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China scientists extend cold-atom entanglement over 420 km
The team said the 420 km result, achieved using two rubidium-atom quantum memory units linked by fiber, surpassed a direct-transmission distance threshold.
Chinese scientists have reported quantum entanglement of cold atoms across a record distance of 420 km, a result they say is intended to support intercity quantum networks. The work was published in the peer-reviewed journal Physical Review Letters on August 11, according to SCMP Economy.
The researchers said the distance was more than four times prior demonstrations and exceeded a threshold where direct transmission faces fundamental physical limits. They used two quantum memory units made from laser-cooled clouds of rubidium atoms placed 420 km apart and connected them through an optical fiber link.
Entanglement, as described in the paper, allows two or more particles to share a joint quantum state regardless of how far apart they are, often involving photons. SCMP Economy also noted that adding quantum memory increases complexity compared with earlier experiments that entangled light particles across large stretches of space or via optical fiber.