A new quantum imaging technique can acquire an image of an object without ever detecting the light used to illuminate it. Typically, to obtain an image of an object it must be illuminated with a light beam and a camera used to sense the light that is either scattered or transmitted through that object. However, a model light for such illumination is one for which cameras do not exist. The new method, based on induced coherence without induced emission, was developed by researchers at the Institute for Quantum Optics and Quantum Information, the Vienna Center for Quantum Science and Technology and the University of Vienna. A new quantum imaging technique generates images with photons that have never touched the object, in this case, a sketch of a cat. Courtesy of Patricia Enigl/IQOQI. The experiment used two separate down-conversion nonlinear crystals, each illuminated by the same laser, which created a pair of photons (one infrared and one red). If the photon pair is created in one of the nonlinear crystals, one photon passes through the object to be imaged and is overlapped with the amplitude created in the other photon; its source is thus undefined. “Interference of the signal amplitudes coming from the two crystals then reveals the image of the object,” the researchers wrote in the study. The infrared photons that pass through the imaged object are never detected, while images are obtained exclusively with the signal photons that do not interact with the object. The experimental setup. Courtesy of Lois Lammerhuber Information about the object is contained in the red photons, even though they never touched the object. Bringing together both paths of the red photons created bright and dark patterns, which formed the exact image of the object. Now, the photons used to illuminate the object do not have to be detected at all, and no coincidence detection is necessary. This versatile method could potentially enable imaging in the mid-infrared as well, and in applications such as biological and medical imaging. The research was published in Nature (doi: 10.1038/nature13586). For more information, visit www.iqoqi.at.