  The linear transient response of a two-level system coupled with an
environmental system is studied under correlated and factorized initial
conditions. We find that the transient response in these cases differs
significantly from each other, especially for strong system-environment
interaction at intermediate temperatures. This means that it is necessary to
pay attention to the initial conditions chosen when analyzing experiments on
transient linear response, because the conventional factorized initial
condition results in an incorrect response, in which the quantum correlation
between the relevant system and the environmental system is disregarded.
