Recognition: unknown
BBQ-mIS: a parallel quantum algorithm for graph coloring problems
Pith reviewed 2026-05-07 04:13 UTC · model grok-4.3
The pith
BBQ-mIS solves graph coloring by iteratively assigning colors to maximal independent sets extracted on quantum hardware while using branch-and-bound to limit the total colors.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
BBQ-mIS combines the natural representation of Maximum Independent Set problems onto the machine Hamiltonian with a Branch&Bound approach to identify a proper graph coloring. The graph representation emerges from qubit interactions, and the coloring is retrieved by iteratively assigning one color to a maximal set of independent vertices of the graph, still minimizing the number of colors with the Branch&Bound approach. Emulations on an IBM Power9-based cluster with MPI-enhanced parallelism show that the problem decomposition is effective in terms of graph coloring solutions quality.
What carries the argument
Iterative extraction of maximal independent sets from a quantum Hamiltonian that encodes graph vertices as qubits and their non-adjacencies as interactions, guided by classical branch-and-bound to minimize the total number of colors.
Load-bearing premise
The quantum hardware will reliably return good maximal independent sets for each decomposed subgraph and the branch-and-bound search will converge to near-minimal color counts without excessive classical cost.
What would settle it
Execute BBQ-mIS on physical Rydberg-atom hardware for standard benchmark graphs, then compare both the number of colors used and the solution quality against known optimal classical colorings and against the classical emulation results.
Figures
read the original abstract
Among the limitations of current quantum machines, the qubits count represents one of the most critical challenges for porting reasonably large computational problems, such as those coming from real-world applications, to the scale of the quantum hardware. In this regard, one possibility is to decompose the problems at hand and exploit parallelism over multiple size-limited quantum resources. To this purpose, we designed a hybrid quantum-classical algorithm, i.e., BBQ-mIS, to solve graph coloring problems on Rydberg atoms quantum machines. The BBQ-mIS algorithm combines the natural representation of Maximum Independent Set (MIS) problems onto the machine Hamiltonian with a Branch&Bound (BB) approach to identify a proper graph coloring. In the proposed solution, the graph representation emerges from qubit interactions (qubits represent vertexes of the graph), and the coloring is then retrieved by iteratively assigning one color to a maximal set of independent vertexes of the graph, still minimizing the number of colors with the Branch&Bound approach. We emulated real quantum hardware onto an IBM Power9-based cluster, with 32 cores/node and 256 GB/node, and exploited an MPI-enhanced library to implement the parallelism for the BBQ-mIS algorithm. Considering this use case, we also identify some technical requirements and challenges for an effective HPC-QC integration. The results show that our problem decomposition is effective in terms of graph coloring solutions quality, and provide a reference for applying this methodology to other quantum technologies or applications.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents BBQ-mIS, a hybrid quantum-classical algorithm for graph coloring on Rydberg-atom quantum hardware. It maps graph vertices to qubits and iteratively extracts maximal independent sets (MIS) from the Rydberg Hamiltonian to assign colors, using a classical Branch-and-Bound (BB) procedure to minimize the total number of colors. The algorithm is emulated on an IBM Power9 cluster with MPI parallelism; the authors conclude that the decomposition produces effective colorings and offers a template for other quantum technologies.
Significance. A validated hybrid decomposition that reliably produces proper colorings while controlling the number of colors could help scale combinatorial problems beyond current qubit limits on near-term Rydberg devices. The combination of hardware-native MIS with classical BB is a plausible direction, and the discussion of HPC-QC integration challenges is potentially useful. However, the absence of quantitative validation means the work currently functions more as a high-level proposal than a demonstrated advance.
major comments (3)
- [Abstract] Abstract: the assertion that 'the results show that our problem decomposition is effective in terms of graph coloring solutions quality' is unsupported by any numerical evidence. No chromatic numbers, approximation ratios, success probabilities, number of test instances, or comparisons to classical baselines (greedy, DSATUR, exact solvers) are reported, rendering the central claim unevaluable.
- [Emulation and results sections] Emulation and results sections: the classical emulation on the IBM Power9 cluster is described only at the level of hardware specifications (32 cores/node, 256 GB/node, MPI). No information is given on the simulation method (exact diagonalization, Monte-Carlo sampling, mean-field), the modeled Rydberg parameters (blockade radius, interaction graph, decoherence), graph sizes tested, or shot statistics. This directly undermines the claim that the observed solution quality would transfer to real hardware.
- [Algorithm description] Algorithm description: the iterative quantum-Hamiltonian MIS extraction plus BB is asserted to produce proper colorings while keeping the number of colors minimal, yet no argument or empirical check is supplied showing that each extracted set is guaranteed to be independent or that the BB search avoids suboptimal color counts. The weakest assumption identified by the stress-test therefore remains unaddressed.
minor comments (2)
- [Abstract] The acronym BBQ-mIS is introduced without expansion; a brief parenthetical definition would improve readability.
- [Discussion] The discussion of 'technical requirements and challenges for an effective HPC-QC integration' is mentioned but not elaborated; adding concrete examples (e.g., latency, data movement, or calibration overhead) would strengthen the reference value claimed in the abstract.
Simulated Author's Rebuttal
We thank the referee for the constructive and detailed feedback on our manuscript describing the BBQ-mIS algorithm. The comments correctly identify areas where additional quantitative support, technical details, and formal arguments are needed to strengthen the presentation. We address each major comment below and will incorporate the suggested improvements in a revised version of the manuscript.
read point-by-point responses
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Referee: [Abstract] Abstract: the assertion that 'the results show that our problem decomposition is effective in terms of graph coloring solutions quality' is unsupported by any numerical evidence. No chromatic numbers, approximation ratios, success probabilities, number of test instances, or comparisons to classical baselines (greedy, DSATUR, exact solvers) are reported, rendering the central claim unevaluable.
Authors: We agree that the abstract claim regarding solution quality lacks supporting numerical evidence in the current manuscript. The work focuses on the hybrid decomposition framework and its emulation on HPC resources, with only qualitative statements about coloring effectiveness. In the revision we will remove or qualify the unsupported assertion in the abstract. We will also add a dedicated results subsection reporting quantitative metrics on the tested instances, including achieved chromatic numbers, approximation ratios relative to known optima, success probabilities from the emulations, the number of graphs evaluated, and direct comparisons against classical baselines such as greedy coloring, DSATUR, and exact solvers where computationally feasible. revision: yes
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Referee: [Emulation and results sections] Emulation and results sections: the classical emulation on the IBM Power9 cluster is described only at the level of hardware specifications (32 cores/node, 256 GB/node, MPI). No information is given on the simulation method (exact diagonalization, Monte-Carlo sampling, mean-field), the modeled Rydberg parameters (blockade radius, interaction graph, decoherence), graph sizes tested, or shot statistics. This directly undermines the claim that the observed solution quality would transfer to real hardware.
Authors: The referee is right that the emulation description is limited to cluster specifications and does not detail the underlying simulation approach or hardware model. The current text emphasizes the MPI-parallel execution of the BBQ-mIS procedure but omits these parameters. In the revised manuscript we will expand the emulation section to specify: the classical simulation technique used to model the Rydberg MIS solver, the Rydberg parameters (blockade radius, interaction strengths, and any decoherence model), the range of graph sizes (vertex counts and densities) employed in the experiments, and the shot statistics or sampling procedure used to emulate quantum measurements. These additions will allow a clearer assessment of how the emulated results relate to actual Rydberg hardware. revision: yes
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Referee: [Algorithm description] Algorithm description: the iterative quantum-Hamiltonian MIS extraction plus BB is asserted to produce proper colorings while keeping the number of colors minimal, yet no argument or empirical check is supplied showing that each extracted set is guaranteed to be independent or that the BB search avoids suboptimal color counts. The weakest assumption identified by the stress-test therefore remains unaddressed.
Authors: We acknowledge that the manuscript does not supply an explicit argument or empirical validation that each extracted set is independent or that the Branch-and-Bound procedure systematically avoids suboptimal color counts. The algorithm relies on the Rydberg Hamiltonian to enforce independence via the blockade interaction and uses BB to prune the search for minimal colorings. In the revision we will add a new subsection (or appendix) that: (i) provides a short proof sketch showing independence is guaranteed by construction of the Hamiltonian (adjacent vertices cannot both be selected), (ii) reports empirical checks on small benchmark graphs where the obtained color counts are compared against known optimal chromatic numbers, and (iii) clarifies how the BB bounding mechanism prevents suboptimal solutions. We will also explicitly discuss the assumptions highlighted by the stress-test. revision: yes
Circularity Check
No circularity: BBQ-mIS hybrid algorithm and emulation results are independent of any internal fitting or self-referential definitions
full rationale
The paper presents a hybrid quantum-classical algorithm that maps graph coloring to iterative maximal independent set extraction via a Rydberg Hamiltonian, then applies classical branch-and-bound to minimize the number of colors. Effectiveness is asserted from the outcomes of a classical MPI emulation on an IBM Power9 cluster. No equations, parameters, or self-citations are shown that reduce the reported solution quality to quantities fitted or defined inside the paper; the central claim rests on the empirical behavior of the described procedure rather than any tautological reduction. The derivation chain combines standard MIS-to-Hamiltonian mappings with established classical search techniques and reports simulation results without internal circularity.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Maximum Independent Set problems can be naturally represented on Rydberg atom quantum machine Hamiltonians.
Reference graph
Works this paper leans on
-
[1]
Comparison of heuristic approaches to pci planning for quantum computers,
G. Barillaro, A. Boella, F. Gandino, M. G. Vakili, E. Giusto, G. Mondo, B. Montrucchio, A. Scarabosio, A. Scionti, O. Terzoet al., “Comparison of heuristic approaches to pci planning for quantum computers,” in2023 IEEE International Conference on Consumer Electronics (ICCE). IEEE, 2023, pp. 1–6
2023
-
[2]
Application of graph colouring to biological networks,
S. Khor, “Application of graph colouring to biological networks,”IET systems biology, vol. 4, no. 3, pp. 185–192, 2010
2010
-
[3]
Optical dipole traps for neutral atoms,
R. Grimm, M. Weidemüller, and Y . B. Ovchinnikov, “Optical dipole traps for neutral atoms,” inAdvances in atomic, molecular, and optical physics. Elsevier, 2000, vol. 42, pp. 95–170
2000
-
[4]
C. Dalyac, L. Henriet, E. Jeandel, W. Lechner, S. Perdrix, M. Porcheron, and M. Veshchezerova, “Qualifying quantum approaches for hard industrial optimization problems. a case study in the field of smart-charging of electric vehicles,”EPJ Quantum Technology, vol. 8, no. 1, May 2021. [Online]. Available: http://dx.doi.org/10.1140/epjqt/ s40507-021-00100-3 ...
-
[5]
Ultracold rubidium atoms excited to rydberg levels,
D. Ciampini, O. Morsch, and E. Arimondo, “Ultracold rubidium atoms excited to rydberg levels,”Journal of Atomic, Molecular, Condensed Matter and Nano Physics, vol. 2, no. 3, pp. 161–167, 2015
2015
-
[6]
Entanglement of neutral-atom qubits with long ground-rydberg coherence times,
C. Picken, R. Legaie, K. McDonnell, and J. Pritchard, “Entanglement of neutral-atom qubits with long ground-rydberg coherence times,”Quantum Science and Technology, vol. 4, no. 1, p. 015011, 2018
2018
-
[7]
Unit disk graphs,
B. N. Clark, C. J. Colbourn, and D. S. Johnson, “Unit disk graphs,”Discrete Mathematics, vol. 86, no. 1, pp. 165–177, 1990. [Online]. Available: https://www.sciencedirect.com/science/article/pii/ 0012365X9090358O
1990
-
[8]
Quantum optimization with arbitrary connectivity using rydberg atom arrays,
M.-T. Nguyen, J.-G. Liu, J. Wurtz, M. D. Lukin, S.-T. Wang, and H. Pichler, “Quantum optimization with arbitrary connectivity using rydberg atom arrays,”PRX Quantum, vol. 4, no. 1, feb 2023. [Online]. Available: https://doi.org/10.1103/2Fprxquantum.4.010316
-
[9]
Neural-powered unit disk graph embedding: qubits connectivity for some qubo problems,
C. Vercellino, P. Viviani, G. Vitali, A. Scionti, A. Scarabosio, O. Terzo, E. Giusto, and B. Montrucchio, “Neural-powered unit disk graph embedding: qubits connectivity for some qubo problems,” in2022 IEEE International Conference on Quantum Computing and Engineering (QCE), 2022, pp. 186–196
2022
-
[10]
The gurobi optimizer,
B. Bixby, “The gurobi optimizer,”Transp. Re-search Part B, vol. 41, no. 2, pp. 159–178, 2007
2007
-
[11]
Hybrid quantum investment optimization with minimal holding period,
S. Mugel, M. Abad, M. Bermejo, J. Sánchez, E. Lizaso, and R. Orús, “Hybrid quantum investment optimization with minimal holding period,” Scientific Reports, vol. 11, no. 1, p. 19587, 2021
2021
-
[12]
Sequential minimal optimization for quantum-classical hybrid algorithms,
K. M. Nakanishi, K. Fujii, and S. Todo, “Sequential minimal optimization for quantum-classical hybrid algorithms,”Physical Review Research, vol. 2, no. 4, p. 043158, 2020
2020
-
[13]
Multi-qubit entanglement and algorithms on a neutral-atom quantum computer,
T. Graham, Y . Song, J. Scott, C. Poole, L. Phuttitarn, K. Jooya, P. Eichler, X. Jiang, A. Marra, B. Grinkemeyeret al., “Multi-qubit entanglement and algorithms on a neutral-atom quantum computer,”Nature, vol. 604, no. 7906, pp. 457–462, 2022
2022
-
[14]
A ship motion forecasting approach based on empirical mode decomposition method hybrid deep learning network and quantum butterfly optimization algorithm,
M.-W. Li, D.-Y . Xu, J. Geng, and W.-C. Hong, “A ship motion forecasting approach based on empirical mode decomposition method hybrid deep learning network and quantum butterfly optimization algorithm,” Nonlinear dynamics, vol. 107, no. 3, pp. 2447–2467, 2022
2022
-
[15]
Pulse based Variational Quantum Optimal Control for hybrid quantum computing,
R. de Keijzer, O. Tse, and S. Kokkelmans, “Pulse based Variational Quantum Optimal Control for hybrid quantum computing,”Quantum, vol. 7, p. 908, Jan. 2023. [Online]. Available: https://doi.org/10.22331/ q-2023-01-26-908
2023
-
[16]
Mapping graph coloring to quantum annealing,
C. Silva, A. Aguiar, P. M. Lima, and I. Dutra, “Mapping graph coloring to quantum annealing,”Quantum Machine Intelligence, vol. 2, pp. 1–19, 2020
2020
-
[17]
Disorder-assisted graph coloring on quantum annealers,
A. Wieckowski, S. Deffner, and B. Gardas, “Disorder-assisted graph coloring on quantum annealers,”Physical Review A, vol. 100, no. 6, p. 062304, 2019
2019
-
[18]
Parameter tuning patterns for random graph coloring with quantum annealing,
O. Titiloye and A. Crispin, “Parameter tuning patterns for random graph coloring with quantum annealing,”PloS one, vol. 7, no. 11, p. e50060, 2012
2012
-
[19]
Constrained quantum annealing of graph coloring,
K. Kudo, “Constrained quantum annealing of graph coloring,”Physical Review A, vol. 98, no. 2, p. 022301, 2018
2018
-
[20]
Quantum annealing of the graph coloring problem,
O. Titiloye and A. Crispin, “Quantum annealing of the graph coloring problem,”Discrete Optimization, vol. 8, no. 2, pp. 376–384, 2011
2011
-
[21]
Planning for compilation of a quantum algorithm for graph coloring,
M. Do, Z. Wang, B. O’Gorman, D. Venturelli, E. Rieffel, and J. Frank, “Planning for compilation of a quantum algorithm for graph coloring,” arXiv preprint arXiv:2002.10917, 2020
-
[22]
Eigenvalues and the max-cut problem,
B. Mohar and S. Poljak, “Eigenvalues and the max-cut problem,” Czechoslovak Mathematical Journal, vol. 40, no. 2, pp. 343–352, 1990
1990
-
[23]
Quantum optimization for the graph coloring problem with space-efficient embedding,
Z. Tabi, K. H. El-Safty, Z. Kallus, P. Hága, T. Kozsik, A. Glos, and Z. Zimborás, “Quantum optimization for the graph coloring problem with space-efficient embedding,” in2020 IEEE International Conference on Quantum Computing and Engineering (QCE). IEEE, 2020, pp. 56–62
2020
-
[24]
Improved complexity of quantum oracles for ternary grover algorithm for graph coloring,
Y . Wang and M. Perkowski, “Improved complexity of quantum oracles for ternary grover algorithm for graph coloring,” in2011 41st IEEE International Symposium on Multiple-Valued Logic. IEEE, 2011, pp. 294–301
2011
-
[25]
Hybrid quantum-classical algorithms for approximate graph coloring,
S. Bravyi, A. Kliesch, R. Koenig, and E. Tang, “Hybrid quantum-classical algorithms for approximate graph coloring,”Quantum, vol. 6, p. 678, Mar
-
[26]
Available: https://doi.org/10.22331/q-2022-03-30-678
[Online]. Available: https://doi.org/10.22331/q-2022-03-30-678
-
[27]
Graph coloring using the reduced quantum genetic algorithm,
S. M. Ardelean and M. Udrescu, “Graph coloring using the reduced quantum genetic algorithm,”PeerJ Computer Science, vol. 8, p. e836, 2022
2022
-
[28]
T. R. Jensen and B. Toft,Graph coloring problems. John Wiley & Sons, 2011
2011
-
[29]
Finding a maximum independent set,
R. E. Tarjan and A. E. Trojanowski, “Finding a maximum independent set,”SIAM Journal on Computing, vol. 6, no. 3, pp. 537–546, 1977
1977
-
[30]
arXiv preprint arXiv:1811.11538
F. Glover, G. Kochenberger, and Y . Du, “A tutorial on formulating and using qubo models,”arXiv preprint arXiv:1811.11538, 2018
-
[31]
Exact algorithms for the graph coloring problem,
A. M. de Lima and R. Carmo, “Exact algorithms for the graph coloring problem,”Revista de Informática Teórica e Aplicada, vol. 25, no. 4, p. 57–73, Nov. 2018. [Online]. Available: https: //seer.ufrgs.br/index.php/rita/article/view/RITA_V ol25_Nr4_57
2018
-
[32]
An algorithm for the chromatic number of a graph,
N. Christofides, “An algorithm for the chromatic number of a graph,” The computer journal, vol. 14, no. 1, pp. 38–39, 1971
1971
-
[33]
On various algorithms for estimating the chromatic number of a graph,
J. Mitchem, “On various algorithms for estimating the chromatic number of a graph,”The Computer Journal, vol. 19, no. 2, pp. 182–183, 1976
1976
-
[34]
An upper bound for the chromatic number of a graph and its application to timetabling problems,
D. J. A. Welsh and M. B. Powell, “An upper bound for the chromatic number of a graph and its application to timetabling problems,”The Computer Journal, vol. 10, no. 1, pp. 85–86, 01 1967. [Online]. Available: https://doi.org/10.1093/comjnl/10.1.85
-
[35]
On eigenvalues and colorings of graphs. ii,
A. Hoffman and L. Howes, “On eigenvalues and colorings of graphs. ii,” Annals of the New York Academy of Sciences, vol. 175, pp. 238 – 242, 03 2007
2007
-
[36]
An inertial lower bound for the chromatic number of a graph,
C. Elphick and P. Wocjan, “An inertial lower bound for the chromatic number of a graph,”arXiv preprint arXiv:1605.01978, 2016
-
[37]
Lower bounds for the clique and the chromatic numbers of a graph,
C. Edwards and C. Elphick, “Lower bounds for the clique and the chromatic numbers of a graph,”Discrete Applied Mathematics, vol. 5, no. 1, pp. 51–64, 1983
1983
-
[38]
Enumerating maximal independent sets with applications to graph colouring,
J. M. Byskov, “Enumerating maximal independent sets with applications to graph colouring,”Operations Research Letters, vol. 32, no. 6, pp. 547–556, 2004
2004
-
[39]
Solving optimization problems with rydberg analog quantum computers: Realistic requirements for quantum advantage using noisy simulation and classical benchmarks,
M. F. Serret, B. Marchand, and T. Ayral, “Solving optimization problems with rydberg analog quantum computers: Realistic requirements for quantum advantage using noisy simulation and classical benchmarks,” Physical Review A, vol. 102, no. 5, p. 052617, 2020
2020
-
[40]
A Quantum Approximate Optimization Algorithm
E. Farhi, J. Goldstone, and S. Gutmann, “A quantum approximate optimization algorithm,”arXiv preprint arXiv:1411.4028, 2014
work page internal anchor Pith review arXiv 2014
-
[41]
H. Silvério, S. Grijalva, C. Dalyac, L. Leclerc, P. J. Karalekas, N. Shammah, M. Beji, L.-P. Henry, and L. Henriet, “Pulser: An open- source package for the design of pulse sequences in programmable neutral-atom arrays,”arXiv:2104.15044 [quant-ph], Jan. 2022
-
[42]
Quantum Computers for High-Performance Computing,
T. S. Humble, A. McCaskey, D. I. Lyakh, M. Gowrishankar, A. Frisch, and T. Monz, “Quantum Computers for High-Performance Computing,” IEEE Micro, vol. 41, no. 5, pp. 15–23, Sep. 2021
2021
-
[43]
Aquila: QuEra’s 256-qubit neutral-atom quantum computer,
J. Wurtz, A. Bylinskii, B. Braverman, J. Amato-Grill, S. H. Cantu, F. Huber, A. Lukin, F. Liu, P. Weinberg, J. Long, S.-T. Wang, N. Gemelke, and A. Keesling, “Aquila: QuEra’s 256-qubit neutral-atom quantum computer,” Jun. 2023
2023
-
[44]
QAOA and QAA to solve a QUBO problem,
“QAOA and QAA to solve a QUBO problem,” Jul. 2023
2023
-
[45]
Acceler- ating HPC With Quantum Computing: It Is a Software Challenge Too,
M. Schulz, M. Ruefenacht, D. Kranzlmuller, and L. B. Schulz, “Acceler- ating HPC With Quantum Computing: It Is a Software Challenge Too,” Computing in Science & Engineering, vol. 24, no. 4, pp. 60–64, Jul. 2022
2022
-
[46]
Adiabatic quantum computation,
T. Albash and D. A. Lidar, “Adiabatic quantum computation,”Reviews of Modern Physics, vol. 90, no. 1, p. 015002, 2018
2018
discussion (0)
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