State Swapping via Semiclassical Gravity

TL;DR

This paper demonstrates that semiclassical gravity can produce effects similar to quantum state swapping, challenging the idea that such phenomena necessarily imply a quantum nature of gravity.

Contribution

It shows that semiclassical gravity can mimic quantum state swapping, questioning previous assumptions about gravity's classical or quantum nature.

Findings

Semiclassical gravity can induce state swapping effects.

Distinguishing classical from quantum gravity based on swapping is inconclusive.

Implications for experimental tests of gravity's quantum properties.

Abstract

The prediction of non-local phenomena is a key attribute of quantum mechanics that distinguishes it from classical theories. It was recently suggested that state swapping is one such effect that a fundamentally classical gravitational field cannot give rise to. The reasoning was that the phenomenology of classical fields is restricted to Local Operations and Classical Communication~(LOCC) whereas swapping is a non-LOCC effect, so gravity must not be a classical channel if it can give rise to such a phenomenon. Here, we show that the Hamiltonian of semiclassical gravity results in an evolution of coherent states that is virtually indistinguishable from swapping them, both theoretically and experimentally. Our results indicate that drawing a definitive conclusion about the nature of gravity based solely on its ability to swap a pair of coherent states would be premature. We discuss the implications of these results regarding proposed experimental tests for the quantum nature of gravity and clarify some conceptual issues.