A few days ago, Pan Jianwei, Bao Xiaohui, Zhang Qiang, etc. of the University of Science and Technology of China, for the first time, used single photon interference to establish entanglement between independent storage nodes, and based on this, built the world's first entanglement based metro three node quantum network. This work has improved the distance of the real quantum entanglement network from tens of meters to tens of kilometers by three orders of magnitude, laying a scientific and technical foundation for the subsequent development of quantum network applications such as blind quantum computing, distributed quantum computing, and quantum enhanced long baseline interference. Relevant research results were published in the international academic journal Nature.
Constructing quantum networks through remote transmission of quantum states is the basic element of large-scale quantum information processing. Based on quantum network, it is possible to realize wide area quantum key distribution, distributed quantum computing and quantum sensing, which forms the technical basis of the future "quantum internet". At present, the quantum key network based on single photon transmission has developed maturely. For further quantum network applications such as distributed quantum computing and distributed quantum sensing, it is necessary to use quantum relay technology to construct quantum entanglement between long-distance quantum memories, and on this basis, connect various quantum information processing nodes through wide area quantum teleportation.
The main challenge of establishing entanglement between independent quantum memories separated at a long distance is how to control the single photon phase. The entanglement scheme based on single photon interference has significant advantages in the entanglement rate, but the experiment is very difficult. Fine phase jitter caused by the control laser of quantum storage, frequency conversion pump laser, long fiber channel, etc. in the entanglement process will lead to the final generation of decoherence of entanglement. In order to solve this problem, the team designed and developed a very sophisticated phase control scheme: first, suppress and control the laser linewidth by stabilizing the frequency of the ultrastable cavity; secondly, construct the phase correlation between the read and write lasers through the optical phase-locked loop; finally, construct the phase correlation between the two nodes through remote time-sharing phase comparison. Using the above phase control technology and quantum frequency conversion, the team successfully realized entanglement between quantum memories that are thousands of meters away. On this basis, the research team has constructed the first metro three node quantum entanglement network in the world, which can establish entanglement between any two quantum memory nodes.
The reviewers of Nature magazine commented that "their achievements have opened a new chapter in the study of quantum Internet" and "paved the way for future large-scale quantum networks". Reporter Ding Yiming
