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Nonequilibrium Probability Currents in Optically-Driven Colloidal Suspensions
by Samudrajit Thapa, Daniel Zaretzky, Ron Vatash, Grzegorz Gradziuk, Chase Broedersz, Yair Shokef, Yael Roichman
This Submission thread is now published as
Submission summary
| Authors (as registered SciPost users): | Yael Roichman · Yair Shokef · Samudrajit Thapa |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202407_00026v2 (pdf) |
| Date accepted: | 2024-09-09 |
| Date submitted: | 2024-08-22 16:28 |
| Submitted by: | Thapa, Samudrajit |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Experimental, Computational |
Abstract
In the absence of directional motion it is often hard to recognize athermal fluctuations. Probability currents provide such a measure in terms of the rate at which they enclose area in the reduced phase space. We measure this area enclosing rate for trapped colloidal particles, where only one particle is driven. By combining experiment, theory, and simulation, we single out the effect of the different time scales in the system on the measured probability currents. In this controlled experimental setup, particles interact hydrodynamically. These interactions lead to a strong spatial dependence of the probability currents and to a local influence of athermal agitation. In a multiple-particle system, we show that even when the driving acts only on one particle, probability currents occur between other, non-driven particles. This may have significant implications for the interpretation of fluctuations in biological systems containing elastic networks in addition to a suspending fluid.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Author comments upon resubmission
We were happy to see that all three referees recommended or leaned toward recommending the acceptance for publication of our paper in SciPost Physics. As detailed below, we have answered all the remaining minor or optional issues mentioned by the referees. We hope that this will enable the journal to accept the paper, and we will be happy to address any further issues if such would arise.
Referee 2 suggested to consider making more quantitative the effect of the confining walls on the hydrodynamic interactions and the resultant suppression of the AER in the experiments compared to the simulations. The presence of walls leads to weaker hydrodynamic interactions between the particles, and causes it to decay faster with the distance between them as compared to the case without walls (Refs. 35-37 in the revised manuscript). Thus, the motion of each particle due to the motion of other particles is smaller, and this results in a lower AER. However, because of the noise in the experimental data, the lack of precise information on the distance to the walls and the limited range of distance between the particles which can be explored, we are unable to provide a quantitative description of the effect of the walls. We have included this discussion on page 9 of the revised manuscript.
Referee 2 also spotted several typographic errors, which we corrected in the revised manuscript.
Referee 3 made two optional comments. The first is about the term “phase space”. Following this comment, we now explicitly state in page 3 of the paper that the entire phase space of the system includes the positions and momenta of all particles, and we clarify that our analysis of the AER is in projections to two-dimensional subspaces of phase space.
The second optional comment made by Referee 3 suggested performing a Taylor series expansion in J, rather than assuming that it is constant. We provide quantitative arguments that the variations in J are very small, and use them to justify why J can be treated as constant. We stress that the numerical simulations took into account the precise locations of the particles, and did not assume that J is constant. The remarkable agreement between simulations with varying J and the theoretical derivations with fixed J, provide another confirmation for the validity of using fixed J in the theory. We have added this explanation to the revised manuscript on page 17.
Sincerely,
Samudrajit Thapa
on behalf of all authors
Published as SciPost Phys. 17, 096 (2024)