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Quenching a Fermi superfluid across the BEC-BCS crossover
by Moritz Breyer, Daniel Eberz, Andreas Kell, Michael Köhl
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Submission summary
| Authors (as registered SciPost users): | Michael Köhl |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202407_00017v3 (pdf) |
| Date accepted: | 2025-01-13 |
| Date submitted: | 2025-01-05 13:52 |
| Submitted by: | Köhl, Michael |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
We study the response of a Fermi superfluid to a rapid change of the interaction strength. For a broad range of quench parameters, the order parameter exhibits damped oscillations, however, we also identify quench regimes in which these oscillations are absent. By comparing our data to a numerical model we find that the damping time constants are explainable by a dephasing in a local density approximation, however, the oscillation frequencies, while being comparable to the superconducting gap parameter, display in detail significant differences to the integrable BCS model.
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Author comments upon resubmission
Dear Editor,
many thanks for sending us the referee comments on our paper. We are very happy that both referees suggest our paper for publication.
Second report of Referee 1: "Maybe it is a question of nomenclature, but within Landau's theory of phase transitions, the order parameter is a quantity that vanishes in one phase and is finite in the other phase. So, condensate fraction of molecules is the order parameter of the BEC - normal gas phase transition." Our response: The referee is correct for the BEC limit. However, throughout the whole BEC-BCS crossover the consensate fraction of molecules is not a suitable choice for the order parameter but instead one chooses the superconducting gap parameter \Delta, which is theoretically defined for any interaction strength.
First report of Referee 2: "1- The theory disagrees with the experiment especially in the BEC side. Is it due to approximations performed in such models? Are there other models which could be considered in such regime? Please add a discussion 2- Is it possible to explore (both theoretically and experimentally) a regime where the system behaves as point-like bosons? In this regime, what would be the predicted outcome of the quench dynamics? Please add a comment and a discussion"
Our response: We have included the requested discussion and an additional reference in our manuscript by the following paragraph in section 3 of the manuscript: "(4) Finally, the integrable BCS model that predicts the phase diagram of Figure 1 only is an approximate solution for the strongly-interacting Fermi gas and alternative theoretical models could be considered for the explanation. For example, in the weakly-interacting BEC limit ($1/(k_Fa) \gg 1$), which, however, is outside the range of our experimental parameters, Bogoliubov theory predicts a prethermalized state after an interaction quench \cite{Menegoz2015}."
We have attached a revised manuscript to this response and we hope that the paper can now be accepted for publication in SciPost.
With best regards, Michael Köhl
Published as SciPost Phys. 18, 053 (2025)