Feng-Yu Lu

Recent studies have revealed critical source-side vulnerabilities in practical quantum key distribution systems. Despite their demonstrated risks, these threats receive limited attention in both academic discussions and practical implementations. To highlight the urgency of addressing source-side vulnerabilities, we will report two widespread but overlooked loopholes: the induced-photorefractive effect and the pattern effect, including a report of the first-time system-level attack against a running MDI-QKD. Except for the attack, we will also report countermeasures against the loopholes, including a fully-passive QKD architecture resistant to encoding side-channels and a correlation-immune QKD protocol mitigating the pattern effect. These works provide essential insights and solutions for advancing the practical deployment of secure QKD systems.

Intensity correlations between neighboring pulses open a prevalent yet often overlooked security loophole in decoy-state quantum key distribution (QKD). As a solution, we present and experimentally demonstrate an intensity-correlation-tolerant QKD protocol that mitigates the negative effect that this phenomenon has on the secret key rate according to existing security analyses. Compared to previous approaches, our method significantly enhances the robustness against correlations, notably improving both the maximum transmission distances and the achievable secret key rates across different scenarios. By relaxing constraints on correlation parameters, our protocol enables practical devices to counter intensity correlations. We experimentally demonstrate this first practical solution that directly overcomes this security vulnerability, establish the feasibility and efficacy of our proposal, taking a major step towards loophole-free and high-performance QKD.