The realization of a global-scale quantum internet is hindered by practical challenges such as high photon loss, decoherence, susceptibility to node failure, and others. We analyze [1] the implications of these practical constraints on the scalability and robustness of the quantum Internet. Considering repeater-based quantum networks, we present bottlenecks for distributing resources among multiple end nodes. We use graph theory to assess network robustness and identify its critical nodes and critical length scales. In particular, we consider repeater-based quantum networks and present practical limitations on distilling secret keys via device-independent quantum key distribution (DI-QKD) protocols and other information processing tasks such as sharing of entanglement between the end nodes, performing Bell-CHSH violation experiments, and implementing quantum teleportation protocols. By considering instances of a hybrid satellite-fiber network for distributing entangled states between far-off cities and considering currently available quantum processor architectures as networks, we analyze the practical limitations and robustness of real-world quantum networks. For such real-world networks, we present algorithms for different network tasks. Overall, the assessment presented in this work can be used to benchmark the critical parameters in the practical realization of a global-scale quantum internet.
The realization of a global-scale quantum internet is hindered by practical challenges such as high photon loss, decoherence, susceptibility to node failure, and others. We analyze [1] the implications of these practical constraints on the scalability and robustness of the quantum Internet. Considering repeater-based quantum networks, we present bottlenecks for distributing resources among multiple end nodes. We use graph theory to assess network robustness and identify its critical nodes and critical length scales. In particular, we consider repeater-based quantum networks and present practical limitations on distilling secret keys via device-independent quantum key distribution (DI-QKD) protocols and other information processing tasks such as sharing of entanglement between the end nodes, performing Bell-CHSH violation experiments, and implementing quantum teleportation protocols. By considering instances of a hybrid satellite-fiber network for distributing entangled states between far-off cities and considering currently available quantum processor architectures as networks, we analyze the practical limitations and robustness of real-world quantum networks. For such real-world networks, we present algorithms for different network tasks. Overall, the assessment presented in this work can be used to benchmark the critical parameters in the practical realization of a global-scale quantum internet.
Abstract The realization of a desirably functional quantum Internet is hindered by fundamental and practical challenges such as high loss during transmission of quantum systems, decoherence due to interaction with the environment, and fragility of quantum states under measurement. We study the implications of these constraints by analyzing the limitations on the scaling and robustness of the quantum Internet. Considering quantum networks, we present practical bottlenecks for secure communication, delegated computing, and resource distribution among end nodes. In particular, we show that the device-independent quantum key distribution (DI-QKD) network of isotropic states with parameter p has a finite diameter depending on p . Motivated by the power of abstraction in graph theory (in association with quantum information theory), that allows us to consider the topology of a network of users spatially separated over long distances around the globe or separated as nodes within the small space over a processor or circuit within a same framework, we consider graph-theoretic quantifiers to assess network robustness and provide critical values of communication lines for viable communication over quantum Internet. We consider some quantum networks of practical interest, ranging from satellite-based networks connecting far-off spatial locations to currently available quantum processor architectures within computers, and analyze their robustness to perform quantum information processing tasks. Some of these tasks form primitives for delegated quantum computing, e.g., entanglement distribution and quantum teleportation, that are desirable for all scale of quantum networks, be it quantum processors or quantum Internet.
Quantum networks play a pivotal role in quantum information science, which not only provide a secure communication platform for remote access to quantum computers but also serve as the strategic core for achieving large-scale quantum information processing, forming the foundational infrastructure for the future global-scale quantum internet. Quantum teleportation, which enables the transmission of unknown quantum states over long distances by employing quantum entanglement together with classical communication, is essential for the distribution of quantum resources in the construction of the global-scale quantum internet. To realize a global-scale quantum internet, quantum repeater protocols represent one of the most promising approaches for enabling quantum communication between any nodes. This concise review presents representative experimental demonstrations of quantum teleportation for constructing quantum networks across different physical platforms. Along this trajectory, the review discusses current challenges, open issues, and future perspectives toward scalable and practical quantum internet.
The scalability of quantum communication networks is crucial for enabling secure information exchange and distributed quantum computing across global infrastructures. However, achieving scalability remains a significant challenge due to the effects of decoherence, photon loss, and fidelity degradation over extended distances. This paper performs a critical investigation into the scalability limits of quantum communication networks, focusing on the interplay between entanglement generation rates, end-to-end fidelity, and network parameters such as node separation, noise levels, and total distance. Leveraging the SeQUeNCe simulation framework, we model adaptable trapped-ion repeater networks to uncover fundamental insights into both homogeneous and heterogeneous configurations. Our findings reveal transformative insights that help reshape system designs for near term quantum networks. We identify maximum node separation thresholds critical for practical implementations, illuminate the non-linear degradation of fidelity with increasing distance, and expose how routing and swapping protocols influence entanglement success rates at scale. Most notably, we demonstrate that while additional repeaters can mitigate distance-induced failures, excessive node counts introduce compounding fidelity losses that threaten network viability under certain architectures. These results provide a roadmap for revolutionizing quantum networks, with actionable design strategies such as optimized node placement, advanced routing algorithms, and the adoption of cutting-edge qubit technologies like topological qubits. By addressing key bottlenecks in quantum communication scalability, our work lays the foundation for the next generation of global quantum networks.
Quantum networks, integrating quantum communication, quantum metrology, and distributed quantum computing, could provide secure and efficient information transfer, high-resolution sensing, and an exponential speed-up in information processing. Deterministic entanglement distribution over long distances is a prerequisite for scalable quantum networks, enabling the utilization of device-independent quantum key distribution (DI-QKD) and quantum teleportation to achieve secure and efficient information transfer. However, the exponential photon loss in optical fibres prohibits efficient and deterministic entanglement distribution. Quantum repeaters, incorporating entanglement swapping and entanglement purification with quantum memories, offer the most promising means to overcome this limitation in fibre-based quantum networks. Despite numerous pioneering efforts toward realizing quantum repeaters, a critical bottleneck remains, as remote memory-memory entanglement suffers from decoherence more rapidly than it can be established and purified over long distances. We overcome this by developing long-lived trapped-ion memories, an efficient telecom interface, and a high-visibility single-photon entanglement protocol. This allows us to establish and maintain memory-memory entanglement over a 10 km fibre within the average entanglement establishment time for the same distance. As a direct application, we demonstrate metropolitan-scale DI-QKD, distilling 1,917 secret keys out of 4.05*10^5 Bell pairs over 10 km. We further report a positive key rate over 101 km in the asymptotic limit, extending the achievable distance by more than two orders of magnitude. Our work provides a critical building block for quantum repeaters and marks an important step toward scalable quantum networks.
This paper investigates the scalability and transmission efficiency of entanglement swapping protocols within multi-node quantum networks. As the realization of a global quantum internet relies heavily on long-distance entanglement distribution, quantum repeaters utilizing entanglement swapping serve as a critical backbone. However, scalability remains a bottleneck due to photon loss, operational infidelities, and quantum memory coherence times. In this study, we analytically model a multi-node quantum chain and evaluate how the end-to-end entanglement fidelity degrades as the number of intermediate nodes scales up. Our analysis highlights the critical thresholds for Bell state measurement (BSM) success rates required to maintain quantum state integrity across large distances. The findings provide optimization constraints for designing scalable and fault-tolerant routing protocols in future quantum information networks.
The quantum internet is one of the frontiers of quantum information science. It will revolutionize the way we communicate and do other tasks, and it will allow for tasks that are not possible using the current, classical internet. The backbone of a quantum internet is entanglement distributed globally in order to allow for such novel applications to be performed over long distances. Experimental progress is currently being made to realize quantum networks on a small scale, but much theoretical work is still needed in order to understand how best to distribute entanglement and to guide the realization of large-scale quantum networks, and eventually the quantum internet, especially with the limitations of near-term quantum technologies. This work provides an initial step towards this goal. The main contribution of this thesis is a mathematical framework for entanglement distribution protocols in a quantum network, which allows for discovering optimal protocols using reinforcement learning. We start with a general development of quantum decision processes, which is the theoretical backdrop of reinforcement learning. Then, we define the general task of entanglement distribution in a quantum network, and we present ground- and satellite-based quantum network architectures that incorporate practical aspects of entanglement distribution. We combine the theory of decision processes and the practical quantum network architectures into an overall entanglement distribution protocol. We also define practical figures of merit to evaluate entanglement distribution protocols, which help to guide experimental implementations.