Infoscience

Thesis

Cavity quantum electrodynamics with systems of site-controlled quantum dots and photonic crystal cavities

The study of light-matter interactions holds an important place in physics and many fields of science including biology, medicine and chemistry. Understanding and exploiting light-matter interactions has become ever more relevant in our modern society which strives for sustainable energy sources and efficient transfer and storage of information. In this context, the realization of novel light harvesting or emitting devices, as well as novel information and computing platforms will demand a thorough understanding and control of nanoscale light-matter interactions. This involves studying the fundamental interactions between quantum emitters and modes of the electromagnetic field, which is undertaken by the field of cavity quantum electrodynamics (cavity-QED). Although initially interactions between isolated atoms and optical cavity modes were investigated, it has recently become possible to realize cavity-QED experiments with solid-state platforms, facilitating the transfer from fundamental studies to applications and device fabrication. In such solid-state platforms, atoms can be substituted by semiconductor quantum dots (QDs), which are nanostructures engineered to have atom-like optical and electronic properties, made to interact with semiconductor nanocavities. The subject of this thesis is the study of semiconductor QDs coupled to optical modes of photonic crystal (PhC) cavities. One of the challenges faced when studying QD-cavity interactions is understanding the impact of the QD environment on its interaction with the cavity mode (CM). Unlike atoms, QDs are embedded in a crystal lattice with which it can interact, leading to quantum decoherence. In this work we rely on site-controlled pyramidal QDs integrated in PhC cavities to study the impact of decoherence on their photoluminescence (PL). Most previous experiments used self-assembled QDs that interact with delocalised electronic states formed in their vicinity during their growth process. This grants them complex electronic states that influence the QD-cavity interaction, overshadowing the impact of solid-state decoherence mechanisms. In contrast, pyramidal QDs possess simpler electronic states that are closer to ideal atom-like states. Using site-controlled pyramidal QDs, we probe the spectral features of a coupled QD-cavity system using PL measurements, and compare them to a theoretical model of a two-level system (TLS) coupled to a CM, providing new insights into the influence of the QD environment on its interaction with a confined CM. A prerequisite demanded of QD-photonic structures to realize on-chip quantum information and computing devices is the possibility to scale-up the system. This requires a good control of the QDs position within the photonic structure as well as a good control of the QDs emission energies. On the one hand this allows the coupling of several QD emitters with the same CM, enabling collective or lasing effects. On the other hand, the QDs can be precisely positioned in an extended photonic structure, permitting the transfer of information, mediated by light, between distant emitters. Within the framework of this thesis, we study such complex photonic structures comprising of multiple quantum emitters embedded in arrays of coupled PhC cavities. We demonstrate the coupling of site-controlled quantum wires (QWRs) to delocalized modes of linear and 2D arrays of cavities. Relying on the high uniformity of pyramidal QDs, we evidence the coupling of the delocalized mode of two coupled cavities to two site-controlled QDs, embedded in each cavity.

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