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Collapse-based models for gravity do not violate the entanglement-based witness of non-classicality

Tianfeng Feng, Vlatko Vedral, Chiara Marletto

TL;DR

The paper defends the entanglement-based witness of non-classicality (GWT) for gravity against claims that collapse-based models like the Diósi–Penrose (DP) framework could yield gravity-induced entanglement while remaining classical. It shows that DP-type dynamics rely on nonlocal hidden monitoring, effectively introducing quantum degrees of freedom and violating locality, so these models do not falsify the GWT. By deriving the DP evolution and performing a negativity analysis for a two-mass setup, the authors demonstrate that entanglement can arise from the monitoring term rather than from gravitational backaction, under realistic parameter choices. Consequently, under locality the presence of gravitationally induced entanglement continues to indicate gravity’s quantum nature, and DP models cannot undermine the GWT. The findings bolster the use of Bose–Marletto–Vedral–type experiments as robust probes of quantum gravity.

Abstract

It is known that an entanglement-based witness of non-classicality can be applied to testing quantum effects in gravity. Specifically, if a system can create entanglement between two quantum probes by local means only, then it must be non-classical. Recently, claims have been made that collapse-based models of classical gravity, i.e. Diósi-Penrose model, can predict gravitationally induced entanglement between quantum objects, resulting in gravitationally induced entanglement is insufficient to conclude that gravity is fundamentally quantum, contrary to the witness statement. Here we vindicate the witness. We analyze the underlying physics of collapse-based models for gravity and show that these models have nonlocal features, violating the principle of locality.

Collapse-based models for gravity do not violate the entanglement-based witness of non-classicality

TL;DR

The paper defends the entanglement-based witness of non-classicality (GWT) for gravity against claims that collapse-based models like the Diósi–Penrose (DP) framework could yield gravity-induced entanglement while remaining classical. It shows that DP-type dynamics rely on nonlocal hidden monitoring, effectively introducing quantum degrees of freedom and violating locality, so these models do not falsify the GWT. By deriving the DP evolution and performing a negativity analysis for a two-mass setup, the authors demonstrate that entanglement can arise from the monitoring term rather than from gravitational backaction, under realistic parameter choices. Consequently, under locality the presence of gravitationally induced entanglement continues to indicate gravity’s quantum nature, and DP models cannot undermine the GWT. The findings bolster the use of Bose–Marletto–Vedral–type experiments as robust probes of quantum gravity.

Abstract

It is known that an entanglement-based witness of non-classicality can be applied to testing quantum effects in gravity. Specifically, if a system can create entanglement between two quantum probes by local means only, then it must be non-classical. Recently, claims have been made that collapse-based models of classical gravity, i.e. Diósi-Penrose model, can predict gravitationally induced entanglement between quantum objects, resulting in gravitationally induced entanglement is insufficient to conclude that gravity is fundamentally quantum, contrary to the witness statement. Here we vindicate the witness. We analyze the underlying physics of collapse-based models for gravity and show that these models have nonlocal features, violating the principle of locality.

Paper Structure

This paper contains 6 sections, 16 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Brief Review of collapse-based models of gravity
  3. Entanglement generation in the DP model
  4. What goes wrong in the argument
  5. Discussions
  6. Conclusions

Figures (1)

  • Figure 1: (a) Schematic representation of the setup for the General Witness Theorem. The two space-like separated quantum probes $A$ and $B$ are coupled only via the unknown mediator $M$, by means of local interactions. Its capability of inducing entanglement between $A$ and $B$ is a witness of its non-classicality. (b) Gravitationally induced entanglement (GIE) between two spatially superposed masses. Observation of GIE suggests the non-classicality of the gravitational field.