Quantum effects in artificial atoms
This thesis contains a theoretical and experimental investigation of semiconductor quantum dots (artificial atoms). The first part presents a numerical study of spin effects in GaAs/AlAs modulation-doped quantum dots containing 0 to 50 electrons. A theoretical model is developed to calculate confinement potentials and ground-state electron density distributions using the Kohn-Sham local spin-density approximation. Spin polarization, defined as the difference between the up- and down-spin electron densities, is predicted to occur spontaneously in symmetric quantum dots and in quantum point contacts in the lowdensity regime as a result of electron exchange interactions. This spontaneous magnetization can be controlled by an applied gate voltage, which opens up applications in spintronics and provides a possible explanation for the non-integer quantization of the quantum point contact conductance. The second part describes experimental techniques to investigate photon-exciton coupling in InAs/GaAs self-assembled quantum dots. Two experiments on resonant excitation of a single quantum dot are proposed, whereby the quantum-dot emission is distinguished from resonant pump light by either photon bunching of collected photons with reference photons, or Michelson interferometry. The feasibility study of the proposed experiments shows that the photon-exciton coupling efficiency must be dramatically increased by putting the quantum dot inside an optical microcavity. Novel types of high-quality, low mode-volume semiconductor microcavities containing quantum dots are designed, fabricated, and studied on a newly built setup. We present the first results of photoluminescence studies of InAs quantum dots inside both GaAs single-defect square-lattice photonic-crystal slabs and GaAs/AlAs micropillars, and InAs artificial molecules formed by vertically coupled strain-assisted quantum dots. The results indicate the potential of these nanostructures for implementing resonant transfer of quantum information, developing quantum repeaters and entangled-photon sources, and studying QED effects in the strong-coupling regime.