Reduction of quantum noise in image estimation by use of twin-photon beams

An estimate of the transmittance of an object is examined in a twin-photon beam setup. The estimate is based on observing both the photons of one beam and the photons of the twin beam after passage through the object. The performance of the estimate (bias, variance, and mean-square error) is compared to the conventional single-beam measurement. The improvement depends on the photon flux, the counting time, the quantum efficiencies of the detectors, and the value of the measured transmittance itself. In general, a performance advantage is achieved for sufficiently high photon flux or long counting time.