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Q: Fachverband Quantenoptik und Photonik

Q 42: Poster – Ultracold Matter (joint session Q/A)

Q 42.4: Poster

Wednesday, March 4, 2026, 17:00–19:00, Philo 2. OG

Universal dynamics of 3D Bose gases near the superfluid transition in the collective-scattering regime — •Anne-Solène Bornens, Elisabeth Gliott, and Nicolas Cherroret — Laboratoire Kastler-Brossel, Sorbonne Université, CNRS, ENS-PSL, Collège de France, Paris, France

Understanding the many-body dynamics of a quantum system after a quench is a central challenge in modern physics. In particular, quantum gases quenched across a phase transition display especially intriguing dynamics, as they generically evolve toward a nonthermal fixed point, i.e. a self-similar evolution of correlations with universal dynamical exponents and a critical slowing down. Recently observed experimentally, this phenomenon compellingly extends the notion of universality classes to nonequilibrium statistical physics.

In this work, we theoretically investigate the universal many-body dynamics of three-dimensional Bose gases suddenly cooled across their superfluid phase transition. Using a quantum kinetic framework that captures the collective-scattering regime emerging in the highly occupied part of the spectrum, we uncover a crossover between two dynamical universality classes controlled by the quench depth. For weak quenches, we find early-time inverse and direct energy cascades characteristic of weak turbulence, where collective scattering plays little role. For deep quenches, collective scattering dominates and a turbulent fixed point emerges, marked by modified dynamical exponents, a more pronounced bidirectional cascade, and an overall slowing down of the dynamics.

Keywords: Quantum gases; Phase transitions; Non-equilibrium quantum dynamics; Nonthermal fixed point; Quantum turbulence