Broadband variational measurement of a classical force using strongly nondegenerate dichromatic optical pump

Maximal sensitivity of classical force detectors utilizing nonlinear opto-mechanical transducers is generally defined by the standard quantum limit resulting from the contamination of the detected signal with noncommuting quantum noises. This restriction can be circumvented by the optimal detection protocols. We here show theoretically that interrogating a resonant opto-mechanical displacement transducer with a strongly nondegenerate dichromatic optical probe enables a quantum back-action evading measurement of a classical force acting on the mechanical oscillator being a part of the opto-mechanical transducer.