Optomechanical backaction-evading measurement without parametric instability

We review a scheme for performing a backaction-evading measurement of one mechanical quadrature in an optomechanical setup. The experimental application of this scheme has been limited by parametric instabilities caused in general by a slight dependence of the mechanical frequency on the electromagnetic energy in the cavity. We find that a simple modification to the optical drive can effectively eliminate the parametric instability even at high intracavity power, allowing realistic devices to achieve sub-zero-point uncertainties in the measured quadrature.

Figure 1

The field envelope $\alpha \left(t\right)$ needed to cancel higher harmonic oscillations in the intracavity energy ${\left|\alpha \left(t\right)\right|}^2$, using (a) 1, (b) 2, (c) 4, and (d) 16 additional drive tones.