Il'in, K. S., Currie, M., Lindgren, M., Milostnaya, I. I., Verevkin, A. A., Gol'tsman, G. N., et al. (1999). Quantum efficiency and time-domain response of superconducting NbN hot-electron photodetectors. IEEE Trans. Appl. Supercond., 9(2), 3338–3341.
Abstract: We report our studies on the response of ultrathin superconducting NbN hot-electron photodetectors. We have measured the photoresponse of few-nm-thick, micron-size structures, which consisted of single and multiple microbridges, to radiation from the continuous-wave semiconductor laser and the femtosecond Ti:sapphire laser with the wavelength of 790 nm and 400 nm, respectively. The maximum responsivity was observed near the film's superconducting transition with the device optimally current-biased in the resistive state. The responsivity of the detector, normalized to its illuminated area and the coupling factor, was 220 A/W(3/spl times/10/sup 4/ V/W), which corresponded to a quantum efficiency of 340. The responsivity was wavelength independent from the far infrared to the ultraviolet range, and was at least two orders of magnitude higher than comparable semiconductor optical detectors. The time constant of the photoresponse signal was 45 ps, when was measured at 2.15 K in the resistive (switched) state using a cryogenic electro-optical sampling technique with subpicosecond resolution. The obtained results agree very well with our calculations performed using a two-temperature model of the electron heating in thin superconducting films.
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Lindgren, M., Currie, M., Zeng, W. - S., Sobolewski, R., Cherednichenko, S., Voronov, B., et al. (1998). Picosecond response of a superconducting hot-electron NbN photodetector. Appl. Supercond., 6(7-9), 423–428.
Abstract: The ps optical response of ultrathin NbN photodetectors has been studied by electro-optic sampling. The detectors were fabricated by patterning ultrathin (3.5 nm thick) NbN films deposited on sapphire by reactive magnetron sputtering into either a 5×10 μm2 microbridge or 25 1 μm wide, 5 μm long strips connected in parallel. Both structures were placed at the center of a 4 mm long coplanar waveguide covered with Ti/Au. The photoresponse was studied at temperatures ranging from 2.15 K to 10 K, with the samples biased in the resistive (switched) state and illuminated with 100 fs wide laser pulses at 395 nm wavelength. At T=2.15 K, we obtained an approximately 100 ps wide transient, which corresponds to a NbN detector response time of 45 ps. The photoresponse can be attributed to the nonequilibrium electron heating effect, where the incident radiation increases the temperature of the electron subsystem, while the phonons act as the heat sink. The high-speed response of NbN devices makes them an excellent choice for an optoelectronic interface for superconducting digital circuits, as well as mixers for the terahertz regime. The multiple-strip detector showed a linear dependence on input optical power and a responsivity =3.9 V/W.
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Zhang, J., Verevkin, A., Slysz, W., Chulkova, G., Korneev, A., Lipatov, A., et al. (2017). Time-resolved characterization of NbN superconducting single-photon optical detectors. In J. C. Armitage (Ed.), Proc. SPIE (Vol. 10313, 103130F (1 to 3)). SPIE.
Abstract: NbN superconducting single-photon detectors (SSPDs) are very promising devices for their picosecond response time, high intrinsic quantum efficiency, and high signal-to-noise ratio within the radiation wavelength from ultraviolet to near infrared (0.4 gm to 3 gm) [1-3]. The single photon counting property of NbN SSPDs have been investigated thoroughly and a model of hotspot formation has been introduced to explain the physics of the photon- counting mechanism [4-6]. At high incident flux density (many-photon pulses), there are, of course, a large number of hotspots simultaneously formed in the superconducting stripe. If these hotspots overlap with each other across the width w of the stripe, a resistive barrier is formed instantly and a voltage signal can be generated. We assume here that the stripe thickness d is less than the electron diffusion length, so the hotspot region can be considered uniform. On the other hand, when the photon flux is so low that on average only one hotspot is formed across w at a given time, the formation of the resistive barrier will be realized only when the supercurrent at sidewalks surpasses the critical current (jr) of the superconducting stripe [1]. In the latter situation, the formation of the resistive barrier is associated with the phase-slip center (PSC) development. The effect of PSCs on the suppression of superconductivity in nanowires has been discussed very recently [8, 9] and is the subject of great interest.
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Verevkin, A., Zhang, J., Pearlman, A., Slysz, W., Sobolewski, R., Korneev, A., et al. (2004). Ultimate sensitivity of superconducting single-photon detectors in the visible to infrared range.
Abstract: We present our quantum efficiency (QE) and noise equivalent power (NEP) measurements of the meandertype ultrathin NbN superconducting single-photon detector in the visible to infrared radiation range. The nanostructured devices with 3.5-nm film thickness demonstrate QE up to~ 10% at 1.3–1.55 µm wavelength, and up to 20% in the entire visible range. The detectors are sensitive to infrared radiation with the wavelengths down to~ 10 µm. NEP of about 2× 10-18 W/Hz1/2 was obtained at 1.3 µm wavelength. Such high sensitivity together with GHz-range counting speed, make NbN photon counters very promising for efficient, ultrafast quantum communications and another applications. We discuss the origin of dark counts in our devices and their ultimate sensitivity in terms of the resistive fluctuations in our superconducting nanostructured devices.
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Shcherbatenko, M., Elezov, M., Manova, N., Sedykh, K., Korneev, A., Korneeva, Y., et al. (2021). Single-pixel camera with a large-area microstrip superconducting single photon detector on a multimode fiber. Appl. Phys. Lett., 118(18), 181103.
Abstract: High sensitivity imaging at the level of single photons is an invaluable tool in many areas, ranging from microscopy to astronomy. However, development of single-photon sensitive detectors with high spatial resolution is very non-trivial. Here we employ the single-pixel imaging approach and demonstrate a proof-of-principle single-pixel single-photon imaging setup. We overcome the problem of low light gathering efficiency by developing a large-area microstrip superconducting single photon detector coupled to a multi-mode optical fiber interface. We show that the setup operates well in the visible and near infrared spectrum, and is able to capture images at the single-photon level.
We thank Philipp Zolotov and Pavel Morozov for NbN film fabrication, ARC coating, and fiber coupling of the detector. We also thank Swabian Instruments GmbH and Dr. Helmut Fedder personally for the kindly provided experimental equipment (Time Tagger Ultra 8). The work in the part of SNSPD research and development was supported by the Russian Foundation for Basic Research Project No. 18-29-20100. The work in the part of the optical setup and imaging was supported by Russian Foundation for Basic Research Project No. 20-32-51004.
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Korneev, A. A. (2021). Superconducting NbN microstrip single-photon detectors. In I. Prochazka, M. Štefaňák, R. Sobolewski, & A. Gábris (Eds.), Proc. Quantum Optics and Photon Counting (Vol. 11771). SPIE.
Abstract: Superconducting Single-Photon Detectors (SSPD) invented two decades ago have evolved to a mature technology and have become devices of choice in the advanced applications of quantum optics, such as quantum cryptography and optical quantum computing. In these applications SSPDs are coupled to single-mode fibers and feature almost unity detection efficiency, negligible dark counts, picosecond timing jitter and MHz photon count rate. Meanwhile, there are great many applications requiring coupling to multi-mode fibers or free space. ‘Classical’ SSPDs with 100-nm-wide superconducting strip and covering area of about 100 µm2 are not suitable for further scaling due to degradation of performance and low fabrication yield. Recently we have demonstrated single-photon counting in micron-wide superconducting bridges and strips. Here we present our approach to the realization of practical photon-counting detectors of large enough area to be efficiently coupled to multi-mode fibers or free space. The detector is either a meander or a spiral of 1-µm-wide strip covering an area of 50x50 µm2. Being operated at 1.7K temperature it demonstrates the saturated detection efficiency (i.e. limited by the absorption in the detector) up to 1550 nm wavelength, about 10 ns dead time and timing jitter in range 50-100 ps.
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Vodolazov, D. Y., Manova, N. N., Korneeva, Y. P., & Korneev, A. A. (2020). Timing jitter in NbN superconducting microstrip single-photon detector. Phys. Rev. Applied, 14(4), 044041 (1 to 8).
Abstract: We experimentally study timing jitter of single-photon detection by NbN superconducting strips with width w ranging from 190 nm to 3μm. We find that timing jitter of both narrow (190 nm) and micron-wide strips is about 40 ps at currents where internal detection efficiency η saturates and it is close to our instrumental jitter. We also calculate intrinsic timing jitter in wide strips using the modified time-dependent Ginzburg-Landau equation coupled with a two-temperature model. We find that with increasing width the intrinsic timing jitter increases and the effect is most considerable at currents where a rapid growth of η changes to saturation. We relate it with complicated vortex and antivortex dynamics, which depends on a photon’s absorption site across the strip and its width. The model also predicts that at current close to depairing current the intrinsic timing jitter of a wide strip could be about ℏ/kBTc (Tc is a critical temperature of superconductor), i.e., the same as for a narrow strip.
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Moshkova, M., Divochiy, A., Morozov, P., Vakhtomin, Y., Antipov, A., Zolotov, P., et al. (2019). High-performance superconducting photon-number-resolving detectors with 86% system efficiency at telecom range. J. Opt. Soc. Am. B, 36(3), B20.
Abstract: The use of improved fabrication technology, highly disordered NbN thin films, and intertwined section topology makes it possible to create high-performance photon-number-resolving superconducting single-photon detectors (PNR SSPDs) that are comparable to conventional single-element SSPDs at the telecom range. The developed four-section PNR SSPD has simultaneously an 86±3% system detection efficiency, 35 cps dark count rate, ∼2 ns dead time, and maximum 90 ps jitter. An investigation of the PNR SSPD’s detection efficiency for multiphoton events shows good uniformity across sections. As a result, such a PNR SSPD is a good candidate for retrieving the photon statistics for light sources and quantum key distribution systems.
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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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Korneeva, Y., Sidorova, M., Semenov, A., Krasnosvobodtsev, S., Mitsen, K., Korneev, A., et al. (2016). Comparison of hot-spot formation in NbC and NbN single-photon detectors. IEEE Trans. Appl. Supercond., 26(3), 1–4.
Abstract: We report an experimental investigation of the hot-spot evolution in superconducting single-photon detectors made of disordered superconducting materials with different diffusivity and energy downconversion time values, i.e., 33-nm-thick NbN and 23-nm-thick NbC films. We have demonstrated that, in NbC film, only 405-nm photons produce sufficiently large hot spot to trigger a single-photon response. The dependence of detection efficiency on bias current for 405-nm photons in NbC is similar to that for 3400-nm photons in NbN. In NbC, large diffusivity and downconversion time result in 1-D critical current suppression profile compared with the usual 2-D profile in NbN.
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Korneeva, Y. P., Manova, N. N., Florya, I. N., Mikhailov, M. Y., Dobrovolskiy, O. V., Korneev, A. A., et al. (2020). Different single-photon response of wide and narrow superconducting MoxSi1−x strips. Phys. Rev. Applied, 13(2), 024011 (1 to 7).
Abstract: The photon count rate (PCR) of superconducting single-photon detectors made of MoxSi1−x films shaped as a 2-μm-wide strip and a 115-nm-wide meander strip line is studied experimentally as a function of the dc biasing current at different values of the perpendicular magnetic field. For the wide strip, a crossover current Icross is observed, below which the PCR increases with an increasing magnetic field and above which it decreases. This behavior contrasts with the narrow MoxSi1−x meander, for which no crossover current is observed, thus suggesting different photon-detection mechanisms in the wide and narrow strips. Namely, we argue that in the wide strip the absorbed photon destroys superconductivity locally via the vortex-antivortex mechanism for the emergence of resistance, while in the narrow meander superconductivity is destroyed across the whole strip line, forming a hot belt. Accordingly, the different photon-detection mechanisms associated with vortices and the hot belt determine the qualitative difference in the dependence of the PCR on the magnetic field.
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Смирнов, К. В., Вахтомин, Ю. Б., Смирнов, А. В., Ожегов, Р. В., Пентин, И. В., Дивочий, А. В., et al. (2010). Приемники терагерцового и инфракрасного диапазонов, основанные на тонкопленочных сверхпроводниковых наноструктурах. Вестник НГУ. Серия: Физика, 5(4).
Abstract: В работе представлены результаты разработки и создания чувствительных и ультрабыстрых приемников, основанных на тонкопленочных сверхпроводниковых наноструктурах: болометрах на эффекте электронного разогрева (HEB – hot-electron bolometer) и детекторах одиночных фотонов видимого и инфракрасного диапазонов волн (SSPD – superconducting singe-photon detector). Представлены основные принципы работы сверхпроводниковых устройств, технология создания и конструкционные особенности приемников, их основные типы и характеристики. Достигнутые рекордные значения параметров приемных систем позволяют использовать созданные приборы при решении различных научно-исследовательских задач в ближнем, среднем и дальнем ИК диапазонах волн.
This work presents the results of the development and fabrication of sensitive and ultrafast detectorsbased on thin film superconducting nanostructures: hot-electron bolometers (HEBs) and visible and infrared superconducting singe photon detectors (SSPDs). The main operational principles of the superconducting devices are presentedas well as the technology of fabrication of the detectors and their main types and parameters. The achieved record parameters of the detectors allow application of the fabricated devices to solution of various research problems in the near, middle and far IR ranges.
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Goltsman, G. (2009). Superconducting NbN hot-electron bolometer mixer, direct detector and single-photon counter: from devices to systems.
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Il'in, K. S., Gol'tsman, G. N., Voronov, B. M., & Sobolewski, R. (1999). Characterization of the electron energy relaxation process in NbN hot-electron devices. In Proc. 10th Int. Symp. Space Terahertz Technol. (pp. 390–397).
Abstract: We report on transient measurements of electron energy relaxation in NbN films with 300-fs time resolution. Using an electro-optic sampling technique, we have studied the photoresponse of 3.5-nm-thick NbN films deposited on sapphire substrates and exposed to 100-fs-wide optical pulses. Our experimental data analysis was based on the two-temperature model and has shown that in our films at the superconducting transition 10.5 K the inelastic electron-phonon scattering time was about (111}+-__.2) ps. This response time indicated that the maximum intermediate-frequency band of a NbN hot-electron phonon-cooled mixer should reach (16+41-3) GHz if one eliminates the bolometric phonon-heating effect. We have suggested several ways to increase the effectiveness of phonon cooling to achieve the above intrinsic value of the NbN mixer bandwidth.
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