AsianScientist (Jun. 18, 2020) – Chinese scientists have reported in Nature the exchange of a ‘secret key’ for encrypting and decrypting messages over a distance of 1,120 kilometers.
This milestone was possible thanks to the use of a satellite to extend the range of entanglement-based quantum key distribution, a theoretically secure communication technique.
Past attempts to directly distribute cryptographic keys between two ground users under real-world conditions have reached distances of only around 100 kilometers due to photon losses, which increase rapidly with distance. Trusted relays or ‘repeaters’ offer a way to extend the distance and avoid photon loss, but the relay stations introduce security risks.
In 2017, Professors Pan Jian-Wei and Peng Cheng-Zhi and colleagues first reported on entanglement success in the field, achieving point-to-point distribution of entangled photon pairs from a satellite to a ground station up to 1,200 kilometers away. Entangled photons are linked in such a way that, even when separated by long distances, outcomes of measurements of their quantum properties are perfectly correlated.
In their latest study, entangled photon pairs were distributed via the Micius satellite to two ground stations built 1,120 kilometers apart in Delingha and Nanshan in China.
“Here we demonstrate entanglement-based quantum key distribution between two ground stations separated by 1,120 kilometers at a finite secret-key rate of 0.12 bits per second, without the need for trusted relays,” the authors write.
Not only does an increase in efficiency and a reduction in error rates make it practical to use quantum entanglement for the relay of cryptographic keys, it is also resistant to attacks from side channels, representing a path towards a secure global quantum communication network.
“Our method not only increases the secure distance on the ground tenfold but also increases the practical security of quantum key distribution to an unprecedented level,” they conclude.
The article can be found at: Yin et al. (2020) Entanglement-based Secure Quantum Cryptography over 1,120 Kilometers.
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Source: Nature; Photo: NASA/Unsplash.
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