Chaotic enhancement of hydrogen atoms excitation in magnetic and   microwave fields
  We numerically investigate multiphoton ionization of excited hydrogen atoms in magnetic and microwave fields when up to 600 photons are required for ionization. The analytical estimates for the quantum localization length in the classically chaotic regime are in agreement with numerical data. The excitation is much stronger as compared to the case with microwave field only due to the chaotic structure of eigenstates in magnetic field. 
G.Benenti, G.Casati and D.L.Shepelyansky