A scalable integrated-photonic twin-field quantum key distribution (TF-QKD) network is demonstrated. The system employs a star topology with a server-side$\text{Si}_{3} ~\mathrm{N}_{4}$optical microcomb and 20 monolithically integrated InP transmitter chips. Coherent comb lines seed client lasers to enable wavelengthdivision multiplexed operation and stable interference. Sequential pairwise TF-QKD is implemented over ten channels among 20 users, each exceeding the repeaterless bound at 370 km. The networking capability reaches$3,700 ~\text{km}$(client pairs × distance), and wafer-scale chip reproducibility confirms a manufacturable platform for large-scale quantum communication networks.
A scalable integrated-photonic twin-field quantum key distribution (TF-QKD) network is demonstrated. The system employs a star topology with a server-sideSi3N4optical microcomb and 20 monolithically integrated InP transmitter chips. Coherent comb lines seed client lasers to enable wavelengthdivision multiplexed operation and stable interference. Sequential pairwise TF-QKD is implemented over ten channels among 20 users, each exceeding the repeaterless bound at 370 km. The networking capability reaches3,700km(client pairs × distance), and wafer-scale chip reproducibility confirms a manufacturable platform for large-scale quantum communication networks.
Quantum key distribution (QKD) makes use of the principles of quantum mechanics to enable provably secure communication1,2. 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 networks5–9, point-to-multipoint networks10,11 and wavelength-multiplexed entanglement networks12,13 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 achieved15–21, 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. A lab-scale proof-of-principle demonstration of a quantum network comprising one server chip and 20 client photonic chips implementing twin-field quantum key distribution shows excellent scalability and reliability and yields a pathway towards future large-scale networks.
Twin-field (TF) quantum key distribution (QKD) has been proved to overcome the linear rate-distance limit of repeaterless quantum communications and has the capability to generate high key rates over long distances compared with other QKD protocols. Photonic integration has proven a promising technique for the large-scale deployment of QKD. While it has been adopted to implement a range of linearly scaling QKD protocols, there is to date no demonstration of TF QKD using photonic integrated chips. One important challenge resides in establishing high coherence between remote laser chips. In this study, we exploit optical injection locking to implement phase dissemination to independent lasers integrated onto photonic circuits and further demonstrate complete phase control on the same chip using electro-optic phase modulators. We achieve high laser coherence between remote transmitter nodes, which lets us demonstrate a quadratic key-rate improvement of the secure key rate beyond 80 dB of channel attenuation. The experimental results are in excellent agreement with the theory in both finite size and asymptotic regimes, in which the fundamental rate-distance limit is overcome. Our work paves the way for the deployment of large-scale TF QKD networks enabled by compact, low-cost, and high-yield chip-based devices.
Quantum key distribution (QKD) is a key application in quantum communication, enabling secure key exchange between parties using quantum states. Twin-field (TF) QKD offers a promising solution that surpasses the repeaterless limits, and its measurement-device-independent nature makes it suitable for star-type network architectures. In this work, we propose a scalable TF-QKD network with adaptable architecture, where users prepare quantum signals and send them to network nodes. These nodes use an optical switch to route the signals to multi-user measurement units, enabling secure key distribution among arbitrary users and adapting to complex connection demands of the network. A proof-of-principle demonstration with three users successfully achieved secure key sharing over simulated link losses of up to 30 dB, with an average rate of 19.57 bit/s. Additionally, simulations show that the proposed architecture can achieve a total secure key rate of 4.84×104 bit/s at 100 km in a symmetric 32-user network. This approach represents a significant advancement in the topology of untrusted-node QKD networks and holds promise for practical, large-scale applications in secure communication.
Photon-number superposition states are a valuable resource for quantum information processing and can be deterministically generated using advanced quantum-dot (QD) platforms. Here, we propose a twin-field quantum key distribution (TF-QKD) protocol that employs photon-number superposition states of the form 1− t |0⟩+ e i ϕ t |1⟩. Numerical simulations show that the protocol outperforms existing laser-based TF-QKD schemes in secret-key rate and transmission distance, surpasses the repeaterless bound, enabling secure communication beyond 210 km under experimentally achievable conditions. A key advantage is its direct compatibility with existing QD technology. As integrated, solid-state, on-demand single-photon sources, QDs inherently provide high stability, scalability, and photon indistinguishability, making them well suited for deployment in large-scale quantum networks. Overall, our work demonstrates a practical pathway toward high-performance long-distance TF-QKD and highlights the broader potential of solid-state non-classical light sources for quantum networking architectures.
Quantum key distribution (QKD) is moving from laboratory demonstrations toward network deployment, and integrated photonic chips provide a hardware route for compact, stable and scalable systems. This review summarizes progress in integrated photonic chips for QKD from protocol requirements to deployable systems. It first examines how decoy-state BB84, measurement-device-independent QKD (MDI-QKD), twin-field QKD (TF-QKD), continuous-variable QKD (CV-QKD) and device-independent QKD (DI-QKD) constrain chip metrics such as loss, modulation accuracy, state indistinguishability, phase stability, synchronization and security monitoring. It then compares planar lightwave circuit (PLC), silicon photonics, silicon nitride, thin-film lithium niobate, indium phosphide (InP) and heterogeneous platforms in terms of routing loss, modulation speed, stable interference, source integration and detector interfaces. Transmitter and receiver architectures, coherent detection, single-photon detection interfaces and on-chip monitoring are discussed as system-level building blocks. The review further analyses phase stability, packaging coupling, thermal management, polarization control, network coexistence and reliability, emphasizing that deployable QKD chips must remain calibratable and compatible with security models under realistic operation. Finally, system demonstrations, network deployment and practical security are discussed within a unified evaluation framework. Throughout, we argue that integration benefits QKD only when compact routing, stable interference, calibration access and manufacturable packaging jointly keep the device inside the assumptions of its security proof; accordingly, chip performance should be judged by mapped, calibratable security parameters rather than by integration density alone.
Twin-field quantum key distribution (TF-QKD) dramatically enhances the secure key rate (SKR) over inter-city distances through its square-root scaling. Further improvements in aggregate SKR can be achieved by wavelength-division multiplexing (WDM) of parallel QKD channels. However, direct implementation in TF-QKD poses significant challenges, as each wavelength channel requires an independent ultra-stable seed laser, narrow-linewidth transmitters, and optical phase-locked loops (OPLLs), which are not easily scalable. Here, we circumvent these limitations by employing two independent, integrated dissipative Kerr soliton (DKS) microcombs at Alice and Bob as multi-wavelength sources. High-visibility single-photon interference across all wavelength channels is achieved by stabilizing the frequencies of every comb line - requiring only the stabilization of the pump wavelength and repetition rates of the two microcombs. Based on this architecture, we perform a full TF-QKD experiment using the sending-or-not-sending protocol, achieving a total SKR of 1.57 Mbps over 201.1 km of fiber using 16 DWDM channels. This result represents more than an order-of-magnitude enhancement compared with single-wavelength TF-QKD at the same distance. Given that a single DKS comb can support over 100 coherent lines across the C-band, this approach offers a scalable pathway toward high-rate quantum key distribution over inter-city distances.