Quantum networks are networks composed of quantum processors that facilitate the exchange of information in the form of quantum bits, also called qubits. Qubits observe a physical phenomenon known as entanglement that enables the transmission of quantum information over long distances as well as the realization of novel protocols and applications that are impossible in classical networks such as the Internet. Due to the limitations of state of the art Noisy Intermediate-Scale Quantum (NISQ) devices, the establishment of entanglement over multi-hop networks demands strict coordination among the network nodes that connect two hosts. The delivery of entanglement in multi-hop quantum networks is further complicated when the network must support Quality of Service requirements for multiple users at the same time. The main challenges are ensuring that connected quantum processors agree when to establish entanglement with their neighbors and that processors use the correct pieces of entanglement to connect source/destination pairs. In this thesis, we propose a novel dynamic time-division multiple access (TDMA) method for multiplexing network resources used to connect multiple users in quantum networks. We investigate the behavior of scheduling heuristics in constructing the TDMA schedules and the effects of resource allocation on network performance. We additionally propose a novel scheduling problem and heuristic based on limited preemption that improves achievable network throughput in the case that devices may tolerate interruptions during connection of users.

In order to bring quantum networks into the real world, we would like to determine the requirements of quantum network protocols including the underlying quantum hardware. Because detailed architecture proposals are generally too complex for mathematical analysis, it is natural to employ numerical simulation. Here we introduce NetSquid, the NETwork Simulator for QUantum Information using Discrete events, a discrete-event based platform for simulating all aspects of quantum networks and modular quantum computing systems, ranging from the physical layer and its control plane up to the application level. We study several use cases to showcase NetSquid’s power, including detailed physical layer simulations of repeater chains based on nitrogen vacancy centres in diamond as well as atomic ensembles. We also study the control plane of a quantum switch beyond its analytically known regime, and showcase NetSquid’s ability to investigate large networks by simulating entanglement distribution over a chain of up to one thousand nodes.@en

Scaling current quantum communication demonstrations to a large-scale quantum network will require not only advancements in quantum hardware capabilities, but also robust control of such devices to bridge the gap in user demand. Moreover, the abstraction of tasks and services offered by the quantum network should enable platform-independent applications to be executed without the knowledge of the underlying physical implementation. Here we experimentally demonstrate, using remote solid-state quantum network nodes, a link layer, and a physical layer protocol for entanglement-based quantum networks. The link layer abstracts the physical-layer entanglement attempts into a robust, platform-independent entanglement delivery service. The system is used to run full state tomography of the delivered entangled states, as well as preparation of a remote qubit state on a server by its client. Our results mark a clear transition from physics experiments to quantum communication systems, which will enable the development and testing of components of future quantum networks.@en