Fig. 1: An integrated-photonics TF-QKD network system.
From: Large-scale quantum communication networks with integrated photonics
a, Schematic diagram for a many-user long-haul TF-QKD WDM-based star network system. This network could support a large number of QKD clients (N) and long client-to-client communication distances (L). It can mitigate detector vulnerabilities at the central (untrusted) server node, while enabling cost-efficient resource sharing among many legitimate QKD users. b, Conceptual diagram of a large-scale integrated-photonics TF-QKD network, ‘Weiming Quantum Chip-Network’, with both large N and long L. QKD client chips integrate local lasers, PMs, IMs and VOAs, delivering high-speed operation, full integration, cost-effectiveness, miniaturization and mass-manufacturability for the TF-QKD network. The server chips encompass an integrated microcomb, as well as linear-optic circuit (LOC; including optical switches, wavelength multiplexers and beamsplitters) modules, single-photon electro-optic frequency shifters (EOFSs), SNSPD modules and electronic logics. The integrated microcomb provides a broad range of ultralow-noise coherent Hz-level comb lines for TF-QKD, enabling WDM-based networks with inherent phase coherence between QKD client chips. Microcomb and client chips are clock synchronized within the network, with the microcomb driving many chip-based transmitters to reliably share quantum-secure keys across long-haul fibre channels. c, Photograph of integrated-photonics quantum chips used in our network, including an integrated Si3N4 microcomb chip (unpackaged) at the centre and 20 copies of identical InP QKD client chips (two InP chips are packaged on one printed circuit board). Both server-side microcomb chips and client-side QKD transmitter chips can be massively manufactured with wafer-scale reproducibility. These 20 InP QKD chips used in this experiment were randomly selected from a set of 24 copies fabricated on a 3-inch wafer, without any preselection.
