Introduction: This article is the result of doctoral research conducted in 2025 on quantum software architecture, addressing the transformative potential of quantum computing and the challenges associated with integrating quantum capabilities into software systems. Problem: The lack of standardized architectural models for hybrid classical–quantum systems limits interoperability, reuse, and systematic software design. Objective: This study proposes a reference architecture to support the design and evolution of hybrid classical–quantum software systems. Methodology: The architecture was derived through a harmonization process. Results: The proposed framework defines ten architectural elements organized across three dimensions: Conceptual, Organizational, and Quality. Conclusion: The architecture provides a structured foundation for designing hybrid classical–quantum solutions. Originality: The work consolidates dispersed knowledge into a unified framework for hybrid classical–quantum systems. Limitations: The model is based on the currently limited body of literature and industrial experience, requiring future validation.
Introduction: This article is the result of doctoral research conducted in 2025 on quantum software architecture, addressing the transformative potential of quantum computing and the challenges associated with integrating quantum capabilities into software systems. Problem: The lack of standardized architectural models for hybrid classical–quantum systems limits interoperability, reuse, and systematic software design. Objective: This study proposes a reference architecture to support the design and evolution of hybrid classical–quantum software systems. Methodology: The architecture was derived through a harmonization process. Results: The proposed framework defines ten architectural elements organized across three dimensions: Conceptual, Organizational, and Quality. Conclusion: The architecture provides a structured foundation for designing hybrid classical–quantum solutions. Originality: The work consolidates dispersed knowledge into a unified framework for hybrid classical–quantum systems. Limitations: The model is based on the currently limited body of literature and industrial experience, requiring future validation.
The rapid development of quantum computing technology has opened new possibilities for solving complex problems beyond the capabilities of classical computing paradigms. However, combining quantum computing with classical systems to create Hybrid Quantum-Classical (HQC) software systems presents unique challenges that require novel approaches in software architecture. This paper proposes a foundation for developing Architecture Description Languages (ADLs) specifically for HQC systems. We aim to provide a robust framework for coherently describing, integrating, and analyzing quantum and classical computing elements. The paper discusses the design principles, methodology, and structural components of the architecture description languages and outlines future research directions.
Quantum software development has largely focused on algorithms, with limited attention to software architecture. As computing moves toward hybrid quantum-classical systems, this gap limits scalability, reusability, and engineering rigor. This study introduces a component-based quantum software architecture framework (QSAF) for hybrid quantum-classical software systems, enabling developers to transition from circuit-level design to system-level reasoning. We identified 34 reusable quantum circuit primitives across seven functional categories and reinterpreted them as architectural components with explicit interfaces and design-relevant constraints. These components are further characterized using non-functional dimensions such as circuit depth, error sensitivity, and information flow, enabling a structured analysis of design trade-offs. The proposed QSAF framework establishes a multi-level abstraction hierarchy linking quantum gates, circuit primitives, algorithmic structures, and hybrid system architectures. Through this approach, common workflows, particularly hybrid quantum-classical workflows such as variational quantum algorithms, can be systematically decomposed, compared, and optimized. By making the architectural structure and trade-offs explicit, this study provides a foundation for quantum software engineering, supporting modular design, reuse, and informed architectural decision-making in quantum application development.
This doctoral dissertation, presented in the form of a compendium of publications, focuses on the design, implementation, and validation of an innovative model for evaluating analyz- ability—understood as a key subcharacteristic of maintainability—in the context of quantum software and, more broadly, hybrid software systems (those integrating classical and quantum components). In a landscape where quantum computing is rapidly advancing and beginning to consolidate in industrial applications, a pressing need arises to adapt and extend traditional software quality models, such as those established in the ISO/IEC 25000 family, to address the specific characteristics of quantum code. The lack of dedicated metrics hinders the rigorous evaluation of critical attributes like analyzability, negatively affecting hybrid systems’ maintainability, evolvability, and reliability in highly complex technical environments. The main objective of this dissertation is the design, implementation, and validation of an evaluation model focused on analyzability, which combines adapted classical metrics with newly defined indicators tailored explicitly for the quantum component. While the model targets hybrid systems, the validation has been exclusively focused on the quantum component, which constitutes the core contribution of this research. The classical part relies on well-established metrics validated and certified by bodies such as ILAC and ENAC and has therefore not been experimentally evaluated in this work. Additionally, an automated technological environment has been developed as a key element of the compendium, facilitating the practical application of the model in real-world projects. This environment enables integrated and real-time measurement of both classical and quantum metrics. However, like the model, its validation has been limited to the novel quantum indicators defined in this thesis. This approach strengthens the proposed methodology and lays the groundwork for future validation of the fully integrated hybrid model. The adopted methodology is grounded in an exhaustive review of the state of the art, the formal and informal definition of metrics, the development of the automated environment, and empirical validation through a family of experiments. The compendium of publications includes, among others, the following articles: Towards a set of metrics for hybrid (quan- tum/classical) systems maintainability, Implementing an environment for hybrid software evaluation, and Environment for the Evaluation of Hybrid (Classical-Quantum) Systems Analyzability. As part of the validation process, a preliminary study has been accepted at the international conference IQSOFT 2025, and an extended version has been submitted to the journal Empirical Software Engineering (EmSE), and is currently under review. The results demonstrate that the proposed model enables precise quantification of quantum software analyzability and that its application in hybrid systems is feasible conceptually and technically. The developed technological environment supports reproducible and systematic evaluation, laying a foundation for future applications in hybrid software engineering. The em- pirical validation conducted thus far has been deliberately limited to the quantum component, given that classical metrics are already widely established and certified. In conclusion, this dissertation represents a significant advance in the evaluation of hybrid software quality. It proposes a validated model that contributes to strengthening maintain- ability and supporting the evolution of complex systems in an ever-changing technological landscape.
Quantum software engineering (QSE) has emerged as a discipline to address the challenges associated with developing software systems in the context of advancing quantum computing technology. This paper explores architectural design patterns specific to QSE. Building on previous work highlighting the need for high-level patterns, we analyze emerging architectural approaches in quantum computing. We identify key challenges unique to hybrid quantum-classical systems and propose a preliminary taxonomy of QSE architectural patterns. These patterns address recurring design problems in areas such as quantum resource management and classical-quantum integration. We describe several potential patterns and discuss their theoretical applications in hybrid software systems. This work aims to provide a foundation for further research into standardizing QSE architectural practices, with the goal of enhancing various quality characteristics of hybrid software (e.g., modularity or maintainability) in the NISQ era and beyond.
Quantum Computing (QC) is transitioning from theoretical frameworks to an indispensable powerhouse of computational capability, resulting in extensive adoption across both industrial and academic domains. QC presents exceptional advantages, including unparalleled processing speed and the potential to solve complex problems beyond the capabilities of classical computers. Nevertheless, academic researchers and industry practitioners encounter various challenges in harnessing the benefits of this technology. The limited accessibility of QC resources for classical developers, and a general lack of domain knowledge and expertise, represent insurmountable barrier, hence to address these challenges, we introduce a framework- Quantum Computing as a Service for Hybrid Classical-Quantum Software Development (QCSHQD), which leverages service-oriented strategies. Our framework comprises three principal components: an Integrated Development Environment (IDE) for user interaction, an abstraction layer dedicated to orchestrating quantum services, and a service provider responsible for executing services on quantum computer. This study presents a blueprint for QCSHQD, designed to democratize access to QC resources for classical developers who want to seamless harness QC power. The vision of QCSHQD paves the way for groundbreaking innovations by addressing key challenges of hybridization between classical and quantum computers.
Quantum computing systems rely on the principles of quantum mechanics to perform a multitude of computationally challenging tasks more efficiently than their classical counterparts. The architecture of software-intensive systems can empower architects who can leverage architecture-centric processes, practices, description languages to model, develop, and evolve quantum computing software (quantum software for short) at higher abstraction levels. We conducted a Systematic Literature Review (SLR) to investigate (i) architectural process, (ii) modelling notations, (iii) architecture design patterns, (iv) tool support, and (iv) challenging factors for quantum software architecture. Results of the SLR indicate that quantum software represents a new genre of software-intensive systems; however, existing processes and notations can be tailored to derive the architecting activities and develop modelling languages for quantum software. Quantum bits (Qubits) mapped to Quantum gates (Qugates) can be represented as architectural components and connectors that implement quantum software. Tool-chains can incorporate reusable knowledge and human roles (e.g., quantum domain engineers, quantum code developers) to automate and customise the architectural process. Results of this SLR can facilitate researchers and practitioners to develop new hypotheses to be tested, derive reference architectures, and leverage architecture-centric principles and practices to engineer emerging and next generations of quantum software.