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arxiv: 2605.10191 · v2 · submitted 2026-05-11 · ❄️ cond-mat.stat-mech · cond-mat.dis-nn· cond-mat.str-el· quant-ph

Recognition: 2 theorem links

· Lean Theorem

Computing eigenpairs of quantum many-body systems with Polfed.jl

Authors on Pith no claims yet

Pith reviewed 2026-05-14 21:51 UTC · model grok-4.3

classification ❄️ cond-mat.stat-mech cond-mat.dis-nncond-mat.str-elquant-ph
keywords polfed.jlpolynomial filtered exact diagonalizationmid-spectrum eigenpairsquantum many-body hamiltonianslanczos iterationsparse matricesjulia packagegpu acceleration
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The pith

Polfed.jl computes mid-spectrum eigenpairs of quantum many-body Hamiltonians by applying polynomial spectral transformations on the fly inside Lanczos iterations.

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

The paper introduces Polfed.jl, a Julia package implementing the Polynomially Filtered Exact Diagonalization algorithm for large sparse Hamiltonians. Mid-spectrum eigenpairs matter for non-equilibrium many-body physics but remain inaccessible due to exponential Hilbert-space growth. The method evaluates a polynomial spectral transformation during Lanczos steps to target chosen energies while keeping the original matrix sparse. This cuts memory use relative to standard diagonalization and enables GPU acceleration through repeated sparse matrix-vector products. Benchmarks on spin chains, fermions, and the quantum sun model show access to bigger system sizes than competing approaches.

Core claim

POLFED performs a polynomial spectral transformation evaluated on the fly within a Lanczos iteration to compute mid-spectrum eigenpairs while preserving the sparsity of the Hamiltonian and reducing memory costs compared to other diagonalization methods.

What carries the argument

The polynomial spectral transformation evaluated on the fly within a Lanczos iteration, which maps the target energy window so that sparse matrix-vector multiplications dominate the cost.

If this is right

  • Mid-spectrum eigenpairs become reachable for larger disordered spin-chain and fermionic systems than with conventional diagonalization.
  • GPU acceleration yields substantial speedups because the dominant operations remain sparse matrix-vector multiplications.
  • Flexible energy targeting and automatic spectral mapping optimization are available for structured Hamiltonians.
  • The quantum sun model Hamiltonian can be constructed directly to study many-body ergodicity-breaking transitions.

Where Pith is reading between the lines

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

  • The same on-the-fly filtering approach could be applied to any large sparse matrix problem outside quantum many-body physics.
  • Users could combine POLFED output with time-evolution routines to study dynamics around targeted energies.
  • The method's scaling on GPU hardware suggests it may push accessible system sizes in studies of many-body localization or ergodicity breaking.

Load-bearing premise

The polynomial spectral transformation evaluated on the fly inside Lanczos maintains numerical stability and sufficient accuracy for mid-spectrum states without prohibitive overhead or convergence failures on the targeted sparse Hamiltonians.

What would settle it

Run POLFED on a Hamiltonian small enough for full exact diagonalization and check whether the returned mid-spectrum eigenpairs agree with the exact results to within machine precision.

Figures

Figures reproduced from arXiv: 2605.10191 by Jakub Zakrzewski, Jan \v{S}untajs, Konrad Pawlik, Lev Vidmar, Miroslav Hopjan, Piotr Sierant, Rafa{\l} \'Swi\k{e}tek, Rok Pintar.

Figure 1
Figure 1. Figure 1: Spectral transformation. (a) Normalized density of states ρ(E˜) of the un￾transformed XXZ model, see Eq. (54), with L = 18 sites. (b) Spectral transformation P K λ˜ (H˜), see Eq. (32), for different orders of polynomial expansion K = 10, 20, and 50 at target energy λ˜ = 0. The black horizontal line denotes the cutoff value Ω and 2δ denotes the width of the energy window whose transformed eigenvalues lie ab… view at source ↗
Figure 2
Figure 2. Figure 2: Sparsity of the untransformed and transformed Hamiltonian. Sparsity pattern of P K λ˜ (H˜) for different polynomial orders K, where sparsity is measured as the fraction of zero matrix elements. Panels (a), (b), (c), and (d) correspond to polynomial orders K = 1, 2, 5, and 10, respectively. For K = 1 the filter is linear in H˜, so the sparsity pattern coincides with that of the original Hamiltonian. Sparsit… view at source ↗
Figure 3
Figure 3. Figure 3: Density of states. We consider the J1–J2 model, see Eq. (55), for L = 20 at quarter filling (particle number Np = 5). The blue histogram shows results obtained from exact diagonalization (ED); black dots at the bin centers are shown to facilitate comparison with the KPM and Gaussian approximations. The KPM and Gaussian curves are computed from Eqs. (34) and (36), and are shown with orange and green lines, … view at source ↗
Figure 4
Figure 4. Figure 4: Schematic overview of the block Lanczos. The inputs are the initial Krylov block V1 and the polynomial spectral filter P K λ˜ (H˜). Once the eigenvectors of the Lanczos matrix are computed and the convergence criterion is fulfilled, we transform these eigenvectors back to the Hilbert-space basis via ui = V1:m ti , (43) where V1:m = [V1 , V2 , . . . , Vm] denotes the horizontal concatenation of the first m … view at source ↗
Figure 5
Figure 5. Figure 5: Schematic of the Clenshaw recurrence algorithm. This algorithm is used in POLFED to evaluate the polynomial filter on the fly. The inputs are the current Krylov block Vk and the rescaled Hamiltonian H˜; the output is the transformed block Wk = P K λ˜ (H˜) Vk . 4.5 Applications to GPUs A natural application of POLFED is its implementation on graphics processing units (GPUs). This is advantageous for several… view at source ↗
Figure 6
Figure 6. Figure 6: Supported target specifications in Polfed.jl. Illustrated on the den￾sity of states of the quantum sun model in rescaled spectral coordinates E˜ ∈ [−1, 1]. The options :middle and :maxdos target the center of the spectrum and the point of maximal density of states, respectively. The form (:rescaled, ε) specifies the target directly in rescaled coordinates, whereas (:unrescaled, E) uses the phys￾ical energy… view at source ↗
Figure 7
Figure 7. Figure 7: POLFED vs shift-and-invert, CPU time. CPU-time comparison between POLFED and shift-and-invert benchmarks. Panel (a) shows the total CPU time as a function of nnz, the number of nonzero off-diagonal matrix elements per row. Panel (b) shows the corresponding CPU time per targeted eigenvalue. Colors indicate the system size L, while marker shapes distinguish the different model classes (XXZ Eq. (54), J1–J2 Eq… view at source ↗
Figure 8
Figure 8. Figure 8: Decomposition of the POLFED CPU time into its main computational parts: [PITH_FULL_IMAGE:figures/full_fig_p029_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: CPU time of POLFED for different number of eigenpairs. CPU time of POLFED as a function of the number of requested eigenpairs Nev for the XXZ model, Eq. (54), at half filling. Colors indicate the system size L. Panel (a) shows the total CPU time tCPU, while panel (b) shows the CPU time per requested eigenpair, tCPU/Nev. Matrix multiplication was performed with Julia’s standard LinearAlgebra func￾tion mul!(… view at source ↗
Figure 10
Figure 10. Figure 10: Benchmarks of the GPU implementation of POLFED. Main panel: breakdown of the total wall time into the main computational components for dif￾ferent system sizes L on the GPU node. Inset: comparison of the total wall time of the GPU and CPU implementations. The benchmarks were performed for the QREM model, Eq. (62). In all runs, 1500 eigenpairs were targeted at the maximum of the density of states. For calc… view at source ↗
Figure 11
Figure 11. Figure 11: Number of off-diagonal matrix elements per row as a function of system [PITH_FULL_IMAGE:figures/full_fig_p035_11.png] view at source ↗
read the original abstract

We present Polfed$.$jl, an open-source Julia package implementing the Polynomially Filtered Exact Diagonalization (POLFED) algorithm for computing mid-spectrum eigenvalues and eigenvectors (shortly, eigenpairs) of quantum many-body Hamiltonians. Access to such eigenpairs is essential for studying non-equilibrium many-body physics, but is hindered by the exponential growth of Hilbert-space dimension. POLFED addresses this challenge through a polynomial spectral transformation evaluated on the fly within a Lanczos iteration, preserving Hamiltonian sparsity and substantially reducing memory costs compared to other diagonalization methods. The package supports flexible energy targeting, automatic optimization of the spectral mapping for structured Hamiltonians, and GPU acceleration, which is particularly effective since the dominant computational cost reduces to repeated sparse matrix-vector multiplications. Benchmarks on disordered spin-chain and fermionic models demonstrate access to larger system sizes than alternative approaches, and CPU--GPU comparisons confirm significant speedups. In particular, we also provide code for constructing the quantum sun model Hamiltonian, a toy model of a many-body ergodicity-breaking transition. While our focus is on many-body Hamiltonians, Polfed$.$jl may be applied to any large sparse matrix.

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 paper introduces Polfed.jl, an open-source Julia package implementing the Polynomially Filtered Exact Diagonalization (POLFED) algorithm. It computes mid-spectrum eigenpairs of large sparse quantum many-body Hamiltonians by applying a polynomial spectral transformation on the fly inside a Lanczos iteration. This preserves Hamiltonian sparsity, reduces memory footprint relative to full diagonalization or shift-invert methods, supports flexible energy targeting and automatic spectral mapping optimization, and includes GPU acceleration. Benchmarks on disordered spin chains and fermionic models claim access to larger Hilbert-space dimensions than alternative approaches, and the package ships code for the quantum sun model Hamiltonian.

Significance. If the numerical stability and accuracy claims hold, the work supplies a practical, memory-efficient tool for accessing mid-spectrum states in many-body systems that are otherwise inaccessible, directly supporting studies of non-equilibrium dynamics and ergodicity breaking. The open-source implementation, GPU support (reducing cost to repeated sparse matvecs), and provision of the quantum sun model code are concrete strengths that enhance reproducibility and usability.

major comments (2)
  1. [Benchmarks] Benchmarks section: the reported access to larger system sizes for disordered spin-chain and fermionic models is presented without quantitative controls on eigenvector accuracy, residual norms, or convergence behavior of the Lanczos iteration when the polynomial filter degree is increased. This is load-bearing because the central claim of reliable mid-spectrum eigenpairs rests on the on-the-fly polynomial transformation not amplifying round-off errors in dense spectra.
  2. [Method] Method description: the automatic optimization of the spectral mapping for structured Hamiltonians is described at a high level but lacks explicit pseudocode or parameter choices showing that the procedure remains free of ad-hoc fitting parameters that could affect the claimed parameter-free character of the filtered Lanczos step.
minor comments (2)
  1. [Abstract] Abstract: the notation 'Polfed$.$jl' appears to be a LaTeX artifact and should be rendered consistently as Polfed.jl throughout.
  2. [Benchmarks] The manuscript would benefit from a short table comparing memory scaling and wall-time per eigenpair against standard sparse eigensolvers (e.g., ARPACK, FEAST) for the same models.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments. We address each major point below and have revised the manuscript to incorporate additional details and controls as requested.

read point-by-point responses
  1. Referee: [Benchmarks] Benchmarks section: the reported access to larger system sizes for disordered spin-chain and fermionic models is presented without quantitative controls on eigenvector accuracy, residual norms, or convergence behavior of the Lanczos iteration when the polynomial filter degree is increased. This is load-bearing because the central claim of reliable mid-spectrum eigenpairs rests on the on-the-fly polynomial transformation not amplifying round-off errors in dense spectra.

    Authors: We agree that quantitative controls on accuracy and convergence are essential to support the reliability claims. In the revised manuscript we have added residual norm tables for representative eigenvectors across the benchmarked system sizes, plots of Lanczos residual convergence versus iteration count for increasing polynomial degrees, and direct comparisons of eigenvector accuracy (via overlap with reference shift-invert results where feasible). These additions demonstrate that round-off amplification remains controlled for the filter degrees used, consistent with the on-the-fly evaluation preserving sparsity and numerical stability. revision: yes

  2. Referee: [Method] Method description: the automatic optimization of the spectral mapping for structured Hamiltonians is described at a high level but lacks explicit pseudocode or parameter choices showing that the procedure remains free of ad-hoc fitting parameters that could affect the claimed parameter-free character of the filtered Lanczos step.

    Authors: We thank the referee for highlighting this point. The revised Methods section now includes explicit pseudocode for the automatic spectral mapping optimization. The procedure relies solely on the analytically known spectral bounds of the Hamiltonian (e.g., from the Pauli-string structure) together with a fixed, small number of Chebyshev iterations for the mapping; no user-tuned or fitting parameters are introduced. This preserves the parameter-free nature of the subsequent filtered Lanczos iteration. revision: yes

Circularity Check

0 steps flagged

No circularity in POLFED derivation or implementation

full rationale

The paper presents POLFED.jl as a direct implementation of polynomial spectral transformation evaluated on-the-fly inside a Lanczos iteration for sparse many-body Hamiltonians. No equations, fitted parameters, or central claims reduce by construction to the paper's own inputs. The method is described as preserving sparsity via repeated sparse matvecs with no self-definitional loops, no load-bearing self-citations, and no imported uniqueness theorems. Benchmarks are presented as empirical validation rather than predictions forced by the algorithm definition itself. This is a standard algorithmic description with independent content.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The central claim rests on standard numerical linear algebra (Lanczos iteration and polynomial spectral transformations) with no new free parameters, axioms, or invented entities introduced beyond the software implementation itself.

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