The time evolution of the squeezing factors of a cascade three-level atom. The atom is initially in the superposition state of | 3 〉 and | 1 〉 with θ = π/4, φ = 0, and the field is the coherent state with initial average photon number n ¯ = | α | 2 = 225 ; (a) entropy squeezing factor E ( S x ) ; (b) entropy squeezing factor E ( S y ) ; (c) variance squeezing factor V ( S x ) ; (d) variance squeezing factor V ( S y ) .