Engineering of heralded narrowband color-entangled states

The efficient generation of entanglement is an essential requirement for quantum communications; however, long distances can only be achieved by utilizing entangled states that can be efficiently mapped into matter. Hence, sources generating states with bandwidths naturally compatible with the linewidths of atomic transitions are crucial. We harness the indistinguishability between two spontaneous four-wave mixing processes to achieve the heralded generation of single-photon frequency-bin entangled states. State manipulation admits entanglement and generation probability optimizations yet with negligible absorption. The scheme could also be adapted to photonic and solid interfaces.