A nonequilibrium statistical quasi-particles thermofield theory.

For quantum systems coupled with Gaussian environment, we observe that the environmental dissipative effect can be represented by statistical quasi-particles. This observation is then exploited to establish universal relations for some important steady state correlation functions, which involve hybrid reservoir modes. All these relations are validated numerically. A simple corollary of them is the transport current expression, which exactly recovers the result obtained from the nonequilibrium Green's function formalism.