New technique allows physicists to place atoms right next to each other

Physicists have managed to arrange atoms 10 times closer than standard methods can. Having atoms in such close proximity is key for technologies such as quantum simulators.

In studying quantum phenomena, proximity is vital. Interactions between atoms are stronger when they are closer together. Quantum simulators, used to model and answer questions about real systems, are made up of atoms arranged as close together as possible. Only then can scientists explore exotic states of matter and build new quantum materials.

Getting atoms to sit so close is usually done by cooling the atoms to a stand-still, then positioning them with lasers. How closely the atoms can be packed is limited by the wavelength of light used.

Up until now, that limit has been about 500 nanometres – about half the width of a red blood cell.

Physicists at the Massachusetts Institute of Technology (MIT) have now developed a technique that can place atoms about 50 nm apart. The research is published in the journal Science.

“At 50 nanometres, the behaviour of atoms is so much different that we’re really entering a new regime here,” says senior author Wolfgang Ketterle, a professor at MIT.

The team is able to place atoms much closer together thanks to a new “trick.”

It starts off the same way – a cloud of atoms is cooled to about one-millionth of a degree above absolute zero. Instead of then using a single laser beam, the team uses two beams of different frequency and electric field direction, or circular polarisation.

The two beams produce two groups of atoms – each with a different spin. Overlaying the two beams creates a new standing wave, like throwing rocks into a pool of water and watching the ripples interact to create new waves on the water’s surface.

Peaks and troughs between the two laser beams could be separated by as little as 50 nm.

To test the new technique, the team used dysprosium atoms. Dysprosium is a rare-earth metal which is one of the strongest magnetic elements on the periodic table. But the magnetic interactions between the atoms is relatively weak at distances of even 500 nm.

Bringing the atoms closer together showed magnetic interactions which otherwise would be almost negligible – almost 1,000 times stronger.

For the first time, the team observed transfer of heat between atoms through magnetic fluctuations alone.

“Until now, heat between atoms could only by exchanged when they were in the same physical space and could collide,” notes first author and MIT graduate student Li Du. “Now we have seen atomic layers, separated by vacuum, and they exchange heat via fluctuating magnetic fields.”

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