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Testing Bell's Inequality with Cosmic Photons

David Kaiser

ABSTRACT: Albert Einstein once dubbed quantum entanglement "spooky action at a distance," and the concept remains one of the most stark examples of how quantum theory differs from our usual intuitions about how matter should behave. John Bell's famous inequality quantifies the degree to which entangled quantum systems exceed correlations that could be expected among classical objects. Many ingenious experiments have found results compatible with the predictions of quantum theory, though each experiment has been subject to one or more "loopholes" that could possibly account for the data even in the absence of genuine quantum entanglement. In this brief talk I will describe a new proposal to use photons from causally disconnected cosmic sources, such as distant quasars, to set the detectors in an experimental test of Bell's inequality, thereby aiming to close the so-called "settings-independence loophole" and hence potentially enable a loophole-free test of Bell's inequality.