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Frieling, Erik Bernard

University of British Columbia

This thesis describes experiments with magnetically and optically trapped ultra-cold gases of ⁶Li and ⁸⁵⁺⁸⁷Rb. We describe three distinct areas of investigation, with a common theme of probing collisions that are universal under certain conditions, with the universality breaking down if these are violated: a study of the reactive collisions of deeply bound ⁶Li₂ dimers, the use of ultra-cold atoms as a pressure sensor by measuring the loss rate due to collisions with background gases at room temperature, and progress towards investigating heteronuclear collisional resonances between ultra-cold ⁶Li and ⁸⁵⁺⁸⁷Rb with the long-term goal of investigating the Efimov effect. We report on the optical synthesis of deeply bound triplet a(1³Σᵤ⁺) ⁶Li₂ molecules in a single quantum state by stimulated Raman adiabatic passage. The ensemble lifetimes for these molecules were limited by dimer-dimer collisions whose rate depends on the rovibrational state of the collision partners. The loss rate observed follows a universal prediction for the |v=0,5,8; N=0,2⟩ states and, remarkably, a sub-universal rate for the |v=9; N=0⟩ state. We find that molecules in the ground state of the triplet potential are also collisionally unstable, consistent with theoretical predictions that molecules in any of the triplet levels are chemically unstable and decay due to a barrier-less trimer formation process. Next, we report on a comparative measurement of the cross-section for trap loss inducing collisions (⟨σlossv⟩) of ⁶Li and ⁸⁷Rb atoms when exposed to various common background gases found in ultra-high vacuum (UHV) environments: H₂, He, Ne, N₂, Ar, Kr and Xe. The quantity ⟨σlossv⟩ exhibits universality for heavy species and is essential for converting the observed loss rate into a sensitive measurement of the background gas density or pressure. Finally, we discuss the production of ultra-cold mixtures of ⁶Li and ⁸⁵⁺⁸⁷Rb atoms and progress toward investigating heteronuclear Feshbach resonances. These resonances allow us to tune the interaction strength, an essential tool for investigating few and many-body physics in these systems. We discuss the particular example of the Efimov effect, which would be a natural topic of study following our investigation of the Feshbach resonance spectrum.

Text

2024-04-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88102

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/