Abstract
One of the most important issues in disordered systems is the interplay of the disorder and repulsive interactions. Several recent experimental advances on this topic have been made with ultracold atoms, in particular the observation of Anderson localization and the realization of the disordered Bose–Hubbard model. There are, however, still questions as to how to differentiate the complex insulating phases resulting from this interplay, and how to measure the size of the superfluid fragments that these phases entail. It has been suggested that the correlation function of such a system can give new insights, but so far very little experimental investigation has been performed. Here, we show the first experimental analysis of the correlation function for a weakly interacting, bosonic system in a quasiperiodic lattice. We observe an increase in the correlation length as well as a change in the shape of the correlation function in the delocalization crossover from Anderson glass to coherent, extended state. In between, the experiment indicates the formation of progressively larger coherent fragments, consistent with a fragmented BEC, or Bose glass.
Highlights
The interplay of disorder and interactions lays at the heart of the behaviour of many physical systems, including superfluid helium in porous media [1], granular and thin-film superconductors [2,3,4,5], and light propagating in disordered media [6,7,8]
A central aspect for ultracold bosonic systems is the competition between disorder, which tends to localize particles, and weak repulsive interactions, which instead have a delocalizing effect
We have characterized the entire delocalization crossover of a disordered bosonic system caused by weak repulsive interactions through study of the spatial localization, phase coherence, and correlation properties
Summary
The interplay of disorder and interactions lays at the heart of the behaviour of many physical systems, including superfluid helium in porous media [1], granular and thin-film superconductors [2,3,4,5], and light propagating in disordered media [6,7,8]. Ultracold atoms in disordered optical potentials are a promising system for such investigations [11, 12] due to their unprecedented control over the disorder strength and interactions They have already enabled the observation of Anderson localization for bosons in the regime of negligible interactions [13, 14], and recent experiments have investigated the effect of interactions on the localization properties, both in the weakly interacting [15, 16] and strongly correlated [17,18,19] regimes. Recent interest has been in the correlation properties of disordered, interacting bosonic systems [41,42,43,44], in order to differentiate insulating phases such as the Bose glass from the superfluid regime.
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