Showing papers on "Open quantum system published in 1990"

Quantum Theory of the Optical and Electronic Properties of Semiconductors

Abstract: This revised second edition on the "Quantum Theory of the Optical and Electronic Properties of Semiconductors" presents the basic elements needed to understand and engage in research in semiconductor physics. In this revised second edition misprints are corrected and some new and more detailed material is added. In order to treat the valence-band structure of semiconductors, an introduction to the k.p. theory and the related description in terms of the Luttinger Hamiltonian is included. An introductory chapter on mesoscopic semiconductor structures discussing the modifications of the envelope function approximation caused by the spatial quantum confinement is also included. Many results are developed in parallel first for bulk material, and then for quasi-two-dimensional quantum wells, and for quasi-one-dimensional quantum wires. Semiconductor quantum dots are treated in a separate chapter. The discussion of time-dependent and coherent phenomena in semiconductors has been considerably extended by including a section dealing with the theoretical description of photon echoes in semiconductors. A new chapter on magneto-absorption has been added, in which magneto-excitons and magneto-plasmas in two-dimensional systems are discussed. The chapter on electron kinetics due to the interaction with longitudinal-optical phonons has been extended. The material is presented in sufficient detail for graduate students and researchers who have a general background in quantum mechanics, and is aimed at solid state physicists, engineers, materials and optical scientists.

Elements of Quantum Optics

Abstract: Classical Electromagnetic Fields.- Classical Nonlinear Optics.- Quantum Mechanical Background.- Mixtures and the Density Operator.- CW Field Interactions.- Mechanical Effects of Light.- to Laser Theory.- Optical Bistability.- Saturation Spectroscopy.- Three and Four Wave Mixing.- Time-Varying Phenomena in Cavities.- Coherent Transients.- Field Quantization.- Interaction Between Atoms and Quantized Fields.- System-Reservoir Interactions.- Resonance Fluorescence.- Squeezed States of Light.- Cavity Quantum Electrodynamics.- Quantum Theory of a Laser.- Entanglement, Bell Inequalities and Quantum Information.

Continuum fields in quantum optics.

Abstract: We formulate the quantum theory of optical wave propagation without recourse to cavity quantization. This approach avoids the introduction of a box-related mode spacing and enables us to use a continuum frequency space description. We introduce a complete orthonormal set of operators that can describe states of finite energy. The set is countable and the operators have all the usual properties of the single-mode frequency operators. With use of these operators a generalization of the single-mode normal-ordering theorem is proved. We discuss the inclusion of material dispersion and pulse propagation in an optical fiber. Finally, we consider the process of photodetection in free space, concluding with a discussion of homodyne detection with both local oscillator and signal fields pulsed.

Quantum mechanics without time: A model.

Abstract: The quantization of a simple dynamical system in which a unitary time evolution appears only within a certain approximation is studied in detail. The probabilistic interpretation of quantum mechanics in the regimes in which time is not defined is discussed and shown to be consistent.

Towards a quantum pump of electric charges.

Abstract: Here we give a critical examination of the possibility of realizing a quantum pump of electric charges. The physics is based on the theory of quantum adiabatic particle transport initially due to Thouless. We present theoretical guidelines on the experimental conditions for observing this phenomenon. We argue that potentially very accurate quantization of charge transport or electron current can be achieved, once these conditions are approximately satisfied. An example of experimental setup is outlined to demonstrate the practical possibilities. Some comments are also made on the scientific significance of such a quantum device.

Neumark's theorem and quantum inseparability

Abstract: The most efficient way of obtaining information about the state of a quantum system is not always a direct measurement. It is sometimes preferable to extend the original Hilbert space of states into a larger space, and then to perform a quantum measurement in the enlarged space. Such an extension is always possible, by virtue of Neumark's theorem. The physical interpretation usually given to that theorem is the introduction of an auxiliary quantum system, prepared in a standard state, and the execution of a quantum measurement on both systems together. However, this widespread interpretation is unacceptable, because the statistical properties of the supposedly standard auxiliary system are inseparably entangled with those of the original, unknown system. A different method of preparing the auxiliary system is proposed, and shown to be physically acceptable.

Direct and heterodyne detection and other applications of quantum stochastic calculus to quantum optics

Abstract: Quantum stochastic calculus is an operator analogue of classical ItG's stochastic calculus which was originally developed for treating quantum noise. However, it turned out to be also useful in other cases of open systems, as in the case of measurement theory in quantum mechanics and in the treatment of quantum input and output channels. In the present paper, this calculus is used for developing a theory of direct, homodyne and heterodyne detection in quantum optics.

Topological phases in quantum mechanics and polarization optics

Abstract: A mathematical treatment is presented of the known Berry, Wilczek-Zee, Aharonov-Anandan, and Pancharatnam topological phases, and simple illustrative examples of their quantum mechanics are presented. The continuity and connection is traced among the various phases, while filling the gap involved with the forgotten works of S. M. Rytov and V. V. Vladimirskiĭ in polarization optics. A set of current experiments in polarization optics where the topological phases are measured is discussed in detail. Additional information on recently obtained results involving manifestations of geometrical phases in quantum mechanics and other fields of physics is contained in the Appendix and in the studies cited there.

Mathematical and Philosophical Questions in the Theory of Open and Macroscopic Quantum Systems

Abstract: It is a curious fact that our popular text books and most discussions of conceptual and philosophical problems of quantum mechanics are still based on the very first attempts to formalize this theory which have been worked out more than 50 years ago. These formulations of nonrelativistic quantum theory do, however, not represent the state of the art.

Non-Hermitian quantum dynamics

Abstract: An algorithm previously obtained for complex-energy modal probabilities in non-Hermitian quantum dynamics is generalized to determine expectation values for arbitrary observables. When cast in conventional form, the formalism including the generalized algorithms appears as a natural generalization of conventional quantum theory, in that conventional quantum theory obtains in the continuous Hermitian limit.

Cosmogenesis: The Growth of Order in the Universe

Abstract: PART I: A THEORY OF ORDER: Science, philosophy, and truth Order and randomness The strong cosmological principle and time's arrow The importance of being discrete Seven steps to quantum physics Alice in quantumland The strong cosmological principle and quantum theory PART II: ASPECTS OF TIMEBOUND ORDER: Cosmic evolution: the standard model Gravitational clustering and structural order Molecules, genes, and evolution Evolution and the growth of order Language, thought, and perception What is consciousness? Mind and body Chance, necessity, and freedom Notes.

Relativistic theory for continuous measurement of quantum fields.

Abstract: We have proposed a formal theory for the continuous measurement of relativistic quantum fields We have also derived the corresponding scattering equations The proposed formalism reduces to known equations in the Markovian case Two recent models for spontaneous quantum state reduction have been recovered in the framework of our theory A possible example of the relativistic continuous measurement has been outlined in standard quantum electrodynamics The continuous measurement theory possesses an alternative formulation in terms of interacting quantum and stochastic fields

Wigner function and decoherence in quantum cosmology

Abstract: We investigate the retrieval of classical behavior from the wave function of the Universe. It has been previously argued that to do this two conditions are necessary: decoherence (or lack of quantum interference) and the existence of classical correlations. Using the Wigner function we study the mutual compatibility of these requirements. Assuming the correlation interpretation of Geroch and Hartle, we show that some form of coarse graining is essential for the theory to predict classical behavior from WKB wave functions. We also show that there must be a compromise between the degree of decoherence and the sharpness of classical correlations. A minisuperspace model is used as an example to illustrate these points.

Quantum theory for continuous photodetection processes.

Abstract: We develop a quantum theory for continuous photodetection processes that describes nonunitary time development of the field under continuous measurement of photon number. Exact expressions are obtained for time evolutions of the photon-field density operator, average and variance of the photon number, and the Fano factor. These are applied to typical quantum states, i.e., number, coherent, thermal, and squeezed states. The continuous photodetection process is made up of two elementary processes in terms of the referring measurement process, that is, one-count and no-count processes. Just after the one-count process in which a photodetector registers one photoelectron, the average photon number 〈n(t)〉 of the remaining field is shown to increase for super-Poissonian states (e.g., thermal state) and decrease for sub-Poissonian states (e.g., number state); for the Poissonian state (e.g., coherent light), 〈n(t)〉 does not change. During the no-count process in which the photodetector registers no photoelectrons, on the other hand, 〈n(t)〉 decreases in time for all states except the number state. The physical origins for these results are clarified from the viewpoint of nonunitary state reduction by continuous measurement of photon number. Furthermore, we introduce a nonreferring measurement process in which the detector registers photocounts, but we discard all readout information. We discuss the difference in the way the photon field evolves in this process compared to the referring measurement process.

New frontiers in quantum electrodynamics and quantum optics

Abstract: A review of recent progress in the borderline areas of quantumelectrodynamics, quantumoptics, and quantum theory of measurement. The first section begins with a review of quantum optics, followed by contributions on the coherence, interference, and squeezing of light. The second section reviews the

Classical limit in quantum cosmology: Quantum mechanics and the Wigner function

Abstract: We study the classical limit of quantum mechanics as applied to quantum cosmology. Conventional wisdom regards the peaking of the Wigner function of the Universe around a classical trajectory as being a quantum prediction of that trajectory. We show that, with quantum interference correctly taken into account, the hoped for "classical correlation" does not exist. There are, therefore, serious difficulties with the notion that a pure quantum state has a classical limit relevant to the description of our world. Some form of quantum decoherence appears necessary for a strict classical limit to exist. This alternative is briefly discussed.

The Path-Integral Simulation of Quantum Systems

Abstract: We explain how Feynman’s path-integral formulation of quantum statistical mechanics gives a natural way of simulating quantum systems in thermal equilibrium. The theory is first outlined for a simple system, consisting of a single particle in one dimension acted on by an external potential. Starting from the standard basic expressions for the partition function and the thermal averages of observables, it is shown how a simple sequence of mathematical operations allows these expressions to be brought into Feynman’s path-integral form. In this form, the quantities of interest are expressed as an integral over cyclic paths of the particle, which can be evaluated by classical simulation methods. This approach, generalized to many particles in three dimensions, gives a simulation technique for quantum many-body systems. We discuss how to calculate some important observables such as the energy and the radial distribution function. In the application of path-integral techniques to systems like liquid helium, the inclusion of quantum exchange is crucial, and we indicate how this can be achieved. We then illustrate the use of the technique by describing simulations that have been performed on (i) an electron dissolved in a molten salt; (ii) hydrogen in metals; and (iii) liquid helium-four.

Barrier Traversal Time in the Quantum Potential Picture

Abstract: We discuss the time taken for a particle to pass through a classically forbidden barrier in the quantum potential approach to quantum mechanics.

Model Apparatus for Quantum Measurements

Abstract: We present a model system that behaves as a measurement apparatus for quantum systems should. The device is macroscopic, it interacts with the microscopic system to be measured, and the results of that interaction affect the macroscopic device in a macroscopic, irreversible way. Everything is treated quantum mechanically: the apparatus is defined in terms of its (many) coordinates, the Hamiltonian is given, and time evolution follows Schrodinger's equation. It is proposed that this model be itself used as a laboratory for testing ideas on the measurement process.

Probabilistic Methods in Quantum Field Theory and Quantum Gravity

Abstract: The meeting encompassed all Euclidean quantum field theory descriptions that make direct reference to concepts from probability theory and statistical mechanics Contributors examine the space-time discretized lattice field theories, and present optimized techniques that combine features of ordinary"

Alternative Hamiltonian Description for Quantum Systems

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

II Quantum Mechanical Limit in Optical Precision Measurement and Communication

Abstract: Publisher Summary This chapter discusses the standard and intrinsic quantum mechanical limits on optical precision measurement and communication. Nonclassical lights, such as a quadrature amplitude squeezed state, number-phase squeezed state (number state), and correlated photon pair circumvent the standard quantum limit (SQL) on photon generation. A quantum mechanical limit on the minimum energy cost per bit emerges if an optical homodyne or heterodyne receiver is used instead of a photon counter. The SQL on photon amplification stems from the fact that an ordinary linear amplifier amplifies the two conjugate observables simultaneously. The chapter discuses the intrinsic quantum limit, which determines the information extraction from a light wave. It emerges in the form of quantum mechanical channel capacity and Bohr's time-energy uncertainty principle. Applications of nonclassical lights, QND measurements, and single-observable amplifiers are also discussed.

Quantum decoherence and classical correlation in quantum mechanics.

Abstract: We study two conditions for the quantum system to behave classically: decoherence in the quantum interference and the establishment of the classical trajectory in phase space. We show, despite the fact that these two conditions partially conflict with each other, the upside-down harmonic oscillator with a diffusion term satisfies them simultaneously. The implications for quantum cosmology and the measurement theory of quantum mechanics are given.