Comment on Classical-Gravity--Quantum-Matter Claims About Gravity-Mediated Entanglement

TL;DR

The paper addresses whether a classical gravitational field can mediate entanglement when matter is fully quantum. It combines a summary of Aziz and Howl’s proposal with a channel-theoretic reformulation to separate entanglement activation in matter from genuine mediation by gravity. In the relevant nonrelativistic limit, the interaction becomes ultra-local and factorizes, implying no gravity-mediated entanglement; the separable-channel form further supports the conclusion that a classical mediator cannot create entanglement from a product input. Consequently, the authors reinforce that observing gravity-mediated entanglement in BMV-type experiments would provide strong evidence for nonclassical gravitational degrees of freedom, preserving the operational test of gravity’s quantum nature.

Abstract

A recent paper by Aziz and Howl (Nature 2025) argues that, once quantum matter is described at the level of quantum field theory and coupled to a classical gravitational field, higher order processes can generate entanglement between two spatially separated masses. A contemporaneous critical note (Marletto, Oppenheim, Vedral, Wilson, arXiv:2511.07348v1) shows that, in the actual nonrelativistic limit employed there, the interaction becomes ultra local, the total unitary factorizes, and no entanglement is generated from a product input. In this comment we (i) restate the core point of that critique, (ii) give a channel theoretic reformulation that makes the conclusion model independent, and (iii) clarify the distinction between activation of entanglement in already quantum matter and genuine mediation of entanglement by a classical field. Once these clarifications are in place, the standard BMV inference that observation of gravity mediated entanglement strongly indicates nonclassical gravitational degrees of freedom remains intact.