"Non-equilibrium quantum dynamics of spin impurities using ultracold atoms."

"Ultracold-atom experiments are suitable to study out-of-equilibrium dynamics of quantum many-body systems. Here I will present the quantum dynamics of deterministically and locally created mobile spin impurities in the one-dimensional bosonic atoms in optical lattices. First, we investigate the dynamics of a single-spin impurity. In the Mott-insulating regime, the coherent propagation of a magnetic excitation, or a magnon, in the Heisenberg model can be observed. Extending the study to the superfluid regime of the bath, we quantitatively determine how the bath affects the motion of the impurity, showing evidence of polaronic behavior. Second, we observe bound states of two magnons in a Heisenberg chain by tracking their dynamics. Such bound states were pointed out theoretically by H. Bethe in 1931, and our novel microscopic study of quantum magnets can directly confirm their existence."