Curator's Take
This breakthrough demonstrates that silicon photonic chips can maintain quantum entanglement over practical telecommunications distances, marking a crucial step toward scalable quantum networks using existing fiber infrastructure. The 80-km chip-to-chip entanglement distribution represents the longest reported distance for path-encoded quantum states between integrated photonic devices, proving that these fragile quantum correlations can survive real-world transmission conditions. What makes this particularly significant is the use of standard telecom components and silicon photonics—the same technology that powers today's internet—suggesting a clear pathway to commercially viable quantum communication networks. The successful quantum key distribution at 2.03 bits per second may seem modest, but it validates the fundamental architecture needed for future quantum internet applications where security is guaranteed by the laws of physics rather than computational complexity.
— Mark Eatherly
Summary
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.