The method of multiple time scales is applied to adiabatic systems. Adiabatic theorems for both classical and quantum systems are derived and expressions for Berry’s phase and its classical counterpart are obtained within the framework of a consistent approximation scheme.
The higher-order adiabatic approximation method of solving the Schr\"odinger equation for slowly transported quantum systems, which contains Berry's improved adiabatic theorem as its zeroth-order step, is generalized to solve evolution equations for a wide class of slowly transported classical systems. It is shown how the adiabatic condition is broken and transitions between different modes take place. Selection rules for such transitions are shown to be a topological property of the evolution path in parameter space.
We present details and expand on the framework leading to the recently introduced degenerate adiabatic perturbation theory [Phys. Rev. Lett. 104, 170406 (2010)], and on the formulation of the degenerate adiabatic theorem, along with its necessary and sufficient conditions [given in Phys. Rev. A 85, 062111 (2012)]. We start with the adiabatic approximation for degenerate Hamiltonians that paves the way to a clear and rigorous statement of the associated degenerate adiabatic theorem, where the non-Abelian geometric phase (Wilczek-Zee phase) plays a central role to its quantitative formulation. We then describe the degenerate adiabatic perturbation theory, whose zeroth-order term is the degenerate adiabatic approximation, in its full generality. The parameter in the perturbative power-series expansion of the time-dependent wave function is directly associated to the inverse of the time it takes to drive the system from its initial to its final state. With the aid of the degenerate adiabatic perturbation theory we obtain rigorous necessary and sufficient conditions for the validity of the adiabatic theorem of quantum mechanics. Finally, to illustrate the power and wide scope of the methodology, we apply the framework to a degenerate Hamiltonian, whose closed-form time-dependent wave function is derived exactly, and also to other nonexactly solvable Hamiltonians whose solutions are numerically computed.