When can gravity path-entangle two spatially superposed masses?

TL;DR

This paper analyzes various models of gravity to determine which predict entanglement between two superposed masses, highlighting that only local linearized quantum gravity models foresee such entanglement, thus guiding experimental tests of gravity's quantum nature.

Contribution

It compares different theoretical models of gravity regarding their predictions for entanglement generation between masses, emphasizing the unique role of local linearized quantum gravity.

Findings

Collapse models and quantum field theory in curved spacetime do not predict entanglement.

Local linearized quantum gravity models predict entanglement can occur.

The paper models a gravity-assisted two-qubit gate mechanism.

Abstract

An experimental test of quantum effects in gravity has recently been proposed, where the ability of the gravitational field to entangle two masses is used as a witness of its quantum nature. The key idea is that if gravity can generate entanglement between two masses then it must have at least some quantum features (i.e., two non-commuting observables). Here we discuss what existing models for coupled matter and gravity predict for this experiment. Collapse-type models, and also quantum field theory in curved spacetime, as well as various induced gravities, do not predict entanglement generation; they would therefore be ruled out by observing entanglement in the experiment. Instead, local linearised quantum gravity models predict that the masses can become entangled. We analyse the mechanism by which entanglement is established in such models, modelling a gravity-assisted two-qubit gate.