Theoretical physicists from Emory University (USA) have developed a method that uses light to detect anyons, unusual quasiparticles that arise from the collective behavior of many electrons. The work was published in the journal Physical Review Letters.
Anyons are interesting because they could become the basis of quantum computing in the future. They are difficult to study: they are not individual fundamental particles but collective excitations of electrons. "Using a specific frequency of light, we created a sensor that can indicate the location of an anyon in a material," explains Luis Santos, a professor of physics and senior author of the study.
For a long time it was believed that electric charge is indivisible: a proton carries a full positive charge and an electron a full negative charge. Later it turned out that in two-dimensional systems charge can split into quasiparticles that do not obey standard rules. They were called anyons, for their "free" behavior.
One possible use of anyons is to create qubits, the elementary units of quantum information. The main problem with quantum computing is that even weak interference, such as the movement of air molecules or solar radiation, destroys fragile quantum states. "Anyons can hide and avoid many external disturbances," Santos says. "This makes them more robust than typical quantum materials."
However, a topological quantum computer that would rely on a special class of anyons remains a purely theoretical idea. Anyons have been observed in the laboratory in the fractional quantum Hall effect: a two-dimensional electron gas is cooled to ultralow temperatures and placed in a strong magnetic field. Later, researchers learned to produce a similar effect under less extreme conditions, but the task of precisely determining the location of anyons remained unsolved.
The authors of the new work proposed a solution. In atomically thin semiconductors, electrons can bind with "holes," or vacancies, to form excitons: neutral quasiparticles that interact strongly with light. The physicists predicted that if an exciton comes close enough to an anyon, they will bind into a new composite particle, an exciton-anyon state. This process should be accompanied by a detectable energy shift that can be recorded.
First the scientists built a model, then ran computer simulations and analyzed the results. "It is interesting to put your ideas into a computer and see that the results match the prediction," says Tianhong Lu, the first author of the paper and a graduate student at Emory University.
The researchers hope that experimentalists will test their theoretical calculations. This would be another step toward creating a topological quantum computer. For now, however, this is only theoretical work: no real devices based on anyons have been created.