Multi-core quantum computing has been identified as a solution to the scalability problem of quantum computing. However, interconnecting quantum chips is not trivial, as quantum communications have their share of quantum weirdness: quantum decoherence and the no-cloning theorem makes transferring qubits a harsh challenge, where every extra nanosecond counts and retransmission is simply impossible. In this paper, we present our first steps towards thorough modeling of quantum communications for multi-core quantum computers, which may be considered as a middle point between the well-known paradigms of Quantum Internet and Network-on-Chip. In particular, we stress the deep entanglement that exists between latency and error rates in quantum computing, and how this affects the quantum network design for this scenario. Moreover, we show the concomitant trade-off between computation and communication resources for a set of parameters out of state-of-the-art experimental research. The observed behavior lets us foresee the potential of multi-core quantum architectures.
Multi-core quantum computing has been identified as a solution to the scalability problem of quantum computing. However, interconnecting quantum chips is not trivial, as quantum communications have their share of quantum weirdness: quantum decoherence and the no-cloning theorem makes transferring qubits a harsh challenge, where every extra nanosecond counts and retransmission is simply impossible. In this paper, we present our first steps towards thorough modeling of quantum communications for multi-core quantum computers, which may be considered as a middle point between the well-known paradigms of Quantum Internet and Network-on-Chip. In particular, we stress the deep entanglement that exists between latency and error rates in quantum computing, and how this affects the quantum network design for this scenario. Moreover, we show the concomitant trade-off between computation and communication resources for a set of parameters out of state-of-the-art experimental research. The observed behavior lets us foresee the potential of multi-core quantum architectures.
(English) Despite its tremendous potential, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Continued progress in the fabrication and control of qubits is certainly required. However, there are hard limits to the number of qubits that can be integrated into a single chip. Multi-core quantum computing has been identified as a solution to the scalability problem of quantum computing, and included in the development roadmaps of the leading industry. Nevertheless, interconnecting quantum chips is not trivial, as quantum communications have their share of quantum weirdness. Quantum data cannot be copied, and decoherence is an unforgiving noise source for every qubit transfer, where every extra nanosecond counts and retransmission is physically impossible. Despite all these challenges, a comprehensive approach to quantum computer design based on multi-core architectures that leverages all the potential of quantum communications is crucial to unlocking the scalability issues. In this context, the present thesis aims to lay the foundations of such a communications-enabled multi-core quantum computing architecture, as a proposed vision for the ultimate success of quantum computing. Our goal is to design a multi-core architecture that entangles computing and communication with a complete understanding of their intertwining requirements. In this way, while putting together dozens of quantum cores (i.e. thousands or millions of qubits collaborating), we alleviate the requirements for control circuits and improve qubit isolation. In order to achieve this goal, we tackle three main tasks. First, we propose a layered approach for a double full-stack comms-enabled many-core quantum computer architecture (chapter 2), aligned with our vision. We aim to provide the basis for an architecture that may be technology-agnostic and intertwine quantum computing and communications. Secondly, using design space exploration, we carry out a scalability and feasibility study of multi-core quantum architectures. The first approach used analytical formulations (chapter 4), while at the end of the thesis, leveraging all the acquired knowledge, code-base analysis, and fully-fledged network simulations are employed, run within a framework developed also for this work (chapter 7). The results of the exploration let us also compare different existing qubit and quantum communication technologies (section 4.4.2). This work might facilitate future work for providing design guidelines and optimal operation ranges for efficient and scalable multi-core quantum computers. Finally, all this work needs to be backed by a study on short-range quantum communications. In particular, we have developed a model of quantum teleportation as a fitting candidate for inter-core communication technology (chapter 5). Moreover, we perform a thorough qubit traffic analysis on several algorithms and architectures that helps us see the bottlenecks and inefficiencies of such a network (sections 6.1 to 6.3). This leads to a latency and throughput analysis with real traffic together with the dimensioning of networking resources, completed by using a fully-fledged simulator developed for this thesis that models with high fidelity the different parts of a multi-core quantum computer (section 7.1). In addition, we have started the development of an efficient MAC protocol specific to our use case (section 6.4), which we believe will complete the architecture design and communications modeling. With the results of this thesis, we hope to contribute with design guidelines that may enable multi-core quantum architectures to unleash the potential of quantum computing. (Español) pesar de su gran potencial, es difícil de prever cómo escalará la computación cuántica para satisfacer los requisitos de sus aplicaciones más poderosas. Sin duda es necesaria la mejora en la fabricación y el control de qubits. Sin embargo, existen límites estrictos para la cantidad de qubits que se pueden integrar en un solo chip. Como solució, se ha propuesta la computación cuántica multinúcleo, que ya protagoniza las hojas de ruta de la industria puntera. Sin embargo, interconectar chips cuánticos no es trivial, al tener las comunicaciones cuánticas sus particularidades. Los datos cuánticos no se pueden copiar y la decoherencia es una fuente de ruido implacable: cada nanosegundo cuenta y la retransmisión es físicamente imposible. A pesar de todos estos desafíos, un enfoque integral para el diseño de computadoras cuánticas basado en arquitecturas multinúcleo que aproveche todo el potencial de las comunicaciones cuánticas es crucial para desbloquear los problemas de escalabilidad. En este contexto, la presente tesis tiene como objetivo sentar las bases de tal arquitectura, en la que las comunicaciones juegan un papel fundamental. Nuestro objetivo es diseñar una arquitectura multinúcleo que combine la informática y la comunicación con una comprensión completa de sus requisitos entrelazados. De esta manera, uniendo decenas de núcleos cuánticos (es decir, miles o millones de qubits colaborando), aliviamos a su vez los requisitos de los circuitos de control y mejoramos el aislamiento de los qubits. Para lograr este objetivo, abordamos tres tareas principales. En primer lugar, proponemos un enfoque en capas para una arquitectura de computadora cuántica multinúcleo que entrelaza computación y comunicación (capítulo 2), alineada con nuestra visión. Nuestro objetivo es proporcionar la base para una arquitectura que pueda ser independiente de la tecnología y entrelace la computación cuántica y las comunicaciones. En segundo lugar, utilizando la técnica de exploración del espacio de diseño, llevamos a cabo un estudio de escalabilidad y viabilidad de arquitecturas cuánticas multinúcleo. En el primer estudio se han utilizado formulaciones analíticas (capítulo 4), mientras que al final de la tesis, aprovechando todo el conocimiento adquirido, se emplean análisis basados en código compilado y en simulaciones completas, ejecutadas dentro de un marco desarrollado también para este trabajo (capítulo 7). Los resultados de la exploración además nos han permitido comparar diferentes tecnologías de comunicación cuántica y qubit existentes (sección 4.4.2). Este trabajo podría facilitar el trabajo futuro para proporcionar pautas de diseño y rangos de operación óptimos para computadoras cuánticas multinúcleo eficientes y escalables. Finalmente, todo este trabajo ha necesitado estar acompañado por un estudio sobre comunicaciones cuánticas de corto alcance. En particular, hemos desarrollado un modelo de teletransportación cuántica como candidato adecuado para la tecnología de comunicación entre núcleos (capítulo 5). Además, hemos realizado un análisis exhaustivo del tráfico de qubits en varios algoritmos y arquitecturas que nos ayuda a ver los cuellos de botella y las ineficiencias de dicha red (secciones 6.1 a 6.3). Esto nos ha conducido a un análisis de latencia y rendimiento con tráfico real junto con el dimensionamiento de los recursos de red, completado mediante el uso de un completo simulador -desarrollado para esta tesis- que modela con alta fidelidad las diferentes partes de un ordenador cuántico multinúcleo (apartado 7.1). Además, hemos dado los primeros pasos en el desarrollo de un protocolo MAC eficiente, específico para nuestro caso de uso (sección 6.4), que creemos completará el diseño de la arquitectura y el modelado de comunicaciones. Con los resultados de esta tesis, esperamos contribuir con pautas de diseño que puede permitir que las arquitecturas cuánticas de múltiples núcleos liberen el potencial de la computación cuántica.
Multi-core quantum computing architectures offer a promising and scalable solution to the challenges of integrating large number of qubits into existing monolithic chip design. However, the issue of transferring quantum information across the cores remains unresolved. Quantum Teleportation offers a potential approach for efficient qubit transfer, but existing methods primarily rely on centralized interconnection mechanisms for teleportation, which may limit scalability and parallel communication. We proposes a decentralized framework for teleportation in multi-core quantum computing systems, aiming to address these limitations. We introduce two variants of teleportation within the decentralized framework and evaluate their impact on reducing end-to-end communication delay and quantum circuit depth. Our findings demonstrate that the optimized teleportation strategy, termed two-way teleportation, results in a substantial 40% reduction in end-to-end communication latency for synthetic benchmarks and a 30% reduction for real benchmark applications, and 24% decrease in circuit depth compared to the baseline teleportation strategy. These results highlight the significant potential of decentralized teleportation to improve the performance of large-scale quantum systems, offering a scalable and efficient solution for future quantum architectures.
Multi-core quantum computing architectures offer a promising and scalable solution to the challenges of integrating large number of qubits into existing monolithic chip design. However, the issue of transferring quantum information across the cores remains unresolved. Quantum Teleportation offers a potential approach for efficient qubit transfer, but existing methods primarily rely on centralized interconnection mechanisms for teleportation, which may limit scalability and parallel communication. We proposes a decentralized framework for teleportation in multi-core quantum computing systems, aiming to address these limitations. We introduce two variants of teleportation within the decentralized framework and evaluate their impact on reducing end-to-end communication delay and quantum circuit depth. Our findings demonstrate that the optimized teleportation strategy, termed two-way teleportation, results in a substantial 40% reduction in end-to-end communication latency for synthetic benchmarks and a 30% reduction for real benchmark applications, and 24% decrease in circuit depth compared to the baseline teleportation strategy. These results highlight the significant potential of decentralized teleportation to improve the performance of large-scale quantum systems, offering a scalable and efficient solution for future quantum architectures.
Scalable quantum computing architectures increasingly rely on multi-core designs, where qubits are distributed across multiple processing cores interconnected through a quantum Network-on-Chip (NoC). In such systems, inter-core communication is typically realized through entanglement-assisted quantum teleportation, making efficient entanglement generation critical for performance. In this paper, we perform a comparative study of three entanglement management paradigms for multi-core quantum processors: reactive on-demand generation (ODG), proactive continuous pre-generation (CGP), and an adaptive continuous pre-generation approach (ACGP). While ODG generates entanglement only when required, CGP reduces average teleportation latency by pre-generating EPR pairs in the background. To improve upon this, we propose ACGP which dynamically adjusts entanglement generation probabilities based on observed inter-core communication patterns. We evaluate these approaches using an extended SeQUeNCe simulator on mesh-based multi-core architectures on real benchmark circuits. Results show that ACGP significantly reduces average teleportation latency compared to ODG and CGP. Although pre-generation introduces fidelity degradation due to storage time, entanglement purification effectively restores fidelity with minimal impact on latency. These results demonstrate that adaptive entanglement managements can substantially improve communication efficiency in scalable quantum multi-core systems.
Modular architectures are a promising approach to scaling quantum computers beyond the limits of monolithic designs. However, non-local communications between different quantum processors might significantly impact overall system performance. In this work, we investigate the role of the network infrastructure in modular quantum computing architectures, focusing on coherence loss due to communication constraints. We analyze the impact of classical network latency on quantum teleportation and identify conditions under which it becomes a bottleneck. Additionally, we study different network topologies and assess how communication resources affect the number and parallelization of inter-core communications. Finally, we conduct a full-stack evaluation of the architecture under varying communication parameters, demonstrating how these factors influence the overall system performance. The results show that classical communication does not become a bottleneck for systems exceeding one million qubits, given current technology assumptions, even with modest clock frequencies and parallel wired interconnects. Additionally, increasing quantum communication resources generally shortens execution time, although it may introduce additional communication overhead. The optimal number of quantum links between QCores depends on both the algorithm being executed and the chosen inter-core topology. Our findings offer valuable guidance for designing modular architectures, enabling scalable quantum computing.
Being a very promising technology, with impressive advances in the recent years, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Although continued progress in the fabrication and control of qubits is required, quantum computing scalability will depend as well on a comprehensive architectural design considering a multi-core approach as an alternative to the traditional monolithic version, hence including a communications perspective. However, this goes beyond introducing mere interconnects. Rather, it implies consolidating the full communications stack in the quantum computer architecture. In this paper, we propose a double full-stack architecture encompassing quantum computation and quantum communications, which we use to address the monolithic versus multi-core question with a structured design methodology. For that, we revisit the different quantum computing layers to capture and model their essence by highlighting the open design variables and performance metrics. Using behavioral models and actual measurements from existing quantum computers, the results of simulations suggest that multi-core architectures may effectively unleash the full quantum computer potential.