3-Mode Detection for Widening the Bandwidth of Resonant Gravitational Wave Detectors

We have implemented a novel scheme of signal readout for resonant gravitational wave detectors. For the first time, a capacitive resonant transducer has been matched to the signal amplifier by means of a tuned high $Q$ electrical resonator. The resulting 3-mode detection scheme widens significantly the bandwidth of the detector. We present here the results achieved by this signal readout equipped with a two-stage SQUID amplifier. Once installed on the AURIGA detector, the one-sided spectral sensitivity obtained with the detector operated at 4.5 K is better than ${10}^{\ensuremath{-}20}\text{ }\text{ }{\mathrm{Hz}}^{\ensuremath{-}1/2}$ over 110 Hz, and in good agreement with the expectations.