Continuous variable quantum discord in a correlated emission laser

A detailed analysis of the nonclassical features of the cavity radiation of a nondegenerate correlated emission laser is presented. Closed mathematical relation that describes the quantum discord in terms of the involved auto- and cross-correlations is provided. It is found that the quantum discord increases with the linear gain coefficient and initially prepared atomic coherent superposition. Although the overall trend of the forward and backward quantum discords turns out to be similar, it is also unequivocally observed that the forward quantum discord is greater or equal to the backward quantum discord. Moreover, comparison of the quantum discord with entanglement shows that there is a very wide range of parameters for which an overlap in capturing the nonclassical nature of the radiation can be observed. However, when the atoms are initially prepared in a maximum coherent superposition, the quantum discord is found to capture the quantumness even when Duan-Giedke-Cirac-Zoller entanglement criterion failed. (C) 2011 Elsevier B.V. All rights reserved.