Quantum secure direct communication (QSDC) based on entanglement can directly transmit confidential information. However, the inability to simultaneously distinguish the four sets of encoded entangled states limits its practical application. Here, we explore a QSDC network based on time–energy entanglement and sum-frequency generation. In total,15 users are in a fully connected QSDC network, and the fidelity of the entangled state shared by any two users is >97%. The results show that when any two users are performing QSDC over 40 km of optical fiber, the fidelity of the entangled state shared by them is still >95%, and the rate of information transmission can be maintained above 1 Kbp/s. Our result demonstrates the feasibility of a proposed QSDC network and hence lays the foundation for the realization of satellite-based long-distance and global QSDC in the future.

基于纠缠的量子安全直接通信（QSDC）可以直接传输机密信息。然而，无法同时区分四组编码纠缠态限制了其实际应用。在这里，我们探索了一种基于时间能量纠缠和和频生成的 QSDC 网络。总共有15个用户处于全连接的QSDC网络中，任意两个用户共享的纠缠态保真度>97%。结果表明，当任意两个用户在40 km光纤上进行QSDC时，其共享的纠缠态保真度仍>95%，信息传输速率可保持在1 Kbp/s以上。我们的结果证明了所提出的QSDC网络的可行性，从而为未来实现星基远距离和全球QSDC奠定了基础。