Large-scale quantum communication networks with integrated photonics.

Quantum key distribution (QKD) makes use of the principles of quantum mechanics to enable provably secure communication. One substantial challenge persists in building large-scale QKD networks with many clients over long communication distances. Although quantum relays continue to pose practical difficulties, existing trusted-node networks, point-to-multipoint networks and wavelength-multiplexed entanglement networks 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 distance. Although long-distance point-to-point TF-QKD has been achieved, 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.