Inhomogeneous broadening of a Mott insulator spectrum

We report an analysis of the inhomogeneous broadening of the excitation spectrum of a three-dimensional (3D) Mott insulator (MI) due to the presence of weak disorder. We present a theoretical model predicting the modification in the spectrum and compare the results to the experimental data obtained for a system of ultracold 87Rb atoms in a 3D optical lattice, where quasi-disorder is added by means of an auxiliary 1D optical lattice with non-commensurate wavelength. The model shows good agreement with the measured points, confirming a significant broadening of the MI spectrum resonances even for a very small height of the disordering potential.