Quantum communication network technology based on quantum relay makes a major breakthrough

Recently, China has made a major breakthrough in the quantum communication network technology based on quantum relays, and achieved quantum entanglement between the memories of optical fibers separated by 50 kilometers for the first time in the world. Scientists from the University of Science and Technology of China, Jinan Institute of Quantum Technology, Shanghai Institute of Microsystems and Information Technology, Chinese Academy of Sciences and other units have cooperated through high-brightness light and atom entanglement sources, low-noise and efficient single-photon frequency conversion and remote single-photon precision interference and other technologies , Successfully entangled two quantum memories separated by 50 kilometers of optical fiber, which laid the foundation for the construction of a quantum network based on quantum relays.

At present, the free space channel of satellites is widely used internationally to achieve wide-area large-scale coverage, and then to achieve urban and inter-city ground coverage through fiber optic networks. Limited to the problem of exponential failure during long-distance transmission of optical signals, the point-to-point ground safety communication distance is only on the order of 100 kilometers. In order to solve the problem of optical signal attenuation in the optical fiber and achieve long-distance ground safety communication, previously tried to use segmented transmission and cascaded through quantum relay technology. The farthest fiber quantum relay transmission is only on the order of kilometers.

The research team used the ring cavity enhancement technology to improve the coupling between single photons and atomic ensemble, and optimize the optical path transmission efficiency, increasing the brightness of the previous light and atom entanglement by an order of magnitude. Subsequently, the self-developed periodically polarized lithium niobate waveguide converted the optical wavelength of the memory from near infrared (795 nm) to the communication band (1342 nm). After 50 kilometers of optical fiber, it only attenuated to 3%. The optical signal in the 50 km fiber will be attenuated to three parts per billion, an increase of 16 orders of magnitude; through the design and implementation of a dual phase locking scheme, remote single photon interference is achieved, which successfully causes the transmission through the 50 km fiber The optical path difference is controlled at about 50nm. The research team finally integrated the above technologies to achieve two-node entanglement transmitted via 50 kilometers of optical fiber, and demonstrated two-node entanglement via 22 kilometers of field fiber. This achievement has received wide attention from internationally renowned scientific media including the US Science magazine, the MIT Science and Technology Review, the US Science News, and the British New Scientist. It is believed that this work makes the realization of the quantum Internet more One step closer.