Two-dimensional Bose-Einstein condensates in a CO2-laser optical lattice

We report on experiments with all‐optically produced Bose‐Einstein condensates in a mesoscopic optical lattice. By retroreflecting the radiation of a CO2‐laser operating near 10.6 μm, a lattice with spacing between sites of λ CO 2/2 ≃ 5.3 μm is realized, for which atom tunneling is negligible. Once cooled to quantum degeneracy by direct evaporative cooling in the lattice, the properties of the trapped microclouds can be studied with far field interference experiments. The microscopic atom clouds are shown to be in the two‐dimensional regime for small atom filling. The realized system has extremely long coherence times, and holds fascinating prospects for both quantum logic and the study of novel collective phenomena.