In the double slit experiment, a particle travels on two different paths at the same time. Something similar can be observed when a helium atom is ionized with a laser beam. The ionization of helium can happen via two different processes, and this leads to characteristic interference effects. A team of scientists has now managed to observe the buildup up of these effects—even though this effect takes place on a time scale of femtoseconds.
It is definitely the most famous experiment in quantum physics: in the double slit experiment, a particle is fired onto a plate with two parallel slits, so there are two different paths on which the particle can reach the detector on the other side. Due to its quantum properties, the particle does not have to choose between these two possibilities, it can pass through both slits at the same time. Something quite similar can be observed when a helium atom is ionized with a laser beam.
Just like the two paths through the plate, the ionization of helium can happen via two different processes at the same time, and this leads to characteristic interference effects. In the case of the helium atom, they are called "Fano resonances". A team of scientists from TU Wien (Vienna, Austria), the Max-Planck Institute for Nuclear Physics in Heidelberg (Germany) and Kansas State University (USA) has now managed to observe the buildup up of these Fano resonances—even though this effect takes place on a time scale of femtoseconds.
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