INVISIBILITY CLOAK WITH ON-OFF SWITCH
Physicist from University of St. Andrews, Scotland, have created an optical invisibility cloak that you can turn on and off as you wish. They used the concept of electromagnetically induced transparency in which certain materials become transparent when zapped by light from two carefully turned lasers.
The cloaking device comprises a transparent mantel that encloses the objects to be hidden.The magnet refracts light around its hidden interior such that light exits as if it had traversed empty or uniform space,thus hiding the object and the act of hiding itself.
This works for material with atoms that can exists in three different electronic states - say a,b and the highest c. The idea here is that the first laser beam is absorbed by the material because it excites the electron from state a to state c. The second laser is also absorbed because it excites the electrons from state b to state c. If the frequencies of the laser are closed together, they can be turned in a way that makes they interfere destructively. And when that happens, their ability to excite the electrons cancels out.