As the works on quantum computing have seen substantial development in recent years, we are on the verge of seeing the fruitful result of the preliminary, early version of quantum computers. Nevertheless, in order to achieve full-fledged, large-scale quantum computers, two aspects still lacking in the existing quantum computers, i.e., scalability and reliability, will need to be more carefully considered and investigated. In this survey, we present a review of existing literature that aims to alleviate the scalability and reliability issues in quantum computers. In particular, we discuss how existing research leads to two main solutions: for advancing scalability, a distributed quantum computing (DQC) paradigm will be the primary direction instead of the general centralized quantum computing (CQC), whereas for attaining reliability, a fault-tolerant quantum computation (FTQC) approach would need to be leveraged instead of the existing noisy intermediate-scale quantum computers (NISQ). Combining both solutions, we highlight the essentiality of fault-tolerant distributed quantum computation (FT-DQC) and present related progress in the field. Furthermore, from the papers that we have gathered, we provide the taxonomy of the works to give a clearer landscape of the field and discuss the key issues in realizing FT-DQC.
As the works on quantum computing have seen substantial development in recent years, we are on the verge of seeing the fruitful result of the preliminary, early version of quantum computers. Nevertheless, in order to achieve full-fledged, large-scale quantum computers, two aspects still lacking in the existing quantum computers, i.e., scalability and reliability, will need to be more carefully considered and investigated. In this survey, we present a review of existing literature that aims to alleviate the scalability and reliability issues in quantum computers. In particular, we discuss how existing research leads to two main solutions: for advancing scalability, a distributed quantum computing (DQC) paradigm will be the primary direction instead of the general centralized quantum computing (CQC), whereas for attaining reliability, a fault-tolerant quantum computation (FTQC) approach would need to be leveraged instead of the existing noisy intermediate-scale quantum computers (NISQ). Combining both solutions, we highlight the essentiality of fault-tolerant distributed quantum computation (FT-DQC) and present related progress in the field. Furthermore, from the papers that we have gathered, we provide the taxonomy of the works to give a clearer landscape of the field and discuss the key issues in realizing FT-DQC.
The limited qubit resources of current quantum processing units (QPUs), together with their susceptibility to operational imperfections, environmental noise, and error propagation, not only degrade computational fidelity but also constrain the scalability required for utility-scale quantum computing. Consequently, the transition from monolithic architectures to distributed quantum computing (DQC), supported by distributed quantum error-correcting codes (QECCs), is emerging as a promising paradigm for large-scale fault-tolerant quantum computing (FTQC). This transition represents a full-stack challenge that requires coordinated advances in quantum architecture, fault-tolerant gate operations, and classical–quantum co-processing and control. In this paper, we review the theoretical foundations and practical realization of large-scale FTQC. We first explore major families of QECCs, including topological, qLDPC, subsystem, and dynamical codes, with emphasis on code construction, syndrome extraction, and decoding. We then review the implementation of fault-tolerant universal gate sets at the physical and logical levels, followed by entanglement generation, distribution, and purification for distributed architectures. Finally, we outline open challenges and future research directions in theory, architecture, and implementation, highlighting the role of distributed fault-tolerant designs in next-generation utility-scale 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.
Emergence of fault-tolerant quantum computers (FTQC) brings about promise of harnessing the power of quantum computing at larger scale. At the same time, as quantum computers are expected to process more sensitive information, there is a need to understand the security issues in fault-tolerant quantum computers, and develop defenses for attacks that may compromise confidentiality or integrity of the data processed by FTQC. While noisy intermediate-scale quantum (NISQ) computers have already been studied from the security perspective, understanding security issues with FTQC is still an open research question. To address the missing research gap, this work presents the first exploration of possible security vulnerabilities of FTQC. The work presents analysis of possible threat models and outlines potential vulnerabilities of FTQC. Understanding the landscape of the threats can help lead to development of safer FTQC design at both software and hardware levels.
The transition from classical to quantum computation marks a shift from deterministic binary logic to a probabilistic, entanglement‑driven framework able to address problems beyond classical reach. Today’s Noisy Intermediate ‑ Scale Quantum era features devices that lack full error correction yet already point toward larger, modular systems designed for fault‑tolerant operation. This paper examines the evolving paradigm shift from classical and NISQ ‑ era machines toward practical fault‑tolerant quantum computing, focusing on how advances in physical qubit technologies, control architectures, and error‑correction strategies are converging to bridge noisy prototypes and scalable, useful machines. We synthesize insights from historical semiconductor scaling trends, contemporary roadmaps from leading institutions and industry, and emerging modular designs with real‑time error decoding. Our analysis shows that while challenges around decoherence, connectivity, and classical co‑processing remain, coordinated progress in hardware, control, and software is laying a coherent foundation for future quantum platforms. The work concludes that quantum computing is maturing into a strategically significant paradigm, poised to redefine the limits of computation in simulation, optimization, and secure communication.
Quantum error correction (QEC) represents the cornerstone technology for realizing fault-tolerant quantum computing, addressing the fundamental challenge of quantum state decoherence in noisy intermediate-scale quantum (NISQ) devices. This comprehensive review examines recent advances in QEC implementations from 2020-2024, spanning theoretical foundations to practical hardware demonstrations. We analyze the evolution from pioneering stabilizer codes to modern topological approaches, with particular emphasis on surface codes and low-density parity-check (LDPC) codes that have demonstrated below-threshold error correction in superconducting and trapped-ion systems. The paper provides a comparative analysis of classical and machine learning-based decoder algorithms, evaluating their performance through complexity analysis and threshold comparisons in real-time error correction scenarios. Through examination of breakthrough experiments by Google, IBM, Quantinuum, and emerging platforms, we assess the current state of fault-tolerant quantum computing and identify critical engineering challenges including correlated noise models, cryogenic control systems, and scalable logical gate implementations. Our quantitative analysis reveals that while significant progress has been made toward practical fault-tolerance thresholds, achieving the resource efficiency and reliability required for large-scale quantum computation remains challenging. We provide detailed resource estimates for key applications including Shor's algorithm and optimization problems, along with analysis of industry roadmaps toward thousand-logical-qubit systems. This review serves as a comprehensive guide for researchers and engineers working toward the next generation of fault-tolerant quantum computers, with particular focus on information-theoretic perspectives relevant to quantum information entropy and syndrome processing.
Quantum error correction (QEC) represents the cornerstone technology for realizing fault-tolerant quantum computing, addressing the fundamental challenge of quantum state decoherence in noisy intermediate-scale quantum (NISQ) devices. This comprehensive review examines recent advances in QEC implementations from 2020-2024, spanning theoretical foundations to practical hardware demonstrations. We analyze the evolution from pioneering stabilizer codes to modern topological approaches, with particular emphasis on surface codes and low-density parity-check (LDPC) codes that have demonstrated below-threshold error correction in superconducting and trapped-ion systems. The paper provides a comparative analysis of classical and machine learning-based decoder algorithms, evaluating their performance through complexity analysis and threshold comparisons in real-time error correction scenarios. Through examination of breakthrough experiments by Google, IBM, Quantinuum, and emerging platforms, we assess the current state of fault-tolerant quantum computing and identify critical engineering challenges including correlated noise models, cryogenic control systems, and scalable logical gate implementations. Our quantitative analysis reveals that while significant progress has been made toward practical fault-tolerance thresholds, achieving the resource efficiency and reliability required for large-scale quantum computation remains challenging. We provide detailed resource estimates for key applications including Shor's algorithm and optimization problems, along with analysis of industry roadmaps toward thousand-logical-qubit systems. This review serves as a comprehensive guide for researchers and engineers working toward the next generation of fault-tolerant quantum computers, with particular focus on information-theoretic perspectives relevant to quantum information entropy and syndrome processing.