Experimental Investigation of Ultracold Atom-Molecule Collisions

Abstract

Ultracold collisions between Cs atoms and ${\mathrm{Cs}}_{2}$ dimers in the electronic ground state are observed in an optically trapped gas of atoms and molecules. The ${\mathrm{Cs}}_{2}$ molecules are formed in the triplet ground state by cw photoassociation through the outer well of the ${0}_{g}^{\ensuremath{-}}({P}_{3/2})$ excited electronic state. Inelastic atom-molecule collisions converting internal excitation into kinetic energy lead to a loss of ${\mathrm{Cs}}_{2}$ molecules from the dipole trap. Rate coefficients are determined for collisions involving Cs atoms in either the $F=3$ or $F=4$ hyperfine ground state, and ${\mathrm{Cs}}_{2}$ molecules in either highly vibrationally excited states (${v}^{\ensuremath{'}}=32--47$) or in low vibrational states (${v}^{\ensuremath{'}}=4--6$) of the $a\text{ }^{3}\ensuremath{\Sigma}_{u}^{+}$ triplet ground state. The rate coefficients $\ensuremath{\beta}\ensuremath{\sim}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ are found to be largely independent of the vibrational and rotational excitation indicating unitary limited cross sections.