One of today’s challenges to realise computing based on quantum mechanics is to reliably and scalably encode information in quantum systems. Here, we present a photon source to on-demand deliver photonic quantum bits of information based on a strongly coupled atom-cavity system. The source operates intermittently for periods of up to 100 <i>μ</i>s, with a single-photon repetition rate of 1 MHz, and an intra-cavity production efficiency of up to 85%. Our ability to arbitrarily control the photons’ wavepackets and phase profiles, together with long coherence times of 500 ns, allows to store time-bin encoded quantum information within a single photon. To do so, the spatio-temporal envelope of a single photon is sub-divided in d time bins which allows for the delivery of arbitrary qu-d-its. This is done with a fidelity of > 95% for qubits, and 94% for qutrits verified using a newly developed time-resolved quantum-homodyne measurement technique. Additionally, we combine two separate fields of quantum physics by using our deterministic single-photon source to seed linear optics quantum computing (LOQC) circuits. As a step towards quantum networking, it is shown that this photon source can be combined with quantum gates, namely a chip-integrated beam splitter, a controlled-NOT (CNOT) gate as well as a CNOT4 gate. We use this CNOT4 gate to entangle photons deterministically emitted from our source and observe non-classical correlations between events separated by periods exceeding the travel time across the chip by three orders of magnitude. Additionally, we use time-bin encoded qubits to systematically study the de- and re-phasing of quantum states as well as the the effects of time-varying internal phases in photonic quantum circuits.

L'objectif de cette thèse CIFRE est de contribuer à la communication véhiculaire autonome et au développement de la mobilité urbaine. Les travaux sont basés sur les limitations et défis de la communication par radio pour les applications de sécurité et envisagent de déployer le système d'éclairage des véhicules en tant que solution de communication de soutien pour le platooning d'IVC-activées par VC Véhicules autonomes. L'objectif principale de cette recherche doctorale consiste à intégrer le système VLC dans l'architecture existante de C-ITS en développant un prototype VLC, ainsi que des algorithmes de transfert suffisants permettant VLC, RF et des solutions basées sur la perception afin d'assurer les exigences de sécurité maximales et l'échange continu d'informations entre les véhicules. La faisabilité et l'efficacité de la mise en oeuvre du système et des algorithmes de transfert ont fait l'objet de recherches approfondies sur six chapitres, destinés à faciliter une progression logique des matériaux et permettre un accès relativement facile. En plus de l'amélioration de la capacité routière en utilisant les systèmes de conduite autonome à la base de convoi. Les simulations réalisées ainsi que les résultats expérimentaux ont montré que l'intégration de VLC avec les solutions existantes RF a un avantage certain dans la qualité du canal de communication et les exigences de sécurité d'un système de platooning quand un algorithme approprié est utilisé. / This thesis effort contributes to the autonomous vehicular communication and urban mobility improvements. The work addresses the main radio-based V2V communication limitations and challenges for ITS hard-safety applications and intends to deploy the vehicular lighting system as a supportive communication solution for platooning of IVC-enabled autonomous vehicles. The ultimate objectives of this Ph.D research are to integrate the VLC system within the existing C-ITS architecture by developing a VLC prototype, together with sufficient, hand-over algorithms enabling VLC, RF, and perception-based solutions in order to ensure the maximum safety requirements and the continuous information exchange between vehicles. The feasibility and efficiency of the VLC-RF system implementation and hand-over algorithms were subjects to deep investigations over six self-contained chapters meant to facilitate a logical progression of materials and to enable a relatively easy access. In addition to the improvement in road capacity by utilizing the convoy-based autonomous driving systems. The carried out simulations followed-up by experimental results proved that the integration of VLC with the existed RF solutions lead to a definite benefit in the communication channel quality and safety requirements of a platooning system when a proper hand-over algorithm is utilized.

Improving road safety and optimizing the traffic flow – these are major challenges at urban intersections. In particular, strengthening the needs of vulnerable road users (VRUs) such as pedestrians, cyclists and e-scooter drivers is becoming increasingly important, combined with support for automated and connected driving. In the LTSA project, a new system is being developed and implemented exactly for this purpose. The LTSA is an intelligent infrastructure system that records the movements of all road users in the vicinity of an intersection using a combination of several locally installed sensors e.g. video, radar, lidar. AI-based software processes the detected data, interprets the movement patterns of road users and continuously analyzes the current traffic situation (digital twin). Potentially dangerous situations are identified, e.g. right turning vehicles and simultaneously crossing VRUs, and warning messages can be sent to connected road users via vehicle-to-infrastructure communication (V2X). Automated vehicles can thus adapt their driving maneuvers. In addition, the collected data is applied to improve traffic light control depending on the current traffic situation, especially for VRUs. This abstract describes the LTSA system and its implementation in the German city of Potsdam. The current project state is presented and an outlook on next steps is given.