Image formation using quantum-entangled photons

The use of quantum-entangled photons in coincidence imaging process is discussed. The features of the process which are quantum and which are understood in terms of classical correlations are also discussed. The entangled photon is created by the excitation of a second-order nonlinear optical crystal by the laser beams through the process of parametric downconversion. Using the process, a sharp image of the object is obtained even though the photons that fall onto the imaging detector have never interacted with the object to be imaged.