Yu-Shuo Lu

Quantum fingerprinting (QF) enables exponential reduction of information transmission in communication complexity tasks. Coherent QF implementations rely upon a direct optical link to maintain coherence between the users, violating the no-shared-randomness rule. Here, we propose and experimentally demonstrate a novel QF protocol based on asynchronous coincidence pairing from the interference results between independent, remotely prepared coherent fields. Over a length of 20 km telecom fiber, our setup has outperformed the classical algorithm, for the first time without being susceptible to shared randomness. This work advances the practical application of QF in communication complexity.

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.