Quantum entanglement dynamics based on composite quantum collision model

By means of composite quantum collision models, we study the entanglement dynamics of a bipartite system, i.e.,two qubits S1 and S2 interacting directly with an intermediate auxiliary qubit SA, while SAis in turn coupled to a thermal reservoir. We are concerned with how the intracollisions of the reservoir qubits influence the entanglement dynamics. We show that even if the system is initially in the separated state, their entanglement can be generated due to the interaction between the qubits. In the long-time limit, the steady-state entanglement can be generated depending on the initial state of S1 and S2 and the environment temperature. We also study the dynamics of tripartite entanglement of the three qubits S1,S2, and SAwhen they are initially prepared in the GHZ state and separated state, respectively. For the GHZ initial state,the tripartite entanglement can be maintained for a long time when the collision strength between the environment qubits is sufficiently large.