Single-photon Cannon (image) University of Copenhagen - Niels Bohr Institute Caption This is an illustration of the single-photon cannon. 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 (light grey). Due to the holes, the photons are not emitted in all directions, but only along the channel where there are no holes. Only 1.6 percent of the emitted photons will be emitted in other directions (illustrated by the upward moving photon) and is thus lost, while 98.4 percent are emitted in the desired direction. Credit Illustration: Marta Arcari, Niels Bohr Institute Usage Restrictions Illustration: Marta Arcari, Niels Bohr Institute Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.