Large-scale quantum communication networks with integrated photonics.

Abstract

Quantum key distribution (QKD) makes use of the principles of quantum mechanics to enable provably secure communication^1,2. One substantial challenge persists in building large-scale QKD networks with many clients over long communication distances³. Although quantum relays continue to pose practical difficulties⁴, existing trusted-node networks^5-9, point-to-multipoint networks^10,11 and wavelength-multiplexed entanglement networks^12,13 encounter issues such as reliance on trusted intermediaries or limited distances. Twin-field quantum key distribution (TF-QKD) provides a compelling architecture that can overcome those issues while enhancing communication distance¹⁴. Although long-distance point-to-point TF-QKD has been achieved^15-21, realizing large-scale networks requires scalable quantum devices. Here we report a proof-of-principle demonstration of an integrated-photonics TF-QKD network with exceptional scalability and reliability. This network includes 20 independent client-side QKD transmitter chips with one server-side optical microcomb chip. The microcomb generates a broad range of ultralow-noise coherent frequency combs with Hz-level linewidths, which serve as seeds and references for all client chips. Each client chip regenerates ultralow-noise light phase-locked to microcombs and prepares quantum keys. We sequentially implement pairwise QKD across 20 client chips through ten wavelength-multiplexed channels, with each surpassing the repeaterless bound at 370 km in spooled fibre, achieving a networking capability (client pairs × communication distance) of 3,700 km. We further demonstrate the wafer-scale reproducibility of both server-side microcomb chips and client-side QKD transmitter chips, together establishing system-level scalability. Combining mass-manufacturability, cost-effectiveness and high scalability of integrated photonics with long-distance quantum communication represents a viable path to large-scale quantum networks.