China builds First space-ground quantum communication network

Moreover, Moreover, The quantum communication distance is limited to a few hundred kilometers, due to the channel loss of fibers or terrestrial free space.

The first quantum-safe video conference  held today. Between President Chunli Bai of the Chinese Academy of Sciences in Beijing and President Anton Zeilinger of the Austria Academy of Sciences in Vienna. As the first real-world demonstration of intercontinental quantum communication.

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Micius satellite

A solution to this problem is exploiting satellite and space-based link. 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. In contrast, quantum key distribution (QKD) uses individual light quanta single photon in quantum superposition states to guarantee unconditional security between distant parties.

A cross-disciplinary multi-institutional team of scientists from the Chinese Academy of Sciences, led by Professor Jian-Wei Pan, has spent more than ten years in developing a sophisticated satellite, named Micius. Dedicated for quantum science experiments  successfully launched on 16th August 2016, from Jiuquan, China, orbiting at an altitude of 500 km.

The satellite equipped with three payloads a decoy-state QKD transmitter, an entangled-photon source, and a quantum teleportation receiver and analyzer. Five ground stations are built in China to cooperate with the Micius satellite, located in Xinglong near Beijing, 40°23"45.12""N, 117°34"38.85""E, altitude 890m), Nanshan (near Urumqi, 43°28"31.66""N, 87°10"36.07""E, altitude 2028m), Delingha (37°22"44.43""N, 97°43"37.01"E, altitude 3153m), Lijiang (26°41"38.15""N, 100°1"45.55""E, altitude 3233m), and Ngari in Tibet (32°19"30.07""N, 80°1"34.18""E, altitude 5047m).

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Within a year after the launch, three key milestones as central to a global-scale quantum internet achieved satellite-to-ground decoy-state QKD with kHz rate over a distance of 1200 km (Liao et al. 2017, Nature 549, 43); satellite-based entanglement distribution to two locations on the Earth separated by ~1200 km and Bell test (Yin et al. 2017, Science 356, 1140), and ground-to-satellite quantum teleportation (Ren et al. 2017, Nature 549, 70). However, the effective link efficiencies in the satellite-based QKD measured to 20 orders of magnitudes. Larger than direct transmission through optical fibers at the same length at 1200 km.

Xinglong station in china now connected to the metropolitan multi-node quantum network in Beijing via optical fibers.

The satellite-based QKD has combined with metropolitan quantum networks. In which fibers used efficiently and conveniently. To connect many users inside a city with a distance scale of 100 km. The Xinglong station has now connected to the metropolitan multi-node quantum network in Beijing via optical fibers.

Very recently, the largest fiber-based quantum communication backbone built in China. By Professor Pan"s team, linking Beijing to Shanghai going through Jinan and Hefei, and 32 trustful relays with a fiber length of 2000 km. The backbone uses decoy-state protocol QKD and achieves an all-pass secure key rate of 20 kbps. Moreover, it is on trial for real-world applications by government, banks, securities and insurance companies.

The Micius satellite 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 has implemented satellite-to-ground QKD in Xinglong. After that, the secure keys stored in the satellite for 2 hours. Until it reached Nanshan station near Urumqi by a distance of 2500 km from Beijing. By performing another QKD between the satellite and Nanshan station. Using one-time-pad encoding, secure key between Xinglong and Nanshan established.

In addition, to test the robustness and versatility of the Micius. QKD from the satellite to Graz ground station near Vienna has also carried out successfully this June. As a collaboration between Professor Pan and Professor Anton Zeilinger"s group.

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Upon request, future similar experiments are also planned between China and Singapore, Italy, Germany, and Russia.