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Events and their Localisation are Relative to a Lab

V. Vilasini, Lin-Qing Chen, Liuhang Ye, Renato Renner

27/5/25 Published in : arXiv:2505.21797

The notions of events and their localisation fundamentally differ between quantum theory and general relativity, reconciling them becomes even more important and challenging in the context of quantum gravity where a classical spacetime background can no longer be assumed. We therefore propose an operational approach drawing from quantum information, to define events and their localisation relative to a Lab, which in particular includes a choice of physical degree of freedom (the reference) providing a generalised notion of "location". We define a property of the reference, relative measurability, that is sensitive to correlations between the Lab's reference and objects of study. Applying this proposal to analyse the quantum switch (QS), a process widely associated with indefinite causal order, we uncover differences between classical and quantum spacetime realisations of QS, rooted in the relative measurability of the associated references and possibilities for agents' interventions. Our analysis also clarifies a longstanding debate on the interpretation of QS experiments, demonstrating how different conclusions stem from distinct assumptions on the Labs. This provides a foundation for a more unified view of events, localisation, and causality across quantum and relativistic domains.

Entire article

Phase I & II research project(s)

  • Quantum Systems

Phase III direction(s)

  • Quantum information and many body theory

The future of secure communications: device independence in quantum key distribution

Superadditivity at Large Charge

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