Scientists entangled quantum memories linked over long distances

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Physicists’ fantasies of a future
quantum internet are a bit closer to reality.

Scientists entangled two quantum “hard drives” that were linked by fibers tens of kilometers long. Entanglement,
a type of ethereal quantum connection, allows two particles to behave as if intertwined
even when distantly separated. The new study entangled two devices called quantum
memories using particles of light that were shuttled across a longer distance
than ever before, the team reports February 12 in Nature.

Like a hard drive in a computer, quantum
memories store quantum information. They’re a necessary part of building a quantum internet, which would facilitate ultrasecure communication and allow distant quantum
computers to work together (SN: 9/19/16).

To be most useful, quantum networks
would need to span the globe. Scientists previously have entangled individual particles of light, or photons, separated by 1,200 kilometers (SN: 6/15/17). But that entanglement couldn’t be stored. Distant
quantum memories could help preserve entanglement over long distances. Quantum
memories, though, had been entangled when separated by just over a kilometer at
most.

In the new study, the researchers entangled quantum memories that, although physically located near one another, required photons to detour either 22 or 50 kilometers though optical fibers to produce the entanglement, depending on the experiment. Made of clouds of laser-cooled rubidium atoms, the quantum memories were first entangled with photons. After traveling for kilometers, those photons were made to interfere with one another and then measured. That interaction caused the two memories to become entangled, showing that quantum memories can go the distance.

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