Physicists have long categorized every elementary particle in our three-dimensional universe as being either a boson or a fermion—the former category mostly capturing force carriers like photons, the latter including the building blocks of everyday matter like electrons, protons, or neutrons. But in lower dimensions of space, the neat categorization starts to break down.

Since the ’70s, a third class capturing anything in between a fermion and a boson, dubbed anyon, has been predicted to exist—and in 2020, these odd particles were observed experimentally at the interface of supercooled, strongly magnetized, one-atom thick (that is, two-dimensional) semiconductors. And now, in two joint papers published in Physical Review A, researchers from the Okinawa Institute of Science and Technology (OIST) and the University of Oklahoma have identified a one-dimensional system where such particles can exist and explored their theoretical properties.

Thanks to the recent developments in experimental control over single particles in ultracold atomic systems, these works also set the stage for investigating the fundamental physics of tunable anyons in realistic experimental settings. “Every particle in our universe seems to fit strictly into two categories: bosonic or fermionic. Why are there no others?” asks Professor Thomas Busch of the Quantum Systems Unit at OIST.