USTC demonstrates successful satellite-enabled quantum key distribution

Quantum secure communication uses quantum mechanisms to secure classical (non-quantum) communication and is fundamental to national information security and socioeconomic development. One of the primary methods of quantum secure communication is quantum key distribution (QKD), which enables two parties to share an encryption key—typically over an insecure channel—while ensuring that any eavesdropping attempt can be detected. Although fiber-based QKD networks have achieved regional deployment, their long-distance use is limited by signal loss and coverage constraints.

Now, however, Chinese researchers have made a major breakthrough by developing the world's first quantum microsatellite and demonstrating real-time QKD between the satellite and multiple compact, mobile ground stations. In collaboration with researchers from South Africa—and using the satellite as a trusted relay—they demonstrated successful secure key sharing and encrypted communication between Beijing and Stellenbosch—two cities separated by 12,900 km.

The study, published in Nature on March 19, was conducted by PAN Jianwei, PENG Chengzhi, and LIAO Shengkai from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), in collaboration with researchers from the Jinan Institute of Quantum Technology, the Shanghai Institute of Technical Physics (CAS), the Innovation Academy for Microsatellites (CAS), and Stellenbosch University in South Africa.

Satellite-based systems using free-space channel offer a viable alternative to fiber networks, potentially enabling QKD on a global scale. USTC pioneered this field with the Micius quantum satellite, achieving the world's first demonstration of space-to-ground QKD. This capability was later integrated with the fiber-based Beijing–Shanghai backbone, creating a space–ground quantum secure communication network. 

For practical applications, however, compact payloads and portable ground stations are essential for widespread deployment and swift implementation. In particular, small-size payloads can be mounted on satellites of various sizes to form a quantum satellite internet constellation capable of providing global services.

Using these insights, the USTC team led the development of several key technologies, including miniaturized decoy-state QKD light sources, real-time key distillation and encrypted communication, and high-precision tracking. On July 27, 2022, Jinan-1, the world's first quantum microsatellite, was successfully launched. The research teams also developed compact optical ground stations, reducing the weight by two orders of magnitude to approximately 100 kg. This lightweight design allows for rapid deployment in different locations, significantly increasing flexibility and practicality.

Jinan-1 established optical links with multiple optical ground stations—in Jinan, Hefei, Nanshan, Wuhan, Beijing, and Shanghai—as well as with a station in Stellenbosch, South Africa. The satellite transmitted approximately 250 million quantum photons per second. During each satellite pass, the system generated up to 1 Mbits of secure keys. It later demonstrated secure key sharing and encrypted communication between Beijing and Stellenbosch.

This study lays a solid foundation for the deployment of a constellation of quantum microsatellites, provides crucial technical support for large-scale quantum communication networks, and holds promise for the global deployment of the quantum internet. 

A Nature reviewer praised it as "a technically impressive accomplishment," marking "considerable progress towards trusted-node constellations for widespread satellite QKD services." The reviewer also noted that "it demonstrates the maturity of satellite QKD technology and represents a milestone for the realization of a satellite constellation for quantum and classical communication."