Cerenkov Wakes in Ultra-Cold Sodium Gases

Abstract

In classical (normal) fluids when a object moves faster than the speed of sound it creates wakes patterns in the form of cones. This phenomenon was also observed in superfluid Bose-Einstein condensates by Cornell [1]. We will redo these experiments using a tightly focused blue detuned laser and moving atomic cloud. Wake formations of both the superfluid and the classical fluid are observed simultaneously in our experiments. These measured angles will be compared with the corresponding angles predicted by theory with a determined speed of sound of 4.8 mm/s. The wake angles generated in the superfluid correspond with theory for an expected speed of sound of 4.8 mm/s. The wake angles generated in the normal fluid however correspond with theory for an unexpected speed of sound of 77 mm/s. We have also extended the existing theory on the formation of supersonic wakes for finite potential barriers. The results predict that the size and speed of the barrier with respect to the condensate will start to suppress higher order wake patterns.