  We investigate a scheme to enhance the sensitivity in detecting weak
variations in a parameter of an optoelectromechanical system by detecting the
system response at radio frequencies. We consider a setup, where either one or
two mechanical modes mediate the interaction between an optical cavity and an
rf resonator. This system can be operated in a regime of impedance matching
where thermal fluctuations are redistributed among the system elements, and, in
particular, rf output noise can be reduced to the quantum vacuum noise level.
We show that this effect can be used to boost the sensitivity in detecting
parameter variations also in regimes of high thermal noise. We characterize the
performance of this protocol in detecting variations in the capacitance of the
rf resonator.
