  The dynamics of a qubit in two different environments are investigated
theoretically. The first environment is a two level system coupled to a bosonic
bath. And the second one is a damped harmonic oscillator. Based on a unitary
transformation, we find that the decoherence of the qubit can be reduced with
increasing temperature $T$ in the first case, which agree with the results in
[Phys. Rev. Lett. 100, 120401], whereas, it can not be reduced with $T$ in the
second case. In both cases, the qubit dynamics are changed substantially as the
coupling increases or finite detuning appears.
