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

Understand

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.