Researchers from the Karlsruhe Institute of Technology (KIT), in Germany, have engineered a portable invisibility cloak powerful enough to be used for demonstrations in classrooms or lecture halls.

While invisibility cloak technology has been around for some time it had, until now, lacked the “wow” factor required to excite and amaze the average person. Prototypes have already been built that can bend light around an object, thereby rendering it invisible. So far though, most are small, function only at tiny wavelength ranges, and are restricted to the lab setting.

While the new cloak couldn’t conceal an entire wizard, it can make smaller objects disappear.

"Our cloak takes advantage of the much lower effective propagation speed in light-scattering media," says Robert Schittny, research leader. "As we seemingly slow down the light everywhere, speeding it up again in the cloak to make up for the longer path around the core is not a problem."

To make an object invisible, one must find a way to overcome the increased distance the light has to travel. To use driving as an analogy, changing one’s speed would solve this problem. For example, there are two roads from point A to point B, one is shorter but has a lower speed limit, while the other is a motorway but is a longer route. The motorway would take less time because the extra distance could be offset by the higher speed limit.

Of course things get a little more complicated with light.

Relativity will not allow mass to travel faster than the vacuum speed of light. So the researchers developed a cloak from a light-scattering material. This material decelerates the speed of the light waves through the object being cloaked. Then the light can accelerate again to offset the longer path that needs to be travelled around the cloaked object.

Accessible prototype

This technology is complex but hugely intriguing. The development of an accessible prototype, therefore, has been eagerly anticipated. “It is a macroscopic cloak that you can look at with your bare eyes and hold in your hands,” says Mr Schittny. “With a reasonably strong flashlight in a not too bright room, it is very easy to demonstrate the cloaking. That means no fancy lab equipment, no microscopes, no post-processing of measurement data. The effect is just there for everyone to see.” Mr Schittny and his team hope their innovation might attract more young students into physics.