Yuan-Mei Xie

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.

Quantum network allows for multi-user applications that bring advantages that are unattainable with a classical network. A crucial application of quantum networks is quantum conference key agreement (QCKA), which enables remote nodes to efficiently share information-theoretic secure group key by leveraging the laws of quantum mechanics. However, the efficacy of QCKA is hampered by inherent losses in optical fibers and the increasing number of users, impacting both bit rate and range. Here we introduce multi-field (MF) QCKA scheme, where independently sets of phase-randomized optical fields are generated at remote locations, later combining them at a central measuring station. Employing the post-measurement pairing technique, we post-select optical fields with the same random phase, establishing Greenberger-Horne-Zeilinger correlations to distill a secret conference key. This method ensures that the communication efficiency of MF-QCKA scales linearly with communication transmittance and remains independent of the number of users. Using components similar to twin-field quantum key distribution, MF-QCKA can be implemented in a practial and scalable fashion. For three-user scenario, our protocol can overcome the performance limitation of QCKA without quantum memory in the finite regime. By mitigating the impact of optical fiber losses and accommodating a larger user base, MF-QCKA protocol represents a promising step forward in the realm of quantum communication, ensuring secure and efficient parallel communication in complex quantum networks.

Quantum conference key agreement facilitates the secure communication among multiple parties through multipartite entanglement, which is anticipated as an important cryptographic primitive for future quantum networks. However, the experimental complexity and low efficiency associated with synchronous detection of multipartite entanglement state have significantly hindered the practical application. Here, we propose a measurement-device-independent conference key agreement protocol utilizing asynchronous Greenberger-Horne-Zeilinger state measurement and achieve a linear scaling of the conference key rate among multiple parties, which has the similar performance with the single-repeater scheme in quantum network. The asynchronous measurement strategy bypasses the necessity for complex global phase-locking technologies, concurrently extending the intercity transmission distance with composable security in finite key regime. Our work also showcases the advantages of the asynchronous pairing concept in multiparty quantum entanglement.