Mainz 2026 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 31: Ultra-cold Atoms, Ions and BEC IV (joint session A/Q)

A 31.7: Vortrag

Donnerstag, 5. März 2026, 16:00–16:15, N 1

Extended Gross-Pitaevskii equation for quantum droplets in cavity BEC systems — •Leon Mixa^1,2,3, Laurenz Timmermann¹, Milan Radonjić^1,4, Axel Pelster³, and Michael Thorwart^1,2 — ¹I. Institut für Theoretische Physik, Universität Hamburg, Germany — ²The Hamburg Center for Ultrafast Imaging, Hamburg, Germany — ³Physics Department and Research Center OPTIMAS, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Germany — ⁴Institute of Physics Belgrade, University of Belgrade, Serbia

Quantum droplets are an exotic state of matter that characterizes a self-bound many-body system emerging from quantum fluctuation energy corrections to the ground state. Here, we present a theoretical framework for a new type of quantum droplet that emerges from a Bose-Einstein condensate in a cavity. Vacuum fluctuations in the cavity mediate an effective, long-range atom-atom interaction that, at the leading order, results in the formation of a distinct roton mode. The zero-point energy of the roton increases proportionally to the volume of the atom gas and thus competes with the repulsive s-wave contact interaction, facilitating the formation of the droplet [PRR 7, 033216; PRR 7, 023204 (2025)]. We present an extended Gross-Pitaevskii equation for the ground state incorporating the quantum fluctuation contribution. We analyze the impact of the roton mode correction term on the droplet wave function. Using a variational ansatz, we evaluate the stability, size, and density of the droplet, comparing it to the homogeneous density profile used in the original derivation.

Keywords: Cavity BEC; Quantum droplets; Ultracold gases; Quantum fluids