These images of a cardboard cutout of a cat were made with light that never touched the object. The technique works a bit like holography, in which a light beam that shines through an object overlaps and interferes with an identical one that passes by it, and that interference is used to encode a 3D image. But physicists in Austria have put a twist on that process, as they report online today in Nature. They begin with two identical photons, one of which shines through the object and the other of which goes by it, and make them overlap perfectly and interfere. But each of these photons is also created together with a photon of shorter wavelength, and the two share a quantum connection called entanglement. That connection allows the researchers to make the shorter wavelength photons also interfere, which can make the pair go one way or the other when it hits a device called a beam splitter. So by scanning the longer wavelength photon pairs over the object, physicists can construct a pair of complementary images, one for each direction out of the beam splitter, using the shorter wavelength photons—even though they never touch the object. Besides being really cool, the technique makes it possible to make an image of an object using a color of light that would normally pass through the thing.
