Wavepacket studies using quasi-one-dimensional Rydberg atoms: Phase-space localization and chaos
Stokely, Christopher Lee
Dunning, F. B.
Doctor of Philosophy
This thesis demonstrates that strongly polarized quasi-one-dimensional very-high-n potassium Rydberg atoms can be produced by photoexcitation of selected Stark states in the presence of a weak dc field. Calculations show that, for m = 0 states, significant photoexcitation occurs only in the vicinity of the Stark-shifted s, p, and d levels, and that those states located near the Stark-shifted d-level have sizable polarizations, i.e., a sizeable dipole moment. These predictions are confirmed experimentally by studying differences in their ionization characteristics when subject to a single pulsed uni-directional electric field of various widths applied parallel and anti-parallel to the do field. A strongly polarized atom behaves as a quasi-one-dimensional atom, and forms an excellent starting point for further control and manipulation of the atomic wavefunctions. Classical and quantum simulations for a one-dimensional atom predict that the wavepacket generated by application of a single very short uni-directional electric field pulse, termed a half-cycle pulse (HCP), which is equivalent to an application of an impulsive momentum transfer or "kick," periodically undergoes a simultaneous strong localization in both position and momentum. This corresponds to a momentary increase in the "statistical coherence" of the system and this phenomenon is analyzed using the course-grained Renyi entropy. The experimental signatures of transient phase space localization are demonstrated using a second probe HCP, applied at different times following the initial impulse. The behavior of Rydberg Stark states subject to a train of identical, equispaced HCPs is also investigated. The periodically kicked quasi-one-dimensional atom is ideally suited to the study of nonlinear Hamiltonian dynamics and chaos in an atomic system. Depending on whether the kicks are parallel or anti-parallel with the applied dc Stark field, theory predicts the phase space of such systems to be either fully chaotic or mixed, with islands of stability in a chaotic sea. The data provide evidence of dynamical stabilization and chaotic diffusion.