  In the following paper, we generalize the geometrical framework of qubit
decoherence to higher dimensions. The quantum mixed state is represented by the
probability distribution, which is the K\"ahler function on the projective
Hilbert space. The Markovian master equation for density operators turns out to
be equivalent to the Fokker-Planck equation for quantum probability
distributions. Several examples are analyzed, featuring different
generalizations of the Pauli channel.
