Paolo Fittipaldi | LIP6 - Équipe QI

Dynamic Scheduling in Fiber and Spaceborne Quantum Repeater Networks

Thu, 18 Sep 2025 00:00:00 +0000

Félicitations Dr.Fittipaldi !

Résumé

In this thesis, we analyze the problem of scheduling in the context of quantum networks. Given a quantum network, the scheduling problem amounts to choosing which entanglement swapping operations to perform to better serve user demand. The choice can be carried out following a variety of criteria (e.g. ensuring all users are served equally vs. prioritizing specific critical applications, properly managing load spikes and node failures, adopting heuristic or optimization-based algorithms…), warranting the need for a method to compare different solutions and choose the most appropriate. We present here a framework to mathematically formulate the scheduling problem over quantum networks and benchmark possible solutions in a variety of environments. Our framework enables the benchmarking of general quantum scheduling policies over arbitrary lossy multicommodity quantum networks. By leveraging the framework, we apply Lyapunov drift minimization (a standard technique in classical network science) to derive a novel class of quadratic optimization based scheduling policies, which we then analyze and compare with a simpler, Max Weight inspired linear class to quantify the performance loss due to the simplification. We start our second chapter with an overview of the pre-existing fiber quantum simulation tools. The rest of the chapter is devoted to the development of numerous extensions to QuISP, an established quantum network simulator focused on scalabil ity and accuracy in modeling the classical communication infrastructure underlying every quantum network. We document the development of our extensions allowing to simulate satellite links and multiple connections in QuISP, with an account of the currently functional extensions (free-space links and connection teardown) and of the ones still under active development (network multiplexing). Since it is likely that a future global-scale quantum network will incorporate satellite interconnections, we devote a chapter to the study of quantum satellite links. We derive an analytical model for the entanglement distribution rates for satellite-to-ground and ground-satellite-ground links and discuss different quantum memory allocation policies for the dual link case. Our findings show that classical communication latency is a major limiting factor for satellite communication, and the effects of physical upper bounds such as the speed of light must be taken into account when designing quantum links, limiting the attainable rates to tens of kHz. We also investigate the issue of differential latency, a Doppler-like effect caused by the displacement of satellite nodes that changes the timing of incoming photons and adds another upper bound to the generation rate. We conclude the thesis by summarizing our findings and highlighting the challenges that still need to be overcome in order to study the quantum scheduling problem over fiber and satellite large scale quantum networks.

Dynamic Scheduling in Fiber and Spaceborne Quantum Repeater Networks

Thu, 18 Sep 2025 00:00:00 +0000

In this thesis, we analyze the problem of scheduling in the context of quantum networks. Given a quantum network, the scheduling problem amounts to choosing which entanglement swapping operations to perform to better serve user demand. The choice can be carried out following a variety of criteria (e.g. ensuring all users are served equally vs. prioritizing specific critical applications, properly managing load spikes and node failures, adopting heuristic or optimization-based algorithms…), warranting the need for a method to compare different solutions and choose the most appropriate. We present here a framework to mathematically formulate the scheduling problem over quantum networks and benchmark possible solutions in a variety of environments. Our framework enables the benchmarking of general quantum scheduling policies over arbitrary lossy multicommodity quantum networks. By leveraging the framework, we apply Lyapunov drift minimization (a standard technique in classical network science) to derive a novel class of quadratic optimization based scheduling policies, which we then analyze and compare with a simpler, Max Weight inspired linear class to quantify the performance loss due to the simplification. We start our second chapter with an overview of the pre-existing fiber quantum simulation tools. The rest of the chapter is devoted to the development of numerous extensions to QuISP, an established quantum network simulator focused on scalability and accuracy in modeling the classical communication infrastructure underlying every quantum network. We document the development of our extensions allowing to simulate satellite links and multiple connections in QuISP, with an account of the currently functional extensions (free-space links and connection teardown) and of the ones still under active development (network multiplexing). Since it is likely that a future global-scale quantum network will incorporate satellite interconnections, we devote a chapter to the study of quantum satellite links. We derive an analytical model for the entanglement distribution rates for satellite-to-ground and ground-satellite-ground links and discuss different quantum memory allocation policies for the dual link case. Our findings show that classical communication latency is a major limiting factor for satellite communication, and the effects of physical upper bounds such as the speed of light must be taken into account when designing quantum links, limiting the attainable rates to tens of kHz. We also investigate the issue of differential latency, a Doppler-like effect caused by the displacement of satellite nodes that changes the timing of incoming photons and adds another upper bound to the generation rate. We conclude the thesis by summarizing our findings and highlighting the challenges that still need to be overcome in order to study the quantum scheduling problem over fiber and satellite large scale quantum networks.

Entanglement Swapping in Orbit: a Satellite Quantum Link Case Study

Sun, 15 Sep 2024 00:00:00 +0000

Satellite quantum communication is a promising way to build long distance quantum links, making it an essential complement to optical fiber for quantum internetworking beyond metropolitan scales. A satellite point to point optical link differs from the more common fiber links in many ways, both quantitative (higher latency, strong losses) and qualitative (nonconstant parameter values during satellite passage, intermittency of the link, impossibility to set repeaters between the satellite and the ground station). We study here the performance of a quantum link between two ground stations, using a quantum-memory-equipped satellite as a quantum repeater. In contrast with quantum key distribution satellite links, the number of available quantum memory slots m, together with the unavoidable round-trip communication latency t of at least a few milliseconds, severely reduces the effective average repetition rate to m/t – at most a few kilohertz for foreseeable quantum memories. Our study uses two approaches, which validate each other: 1) a simple analytical model of the effective rate of the quantum link; 2) an event-based simulation using the open source Quantum Internet Simulation Package (QuISP). The important differences between satellite and fiber links led us to modify QuISP itself. This work paves the way to the study of hybrid satellite- and fiber-based quantum repeater networks interconnecting different metropolitan areas.

A Linear Algebraic Framework for Dynamic Scheduling Over Memory-Equipped Quantum Networks

Mon, 01 Jan 2024 00:00:00 +0000

Quantum Internetworking is a recent field that promises numerous interesting applications, many of which require the distribution of entanglement between arbitrary pairs of users. This work deals with the problem of scheduling in an arbitrary entanglement swapping quantum network - often called first generation quantum network - in its general topology, multicommodity, loss-aware formulation. We introduce a linear algebraic framework that exploits quantum memory through the creation of intermediate entangled links. The framework is then employed to mathematically derive a natural class of quadratic scheduling policies for quantum networks by applying Lyapunov Drift Minimization, a standard technique in classical network science. Moreover, an additional class of Max-Weight inspired policies is proposed and benchmarked, reducing significantly the computation cost, at the price of a slight performance degradation. The policies are compared in terms of information availability, localization and overall network performance through an ad-hoc simulator that admits user-provided network topologies and scheduling policies in order to showcase the potential application of the provided tools to quantum network design.

A Linear Algebraic Framework for Quantum Internet Dynamic Scheduling

Sun, 18 Sep 2022 00:00:00 +0000

Future quantum internet aims to enable quantum communication between arbitrary pairs of distant nodes through the sharing of end-to-end entanglement, a universal resource for many quantum applications. As in classical networks, quantum networks also have to resolve problems related to routing and satisfaction of service at a sufficient rate. We deal here with the problem of scheduling when multiple commodities must be served through a quantum network based on first generation quantum repeaters, or quantum switches. To this end, we introduce a novel discrete-time algebraic model for arbitrary network topology, including transmission and memory losses, and adapted to dynamic scheduling decisions. Our algebraic model allows the scheduler to use the storage of temporary intermediate links to optimize the performance, depending on the information availability, ranging from full global information for a centralized scheduler to partial local information for a distributed one. As an illustrative example, we compare a simple greedy scheduling policy with several Max-Weight inspired scheduling policies and illustrate the resulting achievable rate regions for two competing pairs of clients through a network.