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Non-equilibrium evolution of Bose-Einstein condensate deformation in temporally controlled weak disorder
by Milan Radonjić, Axel Pelster
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|Authors (as registered SciPost users):||Milan Radonjic|
|Preprint Link:||https://arxiv.org/abs/2009.10477v1 (pdf)|
|Date submitted:||2020-09-24 15:58|
|Submitted by:||Radonjic, Milan|
|Submitted to:||SciPost Physics|
We consider a time-dependent extension of a perturbative mean-field approach to the dirty boson problem by considering how switching on and off a weak disorder potential affects the stationary state of an initially homogeneous Bose-Einstein condensate by the emergence of a disorder-induced condensate deformation. We find that in the switch on scenario the stationary condensate deformation turns out to be a sum of an equilibrium part and a dynamically-induced part, where the latter depends on the particular driving protocol. If the disorder is switched off afterwards, the resulting condensate deformation acquires an additional dynamically-induced part in the long-time limit, while the equilibrium part vanishes. Our results demonstrate that the condensate deformation represents an indicator of the generically non-equilibrium nature of steady states of a Bose gas in a temporally controlled weak disorder.
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- Cite as: Anonymous, Report on arXiv:2009.10477v1, delivered 2020-10-26, doi: 10.21468/SciPost.Report.2117
the manuscript "Non-equilibrium evolution of Bose-Einstein condensate
deformation in temporally controlled weak disorder" by Radonjic and Pelster
reports an interesting calculation of the condensation deformation emerging from the switch-on (or -off) of an external disordered potential.
Remarkably, they significantly generalize the seminal calculation by Huang and Meng (Ref.  ) by going beyond the adiabatic limit. Indeed, they report that the condensate deformation is actually defined by two contribution, one of them explicitly dependent on the switch-on/off protocol. This dynamical correction signals that disorder can drive the system towards a stationary out-of-equilibrium states.
In my opinion, this manuscript surely deserves publication in SciPost: the object of the theoretical investigation is timely and clear, while the analytical reasoning are clearly exposed and seemingly easy to reproduce and generalize.
Before final acceptance, I have only few minor remarks, just to improve the readability for a wider audience:
1) The author properly spend a certain amount of words in outlining the experimental possibilities to engineer a disorder landscape for the condensate. It may be also worth to mention how the switch-on/off protocols can be implemented in an actual cold-atom experiment, if there are limitations or technical obstacles to overcome...
2) Eq. (10) is a perturbative approximation up to the second order. Have the authors approached in any way the calculation of the following terms? Do they result in simple shift of the computed profile (for instance in Fig. 1), or there may be dangerous behaviours of the perturbative series?
3) It can be useful to have some conditions stating when a disorder potential is considered "weak", which seems a relevant point since we are actually within a perturbative framework.
- Cite as: Anonymous, Report on arXiv:2009.10477v1, delivered 2020-10-26, doi: 10.21468/SciPost.Report.2115
1) The authors discuss a general approach for dealing with the effects of switching on/off a disordered potential on the density deformation of a Bose-Einstein condensate.
2) The paper is written very clearly, and meets all the General acceptance criteria of this Journal.
3) It proposes a new pathway in this research field.
1) It is limited to the study of homogeneous systems, the effect of trapping potentials are only mentioned in the conclusions at a qualitative level, very briefly.
2) It would have been very interesting to compare the analytical results with the numerical solution of the Gross-Pitaevskii equation. This should be relatively easy to do.
This is a very interesting paper, very clearly written and presented. It represents a timely contribution to the current investigation of ultracold atoms in the presence of disorder. The approach and the results discussed here are likely to trigger further studies along the direction outlined in the paper. Apart from minor suggestion I list below, I would recommend the author to consider comparing their nice analytical results with Gross-Pitaevskii (GP) simulations. This would be the natural completion of this work because it would allow for a verification of the perturbative analytical estimates against the exact behavior of the system (here, the GP equation). With this extension, I would be pleased to recommend the manuscript for publication on SciPost Physics. Otherwise, I reckon this paper more suited for the Physics Core journal.
1) It would be helpful to specify (possibly already in the abstract) that the "equilibrium part" of the the stationary condensate deformation corresponds to adiabatic switching on the disorder potential.
2) The wording "in the frame rotating with the frequency μ0/hbar" may be confusing, there are no _rotating_ frames.
3) I recommend to extend the discussion on how the presence of a trap would affect the present results.
4) A comparison with the results of GP simulations would be very useful.