Dynamics of a single Rydberg shell in time dependent external fields

Probabilities for adiabatic or near-adiabatic state transformation within a highly excited shell of Li(n = 25) were studied experimentally and theoretically for a time dependent electric field, E→(t), and a constant magnetic field, B→. The fields were sufficiently weak and the time dependence slow enough such that only states belonging to the chosen shell were involved. The studies show that the dynamics are governed by the approximate hydrogenic character of the system in most cases, but for some specific time dependences it is influenced strongly by core interactions as expressed through the quantum defects, δ_l. The s-state is effectively decoupled from the rest of the n = 25 manifold due to a very large quantum defect. However the quantum defects of the p, d and f states are shown to play a decisive role in the dynamics. The core interactions lead to avoided crossings, non-adiabatic state transformations, and possibly even phase-interference effects. When a resonance condition pertaining to the hydrogenic character of the system is fulfilled, a linear Stark state is transformed completely into a circular Stark state oriented along E→_f.