Chinese team links quantum memories across 260 miles of fiber

A quantum link has crossed a distance where direct transmission becomes increasingly impractical. Researchers in China maintained entanglement between two quantum memories across 260 miles (420 kilometers) of optical fiber, using clouds of laser-cooled rubidium atoms to hold the quantum states in place.

The obstacle is the fiber itself. Quantum signals weaken as they travel, making direct transmission increasingly impractical beyond roughly 199 miles (320 kilometers). A quantum memory offers a different architecture: it stores the state at network nodes, allowing a longer connection to be divided into smaller sections instead of asking one fragile signal to survive the entire route.

That idea only works if the memories stay synchronized. Temperature changes and mechanical vibrations can disturb the quantum effects, so the team added an active stabilization system that continuously adjusted the setup. The researchers also changed the memories’ operating wavelength, reducing transmission losses and helping preserve the connection.

The result extends work by Pan Jianwei and colleagues at the University of Science and Technology of China. Their group demonstrated quantum-memory entanglement across 31 miles (50 kilometers) in 2020 and established a three-node quantum network in 2024. Another Pan-led group reported secure information transmission across more than 62 miles (100 kilometers) of optical fiber in February, using individual rubidium atoms trapped at separate nodes.

So what, concretely? The experiment gives engineers a longer-range platform for building quantum networks that could eventually connect quantum processors or coordinate sensors across cities and wider areas. It does not yet deliver a working long-distance quantum internet: the latest result is a laboratory demonstration, and the study was published in Physical Review Letters on August 11.