China Focus: Chinese researchers develop system for quantum direct communication

BEIJING -- A team of Chinese researchers proposed a theory of one-way quantum direct communication and successfully developed a practical system, advancing quantum direct communication from a concept to the stage of practical application.

According to a study recently published in Science Advances, researchers from the Beijing Academy of Quantum Information Sciences, Tsinghua University, and North China University of Technology set a record in a standard optical fiber communication test with a transmission distance of 104.8 km. They achieved stable transmission at a rate of 2.38 kilobit per second for 168 consecutive hours.

Quantum direct communication was previously proposed by a team led by Long Guilu from Tsinghua University, one of the corresponding authors of the study paper. It enables secure communication by utilizing quantum states and features characteristics such as eavesdropping detection and prevention, compatibility with existing networks, simplified management processes, and covert transmission.

The core challenge in this field is achieving secure and reliable communication using quantum states with extremely low energy. These states are highly susceptible to interference in quantum channels characterized by high noise, high loss, and the risk of eavesdropping.

Previous research used bidirectional protocols, in which both communicating parties had to transmit quantum states back and forth. This resulted in significant system loss and severely limited communication performance improvement.

"In 2022, we set a world record for quantum direct communication over 100 kilometers, but the rate was only 0.5 bit per second, which allowed transmission of messages with very few characters," Long recalled.

He explained that one-way transmission could halve the distance of quantum state transmission, significantly reducing loss, which is the key to improving the performance of quantum direct communication.

The researchers developed high-noise and high-loss channel coding and other key technologies to propose a theoretical method for one-way quantum direct communication. They resolved the technical challenges and completed the development of the communication terminal.

The new system's communication rate has increased by 4,760 times compared with the one developed in 2022, significantly enhancing the performance of quantum direct communication.

According to Long, quantum direct communication systems are expected to be widely applied in fields with extremely high requirements for information security, such as government affairs and finance.

There are two main types of quantum secure communication. One is quantum key distribution, which uses quantum states to generate keys while transmitting encrypted information through classical communication. Its advantage is the high transmission rate.

The other is quantum direct communication, which directly transmits information using quantum states. In the event of eavesdropping, the quantum states can self-destruct to ensure information security.