Decoherence and the theory of continuous quantum measurements

Abstract

Decoherence of a quantum system (which then starts to displayclassical features) results from the interaction of the system with theenvironment, and is well described in the framework of the theory ofcontinuous quantum measurements (CQM). Reviewed are the vari-ous approaches to the CQM theory, and the approach based on thee ective complex Hamiltonians is discussed in greater detail. Thee ective complex Hamiltonian is derived from the restricted path in-tegral, which emphasizes the role of information in the dynamics ofthe system being measured. The complex Hamiltonian is used for an-alyzing the CQM of energy in a two-level system. Such measurementis demonstrated to be capable of monitoring the quantum transition,and the back e ect of monitoring on the probability of transition isanalyzed. The realization of this type of measurement by a long seriesof soft observations of the system is presented.