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REVIEW 3 major objections 1 minor 1 cited by

Dynamics and rupture of doped Motility Induced Phase Peparation

T0 review · 3 major / 1 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read This paper claims that a small admixture of passive Brownian particles turns the stationary dense slab of a phase-separated active suspension into a self-sustained travelling structure.

desk verdict The full text is an unrelated quantum-compiler paper, so there is no actual MIPS manuscript to referee; the abstract alone is plausible but unverifiable. read the letter →

arxiv 2508.05768 v1 pith:NFJWVJYS submitted 2025-08-07 cond-mat.soft

Rodrigo Fernández-Quevedo García , Enrique Chacón , Pedro Tarazona , Chantal Valeriani This is my paper
classification cond-mat.soft
keywords motility-inducedphaseseparationactiveBrownianparticlespassive-activemixturedenseslabpropagationsymmetrybreakinginterfacedynamicsself-sustainedmotion
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Adding a small number of passive (non-self-propelled) Brownian particles to a two-dimensional suspension of repulsive active Brownian particles does not destroy motility-induced phase separation, but it changes the dynamics of the resulting dense phase. In an elongated box, the dense slab's two interfaces can propagate steadily in one direction for long periods, an effect the authors attribute to the depletion of passive particles on one side of the slab, which breaks left-right symmetry. Using average density profiles and a kinetic decomposition, the paper shows that the apparent slab motion is neither pure evaporation/condensation nor pure rigid translation, but a self-sustained combination of both. The authors also analyze fluctuations that produce, cancel, and abruptly reverse the motion. If correct, the paper establishes a new dynamical regime in doped active matter in which a phase boundary moves without any external drive.

What carries the argument

The central object is the dense slab of active particles in a passive-active mixture, with the passive particles acting as an asymmetric reservoir. The mechanism is the depletion of passive particles on one side of the slab, which breaks the left-right symmetry of the two interfaces and sustains a net flux of active particles through the slab. The kinetic analysis decomposes the interface velocity into a source/sink part and a rigid-translation part, demonstrating that the motion is a self-sustained combination of both.

What would settle it

Simulate the same passive-active mixture in a periodic rectangular box but with passive particles artificially replenished on the depleted side, or with a symmetric bimodal passive distribution; if the steady directed propagation persists, the depletion asymmetry is not the cause. Alternatively, measure the slab velocity as a function of the passive fraction: the proposed mechanism predicts a nonmonotonic dependence that vanishes both at zero and at large passive fractions.

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Extended reading notes

Core claim

The paper claims that passive Brownian particles added to a repulsive active Brownian suspension preserve motility-induced phase separation, but in elongated geometries the dense slab is not static: over long periods it exhibits stable, well-defined propagation of both interfaces. The mechanism proposed is the depletion of passive particles on one side of the slab, creating a symmetry breaking that sustains the motion. The slab movement is not a pure source/sink effect (active particles evaporating from one interface and condensing onto the other) nor a rigid displacement of all particles, but a self-sustained combination of the two. Average density profiles reveal an asymmetry between the t

Load-bearing premise

The claim that slab motion is caused by the depletion of passive particles on one side assumes that the depletion asymmetry is the driving mechanism and not just a side effect; if the asymmetry were absent or the cause were something else, the propagating-slab regime would not be the robust phenomenon described.

Editorial extensions

If this is right

  • Small passive fractions do not destroy motility-induced phase separation but alter its coarsening dynamics.
  • The dense active phase can be made to travel without external forcing by exploiting depletion asymmetry.
  • The slab velocity decomposes into measurable source/sink and drift contributions, enabling quantitative comparison with theory.
  • Fluctuation-driven reversals mean that the direction of motion is not fixed and may be controllable.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The same depletion-asymmetry mechanism might be used to transport the dense phase across a channel, with the passive fraction acting as a steering parameter.
  • Because the effect relies on a long-lived asymmetry, it may be sensitive to box length and total density; varying those could reveal a transition between static and propagating slabs.
  • The identified fluctuation modes that reverse motion could be harnessed or suppressed by engineering the passive-particle concentration or activity.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 1 minor

Summary. The manuscript (arXiv:2508.05768) presents an abstract claiming a new dynamical regime in a 2D suspension of active Brownian particles with a small fraction of passive Brownian particles: the dense slab formed by motility-induced phase separation (MIPS) can develop a stable, directed propagation of its interfaces over long times, driven by depletion of passive particles on one side. The authors state that the motion is not purely a source/sink effect nor a rigid displacement, but a self-sustained combination of both, and that average density profile calculations reveal an asymmetry between the two interfaces, with specific fluctuations producing, cancelling, and reversing the motion. However, the supplied full text is not this paper at all: it is the manuscript 'ConiQ: Enabling Concatenated Quantum Error Correction on Neutral Atom Arrays' (arXiv:2508.05779v1), a quantum compilation paper. None of the active-matter methods, simulations, or analyses described in the abstract appear in the body.

Significance. If the claimed effect is real, it would be a significant contribution to active-matter physics: it identifies a new self-sustained traveling state in a passive-active mixture, with a proposed mechanistic decomposition into source/sink and coherent displacement contributions, and a concrete asymmetry signature. Such a result would be interesting for the dynamics of MIPS interfaces and for designing active suspensions with controllable transport. The manuscript as supplied, however, provides no evidence for any of this. There are no model definitions, simulation parameters, control experiments, density profiles, or fluctuation analyses; there are no machine-checked proofs, reproducible code, or falsifiable quantitative predictions. The significance cannot be assessed beyond the level of the abstract's brief claim.

major comments (3)
  1. [Abstract; full text Sections I–IX] The full text supplied for this submission is an unrelated quantum-computing paper (ConiQ, arXiv:2508.05779v1). The body contains no mention of active Brownian particles, motility-induced phase separation, passive dopants, density profiles, interface asymmetry, or slab propagation. Every load-bearing element claimed in the abstract—model definition, density profile calculations, kinetic analysis, fluctuation and reversal statistics—is absent. This is an internal inconsistency between the abstract and the manuscript body, not a disagreement with scientific consensus.
  2. [Abstract] The abstract attributes the slab propagation to 'symmetry breaking caused by the depletion of passive particles on one side of the slab.' No evidence is presented that this depletion asymmetry is causal rather than a correlated consequence of drift. In particular, no control simulations are reported with passive particles absent, with symmetric depletion, or with reversed initial conditions. The central mechanism is therefore not established.
  3. [Abstract, 'average density profile calculations'] The claimed quantitative support—average density profiles, interface asymmetry, decomposition into source/sink and rigid displacement, and the specific fluctuations that produce, cancel, or reverse motion—is entirely missing from the supplied text. No system size, aspect ratio, activity, passive fraction, boundary conditions, time scales, error bars, or numerical methods are given. The claimed regime is unfalsifiable from the available material.
minor comments (1)
  1. [Title (arXiv listing)] The title contains a typo: 'Peparation' should be 'Separation'.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity identified; the supplied full text is an unrelated quantum-compiler paper, so the abstract's derivation chain is absent rather than circular.

full rationale

The abstract claims a new dynamical regime in doped motility-induced phase separation, with interface propagation caused by passive-particle depletion and a kinetic analysis of slab motion. However, the full text supplied is entirely a different manuscript: 'ConiQ: Enabling Concatenated Quantum Error Correction on Neutral Atom Arrays' (arXiv:2508.05779v1). None of the abstract's model, simulations, density profiles, or fluctuation analyses appear anywhere in the body. Consequently, there is no derivation chain to walk, and no equation, fit, or self-citation can be exhibited that reduces a claimed prediction to its inputs. Circularity requires quoting a specific reduction (e.g., Eq. X = Eq. Y by construction, or a fitted parameter renamed as a prediction); no such reduction exists in the available material. The abstract's causal attribution to passive-particle depletion is an unsupported hypothesis, but unsupported is not circular. Likewise, there are no self-citations in the abstract and no 'uniqueness theorem' imported from prior work. The correct finding is therefore absence of any demonstrable circular reasoning, not positive evidence of non-circularity. The correctness and completeness concerns raised by the mismatch between abstract and full text are substantial, but they fall outside the circularity pass as defined.

Assumptions & free parameters 0 free parameters · 0 assumptions · 0 invented entities

Abstract-only review: the simulation parameters (density, activity, passive fraction, box dimensions) are not stated, so no free parameters can be enumerated. No axioms or invented entities are mentioned in the abstract.

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Cite this review

Pith. "Pith review of Dynamics and rupture of doped Motility Induced Phase Peparation." pith.science (2026). https://pith.science/paper/NFJWVJYS

@misc{pith2026250805768,
  author       = {Pith},
  title        = {Pith review of: Dynamics and rupture of doped Motility Induced Phase Peparation},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/NFJWVJYS}},
  note         = {Machine review of arXiv:2508.05768}
}
read the original abstract

Adding a small amount of passive (Brownian) particles to a two-dimensional dense suspension of repulsive active Brownian particles does not affect the appearance of a motility-induced phase separation into a dense and a dilute phase, caused by the persistence of the active particles' direction of motion. Unlike a purely active suspension, the dense slab formed in an elongated system of a passive-active mixture may show, over long periods of time, a stable and well-defined propagation of the interfaces, because of the symmetry breaking caused by the depletion of passive particles on one side of the slab. We investigate these dynamical structures via average density profile calculations, revealing an asymmetry between the two interfaces, and enabling a kinetic analysis of the slab movement. The apparent movement of the dense slab is not a pure source/sink effect, nor a rigid displacement of all the particles, but a self-sustained combination of both effects. Furthermore, we analyse the specific fluctuations that produce, cancel and abruptly reverse the slab motion.

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Reference graph

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