Interaction of a two-level XY n-spin model with a cavity field

A simplified version of the XY n-spin cyclic model interacting with a single-mode cavity field in the rotating-wave approximation is investigated in the framework of a two-level system. Computation of the energy of the spin system follows from an appropriate tracing of the analytic propagator path integral over Grassmann variables nonorthogonal states in the imaginary time domain. Photon distribution and time evolution of the population inversion for an initial coherent state are computed for an ideal squeezed state of the cavity field.