Quantum gas becomes supersolid

Researchers led by Francesca Ferlaino of the University of Innsbruck and the Austrian Academy of Sciences reported on Physical examination X on the observation of supersolid behavior in quantum dolterium and erbium dysprosium gases. In dysprosium gas, these properties have an unprecedented longevity. This opens the way for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state in which matter is both crystallized and superfluid. Planned 50 years ago, such a counter-intuitive phase, with rather antithetic properties, has long been sought in superfluid helium. However, after decades of theoretical and experimental effort, there is still no compelling evidence of supersolidity in these systems. Two research teams led by Francesca Ferlaino, one at the Institute of Experimental Physics of the University of Innsbruck and the other at the institute of. quantum optics and quantum information of the Austrian Academy of Sciences, are now reporting on the observation of the characteristics of this exotic state in Germany. ultra-cold atomic gases.

Until now, most of the work has been on helium, but researchers have recently turned to atomic gases, especially those with strong dipolar interactions. The team of Francesca Ferlaino has long studied quantum gases made up of atoms with strong dipolar character. "Recent experiments have revealed that these gases have fundamental similarities with superfluid helium," explains Lauriane Chomaz, referring to experimental results in Innsbruck and Stuttgart in recent years. "These characteristics lay the foundation for a state where the tens of thousands of gas particles spontaneously organize into a self-determined crystalline structure, while sharing the same macroscopic wave function, characteristic of supersolidity. . "

Researchers in Innsbruck experimentally created states showing these characteristics of supersolidity by adjusting the force of interaction between particles, in erbium quantum gases and dysprosium. "While in Europe, the supersolid behavior is only transitory – in accordance with the recent good experiences in Pisa and Stuttgart – our achievement in dysprosium shows unprecedented stability," says Francesca Ferlaino. "Here, the supersolid behavior lasts not only long, but can also be obtained directly via evaporative cooling, from a thermal sample." As in the case of a cup of tea, the principle is to remove the particles that carry the most energy so that the gas becomes colder and finally reaches a stationary state with quantum degeneration possessing supersolid properties at thermal equilibrium.

This offers interesting perspectives for future experiments and theories because the supersolid state in this setting is little affected by dissipative dynamics or excitations, thus opening the way for the search for its excitation spectrum and its superfluid behavior. . The works were financially supported by the Austrian Science Fund FWF, the Austrian Academy of Sciences and the European Union.