Physicists Think They Have Found Long-Sought Two-Dimensional Quasiparticles

These may just look like colorful stripes to most of us, but to physicists they represent the interference pattern expected from long-theorized quasiparticles known as anyons, seen for the first time, according to a yet-to-be peer-reviewed paper. James Nakamura and Michael Manfra

Evidence has emerged for long-proposed, but previously unconfirmed quasiparticles called anyons. The concept of anyons goes back 43 years, and physicists have found evidence collections of particles are behaving as anyons for some time, but have lacked confirmation. Now, within months of each other, two teams have found different methods to verify that this is what they are dealing with that look much more conclusive.

The universe's particles are divided into two sorts; fermions and bosons. Fermions, including the components of atoms, cannot occupy the same quantum state as each other while bosons, which include photons of light, have no such problem.

Anyone who has spent much time around physicists will not be surprised to learn that many have wondered if there could be something else. For some, the so-called “particle zoo” is never sufficiently weird and wonderful. This led to the proposal of anyons, which can only exist in two-dimensional space.

In April a team at Sorbonne University published a paper in Science claiming definitive proof of the existence of anyons, although they did not convince everyone. Now Purdue University physicists have published their own paper on the preprint server This work has yet to pass peer-review but has attracted enough excitement to win a detailed discussion in Nature, an unusual accolade for work that has yet to undergo such formal assessment.

As quasiparticles, anyons are formations of smaller particles (in this case electrons) that behave as if they are a single thing. Theoretical models suggest they have characteristics that fall between fermions and bosons, but can only exist when groups of electrons are restricted to movement in just two directions.

We can’t actually see anyons, but if they exist we should be able to detect them statistically from some experiments. The Sorbonne scientists fired beams of clustered electrons cooled close to absolute zero at each other and observed the outputs. As they hoped, the excited electron groups neither repelled each other, as fermions would do, nor collected to the extent bosons would.

Nevertheless, some physicists questioned that conclusion, claiming the observed behavior could be explained without resorting to anyons.

Professor Michael Manfra of Purdue University may have settled such doubts. The defining feature of anyons is that when one travels in a loop around the other it ends up with a wave function that is neither the same as it was, nor the mirror opposite. Manfra etched a layer of gallium arsenide so currents could be carried along two paths and confined groups of electrons inside. At exceptionally low temperatures the interference patterns produced by the quasiparticles were exactly what physicists expect of anyons transported in this way.

“As far as I can tell, it is an extremely solid observation of anyons — directly observing their defining property: that they accumulate a fractional phase when one anyon travels around another,” Oxford University’s Professor Steven Simon, who was not involved in the research, told Nature.

Theoreticians have argued that if anyons can be shown to exist, they could form the basis of quantum computers. Although abundant quantum computing designs are under investigation, with varying progress, most are painfully delicate and need astonishing levels of protection from the outside world. Anyon-based devices could be much more resilient.



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