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Science. 2008 Jul 25;321(5888):541-3. doi: 10.1126/science.1159663.

Entangling the spatial properties of laser beams.

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  • 1Australian Research Council Centre of Excellence for Quantum-Atom Optics, Australian National University, Canberra ACT 0200, Australia.


Position and momentum were the first pair of conjugate observables explicitly used to illustrate the intricacy of quantum mechanics. We have extended position and momentum entanglement to bright optical beams. Applications in optical metrology and interferometry require the continuous measurement of laser beams, with the accuracy fundamentally limited by the uncertainty principle. Techniques based on spatial entanglement of the beams could overcome this limit, and high-quality entanglement is required. We report a value of 0.51 for inseparability and 0.62 for the Einstein-Podolsky-Rosen criterion, both normalized to a classical limit of 1. These results are a conclusive optical demonstration of macroscopic position and momentum quantum entanglement and also confirm that the resources for spatial multimode protocols are available.

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