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arXiv:2507.15588

One-sided Witnesses for the Quantumness of Gravitational Dynamics

Konstantin Beyer, M. S. Kim, Igor Pikovski

Published Jul 21, 2025• 0 citations
arXivHTMLPDF

Abstract

Quantum information concepts and quantum technologies have opened the prospect of probing the quantum nature of gravity in table-top experiments. Most proposals rely on detecting gravitationally mediated entanglement, which requires measurements on both interacting systems. Here we propose an alternative test based on witnessing quantum memory effects in the dynamics of a single system. We show how the quantum memory concept allows the non-classicality of the interaction between two systems to be certified through local measurements on only one of them. We then develop a novel quantum memory witness, making the approach applicable to gravitationally coupled harmonic oscillators. This witness requires no assumptions about the dynamics, such as Gaussianity. Our results show that the quantumness of gravitational dynamics can be certified with access to only one subsystem, opening the door to asymmetric implementations that can offer conceptual and experimental advantages to probing the quantum nature of the gravitational interaction.

DOI
10.48550/arxiv.2507.15588

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Quantum information concepts and quantum technologies have opened the prospect of probing the quantum nature of gravity in table-top experiments. Most proposals rely on detecting gravitationally mediated entanglement, which requires measurements on both interacting systems. Here we propose an alternative test based on witnessing quantum memory effects in the dynamics of a single system. We show how the quantum memory concept allows the non-classicality of the interaction between two systems to be certified through local measurements on only one of them. We then develop a novel quantum memory witness, making the approach applicable to gravitationally coupled harmonic oscillators. This witness requires no assumptions about the dynamics, such as Gaussianity. Our results show that the quantumness of gravitational dynamics can be certified with access to only one subsystem, opening the door to asymmetric implementations that can offer conceptual and experimental advantages to probing the quantum nature of the gravitational interaction.
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Abstract The experimental observation of a clear quantum signature of gravity is believed to be out of the grasp of current technology. However, several recent promising proposals to test the possible existence of non-classical features of gravity seem to be accessible by the state-of-art table-top experiments. Among them, some aim at measuring the gravitationally induced entanglement between two masses which would be a distinct non-classical signature of gravity. We explicitly study, in two of these proposals, the effects of decoherence on the system’s dynamics by monitoring the corresponding degree of entanglement. We identify the required experimental conditions necessary to perform successfully the experiments. In parallel, we account also for the possible effects of the continuous spontaneous localization (CSL) model, which is the most known among the models of spontaneous wavefunction collapse. We find that any value of the parameters of the CSL model would completely hinder the generation of gravitationally induced entanglement.
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Quantum theory is one of the most successful theories in modern physics. It has been extensively tested in the microscopic domain, always with remarkable success. Yet, these tests do not currently extend in a conclusive way to all physical systems and across all scales. This leaves open the question of whether quantum theory provides a truly universal description of reality, especially in regimes where direct experimental access is limited, such as the gravitational field or complex macroscopic biological systems. This Thesis addresses this question through the study of hybrid systems, where a well-controlled quantum sector interacts with an unknown sector whose underlying description may or may not be quantum. It contributes to the emerging framework of information-theoretical witnesses of non-classicality, where the quantum sector is used as a probe to test the nature of the unknown system under minimal assumptions. We first examine spatial entanglement-based witnesses, in which the ability of an unknown system to mediate entanglement between two quantum probes by local means provides a sufficient condition for its non-classicality. We extend this framework by quantitatively showing that locally mediated quantum correlations lower bound the non-commutativity of the observables of the mediator, within quantum theory. We then introduce a novel class of single-probe temporal witnesses, where non-classicality is inferred from the temporal evolution of a probe under a global conservation law. We prove that quantum coherent evolution under such a constraint can only be mediated by a non-classical system, and propose an application to light-harvesting processes in photosynthetic complexes. Finally, we develop a temporal entanglement-based witness. Here, the sufficient condition for the non-classicality of the unknown system is the ability to mediate temporal entanglement relative to the probe's local conserved quantity and a non-commuting observable. This result provides a temporal extension of the spatial entanglement-based witness, representing a promising route for the development of the next generation of tests to probe the universality of quantum theory in previously inaccessible fields such as gravity and biology.
Abstract A general entanglement-based witness of non-classicality has recently been proposed, which can be applied to testing quantum effects in gravity. This witness is based on generating entanglement between two quantum probes via a mediator. In this paper we provide a ‘temporal’ variant of this witness, using a single quantum probe to assess the non-classicality of the mediator. Within the formalism of quantum theory, we show that if a system M is capable of inducing a coherent dynamical evolution of a quantum system Q, in the presence of a conservation law, then M must be non-classical. This argument supports witnesses of non-classicality relying on a single quantum probe, which can be applied to a number of open issues, notably in quantum gravity or quantum biology.