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

TL;DR

This paper presents a low-loss, polarization-maintaining optical router capable of handling single and entangled photons at telecom wavelengths, advancing quantum communication and network scalability.

Contribution

The authors develop a novel interferometer-based router that preserves polarization states of single and entangled photons with minimal optical components and high fidelity.

Findings

Achieved 0.057 dB loss and >22 dB extinction ratio in routing single photons.

Maintained 97% interference visibility for two-photon entangled states.

Enabled polarization-preserving routing for multi-photon quantum states.

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 arbitrarily polarized single photons and, crucially, multi-photon entangled states where the entanglement is encoded in orthogonal polarization bases, 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 with a minimal number of optical components. We demonstrate 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. Moreover, the high-quality router achieves the routing of two-photon N00N-type entangled states with a highly maintained interference visibility of $\approx$ 97%. The demonstrated router scheme preserving multi-photon polarization state paves the way toward polarization-encoded photonic quantum networks as well as multi-photon entanglement synthesis via spatial- and time-multiplexing techniques.