Abstract
The supersolid is an exotic quantum phase of matter featuring both superfluid and crystal-like properties. It was predicted long ago that the superfluid response of a supersolid should be reduced compared to a standard superfluid due to the competing crystal order. The so-called superfluid fraction quantifies this effect, ranging from 1 for a full superfluid to 0 for a classical crystal. I will show our recent experiments aimed to probe the sub-unity superfluid fraction of a supersolid realized in a dipolar Bose-Einstein condensate. Studying the rotational response of the supersolid, we measured its moment of inertia and we demonstrated its non-classical behavior. To measure quantitatively the superfluid fraction, we excited Josephson oscillations between different supersolid sites, demonstrating that it can behave as a self-induced Josephson junction. From the observed Josephson dynamics, we extracted the superfluid fraction, which we can tune from 1 to about 0.1 controlling the interactions. I will also discuss future experiments in annular geometries.
