The incredible display is achieved by using transparent sheets of carbon nanotubes one-molecule thick, dunked in water. When the temperature of the sheets is increased rapidly by an electrical current, the sheet transfers the heat to the water in its immediate vicinity, causing light rays to bend away from the object behind it, rendering it invisible.
“Using these nanotube sheets, concealment can be realized over the entire optical range and rapidly turned on-and-off at will, using either electrical heating or a pulse of electromagnetic radiation,” Aliev explained to the Institute of Physics (IOP).
That’s the same way “the mirage effect” tricks your brain into thinking there is a pool of water in the middle of the road on a blazing sunny day. The hot road heats the air immediately above it to much higher temperatures than the rest of the air, refracting the light from the sky towards your eye.