Researchers at the Helmholtz-Zentrum Berlin (HZB) have moved one step closer to confirming one of quantum physics’ most unusual predictions. Fractons—exotic quasiparticles previously associated with highly theoretical quantum spin liquids—have now appeared in simulations based on more realistic models of quantum solids.
Quasiparticles emerge from the collective behavior of many interacting particles in a solid. For example, vibrations that travel through a crystal lattice can be described as quasiparticles called phonons.
Fractons are far more unusual. These exotic quasiparticles can appear at the corners of domain walls, which separate regions with different spin alignments. Their defining characteristic is restricted mobility: an individual fracton cannot move freely on its own and generally requires interactions with other fractons to change position.
This unusual property could have important practical applications. Because fractons are difficult to move, they may offer a more robust method for storing and protecting quantum information.
Physicists have predicted that fractons could exist in several types of systems, including quantum spin liquids. These unusual states of matter occur in crystals where the magnetic moments of electrons never settle into a fixed arrangement—even at temperatures approaching absolute zero. Instead, the spins continue to fluctuate in a liquid-like state.
Fractons in more realistic quantum models
Fractons in quantum spin liquids have not yet been directly observed in experiments. Until now, theoretical predictions of these quasiparticles have largely depended on highly generalized gauge field theories, including rank-2 U(1) gauge theories.
Research led by Professor Johannes Reuther and Dr. Nils Niggemann has demonstrated that fractons can also emerge in more realistic models of quantum solids, bringing these exotic quasiparticles closer to experimental investigation.
Unlike classical models, the researchers’ simulations incorporate quantum effects. However, their initial studies revealed a significant challenge: when quantum effects became too strong, the fractons disappeared. When the quantum effects were too weak, the excitations survived only as classical particles and no longer displayed genuine quantum behavior.
By improving how interactions between spins are represented, the researchers overcame this difficulty. Their latest numerical simulations provide evidence that the predicted fracton phase can exist under more realistic quantum conditions.
From quantum theory to experimental detection
“In modeling this complex spin interaction, we have benefited from personal interactions with HZB colleagues in experimental solid-state physics,” says Johannes Reuther.
The next challenge is to identify or create a physical system that reproduces the conditions described by the theoretical model. Such a system could allow scientists to test experimentally whether the predicted fractons truly exist.
One possible platform is a Rydberg-atom quantum simulator. This technology could provide a promising pathway toward detecting these elusive quantum quasiparticles and exploring their potential for quantum information storage.
Source: www.sciencedaily.com