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Zolotov, P., Divochiy, A., Vakhtomin, Y., Moshkova, M., Morozov, P., Seleznev, V., et al. (2018). Photon-number-resolving SSPDs with system detection efficiency over 50% at telecom range. In Proc. AIP Conf. (Vol. 1936, 020019).
Abstract: We used technology of making high-efficiency superconducting single-photon detectors as a basis for improvement of photon-number-resolving devices. By adding optical cavity and using an improved NbN superconducting film, we enhanced previously reported system detection efficiency at telecom range for such detectors. Our results show that implementation of optical cavity helps to develop four-section device with quantum efficiency over 50% at 1.55 µm. Performed experimental studies of detecting multi-photon optical pulses showed irregularities over defining multi-photon through single-photon quantum efficiency.
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Vodolazov, D. Y., Korneeva, Y. P., Semenov, A. V., Korneev, A. A., & Goltsman, G. N. (2015). Vortex-assisted mechanism of photon counting in a superconducting nanowire single-photon detector revealed by external magnetic field. Phys. Rev. B, 92(10), 104503 (1 to 9).
Abstract: We use an external magnetic field to probe the detection mechanism of a superconducting nanowire single-photon detector. We argue that the hot belt model (which assumes partial suppression of the superconducting order parameter Δ across the whole width of the superconducting nanowire after absorption of the photon) does not explain observed weak-field dependence of the photon count rate (PCR) for photons with λ=450nm and noticeable decrease of PCR (with increasing the magnetic field) in a range of the currents for photons with wavelengths λ=450–1200nm. Found experimental results for all studied wavelengths can be explained by the vortex hot spot model (which assumes partial suppression of Δ in the area with size smaller than the width of the nanowire) if one takes into account nucleation and entrance of the vortices to the photon induced hot spot and their pinning by the hot spot with relatively large size and strongly suppressed Δ.
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Baselmans, J. J. A., Hajenius, M., Gao, J. R., Baryshev, A., Kooi, J., Klapwijk, T. M., et al. (2004). Hot electron bolometer mixers with improved interfaces: sensitivity, LO power and stability. In Proc. 15th Int. Symp. Space Terahertz Technol. (pp. 17–24).
Abstract: We study twin slot antenna coupled NbN hot electron bolometer mixers with an improved contact structure and a small volume, ranging from 1 µm × 0.1 µm to 2 × 0.3 µm. We obtain a DSB receiver noise temperature of 900 K at 1.6 THz and 940 K at 1.9 THz. To explore the practical usability of such small HEB mixers we evaluate the LO power requirement, the sensitivity and the stability. We find that the LO power requirement of the smallest mixers is reduced to about 240 nW at the Si lens of the mixer. This value is larger than expected from the isothermal technique and the known losses in the lens by a factor of 3-3.5. The stability of these receivers is characterized using a measurement of the Allan Variance. We find an Allan time of 0.5 sec. in an 80 MHz bandwidth. A small increase in stability can be reached by using a higher bias at the expense of a significant amount of sensitivity. The stability is sufficient for spectroscopic applications in a 1 MHz bandwidth at a 1 Hz chopping frequency.
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Baeva, E. M., Titova, N. A., Kardakova, A. I., Piatrusha, S. U., & Khrapai, V. S. (2020). Universal bottleneck for thermal relaxation in disordered metallic films. Jetp Lett., 111(2), 104–108.
Abstract: We study the heat relaxation in current biased metallic films in the regime of strong electron–phonon coupling. A thermal gradient in the direction normal to the film is predicted, with a spatial temperature profile determined by the temperature-dependent heat conduction. In the case of strong phonon scattering, the heat conduction occurs predominantly via the electronic system and the profile is parabolic. This regime leads to the linear dependence of the noise temperature as a function of bias voltage, in spite of the fact that all the dimensions of the film are large compared to the electron–phonon relaxation length. This is in stark contrast to the conventional scenario of relaxation limited by the electron–phonon scattering rate. A preliminary experimental study of a 200-nm-thick NbN film indicates the relevance of our model for materials used in superconducting nanowire single-photon detectors.
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Kuznetsov, K. A., Kornienko, V. V., Vakhtomin, Y. B., Pentin, I. V., Smirnov, K. V., & Kitaeva, G. K. (2018). Generation and detection of optical-terahertz biphotons via spontaneous parametric downconversion. In Proc. ICLO (303).
Abstract: We study spontaneous parametric downconversion (SPDC) in the strongly non-degenerate regime when the idler wave hits the terahertz range. By using the hot-electron bolometer, for the first time the SPDC-generated idler-wave photons were directly detected in the terahertz frequency range. Spectrum of corresponding signal photons was measured using standard technique by the CCD camera. Possible applications of correlated optical-terahertz biphotons are discussed.
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