Mainz 2026 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 28: Ultra-cold Plasmas and Rydberg Systems II (joint session A/Q)

A 28.3: Vortrag

Donnerstag, 5. März 2026, 12:00–12:15, N 2

Stabilizing a Dissipative Non-Equilibrium Phase Transition — •Patrick Mischke, Herwig Ott, and Thomas Niederprüm — Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau

We experimentally investigate the facilitation dynamics in an ultracold Rydberg system. In the facilitation (≡ anti-blockade) regime, a non-equilibrium phase transition emerges from the interplay between driving and excitation decay.

In an off-resonantly driven cloud of atoms, the strong dipole-dipole interactions between two Rydberg states compensates the laser detuning for a specific interatomic distance, allowing resonant excitations to occur. At sufficiently high atomic densities, this facilitation process leads to the spreading of excitations, forming an active phase, whereas at low densities excitations decay faster than they can propagate, resulting in an absorbing phase. Rydberg excitations that decay to ions are lost from the system and observed at our detector. In order to stabilize the system, this loss must be balanced by a gain process. We implement such gain by optically pumping atoms from a different hyperfine state, allowing us to tune the steady-state density. This stabilization enables measurements of the system dynamics, including correlation functions, over time scales orders of magnitude longer than previously accessible, allowing a systematic characterization of the associated dissipative non-equilibrium phase transition.

Keywords: Rydberg; Facilitation; Phase-Transition; Dissipation; Rubidium