Diffusion is ubiquitous in nature, central for transport processes in biology or fluid mechanics. Observing the dynamics of a macroscopic tracer, microscopic interaction mechanisms can be inferred.

We investigate the diffusion dynamics of individual neutral atoms in tailored baths which include ultracold gases and near-resonant light fields. We are particularly interested in dynamics at the edge of standard statistical mechanics or in the cross-over between classical and quantum physics. It is our aim to shed light on such unexplored diffusion phenomena in order to understand and model the underlying dynamics.

Motion of single neutral atoms in a laser field, a so-called optical molasses, shows striking analogy to Brownian motion. An additional periodic potential trapping single atoms, can be realized by a so-called optical lattice. This allows experimentally studying diffusion in structured environments in a highly-controllable system.