Multipump and quasistroboscopic back-action evasion measurements for resonant-bar gravitational-wave antennas

Abstract

A generalization of the back-action evasion (BAE) measurement technique, which we call multipump back-action evasion, has been demonstrated with a parametric electromechanical transducer similar to ones which are used on resonant-bar gravitational-wave detectors. The benefit of a BAE measurement is that the fluctuating back-action force of the transducer readout circuit acting on a test mass is squeezed, i.e., reduced in one of the quadrature phases of the test mass, thus improving the sensitivity for the detection of weak forces. The multipump BAE technique affords even greater noise squeezing than the BAE technique. Measured back-action noise squeezing factors are in quantitative agreement with the predictions of the model of a multipump BAE measurement. Using this system we have also demonstrated a quasistroboscopic position measurement when the number of pumps becomes large. The multipump BAE technique may be used to further improve the sensitivity of resonant-bar gravitational-wave antennas.