Stochastic Liouville equation approach within non-equilibrium thermo field dynamics

The development of non-equilibrium thermo field dynamics, called NETFD in abbreviation, was started in 1983 based on the damping theory in Liouville space. It has progressed considerably since then. Especially, the structural similarity between the framework of NETFD and the framework of the usual quantum field theory was revealed. In this paper, we will show that, within the formalism of NETFD, the quantum Langevin equation and the quantum stochastic Liouville equation approach are also feasible for the construction of the quantum field theory for open systems.