  We investigate the dynamical behavior of the atom-photon entanglement in a
V-type three-level quantum system using the atomic reduced entropy. It is shown
that an atom and photons are entangled at the steady-state; however
disentanglement can also be achieved in an especial condition. It is
demonstrated that in the presence of quantum interference induced by
spontaneous emission, the reduced entropy and the atom-photon entanglement are
phase-dependent. Non-stationary solution is also obtained when the quantum
interference due to the spontaneous emission is completely included.
