  We use one single, few-picosecond-long, variably polarized laser pulse to
deterministically write any selected spin state of a quantum dot confined dark
exciton whose life and coherence time are six and five orders of magnitude
longer than the laser pulse duration, respectively. The pulse is tuned to an
absorption resonance of an excited dark exciton state, which acquires
non-negligible oscillator strength due to residual mixing with bright exciton
states. We obtain a high fidelity one-to-one mapping from any point on the
Poincar\'e sphere of the pulse polarization to a corresponding point on the
Bloch sphere of the spin of the deterministically photogenerated dark exciton.
