  We present a derivation of the integral fluctuation theorem (IFT) for
isolated quantum systems based on some natural assumptions on transition
probabilities. Under these assumptions of "stiffness" and "smoothness" the IFT
immediately follows for microcanonical and pure quantum states. We numerically
check the IFT as well as the validity of our assumptions by analyzing two
exemplary systems. We have been informed by T. Sagawa et al. that he and his
co-workers found comparable numerical results and are preparing a corresponding
paper, which should be available on the same day as the present text. We
recommend reading their submission.
