Quantum computing and distributed systems may enter a mutually beneficial partnership in the future. On the one hand, it is much easier to build a number of small quantum computers rather than a single large one. On the other hand, the best results concerning some of the fundamental problems in distributed computing can potentially be dramatically improved upon by taking advantage of the superior resources and processing power that quantum mechanics offers. This survey has the purpose to highlight both of these benefits. We first review the current results regarding the implementation of arbitrary quantum algorithms on distributed hardware. We then discuss existing proposals for quantum solutions of leader election - a fundamental problem from distributed computing. Quantum mechanics allows leader election to be solved with no communication, provided that certain pre-shared entanglement is already in place. Further, an impossibility result from classical distributed computing is circumvented by the quantum solution of anonymous leader election - a unique leader is elected in finite time with certainty. Finally, we discuss the viability of these proposals from a practical perspective. Although, theoretically, distributed quantum computing looks promising, it is still unclear how to build quantum hardware and how to create and maintain robust large-scale entangled states. Moreover, it is not clear whether the costs of creating entangled states and working with them are smaller than the costs of existing classical solutions.
Quantum computing and distributed systems may enter a mutually beneficial partnership in the future. On the one hand, it is much easier to build a number of small quantum computers rather than a single large one. On the other hand, the best results concerning some of the fundamental problems in distributed computing can potentially be dramatically improved upon by taking advantage of the superior resources and processing power that quantum mechanics offers. This survey has the purpose to highlight both of these benefits. We first review the current results regarding the implementation of arbitrary quantum algorithms on distributed hardware. We then discuss existing proposals for quantum solutions of leader election - a fundamental problem from distributed computing. Quantum mechanics allows leader election to be solved with no communication, provided that certain pre-shared entanglement is already in place. Further, an impossibility result from classical distributed computing is circumvented by the quantum solution of anonymous leader election - a unique leader is elected in finite time with certainty. Finally, we discuss the viability of these proposals from a practical perspective. Although, theoretically, distributed quantum computing looks promising, it is still unclear how to build quantum hardware and how to create and maintain robust large-scale entangled states. Moreover, it is not clear whether the costs of creating entangled states and working with them are smaller than the costs of existing classical solutions.
The exploration of distributed quantum computing (DQC) represents a significant frontier in quantum information science, aiming to harness the unique properties of quantum mechanics to solve complex computational problems effectively. This paper discusses the diverse architectures and models that facilitate the distribution of quantum computing tasks across multiple quantum nodes, thereby addressing the limitations inherent in single quantum devices. DQC systems exploit the principles of superposition and entanglement to enhance computational capabilities beyond what classical computing systems can achieve. We examine various DQC architectures, including both quantum-classical hybrid systems and fully quantum distributed systems, highlighting their respective benefits and challenges. Key issues such as coherence, communication overhead, and error correction are discussed in detail, and we analyze specific use cases where DQC demonstrates superior performance relative to classical computing approaches, including optimization problems in logistics and finance, as well as quantum simulations for material science. Furthermore, we identify future research directions aimed at overcoming existing barriers to the practical implementation of DQC systems. By assessing the current landscape and future possibilities of DQC, this paper underscores the transformative potential of distributed quantum computing in various fields, paving the way for realizing more complex quantum algorithms and applications.
Quantum computing represents a transformative approach to computation leveraging fundamental principles of quantum mechanics such as superposition, entanglement and interference to store and process information in ways that classical computers cannot achieve.This paper attempts to provide a bona fide bibliographic overview of the principles, computational models, hardware technologies, and potential applications of quantum computing.It analyses how quantum algorithms could outperform classical algorithms in cryptographic analysis, optimization, and big data analysis.The survey integrates viewpoints from recent works; it presents system architectures, software development challenges, and quantum-assisted applications in healthcare, artificial intelligence, cybersecurity, and industrial optimization.Meanwhile, it examines hybrid quantum-classical systems that would allow quantum technologies to be deployed in the near term skirted by the limitations currently posed by quantum hardware.Moreover, the paper discusses foremost hurdles in scaling, error-correction, and maintaining coherence.From reviewing the recent developments and whether possible, this present review work informs researchers, engineers, and practitioners alike on the current state, as well as on the long-run viability, of quantum computing.
Nowadays, quantum computing has reached the engineering phase, with fully-functional quantum processors integrating hundreds of noisy qubits. Yet – to fully unveil the potential of quantum computing out of the labs into the business reality – the challenge ahead is to substantially scale the qubit number, reaching orders of magnitude exceeding thousands of fault-tolerant qubits. To this aim, the distributed quantum computing paradigm is recognized as the key solution for scaling the number of qubits. Indeed, accordingly to such a paradigm, multiple small-to-moderate-scale quantum processors communicate and cooperate for executing computational tasks exceeding the computational power of single processing devices. The aim of this survey is to provide the reader with an overview about the main challenges and open problems arising with distributed quantum computing from a computer and communications engineering perspective. Furthermore, this survey provides an easy access and guide towards the relevant literature and the prominent results in the field.
The anonymous network model was introduced by Angluin in [STOC '80, to understand the fundamental properties of distributed computing by examining how much each party in a network needs to know about its own identity and the identities of other parties.In this model, all parties with the same number of communication links are identical.When studying the model, the problem of electing a unique leader is the central problem in the sense that once a unique leader is elected, he can assign a unique identity to each party.It was proved in the literature, however, that it is impossible to deterministically solve the leader election problem with any finite amount of communication.This contrasts sharply with the situation in the quantum setting: the present authors gave quantum algorithms that exactly solve the problem on anonymous quantum networks, where quantum communication and computation can be performed [TOCT, vol.4,no.1, article 1].The core of their algorithm consists of somewhat tricky unitary operators, which eliminate the possibility of ties during (quantum) coin flipping and thereby reduce the number of leader candidates with certainty.This paper presents a new quantum leader election algorithm that is based on quantum reduction via exact amplitude amplification to a classically solvable problem, computing a certain symmetric function, which provides more intuitive reasoning behind the existence of exact quantum algorithms for leader election.The algorithm first achieves a round complexity that is linear in the number of parties, i.e., the largest possible diameter plus one of the underlying graph of the network.
The anonymous network model was introduced by Angluin in (STOC '80, pages 82-93) to understand the fundamental properties of distributed computing by examining how much each party in a network needs to know about its own identity and the identities of other parties. In this model, all parties with the same number of communication links are identical. When studying the model, the problem of electing a unique leader is the central problem in the sense that once a unique leader is elected, he can assign a unique identity to each party. It was proved in the literature, however, that it is impossible to deterministically solve the leader election problem with any finite amount of communication. This contrasts sharply with the situation in the quantum setting: the present authors gave quantum algorithms that exactly solve the problem on anonymous quantum networks, where quantum communication and computation can be performed (TOCT, vol.4, no.1, article 1). The core of their algorithm consists of somewhat tricky unitary operators, which eliminate the possibility of ties during (quantum) coin flipping and thereby reduce the number of leader candidates with certainty. This paper presents a new quantum leader election algorithm that is based on quantum reduction via exact amplitude amplification to a classically solvable problem, computing a certain symmetric function, which provides more intuitive reasoning behind the existence of exact quantum algorithms for leader election. The algorithm first achieves a round complexity that is linear in the number of parties, i.e., the largest possible diameter plus one of the underlying graph of the network.