Another decisive step forward in the development of quantum computers has been successful. For the first time, researchers at Ruhr University and at the Universities of Stuttgart and Texas at Austin in the US have placed two nitrogen atoms at a distance of only a few nanometers so that laser excitation can create a quantum mechanical coupling. The key? It works reliably, with high precision and even at room temperature only in a diamond. The Rubion particle accelerator at Ruhr disposes of the ideal instrumentation for this ion implantation in diamonds and is making implantations available to other universities, including Harvard and MIT. NV centers are immobile in the surrounding carbon lattice. When targeted by a laser, the two nitrogen centers will react. "Initially, numerous groups focused on silicon," said Dr. Jan Meijer at Rubion, "but these researches demonstrated that diamonds are particularly well suited for coupled quantum circuits." The scientists reported their results in the journal Nature Physics. Why diamonds? The research results confirm a hypothesis on the special properties of diamonds that was put forward by two Stuttgart scientists, professor Dr. Jörg Wrachtrup and Dr. Fedor Jelezko, several years ago: Color centers or NV centers are immobile in the surrounding carbon lattice, whereby N stands for nitrogen and V for a vacancy. Because there is actually no “diffusion” inside a diamond, the atoms won’t migrate back and forth. When targeted by a laser, the two nitrogen centers will react, and a manipulable superposition of their spin states – the rotational movement of electrons – results. These highly complex studies were conducted in Stuttgart. Simultaneous multiple states Spin up, spin down: These are primarily the two states that the coupled atoms can assume, comparable with “0” and “1” in a computer. However, the processes in this quantum “circuit” are much more sophisticated. “Microscopical and quantum mechanical systems prepared this way differ totally from our everyday experience and can take on, for example, several states at one and the same time,” Meijer said. “You can almost compare them with two conventional PC memory devices coupled in such a manner that they interfere with each other.” That the coupling of the atoms in the diamond’s color center even works at Room temperature is the crucial requisite for building a quantum computer. “Basically, it is imaginable and possible to create several of these NV centers deliberately by means of ion implantation, couple them together in a scalable fashion and have a classical computer control it all,” Meijer said. The number of couplings is now to be increased step by step. “This is a great challenge because the greater the number of couplings, the faster the system will fall apart.” Unlimited possibilities The possibilities are – theoretically – immeasurable: If we were to connect only 100 of these NV centers with each other, we would get two to the power of 100 coupled memory cells. “Physically, this is considerably more than we need to store the entire knowledge of humankind,” Meijer said. A totally new computer technology can be built by applying the laws of quantum mechanics – with it, we could, for example, calculate the properties of complex biological molecules or crack codes within a fraction of a second. For more information, visit: www.ruhr-uni-bochum.de