Integrated polarization-entangled photon source for wavelength-multiplexed quantum networks

TL;DR

This paper introduces a compact, high-performance on-chip polarization-entangled photon source using thin-film lithium niobate, enabling scalable quantum networks with broad bandwidth and low noise, suitable for real-world deployment.

Contribution

The work presents a novel integrated photon source employing dual quasi-phase matching in a nanophotonic waveguide, simplifying design and enhancing performance for quantum communication.

Findings

Achieved high-fidelity Bell states with broad bandwidth.

Demonstrated wavelength-multiplexed entanglement over 50 km fiber links.

Enabled scalable multi-user quantum networks.

Abstract

Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.