Large-scale combinatorial and continuous optimisation problems remain intractable for classical algorithms as problem dimensionality scales. Quantum computing offers advantages through parallelism, amplitude amplification, and tunnelling, but practical realisation on near-term noisy intermediate-scale quantum (NISQ) devices demands careful algorithm design balancing advantage against noise resilience and circuit depth constraints. This paper presents the Quantum Optimisation Algorithm Suite (QOAS), a systematic framework across four algorithmic paradigms: Adaptive QAOA with dynamic depth scheduling; Variational Quantum Eigensolver (VQE) for QUBO problems; hybrid Quantum Annealing (QA); and Grover-enhanced Branch and Bound (GBB) for constrained integer programming. QOAS is benchmarked on five problem classes (MaxCut, TSP, Portfolio, Drug-Target, Feature Selection) across n = 12-84 qubits on IBM Quantum Eagle (127-qubit) and Falcon (27-qubit). Adaptive QAOA achieves approximation ratio 0.924 (SD = 0.018) for MaxCut at n = 48 -- outperforming standard QAOA (0.848) and Goemans-Williamson (0.878) at equivalent wall-clock time. GBB achieves 28.4x speedup over classical branch-and-bound for the n = 24 drug-target problem. QOAS provides systematic methodology for algorithm selection, circuit depth optimisation, and noise mitigation for NISQ workloads.
Large-scale combinatorial and continuous optimisation problems remain intractable for classical algorithms as problem dimensionality scales. Quantum computing offers advantages through parallelism, amplitude amplification, and tunnelling, but practical realisation on near-term noisy intermediate-scale quantum (NISQ) devices demands careful algorithm design balancing advantage against noise resilience and circuit depth constraints. This paper presents the Quantum Optimisation Algorithm Suite (QOAS), a systematic framework across four algorithmic paradigms: Adaptive QAOA with dynamic depth scheduling; Variational Quantum Eigensolver (VQE) for QUBO problems; hybrid Quantum Annealing (QA); and Grover-enhanced Branch and Bound (GBB) for constrained integer programming. QOAS is benchmarked on five problem classes (MaxCut, TSP, Portfolio, Drug-Target, Feature Selection) across n = 12-84 qubits on IBM Quantum Eagle (127-qubit) and Falcon (27-qubit). Adaptive QAOA achieves approximation ratio 0.924 (SD = 0.018) for MaxCut at n = 48 -- outperforming standard QAOA (0.848) and Goemans-Williamson (0.878) at equivalent wall-clock time. GBB achieves 28.4x speedup over classical branch-and-bound for the n = 24 drug-target problem. QOAS provides systematic methodology for algorithm selection, circuit depth optimisation, and noise mitigation for NISQ workloads.
Designing quantum algorithms that scale gracefully with problem size on NISQ devices -- maintaining useful approximation quality as qubit count, circuit depth, and noise accumulation increase -- remains the central engineering challenge of the NISQ era. Current variational quantum algorithms face two fundamental scalability barriers: barren plateaus (exponentially vanishing gradients that prevent training of deep parameterised circuits) and noise accumulation (gate errors compounding with circuit depth, degrading output fidelity). This paper proposes the Scalable NISQ Algorithm Design (SNAD) framework, a systematic methodology for designing quantum algorithms that remain effective as problem scale increases, comprising four design principles and associated algorithmic techniques: locality-structured ansatz design (LSAD) to avoid barren plateaus through geometric locality constraints; adaptive noise budget allocation (ANBA) distributing gate operations to maximise fidelity within noise constraints; circuit compression and synthesis (CCS) reducing circuit depth through gate cancellation and re-synthesis; and scalability-aware performance prediction (SAPP) using classical simulation to predict NISQ performance at target scale before hardware execution. SNAD is validated on QAOA and VQE circuits across n = 12-84 qubits on IBM Quantum Eagle and Falcon. LSAD eliminates barren plateaus for n up to 84 qubits, maintaining gradient magnitude > 10^-3 where standard random ansatz shows < 10^-8 at n=48. CCS reduces circuit depth by 28.4% (SD = 4.8%) for QAOA circuits on heavy-hex topology. ANBA improves approximation ratio by 6.4pp vs. uniform depth allocation under fixed noise budget. SAPP predicts NISQ approximation ratios with mean error 3.2% (SD = 1.4%) across 284 circuits.
The Quantum Approximate Optimisation Algorithm (QAOA) has emerged as a leading candidate for near-term quantum advantage in combinatorial optimisation, but most evaluations remain confined to synthetic benchmarks such as random MaxCut instances. Translating QAOA to real-world problem instances -- with irregular graph structures, heterogeneous constraint types, and practical scale requirements -- introduces additional challenges including QUBO formulation overhead, hardware embedding costs, and the performance gap between QAOA on structured real instances vs. random benchmarks. This paper presents the Real-World QAOA (RW-QAOA) framework, a systematic methodology for applying QAOA to four real-world application domains: supply chain network optimisation, financial portfolio rebalancing, telecommunications frequency assignment, and traffic signal timing optimisation. RW-QAOA introduces three methodological contributions: a domain-adaptive QUBO formulator (DAQF) encoding real-world constraints as penalised QUBO terms with penalty coefficient auto-tuning; a warm-start initialisation strategy (WSIS) using classical heuristic solutions to seed QAOA parameter search; and a layered noise adaptation protocol (LNAP) adjusting circuit depth based on real-time device calibration data. RW-QAOA is evaluated on real problem instances from industry partners across all four domains on IBM Quantum Eagle (127-qubit). RW-QAOA achieves solution quality within 4.2% of classical exact solvers across all four domains, outperforming classical greedy heuristics by 12.4% (SD = 3.8%) on average. WSIS reduces QAOA parameter convergence iterations by 48.4%. LNAP improves approximation ratio by 8.4pp vs. fixed-depth QAOA under device noise variation.
Claims of quantum advantage for combinatorial optimisation require rigorous comparison against state-of-the-art classical algorithms under controlled experimental conditions -- yet the quantum computing literature frequently benchmarks quantum methods against weak classical baselines such as greedy heuristics or random search, inflating apparent quantum advantage. This paper presents the Quantum-Classical Combinatorial Benchmark (QCCB), a rigorous comparative study of quantum optimisation algorithms (QAOA, VQE-QUBO, hybrid QA) against nine state-of-the-art classical algorithms (Goemans-Williamson SDP, simulated annealing, tabu search, CPLEX branch-and-bound, OR-Tools CP-SAT, Gurobi MIP, Benders decomposition, extremal optimisation, and population-based iterated local search) across six canonical combinatorial problem classes (MaxCut, Vertex Cover, Graph Colouring, Knapsack, Set Cover, and Weighted Max-SAT) at problem sizes n = 12 to n = 256. QCCB finds that no quantum algorithm consistently outperforms all classical baselines across all problem classes at current NISQ scale. QAOA with QOAS adaptive depth (Bianchi, 2024) outperforms all nine classical algorithms on MaxCut at n = 48 (approximation ratio 0.924 vs. GW 0.878). However, classical Gurobi MIP and CPLEX solve MaxCut exactly for n up to n = 84 within the same time budget, eliminating the QAOA advantage at moderate scale. QCCB provides nuanced guidance on problem classes, instance sizes, and time budgets where quantum algorithms offer genuine near-term advantage.
The quantum approximate optimization algorithm (QAOA) is an appealing proposal to solve NP problems on noisy intermediate-scale quantum (NISQ) hardware. Making NISQ implementations of the QAOA resilient to noise requires short ansatz circuits with as few controlled- () gates as possible. Here we present the dynamic adaptive quantum approximate optimization algorithm (Dynamic-ADAPT-QAOA). Our algorithm significantly reduces the circuit depth and the count of standard ADAPT-QAOA, a leading proposal for near-term implementations of the QAOA. Throughout our algorithm, the decision to apply -intensive operations is made dynamically, based on algorithmic benefits. Using density-matrix simulations, we benchmark the noise resilience of ADAPT-QAOA and Dynamic-ADAPT-QAOA. We compute the gate-error probability p gate ★ below which these algorithms provide, on average, more accurate solutions than the classical, polynomial-time approximation algorithm by Goemans and Williamson. For small systems with six to ten qubits, we show that p gate ★ > 10 − 3 for Dynamic-ADAPT-QAOA. Compared to standard ADAPT-QAOA, this constitutes an order-of-magnitude improvement in noise resilience. This improvement should make Dynamic-ADAPT-QAOA viable for implementations on superconducting NISQ hardware, even in the absence of error mitigation. Published by the American Physical Society 2024
This study presents a rigorous empirical evaluation of the Quantum Approximate Optimization Algorithm (QAOA) within a hybrid quantum-classical framework for solving the NP-hard Max-Cut problem. Using Python and Qiskit Aer statevector simulations, we benchmark QAOA (depths p = 2 and p = 3) against established classical algorithms, including simulated annealing, the Goemans–Williamson algorithm, and greedy heuristics, across Erdős–Rényi and regular graphs with 4 to 20 nodes (100 instances per size). Results demonstrate that low-depth QAOA suffers from significant performance degradation, achieving a 0.467 approximation ratio at 20 nodes compared to 0.856 for Goemans–Williamson, alongside a 210× runtime overhead. Convergence analysis further reveals low optimality probabilities and high iteration costs, highlighting limitations of variational optimization in NISQ-era devices. This work provides a reproducible benchmarking framework and contributes to a realistic assessment of near-term quantum advantage.
This paper presents a qualitative analysis of hybrid quantum-classical computing approaches aimed at solving complex optimization problems using near-term quantum processors. Hybrid algorithms leverage the strengths of quantum and classical computing to tackle computationally intensive tasks often constrained by current quantum hardware limitations. Through an extensive literature review and synthesis of recent empirical studies, we benchmark various hybrid algorithms, such as the Quantum Approximate Optimization Algorithm (QAOA) and Variational Quantum Eigensolver (VQE), focusing on their performance, scalability, and practical applicability on noisy intermediate-scale quantum (NISQ) devices. The study highlights the advantages, challenges, and future prospects of integrating hybrid quantum-classical computation in optimization domains, providing a comprehensive framework and qualitative insights into benchmarking methodologies and critical performance metrics.