Single atom shadow

Scientists have been lowering size limits on optical imaging for more than a century, but Australian researchers may have hit the bottom. Optical microscopy relies on matter interacting with light; when you shine a flashlight on your hand, you see an image of your hand on the wall behind it because your hand interacts with and blocks the light. Professor Dave Kielpinski headed the group based out of Griffith University's Centre for Quantum Dynamics in Brisbane, who did an analogous experiment -- with a single atom. "We have reached the extreme limit of microscopy; you can not see anything smaller than an atom using visible light," he said, "we wanted to investigate how few atoms are required to cast a shadow and we proved it takes just one." But the light must be precisely tuned to interact with the atom in question, otherwise it will pass right through; "If we change the frequency of the light we shine on the atom by just one part in a billion, the image can no longer be seen."