Future quantum networks are likely to be heterogeneous both in functionality and quality of service. In this work, we present a routing protocol that takes into account this heterogeneity. While functional heterogeneity can be on several aspects, we divide the quantum computers and repeaters on a quantum network into two classes-those that can perform general-purpose quantum computing, including complex error correction routines and those that can only perform basic operations like entangled pair generation and Bell State Measurements. In terms of quality of service, we categorise the quantum nodes as per the probability of successfully, which we call the node reliability, executing a quantum operation and the expected time taken to do so. The routing protocol that we propose seeks to maximise the reliability of sharing EPR pairs between different nodes of a quantum network, with a minimum guaranteed threshold of fidelity and, optionally, a time constraint. We provide simulation results that indicate the effectiveness of the protocol in achieving these objectives.
Future quantum networks are likely to be heterogeneous both in functionality and quality of service. In this work, we present a routing protocol that takes into account this heterogeneity. While functional heterogeneity can be on several aspects, we divide the quantum computers and repeaters on a quantum network into two classes-those that can perform general-purpose quantum computing, including complex error correction routines and those that can only perform basic operations like entangled pair generation and Bell State Measurements. In terms of quality of service, we categorise the quantum nodes as per the probability of successfully, which we call the node reliability, executing a quantum operation and the expected time taken to do so. The routing protocol that we propose seeks to maximise the reliability of sharing EPR pairs between different nodes of a quantum network, with a minimum guaranteed threshold of fidelity and, optionally, a time constraint. We provide simulation results that indicate the effectiveness of the protocol in achieving these objectives.
Deciding a route for the transfer of quantum information (namely, qubits) on a quantum network is a significant problem that is being studied extensively. In this work, we investigate the problem of routing on a quantum network of heterogeneous nodes both with and without fidelity and timing constraints.We propose a Path Request Packet (PRP) based routing scheme for dynamically selecting a path that maximizes the overall probability of transmission success while maintaining fidelity above a threshold and adhering to time constraints. While the proposed scheme can perform suboptimally under fidelity and timing constraints, we discuss a straightforward proof of optimality in the absence of these constraints. Simulations on random graphs demonstrate that the PRP-based scheme performs better, both in terms of reliability and fidelity, than a non-trivial baseline routing algorithm.
The quantum internet enables distribution of quantum states across distant nodes, supporting secure communication, distributed computing, and quantum sensing. Unlike classical networks, it is constrained by the no cloning theorem, probabilistic entanglement generation, decoherence, and hardware drift, making classical abstractions inadequate. Scalable quantum networking therefore requires new architectures, protocols, and optimisation methods that explicitly account for these limitations.
This thesis studies the architecture, routing, and operation of quantum networks under realistic constraints, focusing on bipartite entanglement distribution over quantum repeater networks. Key metrics include end to end fidelity, throughput, scalability, and fairness. At the network layer, routing strategies are developed beyond assumptions of homogeneous nodes and full network knowledge. Routing under heterogeneous repeater efficiencies shows how partial knowledge of node quality improves fidelity and reduces path blocking. A grey box routing approach is then introduced, where path selection relies only on topology and end to end estimates, achieving robustness and fairness without detailed link information.
At the link layer, calibration and hardware drift are addressed through a calibration aware model separating activation and calibration phases. For linear repeater chains, an optimal calibration schedule is derived to balance operation time and calibration overhead. This is extended to general topologies with shared links, where a greedy orchestration heuristic is proposed.
Finally, the thesis connects network protocols with hardware via an instruction set architecture for programmable quantum repeater nodes based on NV centers, enabling coherent programmability and linking physical operations to higher layer protocols.
This study explores an approach to routing in quantum networks, which targets practical scenarios for quantum networks, mirroring real-world classical networks. By addressing practical constraints, we examine the impact of heterogeneous nodes with mixed efficiency figures on quantum network performance. In particular, we focus on some key parameters in an operational quantum network such as the fraction of nodes with a higher efficiency (called high-quality), path establishment order, end-to-end fidelity, i.e., a measure of the quality of the end-to-end entanglement established. Our simulations show that incorporating knowledge of node quality not only helps boost the fidelity of some of the routing paths but also reduces the number of blocked paths in the quantum network. The study also highlights the critical role of the fraction of high-quality nodes in end-to-end fidelity and explores the trade-offs between upgrading all nodes to high quality or retaining a subset of lower-quality nodes.
Abstract Remote quantum entanglement can enable numerous applications including distributed quantum computation, secure communication, and precision sensing. We consider how a quantum network—nodes equipped with limited quantum processing capabilities connected via lossy optical links—can distribute high-rate entanglement simultaneously between multiple pairs of users. We develop protocols for such quantum “repeater” nodes, which enable a pair of users to achieve large gains in entanglement rates over using a linear chain of quantum repeaters, by exploiting the diversity of multiple paths in the network. Additionally, we develop repeater protocols that enable multiple user pairs to generate entanglement simultaneously at rates that can far exceed what is possible with repeaters time sharing among assisting individual entanglement flows. Our results suggest that the early-stage development of quantum memories with short coherence times and implementations of probabilistic Bell-state measurements can have a much more profound impact on quantum networks than may be apparent from analyzing linear repeater chains. This framework should spur the development of a general quantum network theory, bringing together quantum memory physics, quantum information theory, quantum error correction, and computer network theory.
Future quantum networks will enable the interconnection of multiple users distributed across vast geographic distances. Due to these large separations and limited physical resources, communication will often rely on multi-path routing strategies, where physical resources are distributed across channels of varying lengths and delivered to end users. Efficient long-distance quantum communication therefore requires optimizing the allocation of these resources across available paths. In this work, we introduce a performance-oriented approach to quantum network routing by extending the classical concept of Quality of Service (QoS) to the context of multi-path quantum resources distribution. Unlike prior models that consider entanglement generation or quantum memory coherence in isolation, we investigate the interplay between path assignment strategies, coherence time constraints, and quantum error correction (QEC), and how they jointly impact end-to-end communication fidelity. We analyze both unencoded and encoded transmissions over aggregated network paths, quantifying the effects of resource allocation on transmission success. Our findings show that fidelity cannot be optimized independently of memory lifetimes, and that while QEC can enhance performance under specific conditions, it also imposes additional constraints depending on network topology and path-length asymmetries. This work provides a foundation for developing QoS-aware quantum routing protocols that balance fidelity, throughput, and memory utilization -- key considerations for near-term quantum repeater networks.
We consider the problem of entanglement routing in heterogeneous quantum networks where each link and node may offer a different entanglement generation quality. We consider that each link offers a base rate and fidelity of entanglement generation. These base values can be altered by performing entanglement purification on each link. Furthermore, we consider that each repeater node offers a different probability of a successful entanglement swapping. With this setting, we design a reinforcement learning-based approach for flexible entanglement routing on future quantum networks. Specifically, we formulate the problem of entanglement routing in the Q-learning framework where the main objective of the agent is to deliver end-to-end entanglement while maximizing a user-specified objective function in the form of a weighted sum of achieve fidelity and rate. We demonstrate the efficacy and flexibility of developed framework by simulating random quantum networks where the random requests in fidelity maximizing, rate maximizing, or balanced mode are generated. We also numerically assess the effects of infrastructure developments and technology enhancements in future quantum networks.