Quantum phase space distributions in thermofield dynamics

It is shown that the quantum phase space distributions corresponding to a d ensity operator rho can be expressed, in thermofield dynamics, as overlaps between the state \rho] and 'thermal' coherent states. The usefulness of th is approach is brought out in the context of a master equation describing a nonlinear oscillator for which exact expressions for the quantum phase dis tributions for an arbitrary initial condition are derived.