Feihu Xu

We demonstrate a practical high-performance mode-pairing quantum key distribution system that is able to surpass the repeaterless key rate bound using commercial lasers. We propose a frequency tracking scheme to address phase fluctuations and a theoretical model to analyze the phase noise and optimize the system parameters. Our system achieves a secret key rate of 47.8 bit/s over 403 km standard fiber, which is 2.92 times of the repeaterless bound. Furthermore, we compare the performance between MP-QKD and no-phase-locking TF-QKD under various practical conditions and show that MP-QKD exhibits superior performance at short distances with low error rates, while TF-QKD is more advantageous for long distances with consistent error rates.

We report a quantum key distribution system that is able to generate key at a record high key rate of 115.8 Mb/s over 10-km standard fibre. This attributes to a high-efficiency multi-pixel superconducting nanowire detector, a low-error integrated transmitter, and a fast post-processing algorithm.

Quantum key distribution (QKD) can provide information-theoretic security governed by the law of quantum physics. Toward real-life applications, secret key rate is a key figure of merit of the QKD system. Here we demonstrate a 2.5-GHz polarization-encoding QKD system with an integrated silicon photonic transmitter that is able to generate a secret key rate of 2.42±0.04 Mbps over 101-km standard telecom fibers (19.6-dB loss). Such high rate attributes to the high clock-rate transmission and the ultra-low quantum bit error rate of 0.49%. The scalability, miniaturization and stability offered by silicon photonic technologies along with high-key-rate performance indicate that our system is a promising solution for large-scale deployment of QKD.

The fabrication of quantum key distribution (QKD) systems typically involves several parties, thus providing Eve with multiple opportunities to meddle with the devices. As a consequence, conventional hardware and/or software hacking attacks pose natural threats to the security of practical QKD. Fortunately, if the number of corrupted devices is limited, the security can be restored by using redundant apparatuses. Here, we report on the demonstration of a secure QKD setup with optical devices and classical post-processing units possibly controlled by an eavesdropper. We implement a 1.25 GHz chip-based measurement-device-independent QKD system secure against malicious devices on both the measurement and the users' sides. The secret key rate reaches 137 bps over a 24 dB channel loss. Our setup, benefiting from high clock rate, miniaturized transmitters and a cost-effective structure, provides a promising solution for widespread applications requiring uncompromising communication security.

Measurement-device-independent quantum key distribution (MDI-QKD) removes all detector side channels and enables secure QKD with an untrusted relay. It is suitable for building a star-type quantum access network, where the complicated and expensive measurement devices are placed in the central untrusted relay and each user requires only a low-cost transmitter, such as an integrated photonic chip. Here, we experimentally demonstrate a 1.25 GHz silicon photonic chip-based MDI-QKD system using polarization encoding. The photonic chip transmitters integrate the necessary encoding components for a standard QKD source. We implement random modulations of polarization states and decoy intensities, and demonstrate a finite-key secret rate of 31 bps over 36 dB channel loss (or 180 km standard fiber). This key rate is higher than state-of-the-art MDI-QKD experiments. The results show that silicon photonic chip-based MDI-QKD, benefiting from miniaturization, low-cost manufacture and compatibility with CMOS microelectronics, is a promising solution for future quantum secure networks.

Quantum key distribution (QKD) based on the fundamental laws of quantum physics can allow the distribution of secure keys between distant users. However, the imperfections in realistic devices may lead to potential security risks, which must be accurately characterized and considered in practical security analysis. High-speed optical modulators, being as one of the core components of practical QKD systems, can be used to prepare the required quantum states. Here, we find that optical modulators based on LiNbO3, including phase modulators and intensity modulators, are vulnerable to photorefractive effect caused by external light injection. By changing the power of external light, eavesdroppers can control the intensities of the prepared states, posing a potential threat to the security of QKD. We have experimentally demonstrated the influence of light injection on LiNbO3-based optical modulators and analyzed the security risks caused by the potential green light injection attack, along with the corresponding countermeasures.

We present an analysis for real-life implementations of measurement-device-independent quantum-key-distribution (MDI-QKD): a general system model, an optimized finite-decoy protocol and a rigorous finite-key analysis. This is of particular interest both to researchers hoping to demonstrate MDI-QKD and to others performing non-QKD experiments involving quantum interference.