AsianScientist (Oct. 4, 2017) – The first quantum-secured video conference was held between President Bai Chunli of the Chinese Academy of Sciences in Beijing and President Anton Zeilinger of the Austria Academy of Sciences in Vienna. Held on September 29, 2017, it was the first real-world demonstration of intercontinental quantum communication.
Private and secure communications are fundamental human needs. In particular, with the exponential growth of internet use and e-commerce, it is of paramount importance to establish a secure network with global protection of data.
Traditional public key cryptography usually relies on the perceived computational intractability of certain mathematical functions. In contrast, quantum key distribution (QKD) uses individual light quanta (single photon) in quantum superposition states to guarantee unconditional security between distant parties.
Previously, the quantum communication distance had been limited to a few hundred kilometers due to the channel loss of fibers or terrestrial free space. A promising solution to this problem is exploiting 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 multi-institutional team of scientists from the Chinese Academy of Sciences, led by Professor Pan Jian-Wei, has spent more than ten years in developing a sophisticated satellite, named Micius, dedicated to quantum science experiments. Micius was successfully launched on 16 August 2016, from Jiuquan, China, orbiting at an altitude of approximately 500km. The satellite is equipped with three payloads: a decoy-state QKD transmitter, an entangled-photon source and a quantum teleportation receiver and analyzer.
Five ground stations were built in China to cooperate with the Micius satellite, located in Xinglong, Nanshan, Delingha, Lijiang and Ngari in Tibet.
Within a year after the launch, three key milestones central to a global-scale quantum internet have been achieved: satellite-to-ground decoy-state QKD with kilohertz rate over a distance of about 1,200 km; satellite-based entanglement distribution to two locations on the Earth separated by about 1,200 km, and ground-to-satellite quantum teleportation. The effective link efficiencies in the satellite-based QKD were measured to be around 20 orders of magnitudes larger than direct transmission through optical fibers at the same distance of 1,200 km.
The satellite-based QKD has now been combined with metropolitan quantum networks, where fibers are used to efficiently and conveniently to connect many users inside a city with a distance scale of 100 km. For example, the Xinglong station has now been connected to the metropolitan multi-node quantum network in Beijing via optical fibers.
Very recently, the largest fiber-based quantum communication backbone was also built in China by Pan’s team, linking Beijing to Shanghai with a fiber length of 2,000 km. The backbone uses decoy-state protocol QKD and achieves an all-pass secure key rate of 20 kbps. It is on trial for real-world applications by the Chinese government, banks, securities and insurance companies.
The Micius satellite can be further exploited as a trustful relay to conveniently connect any two points on the earth for high-security key exchange. Early this year, the Chinese team implemented satellite-to-ground QKD in Xinglong. After that, the secure keys were stored in the satellite for two hours until it reached Nanshan station near Urumqi, 2500 km from Beijing.
By performing another QKD between the satellite and Nanshan station, and using one-time-pad encoding, secure keys between Xinglong and Nanshan were then established. To test the robustness and versatility of the Micius, QKD from the satellite to the Graz ground station near Vienna was also carried out successfully in June 2017 as a collaboration between Pan and Zeilinger’s group. Similar experiments are also planned between China and Singapore, Italy, Germany, and Russia.
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Source: Chinese Academy of Sciences; Photo: Shutterstock.
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