An extension to the noise theory of RF SQUIDs with implications for gravitational radiation detectors

The noise theory of an RF SQUID is extended to include those components of flux noise which appear physically linking the SQUID loop. This noise is a consequence of phase fluctuations of the quantum transitions in the SQUID and can react on the system whose parameters are being measured by the SQUID sensor. In particular, gravitational wave detector is considered whose motion is sensed by an RF SQUID system; and it is shown that the back-reaction, combined with other noise, imposes a limit to the detector sensitivity.