Zolotov, P. I., Divochiy, A. V., Vakhtomin, Y. B., Morozov, P. V., Seleznev, V. A., & Smirnov, K. V. (2017). Development of high-effective superconducting single-photon detectors aimed for mid-IR spectrum range. In J. Phys.: Conf. Ser. (Vol. 917, 062037).
Abstract: We report on development of superconducting single-photon detectors (SSPD) with high intrinsic quantum efficiency in the wavelength range 1.31 – 3.3 μm. By optimization of the NbN film thickness and its compound, we managed to improve detection efficiency of the detectors in the range up to 3.3 μm. Optimized devices showed intrinsic quantum efficiencies as high as 10% at mid-IR range.
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Baeva, E., Sidorova, M., Korneev, A., & Goltsman, G. (2018). Precise measurement of the thermal conductivity of superconductor. In Proc. AIP Conf. (Vol. 1936, 020003 (1 to 4)).
Abstract: Measuring the thermal properties such as the heat capacity provide information about intrinsic mechanisms operated inside. In general, the ratio between electron and phonon specific heat Ce/Cp shows how the absorbed energy shared between electron and phonon subsystems. In this work we make estimations for amplitude-modulated absorption of THz radiation technique for investigation of the ratio Ce/Cp in superconducting Niobium Nitride (NbN) at T = Tc. Our results indicates that experimentally the frequency of modulation has to be extra large to extract the quantity. We perform a new technique allowed to work at low frequency with accurately measurement of absorbed power.
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Korneev, A., Korneeva, Y., Florya, I., Voronov, B., & Goltsman, G. (2011). Spectral sensitivity of narrow strip NbN superconducting single-photon detector. In J. Fiurásek, & I. Prochazka (Eds.), Proc. SPIE (Vol. 8072, 80720G (1 to 9)). SPIE.
Abstract: Superconducting single-photon detector (SSPD) is patterned from 4-nm-thick NbN film deposited on sapphire substrate as a 100-nm-wide strip. Due to its high detection efficiency, low dark counts, and picosecond timing jitter SSPD has become a competitor to the InGaAs avalanche photodiodes at 1550 nm and longer wavelengths. Although the SSPD is operated at liquid helium temperature its efficient single-mode fibre coupling enabled its usage in many applications ranging from single-photon sources research to quantum cryptography. In our strive to increase the detection efficiency at 1550 nm and longer wavelengths we developed and fabricated SSPD with the strip almost twice narrower compared to the standard 100 nm. To increase the voltage response of the device we utilized cascade switching mechanism: we connected 50-nm-wide and 10-μm-long strips in parallel covering the area of 10 μmx10 μm. Absorption of a photon breaks the superconductivity in a strip leading to the bias current redistribution between other strips followed their cascade switching. As the total current of all the strips about is 1 mA by the order of magnitude the response voltage of such an SSPD is several times higher compared to the traditional meander-shaped SSPDs. In middle infrared (about 3 μm wavelength) these devices have the detection efficiency several times higher compared to the traditional SSPDs.
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Casaburi, A., Ejrnaes, M., Quaranta, O., Gaggero, A., Mattioli, F., Leoni, R., et al. (2008). Experimental characterization of NbN nanowire optical detectors with parallel stripline configuration. In J. Phys.: Conf. Ser. (Vol. 97, 012265 (1 to 6)). IOP Publishing.
Abstract: We have developed a novel geometrical configuration for NbN-based superconducting single photon optical detector (SSPD) that achieves two goals: a much lower intrinsic impedance, and a consequently greater bandwidth, and a much larger signal amplitude compared to the standard meandered configuration. This has been obtained by implementing a properly designed parallel stripline structure where a cascade switching mechanism occurs when one of the striplines is hit by an optical photon. The overall switching occurs synchronously and in a very short time, giving rise to a strong and fast voltage pulse. The SSPD have been realized using state of the art NbN deposition technology and e-beam lithography. The strips are 100 nm wide and 5 μm long and have been realized with 4 nm NbN film on sapphire and Si substrate. We report on experimental characterization of such novel devices. The performances of the proposed novel type of SSPD are compared with standard SSPD design and results in terms of signal amplitude, risetime and effective detection area.
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Tarkhov, M., Morozov, D., Mauskopf, P., Seleznev, V., Korneev, A., Kaurova, N., et al. (2006). Single photon counting detector for THz radioastronomy. In Proc. 17th Int. Symp. Space Terahertz Technol. (pp. 119–122).
Abstract: In this paper we present the results of the research on the superconducting NbN-ultrathin-film single- photon detectors (SSPD) which are capable to detect single quanta in middle IR range. The detection mechanism is based on the hotspot formation in quasi-two-dimensional superconducting structures upon photon absorption. Spectral measurements showed that up to 5.7 gm wavelength (52 THz) the SSPD exhibits single-photon sensitivity. Reduction of operation temperature to 1.6 K allowed us to measure quantum efficiency of -4% at 60 THz. Although further decrease of the operation temperature far below 1 K does not lead to any significant increase of quantum efficiency. We expect that the improvement of the SSPD's performance at reduced operation temperature will make SSPD a practical detector with high characteristics for much lower THz frequencies as well.
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Smirnov, K., Korneev, A., Minaeva, O., Divochij, A., Rubtsova, I., Antipov, A., et al. (2006). Superconducting single-photon detector for near- and middle IR wavelength range. In Proc. 16th Int. Crimean Microwave and Telecommunication Technology (Vol. 2, pp. 684–685).
Abstract: Presented in this paper are the results of research of NbN-film superconducting single-photon detector. At 2 K temperature, quantum efficiency in the visible light (0.56 mum) reaches 30-40 %. With the wavelength increase quantum efficiency decreases and comes to 20% at 1.55 mum and 0.02% at 5.6 mum. Minimum dark counts rate is 2times10-4s-1. The jitter of detector is 35 ps. The detector was successfully implemented for integrated circuits non-invasive optical testing. It is also perspective for quantum cryptography systems
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Milostnaya, I., Korneev, A., Rubtsova, I., Seleznev, V., Minaeva, O., Chulkova, G., et al. (2006). Superconducting single-photon detectors designed for operation at 1.55-µm telecommunication wavelength. In J. Phys.: Conf. Ser. (Vol. 43, pp. 1334–1337).
Abstract: We report on our progress in development of superconducting single-photon detectors (SSPDs), specifically designed for secure high-speed quantum communications. The SSPDs consist of NbN-based meander nanostructures and operate at liquid helium temperatures. In general, our devices are capable of GHz-rate photon counting in a spectral range from visible light to mid-infrared. The device jitter is 18 ps and dark counts can reach negligibly small levels. The quantum efficiency (QE) of our best SSPDs for visible-light photons approaches a saturation level of ~30-40%, which is limited by the NbN film absorption. For the infrared range (1.55µm), QE is ~6% at 4.2 K, but it can be significantly improved by reduction of the operation temperature to the 2-K level, when QE reaches ~20% for 1.55-µm photons. In order to further enhance the SSPD efficiency at the wavelength of 1.55 µm, we have integrated our detectors with optical cavities, aiming to increase the effective interaction of the photon with the superconducting meander and, therefore, increase the QE. A successful effort was made to fabricate an advanced SSPD structure with an optical microcavity optimized for absorption of 1.55 µm photons. The design consisted of a quarter-wave dielectric layer, combined with a metallic mirror. Early tests performed on relatively low-QE devices integrated with microcavities, showed that the QE value at the resonator maximum (1.55-µm wavelength) was of the factor 3-to-4 higher than that for a nonresonant SSPD. Independently, we have successfully coupled our SSPDs to single-mode optical fibers. The completed receivers, inserted into a liquid-helium transport dewar, reached ~1% system QE for 1.55 µm photons. The SSPD receivers that are fiber-coupled and, simultaneously, integrated with resonators are expected to be the ultimate photon counters for optical quantum communications.
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Okunev, O., Chulkova, G., Milostnaya, I., Antipov, A., Smirnov, K., Morozov, D., et al. (2005). Registration of infrared single photons by a two-channel receiver based on fiber-coupled superconducting single-photon detectors. In Proc. 2-nd CAOL (Vol. 2, pp. 282–285).
Abstract: Single-photon detectors (SPDs) are the foundation of all quantum communications (QC) protocols. Among different classes of SPDs currently studied, NbN superconducting SPDs (SSPDs) are established as the best devices for ultrafast counting of single photons in the infrared (IR) wavelength range. The SSPDs are nanostructured, 100 /spl mu/m/sup 2/ in total area, superconducting meanders, patterned by electron lithography in ultra-thin NbN films. Their operation has been explained within a phenomenological hot-electron photoresponse model. We present the design and performance of a novel, two-channel SPD receiver, based on two fiber-coupled NbN SSPDs. The receivers have been developed for fiber-based QC systems, operational at 1.3 /spl mu/m and 1.55 /spl mu/m telecommunication wavelengths. They operate in the temperature range from 4.2 K to 2 K, in which the NbN SSPDs exhibit their best performance. The receiver unit has been designed as a cryostat insert, placed inside a standard liquid-helium storage dewar. The input of the receiver consists of a pair of single-mode optical fibers, equipped with the standard FC connectors and kept at room temperature. Coupling between the SSPD and the fiber is achieved using a specially designed, precise micromechanical holder that places the fiber directly on top of the SSPD nanostructure. Our receivers achieve the quantum efficiency of up to 7% for near-IR photons, with the coupling efficiency of about 30%. The response time was measured to be <300 ps and it was limited by our read-out electronics. The jitter of fiber-coupled SSPDs is <35 ps and their dark-count rate is below 1 s/sup -1/. The presented performance parameters show that our single-photon receivers are fully applicable for quantum-correlation-type QC systems, including practical quantum cryptography.
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Gol'tsman, G., Korneev, A., Minaeva, O., Rubtsova, I., Milostnaya, I., Chulkova, G., et al. (2005). Superconducting nanostructured detectors capable of single-photon counting in the THz range. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 555–557).
Abstract: We present the results of the NbN superconducting single-photon detector sensitivity measurement in the visible to mid-IR range. For visible and near IR light (0.56 — 1.3μm wavelengths) the detector exhibits 30% quantum efficiency saturation value limited by the NbN film absorption and extremely low level of dark counts (2x10 -4 s -1). The detector manifested single-photon counting up to 6 μm wavelength with the quantum efficiency reaching 10 -2 % at 5.6 μm and 3 K temperature.
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Goltsman, G., Korneev, A., Minaeva, O., Rubtsova, I., Chulkova, G., Milostnaya, I., et al. (2005). Advanced nanostructured optical NbN single-photon detector operated at 2.0 K. In M. Razeghi, & G. J. Brown (Eds.), Proc. SPIE (Vol. 5732, pp. 520–529). Spie.
Abstract: We present our studies on quantum efficiency (QE), dark counts, and noise equivalent power (NEP) of the latest generation of nanostructured NbN superconducting single-photon detectors (SSPDs) operated at 2.0 K. Our SSPDs are based on 4 nm-thick NbN films, patterned by electron beam lithography as highly-uniform 100÷120-nm-wide meander-shaped stripes, covering the total area of 10x10 μm2 with the meander filling factor of 0.7. Advances in the fabrication process and low-temperature operation lead to QE as high as 30-40% for visible-light photons (0.56 μm wavelength)-the saturation value, limited by optical absorption of the NbN film. For 1.55 μm photons, QE was 20% and decreased exponentially with the wavelength reaching 0.02% at the 5-μm wavelength. Being operated at 2.0-K temperature the SSPDs revealed an exponential decrease of the dark count rate, what along with the high QE, resulted in the NEP as low as 5x10-21 W/Hz-1/2, the lowest value ever reported for near-infrared optical detectors. The SSPD counting rate was measured to be above 1 GHz with the pulse-to-pulse jitter below 20 ps. Our nanostructured NbN SSPDs operated at 2.0 K significantly outperform their semiconducting counterparts and find practical applications ranging from noninvasive testing of CMOS VLSI integrated circuits to ultrafast quantum communications and quantum cryptography.
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