| The self-assembled quantum dots (QDs) have been widely used QDs laser and quantum information science (QIS). In experiments the QDs laser with different wave-length has been achieved; In the field of quantum information science, the single photon source, entangled photon source, Rabi oscillation of qubit, initialization, qubit readout and integration et al. Huge progressions both in theory and experiments have been achieved in the past ten years, however, there are still a lot of things to do before prac-tically applications, especially in QIS, we still have a lot of questions that unsolved, such as decoherence of qubits, integration of qubits and theoretical modelling of QDs. These questions are the starting point of this dissertation.In this work, we fist review the application of self-assembled QDs in QDs laser and QIS in Chap.1 and then the basic physics in QDs in Chap.2. In Chap.3 we give three methods in the calculation of electronic structure of QDs, including k·p method, empirical pseudopotential method and tight-binding method. In these methods, we pay much attention to the symmetry and the strain effect, which is of essential importance in determination of optical properties of QDs. We give a detailed description of the empirical pseudopotential method, as it will be used in Chap.4-7. At the last of Chap.3, we discuss the gauge problem under uniform magnetic field, we show that the magnetic field will breakdown the translation symmetry of the periodic lattice, so the Bloch theorem should be modified, we give the method to fix the gauge problems.In this dissertation, we mainly focus on the optical properties of QDs, and the main results we have obtained in this dissertation are as following,1. We systematically study the optical properties of InAs/InP QDs, including the single particle levels, exciton energy, exciton lifetime, many-body effect in QDs and the phase diagrams of electron and hole; We also make a comparative study with that in InAs/GaAs QDs.In Chap.5 and Chap.6, we study the electronic structure and optical properties of InAs/InP and InAs/GaAs QDs using empirical pseudopotential method. We found that the confinement potential of electron(hole) and the strain differs greatly in these two kind of QDs, which render the huge different between the electronic structure and optical properties of QDs. Our results agree well with the available experiments datas.2. We proof that InAs/InP QDs can be used as entangled photon source in the communication regime.The biexciton cascade process in QD can be used as entangled photon source, but in actually QDs the symmetry is C2v, so the two bright state of exciton has a small splitting, know as fine structure splitting, which is about tens ofμeV, so the output two photon states have only classical correlation. In Chap.7 we proof that the fine structure splitting in InAs/InP QDs is very small using empirical potential method, ant the exciton energy is around 1.55μm, so InAs/InP QDs can be used as entangled photon source in the communication regime.3. We show that the spin splitting in (InAs)n/(GaAs)m quantum wellâˆ|k|.In Chap.8 we develops a software to calculate the energy bands using pseudopo-tental method, where the pseudopotential is the same as that used in QDs. In our codes, two method has been used to deal with the spin-orbit interactions. One should know that the spin-orbit interaction in non-local, so the treatment of this is very complex. The method used in codes enable us to calculate the energy bands of very large systems. We use our codes to calculate the band splitting of (InAs)n/(GaAs)m quantum well, and we found that if we choose a suitable width of InAs, we can get spin splittingâˆ|k|. This results may have potential application in spintronics.4. We show that the coupling betwcen exciton and optical phonon in InAs/GaAs QDs has entered the strong coupling regime.In Chap.9 we study the strong exciton-optical phonon coupling in InAs/GaAs QDs. We find a new peak s'on the left side of s shell, and these two peaks can an-ticross with each other. This results is a strong evidence for strong coupling between exciton and optical phonon, hence the optical properties of QDs is greatly modified. Our results show that the Huang-Rhys model, which is based on weak-coupling, can not be used to interpret our results. We use a two-band model to explain the experimen-tal observations, and it work quite well. However, our experiments can not determine the mechanism that render the strong coupling between exciton and optical phonon, and it still ask for further theoretical investigation。... |
