Dynamic Scheduling in Fiber and Spaceborne Quantum Repeater Networks Enables Optimized Entanglement Distribution

Scheduling entanglement distribution in quantum networks presents a significant challenge as demand increases and networks expand, and researchers are now addressing this problem with a new framework for optimising performance. Paolo Fittipaldi from Sorbonne Université, along with colleagues, develops a mathematical approach to compare different scheduling policies across both fibre optic and satellite-based quantum networks. This work introduces novel scheduling policies based on optimisation techniques and benchmarks them against existing methods, revealing that classical communication latency currently limits the speed of satellite links to tens of kilohertz. By extending existing network simulation tools and modelling entanglement distribution rates for satellite links, the team demonstrates a path towards more efficient and scalable quantum communication networks, paving the way for future quantum internet applications.

Quantum Network Simulator Design and Implementation

This research details the development of a sophisticated simulator for quantum networks, a crucial tool for exploring the possibilities of future quantum communication. The team designed a system capable of modelling complex network scenarios, allowing researchers to evaluate different approaches to resource management and network topology. The simulator accurately represents key aspects of quantum networks, including entanglement swapping, quantum memory limitations, and the challenges of establishing links over long distances. It supports various network configurations, such as chain, grid, and probabilistic arrangements, enabling comprehensive performance analysis.

The simulator also incorporates realistic effects, such as signal loss and the delays inherent in satellite communication, providing a highly accurate representation of real-world conditions. Through detailed simulations, researchers can now rigorously test scheduling algorithms and assess the overall performance of quantum networks before physical implementation. The simulator’s capabilities extend to comparing its performance against existing tools, highlighting its strengths and weaknesses in modelling quantum network behaviour. A significant focus of the work lies in exploring the potential of satellite links for extending the reach of quantum networks.

The simulations investigate the performance of entanglement distribution over these links, providing valuable insights into the challenges and opportunities of space-based quantum communication. The research uses the Micius satellite as a case study, evaluating entanglement distribution over a real-world satellite link and providing valuable data for future network designs. The team carefully models free-space loss and differential latency, addressing critical factors that impact the performance of satellite-based quantum communication. This work delivers a powerful tool for advancing the field of quantum networking, paving the way for more efficient and scalable quantum communication systems.

Quantum Network Scheduling Policies Compared and Optimized

This research presents a comprehensive mathematical framework for formulating and evaluating scheduling problems within quantum networks, addressing the critical task of optimising entanglement swapping to meet user demands. Researchers developed a system to assess diverse scheduling policies across complex, lossy quantum networks, enabling rigorous comparison of different approaches. Applying Lyapunov drift minimization, the team derived a novel class of quadratic optimisation-based scheduling policies, offering a sophisticated method for resource allocation. These new policies were then directly compared against a simpler, linear approach inspired by Max Weight, revealing quantifiable performance differences and demonstrating the benefits of the more complex optimisation.

The study extends to modelling realistic network conditions, including an analysis of entanglement distribution rates for satellite-to-ground and ground-satellite-ground links, crucial for expanding quantum network reach. Measurements confirm that classical latency represents a major limiting factor for satellite communication, restricting attainable rates to tens of kHz due to the physical constraints imposed by the speed of light. This finding underscores the need to account for these fundamental limitations when designing future quantum links. To facilitate these analyses, the team significantly extended the QuISP network simulator, a tool known for its scalability and accuracy in modelling classical network infrastructure. This enhanced simulator allows for detailed modelling of quantum network behaviour and provides a platform for testing and refining scheduling algorithms. The research delivers a robust framework and detailed performance data, paving the way for more efficient and scalable quantum networks capable of supporting a wide range of applications.

Quantum Scheduling Policies for Network Optimisation

This research presents a novel framework for mathematically formulating the scheduling problem within quantum networks, addressing a critical gap between physical layer development and potential applications. By establishing a general language to describe scheduling policies, the team demonstrates the relevance of scheduling strategies in optimising quantum resource allocation, building on extensive work in classical networking. The researchers then applied this framework, developing and analysing a new class of quadratic optimisation-based scheduling policies and comparing their performance to existing linear approaches. This work establishes a foundation for designing efficient and scalable quantum networks, paving the way for future advancements in quantum communication technologies.

Furthermore, the study extends to the complexities of integrating satellite links into quantum networks, developing an analytical model to determine entanglement distribution rates for both direct and relayed satellite connections. Results indicate that classical latency, particularly the limitations imposed by the speed of light, represents a significant constraint on satellite-based quantum communication, restricting achievable rates to the kilohertz range. The team acknowledges that further research is needed to address the challenges of scheduling in combined fibre and satellite networks, and they suggest exploring scheduling strategies for distributing multipartite entanglement as a promising future direction.