Two-Parameter Ansatz for the Violation of Eigenstate Thermalization

Kohei Ohgane; Lev Vidmar

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arXiv · 2608.02744

Two-Parameter Ansatz for the Violation of Eigenstate Thermalization

Kohei Ohgane·Lev Vidmar

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Abstract

The eigenstate thermalization hypothesis (ETH) provides the prevailing framework for understanding quantum thermalization and ergodicity in isolated many-body systems. Yet, no general theory describes the continuous onset of ETH violation between the conventional ETH and its complete breakdown. Here, we introduce a two-parameter ansatz for the ETH violation that unifies and distinguishes two mechanisms: fading ergodicity and trapped ergodicity. While fading ergodicity captures the established route to ergodicity breaking, trapped ergodicity describes a distinct scenario in which ETH is violated in finite systems but restored in the thermodynamic limit. We test this framework in the spin-1/2 $J_1$-$J_2$ chains with on-site disorder and linear potential. In both cases, we find that the observed ETH violation is consistent with trapped ergodicity.

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Kohei Ohgane, Lev Vidmar. 2026-08-03. Two-Parameter Ansatz for the Violation of Eigenstate Thermalization. https://arxiv.org/abs/2608.02744

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