Resonance Positions and Widths for Time‐Periodic Hamiltonians by the Complex Coordinate Method

The complex coordinate method combined with the Floquet‐Bloch theory has the advantage of treating the metastable quasi‐energy states (i.e., resonances) of time‐periodic Hamiltonians in terms of bound state formalism. The formalism derived here is a general one. It enables one to use complex basis functions when needed and to calculate the resonance positions and widths for any time‐periodic Hamiltonians. A numerical example is given to illustrate the potential use of the proposed method in the study of the dynamics of laser‐driven systems and of time‐periodic classical chaotic Hamiltonians.