To improve the time resolution of the STM, the researchers modified the tip so that it not only measured electrical current but also supplied it. They fed current to an atom and then measured its state after a fixed period of time. For each such time period, they took 100,000 measurements. They varied the time between pulses and measurements, repeating the process again and again. The images from each measurement were combined as frames in a video. By putting these frames together, the researchers created a moving picture of the spin state of the atom, with a frame taken every five nanoseconds or so.
Loth says the IBM researchers hope to use the fast STM technique for two basic areas of research. First, they’ll continue using it to determine whether different combinations of atoms can store quantum information for longer. Second, by using a stream of photons instead of a stream of electrons as the pulse signal, says Loth, the researchers hope to gain a better understanding of how some organic molecules convert light into electrical energy. This could lead to better solar cells.
Systems like IBM’s for flipping and measuring atomic spins could potentially be part of a future quantum computer, says Alán Aspuru-Guzik, professor of chemistry and chemical biology at Harvard University. Altering and measuring the spin of atoms, and being able to predict how atoms will behave, is an important step towards this goal, he says. Most of the devices that have been made so far, he says, are more like “quantum toys” than computers. But the field is moving steadily forward, he says. “Every week someone demonstrates manipulating the qubit a little better.”