Detection efficiency measurement of single-photon detectors based on spontaneous parametric scattering using the heterodyning method

Abstract

Recent active development of quantum computers and quantum key distribution systems requires characterization of the parameters of single-photon detectors. A key parameter of single-photon detectors is detection efficiency. One of the methods for measuring the detection efficiency given in the international ETSI standard is the Klyshko reference-free method based on the use of the effect of spontaneous parametric downconversion. The signal-to-noise ratio (SNR) of this method depends on a combination of the pump wavelength, the nonlinear crystal axis angle, and the type of detector sensitive element. When the combination is complex, one has to deal with low SNR. In this case, to obtain a high SNR, long-term signal accumulation is necessary. In real detectors, the situation is complicated by the presence of a high noise level at low frequencies. The heterodyning-based method we have proposed consists in introducing modulation into the standard Klyshko scheme and accumulating the signal at a higher frequency. The method was numerically modeled and experimentally tested. A 14 times improvement in SNR was demonstrated compared to simple signal accumulation.