Search Talks

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.

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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.

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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.

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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.

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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. 

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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.

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In virtue of their size and complexity, cosmological and astrophysical data are rapidly becoming intractable by traditional statistical techniques. Unravelling the twin mysteries of dark energy and dark matter requires new data analysis methods capable of extracting robust and reliable knowledge from upcoming data streams, including the Euclid satellite, the Nancy Grace Roman space telescope and the Vera Rubin observatory. I will focus on recent advances in simulation-based inference, probabilistic diffusion models and self-supervised learning, which together are enabling fast, scalable inference that achieves state-of-the-art verifiable performance in a variety of settings, including supernova type Ia cosmology, photometric redshift estimation and weak lensing calibration. Methodological issues like domain shift and model misspecification will also be addressed.

Bio: Roberto Trotta is professor of theoretical physics at the International School for Advanced Study in Trieste, Italy, where is the Director of the Interdisciplinary Laboratory, and a visiting professor at Imperial College London, where he was a professor of Astrostatistics. His research focuses on cosmology, machine learning and data science, with applications to early universe cosmology, dark matter direct and indirect detection, supernova type Ia and large scale structure data. He was awarded the 2018 Chair Lemaître of the University of Louvain for his work on astrostatistics and the 2020 Annie Maunder medal of the Royal Astronomical Society for his contributions to public engagement.

 

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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.

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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.

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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).

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According to QCD calculations on the lattice, at the high energy densities and temperatures reached in ultrarelativistic heavy-ion collisions, nuclear matter undergoes a phase transition to a colour-deconfined state, the quark-gluon plasma (QGP). Heavy quarks, charm and beauty, are produced early in the collision due to their large masses and thus experience the full evolution of the system, serving as excellent probes of QGP properties. As they traverse the expanding medium, heavy quarks interact with its constituents, losing energy and undergoing partial thermalisation. In a QGP, heavy quarks can hadronize via both fragmentation and recombination with lighter quarks from the medium. These mechanisms affect the properties of the observed final-state hadrons. In particular,  the azimuthal anisotropy, primarily quantified by the elliptic-flow coefficient (v2), of heavy-flavour hadrons in non-central collisions is particularly sensitive to the QGP transport coefficients, the heavy-quark degree of thermalisation in the medium, and the underlying hadronisation mechanism. The comparison of the $v_2$ of charm mesons and baryons gives direct insight into hadronisation mechanisms and the partonic origin of collective flow. Charm-baryon $v_2$ measurements remained absent from the experimental landscape until recently, limiting our understanding of heavy-quark hadronisation and QGP transport properties.

This seminar presents new measurements of charm-hadron $v_2$ in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36$ TeV by the ALICE Collaboration. We report precision measurements of prompt non-strange and strange D-meson $v_2$, alongside the first experimental determination of the $\Lambda_c^+$ baryon $v_2$, spanning a wide range of transverse momentum. The results reveal differences between charm baryon and meson $v_2$ at medium-to-high transverse momentum, providing strong support to the partonic origin of collective flow in the heavy-flavour sector. The baryon-meson separation at high transverse momentum is consistent with a scenario where charm quarks combine with light quarks from the medium to form final-state hadrons. The measurements are compared with state-of-the-art transport-model predictions, providing new constraints on QGP transport properties.

 

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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.

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