Picture of the world's smallest diamond ring, measuring 300 nanometers (billionths of a meter) thick and 5 microns (millionths of a meter) across. A diamond is not mounted on a ring: the ring itself is made of diamond. It was made by carving out a circular structure in an artifically made diamond. The ring will be used to access single photons coming out of a tiny impurity region inside the diamond.
Photo credit: P. Olivero, B. Fairchild and S.Prawer, School of
Physics, University of Melbourne.