Experimental studies of a degenerate unitary Bose gas

<p>A dilute Bose-Einstein condensate (BEC) near a Feshbach resonance provides experimental\&nbsp;<span style="line-height: 1.6em;">physics with a clean and controllable system to investigate strongly interacting many-body systems.\&nbsp;</span><span style="line-height: 1.6em;">The ability to tune the scattering length allows BECs to be projected onto strong interactions from\&nbsp;</span><span style="line-height: 1.6em;">an initial weakly interacting state. However, historically, studying a bulk 3D strongly interacting\&nbsp;</span><span style="line-height: 1.6em;">BEC has been difficult, as these systems are inherently unstable due to three-body inelastic collisions.\&nbsp;</span><span style="line-height: 1.6em;">Thus, 2D, 1D, lattice confined, and two component Fermi gases were used to explore the\&nbsp;</span><span style="line-height: 1.6em;">strong interactions in an ultracold gas. In this thesis, I present the first measurement of a strongly\&nbsp;</span><span style="line-height: 1.6em;">interacting 3D <sup>85</sup>Rb BEC. I introduce our experimental system and the techniques we used to probe\&nbsp;</span><span style="line-height: 1.6em;">the BEC. I first report on probes of a BEC in the weakly interacting regime. To probe a spherical\&nbsp;</span><span style="line-height: 1.6em;"><sup>85</sup>Rb BEC with strong interactions we implemented a novel experimental technique that allowed us\&nbsp;</span><span style="line-height: 1.6em;">to quickly change the interactions, bypassing inelastic losses. We projected the BEC onto unitarity,\&nbsp;</span><span style="line-height: 1.6em;">where the scattering length diverges and the interactions are infinite, in order to observe dynamics\&nbsp;</span><span style="line-height: 1.6em;">and the unexpectedly long lifetime of the gas. Additionally, we observe a universality of the gas\&nbsp;</span><span style="line-height: 1.6em;">with respect to the length scale set by the interparticle spacing.</span></p>
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University of Colorado Boulder
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