DECOHERENCE AND THE THEORY OF CONTINUOUS QUANTUM MEASUREMENTS

The decoherence of a quantum system, i.e., its becoming partly classic al, results from its interaction with environment and is well describe d in terms of continuous quantum measurement theory. In the present pa per, various approaches to CQM theory are reviewed, of which that usin g effective complex Hamiltonians is discussed in detail. The effective complex Hamiltonian is obtained from the restricted path integral, th e latter highlighting the role of information in the dynamics of the m easured system, and is applied to the energy measurement on a two-leve l system. For such a measurement, quantum transition monitoring is sho wn to be possible and its backaction on the transition probability ana lyzed. Performing such a measurement using a long series of soft obser vations is described.