Apr 24 2019
Scientists headed by Francesca Ferlaino from the University of Innsbruck and Austrian Academy of Sciences have observed supersolid behavior in dipolar quantum gases of dysprosium and erbium. They have reported the outcomes of their study in Physical Review X.
Several tens of thousands of particles spontaneously organize in a self-determined crystalline structure while sharing the same macroscopic wavefunction—hallmarks of supersolidity. (Image credit: Uni Innsbruck)
These properties are uniquely enduring in the dysprosium gas, thereby setting the stage for future analyses into the nature of this exotic phase of matter.
Supersolidity is a paradoxical state in which the matter exists as a superfluid and a crystal. Proposed five decades ago, a counter-intuitive phase such as this, which features relatively antithetic properties, has been searched for a long time in superfluid helium. However, following many years of theoretical and experimental efforts, an explicit proof of supersolidity in these systems is still lacking.
Two research groups headed by Francesca Ferlaino, one from the Institute for Experimental Physics at the University of Innsbruck and the other from the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, have now reported about observing hallmarks of this strange state in ultracold atomic gases.
Although a majority of the studies to date have focused on helium, recently, scientists have turned to atomic gases—specifically those with strong dipolar interactions. Francesca Ferlaino’s team has been analyzing quantum gases formed of atoms with a strong dipolar character for a long time.
“Recent experiments have revealed that such gases exhibit fundamental similarities with superfluid helium,” stated Lauriane Chomaz referring to experimental achievements in Innsbruck and in Stuttgart over the past few years. “These features lay the groundwork for reaching a state where the several tens of thousands of particles of the gas spontaneously organize in a self-determined crystalline structure while sharing the same macroscopic wavefunction—hallmarks of supersolidity.”
The scientists from Innsbruck experimentally developed states exhibiting these supersolidity characteristics by adjusting the interaction strength between the particles, in both dysprosium and erbium quantum gases.
While in erbium the supersolid behavior is only transient, in line with recent beautiful experiments in Pisa and in Stuttgart, our dysprosium realization shows an unprecedented stability. Here, the supersolid behavior not only lives long but can also be directly achieved via evaporative cooling, starting from a thermal sample.
Francesca Ferlaino, University of Innsbruck.
Similar to blowing over a cup of tea, the idea here is to eliminate the particles that bear much of the energies so that the gas turns more and more cooler and eventually reaches a quantum-degenerate stationary state with supersolid characteristics at thermal equilibrium.
This paves the way for fascinating possibilities for near-future theories and experiments since the supersolid state in this setup is not much affected by dissipative dynamics or excitations, thereby enabling the investigation of its superfluid behavior and its excitation spectrum. The Austrian Science Fund FWF, the Austrian Academy of Sciences, and the European Union financially supported the study.