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±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.
@article{arxiv.2604.26791,
title = {Chip-to-chip entanglement distribution over 80-km multicore fiber link},
author = {Damien Roux and Giulia Guarda and Mujtaba Zahidy and Yunhong Ding and Siyan Zhou and Domenico Ribezzo and Battulga Munkhbat and Francesco Da Ros and Davide Bacco and Caterina Vigliar},
journal= {arXiv preprint arXiv:2604.26791},
year = {2026}
}