Heralded generation of Bell states using atomic ensembles

We propose a scheme that utilizes the collective enhancement of a photonic mode inside an atomic ensemble together with a proper Zeeman manifold to achieve a heralded polarization entangled Bell state. The entanglement is between two photons that are separated in time and can be used as a postselected deterministic source for applications such as quantum repeaters where a subsequent entanglement swapping measurement is employed. We present a detailed analysis of the practical limitation of the scheme.