In general, to obtain an image of an object one has to illuminate it with a light beam and use a camera to sense the light that is either scattered or transmitted through that object. The type of light used to shine onto the object depends on the properties that one would like to image. Unfortunately, in many practical situations the ideal type of light for the illumination of the object is one for which cameras do not exist.
With this crucial step, there is now, in principle, no possibility to find out which crystal actually created the photon pair. Moreover, there is now no information in the infrared photon about the object. However, due to the quantum correlations of the entangled pairs the information about the object is now contained in the red photons – although they never touched the object. Bringing together both paths of the red photons (from the first and the second crystal) creates bright and dark patterns, which form the exact image of the object.
Stunningly, all of the infrared photons (the only light that illuminated the object) are discarded; the picture is obtained by only detecting the red photons that never interacted with the object. The camera used in the experiment is even blind to the infrared photons that have interacted with the object. In fact, very low light infrared cameras are essentially unavailable on the commercial market. The researchers are confident that their new imaging concept is very versatile and could even enable imaging in the important mid-infrared region. It could find applications where low light imaging is crucial, in fields such as biological or medical imaging.
Source: University of Vienna