COLLECTIVE EFFECTS IN THE COLLAPSE-REVIVAL PHENOMENON AND SQUEEZING IN THE DICKE-MODEL

Resonant interaction of a collection of two-level atoms with a single- mode coherent cavity field is considered in the framework of the Dicke model. We focus on the role of collective atomic effects in the pheno menon of collapses and revivals of the Rabi oscillations. It is shown that the behavior of the system strongly depends on the initial atomic state. In the case of the initial half-excited Dicke state we account for a number of interesting phenomena. The correlations between the a toms result in a suppression of the revival amplitude, and the revival time is halved, compared to the uncorrelated fully excited and ground states. The phenomenon of squeezing of the radiation field in the ato m-field interaction is also discussed. For the initial fully excited a nd ground atomic states, the field is squeezed on the short-time scale , and squeezing can be enhanced by increasing the number of atoms. Som e empirical formulas are found which describe the behavior of the syst em in excellent agreement with numerical results. For the half-excited Dicke state, the field can be strongly squeezed on the long-time scal e in the case of two atoms. This kind of squeezing is enhanced by incr easing the intensity of the initial coherent field and is of the same nature as revival-time squeezing in the Jaynes-Cummings model. The app earance of this long-time squeezing can be explained using the factori zation approximation for semiclassical atomic states.