FUSIoN

Non-equilibrium quantum physics is a core challenge of contemporary science, encompassing a variety of systems, with quantum fluids realized in cold-atomic labs at the forefront. In this context, quantum quenches constitute a simple scenario for driving a system out of equilibrium: Following the quench, the system undergoes a dynamical evolution that is generally nontrivial and not captured by conventional equilibrium statistical physics. The central question is whether this dynamics, like for an equilibrium phase, may exhibit universal properties that could be classified in some universality class shared by a broad range of systems. Recently, several such classes have been identified, like Kardar-Parisi-Zhang (KPZ) dynamics or non-thermal fixed points, characterized by universal dynamical scaling laws emerging in the quantum correlations of a many-body system. At a theoretical level, descriptions of non-equilibrium phenomena in many-body physics are still scarce, mainly due to their inherently non-perturbative nature. The goal of this project is to fill this gap by joining the expertises of the two partners, who recently developed complementary approaches addressing the relaxation dynamics of isolated Bose gases: non-equilibrium field theories (LKB) and non-perturbative functional renormalization group schemes (PhLAM). We will combine these methods to characterize universality in two representative yet open problems that currently irrigate many aspects of non-equilibrium physics: (i) quenches of Bose superfluids, where signatures of KPZ physics have been identified but without decisive proof, and (ii) quenches of 2D and 3D Bose gases across their critical temperature, known to induce universal non thermal-fixed points. Beyond providing quantitative descriptions for these non-equilibrium phenomena, the project ultimately aims to explore the robustness and boundaries of their universal properties, in particular with respect to thermalization or a spatial disorder, so to bring predictions ascertainable in state-of-the-art experiments.