Showing papers on "Open quantum system published in 1996"
TL;DR: Feynman's 1982 conjecture, that quantum computers can be programmed to simulate any local quantum system, is shown to be correct.
Abstract: Feynman's 1982 conjecture, that quantum computers can be programmed to simulate any local quantum system, is shown to be correct.
2,678 citations
Book•
01 Jan 1996
TL;DR: In this article, the authors present basic concepts and their interpretation, including Decoherence through Interaction with the Environment, consistent history and decoherence in Quantum Field Theory and Quantum Gravity.
Abstract: 1 Introduction.- 2 Basic Concepts and Their Interpretation.- 3 Decoherence Through Interaction with the Environment.- 4 Decoherence in Quantum Field Theory and Quantum Gravity.- 5 Consistent Histories and Decoherence.- 6 Superselection Rules and Symmetries.- 7 Open Quantum Systems.- 8 Stochastic Collapse Models.- 9 Related Concepts and Methods.- A1 Equation of Motion of a Mass Point.- A2 Solutions for the Equation of Motion.- A3 Elementary Properties of Composite Systems in Quantum Mechanics.- A4 Quantum Correlations.- A5 Hamiltonian Formulation of Quantum Mechanics.- A6 Galilean Symmetry of Non-Relativistic Quantum Mechanics.- A7 Stochastic Processes.- References.
2,042 citations
AT&T1
TL;DR: For any quantum computation with t gates, a polynomial size quantum circuit that tolerates O(1/log/sup c/t) amounts of inaccuracy and decoherence per gate, for some constant c, was shown in this article.
Abstract: It has recently been realized that use of the properties of quantum mechanics might speed up certain computations dramatically. Interest in quantum computation has since been growing. One of the main difficulties in realizing quantum computation is that decoherence tends to destroy the information in a superposition of states in a quantum computer making long computations impossible. A further difficulty is that inaccuracies in quantum state transformations throughout the computation accumulate, rendering long computations unreliable. However, these obstacles may not be as formidable as originally believed. For any quantum computation with t gates, we show how to build a polynomial size quantum circuit that tolerates O(1/log/sup c/t) amounts of inaccuracy and decoherence per gate, for some constant c; the previous bound was O(1/t). We do this by showing that operations can be performed on quantum data encoded by quantum error-correcting codes without decoding this data.
792 citations
TL;DR: In this paper, the authors analyse dissipation in quantum computation and its destructive impact on the efficiency of quantum algorithms and show that the quantum factorization algorithm must be modified in order to be regarded as efficient and realistic.
Abstract: We analyse dissipation in quantum computation and its destructive impact on the efficiency of quantum algorithms. Using a general model of decoherence, we study the time evolution of a quantum register of arbitrary length coupled with an environment of arbitrary coherence length. We discuss relations between decoherence and computational complexity and show that the quantum factorization algorithm must be modified in order to be regarded as efficient and realistic.
752 citations
TL;DR: In this paper, the connections between information, physics, and computation are examined and the computing power of quantum computers is examined, and it is argued that recently studied quantum computers, which are based on local interactions, cannot simulate quantum physics.
Abstract: This paper presents several observations on the connections between information, physics, and computation. In particular, the computing power of quantum computers is examined. Quantum theory is characterized by superimposed states and nonlocal interactions. It is argued that recently studied quantum computers, which are based on local interactions, cannot simulate quantum physics.
708 citations
TL;DR: By using a generalization of the optical tomography technique, the authors describe the dynamics of a quantum system in terms of equations for a purely classical probability distribution which contains complete information about the system.
484 citations
TL;DR: It is shown that under certain conditions the resonant transport in mesoscopic systems can be described by modified (quantum) rate equations, which resemble the optical Bloch equations with some additional terms.
Abstract: It is shown that under certain conditions the resonant transport in mesoscopic systems can be described by modified (quantum) rate equations, which resemble the optical Bloch equations with some additional terms. Detailed microscopic derivation from the many-body Schr\"odinger equation is presented. Special attention is paid to the Coulomb blockade and quantum coherence effects in coupled quantum dot systems. The distinction between classical and quantum descriptions of resonant transport is clearly manifested in the modified rate equations. \textcopyright{} 1996 The American Physical Society.
341 citations
TL;DR: In this article, the decay of quantum coherence for the solvated electron is found to take ≊50% longer in D2O than in H2O, providing a rationalization for a long standing puzzle concerning the lack of experimentally.
Abstract: In this paper, we explore in detail the way in which quantum decoherence is treated in different mixed quantum‐classical molecular dynamics algorithms. The quantum decoherence time proves to be a key ingredient in the production of accurate nonadiabatic dynamics from computer simulations. Based on a short time expansion to a semiclassical golden rule expression due to Neria and Nitzan [J. Chem. Phys. 99, 1109 (1993)], we develop a new computationally efficient method for estimating the decay of quantum coherence in condensed phase molecular simulations. Using the hydrated electron as an example, application of this method finds that quantum decoherence times are on the order of a few femtoseconds for condensed phase chemical systems and that they play a direct role in determining nonadiabatic transition rates. The decay of quantum coherence for the solvated electron is found to take ≊50% longer in D2O than in H2O, providing a rationalization for a long standing puzzle concerning the lack of experimentally...
326 citations
Posted Content•
TL;DR: This document focuses on translating various information-theoretic measures of distinguishability for probability distributions into measures of distin- guishability for quantum states, and gives a way of expressing the problem so that it appears as algebraic as that of the problem of finding quantum distinguishability measures.
Abstract: This document focuses on translating various information-theoretic measures of distinguishability for probability distributions into measures of distin- guishability for quantum states. These measures should have important appli- cations in quantum cryptography and quantum computation theory. The results reported include the following. An exact expression for the quantum fidelity between two mixed states is derived. The optimal measurement that gives rise to it is studied in detail. Several upper and lower bounds on the quantum mutual information are derived via similar techniques and compared to each other. Of note is a simple derivation of the important upper bound first proved by Holevo and an explicit expression for another (tighter) upper bound that appears implicitly in the same derivation. Several upper and lower bounds to the quan- tum Kullback relative information are derived. The measures developed are also applied to ferreting out the extent to which quantum systems must be disturbed by information gathering measurements. This is tackled in two ways. The first is in setting up a general formalism for describing the tradeoff between inference and disturbance. The main point of this is that it gives a way of expressing the problem so that it appears as algebraic as that of the problem of finding quantum distinguishability measures. The second result on this theme is a theorem that prohibits "broadcasting" an unknown (mixed) quantum state. That is to say, there is no way to replicate an unknown quantum state onto two separate quantum systems when each system is considered without regard to the other. This includes the possibility of correlation or quantum entanglement between the systems. This result is a significant extension and generalization of the standard "no-cloning" theorem for pure states.
264 citations
TL;DR: The reconstruction of the quantum state of light from the homodyne photocounting statistics of a single, realistic photodetector is proposed and it is shown that perturbing effects due to classical noise of the local oscillator are small.
Abstract: We propose the reconstruction of the quantum state of light from the homodyne photocounting statistics of a single, realistic photodetector. Contrary to the development of homodyning over the last decade, our approach is based on unbalanced detection with a weak local oscillator. Representing the quantum state in terms of s-parametrized quasiprobability distributions, the method even allows one to determine the Wigner function provided the quantum efficiency of the detector is sufficiently large. We show that perturbing effects due to classical noise of the local oscillator are small. \textcopyright{} 1996 The American Physical Society.
251 citations
TL;DR: In this article, an alternative derivation of the probability distributions for completed homodyne and heterodyne detection schemes is presented, which allows the previously intractable problem of real-time adaptive measurements to be treated.
Abstract: Beyond their use as numerical tools, quantum trajectories can be ascribed a degree of reality in terms of quantum measurement theory. In fact, they arise naturally from considering continuous observation of a damped quantum system. A particularly useful form of quantum trajectories is as linear (but non-unitary) stochastic Schrodinger equations. In the limit where a strong local oscillator is used in the detection, and where the system is not driven, these quantum trajectories can be solved. This gives an alternative derivation of the probability distributions for completed homodyne and heterodyne detection schemes. It also allows the previously intractable problem of real-time adaptive measurements to be treated. The results for an analytically soluble example of adaptive phase measurements are presented, and future developments discussed.
TL;DR: A quantum cryptographic system in which users store particles in a transmission center, where their quantum states are preserved using quantum memories, which allows for secure communication between any pair of users who have particles in the same center.
Abstract: Quantum correlations between two particles show nonclassical properties that can be used for providing secure transmission of information. We present a quantum cryptographic system in which users store particles in a transmission center, where their quantum states are preserved using quantum memories. Correlations between the particles stored by two users are created upon request by projecting their product state onto a fully entangled state. Our system allows for secure communication between any pair of users who have particles in the same center. Unlike other quantum cryptographic systems, it can work without quantum channels and it is suitable for building a quantum cryptographic network. We also present a modified system with many centers. \textcopyright{} 1996 The American Physical Society.
TL;DR: A review of the role played by local fields in the high-frequency electrodynamics of mesoscopic systems exhibiting essential quantum confinement of the electron motion is presented in this article.
TL;DR: The performance of the quantum Fourier transform (QFT) in the presence of decoherence is analysed and it is shown that as far as the peri-1 values are concerned, for some computations an approximation may imply a better performance.
Abstract: We discuss the advantages of using the approximate quantum Fourier transform (AQFT) in algorithms which involve periodicity estimations. We analyze quantum networks performing AQFT in the presence of decoherence and show that extensive approximations can be made before the accuracy of AQFT (as compared with regular quantum Fourier transform) is compromised. We show that for some computations an approximation may imply a better performance. \textcopyright{} 1996 The American Physical Society.
TL;DR: A particular type of generalized quantum measurement is introduced, which is term loss induced generalized (LIGe) quantum measurement, and an experimental realization achieves optimal deterministic separation of two nonorthogonally polarized single photons.
Abstract: Generalized quantum measurements can be used to separate deterministically two nonorthogonal quantum states. However, such measurements also lead to inconclusive results, where the initial state remains unknown. We introduce a particular type of generalized quantum measurement, which we term loss induced generalized (LIGe) quantum measurement, and present an experimental realization. This LIGe measurement achieves optimal deterministic separation of two nonorthogonally polarized single photons. \textcopyright{} 1996 The American Physical Society.
TL;DR: By taking into account both quantum mechanical and general relativistic effects, this article derived an equation that describes some limitations on the measurability of space-time distances. And then discuss possible features of quantum gravity which are suggested by this equation.
Abstract: By taking into account both quantum mechanical and general relativistic effects, I derive an equation that describes some limitations on the measurability of space-time distances. I then discuss possible features of quantum gravity which are suggested by this equation.
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TL;DR: In this paper, the authors suggest that quantum computers can solve quantum many-body problems that are impracticable to solve on a classical computer, such as the one described in this paper.
Abstract: We suggest that quantum computers can solve quantum many-body problems that are impracticable to solve on a classical computer.
TL;DR: The general impossibility of determining the state of a single quantum system is proved for arbitrary measuring schemes, including a succession of measurements, and some recently proposed methods are critically examined.
Abstract: The general impossibility of determining the state of a single quantum system is proved for arbitrary measuring schemes, including a succession of measurements. Some recently proposed methods are critically examined. A scheme for tomographic measurements on a single copy of a radiation field is devised, showing that the system state is perturbed however weak the system-apparatus interaction is, due to the need of preparing the apparatus in a highly ``squeezed'' state.
TL;DR: In this paper, the authors investigated the dynamics of a 2-level atom coupled to a massless bosonic field at positive temperature and proved that, at small coupling, the combined quantum system approaches thermal equilibrium.
Abstract: We investigate the dynamics of a 2-level atom (or spin 1/2) coupled to a mass-less bosonic field at positive temperature. We prove that, at small coupling, the combined quantum system approaches thermal equilibrium. Moreover we establish that this approach is exponentially fast in time. We first reduce the question to a spectral problem for the Liouvillean, a self-adjoint operator naturally associated with the system. To compute this operator, we invoke Tomita-Takesaki theory. Once this is done we use complex deformation techniques to study its spectrum. The corresponding zero temperature model is also reviewed and compared. From a more philosophical point of view our results show that, contrary to the conventional wisdom, quantum dynamics can be simpler at positive than at zero temperature.
TL;DR: In this article, a generic treatment of wave-packet evolution is presented, and conditions under which various types of revivals occur in ideal form are provided, and explicit examples of different types of revival structure are provided.
Abstract: Localized quantum wave packets can be produced in a variety of physical systems and are the subject of much current research in atomic, molecular, chemical, and condensed‐matter physics. They are particularly well suited for studying the classical limit of a quantum‐mechanical system. The motion of a localized quantum wave packet initially follows the corresponding classical motion. However, in most cases the quantum wave packet spreads and undergoes a series of collapses and revivals. We present a generic treatment of wave‐packet evolution, and we provide conditions under which various types of revivals occur in ideal form. The discussion is at a level appropriate for an advanced undergraduate or first‐year graduate course in quantum mechanics. Explicit examples of different types of revival structure are provided, and physical applications are discussed.
TL;DR: The experimental demonstration of a Bell-state analyzer employing two-photon interference effects that generates momentum-entangled Bell states and indicates its readiness for use with quantum communication schemes and in experiments on the foundations of quantum mechanics.
Abstract: We present the experimental demonstration of a Bell-state analyzer employing two-photon interference effects. Photon pairs produced by parametric down-conversion allowed us to generate momentum-entangled Bell states and to demonstrate the properties of this device. The performance obtained indicates its readiness for use with quantum communication schemes and in experiments on the foundations of quantum mechanics.
TL;DR: This work has shown that computers that exploit quantum features could factor large composite integers and that this task is believed to be out of reach of classical computers as soon as the number of digits in the number to factor exceeds a certain limit.
Abstract: Recent theoretical results confirm that quantum theory provides the possibility of new ways of performing efficient calculations. The most striking example is the factoring problem. It has recently been shown that computers that exploit quantum features could factor large composite integers. This task is believed to be out of reach of classical computers as soon as the number of digits in the number to factor exceeds a certain limit. The additional power of quantum computers comes from the possibility of employing a superposition of states, of following many distinct computation paths and of producing a final output that depends on the interference of all of them. This ‘quantum parallelism’ outstrips by far any parallelism that can be thought of in classical computation and is responsible for the ‘exponential’ speed-up of computation. Experimentally, however, it will be extremely difficult to ‘decouple’ a quantum computer from its environment. Noise fluctuations due to the outside world, no matte...
TL;DR: The principles of quantum computing were laid out about 15 years ago by computer scientists applying the superposition principle of quantum mechanics to computer operation as mentioned in this paper, and quantum computing has recently become a hot topic in physics, with the recognition that a two-level system can be presented as a quantum bit, or “qubit,” and that an interaction between such systems could lead to the building of quantum gates obeying nonclassical logic.
Abstract: The principles of quantum computing were laid out about 15 years ago by computer scientists applying the superposition principle of quantum mechanics to computer operation. Quantum computing has recently become a hot topic in physics, with the recognition that a two‐level system can be presented as a quantum bit, or “qubit,” and that an interaction between such systems could lead to the building of quantum gates obeying nonclassical logic. (See PHYSICS TODAY, October 1995, page 24 and March 1996, page 21.)
TL;DR: In this paper, the essential innovation of Bohmian mechanics is the insight that particles move, and the entire quantum formalism, including the uncertainty principle and quantum randomness, emerges from an analysis of this evolution.
Abstract: In order to arrive at Bohmian mechanics from standard nonrelativistic quantum mechanics one need do almost nothing! One need only complete the usual quantum description in what is really the most obvious way: by simply including the positions of the particles of a quantum system as part of the state description of that system, allowing these positions to evolve in the most natural way. The entire quantum formalism, including the uncertainty principle and quantum randomness, emerges from an analysis of this evolution. This can be expressed succinctly – though in fact not succinctly enough – by declaring that the essential innovation of Bohmian mechanics is the insight that particles move!
TL;DR: A quantum theory for mesoscopic electric circuits in accord with the discreteness of electric charges is proposed and the Schrodinger equation for the quantum LC design and L design is solved exactly and a minimum uncertainty state is solved.
Abstract: A quantum theory for mesoscopic electric circuits in accord with the discreteness of electric charges is proposed. On the basis of the theory, the Schr\"odinger equation for the quantum LC design and L design is solved exactly. The uncertainty relation for electric charge and current is obtained and a minimum uncertainty state is solved. By introducing a gauge field, a formula for persistent current arising from magnetic flux is obtained. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the authors introduce measurement quantum mechanics, the theory of a quantum system which undergoes a measurement process, by a loop of mathematical equivalencies connecting previously proposed approaches.
TL;DR: This work considers the exact dynamics of a three-level atom for a resonant form of the atom-environment coupling of the type found in a cavity.
Abstract: The coupling of an atom to its environment can be strongly dependent on frequency when that atom is placed in, for example, a cavity. We consider here the exact dynamics of a three-level atom for a resonant form of the atom-environment coupling of the type found in a cavity. The three-level atom forms a quantum-beat V system in the general model that we consider. Without the use of perturbation theory, we derive a set of three coupled differential equations that describe the system. Results are compared to quantum beats in free space and an interpretation is provided in terms of the coupling of the three-level system to a pseudomode. The pseudomode is defined by the differential equations involving its amplitude and possesses the properties of a finite-Q cavity mode. The signal from a detector is formulated in terms of a resonant coupling between the detector and the cavity modes. Limits for a broadband and a narrow-band detector are considered. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, the authors give an explicit prescription for experimentally determining the evolution operators which completely describe the dynamics of a quantum mechanical black box, and illustrate the general theory by considering one and two quantum bit systems.
Abstract: We give an explicit prescription for experimentally determining the evolution operators which completely describe the dynamics of a quantum mechanical black box -- an arbitrary open quantum system. We show necessary and sufficient conditions for this to be possible, and illustrate the general theory by considering specifically one and two quantum bit systems. These procedures may be useful in the comparative evaluation of experimental quantum measurement, communication, and computation systems.
TL;DR: In this article, the authors derived approximate closed-form expressions to describe the frequency of quantum oscillations in the semiclassical limit of a quantum system, based on general assumptions on the nature of the system.
Abstract: Many transient signals from quantum systems result from beats among a large number of levels whose energies depend nonlinearly on the quantum number. Typical examples range from time-resolved laser femtochemistry to quantum optics of single atoms in cavities. Starting from rather general assumptions on the nature of the system, we derive approximate closed-form expressions, which describe such signals in the semiclassical limit. Our approach brings out in a most natural way the phenomenon of fractional revivals and full revivals and explains the oscillatory structures observed in recent experiments on atomic wave packets [Phys. Rev. Lett. 72, 3783 (1994)].