Thermodynamic Networks: Harnessing Non-Equilibrium Steady States for Computation
Pith reviewed 2026-05-20 19:36 UTC · model grok-4.3
The pith
Negative differential conductance lets thermodynamic networks approximate any function using non-equilibrium steady states.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Thermodynamic networks consisting of finite reservoirs exchanging conserved quantities reach a non-equilibrium steady state that solves chosen computational problems. Negative differential conductance is the property that lifts the restriction to monotonic functions and enables approximation of arbitrary continuous functions. Without NDC the steady-state mapping remains monotonic; with NDC the network becomes a universal approximator. The networks are trained by protocols that harness equilibration, and both quantum-dot and enzymatic platforms are shown to achieve high performance once engineered for NDC.
What carries the argument
Negative Differential Conductance (NDC), the non-monotonic current-voltage response that supplies the non-linearity required for universal approximation in the steady-state mapping of conserved quantities.
If this is right
- Quantum dot and enzymatic networks can be engineered for NDC to perform both regression and classification tasks.
- Computation occurs autonomously once the network relaxes to its steady state, with no ongoing external driving required.
- Training reduces to choosing initial conditions or couplings that let natural equilibration reach the desired encoding.
- The framework applies to any platform where reservoirs exchange conserved quantities and NDC can be realized.
Where Pith is reading between the lines
- Similar NDC-based mechanisms could appear in biological signaling or metabolic networks, offering a physical route to complex computation without explicit programming.
- Energy costs of computation might be analyzed directly from the thermodynamic cost of maintaining the required non-equilibrium steady state.
- Small arrays of quantum dots could serve as an experimental testbed to measure how closely approximation error tracks the strength of engineered NDC.
- The approach suggests a design principle for other physical reservoirs: add tunable negative conductance regions to expand the class of representable functions.
Load-bearing premise
Finite-size reservoirs exchanging conserved quantities can be arranged and tuned so that their non-equilibrium steady state directly encodes the solution once negative differential conductance is present.
What would settle it
Construct a thermodynamic network deliberately lacking NDC and show it still approximates a non-monotonic target such as the sine function to high accuracy after standard equilibration training.
Figures
read the original abstract
We introduce thermodynamic networks, a general framework for autonomous, physics-based computation using non-equilibrium steady states. These networks are modeled as a collection of finite-size reservoirs that exchange conserved quantities--such as electric charge or molecular number--while relaxing to a non-equilibrium steady state, which encodes the solution of a computational problem. We identify Negative Differential Conductance (NDC) as the critical physical property governing the computational expressivity of the thermodynamic network. While networks lacking NDC are restricted to computing monotonic functions, the presence of NDC enables universal function approximation. For the training of the network, we use protocols that take advantage of the natural tendency of the system to equilibrate. We illustrate the versatility of our approach via two different platforms: quantum dot networks and enzymatic reaction networks. Both systems can be engineered to have NDC, enabling high performance in standard benchmarks, including sine function approximation and MNIST digit classification. Overall, our work establishes a rigorous link between non-equilibrium steady states and computational expressivity.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript introduces thermodynamic networks as collections of finite-size reservoirs exchanging conserved quantities (e.g., charge or molecular number) that relax to a non-equilibrium steady state (NESS) encoding the solution to a computational problem. The central claim is that Negative Differential Conductance (NDC) is the key property enabling universal function approximation, while its absence restricts the networks to monotonic functions only. Training exploits natural relaxation dynamics rather than explicit fitting, and the framework is illustrated on quantum-dot and enzymatic-reaction platforms for sine approximation and MNIST classification.
Significance. If the central claims are rigorously established, the work would provide a concrete link between non-equilibrium thermodynamics and computational expressivity, potentially opening routes to autonomous, low-energy physical computers. The emphasis on NDC as the expressivity switch and the use of equilibration for training are distinctive strengths; the two concrete platforms supply falsifiable benchmarks that could be reproduced.
major comments (3)
- [Abstract / central claim on NDC] The universality claim (NDC enables approximation of arbitrary continuous functions via NESS observables) is load-bearing yet unsupported by any derivation or density argument in the provided text. No explicit map from inputs to steady-state currents/potentials is shown to be dense in C[0,1], nor is a reference to a relevant theorem supplied.
- [Discussion of NDC and steady-state encoding] The assumption that engineering NDC yields a unique, asymptotically stable NESS is not justified. Standard circuit theory and non-equilibrium thermodynamics show that NDC regions frequently produce multiple fixed points or limit cycles; the manuscript supplies neither Lyapunov conditions nor numerical evidence confirming uniqueness once NDC is present.
- [Training protocols] The training protocol is described only at the level of 'natural relaxation.' It is unclear how the target function is encoded in the choice of reservoir parameters or boundary conditions without introducing hidden fitting degrees of freedom that undermine the claimed parameter-free character.
minor comments (2)
- Notation for conserved quantities, reservoir indices, and the precise definition of 'thermodynamic network' should be introduced with an explicit diagram or set of equations early in the manuscript.
- Performance numbers for sine approximation and MNIST (error metrics, comparison baselines) are mentioned but not tabulated; a small results table would improve clarity.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive criticism of our manuscript. The comments identify important points that require clarification and strengthening. We respond to each major comment below and indicate the revisions we will make.
read point-by-point responses
-
Referee: [Abstract / central claim on NDC] The universality claim (NDC enables approximation of arbitrary continuous functions via NESS observables) is load-bearing yet unsupported by any derivation or density argument in the provided text. No explicit map from inputs to steady-state currents/potentials is shown to be dense in C[0,1], nor is a reference to a relevant theorem supplied.
Authors: We agree that a fully rigorous density argument establishing that NDC-equipped networks can approximate arbitrary continuous functions is not developed in the current text. The manuscript instead demonstrates the claim through explicit constructions: the quantum-dot and enzymatic examples show that NDC permits non-monotonic steady-state responses (e.g., sine approximation) while its absence restricts the networks to monotonic maps. To address the referee’s concern, we will add a new subsection that sketches a density argument. Specifically, we will show that the steady-state current map, when NDC is present, can realize a family of non-monotonic basis functions whose linear combinations are dense in C[0,1] by appealing to the Stone–Weierstrass theorem after a suitable change of variables induced by the NDC characteristic. We will also cite relevant results from non-equilibrium circuit theory that support the existence of such maps. This addition will be placed after the general framework section. revision: partial
-
Referee: [Discussion of NDC and steady-state encoding] The assumption that engineering NDC yields a unique, asymptotically stable NESS is not justified. Standard circuit theory and non-equilibrium thermodynamics show that NDC regions frequently produce multiple fixed points or limit cycles; the manuscript supplies neither Lyapunov conditions nor numerical evidence confirming uniqueness once NDC is present.
Authors: The referee correctly notes that NDC can destabilize fixed points in general dynamical systems. In the manuscript we implicitly assume that device parameters are chosen so that a unique, globally attractive NESS exists; this assumption is verified numerically for the specific quantum-dot and enzymatic networks we simulate. We acknowledge that a general Lyapunov or contraction-mapping argument is absent. We will therefore revise the stability discussion to include (i) a brief statement of the conditions under which the network equations remain contractive even with NDC (drawing on standard results for monotone systems with bounded negative slopes), and (ii) additional numerical diagnostics (phase portraits and eigenvalue spectra of the Jacobian at the operating point) confirming uniqueness and asymptotic stability for the parameter regimes used in the sine and MNIST examples. These additions will appear in the platform-specific sections. revision: yes
-
Referee: [Training protocols] The training protocol is described only at the level of 'natural relaxation.' It is unclear how the target function is encoded in the choice of reservoir parameters or boundary conditions without introducing hidden fitting degrees of freedom that undermine the claimed parameter-free character.
Authors: We clarify that the term “parameter-free” refers to the absence of iterative numerical optimization (gradient descent, back-propagation, etc.). The physical parameters—reservoir volumes, baseline conductances, and fixed boundary chemical potentials—are chosen once, on the basis of the problem statement, and then held constant while the system relaxes. The target function is encoded by mapping the input variable to a boundary condition (e.g., input voltage or substrate concentration) and reading the desired output from a steady-state observable (current or product flux). Because the mapping is fixed by the physical topology and the NDC characteristic, no additional tunable weights are introduced after the initial design. We will expand the training-protocol paragraph to make this encoding explicit, including a step-by-step description of how the sine and MNIST tasks are mapped onto boundary conditions, and we will add a short paragraph contrasting this approach with conventional machine-learning training to emphasize the lack of hidden fitting degrees of freedom. revision: partial
Circularity Check
No significant circularity; derivation self-contained
full rationale
The paper introduces thermodynamic networks as a framework where non-equilibrium steady states encode computations, with NDC identified as the key property separating monotonic from universal approximation capabilities. Training exploits natural relaxation to equilibrium rather than explicit parameter fitting to target functions. No load-bearing steps reduce claims to self-definitions, fitted inputs renamed as predictions, or self-citation chains; the link between NDC and expressivity is presented via physical modeling and concrete platforms (quantum dots, enzymatic networks) with benchmarks, remaining independent of the target results by construction.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Finite-size reservoirs exchanging conserved quantities relax to a non-equilibrium steady state whose flows encode computational outputs.
invented entities (1)
-
thermodynamic network
no independent evidence
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We identify Negative Differential Conductance (NDC) as the critical physical property governing the computational expressivity... networks lacking NDC are restricted to computing monotonic functions
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Theorem 1 (Kamke-Müller). If the network’s dynamics is cooperative... then μ(t) ≤ μ'(t) for all t > 0
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
Physical setup The network consists of electronic reservoirs (the nodes) connected by single-level quantum dots (the edges), as shown Fig. 2. A reservoirαis characterized by a chemical potentialµ α and temperatureT α. Each quantum dot sitting on the edge connecting two reser- voirs(α, β)has a single discrete energy levelϵαβ through which electrons tunnel ...
-
[2]
Transport through a quantum dot The steady-state current through a quantum dot con- necting reservoirsαandβcan be expressed as the weak- coupling limit of coherent transport through a single res- onant level, Iαβ =γ αβ fα(ϵαβ)−f β(ϵαβ) ,(15) whereγ αβ is the tunnel coupling and fℓ(E) = 1 1 +e (E−µℓ)/kB Tℓ (16) is the Fermi–Dirac distribution of reservoirℓ...
-
[3]
NDC mechanism (electrostatic shift) Under certain conditions, the energy level of a quan- tum dot can be shifted by its electrostatic environment, in particular by the potentialsµα andµ β of the two reser- voirs connected to the dot. Here we model this depen- dence as a linearelectrostatic shift, namely ϵαβ =a αβ +b αβ (µα −µ β),(17) wherea αβ is the bare...
-
[4]
Breaking cooperativity Cooperativity requiresG αβ ≥0for all edges and all operating points (see Sec. IID). Using Eq. (18) it then follows that this is true if and only if Tβ ˜fα Tα ˜fβ ≤ 1 +b αβ bαβ .(19) The right-hand side specifies thecooperativity threshold, namely the maximum asymmetry between source and drain that ensures cooperative behaviour. Nota...
-
[5]
For that we consider a network with architecture 2-2-1, i.e
A minimal example: XOR problem We now test the mechanism of NDC on the simplest non-monotone Boolean function: exclusive-or (XOR). For that we consider a network with architecture 2-2-1, i.e. two input reservoirs(x 1, x2), two hidden reservoirs (h1, h2), and one output(y), fully connected by quantum dots with parameters{w αβ, aαβ, bαβ}. We then train the ...
-
[6]
We now test whether the same prin- ciple can be scaled up to realistic problems
Scaling to image classification The XOR example demonstrates the mechanism of folding due to NDC. We now test whether the same prin- ciple can be scaled up to realistic problems. For that we consider the MNIST handwritten digit classification benchmark [42]: Classifying28×28grayscale images into ten digit categories (0–9). Each input pixel is encoded as t...
-
[7]
There we show the performance of thermodynamic networks operating in different transport regimes as a function of the number of neurons in the hidden layer. Although the high dimensionality of the parameter space leads to challenging training scenarios where the network can converge to multistable solutions, the final networks achieve robust performance o...
-
[8]
reservoirs that contain molecules of different chemical species with varying concentrationsc α
Physical setup The nodes of the network are pools of molecular sub- strates, i.e. reservoirs that contain molecules of different chemical species with varying concentrationsc α. The transport between two nodes is mediated by an enzyme that catalyzes the conversion between compoundαinto another compoundβ. Each such reaction defines an edge of the network, ...
-
[9]
Enzymatic transport A simple and well-studied model of reversible enzyme kinetics is the Michaelis–Menten mechanism [47], which expresses the reaction flux fromαtoβas Iαβ(cα,cβ) = 1 1 + cα Kα + cβ Kβ Vf Kα cα − Vr Kβ cβ ,(22) whereV f /r are the tunable parameters that character- ize the maximal forward and reverse rates, andK α/β, are the Michaelis const...
-
[10]
This is a generic phenomenon made possi- ble bysubstrate inhibition[26]
NDC mechanism (substrate inhibition) Toaccessnon-monotonecomputation, weneedachem- ical analogue of NDC, namely a mechanism that makes the reaction flux respond non-monotonically to substrate concentration. This is a generic phenomenon made possi- ble bysubstrate inhibition[26]. More specifically, at high concentrations, excess substrate molecules bind to...
-
[11]
Function regression ThenumericalexperimentsperformedontheXORand MNIST tasks demonstrated classification with quantum networks. Wenowturntoregression, i.e. fittingacontin- uous mapping rather partitioning the input space using both presented platforms. This is a natural benchmark for thermodynamic networks, as the steady-state output potential is by defaul...
- [12]
-
[13]
L. G. Wright, T. Onodera, M. M. Stein, T. Wang, D. T. Schachter, Z. Hu, and P. L. McMahon, Nature601, 549 (2022)
work page 2022
-
[14]
D. Marković, A. Mizrahi, D. Querlioz, and J. Grollier, Nature Reviews Physics2, 499 (2020)
work page 2020
- [15]
-
[16]
N. Mohseni, P. L. McMahon, and T. Byrnes, Nature Re- views Physics4, 363 (2022)
work page 2022
- [17]
-
[18]
Seifert, Reports on progress in physics75, 126001 (2012)
U. Seifert, Reports on progress in physics75, 126001 (2012)
work page 2012
- [19]
-
[20]
M. Moroder, F. C. Binder, and J. Goold, Digitally opti- mized initializations for fast thermodynamic computing (2026)
work page 2026
-
[21]
P. Lipka-Bartosik, K. Donatella, M. Aifer, D. Melanson, M. Perarnau-Llobet, N. Brunner, and P. J. Coles, in2024 IEEE International Conference on Rebooting Computing (ICRC)(IEEE, 2024) pp. 1–13
work page 2024
-
[22]
P. J. Coles, C. Szczepanski, D. Melanson, K. Donatella, A. J. Martinez, and F. Sbahi, in2023 IEEE Inter- national Conference on Rebooting Computing (ICRC) (IEEE, 2023) pp. 1–10
work page 2023
- [23]
-
[24]
Whitelam, Physical Review Letters136, 037101 (2026)
S. Whitelam, Physical Review Letters136, 037101 (2026)
work page 2026
- [25]
-
[26]
A. Rolandi, P. Abiuso, P. Lipka-Bartosik, M. Aifer, P. J. Coles, and M. Perarnau-Llobet, Energy-time- accuracy tradeoffs in thermodynamic computing (2026), arXiv:2601.04358 [cond-mat.stat-mech]
-
[27]
P. Lipka-Bartosik, M. Perarnau-Llobet, and N. Brunner, Science advances10, eadm8792 (2024)
work page 2024
- [28]
-
[29]
H. L. Smith,Monotone dynamical systems: an introduc- tion to the theory of competitive and cooperative systems: an introduction to the theory of competitive and coopera- tive systems, 41 (American Mathematical Soc., 1995)
work page 1995
-
[30]
X. Liu, X. Han, N. Zhang, and Q. Liu, Advances in Neu- ral Information Processing Systems33, 15427 (2020)
work page 2020
-
[31]
D. Runje and S. M. Shankaranarayana, inInternational Conference on Machine Learning(PMLR, 2023) pp. 29338–29353
work page 2023
-
[32]
D. Chen and W. Ye, inProceedings of the third ACM international conference on AI in finance(2022) pp. 70– 78
work page 2022
- [33]
-
[34]
M. Esposito, U. Harbola, and S. Mukamel, Reviews of modern physics81, 1665 (2009)
work page 2009
- [35]
-
[36]
W. G. Van der Wiel, S. De Franceschi, J. M. Elzerman, T. Fujisawa, S. Tarucha, and L. P. Kouwenhoven, Re- views of modern physics75, 1 (2002)
work page 2002
-
[37]
M. C. Reed, A. Lieb, and H. F. Nijhout, Bioessays32, 422 (2010)
work page 2010
-
[38]
G. Cybenko, Mathematics of Control, Signals, and Sys- tems2, 303 (1989), aDS Bibcode: 1989MCSS....2..303C
work page 1989
- [39]
-
[40]
D. E. Rumelhart, G. E. Hinton, and R. J. Williams, na- ture323, 533 (1986)
work page 1986
-
[41]
B. Scellier and Y. Bengio, Frontiers in Computational Neuroscience11, 24 (2017)
work page 2017
-
[42]
P. Lipka-Bartosik, G. Blasi, J. Lalueza Puértolas, G. Haack, M. Perarnau-Llobet, and N. Brunner, Ther- moNet: A code library for physics-based computation with non-equilibrium steady states,https://github. com/patryk-lb/ThermoNet(2026)
work page 2026
-
[43]
Büttiker, Physical review letters57, 1761 (1986)
M. Büttiker, Physical review letters57, 1761 (1986)
work page 1986
- [44]
- [45]
-
[46]
Y. V. Nazarov and Y. M. Blanter,Quantum transport: introduction to nanoscience(Cambridge university press, 2009)
work page 2009
-
[47]
Datta,Electronic Transport in Mesoscopic Systems (Cambridge university press, 1997)
S. Datta,Electronic Transport in Mesoscopic Systems (Cambridge university press, 1997)
work page 1997
-
[48]
Y. M. Blanter and M. Büttiker, Physics Reports336, 1 (2000)
work page 2000
-
[49]
L. P. Kouwenhoven, C. M. Marcus, P. L. McEuen, S. Tarucha, R. M. Westervelt, and N. S. Wingreen, in Mesoscopic electron transport(Springer, 1997) pp. 105– 214
work page 1997
- [50]
-
[51]
J. P. Sun, G. I. Haddad, P. Mazumder, and J. N. Schul- man, Proceedings of the IEEE86, 641 (1998)
work page 1998
- [52]
- [53]
- [54]
-
[55]
A.Pandi, M.Koch, P.L.Voyvodic, P.Soudier, J.Bonnet, M. Kushwaha, and J.-L. Faulon, Nature communications 10, 3880 (2019)
work page 2019
- [56]
-
[57]
U. T. Bornscheuer, G. Huisman, R. Kazlauskas, S. Lutz, J. Moore, and K. Robins, Nature485, 185 (2012)
work page 2012
-
[58]
Cornish-Bowden,Fundamentals of enzyme kinetics (John Wiley & Sons, 2013)
A. Cornish-Bowden,Fundamentals of enzyme kinetics (John Wiley & Sons, 2013)
work page 2013
-
[59]
J. D. Murray and J. D. Murray,Mathematical biology: II: spatial models and biomedical applications, Vol. 18 (Springer, 2003)
work page 2003
-
[60]
R. A. Copeland,Enzymes: a practical introduction to structure, mechanism, and data analysis(John Wiley & Sons, 2023)
work page 2023
- [61]
-
[62]
A. I. Luppi, Y. Sanz Perl, J. Vohryzek, H. Ali, P. A. Mediano, F. E. Rosas, F. Milisav, L. E. Suárez, S. Gini, D. Gutierrez-Barragan,et al., Nature Neuroscience , 1 (2026)
work page 2026
-
[63]
T. Dou, S. Kumara, J. Burns, E. Sigler, P. Girdhar, D. Petty, G. Milburn, J. Plested, and M. Woolley, arXiv preprint arXiv:2604.10861 (2026)
work page internal anchor Pith review Pith/arXiv arXiv 2026
-
[64]
R. Li, Y. Gong, H. Huang, Y. Zhou, S. Mao, Z. Wei, and Z. Zhang, Advanced Materials37, 2312825 (2025)
work page 2025
- [65]
-
[66]
S. Suderman and G. Rubino, Interpretable rule-based learning in an autonomous thermodynamic network (2026), to appear on arXiv
work page 2026
- [67]
-
[68]
V. Lopez-Pastor and F. Marquardt, Physical Review X 13, 031020 (2023)
work page 2023
-
[69]
P. L. McMahon, Nature Reviews Physics5, 717 (2023)
work page 2023
- [70]
- [71]
-
[72]
R. Martínez-Peña, G. L. Giorgi, J. Nokkala, M. C. So- riano, and R. Zambrini, Physical Review Letters127, 100502 (2021)
work page 2021
-
[73]
D. H. Wolpert, Journal of Physics A: Mathematical and Theoretical52, 193001 (2019)
work page 2019
-
[74]
D. H. Wolpert, J. Korbel, C. W. Lynn, F. Tasnim, J. A. Grochow, G. Kardes, J. B. Aimone, V. Balasub- ramanian, E. De Giuli, D. Doty, N. Freitas, M. Marsili, T. E. Ouldridge, A. W. Richa, P. Riechers, E. Roldan, B. Rubenstein, Z. Toroczkai, and J. Paradiso, Pro- ceedings of the National Academy of Sciences121, 10.1073/pnas.2321112121 (2024)
-
[75]
P. Chattopadhyay, A. Misra, T. Pandit, and G. Paul, Reports on Progress in Physics88, 086001 (2025)
work page 2025
-
[76]
A. de Oliveira Junior, J. B. Brask, and R. Chaves, PRX Quantum6, 10.1103/phkv-wrsd (2025)
-
[77]
S. Campbell, I. D’Amico, M. A. Ciampini, J. Anders, N. Ares, S. Artini, A. Auffèves, L. Bassman Oftelie, L. P. Bettmann, M. V. S. Bonança, T. Busch, M. Campisi, M. F. Cavalcante, L. A. Correa, E. Cuestas, C. B. Dag, S. Dago, S. Deffner, A. Del Campo, A. Deutschmann- Olek, S. Donadi, E. Doucet, C. Elouard, K. Ensslin, P. Erker, N. Fabbri, F. Fedele, G. Fiu...
work page 2026
- [78]
-
[79]
S. Vinjanampathy and J. Anders, Contemporary Physics 57, 545 (2016)
work page 2016
-
[80]
G. Manzano, G. Kardes, E. Roldan, and D. H. Wolpert, Physical Review X14, 10.1103/physrevx.14.021026 (2024)
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.