China News Service, Beijing, June 15 (Reporter Sun Zifa) Following the realization of the safe distribution of 500-kilometer point-to-point optical fiber quantum keys in the laboratory, relying on the trusted relay site to build a 2,000-kilometer optical fiber quantum secret communication backbone network "Beijing-Shanghai Main Line", to After the quantum satellite as a trusted relay to achieve about 7600 kilometers of intercontinental quantum secret communication, the team of academician Pan Jianwei of the University of Science and Technology of China once again achieved a new scientific breakthrough-using the world’s first quantum scientific experimental satellite "Mozi" to achieve entanglement-based Relay thousands of kilometers of quantum secret communications.
Research team composed of Academician Pan Jianwei and colleagues Peng Chengzhi and Professor Yin Juan, together with Artur Ekert of Oxford University in the United Kingdom and Academician Wang Jianyu of Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Microsatellite Innovation Research Institute, Optoelectronic Technology Research Relevant teams, such as the Mozi, used the quantum satellites to achieve quantum key distribution based on entanglement for thousands of kilometers for the first time in the world. This experimental result not only increases the spatial distance of the previous groundless relay quantum secret communication by an order of magnitude, but also ensures that even in the extreme cases where the satellite is attacked and controlled, secure quantum secret communication can still be achieved.
Academician Pan Jianwei of the University of Science and Technology of China introduced the latest quantum communication research breakthroughs to the media through video connection. Photograph by Sun Zifa
A paper on the major breakthrough in the field of quantum communication applications for realizing secure and long-distance quantum secret communications under this realistic condition was published online in the international authoritative academic journal Nature in the late evening of the 15th Beijing time. Reviewers praised the research work as "an important step towards building a global quantum key distribution network or even a quantum Internet" and believed that "the experimental implementation of a long-distance entangled quantum key distribution protocol that does not rely on trusted relays is a milestone" And, as Gilles Brassard, one of the creators of quantum cryptography, said, "This will eventually realize the dream of all cryptographers for thousands of years."
On the eve of the publication of the paper, the Science Communication Bureau of the Chinese Academy of Sciences and Springer Nature Group jointly held a video connection introduction meeting on the afternoon of the 15th. Pan Jianwei said that quantum communication provides an unconditionally safe communication method in principle, but to move from the laboratory to a wide range of applications, two major challenges need to be solved, namely the security problem under real conditions and the long-distance transmission problem. Through the efforts of the international academic community for more than 30 years, the safety distance of the on-site fiber-to-point quantum key distribution on the spot has reached the order of one hundred kilometers. At the current level of technology, the use of trusted relays can effectively extend the distance of quantum communication. For example, the world's first quantum secret communication Beijing-Shanghai trunk line passes through 32 relay nodes and runs through an inter-city optical fiber quantum network with a total length of about 2000 kilometers; The "Mozi" quantum satellite is used as a relay to further expand the intercontinental distance to 7600 kilometers in the free space channel.
Pan Jianwei pointed out that although trusted relays limit the security risks of the entire line in traditional communication methods to a limited range of relay nodes, the safety of relay nodes still needs to be guaranteed. The best solution to achieve long-distance secure quantum communication is to combine quantum relay and entanglement-based quantum key distribution. In principle, quantum relay can be used to achieve long-distance quantum entanglement distribution, but the practical quantum relay still needs For a long time, using satellites as the source of quantum entanglement and distributing the entanglement directly in remote places through free space channels provides a feasible way for realizing quantum secret communication based on entanglement under the existing technical conditions.
The latest breakthrough scientific research achievements of the research team is based on the preliminary experimental work and technical accumulation of the "Mozi" quantum satellite, through the upgrade of the ground telescope's main optics and the rear optical path, to achieve unilateral double and double bilateral reception efficiency Promotion. During the transit of the "Mozi" quantum satellite, it simultaneously established optical links with two ground stations, Urumqi Nanshan Station and Qinghai Delingha Station, at a speed of 2 pairs per second between two stations over 1120 kilometers above the ground. Quantum entanglement, and then generate a key at a final code rate of 0.12 bits per second under a finite code length. In the experiment, the scientific research personnel carefully designed and protected the ground receiving light path and the single photon detector to ensure that the generated key does not depend on the trusted relay and ensure realistic security.
Pan Jianwei also confessed that the scientific breakthrough of the paper published this time is only a demonstration of the principle of science, and it is still far from practical application. It is expected that in six or seven years, combined with the development and progress of quantum entangled source technology and satellite technology, in the future, 1 billion pairs of entangled photons can be generated through satellites in the future, and the final key code rate will be increased to tens of bits per second or single Transit of tens of thousands of bits can lay the foundation for the large-scale application of entangled non-relay long-distance quantum secret communication.
He revealed that the efficient satellite-ground link collection technology developed based on this latest breakthrough can reduce the quantum satellite load weight from hundreds of kilograms to less than tens of kilograms, and reduce the weight of the ground receiving system from more than 10 tons to 100. About kilograms, to achieve the miniaturization and transportability of the receiving system. This will greatly reduce the development and launch costs of quantum communication satellites, and lay a solid foundation for the future scale and commercial application of satellite quantum communications. (Finish)