Spin interaction in semiconductors mediated by optical excitations.

摘要

Circumscribed to the field of condensed matter, this thesis aims to enhance our understanding of optically-induced indirect spin interactions in semiconductor structures, as well as to contribute to the development of solid state proposals for the emerging science of Quantum Information.;The theoretical formalism that is used throughout this thesis is discussed. This mathematical framework describes excitations of the semiconductor, light fields and localized spin states. It is shown how the Hamiltonian is derived from a microscopic model. This resulting Hamiltonian includes the: (i) Interaction between laser light and excitations of the semiconductor; (ii) Kinetic energies of excitations; (iii) interaction of photons and excitons that yield exciton polaritons; (iv) Spin interaction between localized centers and optical excitations in the semiconductor (excitons and/or exciton polaritons).;The formalism is first employed to analyze the spin indirect interaction mediated by excitons in semiconductors and extend the results of previous works in this subject. In contrast to previous works, a full analytical solution valid to all orders in the strength of the interaction between excitations and localized spins is found. New features arise from the non-perturbative solution. One important finding is that both ferromagnetic and anti-ferromagnetic indirect coupling can be achieved.;The indirect interaction for semiconductors embedded in a planar micro-cavity is then considered. This theory follows naturally as an extension of the one for bare semiconductors. The focus is now on different features that are predicted using perturbation theory in the coupling between polaritons and localized spins. It is shown that the indirect interaction presents two distinct regimes, depending on the separation between the localized spins. In each regime, the dominant interaction is of a different type: Ising or Heisenberg. Moreover, the range of the interaction for a semiconductor in a micro-cavity is found to be of longer range when compared to that of a bare semiconductor.;The knowledge gained through the aforementioned investigations opens new possibilities for applications to quantum information. First, a detailed analysis of optical quantum control in a system consisting of quantum dots grown on top of a quantum well is presented. It is shown how this system is a possible candidate for quantum computers. Then a discussion follows; describing how the findings on bare semiconductor and micro-cavity indirect interactions are a rich ground for implementations of quantum computing and other quantum information technologies.;This dissertation ends with comments on the future developments of the research presented here.