REVIEW 4 major objections 5 minor 2 cited by
Enhancing NDAR with Delay-Gate-Induced Amplitude Damping
T0 review · 4 major / 5 minor · reviewed 2026-08-16 · deepseek-v4-flash
Pith's one-line read The paper claims that adding delay gates before measurement strengthens amplitude damping and improves NDAR's best solutions on MaxCut, with QAOA and random circuits performing similarly except on dense weighted instances.
desk verdict Delay-gate control of NDAR is a neat, honestly reported knob, but the central trend rests on one instance per graph class and should be read as a proof-of-concept rather than a general result. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The operational core is the bit-flip gauge transformation $P_y H P_y$, which changes the signs of the Hamiltonian's fields and couplings while preserving its spectrum. Under amplitude damping with $|0\cdots0\rangle$ as the assumed attractor, remapping the best sampled bitstring $y$ to the attractor means that the next iteration's samples concentrate around a higher-quality solution; the delay gate of duration $T_d$ controls how tightly they concentrate. The classical NDAR isolates the same mechanism by setting each bit to 0 with probability $q$, so $q$ plays the role of the damping strength. A supporting assumption is QAOA parameter concentration, which lets the authors fix one set of variational parameters across all NDAR iterations.
What would settle it
On the same device and MaxCut instance, run NDAR at 100 microseconds while measuring the Hamming-weight distribution of the sampled bitstrings each iteration: if EBest improves but the distribution does not shift toward lower Hamming weight, the stated amplitude-damping mechanism is wrong; conversely, if a 100-microsecond delay added to a purely dephasing channel never improves EBest/ESA over zero delay, the claim that delay-gate-induced damping is the cause fails.
Extended reading notes
Core claim
The central claim is that longer delay gates produce stronger amplitude damping, which concentrates measurement outcomes around the all-zeros attractor, and each NDAR gauge transformation remaps the current best solution to that attractor. Under a 100 microsecond delay, EBest/ESA reaches 0.926 on unweighted sparse MaxCut at 80 nodes; under 50 microseconds it reaches 0.908, and without a delay gate NDAR does not improve over iterations. For the fully connected weighted case, QAOA at 100 microseconds reaches 0.717 and at 50 microseconds reaches 0.619, with QAOA slightly outperforming random sampling at 50 microseconds. The similar QAOA and random-circuit trajectories on sparse graphs indicate that the damping-induced neighborhood, not the cost-encoded circuit, is doing most of the work; the classical NDAR result that larger bit-suppress probability q yields better solutions reinforces this interpretation by showing that Hamming-weight concentration around the attractor is the controlling mechanism.
Load-bearing premise
The argument presumes that inserting delay gates strengthens amplitude damping toward the all-zeros attractor fast enough that gauge remapping still focuses sampling on better solutions, rather than merely dephasing the circuit into useless noise; if the delay mostly adds decoherence without a directed Hamming-weight bias, the method's improvement would not follow.
Editorial extensions
If this is right
- If longer delay times genuinely strengthen NDAR, then a delay gate is a zero-cost exploitation dial: one can vary the exploration-exploitation balance without changing the circuit structure or variational parameters.
- Because random circuits match QAOA on sparse unweighted MaxCut, NDAR's gain on these problems does not require the sampler to encode the Hamiltonian; a classically simulable distance-biased sampler can reproduce much of it.
- Classical NDAR at 300 nodes reaching EBest/ESA around 0.955 suggests the same iterative remapping should remain effective beyond the roughly 100-qubit limit of current devices.
- The QAOA advantage seen on dense weighted MaxCut at 50 microseconds indicates that in harder landscapes, Hamiltonian-encoding exploration may raise the ceiling once damping is not so strong that it erases the circuit's information.
Reading between the lines
- An implicit consequence is that NDAR performance can be predicted from the radial distribution of samples in Hamming space, which means classical distance-biased samplers could be used to screen problem instances and delay settings before spending hardware time.
- A testable extension would replace the Bernoulli bit-suppress sampler with an explicit Hamming-distance-targeted sampler or an energy-weighted sampler; comparing these would separate the contribution of proximity to the attractor from the contribution of energy guidance.
- The authors hint at manually constructing attractor states; the classical results suggest that any bias concentrating samples near the current best, not necessarily amplitude damping, should drive the same local-search dynamics, which could be tested by applying NDAR to classical local-search neighborhoods with controlled radii.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a hardware-oriented enhancement of the Noise-Directed Adaptive Remapping (NDAR) method: inserting delay gates before measurement to strengthen amplitude damping noise and thereby steer sampling toward low-Hamming-weight states, which are assumed to be the noise attractor |0...0>. The authors report experiments on IBM's Heron processor for 80-node MaxCut problems in two settings, unweighted-sparse and fully connected weighted graphs, comparing single-layer QAOA and random circuits at delay times Td = 0, 50, and 100 microseconds. They report EBest/ESA values around 0.926(3) for the unweighted sparse case at Td = 100 us, with longer delays giving better trajectories, and a QAOA advantage over random circuits in the weighted dense case at Td = 50 us. They also introduce a classical NDAR variant that samples bits with bit-suppress probability q, showing that higher q (sharper concentration around the attractor) improves solution quality and extends the trend to 300-node instances. The central claim is that increasing delay time improves NDAR performance because stronger amplitude damping focuses sampling near the attractor state.
Significance. If the central claim holds, the paper makes a useful empirical contribution to the emerging line of work that exploits hardware noise rather than mitigating it. The delay-time knob is simple, hardware-relevant, and the comparison between QAOA and random circuits addresses a genuine question about whether problem information in the sampling circuit matters. The classical NDAR variant is a helpful conceptual bridge and provides a concrete, falsifiable baseline with a small number of parameters. The authors are also commendably transparent about limitations: they explicitly note that delay gates affect other noise channels, that parameter transferability may be harmed by noise, and that the classical algorithm is a baseline rather than a simulation of the quantum method. The main weakness is that the headline conclusion is supported by a very narrow empirical base: one graph instance per problem class on the quantum hardware.
major comments (4)
- [§IV-A, Fig. 1 and Fig. 4] The central claim stated in the abstract and in Section IV—that increasing delay time improves the best objective value—rests on a single graph instance per problem class. The 10 independent runs reported in Figs. 1 and 4 are repeated sampling runs on the same instance; they quantify shot noise and run-to-run device drift, not instance-to-instance variability. MaxCut landscapes vary substantially with graph realization even at fixed edge density, so the observed ordering Td = 100 us > Td = 50 us > Td = 0 us may be a property of the particular tested graphs. The authors should either restrict the claim to the tested instances or add multi-instance replication, ideally reporting the fraction of instances on which the delay-time ordering holds and the spread of EBest/ESA across instances.
- [§III, Algorithm 1] The mechanism attributed to the delay gate is amplitude damping toward the all-zeros attractor, but inserting a delay before measurement also increases dephasing, energy relaxation with a different T1/T2 ratio, and any time-dependent gate or measurement drift. The paper acknowledges in Section VI that 'the current delay-gate-induced approach inevitably affects other types of noise besides amplitude damping noise,' but this caveat sits in tension with the title and the causal claim in Section III. Without process characterization (for example, estimating the effective single-qubit channel or comparing with a calibrated amplitude-damping channel), the paper has not established that the observed improvement is specifically due to amplitude damping rather than to a generic reduction of coherence. At minimum, the authors should temper the mechanism language or provide direct evidence that the added delay acts predominantly as amplitude damping.
- [§IV-B, Figs. 5 and 6] The qualitative conclusions about the energy and Hamming-weight distributions—especially the claim that QAOA provides a 'more sophisticated exploration strategy' at Td = 50 us—are based on a single 'representative' run selected from ten runs, with no stated selection criterion. Figure 5 shows one run per configuration, and Figure 6 likewise shows one run per configuration. Because the underlying distributions fluctuate across runs, a hand-picked run can overstate or misstate the typical behavior. The authors should either specify a deterministic selection rule (e.g., the run closest to the mean trajectory) or show the spread across all ten runs for the key comparisons.
- [§IV-B, QAOA parameter setting] The QAOA circuits use fixed parameters optimized once on a noiseless MPS simulator for the original Hamiltonian, then applied unchanged across all NDAR iterations and all delay times. This is an intentional parameter-transfer strategy, and the paper correctly notes that re-optimization at each step was used in the earlier NDAR work [15]. However, the conclusion that 'QAOA outperforms random circuits' in the weighted dense case is sensitive to this choice: the fixed parameters may be poorly adapted to the noisy, delay-affected circuit, making the comparison unfair to QAOA or, conversely, making QAOA look better because its noise-biased output happens to align with the attractor. The authors should either re-optimize parameters per iteration (as in [15]) or explicitly test parameter transferability across Td values before drawing conclusions about the relative merit of QAOA as an exploration strategy.
minor comments (5)
- [Fig. 11 caption] The caption reads 'weighted MaxCut problem on a 300-node graph with edge density dedge ≈ 0.3', but the corresponding text in Section V-B describes the low-density unweighted MaxCut case. This is inconsistent and should be corrected.
- [Algorithm 2] The Require block lists nshots as the number of sampling shots, but line 3 of the pseudocode says 'Sample M bitstrings'; the variable M is not defined in Algorithm 2. Use nshots consistently.
- [§VI] The sentence 'This classical implementation samples solutions near the attractor state and iteratively refines refines it' contains a duplicated word 'refines'. Please fix the typo.
- [§V-B] The classical NDAR results are presented as evidence that 'quantum NDAR would work effectively even for larger problem instances', but the classical algorithm uses independent bit-suppression sampling and does not emulate the correlations or noise structure of the quantum circuit. The paper already says it is a baseline rather than a simulation, so the summary sentence in Section VI should be softened to avoid implying that the classical results validate quantum scaling.
- [§IV-B] The paper reports standard errors such as 0.926(3), but it does not report any statistical test for the ordering of Td values. A paired test across the 10 runs, or a statement that the standard errors make the ordering significant, would strengthen the claim.
Circularity Check
No significant circularity: the paper reports real-device experiments and an external-benchmarked classical baseline; no load-bearing self-citation or fitted prediction.
full rationale
The central claims are empirical rather than derived. The delay-time improvement is read off from device runs (Figs. 1 and 4) and compared against simulated annealing as an external baseline; no parameter is fitted to the target result, so no prediction reduces to its own input by construction. The attractor assumption |0...0> is taken from Maciejewski et al. [15], an external prior work, and it is an input assumption rather than a conclusion of this paper. The classical NDAR algorithm is explicitly defined by sampling with bit-suppress probability q; the observed ordering q=0.95 > q=0.90 > q=0.85 is an empirical finding and is not entailed by the definition of the sampler. The only self-affiliated citation, OpenJij [26], is used merely as a simulated annealing baseline and is not load-bearing. Concerns about generalization across problem instances would be a statistical or external-validity issue, not circularity.
Assumptions & free parameters
free parameters (6)
- QAOA angles gamma and beta =
unweighted: (-0.152, 2.041); weighted: (-0.171, 0.905)
- Delay time Td =
0, 50, 100 microseconds
- Bit-suppress probability q =
0.85, 0.90, 0.95
- Number of shots per iteration =
M=1000 (quantum); nshots=10^3 and 10^4 (classical)
- Maximum iteration count niter =
8 and 12 for 80-node quantum; 12/15 and 20/25 for classical
- MPS maximum bond dimension =
20
assumptions (5)
- domain assumption The noise attractor state under amplitude damping is |0...0>.
- domain assumption Delay gates of 50 and 100 microseconds strengthen amplitude damping without destroying all problem-relevant correlations before measurement.
- standard math Noiseless QAOA is invariant under bit-flip gauge transformations, so the same variational parameters remain optimal for the transformed Hamiltonian in the noiseless limit.
- domain assumption Parameter concentration continues to hold under hardware noise, so the noiseless-MPS-optimized QAOA parameters transfer across NDAR iterations.
- domain assumption High-quality MaxCut solutions tend to be close in Hamming distance to other high-quality solutions.
Cite this review
Pith. "Pith review of Enhancing NDAR with Delay-Gate-Induced Amplitude Damping." pith.science (2026). https://pith.science/paper/42UZ3VNU
@misc{pith2026250412628,
author = {Pith},
title = {Pith review of: Enhancing NDAR with Delay-Gate-Induced Amplitude Damping},
year = {2026},
howpublished = {\url{https://pith.science/paper/42UZ3VNU}},
note = {Machine review of arXiv:2504.12628}
}
abstract
The Noise-Directed Adaptive Remapping (NDAR) method utilizes amplitude damping noise to enhance the performance of quantum optimization algorithms. NDAR alternates between exploration by sampling solutions from the quantum circuit and exploitation by transforming the cost Hamiltonian by changing the signs of its terms. Both exploration and exploitation are important components in classical heuristic algorithm design. In this study, we examine how NDAR performance improves by adjusting the balance between these components. We control the degree of exploitation by varying the delay time to 0, 50, and $100~\mu\text{s}$, and investigate exploration strategies using two quantum circuits, QAOA and a random circuit, on IBM's Heron processor. Our results show that increasing delay time in NDAR improves the best objective value found in each iteration. In single-layer QAOA and random circuits applied to unweighted Max-Cut problem with low edge density, both exploration strategies yield similar objective value trajectories and provide competitive solution quality to simulated annealing for the 80-node problem. Their similar performance indicates that, in most cases, increasing amplitude damping noise via additional delay time results in information loss. On the other hand, QAOA outperforms random circuits in specific cases, such as positive-negative weighted Max-Cut on a fully connected graph. This suggests potential advantages of QAOA in more complex settings. We further develop a classical NDAR to better understand exploration strategies, demonstrating that controlling the Hamming weight distribution of sampled bitstrings yields higher quality solutions. This suggests that identifying suitable quantum circuits for exploration could enhance NDAR performance.
Figures
Figures from the paper (6 more)
Forward citations
Cited by 2 Pith papers
-
Quantum Approximate Optimization via Noise-Directed Adaptive Warm-Starting
Bitflip-gauge warm-start QAOA that aligns the ansatz with amplitude-damping noise improves 100-qubit Ising approximation ratios over non-gauge iterative warm-start at no extra circuit cost.
-
Noise-Directed Adaptive Remapping for Integer Optimization: from qubits to (encoded) qudits
NDAR, a heuristic that turns device noise into a resource, is generalized to integer-domain optimization; qudit-native encodings are argued to be the best fit because their all-zeros attractor is always feasible and t...
Reference graph
Works this paper leans on
-
[15]
Improving quantum approximate opti- mization by noise-directed adaptive remapping,
F. B. Maciejewski, J. Biamonte, S. Hadfield, and D. Venturelli, “Improving quantum approximate opti- mization by noise-directed adaptive remapping,” arXiv preprint, 2024. arXiv: 2404.01412 [quant-ph]
arXiv 2024
-
[1]
C. H. Papadimitriou and K. Steiglitz, Combinatorial Optimization: Algorithms and Complexity . Dover Pub- lications, 1998
work page 1998
-
[2]
Schrijver, Combinatorial Optimization: Polyhedra and Efficiency
A. Schrijver, Combinatorial Optimization: Polyhedra and Efficiency. Springer, 2003
work page 2003
-
[3]
Reducibility among combinatorial prob- lems,
R. M. Karp, “Reducibility among combinatorial prob- lems,” in Complexity of Computer Computations , 1972
work page 1972
-
[4]
M. R. Garey and D. S. Johnson, Computers and In- tractability: A Guide to the Theory of NP-Completeness. W.H. Freeman, 1979
work page 1979
-
[5]
M. Gendreau and J.-Y . Potvin, Eds., Handbook of Meta- heuristics (International series in operations research & management science), en, 3rd ed. Cham, Switzerland: Springer International Publishing, Oct. 2018
work page 2018
-
[6]
Metaheuristics in combinatorial optimization: Overview and conceptual comparison,
C. Blum and A. Roli, “Metaheuristics in combinatorial optimization: Overview and conceptual comparison,” ACM Computing Surveys , vol. 35, no. 3, pp. 268–308, 2003
work page 2003
-
[7]
A brief review of nature-inspired algorithms for opti- mization,
I. Fister, X.-S. Yang, I. F. Jr., J. Brest, and D. Fister, “A brief review of nature-inspired algorithms for opti- mization,” arXiv preprint arXiv:1307.4186 , 2013
arXiv 2013
Show all 30 references
-
[8]
Quantum algorithms: An overview,
A. Montanaro, “Quantum algorithms: An overview,” npj Quantum Information, vol. 2, p. 15 023, 2016
2016
-
[9]
A quantum approximate optimization algorithm,
E. Farhi, J. Goldstone, and S. Gutmann, “A quantum approximate optimization algorithm,” arXiv preprint ,
-
[10]
A review on quantum approximate optimization algorithm and its variants,
K. Blekos, D. Brand, A. Ceschini, et al. , “A review on quantum approximate optimization algorithm and its variants,” Physics Reports , vol. 1068, pp. 1–66, 2024, A review on Quantum Approximate Optimization Algorithm and its variants
2024
-
[11]
Chal- lenges and opportunities in quantum optimization,
A. Abbas, A. Ambainis, B. Augustino, et al. , “Chal- lenges and opportunities in quantum optimization,” en, Nat. Rev. Phys., vol. 6, no. 12, pp. 718–735, Oct. 2024
2024
-
[12]
Error mitigation for short-depth quantum circuits,
K. Temme, S. Bravyi, and J. M. Gambetta, “Error mitigation for short-depth quantum circuits,” Physical Review Letters, vol. 119, no. 18, p. 180 509, 2017
2017
-
[13]
Hybrid quantum-classical algorithms and quantum error mitiga- tion,
S. Endo, Z. Cai, S. C. Benjamin, and X. Yuan, “Hybrid quantum-classical algorithms and quantum error mitiga- tion,” Journal of the Physical Society of Japan , vol. 90, no. 3, p. 032 001, 2021
2021
-
[14]
Scalable mitigation of measurement errors on quantum computers,
P. D. Nation, R. A. Sauer, A. Lubinski, and K. Temme, “Scalable mitigation of measurement errors on quantum computers,” PRX Quantum , vol. 2, no. 4, p. 040 326, 2021
2021
-
[16]
A multilevel approach for solving large-scale qubo problems with noisy hybrid quantum approximate op- timization,
F. B. Maciejewski, B. G. Bach, M. Dupont, et al. , “A multilevel approach for solving large-scale qubo problems with noisy hybrid quantum approximate op- timization,” in 2024 IEEE High Performance Extreme Computing Conference (HPEC) , 2024, pp. 1–10
2024
-
[17]
R. S. Sutton and A. G. Barto, Reinforcement Learning: An Introduction. MIT Press, 1998
1998
-
[18]
On evolutionary ex- ploration and exploitation,
A. E. Eiben and C. A. Schippers, “On evolutionary ex- ploration and exploitation,” Fundamenta Informaticae , vol. 35, no. 1–4, pp. 35–50, 1998
1998
-
[19]
Beitrag zum Verst ¨andnis der magnetischen Erscheinungen in festen K ¨orpern,
W. Lenz, “Beitrag zum Verst ¨andnis der magnetischen Erscheinungen in festen K ¨orpern,” Z. Phys. , vol. 21, pp. 613–615, 1920
1920
-
[20]
Beitrag zur Theorie des Ferromagnetismus,
E. Ising, “Beitrag zur Theorie des Ferromagnetismus,” Z. Phys., vol. 31, pp. 253–258, 1925
1925
-
[21]
Parameter concentrations in quantum approximate op- timization,
V . Akshay, D. Rabinovich, E. Campos, and J. Biamonte, “Parameter concentrations in quantum approximate op- timization,” Phys. Rev. A , vol. 104, no. 1, p. L010401, Jul. 2021. arXiv: 2103.11976 [quant-ph]
2021 arXiv
-
[22]
For Fixed Control Parameters the Quantum Approximate Optimization Algorithm’s Objective Function Value Concentrates for Typical In- stances,
F. G. S. L. Brandao, M. Broughton, E. Farhi, S. Gut- mann, and H. Neven, “For Fixed Control Parameters the Quantum Approximate Optimization Algorithm’s Objective Function Value Concentrates for Typical In- stances,” Dec. 2018. arXiv: 1812.04170 [quant-ph]
2018 arXiv
-
[23]
The Quantum Approximate Optimization Algorithm and the Sherrington-Kirkpatrick Model at Infinite Size,
E. Farhi, J. Goldstone, S. Gutmann, and L. Zhou, “The Quantum Approximate Optimization Algorithm and the Sherrington-Kirkpatrick Model at Infinite Size,” Quantum, vol. 6, p. 759, Jul. 2022. arXiv: 1910.08187 [quant-ph]
2022 arXiv
-
[24]
M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information: 10th Anniversary Edition . Cambridge University Press, 2010
2010
-
[25]
Javadi-Abhari, M
A. Javadi-Abhari, M. Treinish, K. Krsulich, et al. , Quantum computing with Qiskit , 2024. arXiv: 2405 . 08810 [quant-ph]
2024
-
[26]
Openjij: Framework for the ising model and qubo , version 0.6.16, An open source software for the Ising model and quadratic unconstrained binary optimization (QUBO), Jij Inc., 2023
2023
-
[27]
Transfer learning of optimal QAOA parameters in combinatorial optimization,
J. A. Montanez-Barrera, D. Willsch, and K. Michielsen, “Transfer learning of optimal QAOA parameters in combinatorial optimization,” Feb. 2024. arXiv: 2402 . 05549 [quant-ph]
2024
-
[28]
Towards a universal QAOA protocol: Evidence of a scaling advan- tage in solving some combinatorial optimization prob- lems,
J. A. Montanez-Barrera and K. Michielsen, “Towards a universal QAOA protocol: Evidence of a scaling advan- tage in solving some combinatorial optimization prob- lems,” May 2024. arXiv: 2405.09169 [quant-ph]
2024 arXiv
-
[29]
Efficient Online Quantum Circuit Learning with No Upfront Training,
T. O’Leary, P. Czarnik, E. Pelofske, A. T. Sornborger, M. McKerns, and L. Cincio, “Efficient Online Quantum Circuit Learning with No Upfront Training,” Jan. 2025. arXiv: 2501.04636 [quant-ph]
2025
-
[2014]
arXiv: 1411.4028 [quant-ph]
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