Numerical and Experimental Results on Josephson Junctions Irradiated by a Biharmonic Drive

We report some numerical results regarding the characteristics of rf-induced constant voltage steps in a voltage-biased Josephson junction irradiated by a biharmonic drive, namely a rf signal obtained by combining two microwaves of frequency ? and 2?. The maximization of step amplitudes depends strongly on a careful choice of biharmonic drive parameters. We have made experiments on single, large, Josephson junctions, using a biharmonic signal with a fundamental frequency in the range 8-12 GHz. Under these conditions, only a small enhancement of the amplitude of the quantized steps with respect to the single drive case has been observed.