Alkali Rydberg States in Electromagnetic Fields

We study highly excited hydrogen and alkali atoms (’Rydberg
states’) under the influence of a strong microwave field. As the
external frequency is comparable to the highly excited electron’s
classical Kepler frequency, the external field induces a strong
coupling of many different quantum mechanical energy levels and
finally leads to the ionization of the outer electron. While
periodically driven atomic hydrogen can be seen as a paradigm of
quantum chaotic motion in an open (decaying) quantum system, the
presence of the non-hydrogenic atomic core – which unavoidably has
to be treated quantum mechanically – entails some complications.
Indeed, laboratory experiments show clear differences in the
ionization dynamics of microwave driven hydrogen and non-hydrogenic
Rydberg states. In the first part of this thesis, a machinery is
developed that allows for numerical experiments on alkali and
hydrogen atoms under precisely identical laboratory conditions. Due
to the high density of states in the parameter regime typically
explored in laboratory experiments, such simulations are only
possible with the most advanced parallel computing facilities, in
combination with an efficient parallel implementation of the
numerical approach. The second part of the thesis is devoted to the
results of the numerical experiment. We identify and describe
significant differences and surprising similarities in the
ionization dynamics of atomic hydrogen as compared to alkali atoms,
and give account of the relevant frequency scales that distinguish
hydrogenic from nonhydrogenic ionization behavior. Our results
necessitate a reinterpretation of the experimental results so far
available, and solve the puzzle of a distinct ionization behavior
of periodically driven hydrogen and non-hydrogenic Rydberg atoms –
an unresolved question for about one decade. Finally,
microwave-driven Rydberg states will be considered as prototypes of
open, complex quantum systems that exhibit a complicated temporal
decay. However, we find considerable differences in the decay of
such real and experimentally accessible atomic systems, as opposed
to predictions based on the study of quantum maps or other toy
models with mixed regular-chaotic classical counterparts.