The classic mystery of quantum mechanics concerns the passage of a particle through two slits simultaneously. We know from our understanding of the double-slit experiment that the photon must have traveled through both slits, yet we can never actually observe the photon passing through both slits at the same time. If we find the photon in one place, its probability amplitude to be anywhere else immediately vanishes.
At least, that is the familiar story. In a new experiment described in Scientific Reports, Ryo Okamoto and Shigeki Takeuchi of Kyoto University in Japan have shown that under the right conditions, a single photon can have observable physical effects in two places at once.
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