  We have demonstrated experimentally the manipulation of exciton and nuclear
spins in a single self-assembled
In$_{0.75}$Al$_{0.25}$As/Al$_{0.3}$Ga$_{0.7}$As quantum dot. The oscillation of
exciton and nuclear spin polarizations were clearly observed. The switching of
the emissions in Zeeman split pair indicates that the exciton pair with
opposite spins was created coherently via the continuum states and that we can
control the electron and nuclear spin polarizations only by changing the delay
time of the cross-linearly-polarized pulses. These suggest the high
potentiality of electron and nuclear spin manipulation in a single QD via the
continuum state.
