Implementation of Protocols for Quantum Photonic Networks

Congratulations Dr. dos Santos Martins !

Abstract

This thesis is situated in the field of quantum information, with a particular focus on quantum communication networks. The goal of such networks is to enable fundamentally new technologies by facilitating quantum communication between distant parties, eventually leading to a Quantum Internet. These networks allow the transmission of quantum bits (qubits) over long distances, enabling tasks that are provably impossible for any classical communication network. Furthermore, the ability to generate entanglement between remote sites provides a powerful platform for fundamental studies of nature. Photonic resources are central to quantum network infrastructures, as they provide the optimal means for communication between the network nodes. In this thesis, we implement a photonic platform capable of generating high-fidelity Greenberger–Horne–Zeilinger (GHZ) states at telecom wavelengths in a compact and scalable configuration. Our source relies on spontaneous parametric down-conversion within a layered Sagnac interferometer, requiring only a single nonlinear crystal. This design enables the generation of highly indistinguishable photon pairs, leading to high-quality multipartite entangled states. Using this source, we provide the first experimental demonstration of quantum state certification in a device-independent framework, where the quantum states are not assumed to be identically and independently distributed (non-IID regime). This task is a fundamental building block for quantum communication and computation, as it determines whether the involved parties can trust their resources or whether the application should be aborted. We further investigate the efficiency of this protocol with respect to the amount of resources required and analyze how it can be leveraged for robust and reliable quantum information processing. Additionally, we explore the privacy of individual parties in a distributed quantum sensing protocol by certifying the entangled states shared within the network. Our work broadens and enriches the application scope of quantum communication networks.