Moving-obstacle test of atomic superfluidity
= Moving-obstacle test of atomic superfluidity
A repulsive optical obstacle probes dissipation by being moved through a condensate. Heating as a function of speed tests low-speed flow stability; stationary-obstacle and thermal-cloud controls help separate other heating mechanisms. The measured onset need not equal the homogeneous <critical velocity of a homogeneous condensate> because density gradients, obstacle shape and vortex nucleation matter.