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arXiv:1504.04713 · Optics Express

Dark counts of superconducting nanowire single-photon detector under illumination

Sijing Chen, Lixing You, Weijun Zhang, Xiaoyan Yang, Hao Li, Lu Zhang, Zhen Wang, Xiaoming Xie

Published Apr 17, 2015• 30 citations
arXivHTMLPDF

Abstract

An abnormal increase in the SDE was observed for superconducting nanowire single-photon detectors (SNSPDs) when the bias current (I(b)) was close to the switching current (I(sw)). By introducing the time-correlated single-photon counting technique, we investigated the temporal histogram of the detection counts of an SNSPD under illumination. The temporal information helps us to distinguish photon counts from dark counts in the time domain. In this manner, the dark count rate (DCR) under illumination and the accurate SDE can be determined. The DCR under moderate illumination may be significantly larger than the conventional DCR measured without illumination under a high I(b), which causes the abnormal increase in the SDE. The increased DCR may be explained by the suppression of I(sw) under illumination.

DOI
10.1364/oe.23.010786

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An abnormal increase in the SDE was observed for superconducting nanowire single-photon detectors (SNSPDs) when the bias current (I(b)) was close to the switching current (I(sw)). By introducing the time-correlated single-photon counting technique, we investigated the temporal histogram of the detection counts of an SNSPD under illumination. The temporal information helps us to distinguish photon counts from dark counts in the time domain. In this manner, the dark count rate (DCR) under illumination and the accurate SDE can be determined. The DCR under moderate illumination may be significantly larger than the conventional DCR measured without illumination under a high I(b), which causes the abnormal increase in the SDE. The increased DCR may be explained by the suppression of I(sw) under illumination.
Today Superconducting Nanowire Single-Photon Detectors (SNSPDs) are commonly used in different photon-starved applications, including testing and diagnostics of VLSI circuits. Detecting very faint signals in the near-infrared wavelength range requires not only good detection efficiency, but also very low Dark Count Rate (DCR) and jitter. For example, low noise is crucial to enable ultra-low voltage optical testing of integrated circuits. The effect of detector temperature and background thermal radiation on the noise of superconducting single-photon detectors made of NbN meanders is studied in this paper. It is shown that two different regimes can be identified in the DCR vs. bias current characteristics. At high bias, the dark count rate is dominated by the intrinsic noise of the detector, while at low bias current it is dominated by the detection of stray photons that get onto the SNSPD. Changing the detector temperature changes its switching current and only affects the high bias branch of the characteristics: a reduction of the DCR can be achieved by lowering the SNSPD base temperature. On the other hand, changing the temperature of the single-photon light source (e.g. the VLSI circuit under test) only affects the low bias regime: a lower target temperature leads to a smaller DCR.
The realization of an ultralow-dark-count rate (DCR) along with the conservation of high detection efficiency (DE) is critical for many applications using single photon detectors in quantum information technologies, material sciences, and biological sensing. For this purpose, a fiber-coupled superconducting nanowire single-photon detector (SNSPD) with a meander-type niobium nitride nanowire (width: 50 nm) is studied. Precise measurements of the bias current dependence of DE are carried out for a wide spectral range (from 500 to 1650 nm in steps of 50 nm) using a white light source and a laser line Bragg tunable band-pass filter. An ultralow DCR (0.0015 cps) and high DE (32%) are simultaneously achieved by the SNSPD at a wavelength of 500 nm.
We measured the photon count rate (PCR) and dark count rate (DCR) of a superconducting nanowire single photon detector (SNSPD) exposed to either a DC magnetic field (up to 60 mT) or to a low-amplitude oscillating field (0.12–0.48 mT, up to 50 kHz). In both cases, the results show an increase in the PCR and the DCR as the DC field or the frequency of the AC field increase. However, the ratio DCR/(PCR + DCR) increases significantly with an increasing DC field, whereas this ratio is approximately constant as the frequency of the AC field increases up to frequencies in the kHz regime. The results suggest a more favorable effect of AC fields on the operation of the SNSPD.
Abstract In this work we present a study of the dark counts rate in a NbTiN Superconducting Nanowire Single Photon Detectors (SNSPD). We measure the distribution of the time intervals elapsed between two consecutive dark pulses at the fixed temperature of 4,2K. Due to the stochastic nature of the dark counts, the distribution is expected to have a Poisson shape but what we observe is a combination of two Poisson-like processes. A further analysis of the distributions dependence on the bias current highlights that the weight of the two process is not constant. In the scenario presented by Ejrnaes et al. [1], this result can confirm that, in this temperature regime, dark counts are generated mainly by multiple consecutive fluctuation events and the contribution to the dark counts rate coming from single fluctuations increases in the high bias current region.
The dark count is one of the key physical issues for superconducting nanowire single-photon detectors (SNSPDs) that limits various applications for optical quantum information and classical optics. When the bias current approaches the switching current of SNSPDs, the dark count is actually dominated by the intrinsic dark counts (iDCs). However, the origin of iDCs and its relation to constrictions remains unclear for practical SNSPDs. We herein systematically characterize the iDCs of the SNSPDs with and without artificial geometric constrictions by applying the differential readout method. For these devices with constrictions, we have observed distinct Gaussian distributions in the temporal distribution of iDCs, in which the time difference between the distributions is consistent with the geometric distance between constrictions, and the rates of iDCs produced by each constriction are in good agreement with constrictions' widths. With respect to practical SNSPDs, surprisingly, we also observe several Gaussian distributions in the temporal domain and it shows no significant dependence on the devices’ sizes, demonstrating that the iDCs of SNSPDs are mainly dominated by a few specific constrictions.
The dark-count rate (DCR) is a key parameter of single-photon detectors. By introducing a bulk optical band-pass filter mounted on a fiber-to-fiber optical bench cooled at 3 K and blocking down to 5 μm, we suppressed the DCR of a superconducting nanowire single-photon detector by more than three orders of magnitude. The DCR is limited by the blackbody radiation through a signal passband of 20-nm bandwidth. The figure of merit, system detection efficiency, and DCR were 2.7×10(11), 2.3%, and 10(-3) Hz, respectively. Narrowing the bandwidth to 100 GHz suppresses the DCR to 10(-4) Hz, and the figure of merit increases to 1.8×10(12).