Characterization of a Josephson Junction Comb Generator

We present a new type of microwave frequency combs with a potentially calculable pulse shape. The device is an array of 1500 Josephson junctions (JJs) connected in series along a transmission line. The pulse generation is based on the nonlinearity of the JJs. A large-signal network analyzer and a cryogenic probe station are used to characterize the pulses in the frequency domain up to 50 GHz. We compare the measured data to simulations that use the resistively and capacitively shunted JJ model. The amplitude stability of the demonstrated comb generator is better than 0.5 dB per 0.1 dB input drive variation within the operating range. Finally, we observe qualitative agreement between the measured and simulated power spectrum dependence on the input power, and discuss possible improvements to the system model.