Zero-Added-Loss Entangled-Photon Multiplexing for Ground- and Space-Based Quantum Networks

We propose a scheme for optical entanglement distribution in quantum networks based on a quasideterministic entangled photon-pair source. By combining heralded photonic Bell-pair generation with spectral mode conversion to interface with quantum memories, the scheme eliminates switching losses due to multiplexing in the source. We analyze this "zero-added-loss multiplexing"(ZALM) Bell-pair source 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 η 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 O(η). Based on numerical analyses, we estimate our protocol to achieve >10ebit/s at memory multiplexing of 102 spin qubits for ground distance >102km, with the spin-spin Bell-state fidelity exceeding 99%. Our architecture presents a blueprint for realizing global-scale quantum networks in the near term.