Two-collective Mode Entanglement in a Four-level Atomic Ensemble

Abstract

We propose a theoretical method to obtain two-collective mode entanglement in a four-level atomic ensemble. One collective mode is produced due to the Raman atomic coherence, the acquisition of another collective mode is ascribed to the quantum interference in two four-wave mixing processes. We show that two-collective mode and two original single modes are also in the entangled state in experimentally accessible parameter regimes.