Fake violations of Bell tests reinforce importance of closing loopholes

(PhysOrg.com) -- In quantum mechanics, Bell’s inequalities serve as a test of nonclassical behavior: if something (such as a light source) violates Bell’s inequalities, then it can be considered to involve quantum behavior. Ensuring the nonclassicality of a system is important for applications such as quantum cryptography, in which quantum entangled photons ensure the system’s security while non-entangled photons do not. Now in a new study, scientists have shown that they can violate Bell’s inequalities using classical light by taking advantage of two loopholes common in some experiments. This “fake violation” emphasizes the importance of closing all loopholes in Bell tests, even if the detection devices appear to be operating normally.

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