  We study entanglement dynamics of a couple of two-level atoms resonantly
interacting with a cavity mode and embedded in a dispersive atomic environment.
We show that in the absence of the environment the entanglement reaches its
maximum value when only one exitation is involved. Then, we find that the
atomic environment modifies that entanglement dynamics and induces a typical
collapse-revival structure even for an initial one photon Fock state of the
field.
