Differential readout method (IMAGE)
Caption
To probe the spatial information of dark counts, we introduced the differential readout method, which utilizes two identical readout channels for tracing the output signals produced by the same dark count event. Two bias-tees (Mini-Circuits, ZX86-12G-S + ) were applied to separate the bias current and output signals. The signals from the two different terminals of the nanowire, which had opposite polarities, were then amplified. In our experiments, two sets of amplifiers were used for different SNSPDs. For devices with a large active area (65 × 130 μm2 in this paper), commercial room-temperature low-noise amplifiers (RT-LNAs: RFbay, LNA650) were used with a nominal gain of 50 dB. For devices with a smaller active area (≤35 × 35 μm2 in this paper), homemade cryogenic low-noise pre-amplifiers (cryoLNAs) mounted on the 40 K-stage and second-stage homemade RT-LNAs were adopted, as illustrated in Figure(a), to further reduce the contribution of the electrical noise. The cryoLNAs had a nominal gain of 32 dB and power consumption of approximately 20 mW, with a 3-dB bandwidth of 1 GHz, and a noise temperature less than 15 K. The second-stage homemade RT-LNAs had a nominal gain of 20 dB with a 3-dB bandwidth of 600 MHz. The amplified signals, as illustrated in Figure(b), wesre finally recorded by an oscilloscope (Keysight, MOSV204A) simultaneously. The sampling rate of the oscilloscope was set to 80 Giga-samples per second with a discrimination level of approximately 15% of the maximum amplitude to increase the time resolution and reduce the influence of reflections from the meander nanowire.
Credit
Xingyu Zhang, Xiaofu Zhang, Jia Huang, Can Yang, Lixing You, Hao Li, et al.
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License
CC BY