Elusive phase change finally spotted in a quantum simulator

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Elusive phase change finally spotted in a quantum simulator

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An ion trap can control atoms for quantum experiments

Y. Colombe/NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY/SCIENCE PHOTO LIBRARY

After decades of looking, researchers have seen a string of atoms go through a 1D phase change so elusive that it could only happen inside a quantum simulator.

“One motivation [for our experiment] is really trying to understand fundamental physics. We’re trying to understand just the basic states that matter can be in,” says

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at the University of Maryland.

He and his colleagues used electromagnetic fields to arrange 23 ions of the element ytterbium into a line, forming a nearly one-dimensional chain. This device can be used for quantum computing, but in this case, the researchers used the chain as a simulator instead.

Within it, they built a 1D ytterbium magnet one atom at a time. Previous calculations predicted this type of magnet would become unmagnetised when warmed, thanks to quantum effects. But no past experiment had achieved this phase transition.

One reason for the difficulty is that systems like quantum computers and simulators typically only work well when they are very cold. Warming them to make the phase transition occur can thus cause malfunctions, says Schuckert.

To avoid this, he and his colleagues tuned the initial quantum state of the atoms so that, as time went on, the 1D magnet’s collective state changed as if its temperature had been increased. This revealed the never-before-seen phase transition.

The achievement is very exotic because chains of atoms generally shouldn’t undergo phase transitions, says

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at Michigan State University. The researchers were only able to engineer it because they could make each ion interact with others that were far from it, even though they weren’t touching. This pushed the whole line into an unusual collective behaviour.

Because their simulator makes such exotic states of matter possible, it could be used to study theoretical systems that may be very rare – or even not exist – in nature, says Maghrebi.

Schuckert suggests quantum simulators could also help explain odd electric or magnetic behaviours that some materials show in the real world. But to do so, these devices must be able to reach higher temperatures than they can today. They can currently model extremely cold temperatures only, but he says higher-temperature simulations may be possible within five years.

And even more existing and theoretical systems could be studied if the simulators can be made larger, for example by arranging the ions into two-dimensional arrays, says

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at the University of Trieste in Italy. “This will suggest new physics to explore,” he says.

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