Two-Mode Steady-State Entanglement in a Four-Level Atomic System

We investigate the continuous variable entanglement in a four-level atom according to the criterion proposed by Duan et al. [Phys. Rev. Lett. 84 (2000) 2722]. The atomic coherence is introduced using two external classical driving fields. We study the steady-state entanglement of the system in the presence of losses, concluding that the creation of entangled states can be achievable under certain conditions.