SciPost Submission Page
Asymptotic temperature of a lossy condensate
by Isabelle Bouchoule, Max Schemmer
This is not the latest submitted version.
This Submission thread is now published as
Submission summary
Authors (as registered SciPost users):  Isabelle Bouchoule · Maximilian Schemmer 
Submission information  

Preprint Link:  https://arxiv.org/abs/1912.02029v1 (pdf) 
Date submitted:  20191209 01:00 
Submitted by:  Bouchoule, Isabelle 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Experimental 
Abstract
We monitor the time evolution of the temperature of phononic collective modes in a onedimensional quasicondensate submitted to losses. At long times the ratio between the temperature and the energy scale $mc^2$, where $m$ is the atomic mass and $c$ the sound velocity takes, within a precision of 20\%, an asymptotic value. This asymptotic value is observed while $mc^2$ decreases in time by a factor as large as 2.5. Moreover this ratio is shown to be independent on the loss rate and on the strength of interactions. These results confirm theoretical predictions and the measured stationary ratio is in quantitative agreement with the theoretical calculations.
Current status:
Reports on this Submission
Anonymous Report 1 on 2020221 (Invited Report)
 Cite as: Anonymous, Report on arXiv:1912.02029v1, delivered 20200221, doi: 10.21468/SciPost.Report.1524
Strengths
1 Very clear introduction
2 Clear description of the data analysis
Weaknesses
1 The major weakness I see is that, since the main quantity addressed, i.e. the ratio $y=k_B T/(mc_p^2)$, does not change at all, it bears no clear evidence of reaching equilibrium
Report
The manuscript reports on the experimental investigation of the equilibrium properties of a onedimensional quasi BoseEinstein condensate subject to onebody losses. The onebody losses are obtained by exposing the quasiBEC to a microwave radiation coupling atoms out of the magnetic trap. Importantly, the microwave spectrum is sufficiently broad to make the losses homogeneous across the sample and independent of the energy of the removed atoms.
The temperature of the quasiBEC is obtained by the analysis of the density fluctuations in TOF images and it is related to the (peak) sound speed $c_p$, as obtained from the peak density. The results show that the sound speed $c_p$ decreases (as expected) over time when the lossed induced by the microwave radiation are present, and that the ratio $k_B T/mc_p^2$ is consistent with the theoretical equilibrium value 0.75. Actually, as duly acknowledged, the ratio is practically constant over, likely because the sample preparation leads to approximately the same value 0.75.
The experiment is clearly described, as well as the data analysis, still I have some remarks that I would like to be clarified.
1) I miss the difference between the densities $n_0(z)$ and $n_{qBEC}(z)$. How is the latter derived from the former?
2) The asymptotic value $y_\infty$ is defined as the mean of values for $\Gamma t>0.7$, why 0.7?
3) I find counterintuitive that losses, although flat vs energy, lead to a cooling of the gas, it conflicts with the fact that the energy per particle should stay constant. I encourage the Authors to provide some insight on the reason of the observed cooling.
That said, I find the work solid, the results convincing and the limitations clearly described. The manuscript is well written with a clear introduction to the topic. I recommend publication.
Below are listed other minor remarks that the Authors might want to consider:
1end of page 3: the relation between chemical potential and linear density $\mu = \hbar \omega_\perp \sqrt{\dots}$ should be backed by a Reference;
2 page 5, line 10 from bottom: "Results for are close to \dots", the word "for" should be removed;
3 page 7, line 5: "holded" to be replaced by "held".
Requested changes
1end of page 3: the relation between chemical potential and linear density $\mu = \hbar \omega_\perp \sqrt{\dots}$ should be backed by a Reference;
2 page 5, line 10 from bottom: "Results for are close to \dots", the word "for" should be removed;
3 page 7, line 5: "holded" to be replaced by "held".