Miles ahead: China team boosts atom entanglement distance record fourfold

Chinese researchers have set a new record in quantum entanglement, successfully linking cold atoms across an astonishing 420km (260 miles) – four times the previous distance achieved. This groundbreaking development, published in the journal Physical Review Letters on August 11, opens the door for intercity quantum networks and applications beyond the metropolitan scale.

Led by physicist Pan Jianwei from the University of Science and Technology of China in Hefei, Anhui province, the team employed two quantum memory units – each comprising laser-cooled clouds of rubidium atoms – positioned 420km apart and linked by an optical fiber connection. Entanglement, a peculiar quantum phenomenon where two or more particles become intrinsically linked, sharing a joint quantum state irrespective of physical distance, was the primary goal.

While entangling light particles over long distances and through optical fiber has been accomplished before, incorporating quantum memory adds complexity to the process. Transmitting fragile quantum signals over great distances inevitably results in significant signal loss. To circumvent this issue, the research team implemented several advanced techniques, including a continuous correction system to synchronize quantum states and adjusting the operating wavelength of quantum memory units to minimize transmission losses through fiber-optic cables.

The team demonstrated that their system could achieve entanglement beyond 320km, surpassing the theoretical maximum for direct signal transmission over an optical fiber link. This remarkable milestone not only builds upon Pan's earlier research showing entanglement between two quantum memory units across 50km of optical fiber in 2020 but also lays the foundation for scalable quantum communications, computing, and networked sensing.