  The influence of the initial preparation on dephasing in open quantum
dynamics is studied using an exactly solvable model of a two-level system
(qubit) interacting with a bosonic bath. It is found that for some classes of
non-selective preparation measurements, qubit-bath correlations lead to a
significant enhancement of coherence in the qubit at the initial stage of
evolution. The time behavior of the qubit purity and entropy in the regime of
enhancement of coherence is considered for different temperatures and coupling
strengths.

Quantum Physics