  Various aspects of the statistics of work performed by an external classical
force on a quantum mechanical system are elucidated for a driven harmonic
oscillator. In this special case two parameters are introduced that are
sufficient to completely characterize the force protocol. Explicit results for
the characteristic function of work and the respective probability distribution
are provided and discussed for three different types of initial states of the
oscillator: microcanonical, canonical and coherent states. Depending on the
choice of the initial state the probability distributions of the performed work
may grossly differ. This result in particular holds also true for identical
force protocols. General fluctuation and work theorems holding for
microcanonical and canonical initial states are confirmed.
