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Quantum physics

Correlations without parts

Nature volume 474, pages 456–458 (2011)Cite this article

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Quantum correlations between the parts of composite systems have long fascinated physicists. There is now compelling evidence that such correlations can also occur in systems in which no parts can be identified. See Letter p.490

Quantum mechanics is arguably the most accurate and successful theory in the history of science. But unlike the case for special relativity, for which two physical principles suffice to derive the whole theory, physicists are still seeking the entire set of underlying principles for quantum mechanics. Recently1,2, they have been trying to understand one of the most intriguing predictions of quantum mechanics: that quantum correlations violate mathematical relationships known as Bell inequalities, which are valid for any local realistic (classical) theory, but that they do so only up to a certain value, whereas more general theories allow violations up to greater values. On page 490 of this issue, Lapkiewicz et al.3 describe an experiment suggesting that a wider perspective, beyond Bell inequalities, is needed to understand why quantum correlations can attain only certain values.

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Figure 1: Comparing separate and sequential tests.

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  1. Adán Cabello is at the University of Seville, E-41012 Seville, Spain. He is also at Stockholm University, Sweden.,

    Adán Cabello

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  1. Adán Cabello
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Correspondence to Adán Cabello.

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Cabello, A. Correlations without parts. Nature 474, 456–458 (2011). https://doi.org/10.1038/474456a

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