Gravity as an Information Channel: Entanglement Witness, EFT Diagnostics, and the Quantum–Classical Crossover Parameter

We delineate a tripartite diagnostic framework for probing the quantum character of gravitationalinteractions: (i) an entanglement witness based on gravimetrically-induced coherent phase shiftsin spatial superpositions, (ii) an effective field theory (EFT) taxonomy classifying non-universalgravitational couplings, and (iii) a generalized criterion for the breakdown of classical spacetimedescriptions at singular configurations, interpreted as an EFT failure. Central to this work is theintroduction of a dimensionless crossover parameter,Q = κΓtot(1)where κ quantifies the rate of coherent gravitational phase accumulation and Γtot denotes the totalenvironmental decoherence rate. We rigorously demonstrate that Q ≫ 1 delineates regimes ofgenuine quantum gravitational mediation and entanglement generation, whereas Q ≪ 1 characterizeschannels where quantum correlations are suppressed, yielding effectively classical, entanglement-breaking dynamics. This Q-parameter thus serves as a unified discriminant criterion for mappingout the quantum-to-classical transition in gravity.