Qubits in the pink

摘要

Crystal imperfections known as nitrogen-vacancy defects give some diamonds a characteristic pink colour. Appropriately manipulated, these defects might have rosy prospects as the 'qubits' of a quantum computer. A1ccording to materials scientist F. C.Franck, "crystals are like people; it is only the defects that make them interesting". Ronald Hanson and colleagues would probably agree: writing in Physical Review Letters1, they report new developments in the study of negatively charged 'nitrogen-vacancy defects' in diamond. These systems are rapidly becoming a front-runner for use as the basic unit of quantum information - the 'qubif - in a solid-state quantum computer. The lattice of carbon atoms that makes up diamond can contain various substitutional impurities, such as nitrogen or boron atoms. These defects give diamonds their colour, and are often called colour centres. Nitrogen-vacancy (NV) defects give diamond a pink hue, and arise when a nitrogen atom replaces a carbon atom at a position inthe diamond lattice next to a vacant site. It might seem unlikely that these two defects should sit right next to each other, but if the diamond is heated, vacancies can diffuse through the lattice until they encounter nitrogen atoms. When this happens,the 'random walk' comes to a halt because the configuration of the two adjacent defects is extremely stable.