Testing quantum software is challenging because quantum states cannot be directly inspected. Variational quantum algorithms (VQAs) are a particularly important target as they are among the most promising approaches for near-term noisy quantum hardware. Many testing methods rely on classically computed results, which conflicts with the regime where quantum advantage is expected. Although prior studies mitigate this oracle problem, the core difficulty remains that existing approaches do not verify whether the execution deviates from the intended problem or whether the obtained solution is physically plausible. We propose a symmetry-oriented testing framework for VQAs that addresses this gap by using operators commuting with the target Hamiltonian as test specifications. The framework provides two complementary diagnostics: a commutator-based health check that monitors whether each execution step during optimization remains consistent with the symmetry of the target Hamiltonian, and a variance-based acceptance check that assesses the converged solution by examining whether the state is an eigenstate of the symmetry operators. Both diagnostics derive from the problem structure and do not require the exact solution. We evaluate the framework on representative user- and system-side faults, across multiple target systems, and under injected noise. Results show that the two diagnostics detect faulty behavior, provide informative signals of solution quality, and remain useful under noisy execution.
Testing quantum software is challenging because quantum states cannot be directly inspected. Variational quantum algorithms (VQAs) are a particularly important target as they are among the most promising approaches for near-term noisy quantum hardware. Many testing methods rely on classically computed results, which conflicts with the regime where quantum advantage is expected. Although prior studies mitigate this oracle problem, the core difficulty remains that existing approaches do not verify whether the execution deviates from the intended problem or whether the obtained solution is physically plausible. We propose a symmetry-oriented testing framework for VQAs that addresses this gap by using operators commuting with the target Hamiltonian as test specifications. The framework provides two complementary diagnostics: a commutator-based health check that monitors whether each execution step during optimization remains consistent with the symmetry of the target Hamiltonian, and a variance-based acceptance check that assesses the converged solution by examining whether the state is an eigenstate of the symmetry operators. Both diagnostics derive from the problem structure and do not require the exact solution. We evaluate the framework on representative user- and system-side faults, across multiple target systems, and under injected noise. Results show that the two diagnostics detect faulty behavior, provide informative signals of solution quality, and remain useful under noisy execution.
Variational quantum algorithms (VQAs) have established themselves as a central computational paradigm in the Noisy Intermediate-Scale Quantum (NISQ) era. By coupling parameterized quantum circuits (PQCs) with classical optimization, they operate effectively under strict hardware limitations. However, as quantum architectures transition toward early fault-tolerant (EFT) and ultimate fault-tolerant (FT) regimes, the foundational principles and long-term viability of VQAs require systematic reassessment. This review offers an insightful analysis of VQAs and their progression toward the fault-tolerant regime. We deconstruct the core algorithmic framework by examining ansatz design and classical optimization strategies, including cost function formulation, gradient computation, and optimizer selection. Concurrently, we evaluate critical training bottlenecks, notably barren plateaus (BPs), alongside established mitigation strategies. The discussion then explores the EFT phase, detailing how the integration of quantum error mitigation and partial error correction can sustain algorithmic performance. Addressing the FT phase, we analyze the inherent challenges confronting current hybrid VQA models. Furthermore, we synthesize recent VQA applications across diverse domains, including many-body physics, quantum chemistry, machine learning, and mathematical optimization. Ultimately, this review outlines a theoretical roadmap for adapting quantum algorithms to future hardware generations, elucidating how variational principles can be systematically refined to maintain their relevance and efficiency within an error-corrected computational environment.
Variational Quantum Algorithms (VQA) are one of the most promising candidates for near-term quantum advantage. Traditionally, these algorithms are parameterized by rotational gate angles whose values are tuned over iterative execution on quantum machines. The iterative tuning of these gate angle parameters make VQAs more robust to a quantum machine's noise profile. However, the effect of noise is still a significant detriment to VQA's target estimations on real quantum machines - they are far from ideal. Thus, it is imperative to employ effective error mitigation strategies to improve the fidelity of these quantum algorithms on near-term machines.While existing error mitigation techniques built from theory do provide substantial gains, the disconnect between theory and real machine execution characteristics limit the scope of these improvements. Thus, it is critical to optimize mitigation techniques to explicitly suit the target application as well as the noise characteristics of the target machine.We propose VAQEM, which dynamically tailors existing error mitigation techniques to the actual, dynamic noisy execution characteristics of VQAs on a target quantum machine. We do so by tuning specific features of these mitigation techniques similar to the traditional rotation angle parameters -by targeting improvements towards a specific objective function which represents the VQA problem at hand. In this paper, we target two types of error mitigation techniques which are suited to idle times in quantum circuits: single qubit gate scheduling and the insertion of dynamical decoupling sequences. We gain substantial improvements to VQA objective measurements - a mean of over 3x across a variety of VQA applications, run on IBM Quantum machines.More importantly, while we study two specific error mitigation techniques, the proposed variational approach is general and can be extended to many other error mitigation techniques whose specific configurations are hard to select a priori. Integrating more mitigation techniques into the VAQEM framework in the future can lead to further formidable gains, potentially realizing practically useful VQA benefits on today's noisy quantum machines.
Variational Quantum Algorithms (VQA) are one of the most promising candidates for near-term quantum advantage. Traditionally, these algorithms are parameterized by rotational gate angles whose values are tuned over iterative execution on quantum machines. The iterative tuning of these gate angle parameters make VQAs more robust to a quantum machine’s noise profile. However, the effect of noise is still a significant detriment to VQA’s target estimations on real quantum machines — they are far from ideal. Thus, it is imperative to employ effective error mitigation strategies to improve the fidelity of these quantum algorithms on near-term machines.While existing error mitigation techniques built from theory do provide substantial gains, the disconnect between theory and real machine execution characteristics limit the scope of these improvements. Thus, it is critical to optimize mitigation techniques to explicitly suit the target application as well as the noise characteristics of the target machine.We propose VAQEM, which dynamically tailors existing error mitigation techniques to the actual, dynamic noisy execution characteristics of VQAs on a target quantum machine. We do so by tuning specific features of these mitigation techniques similar to the traditional rotation angle parameters -by targeting improvements towards a specific objective function which represents the VQA problem at hand. In this paper, we target two types of error mitigation techniques which are suited to idle times in quantum circuits: single qubit gate scheduling and the insertion of dynamical decoupling sequences. We gain substantial improvements to VQA objective measurements — a mean of over 3x across a variety of VQA applications, run on IBM Quantum machines.More importantly, while we study two specific error mitigation techniques, the proposed variational approach is general and can be extended to many other error mitigation techniques whose specific configurations are hard to select a priori. Integrating more mitigation techniques into the VAQEM framework in the future can lead to further formidable gains, potentially realizing practically useful VQA benefits on today’s noisy quantum machines.
Variational quantum algorithms are hybrid quantum-classical workflows whose results depend on many interacting choices, including the ansatz, Hamiltonian, optimizer, backend, shot count, noise model, mitigation method, random seed, stopping criteria, and software versions. In current practice, this information is often scattered across code, configuration files, logs, backend metadata, and paper descriptions, making executions difficult to reproduce, compare, debug, and reuse. This paper proposes an ontology-supported framework for representing Variational Quantum Algorithm (VQA) execution records as structured and machine-readable software engineering artifacts. The framework defines a Web Ontology Language (OWL) ontology for modeling the main entities involved in VQA experimentation, including algorithms, circuits, ansatzes, Hamiltonians, optimizers, backends, noise models, mitigation techniques, execution steps, software environments, measurement outcomes, and results. It further combines the ontology with Shapes Constraint Language (SHACL) constraints for validating completeness and consistency, and SPARQL Protocol and RDF Query Language (SPARQL) competency queries for retrieving reproducibility-relevant information. We demonstrate the approach using Variational Quantum Eigensolver (VQE) execution records, including a valid record and intentionally incomplete or inconsistent examples. The results show that the framework can represent complete VQA execution contexts, detect missing or malformed metadata, and support query-based inspection of information needed for reproducible quantum software experimentation.
Variational quantum algorithms (VQAs) have established themselves as a central computational paradigm in the Noisy Intermediate-Scale Quantum (NISQ) era. By coupling parameterized quantum circuits with classical optimization, they operate effectively under strict hardware limitations. However, as quantum architectures transition toward early fault-tolerant (EFT) and ultimate fault-tolerant (FT) regimes, the foundational principles and long-term viability of VQAs require systematic reassessment. This review offers a comprehensive analysis of VQAs and their progression toward the FT regime. We deconstruct the core algorithmic framework by examining ansatz design and classical optimization strategies, including cost function formulation, gradient computation, and optimizer selection. Concurrently, we evaluate critical training bottlenecks, notably barren plateaus (BPs), alongside established mitigation strategies. The discussion then explores the EFT phase, detailing how the integration of quantum error mitigation (QEM) and partial error correction can sustain algorithmic performance. Addressing the FT phase, we analyze the inherent challenges confronting current hybrid VQA models. Furthermore, we synthesize recent VQA applications across diverse domains, including many-body physics, quantum chemistry, machine learning, and mathematical optimization. Ultimately, this review outlines a theoretical roadmap for adapting quantum algorithms to future hardware generations, elucidating how variational principles can be systematically refined to maintain their relevance and efficiency within an error-corrected computational environment.
Quantum software testing is essential for the quality assurance of quantum programs. However, existing techniques face many challenges, such as constructing test oracles and distinguishing genuine faults from noise-induced errors. Propertybased testing is a promising solution for dealing with the test oracle issue, which verifies general properties rather than requiring inputs and outputs. However, its effectiveness in noisy quantum environments has not been studied. To this end, we evaluate the feasibility of applying property-based testing in noisy quantum computers by integrating it with a state-of-the-art machine learning-based noise mitigation method called QOIN. Our results show that on average, QOIN mitigates noise for individual circuits, though it may introduce outliers. Crucially, this does not guarantee property preservation: we show that some properties align better with QOIN, while others remain closer under unmitigated noise. To address this, we apply a hybrid approach that selectively applies QOIN during property-based testing. We show that this hybrid approach improves alignment with the ideal execution and significantly reduces false positives in assertion outcomes across most executed mutants. This provides a solid foundation for applying property-based testing to noisy quantum systems.