Polarization properties of excitonic qubits in single self-assembled quantum dots

We investigate polarization properties of neutral exciton emission in single self-assembled InAs/GaAs quantum dots. The in-plane anisotropy of the confinement potential and strain strongly couple the heavy- and light-hole states and lead to large optical anisotropy with nonorthogonal linearly polarized states misaligned with respect to the crystallographic axes. Owing to a waveguiding experimental configuration, luminescence polarized along the growth axis has been observed, revealing the presence of shear components of the deformation tensor out of the growth plane. Resonant luminescence experiments allowed determining the oscillator strength ratio of the two exciton eigenstates. Valence-band mixing governs this ratio and can be very different from dot to dot; however, the polarization anisotropy axis is quite fixed inside a scanned area of 1 mu m(2) and indicates that the in-plane deformation direction to which it is related has a correlation length of the order of magnitude of 1 mu m(2).