Superfluid-to-Mott transition in a Bose-Hubbard ring: Persistent currents and defect formation

We revisit here the Kibble-Zurek mechanism for superfluid bosons slowly driven across the transition toward the Mott-insulating phase. By means of a combination of the time-dependent variational principle and a tree-tensor network, we characterize the current flowing during annealing in a ring-shaped one-dimensional Bose-Hubbard model with artificial classical gauge field on up to 32 lattice sites. We find that the superfluid current shows, after an initial decrease, persistent oscillations which survive even when the system is well inside the Mott insulating phase. We demonstrate that the amplitude of such oscillations is connected to the residual energy, characterizing the creation of defects while crossing the quantum critical point, while their frequency matches the spectral gap in the Mott insulating phase. Our predictions can be verified in future atomtronics experiments with neutral atoms in ring-shaped traps. We believe that the proposed setup provides an interesting but simple platform to study the nonequilibrium quantum dynamics of persistent currents experimentally.