Fengyu Lu

Measurement-device-independent quantum key distribution (MDIQKD) can resist all attacks on the detection devices, but there are still some security issues related to the source side. One possible solution is to use the passive protocol to eliminate the side channels introduced by active modulators at the source. Recently, a fully passive QKD protocol was proposed that could simultaneously achieve passive encoding and passive decoy-state modulation using linear optics. In this work, we propose a fully passive MDIQKD scheme that can protect the system from both side channels of source modulators and attacks on the measurement devices, which can significantly improve the implementation security of the QKD systems. We provide a specific passive encoding strategy and a method for decoy-state analysis, followed by simulation results for the secure key rate in the asymptotic scenario. Our work offers a feasible way to improve the implementation security of QKD systems and serves as a reference for achieving passive QKD schemes using realistic devices.

Measurement-device-independent quantum key distribution (MDI-QKD) is considered one of the most promising protocols due to its high performance and security. To implement the MDI-QKD system in practice, clock synchronization is a crucial step to correctly generate the secret keys. However, as practical applications advance, the complexity and cost of synchronization have become significant challenges for the implementation of MDI-QKD. In this study, we introduce a qubit-based synchronization algorithm specifically designed for MDI-QKD. By utilizing the property of Hong-Ou-Mandel interference, we achieve clock synchronization between parties of MDI-QKD without the need for additional hardware. The cost-effectiveness and simplicity of this approach are expected to significantly facilitate the practical deployment of MDI-QKD.

High-speed quantum key distribution (QKD) systems have achieved repetition frequencies above gigahertz through advanced technologies and devices, laying an important foundation for the deployment of high-key-rate QKD system. However, these advancements may introduce unknown security loopholes into the QKD system. For an eavesdropper Eve, it is challenging to exploit these security loopholes performing the intercept-and-resend attacks due to the limited time window under the high repetition frequency. Here, we propose a muted attack that does not require intercept-and-resend operation, which is applicable to high-speed QKD systems. By exploiting the security loophole of the width discriminator on the single photon avalanche detector (SPAD), Eve can control whether Bob’s detector is capable of receiving photons from Alice, allowing her to learn nearly all the keys. Additionally, we verified through experimental tests that Eve only needs to match the period of the hacking pulse with the dead time of the SPAD and ensure that each pulse contains hundreds of photons. This study reveals the security loopholes introduced by the state-of-the-art devices in high-speed QKD systems.