| Coherent continuous-wave laser fields are used to excite and probe GaAs quantum dots formed by interface fluctuations. Experiments are carried out both at the single quantum dot level and on an ensemble of dots. An external magnetic field is used as an additional tool for this investigation.; The three-dimensional quantum confinement leads to discrete exciton and biexciton states in a dot. Four states, including the crystal ground state, two excitonic states, and the biexciton state, are experimentally identified. This thesis shows that the quantum coherences between any two of the four states can be optically manipulated and give rise to unique signatures in the coherent nonlinear optical response. These coherences are maintained within the exciton and biexciton lifetimes due to the absence of pure dephasing in these systems.; These experiments provide a direct measure of the strength of the exciton-exciton Coulomb correlation in a QD. This correlation leads to conditional dynamics in the excitation that are critical for demonstrating of two-bit quantum logic operations in interface fluctuation QD systems. It allows for optically inducing a two-exciton entangled state, one of the core elements in a quantum logic device. The entanglement is relatively long-lived due to the absence of pure dephasing.; Other parameters of importance to both QD physics and QD-based quantum computing are also measured, including the exciton and biexciton dipole moments, the exciton g-factor and diamagnetic coefficient. |
