Abstract

We report the experimental violation of Cauchy-Schwarz (CS) inequality by the nonclassical intensity twin beam. It’s particularly of interest to demonstrate the nonclassical behaviours of the electromagnetic field. The most well-known examples of nonclassical effects are photon antibunching^[1], sub-poissonian photon statistics^[2], squeezing^[3] and nonclassical correlation between light beams indicated by violation of CS inequality ^[4]. The violation of the CS inequality has been observed by Clauser^[4] in the radiation emitted in an atomic two-photon cascade with coincidence counting technique, and expected theoretically in a two-photon laser^[5], parametric amplifier^[6], resonance fluorescence^[7] and other systems^[8,9]. Intense intensity twin beam with nonclassical correlation has been also obtained in OPO experiments^[10]. In this letter, we give a new method to establish nonclassical correlation between macrosopic light beams and demonstrate violation of CS inequality.

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