The world’s first integrated quantum communications network has been developed by Chinese scientists, integrating more than 700 ground-based optical fibers with two ground-to-satellite connections to achieve quantum key delivery for users throughout the country over a total distance of 4,600 kilometers.
In Nature, the team, led by Jianwei Pan, Yuao Chen and Chengzhi Peng of the Chinese University of Science and Technology in Hefei, reports on their recent progress towards a global, realistic application for future communications of such a network.
Quantum communication is considered unhackable, unlike traditional encryption, making it the future of protected transmission of information for banks, power grids, and other fields.
Quantum key distribution (QKD), which uses the quantum states of particles – such as photons – to form a sequence of zeros and ones, is at the heart of quantum communications, with any eavesdropping between the sender and receiver altering this chain, or key, and being instantly detected. For transmissions over several hundred kilometers, with high stability but substantial channel loss, the most popular QKD technology to date uses optical fibers.
Free space between satellites and ground stations for transmissions over thousands of kilometers is used by another significant QKD technology.
China launched the world’s first quantum communications satellite (QUESS, or Mozi/Micius) in 2016 and achieved QKD with two 2600 km apart ground stations.
In 2017, for QKD between Beijing and Shanghai, a fiber-optic network of over 2,000 km was completed.
The ground-based fiber network and satellite-ground connections have been incorporated using trusted relays to serve more than 150 industrial users across China, including state and local banks, regional power grids, and websites for e-government. “Our work shows that quantum communication technology is sufficiently mature for practical large-scale applications,” said Jianwei Pan, a professor at USTC. Similarly, if national quantum networks from different countries are combined and if universities, organizations and companies join hands to standardize the related protocols, hardware, etc., a global quantum communication network can be constructed, he added.
The team has thoroughly evaluated and enhanced the efficiency of the different parts of the interconnected network in recent years.
For example, the satellite-to-ground QKD now has an average key generation rate of 47.8 kilobits per second, which is 40 times higher than the previous rate, with an improved clock rate and a more powerful QKD protocol.
The researchers also increased the ground-based QKD record by using a new technology called Twin-Field QKD to more than 500 km (TF-QKD).
Next, the team will continue to expand its network in China and with its Austria, Italy, Russia and Canada foreign partners.
Low-cost QKD small satellites and ground-based receivers will also be built, as well as medium and high-earth orbit satellites to reach QKD at altitudes of 10,000 kilometers.
Reference: Nature, January 6, 2021.
The work was funded by the China National Commission for Growth and Reform, the Shandong, Anhui and Shanghai provincial/municipal governments, the China Banking Regulatory Commission, the Chinese Academy of Sciences, the China Ministry of Science and Technology, and the China National Science Foundation.