China's experiment in quantum communication brings Beijing closer to creating a hack-proof network
China's hack-proof quantum communication technology is "primarily ready" for practical use after a 4,600km network was put through two years of experimental service, researchers announced.
Since early 2019, the integrated space-to-ground quantum communication network has proved its "practical security", and "maintained long-term reliability and stability" through ground fibres and achieved an adequately fast link with a satellite, according to a paper by the researchers published in the science journal Nature on Wednesday.
It is a milestone for China in its mission to develop a secure communications network free from hacking, and also provides an opportunity for China to take a lead role in quantum technology internationally.
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The Chinese scientists have been drafting international standards for relevant technologies with the International Organization for Standardization and other groups.
"Such a prototype of integrated space-to-ground network has laid a scientific and technological foundation for a secure quantum communication global network in the future," said Science and Technology Daily, the official newspaper of the Ministry of Science and Technology.
In theory, the laws of physics ensure hacking attempts on the messages transmitted through quantum entanglement-based channels cause a physical change allowing them to be discovered and an alert raised. When fully developed, quantum communication can be applied in fields such as finance, defence, government administration and electronic information, according to scientists.
In the Nature article the team led by Professor Pan Jianwei from the University of Science and Technology of China summarised their work and reviewed the operation of the network that was used by an unprecedented number of users distributed over a wide area.
This network consisted of the Micius satellite - the world's first quantum communication satellite launched in 2016 - and more than 700 optical fibres covering 2,000km (1,240 miles) and connecting 32 nodes across four provinces and three municipalities in China. It was completed in 2017 and has realised communication up to a distance of 4,600km.
The integrated space-to-ground quantum communication network "maintained long-term reliability and stability" through ground fibres and a speedy enough link with the satellite, according to Chinese researchers. Image: Weibo alt=The integrated space-to-ground quantum communication network "maintained long-term reliability and stability" through ground fibres and a speedy enough link with the satellite, according to Chinese researchers. Image: Weibo
It was the world's first quantum communication experiment of this scale and as such the network on trial applied the technology of quantum key distribution (QKD). QKD is a secure communication and information transfer technology that encrypts based on the phenomenon of "quantum entanglement", in which a pair of entangled particles remain connected and affect each other even when separated by great distances.
It created links between the ground nodes as well as high-speed satellite-to-ground free-space QKD links with the satellite.
"Using a trusted relay structure, the fibre network on the ground covers more than 2,000km, provides practical security against the imperfections of realistic devices, and maintains long-term reliability and stability," the Chinese team reported in Nature.
The satellite-to-ground QKD became more than 40 times higher than previous technologies in its "secret-key" rate, at 47.8 kilobits per second, the article said.
The satellite-to-ground QKD channel loss was comparable to the loss between a geostationary satellite and the ground. It could be feasible to construct more versatile and ultralong quantum links via geosynchronous satellites, the article said.
More than 150 users from industries, including finance, electric power and the government took part in the trial and aspects of the experiment. The State Grid's Beijing headquarters sent encrypted data to its branch in far western Xinjiang through the QKD channel.
The researchers have developed portable ground stations - weighing about 100kg (220 pounds) - to connect with the Micius satellite as well as other ground stations overseas. Their goal is to further miniaturise transmission stations to eventually be carried by a person. Meanwhile, transmission modules that could be loaded on to other satellites were also ready.
In December, a team of Chinese physicists, also led by Pan, said they had built a quantum computer one trillion times faster than the most powerful supercomputer, claiming "quantum supremacy".
This article originally appeared on the South China Morning Post (SCMP).
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