Abstract Quantum computing offers the potential for exponential speed-ups for classically intractable problems, yet quantum programming is still susceptible to bugs. Classical debugging methods are often inadequate, as quantum mechanical principles make state inspection disruptive and classical simulation has exponential time complexity. This survey explores the landscape of quantum assertions as a key technique for identifying and locating bugs in quantum programs. We classify these techniques into two primary categories based on their evaluation stage: classical runtime and quantum runtime assertions. For each category, we analyze the strengths, limitations, time complexity, and applicability of current methods. Our findings show that scalable quantum debugging remains an open problem—a challenge that will persist even with the advent of fault-tolerant hardware. Finally, this work highlights key challenges and proposes future directions for the development of novel quantum debugging techniques.
Abstract Quantum computing offers the potential for exponential speed-ups for classically intractable problems, yet quantum programming is still susceptible to bugs. Classical debugging methods are often inadequate, as quantum mechanical principles make state inspection disruptive and classical simulation has exponential time complexity. This survey explores the landscape of quantum assertions as a key technique for identifying and locating bugs in quantum programs. We classify these techniques into two primary categories based on their evaluation stage: classical runtime and quantum runtime assertions. For each category, we analyze the strengths, limitations, time complexity, and applicability of current methods. Our findings show that scalable quantum debugging remains an open problem—a challenge that will persist even with the advent of fault-tolerant hardware. Finally, this work highlights key challenges and proposes future directions for the development of novel quantum debugging techniques.
Quantum computing has existed in the theoretical realm for several decades. Recently, quantum computing has re-emerged as a promising technology to solve problems that a classical computer could take hundreds of years to solve. However, there are challenges and opportunities for academics and practitioners regarding software engineering practices for testing and debugging quantum programs. This article presents a roadmap for addressing these challenges, pointing out the existing gaps in the literature and suggesting research directions. We discuss the limitations caused by noise, the no-cloning theorem, the lack of a standard architecture for quantum computers, among others. Regarding testing, we highlight gaps and opportunities related to transpilation, mutation analysis, input states with hybrid interfaces, program analysis, and coverage. For debugging, we present the current strategies, including classical techniques applied to quantum programs, quantum-specific assertions, and quantum-related bug patterns. We introduce a conceptual model to illustrate concepts regarding the testing and debugging of quantum programs and the relationship between them. Those concepts are used to identify and discuss research challenges to cope with quantum programs through 2030, focusing on the interfaces between classical and quantum computing and on creating testing and debugging techniques that take advantage of the unique quantum computing characteristics.
Advances in NISQ devices have allowed quantum researchers and enthusiasts to design and develop quantum programs for different applications. As the hardware progresses from noisy to fault-tolerant, the size of the programs implemented will increase. As the circuits get larger, testing and debugging these circuits will become more complex. To overcome the counterintuitive nature of quantum circuits and help developers better understand their programs and locate bugs during the development process's testing and debugging stages, we must understand the different types of bugs that occur in quantum circuits and how they affect the state of the qubits and propagate through the circuit. In this work, we categorize some bugs that could occur when implementing quantum circuits. This poster is part of a bigger work that aims to assist developers in debugging their circuits. This is done by bridging some testing and debugging techniques from the classical world, such as hypothesis and binary-like testing, and debugging-assistance functions, such as tracking gates and detecting qubits' light cones. In addition, we collected and studied bugs from Stack Exchange, Stack Overflow, and GitHub and categorized these bugs based on their source to provide developers with tools and information for an efficient and systematic debugging process for their programs.
With recent breakthroughs in quantum computing, it has become a coming reality instead of a promising future. Quantum computing applications offer revolutionary potential across multiple domains including artificial intelligence (AI), optimization, healthcare, energy, and space, known as quantum advantage. The power of quantum computing relies on novel quantum algorithms, quantum software, and hardware. Unlike classical software, quantum software has unique features because of quantum mechanics such as superposition and noncloning. This opens a new research field - quantum software engineering (QSE). While the software engineering (SE) research community became aware of this need in 2019, we noticed the lack of a comprehensive investigation of state-of-the-art technologies and tools to improve quantum software quality. Testing and debugging are the two most efficient approaches to assure software quality in classical SE. In QSE, testing and debugging quantum programs become challenging due to quantum mechanics. While we can leverage some best practices from the classical world, new techniques and tools are needed to address the concerns in QSE. In this chapter, we first conduct a survey study of the state-of-the-art technologies and tools for testing and debugging quantum software. This study includes but is not limited to quantum bug pattern analysis and detection, quantum software testing techniques and classification, and quantum debugging techniques. In the second place, we provide our visions and insights of testing and debugging quantum software in terms of challenges and opportunities for improving quantum software quality. This survey has the potential to foster a research community committed to developing novel methods and tools for QSE.
Abstract As quantum computers continue to improve in quality and scale, there is a growing need for accessible software frameworks for programming them. However, the unique behavior of quantum systems means specialized approaches, beyond traditional software development, are required. This is particularly true for debugging due to quantum bugs, i.e., bugs that occur precisely because an algorithm is a quantum algorithm. Pinpointing a quantum bug’s root cause often requires significant developer time, as there is little established guidance for quantum debugging techniques. Developing such guidance is the main challenge we sought to address. In this work, we describe a set of 14 quantum bugs, sourced primarily from our experience as quantum software developers, and supplemented by analysis of open-source GitHub repositories. We detail their context, symptoms, and the techniques applied to identify and fix them. While classifying these bugs based on existing schemes, we observed that most emerged due to unique interactions between multiple aspects of an algorithm or workflow. In other words, they occurred because more than one thing went wrong, which provided important insight into why quantum debugging is more challenging. Furthermore, based on this clustering, we found that—unexpectedly—there is no clear relationship between debugging strategies and bug classes. Further research is needed to develop effective and systematic quantum debugging strategies.
Quantum simulators are a foundational component of the quantum software ecosystem. They are widely used to develop and debug quantum programs, validate compiler transformations, and support empirical claims about correctness and performance. In the absence of large-scale quantum hardware, simulator outputs are often treated as ground truth for algorithm development and system evaluation. However, quantum simulators also introduce unique implementation challenges. They must faithfully emulate quantum behavior while executing on classical hardware, requiring complex representations of quantum state evolution, operator composition, and noise modeling. Yet, we still lack a large-scale and in-depth study of failures in quantum simulators.
To bridge this gap, this work presents a comprehensive empirical study of bugs in widely used open-source quantum simulators. We analyze 394 confirmed bugs from 12 simulators and manually categorize them based on root causes, failure manifestations, affected components, and discovery mechanisms. Our study reveals several key findings. First, bug discovery is largely user-driven, with most crashes, exceptions, and resource-related failures not detected by automated testing and identified after deployment. Second, logical correctness failures are widespread and often silent, producing plausible but incorrect outputs without triggering crashes or explicit error signals. Third, many critical failures originate in classical simulator infrastructure, such as memory management, indexing, configuration, and dependency compatibility, rather than in core quantum execution logic. These findings provide new insights into the reliability challenges of quantum simulators and highlight opportunities to improve testing and validation practices in the quantum software ecosystem.
The continuous growth of quantum computing and the increasingly complex quantum programs resulting from it lead to unprecedented obstacles in ensuring program correctness. Runtime assertions are, therefore, becoming a crucial tool in the development of quantum programs. They assist developers in the debugging process and help to test and verify the program. However, while assertions can be implemented in a straightforward manner on classical computers, physical limitations of quantum computers pose considerable challenges for the evaluation of quantum assertions. Access to the quantum state of a program is limited, execution time is expensive and noise can significantly distort measurement outcomes. To address these problems, this work proposes a framework that assists developers in the evaluation of runtime assertions on real quantum computers. It translates a variety of assertions into sets of measurements, reduces execution overhead where possible and evaluates the measurement results after the execution even in the presence of noise. This approach substantially aids developers in the debugging process, enabling efficient assertion-driven debugging even in large programs. The proposed framework is available as an open-source implementation at https://github.com/munich-quantum-toolkit/debugger