TY - JOUR A1 - Nalbach, Peter A1 - Leyton, Vicente T1 - Magnus expansion for a chirped quantum two-level system T2 - Physical Review A N2 - We 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. Y1 - 2018 UR - https://whge.opus.hbz-nrw.de/frontdoor/index/index/docId/3129 VL - 98 IS - 2 SP - 023855 ER -