• The experiment involved holding the atoms over a sensor using an optical trap. Because of the way the trap was set up, the atoms would start off moving upward at two different velocities until the influence of gravity started pulling them back downward.
  • While they were moving upward, the atoms were hit with photons that would exchange their momenta. This causes them to cross paths before they begin to fall. At the precise point where the paths cross, the atoms were hit with photons again. But this time, the photons were only half the intensity, leading to a 50/50 chance that their momenta would change.
  • Our classically trained expectations would predict a Gaussian (bell) curve, with momenta distributed around the two starting speeds due to random error and noise. And that's similar to what the results look like. Except if you look at the correlations between when particles land, you see the same sort of bias that Hong, Ou, and Mandel saw: the atoms seem to show up at one or the other of the two speeds, but not both.

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