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Quantum Ergodicity: Stability and Transitions

Project description

A new approach to study how quantum systems reach equilibrium

Ergodicity is a fundamental concept in statistical mechanics describing how systems evolve over time to explore all accessible states, ensuring equilibrium properties emerge. The ERC-funded QUEST project will further understanding of quantum ergodicity in many-body systems, proving its stability against small perturbations, and study transitions where ergodicity breaks owing to diverse factors such as integrability, disorder and impurities. QUEST will examine weak perturbations in specific types of systems already well understood and chaotic like dual-unitary quantum circuits. This method differs from traditional approaches that often rely on simpler, less chaotic systems. Furthermore, QUEST will create special models where the eigenstate thermalisation hypothesis – explaining how systems reach equilibrium – can be proven. Project advancements could boost quantum simulations and chaos theory, with applications spanning from quantum technologies to black hole physics.

Objective

We shall develop methods and models for analyzing quantum ergodicity in many-body systems, proving its stability against small perturbations, and studying ergodicity-breaking transitions due to integrability, disorder, or localized impurities. Ergodicity is a cornerstone of statistical mechanics and a key manifestation of many-body quantum chaos, while manipulating ergodicity and engineering ergodicity-breaking transitions will have immense applications (cf.scarred states in Rydberg arrays, heating transitions in Floquet systems, time crystalline phases of matter). PI proposed groundbreaking methods for establishing quantum ergodicity by rigorous analysis of spectral statistics, correlation functions, dynamical complexity indicators and entanglement on the basis of space-time duality. Most of current understanding of many-body physics or quantum fields is based on perturbative expansions around free, integrable or localized models. Here we propose a twist of paradigm: We shall study weak perturbations of statistically exactly solvable ergodic models, such as dual-unitary chaotic quantum circuits proposed by PI. An intuitive expectation of structural stability of ergodic dynamics (in analogy to rigorous results in classical ergodic theory) implies that such expansions typically have, unlike expansions around free/integrable models, finite radii of convergence. Various order parameters of the ergodic phase shall be developed and compared in their utility to signal and characterize ergodicity-breaking transitions. A related goal is a construction of exactly solvable models in which the eigenstate thermalization hypothesis can be proven. Being of fundamental importance in mathematical and statistical physics, the results are expected to have widespread applications across fields: from studying localization transitions in disordered systems, benchmarking quantum simulators and certifying quantum supremacy, to rigorous proofs of chaos in holographic models of black holes.

Fields of science (EuroSciVoc)

Keywords

Programme(s)

Topic(s)

Funding Scheme

HORIZON-ERC - HORIZON ERC Grants

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Call for proposal

(opens in new window) ERC-2022-ADG

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Host institution

UNIVERZA V LJUBLJANI
Net EU contribution
€ 1 944 625,00
Address
KONGRESNI TRG 12
1000 Ljubljana
Slovenia
Region
Slovenija Zahodna Slovenija Osrednjeslovenska
Activity type
Higher or Secondary Education Establishments
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Total cost
€ 1 944 625,00

Beneficiaries (1)