  We present a comprehensive examination of optical pumping of spins in
individual GaAs quantum dots as we change the charge from positive to neutral
to negative using a Schottky diode. We observe that photoluminescence
polarization memory has the same sign as the net charge of the dot. Optical
pumping of ground state electron spins enhances this effect, as demonstrated
through the first measurements of the Hanle effect on an individual quantum
dot. With the Overhauser effect in a high longitudinal magnetic field, we
demonstrate efficient optical pumping of the quantum dot's nuclear spins for
all three charge states.
