Physicists Use Light to Detect Anyons
'Spectral fingerprints' point to path for quantum computing
Physicists have discovered a way to use light to detect the “spectral fingerprints” of anyons — exotic quasiparticles that emerge from the collective behavior of many electrons.
Physical Review Letters published the finding by theoretical physicists at Emory University. Their work offers a new tool for the study of anyons, which hold potential as fundamental building blocks for quantum computing.
“Using a particular frequency of light, we’ve developed a sensor that can pinpoint the location of an anyon in a material,” says Luiz Santos, professor of physics at Emory University and senior author of the study.
“The dream goal is the ability to manipulate anyons to achieve topological quantum computation,” says Tianhong Lu, first author of the paper and an Emory PhD candidate in physics. “Our theoretical work takes another step in that direction.”
‘Anything goes’ behavior
For nearly 100 years, it was believed that every electrical charge in the universe, whether on Earth or in the next galaxy, has the same magnitude of charge: protons have a full-positive electrical charge, for example, while electrons have a full-negative electrical charge.
“People thought that all charge excitations had to carry multiples of magnitude — in other words, the charges could not be split into fractional charges,” Santos explains.
During the 1980s, however, scientists discovered that — in two-dimensional systems — electron charges can fractionalize into quasiparticles that defy the standard rules of particles. These newly discovered phenomena were dubbed “anyons,” for their “anything goes” behavior.
"When we can literally shed light on how things work at a fundamental level, that makes me quite happy," says Luiz Santos, Emory professor of physics.
"When we can literally shed light on how things work at a fundamental level, that makes me quite happy," says Luiz Santos, Emory professor of physics.
One of the more interesting potential applications for anyons is to create qubits, or the bits of information needed for quantum computing.
A major challenge in developing quantum computing is that even the slightest disturbances — from the movement of air molecules or radiation from the sun — create disturbances that cause havoc at such a tiny scale.
“Anyons can hide themselves and avoid being perturbed by many environmental disturbances,” Santos says. “That makes them more stable than typical quantum materials.”
However, topological quantum computation —a system that relies on a particular class of anyons — remains in the theoretical realm.
Studying anyons to find ways to harness their power is incredibly challenging because they don’t exist as fundamental, isolated particles. Instead, they emerge as collective excitations of electrons.
A quantum dance
“It’s quantum choreography,” Santos says. “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.”
Physicists have observed this quantum dance under laboratory conditions. A strong magnetic field is applied to a two-dimensional electron gas which is cooled to an ultra-low temperature. That produces what is called the fractional quantum Hall effect — a quantum fluid with fractionally charged excitations, or anyons.
Around three years ago, researchers discovered they could produce the effect without a strong magnetic field and under less extreme conditions. The challenge of pinpointing the location of the anyons, however, remained.
The Emory physicists showed how light can help.
"I like the clarity of physics," says Tianhong Lu, an Emory PhD candidate who plans for a career as an academic researcher. "Physics is a systematic way of explaining things with very few parameters."
"I like the clarity of physics," says Tianhong Lu, an Emory PhD candidate who plans for a career as an academic researcher. "Physics is a systematic way of explaining things with very few parameters."
Imagining a model
In certain atomically thin semiconductor materials, electrons can pair with holes, or imperfections, 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 to form a new composite object: an exciton-anyon state. This process, in turn, should emit a detectable shift in energy.
The challenge began on the blackboard as the physicists worked out potential ways to model their proposed system on a computer.
Many early physics breakthroughs relied on direct observation, giving rise to the apocryphal story of an apple falling onto Isaac Newton’s head, inspiring him to come up with gravitational theory.
In contrast, much of modern-day physics involves processes occurring in invisible, untouchable realms.
“You can feel an apple hitting your head but not an anyon,” Lu says.
Watch animation of the theoretical concept for how to pinpoint anyons using light. Tianhong Lu created the animation using ChatGPT's Codex.
Watch animation of the theoretical concept for how to pinpoint anyons using light. Tianhong Lu created the animation using ChatGPT's Codex.
Abstract thinking about physics, he adds, was the hardest, and most rewarding, part of the current paper.
“We had to do qualitative analyses to come up with trends for the binding energy and quantum entanglements involved,” Lu says.
After they came up with a model, they developed a simulation for it and, finally, analyzed the results.
“It’s interesting to enter your ideas into a computer and see that the results fit your prediction,” Lu says.
The researchers hope that experimentalists will now build on their work, providing real-world confirmation of their theory, to help move topological quantum computing yet another step closer to reality.
The work was funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Grant No: DE-SC0023327).
Story and photos by Carol Clark.
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