Quantum communication: the “unbreakable” satellite network from China to South Africa - Analysis

A team of Chinese and South African scientists has made the world's longest quantum satellite link, marking a milestone in secure communications and the advancement of QKD technology for protecting information

Chinese and South African scientists have succeeded in creating the world's longest intercontinental quantum satellite link, stretching 12,900 kilometers between China and South Africa. This discovery, using China's Jinan-1 micro-nano satellite in low Earth orbit, represents the first quantum satellite communication link established in the Southern Hemisphere. The research results were published in Nature, documenting a significant advance in secure global communications technology. The journal's reviewer called the new link "a technically impressive achievement" that "demonstrates the maturity of QKD satellite technology and represents a milestone in the development of quantum and classical satellite constellations." 

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Quantum communication offers a secure means of transferring information, exploiting components of quantum mechanics in a way that prevents eavesdropping. This scientific achievement, therefore, lays the foundation for a future financial, national defense, military, or other intercontinental communications service that is impossible to hack. 

Technical results 

The international team, led by experts from the University of Science and Technology of China, demonstrated real-time quantum key generation through Quantum Key Distribution (QKD) technology. This process allowed images transmitted between ground stations in China and South Africa to be securely encrypted using one-time pad encryption, a method considered mathematically unbreakable if implemented correctly.

The ground station at Stellenbosch University, South Africa, achieved an exceptional key generation rate of 1.07 million secure bits during a single satellite pass, attributed to the region's ideal environmental conditions, including clear skies and low atmospheric humidity. These conditions minimize photon scattering and absorption, critical factors for the success of quantum communication.

The Jinan-1 quantum microsatellite in low Earth orbit was the intermediary of this quantum link. The satellite's specialized quantum communications payload allows it to generate and distribute quantum keys to ground stations, creating a hacker-proof connection despite the great distance between continents.

“We have multiplexed satellite-to-ground two-way optical communication with quantum communication, enabling key distillation and secure real-time communication,” the scientists say. The compact quantum payload can be easily assembled on existing space stations or small satellites, paving the way for a quantum and classical network based on a constellation of satellites for widespread real-world applications. The microsatellite, in fact, weighs approximately 23 kilograms and the portable ground station approximately 100 kilograms, with reductions of over 1 and 2 orders of magnitude respectively compared to traditional ones.

In summary, Chinese scientists have achieved remarkable success in designing, developing and launching 500 kbit packages, which represent a compromise between a lightweight microsatellite with a payload weight of 22.7 kg, significantly lighter than conventional satellites. On land, transmission occurred thanks to portable 100 kg class OGS positioned in the Chinese urban areas of Jinan, Hefei, Wuhan and Nanshan. 

The security of quantum communication

The security of quantum communication derives from the fundamental principles of quantum mechanics. In quantum key distribution, single photons encode and transmit secure cryptographic keys. According to the principles of quantum physics, any attempt to intercept, copy or measure these photons would inevitably alter their quantum states, immediately warning legitimate users of potential eavesdropping.

Quantum communication, therefore, offers a secure means of transferring information, exploiting components of quantum mechanics in a way that prevents eavesdropping.

One type of quantum communication is quantum key distribution, a cryptographic protocol that relies on the generation and distribution of a secret key shared between parties to secure communication.

This inherent security feature makes quantum communication particularly resistant to computational attacks, including those potentially enabled by future quantum computers. The single-photon nature of the transmission creates a physically secure channel that remains protected even against adversaries with significant computational resources.

The research group

The collaborative research initiative brought together scientists from Stellenbosch University in South Africa and the University of Science and Technology of China (USTC). The Chinese research team was led by Professor Juan Yin, who previously played a crucial role in the development of China's first quantum satellite, the Better, developed to begin long-distance quantum transmissions. In 2017, this satellite demonstrated a 7,600 km intercontinental quantum link between China and Austria.

On the South African side, Dr Yaseera Ismail led the research team at the Department of Physics at Stellenbosch University, serving as the principal investigator responsible for establishing the quantum satellite link. Professor Francesco Petruccione, professor of quantum computing in the School of Data Science and Computational Thinking and director of the National Institute for Theoretical and Computational Sciences (NITheCS) at Stellenbosch University, has been instrumental in the development of quantum communications infrastructure in South Africa.

Juan Yin, deputy of the National People's Congress (NPC), scientist and professor of experimental physics at the University of Science and Technology of China, announced the discovery at the annual plenary meeting of the NPC in Beijing in March.

“It is the first time that this type of secure quantum key distribution experiment has been implemented in the Southern Hemisphere,” said Yin. The feat was made possible by “achieving secure real-time communication between low-cost quantum micro-nano satellites and mobile ground stations.”

The development of quantum infrastructure in China

According to the draft economic and social development plan issued by the National Development and Reform Commission during the annual plenary session, the quantum technology for satellite communications is one of the industries of the future” which Beijing will particularly focus on in 2025.

In the global race to develop quantum communications, Chinese scientists have made several advances in recent years, including using the Micius satellite and a network of ground stations to establish secure communications between Russia and China.

China intends to exploit its quantum satellites to establish secure communications between emerging markets in the Brics block, which also includes South Africa.

The Chinese leadership in quantum communication technology 

Beijing is currently leading the global development of quantum communication technology under the leadership of famous quantum physicist Professor Jian-Wei Pan. The country has built a vast quantum infrastructure with a 2,000km terrestrial fiber optic network connecting 32 reliable nodes in major cities from Beijing to Shanghai.

The physicist Jianwei, known as the “father of quantum physics” who helped build the Micius satellite, said the country aims to launch an ultra-secure global communications service by 2027 after completing its constellation of quantum satellites.

Existing Chinese infrastructure has provided critical technical expertise and support systems for the intercontinental quantum satellite link with South Africa. China's continued investment in quantum technology has positioned it as a leader in this emerging field, with applications ranging from secure communications to computing and sensing.

In his speech at the NPC, Yin made several recommendations on how Beijing should improve quantum research and development to become an undisputed world leader in the field, including increasing investment in basic research and promoting a development pipeline from basic to applied research. He also added that China's policy to attract and develop skilled talent should be optimized to better train experts in the field of quantum computing technology and to help attract top international scientists to China. Since science and technology is "still a global issue", China should promote high-level international exchanges and cooperation in quantum technology, Yin said. “Helping formulate international quantum standards could help China master the ‘power of speech’ for a future global quantum communications network.”