Inference of gravitational field superposition from quantum measurements

TL;DR

This paper discusses how recent quantum experiments challenge classical gravity theories, providing evidence that gravity exhibits quantum properties and proposing future experiments to further test this nonclassical nature.

Contribution

It demonstrates that alternative gravity theories must decouple gravitational energy from quantum states and require a preferred frame, which are considered implausible, supporting gravity's quantum nature.

Findings

Alternative gravity theories cannot avoid superposition without decoupling gravitational energy.

Recent experiments provide indirect evidence of gravity's quantum features.

Proposed experiments could offer stronger evidence of gravity's nonclassical behavior.

Abstract

Experiments are beginning to probe the interaction of quantum particles with gravitational fields beyond the uniform-field regime. In non-relativistic quantum mechanics, the gravitational field in such experiments can be written as a superposition state. We empirically demonstrate that alternative theories of gravity can avoid gravitational superposition states only by decoupling the gravitational field energy from the quantum particle's time evolution. Furthermore, such theories must specify a preferred quantum reference frame in which the equations of motion are valid. To the extent that these properties are theoretically implausible, recent experiments provide indirect evidence that gravity has quantum features. Proposed experiments with superposed gravitational sources would provide even stronger evidence that gravity is nonclassical.