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  • After forty years, the creator of quantum scar theory has observed the phenomenon in real time.
  • Quantum scarring is a phenomenon in which traveling electrons end up following the same repeating path.
  • Electrons are chaotic and show duality, so they don’t typically behave in an orderly way.

Scientists from California, Massachusetts, England, and Japan have used microdots of carbon graphene to directly observe a long-theorized phenomenon called a quantum scar. By trapping electrons in a particular way, physicists can apparently observe how they move, and then see that this movement continues in a predictable way. These predictable orbits are known as scars, and they function similarly to how people in a park or college campus will wear their own paths into the grass by walking the same way every day. The quantum scar is an electron’s own desire path.

The paper describing this research was recently published in the journal Nature.

In a press statement, coauthor Eric Heller from Harvard University describes quantum scarring as “a window onto the strange quantum world.” Electrons are peculiar, even among the subatomic crowd—perhaps especially in that they behave in a chaotic way because (like photons) they show wave-particle duality.

With that in mind, scientists are tantalized by the idea of phenomena that could corral electrons into more predictable patterns of behavior. Even inside high-quality conducting materials, electrons often behave very randomly (in the proverbial sense), and aren’t traveling on efficient paths–except when that’s the quickest way through a solid material. On the quantum nano scale, when building quantum computers and other microstructures designed for precision, those macro solid matter techniques just won’t work.

It was Heller who originally coined the term “scarring” in 1984, to describe how an electron’s behavior could create an area of higher probability density and cause the same electron to continue to follow that path on repeat. Now, a team—including Heller and eleven other scientists—has used emerging particle control technology to confine and directly observe this scarring in situ for the first time.

To do this, they narrowed their research down to Dirac electrons, which somehow act even lighter than the regular kind. These electrons are proving useful in quantum research because of their very free and energetic motion—something that can be easier to spot now that scientists are peering at these experiments through high-powered observational tools like electron microscopes.

This time, the scientists placed graphene quantum dots into a controlled environment. These graphene dots are nanoscale materials made by arranging a single layer of graphene—which, like diamonds or graphite in pencils, is a different format of regular old carbon atoms. The resulting dots act like solid materials or molecules in some ways, but have novel properties that scientists are continuing to explore in emerging research.

The material was shaped like a stadium, and when the scientists zoomed way in and hovered over the ‘stadium’ surface, they could see a ghostly image of an electron repeating a figure-8 shape. This is called lemniscate, from the Latin for a ribbon bow. What results is more predictable than any freewheeling electron, with less energy loss.

Particles often exhibit strange or novel behaviors within this kind of confinement. But before these behaviors can be turned into usable technologies, scientists must probe their boundaries to find which particular parameters and situations lead to those behaviors. In this case, it’s taken forty years for lab equipment to catch up to Heller’s idea in a way that he and his collaborators can observe directly. That seems like a very special moment within one long career.

Headshot of Caroline Delbert

Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She’s also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all. 

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2024-12-16 14:30:00

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