  A fluctuation theorem for the nonequilibrium entropy production in quantum
phase space is derived, which enables the consistent thermodynamic description
of arbitrary quantum systems, open and closed. The new treatment naturally
generalizes classical results to the quantum domain. As an illustration the
harmonic oscillator dragged through a thermal bath is solved numerically.
Finally, the significance of the new approach is discussed in detail, and the
phase space treatment is opposed to the two time energy measurement approach.
