Lai Zhou

Asynchronous measurement-device-independent quantum key distribution (AMDI-QKD) stands out for its experimental simplicity and high key rate generation. To simplify the system further, we devise a post-measurement compensation scheme to accurately estimate the mutual frequency offset between two compact lasers using just the announced quantum-signal detection results, thereby obviating the need for optical reference light. As a result, we demonstrate an AMDI-QKD system operating at 2.5 GHz and achieving secure key rates (SKRs) of 537 and 101 kbit/s at distances of 100 and 201 km, respectively. By leveraging ultra-stable lasers, we achieve the highest SKRs with measurement-device-independent security within the 100 to 400 km range.

Owing to its repeaterlike rate-loss scaling, twin-field quantum key distribution (TF-QKD) has repeatedly exhibited in the laboratory its superiority for secure communication over record fiber lengths. Field trials pose a new set of challenges, however, which must be addressed before the technology’s roll-out into the real world. Here, we verify in the field the viability of using independent optical frequency combs, installed at sites separated by a straight-line distance of 300 km, to achieve a versatile TF-QKD setup that has no need for optical frequency dissemination and thus enables an open and network-friendly fiber configuration. Our work represents an important step toward incorporation of long-haul fiber links into large quantum networks.

A post-measurement coincidence pairing technique is proposed to hold a repeater-like advantage and simultaneously mitigate the global phase tracking. Here, we demonstrate a practical asynchronous MDI-QKD system with an excellent long-term stability. With the use of two independent economical acetylene-stabilized fiber lasers, we achieve a secure key rate (SKR) of 14.65 bit/s over 504 km fiber, beating the absolute repeaterless bound by 1.18 times. Our work will advance the development of economical and efficient quantum network.

Quantum fingerprinting (QF) enables exponential reduction of information transmission in communication complexity tasks. Coherent QF implementations rely upon a direct optical link to maintain coherence between the users, violating the no-shared-randomness rule. Here, we propose and experimentally demonstrate a novel QF protocol based on asynchronous coincidence pairing from the interference results between independent, remotely prepared coherent fields. Over a length of 20 km telecom fiber, our setup has outperformed the classical algorithm, for the first time without being susceptible to shared randomness. This work advances the practical application of QF in communication complexity.

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.