Stationary two-atom entanglement induced by nonclassical two-photon correlations

Abstract

A system of two two-level atoms interacting with a squeezed vacuum field can\nexhibit stationary entanglement associated with nonclassical two-photon\ncorrelations characteristic of the squeezed vacuum field. The amount of\nentanglement present in the system is quantified by the well known measure of\nentanglement called concurrence. We find analytical formulas describing the\nconcurrence for two identical and nonidentical atoms and show that it is\npossible to obtain a large degree of steady-state entanglement in the system.\nNecessary conditions for the entanglement are nonclassical two-photon\ncorrelations and nonzero collective decay. It is shown that nonidentical atoms\nare a better source of stationary entanglement than identical atoms. We discuss\nthe optimal physical conditions for creating entanglement in the system, in\nparticular, it is shown that there is an optimal and rather small value of the\nmean photon number required for creating entanglement.\n