Experiments

Ultra-cold dipolar gases in optical lattices

Dipolar gases are characterized by anisotropic and long-range interactions. In our group the study of dipolar physics has been focused on the emergence of new quantum phases, the effects of the dipolar drag and the physics of polarons. Special attention has been devoted to the study of dipolar atoms or molecules in optical lattices, which provide a realistic implementation of Hubbard-like models. This opens challenging possibilities of using ultra-cold gases as quantum simulators of known solid-state Hamiltonians and beyond.
The anisotropic character of the dipolar interaction is responsible for a dipolar induced resonance (DIR) related to the formation of a bound state of two dipoles, which affects crucially both the two-body and the many-body physics of the system. As the simplest many-body model accounting for the DIR, we have suggested an extended Bose-Hubbard two-bands atom-dimer model. We have investigated the effects of the DIR on the phase diagram and discussed under which conditions the atom-dimer extended Bose-Hubbard model can be mapped onto an effective atomic single-band extendend Bose-Hubbard model.
We are also investigating the dynamics of few dipolar particles in a lattice. The dynamics is crucially affected by the underlying presence of bound states. For long-range interactions, in the presence of the lattice, there exists several (attractive or repulsive) bound states whose wavefunction can be extended over several lattice wells. During the dynamics, in the case of attractive interactions, the bound states or equivalently the energy conservation underlying their existence, strongly affect the correlations at short distances, preventing two particles to come closer than a critical range.
Dipolar particles in optical lattices can also be exploited to create a disordered potential marked both by short- and long-range correlations. We have shown that when short-range correlations are dominant, extended states can appear in the spectrum. Introducing long-range correlations, the extended states, if any, are wiped out and localization is restored over the whole spectrum.

Quasi-analytical phase numerical phase diagram for N particles and N lattice sites showing the boundaries between SF, MDW and collapse phases in good agreement with the numerical exact diagonalization results..

The dipolar impurities trapped at random position in the optical lattice induce a long- and shor-range correlated disorder on the test dipole, free to move in the lattice.