In 1929 the Swedish physicist Oskar Klein made a surprising prediction: if you fire an electron over a barrier, it can slip off the bus. Actually, this tunnel effect is nothing unusual. In the quantum world this is always a possibility when a particle encounters an obstacle.
Generally, in such a situation, one particle can only get to the other side with great luck. Oskar Klein, on the other hand, came up with a 100 percent probability in his calculations: if the electron moves almost at the speed of light, it practically does not experience a barrier – exactly how big it is.
For a long time, physicists argued about whether Klein’s hypothesis had anything to do with reality. In fact, it was practically impossible to recreate the situation he described. For many years now, researchers have been investigating indirect clues in 2-D content graphs. In wafer-thin carbon lattice, multi-particle assemblies – so-called casiparticles – can tunnel through a barrier in small ways under special conditions.
Researchers working with Jiang Zhang of the University of California at Berkeley now want to directly observe the phenomenon for the first time, but in a completely different setting: they arranged acrylic cylinders a few centimeters larger on the surface and then sound waves. Let him pass by. This is how researchers said about a “phononic crystal” from the class of metametris. They contain many similar components that take shape in such a way that they change the waveform in a targeted manner.
In Jiang Zhang’s experiment, the components bound the sound waves so that they follow the same equations as the quipiparticles in the graph. Physicists report that excitation passes through a small cylinder region without loss, although normal sound waves should actually be weak here «Science in the journal«. This acoustic tunnel became 100 percent successful when researchers predicted the obstacle, which Oscar Klein predicted.
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