Enhanced steady-state coherence via repeated system-bath interactions

The appearance of steady-state coherence (SSC) from system-bath interactions proves that quantum effects can appear without an external drive. Such SSC could become a resource to demonstrate a quantum advantage in the applications. We predict the generation of SSC if the target system repeatedly interacts with independent and noncorrelated bath elements. To describe their behavior, we use the collision model approach of system-bath interactions, where the system interacts with one bath element (initially in an incoherent state) at a time, asymptotically (in the fast-collision regime) mimicking a macroscopic Markovian bath coupled to the target system. Therefore, the SSC qualitatively appears to be the same as if the continuous Markovian bath were used. We confirm that the presence of composite system-bath interactions under the rotating-wave approximation is the necessary condition for the generation of SSC using thermal resources in collision models. Remarkably, we show that SSC substantially increases if the target system interacts collectively with more than one bath element at a time. A few bath elements collectively interacting with the target system is sufficient to increase SSC at nonzero temperatures at the cost of a tolerable lowering of the final state purity. From the thermodynamic perspective, the SSC generation in our collision models is inevitably linked to a nonzero power input (and thus heat dissipated to the bath) necessary to reach the steady state, although such energetic cost can be lower compared to cases relying on SSC nongenerating interactions.