Mobile impurity near the superfluid-Mott insulator quantum critical   point in two dimensions
  We consider bosonic atoms in an optical lattice at integer filling, tuned to the superfluid-Mott insulator critical point, and coupled to a single, mobile impurity atom of a different species. This setup is inspired by current experiments with quantum gas microscopes, which enable tracking of the impurity motion. We describe the evolution of the impurity motion from quantum wave packet spread at short times, to Brownian diffusion at long times. This dynamics is controlled by the interplay between dangerously irrelevant perturbations at the strongly-interacting field theory describing the superfluid-insulator transition in two spatial dimensions. 
Matthias Punk, Subir Sachdev
cond-mat.quant-gas