Gravitationally-Induced Photon Entanglement in an FLRW Cosmological Background

TL;DR

This paper proposes a novel method to test the quantum nature of gravity by observing gravitationally induced entanglement between photons produced in astronomical events, offering a new approach to quantum gravity experiments.

Contribution

It introduces a photon-based QGEM protocol in curved spacetime, providing a new experimental avenue to test the nonclassical nature of gravity using relativistic particles.

Findings

Gravitationally induced photon entanglement is theoretically quantifiable.

Photon entanglement features depend on astronomical gravitational interactions.

The proposed method could inspire future photon entanglement experiments in astrophysics.

Abstract

In order to detect the quantum nature of gravity, the quantum gravity induced entanglement of masses(QGEM) has been proposed both in flat and curved spacetime. In this paper we propose an analogous QGEM protocol using photons produced in astronomical processes as the quantum systems. Unlike massive particles, the gravitational interaction between photons-intrinsically relativistic particles-simultaneously satisfies both the event and system localities. So it can provide a clear test of whether the gravitational mediator must be nonclassical based on the Local Operations and Classical Communication (LOCC) principle. Although the gravitationally induced entanglement between massless relativistic photons is extremely small, our quantitative calculations clarify the characteristic features of the entanglement induced by the photon's own gravitational field in astronomical process and may inspire other photon entanglement experiments.