We report on the observation of unusually strong interactions in a thermal mixture of ultracold atoms which cause a significant modification of the spatial distribution. A mixture of ${}^{87}\mathrm{Rb}$ and ${}^{174}\mathrm{Yb}$ with a temperature of a few $\mu$K is prepared in a hybrid trap consisting of a bichromatic optical potential superimposed on a magnetic trap. For suitable trap parameters and temperatures, a spatial separation of the two species is observed. We infer that the separation is driven by a large interaction strength between ${}^{174}\mathrm{Yb}$ and ${}^{87}\mathrm{Rb}$ accompanied by a large three-body recombination rate. Based on this assumption we have developed a diffusion model which reproduces our observations.

• Received 2 August 2010

DOI:https://doi.org/10.1103/PhysRevA.83.040702