Ionization of high-nH atoms by bichromatic microwave fields

We present the first quantum-mechanical calculations of the ionization probability of high-n H Rydberg atoms perturbed by strong bichromatic microwave fields. The quantum-mechanical ionization thresholds agree very well with the experimental findings. The effect of rational approximants to the experimental frequency ratio is studied. We provide evidence to show that for the range of principal quantum numbers and field parameters investigated experimentally, the response of the H atoms to the bichromatic microwave field is quasiperiodic.