Underdamped long Josephson junction coupled to overdamped single-flux-quantum circuits

We report a circuit that integrates an underdamped long Josephson junction with overdamped single-flux-quantum (SFQ) circuits. We confirm that the resonant soliton modes in the long junction are not affected by SFQ cells coupled to the junction, and demonstrate that the radiation frequency and linewidth of the soliton resonances can be measured with SFQ T-flip-flops. Our experimental results also show that a 4π quantum mechanical phase leap at the end of the long junction, which is due to the reflection of a soliton, creates two single flux quanta propagating in the overdamped Josephson transmission line.