Cavity-QED studies of composite semiconductor nanostructure and dielectric microsphere systems

Spontaneous emission, which reflects fundamental dynamical interactions between matter and vacuum, can be controlled by using optical microcavities with dimensions of optical wavelength. This dissertation presents experimental studies aimed at controlling the spontaneous emission process in semiconductor quantum dots by coupling colloidal core/shell CdSe/ZnS nanocrystals to whispering gallery modes of a dielectric microsphere. Extensive cavity-QED studies are carried out in both the low-Q regime where the spontaneous emission features modified decay rate and the high-Q regime where dynamics of the cavity is sensitive to absorption occurring in a single nanocrystal.; For studies in the low-Q regime, we have embedded CdSe/ZnS nanocrystals in the interior surface of a polystyrene sphere. We have demonstrated pronounced enhancement in spontaneous emission rates when the nanocrystals are resonant with a whispering gallery mode. The manifestation of these cavity-QED effects depends sensitively on temperature and especially on nanocrystal sizes, providing a unique probe to the underlying radiative dynamics. We show that emissions from the lowest dipole-allowed transition represent a predominant contribution to the photoluminescence. Comparison between the theoretically expected Purcell factor and the observed enhancement in the photoluminescence decay rate also indicates that quantum yield for the lowest dipole-allowed transition in large nanocrystals (D > 6 nm) is near unity, which reflects the high surface quality of core/shell nanocrystals and is also important for using these nanocrystals as artificial atoms for applications in photonics and quantum optics.; For studies in the high-Q regime, we have deposited nanocrystals to the surface of a fused silica microsphere. We have demonstrated that the Q-factor of this composite nanocrystal-microcavity system can exceed 108, four orders of magnitude greater than Q-factors of other monolithic semiconductor microcavities. We find that the Q-factor is primarily limited by surface adsorption of chloroform solution used in the deposition process. The extremely high Q-factor puts us in a regime where cavity-QED at the level of a single nanocrystal can be pursued. This composite nanocrystal-fused silica microsphere system should open up a new avenue to a variety of physical phenomena including single-quantum-dot lasers, vacuum Rabi oscillation of nanocrystals and nanocrystal-based quantum information processing.