Zeng-Bin Chen

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.