Chip-to-chip entanglement distribution over 80-km multicore fiber link

TL;DR

This paper demonstrates chip-to-chip distribution of path-encoded entangled states over 80 km of fiber, achieving high fidelity and secure key rates, advancing scalable quantum networks.

Contribution

First successful long-distance chip-to-chip distribution of path-encoded entanglement using integrated silicon photonics over 80 km fiber.

Findings

Achieved Bell state fidelity of 85.7%.

Generated secure key rate of 2.03 bits/sec.

Distributed entanglement over 80 km fiber link.

Abstract

Long-range quantum entanglement is essential for building large-scale quantum networks and unconditionally secure cryptographic systems based on quantum key distribution (QKD). While photonic integrated circuits offer a highly scalable platform, the fragility of phase coherence between spatial modes has prevented the distribution of path-encoded entanglement over long distances. Here, we report chip-to-chip distribution of path-encoded entangled states over 80 km between fully integrated silicon photonic transmitter and receiver chips. Telecom-band entangled photon pairs are generated via spontaneous four-wave mixing in on-chip spiral waveguides and distributed between chips over a dual-core, actively stabilized fiber link. Upon distribution, we measure a Bell state fidelity of $85.7 \pm 0.2 \%$. Implementing the BBM92 protocol with the same source, we obtain a secure key rate of 2.03 bit/s in the infinite-key regime. These results establish silicon photonic chips as a viable platform for long-distance path-encoded entanglement-based quantum key distribution, paving the way toward scalable, device-independent quantum networks.