Degenerate Polar Molecules with Controlled Interactions and Reactivity


Ultracold polar molecules, which have complex internal structures and dipole moments tunable with external electric fields, are a promising system for studying many-body physics. Producing degenerate molecules and observing quantum effects has been a long-standing goal. Technical barriers that have prevented reaching degeneracy include inelastic loss of molecules from chemical reactions and relatively high temperatures, since standard methods of cooling atomic gases are not effective for molecules. This thesis documents the creation of degenerate potassium-rubidium (KRb) molecules and the control of intermolecular interactions using electric fields. In three dimensions, molecules are produced by pairing in a degenerate atomic mixture and reach thermal equilibrium through elastic collisions with unpaired atoms. We probe the fermionic statistics of the degenerate molecules by measuring reduced number fluctuations in the momentum state occupation, a direct consequence of the Pauli exclusion principle. In two dimensions, we apply an external electric field to induce repulsive dipolar interactions, suppressing inelastic collisions and enabling direct evaporation to degeneracy. At particular electric fields, pairs of rotational states can be tuned into resonance, generating strongly attractive or repulsive intermolecular potentials and modifying the chemical reaction rate by orders of magnitude. We also develop the capability to address the molecule distribution with nanometer-scale precision using electric field gradients, enabling sub-wavelength field sensing and microscopic control of interacting ultracold molecules.

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Department of Physics
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University of Colorado Boulder
Boulder, CO
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