Perturbative expansion for the master equation and its applications - art.no. 013819

We construct generally applicable small-loss rate expansions for the densit y operator of an open system. Successive terms of those expansions yield ch aracteristic loss rates for dissipation processes. Three applications are p resented in order to give further insight into the context of those expansi ons. The first application, of a two-level atom coupling to a bosonic envir onment, shows the procedure and the advantage of the expansion, whereas the second application that consists of a single mode field in a cavity with l inewidth kappa due to partial transmission through one mirror illustrates a practical use of those expansions in quantum measurements, and the third o ne, for an atom coupled to modes of a lossy cavity shows another use of the perturbative expansion.