Dynamics and quasi-stationary states of N-atom micromaser

Summary form only given. We consider a N-atom micromaser model described by a hamiltonian. Taking into account field relaxation between consecutive N-atom packets we study dynamics and quasi-stationary states of subsystems in the model. Experimentally, such a system may be realized on a high-density atom flux prepared with help of ultrashort time pulses of exciting laser, in order to achieve small packets and avoid large dispersion of entrance times. For initially diagonal density operator of atoms, the system dynamics and particularly of the field reduced density matrix (RDM) have significant simplification, called diagonal invariance. Under such conditions it was found that the field dynamics might be divided into two stages, a rapid stage and a quasi-stationary stage. This behavior is determined by quasi-trapped states, which are a generalization of well known trapped states in the one-atom micromaser. We want to emphasize that our work raises important questions on a possibility to apply formalism of density matrix for description of such experiments.