Bose Polarons in a Homogenous Bose-Einstein Condensate

We study Bose polarons in a homogeneous BEC of ³⁹K atoms, produced in an optical-box trap. The impurities are formed using rf-injection between spin states, and the interstate interactions are tuned using magnetic Feshbach resonances. Leveraging the suppression of inhomogeneous broadening in a box-trapped gas, we use a combination of injection spectroscopy and Ramsey-like many-body interferometry to access the injection spectrum (frequency domain) and the impurity-coherence function (time domain) for both attractive and repulsive interactions. On the repulsive side of the resonance, we resolve two energy branches, corresponding to a repulsive polaron and a many-body state connected to the Feshbach dimer, whose energy shifts with density. Finally, we obtain first measurements of the Bose-polaron quasiparticle residue using the many-body interferometry.