Tailored quantum dots for entangled photon pair creation

Abstract

We compare the asymmetry-induced exchange splitting ${\ensuremath{\delta}}_{1}$ of the bright-exciton ground-state doublet in self-assembled $(\mathrm{In},\mathrm{Ga})\mathrm{As}∕\mathrm{GaAs}$ quantum dots, determined by Faraday rotation, with its homogeneous linewidth $\ensuremath{\gamma}$, obtained from the radiative decay in time-resolved photoluminescence. Postgrowth thermal annealing of the dot structures leads to a considerable increase of the homogeneous linewidth, while a strong reduction of the exchange splitting is simultaneously observed. The annealing can be tailored such that ${\ensuremath{\delta}}_{1}$ and $\ensuremath{\gamma}$ become comparable, whereupon the carriers are still well confined. This opens the possibility to observe polarization entangled photon pairs through the biexciton decay cascade.