Violation of the Leggett-Garg inequality in photon-graviton conversion

TL;DR

This paper demonstrates that photon-graviton conversion in a magnetic field can violate the Leggett-Garg inequality, offering a potential experimental test for the quantum nature of gravity through temporal correlation measurements.

Contribution

It provides an analytical demonstration that photon-graviton conversion can lead to LGI violation, linking quantum optics with gravitational phenomena.

Findings

Photon-graviton conversion can violate the LGI.

Temporal correlations reveal nonclassicality of gravity.

Potential for experimental tests of quantum gravity.

Abstract

The Leggett-Garg inequality (LGI) is a temporal analogue of Bell's inequality and provides a quantitative test of the nonclassicality of a system through its violation. We analytically investigate the violation of the LGI in the context of photon-graviton conversion in a magnetic field background, motivated by its potential applications to testing the nonclassicality of gravity. When gravitational perturbations are quantized as gravitons, the conversion of an initial single photon state gives rise to a superposition of photon and graviton states. We show that the temporal correlations obtained from successive projective measurements on the photon-graviton system violate the LGI. Observation of such a violation would provide a novel avenue for probing the quantum nature of gravity.