Phase diagram of the Bose-Hubbard model on a ring-shaped lattice with tunable weak links

Motivated by recent experiments on toroidal Bose-Einstein condensates in all-optical traps with tunable weak links, we study the one-dimensional Bose-Hubbard model on a ring-shaped lattice with a small region of weak hopping integrals using quantum Monte Carlo simulations. Besides the usual Mott insulating and superfluid phases, we find a phase which is compressible but nonsuperfluid with a local Mott region. This “local Mott” phase extends in a large region of the phase diagram. These results suggest that the insulating and conducting phases can be tuned by a local parameter, which may provide additional insight into the design of atomtronic devices.