  We investigate some aspects of the dynamics and entanglement of bipartite
quantum system (atom-quantized field), coupled to a third ``external" subsystem
(quantized field). We make use of the Raman coupled model; a three-level atom
in a lambda configuration interacting with two modes of the quantized cavity
field. We consider the far off resonance limit, which allows the derivation of
an effective Hamiltonian of a two-level atom coupled to the fields. We also
make a comparison with the situation in which one of the modes is treated
classically rather than prepared in a quantum field (coherent state).
