Quantum coordinates, localisation of events, and the quantum hole argument

Abstract The study of quantum reference frames (QRFs) is motivated by the idea of taking into account the quantum properties of the reference frames used, explicitly or implicitly, in our description of physical systems. Like classical reference frames, QRFs can be used to define physical quantities...

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Main Authors: Viktoria Kabel, Anne-Catherine de la Hamette, Luca Apadula, Carlo Cepollaro, Henrique Gomes, Jeremy Butterfield, Časlav Brukner
Format: Article
Language:English
Published: Nature Portfolio 2025-04-01
Series:Communications Physics
Online Access:https://doi.org/10.1038/s42005-025-02084-3
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author Viktoria Kabel
Anne-Catherine de la Hamette
Luca Apadula
Carlo Cepollaro
Henrique Gomes
Jeremy Butterfield
Časlav Brukner
author_facet Viktoria Kabel
Anne-Catherine de la Hamette
Luca Apadula
Carlo Cepollaro
Henrique Gomes
Jeremy Butterfield
Časlav Brukner
author_sort Viktoria Kabel
collection DOAJ
description Abstract The study of quantum reference frames (QRFs) is motivated by the idea of taking into account the quantum properties of the reference frames used, explicitly or implicitly, in our description of physical systems. Like classical reference frames, QRFs can be used to define physical quantities relationally. Unlike their classical analogue, they relativise the notions of superposition and entanglement. Here, we explain this feature by examining how configurations or locations are identified across different branches in superposition. We show that, in the presence of symmetries, whether a system is in “the same” or “different” configurations across the branches depends on the choice of QRF. Hence, sameness and difference — and thus superposition and entanglement — lose their absolute meaning. We apply these ideas to the context of semi-classical spacetimes in superposition and use coincidences of four scalar fields to construct a comparison map between spacetime points in the different branches. This reveals that the localisation of an event is frame-dependent. We discuss the implications for indefinite causal order and the locality of interaction and conclude with a generalisation of Einstein’s hole argument to the quantum context.
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spelling doaj-art-9708af6356e5409cab12ad85ea77b14d2025-08-20T02:55:23ZengNature PortfolioCommunications Physics2399-36502025-04-018111810.1038/s42005-025-02084-3Quantum coordinates, localisation of events, and the quantum hole argumentViktoria Kabel0Anne-Catherine de la Hamette1Luca Apadula2Carlo Cepollaro3Henrique Gomes4Jeremy Butterfield5Časlav Brukner6Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of SciencesInstitute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of SciencesInstitute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of SciencesInstitute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of SciencesOriel College, University of OxfordTrinity College, University of CambridgeInstitute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of SciencesAbstract The study of quantum reference frames (QRFs) is motivated by the idea of taking into account the quantum properties of the reference frames used, explicitly or implicitly, in our description of physical systems. Like classical reference frames, QRFs can be used to define physical quantities relationally. Unlike their classical analogue, they relativise the notions of superposition and entanglement. Here, we explain this feature by examining how configurations or locations are identified across different branches in superposition. We show that, in the presence of symmetries, whether a system is in “the same” or “different” configurations across the branches depends on the choice of QRF. Hence, sameness and difference — and thus superposition and entanglement — lose their absolute meaning. We apply these ideas to the context of semi-classical spacetimes in superposition and use coincidences of four scalar fields to construct a comparison map between spacetime points in the different branches. This reveals that the localisation of an event is frame-dependent. We discuss the implications for indefinite causal order and the locality of interaction and conclude with a generalisation of Einstein’s hole argument to the quantum context.https://doi.org/10.1038/s42005-025-02084-3
spellingShingle Viktoria Kabel
Anne-Catherine de la Hamette
Luca Apadula
Carlo Cepollaro
Henrique Gomes
Jeremy Butterfield
Časlav Brukner
Quantum coordinates, localisation of events, and the quantum hole argument
Communications Physics
title Quantum coordinates, localisation of events, and the quantum hole argument
title_full Quantum coordinates, localisation of events, and the quantum hole argument
title_fullStr Quantum coordinates, localisation of events, and the quantum hole argument
title_full_unstemmed Quantum coordinates, localisation of events, and the quantum hole argument
title_short Quantum coordinates, localisation of events, and the quantum hole argument
title_sort quantum coordinates localisation of events and the quantum hole argument
url https://doi.org/10.1038/s42005-025-02084-3
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