Exciton and spin coherence in quantum dot lattices

Abstract

AbstractWe theoretically investigate the optical properties of different semiconductor systems containing two dimensional lattices of neutral and charged quantum dots embedded in planar and arrays of optical cavities. The strong exciton (trion)- photon coupling is described in terms of polariton quasiparticles. First, we focus on a lattice of neutral dots in a planar microcavity. We show that Bragg polariton modes can be obtained by tuning the exciton and the cavity modes into resonance at high symmetry points of the Brillouin zone. The effective mass of these polaritons can be extremely small and makes of them the lightest exciton-like quasiparticles in solids. We analyze how disorder affects the properties of these Bragg polariton modes. It is found that in some cases weak disorder increases the light matter coupling and it leads to a larger polariton splitting. The second system investigated is similar to the first, but each dot has been charged with one electron. The electron spin determines the polarization of the cavity photon that couples to the dot. Such spin lattice can be used for quantum information processing and we show that a conditional phase shift gate with high fidelity can be obtained. Finally, we investigate exciton-photon quantum phase transitions in a planar lattice of one-mode cavities containing one neutral quantum dot each. Adopting the mean-field approximation we calculate exciton- and photon-phase diagrams and demonstrate that by controlling exciton- and photon-hopping energies a very rich scenario of coupled fermionic-bosonic quantum phase transitions appears.KeywordsQuantum WellQuantum Phase TransitionExciton EnergyCoherence ParameterSpin CoherenceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.