Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots

TL;DR

This paper demonstrates long-lived exciton spin memory in individual InAs/GaAs quantum dots through optical polarization techniques, with high polarization conservation and conversion efficiency, supported by a pseudo-spin model.

Contribution

It introduces a method to control and measure exciton spin polarization in quantum dots, revealing long spin relaxation times and polarization conversion efficiencies.

Findings

Up to 90% linear polarization conservation

Up to 47% circular-to-linear polarization conversion

Long exciton spin relaxation times relative to radiative lifetime

Abstract

We investigate exciton spin memory in individual InAs/GaAs 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 with a model of pseudo-spin 1/2 including heavy-to-light hole mixing.