A highly accurate method for the determination of the detection efficiency of a silicon single-photon avalanche diode (Si-SPAD) is presented. This method is based on the comparison of the detected count rate of the Si-SPAD compared to the photon rate determined from a calibrated silicon diode using a modified attenuator technique, in which the total attenuation is measured in two attenuation steps. Furthermore, a validation of this two-step method is performed using attenuators of higher transmittance. The setup is a tabletop one, laser-based, and fully automated. The measurement uncertainty components are determined and analyzed in detail. The obtained standard measurement uncertainty is < 0.5%. Main contributions are the transmission of the neutral density filters used as attenuators and the spectral responsivity of the calibrated analog silicon diode. Furthermore, the dependence of the detection efficiency of the Si-SPAD on the mean photon number of the impinging laser radiation with Poissonian statistics is investigated.
Single‐photon sources (SPSs) based on quantum emitters hold promise in quantum radiometry as metrology standard for photon fluxes at the low light level. Ideally this requires control over the photon flux in a wide dynamic range, sub‐Poissonian photon statistics, and narrow‐band emission spectrum. In this work, a monochromatic SPS based on an organic dye molecule is presented, whose photon flux is traceably measured to be adjustable between 144 000 and 1320 000 photons per second at a wavelength of (785.6 ± 0.1) nm, corresponding to an optical radiant flux between 36.5 and 334 fW. The high purity of the single‐photon stream is verified, with a second‐order autocorrelation function at zero time delay below 0.1 throughout the whole range. Such molecule‐based SPS is hence used for the calibration of a single‐photon avalanche detector against a low‐noise analog photodiode traceable to the primary standard for optical radiant flux (i.e., the cryogenic radiometer). Due to the narrow bandwidth of the source, corrections to the detector efficiency arising from the spectral power distribution are negligible. With this major advantage, the developed device may finally realize a low‐photon‐flux standard source for quantum radiometry.
Here we present a reconstruction of the Positive Operator-Value Measurement of a photon-number-resolving detector comprised of three 50:50 beamsplitters in a tree configuration, terminated with four single-photon avalanche detectors. The four detectors' outputs are processed by an electronic board that discriminates detected photon number states from 0 to 4 and implements a "smart counting" routine to compensate for dead time issues at high count rates. c 2018 Optical Society of America OCIS codes: 270.0270, 270.5570, 270.5585.Photon-number-resolving (PNR) detectors [1, 2], i.e. photodetectors that can resolve the number of photons that are impinging on them, have achieved a critical role in a wide variety of research fields, ranging from quantum mechanics foundations experiments [3] to quantum metrology [4,5], imaging [6,7] and information [8,9]. As a consequence, a precise quantum characterization of these devices has become crucial [3][4][5][6][7][8][9][10][11]. In a quantum mechanical framework, a full operational description of a PNR device is its positive operator-valued measure (POVM), i.e. the set of operators Ξ n describing a physical process that leads to a particular measurement outcome n. A measurement of the elements of a detector's POVM can be quite non-trivial, because one has to carefully choose the best-suited technique for a tomographic reconstruction of the POVM of the device under test, depending on its particular properties [12][13][14][15][16][17][18].There exist different types of PNR detectors, e.g. photo-multiplier tubes [19,20] [28][29][30][31][32][33][34][35][36][37][38]. Some of those detector families hold a significant promise for future applications, even if their use at present is very difficult because of a large experimental overhead associated with their operation. On the other hand, even though traditional single-photon avalanche detectors (SPADs) are only capable to discriminate between zero and one (or more) detected photons, photon number resolution can be obtained by multiplexing those detectors spatially [39,40] or temporally [41][42][43][44]. At present, this solution is by far the easiest and cheapest way to achieve a photon number resolving capability, even though at a cost of sacrificing linearity due to detector saturation [45]. Here we present the POVM reconstruction of a multiplexed PNR detector (at 1550 nm) composed of four Indium/Gallium arsenide (InGaAs) SPADs connected to a beam-splitter (BS) tree made with three 50:50 fiber BSs. The output of the InGaAs SPADs is processed with a field-programmable gate array (FPGA) board, giving as output the detected photon number (up to 4 detected photons per pulse).Because this detector is not phase-sensitive, its POVM is diagonal in the Fock states basis:where the Ξ nm = m| Ξ n |m elements give the detector tree probability of counting n = 0, ..., 4 photons with m impinging photons per pulse. To reconstruct Ξ nm , we test the response of our device to a set of J coherent states. The response of our PNR detector to the j-th...
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