Weak-Coupling Theory for Low-Frequency PeriodicallyDriven Two-Level Systems

We generalize the Wu-Yang strong-coupling theory to solveanalytically periodically driven two-level systems in the weak-coupling andlow-frequency regimes for single- and multi-period periodic driving ofcontinuous-wave-type and pulse-type including ultrashort pulses of a fewcycles. We also derive a general formula of the AC Stark shift suitable for such diverse situations.