feedback. As examples, we demonstrate a 53-fold speed increase for the simulation of the feedback cooling of a single trapped particle, and the feedback cooling of a quantum field with 32 modes, which would be impractical using previous brute force methods.

343

Role of quantum fluctuations in a system with strong fields

In this work we study how quantum fluctuations modify the quantum evolution of an initially classical field theory. We consider a scalar $\\phi^4$ theory coupled to an external source as a toy model for the Color Glass Condensate description of the early time dynamics of heavy-ion collisions. We demonstrate that quantum fluctuations considerably modify the time evolution driving the system to evolve in accordance with ideal hydrodynamics. We attempt to understand the mechanism behind this relaxation to ideal hydrodynamics by using modified initial spectra and studying the particle content of the theory.

Dusling, Kevin

2011-01-01

344

A short review on entanglement in quantum spin systems

We review some of the recent progress on the study of entropy of entanglement in many-body quantum systems. Emphasis is placed on the scaling properties of entropy for one-dimensional multi-partite models at quantum phase transitions and, more generally, on the concept of area law. We also briefly describe the relation between entanglement and the presence of impurities, the idea of particle entanglement, the evolution of entanglement along renormalization group trajectories, the dynamical evolution of entanglement and the fate of entanglement along a quantum computation.

Latorre, J I

2009-01-01

345

Quantum information transfer between topological and spin qubit systems

International Nuclear Information System (INIS)

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

346

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

Shushin, A. I.

2011-02-01

347

Some statistical properties of simple classically stochastic quantum systems

International Nuclear Information System (INIS)

Numerical studies are made of simple one- and two-dimensional quantum models which are stochastic in the classical limit. It is shown that the correlation properties of the quantum and corresponding classical motions are only similar for very short time intervals tsub(s), and that the evolution of the quantum system, unlike the classical one, is stable. The diffusive excitation of the quantum system under a periodic perturbation is limited to a specific time interval tsup(*)>>tsub(s), during which the diffusion rate is similar to the corresponding classical diffusion rate. For the two-dimensional model, a continuous component in the correlation spectrum survives for an indefinite period tsub(w)>>tsup(*). It is shown that when the perturbation is quasiperiodic the interval tsup(*) increases sharply. (orig.)

348

Symmetry and the thermodynamics of currents in open quantum systems

Symmetry is a powerful concept in physics, and its recent application to understand nonequilibrium behavior is providing deep insights and groundbreaking exact results. Here we show how to harness symmetry to control transport and statistics in open quantum systems. Such control is enabled by a first-order-type dynamic phase transition in current statistics and the associated coexistence of different transport channels (or nonequilibrium steady states) classified by symmetry. Microreversibility then ensues, via the Gallavotti-Cohen fluctuation theorem, a twin dynamic phase transition for rare current fluctuations. Interestingly, the symmetry present in the initial state is spontaneously broken at the fluctuating level, where the quantum system selects the symmetry sector that maximally facilitates a given fluctuation. We illustrate these results in a qubit network model motivated by the problem of coherent energy harvesting in photosynthetic complexes, and introduce the concept of a symmetry-controlled quantum thermal switch, suggesting symmetry-based design strategies for quantum devices with controllable transport properties.

Manzano, Daniel; Hurtado, Pablo I.

2014-09-01

349

Experimental quantum computing to solve systems of linear equations.

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

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

2013-06-01

350

Open quantum system of two coupled harmonic oscillators

International Nuclear Information System (INIS)

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

351

Quantum and classical eigenfunctions in Calogero and Sutherland systems

Energy Technology Data Exchange (ETDEWEB)

An interesting observation was reported by Corrigan-Sasaki that all the frequencies of small oscillations around equilibrium are 'quantized' for Calogero and Sutherland (CS) systems, typical integrable multi-particle dynamics. We present an analytic proof by applying recent results. Explicit forms of 'classical' and quantum eigenfunctions are presented for CS systems based on any root system.

Loris, I [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Sasaki, R [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

2004-01-09

352

Photon Statistics; Nonlinear Spectroscopy of Single Quantum Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

A unified description of multitime correlation functions, nonlinear response functions, and quantum measurements is developed using a common generating function which allows a direct comparison of their information content. A general formal expression for photon counting statistics from single quantum objects is derived in terms of Liouville space correlation functions of the material system by making a single assumption that spontaneous emission is described by a master equ...

Mukamel, Shaul

2003-01-01

353

Quantum Cost Efficient Reversible BCD Adder for Nanotechnology Based Systems

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Islam, Md Saiful; Hafiz, Mohd Zulfiquar; Begum, Zerina

2011-01-01

354

Quantum integrable systems: basic concepts and brief overview

International Nuclear Information System (INIS)

An overview of the quantum integrable systems (QIS) is presented. Basic concepts of the theory are highlighted stressing on the unifying algebraic properties, which not only helps to generate systematically the representative Lax operators of different models, but also solves the related eigenvalue problem in an almost model independent way. Difference between the approaches in the integrable ultra local and nonultralocal quantum models are explained and the interrelation between the QIS and other subjects are focused on. (author)

355

Computer simulation of mixed classical-quantum systems

International Nuclear Information System (INIS)

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

356

GRAVITATIONAL WAVES AND STATIONARY STATES OF QUANTUM AND CLASSICAL SYSTEMS

Directory of Open Access Journals (Sweden)

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

Trunev A. P.

2014-03-01

357

Bipartite quantum systems: on the realignment criterion and beyond

Digital Repository Infrastructure Vision for European Research (DRIVER)

Inspired by the `computable cross norm' or `realignment' criterion, we propose a new point of view about the characterization of the states of bipartite quantum systems. We consider a Schmidt decomposition of a bipartite density operator. The corresponding Schmidt coefficients, or the associated symmetric polynomials, are regarded as quantities that can be used to characterize bipartite quantum states. In particular, starting from the realignment criterion, a family of neces...

Lupo, Cosmo; Aniello, Paolo; Scardicchio, Antonello

2008-01-01

358

Heat-exchange statistics in driven open quantum systems

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

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

2014-11-01

359

Non-Hermitian Quantum Systems and Time-Optimal Quantum Evolution

Directory of Open Access Journals (Sweden)

Full Text Available Recently, Bender et al. have considered the quantum brachistochrone problem for the non-Hermitian PT-symmetric quantum system and have shown that the optimal time evolution required to transform a given initial state |?_i> into a specific final state |?_f> can be made arbitrarily small. Additionally, it has been shown that finding the shortest possible time requires only the solution of the two-dimensional problem for the quantum system governed by the effective Hamiltonian acting in the subspace spanned by |?_i> and |?_f>. In this paper, we study a similar problem for the generic non-Hermitian Hamiltonian, focusing our attention on the geometric aspects of the problem.

Alexander I. Nesterov

2009-07-01

360

Numerical approaches to complex quantum, semiclassical and classical systems

Energy Technology Data Exchange (ETDEWEB)

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

Schubert, Gerald

2008-11-03

361

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 Schr\\"odinger probability density. First, we examine these concepts and its application to quantum systems with central potentials. Then, we calculate these measures for hydrogenic systems, emphasizing their predictive power for various physical phenomena. Finally, some recent open problems are pointed out.

Dehesa, J S; Sánchez-Moreno, P S; Yáñez, R J

2010-01-01

362

A generalization of Fermat's principle for classical and quantum systems

The analogy between dynamics and optics had a great influence on the development of the foundations of classical and quantum mechanics. We take this analogy one step further and investigate the validity of Fermat's principle in many-dimensional spaces describing dynamical systems (i.e., the quantum Hilbert space and the classical phase and configuration space). We propose that if the notion of a metric distance is well defined in that space and the velocity of the representative point of the system is an invariant of motion, then a generalized version of Fermat's principle will hold. We substantiate this conjecture for time-independent quantum systems and for a classical system consisting of coupled harmonic oscillators. An exception to this principle is the configuration space of a charged particle in a constant magnetic field; in this case the principle is valid in a frame rotating by half the Larmor frequency, not the stationary lab frame.

Elsayed, Tarek A.

2014-09-01

363

Quantum dynamics of bio-molecular systems in noisy environments

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

Plenio, M B

2012-01-01

364

Strongly interacting confined quantum systems in one dimension.

In one dimension, the study of magnetism dates back to the dawn of quantum mechanics when Bethe solved the famous Heisenberg model that describes quantum behaviour in magnetic systems. In the last decade, one-dimensional (1D) systems have become a forefront area of research driven by the realization of the Tonks-Girardeau gas using cold atomic gases. Here we prove that 1D fermionic and bosonic systems with strong short-range interactions are solvable in arbitrary confining geometries by introducing a new energy-functional technique and obtaining the full spectrum of energies and eigenstates. As a first application, we calculate spatial correlations and show how both ferro- and antiferromagnetic states are present already for small system sizes that are prepared and studied in current experiments. Our work demonstrates the enormous potential for quantum manipulation of magnetic correlations at the microscopic scale. PMID:25366925

Volosniev, A G; Fedorov, D V; Jensen, A S; Valiente, M; Zinner, N T

2014-01-01

365

Equivalence of the Symbol Grounding and Quantum System Identification Problems

Directory of Open Access Journals (Sweden)

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

Chris Fields

2014-02-01

366

Applications of Lie systems in Quantum Mechanics and Control Theory

Some simple examples from quantum physics and control theory are used to illustrate the application of the theory of Lie systems. We will show, in particular, that for certain physical models both of the corresponding classical and quantum problems can be treated in a similar way, may be up to the replacement of the involved Lie group by a central extension of it. The geometric techniques developed for dealing with Lie systems are also used in problems of control theory. Specifically, we will study some examples of control systems on Lie groups and homogeneous spaces.

Cariñena, José F; Cari\\~nena, Jos\\'e F.; Ramos, Arturo

2003-01-01

367

Chaotic Dynamics and Transport in Classical and Quantum Systems

This book offers a modern updated review on the most important activities in today dynamical systems and statistical mechanics by some of the best experts in the domain. It gives a contemporary and pedagogical view on theories of classical and quantum chaos and complexity in hamiltonian and ergodic systems and their applications to anomalous transport in fluids, plasmas, oceans and atom-optic devices and to control of chaotic transport. The book is issued from lecture notes of the International Summer School on "Chaotic Dynamics and Transport in Classical and Quantum Systems" held in Cargèse (Corsica) 18th to the 30th August 2003.

Collet, P.; Courbage, M.; Metens, S.; Neishtadt, A.; Zaslavsky, G.

368

Alternative routes to equivalent classical models of a quantum system

International Nuclear Information System (INIS)

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

369

Unifying relation for quantum systems driven out of equilibrium

We extend a classical relation derived by Crooks to quantum systems driven out of equilibrium and show that it provides a unified way of deriving both known and new results for these systems. For a fluid driven to a steady state with a shear flow, we use it to prove the fluctuation theorem for shear stress to obtain the Green-Kubo formula for shear viscosity in terms of the symmetrized correlation function of the shear stress operator. We also show that a generalized entropy for a quantum system in a steady heat conduction state satisfies extensions of the Clausius and the Gibbs relations.

Matsuoka, Hiroshi

2011-01-01

370

An Online Banking System Based on Quantum Cryptography Communication

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

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

2014-07-01

371

Nonlinear Dynamics and Quantum Entanglement in Optomechanical Systems

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

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

2014-03-01

372

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

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

Yuen, H. P. H.

1971-01-01

373

Bipartite quantum systems: on the realignment criterion and beyond

International Nuclear Information System (INIS)

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

374

Quantifying Quantum Correlations in Fermionic Systems using Witness Operators

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 entan- glement witness of a state with a class of problems known as semidefinite programs (SDPs), 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 Robust- ness 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 con- currence presents itself as an upper bound for the Generalized Robustness. The quantum discord is also found to be an upper bound for the entangl...

Iemini, Fernando; Debarba, Tiago; Vianna, Reinaldo O

2012-01-01

375

Quantum maximum entropy principle for a system of identical particles

International Nuclear Information System (INIS)

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

376

RKKY interaction in a chirally coupled double quantum dot system

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-04

377

Fluorescence from a quantum dot and metallic nanosphere hybrid system

Energy Technology Data Exchange (ETDEWEB)

We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

Schindel, Daniel G. [Department of Mathematics and Statistics, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB, R3B 2E9 (Canada); Singh, Mahi R. [Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 3K7 (Canada)

2014-03-31

378

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2007-01-01

379

The 20th century saw the first revolution of quantum mechanics, setting the rules for our understanding of light, matter, and their interaction. The 21st century is focused on using these quantum mechanical laws to develop technologies which allows us to solve challenging practical problems. One of the directions is the use quantum devices which promise to surpass the best computers and best known classical algorithms for solving certain tasks. Crucial to the design of realistic devices and technologies is to account for the open nature of quantum systems and to cope with their interactions with the environment. In the first part of this dissertation, we show how to tackle classical optimization problems of interest in the physical sciences within one of these quantum computing paradigms, known as quantum annealing (QA). We present the largest implementation of QA on a biophysical problem (six different experiments with up to 81 superconducting quantum bits). Although the cases presented here can be solved on a classical computer, we present the first implementation of lattice protein folding on a quantum device under the Miyazawa-Jernigan model. This is the first step towards studying optimization problems in biophysics and statistical mechanics using quantum devices. In the second part of this dissertation, we focus on the problem of excitonic energy transfer. We provide an intuitive platform for engineering exciton transfer dynamics and we show that careful consideration of the properties of the environment leads to opportunities to engineer the transfer of an exciton. Since excitons in nanostructures are proposed for use in quantum information processing and artificial photosynthetic designs, our approach paves the way for engineering a wide range of desired exciton dynamics. Finally, we develop the theory for a two-dimensional electronic spectroscopic technique based on fluorescence (2DFS) and challenge previous theoretical results claiming its equivalence to the two-dimensional photon echo (2DPE) technique which is based on polarization. Experimental realization of this technique confirms our theoretical predictions. The new technique is more sensitive than 2DPE as a tool for conformational determination of excitonically coupled chromophores and offers the possibility of applying two-dimensional electronic spectroscopy to single-molecules.

Perdomo, Alejandro

380

Cooling of quantum systems through optimal control and dissipation

International Nuclear Information System (INIS)

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.

381

Stochastic pure state representation for open quantum systems

International Nuclear Information System (INIS)

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

382

GRAVITATIONAL WAVES AND EMERGENCE PARAMETER OF CLASSICAL AND QUANTUM SYSTEMS

Directory of Open Access Journals (Sweden)

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

Trunev A. P.

2014-03-01

383

Dissipation and entropy production in open quantum systems

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-11-01

384

On the complete ionization of a periodically perturbed quantum system

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the time evolution of a one-dimensional quantum system with zero range potential under time periodic parametric perturbation of arbitrary strength and frequency. We show that the projection of the wave function on the bound state vanishes, i.e. the system gets fully ionized, as time grows indefinitely.

Costin, O.; Lebowitz, J. L.; Rokhlenko, A.

2000-01-01

385

Hidden symmetry of the quantum Calogero-Moser system.

DEFF Research Database (Denmark)

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

Kuzentsov, Vadim b

1996-01-01

386

Active optical clock based on four-level quantum system

Active optical clock, a new conception of atomic clock, has been proposed recently. In this report, we propose a scheme of active optical clock based on four-level quantum system. The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam. To three-level quantum system, they are mainly limited by light shift of pumping laser field. These limitations can be avoided effectively by applying the scheme proposed here. Rubidium atom four-level quantum system, as a typical example, is discussed in this paper. The population inversion between $6S_{1/2}$ and $5P_{3/2}$ states can be built up at a time scale of $10^{-6}$s. With the mechanism of active optical clock, in which the cavity mode linewidth is much wider than that of the laser gain profile, it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory. An experimental configuration is designed to realize this active optical clock.

Zhang, Tonggang; Zang, Xiaorun; Zhuang, Wei; Chen, Jingbiao

2012-01-01

387

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

International Nuclear Information System (INIS)

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

388

International Nuclear Information System (INIS)

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

389

Simulations are performed of a small quantum system interacting with a quantum environment. The system consists of various initial states of two harmonic oscillators coupled to give normal modes. The environment is "designed" by its level pattern to have a thermodynamic temperature. A random coupling causes the system and environment to become entangled in the course of time evolution. The approach to a Boltzmann distribution is observed, and effective fitted temperatures close to the designed temperature are obtained. All initial pure states of the system are driven to equilibrium at very similar rates, with quick loss of memory of the initial state. The time evolution of the von Neumann entropy is calculated as a measure of equilibration and of quantum coherence. It is pointed out using spatial density distribution plots that quantum interference is eliminated only with maximal entropy, which corresponds thermally to infinite temperature. Implications of our results for the notion of "classicalizing" behavior in the approach to thermal equilibrium are briefly considered. PMID:24320365

Barnes, George L; Kellman, Michael E

2013-12-01

390

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-07

391

Area laws in quantum systems: mutual information and correlations

The holographic principle states that on a fundamental level the information content of a region should depend on its surface area rather than on its volume. This counterintuitive idea which has its roots in the nonextensive nature of black-hole entropy serves as a guiding principle in the search for the fundamental laws of Planck-scale physics. In this paper we show that a similar phenomenon emerges from the established laws of classical and quantum physics: the information contained in part of a system in thermal equilibrium obeys an area law. While the maximal information per unit area depends classically only on the number of microscopic degrees of freedom, it may diverge as the inverse temperature in quantum systems. A rigorous relation between area laws and correlations is established and their explicit behavior is revealed for a large class of quantum many-body states beyond equilibrium systems.

Wolf, M M; Hastings, M B; Cirac, J I

2007-01-01

392

Coherent oscillations in a superconducting multilevel quantum system.

We have observed coherent oscillations in a multilevel quantum system, formed by a current-biased dc SQUID. These oscillations have been induced by applying resonant microwave pulses of flux. Quantum measurement is performed by a nanosecond flux pulse that projects the final state onto one of two different voltage states of the dc SQUID, which can be read out. The number of quantum states involved in the coherent oscillations increases with increasing microwave power. The dependence of the oscillation frequency on microwave power deviates strongly from the linear regime expected for a two-level system and can be very well explained by a theoretical model taking into account the anharmonicity of the multilevel system. PMID:15525198

Claudon, J; Balestro, F; Hekking, F W J; Buisson, O

2004-10-29

393

SU(2)-coherent states of the quantum systems

International Nuclear Information System (INIS)

The coherent states of a nonstationary quantum system connected with the representation of Lie group in Hilbert space are investigated. The method developed earlier for constructing some types of coherent states of nonstationary quantum systems is generalized. In the concrete considerations the SU(2) group is used. The coherent states, connected with the nonunitary irreducible representations of SU(2) group in Hilbert space of a nonstationary harmonic oscillator, are obtained in an explicite form. The corresponding complete set of U(2)-coherent states is also given. The time-stability of the obtained SU(2)-set is studied. In the particular case of circular orbits the most general explicite form of Hamiltonian, for which the SU(2)-coherent states are time-stable, is given. It is also shown that if Hamiltonian of the quantum system is a linear combination of the group generators, the corresponding coherent states connected with the representation of this group are stable

394

An order parameter for impurity systems at quantum criticality.

A quantum phase transition may occur in the ground state of a system at zero temperature when a controlling field or interaction is varied. The resulting quantum fluctuations which trigger the transition produce scaling behaviour of various observables, governed by universal critical exponents. A particularly interesting class of such transitions appear in systems with quantum impurities where a non-extensive term in the free energy becomes singular at the critical point. Curiously, the notion of a conventional order parameter that exhibits scaling at the critical point is generically missing in these systems. Here we explore the possibility to use the Schmidt gap, which is an observable obtained from the entanglement spectrum, as an order parameter. A case study of the two-impurity Kondo model confirms that the Schmidt gap faithfully captures the scaling behaviour by correctly predicting the critical exponent of the dynamically generated length scale at the critical point. PMID:24807201

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

2014-01-01

395

Engineered Open Systems and Quantum Simulations with Atoms and Ions

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

Müller, M; Pupillo, G; Zoller, P

2012-01-01

396

Einstein, De Broglie and others hoped that the schism between classical and quantum physics might one day be overcome by a theory taking into account the essential nonlinearity of elementary physical processes. However, neither their attempts, nor subsequent ones were able to supply a unifying principle that could serve as a starting-point for a coherent understanding of both microphysical and macroscopic phenomena. In the late 1960s the phenomenon of amplitude quantization, or Macroscopic Quantum Effect (MQE), was discovered in a class of nonlinear oscillating systems in which two or more subsystems are coupled to each other by interactions having a specific phase-dependent character -- so-called argumental interactions. Experimental and theoretical studies of the MQE, carried out up to the present time, suggest the possibility of a new conceptual framework for physics, which would provide a bridge between classical and quantum physics, replacing the Newtonian notion of "force" by a new conception of physica...

Doubochinski, Danil

2007-01-01

397

Strongly coupled coulomb systems in graphene quantum dots

International Nuclear Information System (INIS)

Complete text of publication follows. We review here our recent work on strongly coupled Coulomb systems in gated graphene quantum dots. The effect of Coulomb interactions, size, shape, edge and carrier density on the electronic, magnetic and optical properties of graphene quantum dots will be described. We will focus on a special class of triangular quantum dots (GTQD) with zig-zag edges. Such structures lead to a shell of degenerate zero-energy states at the Fermi level (Dirac point). The degeneracy is proportional to the edge size and can be made macroscopic. Using a combination of tight-binding, density functional, Hartree-Fock and configuration interaction methods we will describe the strongly coupled Coulomb system, a degenerate shell, as a function of the fractional filling, drawing on analogy with the FQHE. In particular, we will show that at half-filling the shell is fully spin polarised but polarization can be modulated by controlling the filling of the shell with the external gate. In particular, addition of a single electron leads to spin depolarisation due to electronic correlations and strong Coulomb interaction with the gate. The effect of shell filling and magnetic moment on transport and optical properties of a single quantum dot will be described. We will show that the magnetic moments of triangular quantum dots interact ferromagnetically in bi-layer quantum dots. The tunability of this magnetic moment with vertical electric field and the possibility of isolating a single electron spin will be demonstrated. These results show that it is possible to combine electronic, photonic and magnetic functionalities in a single material system by engineering graphene quantum dot size, shape and character of the edge.

398

Room-temperature resonant quantum tunneling transport of macroscopic systems.

A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (?10(2) V cm(-1)) could be enhanced by three orders of magnitude (?10(5) V cm(-1)) between the Ni QDA because of the higher permittivity of BaTiO3 and the 'hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (?-T curves) construction. PMID:25307500

Xiong, Zhengwei; Wang, Xuemin; Yan, Dawei; Wu, Weidong; Peng, Liping; Li, Weihua; Zhao, Yan; Wang, Xinmin; An, Xinyou; Xiao, Tingting; Zhan, Zhiqiang; Wang, Zhuo; Chen, Xiangrong

2014-10-24

399

Universal quench dynamics of interacting quantum impurity systems

The equilibrium physics of quantum impurities frequently involves a universal crossover from weak to strong reservoir-impurity coupling, characterized by single-parameter scaling and an energy scale TK (Kondo temperature) that breaks scale invariance. For the noninteracting resonant level model, the nonequilibrium time evolution of the Loschmidt echo after a local quantum quench was recently computed explicitly [R. Vasseur, K. Trinh, S. Haas, and H. Saleur, Phys. Rev. Lett. 110, 240601 (2013), 10.1103/PhysRevLett.110.240601]. It shows single-parameter scaling with variable TKt. Here, we scrutinize whether similar universal dynamics can be observed in various interacting quantum impurity systems. Using density matrix and functional renormalization group approaches, we analyze the time evolution resulting from abruptly coupling two noninteracting Fermi or interacting Luttinger liquid leads via a quantum dot or a direct link. We also consider the case of a single Luttinger liquid lead suddenly coupled to a quantum dot. We investigate whether the field-theory predictions for the universal scaling as well as for the large-time behavior successfully describe the time evolution of the Loschmidt echo and the entanglement entropy of microscopic models. Our study shows that for the considered local quench protocols the above quantum impurity models fall into a class of problems for which the nonequilibrium dynamics can largely be understood based on the knowledge of the corresponding equilibrium physics.

Kennes, D. M.; Meden, V.; Vasseur, R.

2014-09-01

400

From Quantum Spectra to Classical Orbits: the Circular Billiards Systems

Directory of Open Access Journals (Sweden)

Full Text Available The semi-classical method has become a necessary instrument to study the classical movement of the particle. Periodic orbit theory is repidly becoming one of most useful semi-classical tools which can be used to make direct connections between the quantized energy eigenvalues of a bound state and the classical motions for the corresponding point particle. We use a quantum spectral function which contain rich information of classical orbits in well. We study the correspondence between quantum spectra and classical orbits in the circular Two-dimensional billiard systems have provided easily visualization examples relevant for both types of analyses. As a simple example of the application to a billiard or infinite well system of Periodic orbit theory, we compute the Fourier transform (p(L of the quantum mechanical energy level density of two-dimensional circular billiard system The resulting peaks in plots of |p(L|2 versus L are compared to lengths of the classical trajectories in these geometries. The locations of peaks in p(L agree with the lengths of classical orbits perfectly, which testifies the correspondence of quantum mechanics and classical mechanics. This examples show evidently that semi-classical methods provides a brdge between quantum and classical mechanics.

ZHANG Ye-bing

2011-01-01

401

Quantum spin ladder systems associated with SU(2|2)

International Nuclear Information System (INIS)

Two integrable quantum spin ladder systems will be introduced associated with the fundamental SU 92/20 solution of the Yang-baxter equation. The first model is a generalized quantum Ising system with Ising rung interactions. In the second model the addition of extra interactions allows us to impose Heisenberg rung interactions without violating integrability. The existence of a Bethe ansatz solution for both models allows us to investigate the elementary excitations for antiferromagnetic rung couplings. We find that the first model does not show a gap whilst in the second case there is a gap for all positive values of the rung coupling. (author)

402

Bayesian parameter inference from continuously monitored quantum systems

DEFF Research Database (Denmark)

We review the introduction of likelihood functions and Fisher information in classical estimation theory, and we show how they can be defined in a very similar manner within quantum measurement theory. We show that the stochastic master equations describing the dynamics of a quantum system subject to a definite set of measurements provides likelihood functions for unknown parameters in the system dynamics, and we show that the estimation error, given by the Fisher information, can be identified by stochastic master equation simulations. For large parameter spaces we describe and illustrate the efficient use of Markov chain Monte Carlo sampling of the likelihood function.

Gammelmark, SØren; MØlmer, Klaus

2013-01-01

403

Quantum dynamics and transport in a double well system

The simplest one-dimensional model for the studying of non-trivial geometrical effects is a ring shaped device which is formed by joining two arms. We explore the possibility to model such a system as a two level system (TLS). Of particular interest is the analysis of quantum stirring, where it is not evident that the topology is properly reflected within the framework of the TLS modeling. On the technical side we provide a practical "neighboring level" approximation for the analysis of such quantum devices, which remains valid even if the TLS modeling does not apply.

Sela, Itamar

2008-01-01

404

Arbitrarily Accurate Dynamical Control in Open Quantum Systems

We show that open-loop dynamical control techniques may be used to synthesize unitary transformations in open quantum systems in such a way that decoherence is perturbatively compensated for to a desired (in principle arbitrarily high) level of accuracy, which depends only on the strength of the relevant errors, and the achievable rate of control modulation. Our constructive and fully analytical solution employs concatenated dynamically corrected gates, and is applicable independently of detailed knowledge of the system-environment interactions and environment dynamics. Explicit implications for boosting quantum gate fidelities are addressed.

Khodjasteh, Kaveh; Viola, Lorenza

2009-01-01

405

On the Supersymmetric Spectra of two Planar Integrable Quantum Systems

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

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

2011-01-01

406

Sign rules for anisotropic quantum spin systems

International Nuclear Information System (INIS)

We present exact ''sign rules'' for various spin-s anisotropic spin-lattice models. It is shown that, after a simple transformation which utilizes these sign rules, the ground-state wave function of the transformed Hamiltonian is positive definite. Using these results exact statements for various expectation values of off-diagonal operators are presented, and transitions in the behavior of these expectation values are observed at particular values of the anisotropy. Furthermore, the importance of such sign rules in variational calculations and quantum Monte Carlo calculations is emphasized. This is illustrated by a simple variational treatment of a one-dimensional anisotropic spin model

407

Equilibration implies asymptotic stationarity for open quantum systems

International Nuclear Information System (INIS)

We use the exact Nakajima–Zwanzig form of the master equation to show that open quantum systems which exhibit equilibration (or thermalization) by evolving to a time independent asymptotic state, have under certain conditions a reduced density matrix for the system which commutes with the effective system Hamiltonian. We also show that if the initial system–bath density matrix is of product form then the asymptotic reduced density matrix of the system depends only on the diagonal elements of the initial system density matrix in the eigenbasis of the effective Hamiltonian. -- Highlights: ? Quantum open systems which equilibrate are also stationary. ? Equilibrium state commutes with Hamiltonian. ? For product initial state, equilibrium state depends only on diagonal elements of initial density matrix.

408

Quantum Tunneling and Quantum-Classical Transitions in Large Spin Systems

We have studied quantum tunneling of large spins in a biaxial spin system and in a single-axial spin system with a transverse magnetic field. The asymptotically exact eigenvalues and eigenstates of the spin systems are obtained by solving the Mathieu equation. When the height $4q$ of energy barrier formed by the anisotropy and the magnetic field exceeds some critical values $4q_{1T}(r)$, the ground states and the excited states split due to tunneling of large spins. We also have presented the phase diagram of these spin systems in the extremely weak spin-phonon coupling limit. The crossover from thermal to quantum regime is second order. With further decreasing temperature, the first order phase transition occurs from a thermally-assisted resonant tunneling to thermal regime as $q

Hu, B; Li, B; Hu, Bambi; Zhang, De-gang; Li, Bo-zang

2000-01-01

409

Classical representation of a quantum system at equilibrium

International Nuclear Information System (INIS)

Complete text of publication follows. A quantum system at equilibrium is represented by a corresponding classical system, chosen to reproduce the thermodynamic and structural properties. The objective is to develop a means for exploiting strong coupling classical methods (e.g., MD, integral equations, DFT) to describe quantum systems. The classical system has an effective temperature, local chemical potential, and pair interaction that are defined by requiring equivalence of the grand potential and its functional derivatives with respect to the external and pair potentials for the classical and quantum systems. Practical inversion of this mapping for the classical properties is effected via the hypernetted chain approximation, leading to representations as functionals of the quantum pair correlation function (similar in spirit to the approach of Dharma-wardana and Perrot). The parameters of the classical system are determined such that ideal gas, weak coupling RPA, and strong coupling pair limits are preserved. The potential advantages of this approach are discussed. Research supported by NSF/DOE Partnership in Basic Plasma Science Award DE-FG02-07ER54946, and by US DOE Grant DE-SC0002139.

410

Generalized Kronig-Penney model for ultracold atomic quantum systems

We study the properties of a quantum particle interacting with a one-dimensional structure of equidistant scattering centers. We derive an analytical expression for the dispersion relation and for the Bloch functions in the presence of both even and odd scattering waves within the pseudopotential approximation. This generalizes the well-known solid-state physics textbook result known as the Kronig-Penney model. Our generalized model can be used to describe systems such as degenerate Fermi gases interacting with ions or with another neutral atomic species confined in an optical lattice, thus enabling the investigation of polaron or Kondo physics within a simple formalism. We focus our attention on the specific atom-ion system and compare our findings with quantum defect theory. Excellent agreement is obtained within the regime of validity of the pseudopotential approximation. This enables us to derive a Bose-Hubbard Hamiltonian for a degenerate quantum Bose gas in a linear chain of ions.

Negretti, A.; Gerritsma, R.; Idziaszek, Z.; Schmidt-Kaler, F.; Calarco, T.

2014-10-01

411

The geometry emerging from the symmetries of a quantum system

We investigate the relation between the symmetries of a quantum system and its topological quantum numbers, in a general C*-algebraic framework. We prove that, under suitable assumptions on the symmetry algebra, there exists a generalization of the Bloch-Floquet transform which induces a direct-integral decomposition of the algebra of observables. Such generalized transform selects uniquely the set of "continuous sections" in the direct integral, thus yielding a Hilbert bundle. The emerging geometric structure provides some topological invariants of the quantum system. Two running examples provide an Ariadne's thread through the paper. For the sake of completeness, we review two related theorems by von Neumann and Maurin and compare them with our result.

De Nittis, G

2009-01-01

412

The phase diagram of quantum systems Heisenberg antiferromagnets

A novel approach for studying phase transitions in systems with quantum degrees of freedom is discussed. Starting from the microscopic hamiltonian of a quantum model, we first derive a set of exact differential equations for the free energy and the correlation functions describing the effects of fluctuations on the thermodynamics of the system. These equations reproduce the full renormalization group structure in the neighborhood of a critical point keeping, at the same time, full information on the non universal properties of the model. As a concrete application we investigate the phase diagram of a Heisenberg antiferromagnet in a staggered external magnetic field. At long wavelengths the known relationship to the Quantum Non Linear Sigma Model naturally emerges from our approach. By representing the two point function in an approximate analytical form, we obtain a closed partial differential equation which is then solved numerically. The results in three dimensions are in good agreement with available Quant...

Gianinetti, P; Gianinetti, Pietro; Parola, Alberto

2000-01-01

413

Scalable quantum computation in systems with Bose-Hubbard dynamics

Several proposals for quantum computation utilize a lattice type architecture with qubits trapped by a periodic potential. For systems undergoing many body interactions described by the Bose-Hubbard Hamiltonian, the ground state of the system carries number fluctuations that scale with the number of qubits. This process degrades the initialization of the quantum computer register and can introduce errors during error correction. In [1] we proposed a solution to this problem tailored to the loading of cold atoms into an optical lattice via the Mott Insulator phase transition. It was shown that by adding an inhomogeneity to the lattice and performing a continuous measurement, the unit filled state suitable for a quantum computer register can be maintained. Here, we give a more rigorous derivation of the register fidelity in homogeneous and inhomogeneous lattices and provide evidence that the protocol is effective in the finite temperature regime.

Pupillo, G; Brennen, G; Williams, C J; Clark, C W; Pupillo, Guido; Rey, Ana Maria; Brennen, Gavin; Williams, Carl J.; Clark, Charles W.

2004-01-01

414

Hacking commercial quantum cryptography systems by tailored bright illumination

The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built from off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies.

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

2010-10-01

415

Natural Light Harvesting Systems: Unraveling the quantum puzzles

In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies (> 95 %) at which excitation is transferred from the illuminated protein complex site to the reaction centers. Such high exciton propagation rates within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observation of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes, even in noisy environmental baths. A number of experimental and theoretical studies have been devoted to unlocking the links between quantum processes and information protocols, in the hope of finding answers...

Thilagam, A

2013-01-01

416

Theoretical discussion for quantum computation in biological systems

Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ? interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.

Baer, Wolfgang

2010-04-01

417

Locality, entanglement, and thermalization of isolated quantum systems

A way to understand thermalization in an isolated system is to interpret it as an increase in entanglement between subsystems. Here we test this idea through a combination of analytical and Krylov-subspace-based numerical methods applied to a quantum gas of bosons. We find that the entanglement entropy of a subsystem is rapidly generated at the initial state of the evolution, to quickly approach the thermal value. Our results also provide an accurate numerical test of the eigenstate thermalization hypothesis (ETH), according to which a single energy eigenstate of an isolated system behaves in certain respects as a thermal state. In the context of quantum black holes, we propose that the ETH is a quantum version of the classical no-hair theorem.

Khlebnikov, S.; Kruczenski, M.

2014-11-01

418

Harnessing quantum superposition and interference in atomic systems.

We propose resilient quantum superposition states in closed-loop multilevel system which result in myriad quantum interference phenomena. An interplay of these superposition states results in a whole gamut of atomic phenomena including coherent population trapping (CPT), electromagnetically induced transparency (EIT), electromagnetically induced absorption (EIA), amplification without inversion (AWI) and enhancement of refractive index accompanied with negligible absorption. The polarization and the phases of the fields transform the underlying superposition of the excited states leading to all these effects, where, given the macroscopic nature of these phenomena the quantum superposition states as well as the synergy between them can be ascertained. Numerical simulations for D1 transition in room temperature Rb87 atomic vapour system bear out these findings. PMID:24977621

Kani, A; Wanare, Harshawardhan

2014-06-16

419

Complete controllability of quantum systems with energy level degeneracy

Complete controllability of finite dimensional quantum systems with energy level degeneracy is investigated. Two approaches are presented. The first is to apply a week constant field to eliminate the degeneracy first and then control it using techniques developed for non-degenerate quantum system. Conditions for the elimination of degeneracy are found and the issue of influence of relaxation time of constant external field to the target state are addressed by calculating the fidelity. Another approach is to control the degenerate system by a single control field directly. It is found that the system with two fold degenerate excited states and non-degenerate ground states are completely controllable except for the two-level system. Conditions of complete controllability are found for both systems with different energy gaps and with equal energy gaps.

Zhang, Zhedong

2009-01-01

420

Plasmonic antennas, positioning, and coupling of individual quantum systems

Energy Technology Data Exchange (ETDEWEB)

Plasmonic nanoantennas can enhance the radiative decay rate of quantum emitters via the Purcell-effect. Similar to their radiofrequency equivalents, they can also direct the emitted light into preferential directions. In this paper we first investigate plasmonic Yagi-Uda antennas that are able to confine light to and direct light from subwavelength size volumes. Hence, enhanced transition rates and directed emission are expected when near-field coupling between quantum emitters and the antennas is achieved. Second, we present suitable techniques to couple different quantum systems to plasmonic antennas. We use top-down fabrication techniques to achieve positioning of individual quantum emitters relative to plasmonic nanostructures with an accuracy better than 10 nm. We assure a sufficiently small distance for an efficient near-field coupling of the transition dipole to the plasmonic nanoantenna, which is, however, large enough not to quench the transition. The hybrid system using quantum dots, molecules, or nitrogen-vacancy (NV)-centers in diamond can serve as an efficient single photon source. It is suitable for high-speed information transfer at optical frequencies on the nanoscale for future applications. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Dregely, Daniel; Dorfmueller, Jens; Giessen, Harald [4. Physikalisches Institut und Forschungszentrum SCoPE, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Lindfors, Klas; Hentschel, Mario; Lippitz, Markus [4. Physikalisches Institut und Forschungszentrum SCoPE, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Becker, Merle; Wrachtrup, Joerg [3. Physikalisches Institut und Forschungszentrum SCoPE, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Vogelgesang, Ralf [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)

2012-04-15

421

Environmentally induced effects and dynamical phase transitions in quantum systems

International Nuclear Information System (INIS)

The dynamics of open quantum systems is determined by singularities in the continuum of scattering wavefunctions which are related to avoided and true crossings of eigenvalue trajectories of a non-Hermitian Hamiltonian. The phases of the eigenfunctions are not rigid in approaching the crossing points so that environmentally induced spectroscopic redistribution processes may take place and a dynamical phase transition may occur. Due to the formal equivalence between the quantum mechanical Schrödinger equation and the optical wave equation in PT symmetric lattices, the dynamics of the system is determined also in this latter case by avoided and true crossings of eigenvalue trajectories of the non-Hermitian Hamiltonian. In contrast to the eigenvalues characterizing an open quantum system, the eigenvalues describing the PT symmetric optical lattice are real as long as the influence of the environment (lattice) on the optical wave equation is small. In the regime of avoided level crossings, the symmetry is broken, the eigenvalues become complex and a dynamical phase transition occurs, similar as in the open quantum system. These results can be proven experimentally by tracing the phase rigidity of the eigenfunctions of the Hamiltonian and its correlation with the transparency. The redistribution processes in the regime of avoided level crossings allow us to design systems with desired properties in a broad parameter range

422

Large quantum systems: a mathematical and numerical perspective

International Nuclear Information System (INIS)

This thesis is devoted to the mathematical study of variational models for large quantum systems. The mathematical methods are that of nonlinear analysis, calculus of variations, partial differential equations, spectral theory, and numerical analysis. The first part contains some results on finite systems. We study several approximations of the N-body Schroedinger equation for electrons in an atom or a molecule, and then the so-called Hartree-Fock- Bogoliubov model for a system of fermions interacting via the gravitational force. In a second part, we propose a new method allowing to prove the existence of the thermodynamic limit of Coulomb quantum systems. Then, we construct two Hartree-Fock-type models for infinite systems. The first is a relativistic theory deduced from Quantum Electrodynamics, allowing to describe the behavior of electrons, coupled to that of Dirac's vacuum which can become polarized. The second model describes a nonrelativistic quantum crystal in the presence of a charged defect. A new numerical method is also proposed. The last part of the thesis is devoted to spectral pollution, a phenomenon which is observed when trying to approximate eigenvalues in a gap of the essential spectrum of a self-adjoint operator, for instance for periodic Schroedinger operators or Dirac operators. (author)

423

Open quantum system of two coupled harmonic oscillators

International Nuclear Information System (INIS)

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

424

Quantum systems with positions and momenta on a Galois field

International Nuclear Information System (INIS)

Quantum systems with positions and momenta in the Galois field GF(pe), are considered. The Heisenberg-Weyl group of displacements and the Sp(2,GF(pe)) group of symplectic transformations, are studied. Frobenius symmetries, are a unique feature of these systems and lead to constants of motion. The engineering of such systems from l spins with j = (p - 1)/2, which are coupled in a particular way, is discussed

425

Quantum Phase Transitions in Spin-Boson Systems: Dissipation and Light Phenomena

Digital Repository Infrastructure Vision for European Research (DRIVER)

Spin-boson models are essentially useful in the understanding of quantum optics, nuclear physics, quantum dissipation, and quantum computation. We discuss quantum phase transitions in various spin-boson Hamiltonians, compare, and contrast them. We summarize the theoretical concepts and results, open questions and implementations of those ideas in cold atomic and QED cavity systems are also addressed.

Hur, Karyn Le

2009-01-01