Classical Gravity Cannot Mediate Entanglement: Study Shows Models Fail to Produce Results for 646 and 813

The question of whether gravity can directly induce quantum entanglement has long fascinated physicists, and recent claims suggested a possible mechanism for this phenomenon. Chiara Marletto, Jonathan Oppenheim, Vlatko Vedral, and Elizabeth Wilson investigate these claims, demonstrating that a previously proposed model fails to produce genuine entanglement. Their work reveals that even if such a model did generate entanglement, it would arise from the interactions of matter itself, not from gravity’s influence. This finding clarifies that entanglement demonstrably mediated by gravity would serve as a definitive signature of quantum gravity, offering a crucial pathway for understanding the interplay between these fundamental forces.

Therefore, detecting entanglement mediated by gravity would represent unambiguous evidence of gravity’s quantum properties. Recent proposals aimed to detect these quantum effects in gravity utilise Gravitationally Mediated Entanglement (GME) between massive probes, predicated on the idea that if gravity can entangle quantum systems, it must possess non-classical features. This research presents a rigorous analysis of a proposed Hamiltonian, demonstrating that it cannot generate entanglement under its stated assumptions.

Entanglement Fails with Negligible Mass Coupling

The research demonstrates that a previously proposed mechanism for generating entanglement between massive particles cannot, in fact, create entanglement under its stated assumptions. The core argument centres on the interaction between a classical Newtonian potential and a quantum scalar field. However, this analysis reveals that the interaction effectively acts on each particle individually, preventing the creation of entanglement because the term directly coupling the two masses is negligible in the non-relativistic limit. The authors initially posited that the matter Hamiltonian alone should not create entanglement, and that any entanglement must arise from the interaction term.

However, this criterion proves insufficient, as either the matter Hamiltonian does not directly couple the particles, leading to a simple product of individual particle states, or it does couple them, directly generating entanglement without the need for the interaction term. The analysis shows that the proposed mechanism inconsistently removes momentum terms crucial for propagating quantum information between particles, and then reintroduces them later in the calculation, leading to unphysical results. Specifically, the correct mathematical description of particle behavior yields a term proportional to a delta function, indicating no entanglement unless the wavepackets of the particles overlap. The research clarifies that even if the proposed mechanism were to function, it would resemble a standard quantum interaction initiated by a classical perturbation, rather than gravitationally mediated entanglement.

The authors’ criterion for identifying gravity as the source of entanglement is therefore inadequate, failing to distinguish their mechanism from any standard quantum interaction triggered by a classical system. Further analysis demonstrates that approximations in mathematical calculations can falsely indicate entanglement when none exists, and that the fundamental principles underpinning tests for non-classicality do not rely on assumptions specific to standard quantum mechanics. The findings confirm that models where quantum matter degrees of freedom interact directly can generate entanglement, but that any classical field modulating this interaction does not mediate the entanglement itself. Detecting entanglement through these methods remains a clear indication of quantum effects in gravity, and the research emphasizes the importance of exploring all possible routes to entanglement between massive particles, including those involving correlated environmental noise. Ultimately, superpositions of massive particles offer powerful tools for probing the quantum nature of spacetime.

Gravity Fails to Generate Quantum Entanglement

This work demonstrates that a previously proposed model for generating entanglement via gravity cannot, in fact, produce this quantum correlation. Researchers rigorously tested the theoretical framework, revealing that their model fails to generate entanglement under its stated assumptions. The analysis shows that even if entanglement were to appear, it would arise from direct interactions between quantum matter, not from gravity itself. This finding is crucial because it clarifies that detecting entanglement remains a definitive signature of genuine quantum effects within gravitational systems. The team’s investigation focused on the mathematical mechanisms proposed to induce entanglement, specifically examining the role of the gravitational potential.

They discovered that a key step in the original model, dropping a momentum term, inconsistently removes the propagation of quantum information between particles. Reintroducing this term reveals that the resulting mathematical description of particle behavior cannot support entanglement. Instead, the calculations demonstrate that any apparent entanglement would be mediated by quantum matter, triggered by a classical perturbation, mirroring standard quantum interactions initiated by external systems. Furthermore, the research highlights that simply observing entanglement when a gravitational interaction is “switched on” is insufficient to prove gravity’s role.

The team established that any classical field modulating quantum interactions does not mediate entanglement, a principle consistent with established quantum field theory. They demonstrated this by showing that a simplified mathematical description, while appearing to generate entanglement at specific stages of calculation, ultimately fails to do so, illustrating how mathematical approximations can create misleading results. This work confirms that detecting entanglement through gravitational means remains an unambiguous witness of quantum effects, distinguishing it from entanglement generated by classical interactions.

Gravity Fails to Entangle Massive Particles

This research rigorously demonstrates that classical theories of gravity cannot produce entanglement between massive particles. The team conclusively showed that a previously proposed model, suggesting classical gravity could induce entanglement, does not, in fact, generate this quantum correlation. Importantly, even if such a model did produce entanglement, it would arise from interactions between the quantum properties of matter, not from gravity itself. This finding reinforces the principle that detecting entanglement remains a clear signature of genuine quantum effects within gravity. The work builds upon fundamental information-theoretic axioms and confirms that consistent quantum field theories interacting with classical fields do not generate entanglement via the classical field.

Through detailed analysis, the researchers validated earlier findings demonstrating the absence of entanglement generation when solving the relevant equations exactly. This establishes a firm theoretical basis for distinguishing entanglement arising from quantum gravity from other potential sources. While acknowledging the importance of exploring all possible routes to entanglement, the authors emphasize that any entanglement generated through alternative mechanisms, such as correlated environmental noise, would likely exhibit different characteristics than that predicted by quantum theories of gravity. Future research, they suggest, should focus on refining experimental techniques to differentiate between these various entanglement sources, ultimately leveraging superpositions of massive particles as powerful sensors to probe the quantum nature of spacetime.