Researchers have bent one of the most fundamental rules of quantum mechanics, by observing light as both a wave and a particle simultaneously. According to quantum theory, light behaves as both, but can only be observed acting as one at a time.
Now, Aephraim Steinberg of the University of Toronto and his colleagues have sidestepped this limitation by undertaking “weak measurements” of the photons’ momentum.
The team allowed the photons to pass through a thin sliver of the mineral calcite which gave each photon a tiny nudge in its path, with the amount of deviation dependent on which slit it passed through.
By averaging over a great many photons passing through the apparatus, and only measuring the light patterns on a camera, the team was able to infer what paths the photons had taken.