Nonclassical properties of a two-mode SU(2) coherent field resonantly interacting with a three-level Λ-type atom

Nonclassical properties of a two-mode field initially in an SU(2) coherent state resonantly interacting with a three-level Λ-type atom are investigated by means of the quantum theory and numerical calculations. The dependence of the nonclassical properties on the total photon number of the two-mode, the partition parameter and the coupling constant is discussed for three cases: (1) no state-selective atomic measurement; (2) direct state-selective atomic measurement; and (3) state-selective atomic measurement after the application of a classical field. The results indicate that when the total photon number of the two-mode is increased or the state-selective measurement is performed on the atom, the difference squeezing of two-mode is distinctly enhanced; and when the partition parameter is decreased or the state-selective measurement is performed on the atom after the application of a classical field, the average intensity of the sub-Poisson statistic distribution of mode a is reduced and that of mode b is enhanced; when the total photon number of the two modes is increased or the direct state-selective measurement is performed on the atom, the anti-correlation character between the two modes is preserved, but the average intensity of the anti-correlation is reduced; and when the direct state-selective measurement is performed on the atom, the Cauchy-Schwartz inequality is violated.