Scientists at the University of Science and Technology of China (USTC) have made major advances in scalable quantum networks, bringing the technology closer to real-world use. Their findings have been published in Nature and Science.
Quantum information science aims to create highly efficient and ultra-secure networks, which require the long-distance distribution of quantum entanglement – a phenomenon where particles share a unique connection.
This entanglement is vital for secure quantum communication and linking future quantum computers. A major hurdle has been signal loss in optical fibers, where transmission efficiency drops sharply with distance, making large-scale networks difficult to implement.
To overcome this, the USTC team focused on a “quantum repeater,” which divides a long communication link into shorter segments, establishes entanglement in each, and then connects them. The main challenge has been that quantum entanglement is usually too short-lived to last long enough to connect the segments, preventing repeaters from functioning effectively.
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The researchers solved this problem by developing a long-lived trapped-ion quantum memory, a highly efficient ion-photon interface, and a high-fidelity experimental protocol.
These innovations allowed entanglement to persist long enough to link segments successfully. USTC said this is the first demonstration of a scalable building block for a quantum repeater, a critical step toward long-distance quantum networks.
In a related experiment, the team used similar technology to create high-fidelity entanglement between two distant rubidium atoms. Using this, they implemented device-independent quantum key distribution (DI-QKD) over city-scale fiber networks for the first time.
DI-QKD is considered the most secure form of communication, as its security is ensured by the principles of quantum physics, regardless of potential device flaws.
The team successfully carried out DI-QKD over 11 kilometers of fiber, extending the practical distance about 3,000 times beyond previous records. They also demonstrated the feasibility of secure key generation over 100 kilometers, surpassing the previous international record by more than 100 times.
The researchers described these achievements as landmark milestones for China in quantum communication, signaling that fiber-based quantum networks are moving from theory toward practical application.