  We derive the general probability distribution function of stochastic work
for quantum Otto engines in which both the isochoric and driving processes are
irreversible due to finite time duration. The time-dependent power
fluctuations, average power, and thermodynamic efficiency are explicitly
obtained for a complete cycle operating with an analytically solvable two-level
system. We show that, there is a trade-off between efficiency (or power) and
power fluctuations.
