Dresden 2026 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 2: Focus Session: New Routes to Localization and Quantum Non-Ergodicity I (joint session TT/DY)

DY 2.5: Topical Talk

Montag, 9. März 2026, 11:45–12:15, HSZ/0003

Fock-space cages and their spectral signatures — •Cheryne Jonay — University of Ljubljana

Generic quantum many-body systems thermalize. Yet several mechanisms can prevent this, notable examples include integrability, many-body localization, Hilbert-space fragmentation, and scars. We will discuss a new mechanism of ergodicity breaking that arises from destructive interference in Fock space. This leads to exact eigenstates localized on polynomially many configurations within an exponentially large, fully connected Hilbert space sector. We call these states Fock-space cages. They emerge naturally in kinetically constrained models with chiral symmetry. We will present graph-theoretic methods to explicitly construct cages with support ranging from O(1) to O(L) sites, and examine how their dynamical signatures, such as return probabilities and magnetization, resist thermalization. Finally, we will explore the spectral statistics through the lens of chiral random matrix theory. The exponentially degenerate zero-energy manifold produces distinctive signatures, yet the agreement with random matrix predictions varies across energy scales - a direct consequence of localized and thermal eigenstates coexisting within the same Hilbert space sector. We will also probe the stability of these phenomena: the gap between the zero-energy manifold and the spectral bulk may give rise to protected slow dynamics.

Keywords: Ergodicity Breaking; Kinetically Constrained Models; Fock Space Cages; Chiral Random Matrix Theory; Loschmidt Echo