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We provide a pedagogical introduction to eigenstate thermalization. This phenomenon, which occurs in generic quantum systems, allows one to understand why thermalization takes place in isolated systems under unitary dynamics. We motivate…

Quantum Physics · Physics 2026-04-29 Rohit Patil , Marcos Rigol

Analytical treatments of far-from-equilibrium quantum dynamics are few, even in well-thermalizing systems. The celebrated eigenstate thermalization hypothesis (ETH) provides a post hoc ansatz for the matrix elements of observables in the…

Quantum Physics · Physics 2025-10-06 Dominik Hahn , David M. Long , Marin Bukov , Anushya Chandran

We study the Eigenstate Thermalization Hypothesis (ETH) in chaotic conformal field theories (CFTs) of arbitrary dimensions. Assuming local ETH, we compute the reduced density matrix of a ball-shaped subsystem of finite size in the infinite…

High Energy Physics - Theory · Physics 2018-06-14 Nima Lashkari , Anatoly Dymarsky , Hong Liu

We investigate a weak version of subsystem eigenstate thermalization hypothesis (ETH) for a two-dimensional large central charge conformal field theory by comparing the local equivalence of high energy state and thermal state of canonical…

High Energy Physics - Theory · Physics 2017-11-22 Song He , Feng-Li Lin , Jia-ju Zhang

We study the entanglement Hamiltonian for finite intervals in infinite quantum chains for two different free-particle systems: coupled harmonic oscillators and fermionic hopping models with dimerization. Working in the ground state, the…

Statistical Mechanics · Physics 2020-10-20 Viktor Eisler , Giuseppe Di Giulio , Erik Tonni , Ingo Peschel

Ergodic isolated quantum many-body systems satisfy the eigenstate thermalization hypothesis (ETH), i.e., the expectation values of local observables in the system's eigenstates approach the predictions of the microcanonical ensemble.…

Disordered Systems and Neural Networks · Physics 2025-11-25 Adith Sai Aramthottil , Ali Emami Kopaei , Piotr Sierant , Lev Vidmar , Jakub Zakrzewski

If and how an isolated quantum system thermalizes despite its unitary time evolution is a long-standing, open problem of many-body physics. The eigenstate thermalization hypothesis (ETH) postulates that thermalization happens at the level…

Quantum Gases · Physics 2018-11-06 Anna Posazhennikova , Mauricio Trujillo-Martinez , Johann Kroha

We investigate off-diagonal matrix elements of local operators in integrable spin chains, focusing on the isotropic spin-$1/2$ Heisenberg chain ($XXX$ chain). We employ state-of-the-art Algebraic Bethe Ansatz results, which allow us to…

Statistical Mechanics · Physics 2026-02-18 Federico Rottoli , Vincenzo Alba

We consider the statistical properties of eigenstates of the time-evolution operator in chaotic many-body quantum systems. Our focus is on correlations between eigenstates that are specific to spatially extended systems and that…

Quantum Physics · Physics 2024-08-21 Dominik Hahn , David J. Luitz , J. T. Chalker

In the present note, we discuss a simple example of a macroscopic quantum many-body system in which the approach to thermal equilibrium from an arbitrary initial state in the microcanonical energy shell is proved without relying on any…

Statistical Mechanics · Physics 2024-04-09 Hal Tasaki

Local observables in generic periodically driven closed quantum systems are known to relax to values described by periodic infinite temperature ensembles. At the same time, ergodic static systems exhibit anomalous thermalization of local…

Disordered Systems and Neural Networks · Physics 2018-08-15 Sthitadhi Roy , Yevgeny Bar Lev , David J. Luitz

We study the entanglement spectrum in the many body localizing and thermalizing phases of one and two dimensional Hamiltonian systems, and periodically driven `Floquet' systems. We focus on the level statistics of the entanglement spectrum…

Statistical Mechanics · Physics 2016-05-25 Scott D. Geraedts , Rahul Nandkishore , Nicolas Regnault

The Eigenstate Thermalization Hypothesis (ETH) is a framework for discussing thermal behavior originating from chaotic dynamics in isolated many-body quantum systems. The PXP model, where certain states do not thermalize, has been compared…

Quantum Physics · Physics 2025-03-17 Maanav Srihari , Anil Shaji

We show, without relying on any unproven assumptions, that a low-density free fermion chain exhibits thermalization in the following (restricted) sense. We choose the initial state as a pure state drawn randomly from the Hilbert space in…

Statistical Mechanics · Physics 2026-04-13 Naoto Shiraishi , Hal Tasaki

We use the eigenstate thermalization hypothesis to derive a quantum master equation for a system weakly coupled to a chaotic finite-sized bath prepared in a pure state. We show that the emergence of Markovianity is controlled by the…

Quantum Physics · Physics 2025-09-03 Peter O'Donovan , Philipp Strasberg , Kavan Modi , John Goold , Mark T. Mitchison

Ability of dynamical systems to relax to equilibrium has been investigated since the invention of statistical mechanics, which establishes the connection between dynamics of many-body Hamiltonian systems and phenomenological thermodynamics.…

Statistical Mechanics · Physics 2019-07-01 K. S. Glavatskiy , V. L. Kulinskii

We study general entanglement properties of the excited states of the one dimensional translational invariant free fermions and coupled harmonic oscillators. In particular, using the integrals of motion, we prove that these Hamiltonians…

Strongly Correlated Electrons · Physics 2019-11-13 Arash Jafarizadeh , M. A. Rajabpour

Motivated by recent ion experiments on tunable long-range interacting quantum systems [B.Neyenhuis et al., Sci.Adv.3, e1700672 (2017, https://doi.org/10.1126/sciadv.1700672 )], we test the strong eigenstate thermalization hypothesis (ETH)…

Statistical Mechanics · Physics 2022-07-27 Shoki Sugimoto , Ryusuke Hamazaki , Masahito Ueda

An isolated quantum system is said to thermalize if ${\rm Tr} (A \rho(t)) \to {\rm Tr} (A \rho_{\rm eq})$ for time $t \to \infty$. Here $\rho(t)$ is the time-dependent density matrix of the system, $\rho_{\rm eq}$ is the time-independent…

Quantum Physics · Physics 2024-04-22 Hans A. Weidenmüller

Many phases of matter, including superconductors, fractional quantum Hall fluids and spin liquids, are described by gauge theories with constrained Hilbert spaces. However, thermalization and the applicability of quantum statistical…

Statistical Mechanics · Physics 2016-12-09 A. Chandran , M. D. Schulz , F. J. Burnell