Second-order effects for the hydrogen atom in perpendicular electric and magnetic fields and instability of classical electron trajectories

摘要

Degeneracy of energy levels of excited hydrogen atoms is not fully lifted by external perpendicular electric and magnetic fields in the first order of perturbation theory. Within the submanifold of residual degeneracy the levels splitting is governed by the second-order effects. The related classical electron trajectories exhibit instabilities characterized by the Lyapunov exponent. The present study establishes quantum mechanical implications of these instabilities. In particular, we derive from a quantum framework a simple analytical approximation for the Lyapunov exponent. The classical instabilities are linked to the presence of a diabatic quasistationary state in the quantum mechanical problem. Its meaning is elucidated by considering a related non-stationary quantum system with time-dependent field parameter. Some of the state-to-state transition probabilities are approximately expressed via Lyapunov exponents. Exact formulae for these probabilities are derived in the framework of multistate generalization of the Landau-Zener model. Non-adiabatic transitions are interpreted in terms of analytical properties of adiabatic potential curves.