Physicists Move Closer to Detecting Fractons in Quantum Spin Liquids

A team of physicists has taken a step toward bringing fractons, an unusual prediction of quantum physics, closer to experimental reality. Fractons are exotic quasiparticles previously predicted in quantum spin liquids. A new study shows they can also emerge in a more realistic quantum solid-state model.

Quasiparticles arise from the collective behavior of many interacting particles in a solid; vibrations moving through a crystal lattice are described as quasiparticles called phonons. Fractons are stranger: they appear at the corners of magnetic domain walls separating different spin arrangements, and their defining feature is extremely limited mobility. A single fracton is essentially unable to move on its own and can only shift through interactions with other fractons, a restriction researchers say could help store quantum information more robustly.

Fractons are predicted to occur in several systems, including quantum spin liquids, unusual states of matter in crystals where the magnetic moments of electrons never settle into a fixed arrangement, even at 0 degrees Kelvin, but keep fluctuating like atoms in a liquid. Such predictions have relied on highly generalized gauge field theories, and no direct experimental observation of these fractons exists.

A study led by Professor Johannes Reuther and Dr. Nils Niggemann showed fractons can also emerge in a more realistic quantum solid model, whose simulations account for quantum effects that classical models ignore. Earlier work by the group ran into trouble: when quantum effects were too strong, fractons disappeared; when too weak, they survived only as classical particles. Improving how the model represents interactions between spins let the researchers overcome this problem.

Reuther said modeling this complex spin interaction benefited from personal exchanges with colleagues in experimental solid-state physics. The next challenge is to identify or create real physical systems matching the model's conditions; Rydberg atom simulators are one possible platform for testing whether the predicted fractons actually appear.