Uniform semiclassical approach to fidelity decay

We use uniform semiclassical approximation for fidelity in order to derive its decay in the regime of large perturbations. Numerical computations agree with our theoretical predictions. Moreover, our theory allows to explain previous findings, such as exponential decay with twice the Lyapunov rate, and deviations from the Lyapunov decay rate in cases where the classical finite-time instability is non-uniform in phase space