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 quantized electromagnetic field through a dispersive coupling fulfilling quantum nondemolition criteria. Two schemes of measurements are examined. The first one consists in measuring the atomic electric dipole, which indirectly allows one to infer the photon distribution inside the cavity. The second one schematizes a measurement of photon momentum, which permits to describe the atomic level distribution. Decoherence of the corresponding reduced density matrices is studied in detail for both cases, and its relationship to recent experiments is finally discussed. 
Roberto Onofrio and Lorenza Viola