The problem we wish to solve is how to optically detect the presence of something, but with no photons hitting it. The something could be many things, like a hand, a detector, an ultrasensitive piece of film, or a single atom. The two physicists who brought this topic to light in 1993, Elitzur and Vaidman (EV), considered a "superbomb", which, if it possessed the trigger/detonator element, would explode whenever hit by even a single photon. Some of the bombs possess the element, and some do not. (The former are the so-called "good" bombs, the latter are the "bad" bombs [please do not get on my case about which ones are really the good ones!]). The goal now is, given a supply of these bombs in sealed crates, find out which ones are the good bombs. (Also, we aren't allow to shake the crates, or otherwise risk disturbing the bombs.)
http://physics.illinois.edu/people/kwiat/interaction-free-measurements.asp