We demonstrate a low-loss and polarization-entanglement-preserving photonic router at the telecom C-band. The router enables switching an optical path of two-photon polarization-mode N00N states while maintaining its high degree of entanglement.
Abstract In photonic quantum applications, optical routers are required to handle single photons with low loss, high speed, and preservation of their quantum states. Single-photon routing with maintained polarization states is particularly important for utilizing them as qubits. Here, we demonstrate a polarization-maintaining electro-optic router compatible with single photons. Our custom electro-optic modulator is embedded in a configuration of a Mach–Zehnder interferometer, where each optical component achieves polarization-maintaining operation. We observe the performance of the router with 2%–4% loss, 20 dB switching extinction ratio, 2.9 ns rise time, and >99% polarization process fidelity to an ideal identity operation.
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, a low‐loss, noiseless, polarization‐maintaining routing of arbitrarily polarized single photons and, crucially, multi‐photon entangled states is demonstrated where the entanglement is encoded in orthogonal polarization bases, at the telecom L‐band. The interferometer‐based router is constructed by optics with a low angle of incidence and cross‐aligned electro‐optic crystals, achieving the polarization‐maintaining operation with a minimal number of optical components. The routing of arbitrarily‐polarized heralded single photons with a 0.057 dB (1.3%) loss, a 22 dB switching extinction ratio, and 99% polarization process fidelity to ideal identity operation is demonstrated. Moreover, the high‐quality router achieves the routing of two‐photon N00N‐type entangled states with a highly maintained interference visibility of 97%. The demonstrated router scheme preserving multi‐photon polarization state paves the way toward polarization‐encoded photonic quantum network as well as multi‐photon entanglement synthesis via spatial‐ and time‐multiplexing techniques.