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arXiv:2406.18494 · New Journal of Physics

On the effectiveness of the collapse in the Diósi–Penrose model

Laria Figurato, Marco Dirindin, José Luis Gaona-Reyes, Matteo Carlesso, Angelo Bassi, Sandro Donadi

Published Oct 29, 2024• 12 citations
arXivHTMLPDF

Abstract

Abstract The possibility that gravity plays a role in the collapse of the quantum wave function has been considered in the literature, and it is of relevance not only because it would provide a solution to the measurement problem in quantum theory, but also because it would give a new and unexpected twist to the search for a unified theory of quantum and gravitational phenomena, possibly overcoming the current impasse. The Diósi–Penrose model is the most popular incarnation of this idea. It predicts a progressive breakdown of quantum superpositions when the mass of the system increases; as such, it is susceptible to experimental verification. Current experiments set a lower bound R 0 ≳ 4 Å for the free parameter of the model, excluding some versions of it. In this work we search for an upper bound, coming from the request that the collapse is effective enough to guarantee classicality at the macroscopic scale: we find out that not all macroscopic systems collapse effectively. If one relaxes this request, a reasonable (although to some degree arbitrary) bound is found to be: R 0 ≲ 10 6 Å. This will serve to better direct future experiments to further test the model.

DOI
10.1088/1367-2630/ad8c77

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Abstract The possibility that gravity plays a role in the collapse of the quantum wave function has been considered in the literature, and it is of relevance not only because it would provide a solution to the measurement problem in quantum theory, but also because it would give a new and unexpected twist to the search for a unified theory of quantum and gravitational phenomena, possibly overcoming the current impasse. The Diósi–Penrose model is the most popular incarnation of this idea. It predicts a progressive breakdown of quantum superpositions when the mass of the system increases; as such, it is susceptible to experimental verification. Current experiments set a lower bound R 0 ≳ 4 Å for the free parameter of the model, excluding some versions of it. In this work we search for an upper bound, coming from the request that the collapse is effective enough to guarantee classicality at the macroscopic scale: we find out that not all macroscopic systems collapse effectively. If one relaxes this request, a reasonable (although to some degree arbitrary) bound is found to be: R 0 ≲ 10 6 Å. This will serve to better direct future experiments to further test the model.
The possibility that the collapse of the wave function in quantum mechanics is real and ultimately connected to (classical) gravity has been debated for decades with main contributions by Diósi and Penrose (DP). In particular, Diósi proposed a noise-based dynamical reduction model, which captures the same order of magnitudes for the collapse time suggested by Penrose based on heuristic arguments. This is known in the literature as the DP model (Diósi–Penrose). A peculiarity of the DP model is the prediction of spontaneous heating of matter, which can be tested without the need for massive quantum superpositions. Notably, a very similar effect is predicted by recent theoretical approaches to gravity as a classical-only information channel. Here, we reconsider the current constraints on the DP model from spontaneous heating by analyzing experimental situations not properly considered before. We argue that the parameter-free version of the DP model is close to be ruled out by standard heat leak measurements at ultralow temperatures with a conclusive exclusion likely within reach with existing technology. This result would strengthen a recent claim of exclusion inferred by spontaneous x-ray emission experiments, which relies on the somewhat stronger assumption that the DP noise field is white up to x-ray frequencies.
Probing gravity-related decoherence with a 16 μμμg Schrödinger cat state
The Schrödinger equation predicts the validity of the superposition principle at any scale, yet we do not experience cats being in a superposition of "dead" and "alive" in our everyday lives. Modifications to quantum theory at the fundamental level may be responsible for the objective collapse of the wave function above a critical mass, thereby breaking down the superposition principle and restoring classical behavior at the macroscopic scale. One possibility is that these modifications are related to gravity, as described by the Diósi-Penrose wavefunction collapse model. Here, we investigate this model using experimental measurements on the decoherence of a Schrödinger cat state of a mechanical resonator with an effective mass of 16 micrograms.
We analyze gravitational collapse models within the Diósi–Penrose framework against current experimental bounds and macroscopic classicality requirements. We show that, among the six constraints considered (three interferometry bounds from MAQRO, Vienna, and Delft, and three macroscopic classicality requirements), only the Vienna bound is active in the vicinity of the optimum: the other five are satisfied with margins of 1–13 orders of magnitude and do not constrain the cutoff radius Rc. Saturating the Vienna bound alone fixes Rc = (5.3 ± 0.1) × 10^−5 m (53 µm). We present this value not as an emergent consequence of multiple independent constraints, but as the current experimental upper bound on Rc under the Diósi model with a Gaussian cutoff—the largest cutoff radius consistent with the absence of observed collapse in the Vienna levitation experiment. This is a more modest, but equally falsifiable, claim: any future experiment probing Rc ≲ 53 µm without observing the predicted collapse signature would rule out this specific parameter choice. We give the resulting testable predictions for next-generation nano-interferometry and discuss the sensitivity of the bound to the single dominant experimental input.
The Diósi-Penrose model states that the wave function collapse ending a quantum superposition occurs due to the instability of coexisting gravitational potentials created by distinct geometric conformations of the system in different states. The Heisenberg time-energy principle can be invoked to estimate the collapse time for the energy associated with this instability, the gravitational self-energy. This paper develops atomistic models to calculate the Diósi-Penrose collapse time. It applies them to a range of systems, from small molecules to large biological structures and macroscopic systems. An experiment is suggested to test the Diósi-Penrose hypothesis, and we critically examine the model, highlighting challenges from an atomistic perspective, such as gravitational self-energy saturation and limited extensivity.
The physical mechanism underlying quantum wave-function collapse remains a central problem in foundational physics. Objective collapse theories, notably the Penrose-Diósi (DP) model,propose that macroscopic superposition is destroyed by gravitational self-energy (∆EG), predicting that collapse scales strictly with mass.We propose an entirely distinct physical mechanism: Topological Representation Collapse.Within the Deterministic Spectral Manifold (DSM-861) framework, wave-function collapse istriggered not by static gravity, but by dynamic enstrophy strain exceeding a specific topologicalmelting threshold (Em ≈ 695.74 eV). This establishes a falsifiable experimental demarcationline in the mesoscopic regime. We demonstrate that highly strained, rapidly rotating, or topologically complex mesoscopic systems (such as driven nanomechanical rotors or rapidly foldingproteins) will undergo spontaneous decoherence significantly faster than predicted by gravityinduced models, while perfectly rigid macroscopic masses may maintain coherence longer.
Quantum mechanics is grounded on the superposition principle, which is the source both of its tremendous success and technological power, as well as of the problems in understanding it. The reason why superpositions do not propagate from the microscopic to the macroscopic world are unclear. Spontaneous wave function collapse models have been formulated to take into account a progressive breakdown of quantum superpositions when systems are large enough; they do so by modifying the Schrödinger dynamics, and therefore they are empirically testable. Deviations are tiny, and require precision measurements. I will review the most recent tests of such models, spanning from optomechanical to underground experiments. I will conclude by presenting possible future experiments.