Third order correction to localization in a two-level driven system
  A general result is presented on the lack of second order corrections and on the form of the leading order Floquet quasi-energies in the high-frequency approximation for a two-level driven system. Then, by a perturbative approach in the high-frequency approximation that uses dual Dyson series and renormalization group techniques [M. Frasca, Phys. Rev. B 68, 165315 (2003)], we obtain a third order correction for a sinusoidal driving field that is the same obtained by Barata and Wreszinski [Phys. Rev. Lett. 84, 2112 (2000)], confirming their result that localization deviates from the zeros of the zero-th order Bessel function when higher order terms are taken into account. Three different expressions for this correction are compared. An important consequence of this result is that gives complete support to the correctness of both methods. Finally, the limitation of high-frequency approximations is presented by comparison with numerical results for a sinusoidal driving field. 
Marco Frasca