Influence of an external radiation on a Josephson oscillator and phase locking effects

The frequency conversion signal of a Josephson junction operating as an oscillator mixer is not observable when the intermediate frequency is too low. To test experimentally the possibility of phase-locking effects a superconducting point contact oscillating atf_{0} \sim 9GHz is irradiated with an external radiation of frequency f1between 8 and 18 GHz. The Josephson oscillation level and linewidth are measured as a function of the power level P1of the external signal at f1with\deltaf = |f_{0}-f_{1}|as a parameter. With large\deltafvalues, the variations of the Josephson oscillation and linewidth are the consequence of the V-I characteristic modification. With low δf, the operating point in the VIC is in the induced step curvature and the observed variations show that progressive phase looking occurs.