  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 phenomenon 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 atoms 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 atom-field interaction is also discussed. For the initial
fully-excited and ground atomic states, the field is squeezed on the short-time
scale, and squeezing can be enhanced by increasing the number of atoms. Some
empirical formulas are found which describe the behavior of the system in
excellent agreement with numerical results. For the half-excited Dicke state,
the field can be strongly squeezed on the long-time scale in the case of two
atoms. This kind of squeezing is enhanced by increasing the intensity of the
initial coherent field and is of the same nature as revival-time squeezing in
the Jaynes-Cummings model. The appearance of this long-time squeezing can be
explained using the factorization approximation for semiclassical atomic
states.
