A recent theoretical study has investigated the possibility of detecting cosmic gravitons, the hypothetical particles mediating the gravitational interaction, through their effects on photon correlations. Unlike gravitational waves classically generated by moving macroscopic masses, diffuse graviton backgrounds are postulated to arise from zero-point fluctuations of the gravitational field, amplified by the evolution of spacetime curvature. These gravitons, which would be in entangled states, could produce potentially detectable second-order correlation effects.

To quantitatively analyze this empirical expectation, researchers scrutinized the interactions between cosmic gravitons and the fundamental mode of a quantized electromagnetic field. This field was confined inside a closed optical resonator with perfectly reflecting walls. The aim was to determine if Hanbury-Brown Twiss (HBT) correlations of photons within the cavity could serve as an indicator of the gravitons' statistical properties.

The analysis results showed that the HBT correlations of photons are insensitive to the second-order coherence degrees of the gravitons. This insensitivity holds even when accounting for the exceedingly small couplings between gravitons and the electromagnetic field. Consequently, the second-order coherence degree of the photons does not reflect the correlation properties of the gravitons. This implies that the statistical properties of gravitons, including their potential super-Poissonian statistics, cannot be inferred, even in principle, from the intensity correlations of the cavity modes.