The multiphoton ionization of hydrogen Rydberg atoms in strong
microwave fields is a seemingly simple system with complex
dynamics. Here we investigate ionization with bichromatic pulses using
methodology of chaos.
1.Reducing multiphoton ionization by local control:
We present a control procedure to reduce the stochastic ionization
of hydrogen atom in a strong microwave field by adding to the
original Hamiltonian a comparatively small control term which
might consist of an additional set of microwave fields. This
modification restores select invariant tori in the dynamics and
prevents ionization. We demonstrate the procedure on the
one-dimensional model of microwave ionization.
2.How periodic orbit bifurcations drive multiphoton ionization:
The multiphoton ionization of hydrogen by a strong bichromatic microwave
field is a complex process prototypical for atomic control research. Periodic
orbit analysis captures this complexity: Through the stability of periodic
orbits we can match qualitatively the variation of experimental ionization
rates with a control parameter, the relative phase between the two modes of the
field. Moreover, an empirical formula reproduces quantum simulations to a high
degree of accuracy. This quantitative agreement shows how short periodic orbits
organize the dynamics in multiphoton ionization.