Casper becomes the quantum, friendly ghost.

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In a spooky new study, a team found telltale signs of quantum weirdness lurking in an optical trick called ghost imaging. The trick allows researchers to create an image of something using light that never bounced off the actual object. To look for evidence of quantum behavior, Miles Padgett of the University of Glasgow in Scotland and colleagues designed a system to create a ghost image of an appropriately ghoulish object (above). Photons in two light streams, one of which bounced off a hologram and never touched the object, were intimately linked, a property known as entanglement, the team found. This "spooky action at a distance" allowed contrast information from the hologram to improve the image of the ghost. The results are "the clearest demonstration that at least some forms of ghost imaging are quantum," Padgett says. "That's not to say that all systems are quantum, but ours is."