Tunable steady-state coherence via composite system–environment interactions beyond weak tunnel coupling

We study a two-level system with an additional tunneling effect, where the general interaction with an Ohmic-class spectrum can be controlled by adjusting the coupling angle. We outline the derivation of the time-local microscopic non-Markovian master equation after renormalizing the eigenstates in the two-level system, hence removing the restriction of weak tunneling coupling. Further, two quantum coherence measures are exploited to analyze steady-state coherences (SSC). We identify that under strong tunneling effects, a specific coupling angle enables SSC generation that is both independent of the Ohmic-like spectral density and capable of reaching substantial magnitudes. Moreover, in the vicinity of this critical angle, SSC exhibits an opposite dependence on the Ohmic parameter in different regions. In addition, we examine the impact of Ohmic parameters and environmental temperature on SSC, demonstrating that optimizing these factors provides an effective strategy to maximize SSC.