In 2021, a low-background experiment at the Gran Sasso National Laboratory searched for spontaneous radiation predicted by the standard Markovian Diósi-Penrose (DP) dynamics and obtained the new bound
R0>5.4×10−11m at
95% probability for the short-length cutoff parameter. For germanium at the experimental temperature, the parameter-free prescription identifying
R0 with the spatial quantum spread of a nucleus gives
R0≃5×10−12m. That particular combination, Diósi's stochastic dynamics and the Penrose-motivated mass-density resolution, was therefore excluded. Subsequent searches strengthened the cutoff bound. The Majorana Demonstrator improved it in 2022, and XENONnT has now obtained the world-leading limits
R0>4.9×10−10m at
90% confidence level and
R0>4.5×10−10m at
95% confidence level. These advances reinforce the 2021 exclusion but do not alter its logical scope: they \emph{parametrically constrain} the Markovian, effectively white-noise DP dynamics, not Penrose's (and Diósi's) lifetime criterion independently of a dynamics, and not all colored-noise, dissipative, or otherwise modified gravity-related spontaneous collapse theories. We reconstruct what Gran Sasso did and did not rule out and place that conclusion in the present experimental context.
We show that the dynamics of the Diósi-Penrose (DP) model of classical gravity can entangle the mechanical degrees of freedom of two separate particles. For standard experiments of gravitationally induced entanglement (GIE), we find that entanglement can be generated if and only if the particles are separated by a distance smaller than some limiting value d c , proportional to the only free parameter of the DP model. Greater distances can be achieved through new experimental configurations, where the initial wave functions of the particles are allowed to spread perpendicularly to the separation axis. Although the DP dynamics asymptotically drives the system to a separable state, we observe that, for reasonable experimental parameters, GIE can survive for more than a day. Our results therefore imply that GIE detection is not enough to validate quantum gravity. Experimental tests of GIE dynamics have nonetheless the potential to falsify the DP model.
This note asks what a threshold picture of objective collapse predicts for Bose–Marletto–Vedral (BMV) tests of gravity-mediated entanglement. A collapse rate that switches on sharply violates complete positivity. For homogeneous spheres, Markovian Diósi–Penrose (DP) collapse forbids BMV entanglement at all times. If the threshold is instead modeled as a build-up in time, using Ornstein–Uhlenbeck colored DP noise with correlation time τ_c, the dynamics stays completely positive and evades the non-interferometric bounds we considered for τ_c ≳ 1.7×10³ s. Colored CSL cannot do this. The prediction is transient entanglement, which rises, peaks and vanishes at about 1.46×10⁻³ τ_c. The time profile alone matches slow classical noise. A superposition-size scan of about 90 single-mass runs separates the two. The window requires a heavier effective collapse threshold and closes under minimal-measurement-time criteria. This is a modest, testable prediction, not evidence for collapse. Computations assisted by AI tools.