External Field Control of Ultracold Atom-Molecule Mixtures: Quantum Collision Dynamics, Chemical Reactions, and Sympathetic Cooling

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This project aims at the development of a new, rigorous, and computationally efficient quantum scattering methodology for the theoretical description of low-temperature atom-molecule collisions and chemical reactions in the presence of external electromagnetic fields. A new methodology is needed in order to expand the number and variety of molecular species that can be cooled to the ultra-cold temperatures at which quantum phenomena become dominant. Until recently, the range of molecular species available for experiments in the ultra-cold domain has been limited to those diatomic molecules which can be produced by laser-induced binding of ultra-cold alkali-metal atoms. Expanding this range to include more complex molecular species requires the adoption of appropriate cooling techniques, especially so-called sympathetic cooling, by which elastic atom-molecule collisions within an ultra-cold alkali-metal atom "bath" serve to reduce the temperature of the participating molecules. The process of sympathetic cooling is effective providing that inelastic collisions which could internally heat the molecules, or which might expel them from the trapping environment, can be suppressed. The computational requirements for the accurate description of the relevant collisional processes are stringent, because the molecules involved are highly anisotropic, and because the trapping field environment of the molecule is also generally anisotropic. This project will provide much needed theoretical support to experimental groups honing the sympathetic cooling technique. If the technique is successful, it will drastically extend the range of molecular species available in the ultra-cold regime, with far-reaching implications for ultra-cold molecule-based quantum information processing, quantum simulation, controlled chemistry, and fundamental symmetry tests. As a basis for the improved methodology, the total angular momentum representation of molecular scattering states will be used. The methodology will be applied to elucidate the prospects for sympathetic cooling of the experimentally relevant polar molecules CaH, SrF, and SrOH with the alkali-metal atoms Li and Rb in magnetic and magneto-optical traps. The scientists will also explore new scenarios for controlling atom-molecule chemical reactions via tuning molecular Zeeman states, inducing vibrational Feshbach resonances, and applying superimposed electric and magnetic fields. The graduate students supported by this project will get extensive training in quantum scattering theory, molecular physics, numerical analysis, and computer programming, which will allow them to engage in collaboration with leading experimental groups, and gain international recognition for their research. The proposed work connects the fields of atomic and molecular physics and physical chemistry, thereby enhancing research collaborations between the Physics and Chemistry Departments of the University of Navada, Reno.