Broadband quantum back action evading measurements of a resonant force (Q2064212)

The authors propose a technique to improve the measurement of a classical force acting on a massive mechanical oscillator via an optimal meter beyond the standard quantum limit. The proposed strategy exploits a dichromatic rather than monocromatic field probe in a variational approach. The dichromatic probe allows to decouple the measured signal from the back action noise, so that the latter can be separately detected and subtracted from the measurement result. This improves the ordinary scheme in which the back action results from the amplitude fluctuations of the monochromatic probe wave while the signal is recorded in its phase, so that they cannot be measured simultaneously in the same frequency band.