Dynamics of Component Separation in a Binary Mixture of Bose-Einstein Condensates

We describe the first experiments that study in a controlled way the dynamics of distinguishable and interpenetrating bosonic quantum fluids. We work with a two-component system of Bose-Einstein condensates in the $|{F=1,m}_f=-1\mathrm{}〉$ and $|2,1〉$ spin states of ${}^{87}\mathrm{Rb}$. The two condensates are created with complete spatial overlap, and in subsequent evolution they undergo complex relative motions that tend to preserve the total density profile. The motions quickly damp out, leaving the condensates in a steady state with a non-negligible (and adjustable) overlap region.