Welcome

• Enrique Rico Ortega (CERN)

Room: 4/3-006 - TH Conference Room

Non-ergodic dynamics in SU(2) lattice gauge theory: scars, fragmentation, and disorder-free localization

• Giovanni Cataldi (Max Planck Institute of Quantum Optics)

Room: 4/3-006 - TH Conference Room Non-Abelian lattice gauge theories provide a setting where local constraints reshape far-from-equilibrium quantum many-body dynamics and can obstruct thermalization. In a (1+1)D SU(2) lattice gauge theory with dynamical matter, three non-ergodic phenomena are identified, each with a different origin. In regimes where the gauge-invariant dynamics is otherwise ergodic, low-overhead product-state quenches exhibit robust quantum many-body scarring, seen as long-lived coherent oscillations in local observables and pronounced fidelity revivals enabled by non-Abelian meson and baryon–antibaryon excitations. In a separate region of parameters, the gauge-invariant model becomes nonthermal yet delocalized due to Hilbert-space fragmentation into disconnected Krylov subsectors. Finally, when static SU(2) background charges are introduced to encode gauge superselection sectors, and the system is initialized in a coherent superposition of these sectors, disorder-free localization emerges even where a fixed sector is ergodic: spatial matter inhomogeneities persist at long times, and entanglement exhibits MBL-like (logarithmic) growth. These results provide a unified benchmark suite for non-ergodic far-from-equilibrium dynamics in non-Abelian constrained systems and are compatible with digital quantum simulation on existing qudit platforms.

Quasiparticle wavepackets for glueball scattering on a qutrit chain

• Marco Rigobello (Max-Planck Quantum Optics)

Room: 4/3-006 - TH Conference Room We introduce a model-independent method for preparing and detecting quasiparticle wavepackets in (quasi-)1D quantum many-body systems. We exploit maximally localized Wannier functions obtained from exact diagonalization to construct unitary quasiparticle creation operators. These can then be applied to larger systems, encoded using tensor networks or quantum simulators. Detection further distinguishes single-particle contributions from resonances. We benchmark the method in real-time matrix-product-state simulations of glueball-glueball scattering in a truncated SU(3) gauge theory on a ladder. By encoding the model in a qutrit chain, we provide a minimal setup for studying dynamical pure-gauge excitations.

Group Invariant Quantum Many-Body Scars and Unconventional Electron Pairing

• Kiryl Pakrouski (ETH Zurich)

Room: 4/3-006 - TH Conference Room Many-body scar subspaces decouple from the rest of the Hilbert space which protects the order present in scar states from thermalisation. I will discuss a form of general conditions leading to this phenomenon known as the Group Invariant formalism. As an example, I will show that the Yang’s eta-pairing states are many-body scars in many standard condensed matter models such as the 1-orbital Fermi-Hubbard model of spin-1/2 electrons on a lattice. In the 2-orbital case scar states feature strong unconventional superconducting pairing. I will also show that scars themselves may be non-integrable, forming an independent thermal bath with distinct thermal expectation values.

Emergent spacetime geometry for quantum matter

• Stefan Floerchinger (University of Jena)

Room: 4/3-006 - TH Conference Room Quantum excitations or quasiparticles in a material, like for example phonons in a Bose-Einstein condensate, or fermions in the vicinity of a Dirac point in materials like graphene, can be subject to non-trivial spacetime geometries that differ from the Minkowski spacetime of the laboratory. These geometries are determined by material properties like the speed of sound, fluid velocity, or Fermi velocity, and they can depend themselves on space and time. Geometries of this kind are emergent in the sense that they appear in the low energy sector of macroscopic pieces of matter consisting of many atoms or other constituents. The talk reviews this physics and discusses how it allows quantum simulation of quantum fields in curved spacetime, as it plays a role for example in the early universe.

Hydrodynamic attractors in ultracold atoms

• Tilman Enss (Heidelberg)

Room: 4/3-006 - TH Conference Room Hydrodynamic attractors are a universal phenomenon of strongly interacting systems that describe an hydrodynamic-like evolution far from local equilibrium. We describe how such behavior might be observed in real time in ultracold atomic gases. Although ultracold atomic gases are dilute, they have remarkable transport properties exhibiting hydrodynamics and nearly perfect fluidity. We show by explicit microscopic calculations how such systems relax toward equilibrium. On relevant time scales, the dynamics is well represented by analytical attractor solutions valid at short times before the onset of Navier-Stokes hydrodynamics. [1] Keisuke Fujii and Tilman Enss, Phys. Rev. Lett. 133, 173402 (2024). [2] Aleksas Mazeliauskas and Tilman Enss, Phys. Rev. Lett. 136, 103402 (2026).

From projected to observable-projected ensembles

• Sara Murciano

Room: 4/3-006 - TH Conference Room Local measurements offer a powerful way to probe novel quantum phenomena, thermalization, and universal distributions in many-body quantum systems. In this talk, I will introduce the observable-projected ensemble, in which the subsystem state is conditioned on the outcome of measuring a single local Hermitian operator on part of its complement, rather than on a complete projective measurement of the whole complement. This protocol avoids the exponential complexity of conventional projected ensembles while remaining analytically tractable. I will discuss how its k-th moments compare with those of the Haar ensemble and show that, rather than approaching the Haar ensemble, the observable-projected ensemble can become exponentially distinguishable from it as the bath size grows. I will also describe its field-theoretic formulation in critical systems and illustrate the construction with the free compact boson.

From phase space to Krylov space: complexity and the geometry of chaos

• Julian Sonner (Universite de Geneve (CH))

Room: 4/3-006 - TH Conference Room We develop a classical counterpart of the Krylov complexity framework by running the Lanczos algorithm directly on the algebra of observables of a Hamiltonian system on a compact symplectic manifold. This construction arises naturally as the semiclassical limit of the quantum Lanczos algorithm. We demonstrate the usefulness of classical Krylov complexity in characterisation early-time dynamics in chaotic quantum systems with a semiclassical limit, and derive a Krylov-Ehrenfest theorem, which captures the eventual divergence of semiclassical and exact Krylov dynamics.

Tensor Network methods for real-time dynamics of Gauge Field Theories

• Giuseppe Magnifico

Room: 4/3-006 - TH Conference Room Gauge theories lie at the heart of our description of nature’s fundamental building blocks and their interactions, ranging from high-energy particle physics to emergent phenomena in low-temperature quantum matter. However, the complete characterization of their phase diagrams and the full understanding of non-perturbative effects remain open challenges, especially at finite charge density, largely due to the sign problem affecting Monte Carlo simulations. In recent years, a complementary numerical approach based on Tensor Network (TN) methods, in synergy with emerging quantum technologies, has shown great potential for the study of Lattice Gauge Theories (LGTs). In this talk, I will primarily focus on the real-time dynamics of LGTs with fermionic matter, emphasizing genuinely non-equilibrium phenomena. In particular, I will discuss dynamical processes such as string breaking, scattering, and thermalization in open quantum systems, where gauge degrees of freedom interact with an external environment. I will also briefly comment on recent progress in equilibrium properties and phase diagrams.

Color Glass to Color Fluid: Thermalization in ultrarelativistic heavy-ion collisions

• Raju Venugopalan (BNL and Univ. of Edinburgh)

Room: 4/3-006 - TH Conference Room From a first principles QFT perspective, the problem of thermalization in heavy-ion collisions may appear to be intractable. However, at very high energies, a semi-classical "shockwave" description of ultrarelativistic nuclei (and their scattering) emerges, described by the Color Glass Condensate (CGC) EFT. We first discuss how such shockwaves form in QCD, and how they decay, and the rich insights provided by examining this process in the language of broken global symmetries. We then discuss multi-particle production in collisions of the shockwave coherent states. The radiated glue initially forms a far-from-equilibrium Glasma, which can be understood as a generalized Susskind-Glogower squeezed state. The subsequent evolution of the Glasma after it decoheres is characterized by turbulent IR and UV flows with universal features in common with ultracold atomic gases. We discuss some of the unresolved open questions in this description of thermalization in heavy-ion collisions.

New ideas for nonthermal fixed points

• Michal Heller

Room: 4/3-006 - TH Conference Room Nonthermal fixed points are paradigmatic far-from-equilibrium phenomena, relevant experimentally in cold atomic gases and theoretically in ultrarelativistic nuclear collisions and cosmology. I will show how insights from other areas, including holographic studies of thermalization, enable predictions of new features and phenomena associated with their self-similar time evolution.

Ergodicity-breaking scenarios in quantum link lattice gauge theories

• Debasish Banerjee (University of Southampton)

Room: 4/3-006 - TH Conference Room While the widespread applicability of statistical mechanics indicates the ubiquitous occurrence of thermalization, guided by the Eigenstate Thermalization Hypothesis (ETH), there are increasing examples of violations of the ETH paradigm; both for translational invariant and disordered systems. In this talk, we will discuss various such examples occurring in pure U(1) quantum link gauge theories in two and three spatial dimensions involving exotic phenomena such as scarring and fragmentation.

Interface phases and dynamics in two-dimensional quantum magnets: Theory and novel quantum simulation opportunities

• Alessio Lerose

Room: 4/3-006 - TH Conference Room We introduce a rigorous framework to classify phases and phase transitions of interfaces separating ordered regions in 2D Ising-type quantum magnets --- or, equivalently, confining strings in the dual lattice gauge theories --- based on effective 1D fermionic Hamiltonians governing transversal quantum fluctuations. Building on the `holographic' approach from [Balducci et al., Phys. Rev. Lett. 129, 120601], here reinterpreted as an exact lattice bosonization, we systematically classify the fermionic interactions arising from various symmetry-preserving bulk Hamiltonians. We find that irrelevant bulk perturbations give rise to a rich variety of interface/string behaviors, with various distinct `stiff' and `rough' phases described by `insulating' and `metallic' fermionic ground states, respectively, distinguished by their symmetry and dynamical character. Furthermore, we map out the universal 2D curvature-driven relaxation laws of the interfaces/strings in terms of the non-equilibrium charge-transport properties of the underlying 1D chains, including ballistic, diffusive, and super-diffusive flattening dynamics. Finally, building on recent advances with 2D neutral atom arrays [Manovitz et al., Nature 638, 86–92], we discuss how our approach enables unprecedented experimental opportunities for quantum simulation, including a straightforward access to the charge full counting statistics via simple local measurements as well as an analog implementation of full (untruncated) gauge-invariant continuum quantum field theory (QED2). Based on work in preparation with Abhishodh Prakash (Oxford -> HRI), Jaydev S. Rao (KU Leuven), Sid Parameswaran (Oxford)

False vacuum decay in quantum spin chains and quantum simulators

• Gianluca Lagnese

Room: 4/3-006 - TH Conference Room Confinement and false vacuum decay are cornerstone non-perturbative phenomena in quantum field theory. Both emerge when an explicit symmetry breaking field lifts the degeneracy of a vacuum. In this framework, confined states act as droplets of the "false" vacuum, while decay occurs through the nucleation of "true" vacuum bubbles via quantum tunneling. Recent breakthroughs in controllable quantum platforms, including trapped ions and Rydberg atom arrays, have moved these concepts from theory to the lab. While confinement has already been observed, real time investigations of false vacuum decay are now on the horizon. I will discuss how these phenomena manifest in quantum spin chains, focusing on real time dynamics following a quantum quench and experimental setups that provide a controlled environment to study quantum tunneling and bubble nucleation.

Bubble nucleation in long-range systems

• Laura Batini (ETH Zürich)

Room: 4/3-006 - TH Conference Room Metastable states are ubiquitous in systems undergoing first-order transitions, where the decay proceeds via the nucleation of critical droplets. This phenomenon has attracted renewed interest driven by experiments with analog quantum simulators, which enable direct access to real-time nucleation dynamics. Many of these platforms, trapped-ion Ising simulators, Rydberg-atom arrays with dipolar or van der Waals tails, exhibit long-range power-law couplings. Understanding how such interactions reshape the nucleation process is an open challenge. To address it, we introduce a numerical method based on solving the fractional-Laplacian saddle-point equation for the nucleating droplet, applicable to both thermal and quantum decay regimes. After benchmarking against the local case, we turn to the weak long-range setting. We find that the critical droplet profile develops distinctive algebraic tails, in stark contrast to the sharp domain walls of short-range models. In the classical regime, we observe a metastability transition as a function of the interaction range: for sufficiently long-range couplings, the metastable state becomes arbitrarily long-lived as the energy splitting between the two phases vanishes, mirroring the equilibrium phase transition of the one-dimensional long-range Ising model. In the quantum (1+1)-dimensional case, the physics is qualitatively different: the interplay between long-range interactions and quantum fluctuations modifies the nucleation process in ways that have no classical analog, with distinct regimes emerging as the interaction range is varied.

Quantum computation of Quantum Electrodynamics beyond one spatial dimension

• Bipasha Chakraborty (University of Southampton)

Room: 4/3-006 - TH Conference Room Quantum computing provides a promising framework for simulating strongly coupled gauge theories relevant to high-energy physics. In this talk, I will discuss quantum simulations of lattice gauge theories, focusing on the Schwinger model implementing on higher than one spatial dimension. I will outline gauge-invariant encodings and circuit implementations suitable for near-term quantum hardware, and comment on prospects for using quantum algorithms to study real-time dynamics and other regimes challenging for classical methods.

Thermalization Under Generalized Symmetries

• Joao C. Pinto Barros (Institute for Theoretical Physics, ETH Zurich)

Room: 4/3-006 - TH Conference Room In the last few years, many instances of local Hamiltonians with abnormal thermalization properties have been found. These include models with Hilbert space fragmentation and quantum many-body scars. In an ideal scenario, we would like to characterize the conditions under which abnormal thermalization can occur and, if it does, predict its characteristics. In this talk, I will demonstrate how generalized symmetries can lead to an exponential increase in the number of disconnected sectors of the Hilbert space, which has been taken as evidence of ergodicity breaking. I will argue that, in certain instances, this should not be regarded as ergodicity-breaking, namely when it can be fully explained within the framework of generalized symmetries, including non-invertible symmetries, that have been largely unexplored in this context. Notable examples include the PXP model and gauge theories, particularly Quantum Link Models in higher dimensions.