Ghost Imaging

Just imagine that you have taken a photograph with a digital camera. Suddenly you see an unknown image in your photograph. It looks like as if there is a ghost upon the screen. The camera does not see this object in front of it. Yet here is this amazing manifestation upon your screen. This is known as ghost imaging, and it is a technique, which focuses upon light’s quantum or particle nature. First a pair of photons are taken and the quantum correlations between them are exploited, so that an image of an object that is not present in reality is built upon the screen.

Photons have a tendency to move in the opposite directions to each other and that is why when 1 photon is hitting the camera lens, the other photon is hitting the object. If your camera is constructed in such a way that only the photons, which hit the image, plane as well as the object simultaneously, there is an immediate formation of the object. However, this correlation between the light beam hitting the object and the light beam hitting the plane of the object is quite classical and cannot be found in real life. That is why this phenomenon is exploited so that ghost imaging can be done by using a detector of just one single pixel.

In some experiments, there has been a correlation of the outputs from two detectors, out of which one is a scanning pinhole camera and the other is a single pixel detector. The image, which is collected now, is completely free of a background.