World's Smallest MRI Machine Captures Image of Magnetic Field of a Single Atom

Scientists announced this month that they were able to capture an image of the magnetic field of an atom for the first time in the world.

In a world-first, scientists have captured an image of the magnetic field of an atom, opening the door to new ways to interacting with matter on a quantum level for researchers and commercial applications of quantum phenomenon, like quantum computing.

World's Smallest MRI Machine Images an Atom's Magnetic Field for First Time

Researchers at the Center for Quantum Nanoscience (QNS) at the Institute for Basic Science, part of Ewha Womans University in Seoul, South Korea, have used the smallest magnetic resonance imaging (MRI) machine in the world to capture the magnetic fields of individual atoms for the first time.

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Published this month in the journal Nature Physics, the QNS team's work opens the door to a whole new way of interacting with matter on a quantum level, implicating everything from basic research to the commercial and industrial applications of quantum phenomenon, like lasers, quantum computing, and medical diagnostics. “I am very excited about these results," said Professor Andreas Heinrich, director of QNS. "It is certainly a milestone in our field and has very promising implications for future research.”

MRI machines work by measuring the relative densities of 'spins,' the source of the magnetic force between electrons and protons. Normally, MRI machines need many billions of these spins to make an image, but the process at the macro level is the same as for a single atom, so recording the magnetic field of a single atom requires creating a way of detecting a single magnetic field among billions of others.

Atom MRI STM Setup
Source: Philip Willke et al/Institute for Basic Science

To do this, the QNS scientists used a scanning tunneling microscope (STM), the tip of which is as sharp as a single atom and which allows scientists to interact with individual atoms as they scan along a surface. The researchers chose to focus on two atoms in particular, iron and titanium, that are both magnetically active and thanks to their precision placement on a surface of magnesium oxide, the atoms themselves were already visible to researchers using the STM as normal.

To detect the magnetic fields of the atoms, the scientists attached another magnetically active 'spin cluster' to the metal tip of the STM, which they then passed over the atoms like before. Now, however, the researchers could record the pull or repulsion of the atom's magnetic field, exactly the way commonly used magnets of opposite or similar charge behave, as detected by the spin cluster on the STM's tip.

Doing so gave the researchers an incredibly detailed, 3D view of the magnetic field being generated by the single atom they were passing over. What's more, the iron atoms and the titanium atoms interacted with the spin cluster on the tip in characteristically different ways and to different degrees, making it possible to determine the type of atom being passed over from its interaction with the spin cluster on the tip of the STM.

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Atom MRI Fields
Source: Philip Willke et al/Nature Physics

"It turns out that the magnetic interaction we measured depends on the properties of both spins, the one on the tip and the one on the sample," said lead author Dr. Philip Willke. "For example, the signal that we see for iron atoms is vastly different from that for titanium atoms. This allows us to distinguish different kinds of atoms by their magnetic field signature and makes our technique very powerful.”

The researchers hope that their technique will make it possible to explore even more complex structures on the nanoscale, such as the spin distributions of atoms within chemical compounds or allow for precision control of magnetic material such as those used by modern magnetic storage devices. "Many magnetic phenomena take place on the nanoscale, including the recent generation of magnetic storage devices,” said study co-author Dr. Yujeong Bae. “We now plan to study a variety of systems using our microscopic MRI."

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The researchers hope that their technique could even help control and further the development of quantum systems of communications or computing, something that has been a major problem for quantum computing systems that still has no real, satisfactory solution.

Whether that solution lies in the QNS team's new MRI technique remains to be seen, but it certainly opens up a new avenue of research worth exploring. “The ability to map spins and their magnetic field with previously unimaginable precision allows us to gain deeper knowledge about the structure of matter and opens new fields of basic research,” said Heinrich.

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