Harry Potter has one. Frodo Baggins used one in Lord of the Rings. Han Solo had one big enough to use on his entire space ship in Star Wars. Invisibility cloaks have had a significant presence in fiction and now it seems that reality has finally caught up.
Over the last few years researchers have been getting close to developing an invisibility cloak and now some researchers appear to have designed one.
In the real world invisibility cloaks make objects invisible by bending light rays as they enter the cloak and then again when they exit it. The light is deviated in such a way that the rays seem to have been reflected directly from the ground underneath the object so that to the observer it appears that the object is not there.
If you want to build such a cloak then you need material that will bend the incoming and outgoing light rays by different amounts determined the size and shape of the object that is to be hidden. Researchers have found that a material called calcite is perfect for this job because the speed at which light passes through it depends on the orientation of the crystals in the calcite. By sticking together two pieces of calcite crystal it is possible to create a cloak that bends incoming and outgoing light by the required amount to make it appear invisible.
The researchers in Singapore from the MIT Alliance for Research and Technology have built a calcite invisibility cloak that can shield a steel wedge that is 3.8cm long and two millimetres think from red, green, and blue visible light. The cloak has been specifically designed to work underwater which will get all of military-sci-fi types thinking about invisible submarines which is all very fine provided suitable submariners can be found since those subs will have to be under four centimetres long.
At the same time researchers from the University of Birmingham (UK) and the Imperial College London have built a calcite invisibility cloak that works in air and will cover objects up to a few centimetres high.
The cloaks at the moment cost approximately US$1000 to make. So they could conceivably be available for consumers sometime soon. At the moment their most obvious use will be to render invisible from prying eyes that piece of chocolate cake that you have earmarked for yourself for later. No doubt more significant, and possibly insidious, applications will be arrived at soon.