LONDON — Researchers at the Kavli Institute of NanoScience (Delft, the Netherlands) have captured a single electron in a highly tunable carbon nanotube double quantum dot. The researchers suggest they are the first to do this successfully.

The breakthrough was made possible through a new approach for producing ultraclean nanotube quantum dots.

The team of researchers, led by Spinoza prize winner Leo Kouwenhoven, also say they discovered a new kind of tunneling as a result of which electrons can fly straight through obstacles.

The researchers used silicon electrodes positioned close to the ultraclean nanotube to control precisely the number of electrons of the quantum dot.

Three electrodes were used in the research, although more electrodes can be incorporated. The ultraclean tube ensures that no disruption occurs in the manipulation of the electrons.

Whilst studying the double quantum dot, the researchers discovered a new type of tunneling that is analogous to tunneling according to the so-called Klein paradox.

Tunneling is an effect in which rapidly moving electrons can fly straight through obstacles. The particle goes straight through a barrier even though it does not have enough energy to go over the barrier. Normally tunneling ceases as soon as the barrier is too large.

The Klein paradox predicts that if the barrier is made even bigger still, tunneling can once again take place due to the influence of relativistic quantum mechanics. In the case of normal tunneling, electrons can only move from one quantum dot to another due to the tunnel coupling of the wave functions on both sides of the energy barrier within the double quantum dot.

The researchers used the silicon gate electrodes to manipulate the barrier and observed tunneling could become enhanced even though the barrier was increasing, as predicted in the Klein paradox.