Repulsive Gravitational Force as a Witness of the Quantum Nature of Gravity

TL;DR

This paper proposes an experimental scheme where a superposed mass can produce a repulsive gravitational force on a probe, providing evidence of the quantum nature of gravity through quantum interference effects.

Contribution

It introduces a novel method using superposition and postselection to detect quantum gravitational effects, specifically repulsive forces, which cannot occur classically.

Findings

Superposition of mass states can lead to repulsive gravity effects.

Quantum interference is essential for observing repulsion, indicating quantum gravity.

Feasible parameter ranges are estimated for experimental realization.

Abstract

We show that a single spatially superposed 'source' mass acting on a 'probe' matter wavepacket can reveal the quantum nature of the gravitational field. For this we use a specific state preparation and measurement of the superposed source mass, including a postselection, which altogether results in a repulsive gravitational force on the probe particle. A classical gravitational field can never lead to repulsion, as the effect requires quantum interference of two distinct states of gravity. We also present a calculation in the Heisenberg picture under the formalism of weak values that illustrates how repulsion is achieved. Finally, we estimate the range of parameters (masses and the spatio-temporal extent of interference) for which the experiment is feasible.