Nuclear polarization dynamics are measured in the nuclear spin bi-stability regime in a single optically pumped InGaAs/GaAs quantum dot. The controlling role of nuclear spin diffusion from the dot into the surrounding material is revealed in pump-probe measurements of the non-linear nuclear spin dynamics. We measure nuclear spin decay times in the range 0.2-5 sec, strongly dependent on the optical pumping time. The long nuclear spin decay arises from polarization of the material surrounding the dot by spin diffusion for long (>5sec) pumping times. The time-resolved methods allow the detection of the unstable nuclear polarization state in the bi-stability regime otherwise undetectable in cw experiments.
@article{arxiv.0708.2792,
title = {Long nuclear spin decay times controlled by optical pumping in individual quantum dots},
author = {M. N. Makhonin and A. I. Tartakovskii and I. Drouzas and A. B. Van'kov and T. Wright and J. Skiba-Szymanska and A. Russell and V. I. Fal'ko and M. S. Skolnick and H. -Y. Liu and M. Hopkinson},
journal= {arXiv preprint arXiv:0708.2792},
year = {2011}
}