using the operator Uˆ(t). This time-development operator Uˆ(t) includes the thermal noise R(t). Clearly, by reducing the
random operator R(t), we can obtain such an effective interaction between S0 and S˜
0 as it includes thermal dissipation. This
yields, as will be seen below, the new point of view that introducing the effective interaction enables us to study dissipative
systems