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The Bose--Marletto--Vedral experiment is a family of proposals to test gravitationally induced entanglement between initially independent masses. Sougato Bose and collaborators, and independently Chiara Marletto and Vlatko Vedral, described the idea in 2017. Each mass occupies two distinguishable spatial branches, encoding a qubit. Different branch separations give different Newtonian gravitational potential energies and hence different relative phases.^[ref]

For stationary branches at separations $r_{ab}$ held for duration $\tau$, the ideal model givesThe positive phase follows from negative Newtonian gravitational potential energy in $e^{-iV\tau /\hslash }$. A direct algebraic check separates local rephasing from genuine entanglement: the determinant of the two-by-two coefficient matrix vanishes exactly whenThus a large common phase alone is insufficient. For this ideal pure state, the concurrence is $|\sin (\Delta \varphi /2)|$, reaching one at an odd multiple of $\pi$.

The spin-based proposal uses two Stern-Gerlach interferometers: embedded spins label the spatial branches, the masses interact, and recombination transfers the branch information into measurable spin correlations. Measurements in different spin bases supply an entanglement witness. Unwanted electromagnetic interactions and quantum decoherence must be controlled for the gravitational interpretation.^[ref]

The mediator inference assumes initially unentangled systems, local coupling through a mediator, and no other entangling interaction. Under those assumptions, a mediator described only by commuting observables cannot generate the observed entanglement; at least two incompatible observables are required. This is an indirect test of nonclassical mediation, without selecting a complete high-energy theory of quantum gravity.^[ref]

Chiara Marletto and Vlatko Vedral developed a quantum-information route to testing gravity without detecting an individual graviton. Their proposal uses quantum entanglement between two initially independent masses to witness nonclassical properties of the interaction mediating it.^[ref]

The experimental question is stronger than measuring a gravitational phase shift alone. It requires establishing the appropriate quantum entanglement and controlling alternative couplings. The inference concerns the mediator under the stated assumptions, rather than uniquely selecting a complete microscopic theory of gravity.

Vlatko Vedral, with Chiara Marletto, proposed using gravitationally generated quantum entanglement as an indirect witness of quantum features of gravity. Their 2017 argument considers two masses in spatial quantum superpositions and asks whether their gravitational interaction can entangle them.^[ref]

Under the assumed local mediation and initial-independence conditions, a mediator restricted to classical commuting information cannot generate the required quantum entanglement. The conclusion is conditional on that model of mediation and exclusion of other entangling interactions. The paper proposes a test; it does not report an observed laboratory detection of quantum gravity.