Fractional photon-assisted tunneling in an optical superlattice: a leading order effect

Fractional photon-assisted tunneling is investigated both analytically and numerically for few interacting ultra-cold atoms in the double-wells of an optical superlattice. This could be realized experimentally by adding periodic shaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404 (2008)]. In order to understand the physics of the photon-assisted tunneling, an effective model based on the rotating wave approximation is introduced. The validity of this effective approach is tested for wide parameter ranges which are accessible to experiments in double-well lattices. The effective model goes well beyond previous perturbation theory approaches and is useful to investigate in particular the fractional photon-assisted tunneling resonances. Analytic results on the level of the experimentally realizable two-particle quantum dynamics show very good agreement with the numerical solution of the time-dependent Schrodinger equation. Far from being a small effect, both the one-half-photon and the one-third-photon resonance are shown to be leading order effects.