Approaching the Key Rate Limit in Continuous-Variable Quantum Key Distribution Network

Abstract: A quantum key distribution network enables pairs of users to generate independent secret keys by leveraging the principles of quantum physics. For end-to-end secure communication, a user pair's secret key must remain secure against any third parties, including both external eavesdroppers and other network users. However, isolating a given user pair from the remaining users while maintaining a high key rate is challenging when all users are intrinsically coupled and correlated, particularly in continuous-variable networks. This results in either a low key rate, or incomplete end-to-end security. Here, we introduce a multi-user security framework, offering a general and comprehensive end-to-end key rate formula, against the collaboration of the other network users and eavesdropper. Building on this framework, we propose a multi-user protocol that achieves the theoretical upper limit in all practical deployments within a 100 km range. Applied to a three-node network, it achieves an Mbps-level per-user key rate and an overall network key rate reaching 90\% of the upper limit. The proposed solution supports scalable implementations using telecom-compatible components, while the method for obtaining the accessible information in the network is broadly applicable and can be extended to various multipartite quantum information systems.