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 distributed 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 structure. In this paper, we propose a double full-stack architecture encompassing quantum computation and quantum communications, which we use to address the monolithic versus distributed 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 multicore architectures may effectively unleash the full quantum computer potential.
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 distributed 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 structure. In this paper, we propose a double full-stack architecture encompassing quantum computation and quantum communications, which we use to address the monolithic versus distributed 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 multicore architectures may effectively unleash the full quantum computer potential.
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.
Despite its tremendous potential, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Among other issues, there are hard limits to the number of qubits that can be integrated into a single chip. Multicore architectures are a firm candidate for unlocking the scalability of quantum processors. Nonetheless, the vulnerability and complexity of quantum communications make this a challenging approach. A comprehensive design should imply consolidating the communications stack in the quantum computer architecture. In this article, we explain how this vision, by entangling communications and computation in the core of the design, may help to solve the open challenges. We also summarize the first results of our application of structured design methodologies backing this vision. With our work, we hope to contribute with design guidelines that may help unleash the potential of quantum computing.
In the quest of large-scale quantum computers, multi-core distributed architectures are considered a compelling alternative to be explored. A crucial aspect in such approach is the stringent demand on communication among cores when qubits need to interact, which conditions the scalability potential of these architectures. In this work, we address the question of how the cost of the communication among cores impacts on the viability of the quantum multi-core approach. Methodologically, we consider a design space in which architectural variables (number of cores, number of qubits per core), application variables for several quantum benchmarks (number of qubits, number of gates, percentage of two-qubit gates) and inter-core communication latency are swept along with the definition of a figure of merit. This approach yields both a qualitative understanding of trends in the design space and companion dimensioning guidelines for the architecture, including optimal points, as well as quantitative answers to the question of beyond which communication performance levels the multi-core architecture pays off. Our results allow to determine the thresholds for inter-core communication latency in order for multi-core architectures to outperform single-core quantum processors.
(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.
Modular quantum processor architectures are envisioned as a promising solution for the scalability of quantum computing systems beyond the Noisy Intermediate Scale Quantum (NISQ) era. Based upon interconnecting tens to hundreds of quantum processors (i.e cores) via quantum coherent and classical links, this approach unravels the pressing limitations of densely qubit-packed monolithic processors, mainly by mitigating the requirements of qubit control and enhancing qubit isolation. Therefore, this new architectural design enables executing large-scale algorithms in a distributed manner. In order to assess the performance and optimize such architectures, it is crucial to analyze the quantum state transfers occurring via inter-core communication networks, referred to as inter-core qubit traffic. This would provide insights to improve the software and hardware stack for multi-core quantum computers. To this aim, we present a characterization of the spatio-temporal inter-core qubit traffic for different large-scale quantum algorithms. The programs are compiled on an all-to-all connected multi-core architecture that supports up to around 1000 qubits. We characterize the qubit traffic based on multiple performance metrics to assess the computational process and the communication overhead. Based on the showcased results, we conclude on the parallelization and scalability of presented algorithms, qualitatively evaluate the resource requirements as we scale circuit sizes, and lay the foundations of application-oriented benchmarking of large-scale multi-core architectures.
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.