Carbon nanotubes can create a 'perfect black' that visually wipes out a dimension, making 3D objects look 2D. When draped over a substance, a thin coat of them renders the object invisible by absorbing all the light coming in. Scientists think that similar substances might be responsible for much of the 'missing matter' in the universe, and would make dandy space ship cloaks.
To pull off magic tricks, often magicians will stand in front of a black curtain. This isn't just showmanship or style, it's a necessary part of the act. If an assistant, wearing all black and carrying black-covered instruments, were to come in behind them and stand just out of the spotlight, the audience would have a hard time seeing them, and objects would appear out of nowhere. That being said, if one of the assistants blundered into the spotlight, the audience would know, and the more careful viewers might pick them out anyway, if they weren't distracted by the show.
Dress an assistant in a coating of carbon nanotubes and put them against a background curtain, and they could wander freely. No one would see them. Researchers at the University of Michigan, found that carbon nanotubes can create a 'perfect black,' which not only absorbs 99.9 percent of infrared, ultraviolet, and visible wavelengths of light, but has an index of refraction similar to that of air. As seen in this classic io9 post, matching indices of refraction is a big deal. In that clip, an entire pyrex beaker disappeared because it was dipped in vegetable oil. Light travels through vegetable oil at the exact same rate it travels through pyrex, which means when it hits the dish it doesn't bend or scatter. We only see the light that's bent, scattered, or reflected back to us, so the solid object is rendered invisible.