Chink found in armor of perfect cloak

Tiny charged particles could reveal the location of a perfect invisibility cloak. Such a cloak — which exists only in theory at the moment — would render an object invisible by gently deflecting photons around it. But charged particles wouldn’t be fooled: they would interact with the cloak in a telltale way, giving up the cloak’s location, researchers report in a paper to appear in an upcoming Physical Review Letters.