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arxiv: 2512.01654 · v2 · submitted 2025-12-01 · ❄️ cond-mat.stat-mech

Quasistatic response for nonequilibrium processes: evaluating the Berry potential and curvature

Pith reviewed 2026-05-17 03:00 UTC · model grok-4.3

classification ❄️ cond-mat.stat-mech
keywords nonequilibrium thermodynamicsBerry phaseMarkov jump processesquasistatic responseBerry curvatureClausius theoremMaxwell relationsentropy flux
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The pith

Cyclic changes in nonequilibrium steady states produce excess responses given by a geometric Berry phase.

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

The paper examines how slow time-dependent perturbations change the expected excesses in observables such as dynamical activity and entropy flux for systems already in a nonequilibrium steady state. For closed cycles in the space of control parameters, these excesses take the form of a Berry phase computed directly from the instantaneous steady-state distribution. The associated Berry potential and curvature then quantify the geometric contribution to the response. Nonzero curvature implies that standard thermodynamic identities, including Maxwell relations and the Clausius heat theorem, cease to hold. The work also identifies a parameter-space analogue of the Aharonov-Bohm effect and sufficient conditions, based on mean first-passage times, under which the geometric quantities vanish at absolute zero.

Core claim

When slow cyclic perturbations are applied to a Markov jump process in a nonequilibrium steady state, the excess values of observables are expressed through a Berry phase extracted from the steady-state probability distribution. The Berry potential and its curvature serve as the response functions that measure this geometric excess. Nonzero curvature produces a breakdown of the thermodynamic Maxwell relations and of the Clausius heat theorem. The same framework yields a parameter-space version of the Aharonov-Bohm effect in which a nonzero phase accumulates along a path with vanishing curvature, and it supplies sufficient no-localization conditions, stated in terms of mean first-passage time

What carries the argument

The Berry phase extracted from the nonequilibrium steady-state distribution of a Markov jump process, which defines the potential and curvature that quantify excess responses to slow cyclic driving.

If this is right

  • Excesses in dynamical activity and entropy flux during a cycle equal the Berry phase accumulated along the closed path in parameter space.
  • Nonzero Berry curvature implies that thermodynamic Maxwell relations no longer hold.
  • The Clausius heat theorem is violated whenever the Berry curvature is nonzero.
  • Under no-localization conditions expressed via mean first-passage times, both Berry potential and curvature vanish at absolute zero for arbitrary driving protocols.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same geometric construction could be tested in other driven classical systems whose steady states are known analytically or numerically.
  • Measuring the curvature in an experiment would give a direct signature that standard equilibrium thermodynamic identities must be replaced by nonequilibrium versions.
  • The Aharonov-Bohm analogue suggests that phase accumulation can occur even when local curvature is zero, which might be observable in systems with topologically nontrivial parameter spaces.

Load-bearing premise

The perturbations must be slow enough that the system remains in a well-defined nonequilibrium steady state at every instant so that the Berry quantities can be read off from the steady-state distribution alone.

What would settle it

Perform a slow cyclic protocol on a concrete Markov jump process, compute the excess entropy flux from direct simulation or experiment, and compare it with the line integral of the Berry potential around the same cycle; a statistically significant mismatch would falsify the claimed geometric description.

Figures

Figures reproduced from arXiv: 2512.01654 by Aaron Beyen, Christian Maes, Faezeh Khodabandehlou.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: shows these responses as function of β2 for α = 1, β1 = 0.5 and β1 = 3. R1 α , β1=0.5 R1 α , β1=3 R2 α , β1=0.5 R2 α , β1=3 0 1 2 3 4 5 -0.025 -0.020 -0.015 -0.010 -0.005 0.000 0.005 β2 FIG. 4: The response RPi α of the excess heat to each of the heat baths upon changing the switching rate α in [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p012_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6 [PITH_FULL_IMAGE:figures/full_fig_p013_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: (b) shows that the driving E does not significantly affect the excess reactivity for large driving, since the corresponding response RA E becomes small. Example 3: Excess current To illustrate how to calculate the excess current (27), consider the jump process on the graph in [PITH_FULL_IMAGE:figures/full_fig_p013_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8 [PITH_FULL_IMAGE:figures/full_fig_p014_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: j(1,2)/a j(4,6)/a 0 2 4 6 8 10 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 α Steady current (a) β=1 β=1.5 0 2 4 6 8 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 α exc(4,6) (b) FIG. 9: (a) Steady currents jλ (in units of a) in the left and right triangles in [PITH_FULL_IMAGE:figures/full_fig_p014_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10 [PITH_FULL_IMAGE:figures/full_fig_p016_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: FIG. 11 [PITH_FULL_IMAGE:figures/full_fig_p020_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: FIG. 12 [PITH_FULL_IMAGE:figures/full_fig_p024_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: FIG. 13 [PITH_FULL_IMAGE:figures/full_fig_p025_13.png] view at source ↗
read the original abstract

We investigate how introducing slow, time-dependent perturbations to a steady, nonequilibrium process alters the expected (excess) values of important observables, such as the dynamical activity and entropy flux. When we make a cyclic thermodynamic transformation, the excesses are described in terms of a (geometric) Berry phase with corresponding Berry potential and Berry curvature quantifying the response. Focussing on Markov jump processes, we show how a non-zero Berry curvature leads to a breakdown of the thermodynamic Maxwell relations and of the Clausius heat theorem. We also present a variant of the Aharonov-Bohm effect in which the parameters follow a curve with vanishing Berry curvature, but the system still experiences a nonzero Berry phase. Finally, we identify (sufficient) no-localization conditions in terms of mean first-passage times under which the corresponding Berry potentials and curvatures vanish at absolute zero, extending, for arbitrary driving, e.g., the case of vanishing heat capacity as for the Nernst postulate.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript develops a geometric framework for the quasistatic response of nonequilibrium steady states under slow time-dependent driving, focusing on Markov jump processes. Excess dynamical activity and entropy flux for cyclic protocols are expressed as a Berry phase computed from the instantaneous steady-state distribution, with the associated Berry potential and curvature quantifying the response. Nonzero curvature is shown to violate thermodynamic Maxwell relations and the Clausius heat theorem. The work also presents an Aharonov-Bohm-like effect with vanishing curvature but nonzero phase, and derives sufficient no-localization conditions (via mean first-passage times) under which the Berry quantities vanish at absolute zero, extending the Nernst postulate.

Significance. If the central derivations are free of gaps, the paper supplies a parameter-free geometric interpretation of excess observables in driven nonequilibrium systems. This could unify aspects of stochastic thermodynamics with Berry-phase concepts, offering falsifiable predictions for the breakdown of equilibrium-like relations under cyclic driving and concrete conditions for zero-temperature behavior. The explicit treatment of Markov processes and the Aharonov-Bohm variant add technical value.

major comments (2)
  1. [Derivation of excess observables and Berry curvature (around the quasistatic expansion)] The central identification of excess entropy flux and dynamical activity with a Berry phase (computed solely from the instantaneous nonequilibrium steady-state distribution) is load-bearing for the claimed breakdown of Maxwell relations and Clausius theorem. The derivation must explicitly demonstrate that the O(ε) correction in the adiabatic parameter ε is purely geometric and independent of the relaxation spectrum; if mean first-passage times remain comparable to the driving period, transient currents enter at the same order and the curvature interpretation does not hold.
  2. [Zero-temperature section on mean first-passage times] The no-localization conditions stated in terms of mean first-passage times are used to conclude vanishing Berry potential/curvature at T=0 for arbitrary driving. It is necessary to show that these conditions are sufficient to eliminate all non-geometric contributions uniformly along the cycle, rather than only for specific protocols or equilibrium limits.
minor comments (2)
  1. [Introduction and definitions] Notation for the Berry potential and curvature should be introduced with explicit formulas early in the text to aid readability, especially when contrasting with equilibrium thermodynamic potentials.
  2. [Discussion of Maxwell relations] The manuscript would benefit from a brief comparison table or explicit example contrasting the new nonequilibrium Maxwell relations with their equilibrium counterparts.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive report. The comments raise important points regarding the rigor of the quasistatic expansion and the zero-temperature analysis. We address each major comment below and indicate planned revisions to strengthen the manuscript.

read point-by-point responses
  1. Referee: [Derivation of excess observables and Berry curvature (around the quasistatic expansion)] The central identification of excess entropy flux and dynamical activity with a Berry phase (computed solely from the instantaneous nonequilibrium steady-state distribution) is load-bearing for the claimed breakdown of Maxwell relations and Clausius theorem. The derivation must explicitly demonstrate that the O(ε) correction in the adiabatic parameter ε is purely geometric and independent of the relaxation spectrum; if mean first-passage times remain comparable to the driving period, transient currents enter at the same order and the curvature interpretation does not hold.

    Authors: We agree that an explicit demonstration of timescale separation is essential for the geometric interpretation. In the manuscript the quasistatic expansion is performed under the assumption that the driving rate ε is small compared with the inverse of the longest relaxation time set by the mean first-passage times of the Markov generator. Under this condition the probability distribution follows the instantaneous steady state plus an O(ε) correction whose leading term is the Berry connection evaluated on the manifold of steady-state distributions; transient currents decay exponentially and do not contribute at order ε. We will revise the derivation section to include a short paragraph that states this spectral-gap assumption explicitly and shows that the O(ε) excess is thereby independent of further details of the relaxation spectrum beyond the existence of a gap. This clarification will also be cross-referenced to the discussion of the Aharonov-Bohm variant. revision: yes

  2. Referee: [Zero-temperature section on mean first-passage times] The no-localization conditions stated in terms of mean first-passage times are used to conclude vanishing Berry potential/curvature at T=0 for arbitrary driving. It is necessary to show that these conditions are sufficient to eliminate all non-geometric contributions uniformly along the cycle, rather than only for specific protocols or equilibrium limits.

    Authors: The no-localization conditions are formulated directly on the instantaneous generator at each point of the parameter manifold and require that the mean first-passage times diverge as T→0 for every admissible driving protocol. Because the conditions are uniform in the control parameters and the cycle is compact, the localization (and consequent vanishing of the Berry quantities) holds uniformly along the entire path. Non-geometric contributions, which rely on finite relaxation rates, are likewise suppressed uniformly once the mean first-passage times become arbitrarily large. We will expand the zero-temperature section with a brief argument making this uniformity explicit and noting that the argument applies to arbitrary cyclic protocols, thereby extending the Nernst-like statement beyond equilibrium. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation applies standard Berry geometry to parameter-dependent steady states

full rationale

The paper constructs the Berry potential and curvature directly from the instantaneous nonequilibrium steady-state distribution via the standard adiabatic phase definition for Markov jump processes. Excess observables are then obtained as first-order corrections in the slow-driving expansion of the master equation, which is an independent dynamical calculation rather than a redefinition or fit. No load-bearing self-citations, no fitted parameters renamed as predictions, and no ansatz smuggled via prior work; the claimed breakdown of Maxwell relations follows mathematically from nonzero curvature in the quasistatic limit.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The claims rest on the standard mathematical definition of Berry phase for a parameter-dependent family of steady-state distributions of Markov processes, plus the assumption that slow driving allows adiabatic following of the instantaneous steady state.

axioms (2)
  • domain assumption The system is described by a continuous-time Markov jump process whose transition rates depend smoothly on external parameters.
    Invoked to define the steady-state distribution from which the Berry connection is constructed.
  • domain assumption The driving is slow enough that the system stays close to the instantaneous nonequilibrium steady state throughout the cycle.
    Required for the quasistatic excess to be captured by the geometric Berry phase rather than transient dynamics.

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Forward citations

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