The research team of the University of Science and Technology of China and their collaborators achieved the first real-time satellite-to-ground quantum key distribution between quantum micro-nano satellites and miniaturized and mobile ground stations in the world, and realized key sharing and data relay between China and South Africa, which are more than 12,900 kilometers apart.The international academic journal Nature published relevant research results online on March 20.

Stellenbosch University in South Africa implements the Southern Hemisphere’s first quantum satellite link. The microsatellite Jinan-1 was launched into low Earth orbit and transmitted security keys via a portable ground station installed on the roof of the University of Stellenbosch's engineering building. The experiment will be conducted in October 2024. Image source: IgnusDreyer

Quantum secure communication based on quantum key distribution is the only communication method that can achieve "information theory provable" security so far. At present, metropolitan intercity quantum communication based on optical fiber links has matured and has been initially applied. In order to achieve long-distance and even global quantum secure communication, it is necessary to overcome the inherent loss of optical fiber and the difficulty of global coverage.

Researchers from the University of Science and Technology of China, including Pan Jianwei, Peng Chengzhi, and Liao Shengkai, collaborated with a number of scientific research institutions to tackle key problems and carried out a series of groundbreaking research in satellite-to-ground quantum communications. For example, in terms of "stars", it has made breakthroughs in a series of key technologies and developed the world's first quantum micro-nano satellite "Jinan-1"; in terms of "ground", it has further developed a miniaturized ground station system, significantly reducing its weight to facilitate rapid deployment.

Dr. Yaseera Ismail, a quantum physicist at the Department of Physics at the University of Stellenbosch in South Africa, led the South African team on the project. Image source: StefanEls

In this research work, quantum micro-nano satellites established optical links with ground optical stations such as Jinan, Hefei, Beijing, and Stellenbosch, South Africa, to achieve real-time satellite-to-ground quantum key distribution experiments. The spaceborne quantum decoy state light source sends an average of 250 million signal photons per second, combined with uplink and downlink optical communications to achieve real-time extraction of keys; and using satellites as trusted relays, the research team further realized key sharing and data relay between the Beijing Station on the ground and the Stellenbosch Station in South Africa.

This research work lays a solid foundation for the future launch of multiple micro-nano satellites to build a "quantum constellation". It not only provides key technical support for the construction of large-scale practical quantum communication networks, but also opens up a new development path for the global deployment of quantum Internet.

The reviewer of "Nature" magazine believes that this achievement "demonstrates the maturity of satellite quantum key distribution technology and represents a milestone in the realization of quantum and classical communication satellite constellations."