Resonant photon-exciton interaction in semiconductor quantum dots

Semiconductor self-assembled quantum dots form a three dimensional confinement for charge carriers in the solid state matrix. The confinement modifies the density of states, leading to atom like optical properties of quantum dots that can be studied by absorption or emission of photons. Due to the sharp resonance lines that are observed in optical spectra, quantum dots are often referred to as artificial atoms. However, self-assembled quantum dots are semiconductor nanostructures and they are incorporated into a solid state crystal yielding physical properties given by their solid state nature. By tailoring the semiconductor heterostructure around the quantum dot a charge tunable device can be fabricated. As a result, the quantum dot can be charged with single electrons in a controlled way via an applied bias. Furthermore, the device can be designed such that the quantum dot states are coupled to continuum states in the vicinity of the quantum dot. In this thesis, the two-level atom like optical properties of single charge tunable quantum dots are investigated as well as their solid state nature. This, on one hand, leads to the observation of Rabi splitting of the quantum dot states, a typical feature of a two-level system. On the other hand, the introduction of a tunnel coupled continuum of states into the device leads to the discovery of the nonlinear Fano effect. An effect that can be explored on quantum dots in a different, nonlinear regime that is not easily accessible by atom spectroscopy. Furthermore, the dynamics of a single electron or hole spin in a quantum dot are investigated. Here, again, the solid state nature of the quantum dot manifests itself in a single electron spin resonance experiment adopted from quantum optical experiments on atoms. We find that the spin dynamics of electrons and holes in a semiconductor quantum dot are dominated by coupling to the electron reservoir or finally by the hyperfine interaction. The experiments presented in this thesis were performed with diffraction-limited cryogenic microscopes. The microscopes were designed such that they operate in a magnetic field that can be applied parallel or perpendicular to the light propagation direction. The sample was cooled to liquid helium temperature (4.2 K). Resonant Rayleigh scattering spectroscopy is used to gain high spectral resolution, yielding the natural resonance linewidth of the excitonic transition in a quantum dot (1 − 2 μeV). This method is applied to neutral, negatively, and positively charged states on the very same quantum dot for the first time. Furthermore, resonant optical pumping of the electron or hole ground state into a shelving state is presented in this work. This optical pumping allows the alignment of electron or hole spins in the quantum dot with near-unity fidelity, parallel or antiparallel to an applied magnetic field.