Frank Leymann

University of Stuttgart · Institute of Architecture of Application Systems

Quantum computers are available via a variety of different quantum cloud offerings. These offerings are heterogeneous and differ in features, such as pricing models or types of access to quantum computers. Furthermore, quantum circuits can be implemented using different quantum programming languages, which are typically only supported by a small su...

Distributed quantum computing leverages the collective power of multiple quantum devices to perform computations exceeding the capabilities of individual quantum devices. A currently studied technique to enable this distributed approach is wire cutting, which decomposes a quantum circuit into smaller subcircuits by cutting their connecting wires. T...

Nowadays, predominant asymmetric cryptographic schemes are considered to be secure because discrete logarithms are believed to be hard to be computed. The algorithm of Shor can effectively compute discrete logarithms, i.e. it can brake such asymmetric schemes. But the algorithm of Shor is a quantum algorithm and at the time this algorithm has been...

Quantum Neural Networks (QNNs) use sets of training samples supplied as quantum states to approximate unitary operators. Recent results show that the average quality, measured as the error of the approximation, depends on the number of available training samples and the degree of entanglement of these samples. Furthermore, the linear structure of t...

Due to low numbers of qubits and their error-proneness, Noisy Intermediate-Scale Quantum (NISQ) computers impose constraints on the size of quantum algorithms they can successfully execute. State-of-the-art research introduces various techniques addressing these limitations by utilizing known or inexpensively generated approximations, solutions, or...

The Boolean satisfiability problem (SAT), in particular 3SAT with its bounded clause size, is a well-studied problem since a wide range of decision problems can be reduced to it. The Quantum Approximate Optimization Algorithm (QAOA) is a promising candidate for solving 3SAT for Noisy Intermediate-Scale Quantum devices in the near future due to its...

The introduction of smart contracts has expanded the applicability of blockchains to many domains beyond finance and cryptocurrencies. Moreover, different blockchain technologies have evolved that target special requirements. As a result, in practice, often a combination of different blockchain systems is required to achieve an overall goal. Howeve...

Noisy Intermediate-Scale Quantum (NISQ) devices are restricted by their limited number of qubits and their short decoherence times. An approach addressing these problems is quantum circuit cutting. It decomposes the execution of a large quantum circuit into the execution of multiple smaller quantum circuits with additional classical postprocessing....

The application of quantum computing to combinatorial optimization problems is attracting increasing research interest, resulting in diverse approaches and research streams. This study aims at identifying, classifying, and understanding existing solution approaches as well as typical use cases in the field. The obtained classification schemes are b...

Blockchains have become increasingly important in recent years and have expanded their applicability to many domains beyond finance and cryptocurrencies. This adoption has particularly increased with the introduction of smart contracts, which are immutable, user-defined programs directly deployed on blockchain networks. However, many scenarios requ...

Distributed quantum computing combines the computational power of multiple devices to overcome the limitations of individual devices. Circuit cutting techniques enable the distribution of quantum computations through classical communication. These techniques involve partitioning a quantum circuit into smaller subcircuits, each containing fewer qubi...

Quantum processing units (QPUs) are currently exclusively available from cloud vendors. However, with recent advancements, hosting QPUs is soon possible everywhere. Existing work has yet to draw from research in edge computing to explore systems exploiting mobile QPUs, or how hybrid applications can benefit from distributed heterogeneous resources....

Automation is the key to enable an efficient, fast, and reliable deployment of applications. Therefore, several deployment automation technologies emerged in recent years whereby each technology has its specific field of application: While some are bound to cloud providers and offer provider-specific functionalities, others enable multi-cloud deplo...

With the emergence of quantum computing, a growing number of quantum devices is accessible via cloud offerings. However, due to the rapid development of the field, these quantum-specific service offerings vary significantly in capabilities and requirements they impose on software developers. This is particularly challenging for practitioners from o...

Due to low numbers of qubits and their error-proneness, Noisy Intermediate-Scale Quantum (NISQ) computers impose constraints on the size of quantum algorithms they can successfully execute. State-of-the-art research introduces various techniques addressing these limitations by utilizing known or inexpensively generated approximations, solutions, or...

The Boolean satisfiability problem (SAT), in particular 3SAT with its bounded clause size, is a well-studied problem since a wide range of decision problems can be reduced to it. Due to its high complexity, examining potentials of quantum algorithms for solving 3SAT more efficiently is an important topic. Since 3SAT can be formulated as unstructure...

Quantum applications are hybrid, i.e., they comprise quantum and classical programs, which must be orchestrated. Workflows are a proven solution for orchestrating heterogeneous programs while providing benefits, such as robustness or scalability. However, the orchestration using workflows can be inefficient for some quantum algorithms, requiring th...

Noisy Intermediate-Scale Quantum (NISQ) devices are restricted by their limited number of qubits and their short decoherence times. An approach addressing these problems is quantum circuit cutting. It decomposes the execution of a large quantum circuit into the execution of multiple smaller quantum circuits with additional classical postprocessing....

Most of existing production-ready deployment automation technologies enable declaratively specifying the target deployment for a multi-service application, which can then be automatically enforced. Each technology however relies on a different deployment modelling language, hence hampering the portability of an application deployment from one techn...

The rise of the IoT and Industry 4.0 has increased the complexity of collaborating business processes, i. e., choreographies, as more partners and assets are involved. However, maintaining and executing business choreographies are complex tasks. Moreover, enabling robust and reliable execution is important, as failures or delays cause high costs am...

For automating the deployment of composite applications, typically, declarative deployment models are used. Depending on the context, the deployment of an application has to fulfill different requirements, such as costs and elasticity. As a consequence, one and the same application, i.e., its components, and their dependencies, often need to be dep...

This chapter discusses that the development of quantum applications typically incorporates the development of quantum programs, classical programs, and workflows to orchestrate them. Thus, the lifecycles of these software artifacts with their included phases, related concepts, and tools are described. Finally, the points of connection between the v...

The performance of current quantum computers is limited by high error rates and few qubits. Nevertheless, more and more quantum computers are available in the cloud. Selecting a suitable quantum computer to execute a specific quantum circuit and receive precise results can be difficult. At the same time, it is crucial to choose an available quantum...

Various cloud service models with different management requirements can be used for hosting a certain application component. For instance, more consumer-managed serverful options can be preferred if a component has special requirements related to deployment stack or scaling configuration management, whereas more provider-managed serverless alternat...

Plugins can be used to extend applications with new functionality without requiring expensive code changes for the application. To enable users to interact with the new functionality, plugins must be able to contribute new elements to the user interface of the application. However, as plugins are built for specific applications, they are not reusab...

Quantum applications play an essential role in exploiting the full potential of quantum computers. However, quantum applications are typically hybrid, i.e., they consist of classical and quantum processing steps that must be orchestrated. Workflow technologies enable such orchestration and offer several advantages such as robustness, reusability, a...

Current quantum computers are still error-prone, with measurement errors being one of the factors limiting the scalability of quantum devices. To reduce their impact, a variety of readout error mitigation methods, mostly relying on classical post-processing, have been developed. However, the application of these methods is complicated by their hete...

The algorithm of Shor for prime factorization is a hybrid algorithm consisting of a quantum part and a classical part. The main focus of the classical part is a continued fraction analysis. The presentation of this is often short, pointing to text books on number theory. In this contribution, we present the relevant results and proofs from the theo...

Today’s quantum computers are limited in their capabilities, e.g., the size of executable quantum circuits. The Quantum Approximate Optimization Algorithm (QAOA) addresses these limitations and is, therefore, a promising candidate for achieving a near-term quantum advantage. Warm-starting can further improve QAOA by utilizing classically pre-comput...

Infrastructure-as-Code (IaC) technologies are used to automate the deployment of cloud applications. They promote the usage of code to define and configure the IT infrastructure of cloud applications allowing them to benefit from conventional software development practices, which facilitates the rapid deployment of new versions of application infra...

Infrastructure-as-Code (IaC) technologies are used to automate the deployment of cloud applications. They promote the usage of code to define and configure the IT infrastructure of cloud applications allowing them to benefit from conventional software development practices, which facilitates the rapid deployment of new versions of application infra...

Function‐as‐a‐Service (FaaS) is a cloud service model enabling to implement serverless applications for a variety of use cases. These range from scheduled calls of single functions to complex function orchestrations executed using orchestration services such as AWS step functions. However, since the available function orchestration technologies var...

Abstract As quantum computers are based on the laws of quantum mechanics, they are capable of solving certain problems faster than their classical counterparts. However, quantum algorithms with a theoretical speed‐up often assume that data can be loaded efficiently. In general, the runtime complexity of the loading routine depends on (i) the data e...

Quantum computers have the potential to solve certain problems faster than classical computers. However, the computations that can be executed on current quantum devices are still limited. Hybrid algorithms split the computational tasks between classical and quantum computers circumventing some of these limitations. Therefore, they are regarded as...

For very specific problems, quantum advantage has recently been demonstrated. However, current NISQ computers are error-prone and only support small numbers of qubits. This limits the executable circuit size of an implemented quantum algorithm. Due to this limitation, it is important that compiled quantum circuits for a specific quantum computer ar...

Abstract Quantum computing promises breakthroughs in various application areas, such as machine learning, chemistry, or simulations. However, today’s quantum computers are error‐prone and have limited capabilities. This leads to various challenges when developing and executing quantum algorithms, for example, the mitigation of occurring errors or t...

With recent advances in the development of more powerful quantum computers, the research area of quantum software engineering is emerging, having the goal to provide concepts, principles, and guidelines to develop high-quality quantum applications. In classical software engineering, lifecycles are used to document the process of designing, implemen...

Quantum computers have been significantly advanced in recent years. Offered as cloud services, quantum computers have become accessible to a broad range of users. Along with the physical advances, the landscape of technologies supporting quantum application development has also grown rapidly in recent years. However, there is a variety of tools, se...

Most of today’s deployment automation technologies enable the deployment of distributed applications in distributed environments, whereby the deployment execution is centrally coordinated either by a central orchestrator or a master in a distributed master-workers architectures. However, it is becoming increasingly important to support use cases wh...

Function-as-a-Service (FaaS) is a cloud service model enabling developers to offload event-driven executable snippets of code. The execution and management of such functions becomes a FaaS providerâs responsibility, therein included their on-demand provisioning and automatic scaling. Key enablers for this cloud service model are FaaS platforms, e.g...

The execution of a quantum algorithm typically requires various classical pre- and post-processing tasks. Hence, workflows are a promising means to orchestrate these tasks, benefiting from their reliability, robustness, and features, such as transactional processing. However, the implementations of the tasks may be very heterogeneous and they depen...

Pattern languages are well-established in the software architecture community. Many different aspects of creating a software architecture are addressed by such languages. Thus, several pattern languages have to be considered when building a particular architecture. But these pattern languages are isolated, i.e. it is hard to determine the relevant...

As quantum computers are becoming real, they have the inherent potential to significantly impact many application domains. In this paper we outline the fundamentals about programming quantum computers and show that quantum programs are typically hybrid consisting of a mixture of classical parts and quantum parts. With the advent of quantum computer...

Quantum applications are most often hybrid, i.e. they are not only made of implementations of pure quantum algorithms but also of classical programs as well as workflows and topologies as key artifacts, and data they process. Since workflows and topologies are referred to as orchestrations in modern terminology (but with very different meaning), tw...

Function-as-a-Service (FaaS) is a cloud service model enabling developers to offload event-driven executable snippets of code. The execution and management of such functions becomes a FaaS provider’s responsibility, therein included their on-demand provisioning and automatic scaling. Key enablers for this cloud service model are FaaS platforms, e.g...

The growing trend of integrating software processes and the physical world created new paradigms, such as, the Internet of Things and Cyber-Physical Systems. However, as applications of these paradigms are rolled out, the management of their software and hardware components becomes a challenge, e.g., an update of a mobile system must not only consi...

Quantum computing can enable a variety of breakthroughs in research and industry in the future. Although some quantum algorithms already exist that show a theoretical speedup compared to the best known classical algorithms, the implementation and execution of these algorithms come with several challenges. The input data determines, for example, the...

Patterns describe proven solutions for recurring problems. Typically, patterns in a particular domain are interrelated and can be organized in pattern languages. As real-world problems often require to combine patterns of multiple domains, different pattern languages have to be considered to address these problems. However, cross-domain knowledge a...

Although historically the term serverless was also used in the context of peer-to-peer systems, it is more frequently associated with the architectural style for developing cloud-native applications. From the developer's perspective, serverless architectures allow reducing management efforts since applications are composed using provider-managed co...

Microservice-based architectures (MSAs) gained momentum in industrial and research communities since finer-grained and more independent components foster reuse and reduce time to market. However, to come from the design of MSAs to running applications, substantial knowledge and technology-specific expertise in the deployment and integration of micr...

Implementing a gate-based quantum algorithm on a NISQ device has several challenges that arise from the fact that such devices are noisy and have limited quantum resources. Thus, various factors contributing to the depth and width as well as to the noise of an implementation of a gate-based algorithm must be understood in order to assess whether an...

The OASIS standard TOSCA provides a portable means for specifying multi-service applications and automating their deployment. Despite TOSCA is widely used in research, it is currently not supported by the production-ready deployment technologies daily used by practitioners, hence resulting in a gap between the state-of-the-art in research and the s...

The establishment of digital humanities as a research field has shown that the use of computers as tools, but also the use of methods and techniques from computer science, can contribute enormously to research done in the humanities. Since quantum computers are expected to become generally available in the next few years, it is promising to use the...

With the continuous growth of IT application systems, the complexity of architecture modeling and development increases. Patterns document proven solutions for recurring problems in an abstract and human readable manner. Within the domain of IT architectures, they should support the architecture modeling and development process. Due to the document...