  The interaction between the electric dipole moments of a quantum emitter and
a metal nanoparticle gives rise to unique optical properties, such as
interference-induced photon correlations, that could be useful for enhanced
intensity-based sensing. Using the quantum theory of photodetection, we propose
a nanosensor system comprising a quantum emitter and a metal nanoparticle that
explores the possibility of utilizing higher-order photon correlations for
refractive index sensing. Both the refractive index sensitivity and resolution
of the nanosensor, whose scattering spectrum lies within the visible region,
are predicted. The sensor is supported by a substrate and driven weakly by a
coherent field. By calculating the mean photocount and its second factorial
moment resulting from the scattered field of the system, the sensing
performance of the intensity and intensity-intensity correlation, are compared
at optimal driving wavelengths. The mean photocount was found to be inherently
low, inhibiting the role of interference-induced photon antibunching in
minimizing the sensor's intensity shot noise. However, a regime in which the
noise could be reduced below the shot noise limit is identified, leading to a
quantum enhancement in the sensing performance.
