Mutual Friction and Coarsening in a Two-Component BEC

In a two-component Bose-Einstein condensate with relative flow, the counterflow instability spontaneously breaks translational symmetry after a critical relative velocity. The turbulence that develops produces an effective mutual friction between the two components, allowing momentum exchange and dissipating their bulk velocity despite the absence of viscosity. By applying a constant force, experimentalists can control the amount of mutual friction, providing experimental access to the underlying turbulence. We will discuss the nature of this mutual friction seen in simulations, and an interesting coarsening dynamic seen in the experiments when the forcing is stopped.