Chinese researchers have made a crucial breakthrough in quantum communication, boosting the future development of secure satellite-based long-distance and global quantum communication networks.
The research team comprising Chen Xianfeng from Shanghai Jiaotong University and Li Yuanhua from Jiangxi Normal University constructed a 15-user quantum secure direct communication (QSDC) network. The network enabled the direct transmission of confidential information among the users connected by the network for the first time.
Their study titled “A 15-user quantum secure direct communication network” was published in the scientific journal Light: Science and Application.
Quantum communication is a cutting-edge information technology that promises ultra-secure transmission of data. Scientists have developed many models for such transmission, including quantum key distribution (QKD), quantum teleportation, and QSDC.
Based on QKD technology, many different types of quantum communication networks have been proposed. However, such communication networks only transmit the key but do not directly transmit information.
In contrast, QSDC sends secret information directly over a secure quantum channel. Any attack of QSDC results in only a random number, and cannot obtain any useful information from it, according to the researchers.
“Therefore, QSDC has simple communication steps and reduces potential security loopholes, and offers higher security guarantees,” they wrote in the study. 
Composition of the quantum network. /Illustration from the study
In recent years, the experimental QSDC has been developed significantly. “However, the inability to simultaneously distinguish the four sets of encoded orthogonal entangled states in entanglement-based QSDC protocols limits its practical application,” researchers said. “Experimental demonstration of QSDC is badly required,” they added.
To achieve wide applications of QSDC, they constructed the fully connected entanglement-based QSDC network, including five subnets, with 15 users.
“The fidelity of the entangled state shared by any two users is higher than 97 percent,” the researchers wrote.
“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 over 95 percent, and the rate of information transmission can be maintained above 1 Kbp/s,” they said. “The result demonstrates the feasibility of a proposed QSDC network.”
