  An ultracold gas of interacting fermionic atoms in a three-dimensional
optical lattice is considered, where the lattice potential strength is
periodically modulated. This non-equilibrium system is non-perturbatively
described by means of a Keldysh-Floquet-Green's function approach for
Mott-Hubbard systems employing a generalized dynamical mean field theory
(DMFT). Strong repulsive interactions between different atoms lead to a Mott
insulator state for the equilibrium system, but the additional external driving
at zero temperature yields a non-equilibrium quantum critical behavior, where
an infinite number of Floquet states arise and a transition to the liquid and
conducting phase is given.
