On February 6, it was learned from the University of Science and Technology of China (USTC) that a team led by Pan Jianwei, Wang Ye, Bao Xiaohui, Zhang Qiang, and Wan Yong, in collaboration with numerous industry experts, has achieved a significant breakthrough in the research of scalable quantum networks. For the first time internationally, they have constructed a fundamental module for scalable quantum repeaters, making long-distance quantum networks a realistic possibility. Simultaneously, they have achieved long-distance, high-fidelity entanglement between single-atom nodes and, based on this, have broken the 100-kilometer barrier for device-independent quantum key distribution (QKD) transmission for the first time. The related findings were published in the international academic journals Nature and Science on February 6.

The ultimate goal of quantum information science is to build efficient and secure quantum networks. The fundamental element for constructing quantum networks is long-distance deterministic quantum entanglement distribution. Based on quantum entanglement, not only can secure transmission of classical information be achieved through quantum key distribution, but quantum teleportation also provides the only effective pathway for the interaction of quantum information between quantum computers and users. The inherent loss in optical fibers causes the transmission efficiency of quantum entanglement to decay exponentially with distance, posing the greatest challenge in building scalable quantum networks. The quantum repeater scheme is an effective solution to address optical fiber transmission losses. Using this scheme for entanglement distribution over a distance of 1,000 kilometers in optical fibers can improve efficiency by a factor of 10^18 compared to direct transmission in optical fibers. However, in the past, the lifetime of quantum entanglement was far shorter than the time required to generate entanglement, making it impossible to achieve effective entanglement connections and limiting the scalability of quantum repeaters.

To address this challenge, the research team developed long-lived trapped-ion quantum memories, high-efficiency ion-photon communication interfaces, and high-fidelity single-photon entanglement protocols. For the first time, they achieved long-lived quantum entanglement, with the entanglement lifetime significantly exceeding the time required to establish entanglement. This successfully constructed the fundamental module for scalable quantum repeaters, making long-distance quantum networks possible.

Furthermore, based on scalable quantum repeater technology, the research team achieved long-distance, high-fidelity entanglement between two rubidium atoms. On this basis, they broke the 100-kilometer barrier for device-independent quantum key distribution for the first time, surpassing the previous best international experimental results by more than two orders of magnitude and greatly advancing the practical application of this technology.

The researchers stated that these breakthroughs mark the transition of fiber-based quantum networks based on quantum entanglement from theoretical concepts to realistic possibilities.