BEIJING -- A group of Chinese researchers has achieved a new milestone in quantum communication by constructing a quantum secure direct communication (QSDC) network spanning about 300 kilometers, a practical inter-city application range.

The breakthrough, led by a team from Shanghai Jiao Tong University, maintains over 85 percent quantum state fidelity after transmission between pairs of users in the network, according to Science and Technology Daily.

Published in the journal Science Bulletin, the research addresses key limitations of quantum networks -- transmission distance and user capacity.

The team has developed a double-pumped, expandable, fully connected QSDC network that operates effectively in noisy environments. The system achieved a stable photon pair rate of 300 to 400 Hz, theoretically allowing for communication speeds of several bits per second.

The achievement came after a team from Beijing reported a record in February in a quantum direct communication test via standard optical fiber with a transmission distance of 104.8 km.

Quantum direct communication was previously proposed by researchers from Tsinghua University. It enables secure communication by utilizing quantum states and features such as eavesdropping detection and prevention, compatibility with existing networks, simplified management processes, and covert transmission.

The QSDC systems are expected to be widely applied in fields with extremely high information security requirements, such as finance.

The technique is complementary to another type of quantum secure communication: quantum key distribution (QKD). These technologies have the potential to form the backbone of a future global quantum internet.

In a world first, an international team led by Chinese scientists has successfully demonstrated real-time QKD communication across over 12,900 km between China and South Africa, utilizing a satellite.