A new photonic “cannon” could provide the necessary light control for quantum encryption and computing. Researchers at the Niels Bohr Institute at the University of Copenhagen have created an optical chip that produces a steady stream of photons, emitted one at a time and in a determined direction. The optical chip consists of a quantum-dot light source and a photonic crystal waveguide 10-µm wide and 160-nm thick. A quantum dot (illustrated with the yellow symbol) emits one photon (red wave packet) at a time. The quantum dot is embedded in a photonic-crystal structure, which is obtained by etching holes (black circles) in a semiconducting material. Due to the holes, the photons are not emitted in all directions, but only along the channel where there are no holes. Courtesy of Soren Stobbe, Niels Bohr Institute. The quantum dot functions as an artificial atom whose electrons emit photons after laser excitation. The individual photons can be directed with a 98.43 ±0.04 percent success rate. The researchers are in the process of patenting several parts of their work, with a goal of developing a prototype high-efficiency single-photon source for encryption or for calculations of complex quantum mechanical problems. The research was published in Physical Review Letters. For more information, visit www.nbi.ku.dk.