Quantum correlations beyond entanglement in a classical-channel model of gravity

TL;DR

This paper demonstrates that classical-channel gravity models can generate quantum correlations like discord between masses, even without entanglement, challenging the notion that entanglement is necessary to witness quantum gravity effects.

Contribution

It shows that classical-channel models of gravity can produce quantum discord, expanding the understanding of quantum correlations beyond entanglement in gravitational systems.

Findings

Classical-channel gravity models can generate quantum discord.

Discord decays or stabilizes depending on the model extension.

Local squeezing enhances the generated quantum discord.

Abstract

A direct quantization of the Newtonian interaction between two masses is known to establish entanglement, which if detected would witness the quantum nature of the gravitational field. Gravitational interaction is yet compatible also with gravitational decoherence models relying on classical channels, hence unable to create entanglement. Here, we show in paradigmatic cases that, despite the absence of entanglement, a classical-channel model of gravity can still establish quantum correlations in the form of quantum discord between two masses. This is demonstrated for the Kafri-Taylor-Milburn (KTM) model and a recently proposed dissipative extension of this. In both cases, starting from an uncorrelated state, a significant amount of discord is generally created. This eventually decays in the KTM model, while it converges to a small stationary value in its dissipative extension. We also find that initial local squeezing on the state of the masses can significanlty enhance the generated discord.