Exploring initial correlations in a Gibbs state by application of external field

We study the time evolution of trace distance between the quantum states which evolve from two kinds of initial states, a correlated Gibbs state and its uncorrelated marginal state. We consider the case where a two-level system linearly and adiabatically interacts with an infinite number of bosons. We find that the trace distance increases above its initial value for any and all parameter settings when a weak external field is applied to the two-level system. This indicates that we can explore the existence of initial system-environment correlations with the breakdown of the contractivity induced by the external field.