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arXiv:2502.12554 · Advanced Quantum Technologies

Low‐Loss Polarization‐Maintaining Router for Single and Entangled Photons at a Telecom Wavelength

Pengfei Wang, So-Young Baek, Masahiro Yabuno, Shigehito Miki, Hirotaka Terai, Fumihiro Kaneda

Published Sep 2, 2025• 5 citations

Abstract

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.

DOI: 10.1002/qute.202500355

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An essential component of future quantum networks is an optical switch capable of dynamically routing single photons. Here we implement such a switch, based on a fiber-optical Sagnac interferometer design. The routing is implemented with a pair of fast electro-optical telecom phase modulators placed inside the Sagnac loop, such that each modulator acts on an orthogonal polarization component of the single photons, in order to yield polarization-independent capability that is crucial for several applications. We obtain an average extinction ratio of more than 19 dB between both outputs of the switch. Our experiment is built exclusively with commercial off-the-shelf components, thus allowing direct compatibility with current optical communication systems.

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