A 15-user quantum secure direct communication network

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.

Automated summary

The study explores a QSDC network based on time-energy entanglement, with 15 users fully connected and sharing entangled states of high fidelity. Results show that QSDC can be maintained over 40 km of optical fiber with an information transmission rate above 1 Kbp/s.