Entanglement distribution over 155 km metropolitan fiber using a CMOS-compatible silicon chip

TL;DR

This paper demonstrates long-distance entanglement distribution over 155 km of fiber using a CMOS-compatible silicon chip, achieving high brightness and fidelity, advancing scalable quantum network technology.

Contribution

It introduces a silicon chip platform with significantly higher brightness for entangled photon pairs, enabling practical long-distance quantum communication.

Findings

Entangled photons distributed over 155 km fiber with 66 dB loss.

Achieved entanglement fidelity of approximately 98%.

Off-chip brightness exceeds previous reports by three orders of magnitude.

Abstract

Transmitting entangled states over long distances is crucial for developing quantum networks. Previous demonstrations using satellites or fibers relied on photon pairs generated from bulk crystal arrangements. Polarization entanglement distribution based on CMOS-compatible silicon chips has long been restricted to lab-scale demonstrations spanning only a few meters, due to the difficulty of achieving sufficient off-chip brightness. We report a silicon chip platform that provides an off-chip entangled photon pair brightness ranging from 8,000 to 460,000 pairs per second, exceeding previous reports by three orders of magnitude. The entanglement fidelity reaches 99.85(6)% and 97.90(3)%, respectively. After addressing key challenges in long distance entanglement distribution over deployed fiber, including phase drift and chromatic dispersion, entangled photons were successfully distributed over 155 km (66 dB loss). These results demonstrate that CMOS-compatible silicon chips can perform competitively with bulk crystal sources and represent an important step toward scalable, chip-based quantum networks.