Measurement of forward and reverse signal transfer coefficients for an rf-biased SQUID

Abstract
Comprehensive measurements of the parameters characterizing an rf‐biased SQUID as a linear twoport are described. The behavior of the device corresponds in detail to the predictions of a recently published model of SQUID operation and is unexpectedly similar to that of a conventional reactive parametric amplifier. The measurements have been used to make the first reliable predictions of the noise temperature and optimum source impedance of an rf‐biased SQUID.