The Axion Dark Matter eXperiment (ADMX) was designed to detect ultra-weakly interacting relic axion particles by searching for their conversion to microwave photons in a resonant cavity positioned in a strong magnetic field. Given the extremely low e
xpected axion-photon conversion power we have designed, built and operated a microwave receiver based on a Superconducting QUantum Interference Device (SQUID). We describe the ADMX receiver in detail as well as the analysis of narrow band microwave signals. We demonstrate the sustained use of a SQUID amplifier operating between 812 and 860 MHz with a noise temperature of 1 K. The receiver has a noise equivalent power of 1.1x10^-24 W/sqrt(Hz) in the band of operation for an integration time of 1.8x10^3 s.
Hidden U(1) gauge symmetries are common to many extensions of the Standard Model proposed to explain dark matter. The hidden gauge vector bosons of such extensions may mix kinetically with Standard Model photons, providing a means for electromagnetic
power to pass through conducting barriers. The ADMX detector was used to search for hidden vector bosons originating in an emitter cavity driven with microwave power. We exclude hidden vector bosons with kinetic couplings {chi} > 3.48x10-8 for masses less than 3 {mu}eV. This limit represents an improvement of more than two orders of magnitude in sensitivity relative to previous cavity experiments.
