Abstract Quantum computing is getting closer and closer to bringing all its potential applications to our lives. This means that in a few years the current IT will evolve into hybrid software systems where quantum and classical computing paradigms should be designed, developed, and operated together. This is a big challenge that will require software modernization processes for transforming and migrating legacy software systems (which may include adding new existing quantum software) toward such hybrid software systems. This chapter discusses the challenges of hybrid software and how software modernization (based on architecture-driven modernization) can be used as a reengineering solution for an effective evolution of classical and quantum software.
Abstract Quantum computing is getting closer and closer to bringing all its potential applications to our lives. This means that in a few years the current IT will evolve into hybrid software systems where quantum and classical computing paradigms should be designed, developed, and operated together. This is a big challenge that will require software modernization processes for transforming and migrating legacy software systems (which may include adding new existing quantum software) toward such hybrid software systems. This chapter discusses the challenges of hybrid software and how software modernization (based on architecture-driven modernization) can be used as a reengineering solution for an effective evolution of classical and quantum software.
As quantum computing continues to advance, the development of reliable and scalable quantum software systems becomes increasingly crucial. However, designing and implementing hybrid (quantum-classical) software systems poses unique challenges that require novel approaches and best practices. This position paper argues for the importance of developing architectural and design patterns specific to Quantum Software Engineering (QSE). We provide an overview of existing quantum software design patterns (more focused on low-level, programming details) and highlight the lack of patterns addressing hybrid software systems and architectural patterns. We discuss the key challenges that architectural patterns should address, including quantum-classical integration, maintainability, efficiency, and security. We also discuss the implications for practitioners, providing guidance on how to think high-level about hybrid software development process. Finally, we outline future research directions and emphasize the need for collaboration between the quantum computing and software engineering communities to establish a comprehensive high-level patterns framework for QSE.
The emergence of quantum computing proposes a revolutionary paradigm that can radically transform numerous scientific and industrial application domains. The ability of quantum computers to scale computations exponentially imply better performance and efficiency for certain algorithmic tasks than current computers provide. However, to gain benefit from such improvement, quantum computers must be integrated with existing software systems, a process that is not straightforward. In this paper, we investigate challenges that emerge from building larger hybrid classical-quantum computers, and discuss some approaches that could be employed to overcome these challenges.
Quantum computing has gained a lot of interest in recent years, thanks to its ability to solve certain problems that classical computing cannot address. These applications will only be achieved through the development of quantum software. Thus, many organizations are starting projects to integrate this new software into their existing systems. Software modernization (as based on Model-Driven Engineering) can be used to migrate from/to the so-called hybrid software systems, which integrate classical and quantum software. In that process, reverse engineering and restructuring phases have already been addressed, but the forward engineering phase for hybrid software has not yet been addressed. This paper presents a preliminary code generation technique from extended UML design models. It proposes an EGL transformation to generate Python and Qiskit code by integrating classical and quantum code. The transformation has been preliminarily validated with an example of application with the design model of a hybrid system for a financial web application. The implication of this work is that the software modernization process for hybrid software systems is completed, which facilitates the adoption of this new paradigm in the industry.
Despite the promise and potential of quantum computing, most of the current day developments of quantum computing have several limitations for relevant practical use. As a result, hybrid classical-quantum computing has emerged as a viable solution. This paper discusses the software aspects of hybrid classical-quantum computing solutions to understand and examine how hybrid computing solutions can be expected to work in practice. This paper examines existing software solutions (cloud applications, middleware frameworks, and API gateways) that can enable classical and quantum computing to work together. For practitioners the paper provides a curated list of algorithms, full stack libraries, simulators, and cloud service providers that are likely to be central to the development of any hybrid computing solutions. We conclude by identifying an agenda for future research on classical-quantum hybrid software engineering, and some near-term priorities for development of functional, robust hybrid software systems. The paper argues that due to the deep dependency of quantum execution on classical pre- and post-processing, hybrid computing may represent a near-permanent outcome of classical-quantum computing rather than a transitional workaround.
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.
This article provides an overview of the current state and future challenges of quantum software engineering as quantum computing transitions from proof-of-concept to potential industrial adoption. While significant progress has been made in quantum hardware and cloud-based execution platforms, the article argues that innovation will depend critically on advances in software tools, programming abstractions, and engineering methodologies. Focusing on the constraints of the Noisy Intermediate-Scale Quantum (NISQ) era, it examines challenges related to hardware heterogeneity, software portability, hybrid classical–quantum architectures, and the lack of mature development environments. The article also highlights the urgent need for a new generation of quantum software engineers and coherent educational programmes, particularly in Europe, to bridge skills gaps and support the long-term evolution toward fault-tolerant quantum computing.