Parametric amplification with self-pumped Josephson junctions

The parametric nature of supercurrent in Josephson junctions may be exploited for amplification of high frequency signals in several modes of operation, where in each case the reactance variation is provided by the internal oscillations due to the average contact potential, a)One mode is negative resistance amplification with a single idler. This mode is entirely equivalent to that generally employed in conventional parametric amplifiers with varactor diodes. b)Negative resistance amplification with several idlers at further combination frequencies. This mode of operation is typical for the resistively shunted junction model, c)Amplification by upconversion, which is conceptually employed in the rf SQUID used in magnetometry. Experimental verifications of these various modes are described and their suitability for low noise amplification discussed. The upconverter experiment permitted the measurement of device noise by variation of the temperature of the input termination. An upper noise limit of 15°K is established. This experiment demonstrates that in high frequency application of active self-oscillating Josephson junctions the fundamental noise achievable is not greatly in excess of the thermal limit.