Gravity generates quantum entanglement via two-qubit systems

The fundamental connection between gravity and quantum mechanics remains one of the most challenging problems in physics, and researchers continually seek ways to bridge these seemingly disparate realms. Feng-Li Lin of National Taiwan Normal University and Sayid Mondal of Universidad Arturo Prat, along with their colleagues, now demonstrate that even Newtonian gravity, the classical description of gravitational force, can generate quantum entanglement between objects. This achievement establishes a framework for understanding how classical gravity influences quantum phenomena, revealing that entanglement arises from the way objects interact gravitationally through a non-local coupling. The discovery offers a novel perspective on the interplay between gravity and quantum mechanics, potentially paving the way for exploring quantum gravity effects in macroscopic systems.

Gravity Entangles Quantum Bodies via Superposition

Generating quantum entanglement via gravitational interactions

Inducing Entanglement using Classical Gravity Principles

Scientists have demonstrated that Newtonian gravity can induce quantum entanglement between two distant bodies, a result achieved through a novel combination of classical gravity and quantum superposition. The research centers on preparing “quantum bodies”, objects in a superposition of two mass distributions, and examining their interaction via gravity. These quantum bodies are created using N00N states, which distribute quantum properties across spatial locations, effectively creating a qubit representing the object’s mass configuration. The team derived an effective field theory describing the interaction, revealing a two-qubit interaction governed by a Newtonian, nonlocal quadrupole-quadrupole coupling.

This interaction, stemming from the gravitational force between the mass distributions, produces entanglement, as evidenced by a non-zero entanglement entropy in the final state after the system evolves. Measurements confirm that the entanglement is governed by a coupling constant that is nonlocal, meaning the interaction doesn’t diminish with distance as expected in classical physics. The team calculated the entanglement generated, finding it scales with the gravitational coupling constant, the mass fluctuations, the interaction time, and is inversely proportional to both the distance between the bodies and their size. The calculations demonstrate that the entanglement strength is approximately proportional to GδM1δM2 r12 -4 T, where G is the gravitational constant, δM1 and δM2 represent the mass fluctuations, r12 is the distance between the bodies, and T is the interaction time.

Mapping the generation of quantum correlations

Mapping Direct Links Between Gravity and Entanglement

This work establishes a direct link between Newtonian gravity and quantum entanglement, suggesting that even classical gravity can generate quantum correlations under specific conditions. Importantly, the team identified specific parameter values, termed “magic points”, where entanglement production vanishes entirely, suggesting a nuanced relationship between gravitational interaction and quantum coherence. While acknowledging the limitations of restricting calculations to Newtonian order, the authors suggest that incorporating higher-order post-Newtonian interactions could further refine the understanding of entanglement production. Future research may focus on exploring the physical implications of these “magic points” and investigating the role of higher-order interactions in mediating quantum entanglement through classical gravity.

Implications for quantum gravity research

The theoretical underpinning of this interaction is rooted in the derivation of an effective Hamiltonian, which effectively models the gravitational coupling between the two spatially extended quantum mass distributions. This Hamiltonian formulation reveals that the leading interaction term is proportional to the quadrupole moments of the mass configurations. Understanding the symmetries and renormalization group flow of this effective theory is crucial, as it dictates how higher-order multipole interactions, which are typically neglected in simplified models, must be included to achieve a comprehensive description of the entanglement evolution.

From an experimental feasibility standpoint, generating and maintaining the required quantum superposition states—particularly robust N00N states of macroscopic mass—presents formidable technological challenges. These states are inherently fragile, making the system highly susceptible to decoherence caused by environmental noise or uncontrolled gravitational gradients. Therefore, realizing this effect necessitates the development of ultracold atom trapping techniques or advanced quantum state preparation methods capable of ensuring a coherence time significantly longer than the calculated interaction time $T$.

The non-local nature of the observed coupling suggests that the interaction cannot be fully described solely by the standard Poisson equation approximations. Analyzing this non-local term requires addressing the associated field equations in momentum space, where the coupling constant’s dependence on distance $r_{12}^{-4}$ becomes explicitly evident. This departure from typical inverse-square law decay provides key insights into how quantum superposition affects the mediating gravitational field structure itself, potentially requiring modifications to general relativity’s metric assumptions at the quantum level.

Furthermore, the ability to manipulate the “magic points” where entanglement vanishes opens avenues for active quantum control. By tuning system parameters—such as the internal state coupling or the relative mass fluctuation magnitudes—researchers can potentially switch the entanglement generation process ‘on’ or ‘off.’ This capability moves the theory from a passive demonstration toward an active paradigm for quantum state engineering, making gravitational interactions a controllable resource for quantum information processing protocols.