  In this paper, we investigate the entanglement dynamics and decoherence in
the interacting system of a strongly driven two-level atom and a single mode
vacuum field in the presence of dissipation for the cavity field. Starting with
an initial product state with the atom in a general pure state and the field in
a vacuum state, we show that the final density matrix is supported on ${\mathbb
C}^2\otimes{\mathbb C}^2$ space, and therefore, the concurrence can be used as
a measure of entanglement between the atom and the field. The influences of the
cavity decay on the quantum entanglement of the system are also discussed. We
also examine the Bell-CHSH violation between the atom and the field and show
that there are entangled states for which the Bell-BCSH inequality is not
violated. Using the above system as a quantum channel, we also investigate the
quantum teleportation of a generic qubit state and also a two-qubit entangled
state, and show that in both cases the atom-field entangled state can be useful
to teleport an unknown state with fidelity better than any classical channel.
