Noise in Josephson Junction Amplifiers

摘要

A Josephson junction amplifier working at cryogenic temperature based on Josephson effect was studied and a prototype amplifier at 30 MHz carrier frequency was made. The noise performance of the amplifier was poorer than expected because of the multiple quantum transition oscillations. The noise power per unit bandwidth S sub v sub n(f) of this amplifier is proportional to N(a) where N is quantum transition number; alpha is measured to be about 2.77. The noise level of this amplifier was calibrated by an f.m. noise calibration method. The input noise voltage per unit bandwidth square root of S sub v sub n(f) is typically 0.5 x 10 to the minus 9th power volt/square root of Hz at N = 1000 and 30 MHz carrier frequency, which is better than the best transistor amplifier presently available. The sensitivity may be improved considerably by going to a higher carrier frequency and a more careful design of the junction and the system. (Author)