Quantum engineering of photon states with atomic ensembles

The deterministic generation of collimated single and entangled photons is of crucial importance in several applications in quantum information. Most of the methods require the use of high-Q cavities, something which is very demanding in practice. In this work we propose a new method to produce single-and entangled-photons in a deterministic way which does not require the use of cavities. It relies on the collective light emission in some particular directions as a consequence of the presence of entanglement in an atomic ensemble. This light emission is triggered by a laser pulse, and therefore our scheme is deterministic. Furthermore, it allows one to produce a variety of photonic entangled states by first preparing certain classes of atomic entangled states.