Two-mode multiphoton transitions

Abstract

We have investigated multiphoton transitions driven by two harmonically related microwave fields in a two-level system. We observed pronounced dependence of the Rabi frequency on the amplitudes and relative phase of the fields in the low field limit and found that the Rabi frequency of the combined fields was given by the phasor sum of the Rabi frequencies of the individual fields. For strong fields, each individual Rabi frequency is modified by the presence of the other field and this intuitive phasor addition is no longer valid.