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Gravitational Decoherence as a Fundamental Limit on Massive Quantum Technologies

Marc Sperzel

Published Mar 22, 2026• 0 citations
Publisher

Abstract

We analyze implications of the Diósi-Penrose hypothesis for quantum computing platforms. Conventional qubits are entirely unaffected, but emerging massive quantum technologies approach a regime where gravitational decoherence could become the dominant coherence-limiting mechanism. Three experimental signatures uniquely distinguish gravitational from environmental decoherence. Part of the Quantum-Geometric Duality series (Paper J).

DOI
10.5281/zenodo.19181596

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We analyze implications of the Diósi-Penrose hypothesis for quantum computing platforms. Conventional qubits are entirely unaffected, but emerging massive quantum technologies approach a regime where gravitational decoherence could become the dominant coherence-limiting mechanism. Three experimental signatures uniquely distinguish gravitational from environmental decoherence. Part of the Quantum-Geometric Duality series (Paper J).
Why do macroscopic objects appear classical? The Diósi-Penrose conjecture proposes that the classical gravitational self-energy directly determines the decoherence rate for spatial superpositions. We present an exposition and experimental analysis of this hypothesis, interpreting the mechanism in terms of environmental decoherence compatible with unitarity. We identify four distinctive experimental signatures that no other decoherence mechanism exhibits simultaneously. Part of the Quantum-Geometric Duality series (Paper A).
Real world quantum systems are open to perpetual influence from the wider environment. Quantum gravitational fluctuations provide a most fundamental source of the environmental influence through their universal interactions with all forms of energy and matter causing decoherence. This may have subtle implications on precision laboratory experiments and astronomical observations and could limit the ultimate capacities for quantum technologies prone to decoherence. To establish the essential physical mechanism of decoherence under weak spacetime fluctuations, we carry out a sequence of analytical steps utilizing the Dirac constraint quantization and gauge invariant influence functional techniques resulting in a general master equation of a compact form that describes an open quantum gravitational system with arbitrary bosonic fields. An initial application of the theory is illustrated by the implied quantum gravitational dissipation of light as well as (non)relativistic massive or massless scalar particles. Related effects could eventually lead to important physical consequences including those on a cosmological scale and for a large number of correlated particles.
Space offers exciting opportunities to test the foundations of quantum physics using macroscopic quantum superpositions. It has been proposed to perform such tests in a dedicated space mission (MAQRO) using matter-wave interferometry with massive test particles or monitoring how the wave function of a test particle expands over time. Such experiments could test quantum physics with sufficiently high precision to resolve potential deviations from its unitary evolution due to gravitational decoherence. For example, such deviations have been predicted by the Diósi–Penrose (DP) model and the Károlyházy (K) model. The former predicts the collapse of massive or large superpositions due to a nonlinear modification of quantum evolution. The latter predicts decoherence because of an underlying uncertainty of space time. Potential advantages of a space environment are (1) long free-fall times, (2) low noise, and (3) taking a high number of data points over several years in a dedicated space mission. In contrast to interferometric tests, monitoring wave function expansion is less complex, but it does face some practical limitations. Here, we will discuss limitations of such non-interferometric experiments due to the limited number of data points achievable during a mission lifetime. Our results show that it will require an interferometric approach to conclusively test for gravitational decoherence as predicted by the DP or K models. In honor of the Nobel prize of Sir Roger Penrose, we will focus our discussion on the Diósi–Penrose model.