Optical alignment and polarization conversion of the neutral-exciton spin in individualInAs∕GaAsquantum dots

Abstract

We investigate exciton spin memory in individual $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ self-assembled quantum dots via optical alignment and conversion of exciton polarization in a magnetic field. Quasiresonant phonon-assisted excitation is successfully employed to define the initial spin polarization of neutral excitons. The conservation of the linear polarization generated along the bright exciton eigenaxes of up to 90% and the conversion from circular to linear polarization of up to 47% both demonstrate a very long spin relaxation time with respect to the radiative lifetime. Results are quantitatively compared to a model of pseudospin $1∕2$ including heavy-to-light hole mixing.