Quantum communication breakthrough: China sends 'hack-proof' cipher from space

Chinese scientists have successfully sent an unbreakable code from its quantum satellite to the Earth in what is considered to be a major breakthrough in the development of a "hack-proof" global quantum communication network.

The satellite, called Quantum Experiments at Space Scale (QUESS), is claimed to be the world's first of its kind, and was sent into a sun-synchronous orbit on Aug. 16, 2016. Nicknamed "Micius," the satellite weighs over 600 kilograms and is situated nearly 500 kilometres above the Earth's surface.

According to scientists, Micius sent quantum keys to ground stations in Xinglong, in China's northern Hebei province, and in Nanshan near Urumqi, the capital of northwest China's Xinjiang Uygur region.

The communication from the satellite to ground stations happened over a distance of up to 1,200 kilometres. Scientists claimed that this quantum key transmission was up to 20 orders of magnitudes more efficient than that expected using an optical fibre of the same length.

"Satellite-based QKD promises to establish a global-scale quantum network by exploiting the negligible photon loss and decoherence in the empty out space," scientists said in a related study, published in the journal Nature, on Thursday. "The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission paves the way to global-scale quantum networks."

Pan Jianwei, lead scientist of QUESS and an academician of the Chinese Academy of Sciences (CAS), said that the quantum satellite provides an experiment window of about 10 minutes when it flies over China. Within this short time period, Micius can generate and send as many as 300 kbit secure keys, enough to make a highly secure phone call or transmit a large amount of bank data.

It was in June when Chinese scientists managed to transmit "entangled" photons -- tiny particles acting in sync -- over long distances from space to Earth for the first time. The scientists claimed at the time that they had successfully beamed about six billion photon pairs per second to separate ground telescopes that were about 1,200 kilometres apart.

"Satellite-based quantum key distribution can be linked to metropolitan quantum networks where fibres are sufficient and convenient to connect numerous users within a city over 100 km. We can thus envision a space-ground integrated quantum network, enabling quantum cryptography - most likely the first commercial application of quantum information - useful at a global scale," Xinhua quoted Pan as saying.