REVIEW 1 major objections 5 minor 46 references
Continuously measuring local electric-flux and mass-density observables in a 1+1D Z2 lattice gauge theory yields no measurement-induced entanglement transition: the late-time entanglement entropy saturates to a value that does not grow with
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-02 17:00 UTC pith:EDTUAXS4
load-bearing objection Solid numerics, unsupported scaling claim: the paper asserts a size-independent saturation entropy without showing any system-size dependence data. the 1 major comments →
Dynamics of entanglement entropy for a locally monitored lattice gauge theory
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that in the no-click limit of the 1+1D Z2 gauge theory, projective measurements of local diagonal observables in the computational basis — the electric flux on each link and the staggered fermion number on each site — do not produce a measurement-induced phase transition. The evidence offered is that the late-time bipartite entanglement entropy, after early oscillations, saturates to a finite value, and this saturation value stays the same as the subsystem is placed in lattices of different size, for all measurement rates and couplings explored. The saturation value decreases monotonically with measurement strength and increases linearly with the gauge coupling x. Absent
What carries the argument
The engine is the no-click effective Hamiltonian H_eff = H0 - i γ H1, where H0 is the 1+1D Z2 gauge Hamiltonian and H1 is the measured observable — either the electric-flux operator τ^Z on links or the staggered mass-density operator on sites, with γ the measurement rate. This replaces random projective clicks with a deterministic imaginary potential, making the monitored dynamics non-unitary but tractable with matrix-product-state tensor networks. The entanglement entropy across the central bond, computed from Schmidt coefficients after time evolution, is the diagnostic: a phase transition would show up as a crossing between area-law and volume-law scaling of this entropy with subsystem siz
Load-bearing premise
The no-transition conclusion assumes that the flat late-time value seen by t=60 at L=64 is the true steady-state entropy and that it does not grow with lattice size; the paper presents no explicit scan of saturation entropy against system size to establish this.
What would settle it
Fix x=0.5 and γ=0.5 and compute the late-time bipartite entanglement entropy for L=32, 48, 64, 96, and 128 sites at T=60 and T=200, for both electric-flux and mass-density measurement. If the saturation value increases with L (linearly, logarithmically, or otherwise), or creeps upward between T=60 and T=200, the claimed system-size independence and the absence of an MIPT would be contradicted.
If this is right
- If correct, the monitored 1+1D Z2 gauge theory in the no-click limit sits in a single, area-law-like entanglement phase for local diagonal measurements, with no volume-to-area crossing to tune around.
- The saturation value of entanglement gives a practical cost bound: tensor-network simulations of gauged dynamics under local monitoring remain efficient because the bond dimension needed stays controlled.
- The quantum-Zeno behavior — earlier oscillations suppressed by larger γ — means measurement strength can be used as a smooth dial on late-time entanglement without triggering a phase transition.
- The result separates gauge-theory dynamics from unconstrained spin-chain monitored dynamics, where no-click models of the same type do exhibit volume-to-area transitions.
- It establishes a baseline against which future studies of nonlocal, stochastic, or non-Abelian monitoring in lattice gauge theories can be compared.
Where Pith is reading between the lines
- The paper's no-MIPT conclusion is limited to local diagonal observables and the no-click limit; a natural extension, not tested here, is whether measuring nonlocal string or plaquette operators, or including actual click outcomes in full quantum trajectories, restores a measurement-induced transition.
- The independence of the saturation entropy from system size, if it survives longer times and larger lattices, suggests that local measurements effectively act as a spatially uniform decoherence source in this gauge theory, which could be probed further with mutual-information or negativity measures rather than only bipartite von Neumann entropy.
- One practical implication the authors leave implicit: error-mitigation protocols for quantum simulators of Z2 gauge theories can safely add local measurements for state preparation or readout without expecting a critical slowdown in convergence.
- Because the claim rests on saturation at t=60 and L=64, the most direct testable extension is a systematic S_sat(L,T) scan at fixed x and γ, which would either confirm the plateau or reveal a slow multiplicative growth that the current data cannot exclude.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript studies the non-unitary ('no-click') dynamics of a 1+1D Z2 lattice gauge theory coupled to staggered fermions, under continuous projective monitoring of local diagonal observables (electric flux and staggered fermion density). The evolution is implemented with MPS and second-order TDVP, and the half-chain bipartite entanglement entropy is computed as a function of time, measurement rate γ, and coupling x. The paper reports that the entropy saturates at late times, that the saturation value decreases monotonically with γ, and that the saturation value is independent of system size, which is taken as evidence for the absence of a measurement-induced phase transition (MIPT) in the no-click limit. The numerical protocol is benchmarked against exact diagonalization for a small system, with stated bond-dimension convergence of 10^-8 and explicit verification of Gauss's law.
Significance. If the central scaling claim were established, this would be a valuable first exploration of measurement-induced entanglement dynamics in a lattice gauge theory, with potentially broad interest for quantum simulation of gauge theories. The paper's numerical care—benchmarking, Gauss-law verification, and a stated convergence criterion—is a strength. However, the manuscript's central conclusion is a negative scaling statement, and the evidence presented is currently limited to a single system size at a single final time. With an explicit system-size scan and a time-convergence check, the work could become a solid null-result contribution; as it stands, the main claim is not supported by the displayed data.
major comments (1)
- [Figs. 4(b), 5(b); Sec. 3 bullet 1] The four-parameter fits of S_sat(γ) are purely descriptive. No fit function, error bars, or uncertainty estimates are given, and no statistical or finite-size criterion is used to distinguish a smooth crossover from a phase transition. The claim that 'there is no MIPT' cannot be inferred from the monotonicity of S_sat(γ) at a single system size. The authors should define how S_sat is extracted (e.g., time-averaging window, extrapolation in t), show the L-dependence of these fits, and test for crossing or collapse behavior if a transition were present.
minor comments (5)
- [Eq. (4)] The operator H1 encoding the measured observable is not explicitly defined. For reproducibility, please give the explicit forms of the electric-flux and staggered-mass measurement operators used in the non-Hermitian evolution.
- [Fig. 6 caption] The caption says 'for different x=0.5 and L=64 with (a) γ=0.5 and (b) γ=1.5.' This appears to be a typo; presumably the panel varies x while fixing γ. Please correct.
- [Sec. 2.1] The paper fixes m/g=1 throughout and states in the Introduction that strong- and weak-coupling regimes are compared, but no mass-ratio scan is presented. If the conclusion is meant to hold beyond m/g=1, please state this limitation explicitly or provide supporting data.
- [Figs. 4(b), 5(b)] The figure captions list fit coefficients but do not show the fitted curve or residuals. Adding the fitted function and data points with error bars would make the fits and their interpretation transparent.
- [Throughout] There are several typographical issues (e.g., 'cleary' in Fig. 3 caption, inconsistent spacing). A careful proofread is recommended.
Circularity Check
No significant circularity: the no-MIPT claim is a direct numerical observation; the only self-citation is not load-bearing. Evidentiary gaps exist but do not constitute circularity.
full rationale
The paper's central claim — absence of an MIPT under local computational-basis measurements — is a numerical observation reported from MPS/TDVP time evolution (Section 3, Figs. 4-6), not a derived result, so there is no derivation chain that could reduce to its inputs. The four-parameter fits of S_sat(γ) in Figs. 4(b)/5(b) are descriptive only and are not used to infer system-size independence. The self-citation [42] (N. Chakrabarti, N. Nirbhan, A. Bhattacharyya, JHEP 2025) is cited solely as background that the no-click limit 'has been shown to exhibit MIPTs in spin-chain models [41,42]'; it does not supply the present no-MIPT conclusion, so it is not load-bearing. What remains is an evidentiary gap, not circularity: the abstract's system-size-independence claim is supported only by Section 3 bullet 3 ('We have exhaustively scanned over values of γ for fixed values of x, and vice versa. This remains robust'), and all displayed curves are for L=64 at t_sat=60, so the L-dependence of the steady-state entropy is asserted rather than exhibited. A finite-time saturation at t=60, or a slowly growing S_sat(L), would undermine the null result, but the claim does not reduce by construction to its inputs. The manuscript also labels itself 'preliminary results' in the introduction, further indicating that the scaling evidence is not yet fully presented.
Axiom & Free-Parameter Ledger
free parameters (3)
- m/g (fermion mass to gauge coupling ratio) =
1
- S_sat(gamma) fit coefficients a,b,c,d for electric-flux measurement =
a=0.9735, b=0.0358, c=0.0267, d=-0.9447
- S_sat(gamma) fit coefficients a,b,c,d for mass-density measurement =
a=-0.0032, b=1.6452, c=-0.0039, d=0.0301
axioms (5)
- domain assumption The no-click (no-jump) non-Hermitian evolution defined by H_eff = H0 - i gamma H1 and the normalized state in Eq. (5) faithfully represents monitored dynamics relevant for MIPTs.
- domain assumption Entanglement entropy of the half-chain at the central bond is the correct order parameter for an MIPT in this open-boundary, fixed-charge system.
- domain assumption The computational-basis local diagonal observables (electric flux and mass density) are the relevant measurement class for probing an MIPT.
- domain assumption MPS/TDVP with bond dimension up to chi=1000, time step delta=0.1, and T=60 gives converged dynamics sufficient to define late-time saturation.
- ad hoc to paper Fixing m/g=1 is a representative choice for the continuum limit, and the conclusions hold for other mass ratios.
read the original abstract
The $1+1$ dimensional $Z_2$ gauge theory is the simplest model that allows for quantum computation or quantum simulation to probe the fundamental aspects of a gauge theory coupled with dynamical fermions. To reliably benchmark such a system, it is crucial to understand the non-unitary quantum dynamics arising from the underlying non-Hermitian evolution and to model the effects of quantum measurements. In this work, we study post-selected filtering dynamics of physical observables for a $\mathbb {Z} _2$ gauge theory. Tensor network calculations are performed to dynamically probe entanglement entropy at larger lattice sizes. We report that projective measurement of local and diagonal observables (electric and mass energy densities) in the computational basis demonstrates the absence of any measurement-induced phase transition like phenomenon, as indicated by the system-size independence of the late-time saturation value of the bipartite entanglement entropy.
Figures
Reference graph
Works this paper leans on
-
[1]
Kogut,An introduction to lattice gauge theory and spin systems,Rev
J.B. Kogut,An introduction to lattice gauge theory and spin systems,Rev. Mod. Phys.51 (1979) 659
1979
-
[2]
Wegner,Duality in Generalized Ising Models and Phase Transitions without Local Order Parameters,Journal of Mathematical Physics12(1971) 2259
F.J. Wegner,Duality in Generalized Ising Models and Phase Transitions without Local Order Parameters,Journal of Mathematical Physics12(1971) 2259
1971
-
[3]
Fradkin and S.H
E. Fradkin and S.H. Shenker,Phase diagrams of lattice gauge theories with higgs fields, Phys. Rev. D19(1979) 3682
1979
-
[4]
Senthil and M.P.A
T. Senthil and M.P.A. Fisher,𝑍2 gauge theory of electron fractionalization in strongly correlated systems,Phys. Rev. B62(2000) 7850
2000
-
[5]
Lai and O.I
H.-H. Lai and O.I. Motrunich,Majorana spin liquids on a two-leg ladder,Phys. Rev. B84 (2011) 235148
2011
-
[6]
Zohar, J.I
E. Zohar, J.I. Cirac and B. Reznik,Quantum simulations of lattice gauge theories using ultracold atoms in optical lattices,Reports on Progress in Physics79(2015) 014401
2015
-
[7]
M. Kormos, M. Collura, G. Takács and P. Calabrese,Real-time confinement following a quantum quench to a non-integrable model,Nature Physics13(2017) 246 [1604.03571]
Pith/arXiv arXiv 2017
-
[8]
Smith, J
A. Smith, J. Knolle, D.L. Kovrizhin and R. Moessner,Disorder-free localization,Phys. Rev. Lett.118(2017) 266601
2017
-
[9]
Smith, J
A. Smith, J. Knolle, R. Moessner and D.L. Kovrizhin,Dynamical localization in𝑍2 lattice gauge theories,Phys. Rev. B97(2018) 245137
2018
-
[10]
Frank, E
J. Frank, E. Huffman and S. Chandrasekharan,Emergence of gauss’ law in a z2 lattice gauge theory in 1+1 dimensions,Physics Letters B806(2020) 135484
2020
-
[11]
Borla, R
U. Borla, R. Verresen, F. Grusdt and S. Moroz,Confined phases of one-dimensional spinless fermions coupled to𝑍2 gauge theory,Phys. Rev. Lett.124(2020) 120503
2020
-
[12]
Grusdt and L
F. Grusdt and L. Pollet,𝑍2 parton phases in the mixed-dimensional𝑡−𝐽𝑧 model,Phys. Rev. Lett.125(2020) 256401
2020
-
[13]
Surace, P.P
F.M. Surace, P.P. Mazza, G. Giudici, A. Lerose, A. Gambassi and M. Dalmonte,Lattice gauge theories and string dynamics in rydberg atom quantum simulators,Phys. Rev. X10 (2020) 021041. 8 Effects of measurements on entanglement dynamics for a lattice gauge theoryNisa Ara
2020
-
[14]
Bañuls et al.,Simulating Lattice Gauge Theories within Quantum Technologies,Eur
M.C. Bañuls et al.,Simulating Lattice Gauge Theories within Quantum Technologies,Eur. Phys. J. D74(2020) 165 [1911.00003]
Pith/arXiv arXiv 2020
-
[15]
Borla, R
U. Borla, R. Verresen, J. Shah and S. Moroz,Gauging the Kitaev chain,SciPost Phys.10 (2021) 148
2021
-
[16]
J.C. Halimeh, L. Homeier, C. Schweizer, M. Aidelsburger, P. Hauke and F. Grusdt, Stabilizing lattice gauge theories through simplified local pseudogenerators,Phys. Rev. Res. 4(2022) 033120 [2108.02203]
Pith/arXiv arXiv 2022
-
[17]
J. Mildenberger, W. Mruczkiewicz, J.C. Halimeh, Z. Jiang and P. Hauke,Confinement in a Z2 lattice gauge theory on a quantum computer,Nature Phys.21(2025) 312 [2203.08905]
arXiv 2025
- [18]
-
[19]
I.-C. Chen, J.C. Getelina, K. Pollock, A. Khindanov, S. Sen, Y.-X. Yao et al.,Classical and quantum simulations of 1+1-dimensionalZ2 gauge theory at finite temperature and density, Commun. Phys.8(2025) 375 [2407.11949]
Pith/arXiv arXiv 2025
-
[20]
Alexandrou, A
C. Alexandrou, A. Athenodorou, K. Blekos, G. Polykratis and S. Kühn,Realizing string breaking dynamics in a𝑍2 lattice gauge theory on quantum hardware,Phys. Rev. D112 (2025) 114506
2025
-
[21]
Casini, M
H. Casini, M. Huerta and J.A. Rosabal,Remarks on entanglement entropy for gauge fields, Phys. Rev. D89(2014) 085012
2014
-
[22]
Pichler, E
T. Pichler, E. Rico, M. Dalmonte, S. Montangero and P. Zoller,Real-time dynamics in lattice gauge theories with tensor networks,Physical Review X6(2016) 011023
2016
-
[23]
M.C. Bañuls, K. Cichy, J.I. Cirac, K. Jansen and S. Kühn,Tensor Networks and their use for Lattice Gauge Theories,PoSLATTICE2018(2018) 022 [1810.12838]
Pith/arXiv arXiv 2018
-
[24]
G. Magnifico, M. Dalmonte, P. Facchi, S. Pascazio, F.V. Pepe and E. Ercolessi,Real Time Dynamics and Confinement in theZ𝑛 Schwinger-Weyl lattice model for 1+1 QED,Quantum 4(2020) 281 [1909.04821]
Pith/arXiv arXiv 2020
-
[25]
E. Mathew, N. Gupta, S.V. Kadam, A. Bapat, J. Stryker, Z. Davoudi et al.,Tensor-network toolbox for probing dynamics of non-Abelian gauge theories,PoSLATTICE2024(2025) 472 [2501.18301]
Pith/arXiv arXiv 2025
-
[26]
Skinner, J
B. Skinner, J. Ruhman and A. Nahum,Measurement-induced phase transitions in the dynamics of entanglement,Phys. Rev. X9(2019) 031009
2019
-
[27]
Y. Li, X. Chen and M.P.A. Fisher,Quantum zeno effect and the many-body entanglement transition,Phys. Rev. B98(2018) 205136
2018
-
[28]
Y. Li, X. Chen and M.P.A. Fisher,Measurement-driven entanglement transition in hybrid quantum circuits,Phys. Rev. B100(2019) 134306. 9 Effects of measurements on entanglement dynamics for a lattice gauge theoryNisa Ara
2019
-
[29]
Chan, R.M
A. Chan, R.M. Nandkishore, M. Pretko and G. Smith,Unitary-projective entanglement dynamics,Phys. Rev. B99(2019) 224307
2019
-
[30]
Dalibard, Y
J. Dalibard, Y. Castin and K. Mølmer,Wave-function approach to dissipative processes in quantum optics,Phys. Rev. Lett.68(1992) 580
1992
-
[31]
Carmichael,Quantum trajectory theory for cascaded open systems,Phys
H.J. Carmichael,Quantum trajectory theory for cascaded open systems,Phys. Rev. Lett.70 (1993) 2273
1993
-
[32]
M.B. Plenio and P.L. Knight,The Quantum jump approach to dissipative dynamics in quantum optics,Rev. Mod. Phys.70(1998) 101 [quant-ph/9702007]
Pith/arXiv arXiv 1998
-
[33]
Davoudi, C.-C
Z. Davoudi, C.-C. Hsieh and S.V. Kadam,Scattering wave packets of hadrons in gauge theories: Preparation on a quantum computer,Quantum8(2024) 1520
2024
-
[34]
Mildenberger, W
J. Mildenberger, W. Mruczkiewicz, J.C. Halimeh, Z. Jiang and P. Hauke,Confinement in a Z2 lattice gauge theory on a quantum computer,Nature Physics21(2025) 312
2025
-
[35]
H.M. Wiseman and G.J. Milburn,Quantum Measurement and Control, Cambridge University Press (2009), https://doi.org/10.1017/CBO9780511813948
-
[36]
H. Carmichael,An open systems approach to quantum optics, Springer, Berlin, Germany (1993), 10.1007/978-3-540-47620-7
-
[37]
Gardiner and P
C. Gardiner and P. Zoller,Quantum noise, Springer Science & Business Media (2004)
2004
-
[38]
Daley,Quantum trajectories and open many-body quantum systems,Adv
A.J. Daley,Quantum trajectories and open many-body quantum systems,Adv. Phys.63 (2014) 77
2014
-
[39]
K. Jacobs,Quantum Measurement Theory and its Applications, Cambridge University Press (Aug., 2014), 10.1017/cbo9781139179027
-
[40]
Yamamoto, M
K. Yamamoto, M. Nakagawa, M. Tezuka, M. Ueda and N. Kawakami,Universal properties of dissipative tomonaga-luttinger liquids: Case study of a non-hermitian xxz spin chain, Phys. Rev. B105(2022) 205125
2022
-
[41]
Y.L. Gal, X. Turkeshi and M. Schirò,Volume-to-area law entanglement transition in a non-Hermitian free fermionic chain,SciPost Phys.14(2023) 138
2023
-
[42]
N. Chakrabarti, N. Nirbhan and A. Bhattacharyya,Dynamics of monitored SSH model in Krylov space: from complexity to quantum Fisher information,JHEP07(2025) 203 [2502.03434]
Pith/arXiv arXiv 2025
-
[43]
Fishman, S.R
M. Fishman, S.R. White and E.M. Stoudenmire,The ITensor Software Library for Tensor Network Calculations,SciPost Phys. Codebases(2022) 4
2022
-
[44]
I. Raychowdhury and J.R. Stryker,Loop, string, and hadron dynamics in SU(2) Hamiltonian lattice gauge theories,Phys. Rev. D101(2020) 114502 [1912.06133]. 10 Effects of measurements on entanglement dynamics for a lattice gauge theoryNisa Ara
Pith/arXiv arXiv 2020
- [45]
-
[46]
F. Ilčić, R. Majumdar, E. Mathew, M.O. Ali, N. Earnest-Noble and I. Raychowdhury, Observation of Robust and Coherent Non-Abelian Hadron Dynamics on Noisy Quantum Processors,2602.18080. 11
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.