1 Department of Photonics Engineering, Technical University of Denmark2 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
In this thesis we have performed quantum-electrodynamics experiments on quantum dots embedded in photonic-crystal cavities. We perform a quantitative comparison of the decay dynamics and emission spectra of quantum dots embedded in a micropillar cavity and a photonic-crystal cavity. The light-matter interaction in the micropiller caivty is so strong that we measure non-Markovian dynamics of the quantum dot, and we compare to the Jaynes-Cummings model with all parameters independently determined. We find an excellent agreement when comparing the dynamics, but the emission spectra show significant deviations. Similar measurements on a quantum dot in a photonic-crystal cavity sow a Rabi splitting on resonance, while time-resolved measurements prove that the system is in the weak coupling regime. Whle tuning the quantum dot through resonance of the high-Q mode we observe a strong and surprisingly broadband Purcell enhancement of the decay rate, which cannot be described by the Jaynes-Cummings model. The broadband Purcell enhancement occurs because the quantum dot emits or absorbs a longitudinal acoustic phonon with the energy corresponding to the detuning between the quantum dot and cavity. We Successfully model the decay rates with a microscopic model that allows us to for the first time extract the effective phonon density of states, which we can model with bulk phonons. Studies on a quantum dot detuned from a low-Q mode of a photonic-crystal cavity show a high collection efficiency at the first lens of (44.3±2.1)%, while emission exhibits a very strong anti-bunching. We demonstrate how the quantum dot can be efficiently and selectively excited through longitudinal optical and acoustic phonon-mediated excitation. Indistinguishability measurements of the emitted photons under these two excitation schemes reveal low dephasing rates of 0.82±0.41µeV and 0.42±0.18µeV respectively.