Showing papers on "Open quantum system published in 1989"
TL;DR: The theory of quantum computational networks is the quantum generalization of the theory of logic circuits used in classical computing machines, and a single type of gate, the universal quantum gate, together with quantum ‘unit wires' is adequate for constructing networks with any possible quantum computational property.
Abstract: The theory of quantum computational networks is the quantum generalization of the theory of logic circuits used in classical computing machines. Quantum gates are the generalization of classical logic gates. A single type of gate, the universal quantum gate, together with quantum ‘unit wires’, is adequate for constructing networks with any possible quantum computational property.
1,248 citations
TL;DR: In this paper, the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers, are reviewed.
Abstract: In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.
791 citations
TL;DR: In this article, a procedure for computing the thermal rate constants for infrequent events that occur in complicated quantum mechanical systems is described, based on the equilibrium statistics of the centroids for the imaginary time quantum paths.
Abstract: We describe a procedure for computing the thermal rate constants for infrequent events that occur in complicated quantum mechanical systems. Following the ideas of Gillan, the procedure focuses on the equilibrium statistics of the centroids for the imaginary time quantum paths. We argue that the imaginary time statistics can be used to efficiently bias Monte Carlo sampling of the real time reaction dynamics. Consideration of imaginary time paths or equilibrium statistics alone leads to a quantum transition state theory. Analytical versions of this transition state theory are developed with the aid of a variational principle. Numerical applications of the quantum transition state theory are given for the one‐dimensional Eckart barrier problem and for the nonseparable two‐dimensional collinear H2+H reaction. Remarkably accurate results are obtained. The quantum transition state theory we describe provides a rigorous basis and generalizes algorithms recently employed to treat electron transfer and also ionization in polar media.
470 citations
TL;DR: In an open quantum system, dissipation can cause decorrelation on a time scale significantly shorter than the relaxation time which characterizes the approach of the system to thermodynamic equilibrium, and it is demonstrated that the density matrix decays rapidly toward a mixture of ``approximate eigenstates'' of the ``pointer observable,'' which commutes with the system-environment interaction Hamiltonian.
Abstract: The effect of the environment on a quantum system is studied on an exactly solvable model: a harmonic oscillator interacting with a one-dimensional massless scalar field. We show that in an open quantum system, dissipation can cause decorrelation on a time scale significantly shorter than the relaxation time which characterizes the approach of the system to thermodynamic equilibrium. In particular, we demonstrate that the density matrix decays rapidly toward a mixture of ``approximate eigenstates'' of the ``pointer observable,'' which commutes with the system-environment interaction Hamiltonian. This observable can be regarded as continuously, if inaccurately, monitored by the scalar field environment. Both because in a harmonic oscillator the state of the system rotates in the phase space and because the effective environment ``measurement'' is weak, the system, on the short ``collision'' time scale (1/\ensuremath{\Gamma}), maintains a coherence in this pointer observable on time scales of order [\ensuremath{\gamma}/\ensuremath{\Omega}ln(\ensuremath{\Gamma}/\ensuremath{\Omega}${)]}^{1/2}$ and on longer time scales settles into a mixture of coherent states with a dispersion approximately consistent with the vacuum state. The master equation satisfied by the exact solution differs from the other master equations derived both for the high-temperature limit and for T=0. We discuss these differences and study the transition region between the high- and low-temperature regimes. We also consider the behavior of the system in the short-time ``transient'' regime. For T=0, we find that, in the long-time limit, the system behaves as if it were subject to ``1/f noise.'' The generality of our model is considered and its predictions are compared with previous treatments of related problems. Some of the possible applications of the results to experimentally realizable situations are outlined. The significance of the environment-induced reduction of the wave packet for cosmological models is also briefly considered.
460 citations
Book•
01 Jan 1989
TL;DR: In this article, a review of various mathematical formulations of the uncertainty relations in quantum mechanics and of equivalent relations in optics and radiophysics is presented, together with invariants and correlated states of nonstationary quantum systems.
Abstract: The book contains three papers. The first is a review of various mathematical formulations of the uncertainty relations in quantum mechanics and of equivalent relations in optics and radiophysics. The second deals with invariants and correlated states of nonstationary quantum systems; the third is on the evolution of multidimensional systems.
208 citations
TL;DR: A quantum optical model that obeys the nonlinear rotator dynamics and can generate superpositions of SU(2) coherent states of the two-mode electromagnetic field is presented.
Abstract: The quantum and classical dynamics of the nonlinear oscillator are contrasted by comparing the evolution of the quantum Q function with that of a similar classical probability distribution. The quantum nonlinear rotator is shown to generate a superposition of two distinct coherent states from a coherent-state input. Measurements of the angular-momentum components and the signature of a superposition state are discussed. The effects of a continual measurement of one angular-momentum component are introduced into the model, and its effects on quantum coherences are shown to degrade the quantum coherence effects. We present a quantum optical model that obeys the nonlinear rotator dynamics and can generate superpositions of SU(2) coherent states of the two-mode electromagnetic field.
156 citations
TL;DR: There is no quantum chaos, in the sense of exponential sensitivity to initial conditions, but there are several novel quantum phenomena which reflect the presence of classical chaos as mentioned in this paper, and the study of these phenomena is quantum chaology.
Abstract: There is no quantum chaos, in the sense of exponential sensitivity to initial conditions, but there are several novel quantum phenomena which reflect the presence of classical chaos. The study of these phenomena is quantum chaology.
143 citations
01 Jan 1989
TL;DR: The 7th Jerusalem Winter School 1990 on Quantum Cosmology and Baby Universes as mentioned in this paper discussed quantum mechanics for closed systems like the universe, generalized quantum mechanics, time in quantum mechanics and quantum mechanics spacetime.
Abstract: Notes from the lectures by the author at the 7th Jerusalem Winter School 1990 on Quantum Cosmology and Baby Universes. The lectures covered quantum mechanics for closed systems like the universe, generalized quantum mechanics, time in quantum mechanics, the quantum mechanics spacetime, and practical quantum cosmology. References have not been updated.
113 citations
101 citations
TL;DR: In this article, it was shown that, within the framework of quantum field theory, no faster-than-light communication can be established between observers, and the steps of the demonstration are detailed enough to pinpoint which properties of the theory have been misinterpreted in previous papers claiming the existence of effects that could permit such communication.
Abstract: We spell out a demonstration that, within the framework of quantum field theory, no faster-than-light communication can be established between observers. The steps of the demonstration are detailed enough to pinpoint which properties of the theory have been misinterpreted in previous papers claiming the existence of effects that could permit such communication. The developments described here can also be used to analyze future papers making similar claims.
TL;DR: In this paper, the authors present a formalism for treating one-dimensional problems in quaternionic quantum mechanics, and derive an explicit form for the T matrix for scattering from a square barrier, and use this result to calculate the transmission and reflection coefficients.
Abstract: We present a formalism for treating one-dimensional problems in quaternionic quantum mechanics. As an example, we derive an explicit form for the T matrix for scattering from a square (quaternionic) barrier, and use this result to calculate the transmission and reflection coefficients. We show that the qualitative form of these coefficients is the same as in complex quantum mechanics, even when the barrier has a nonzero value for the quaternionic components of the potential.
Book•
01 Jan 1989
TL;DR: In this paper, the major problems of the quantum physics of solids, ranging from fundamental concepts to topical issues, are considered and analyzed, rather than use a deductive method of exposition.
Abstract: This book treats the major problems of the quantum physics of solids, ranging from fundamental concepts to topical issues. Rather than use a deductive method of exposition, the authors consider and analyze simple empirically established properties of solids and employ more complicated models only as the need arises. Detailed treatment is given of classical problems such as chemical bonding in crystals, the one-dimensional Schrodinger equation with a periodic potential, the metal-insulator criterion, and the quantum theory of band electron motion in external fields. Consideration is also given to topical problems such as neutron scattering by the crystal lattice, plasma and Fermi liquid effects, the theory of disordered systems, and the polaron. The reader is expected to know only the fundamentals of quantum mechanics and statistical physics. Compared with the Russian edition (Nauka, Moscow 1983), the book has been substantially revised and enlarged, new sections have been written and recent results have been incorporated."
TL;DR: In this paper, the authors present the quantum analysis of a scattering problem which displays chaotic (irregular) features when analyzed classically and show that the "finger print" of the classical chaos on the quantum description in the appearance of universal fluctuations in the cross section is analogous to the one expected from a random matrix description.
TL;DR: In this paper, the possibilities of a realistic interpretation of quantum mechanics are investigated by means of a statistical analysis of experiments performed on the simplest type of quantum systems carrying spin or helicity.
Abstract: The possibilities of a realistic interpretation of quantum mechanics are investigated by means of a statistical analysis of experiments performed on the simplest type of quantum systems carrying spin or helicity. To this end, fundamental experiments, some new, for measuring polarization are reviewed and (re)analyzed. Theunsharp reality of spin is essential in the interpretation of some of these experiments and represents a natural motivation for recent generalizations of quantum mechanics to a theory incorporating effect-valued measures as unsharp observables and generalized systems of imprimitivity.
TL;DR: In this paper, the theoretical and physical meaning of dissipation of background fields due to particle creation and statistical effects in interacting quantum field theories and in semiclassical gravitational theories is discussed.
Abstract: We discuss the theoretical and physical meaning of dissipation of background fields due to particle creation and statistical effects in interacting quantum field theories and in semiclassical gravitational theories. We indicate the possible existence of a fluctuation-dissipation relation for non-equilibrium quantum fields as occuring in cosmological particle creation and backreaction processes. We also conjecture that all effective theories, including quantum gravity, could manifest dissipative behavior.
TL;DR: This paper discusses the concepts of quantum integrability and nonintegrability based on the concept of a complete set of commuting observables and the Hilbert-space structure of a quantum system and the definitions are given for the quantum-dynamical degrees of freedom and quantum phase space.
Abstract: In this paper we discuss the concepts of quantum integrability and nonintegrability. Based on the concept of a complete set of commuting observables and the Hilbert-space structure of a quantum system, the definitions are given for the quantum-dynamical degrees of freedom and quantum phase space from which the quantum integrability is defined. A criterion for quantum integrability then emerges; the system is integrable if it possesses dynamical symmetry. Breaking of dynamical symmetry is connected with the nonintegrability of systems and thus is the inherent mechanism of chaotic motion. A number of examples are discussed.
01 Jan 1989
TL;DR: In this article, different ways of expressing quantum properties as stochastic averages are discussed and a formal mathematical connection between quantum mechanics and Stochastic processes may be used to compute quantum observables (Monte Carlo simulation).
Abstract: This paper discusses different ways of expressing quantum properties as stochastic averages. It is explained how such a formal mathematical connection between quantum mechanics and stochastic processes may be used to compute quantum observables (Monte Carlo simulation). The problems in applying stochastic methods to fermion systems are discussed and a few illustrative results for atoms and molecules are presented.
TL;DR: In this article, a toy quantum mechanical model with two degrees of freedom (which mimics the features of gravity interacting with quantum fields) is used for illustration, and the Born-Oppenheimer approximation (BOA) and the effective action approach (h(cross) to 0 at fixed G) and their combinations are compared.
Abstract: Semiclassical approximations, which are useful in the study of a quantum system interacting with a classical system, are studied and compared. A toy quantum mechanical model with two degrees of freedom (which mimics the features of gravity interacting with quantum fields) is used for illustration. In particular, the author considers the Born-Oppenheimer approximation (BOA) (corresponding to G to 0 at fixed h(cross)), the effective action approach (h(cross) to 0 at fixed G) and their combinations. He shows that in the strict BOA limit there is no backreaction on gravity. Gravity is described by classical equations and the fields are quantised in that background. In the effective action approach one can obtain a semiclassical description for gravity, if certain stringent requirements are satisfied. In most situations of interest these conditions will not be met and the O(h(cross)) contribution from gravitons will be comparable to that from quantum fields. He studies the system using both the Schrodinger equation and path integrals and indicates the correspondence.
TL;DR: In this paper, the authors discuss the instability and chaos in Quantum Optics, and propose a method to solve the problem of quantum instability and Chaos in quantum Optics (COCO).
Abstract: (1989). Instabilities and Chaos in Quantum Optics. Journal of Modern Optics: Vol. 36, No. 1, pp. 149-149.
TL;DR: Ghirardi, Rimini and Weber as mentioned in this paper presented a statistical modification of non-relativistic quantum mechanics which unifies the description of microscopic and macroscopic systems of distinct particles.
Abstract: Ghirardi, Rimini and Weber have presented a statistical modification of non-relativistic quantum mechanics which unifies the description of microscopic and macroscopic systems of distinct particles. We revise their proposal to cover systems of indistinguishable particles. Testable, mathematically precise, realist models of non-relativistic physics result. We give empirically derived bounds on the model parameters.
01 Jan 1989
TL;DR: In this paper, the authors present a collection of papers that apply the theory of self-adjoint extensions of symmetry operators in various areas of physics, including quantum mechanics, quantum field theory, high energy physics, solid-state physics, microelectronics and other fields.
Abstract: The shared purpose in this collection of papers is to apply the theory of self-adjoint extensions of symmetry operators in various areas of physics. This allows the construction of exactly solvable models in quantum mechanics, quantum field theory, high energy physics, solid-state physics, microelectronics and other fields. The 20 papers selected for these proceedings give an overview of this field of research unparallelled in the published literature; in particular the views of the leading schools are clearly presented. The book will be an important source for researchers and graduate students in mathematical physics for many years to come. In these proceedings, researchers and graduate students in mathematical physics will find ways to construct exactly solvable models in quantum mechanics, quantum field theory, high energy physics, solid-state physics, microelectronics and other fields.
TL;DR: In this paper, the authors give a description of the reduced dynamics of an open quantum system whose initial state is correlated with the surroundings and use the averaging method to construct a series expansion of reduced dynamics in powers of the ratio τ 1 /τ 0 of the characteristic relaxation times τ 1 and τ 0, respectively.
Abstract: We give a description of the reduced dynamics of an open quantum system whose initial state is (in general) correlated with the surroundings. The averaging method (whose mathematical theory was developed in another paper) is used to construct a series expansion of the reduced dynamics in powers of the ratio τ 1 /τ 0 of the characteristic relaxation times τ 1 and τ 0 of the surroundings and of the system respectively. To first order in τ 1 /τ 0 we obtain the well-known Markovian approximation which corresponds to the weak coupling limit. Starting from second order in τ 1 /τ 0 there appear various kinds of non-Markovian effects including initial slips which have attracted much attention in the recent literature. The relevance of these higher-order corrections stems from the fact that the characteristic time τ 1 cannot be much smaller than h kT for quantum surroundings at temperature T .
TL;DR: In this article, a nonlinear wave equation is derived in the context of quantum cybernetics, which is made responsible for the generation of such "order out of chaos", and an explanation of the quantization of action is given.
Abstract: The discussion of nonadiabatic changes of eigenstates of quantum-mechanical Hamiltonians leads to a straightforward interpretation of pure quantum states as ordered structures on top of a (hypothetical) stochastic subquantum medium. A nonlinear wave equation is derived in the context of quantum cybernetics, which is made responsible for the generation of such «order out of chaos». An explanation of the quantization of action is given. Finally, a concrete «late choice» experiment is proposed and further experimental consequences are discussed.