A disordered insulator in an optical lattice

Disorder can profoundly affect the transport properties of a wide range of quantum materials. At present, significant disagreement exists regarding features of the disordered Bose-Hubbard model, which is used to study disorder in strongly correlated bosonic systems(1,2). Here, by measuring transport(3) in a disordered optical lattice(4), we discover a disorder-induced superfluid-to-insulator transition in this system, in quantitative agreement with a predicted superfluid-Bose-glass transition from recent numerical simulations(5). Both the superfluid-to-insulator transition and correlated changes in the atomic quasimomentum distribution-which verify a simple model for the interplay of disorder and interactions in this system-are phenomena new to the unit-filling regime explored in this work. We find that increasing disorder strength generically leads to greater dissipation, excluding predictions of a disorder-induced or 're-entrant' superfluid. Whereas the absence of a re-entrant superfluid may be explained by finite temperature, the measured bounds on entropy strongly constrain theory.