Observer-Dependent Entropy and Diagonal R\'enyi Invariants in Quantum Reference Frames

Quantum Physics [Submitted on 24 Mar 2026] Observer-Dependent Entropy and Diagonal Rényi Invariants in Quantum Reference Frames Anne-Catherine de la Hamette Quantum reference frames provide a relational description of multipartite quantum systems in which physical states and observables are defined relative to quantum observers. Yet different observers can assign different entropies to the same system, raising the question of how such observer-dependence is constrained. We identify a family of frame-independent diagonal Rényi entropies for arbitrary subsystems, yielding a generalized multipartite coherence-entanglement tradeoff. For ideal frames, the observer-dependence of subsystem entropy admits an exact decomposition into a sum of single-frame coherences and inter-frame correlations; for non-ideal frames, it is instead bounded by the dimension of an effective relational Hilbert space determined by the representation structure of the frames. Our results place quantitative limits on how much quantum observers can disagree about subsystem entropy, with potential implications for observer-dependent entropy assignments in gravitational settings. Comments: 5+4 pages, 1 figure Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2603.23598 [quant-ph]   (or arXiv:2603.23598v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2603.23598 Focus to learn more Submission history From: Anne-Catherine De La Hamette [view email] [v1] Tue, 24 Mar 2026 18:00:01 UTC (482 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-03 References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)