DYNAMICS OF DECOHERENCE IN CONTINUOUS ATOM-OPTICAL QUANTUM-NONDEMOLITION MEASUREMENTS

The Lindblad approach to continuous quantum measurements is applied to a system composed of a two-level atom interacting with a stationary q uantized electromagnetic held through a dispersive coupling, fulfillin g quantum nondemolition criteria. Two schemes of measurements are exam ined. The first one consists of measuring the atomic electric dipole, which indirectly allows one to infer the photon distribution inside th e cavity. The second one schematizes a measurement of photon momentum, which permits one to describe the atomic level distribution; Decohere nce of the corresponding reduced density matrices is studied in detail for both cases, and its relationship to recent experiments is finally discussed.