Local quantum coherence with intersource interactions at nonzero temperature

Abstract: Local quantum coherence in a two-level system (TLS) is typically generated via time-dependent driving. However, it can also emerge autonomously from symmetry-breaking interactions between the TLS and its surrounding environment at a low temperature. Although such environments often consist of interacting atoms or spins, the role of interactions within the environment in generating the autonomous local coherence has remained unexplored. Here, we address this gap by analyzing an exactly solvable model, which comprises a target TLS coupled to $N$ interacting source TLSs that represent the environment, with the whole system being in thermal equilibrium. We show that the local coherence not only persists but can be enhanced at finite temperatures of the environment compared to the case of no inter-source interactions. The temperature dependence of the coherence bears signatures of a quantum phase transition, and our analytical results suggest strategies for its optimization. Our findings reveal generic properties of the autonomously generated quantum coherence and point to viable routes for observing the coherence at nonzero temperatures.