记录量子安全通信距离

Researchers in China have demonstrated quantum secure communications running over a record length of over 100km to provide intercity links

The team, led by Haoran Zhang from the State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics at Tsinghua University in Beijing, China, used a new technique called Quantum secure direct communication (QSDC) rather than quantum key distribution (QKD), which negotiates a secure key using quantum technology.

Rapid progress has been made in quantum secure direct communication in recent years. For practical application, it is important to improve the performances, such as the secure information rate and the communication distance. Researchers from Austria and China demonstrated the first quantum secure video call using QKD back in 2017.

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QSDC and QKD perform different tasks. QSDC securely and reliably transmits information through a quantum channel with both noise and eavesdropping. Compared to classical communication where reliable transmission of information over a noisy channel is concerned, QSDC has the additional capability to ensure its security using the properties of quantum information carriers. As QSDC is a kind of communication, it is flexible to construct networks using techniques such as packet switching, and the researchers see potential for 6G wireless communication as well.

Using QSDC increased the secrecy capacity greatly by achieving an ultra-low quantum bit error rate of <0.1%, an order of magnitude smaller than that of existing systems. The 50 MHz system can be easily upgraded to over 1 GHz using current on-the-shelf technology and can tolerate more channel loss, from 5.1 dB, which is about 28.3 km in fibre previously to 18.4 dB, which corresponds to fibre length of 102.2 km.

The experiment, published in Nature, shows that intercity quantum secure direct communication through fibre is feasible with present-day technology.