Experiments

Interacting bosons in a disordered potential

Owing to the ongoing impressive progress in the field of ultracold atoms, the simple ideal models appearing in condensed matter textbooks are being promoted from rough toy models to actual simulation tools.
Among the many avenues of research that this new field has opened, of particular interest is the study of the effects of disorder on the coherence and transport properties of quantum systems. The phase coherence and interference effects taking place in these systems underlie important phenomena, such as superfluidity, and can affect high precision devices such as interferometers, accelerometers and gyroscopes.
A clear picture of the role played by small random imperfections in this setting is hence important, and the controlled environment provided by the “cold atom toolbox” is an ideal setting to develop it.
Our research activity in this field focuses on the theoretical characterization of the quantum phases arising in ultracold lattice system as a result of the competition between disorder and interactions. In order to make closer contact with ongoing experiments, we do no restrict ourselves to a thermodynamic study of the quantum phases, but rather we employ dynamical probes such as current-carrying states. Other than the uncorrelated disorder typical of standard textbook models, we plan to investigate the correlated yet highly controllable disordered potentials appearing in current experiments, typically obtained from the light-matter interaction between atoms and speckle-field patterns or quasi-random bichromatic lattices.
In a parallel, related investigation we aim at the characterization of the statistical properties of the disorder arising from the presence of a secondary species whose kinetic degrees of freedoom are quenched.

Superfluid fraction in a 3D Bose-Hubbard model at filling 1. The circles, obtained from QMC simulations and signaling the boundaries of the superfluid phase, confirm the reliability of the Gutzwiller approximation used to obtain the density plot.

Boundary of the superfluid phase for a filling-2 Bose-Hubbard model, as provided by our dynamical analysis. The black and white boundaries correspond to adiabatic and diabatic protocols, respectively.