Continuous Variable Entanglement Via Four-Wave Mixing

Quantum entanglement is a fundamental resource for the manipulation, storage and transfer of quantum information. Entanglement as non-localization quantum correlations among subsystems of multi-quantum-systems is a key element beyond the classical mechanics. In recent years, the preparation of continuous variable entanglement has attracted a lot of attention in quantum optics and quantum information process. Any attempt to exploit the entanglement have to, however, face the corruption of the entanglement by unavoidable decoherence. As a result, how to produce the robust, steady and high entanglement is an interesting research issue.We first study that the steady continuous variable entanglement is obtained via four-wave mixing in the driven two-level atomic sytem. Our scheme applies the method for the combination of the squeeze transformed modes with the dressed atoms and discusses the entanglement features of the two-mode cavity fields. It is found that only one squeeze transformed mode interacts resonantly with the dressed atoms at a time. The steady continuous variable entanglement can be implemented via the dissipation process, where the atoms always absorb in average excitations from the transformed mode and the degree of entanglement depends on the parameters of the classical field. The present scheme does not requires the preparation of the initial states of the incoming atoms, nor atomic detection and velocity selection. Secondly, we discuss the entanglement features of the high-Q optical cavity, in which an ensemble of N V-type three-level atoms interact with two strong pump fields. In three-level scheme, two different channels are identified, throuth which two squeeze transformed modes simultaneously interact resonantly with the dressed atoms. The entanglement between two cavity modes is enhanced and the close Einstein-Podolsky-Rosen entangled state is achieved. The scheme does not require the preparation of the initial atomic state nor the two-step procedure. In sharp contrast, one-channel is present in the two level scheme, through which only one squeeze transformed mode interact with the dressed atoms. To obtain the Einstein-Podolsky-Rosen entanglement, two steps are implemented.