REVIEW 3 major objections 5 minor 45 references
Microscopic study of topological phase transitions: Percolation point of view
T0 review · 3 major / 5 minor · reviewed 2026-08-04 · deepseek-v4-flash
Pith's one-line read Decoherence-induced topological phase transitions are percolation events, and a new quasi-local negativity (QLTEN) makes this visible at the microscopic scale.
desk verdict QLTEN is a genuinely useful new probe and the color-code/toric-code contrast under explosive percolation is real, but the labeling rule that defines QLTEN regions is heuristic and needs proof before the extracted thresholds are trusted. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
QLTEN: the topological entanglement negativity computed locally on adjacent 7-plaquette hexagonal subsystems (A,B,C) via γ_N = −N_A − N_B − N_C − N_ABC + N_AB + N_BC + N_AC; γ_N=1 marks a toric-code-like region, γ_N=0 a Higgs region. The homological reading: TEN answers to (quasi-)closed loops of merged S^Z stabilizers (first simplicial homology), while the 1-form disorder parameter D_X(Γ) answers to connected clusters of merged stabilizers (zeroth homology). The explosive-percolation decoherence schedule selects, at each step, the bond whose attached clusters have the smallest size product, so large decohered clusters are suppressed.
What would settle it
Enumerate all decoherence patterns on a small patch of the triangular lattice, and for each 7-plaquette hexagon in each pattern compute both the exact QLTEN value and whether a (quasi-)closed loop of merged S^Z stabilizers encircles it; find one pattern with QLTEN=1 but no encircling loop, or the reverse, and the heuristic rule is refuted. A coarser check: in many decoherence realizations, compare the percolation threshold read from QLTEN clusters with the threshold read from the exact global TEN; if the two transitions drift apart, QLTEN is not faithfully representing the global topological t
Extended reading notes
Core claim
On the paper's own terms: the decoherence-induced transition from the color code to the toric code is a percolation transition in the space of anyon-proliferation events. Each red-link XX-decoherence merges two red plaquette stabilizers, so the state's evolution is a growing bond network on a triangular lattice; when a (quasi-)closed loop of merged S^Z stabilizers surrounds a 7-plaquette hexagon, the local TEN drops from 2 to 1, marking a 'TC region.' QLTEN snapshots reveal these regions, and their largest cluster percolates at p≈0.22, earlier than the 1-form disorder parameter's critical point p_s≈0.31. In the toric code under Z-decoherence, QLTEN shows γ_N=0 Higgs regions, and the death of
Load-bearing premise
The load-bearing premise is that a 7-plaquette hexagon has γ_N=1 (the toric-code value) exactly when a (quasi-)closed loop of merged S^Z stabilizers encircles it; the paper checks this rule for selected configurations and explicitly says general cases are difficult to analyze analytically, so if other configurations violate it, QLTEN's snapshots mislabel the local topological order and the conclusions built on those labels weaken.
Editorial extensions
If this is right
- QLTEN configurations can be assembled from the stabilizer syndrome on a classical computer, making the percolation of TC or Higgs regions observable as an early warning that logical qubits are about to fail.
- The non-coincidence of the 1-form critical point (p_s≈0.31, ν≈1.2, close to bond percolation) and the TEN-variance peak (p≈0.22) is explained by their different homological character: cluster vs loop.
- In the toric code, the moment the largest QLTEN 'Higgs' cluster spans the system is the moment the logical qubit disappears; QLTEN is precocious relative to the non-contractible-loop order.
- Biased decoherence results imply that fault-tolerance thresholds and noise-bias strategies are code-specific and will not transfer between the color code and the toric code.
- The operator ∏_{⟨i,j⟩∈loop}(λ+X_i X_j) is introduced as a second-homology probe for the emergence of the Z2 gauge theory in the color-code-to-toric-code transition.
Reading between the lines
- Because QLTEN uses a fixed 7-plaquette resolution, its cluster statistics (thresholds, exponents) may drift as the subsystem size changes; a natural test is to repeat the percolation analysis with larger and smaller hexagonal subsystems and check convergence.
- The color code's insensitivity to explosive percolation hints that its transition is driven by local anyon-pair creation rather than by the growth of global decohered clusters; this could be tested in other stabilizer codes, such as the surface code with different boundary conditions.
- If QLTEN is a genuine percolation order parameter, its cluster-size distribution should obey standard percolation scaling; comparing its cluster-size exponent with bond percolation on the triangular lattice would be a quantitative check.
- The paper leaves open whether the second-homology loop operator restores a universal description; a direct test is to measure its expectation value in both codes under the same explosive-percolation schedule and see whether it tracks a common threshold.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies decoherence-induced transitions from the color code to an emergent toric code, and from the toric code to a Higgs-like phase, using the stabilizer formalism on lattices of up to a few hundred qubits. It introduces QLTEN, the topological entanglement negativity of a 7-plaquette hexagon, as a local probe, and interprets global TEN and the 1-form disorder parameter as first- and zeroth-homology observables. Under uniform and n-trial explosive-percolation (EP) biased decoherence, the authors report that in the color code the QLTEN clusters and global observables are nearly EP-insensitive, while in the toric code QLTEN clusters, TEN, and logical loop operators show clear n-dependence. The central claim is that QLTEN clusters react before the 1-form symmetry and logical-order parameters, and that the two models' different responses to EP indicate the absence of a simple universal microscopic description of these transitions.
Significance. The paper's exact stabilizer-formalism numerics are a strength, as are the multiple independent observables (TEN, string operator, logical loops, QLTEN cluster statistics) and the explicit finite-size scaling with data collapse for the disorder parameter. The percolation/homology analogy is appealing and the QLTEN proposal is a natural way to visualize spatial structure in a topological transition. If the interpretation is substantiated, the work could provide a practical diagnostic for quantum error mitigation in topological codes. However, the central interpretive step—identifying QLTEN γ_N=1 regions with quasi-closed loops—is only heuristic, and the extracted event-based thresholds are quoted without uncertainties. These issues are fixable and do not undermine the exactness of the computed QLTEN values, but they must be addressed before the microscopic claims can be regarded as established.
major comments (3)
- [Sec. III.C, Fig. 8] The identification of QLTEN γ_N=1 with 'at least one of A,B,C is encircled by a (quasi-)closed loop' is verified only for selected configurations; the text concedes that 'general cases are rather difficult to examine analytically' and calls the consideration a 'heuristic reflection.' This is load-bearing because the percolation interpretation, the extraction of p_QL/p_UF, and the claimed color-code/toric-code contrast all use QLTEN clusters as TC/Higgs regions. Since the QLTEN values themselves are computed exactly, the gap is testable: for random decoherence configurations in both codes and a range of p and L, compare the loop-encirclement criterion with the directly computed 7-plaquette TEN and report false-positive/false-negative rates. If the rule has exceptions, the homology-based interpretation and the thresholds must be qualified accordingly.
- [Sec. IV.A, IV.D, Fig. 13] The thresholds p_QL and p_UF are reported as point values (e.g., p_QL=0.22 for n=1 and 96; p_UF=0.29 and 0.54) without error bars or finite-size analysis. The event-based ensemble estimator (peak of Δ(t)=C_1(t+1)-C_1(t)) is nonstandard, and no distribution of t_max or sample-to-sample spread is shown. Because the paper uses the difference between p_QL and p_UF to argue that QLTEN 'reacts to decoherence faster than the 1-form symmetry and the non-contractible logical orders,' statistical uncertainties and system-size dependence are needed. Please provide bootstrap or similar errors, the t_max distribution, and a scaling test for at least two additional system sizes.
- [Sec. V, Figs. 15-19] The qualitative contrast between the color code (QLTEN insensitive to n-trial EP) and the toric code (clearly n-dependent) is central to the conclusion that a universal microscopic description is challenging. However, the two simulations use different system sizes (color code (12,8), toric code (12,12)) and different maximal n (96 versus 120). Please confirm the contrast at matched system sizes and n, or explain quantitatively why the mismatch cannot affect the comparison. This is particularly relevant to the 'precocious QLTEN' claim in Sec. V, which relies on the timing of QLTEN-cluster growth relative to logical-order disappearance.
minor comments (5)
- [Sec. III.C, Eq. (21)] The proposed operator with arbitrary λ is not used anywhere in the paper. If it is only an outlook remark, say so explicitly; otherwise its presence introduces an unused free parameter and distracts from the main results.
- [Sec. VI] Typos: 'holomogical' should be 'homological'; 'extra-ordinary' is nonstandard. The manuscript would also benefit from a careful pass for minor grammatical errors.
- [Figs. 5, 12, 13] Several variance/largest-cluster panels would be easier to read if the legend explicitly identified the subsystem size or n value inside the panel; currently some identification is only in the caption. Also state in captions whether error bars represent standard error or standard deviation.
- [Sec. II.C.1, Eq. (13)] The disorder parameter D_X(Γ) is defined with ρ_D in both the numerator and denominator; this is clear enough, but for reproducibility please specify the string shape and boundary conditions more explicitly than 'details are specified in the practical calculation.'
- [Data Availability] The statement 'available from the authors on reasonable request' is acceptable, but for a numerical paper of this type, providing the stabilizer-formalism code (or a minimal example) would strengthen reproducibility. This is a suggestion, not a requirement.
Circularity Check
No significant circularity: QLTEN is a direct local observable, and the paper's correlations are numerical, not fitted into themselves.
full rationale
The paper's central new quantity, QLTEN, is not defined in terms of the global quantities it is compared with. It is computed directly from the stabilizer-rank negativity formula, Eq. (15), via the TEN combination, Eq. (18), applied to 7-plaquette subsystems. The paper explicitly notes that the spatial rule linking gamma_N=1 to (quasi-)closed loops of merged stabilizers is heuristic ('General cases are rather difficult to examine analytically, but the above consideration provides us with a heuristic reflection'), which is an unproven-lemma limitation rather than a reduction of the result to its inputs. The claimed correlations between QLTEN clusters, string operators, 1-form disorder parameters, and logical-qubit survival are numerical observations made on independently generated decoherence configurations; no parameter is fitted to one of these observables and then renamed as another. Self-citations, including Refs. [6], [20], and [26], provide previously established stabilizer-rank methods and the disorder-parameter construction, but the paper's new results—the EP behavior, the QLTEN snapshots, and the toric-code logical-qubit timing—are generated by direct simulation and not forced by those citations alone. The absence of a machine-checked proof of the QLTEN labeling rule is a correctness risk, not circularity.
Assumptions & free parameters
free parameters (6)
- n-trial EP trial count n =
1, 2, 4, 96, 120, 384
- QLTEN subsystem size =
7-plaquette hexagon
- event-based and Union-Find thresholds p_QL, p_UF =
p_QL≈0.22 (n=1 and 96), p_UF≈0.29 (n=1), 0.54 (n=96)
- EP pseudo-critical p_max =
⟨p_max⟩≈0.320 (n=1), 0.365 (n=4), 0.652 (n=384)
- disorder-parameter critical point and exponent =
p_s≈0.31, ν≈1.2 (n=1); p_s≈0.32, ν≈1.19 (n=384)
- λ in proposed loop operator Eq. (21) =
unspecified positive real
assumptions (5)
- standard math Rank formula for negativity of stabilizer states (Eqs. 15-16)
- domain assumption Area-law scaling N_A = c|∂A| − γ_N (Eq. 17) with universal TEN
- ad hoc to paper A 7-plaquette subsystem has γ_N=1 iff one of A,B,C is encircled by a (quasi-)closed loop of merged S^Z stabilizers
- domain assumption Color code is equivalent to two toric codes; red XX decoherence at p=1 yields a TC on the red triangular lattice
- standard math Triangular-lattice bond percolation threshold ~0.3473 and EP cluster statistics
Cite this review
Pith. "Pith review of Microscopic study of topological phase transitions: Percolation point of view." pith.science (2026). https://pith.science/paper/5I677F5J
@misc{pith2026260726707,
author = {Pith},
title = {Pith review of: Microscopic study of topological phase transitions: Percolation point of view},
year = {2026},
howpublished = {\url{https://pith.science/paper/5I677F5J}},
note = {Machine review of arXiv:2607.26707}
}
read the original abstract
We investigate microscopic mechanisms underlying decoherence-induced transitions between topologically ordered states. As a first case study, we analyze the color code using topological entanglement negativity (TEN) and a disorder parameter associated with 1-form symmetry. We interpret these quantities as first- and zeroth-dimensional simplicial homological objects, respectively, and show that the transition can be understood in terms of decoherence percolation. To resolve its local structure, we introduce quasi-local TEN (QLTEN), which visualizes the spatial distribution of local topological properties and the growth of decohered regions. We further introduce explosive percolation (EP), corresponding here to biased decoherence that suppresses the formation of large decohered clusters. As a second case study, we consider the toric code on a triangular lattice under external-field-type decoherence. Numerical results show that QLTEN faithfully captures the emergence of Higgs regions and the survival of logical qubits. Although global TEN, QLTEN clusters, and string operators are strongly correlated in both models, the color code and toric code respond differently to EP patterns. This difference indicates that a universal microscopic description of decoherence-induced topological phase transitions remains challenging even for closely related systems.
Figures
Figures from the paper (15 more)
Reference graph
Works this paper leans on
-
[1]
Explicitly, W rX (γc)≡ Y ℓ∈γc (XX) ℓ,(9) whereγ c is a closed loop on red links and(XX) ℓ stands for theXXoperator on the red linkℓ
Disorder parameter of 1-form symmetry We first consider the 1-form symmetry [3, 4], in particular the redX-1-form symmetry, whose charge is an arbitrary loop composite of redXXoperators. Explicitly, W rX (γc)≡ Y ℓ∈γc (XX) ℓ,(9) whereγ c is a closed loop on red links and(XX) ℓ stands for theXXoperator on the red linkℓ. It is not difficult to show thatW rX ...
-
[2]
For pure systems, TEE is believed to be a good measure, whereas it includes classical correlation as well for mixed states
Topological entanglement negativity Moving on, let us discuss the quantum entanglement prop- erty of the system. For pure systems, TEE is believed to be a good measure, whereas it includes classical correlation as well for mixed states. TEN was proposed as a measure of quantum entanglement, and recent studies indicate its utility. We employ TEN for the pr...
2026
-
[3]
As explained in the main text, we have to specify the shapes of the subsystemsA, B.C
Prescription of TEN and QLTEN We show the protocol for calculating TEN and QLTEN. As explained in the main text, we have to specify the shapes of the subsystemsA, B.C. Essential points are the same for the color code and the TC, whereas the color code (TC) is defined on the honeycomb (triangular) lattice. The first step is to construct a hexagonal complex...
-
[4]
5 and 12 [5, 20]
the finite-size scaling analysis In this subsection, we explain the finite-size scaling (FSS) analysis for the string data in Figs. 5 and 12 [5, 20]. We employ the following Ansatz, DX (Γ) =ℓ −ζF((p−p c)ℓ1/ν),(A1) whereℓ=|Γ|=length ofΓ,Fis a scaling function andνis the critical exponent. We tried to apply FSS to the variance of DX (Γ), but could not obtai...
-
[5]
Levin and X.-G
M. Levin and X.-G. Wen, Detecting topological order in a ground state wave function, Phys. Rev. Lett.96, 110405 (2006)
2006
-
[6]
Kitaev and J
A. Kitaev and J. Preskill, Topological entanglement entropy, Phys. Rev. Lett.96, 110404 (2006)
2006
-
[7]
D. Gaiotto, A. Kapustin, N. Seiberg, and B. Willett, General- ized global symmetries, Journal of High Energy Physics2015, 10.1007/jhep02(2015)172 (2015)
-
[8]
McGreevy, Generalized symmetries in condensed matter, An- nual Review of Condensed Matter Physics14, 57–82 (2023)
J. McGreevy, Generalized symmetries in condensed matter, An- nual Review of Condensed Matter Physics14, 57–82 (2023)
2023
Show all 45 references
-
[9]
Kataoka, Y
K. Kataoka, Y . Kuno, T. Orito, and I. Ichinose, Measurement- only circuit of perturbed toric code on triangular lattice: Topo- logical entanglement, 1-form symmetry, and logical qubits, Physical Review B113, 024111 (2026)
2026
-
[10]
Kataoka, Y
K. Kataoka, Y . Kuno, T. Orito, and I. Ichinose, Decohered color code and emerging mixed toric code by anyon prolifer- ation: Topological entanglement negativity perspective, arXiv preprint arXiv:2604.22521 (2026)
2026 arXiv
-
[11]
A. Y . Kitaev, Quantum computations: algorithms and error cor- rection, Russian Mathematical Surveys52, 1191 (1997)
1997
-
[12]
Kitaev, Fault-tolerant quantum computation by anyons, An- nals of Physics303, 2–30 (2003)
A. Kitaev, Fault-tolerant quantum computation by anyons, An- nals of Physics303, 2–30 (2003)
2003
-
[13]
Bombin and M
H. Bombin and M. A. Martin-Delgado, Topological quantum distillation, Phys. Rev. Lett.97, 180501 (2006)
2006
-
[14]
Bombin, R
H. Bombin, R. S. Andrist, M. Ohzeki, H. G. Katzgraber, and M. A. Martin-Delgado, Strong resilience of topological codes to depolarization, Phys. Rev. X2, 021004 (2012)
2012
-
[15]
Bomb ´ın, Gauge color codes: optimal transversal gates and gauge fixing in topological stabilizer codes, New Journal of Physics17, 083002 (2015)
H. Bomb ´ın, Gauge color codes: optimal transversal gates and gauge fixing in topological stabilizer codes, New Journal of Physics17, 083002 (2015)
2015
-
[16]
Yoshida, Topological color code and symmetry-protected topological phases, Phys
B. Yoshida, Topological color code and symmetry-protected topological phases, Phys. Rev. B91, 245131 (2015)
2015
-
[17]
Kubica, B
A. Kubica, B. Yoshida, and F. Pastawski, Unfolding the color code, New Journal of Physics17, 083026 (2015)
2015
-
[18]
M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, 10th ed. (Cambridge University Press, USA, 2011)
2011
-
[19]
Z. Wang, Z. Wu, and Z. Wang, Intrinsic mixed-state topological order, PRX Quantum6, 010314 (2025)
2025
-
[20]
Sohal and A
R. Sohal and A. Prem, Noisy approach to intrinsically mixed- state topological order, PRX Quantum6, 010313 (2025)
2025
-
[21]
Bombin, G
H. Bombin, G. Duclos-Cianci, and D. Poulin, Universal topo- logical phase of two-dimensional stabilizer codes, New Journal of Physics14, 073048 (2012)
2012
-
[22]
A. B. Aloshious and P. K. Sarvepalli, Local equivalence of qudit color codes and toric codes, Phys. Rev. A100, 012348 (2019)
2019
-
[23]
M. S. Kesselring, J. C. Magdalena de la Fuente, F. Thomsen, J. Eisert, S. D. Bartlett, and B. J. Brown, Anyon condensation and the color code, PRX Quantum5, 010342 (2024)
2024
-
[24]
Y . Kuno, T. Orito, and I. Ichinose, Intrinsic mixed-state topolog- ical order in a stabilizer system under stochastic decoherence: Strong-to-weak spontaneous symmetry breaking from a perco- lation point of view, Physical Review B111, 064111 (2025)
2025
-
[25]
Bu ˇca and T
B. Bu ˇca and T. Prosen, A note on symmetry reductions of the lindblad equation: transport in constrained open spin chains, New J. of Phys.14, 073007 (2012)
2012
-
[26]
V . V . Albert and L. Jiang, Symmetries and conserved quantities in lindblad master equations, Phys. Rev. A89, 022118 (2014)
2014
-
[27]
de Groot, A
C. de Groot, A. Turzillo, and N. Schuch, Symmetry protected topological order in open quantum systems, Quantum6, 856 (2022)
2022
-
[28]
This comes from the fact Tr(DrX ρD) = 0for anyp, as the decoherence does not expand stabilizer group
The strong 1-form symmetry is always SSB. This comes from the fact Tr(DrX ρD) = 0for anyp, as the decoherence does not expand stabilizer group
-
[29]
T.-C. Lu, T. H. Hsieh, and T. Grover, Detecting topological or- der at finite temperature using entanglement negativity, Phys. Rev. Lett.125, 116801 (2020)
2020
-
[30]
S. Sang, Y . Li, T. Zhou, X. Chen, T. H. Hsieh, and M. P. Fisher, Entanglement negativity at measurement-induced crit- icality, PRX Quantum2, 030313 (2021)
2021
-
[31]
Weinstein, Y
Z. Weinstein, Y . Bao, and E. Altman, Measurement-induced power-law negativity in an open monitored quantum circuit, Phys. Rev. Lett.129, 080501 (2022)
2022
-
[32]
B. Shi, X. Dai, and Y .-M. Lu, Entanglement negativity at the critical point of measurement-driven transition (2021), arXiv:2012.00040 [cond-mat.stat-mech]
2021 arXiv
-
[33]
Sharma, X
S. Sharma, X. Turkeshi, R. Fazio, and M. Dalmonte, Measurement-induced criticality in extended and long-range unitary circuits, SciPost Phys. Core5, 023 (2022)
2022
-
[34]
Y . Kuno, T. Orito, and I. Ichinose, Phase transition and evi- dence of fast-scrambling phase in measurement-only quantum circuits, Phys. Rev. B108, 094104 (2023)
2023
-
[35]
R. Fan, Y . Bao, E. Altman, and A. Vishwanath, Diagnostics of mixed-state topological order and breakdown of quantum mem- ory, PRX Quantum5, 10.1103/prxquantum.5.020343 (2024)
2024 doi
-
[36]
M. Li, J. Wang, and Y . Deng, Explosive percolation in finite dimensions, Physical Review Research6, 033319 (2024)
2024
-
[37]
Achlioptas, R
D. Achlioptas, R. M. D’souza, and J. Spencer, Explosive perco- lation in random networks, science323, 1453 (2009)
2009
-
[38]
K. G. Wilson, Confinement of quarks, Phys. Rev. D10, 2445 (1974)
1974
-
[39]
’t Hooft, On the phase transition towards permanent quark confinement, Nuclear Physics B138, 1 (1978)
G. ’t Hooft, On the phase transition towards permanent quark confinement, Nuclear Physics B138, 1 (1978)
1978
-
[40]
Botzung, M
T. Botzung, M. Buchhold, S. Diehl, and M. M ¨uller, Robust- ness and measurement-induced percolation of the surface code, 21 Journal of Physics A: Mathematical and Theoretical58, 205304 (2025)
2025
-
[41]
F. Ares, S. Murciano, and P. Calabrese, Entanglement asymme- try as a probe of symmetry breaking, Nature Communications 14, 2036 (2023)
-
[42]
Benini, P
F. Benini, P. Calabrese, M. Fossati, A. H. Singh, and M. Venuti, Entanglement asymmetry for higher and noninvertible symme- tries, arXiv preprint arXiv:2509.16311 (2025)
2025
-
[43]
A. G. Lamas, J. Gliozzi, and T. L. Hughes, Higher-form en- tanglement asymmetry and topological order, arXiv preprint arXiv:2510.03967 (2025)
2025 arXiv
-
[44]
Benini, E
F. Benini, E. Garc ´ıa-Valdecasas, and S. Vitouladitis, Higher- form entanglement asymmetry. part I. the limits of symmetry breaking, Journal of High Energy Physics2026, 202 (2026)
2026
-
[45]
Yang and C
M. Yang and C. H. Lee, Percolation-inducedPTsymmetry breaking, Phys. Rev. Lett133, 136602 (2024)
2024
Reviewed August 4, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.