Lessons and complications from gravitationally induced entanglement

Abstract

We critically review arguments depicting entanglement generated between exclusively gravitationally interacting particles as evidence for the necessity of a quantized gravitational field. For proposed experiments which are supposed to witness this gravitationally induced entanglement, we discuss the implications of a positive result and defend the possibility of a semiclassical theory of quantum matter on a classical spacetime which cannot be conclusively ruled out by witnessing entanglement. For thought experiments that resolve apparent causality issues with quantum systems entangled via the Newtonian gravitational interaction by considering a quantized gravitational field, we demonstrate that quantization of gravitational degrees of freedom is not only unnecessary but may result in remaining paradoxical behavior, unless a previously disregarded decoherence channel is taken into consideration.