Anomalous diffusion of atoms in a 1D damped lattice

We study experimentally the anomalous diffusion of atoms in one dimension. The ultra-cold atoms continuously scatter photons from a lattice which is in a configuration identical to the one used in the well-known Sisyphus cooling scheme. This produces a steady-state atomic velocity distribution which is a power law, with an exponent that depends on the lattice depth [1]. We image the atomic density distribution after a varying waiting time. The width of the atomic cloud exhibits a power law time dependence, and we extract its characteristic exponent for various lattice depths. We also show that the density distribution at different times is self-similar with the same characteristic exponent, in accordance with the predictions of a fractional diffusion equation [2]. \\[4pt] [1] P. Douglas, S. Bergamini, and F. Renzoni, Phys. Rev. Lett. 96, 110601 (2006). \newline [2] R. Metzler and J. Klafter, Physics Reports 339, 1 (2000).