Entanglement, the spooky link that makes disparate quantum objects act as one, can now be topped up for as long as necessary.

In recent years, physicists have learned to exploit entanglement to communicate, compute and even teleport. But these experiments have always been hard because entanglement rapidly leaks into the environment. Blink and it’s gone.

Now Hanna Krauter at the Niels Bohr Institute in Copenhagen and colleagues have worked out how to entangle two clouds of caesium atoms and maintain the link for as long as they keep their experiment running.

The team bathe both clouds of atoms in a laser beam, which simultaneously aligns their collective spins. This entangles the clouds. But the clouds emit photons, which allow the entanglement to leak away. Their trick, described in a paper to appear in Physical Review Letters, is to replenish the entanglement as it escapes.


Record breaker

Using the new technique, the team has entangled the clouds for up to an hour, vastly improving on the few seconds that have been possible up to now. “We’ve beaten all previous records,” says Ignacio Cirac, a member of the team at the Max Planck Institute for Quantum Optics in Germany.

Franck Laloë, a physicist at the Laboratoire Kastler Brossel in Paris, France, says that although the technique was known theoretically, it has never been demonstrated experimentally.

The breakthrough should help to turn entanglement from a laboratory workhorse to a technology capable of working in the wider world. One possible application is in making quantum routers for internet-style quantum communication.

Hard to handle

These work like ordinary routers, receiving signals and sending them onwards. But when the information being transmitted is encoded in the quantum properties of a particle, the routers must pass it on using entanglement.

Nobody has built a practical quantum router because entanglement has been so hard to handle. That’s why a technique that can maintain entanglement indefinitely might change this.

Rainer Blatt, an experimental physicist The Institute for Quantum Optics and Quantum Information in Innsbruk, Austria, has done similar work. “The experiment is a useful advance and may become important for quantum communication protocols,” he says.