When Cavendish meets Feynman: A quantum torsion balance for testing the quantumness of gravity

TL;DR

This paper proposes a thought experiment using a quantum torsion balance with an optically levitated rotor to test the quantum nature of gravity by observing gravity-induced decoherence effects.

Contribution

It introduces a novel experimental scheme combining quantum superposition and gravity to distinguish classical from quantum gravitational effects with reduced control requirements.

Findings

Gravity causes measurable decoherence differences in quantum vs. classical scenarios.

The proposed method simplifies testing quantum gravity by integrating source and probe mechanisms.

Potential to experimentally verify the quantum nature of gravity using existing quantum technologies.

Abstract

We propose a thought experiment, based on a mechanism that is reminiscent of Cavendish's torsion balance, to investigate the possible quantum nature of the gravitational field generated by the quantum superposition state of a massive system. Our proposal makes use of the dynamics of a ultra-stable optically levitated nanomechanical rotor endowed with a spin to generate a quantum angular superposition that is then tested through standard Ramsey-like scheme. Gravity manifests itself as an effective decoherence mechanism, whose strength is different-and, as we show, appreciable-in the classical and quantum case. By incorporating both the source for decoherence and the mechanism to probe it, the experiment that we propose allows for a much reduced degree of control and dynamical engineering.