Coherent State Combined with Mixed State for an Imperfect Boson System. I --- Thermalization of Pure Squeezed Coherent State ---

A pure squeezed coherent state is amalgamated with a mixed state for the purpose of describing bose condensation in an imperfect spinless boson system at non-zero temperature. Three types of variables are introduced: One describes the bose condensation, one describes the quantum fluctuations of a condensed pair induced by the interaction, and one describes the thermal properties. We define an entropy in association with the amalgamated state. Then, the thermal equilibrium state is defined through a variational principle with a fixed boson number and entropy.