Nuclear polarization dynamics are measured in the nuclear spin bistability 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 nonlinear nuclear spin dynamics. We measure nuclear spin polarization decay times in the range of 0.2-5 s, 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 (>5s) pumping times. The time-resolved methods allow the detection of the unstable nuclear polarization state in the bistability regime otherwise undetectable in cw experiments.

We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a thresholdlike enhancement or reduction of the local nuclear field by up to 3 T can be generated by varying the pumping intensity. The excitation power threshold for such a nuclear spin "switch" is found to depend on both the external magnetic and electric fields. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of the spin transfer from electrons to the nuclei of the dot.

Control of the dynamic nuclear polarization is achieved in individual InGaAs dots embedded in a p-i-n diode by employing the vertical electric field controlling carrier tunneling rates. Nuclear magnetic fields up to 1.7 T are observed.

A high degree of spin polarization (or spin memory) is achieved using quasiresonant optical excitation at zero magnetic field (B=0) for singly positively charged excitons (X+) in individual quantum dots embedded in a Schottky diode. The high degree of spin memory indicates highly efficient optical excitation ("writing") of long-lived spin-polarized electrons, determining the X+ spin orientation. We demonstrate control of the degree of spin polarization by the applied bias, controlling carrier tunneling rates in the device. In addition, efficient spin-selective optical excitation of neutral excitons is achieved for B > 1 T.

We report neutral (X-0) and charged excitons (X+) with high degrees of linear polarization (>= 70%) in charge-tunable InGaAs quantum dots (QDs). The QD emission exhibits a small Zeeman splitting for magnetic fields parallel to the growth direction, in contrast to "conventional" dots in the same sample, and remains predominantly linearly polarized up to 5 T. With the aid of in-plane field measurements, the observations are explained in terms of heavy-light-hole mixing due to QD anisotropy. This results in elliptical polarization of the QD emission and strong reduction of the exciton g factor. A combination of the data obtained for magnetic fields in Faraday and Voigt configurations allows a full determination of the electronic properties.

Control of electronic spins in individual InGaAs quantum dots is achieved by applying vertical electric and magnetic fields. In addition, dots with anomalously large degree of linear polarization are found weakly affected by magnetic field.

We report neutral $({X}^{0})$ and charged excitons $({X}^{+})$ with high degrees of linear polarization $(\ensuremath{\geqslant}70%)$ in charge-tunable InGaAs quantum dots (QDs). The QD emission exhibits a small Zeeman splitting for magnetic fields parallel to the growth direction, in contrast to ``conventional'' dots in the same sample, and remains predominantly linearly polarized up to $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. With the aid of in-plane field measurements, the observations are explained in terms of heavy\char21{}light-hole mixing due to QD anisotropy. This results in elliptical polarization of the QD emission and strong reduction of the exciton $g$ factor. A combination of the data obtained for magnetic fields in Faraday and Voigt configurations allows a full determination of the electronic properties.