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Martin Eckstein (University of Hamburg)24/08/2026, 09:20Invited Talk
Accurate diagrammatic simulations of nonequilibrium quantum many-body systems are often limited by the evaluation of multidimensional integrals involving high-order correlation functions. In this work, I present a tensor-network acceleration scheme for diagrammatic calculations based on tensor cross interpolation (TCI). The method is applied to the strong-coupling expansion for quantum...
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Hiroshi Shinaoka (Saitama University)24/08/2026, 09:55Invited Talk
Nonequilibrium Green's function (NEGF) simulations face a steep growth of memory and computational cost with the number of time steps. Tensor networks offer a general solution: the quantics tensor train (QTT) representation compresses multi-time correlation functions by exploiting scale separation, and tensor cross interpolation (TCI) learns compressed tensor-train representations of functions...
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Yaroslav Pavlyukh (Independent researcher)24/08/2026, 11:00Invited Talk
The exact dynamics of many-particle quantum systems coupled to an environment is governed by the Kadanoff-Baym equations. While these equations can, in principle, be solved exactly for small systems, the numerical cost grows rapidly and becomes prohibitive for longer times or larger systems. Beyond many-body correlations, the primary computational challenge arises from memory effects, which...
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Prof. Hendrik van Hees (Goethe University Frankfurt)24/08/2026, 11:35Invited Talk
In recent years the problem of bound-state formation in hot and dense medium in has become of high
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interest in heavy-ion-collision theory due to the discovery at the LHC that the production rate of
light nuclei in ultra-relativistic heavy-ion collisions follows the statistical hadronization model with
abundancies consistent with the conditions at chemical freeze-out. Despite the small... -
Jan-Philip Joost (University of Kiel)24/08/2026, 12:10Invited Talk
Computational many-body physics is governed by a persistent model–method dilemma. The finite resources available to a simulation must be divided between representing the physical system and solving its dynamics. A realistic Hamiltonian may require large basis sets, spatial inhomogeneity, and nonlocal interactions, whereas an accurate real-time propagation method must retain correlations,...
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Erik Schroedter (Kiel University)24/08/2026, 12:45Contributed Talk
Correlated real-time dynamics in large, spatially inhomogeneous quantum systems remain a major challenge for nonequilibrium many-body approaches. Nonequilibrium Green functions (NEGF) provide a systematic and highly accurate framework for addressing this problem, but their practical application has long been limited by the cubic scaling of the computational runtime with the number of time...
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Prof. Claude Monney (University of Fribourg)24/08/2026, 14:35Invited Talk
Time- and angle-resolved photoemission spectroscopy (ARPES) is an ideal experimental technique to access the transient electronic structure of quantum materials. Moreover, the simulation of ARPES spectra can be well achieved by calculating the spectral function through Green’s function-based methods.
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Here I will exemplify how quantum material can be probed with time-resolved ARPES using two... -
Dr Hiroki Ueda (PSI - Paul Scherrer Institut)24/08/2026, 15:10Invited Talk
Low-energy collective excitations, such as phonons and magnons, are essential for understanding physics across a wide range of time and length scales. Energy flow among correlated subsystems, mediated by these collective excitations, is essential for ultrafast dynamics and high-speed technologies. Yet momentum-resolved access to low-energy magnons in non-equilibrium states has been lacking. In...
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Juan Felipe Pulgarin Mosquera (University of Fribourg)24/08/2026, 15:45Contributed Talk
Understanding how magnetic phase transitions in correlated quantum systems respond to external perturbations requires a rigorous many-body description of localized states and ligand coordination. Because these macroscopic states emerge from a subtle interplay between crystal-field effects, spin-orbit coupling, and strong electronic correlations, core-level techniques like X-ray absorption...
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Gianluca Stefanucci (University of Rome Tor Vergata)25/08/2026, 09:00Invited Talk
Dissipation is usually associated with decoherence and loss of quantum properties. However, in interacting many-body systems it can also stabilize unconventional states, and profoundly modify electronic, optical and topological properties. Describing these phenomena requires a framework capable of treating interactions, external driving, and environmental effects on the same footing.
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In this... -
Prof. Vojtěch Vlček (UC Santa Barbara)25/08/2026, 09:35Invited Talk
Time-resolved spectroscopies provide direct access to observables that encode information about transient excited states and dynamical correlations in quantum materials. In this talk, I will present recent developments in efficient diagrammatic approaches for computing time-resolved spectral functions, centered on the Real-Time Dyson Expansion (RTDE), which reconstructs the time-nonlocal...
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Thomas Blommel (UCSB)25/08/2026, 10:10Contributed Talk
We present a unified many-body perturbation theory for open quantum systems, that treats dissipation, correlations, and external driving on equal footing. Using a Keldysh–Lindblad formalism, we introduce diagrammatic treatment of dissipative interaction lines representing quasiparticle flows and fluctuations. Two new Feynman rules render the evaluation of dissipative diagrams compact and...
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Zhenlin Zhang (University of Science and Technology of China)25/08/2026, 11:00Contributed Talk
In open quantum systems hosting excitons, dissipation mechanisms critically shape the excitonic dynamics, band-structure and topological properties. A microscopic understanding of excitons in such non-Hermitian settings demands a first-principles generalization of the Bethe-Salpeter equation (BSE). Building on a recently introduced nonequilibrium Green’s function formalism compatible with...
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Enrico Perfetto (University of Rome Tor Vergata)25/08/2026, 11:20Invited Talk
Exciton dynamics—including ultrafast photogeneration, diffusion, and thermalization—plays a central role in optoelectronic, photovoltaic, and photocatalytic processes. In this talk, I will present a novel first-principles many-body framework for describing exciton dynamics driven by electron–phonon interactions. A key ingredient of the theory is the introduction of an auxiliary excitonic...
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Nicola Colonna (PSI - Paul Scherrer Institut)25/08/2026, 11:55Contributed Talk
We present an efficient first-principles approach to nonequilibrium electron dynamics in extended systems, leveraging Koopmans-compliant spectral functionals and Wannier functions. Koopmans functionals provide an accurate description of the quasiparticle band structure, which serves as the static starting point for real-time propagation of the electronic density matrix within the...
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Anna Hehn (Christian-Albrechts-University Kiel)25/08/2026, 12:15Contributed Talk
An accurate description of adsorption on metal surfaces requires to take into account the image charge which is generated within the metal surface [1]. State-of-the-art semilocal and hybrid exchange-correlation functionals are incapable to capture the substrate polarization, thus emphasizing the necessity of dynamical screening as incorporated in GW and Bethe-Salpeter ansätze. Based on our...
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Kai Wu (Institute of Structure of Matter, National Research Council of Italy)25/08/2026, 12:35Contributed Talk
The time-resolved angle-resolved photoemission spectra of WSe$_2$, a paradigmatic transition metal dichalcogenide, are dominated by a transient signal that, after being initially observed in the gap at the $K$ valley, scatters, on an ultra-fast time scale of $\sim\,30$ fs, to the $\Sigma$ valley. In this work we question the common interpretation of the experimental dynamics in terms of a...
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Jin Zhao (University of Science & Technology of China)25/08/2026, 14:30Invited Talk
Understanding nonequilibrium quasiparticle dynamics in materials requires going beyond static electronic structure. Here, we present an ab initio framework that combines GW/BSE with real-time quantum dynamics to simulate exciton dynamics in different materials. It is shown that exciton dynamics is fundamentally driven by different many-body interactions. In transition metal dichalcogenides,...
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Fabio Caruso25/08/2026, 15:05Invited Talk
First-principles simulations of electron–phonon interactions (EPI) are key to clarifying the microscopic origin of the ultrafast electron and phonon dynamics revealed by pump–probe experiments. In this talk, I will discuss recent advances in ab-initio simulations of the EPI and their application to light-driven electron and lattice dynamics. Building on recent progress in many-body theory and...
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Emanuel Gull (University of Warsaw & University of Michigan)26/08/2026, 09:00Invited Talk
Response functions are fundamental objects in quantum many-body theory. For equilibrium and steady-state systems, retarded response functions are analytic in the upper half of the complex plane, and their imaginary part has a definite sign. These analytic properties enable compact and systematically improvable representations based on pole approximants and moment theory, allowing...
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Dr Ken Inayoshi (Department of Physics, Saitama University)26/08/2026, 09:35Contributed Talk
Recent developments in time-resolved Raman scattering [1] and resonant inelastic X-ray scattering [2,3] have enabled the observation of the time evolution of various low-energy excitations, such as charge, spin, and phonon excitations, in materials. From a theoretical perspective, the spectra of these excitations can be computed from the nonequilibrium two-particle correlation functions. To...
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Mr Shuta Matsuura (The University of Tokyo)26/08/2026, 09:55Contributed Talk
Nonequilibrium dynamical mean-field theory (DMFT) is a powerful framework for studying the real-time dynamics of strongly correlated electron systems. In this approach, an interacting lattice model such as the Hubbard model is mapped onto a quantum impurity problem, but solving this impurity problem accurately remains the central numerical bottleneck. Continuous-time quantum Monte Carlo...
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Hugo U. R. Strand (Örebro University)26/08/2026, 10:15Contributed Talk
In recent years, several non-stochastic algorithms have been developed for solving impurity models using the hybridization expansion, such as tensor cross interpolation, quasi–Monte Carlo integration, and sum-of-exponentials-based separation of variables.
While it is extremely hard to outperform Philipp Werner's (stochastic) continuous-time quantum Monte Carlo hybridization expansion in...
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Paul Fadler (University of Bremen)26/08/2026, 11:05Invited Talk
The influence of the dielectric environment on material properties has been studied theoretically mostly within two different contexts: Within Coulomb engineering one uses electrostatic screening of the longitudinal electromagnetic field to renormalize interactions. In contrast, within cavity material engineering one tries to shape the modes of the enveloping electromagnetic field to produce...
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Philipp Werner (University of Fribourg)26/08/2026, 11:40Invited Talk
We use nonequilibrium dynamical mean field theory (DMFT) in combination with strong-coupling impurity solvers to study eta-pairing states in photo-doped Mott insulators. To achieve reasonably accurate DMFT solutions, the strong coupling technique is combined with quantics tensor cross interpolation for the efficient evaluation of the diagram weights.
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Dr Denis Golez (Jožef Stefan Institute)26/08/2026, 12:15Invited Talk
We present recent developments in hierarchical representations of nonequilibrium Green’s functions, including applications and open challenges. We begin by comparing global iterative solvers, which suffer from error-front propagation, with time-stepping approaches that avoid this limitation. We show that hierarchical representations have become a practical tool for contemporary problems,...
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Riku Tuovinen (University of Jyväskylä)27/08/2026, 09:00Invited Talk
Accurate modeling of nanoscale transport requires a simultaneous treatment of quantum coherence, interactions, and nonequilibrium environments. While the wide-band limit often enables substantial simplifications, it neglects reservoir spectral structure and can limit the quantitative description of transport and thermodynamic processes. We present a nonequilibrium Green's function framework...
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Lei Geng (University of Fribourg)27/08/2026, 09:35Contributed Talk
The nonlinear Hall effect in quantum materials has attracted broad interest; yet most existing studies focus on the weak-field, perturbative regime.
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Here we develop a nonperturbative approach based on nonequilibrium steady-state Green's functions for dc-field-driven lattice systems, with dissipation and interactions incorporated through self-energies beyond the constant relaxation-time... -
Mathieu Luisier (ETH Zurich)27/08/2026, 09:55Invited Talk
Computer-aided design tools dedicated to the modelling of nano-devices, e.g., transistors, memory cells, or photo-detectors, should capture quantum mechanical effects from first-principles and account for non-ideal phenomena such as electron-phonon or electron-electron interactions. In this presentation, a framework called QuaTrEx that fulfils these criteria will be presented, focusing on its...
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Andrea Marini (CNR-ISM)27/08/2026, 11:00Invited Talk
Enrico Fermi in 1932, used classical Gauss equation to derive the Coloumb density–density interaction from the longitudinal electro–magnetic potential, in a gauge–invariant way. In this work we extend the Fermi procedure to the transverse component of the vector potential. By using a fully quantistic canonical transformation we replace the transverse vector potential with a current– current...
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Nils Jacobsen (Universität Bremen, MPSD Hamburg)27/08/2026, 11:35Contributed Talk
Periodic driving of solids offers new opportunities for controlling and designing quantum phases of matter. Floquet engineering has, for example, been proposed as a route to induce topological states in graphene through circularly polarized light [1, 2] . However, the persistence of Floquet states under realistic conditions, including interactions, screening, and decoherence, remains an open...
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Oscar Moreno Segura (University of Jyväskylä)27/08/2026, 11:55Contributed Talk
Scanning tunneling microscopy and spectroscopy (STM/STS) provide powerful tools for probing electronic properties at the atomic scale. On the theoretical side, density functional theory (DFT) and Wannier-based methods allow realistic first-principles descriptions of complex nanosystems. However, modeling nonequilibrium transport remains a significant challenge, especially in superconducting...
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Marie Eder27/08/2026, 12:15Contributed Talk
Capturing correlation effects in quantum many-body systems remains a major challenge in the physical description of molecules. Coupled cluster theory has proven to be very accurate in a weakly interacting, weakly correlated setting while scaling comparatively favourably with system size. However, it struggles with systems with large static correlations. This issue is known as the...
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Invited Talk
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Ayan Pal (Lund University)Contributed Talk
The Floquet theory of time-periodic systems provides a middle ground between equilibrium and far-from-equilibrium physics, making it ideal for studying non-equilibrium steady states. We employ this framework to interacting electrons exposed to spatially and time-periodic potentials by combining Floquet theory with RPA and GW. This is applied to both the homogeneous electron gas under moving...
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