We present a stack model for breaking down the complexity of entanglement-based quantum networks.More specifically, we focus on the structures and architectures of quantum networks and not on concrete physical implementations of network elements.We construct the quantum network stack in a hierarchical manner comprising several layers, similar to the classical network stack, and identify quantum networking devices operating on each of these layers.The layers responsibilities range from establishing point-to-point connectivity, over intra-network graph state generation, to inter-network routing of entanglement.In addition we propose several protocols operating on these layers.In particular, we extend the existing intra-network protocols for generating arbitrary graph states to ensure reliability inside a quantum network, where here reliability refers to the capability to compensate for devices failures.Furthermore, we propose a routing protocol for quantum routers which enables the generation of arbitrary graph states across network boundaries.This protocol, in correspondence with classical routing protocols, can compensate dynamically for failures of routers, or even complete networks, by simply re-routing the given entanglement over alternative paths.We also consider how to connect quantum routers in a hierarchical manner to reduce complexity, as well as reliability issues arising in connecting these quantum networking devices.
We present a stack model for breaking down the complexity of entanglement-based quantum networks.More specifically, we focus on the structures and architectures of quantum networks and not on concrete physical implementations of network elements.We construct the quantum network stack in a hierarchical manner comprising several layers, similar to the classical network stack, and identify quantum networking devices operating on each of these layers.The layers responsibilities range from establishing point-to-point connectivity, over intra-network graph state generation, to inter-network routing of entanglement.In addition we propose several protocols operating on these layers.In particular, we extend the existing intra-network protocols for generating arbitrary graph states to ensure reliability inside a quantum network, where here reliability refers to the capability to compensate for devices failures.Furthermore, we propose a routing protocol for quantum routers which enables the generation of arbitrary graph states across network boundaries.This protocol, in correspondence with classical routing protocols, can compensate dynamically for failures of routers, or even complete networks, by simply re-routing the given entanglement over alternative paths.We also consider how to connect quantum routers in a hierarchical manner to reduce complexity, as well as reliability issues arising in connecting these quantum networking devices.
The emergence of quantum networks promises revolutionary advancements in secure communication, computational power, and information processing. This paper provides insights into the essential components and architecture of quantum networks. We systematically examine each layer of the quantum protocol stack, from the physical layer responsible for qubit transmission and entanglement generation to the transport layer ensuring reliable qubit communication, up to the application layer enabling quantum key distribution and quantum computing applications. In this work, we introduce the E-QNet framework, an entanglement-assisted quantum network protocol stack designed to facilitate quantum communication. Key devices such as quantum transceivers, entanglement sources, quantum memories, quantum repeaters, and quantum routers are analyzed in the context of their specific roles and functionalities. We draw parallels with classical network architecture, highlighting both the unique challenges and novel solutions inherent in quantum networking. By elucidating the interplay between hardware devices and protocol layers, this article provides a comprehensive overview of the current state and future directions in quantum network design, offering valuable insights for researchers and engineers in the field. This work aims to contribute to the foundational understanding required for the development and implementation of robust quantum networks.
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.
Over the course of the last five decades, there has been substantial growth in conventional network routing design, transitioning from small static node networks to vast systems connecting billions of devices. This evolution has been facilitated by the separation of concerns principle, which involves integrating network functionalities into graph or random network designs and utilizing specific protocols to enable diverse communication capabilities. The landscape of quantum networks is rapidly evolving, presenting new paradigms in information transmission and processing. Routing protocols play a pivotal role in establishing efficient communication pathways within quantum networks, enabling the transmission of quantum states and entanglement across interconnected nodes. The objective of this paper is to shed light on existing entanglement routing design techniques within quantum networks. The design of quantum entanglement routing necessitates a departure from conventional network protocols due to its unique considerations of quantum entanglement and entanglement swapping. However, the implementation of these techniques is fraught with significant challenges, including quantum system decoherence and noise, limitations on communication ranges, and the need for specialized hardware. The paper initiates by surveying critical research in quantum routing design techniques, then delves into essential aspects of the routing concept, associated quantum operations, and the step-wise process for establishing efficient and resilient quantum networks. In summary, this paper provides an overview of the current landscape of quantum entanglement routing techniques. It outlines their core principles, protocols, and challenges, while also highlighting potential applications and charting future directions for research and development.
This paper proposes a novel distributed routing protocol for quantum networks leveraging the topological properties of quantum entanglement. The core idea is to construct a network topology based on entangled states between nodes, enabling communication through the instantaneous correlation inherent in entanglement. This approach aims to overcome the limitations of traditional routing protocols, particularly in terms of speed and security. We define a routing algorithm that dynamically adjusts the entanglement states to facilitate data transmission, effectively creating a network with inherently high bandwidth and resilience to eavesdropping. The algorithm is based on a graph theory framework where nodes represent quantum devices and edges represent entangled pairs. The routing process involves identifying the shortest path through the entanglement network, leveraging the correlated states for rapid information transfer. We explore the mathematical underpinnings of this protocol, outlining key formulas for calculating entanglement metrics, path distances, and routing decisions. The theoretical framework presented here provides a foundation for future research and development in quantum network architecture and routing strategies.
This paper proposes a dynamic routing protocol for quantum networks based on the fluctuating entanglement states between quantum nodes. The core of the protocol lies in real-time monitoring of entanglement strength and dynamically adjusting routing paths based on these changes. This approach aims to mitigate the risk of information loss due to entanglement decay, ultimately achieving high reliability in quantum routing. Unlike traditional protocols relying on fixed topologies, this protocol adapts to the dynamic nature of entanglement, enhancing routing efficiency and resilience. The protocol utilizes a graph-based representation of the quantum network and employs algorithms for entanglement assessment and path optimization. Mathematical models are presented to formalize the routing process, including the calculation of entanglement fidelity and path cost. The proposed system demonstrates improved routing performance and fault tolerance compared to static routing schemes. The key contribution is a dynamic, adaptive routing strategy that leverages the inherent properties of quantum networks for reliable quantum information transmission.
Quantum networks create a completely new way for communication, and the most important function of a quantum network is to generate long-distance quantum entanglement to serve a number of quantum applications. As the scale of the network expands, in order to establish end-to-end entanglement between two remote nodes, entangled pairs need to be generated and distributed among multiple repeaters along the path from the source to the destination, which requires a specific protocol to negotiate resource allocations and quantum operations among the repeaters. Thus, to realize such remote entanglement distribution in a quantum network, designing a stable and reliable protocol becomes urgent and necessary. In this article, we focus on how to guarantee the generation rate of entangled pairs between any two quantum nodes to meet the requirements of various quantum applications in a large-scale quantum network. We present a connection-oriented entanglement distribution protocol inspired by the connection-oriented communication model in classical networks. Our protocol is located in the network layer of the quantum network to enable end-to-end quantum communication. Three main features are provided by the proposed protocol: 1) it is reliable and can guarantee the successful entanglement generation; 2) it can reduce the influence of quantum decoherence via reducing the latency caused by resource competition; and 3) it can guarantee the rate of generating entanglement between two quantum nodes according to the requirement of quantum applications.