Catherine Tonin

Addressing and manipulating an individual spin in single quantum dots is a fundamental step to achieve for eventual information processing based on quantum mechanics. Neutral excitons can also be used as single qu-bits but their polarization properties have to be well known in order to address a specific state. It is well established now that for self-assembled QDs, in-plane shape asymmetry induced during growth and anisotropic strain effects create linearly polarized exciton states with mixed heavy and light hole states. Moreover, the polarization directions are not always aligned along the crystallographic axes. It then becomes essential to know precisely the optical alignment of the QD exciton eigenstates.

We investigate the optical emission polarization dependence of single InGaAs/GaAs self-assembled QDs embedded in a one-dimensional GaAlAs monomode waveguide, in the dots plane (x, y) and along the growth axis z. This original geometry allows to study the resonant emission properties and to investigate the polarization properties along the z-axis which is impossible in usual backscattering excitation-detection geometry. If luminescence polarized along the z-axis exists, it reflects directly the mixing between heavy and light hole states with opposite spins due to the different off-plane strain components.

Using the valence band mixing and the misorientation angle determined independently in non-resonant experiments, we used resonant excitation experiments to evaluate the oscillator strength ratio between the two linearly polarized exciton eigenstates. Preliminary results show that the valence band mixing induces different oscillator strengths for the two optically allowed exciton states with a ratio between 0.2 and 1.