Quantum Communication Goes Intercontinental

Combining the Micius satellite’s capabilities with metropolitan quantum networks, Chinese scientists have securely transmitted images and video between China and Austria.

AsianScientist (Feb. 1, 2018) – Scientists in China have successfully used the Micius satellite to conduct intercontinental quantum communication. Their results have been published in Physical Review Letters.

Traditional public key cryptography relies on the computational intractability of certain mathematical functions to protect the information being exchanged between senders and recipients. In contrast, quantum key distribution (QKD) uses individual ‘packets’ of light (photons) in quantum superposition states to guarantee unconditional security between distant parties.

Previously, quantum communication was limited to a few hundred kilometers due to the loss of signal within optical fibers, or because of interference from terrestrial free space. A promising solution to these problems exploits satellite and space-based links, which can conveniently connect two remote points on the Earth with greatly reduced channel loss because most of the photons’ propagation path is in empty space, with negligible loss and decoherence.

A cross-disciplinary and multi-institutional team of scientists from the Chinese Academy of Sciences, led by Professor Pan Jian-Wei, has spent more than a decade developing a sophisticated satellite, Micius, dedicated to quantum science experiments. The Micius was launched in August 2016 and orbits the Earth at an altitude of about 500 km. Five ground stations are being built in China to cooperate with the Micius satellite, located in Xinglong (near Beijing), Nanshan (near Urumqi), Delingha, Lijiang and Ngari in Tibet.

The Micius satellite was successfully used for QKD between itself and the Graz ground station near Vienna in mid-2017. In this study, the satellite also established QKD with ground stations in China via metropolitan quantum networks, whose nodes are connected by optical fibers spanning a distance of approximately 100 km.

With this latest development, upon request from the ground stations, Micius can now function as a trusted relay, creating a secret key between China and Europe at locations separated by 7,600 km on Earth. To test this capability, a picture of Micius (with a size of 5.34 kilobytes) was transmitted from Beijing to Vienna, and a picture of Schrödinger (with a size of 4.9 kilobytes) was sent from Vienna to Beijing, over the space-based link.

An intercontinental video conference was also held between the Chinese Academy of Sciences and the Austria Academy of Sciences, employing the Advanced Encryption Standard (AES)-128 protocol that refreshed the 128-bit seed keys every second. The video conference lasted for 75 minutes, with a total data transmission of an estimated two gigabytes.

The article can be found at: Liao et al. (2018) Satellite-Relayed Intercontinental Quantum Network.

Source: University of Science and Technology of China.
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