The wide range of emergent phenomena and quasiparticles arising from excitation, correlation, and coherence of electrons, spin, photons, and nuclei provides a wealth of largely unexplored possibilities to achieve properties on demand in advanced materials [4]. Achieving control of these phenomena constitutes the key to the formulation of novel technology concepts based on quantum materials [12]. However, this requires a detailed understanding of light-matter coupling in many-body systems out of equilibrium via predictive ab-initio methods and semi-empirical approaches suitable to simulate time-resolved ultrafast dynamics [26].

Modelling non-equilibrium dynamics in solids involves capturing a wide and diverse landscape of excitations (Floquet states, excitons, polaritons, magnons) and fundamental interaction mechanisms (light-matter, electron-exciton-phonon, spin-phonon, etc.) spanning different time and length scales, as well as different levels of complexity. In recent years, a significant progress was attained in experimental [23], theoretical [17], and computational [20] capabilities to explore ultrafast processes ranging from attoseconds to nanoseconds [11, 17, 6, 25, 8, 5,  20, 13] thus enabling new routes and perspectives for the reliable prediction of excited-state dynamics in advanced materials. The extension of quantum electrodynamics and non-equilibrium Green functions [15, 17] to the domain of ab-initio methods has enabled to describe the quantum kinetics of electrons and photons at the atto- and femtosecond timescales, respectively, yielding unprecedented information on the formation, dynamics, and decay of coupled light-matter states and many-body excitations. Ab-initio molecular dynamics and perturbative techniques can provide insight into the non-equilibrium phonon and structural dynamics for timescales up to tens or hundreds of picoseconds.

Many-body interactions among electrons, magnons, excitons, phonons, and photons in systems out of equilibrium constitute a major challenge for both ab-initio [3, 6, 2] and semi-empirical approaches [7,16, 18]. In spite of the remarkable progress in the theoretical description of ultrafast processes – such as, e.g., coherent phonon excitations [14, 24, 27], driven topological insulators [10, 22], two dimensional semiconductors [1] and  magnetic systems [9, 19] –, the rich interplay of several coupling mechanisms and many-body interactions across multiple length and time scales often hinders a thorough theoretical understanding of non-equilibrium phenomena in advanced materials. These considerations outline the urgency of establishing novel concepts to bridge spatio-temporal scales in the theory of ultrafast phenomena and their implementation in efficient computational methods.

This workshop aims at bringing together researchers with complementary expertise in the field of experimental and theoretical ultrafast science. In particular, the goal of this event is to stimulate discussion and exchange on bridging time-scales in both ab-initio and semi-empirical approaches for non-equilibrium phenomena, focusing on time-scales ranging from attoseconds to nanoseconds. While the primary focus of the workshop will be on theoretical and numerical modelling of ultrafast dynamics, we intend to foster participation of few leading experimentalists from the area of time-resolved spectroscopy and microscopy. Our aim is to generate an open and diverse environment that will stimulate discussions and collaborations on new theoretical and computational horizons for the description of non-equilibrium dynamics and time-resolved excited-state phenomena.