ENHANCED JOSEPHSON RADIATION AND LINEWIDTH-NARROWING OF SUPERCONDUCTING MICROBRIDGES IN A RESONANT CAVITY

Abstract

Josephson radiation emitted from superconducting microbridges and coupled two-bridge junctions has been investigated at microwave frequencies. The radiation linewidth Ɗf and total radiation power P are found to vary with the output coupling controlled by a tuning stub in the cavity, indicating feedback-induced effects due to the radiation fields. We have found (Ɗf)min ~ 900 kHz, Pmax ~ 0.9 x 10-12 W for the single microbridge and (Ɗf)min ~ 60 kHz, Pmax ~ 5 x 10-12 W for the coupled bridges. The enhancement of radiated power and line-narrowing in the coupled bridges are attributed to coherent behaviour of the junctions