The main contribution of the decoherence of ρ +-, on the other hand, originates from the population transfer from the |+⟩ state to the dark states manifold {|D k ⟩}. This population transfer process happens within the same timescale of the ρ +-(t) decoherence process, as shown in Fig. and Fig. . This transition is caused by the phonon coupling term Ĥ{±,D} in Eq. 21b. One can estimate the transition rate constant for the process |+⟩ → {|D k ⟩} using Fermi's Golden Rule (FGR), which gives