Manipulating non-Markovianity via bath's coherence in a collision model

In this paper, we propose a structured collision model where the system qubit directly interacts with a nonthermal bath simulated by an ensemble of ancillas, and each ancilla consists of N correlated qubits. Based on this collision model, we systematically investigate the effects of three distinct types of coherence, namely displacement coherence in the single-qubit bath, along with squeezing and heat-exchange coherences in the two-qubit bath, on non-Markovianity in open quantum dynamics. The research findings demonstrate that injecting any of these three types of coherence into the environment can enhance the non-Markovianity in dynamics and make it more easily activated as long as the parameters (including the magnitude and phase of coherence) are appropriately selected. When the intracollision strength is relatively small, manipulating the coherence embedded in the bath can induce successive transitions of the system's dynamics between Markovian and non-Markovian regimes. In particular, we show that compared to the displacement coherence in the single-qubit bath, injecting the heat-exchange coherence or squeezing coherence into the two-qubit bath is more effective for improving the non-Markovianity.