The rapid evolution of quantum computing has led to growing interest in the development of systematic approaches to assess and manage quantum software. Among these, functional size measurement (FSM) offers a promising pathway for establishing metrics that can support project estimation, benchmarking, and quality assessment. This paper provides an overview of emerging efforts in quantum software functional size measurement with a focus on key concepts, challenges, and motivations. First, we examine the foundational principles of quantum computing in relation to the existing FSM methods, identifying both compatibilities and unique constraints. Building on this, we discuss the challenges that arise when applying FSM to quantum software, including the hardware-coupled nature of functionality, evolving semantics of data and measurement abstractions, gaps in tooling and standardization, and evolving role of FSM across the Noisy Intermediate-Scale Quantum (NISQ) and future faulttolerant eras. We then outline community-driven initiatives, such as the COSMIC Quantum Software Taskforce and the Fall 2024 Workshop, which highlight the increasing demand for structured measurement practices. By articulating these issues, this paper aims to present initial research efforts for quantum software functional size measurement and stimulate further exploration of measurement approaches that are both theoretically grounded and practically applicable in quantum software engineering.
The rapid evolution of quantum computing has led to growing interest in the development of systematic approaches to assess and manage quantum software. Among these, functional size measurement (FSM) offers a promising pathway for establishing metrics that can support project estimation, benchmarking, and quality assessment. This paper provides an overview of emerging efforts in quantum software functional size measurement with a focus on key concepts, challenges, and motivations. First, we examine the foundational principles of quantum computing in relation to the existing FSM methods, identifying both compatibilities and unique constraints. Building on this, we discuss the challenges that arise when applying FSM to quantum software, including the hardware-coupled nature of functionality, evolving semantics of data and measurement abstractions, gaps in tooling and standardization, and evolving role of FSM across the Noisy Intermediate-Scale Quantum (NISQ) and future faulttolerant eras. We then outline community-driven initiatives, such as the COSMIC Quantum Software Taskforce and the Fall 2024 Workshop, which highlight the increasing demand for structured measurement practices. By articulating these issues, this paper aims to present initial research efforts for quantum software functional size measurement and stimulate further exploration of measurement approaches that are both theoretically grounded and practically applicable in quantum software engineering.
Quantum computing promises to offer significant computational advantages over classical computing, leveraging principles such as superposition and entanglement. This necessitates effective metrics and measurement techniques for evaluating quantum systems, aiding in their development and performance optimization. However, due to fundamental differences in computing paradigms, and current immaturity of quantum software abstractions, classical software and hardware metrics may not directly apply to quantum computing, where the distinction between software and hardware can still be somewhat indiscernible compared to classical computing. This paper provides a comprehensive review of existing quantum software and hardware metrics in the scientific literature, highlighting key challenges in the field. Additionally, it investigates the application of Functional Size Measurement (FSM) based on COSMIC ISO 19761 to measure quantum software. Three FSM approaches are analyzed by applying them to Shor’s and Grover’s algorithms, with measurement results compared to assess their effectiveness. A comparative analysis highlights the strengths and limitations of each approach, emphasizing the need for further refinement. The insights from this study contribute to the advancement of quantum metrics, especially software metrics and measurement, paving the way for the development of a unified and standardized approach to quantum software measurement and assessment.
Rapid growth in quantum computing has created an urgent need to adapt traditional software engineering methodologies. Among these methodological challenges, software size measurement plays a central role in project estimation, quality assurance, and software engineering management. However, there is no consolidated understanding of how it should be applied to quantum software systems. This paper presents the first systematic literature review on quantum software size measurement, synthesizing existing approaches, and identifying key research gaps. An analysis of 16 studies shows that size measures span multiple abstraction levels, with most research focusing on adapting classical metrics, such as Lines of Code (LOC) and functional size, to quantum software systems. LOC continues to be used for sizing quantum code, while COSMIC Function Points (ISO 19761) have been extended to capture data movements in quantum components, enabling their application at the requirement, code, and circuit levels. At the specification and architectural design levels, the proposed measures include counts of quantum classes and methods as well as lines of architectural specifications. At the circuit level, quantum-specific constructs, such as qubits, gates, and measurements, are also incorporated. Additionally, software structure metrics, including cyclomatic complexity and Halstead metrics, are used to measure quantum software at both the code and design levels. Research output has grown since 2024, and is driven by academic groups, with minimal industrial participation. However, most metrics remain conceptual, lack empirical validation, and are not integrated into development life cycles, highlighting the immaturity and fragmentation of current proposals and the need for standardized frameworks.
As quantum computing evolves, the need for quantum software measurement techniques has increased. Functional Size Measurement (FSM) has been adopted to measure quantum Software in three different approaches based on COSMIC ISO 19761. We examine the proposed approaches by analyzing the measurement results of their application on Shor’s and Grover’s algorithms. A comparative analysis reveals the strengths and limitations of each approach, emphasizing the need for continued refinement. The insights gained from this study are critical for developing a more unified approach for quantum software and pave the way to a standardized approach.
Abstract Quantum computing is an emerging field in which theoretical principles are being transformed into practical applications, largely due to the efforts of the developer community. In order to ensure that quantum software engineering continues to advance, it is vital to understand the experiences, challenges, and aspirations of developers. This chapter is a continuation of our previous work, which provided a comprehensive survey exploring the adoption patterns and common challenges in quantum software engineering. In addition to the survey, we conducted in-depth, semi-structured interviews with practitioners in the field to gain a deeper and more detailed understanding of their perspectives. Through the interviews and survey findings, we have gained nuanced insights into the motivations, hurdles, and outlook of developers toward the rapidly evolving quantum computing landscape. We describe the research methodology in detail, including the tools and techniques used, in order to provide a comprehensive understanding of the research process. Furthermore, we present critical insights from both the survey and interviews, enriching the narrative with fresh perspectives obtained from the post-publication interviews. This chapter is a blend of academic investigation and real-world practitioner insights, aiming to provide a comprehensive understanding of the current state of quantum software engineering. By illuminating the path for future research and development in this dynamic field, we hope to guide the way toward continued progress and innovation.
Accurate sizing of software systems is essential for effective project management and resource allocation. Hybrid classical-quantum software systems consist of a quantum component, which executes quantum algorithms and incorporates error correction mechanisms (overhead)-a critical aspect in the Noisy Intermediate-Scale Quantum (NISQ) era-and a classical component, which controls quantum operations and manages error propagation. This paper explores functional sizing for hybrid classical-quantum software. It highlights the challenges arising from the interaction between the classical and quantum components, particularly with respect to the abstraction layers and granularity levels. A key principle emphasized is that functional sizing should not extend across multiple abstraction layers within a single measurement scope. While quantum software typically operates at a low-level implementation-specific layer, classical software generally functions at a higher level of abstraction. This divergence emphasizes the need to clarify how functional size measurement should be applied using set theory to account for requirements specified at different abstraction layers in hybrid computing environments.
Quantum engineering seeks to exploit quantum information to build, among others, computing, cybersecurity, and metrology technologies. Quantum Software Engineering (QSE) focuses on the information processing side of these technologies. Historically, quantum (software) engineering has focused on development in controlled research environments and 'in the small'. As the field progresses, we should expect to see more large-scale quantum systems to be deployed as 'real-world' products and services. An essential tool in (classical) software engineering and development has been software size metrics. Calculating/estimating the size of a piece of software, to be developed or pre-existing, is an essential step in its engineering. Quantum software will be no different. Here we introduce Q-COSMIC, a technique for measuring the functional size of quantum software, based on the well-regarded COSMIC standard (ISO/IEC19761) for classical software