Nonlinear parametric interaction and higher-order squeezing in coherent population trapping

In this paper, we show that coherent population trapping (CPT) system can act as a nonlinear parametric interaction process, in which higher-order nonlinear effects are included, giving rise to the occurrence of nonclassical quantum correlation. Furthermore, our numerical results confirm that single- and two-mode higher-order squeezing are possible to obtain under different conditions because of the higher-order nonlinear effects, which are strongly determined by the atomic coherence. The higher-order squeezing obtained in CPT is robust against dissipation since the atoms are nearly trapped into the ground state, which may be useful for high-precision measurement. Copyright (C) EPLA, 2014