Quantum theory has been put to many tests and it has passed them all, but it is not the only possible theory to explain the physical world. Unlike classical theories, quantum mechanics does not rest on clear physical principles, and it is therefore difficult to identify it as the one correct theory. Mirjam Weilenmann and Roger Colbeck have now suggested an alternative approach to single out quantum mechanics: they proposed to extend the concept of self-testing quantum states to the theory itself.

When two particles are entangled, separate measurements of each particle are correlated in a way that cannot be reproduced classically. Observing these correlations provides a ‘self-test’ that shows entanglement is present without the need to know any details of the measurement.

Weilenmann and Colbeck proposed searching for self-tests that are satisfied by quantum mechanics but exclude alternative theories. Defining quantum theory via self-tests could provide a more intuitive basis for quantum mechanics, and self-tests could be used to experimentally confirm the validity of quantum theory.

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Richard Brierley.

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Brierley, R. Test your theory.
Nat. Phys. 16, 819 (2020).

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