# Heidelberg 2015 – wissenschaftliches Programm

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# A: Fachverband Atomphysik

## A 18: Poster: Ultra-cold atoms, ions and BEC (with Q)

### A 18.15: Poster

### Dienstag, 24. März 2015, 17:00–19:00, C/Foyer

**Quench Dynamics of a Superfluid Fermi Gas in the BCS-BEC Crossover Regime** — •Simon Hannibal^{1}, Peter Kettmann^{1}, Mihail Croitoru^{2}, Alexei Vagov^{3}, 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 in these systems. Furthermore, the transition between these two states is well controllable by means of a Feshbach resonance, which allows one to tune the interaction strength over a wide range from negative to positive scattering lengths. The divergence of this quantity marks the unitary point associated with the BCS-BEC crossover.

We calculate the dynamics of the BCS gap of a confined ultracold Fermi gas after a quantum quench, i.e., a sudden change of the coupling constant induced by switching the magnetic field. We show that the excitation induces an oscillation of the BCS gap which can be classified into the Higgs and Goldstone mode. Here we concentrate on the Higgs mode in the BCS-BEC crossover regime.

We find damped collective amplitude oscillations of the gap breaking down after a certain time. Afterwards rather irregular dynamics occur. The obtained frequencies are connected to the BCS gap and the size of the gas cloud. A linearization of the equations of motion is exploited to understand the origin of the observed behavior.