Hello! If I have an ion which can be treated as a 2 level system, in a time varying electric field (the variation of the field doesn't need to be on or close to resonance, but for simplicity we can assume it is an oscillatory field) can I simply separate the problem into a center of mass motion and an internal 2 level system motion. Basically the ion would move up and down under the influence of the field, but in the ion's rest frame we would just have a normal time varying field, as if the ion wouldn't move at all. Would this work or am I missing some coupling between the internal and external degrees of freedom? Thank you!