NEW APPLICATION OF THERMO FIELD DYNAMICS IN SIMPLIFYING THE CALCULATION OF WIGNER FUNCTIONS
Hong-Yi Fan · Modern Physics Letters A · 2003
We find that the Thermo Field Dynamics, invented by Takahashi and Umezawa, can simplify calculations of Wigner functions for density matrices ρ. Using the coherent thermal state representation (Phys. Lett.A246, 242 (1998)), we show that the Wigner function W = Tr (Δρ) (an ensemble average of the Wigner operator Δ) can be expressed as a matrix element of ρ in the pure coherent thermal states. Wigner functions for some complicated density matrices are derived in this way.