Quantum dynamics of a strongly coupled dissipative system toward thermal equilibrium II

The quantum dynamics of the Jaynes-Cummings model toward thermal equilibrium is studied in detail from the viewpoint of phase and energy relaxation, continuing the previous work of the authors, Physica A 217 (1995) 348. The dynamics of the spin subsystem and the Hushimi functions of the boson subsystem are clarified by calculating the reduced density matrix including the off-diagonal part with respect to the boson quantum number. The decoherence of the coupled system is investigated using the purity. The Hushimi function and purity are divided into two parts from the diagonal and off-diagonal elements. The effects of phase and enenry relaxation are analysed quantitatively.