An important step towards detecting fractons in quantum spin liquids
The distribution of the Fourier transform of the spin correlation in momentum space, shown here, can be used as an indicator of the existence of fractons. The numerical simulation using the newly developed GFMC solid-state model (left) shows a distribution that is almost identical to that of the established but non-specific model of gauge field theory (right). © HZB
Following predictions of the existence of fractons in quantum spin liquids by more general gauge field theories, researchers at HZB succeeded in detecting these quasi-particles also in a quantum solid-state model.
Exotic material phase as an information storage medium
Quasiparticles arise from the complex interaction of many particles in solids; for example, we describe the lattice vibrations in crystals as phonons. Fractons are exotic quasi-particles that occur at the vertices of magnetic domain walls between different spin orders. What makes them special is that they are virtually immobile and can only be displaced by other fractons. In theory, this limited mobility could be exploited to store quantum information robustly.
Theoretical physicists postulate the existence of fractons in various systems, such as quantum spin liquids. These are exotic states of matter in crystals in which the magnetic moments of the electrons do not assume a fixed order even at 0° K, but remain in constant motion, just like the atoms in a liquid.
From gauge field theories to quantum solid-state models
The postulated fractons in a quantum spin liquid have not yet been observed experimentally, and their theoretical prediction was only possible within highly generalised gauge field theories (rank-2 U(1) gauge theories). The study led by Professor Johannes Reuther and Dr Nils Niggemann has now taken a major step towards experimental verification by extending the theoretical prediction to a more realistic solid-state model.
Unlike classical models, they also simulate quantum effects; however, this led to disappointing results in the groups’ previous publications. The quantum effects were either too strong or too weak, with the result that the fractons were either destroyed or could only exist as classical particles without any quantum properties. Thanks to improved modelling, for example that of spin interactions, numerical simulations have now provided evidence for this phase of matter.
From theory to experiment
'When modelling this complex spin interaction, we benefit from personal exchanges with HZB colleagues in experimental solid-state physics,' said Johannes Reuther. Now, the next step toward experimental verification is to develop real materials that reproduce the properties assumed in the theoretical model. In this context, Rydberg atom simulators could be an interesting candidate for the experimental realisation of a detection experiment.
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