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We derive an upper bound on the difference between the long-time average and the microcanonical ensemble average of observables in isolated quantum systems. We propose, numerically verify, and analytically support a new hypothesis,…

Statistical Mechanics · Physics 2011-08-24 Tatsuhiko N. Ikeda , Yu Watanabe , Masahito Ueda

The Eigenstate Thermalization Hypothesis (ETH) implies a form for the matrix elements of local operators between eigenstates of the Hamiltonian, expected to be valid for chaotic systems. Another signal of chaos is a positive Lyapunov…

Statistical Mechanics · Physics 2019-05-01 Laura Foini , Jorge Kurchan

A plausible mechanism of thermalization in isolated quantum systems is based on the strong version of the eigenstate thermalization hypothesis (ETH), which states that all the energy eigenstates in the microcanonical energy shell have…

Statistical Mechanics · Physics 2018-05-23 Toru Yoshizawa , Eiki Iyoda , Takahiro Sagawa

The Eigenstate Thermalization Hypothesis (ETH) provides a way to understand how an isolated quantum mechanical system can be approximated by a thermal density matrix. We find a class of operators in (1+1)-$d$ conformal field theories,…

High Energy Physics - Theory · Physics 2017-08-30 Pallab Basu , Diptarka Das , Shouvik Datta , Sridip Pal

The Eigenstate Thermalization Hypothesis explains thermalization in isolated quantum systems through the statistical properties of observables in the energy eigenbasis. We investigate the crossover from integrability to chaos in the…

Quantum Physics · Physics 2026-01-15 Shivam Mishra , C Jisha , Ravi Prakash

The eigenstate thermalization hypothesis (ETH) explains why chaotic quantum many-body systems thermalize internally if the Hamiltonian lacks symmetries. If the Hamiltonian conserves one quantity ("charge"), the ETH implies thermalization…

The Eigenstate Thermalization Hypothesis (ETH) represents a cornerstone in the theoretical understanding of the emergence of thermal behavior in closed quantum systems. The ETH asserts that expectation values of simple observables in energy…

Statistical Mechanics · Physics 2024-05-15 Giorgio Cipolloni , Jonah Kudler-Flam

The eigenstate thermalization hypothesis (ETH) provides a powerful framework for understanding thermalization in isolated quantum many-body systems, yet a complete and conceptually transparent derivation has remained elusive. In this work,…

Statistical Mechanics · Physics 2025-12-23 Yucheng Wang

Deriving conditions under which a macroscopic system thermalizes directly from the underlying quantum many-body dynamics of its microscopic constituents is a long-standing challenge in theoretical physics. The well-known eigenstate…

Statistical Mechanics · Physics 2022-02-02 Lennart Dabelow , Patrick Vorndamme , Peter Reimann

The strong eigenstate thermalization hypothesis (ETH) provides a sufficient condition for thermalization and equilibration. Although it is expected to be hold in a wide class of highly chaotic theories, there are only a few analytic…

High Energy Physics - Theory · Physics 2026-01-19 Taishi Kawamoto

The Eigenstate Thermalization Hypothesis (ETH) has played a major role in understanding thermodynamic phenomena in closed quantum systems. However, its connection to the timescale of thermalization for open system dynamics has remained…

Quantum Physics · Physics 2023-03-30 Chi-Fang Chen , Fernando G. S. L. Brandão

The eigenstate thermalization hypothesis (ETH) attempts to bridge the gap between quantum mechanical and statistical mechanical descriptions of isolated quantum systems. Here, we define unbiased measures for how well the ETH works in…

Statistical Mechanics · Physics 2016-05-04 Pavan Hosur , Xiao-Liang Qi

The eigenstate thermalization hypothesis (ETH) explains how generic quantum many-body systems thermalize internally. It implies that local operators' time-averaged expectation values approximately equal their thermal expectation values,…

Quantum Physics · Physics 2024-12-12 Aleksander Lasek , Jae Dong Noh , Jade LeSchack , Nicole Yunger Halpern

Despite the unitary evolution of closed quantum systems, long-time expectation of local observables are well described by thermal ensembles, providing the foundation of quantum statistical mechanics. A promising route to understanding this…

Quantum Physics · Physics 2026-02-03 Yuke Zhang , Pengfei Zhang

The eigenstate thermalisation hypothesis (ETH) is a statistical characterisation of eigen-energies, eigenstates and matrix elements of local operators in thermalising quantum systems. We develop an ETH-like ansatz of a partially…

Quantum Physics · Physics 2022-08-01 Philip JD Crowley , Anushya Chandran

We ask whether the Eigenstate Thermalization Hypothesis (ETH) is valid in a strong sense: in the limit of an infinite system, {\it every} eigenstate is thermal. We examine expectation values of few-body operators in highly-excited many-body…

Statistical Mechanics · Physics 2014-11-13 Hyungwon Kim , Tatsuhiko N. Ikeda , David A. Huse

Under the Eigenstate Thermalization Hypothesis (ETH), quantum-quenched systems equilibrate towards canonical, thermal ensembles. While at first glance the ETH might seem a very strong hypothesis, we show that it is indeed not only…

Quantum Physics · Physics 2016-02-03 Giacomo De Palma , Alessio Serafini , Vittorio Giovannetti , Marcus Cramer

According to the eigenstate thermalization hypothesis (ETH), the eigenstate-to-eigenstate fluctuations of expectation values of local observables should decrease with increasing system size. In approaching the thermodynamic limit - the…

Statistical Mechanics · Physics 2021-04-14 Goran Nakerst , Masudul Haque

The eigenstate thermalization hypothesis (ETH) has been highly influential in explaining thermodynamic behavior of closed quantum systems. As of yet, it is unclear whether and how the ETH applies to non-Hermitian systems. Here, we introduce…

The validity of the ergodic hypothesis in quantum systems can be rephrased in the form of the eigenstate thermalisation hypothesis (ETH), a set of statistical properties for the matrix elements of local observables in energy eigenstates,…

Statistical Mechanics · Physics 2024-10-16 Miha Srdinšek , Tomaž Prosen , Spyros Sotiriadis