Nalbach, P.Leyton, V.2020-02-102020-02-102018-06-0724699926https://repositorio.usc.edu.co/handle/20.500.12421/2708We derive a Magnus expansion for a frequency chirped quantum two-level system. We obtain a time-independent effective Hamiltonian which generates a stroboscopic time evolution. At lowest order the according dynamics is identical to results from using a rotating wave approximation. We determine, furthermore, also the next higher-order corrections within our expansion scheme in correspondence to the Bloch-Siegert shifts for harmonically driven systems. Importantly, our scheme can be extended to more complicated systems, i.e., even many-body systems.enQuantum opticsBloch-Siegert shiftComplicated systemsMagnus expansionArticle