High Resolution Imaging of Quantum Gases: Tracking Impurities in 2D Bose Gases

We report on our recent experiments on impurities in a degenerate two-dimensional K39 Bose gas.

For both 3D and 2D, we measure the polaron spectrum over a wide range over interactions by employing a interstate Feshbach resonance, and can model the line shapes in good agreement with observation when including excited polaronic states.

Furthermore, we experimentally investigated spatially and temporally resolved impurity dynamics in the 2D BKT gas.

For repulsive interactions we observe an outward motion of the impurities and ultimately the expulsion of the impurities from the bath. We can accurately describe this motion when including friction of the impurities with the superfluid for velocities above the speed of sound.