Gaussian theory for estimating fluctuating perturbations with backaction-evading oscillator variables

We apply a Gaussian state formalism to track fluctuating perturbations that act on the position and momentum quadrature variables of harmonic oscillator. Following seminal proposal by Tsang Caves [Phys. Rev. Lett. 105, 123601 (2010)], Einstein-Podolsky-Rosen correlations with an ancillary oscillator are leveraged significantly improve estimates as relevant sensor can be arbitrarily squeezed while evading adverse effects from conjugate, antisqueezed variables. Our real-time analysis continuous monitoring system employs hybrid quantum-classical description quantum probe unknown classical perturbations, it provides general establish achievements sensing scheme how they depend different parameters.