Direct observation of atomic localization in optical superlattices

We present direct experimental evidence for the localization of atoms cooled and trapped in a three- dimensional optical superlattice. As in the case of solid-state superlattices, we are able to tailor the characteristics of the optical potential wells. In particular, we impose a long-range modulation to the depth of the potential wells whose size remains in the optical wavelength range. The cooling mechanism in this configuration accumulates the atoms in the deepest wells. Images of the resulting separated denser atomic planes (distance $\simeq 70$ $\mu \mathrm{m}$) have been obtained both by detecting the fluorescence and by observing the shadow of the cloud.