Quantum Correlation And Spin Squeezing In Dressed Three Level Systems

The study of the atomic spin squeezing and the quantum correlation between atomic and cavity field is essential and significant for quantum information. This paper is about the investigation of the atomic spin squeezing and the quantum corre-lation between the atoms and the cavity in four-wave mixing in a lambda three-level system. We derive the master equation of the system, and use the Langevin theory to deal with the strong interaction between dressed atoms and drive field. Finally, we get the results as follow:The first one is that, when we select the parameters of the bad cavity and strong coupling, the atomic spin squeezing strength is better. When the cavity decay rate is small (κ<0.1γ), there is no atomic spin squeezing. When the coupling degree of the atomic-field is small (g<γ), there is no atomic spin squeezing either. The increase of the field decay rate and coupling strength leads to the widening of the spin squeezing range and the increase of atomic spin squeezing degree. However, when the parameters are increased beyond critical values (κ>5γ, g>10γ), atomic spin squeezing degree and the range are no longer changed.The second one is that, no matter what cavity decay and atom-field coupling parameters we select, the system does not exist any atoms-field entanglements; When field decay is small (κ<γ), the system exists the atomic-field hybrid squeezing. As the field decay rate decreases, the atomic-field hybrid squeezing degree would increase. In this four-wave mixing system, the atomic-field entanglement does not exist, but the atomic-field hybrid squeezing exists, to prove that squeezing is a necessary but not sufficient condition of the entanglement.