Stellenbosch University (SU) Physics Department researchers, working in collaboration with Chinese colleagues at the University of Science and Technology of China, have successfully established the longest intercontinental ultra-secure quantum communications satellite link yet achieved. The link, via Chinese low Earth orbit quantum microsatellite Jinan-1, spans 12 900 km. It is also the first ever quantum satellite communication link established in the southern hemisphere.

“International and national collaborations are essential to drive cutting-edge research and push scientific boundaries,” highlighted SU research team leader Dr Yaseera Ismail. “Implementing the first quantum satellite link in the southern hemisphere is an outstanding achievement for South Africa, demonstrating the significant potential to develop a thriving quantum ecosystem.”

In the demonstration, encrypted images were transmitted between ground stations in China and South Africa. Encryption was achieved by using Quantum Key Distribution (QKD), which creates secure quantum cryptographic keys, which were used to create one-time pad encryption.

(One-time pad is an encryption system that is considered unbreakable, regardless of the method of information transmission, whether quantum, digital, radio, or written. Basically, each message is sent using a unique encryption key, which is not reused for any subsequent messages, so each message is encrypted differently. Naturally, both sender and receiver have to have the same encryption keys, and in the same order.) 

Quantum technology, by its very nature, adds even more security to one-time pad. QKD uses single photons to encode and transmit the secure keys. And single photons cannot be intercepted, copied or measured without changing their quantum states, meaning that they can’t be “read”, so that even the most sophisticated and capable eavesdropper can’t determine what the key is.

“This successful demonstration of quantum satellite technology firmly positions South Africa as a significant player in the rapidly evolving global quantum technology ecosystem,” affirmed National Institute for Theoretical and Computational Sciences director and SU School of Data Science and Computational Thinking Quantum Computing Professor Francesco Petruccione. “Collaborations such as this accelerate scientific breakthroughs, build local expertise, and enable translating advanced quantum research into tangible technological solutions.”

“This breakthrough underscores the importance of supporting and investing in the basic sciences such as quantum computing,” stressed SU Deputy Vice-Chancellor for Research, Innovation and Post-Graduate Studies Professor Sibusiso Moyo. “We are proud that our researchers are pushing the frontiers of science. This work is in line with SU’s Vision 2040, to be Africa’s leading research-intensive university recognised for its excellence and advancing knowledge in service of society.”

China is a world-leading centre, perhaps the world-leader, in quantum communications technology. The country already has a 2 000 km fibre-based terrestrial quantum network, which links 32 nodes in major cities, from Beijing to Shanghai. A previous intercontinental satellite-based quantum link was established between China and Austria in 2017, which spanned 7 600 km.

In South Africa, Petruccione has led ground-breaking quantum communication projects, including the development of a fibre-optic quantum communication network in Durban, KwaZulu-Natal province, which is one of the first in the world. SU will soon launch its Centre for Quantum Science and Technology, to reinforce the country’s leading role in quantum research and innovation.