  We study the entanglement properties of two three-level Rydberg atoms passing
through a single-mode cavity. The interaction of an atom with the cavity field
allows the atom to make a transition from the upper most (lower most) to the
lower most (upper most) level by emission (absoprtion) of two photons via the
middle level. We employ an effective Hamiltonian that describes the system with
a Stark shifted two-photon atomic transition. We compute the entanglement of
formation of the joint two-atom state as a function of Rabi angle $gt$. It is
shown that the Stark shift can be used to enhance the magnitude of atomic
entanglement over that obtained in the resonant condition for certain parameter
values. We find that though the two-atom entanglement generally diminishes with
the increase of the two-photon detuning and the Stark shift, it is possible to
sustain the entanglement over a range of interaction times by making the
detuning and the Stark shift compensate each other. Similar characteristics are
obtained for a thermal state cavity field too.

Quantum Physics