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Abstract
In this thesis, I study dielectric structures with great subwavelength confinement, termed extreme dielectric confinement (EDC), and deal with their design and quantum optical properties through finite element and finitedifference timedomain calculations. I begin with a short background on these novel structures in a first introductory section, where I also discuss the content and purpose of this work. In part I, I start by introducing the quasinormal mode (QNM) formulation, which is fundamental for both parts I and II. I then describe and motivate the intuitive design simplification approach I have used to derive simpler designs from original complicated topologyoptimized designs. In the following chapter, I use QNMs for calculations using firstorder perturbation theory, showing that an EDC structure is extremely sensitive to local perturbations to its bowtie. In the final chapter, I introduce three numerical methods for calculating the point dipole response, and I calculate the spontaneous emission factor of EDC structures by comparing the singlemode response to the total response, showing that the beta factor is close to unity for a broad spectral region and in a relatively broad spatial region around the bowtie. In part II, I introduce the challenge of deterministic quantum dot (QD) fabrication, and suggest creating a lithographically defined quantum dot in the region of the bowtie hotspot. The motivation in doing this is to address deterministic fabrication, and to take advantage of the high radiative enhancement to improve the performance of etched quantum dots, that have historically suffered from high nonradiative rates. By modifying the central bowtie feature, we can achieve localized, finitelifetime electronic states in the region of the optical hotspot, enabling simultaneous optical and electronic confinement. I introduce a method for calculating the coupling strength between the exciton in the mesoscopic dot and the optical field, resulting in an intuitive overlap integral with simple selection rules for allowed radiative transitions. In the last chapter, I describe one possible design process and the characterization of the resulting device in terms of radiative rate and radiative quantum efficiency. In Part III, I explore dynamics of QDs placed in a bowtie cavity, using a selfconsistent MaxwellBloch  FDTD (MBFDTD) solver. I first generally discuss the validity of the semiclassical approach, introduce the concepts of nonMarkovianity and the rotatingwave approximation, and describe the selfconsistent MBFDTD solver while outlining some numerical challenges. I then show transient Purcell factor dynamics for a single QD coupled to a lowQ bowtie cavity – transient enhancement and suppression for a single short exciting pulse, and oscillatory dynamics under periodic pulse excitation. Additionally, I compare these results with Markovian Master equation results and show that the MBFDTD solver captures counterintuitive features that are not present in the Markovian solution.
Original language  English 

Publisher  Technical University of Denmark 

Number of pages  220 
Publication status  Published  2024 
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 1 Finished

Quantum theory of extreme dielectric confinement structures
Kountouris, G. (PhD Student), Mork, J. (Main Supervisor), Denning, E. V. (Supervisor), Kristensen, P. T. (Supervisor), Mortensen, N. A. (Examiner) & Sapienza, R. (Examiner)
01/06/2020 → 10/06/2024
Project: PhD