Raman sideband cooling and cold atomic collisions in optical lattices

The next generation of laser-cooled atomic frequency standards, atom-interferometer based inertial force sensors and precision measurements, atom-optical devices, and Bose-Einstein condensation experiments can benefit greatly from enhanced laser-cooling techniques capable of preparing a high flux of ultracold atoms at high phase-space density. In this work, we have demonstrated a method known as Raman-sideband cooling, which we have used to produce atomic samples at temperatures near the single-photon recoil limit, and at phase-space densities within a factor of 30 of Bose-Einstein condensation. This method is an extension of the sideband cooling used previously on electrostatically trapped ions, and involves stimulated Raman transitions between the well-resolved, quantized vibrational levels of atoms in a tightly confining potential. The confinement is provided by a so-called “optical lattice”, which consists of a lattice-like potential created by the atomic ground-state AC stark shift induced by a three-dimensional interference pattern of several laser beams.; We have also used this technique to prepare extremely high densities of trapped cesium atoms to study their interactions at ultracold temperatures. These interactions are responsible for a frequency shift in the ground-state hyperfine splitting of cesium, which is currently an important stability limit for advanced frequency standards based on laser-cooled cesium atoms. Ultracold atomic interactions are also important for Bose-Einstein condensation, as well as cold-atom based realizations of quantum phase-transitions and quantum computation schemes. In the present work, we have observed with high precision a large number of narrow resonances in the elastic and inelastic collision cross-sections of trapped cesium atoms; these features arise from an effect known as Feshbach resonance, which occurs when two colliding atoms form a weakly-bound virtual molecule during a collision. Using the measured positions of these resonances, a self-consistent and fully predictive model of binary cesium collisions at ultracold temperatures can for the first time be constructed.