According to the University of Science and Technology of China (USTC), important new progress has been made in the research of quantum communication and quantum networks. Taking advantage of high-quality entangled photon pair sources, scientists have realized long-distance quantum entanglement purification through 11 km fiber for the first time, with purification efficiency more than 6,000 times higher than the international level. 

The work was conducted by a research group headed by Li Chuanfeng and Liu Biheng as part of Academician Guo Guangcan's team at USTC, in cooperation with researchers from Nanjing University of Posts and Telecommunications. The results were published in the internationally renowned journal Physical Review Letters on Jan. 8.

High-quality long-distance entanglement is essential for both quantum communication and scalable quantum networks. The previous significant entanglement purification experiments require two pairs of low-quality entangled states and were demonstrated in tabletop. 

The USTC researchers proposed a high-efficiency and long-distance entanglement purification using only one pair of hyperentangled state. In their studies, one pair of polarization spatial-mode hyperentanglement was distributed over 11 km multicore fiber (noisy channel). 

The results show that after purification, the fidelity of polarization entanglement increased from 0.771 to 0.887. Moreover, by using one pair of hyperentanglement, the total purification efficiency can be estimated as 6.6×103 times the experiment using two pairs of entangled states with spontaneous parametric down-conversion sources.

The research results provide important technical support for the realization of highly efficient quantum relay in the future.

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