Pair-wise Entanglement Characterizing a Quantum State of an Atomic Ensemble Storing a Squeezed Light

This paper characterizes a pair-wise quantum spin correlation formed in an atomic ensemble that stores a phase or amplitude squeezed state of light on the framework of the electromagnetically induced transparency (EIT). The photonic quantum correlation in the squeezed light is transformed into an atomic quantum correlation between N atoms. If we regard the atomic state as a 1/2-spin and utilize the pair-wise spin entanglement to analyze the atomic quantum correlation, we can specify a certain entangled state of a spin pair as the signature of the squeezed light.