Some aspects of the irreversible dynamics of a generalized Jaynes–
Cummings model are addressed. By working in the dressed-state
representation, it is possible to split the dynamics of the entanglement
and coherence. The exact solution of the master equation in
the case of a high-Q cavity with atomic decay is found. Effects of
the atomic spontaneous decay on the temporal evolution of partial
entropies of the atom or the field and the total entropy as a quantitative
measure entanglement are elucidated. The degree of entanglement,
through the sum of the negative eigenvalues of the
partially transposed density matrix and the negative mutual information
has been studied and compared with other measures.