The Scattering and Coherence of a Fermi Polaron*

We probe the coherence of a strongly interacting $^{40}$K impurity in a Fermi sea of ${^6}$Li atoms using time-resolved Ramsey spectroscopy. The measured variation of the coherence with the interaction strength and temperature is well-explained by the low-energy scattering of the impurity in the Fermi liquid picture. For very strong interactions, we observe additional dynamics arising from the dressing of the impurity by its environment.