Optical Properties Of Self-assembled Semiconductor Quantum Dots And Its Applications In Quantum Information

Quantum dots, the so called "artificial atoms", possess many quantum effects and optical properties similar with atoms. Besides, because of the stability and compati-bility with modern semiconductor technologies and devices, it is relatively easy to be manufactured and integrated. Therefore, it is a prospective solid state system in quan-tum information and computation. To study the optical properties of quantum dots, on the one hand we can investigate the intrinsic energy level structure making it as a qubit in quantum computation. On the other hand, the emitted single photon and entangled photon pairs can be tools for quantum communications. So I selected the optical prop-erties as the main topic of this thesis. We also make discussions on some fundamental growth techniques and solid state theory on self-assembled semiconductor quantum dots.1. We experimentally discovered the exciton-phonon interaction in quantum dots ensemble, and gave further experimental proofs and theoretical explanation. We find under certain temperatures, a exciton in quantum dots ensemble can be coupled to a phonon, thus provide a new relaxation window for the carriers. Form the photo-luminescence picture, a new peak appears separating from the origin s-shell peak with one phonon energy. The relative intensity changes with the temperature. Finally, al-most all the carriers decays through the new window. We put forward a new technique to measure the lifetime of excitons in quantum dots, and the results show that under certain temperatures, the exciton indeed combines with phonon resulting in longer life-time.2. We discuss the probability of single quantum dots to be single photon source, and propose a scheme to realize quantum random walk algorithm. Single photon can carry coherent state and propagate decoherence-freely in free space, so it can be an important tool for quantum state engineering and for transporting. Single quantum dot excited by a pulse laser can provide single photons effectively on demand, thus can be used as the carrier of walk qubit to realize scalable quantum random walk.3. We propose a scheme to generate hyper-entangled photon pairs taking use of the cascaded photon emitting from biexciton state. In this scheme, exciton fine-structure splitting, which was previously deemed undesirable in similar schemes, is used here to produce photon pairs entangled in both frequency and polarization degrees of freedom.4. We study the orbital angular momentum distribution of the photon emitted by quantum dots, to explore the probability of single quantum dot as entanglement source in orbital angular momentum dimension. The photons from quantum dots are not in single Gaussian mode but superposition of Gaussian mode and high order LG modes.