Qin Wang

The measurement-device-independent quantum key distribution (MDI-QKD) protocol plays an important role in quantum communications due to its high level of security and practicability. It can be immune to all side-channel attacks directed on the detecting devices. However, the protocol still contains strict requirements during state preparation in most existing MDI-QKD schemes, e.g., perfect state preparation or perfectly characterized sources, which are very hard to realize in practice. In this letter, we investigate uncharacterized MDI-QKD by utilizing a three-state method, greatly reducing the finite-size effect. The only requirement for state preparation is that the state are prepared in a bidimensional Hilbert space. Furthermore, a proof-of-principle demonstration over a 170 km transmission distance is achieved, representing the longest transmission distance under the same security level on record.

Nowadays, quantum key distribution (QKD) is gradually moving from the laboratory to practical applications. However, imperfections of practical QKD devices inevitably cause side-channel information leakage, and thus hinder its practical implementations. Among them, there is one critical vulnerability that is often neglected, i.e., leakage of electromagnetic field (LEMF). In this work, we carry out investigations on the impact of LEMF by using a phase-coding QKD system as an example, and give corresponding security analysis. Simulation results show that LEMF may cause fatal security issues if it is ignored. Finally, to address this security issue, we provide corresponding solutions.

Quantum key distribution (QKD) serves as a cornerstone of secure quantum communication, providing unconditional security grounded in quantum mechanics. While trusted-node networks have facilitated early QKD deployment, their vulnerability to node compromise underscores the need for untrusted-node architectures. Measurement-device -independent QKD (MDI-QKD) and twin-field QKD (TF-QKD) have emerged as leading candidates, addressing security vulnerabilities and extending transmission distances. Despite the wide adoptions in various fiber scaling, no integrated implementation of these two protocols has been demonstrated to date. Here, we present a multi-protocol system that seamlessly integrates TF-QKD and MDI-QKD into one untrusted-node-based architecture. Utilizing an efficient phase estimation method based on asymmetric interferometers, we convert twin-field global phase tracking to relative phase calibration, allowing near continuous running of both protocols. Experiments demonstrate secure key rates for sending -or-not-sending QKD and MDI-QKD protocol over fiber distances of 710 km and 501 km in the asymptotic case, respectively. The results align with theoretical simulations and show the ability to surpass the absolute repeaterless key capacity. Our work offers an unified framework for deploying multi-protocol QKD networks, laying the foundation for scalable quantum infrastructures that can meet a wide range of security and performance needs.

At present, the performance of quantum digital signatures (QDSs) is limited by key generation protocols (e.g., BB84 or measurement-device-independent protocols), which are fundamentally limited in terms of channel capacity. Fortunately, the recently proposed twin-field quantum key distribution can overcome this limit. Here, we for the first time propose a twin-field QDS (TF-QDS) protocol and give a corresponding security analysis. It can not only possess the highest security among all existing QDS protocols, but also exhibit outstanding performance in terms of both signature rates and secure transmission distances. Therefore, our work represents another step towards practical implementation of QDSs.