Low noise, permanently adjusted UHF SQUID magnetometer

We report the development of a simple 450MHz SQUID magnetometer, utilizing a symmetric two-hole permanently adjusted point contact SQUID ring. One hole of the SQUID ring is coupled to the center conductor of a resonant superconducting coaxial cavity. A superconducting coil, inserted into the other hole, allows us to couple an external flux into the SQUID system. The sensitivity is an order of magnitude better than that attained with identical SQUID rings biased at ∼10MHz. We show that this improvement can be achieved simply and relatively inexpensively, and without sacrificing the excellent flux coupling attainable with such SQUID rings.