scientists create double-slit thought experiment
Physicists using the SOLEIL synchrotron in France are the closest yet to realizing a thought experiment first proposed in 1927 by Albert Einstein. A variation on the much-loved double-slit experiment, the measurement confirms an aspect of quantum theory that Einstein had sought to discredit. The SOLEIL experiment uses two excited atoms in place of the two slits of Einstein's experiment and shows that when one can determine which atom has emitted an electron, a quantum interference pattern vanishes.
Einstein made several attempts to refute the inherent uncertainty of quantum mechanics by proposing thought experiments, which could not be performed in the lab at the time. One involved the principle of wave–particle duality, which predicts that a succession of single particles passing through two slits will build up a wave-like diffraction pattern on a screen. This occurs because the wave-like property of each particle allows it to travel through both slits at once. Einstein pointed out that an extremely sensitive sensor could detect the recoil of the individual slit that each electron passed through, while not disturbing the diffraction pattern. This flew in the face of quantum mechanics, and Einstein's great rival, Niels Bohr, countered by arguing that the diffraction pattern would simply not occur if the experimenter knew which slit each electron had passed through.
While this was a pure thought experiment at the time, its combination of conceptual simplicity and formidable experimental difficulty has provided an irresistible challenge for modern-day experimentalists. In 2001 Serge Haroche and colleagues at the Ecole Normale Supéérieure in Paris demonstrated the principle in an analogue system, using a microwave pulse to split the internal state of a small number of Rydberg atoms into two separate states that evolved at different rates before being recombined. Then in 2011 Jörg Schmiedmayer and colleagues at the Vienna University of Technology achieved a closer approximation.
Double-atom experiment
http://physicsworld.com/cws/article/news/2014/dec/01/soleil-scientists-create-double-slit-thought-experiment
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