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PreprintCC BY-NC-ND 4.0arXiv

Broken-Symmetry Reference States for Sample-Based Quantum Diagonalization with Near-DMRG Accuracy

  • Kunal Kumar
  • Tomonori Shirakawa
  • Boseong Kim
  • Ryo Wakizaka
  • Ikko Hamamura
  • Mitsuhisa Sato
  • Seiji Yunoki
  • Mario Motta
  • Hiroshi Horii
  • Yuri Kobayashi
Open at sourcePDFDOICite

Abstract

Sample-based quantum diagonalization (SQD) accuracy remains limited for strongly correlated systems like iron-sulfur clusters. This accuracy heavily depends on the mean-field reference state, which determines the sampling ansatz and configuration-recovery target. We extend the qcsc-prefect workflow to support a broken-symmetry unrestricted Hartree-Fock (BS-UHF) starting point, derived from atom-localized antiferromagnetic initial guesses. For the [Fe4S4(SCH3)4]2− cubane (54 electrons, 36 orbitals, 72 data qubits; 88 total qubits), this lowers the mean-field reference by ≈ 534 mHa relative to the Restricted Hartree-Fock (RHF) solution (-327.0809 vs. -326.5474 Ha). Combined with deep multi-step configuration recovery on ROQUO GPU nodes at subspace dimension d = 3 × 1010, we reach E = −327.235076 Ha. This is 4.3 mHa above the finite-D = 4000 DMRG value (-327.2393952 Ha) and ∼ 512−517 mHa below a previous same-active-space RHF-reference SQD calculation. Extrapolating to the d → ∞ limit via a Gaussian-in-log d fitting ansatz gives an asymptotic estimate E∞ = −327.244468 Ha ± 1.05 mHa, just 0.33 mHa above our discarded-weight-extrapolated DMRG estimate (ED→∞ = −327.244797 Ha ± 0.46 mHa), well within their combined 1σ uncertainty. We characterize the determinant-subspace composition driving convergence, show matching validation on [Fe2S2(SCH3)4]2−, and report multi-HPC execution on Fugaku, Miyabi-G, and ROQUO. We conclude that reference-state preparation, rather than subspace size alone, is a key driver of SQD energy accuracy under strong electronic correlation.

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Cite

BibTeXRIS
BibTeX
@misc{kumar2026brokensymmetry,
  title = {{Broken-Symmetry Reference States for Sample-Based Quantum Diagonalization with Near-DMRG Accuracy}},
  author = {Kunal Kumar and Tomonori Shirakawa and Boseong Kim and Ryo Wakizaka and Ikko Hamamura and Mitsuhisa Sato and Seiji Yunoki and Mario Motta and Hiroshi Horii and Yuri Kobayashi},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.04496},
  eprint = {2611.04496},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.04496},
  note = {CC BY-NC-ND 4.0},
}
RIS
TY  - UNPB
TI  - Broken-Symmetry Reference States for Sample-Based Quantum Diagonalization with Near-DMRG Accuracy
AU  - Kunal Kumar
AU  - Tomonori Shirakawa
AU  - Boseong Kim
AU  - Ryo Wakizaka
AU  - Ikko Hamamura
AU  - Mitsuhisa Sato
AU  - Seiji Yunoki
AU  - Mario Motta
AU  - Hiroshi Horii
AU  - Yuri Kobayashi
PY  - 2026
DA  - 2026/11/03
PB  - arXiv
DO  - 10.48550/arxiv.2611.04496
UR  - https://arxiv.org/abs/2611.04496
AB  - Sample-based quantum diagonalization (SQD) accuracy remains limited for strongly correlated systems like iron-sulfur clusters. This accuracy heavily depends on the mean-field reference state, which determines the sampling ansatz and configuration-recovery target. We extend the qcsc-prefect workflow to support a broken-symmetry unrestricted Hartree-Fock (BS-UHF) starting point, derived from atom-localized antiferromagnetic initial guesses. For the [Fe_4S_4(SCH_3)_4]^2− cubane (54 electrons, 36 orbitals, 72 data qubits; 88 total qubits), this lowers the mean-field reference by ≈ 534 mHa relative to the Restricted Hartree-Fock (RHF) solution (-327.0809 vs. -326.5474 Ha). Combined with deep multi-step configuration recovery on ROQUO GPU nodes at subspace dimension d = 3 × 10^10, we reach E = −327.235076 Ha. This is 4.3 mHa above the finite-D = 4000 DMRG value (-327.2393952 Ha) and ∼ 512−517 mHa below a previous same-active-space RHF-reference SQD calculation. Extrapolating to the d → ∞ limit via a Gaussian-in-log d fitting ansatz gives an asymptotic estimate E_∞ = −327.244468 Ha ± 1.05 mHa, just 0.33 mHa above our discarded-weight-extrapolated DMRG estimate (E_D→∞ = −327.244797 Ha ± 0.46 mHa), well within their combined 1σ uncertainty. We characterize the determinant-subspace composition driving convergence, show matching validation on [Fe_2S_2(SCH_3)_4]^2−, and report multi-HPC execution on Fugaku, Miyabi-G, and ROQUO. We conclude that reference-state preparation, rather than subspace size alone, is a key driver of SQD energy accuracy under strong electronic correlation.
ER  -