  We demonstrate how noise can be turned into an advantage for optical sensing
using a nonlinear cavity. The cavity is driven by a continuous wave laser into
the regime of optical bistability. Due to the influence of fluctuations, the
cavity randomly switches between two states. By analyzing residence times in
these two states, perturbations to the resonance frequency of the cavity can be
detected. Here, such an analysis is presented as a function of the strength of
the perturbation and of the noise. By increasing the standard deviation of the
noise, we find that the detection speed increases monotonically while the
sensitivity peaks at a finite value of the noise strength. Furthermore, we
discuss how noise-assisted sensing can be optimized in state-of-the-art
experimental platforms, relying solely on the minimum amount of noise present
in the cavity due to its dissipation. These results open new perspectives for
the ultrafast detection of nanoparticles, contaminants, gases, or other
perturbations to the resonance frequency of an optical resonator, at low powers
and in noisy environments.
