Phase properties of a coherent field interacting with two two-level atoms in a cavity

We use the Hermitian phase formalism of Pegg and Barnett to study phase properties of a coherent field interacting with a cooperative system. We show that if the number of eigenvalues in a subspace with fixed photon number n is large, as the evolution proceeds, the phase probability distribution exhibits a multi-peaked structure, each of them is associated with one eigenvalue or corresponding eigenstate. We consider in detail the field phase in the system consisting of two two-level atoms and show that its time behaviour reflects the collapses and revivals of the level occupation probabilities.