Improving the rate-loss scaling in polarization entanglement distribution using single-click entanglement swapping

Polarization entanglement is widely used in optical quantum information processing as well as quantum communication due to its compatibility with standard optical components. However, distributing polarization entanglement is severely limited by photon loss in the channels. In conventional methods, the distribution rate of polarization entanglement scales linearly with the end-to-end channel transmittance, which decreases exponentially with distance. Here, we propose and experimentally demonstrate a protocol for distributing polarization entanglement with improved rate-loss scaling. The protocol combines single-click entanglement swapping with polarization–photon-number hybrid entanglement, in which the photon-number-basis modes are sent to a central swapping node while the polarization qubits are retained by the end users. In our experiment, we observed a square-root improvement in the rate-loss scaling compared with conventional methods and achieved a fidelity of 0.843 for distributed polarization-entangled photon pairs. These results provide a proof-of-principle demonstration that the favorable rate-loss scaling of single-click entanglement swapping can be transferred to polarization entanglement distribution.