External quantum fluctuations select measurement contexts
1Quantum Group, School of Computing, Newcastle University, 1 Science Square, Newcastle upon Tyne, NE4 5TG, UK
2Quantum Engineering Technology Laboratories, Department of Electrical and Electronic Engineering, University of Bristol, Woodland Road, Bristol, BS8 1US, UK
3QICI Quantum Information and Computation Initiative, School of Computing and Data Science, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
4Graduate School of Advanced Science and Engineering, Hiroshima University, Kagamiyama 1-3-1, Higashi Hiroshima 739-8530, Japan
| Published: | 2026-05-13, volume 10, page 2106 |
| Editor: | Leon Loveridge |
| Eprint: | arXiv:2501.04664v2 |
| Doi: | https://doi.org/10.22331/q-2026-05-13-2106 |
| Citation: | Quantum 10, 2106 (2026). |
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Abstract
Quantum paradoxes show that the outcomes of different quantum measurements cannot be described by a single measurement-independent reality. Any theoretical description of a quantum measurement implies the selection of a specific measurement context. Here, we investigate generalised quantum measurements, in order to identify the mechanism by which this specific context is selected. We show that external quantum fluctuations, represented by the initial state of the measurement apparatus, play an essential role in the selection of the context. This has the non-trivial consequence that, when considering measurements other than just idealised projection-valued measures, different outcomes of a single measurement setup can represent different measurement contexts. We further show this result underpins recent claims that contextuality can occur in scenarios without measurement incompatibility.
Featured image: The three-path interferometer introduced by Hofmann to illustrate quantum contextuality. We use this in the paper as a toy model to illustrate how external quantum fluctuations in the environment (here modelled through the polarisation degree of freedom of the photon traversing the interferometer) can select different measurement contexts in what is otherwise the same apparatus.
Popular summary
Here, we investigate generalised quantum measurements, which don't require that the different measurement outcomes are mutually-exclusive (e.g., "yes", "maybe", and "no"), in order to identify the mechanism by which this specific context is selected. We show that external quantum fluctuations (from the immediate environment outside our system), represented by the initial state of the measurement apparatus, play an essential role in the selection of the context.
This has the non-trivial consequence that, when considering measurements other than just idealised projection-valued measures (e.g., measurements where the measurement outcomes aren't incompatible, so can overlap), different outcomes of a single measurement setup can represent different measurement contexts. We further show this result underpins recent claims that contextuality can occur in scenarios without measurement incompatibility.
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Cited by
[1] Alisson Tezzin, Bárbara Amaral, and Jonte R. Hance, "Sufficiency of the counterfactual account of Lüders' rule to rule out ontological models of quantum mechanics", Physical Review A 112 5, 052208 (2025).
[2] Partha Patra, Sumit Mukherjee, and A. K. Pan, "Contextuality sans incompatibility in the simplest scenario: Communication supremacy of a qubit", arXiv:2503.09534, (2025).
[3] Enrico Bozzetto and Jonte R. Hance, "Warring Contextualities -- Provably Classical vs Provably Nonclassical", arXiv:2604.14319, (2026).
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