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| Theory dot GSI dot De |
Like Schrödinger’s cat, it was only supposed to be a thought experiment to elucidate the strange mathematics of quantum mechanics.
Now, the 46-year-old Kochen–Specker theorem, which describes the quantum dance of observer and observed,has passed its toughest test yet in the real world. The test, published in February (V. D’Ambrosio et al. Phys. Rev. X 3, 011012; 2013), is indicative of growing interest in the theorem, triggered by new capabilities for manipulating photons and cold atoms (see ‘A quantum revival’).
“We can test things that until now were just mathematics,” says Adán Cabello, a physicist at the University of Seville in Spain, and a co-author of the paper. “We’ve been waiting for the technology.” Although his team has focused on the pure maths of the theorem, follow-up work may eventually find practical use in defending encrypted conversations against attack, and in improving random-number generators.
The theorem, first published in 1967 by the mathematicians Simon Kochen and Ernst Specker, shows that it is incorrect to assume, before measurements are made, that the results of a quantum mechanics experiment are already determined (S. Kochen and E. P. Specker J. Math. Mech. 17, 59–87; 1967). That assumption is valid in classical physics; for example, the heat content of a cup of tea is unaffected by the thermometer measuring it. But it breaks down in quantum mechanics, where measurements change their subjects in ways that depend on what else is being measured — as if a set of thermometers conspired to create the heat that they measure.
Nature: Photons test quantum paradox
Physics arXiv:
Proofs of the Kochen-Specker theorem based on a system of three qubits
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