Beijing Institute of Quantum has made breakthroughs in real-world dual-field quantum key distribution
The dual-field quantum key distribution protocol has the advantage that the key rate decreases with the square root scale of the channel transmittance, and is a new direction for ultra-long-distance quantum key distribution. Recently, Yuan Zhiliang, chief scientist of the Beijing Institute of Quantum Information Science, and Italian and British scientists combined quantum metrology technology with key requirements in the field of quantum communication, and successfully demonstrated the precise transmission of coherent phases on a 206-kilometer fiber-optic transmission line in three places in Italy. , which provides an efficient and practical solution for dual-field quantum key distribution. On January 10, 2022, the related work was published in Nature Communications under the title "Coherent phase transfer for real-world twin-field quantum key distribution".
The code rate of traditional quantum key distribution (QKD) decreases by about 100 times per 100 kilometers of fiber distance, and will decrease by 100 million times after 400 kilometers, and the remaining code rate becomes negligible. The two-field protocol published in 2018 [Nature 557, 400 (2018)] reversed this situation, and the same 400 km code rate has only 10,000 times of attenuation, instead of the previous 100 million times. This is because both sides of the communication are transmitters, and their optical signals meet in the middle of the fiber channel, and only receive half of the channel loss. Due to the huge advantages in long-distance communication, the dual-field protocol has been quickly adopted by many international teams, and the optical fiber transmission distance has exceeded 600 kilometers in both the laboratory and the field.
The difficulty of the double-field experiment is that after the optical signals of the two communication parties pass through hundreds of kilometers of optical fiber, the mutual phase must remain stable. The existing solution is laser frequency cloning plus real-time phase feedback. In order to ensure that the phase stability is not affected by the laser frequency drift, the lengths of the two independent hundreds of kilometers of optical paths on both sides of the communication must be consistent. In actual deployment, additional optical fibers need to be used for length compensation, which is very inconvenient.
Yuan Zhiliang, chief scientist of Beijing Institute of Quantum, and his collaborators used dual-band phase stabilization technology to introduce optical frequency comb technology in quantum metrology into the field of quantum communication for the first time, which solved the requirement for phase stabilization of dual-field protocols, thus significantly improving dual-band phase stabilization. The practicality of field QKD. In the Italian quantum trunk network, Bardonecchia, Torino and Santhia have successfully demonstrated the precise transmission of coherent phases on the 206-kilometer fiber-optic transmission line. A difference of 22 kilometers. The ultra-stable frequency transmission technology in quantum metrology is expected to become a key technology supporting distributed quantum sensor networks and quantum key distribution networks in the future.
Yuan Zhiliang participated in the design of the experimental program.
Figure 1: a) Map of the experimental site. b) The Italian Quantum Backbone map, the red part is the experimental route. c) Experimental setup.
Article link:https://www.nature.com/articles/s41467-021-27808-1
