Non-Markovianity in a dressed qubit with local dephasing

We study the dynamics of a dressed qubit implemented by a spinless fermion hopping between two lattice sites with each site strongly coupled to a bath of phonons. We employ Lang-Firsov transformation to make the problem tractable perturbatively. Applying time-convolutionless master equation within the polaron frame, we investigate decoherence dynamics of the dressed qubit within the singlet-triplet basis of the system for a wide range of bath spectral densities. It is shown that the coherence persists for longer time scales for large coupling values and shows non-monotonic behaviour reflecting the presence of non-Markovianity in the dynamics. Non-Markovianity, characterized by coherence revivals and non-monotonic decay patterns, emerges distinctly depending on the bath spectrum and coupling strengths. Systems coupled to sub-Ohmic baths, whether both or in combination with another type, display pronounced memory effects at relatively small values of couplings. In contrast, combinations involving Ohmic and super-Ohmic baths exhibit noticeable non-Markovianity only at higher couplings.

💡 Research Summary

The paper investigates the open‑system dynamics of a “dressed” qubit realized as a spin‑less fermion that tunnels between two lattice sites, each of which is locally coupled to an independent phonon bath. Because the system‑bath coupling is strong, the authors first apply the Lang‑Firsov (polaron) transformation, which eliminates the explicit fermion‑phonon interaction and renormalizes the hopping amplitude J to an effective value (\tilde J = J \exp