January 13, 2025
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Exotic “paraparticles” that defy categorization can exist in many dimensions
Theoretical physicists predict the existence of exotic “paraparticles” that defy classification and may have applications in quantum computing.
particles known as fermions (shown in this illustration) cannot share the same status.
Roman Andrade 3Dcienca/Science Photo Library
Theoretical physicists have proposed the existence of a new type of particle that does not fit into the usual classifications of fermions and bosons. Their “paraparticle”, described in Sect nature on January 8, is not the first to be suggested, but the precise mathematical model that characterizes it could lead to experiments created using a quantum computer. The research also suggests that undiscovered fundamental paraparticles may exist in nature.
In a separate development published late last year sciencephysicists experimentally demonstrated for the first time a type of particle—”anything”—that is neither a boson nor a fermion in a one-dimensional virtual universe. It was previously created by Anyons Only in 2D systems.
Because of their unusual behavior, paraparticles and everyone else could one day play a role in making quantum computers less error-prone.
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Particle properties
When physicists began to understand the structure of atoms, a century agoAustrian-born theorist Wolfgang Pauli suggested that no two electrons can occupy the same state, and that if two electrons come close to being in the same state, a repulsive force is created between them. This “Pauli exclusion principle” is fundamental to the way electrons orbiting an atomic nucleus are organized into shells, rather than all falling into the lowest possible energy state.
Pauli and others soon realized that this empirical exclusion rule applied not only to electrons, but to a wider class of particles, including protons and neutrons, which they called fermions. Conversely, particles that like to share the same state—including photons from a laser beam, for example—became known as bosons. (Pauli and his collaborators also worked out why being a fermion or boson seemed to have a particle’s intrinsic angular momentum, or ‘spin’).
Mathematically, the fundamental property of fermions is this: when two of them change positions, the “wave function” that represents their collective quantum state changes sign, that is, it is multiplied by –1. In the case of bosons, the wave function remains unchanged. Early quantum theorists knew, in principle, that there could be other kinds of particles whose wave functions changed in more complicated ways when they exchanged positions. In the 1970s, researchers discovered that anything can exist only in one-dimensional or two-dimensional universes.
Physicists Zhiyuan Wang, now at the Max Planck Institute for Quantum Optics in Garching, Germany, and Kaden Hazzard at Rice University in Houston, Texas, have now built a model of paraparticles that can exist in any dimension and have properties. different from fermions or bosons. In particular, these paraparticles fulfill their own type of Pauli exclusion. “It’s not entirely surprising that it’s possible,” says Kasia Rejzner, a mathematical physicist at the University of York in the UK. “But it’s still cool.”
Wang says he came up with the exotic trading rules by accident in 2021, when he was doing his Ph.D. “It was the most exciting moment of my life,” he says. Wang added that it should be possible—albeit challenging—to realize these paraparticle states on a quantum computer.
1D anyone
Paraparticles share a property with fermions: if two particles are exchanged, they are restored to their original state by exchanging them again. Everyone generally has a different quantum state even when returned to their original positions, so they are not classified as paraparticles.
in the year science In the study, physicists Joyce Kwan and Markus Greiner of Harvard University in Cambridge, Massachusetts, and their colleagues suspended atoms of the isotope rubidium-87 in a vacuum using light waves. The atoms tended to stay in the troughs of the waves and only occasionally jumped from one to the other, less than a micrometer apart. In these circumstances, the rubidium-87 atoms would normally behave like bosons, so two of them would not mind sharing the same trough. But by periodically adjusting the intensity of the light, the researchers were able to change the behavior of the atoms so that when two atoms swapped places, their wave functions were bent by a prescribed angle, a defining property of any. Analyzing the wave functions required many repetitions of the experiment, allowing the atoms to drift and then freezing them and imaging the position of each atom, Kwan says.
“I’m very excited that the Greiner group has brought everyone in 1D to life,” says Martin Greiter, a theoretical physicist at Julius Maximilian University in Würzburg, Germany.
Since anyone’s wavefunctions “remember” how two of them were swapped, they can provide a robust way to encode information. This property of memory has already been exploited in 2D virtual machines built by Google physicists and other groups.
Paraparticles are unlikely to be as robust as any, but they could also be useful in quantum computing, Wang says. Oddly enough, they can be in 3D. In principle, some undiscovered elementary particles could be paraparticles, he added.
This article is and was reproduced with permission first published January 8, 2025.
