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.