| Issue |
EPL
Volume 152, Number 2, October 2025
|
|
|---|---|---|
| Article Number | 28001 | |
| Number of page(s) | 5 | |
| Section | Quantum information | |
| DOI | https://doi.org/10.1209/0295-5075/ae1639 | |
| Published online | 06 November 2025 | |
Toy model challenging prevailing definitions of classicality
1 Física Teòrica: Informació i Fenòmens Quàntics, Departament de Física, Universitat Autònoma de Barcelona 08193 Bellaterra (Barcelona), Spain
2 Department of Physics & Astronomy, University of Manchester - Manchester M13 9PL, UK
3 Instituto de Física de Cantabria (IFCA), Universidad de Cantabria-CSIC - 39005 Santander, Spain
Received: 22 August 2025
Accepted: 22 October 2025
Abstract
We analyze a toy model that obeys environmentally induced decoherence and quantum Darwinism and satisfies the decoherent histories criterion and Leggett-Garg inequalities with respect to the pointer basis. Yet, the resulting “classical” dynamics are extremely fragile and recohere after a seemingly innocent control operation. This challenges the idea that classical behaviour or the Multiverse branches can be identified by looking at the universal wave function alone. It also demonstrates that quantum Darwinism is compatible with strong non-Markovianity. Possible solutions related to Markovianity, non-integrability and an operational definition of pointer states are briefly discussed.
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