Beyond Exact Recovery: Operational Success Probability and Sampling Cost for Approximate Quantum Optimization under Stochastic Uncertainty
Roberto Garrone
Abstract
Abstract Approximate optimization algorithms are commonly evaluated through exact optimum recovery or objective-space approximation, although these criteria need not coincide with the quality of the resulting decision in its downstream operating environment. This paper develops an end-to-end evaluation framework that separates three notions of solver success: exact recovery of the mathematical optimum, near-optimality with respect to the optimization surrogate, and operational acceptability under stochastic downstream evaluation. We study the framework using a small binary inventory-control benchmark represented by a calibrated and held-out-validated QUBO surrogate and solved with exact enumeration, greedy search, simulated annealing, uniform feasible sampling, and ideal QAOA at depths p=1,2,3. The results show that mathematical near-optimality and downstream operational acceptability define distinct solution sets. For QAOA, the probability mass assigned to operationally acceptable solutions can differ materially from both exact-recovery and QUBO-near-optimal probability, producing substantial differences in the number of measurements required to observe an acceptable solution. For n=8 at p=2, the median number of shots required for 95% observation probability decreases from 392 under exact recovery to 84 under QUBO near-optimality and 31 under the operational criterion. However, operational success alone can be misleading when acceptable states are abundant. We therefore use a descriptive enrichment comparison against uniform feasible sampling. Statistically supported enrichment is observed only in selected regimes, while classical greedy and simulated-annealing baselines outperform QAOA on these small instances. The results therefore do not indicate quantum advantage; rather, they show that solver evaluation can change materially when success is defined in terms of downstream decision consequences rather than surrogate-objective recovery alone. The QAOA statevector implementation and selected frozen confirmatory cases were independently reproduced with Qiskit and Qiskit Aer to floating-point precision.