Gravity is not a Pairwise Local Classical Channel

TL;DR

Large-scale single-atom interference experiments challenge the notion that gravity is a purely classical, non-entangling interaction, suggesting gravity may have inherently quantum features capable of generating entanglement.

Contribution

This work demonstrates experimentally that gravity cannot be solely a classical information channel, providing evidence that gravity may be fundamentally quantum in nature.

Findings

Single-atom interference experiments rule out classical gravity as an entanglement-preserving channel.

Classical channel models of gravity cannot account for observed quantum effects.

Gravity, if Newtonian at low energies, must have quantum features capable of entanglement creation.

Abstract

It is currently believed that there is no experimental evidence on possibly quantum features of gravity or gravity-motivated modifications of quantum mechanics. Here we show that single-atom interference experi- ments achieving large spatial superpositions can rule out a framework where the Newtonian gravitational inter- action is fundamentally classical in the information-theoretic sense: it cannot convey entanglement. Specifically, in this framework gravity acts pairwise between massive particles as classical channels, which effectively induce approximately Newtonian forces between the masses. The experiments indicate that if gravity does reduce to the pairwise Newtonian interaction between atoms at the low energies, this interaction cannot arise from the exchange of just classical information, and in principle has the capacity to create entanglement. We clarify that, contrary to current belief, the classical-channel description of gravity differs from the model of Diosi and Penrose, which is not constrained by the same data.