1D bosons in optical lattices: from Superfluid to Bose glass

In this thesis we experimentally study fundamental problems related to the physics of bosonic systems at very low temperatures, close to the absolute zero, in the presence of both an ordered and a disordered optical lattice. We focus our study on one-dimensional (1D) systems which, besides being more accessible from a theoretical view point, exhibit very peculiar features such as, for instance, strong quantum phase fluctuations. Such phase fluctuations significantly affect the properties of a superfluid, leading to a new, quantum source of dissipation, the phase slips, besides the known classical energetic and dynamical instabilities. The first experimental evidence of quantum phase slips in a 1D atomic superfluid sample is reported in this thesis. We explore for the first time the phase diagram describing the low-temperature properties of 1D disordered bosonic systems. Measurements of coherence, transport and excitation spectra highlight the features of a disordered insulator that extends from weak to strong interactions sorrounding the superfluid phase. Such a finite-T disordered insulator strongly resembles the T = 0 Bose glass phase predicted by theory. A comparison with theoretical analysis taking into account finite temperature and inhomogeneity effects, confirm the experimental results.