Long-range tunneling of quantum particles

The quantum tunnel effect manifests itself in a multitude of well-known phenomena. Experimental physicists in Innsbruck, Austria, have now directly observed quantum particles transmitting through a whole series of up to five potential barriers under conditions where a single particle could not do the move. One of the most remarkable consequences of the rules in quantum mechanics is the capability of a quantum particle to penetrate through a potential barrier even though its energy would not allow for the corresponding classical trajectory. This is known as the quantum tunnel effect and manifests itself in a multitude of well-known phenomena. For example, it explains nuclear radioactive decay, fusion reactions in the interior of stars, and electron transport through quantum dots. Tunneling also is at the heart of many technical applications, for instance it allows for imaging of surfaces on the atomic length scale in scanning tunneling microscopes. All the above systems have in common that they essentially represent the very fundamental paradigm of the tunnel effect: a single particle that penetrates through a single barrier.