I will showcase two series of experiments using ultracold box-trapped 39K Bose gases, which offer widely tuneable interparticle interactions using so-called Feshbach resonances.
In the first series, we use conveniently situated interstate Feshbach resonances to create Bose polarons in a homogeneous Bose-Einstein condensate and map out the impurity-boson interactions from weak to strong. We measure the polaron energy and spectral response, observing reduced inhomogeneous broadening compared to previous harmonic-trap experiments. We also study the polaron formation dynamics using many-body interferometry.
In the second series, we turn off the interparticle interactions and violently drive the gas out of equilibrium. This realizes a novel far-from-equilibrium state that displays subdiffusive dynamic scaling behavior. The dynamics arise due to the interplay of a driven chaotic state and the presence of weak disorder. The resultant momentum distribution is essentially isotropic and features a remarkably uniform low-momentum population. Finally, I will discuss the prospects of using this novel state for other experiments.