Stable entanglement in a quadripartite cavity optomechanics

Abstract

In this paper, making use of negativity, we study bipartite entanglements in a quadripartite system composed of two two-level atoms and a cavity optomechanics. An atom is inside a single-mode cavity with a movable mirror and the other one is isolated outside, i.e., there is no direct interaction between this atom and cavity optomechanics with the atom therein. The entanglement dynamics of various types of bipartite systems obtained has been numerically investigated to understand the roles of initial state of cavity field, movable mirror and atoms, the ratio of the atom-field coupling strength to the optomechanical coupling coefficient on physical properties. The results amazingly show the bipartite entanglement between the interior and exterior isolated atoms. Depending on the above-mentioned ratio and different initial states adopted to the system, the relatively stable entanglement can be generated between the atoms. Furthermore, the so-called atomic entanglement sudden death, which is independent of the degree of entanglement of the initial state, occurs in some situations.