Quantum Measurements and Decoherence

The theory of quantum measurements is an area that has attracted attention because of its new applications for quantum information technology. The phenomenon of decoherence of a measured system is investigated and simple techniques for the description of a wide class of measurements are developed. An individual continuously measured (decohering) system is presented by an effective complex Hamiltonian which supplies a phenomenological theory of gradual decoherence. The work, which features a presentation of physical processes leading to quantum measurement (decoherence) and simple mathematical formalisms, concentrates on the physical nature of quantum measurements and the behaviour of measured (open) quantum systems, but conceptual problems are also treated. The analysis of interrelations between different approaches to quantum measurement is given. The methods developed in this volume are applicable for the description of individual continuously measured (decohering) systems, not only to a whole set of such systems.