  Models of gravitational decoherence are not commonly applied to
ultra-relativistic systems, including photons. As a result, few quantum optical
tests of gravitational decoherence have been developed. In this paper, we
generalize the gravitational decoherence model of Anastopoulos and Hu
(arXiv:1305.5231) to photons. In this model, decoherence originates from a bath
of stochastic gravitational perturbations, possibly of fundamental origin. We
derive a master equation for general states of the electromagnetic (EM) field;
the only free parameter is a noise temperature $\Theta$ of the gravitational
fluctuations. We find that interference experiments with long baselines,
accessible in near-future experiments, can, in principle, lead to strong
constraints in $\Theta$.
