Creating a nano-sized mirror

Science : Physicists at the University of Innsbruck, Austria, have turned a single atom into a mirror. Gabriel Hétet, Rainer Blatt, and colleagues set up a Fabry–Pérot interferometer , replacing one of the device’s two mirrors with a barium ion. Using an electronic trap to hold the ion in place and a lens to focus the laser light, they tuned the wavelength of the light entering the interferometer so that it could excite the atom from a particular low-energy state to a higher-energy one. Without such a light–atom interaction, the atom can’t affect the light, writes Adrian Cho for Science. Although the interferometer wasn’t perfect—as the researchers moved the ion away from the mirror, the amount of light coming through the system varied by about 6%—the atom still managed to work as a mirror. Such work in quantum electrodynamics could lead to ever smaller optical devices, such as an atom-sized transistor for light. The team reports its results in a paper to be published in Physical Review Letters.