Jack Featherstone
Graphic illustration of the article’s conclusions. A rotary knob, labeled α, can be adjusted between 0 and 1, showing how it affects the symmetry of two particles during a swap operation.
A team of researchers has described, for the first time, the properties of one-dimensional anions — and outlined how these particles can be observed using existing experimental setups.
Physicists have traditionally classified all elementary particles in our three-dimensional universe into two groups: bosons and fermions. Bosons typically include force-carrying particles such as photons, while fermions make up matterincluding electrons, protons and neutrons.
In systems of lower dimensionalityhowever, this clear distinction begins to fade, explains .
In the 1970s, scientists predicted the existence of a third category of particles, located between bosons and fermions, known as anions. These particles were observed experimentally for the first time in 2020, in ultrathin and strongly magnetized semiconductor systems.
Building on that work, a team of researchers from the Okinawa Institute of Science and Technology (OIST) and the University of Oklahoma has now identified a one-dimensional system where anions can existand analyzed its theoretical properties.
Advances in the control of individual particles in ultracold atomic systems have made it possible to explore these ideas experimentally.
“All particles in our universe appear to fall strictly into two categories: bosonic or fermionic. Why aren’t there others?“, asks the teacher Thomas Buschfrom the Quantum Systems Unit at OIST.
“With these works, we have now opened the door to improving our understanding of the fundamental properties of the quantum world, and it is very exciting to see Where theoretical and experimental physics take us from here”, he adds.
Break the boson/fermion duality
Traditional classification depends on the behavior of identical particles when they exchange positions. In three-dimensional space, experiments show only two possible outcomes: or the system remains unchangedo, as with bosons, or changes sign, as happens with fermions.
This behavior is rooted in the quantum principle of indistinguishability. Unlike classical objects, identical quantum particles cannot be labeled nor distinguished from each other.
When two of these particles change positionsthe system must remain physically the same.
“Since This exchange is equivalent to doing nothingthe mathematical statistics that governs the event, known as exchange factormust necessarily comply with a simple rule: the square of the exchange factor must be equal to 1″, explains Raúl Hidalgo-SacotoPhD student at the OIST unit.
“The only two numbers that satisfy this rule are +1 and -1. This is why all particles must be, respectively, bosons, for which the factor is 1, or fermions, for which the factor is -1”, he adds.
This distinction leads to very different physical behaviors. Bosons tend to act collectively, as observed in lasers or Bose-Einstein condensates, where particles share the same state.
Fermions, on the contrary, cannot occupy the same statea property that underlies the structure of atoms and the periodic table.
In lower dimensions, the situation changes. Particles have fewer ways to move around each other, and exchanges are linked to their trajectories through space and time. This means that the system can no longer return to an identical state after exchanging particles.
“In lower dimensions, this exchange is no longer topologically equivalent to doing nothing. To satisfy the law of indistinguishabilitywe need exchange factors in a continuous range that account for the exchange, depending on the exact twists and turns of the trajectories”, explains Hidalgo-Sacoto.
This allows a new class of particles with exchange factors that are not limited to +1 or -1. These particles are called anions.
A recipe for tunable anions
In their , Hidalgo-Sacoto and colleagues demonstrate that, in one-dimensional systems, this broad range of behavior persists and can even be in Athens.
In one dimension, particles cannot move around each other, and they have to pass through each other instead, which changes the way your exchange is defined.
The researchers show that the exchange factor, in this case, is directly linked to the intensity of interactions between particles at short distances. This relationship allows scientists to adjust switching behavior in a controlled way, opening up new possibilities for experiments.
“We not only identified the possibility of one-dimensional anions, but also showed cHow your trade statistics can be mapped and, excitingly, how its nature can be observed through its momentum distribution”, summarizes Professor Busch.
“The experimental setups needed to perform these observations already exist. We look forward to seeing what future discoveries will be made in this area and what they can reveal to us about the fundamental physics of our universe.”
