Resonator coupled Josephson junctions; parametric excitations and mutual locking

Self-pumped parametric excitations and mutual locking in systems of Josephson tunnel junctions coupled to multimode resonators are reported. For the very large values of the coupling parameter, obtained with small Nb-Al/sub 2/O/sub 3/-Nb junctions integrated in superconducting microstrip resonators, the DC I-V characteristic shows an equidistant series of current steps generated by subharmonic pumping of the fundamental resonator mode. This is confirmed by measurement of frequency and linewidth of the emitted Josephson radiation.