  The energy states in semiconductor quantum dots are discrete as in atoms, and
quantum states can be coherently controlled with resonant laser pulses. Long
coherence times allow the observation of Rabi-flopping of a single dipole
transition in a solid state device, for which occupancy of the upper state
depends sensitively on the dipole moment and the excitation laser power. We
report on the robust preparation of a quantum state using an optical technique
that exploits rapid adiabatic passage from the ground to an excited state
through excitation with laser pulses whose frequency is swept through the
resonance. This observation in photoluminescence experiments is made possible
by introducing a novel optical detection scheme for the resonant electron hole
pair (exciton) generation.
