Delayed-choice quantum eraser

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A delayed-choice quantum eraser experiment is an elaboration on the quantum eraser experiment that incorporates concepts considered in John Archibald Wheeler's delayed-choice experiment. The experiment was designed to investigate peculiar consequences of the well-known double-slit experiment in quantum mechanics, as well as the consequences of quantum entanglement. Delayed-choice quantum eraser experiments are designed to investigate the following apparent paradox arising from the traditional double-slit experiment: if, upon observing a photon, one can deduce that it arrived at a detector by following a particular path, then "common sense" (which Wheeler and others challenge) says that it must have entered the double-slit device as a particle, whereas if the photon's path cannot be deduced, then it must have entered the double-slit device as a wave. By this logic, a spontaneous change in the mode of observation while the photon is in transit may force it to retroactively alter its initial...

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