Scientific Calendar Event

The interplay of disorder and interactions can have a large impact on the properties of quantum systems.  It is well known that, whereas non-interacting particles can be localized by the destructive interference in a disordered potential, a weak repulsive interaction tends to establish coherence between single-particle localized states, thus weakening or destroying such localization.  The interplay of disorder and strong interactions is instead still a challenging problem.  One paradigmatic problem is that of low-temperature bosonic particles confined to a one-dimensional disordered environment, which, in addition to the standard superfluid and Mott phases, has been predicted to show a peculiar gapless insulating phase, the Bose glass [1,2], that is still proving to be elusive in experiments.  We investigate the behavior of a bosonic quantum gas close to T=0 confined in a one-dimensional quasi-periodic lattice, where interactions and disorder can be independently tuned.  By studying its momentum distribution, mobility and excitation spectrum features, we trace out a phase diagram showing a coherent phase surrounded by a gapless insulator.  The latter has a bosonic character at low interactions, and a fermionic one at large interactions, consistently with the expectations for the presence of a Bose glass phase.  Our results confirm long-standing theoretical predictions and indicate the way to study still open questions in 1D bosons and analogous disordered problems in higher dimensions and/or with fermions.

[1] D. S. Fisher, Phys.Rev. B 40, 546 (1989).
[2] T. Giamarchi, Phys. Rev. A 78, 023628 (2008).
Go to day