The Cauchy-Schwarz (CS) inequality-one of the most widely used and important inequalities in mathematics-can be formulated as an upper bound to the strength of correlations between classically fluctuating quantities. Quantum-mechanical correlations can, however, exceed classical bounds. Here we realize four-wave mixing of atomic matter waves using colliding Bose-Einstein condensates, and demonstrate the violation of a multimode CS inequality for atom number correlations in opposite zones of the collision halo. The correlated atoms have large spatial separations and therefore open new opportunities for extending fundamental quantum-nonlocality tests to ensembles of massive particles. © 2012 American Physical Society.
CITATION STYLE
Kheruntsyan, K. V., Jaskula, J. C., Deuar, P., Bonneau, M., Partridge, G. B., Ruaudel, J., … Westbrook, C. I. (2012). Violation of the Cauchy-Schwarz inequality with matter waves. Physical Review Letters, 108(26). https://doi.org/10.1103/PhysRevLett.108.260401
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