Rydberg atoms as sensitive magnetic probes

The multiphoton ionization of hydrogen in strong parallel microwave and sta tic fields is a fundamental problem of great complexity which has been the subject of recent experimental and theoretical studies. We show that the su perposition of an additional held, namely a static, relatively weak magneti c field, results in rapid oscillations of the ionization survival probabili ty. These rapid oscillations can be used as a very sensitive method for mea suring weak magnetic fields.