# Mainz 2017 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 46: Quantum Gases: Fermions I

### Q 46.4: Vortrag

### Donnerstag, 9. März 2017, 12:00–12:15, P 204

**Vanishing order parameter oscillations of the Higgs mode in a cigar-shaped ultracold Fermi gas** — •Simon Hannibal^{1}, Peter Kettmann^{1}, Mihail Croitoru^{2}, Vollrath Martin Axt^{3}, and Tilmann Kuhn^{1} — ^{1}Institute of Solid State Theory, University of Münster — ^{2}Condensed Matter Theory, University of Antwerp — ^{3}Theoretical Physics III, University of Bayreuth

Ultracold Fermi gases in optical traps provide a unique system to study the many body physics of systems composed of fermionic constituents. Both, the BEC and the BCS superfluid state are observed. Furthermore, the transition between these states is well controllable by means of a Feshbach resonance, which allows to tune the scattering length over a wide range from negative to positive values.

We employ an inhomogeneous BCS mean field theory and calculate the dynamics of the BCS gap of a confined ultracold Fermi gas after an interaction quench. Due to the spontaneously broken U(1) symmetry in the superfluid phase two fundamental modes of the BCS gap evolve, i.e., the amplitude (Higgs) and phase (Goldstone) mode. Here, we focus on the Higgs mode on the BCS side of the BCS-BEC crossover.

We investigate the dynamics after a large quench from strong to weak interactions. For large aspect ratios we find a dynamical vanishing of the order parameter similar to what has been predicted in the case of a homogeneous system. However, for smaller aspect ratios transverse trap modes are excited preventing a complete vanishing of the order parameter.