  We propose an optical cavity-QED scheme for the deterministic generation of
polarization entangled photon pairs that operates with high fidelity even in
the bad cavity limit. The scheme is based on the interaction of an excited
four-level atom with two empty optical cavity modes via an adiabatic passage
process. Monte-Carlo wave function simulations are used to evaluate the
fidelity of the cavity-QED source and its entanglement capability in the
presence of decoherence. In the bad cavity limit, fidelities close to one are
predicted for state-of-the-art experimental parameter values.
