Research from Ruben Esteban and Javier Aizpurua published in Nature

Ruben Esteban and Javier Aizpurua from the Donostia International Physics Center (DIPC) and the Materials Physics Center (CFM), in collaboration with researchers from the research group of Jeremy Baumberg from University of Cambridge and Andrei Borisov from Universite Paris-Sud, have observed for the first time with optical methods, the quantum regime in the interaction between nano-sized spheres of gold. This quantum regime has been identified thanks to the change of colour of the gap or empty space between these particles when they are at distances of less than one nanometre. This work, published in Nature journal, enables literally “seeing” a quantum kiss between nanoparticles.

Quantum ‘kisses’ change the colour of space

The gap generated between two opposing nanospheres of gold can change its colour when the distance between them is less than one nanometre, according to a recent investigation by researchers from the DIPC and the CFM (a joint center between the CSIC-UPV/EHU). This work published in Nature, confirmes that electrons accumulated on the gold surfaces around the illuminated gap between the two spheres can “jump” from one to the other, thanks to the tunnel effect, thus reducing the accumulated charge on the surface of each of these spheres and changing the colour of the gap from red to blue, seen as a blueshifting.

This work enables the observation of quantum mechanics in action and shows how light interacts with matter at subnanometre scales. The change in colour of the gap is the “chromatic fingerprint” that identifies the initiation of the quantum regime therein – an effect that had been predicted by the theoretical team of Dr. Aizpurua, the lead researcher in Donostia, and now fully identified as a result of this research. To this end, tour de force experiments have been combined with very advanced theories.

The paper: Revealing the quantum regime in tunnelling plasmonics, Nature 491, 574–577 (2012).