Physicists measure quantum geometry for the first time

Jan. 14 () –

Physicists at MIT and colleagues at other institutions have for the first time measured the geometry, or shape, of electrons in solids at the quantum level.

Scientists have long known how to measure the energies and velocities of electrons in crystalline materials, but until now, the quantum geometry of these systems could only be inferred theoreticallyor sometimes it could not even be inferred.

The work, recently published in Nature Physics“opens new avenues for understanding and manipulating the quantum properties of materials,” says Riccardo Comin, MIT Class of 1947 career development associate professor of physics and leader of the work.

“Basically, we have developed a plan to obtain completely new information that could not be obtained before”, says Comin, who is also affiliated with the Materials Research Laboratory and the Electronics Research Laboratory at MIT.

The work could be applied to “any type of quantum material, not just the one we work with,” says Mingu Kang, first author of the Nature Physics paper, who did the work as a graduate student at MIT and is now a Kavli Postdoctoral Fellow at the Laboratory of Atomic and Solid State Physics at Cornell University.

In the strange world of quantum physics, an electron can be described as a point in space and as a wave-like shape. At the center of the current work is a fundamental object known as a wave function that describes the latter. “You can think of it as a surface in three-dimensional space”says Comin.

There are different types of wave functions, ranging from simple to complex. “Let’s think of a ball. That is analogous to a simple or trivial wave function. Now let’s imagine a Möbius strip, the type of structure that MC Escher explored in his art. It is analogous to a complex or non-trivial wave function. And the quantum world is full of materials composed of the latter,” MIT states in a statement.

But until now, the quantum geometry of wave functions could only be inferred theoretically, or sometimes not even at all. And the property is becoming increasingly important as physicists find more and more quantum materials with potential applications in everything from quantum computers to advanced electronic and magnetic devices.

The MIT team solved the problem using a technique called angular-resolved photoemission spectroscopy, or ARPES. Comin, Kang and some of the same colleagues had used the technique in other research. For example, in 2022 they reported on the discovery of the “secret sauce” behind the exotic properties of a new quantum material known as kagome metal. That work also appeared in Nature Physics. In the current work, the team adapted ARPES to measure the quantum geometry of a kagome metal.

Kang emphasizes that the new ability to measure the quantum geometry of materials “comes from the close collaboration between theorists and experimentalists.”