Recognition: unknown
Protein folding on a 64 qubit trapped-ion hardware via counterdiabatic quantum optimization
Pith reviewed 2026-05-07 13:15 UTC · model grok-4.3
The pith
Bias-field counterdiabatic optimization on 64 trapped-ion qubits produces lower-energy lattice protein configurations than random sampling.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
BF-DCQO uses low-energy samples from each round to define longitudinal fields that steer subsequent quantum evolutions on 46-61 qubit instances of 14-16 residue peptides. The resulting distributions improve over uniform random sampling, most noticeably in the contact variables. When these samples enter a consensus pipeline that enforces feasible backbone geometries, the hybrid workflow reaches the classical reference energy on multiple instances and outperforms the corresponding random-seeded pipeline.
What carries the argument
Bias-field digitized counterdiabatic quantum optimization (BF-DCQO), a non-variational feedback loop in which low-energy samples from one evolution round set longitudinal bias fields for the next round, paired with a consensus post-processing pipeline that combines quantum contact predictions and feasible backbone geometries.
If this is right
- Raw BF-DCQO samples already concentrate on lower energies than random sampling, particularly among residue-contact variables.
- The hybrid workflow reaches classical reference energies on multiple 14-16 residue instances encoded with up to five-body terms.
- Structured samples emerge at trapped-ion scales of 46-61 qubits for Hamiltonians that enforce both contact optimization and backbone constraints.
- The non-variational bias feedback mechanism avoids parameter optimization while still guiding the evolution toward better regions.
Where Pith is reading between the lines
- The same bias-feedback pattern could be tested on other dense combinatorial problems whose Hamiltonians contain long-range higher-order terms.
- Increasing the number of bias rounds might further narrow the sampled distribution before post-processing is applied.
- Hardware with native all-to-all connectivity, such as the reported barium ions, appears especially suited to the long-range interactions that appear in the lattice protein models.
Load-bearing premise
The consensus post-processing step that merges quantum contact information with feasible backbone geometries does not itself account for the reported energy improvements over random baselines.
What would settle it
Run the identical consensus post-processing pipeline on contact information drawn only from uniform random samples with no quantum data and check whether the final energies still reach the classical reference values reported for the BF-DCQO runs.
Figures
read the original abstract
We report the largest trapped-ion hardware demonstration of lattice protein-folding optimization to date, using bias-field digitized counterdiabatic quantum optimization (BF-DCQO) on a fully connected 64-qubit Barium development system similar to the forthcoming IonQ Tempo line. Six peptide sequences with 14-16 amino-acid residues are encoded using a coarse-grained tetrahedral lattice model, yielding higher-order spin-glass Hamiltonians with long-range interactions involving up to five-body terms and mapped to 46-61 qubits. The resulting instances are demanding for near-term quantum hardware because low-energy configurations must satisfy backbone-geometry constraints while optimizing dense residue-contact interactions. BF-DCQO uses a non-variational bias-feedback mechanism, where low-energy samples from each round define longitudinal fields that guide subsequent quantum evolutions. Across the studied instances, BF-DCQO shifts raw sampled energy distributions toward lower energies than uniform random sampling, with the strongest improvements appearing in residue-contact variables. To preserve this signal, we introduce a consensus-based post-processing pipeline that combines quantum-learned contact information with feasible backbone geometries. The resulting hybrid workflow reaches the classical reference energy in multiple instances and improves over the corresponding random-seeded pipeline. These results show that BF-DCQO can generate structured samples for dense protein-folding Hamiltonians at previously unexplored trapped-ion scales.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports the largest trapped-ion hardware demonstration to date of lattice protein-folding optimization, using bias-field digitized counterdiabatic quantum optimization (BF-DCQO) on a 64-qubit Barium system. Six 14-16 residue peptides are encoded as higher-order spin-glass Hamiltonians (up to five-body terms) on 46-61 qubits. BF-DCQO is shown to shift raw sampled energy distributions lower than uniform random sampling, with strongest gains in residue-contact variables. A consensus-based post-processing pipeline then merges quantum-learned contacts with feasible backbone geometries, enabling the hybrid workflow to reach classical reference energies in multiple instances and to outperform the corresponding random-seeded pipeline.
Significance. If the structured samples generated by BF-DCQO are shown to be the primary source of the observed gains rather than an artifact of the classical post-processing, the work would constitute a meaningful step toward applying counterdiabatic quantum optimization to dense, long-range combinatorial problems at previously inaccessible trapped-ion scales. The bias-feedback mechanism and the hybrid pipeline design could serve as templates for future quantum-classical solvers in protein folding and related spin-glass instances.
major comments (2)
- [Results / Methods (post-processing pipeline)] The central performance claims rest on the hybrid workflow (abstract and Results section). The manuscript does not present an ablation in which the identical consensus post-processing pipeline is applied to samples drawn from uniform random sampling (or from a classical heuristic) without any BF-DCQO input. Without this control, it remains unclear whether the reported improvements over the random-seeded baseline are driven by structure in the quantum samples or by the classical merging and geometry-enforcement steps.
- [Results (energy distributions)] The raw energy-distribution shifts attributed to BF-DCQO (abstract and Figure 2 or equivalent) are presented without reported statistical tests, error bars on the distribution means, or quantification of run-to-run variability across the multiple rounds of bias feedback. This weakens the claim that BF-DCQO systematically produces lower-energy samples than random sampling for the contact variables.
minor comments (2)
- [Methods (Hamiltonian encoding)] The mapping from the tetrahedral lattice model to the qubit Hamiltonian (including the treatment of five-body terms) is only sketched; an explicit equation or supplementary table listing the interaction coefficients for at least one instance would improve reproducibility.
- [Methods (BF-DCQO)] Notation for the bias fields and the feedback schedule is introduced without a compact summary table; readers must cross-reference multiple paragraphs to reconstruct the precise BF-DCQO protocol.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed comments. These have highlighted opportunities to strengthen the clarity and rigor of our presentation regarding the hybrid workflow and the evidence for BF-DCQO sample quality. We address each major comment below and will incorporate the suggested additions in the revised manuscript.
read point-by-point responses
-
Referee: [Results / Methods (post-processing pipeline)] The central performance claims rest on the hybrid workflow (abstract and Results section). The manuscript does not present an ablation in which the identical consensus post-processing pipeline is applied to samples drawn from uniform random sampling (or from a classical heuristic) without any BF-DCQO input. Without this control, it remains unclear whether the reported improvements over the random-seeded baseline are driven by structure in the quantum samples or by the classical merging and geometry-enforcement steps.
Authors: We acknowledge the value of this control. The manuscript already compares the full hybrid workflow (BF-DCQO samples plus consensus post-processing) against a random-seeded pipeline that applies the same consensus merging and geometry-enforcement steps. However, we agree that an explicit ablation applying the identical post-processing pipeline to purely uniform random samples (with no BF-DCQO input at any stage) would more cleanly isolate the contribution of structured quantum samples. We will add this ablation to the revised Results section, reporting the energies obtained when the consensus pipeline is seeded exclusively with random samples. This will allow direct comparison and confirm that the observed gains originate from the bias-feedback mechanism rather than the classical steps alone. revision: yes
-
Referee: [Results (energy distributions)] The raw energy-distribution shifts attributed to BF-DCQO (abstract and Figure 2 or equivalent) are presented without reported statistical tests, error bars on the distribution means, or quantification of run-to-run variability across the multiple rounds of bias feedback. This weakens the claim that BF-DCQO systematically produces lower-energy samples than random sampling for the contact variables.
Authors: We agree that the current presentation would benefit from greater statistical rigor. In the revised manuscript we will augment the energy-distribution analysis (Figure 2 and associated text) with error bars on the reported means, run-to-run standard deviations across the bias-feedback rounds, and appropriate statistical tests (e.g., two-sample t-tests or Wilcoxon rank-sum tests with p-values) comparing the BF-DCQO and uniform-random distributions for both total energy and the contact-variable subset. These additions will quantify the systematic shift and variability, thereby strengthening the evidence that BF-DCQO produces lower-energy samples than random sampling. revision: yes
Circularity Check
No significant circularity; iterative bias feedback compared to random baseline
full rationale
The derivation chain is self-contained. BF-DCQO bias fields are iteratively defined from prior-round low-energy samples, but the paper explicitly compares resulting energy distributions and post-processed outcomes against uniform random sampling under the identical consensus pipeline. This control prevents the final improvements from reducing to the inputs by construction. No equations equate a claimed prediction to a fitted parameter from the target data, and while the method likely cites prior author work on DCQO, the hardware demonstration at 46-61 qubits supplies independent empirical content. The post-processing is applied equally to quantum and random seeds, preserving the comparison.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
-
[1]
K. A. Dill and J. L. MacCallum, “The protein-folding problem, 50 years on,”Science, vol. 338, no. 6110, pp. 1042–1046, 2012. [Online]. Available: https://www.science.org/doi/abs/10.1126/science.1219021
-
[2]
Principles that govern the folding of protein chains,
C. B. Anfinsen, “Principles that govern the folding of protein chains,” Science, vol. 181, no. 4096, pp. 223–230, 1973. [Online]. Available: https://www.science.org/doi/abs/10.1126/science.181.4096.223
-
[3]
Finding low-energy conformations of lattice protein models by quantum annealing,
A. Perdomo-Ortiz, N. Dickson, M. Drew-Brook, G. Rose, and A. Aspuru-Guzik, “Finding low-energy conformations of lattice protein models by quantum annealing,”Scientific Reports, vol. 2, no. 1, p. 571,
-
[4]
Finding low-energy conformations of lattice protein models by quantum annealing
[Online]. Available: https://doi.org/10.1038/srep00571
-
[5]
Resource-efficient quantum algorithm for protein folding,
A. Robert, P. K. Barkoutsos, S. Woerner, and I. Tavernelli, “Resource-efficient quantum algorithm for protein folding,”npj Quantum Information, vol. 7, no. 1, p. 38, 2021. [Online]. Available: https://doi.org/10.1038/s41534-021-00368-4
-
[6]
Coarse-grained lattice protein folding on a quantum annealer,
T. Babej, C. Ing, and M. Fingerhuth, “Coarse-grained lattice protein folding on a quantum annealer,” 2018. [Online]. Available: https://arxiv.org/abs/1811.00713
-
[7]
Digitized-counterdiabatic quantum approximate optimization algorithm,
P. Chandarana, N. N. Hegade, K. Paul, F. Albarr ´an-Arriagada, E. Solano, A. del Campo, and X. Chen, “Digitized-counterdiabatic quantum approximate optimization algorithm,”Phys. Rev. Res., vol. 4, p. 013141, Feb 2022. [Online]. Available: https://link.aps.org/doi/10. 1103/PhysRevResearch.4.013141
2022
-
[8]
Protein folding with an all- to-all trapped-ion quantum computer,
S. V . Romero, A. G. Cadavid, P. Nika ˇcevi´c, E. Solano, N. N. Hegade, M. A. Lopez-Ruiz, C. Girotto, M. Yamada, P. K. Barkoutsos, A. Kaushik, and M. Roetteler, “Protein folding with an all- to-all trapped-ion quantum computer,” 2025. [Online]. Available: https://arxiv.org/abs/2506.07866
-
[9]
Peptide conformational sampling using the quantum approximate optimization algorithm,
S. Boulebnane, X. Lucas, A. Meyder, S. Adaszewski, and A. Montanaro, “Peptide conformational sampling using the quantum approximate optimization algorithm,”npj Quantum Information, vol. 9, no. 1, p. 70,
-
[10]
Available: https://doi.org/10.1038/s41534-023-00733-5
[Online]. Available: https://doi.org/10.1038/s41534-023-00733-5
-
[11]
Resource analysis of quantum algorithms for coarse-grained protein folding models,
H. Linn, I. Brundin, L. Garc ´ıa-´Alvarez, and G. Johansson, “Resource analysis of quantum algorithms for coarse-grained protein folding models,”Phys. Rev. Res., vol. 6, p. 033112, Jul 2024. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRevResearch.6.033112
-
[12]
Protein structure prediction with high degrees of freedom in a gate-based quantum computer,
J. V . Pamidimukkala, S. Bopardikar, A. Dakshinamoorthy, A. Kannan, K. Dasgupta, and S. Senapati, “Protein structure prediction with high degrees of freedom in a gate-based quantum computer,”Journal of Chemical Theory and Computation, vol. 20, no. 22, pp. 10 223–10 234, 11 2024. [Online]. Available: https://doi.org/10.1021/acs.jctc.4c00848
-
[13]
Quantum algorithm for protein structure prediction using the face-centered cubic lattice,
R.-H. Li, H. Doga, B. Raubenolt, S. Mostame, N. DiSanto, F. Cumbo, J. Joshi, H. Linn, M. Gaffney, A. Holden, V . Kulkarni, V . Chaudhary, K. M. M. Jr, A. A. Saki, T. Radivoyevitch, F. DiFilippo, J. Qin, O. Shehab, and D. Blankenberg, “Quantum algorithm for protein structure prediction using the face-centered cubic lattice,” 2025. [Online]. Available: http...
-
[14]
Efficient quantum protein structure prediction with problem-agnostic ansatzes,
H. Linn, R.-H. Li, A. Holden, A. A. Saki, F. DiFilippo, T. Radivoyevitch, D. Blankenberg, L. Garc ´ıa-´Alvarez, and G. Johansson, “Efficient quantum protein structure prediction with problem-agnostic ansatzes,”
-
[15]
Available: https://arxiv.org/abs/2509.18263
[Online]. Available: https://arxiv.org/abs/2509.18263
-
[16]
A Quantum Approximate Optimization Algorithm
E. Farhi, J. Goldstone, and S. Gutmann, “A quantum approximate optimization algorithm,” 2014. [Online]. Available: https://arxiv.org/abs/ 1411.4028
work page internal anchor Pith review arXiv 2014
-
[17]
A variational eigenvalue solver on a photonic quantum processor,
A. Peruzzo, J. McClean, P. Shadbolt, M.-H. Yung, X.-Q. Zhou, P. J. Love, A. Aspuru-Guzik, and J. L. O’Brien, “A variational eigenvalue solver on a photonic quantum processor,”Nature Communications, vol. 5, no. 1, p. 4213, 2014. [Online]. Available: https://doi.org/10. 1038/ncomms5213
2014
-
[18]
Stochastic properties of the frequency dynamics in real and synthetic power grids,
N. N. Hegade, X. Chen, and E. Solano, “Digitized counterdiabatic quantum optimization,”Phys. Rev. Res., vol. 4, p. L042030, Nov 2022. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRevResearch. 4.L042030
-
[19]
Minimizing irreversible losses in quantum systems by local counterdiabatic driving,
D. Sels and A. Polkovnikov, “Minimizing irreversible losses in quantum systems by local counterdiabatic driving,”Proceedings of the National Academy of Sciences, vol. 114, no. 20, pp. E3909–E3916,
-
[20]
Proceedings of the National Academy of Sciences120(33) (2023) https://doi.org/10.1073/pnas
[Online]. Available: https://www.pnas.org/doi/abs/10.1073/pnas. 1619826114
-
[21]
Floquet- engineering counterdiabatic protocols in quantum many-body systems,
P. W. Claeys, M. Pandey, D. Sels, and A. Polkovnikov, “Floquet- engineering counterdiabatic protocols in quantum many-body systems,” Phys. Rev. Lett., vol. 123, p. 090602, Aug 2019. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRevLett.123.090602
-
[22]
Bias-field digitized counterdiabatic quantum optimization,
A. G. Cadavid, A. Dalal, A. Simen, E. Solano, and N. N. Hegade, “Bias-field digitized counterdiabatic quantum optimization,” Phys. Rev. Res., vol. 7, p. L022010, Apr 2025. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRevResearch.7.L022010
-
[23]
Bias-field digitized counterdiabatic quantum algorithm for higher-order binary optimization,
S. V . Romero, A.-M. Visuri, A. G. Cadavid, A. Simen, E. Solano, and N. N. Hegade, “Bias-field digitized counterdiabatic quantum algorithm for higher-order binary optimization,”Communications Physics, vol. 8, no. 1, p. 348, 2025. [Online]. Available: https: //doi.org/10.1038/s42005-025-02270-3
-
[24]
Experimental comparison of two quantum computing architectures,
N. M. Linke, D. Maslov, M. Roetteler, S. Debnath, C. Figgatt, K. A. Landsman, K. Wright, and C. Monroe, “Experimental comparison of two quantum computing architectures,”Proceedings of the National Academy of Sciences, vol. 114, no. 13, pp. 3305–3310, 2017
2017
-
[25]
S. Miyazawa and R. L. Jernigan, “Estimation of effective interresidue contact energies from protein crystal structures: quasi-chemical approximation,”Macromolecules, vol. 18, no. 3, pp. 534–552, 03 1985. [Online]. Available: https://doi.org/10.1021/ma00145a039
-
[26]
T. U. Consortium. (2025) Masti polpi (polybia-mastoparan-i), *polybia paulista* — uniprotkb entry p0c1q4. Protein evidence at protein level; 14 amino acids; antimicrobial and chemotactic peptide for polymorphonucleated leukocytes. :contentReference[oaicite:0]index=0. [Online]. Available: https://www.uniprot.org/uniprotkb/P0C1Q4/entry
2025
-
[27]
10 structure ensemble of the 14-residue peptide rg-kwty-ng-itye-gr (mbh12) (pdb id: 1k43),
M. T. Pastor, M. Lopez de la Paz, E. Lacroix, L. Serrano, and E. Perez-Paya, “10 structure ensemble of the 14-residue peptide rg-kwty-ng-itye-gr (mbh12) (pdb id: 1k43),” 2001, pDB entry 1K43. [Online]. Available: https://www.rcsb.org/structure/1K43
2001
-
[28]
Mapping the orientation of helices in micelle-bound peptides by paramagnetic relaxation waves,
M. Respondek, T. Madl, C. Goebl, R. Golser, and K. Zangger, “Mapping the orientation of helices in micelle-bound peptides by paramagnetic relaxation waves,”Journal of the American Chemical Society, vol. 129, no. 17, pp. 5228–5234, 2007, pDB entry: 2JMY; method: solution NMR; CM15 in DPC micelles; 15 residues
2007
-
[29]
T. U. Consortium. (2025) Tissue transglutaminase (tgm2), homo sapiens (human) — uniprotkb entry q9bxq0. UniProtKB/Swiss- Prot; entry version 205 (updated 2025-07-01). [Online]. Available: https://www.uniprot.org/uniprotkb/Q9BXQ0/entry
2025
-
[30]
(2025) Mitochondrial-derived peptide mots-c (mt-rnr1), homo sapiens (human) — uniprotkb entry a0a0c5b5g6
——. (2025) Mitochondrial-derived peptide mots-c (mt-rnr1), homo sapiens (human) — uniprotkb entry a0a0c5b5g6. UniProtKB/Swiss- Prot; entry version 29 (updated 2025-06-18). [Online]. Available: https://www.uniprot.org/uniprotkb/A0A0C5B5G6/entry
2025
-
[31]
Nmr structure ofvg16krkp, an antimicrobial peptide in lipopolysaccharide (lps),
A. Bhunia, A. Datta, C. Airoldi, P. Sperandeo, K. H. Mroue, J. Jimenez- Barbero, P. Kundu, and A. Ramamoorthy, “Nmr structure ofvg16krkp, an antimicrobial peptide in lipopolysaccharide (lps),”Scientific Reports, vol. 5, p. 11951, 2015, pDB entry: 2MWL; method: solution NMR; submitted 2014-11-13; released 2014-12-24; latest revision May 15, 2024
2015
-
[32]
A. G. Cadavid, I. Montalban, A. Dalal, E. Solano, and N. N. Hegade, “Efficient digitized counterdiabatic quantum optimization algorithm within the impulse regime for portfolio optimization,”Phys. Rev. Appl., vol. 22, p. 054037, Nov 2024. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRevApplied.22.054037
-
[33]
doi:10.22331/q-2024-11-07-1516 , url =
J.-S. Chen, E. Nielsen, M. Ebert, V . Inlek, K. Wright, V . Chaplin, A. Maksymov, E. P ´aez, A. Poudel, P. Maunz, and J. Gamble, “Benchmarking a trapped-ion quantum computer with 30 qubits,” Quantum, vol. 8, p. 1516, Nov. 2024. [Online]. Available: https: //doi.org/10.22331/q-2024-11-07-1516
-
[34]
Scalable multispecies ion transport in a grid-based surface-electrode trap,
R. D. Delaney, L. R. Sletten, M. J. Cich, B. Estey, M. I. Fabrikant, D. Hayes, I. M. Hoffman, J. Hostetter, C. Langer, S. A. Moses, A. R. Perry, T. A. Peterson, A. Schaffer, C. V olin, G. Vittorini, and W. C. Burton, “Scalable multispecies ion transport in a grid-based surface- electrode trap,”Phys. Rev. X, vol. 14, p. 041028, Nov 2024. [Online]. Availabl...
-
[35]
Doppler- free, multiwavelength acousto-optic deflector for two-photon addressing arrays of Rb atoms in a quantum information processor,
S. Kim, R. R. McLeod, M. Saffman, and K. H. Wagner, “Doppler- free, multiwavelength acousto-optic deflector for two-photon addressing arrays of Rb atoms in a quantum information processor,”Appl. Opt., vol. 47, no. 11, pp. 1816–1831, Apr. 2008
2008
-
[36]
Compact Ion-Trap Quantum Computing Demonstrator,
I. Pogorelov, T. Feldker, C. D. Marciniak, L. Postler, G. Jacob, O. Krieglsteiner, V . Podlesnic, M. Meth, V . Negnevitsky, M. Stadler et al., “Compact Ion-Trap Quantum Computing Demonstrator,”PRX Quantum, vol. 2, no. 2, p. 020343, Jun. 2021
2021
-
[37]
Enhancing quantum computer performance via symmetrization,
A. Maksymov, J. Nguyen, Y . Nam, and I. Markov, “Enhancing quantum computer performance via symmetrization,” 2023. [Online]. Available: https://arxiv.org/abs/2301.07233
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.