THE SYSTEM OF N 2-LEVEL ATOMS INTERACTING WITH A FIELD MODE - ENTANGLEMENT AND PARAMETRIC APPROXIMATION

We study the entanglement of the cavity field mode to the ensemble of two-level atoms when their interaction is ruled by the Dicke model. Our investigation is focused mainly on initial states with fully excited atomic system and an intense cavity field mode. We give an analysis of the entanglement on the short as well as the long time scale. We derive limit expressions for the entanglement for the first moments of the evolution where the entanglement reaches constant value. We show that in the early moments of the evolution an almost pure state can be generated under suitable conditions when the intensity of the field is approximately N. On the long time scale we point out the appearance of a clear decrease of the entanglement associated with the collapse-revival phenomenon of the mean photon number in this model. The bifurcation of initially a gaussian Q-function of the field mode into N + 1 peaks of different weight factors is shown. Finally the results known for the Jaynes-Cummings model are compared with the obtained results.