Scientists have discovered that Plasmons can be used to make very small items invisible. From the article:
The proposal involves using plasmons — tiny electronic excitations on the surfaces of some metals — to cancel out the visible light or other radiation coming from an object.
“A proper design … may induce a dramatic drop in the scattering cross-section, making the object nearly invisible to an observer,” Nader and Alu write in a scientific paper that was made available to the public Feb. 14.
But cloaking ability would depend on an object’s size, so that only with very small things — items that are already microscopic or nearly so — could the visible light be rendered null. A human could be made impossible to detect in longer-wavelength radiation such as microwaves, but not from visible light.
So, don’t go planning on a Harry Potter invisibility cloak just yet…