Quantum key distribution (QKD) enable different users to generate secure keys. It is one of the crucial technologies in modern quantum secure communication. With the practical applications of quantum secure communication, how to realize QKDs among multiple users in an effective and simple way has become the focus of researchers. In this work, we propose a layered, fully connected QKD network architecture without trusted node for large number of users. Using flexible wavelength division multiplexing/demultiplexing and space division multiplexing, entanglement resources are flexibly distributed to users in the network. Based on this architecture, we experimentally realize a 40-user fully connected quantum entanglement distribution network based on a broadband energy-time entangled quantum light source. Using symmetric entanglement-based dispersive optics QKD, we generate secure keys between any two users in the network. Without trusted node, this is the entanglement-based QKD network experiment with the largest number of users to date. The theoretical analysis and experimental results show its potential on developing quantum communication networks with large user numbers.

This paper was accepted by PhotoniX (Volume 3, Article number 2; https://doi.org/10.1186/s43074-022-00048-2; DOI: 10.1186/s43074-022-00048-2) and on-line published in Jan. 24th, 2022. The co-first authors of this paper are Dr. Xu Liu and Ph.D candidate Jingyuan Liu. The corresponding author of this paper is Prof. Wei Zhang.