This thesis treats networks providing quantum computation based on distributed paradigms. Compared to architectures relying on one processor, a network promises to be more scalable and less fault-prone. Developing a distributed system able to provide practical quantum computation comes with many challenges, each of which need to be faced with careful analysis in order to create a massive integration of several components properly engineered. In accordance with hardware technologies, currently under construction around the globe, telegates represent the fundamental inter-processor operations. Each telegate consists of several tasks: i) entanglement generation and distribution, ii) local operations, and iii) classical communications. Entanglement generation and distribution is an expensive resource, as it is time-consuming. The main contribution of this thesis is on the definition of compilers that minimize the impact of telegates on the overall fidelity. Specifically, we give rigorous formulations of the subject problem, allowing us to identify the inter-dependence between computation and communication. With the support of some of the best tools for reasoning -- i.e. network optimization, circuit manipulation, group theory and ZX-calculus -- we found new perspectives on the way a distributed quantum computing system should evolve.
This thesis treats networks providing quantum computation based on distributed paradigms. Compared to architectures relying on one processor, a network promises to be more scalable and less fault-prone. Developing a distributed system able to provide practical quantum computation comes with many challenges, each of which need to be faced with careful analysis in order to create a massive integration of several components properly engineered. In accordance with hardware technologies, currently under construction around the globe, telegates represent the fundamental inter-processor operations. Each telegate consists of several tasks: i) entanglement generation and distribution, ii) local operations, and iii) classical communications. Entanglement generation and distribution is an expensive resource, as it is time-consuming. The main contribution of this thesis is on the definition of compilers that minimize the impact of telegates on the overall fidelity. Specifically, we give rigorous formulations of the subject problem, allowing us to identify the inter-dependence between computation and communication. With the support of some of the best tools for reasoning -- i.e. network optimization, circuit manipulation, group theory and ZX-calculus -- we found new perspectives on the way a distributed quantum computing system should evolve.
Practical distributed quantum computing requires the development of efficient compilers, able to make quantum circuits compatible with some given hardware constraints. This problem is known to be tough, even for local computing. Here, we address it on distributed architectures. As generally assumed in this scenario, telegates represent the fundamental remote (inter-processor) operations. Each telegate consists of several tasks: (i) entanglement generation and distribution, (ii) local operations, and (iii) classical communications. Entanglement generations and distribution is an expensive resource, as it is time-consuming. To mitigate its impact, we model an optimization problem that combines running-time minimization with the usage of distributed entangled states. Specifically, we formulated the distributed compilation problem as a dynamic network flow. To enhance the solution space, we extend the formulation, by introducing a predicate that manipulates the circuit given in input and parallelizes telegate tasks. To evaluate our framework, we split the problem into three sub-problems, and solve it by means of an approximation routine. Experiments demonstrate that the run-time is resistant to the problem size scaling. Moreover, we apply the proposed algorithm to compile circuits under different topologies, showing that topologies with a higher ratio between edges and nodes give rise to shallower circuits.
This paper presents a comprehensive review of quantum computing and the technological foundations of quantum processors. Quantum computing represents a transformative computational paradigm that leverages the fundamental principles of quantum mechanics—such as superposition, entanglement, and quantum interference—to solve complex problems that are intractable for classical computers. At the core of this paradigm lies the quantum processor, a specialized hardware system designed to initialize, control, and measure quantum bits (qubits) through precise gate operations and coherent interactions. The survey examines the essential theoretical concepts underlying quantum computation and provides a structured comparison of leading quantum processor platforms. Prominent architectures, including superconducting circuits, trapped-ion systems, and photonic implementations, are analyzed in terms of their physical mechanisms, scalability, coherence properties, and engineering challenges. Each platform offers distinct advantages and faces specific technical limitations related to noise, error correction, and fabrication complexity. In addition to reviewing hardware developments, this study highlights key obstacles in advancing quantum processors toward large-scale, fault-tolerant systems. Issues such as qubit stability, error mitigation, thermal management, and system integration are discussed to present a realistic perspective on current progress. Performance indicators including gate fidelity, coherence time, connectivity, and scalability are used to compare architectural approaches. The objective of this paper is to provide a clear and organized synthesis of recent advancements in quantum computing hardware, thereby offering researchers and practitioners a foundational reference to support continued innovation and development in this rapidly evolving field.
Scalable quantum computing requires execution models that go beyond the capacity of a single quantum processing unit (QPU). Although current hardware platforms continue to increase in qubit count, large fault-tolerant applications require substantially more physical qubits, stronger connectivity, and lower effective error rates than a monolithic near-term device can provide. Multi-QPU and multi-core architectures therefore form an important route towards larger quantum systems. However, distributing a quantum computation introduces compiler and architecture constraints that do not arise in conventional classical distribution. A partitioned quantum circuit separates gates and qubits that may still be logically entangled or mutually dependent. The system must therefore provide quantum resources that support entanglement between the distributed circuit fragments, while each local subcircuit must remain executable on the hardware topology of its assigned QPU. In this thesis, graph states serve as the explicit interconnection resources for these nonlocal dependences: they encode the entanglement structure required to support teleportation-based operations across QPUs. This thesis studies scalable quantum execution as an architecture-driven compilation problem. It develops a staged framework in which distribution, graph-state-based interconnection, and interconnection robustness are treated as dependent compiler decisions. The framework addresses three connected questions: 1) how a large quantum circuit should be divided when the resulting subcircuits must match real QPU topologies; 2) how the graph states required to entangle and operate across the distributed circuit boundaries can be prepared efficiently on constrained hardware; and 3) how those graph-state resources can remain useful under the loss and fusion failures that arise during preparation and use. These questions define an execution path from a large logical circuit to distributed local workloads connected by explicit entanglement resources. The thesis makes three main technical contributions that instantiate this framework. 1) It introduces hardware-aware circuit cutting, which incorporates the relationship between subcircuit interaction graphs and target QPU topology into the partitioning objective. This stage produces distributed workloads and explicit cut boundaries where quantum entanglement must be supplied across QPUs. 2) It formulates graph-state preparation as the resource-generation stage for those boundaries and develops methods that reduce preparation depth and emitter usage by exploiting graph-state equivalence and divide-and-conquer construction. 3) It develops a robust graph-state interconnection scheme that uses tree-encoded fusion and spin-memory-assisted compilation to tolerate photon loss and probabilistic fusion failures, so that the graph state can serve as a reliable connection between distributed quantum program fragments.
For most practical applications, quantum algorithms require large resources in terms of qubit number, much larger than those available with current NISQ processors. With the network and communication functionalities provided by the Quantum Internet, Distributed Quantum Computing (DQC) is considered as a scalable approach for increasing the number of available qubits for computational tasks. For DQC to be effective and efficient, a quantum compiler must find the best partitioning for the quantum algorithm and then perform smart remote operation scheduling to optimize EPR pair consumption. At the same time, the quantum compiler should also find the best local transformation for each partition. In this paper we present a modular quantum compilation framework for DQC that takes into account both network and device constraints and characteristics. We implemented and tested a quantum compiler based on the proposed framework with some circuits of interest, such as the VQE and QFT ones, considering different network topologies, with quantum processors characterized by heavy-hexagon coupling maps. We also devised a strategy for remote scheduling that can exploit both TeleGate and TeleData operations and tested the impact of using either only TeleGates or both. The evaluation results show that TeleData operations can have a positive impact on the number of consumed EPR pairs, depending on the characteristic of compiled circuit. Meanwhile, choosing a more connected network topology helps reduce the number of layers dedicated to remote operations.
Quantum mechanics shows that if one is able to generate and manipulate entanglement over a distance, one is able to perform certain tasks which are impossible using only classical communication. Classical communication refers to what is used in the Internet of today. A quantum internet would therefore bring new capabilities to our highly connected world. These capabilities both involve (1) the ability to perform tasks with are provably impossible in the current Internet, such as unconditionally secure communication, and (2) the ability to perform certain tasks much more efficient, such as distributed (quantum) computing or extending the baseline of telescopes. To be able to build a quantum internet, two main components are needed: (i) hardware that can store, manipulate and entangle qubits and (ii) a software stack to control the hardware. The core task of both of these is to generate entanglement to be used by applications. In this thesis we focus on the latter, i.e. the development of software and protocols that enable entanglement generation using capable hardware. To enable a certain application, one can certainly, in theory, manually specify each operation the hardware should perform, involving micro-wave pulses, lasers etc. However, in practice this is not feasible, if not to say impossible, due to the complexity of the operations needed, especially in a distributed system such as a quantum network. What is needed is a software stack, which can help with abstracting complexity away in multiple layers. This allows for someone to program a protocol in one layer without knowing all the details of the lower layers. In particular, one can abstract away the hardware details, in order to make higher-layer protocols and applications hardware-agnostic. Therefore, to be able to build a universal, efficient and scalable quantum internet, a software stack is crucial. In chapter 2 we start discussing the networking part of a software stack. Namely, we introduce a network stack for a quantum internet, drawing parallels to the IP/TCP-suite of the classical Internet. We continue with proposing a service and interface of the lowest layer of the network stack: the link layer. The link layer is here responsible for generating entanglement between nodes in a quantum network which are directly connected by a quantum link, i.e. a fiber cable. When developing a protocol or application it is very useful to be able to run it. Both to see if the intended ideas make sense and also to check that the implementation is actually correct. Currently we do not have quantum hardware that exposes a full-fledge API that can be used to execute applications. For this reason, it is very useful to be able to instead simulate the hardware in a way that exposes the same API as the hardware being developed. In chapter 3 we introduce SimulaQron for this exact purpose. Any application of a quantum internet will need entanglement in one way or another. However, entanglement is generally hard to generate and is usually the bottleneck when executing an application. We would therefore like to make use of the generated entanglement in the most optimal way. To be able to do this we need to understand how entanglement can be transformed and distributed in a quantum network. We study the entanglement of a particular class of states called graph states in chapters 4 to 9 and how these states can be transformed in a quantum network.
This paper proposes a novel distributed computing architecture predicated on the precise control of quantum entanglement. The core claim is that by leveraging entanglement, it is possible to design a computing paradigm that surpasses the limitations of classical parallel computing. The proposed architecture utilizes entangled states to connect multiple quantum processors, enabling instantaneous state transfer and information sharing. This approach involves the development of new entanglement generation and control algorithms, optimized to manipulate quantum superposition and interference, thereby enhancing computational efficiency. The key innovation lies in moving beyond the bottleneck of classical communication inherent in traditional distributed systems. This architecture promises a fundamentally different approach to parallel computation, exploiting the unique properties of quantum mechanics. The presented framework offers a potential pathway towards scalable and highly efficient quantum computation, though significant technological challenges remain. The theoretical framework outlines the key components and operational principles of this new architecture.