The fridge-sized satellite Jinan-1, pictured before its launch in 2022. Credit: Y. Li et al./Nature
Researchers have broken a distance record in quantum communication by sending a secret encryption key nearly 13,000 km from China to South Africa, using a cheap, lightweight ‘microsatellite’.
The satellite was able to send pulses of laser light, put into special quantum states, from a rooftop in Beijing to another at Stellenbosch University near Cape Town. The pulses formed a quantum key that was used to encrypt two images — one of China’s Great Wall and one showing part of Stellenbosch’s campus. The feat, a kind of encryption known as quantum key distribution (QKD), is a step towards being able to send ultra-secure messages between any two locations, however distant. It was described in Nature on 19 March1.
Quantum network is step towards ultrasecure internet
The satellite, called Jinan-1, is ten times lighter, 45 times cheaper and much more efficient than its predecessor, Micius, which launched in 2016, says Jian-Wei Pan, a quantum physicist at the University of Science and Technology in Hefei, China, who led the work.
Pan’s team also shrank the ground-station receiver from 13,000 kg to a portable 100 kg . “We want to improve the technology from proof-of-principle to really practical and useful,” he says. Pan adds that his team is working with the Beijing-based telecommunications firm China Telecom to launch four more microsatellites for commercial applications in 2026.
“This is another milestone in the development of a global QKD network,” says Alexander Ling, a quantum physicist at the National University of Singapore. The satellite is “a significant step forward” in deploying this kind of encryption in real time, adds Katanya Kuntz, a quantum physicist and co-founder of Qubo Consulting, a firm based in Calgary, Canada, that helps other companies to adopt quantum technologies.
Researchers encrypted these two images using a quantum key, which they transmitted from China to South Africa.Credit: University of Science and Technology of China
Uncrackable codes
Physicists think that future quantum computers will be able to break many types of encryption, but techniques such as QKD provide “very strong assurance that a future quantum computer cannot read confidential communications”, says Ling.
QKD is already used by banks and governments to transmit keys over fibre optics. But these cables absorb photons, limiting the distance over which the signal can travel. Because light is absorbed at a much lower rate when travelling through the air than in a fiber-optic cable, satellites could act as a relay to send secret keys between two locations almost anywhere on the planet.
Quantum encryption rests on the idea that if two parties share a secret key, they can scramble a message so that only they can decode it.
Pan’s experiment involved sending pulses of laser light that are each in a ‘superposition’, where they exist at once in two quantum states, representing 1 or 0. By comparing the settings that the sender uses with those used by the receiver to measure the pulses, the two parties can work out a selection of measured 1s or 0s to use as a secure key. If an eavesdropper tries to intercept the message, this disturbs the quantum states and creates noise, revealing that the key has been compromised.
