Abstract: Entangled optical outputs are generated using one or more heralded entanglement sources, each comprising: first and second free-running entanglement sources, each providing a first (third) optical output comprising a quantum superposition of a pair of orthogonal optical modes, and a second (fourth) optical output comprising a quantum superposition of a pair of orthogonal optical modes; an optical module configured to perform an interferometric measurement based on optical interference between at least a portion of the first optical output and at least a portion of the third optical output, and to generate one or more detection signals based on the interferometric measurement in a series of time slots; and a trigger module configured to generate a trigger signal based on the one or more detection signals to indicate one or more time slots in which the second optical output and the fourth optical output are entangled with each other.

Abstract: We disclose optical entanglement distribution in quantum networks based on a quasi-deterministic entangled photon pair source. Combining heralded photonic Bell pair generation with spectral mode conversion to interface with quantum memories eliminates switching losses due to multiplexing in the source. This zero-added-loss multiplexing (ZALM) Bell pair source is especially useful for the particularly challenging problem of long-baseline entanglement distribution via satellites and ground-based memories, where it unlocks additional advantages: (i) the substantially higher channel efficiency ? of downlinks versus uplinks with realistic adaptive optics, and (ii) photon loss occurring before interaction with the quantum memory—i.e., Alice and Bob receiving rather than transmitting—improve entanglement generation rate scaling by (?{square root over (?)}).