Emergent classicality and wavefunction branching in an isolated quantum many-body system

Quantum Physics arXiv:2609.19254 (quant-ph) [Submitted on 16 Sep 2026] Title:Emergent classicality and wavefunction branching in an isolated quantum many-body system Authors:Saúl Pilatowsky-Cameo, Jordan Cotler, Daniel Ranard, C.

Jess Riedel View a PDF of the paper titled Emergent classicality and wavefunction branching in an isolated quantum many-body system, by Sa\'ul Pilatowsky-Cameo and 3 other authors View PDF HTML (experimental) Abstract:Decoherence in quantum systems is conventionally modeled as the effect of interactions with an external environment. However, such a prescription excludes isolated many-body systems, which are also expected to display classical behavior at macroscopic scales. In isolated systems, decoherence must emerge internally from microscopic degrees of freedom that are invisible to the macroscopic description. Here we explicitly show that classicality can emerge in such a fashion. We consider a weakly disordered, $3$-local chaotic kicked top of $N$ qubits, where the collective spin sector serves as the macroscopic description, while the microscopic permutation sector acts as an internal bath, decohering the collective spin sector. Starting from closed unitary dynamics, we derive and numerically confirm an effective Lindblad equation for the collective spin variables. In the thermodynamic limit these reduced dynamics converge to a classical chaotic Fokker--Planck equation with vanishingly small diffusion on the spherical phase space, producing a quantum-classical correspondence beyond the Ehrenfest time. The chaotic dynamics evolve the pure many-body wavefunction into continuously branching components associated with distinct classical trajectories. These branches acquire nearly orthogonal microscopic records in the permutation sector, preventing quantum interferences and ensuring the corresponding histories remain consistent. Comments: Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph) Report number: MIT-CTP/6114 Cite as: arXiv:2609.19254 [quant-ph] (or arXiv:2609.19254v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2609.19254 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Saúl Pilatowsky-Cameo [view email] [v1] Wed, 16 Sep 2026 18:00:01 UTC (3,592 KB) Full-text links: Access Paper: View a PDF of the paper titled Emergent classicality and wavefunction branching in an isolated quantum many-body system, by Sa\'ul Pilatowsky-Cameo and 3 other authorsView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-09 Change to browse by: cond-mat cond-mat.str-el math math-ph math.MP References & Citations INSPIRE HEP NASA ADSGoogle Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... Data provided by: 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 Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv (What is alphaXiv?) Links to Code Toggle CatalyzeX Code Finder for Papers (What is CatalyzeX?) DagsHub Toggle DagsHub (What is DagsHub?) GotitPub Toggle Gotit.pub (What is GotitPub?) Huggingface Toggle Hugging Face (What is Huggingface?) ScienceCast Toggle ScienceCast (What is ScienceCast?) Demos Demos Replicate Toggle Replicate (What is Replicate?) Spaces Toggle Hugging Face Spaces (What is Spaces?) Spaces Toggle TXYZ.AI (What is TXYZ.AI?) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower (What are Influence Flowers?) Core recommender toggle CORE Recommender (What is CORE?) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them. Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs. Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)