All optical manipulation of a single nitrogen-vacancy centre in nanodiamond

The efficient interaction of photons with single quantum emitters like nitrogen vacancy (NV) centres is essential for the elaboration of future integrated quantum optical devices. A promising strategy towards this goal capitalizes on the latest advances of nano-optics to boost the interaction with single emitters as well as strengthen coupling between several of them. However, fully exploiting the capabilities of this marriage between NV centres and optical nanostructures requires suitable tools to accurately control their interaction. In this thesis, we use optical manipulation to trap and manipulate in 3D individual nanodiamonds containing a single NV. We first demonstrate the use of optical tweezers as a tool to achieve deterministic trapping and three-dimensional spatial manipulation of individual nanodiamonds hosting a single NV spin. Remarkably, we find that the NV axis is nearly fixed inside the trap and can be controlled in situ by adjusting the polarization of the trapping light. By combining this unique spatial and angular control with coherent manipulation of the NV spin and fluorescence lifetime measurements near an integrated photonic system, we demonstrate individual optically trapped NV centers as a novel route for both three-dimensional vectorial magnetometry and sensing of the electromagnetic local density of states. In a second step, our manipulation technique is further developed to deterministically position a single nanodiamond into the hotspot of a plasmonic antenna. The gradient force of electromagnetic field of the excited plasmon acts as localized optical tweezers to drive the functionalized nanodiamonds to the regions of largest field enhancement of the antenna, where they are adsorbed. The proximity of the immobilized NV to the nano-antenna is corroborated by the observed decrease in its fluorescence lifetime. Last but not least, we observe a NV fluorescence decrease upon near-infrared (NIR) illumination. We identify the promotion of the excited electron to a so far unknown dark band with a fast decay channel as the origin of the fluorescence decrease. This assumption is verified by the excellent agreement between our simple rate equation model and the experiment. With this mechanism we demonstrate that a single NV can operate as an efficient and fast optical switch controlled through an independent NIR gating laser. Furthermore the hybrid system formed by a single NV coupled to a gold gap antenna enhances the modulation depth. The results presented in this thesis show the ability to manipulate and position NV centres in nanodiamond with optical tweezers. This paves the way towards spin based magnetic field and temperature sensing in liquid environment. Furthermore, the control of positioning and coupling to photonic and plasmonic nanostructures may play a role for potential applications in all-optical circuits or quantum optical devices.La interacción de fotones con emisores cuánticos individuales como los centros de nitrógeno-vacante (NV) es esencial para la elaboración de futuros dispositivos integrados de óptica cuántica. Una estrategia prometedora para alcanzar este objetivo es de aprovechar de los últimos avances de la nano-óptica para aumentar la interacción con emisores individuales, así como fortalecer el acoplamiento entre varios de ellos. Sin embargo, para aprovechar al máximo las capacidades de este matrimonio entre centros de NV y nano-estructuras ópticas se requiere de herramientas adecuadas para controlar con precisión su interacción. En esta tesis, se utiliza la manipulación óptica para atrapar y manipular en 3D nano-diamantes individuales que contienen un solo centro de NV. En primer lugar, demostramos el uso de pinzas ópticas como una herramienta para lograr la captura precisa y manipulación espacial tridimensional de nano-diamantes individuales conteniendo un solo centro de NV. Sorprendentemente, encontramos que el eje del centro de NV está casi fija dentro de la trampa y puede controlarse in situ mediante el ajuste de la polarización de la luz del láser de captura. Combinamos este control espacial y angular con la manipulación coherente del espín del centro NV y con medidas de tiempo de vida de fluorescencia de un sistema fotónico integrado. Demostramos que los centros NV atrapados ópticamente pueden servir como una nueva ruta para ambos magnetometría vectorial tridimensional y de detección de la densidad local de estados electromagnéticos. En un segundo paso, nuestra técnica de manipulación se desarrolló aún más hacia el posicionamiento de un nano-diamante individual en una antena plasmónica. La fuerza de gradiente del campo electromagnético del plasmon excitado actúa como una pinza óptica local para atraer los nano-diamantes funcionalizados a las regiones de mayor aumento del campo de la antena, donde quedan adsorbidos. La proximidad del centro NV inmovilizado en la nanoantena es corroborado por la disminución observada del tiempo de vida de la fluorescencia. Por otra parte, se observa una disminución de la fluorescencia NV tras la iluminación infrarroja. Identificamos como origen de la disminución de la fluorescencia la promoción del electrón excitado a una banda, que tiene un canal de decaimiento rápido. Esta hipótesis es comprobada por el excelente acuerdo entre nuestro modelo simple de ecuación cinética y el experimento. Por último, demostramos que un centro NV puede funcionar como un interruptor óptico eficiente y rápido controlado a través de un láser de control infrarrojo independiente. Además, el sistema híbrido formado por un solo NV acoplado a una nano-antena de oro aumenta la profundidad de modulación. Los resultados presentados en esta tesis demuestran la capacidad de manipular y posicionar nano-diamantes conteniendo un centro NV con pinzas ópticas. Esto allana el camino hacia un sensor de campo magnético y de temperatura en ambiente liquido usando el espín del centro NV. Además, el control de posicionamiento y acoplamiento a nano-estructuras fotónicas y plasmónicas podría tener un impacto para aplicaciones potenciales en circuitos completamente ópticos o dispositivos de óptica cuántica

Cybersecurity Research: Challenges and Course of Action

The European society faces numerous disruptive changes due to the progressing digitalisation. These changes have the potential to lead to a fair digitalised world if they are based on the ideal of digital sovereignty as a guiding principle at the citizen, economic and state levels. Research in cybersecurity creates the technological prerequisites for addressing the challenges of digitalisation in this spirit. Researchers in academia and industry from all over Europe met in Darmstadt and Berlin to identify the main challenges of cybersecurity research. Irrespective of their scientific backgrounds, all authors agreed that effective security and privacy measures require a systematic and holistic approach which considers security and privacy from the ground up. They stressed that in addition to the proposed research agenda, it is necessary to improve education across the board. During the discussions, it became also clear that various important scientific questions remain open, and that only long-term research across all disciplines can solve these problems. In the first chapter, we outline the major challenges in the fundamental research of the IT security fields in computer and engineering sciences. In the second chapter, we look at the cybersecurity challenges from the perspective of economic, legal and social sciences. In the last chapter, we analyse various examples of applications and technologies which combine the different research areas. Each section of the roadmap is dedicated to a specific challenge. The order of the sections is not intended to reflect their rel ative importance. For each challenge, we propose concrete next steps based on the state of the art in the scientific and industrial research landscape. We hope to reach out to all interested parties who endeavour to strengthen cybersecurity and enhance digital sovereignty in Europe