Huihong Yuan

We demonstrate a scalable integrated photonic network for twin-field quantum key distribution (TF-QKD). The architecture employs a star topology, utilizing a server-side Si3N4 optical microcomb and 20 monolithically integrated InP transmitter chips. Coherent comb lines are used to seed client lasers, enabling wavelength-division multiplexing and ensuring stable interference. Sequential pairwise TF-QKD is performed across ten channels among 20 users, with each channel surpassing the repeaterless secret-key-capacity bound at a distance of 370 km. This yields an overall networking capability of 3,700 km. Wafer-scale chip reproducibility confirms the platform’s practicability for building large-scale quantum communication networks. Furthermore, we demonstrate a design utilizing a broadly tunable on-chip laser, which is expected to cover the entire telecommunication C-band. This approach enables dozens of wavelength channels to operate in parallel, thereby scaling the network capacity up to hundred-user-level.

Twin-field quantum key distribution (TF-QKD) promises long-distance quantum networks, but practical deployment demands compact and phase-stable hardware--requirements well matched by thin-film lithium niobate (TFLN) electro-optic photonics. Here, we propose and demonstrate a coherent dual-band TFLN chip to enable system miniaturization and an open-channel architecture. EO-comb generation and quantum signal encoding are monolithically integrated on a single chip. Coherent on-chip comb lines serve as channel references for fast and robust phase stabilization. Using this integrated platform, we demonstrate TF-QKD over a 508 km fiber link, achieving a quantum bit error rate below 0.5% and a secure key rate that surpasses the linear rate limit by a factor of 2.67. These results establish integrated TFLN photonics as a scalable and robust solution for practical, long-distance quantum communication.

Photonic integration in quantum communication holds significant potential for miniaturization and enabling commercial applications. Among various platforms, thin-film lithium niobate (TFLN) stands out due to its exceptional combination of high electro-optical efficiency, low propagation loss, and compact footprint. Here, we demonstrate a 2.5 GHz chip-to-chip fully integrated quantum key distribution (QKD) system based on a TFLN platform, which incorporates high-speed dual-polarization time-bin phase encoding and decoding functionalities. We achieve an extremely low quantum bit error rate of 0.53% and a secret key rate exceeding 10 Mbps over 25 km fiber spools. The design of cascaded Mach–Zehnder modulators effectively suppresses the patterning effect in high speed QKD. Notably, the TFLN chips used in both the transmitter and receiver share a similar architecture, highlighting the potential for creating a homogeneous transceiver. This work paves the way for high-speed, miniaturized QKD systems based on the lithium niobate integrated platform.

Nonlocal correlation represents the key feature of quantum mechanics, which is exploited as a resource in quantum information processing. However, the loophole issues hamper the practical applications. We report the first demonstration of steering nonlocality with detection loophole closed at telecommunication wavelengths. In this endeavour, we design and fabricate a low-loss silicon chip for efficient entanglement generation, and further apply direct modulation technique to its optical pump to eliminate phase-encoding loss at the steering side. The newly proposed phase-encoding measurement setting adapts to an ultra fast modulation rate (GHz). Consequently, we build a fiber-optic setup that can overcome the detection efficiency that is required by quantum steering with multiple measurement settings. Our setup provides an immediate platform for exploring applications based on steering nonlocality, especially for quantum communication.

We propose and demonstrate an upgraded quantum key distribution protocol based on time-bin entanglement source with access control through introducing phase randomization. The upgraded source can protect users from memory attacks at a negligible cost.