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Applied Optics

Photon number measurement using heterodyne method for a detector’s quantum efficiency determination based on spontaneous parametric down-conversion

A. A. Samoĭlenko, Gennady G. Levin

Published Dec 10, 2019• 2 citations
Publisher

Abstract

Active development of quantum informational components such as quantum computers and quantum key distribution systems requires parameter characterization of single photon detectors. A key property of the single photon detectors is detection efficiency. One of the methods of the detection efficiency measurement, as listed in the international standard ETSI, is the reference-free twin-photon-based Klyshko method. The signal-to-noise ratio (SNR) of this method depends on the combination of the pump wavelength, the nonlinear crystal's axis angle, and the type of detector's sensitive element. When the combination is difficult, one has to deal with the low SNR of the detector counts measurement. To gain the high SNR, one has to average the long record complicated with the "random telegraph signal" noise. This type of noise exhibits high spectral density at a zero frequency, where simple averaging works. The heterodyne based method we have proposed is to perform averaging at the higher frequency of the modulation introduced to the standard Klyshko measurement scheme. The method was numerically simulated and experimentally tested. The 14 times improvement in SNR for the proposed method relative to the simple averaging was demonstrated by the numerical simulation and confirmed experimentally.

DOI
10.1364/ao.58.009856

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Active development of quantum informational components such as quantum computers and quantum key distribution systems requires parameter characterization of single photon detectors. A key property of the single photon detectors is detection efficiency. One of the methods of the detection efficiency measurement, as listed in the international standard ETSI, is the reference-free twin-photon-based Klyshko method. The signal-to-noise ratio (SNR) of this method depends on the combination of the pump wavelength, the nonlinear crystal's axis angle, and the type of detector's sensitive element. When the combination is difficult, one has to deal with the low SNR of the detector counts measurement. To gain the high SNR, one has to average the long record complicated with the "random telegraph signal" noise. This type of noise exhibits high spectral density at a zero frequency, where simple averaging works. The heterodyne based method we have proposed is to perform averaging at the higher frequency of the modulation introduced to the standard Klyshko measurement scheme. The method was numerically simulated and experimentally tested. The 14 times improvement in SNR for the proposed method relative to the simple averaging was demonstrated by the numerical simulation and confirmed experimentally.
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.
Single-photon detectors are of great importance in spectroscopy, laser ranging, astronomy and wherever weak light detection is required, so a precise knowledge of their quantum efficiency is essential, but their calibration is by no means trivial. Traditional methods need a black body radiation source or a highly attenuated laser beam as a reference standard, or an already calibrated reference detector. It is well known that absolute measurement of the quantum efficiency, absolute in the sense that the calibration is independent of any radiometric standard or the properties of another detector, can be performed using entangled twin photons generated in optical spontaneous parametric down-conversion together with a reference detector. We have performed the first proof-of-principle experiment to determine the quantum efficiency by which no second detector or reference standard is required. This absolute self-calibration method is also based on the time correlation of photons emitted in parametric down-conversion, but with the introduction of a suitable time delay between the arrival times of the twin photons. Furthermore, we describe a scheme for absolute self-calibration of the quantum efficiency at different wavelengths by means of a pulsed source of nondegenerate down-converted photons. This method should have even greater potential for applications.
Single-photon detectors are of great importance in spectroscopy, laser ranging, astronomy and wherever weak light detection is required, so a precise knowledge of their quantum efficiency is essential, but their calibration is by no means trivial. Traditional methods need a black body radiation source or a highly attenuated laser beam as a reference standard, or an already calibrated reference detector. It is well known that absolute measurement of the quantum efficiency, absolute in the sense that the calibration is independent of any radiometric standard or the properties of another detector, can be performed using entangled twin photons generated in optical spontaneous parametric down-conversion together with a reference detector. We have performed the first proof-of-principle experiment to determine the quantum efficiency by which no second detector or reference standard is required. This absolute self-calibration method is also based on the time correlation of photons emitted in parametric down-conversion, but with the introduction of a suitable time delay between the arrival times of the twin photons. Furthermore, we describe a scheme for absolute self-calibration of the quantum efficiency at different wavelengths by means of a pulsed source of nondegenerate down-converted photons. This method should have even greater potential for applications.
A method to measure the correlation function of a biphoton field, which does not require single-photon detectors and photocount coincidence schemes, has been proposed and experimentally approved. It is based on the statistical analysis of current data from analog detectors. On an example of the operation of a scheme with analog photomultiplier tubes in the signal and idler channels of degenerate parametric down conversion, it has been shown that this new approach allows one to obtain correlation function values coinciding with the results of the standard photon counting technique. It has been shown how the absolute values of photon numbers and radiation power in the signal channel of the down conversion scheme are determined from the measured correlation function. Analog detection can expand the spectral and dynamic ranges of electromagnetic radiation for the application of quantum optic technologies. A method for the reference-free measurement of the spectral sensitivity of an analog photosensor module has been demonstrated as the first example of application.
By constructing an experimental system, the heterodyne detection of the photon counting system is realized. The effects of photon counting rate, sampling rate, background light noise and beam mismatching angle on the single-photon heterodyne detection performance based on power spectrum averaging are studied experimentally. The results show that the power spectrum average results have a saturated signal-to-noise ratio (SNR) at a certain count rate, and the saturation SNR increases with the increase of the count rate. As the sampling rate increases, a higher saturation SNR can be obtained. The local oscillator and signal light mismatch angles have the same effect on single photon heterodyne detection compared to linear detection. The research results in this paper have a promoting significance for the practical application of single-photon heterodyne detection technology.
A modified Klyshko method for standardless calibration of analog photodetector efficiencies is suggested and experimentally implemented. The method is based on the measurement of the number of incident photons using correlation properties of biphotons generated under spontaneous parametric downconversion, and on the determination of the mean number of discrete elementary responses of a photodetector by deconvoluting the statistical distribution of the output photocurrents. As an example, the generalized efficiency of an analog photomultiplier is measured as the ratio of the average number of elementary current responses to the average number of incident photons. The statistical properties of the elementary responses of an analog photodetector depend not only on the detector itself, but also on the parameters of the subsequent electronic circuit. Nevertheless, it has been shown that the generalized efficiency determined by this way allows one to calibrate the photon fluxes by the analog photodetector without involvement of any reference sources or detectors.