Emory Physicists Propose Using Light to Pinpoint Anyons, Quantum Computing's Hidden Building Blocks
A theory paper in Physical Review Letters predicts that excitons in atomically thin semiconductors bind to anyons, shifting the light spectrum in a way that could locate them. Experiments have yet to test it.
Theoretical physicists at Emory University say they have found a way to use light to detect the "spectral fingerprints" of anyons, exotic quasiparticles that emerge from the collective behavior of many electrons. The work, published in Physical Review Letters, offers a new tool for studying particles that could become building blocks for quantum computers.
"Using a particular frequency of light, we've developed a sensor that can pinpoint the location of an anyon in a material," said Luiz Santos, a professor of physics at Emory and senior author of the study. First author Tianhong Lu, an Emory Ph.D. candidate, said the long-term target is "the ability to manipulate anyons to achieve topological quantum computation."
Anyons overturn a century-old assumption. For nearly 100 years, physicists believed every electrical charge in the universe came in whole multiples of the electron's charge. "People thought that all charge excitations had to carry multiples of magnitude," Santos said, so charge could not be split into fractions. In the 1980s, researchers found that in two-dimensional systems electron charge can fractionalize into quasiparticles that break the standard rules. They were named anyons for their "anything goes" behavior.
The appeal for computing is stability. Quantum computers are fragile, and even small disturbances, from moving air molecules to radiation from the sun, can ruin a calculation. "Anyons can hide themselves and avoid being perturbed by many environmental disturbances," Santos said. "That makes them more stable than typical quantum materials."
Anyons are hard to study because they never exist as isolated particles. Santos described them as ripples in a crowd of electrons. "The electrons are dancing around, which creates ripples that carry anyons, or a fraction of the charges. You can think of the ripples like waves on the surface of water. Instead of water molecules moving around, billions of electrons are moving together," he said.
Labs have long seen this behavior by applying a strong magnetic field to a two-dimensional electron gas cooled to ultralow temperatures. About three years ago, researchers found they could produce the effect without a strong magnetic field and under less extreme conditions. Pinpointing where the anyons sit, however, remained an open problem.
The Emory proposal uses atomically thin semiconductors, where electrons pair with holes to form excitons, neutral quasiparticles that interact strongly with light. The researchers predicted that when an exciton gets close enough to an anyon, it will bind to it and form a new composite object, an exciton-anyon state. That binding should produce a detectable shift in energy in the material's optical spectrum.
Lu said the work started on a blackboard, with the team modeling the system on a computer. "We had to do qualitative analyses to come up with trends for the binding energy and quantum entanglements involved," he said.
The result is a prediction, not a measurement. The researchers hope experimentalists will now build on it with real-world confirmation, moving topological quantum computing one more step closer to reality.
