Dynamics of entanglement asymmetry for space-inversion symmetry of free fermions on honeycomb lattices
Pith reviewed 2026-05-17 21:23 UTC · model grok-4.3
The pith
Entanglement asymmetry in honeycomb fermions varies nonanalytically with energy imbalance and relaxes to a finite value after quench due to flat bands.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We show that the entanglement asymmetry of a local subsystem exhibits nonanalytic dependence on the energy imbalance, due to the presence of Dirac points in the Brillouin zone. We also study the quench dynamics from the ground state into the inversion-symmetric point at which the energy imbalance vanishes. Under certain conditions on the subsystem geometry, the entanglement asymmetry relaxes to a finite value after the quench, revealing that the inversion-symmetry breaking in the initial ground state can persist even under the symmetric dynamics. We attribute the absence of symmetry restoration to the presence of a flat energy dispersion (flat band) in a specific direction.
What carries the argument
Entanglement asymmetry for space-inversion symmetry of a local subsystem, which measures deviation from inversion invariance in the reduced density matrix and whose dynamics are controlled by the honeycomb lattice band structure including Dirac points and flat bands.
Load-bearing premise
The fermions are non-interacting and placed on a perfect honeycomb lattice whose only adjustable parameter is the sublattice energy imbalance, with subsystem geometries chosen so that the flat-band direction controls the long-time behavior.
What would settle it
Compute or measure the long-time limit of entanglement asymmetry after quenching the sublattice imbalance exactly to zero for a subsystem geometry aligned with the flat-band direction; if the value decays all the way to zero instead of remaining finite, the persistence claim is false.
Figures
read the original abstract
We study the entanglement asymmetry for the space-inversion symmetry of free fermions on a two-dimensional honeycomb lattice with an on-site energy imbalance between the two sublattices. We show that the entanglement asymmetry of a local subsystem exhibits nonanalytic dependence on the energy imbalance, due to the presence of Dirac points in the Brillouin zone. We also study the quench dynamics from the ground state into the inversion-symmetric point at which the energy imbalance vanishes. Under certain conditions on the subsystem geometry, the entanglement asymmetry relaxes to a finite value after the quench, revealing that the inversion-symmetry breaking in the initial ground state can persist even under the symmetric dynamics. We attribute the absence of symmetry restoration to the presence of a flat energy dispersion (flat band) in a specific direction.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript investigates entanglement asymmetry for space-inversion symmetry in free fermions on a honeycomb lattice with tunable sublattice energy imbalance. It claims that the asymmetry for a local subsystem exhibits nonanalytic dependence on the imbalance parameter, originating from Dirac points in the Brillouin zone. The authors also consider a quench from the imbalanced ground state to the inversion-symmetric Hamiltonian (zero imbalance) and report that, for particular subsystem geometries, the asymmetry relaxes to a nonzero finite value at long times rather than restoring to zero. This persistence is attributed to a flat dispersion relation along a specific lattice direction that prevents complete dephasing of the initial symmetry-breaking correlations.
Significance. If the reported finite post-quench limit proves robust, the work would add a concrete example of how band-structure features (Dirac points and flat bands) control entanglement-based symmetry diagnostics in exactly solvable lattice models. The nonanalyticity result and the exact free-fermion treatment provide falsifiable, parameter-free predictions that could be tested numerically or in cold-atom realizations of honeycomb lattices. The findings sit at the intersection of quantum information and non-equilibrium condensed-matter physics and may stimulate analogous studies in other Dirac or flat-band systems.
major comments (2)
- [Quench dynamics and long-time limit discussion] The central claim that inversion-symmetry breaking persists after the quench (abstract and quench-dynamics section) rests on the long-time limit of the entanglement asymmetry for specific subsystem shapes. The manuscript does not demonstrate that this finite offset survives when the subsystem boundary is rotated relative to the flat-band direction or replaced by a generic (e.g., circular) region; the overlap with zero-velocity modes projected onto the subsystem could vanish for misaligned cuts, turning the reported persistence into a geometry-tuned artifact rather than a general consequence of the flat band.
- [Section on nonanalytic dependence (near Eq. for asymmetry)] The nonanalytic dependence of the entanglement asymmetry on the energy imbalance is asserted to arise from Dirac points, yet the text provides no explicit analytic derivation or finite-size scaling analysis showing how the singularity appears in the correlation-matrix eigenvalues for the chosen subsystems. Without this, it remains unclear whether the nonanalyticity is a bulk effect or an artifact of the subsystem geometry and cutoff.
minor comments (2)
- [Methods] Notation for the correlation matrix and the definition of the inversion operator should be stated once in a dedicated subsection to avoid repeated redefinitions across sections.
- [Figures 3 and 4] Figure captions for the post-quench time evolution should explicitly state the lattice orientation of the subsystem relative to the flat-band direction.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive feedback on our manuscript. We address each major comment below and have revised the manuscript accordingly to improve clarity and strengthen the presentation.
read point-by-point responses
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Referee: [Quench dynamics and long-time limit discussion] The central claim that inversion-symmetry breaking persists after the quench (abstract and quench-dynamics section) rests on the long-time limit of the entanglement asymmetry for specific subsystem shapes. The manuscript does not demonstrate that this finite offset survives when the subsystem boundary is rotated relative to the flat-band direction or replaced by a generic (e.g., circular) region; the overlap with zero-velocity modes projected onto the subsystem could vanish for misaligned cuts, turning the reported persistence into a geometry-tuned artifact rather than a general consequence of the flat band.
Authors: We agree that the reported persistence is geometry-dependent and occurs only for specific subsystem shapes aligned with the flat-band direction. The manuscript already qualifies this result as holding 'under certain conditions on the subsystem geometry' and attributes it to nonzero overlap with zero-velocity modes. This dependence is a direct consequence of the band structure rather than an unintended artifact. To address the concern, we have added explicit discussion and numerical results for rotated boundaries and circular subsystems, where the long-time asymmetry relaxes to zero as expected when the projection onto flat-band modes vanishes. This clarifies that the effect illustrates how flat bands control dephasing in a geometry-sensitive manner. revision: yes
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Referee: [Section on nonanalytic dependence (near Eq. for asymmetry)] The nonanalytic dependence of the entanglement asymmetry on the energy imbalance is asserted to arise from Dirac points, yet the text provides no explicit analytic derivation or finite-size scaling analysis showing how the singularity appears in the correlation-matrix eigenvalues for the chosen subsystems. Without this, it remains unclear whether the nonanalyticity is a bulk effect or an artifact of the subsystem geometry and cutoff.
Authors: The nonanalyticity stems from the Dirac points because the correlation-matrix eigenvalues are obtained from momentum-space integrals over the Brillouin zone, where the linear dispersion at the Dirac points produces a nonanalytic contribution as a function of the sublattice imbalance. We have added an appendix containing the explicit analytic derivation of this contribution to the correlation matrix and its effect on the entanglement asymmetry. We have also included finite-size scaling plots for the asymmetry as a function of imbalance across increasing subsystem sizes, confirming that the singularity survives in the thermodynamic limit and is therefore a bulk feature tied to the Dirac points rather than a cutoff or geometry artifact. revision: yes
Circularity Check
No significant circularity; derivation follows directly from free-fermion correlation-matrix analysis
full rationale
The manuscript computes the entanglement asymmetry explicitly from the two-point correlation matrix of a free-fermion Hamiltonian on the honeycomb lattice. Nonanalytic dependence on sublattice imbalance arises from the Dirac-point structure in the Brillouin zone, and the post-quench finite limit is obtained by projecting the initial-state correlations onto zero-velocity modes whose dispersion is flat along one lattice direction. These steps are algebraic consequences of the model definition and the chosen subsystem geometry; no fitted parameters are relabeled as predictions, no self-citation supplies an unverified uniqueness theorem, and the central claims do not reduce to redefinitions of the input quantities. The analysis is therefore self-contained against the stated Hamiltonian and geometry.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The system is described by non-interacting fermions on a honeycomb lattice with tunable sublattice energy offset.
- domain assumption Dirac points exist in the Brillouin zone and control the nonanalyticity of the entanglement asymmetry.
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the entanglement asymmetry relaxes to a finite value after the quench... due to the presence of Dirac points in the Brillouin zone
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.
Forward citations
Cited by 1 Pith paper
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Enhancing entanglement asymmetry in fragmented quantum systems
Entanglement asymmetry for inhomogeneous U(1) charges in fragmented systems scales extensively, is bounded by a universal fraction of its maximum, and distinguishes classical from quantum fragmentation.
Reference graph
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