Small Dayem Bridges as Active Components in Microwave Circuits

We report X-band microwave measurements on superconducting thin film micro-bridges (Dayem bridges), mounted in a half wavelength cavity with an adjustable coupling to match the bridge properly. Power emission from the bridge of 10¿13 W in a 10 MHz bandwidth was measured. Current noise fluctuations caused a total voltage line width corresponding to 150-200 MHz, when the voltage across the bridge was swept through the resonance; from this we estimate a total power emission of 1-2·10¿12 W into this frequency interval. Transmission measurements and comparison with analogue computer calculations have revealed that an equivalent diagram consisting of an inductance in series with the resistively shunted Josephson junction model can account for the experimental results. A conclusion from these measurements is that there is a possibility for amplification in the device. Moreover, the nonlinearity of the device was used in a mixing experiment with the Josephson oscillation as local oscillator.