Seminario
"Analytical Phase Diagram for the CurrentCarrying States of the Quantum Phase Model"
Relatore: Pierfrancesco Buonsante Istituto Nazionale di Ottica e LENS, Firenze
Aula Feynman
30 Ottobre 2012 ore 16.30
Abstract

A gas of (bosonic) alkhali atoms can be spatially confined, cooled down to virtually zero temperature and trapped in a "crystal of light" periodic potential. Under suitable
conditions a tightbinding approximation applies, and the
system can "simulate" the bosonic Hubbard model with a high degree of ideality and control over the parameters.
Besides the superfluidinsulator transition taking place in the groundstate at a critical value of the effective interaction, a transition to a "dynamical insulator" has been observed for the currentcarrying excited states of the model. The interactiondependent critical momentum $p_{\rm c}$ for such transition interpolates between the value for the modulational instability in the semiclassical dynamics of the model, $p_c=\pi/2$ in the noninteracting limit, and $p_c=0$ at the critical interaction for
the groundstate. We analyze the properties of the currentcarrying states in the Quantum
Phase Model, which is equivalent to the BoseHubbard
model for strong interactions and large average occupation numbers. A variational approach based on a simple Gutzwiller trial state allows us to derive the critical lines in the phase diagram of the system analytically.


