Recently, the research team led by Academician Guo Guangcan from the University of Science and Technology of China (USTC) has successfully built the Xinghan-II multimode quantum repeater network in Hefei, Anhui Province, realizing matter entanglement over a distance of 14.5 kilometers. This technology is expected to become the fundamental technical route for future quantum networks. The relevant research findings were published online in the international academic journal Nature Photonics on May 7.

Quantum repeaters serve as a core technology for constructing the future quantum internet. Quantum signals suffer rapid attenuation when transmitted through optical fibers. Scientists use quantum repeaters to split long-distance channels into multiple short links, establish matter entanglement segment by segment and then connect them together, so as to overcome the exponential photon loss inside fiber channels.

Previously, quantum repeater protocols mainly fall into two categories: single-photon interference and two-photon interference. The single-photon interference scheme only requires detection of one photon at the intermediate station and delivers a high entanglement generation rate, yet it is sensitive to channel phase jitter and limited by entanglement fidelity. By contrast, the two-photon interference scheme requires simultaneous detection of a photon pair, offering high fidelity but at a low rate. The trade-off between rate and fidelity has long been a fundamental bottleneck restricting the performance and practical deployment of quantum repeaters.

To tackle this dilemma, researchers including Li Chuanfeng, Zhou Zongquan and Huang Yunfeng from Academician Guo Guangcan’s team at USTC originally proposed a multimode quantum repeater protocol based on time measurement. Instead of requiring a photon pair to arrive at the intermediate station simultaneously, the protocol allows the two photons to arrive one after another. Researchers can herald entanglement by precisely measuring their time-of-arrival difference, and realize on-demand readout of arbitrarily delayed entangled photons via multimode quantum memory. This protocol successfully combines the high rate of single-photon interference and the high fidelity of two-photon interference, enabling high-speed, high-fidelity entanglement distribution and native compatibility with existing fiber-optic network infrastructure.

The multimode Xinghan-II quantum repeater network realizes matter entanglement between nodes separated by 14.5 kilometers.

The team constructed the Xinghan-II multimode quantum repeater network in Hefei. The system achieves an entanglement fidelity of 78.6%, with a straight-line separation of 14.5 kilometers between the two quantum memories. Reviewers of Nature Photonics commented that this protocol resolves the longstanding conflict between rate and fidelity in quantum repeater schemes, and its entanglement distribution rate is over a hundred times higher than that of previous metropolitan-scale quantum repeaters.

Artistic schematic of the Xinghan-II multimode quantum repeater.

According to Li Chuanfeng, this work realizes the longest-distance matter entanglement reported publicly to date. It marks the advancement of the team’s earlier Xinghan-I multimode quantum repeater from laboratory proof-of-principle verification to practical demonstration within an urban network environment, demonstrating that multimode multiplexing technology is poised to become the foundational technical route for future quantum networks.

Article link: https://www.nature.com/articles/s41566-026-01911-5

(English translation provided by AI)