Some very interesting research out of University of Rochester. Researchers there have found a way to record and later retrieve an image using only a single photon. This is cool enough -- but wait, there's more -- they did this by leveraging the famous "double slit" experiment of quantum mechanics in a really smart way. Why didn't I think of this??? Duh!
To produce the UR image, Howell simply shone a beam of light through a stencil with the U and R etched out. Anyone who has made shadow puppets knows how this works, but Howell turned down the light so much that a single photon was all that passed through the stencil.
Quantum mechanics dictates some strange things at that scale, so that bit of light could be thought of as both a particle and a wave. As a wave, it passed through all parts of the stencil at once, carrying the "shadow" of the UR with it. The pulse of light then entered a four-inch cell of cesium gas at a warm 100 degrees Celsius, where it was slowed and compressed, allowing many pulses to fit inside the small tube at the same time.