New evidence confirms supersolid’s dual nature in quantum physics breakthrough

Innsbruck researchers have observed quantized vortices in supersolids, providing key insight into this paradoxical state of quantum matter.

Physicists at the University of Innsbruck have experimentally confirmed that supersolids, a unique quantum state of matter, can display a hallmark feature of superfluidity—quantized vortices—when exposed to rotation. This finding reveals how supersolids can paradoxically act as both a rigid structure and a frictionless fluid, marking a critical advancement in quantum matter research.

The concept of a supersolid, first hypothesised over 50 years ago, suggests a material with both crystalline order (solid-like rigidity) and superfluid properties (fluidity without resistance). Francesca Ferlaino, who leads the team at the Department of Experimental Physics at the University of Innsbruck and the Austrian Academy of Sciences, compares this paradox to Schrödinger’s cat, which is “both alive and dead”: “A supersolid is both rigid and liquid,” she explains. Until now, scientists have struggled to directly observe this behaviour in action.

Researchers have previously observed some signs of superfluidity in supersolids, such as coherence in particle phases and other low-energy properties. However, finding direct evidence of quantized vortices—tiny, whirlpool-like structures that mark a material’s superfluid state—has remained elusive. Achieving this breakthrough required precise experiments with dipolar quantum gases, a technically demanding process that only recently became feasible.

Precision rotation and the emergence of vortices

In 2021, the Innsbruck team successfully created a stable, two-dimensional supersolid with ultracold erbium atoms, marking a significant step forward. However, the recent breakthrough involved rotating this fragile supersolid without destroying its structure. Lead author Eva Casotti explained, “The next step—developing a way to stir the supersolid without destroying its fragile state—required even greater precision”

By applying carefully calibrated magnetic fields to induce rotation, the researchers were able to trigger the formation of quantized vortices, confirming the superfluid nature of supersolids. This breakthrough allows for deeper exploration of quantum states that are otherwise found only under extreme cosmic conditions, enabling scientists to study these phenomena under controlled conditions in the laboratory.

Potential insights for superconductors and neutron stars

The impact of this research extends beyond fundamental quantum mechanics. According to Thomas Bland, who led the theoretical work, this discovery “Our findings open the door to studying the hydrodynamic properties of exotic quantum systems with multiple broken symmetries, such as quantum crystals and even neutron stars”. The findings could help clarify the mechanics behind rotational changes in neutron stars, where superfluid vortices are believed to play a role.

Further implications exist for superconductors, materials that conduct electricity without energy loss and may contain similar vortex structures under specific conditions. Ferlaino adds, “Our findings open the door to studying the hydrodynamic properties of exotic quantum systems with multiple broken symmetries, such as quantum crystals and even neutron stars.”

The research, published in Nature, was supported by the Austrian Science Fund (FWF), the Austrian Research Promotion Agency (FFG), and the European Union.