A Single Atom Can Store Information, At Least For A Little While


Sam Lemonick

April 18, 2016

Data is big business and storing it takes big infrastructure: hard drives, server racks and warehouses across the globe. We’re generating so much new data so quickly that in the next few decades we could run out of physical space in which to store it. Now scientists have found a way to encode data in what might be the smallest place possible: a single atom.

Harald Brune of the Ecole Polytechnique Fédérale de Lausanne and Pietro Gambardella of ETH Zurich found a way to make atoms of the rare earth metal holmium hold their magnetic orientation for nearly half an hour at temperatures about 10 degrees above absolute zero. They reported their research in Science.

“How small can you make a magnetic bit and still make it useful for data storage? What Brune and coworkers show is that the answer is one atom,” says IBM researcher Andreas Heinrich in an email. Heinrich and Alex Khajetoorians of Radboud University wrote a perspective that accompanies the paper.

A bit is a device that can be assigned a value of 1 or 0. These 1s and 0s add up to pictures, music and the words on this page.

For computer memory to work well, these bits have to hold on to their assigned 1 or 0 for a long time. Magnets, which can be polarized in one of two directions to represent a 1 or 0, have been the material of choice for digital storage for decades in the form of tapes and disks.

Theoretically, the smallest possible magnet is one atom. Individual atoms, after all, are what make up the magnets on your fridge, all aligned in the same magnetic orientation.

In practice, it’s proven very hard to get single atom magnets to maintain a magnetic orientation. In a bit on a hard disk drive, the magnetic field created by the collective atoms prevents any one atom from changing its orientation.

But for a single atom magnet there is no field to freeze its orientation. What’s more, when you get down to a single atom the rules of classical physics start to break down and the rules of quantum mechanics rear their weird head.

At this scale, electrons can tunnel through energy barriers that should keep them in one place. In the holmium atoms the researchers used as magnets, an electron can shortcut the energy barrier that separates the 1 and 0 orientations, erasing the information the atom is carrying.

A holmium electron only needs a little bit of energy to find that shortcut. The energy can come from an interaction with an electron in a neighboring atom or from vibrations in the surface the holmium is sitting on.

The group’s solution was an electron dead end. They arranged the magnesium and oxygen atoms around the holmium atom in a way that forces any electrons headed for that shortcut into an electronic cul-de-sac.

If one electron was in that dead end, a second would need to be perturbed to access the shortcut that could flip the holmium from 1 to 0. Khajetoorians explains there’s a low probability of two electrons being perturbed like that at the same time. That’s what keeps the holmium atoms frozen in the 1 or 0 position they’re assigned.

He says the research opens up new ways to think about how to store data.

“The whole hard drive industry is still kind of in this classical world,” says Khajetoorians. He and Heinrich are convinced that this research is a breakthrough for single atom memory, possibly in combination with quantum computing. But there are still a number of questions to answer before that happens.

For one, the low temperatures and short time lengths Brune and Gambardella demonstrated aren’t practical for real-world applications. For two, nobody knows how closely individual atom bits could be spaced and not interfere with each other. And there’s the matter of how to read and write information to them. That’s something Heinrich and Khajetoorians are excited about working on.

Not all researchers in the field share their enthusiasm. Wolfgang Wernsdorfer of the Institut Néel praised the work for its daring, but he says in an email that even after talking with Brune and Gambardella, he can’t reconcile their conclusions with his understanding of how magnets should work.

Brune and Gambardella are cautious as well, but they still see enormous potential in their work.

“In my view, holmium and magnesium-oxygen is just the first atom/surface combination where the atom exhibits remanence on human time scales such as hours,” says Brune in an email. He says his group is already working on two other promising systems.

This article was written by Sam Lemonick from Forbes and was legally licensed through the NewsCred publisher network.

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