WIGNER FUNCTIONS FOR COHERENT AND SQUEEZED STATES WITH THERMAL NOISE

A generalized Wigner function W(T)(alpha, alpha) including the thermal degrees of freedom is presented to calculate the 'reduced' Wigner functions for all kinds of coherent and squeezed states with thermal noise by the formalism of thermofield dynamics. The results show that the different definitions of coherent and squeezed state with the same corresponding density matrix give rise to the same reduced Wigner function. By our method, the reduced Wigner function can be calculated for an arbitrary vector in the thermal Fock space, of which the density matrix is too complicated to use.