Zolotov, P., Semenov, A., Divochiy, A., & Goltsman, G. (2021). A comparison of VN and NbN thin films towards optimal SNSPD efficiency. IEEE Trans. Appl. Supercond., 31(5), 1–4.
Abstract: Based on early phenomenological ideas about the operation of superconducting single-photon detectors (SSPD or SNSPD), it was expected that materials with a lower superconducting gap should perform better in the IR range. The plausibility of this concept could be checked using two popular SSPD materials – NbN and WSi films. However, these materials differ strongly in crystallographic structure (polycrystalline B1 versus amorphous), which makes their dependence on disorder different. In our work we present a study of the single-photon response of SSPDs made from two disordered B1 structure superconductors – vanadium nitride and niobium nitride thin films. We compare the intrinsic efficiency of devices made from films with different sheet resistance values. While both materials have a polycrystalline structure and comparable diffusion coefficient values, VN films show metallic behavior over a wide range of sheet resistance, in contrast to NbN films with an insulator-like temperature dependence of resistivity, which may be partially due to enhanced Coulomb interaction, leading to different starting points for the normal electron density of states. The results show that even though VN devices are more promising in terms of theoretical predictions, their optimal performance was not reached due to lower values of sheet resistance.
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Smirnov, K., Moshkova, M., Antipov, A., Morozov, P., & Vakhtomin, Y. (2021). The cascade switching of the photon number resolving superconducting single-photon detectors. IEEE Trans. Appl. Supercond., 31(2), 1–4.
Abstract: In this article, present the first detailed study of cascade switching in superconducting photon number resolving detectors. The detectors were made in the form of four parallel nanowires, coupled with the single-mode optical fiber and mounted into a closed-cycle refrigerator with a temperature of 2.1 K. We found out the value of additional false pulses (N cas.sw. ) appearing due to cascade switching and showed that it is possible to set up the detector bias current that corresponds to a high level of the detection efficiency and a low level of N cas.sw. simultaneously. We reached the detection efficiency of 60% and N cas.sw. = 0.3%.
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Polyakova, M., Semenov, A. V., Kovalyuk, V., Ferrari, S., Pernice, W. H. P., & Gol'tsman, G. N. (2019). Protocol of measuring hot-spot correlation length for SNSPDs with near-unity detection efficiency. IEEE Trans. Appl. Supercond., 29(5), 1–5.
Abstract: We present a simple quantum detector tomography protocol, which allows, without ambiguities, to measure the two-spot detection efficiency and extract the hot-spot interaction length of superconducting nanowire single photon detectors (SNSPDs) with unity intrinsic detection efficiency. We identify a significant parasitic contribution to the measured two-spot efficiency, related to an effect of the bias circuit, and find a way to rule out this contribution during data post-processing and directly in the experiment. From the data analysis for waveguide-integrated SNSPD, we find signatures of the saturation of the two-spot efficiency and hot-spot interaction length of order of 100 nm.
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Korneev, A., Korneeva, Y., Florya, I., Semenov, A., & Goltsman, G. (2018). Photon switching statistics in multistrip superconducting single-photon detectors. IEEE Trans. Appl. Supercond., 28(7), 1–4.
Abstract: We study photon count statistics in superconducting single-photon detectors consisting of up to 70 narrow superconducting strips connected in parallel. Using interarrival time analysis, we demonstrate that our samples are operated in the “arm-trigger” regime and require up to seven subsequently absorbed photons to form a resistive state in the whole sample. We also performed numerical simulation of the light and dark count rates versus detector bias current, which are in good agreement with the experimental results.
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Reiger, E., Pan, D., Slysz, W., Jukna, A., Sobolewski, R., Dorenbos, S., et al. (2007). Spectroscopy with nanostructured superconducting single photon detectors. IEEE J. Select. Topics Quantum Electron., 13(4), 934–943.
Abstract: Superconducting single-photon detectors (SSPDs) are nanostructured devices made from ultrathin superconducting films. They are typically operated at liquid helium temperature and exhibit high detection efficiency, in combination with very low dark counts, fast response time, and extremely low timing jitter, within a broad wavelength range from ultraviolet to mid-infrared (up to 6 mu m). SSPDs are very attractive for applications such as fiber-based telecommunication, where single-photon sensitivity and high photon-counting rates are required. We review the current state-of-the-art in the SSPD research and development, and compare the SSPD performance to the best semiconducting avalanche photodiodes and other superconducting photon detectors. Furthermore, we demonstrate that SSPDs can also be successfully implemented in photon-energy-resolving experiments. Our approach is based on the fact that the size of the hotspot, a nonsuperconducting region generated upon photon absorption, is linearly dependent on the photon energy. We introduce a statistical method, where, by measuring the SSPD system detection efficiency at different bias currents, we are able to resolve the wavelength of the incident photons with a resolution of 50 nm.
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