  A method for the determination of absolute quantum detection efficiency is
suggested based on the measurement of photocount statistics of twin beams. The
measured histograms of joint signal-idler photocount statistics allow to
eliminate an additional noise superimposed on an ideal calibration field
composed of only photon pairs. This makes the method superior above other
approaches presently used. Twin beams are described using a paired variant of
quantum superposition of signal and noise.
