Chinese mini-satellite transmits quantum key over 12,000 km
A Chinese microsatellite has transmitted tap-proof quantum keys over a distance of 12,000 kilometers to a mobile ground station.
Symbolic image of a small satellite in orbit
(Image: Andrey Armyagov/Shutterstock.com)
Encryption is not just for spies or dissidents – Encryption algorithms are found in every browser session, every internet purchase and payment process and every patch that is installed. However, classic cryptography is essentially based on mathematical "one-way functions". Although two prime numbers can be easily multiplied together, it is very difficult to calculate back to the prime numbers from the result. However, this assumption will no longer apply once practical quantum computers are available. Then one-way functions can also be cracked.
Tap-proof with quantum cryptography
In quantum cryptography, each session is theoretically encrypted with a new key. To do this, the key is first transmitted on the secure quantum channel. This is protected against eavesdropping – at least in theory. This is because the transmission uses the quantum superposition of states to transfer data. If the bits are branched off in between, this quantum superposition is lost, which means that the sender and receiver know that they are being intercepted.
Theoretically secure in this context means that because every quantum encryption must be implemented in both hardware and software, there are of course also gaps that can be exploited by attackers. However, quantum hacking is much more complex than normal eavesdropping.
Limited range
Quantum cryptography can be implemented in many different ways. Commercial use is still limited to niches. There are two reasons for this. Firstly, the data transmission rate is relatively low. In practice, therefore, only the cryptographic key is exchanged via the quantum connection. The encrypted data is then transmitted conventionally. Secondly, the range of quantum cryptographic connections via optical fiber is relatively short – around 100 kilometers. An intermediate station must then be set up.
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Quantum satellite vs. microsatellite
However, Chinese researchers were able to show back in 2016 that such connections can also be established over very long distances using a satellite. In cooperation with the Institute of Quantum Optics and Quantum Information (IQOQI) in Vienna, they were able to establish an intercontinental quantum connection for the first time using the Micius satellite. In the satellite, a high-intensity ultraviolet laser shone into a special crystal. This created two "entangled" photons with half the energy from one light particle. One photon was sent to Beijing, the other to Vienna. If the polarization of one of the particles was measured in Vienna, this also determined the polarization of the second particle in Beijing – and vice versa.
However, not only the satellite but also the ground station were large, heavy, very complex and expensive. The team led by Jian-Wei Pan from the University of Science and Technology of China, who had already worked on Micius, therefore developed a quantum microsatellite and a portable ground station. The satellite, named Jinan-1, was launched into a sun-synchronous orbit 500 kilometers above the Earth in July 2022. It has a payload of just 23 kilograms. The portable ground station weighs around 100 kilograms.
The technical progress was made possible by greater integration of the components, but also by technical simplification. Unlike Micius, Jinan-1 does not work with entangled photons, but uses a simpler protocol. During a single overflight (the period during which the satellite is above the local horizon), the satellite was able to exchange up to 1.07 million bits of secret keys with the portable ground stations.
At the same time as exchanging the quantum key, the satellite can also establish the encrypted data connection with the base via another laser. The researchers now describe the technical details in a paper in Nature(pre-publication of August 20, 2024 on ArXiv). By 2027 at the latest, the Chinese want to have at least four of these quantum mini-satellites in space, which will then also exchange encrypted data with each other. They also want to place a satellite in geostationary orbit.
International race
In the Nature podcast, Jian-Wei Pan was emphatically open and explained that his working group would like to cooperate with others. In fact, the Chinese are working together with the Russians. In the West, however, secure quantum communication in space has long since become a question of technical sovereignty. However, it is obviously being pursued with varying degrees of urgency. The Europeans want to launch the first quantum satellite into space in 2026. In the USA, the technology is still at an early stage.
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This article first appeared on t3n.de .
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