The double-slit experiment is the most famous and probably the most important experiment in quantum physics: individual particles are shot at a wall with two openings, behind which a detector measures where the particles arrive. This shows that the particles do not move along a very specific path, as is known from classical objects, but along several paths simultaneously: Each individual particle passes through both the left and the right opening.
Normally, however, this can only be proven by carrying out the experiment repeatedly and evaluating the results of many particle detections at the end. At TU Wien, researchers developed a new variant of such a two-way interference experiment that can correct this flaw: A single neutron is measured at a specific position—and due to the sophisticated measurement setup, this single measurement proofs already that the particle moved along two different paths at the same time. It is even possible to determine the ratio in which the neutron was distributed between the two paths. Thus, the phenomenon of quantum superposition can be proven without having to resort to statistical arguments. The results have now been published in the journal Physical Review Research.
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