The spin of a single electron confined in a semiconductor quantum dot is a possible candidate for a qubit to realize quantum information processing. Here we discuss the initialization of the electron spins in single quantum dots using a semi-magnetic spin aligner layer. We have succeeded in the concurrent initialization of five quantum dots with near-unity fidelity. The electron spin is read-out by observing the polarization of the emitted photons. These originate from excitonic recombination of the electron with an unpolarized hole in the dot. We find dots emitting highly polarized photons over the whole inhomogeneously broadened quantum-dot ensemble emission spectrum. However, a pronounced dependency between the statistical average of the polarization degree and the quantum-dot ground-state energy is found. The influence of charged-exciton recombination due to donors and defects is discussed.
W. Löffler, M. Hetterich, C. Mauser, S. Li, J. Leuthold, H. Kalt
phys. stat. sol. (b) 245, 1102 (2008)