Low-loss polarization-maintaining router for single and entangled photons at a telecom wavelength

Abstract: Photon polarization serves as an essential quantum information carrier in quantum information and measurement applications. Routing of arbitrarily polarized single photons and polarization-entangled photons is a crucial technology for scaling up quantum information applications. Here, we demonstrate a low-loss, noiseless, polarization-maintaining routing of single and entangled photons at the telecom L-band. Our interferometer-based router is constructed by optics with a low angle of incidence and cross-aligned electro-optic crystals, achieving the polarization-maintaining operation without additional polarization-compensation optics. We demonstrate the routing of arbitrary-polarized heralded single photons with a 1.3% loss, a $>$ 22 dB switching extinction ratio, and $>$ 99% polarization process fidelity to ideal identity operation. Moreover, the high-quality router achieves the routing of two-photon N00N-type entangled states with a highly maintained interference visibility of $\sim$ 97%. The demonstrated router scheme paves the way toward polarization-encoded photonic quantum network as well as multi-photon entanglement synthesis via spatial- and time-multiplexing techniques.