Although nonclassical quantum states are important both conceptually and as a resource for quantum technology, it is often difficult to test whether a given quantum system displays nonclassicality. A simple method to certify nonclassicality is introduced, based on easily accessible collective atomic quadrature measurements, without the need of full state tomography. The statistics is analyzed beyond the ground-state noise level by direct sampling of a regularized atomic quadrature quasiprobability. Nonclassicality of a squeezed ensemble of $2\times {10}^5$ cesium atoms is demonstrated, with a significance of up to 23 standard deviations.

• Received 12 July 2012

DOI:https://doi.org/10.1103/PhysRevA.86.042108