PhD Dissertation Defense
Department of Physics, University of Connecticut
This thesis comprises two topics in the field of the ultracold atomic and molecular physics, both involving formation of ultracold 85Rb2 by photoassociation (PA). Typically, these ground-state molecules are formed mainly in the very highest vibrational levels, rather than the low-v levels that will be required for most future investigations of ultracold molecular physics and chemistry. The first topic of my research is a method for circumventing this problem: resonant enhancement (RE) of photoassociative ground state molecule production. The key idea of RE is to photoassociate pairs of colliding atoms into an excited state that has a bimodal vibrational probability distribution, with one peak at long range to enhance the photoassociation rate and another at shorter range to enhance radiative decay into deeply bound levels of the ground-state. This can be arranged thanks to the strong spin-orbit perturbative interaction between the two 0+u states converging to two different asymptotes, (5s+5p1/2) and (5s+5p3/2). This method enhances ground-state molecule formation in the region well below the dissociation limit. The experimental work described here was done at the University of Connecticut in collaboration with C.P. Koch at the Institut fu ̈r Theoretische Physik, Freie Universitat Berlin, Germany, who performed a on the theoretical analysis.
The second part of my thesis is the investigation of ultracold molecules in an optical dipole trap. We have constructed a quasi-electrostratic optical trap (QUEST) for 85Rb using a focused CO2 laser. This provides a very high density of ultracold atoms, up to 1012 cm−3, providing much higher photoassociation rates. It also keeps the molecules trapped once they have formed. The QUEST provides an ample trapping lifetime for both trapped atoms and molecules, about 106 for atoms and about 105 for high-v molecules. The long lifetime of the trapped molecules and atoms, combined with their high density, allows us to study interactions such as atom-molecule or molecule-molecule collisions in the ultracold regime. A preliminary experiment on Rb2 molecular decay is described.