The behaviour of a mobile impurity particle
interacting with a quantum-mechanical medium is of fundamental
importance in physics. Ultracold atomic gases have greatly
improved our understanding of the impurity problem owing to the
high degree of control over experimental parameters such as
interactions and atom population. I will discuss recent
theoretical and experimental progress in exploring the
properties of impurities interacting with a fermonic medium. In
particular, I will present a theoretical approach for describing
the coherent non-perturbative quantum evolution following a
quench of the impurity-medium interactions.
 M. Cetina, M. Jag, R. S. Lous, I. Fritsche,
J. Walraven, R. Grimm, J. Levinsen, M. Parish, R. Schmidt, M.
Knap, E. Demler, Science 354, 96 (2016).
 M. M. Parish and J. Levinsen, Phys. Rev. B
94, 184303 (2016).
 W. E. Liu, J. Levinsen and M. M. Parish,