In situ velocity imaging of ultracold atoms using slow light

The optical response of a moving medium suitably driven into a slow-light propagation regime strongly depends on its velocity. This effect can be used to devise a scheme for imaging ultraslow velocity fields. The scheme turns out to be amenable to study in situ the dynamics of collective and topological excitations of a trapped Bose-Einstein condensate. We illustrate how slow-light imaging works specifically for sloshing oscillations and bent vortices in a stirred condensate.