Quantum Chaos in Many-Body Systems: Theory and Experiment

Diplôme Thèse Quantum Chaos in Many-Body Systems: Theory and Experiment eng 2026-01-30 2026-02-23 author Baumgartner Rahel Lea 0009-0006-2892-8099 838301 Département de physique théorique (FITEO) director Sonner Julian 843498 Département de physique théorique (FITEO) 215 10.13097/archive-ouverte/unige:192463 urn:nbn:ch:unige-1924634 Sc. 5979 Quantum chaos concerns the emergence of universal statistical and dynamical prop- erties in quantum systems whose classical counterparts exhibit chaotic behavior. Unlike classical chaos, which can be characterized by sensitivity to initial conditions and exponential divergence of trajectories, quantum chaos manifests itself through a variety of indirect diagnostics, including spectral correlations, operator growth, and information scrambling. Understanding how these signatures arise from microscopic dynamics, and how they can be accessed in realistic many-body systems, is a central challenge in modern physics. This thesis investigates quantum chaos from complementary theoretical and practical perspectives. On the theoretical side, it develops effective descriptions of chaotic dy- namics in many-body systems with approximate symmetries, focusing on how weak symmetry breaking controls the exploration of Hilbert space and the crossover to random-matrix universality. Using perturbative arguments, numerical simulations, and a nonlinear sigma-model formulation, we identify a regime of Hilbert-space dif- fusion in which chaotic dynamics unfolds through a slow, collective spreading across nearly decoupled symmetry sectors. On the practical side, the thesis addresses the question of how paradigmatic chaotic models can be realized and probed in controlled experimental platforms. In partic- ular, it explores quantum simulation schemes for Sachdev–Ye–Kitaev (SYK) models using cavity quantum electrodynamics. By employing time-dependent disorder and Trotterized evolution in single-mode optical cavities, we demonstrate how low-rank interactions can be systematically promoted to effective all-to-all randomness, re- producing the spectral and dynamical signatures of SYK physics. Extensions to open-system dynamics are discussed, including Lindbladian realizations and the role of dissipation. The thesis thus highlights the connections between effective descriptions of quantum chaos and their implementation in controlled quantum simulation settings. Quantum Chaos Quantum Simulation Holography Dewey 500.2 37 Département de physique théorique 133 false 968 Groupe Sonner 018cde2f-b226-4cca-a4ac-61757ed4a064 Thesis Restricted Thesis.pdf 22333576 application/pdf 18877b0c3ab443e99d1d8a7b944771234baf93dbf43a75fb275263b3781284eb 799aa686-a64c-4672-9a0b-deb513638a0f Imprimatur Public imprimatur.pdf 41460 application/pdf 299d8a3c738cf2464e9a75c3d5456698888a8d9d039075f75980f631160dd5fd restrictedAccess Faculté des sciences / Section de physique / Département de physique théorique

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Baumgartner, Rahel

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