Photon-number-resolving (PNR) single-photon detectors are an enabling technology in many areas, such as photonic quantum computing, nonclassical light-source characterization, and quantum imaging.Here, we demonstrate high-efficiency PNR detectors using a parallel superconducting nanowire singlephoton-detector (P-SNSPD) architecture that does not suffer from crosstalk between the pixels and that is free of latching. The behavior of the detector is modeled and used to predict the possible outcomes given a certain number of incoming photons. We apply our model to a four-pixel P-SNSPD with a system detection efficiency of 92.5%. We also demonstrate how this detector allows reconstructing the photonnumber statistics of a coherent source of light, which paves the way towards the characterization of the photon statistics of other types of light source using a single detector.

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Reactive ion etching (RIE) used to fabricate high‐aspect‐ratio (HAR) nano/microstructures is known to damage semiconductor surfaces which enhances surface recombination and limits the conversion efficiency of nanostructured solar cells. Here, defect passivation of ultrathin Al2O3‐coated Si micropillars (MPs) using different surface pretreatment steps is reported. Effects on interface state density are quantified by means of electrochemical impedance spectroscopy which is used to extract quantitative capacitance–voltage and conductance–voltage characteristics from HAR dielectric–semiconductor structures which would otherwise suffer from high gate leakage currents if tested using solid‐state metal–insulator–semiconductor structures. High‐temperature thermal oxidation to form a sacrificial oxide on RIE‐fabricated Si MPs, followed by atomic layer deposition of 4 nm thick Al2O3 after removal of the sacrificial layer produces an interface trap density (D it) as low as 1.5 × 1011 cm−2 eV−1 at the mid‐gap energy of silicon. However, a greatly reduced mid‐gap D it (2 × 1011 cm−2 eV−1) is possible even with a simple air annealing procedure having a maximum temperature of 400 °C.

We present a full characterization (efficiency, dark count, recovery time, jit-ter, POVM matrix) of a photon-number-resolving detector based on parallel SNSPD. We construct a model based only on the pixels efficiencies to compute the POVM.