Formation of ultracold Rb$_2$ in the ground X$^1$$\Sigma$$^+_g$ state in an optical dipole trap

We present a study of the formation of ultracold ground-state Rb$_2$ molecules in an optical dipole trap formed by a focused CO$_2$ laser. Rubidium atoms are efficiently loaded from a magneto-optical trap (MOT) into the dipole trap, after a brief cooling and compression stage. The atomic sample is cooled significantly from 100 $\mu$K to 30 $\mu$K and the density is increased up to 10$^{12}$ cm$^{-3}$. After loading atoms into the dipole trap, a photoassociation laser is introduced to form ultracold molecules. The excited ultracold molecules spontaneously decay to the ground-state, which is subsequently detected by resonance-enhanced two-photon ionization using a pulsed dye laser. With the ultracold molecules trapped, we will pursue an experiment involving vibrational quenching of the molecules due to collisions with $^{85}$Rb atoms. With our state-selective detection, we will be able to measure the individual loss rates of each vibrational level. This work is supported by NSF.