  We demonstrate a method which allows the stochastic modelling of quantum
systems for which the generalised Fokker-Planck equation in the phase space
contains derivatives of higher than second order. This generalises quantum
stochastics far beyond the quantum-optical paradigm of three and four-wave
mixing problems to which these techniques have so far only been applicable. To
verify our method, we model a full Wigner representation for the optical
parametric oscillator, a system where the correct results are well known and
can be obtained by other methods.
