Estimates of Collisional Cooling and Quenching Rates for Atomic and Molecular Ion Collisions with Ultracold Atoms.

Translational cross sections and rate coefficients for cold ion-neutral elastic and charge-exchange collisions (either atomic or molecular) are $>>$ larger ($\sim$10$^6$ a.u.) than neutral-neutral collisions at the same CM energy. This is due to the long range polarization potential V(R) = -C$_{4}$/R$^{4}$, where C$_{4}$ is proportional to the polarizability of the neutral partner. Thus collisions between ultracold alkali atoms (trapped in a magneto-optic trap or MOT) and low-energy ions can be used for sympathetic cooling experiments. We are building a prototype hybrid-trap apparatus [1] that applies these principles to collisions of Ca$^{+}$ ions (which can be laser pre-cooled) with MOT-trapped ultracold Na atoms. Some calculations on this system and other related ion-neutral systems have been published [2] and some initial experiments on other ion-neutral species have begun [3]. Estimates of cooling and quenching rates in the low K-mK CM energy range for Ca+ on Na and other cases will be presented and possible experiments described. [1] Winthrop W. Smith, Oleg P. Makarov and Jian Lin, J. Modern Optics \textbf{52}, 2253 (2005). [2] R. C\^{o}t\'{e} and A. Dalgarno, Phys. Rev. A \textbf{62}, 012709 (2000); R. C\^{o}t\'{e}, Phys. Rev. Lett. \textbf{85}, 5316 (2000). [3] A. Grier, M. Cetina, F.Orucevic, and V. Vuletic, ArXiv atom-ph/0808.3620.