Collinear degenerate spontaneous parametric down-conversion type-II scheme for measuring quantum efficiencies

Discrepancies between the results of absolute standardless quantum photometry and traditional methods of quantum efficiency calibration are discussed. Possible physical reasons for these discrepancies may include the limited accuracy of the commonly used phenomenological approach for detector count treatment in quantum photometry calibration, as well as an asymmetrical optical setup in the calibration process. Additional uncertainty may stem from not considering the correlated nature of optical losses when a biphoton passes through a finite aperture. A collinear degenerate optical scheme is proposed to minimize calibration errors and reduce discrepancies with traditional calibration methods.