© Martin Zwierlein.
This is a picture of a rotating BEC, stirred by a laser. These sodium atoms were laser cooled, trapped, and cooled further until they condensed into a BEC. Then the cloud of atoms was stirred with a laser to determine whether it was in a superfluid state. One unmistakable characteristic of superfluids is that quantized vortices form when they rotate too quickly. The bright areas in this image are atoms in the BEC, and the dark areas are vortices, which form in a lattice pattern as the cloud is rotated faster and faster. This picture demonstrates unmistakably that this cloud of atoms is in a superfluid state. (Unit: 6)