FIELD-THEORETICAL DERIVATION OF THE MASTER EQUATION IN QUANTUM OPTICS

The basic tool in quantum optics for the description of atomic systems interacting with coherent and incoherent radiation fields is the atom ic density matrix governed by the master equation. In the present pape r we apply standard condensed-matter nonequilibrium many-body methods to the problem of a two-level atom driven by an external laser field a nd relaxing by interaction with the radiation field. We recover the we ll-known dressed-atom picture and, in particular, we present an altern ative derivation of the master equation for the atomic density matrix which allows simple generalizations.