This book treats modern aspects of open systems, measurement, and decoherence in relativistic quantum theory. It starts with a comprehensive introduction to the problems related to measuring local and nonlocal observables and the constraints imposed by the causality principle. In the articles that follow, the emphasis lies on new theoretical models. Quantum dynamical semigroups and stochastic processes in Hilbert space are introduced, as are dynamical reduction models. Further topics include relativistic generalizations of the continuous spontaneous localization model and of the quantum state diffusion model and decoherence and the dynamical selection of preferred basis sets in the framework of continuous measurement theory and of the decoherent histories approach. Mathematical aspects of quantum measurement theory and dynamical entropies are also studied from the viewpoint of the operational approach to quantum mechanics.

Quantum mechanics has shown unprecedented success as a physical theory, but it has forced a new view on the description of physical reality. In recent years, important progress has been achieved both in the theory of open quantum systems and in the experimental realization and control of such systems. A great deal of the new results is concerned with the characterization and quantification of quantum memory effects. From this perspective, the 684. WE-Heraeus-Seminar has brought together scientists from different communities, both theoretical and experimental, sharing expertise on open quantum systems, as well as the commitment to the understanding of quantum mechanics. This book consists of many contributions addressing the diversified physics community interested in foundations of quantum mechanics and its applications and it reports about recent results in open quantum systems and their connection with the most advanced experiments testing quantum mechanics.

The physics of open quantum systems plays a major role in modern experiments and theoretical developments of quantum mechanics. Written for graduate students and readers with research interests in open systems, this book provides an introduction into the main ideas and concepts, in addition to developing analytical methods and computer simulation techniques.

The development of a consistent picture of the processes of decoherence and quantum measurement is among the most interesting fundamental problems with far-reaching consequences for our understanding of the physical world. A satisfactory solution of this problem requires a treatment which is c- patiblewiththetheoryofrelativity, andmanydiverseapproachestosolveor circumvent the arising di?culties have been suggested. This volume collects the contributions of a workshop on Relativistic Quantum Measurement and Decoherence held at the Istituto Italiano per gli Studi Filoso?ci in Naples, April9-10,1999. Theworkshopwasintendedtocontinueapreviousmeeting entitled Open Systems and Measurement in Relativistic Quantum Theory, the talks of which are also published in the Lecture Notes in Physics Series (Vol. 526). The di?erent attitudes and concepts used to approach the decoherence and quantum measurement problem led to lively discussions during the wo- shop and are re?ected in the diversity of the contributions. In the ?rst article the measurement problem is introduced and the various levels of compatibility with special relativity are critically reviewed. In other contributions the r oles of non-locality and entanglement in quantum measurement and state vector preparation are discussed from a pragmatic quantum-optical and quant- information perspective. In a further article the viewpoint of the consistent histories approach is presented and a new criterion is proposed which re?nes thenotionofconsistency. Also, thephenomenonofdecoherenceisexamined from an open system's point of view and on the basis of superselection rules employing group theoretic and algebraic methods. The notions of hard and softsuperselectionrulesareaddressed, aswellasthedistinctionbetweenreal andapparentlossofquantumcoherence."

This book treats modern aspects of open systems, measurement, and decoherence in relativistic quantum theory. It starts with a comprehensive introduction to the problems related to measuring local and nonlocal observables and the constraints imposed by the causality principle. In the articles that follow, the emphasis lies on new theoretical models. Quantum dynamical semigroups and stochastic processes in Hilbert space are introduced, as are dynamical reduction models. Further topics include relativistic generalizations of the continuous spontaneous localization model and of the quantum state diffusion model and decoherence and the dynamical selection of preferred basis sets in the framework of continuous measurement theory and of the decoherent histories approach. Mathematical aspects of quantum measurement theory and dynamical entropies are also studied from the viewpoint of the operational approach to quantum mechanics.

Quantum mechanics has shown unprecedented success as a physical theory, but it has forced a new view on the description of physical reality. In recent years, important progress has been achieved both in the theory of open quantum systems and in the experimental realization and control of such systems. A great deal of the new results is concerned with the characterization and quantification of quantum memory effects. From this perspective, the 684. WE-Heraeus-Seminar has brought together scientists from different communities, both theoretical and experimental, sharing expertise on open quantum systems, as well as the commitment to the understanding of quantum mechanics. This book consists of many contributions addressing the diversified physics community interested in foundations of quantum mechanics and its applications and it reports about recent results in open quantum systems and their connection with the most advanced experiments testing quantum mechanics.

This book treats the central physical concepts and mathematical techniques used to investigate the dynamics of open quantum systems. To provide a self-contained presentation the text begins with a survey of classical probability theory and with an introduction into the foundations of quantum mechanics with particular emphasis on its statistical interpretation. The fundamentals of density matrix theory, quantum Markov processes and dynamical semigroups are developed. The most important master equations used in quantum optics and in the theory of quantum Brownian motion are applied to the study of many examples. Special attention is paid to the theory of environment induced decoherence, its role in the dynamical description of the measurement process and to the experimental observation of decohering Schrodinger cat states. The book includes the modern formulation of open quantum systems in terms of stochastic processes in Hilbert space. Stochastic wave function methods and Monte Carlo algorithms are designed and applied to important examples from quantum optics and atomic physics, such as Levy statistics in the laser cooling of atoms, and the damped Jaynes-Cummings model. The basic features of the non-Markovian quantum behaviour of open systems are examined on the basis of projection operator techniques. In addition, the book expounds the relativistic theory of quantum measurements and discusses several examples from a unified perspective, e.g. non-local measurements and quantum teleportation. Influence functional and super-operator techniques are employed to study the density matrix theory in quantum electrodynamics and applications to the destruction of quantum coherence are presented. The text addresses graduate students and lecturers in physics and applied mathematics, as well as researchers with interests in fundamental questions in quantum mechanics and its applications. Many analytical methods and computer simulation techniques are developed and illustrated with the help of numerous specific examples. Only a basic understanding of quantum mechanics and of elementary concepts of probability theory is assumed.