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Nebosis, R. S., Heusinger, M. A., Schatz, W., Renk, K. F., Gol’tsman, G. N., Karasik, B. S., et al. (1993). Ultrafast photoresponse of a structured YBa2Cu3O7-δ thin film to ultrashort FIR laser pulses. IEEE Trans. Appl. Supercond., 3(1), 2160–2162.
Abstract: The authors have investigated the photoinduced voltage response of a current-carrying structured YBa2Cu3O7-δ thin film to ultrashort far-infrared (FIR) laser pulses in the frequency range from 0.7 THz to 7 THz. The detector has shown an almost constant sensitivity of 1 mV/W and a noise equivalent power of less than 5*10/sup -7/ W/ square root Hz. The temperature dependence of the decay time of the detector signal was studied for temperatures around the transition temperature of the film ( approximately 80 K). For a detector temperature where dR/dT had its maximum, the authors observed bolometric signals with decay times of about 2 ns, and for lower temperatures they observed nonbolometric signals with decay times of approximately 120 ps; the duration of the nonbolometric signals was limited by the time resolution of the electronic registration equipment.
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Gol’tsman, G., Okunev, O., Chulkova, G., Lipatov, A., Dzardanov, A., Smirnov, K., et al. (2001). Fabrication and properties of an ultrafast NbN hot-electron single-photon detector. IEEE Trans. Appl. Supercond., 11(1), 574–577.
Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film’s supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.
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Kawamura, J., Tong, C. - Y. E., Blundell, R., Papa, D. C., Hunter, T. R., Patt, F., et al. (2001). Terahertz-frequency waveguide NbN hot-electron bolometer mixer. IEEE Trans. Appl. Supercond., 11(1), 952–954.
Abstract: We have developed a low-noise waveguide heterodyne receiver for operation near 1 THz using phonon-cooled NbN hot-electron bolometers. The mixer elements are submicron-sized microbridges of 4 nm-thick NbN film fabricated on a quartz substrate. Operating at a bath temperature of 4.2 K, the double-sideband receiver noise temperature is 760 K at 1.02 THz and 1100 K at 1.26 THz. The local oscillator is provided by solid-state sources, and power measured at the source is less than 1 /spl mu/W. The intermediate frequency bandwidth exceeds 2 GHz. The receiver was used to make the first ground-based heterodyne detection of a celestial spectroscopic line above 1 THz.
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Chulkova, G., Milostnaya, I., Korneev, A., Minaeva, O., Rubtsova, I., Voronov, B., et al. (2005). Superconducting nanostructures for counting of single photons in the infrared range. In Proc. 2-nd CAOL (Vol. 2, pp. 100–103).
Abstract: We present our studies on ultrafast superconducting single-photon detectors (SSPDs) based on ultrathin NbN nanostructures. Our SSPDs are patterned by electron beam lithography from 4-nm thick NbN film into meander-shaped strips covering square area of 10/spl times/10 /spl mu/m/sup 2/. The advances in the fabrication technology allowed us to produce highly uniform 100-120-nm-wide strips with meander filling factor close to 0.6. The detectors exploit a combined detection mechanism, where upon a single-photon absorption, an avalanche of excited hot electrons and the biasing supercurrent, jointly produce a picosecond voltage transient response across the superconducting nanostrip. The SSPDs are typically operated at 4.2 K, but they have shown that their sensitivity in the infrared radiation range can be significantly improved by lowering the operating temperature from 4.2 K to 2 K. When operated at 2 K, the SSPD quantum efficiency (QE) for visible light photons reaches 30-40%, which is the saturation value limited by optical absorption of our 4-nm-thick NbN film. For 1.55 /spl mu/m photons, QE was /spl sim/20% and decreases exponentially with the increase of the optical wavelength, but even at the wavelength of 6 /spl mu/m the detector remains sensitive to single photons and exhibits QE of about 10/sup -2/%. The dark (false) count rate at 2 K is as low as 2 /spl times/ 10/sup -4/ s/sup -1/, what makes our detector essentially a background-limited sensor. The very low dark-count rate results in the noise equivalent power (NEP) as low as 10/sup -18/ WHz/sup -1/2/ for the mid-infrared range (6 /spl mu/m). Further improvement of the SSPD performance in the mid-infrared range can be obtained by substituting NbN for the other, lower-T/sub c/ superconductors with the narrow superconducting gap and low quasiparticle diffusivity. The use of such materials will shift the cutoff wavelength towards the values even longer than 6 /spl mu/m.
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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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Xu, Y., Zheng, X., Williams, C., Verevkin, A., Sobolewski, R., Chulkova, G., et al. (2001). Ultrafast superconducting hot-electron single-photon detector. In CLEO (345).
Abstract: Summary form only given. The current most-pressing need is to develop a practical, GHz-range counting single-photon detector, operational at either 1.3-/spl mu/m or 1.55-/spl mu/m radiation wavelength, for novel quantum communication and quantum cryptography systems. The presented solution of the problem is to use an ultrafast hot-electron photodetector, based on superconducting thin-film microstructures. This type of device is very promising, due to the macroscopic quantum nature of superconductors. Very fast response time and the small, (meV range) value of the superconducting energy gap characterize the superconductor, leading to the efficient avalanche process even for infrared photons.
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Rosfjord, K. M., Yang, J. K. W., Dauler, E. A., Anant, V., Berggren, K. K., Kerman, A. J., et al. (2006). Increased detection efficiencies of nanowire single-photon detectors by integration of an optical cavity and anti-reflection coating. In CLEO/QELS (JTuF2 (1 to 2)).
Abstract: We fabricate and test superconducting NbN-nanowire single-photon detectors with an integrated optical cavity and anti-reflection coating. We design the cavity and coating such as to maximize absorption in the NbN film of the detector.
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Minaeva, O., Divochiy, A., Korneev, A., Sergienko, A. V., & Goltsman, G. N. (2009). High speed infrared photon counting with photon number resolving superconducting single-photon detectors (SSPDs). In CLEO/Europe – EQEC.
Abstract: A review of development and characterization of the nanostructures consisting of several meander sections, all connected in parallel was presented. Such geometry leads to a significant decrease of the kinetic inductance, without a decrease of the SSPD active area. A new type of SSPDs possess the QE of large-active- area devices, but, simultaneously, allows achieving short response times and the GHz-counting rate. This new generation of superconducting detectors has another significant advantage for quantum key distribution, they have a photon number resolving capability and can distinguish more photons.
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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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Svechnikov, S. I., Finkel, M. I., Maslennikov, S. N., Vachtomin, Y. B., Smirnov, K. V., Seleznev, V. A., et al. (2006). Superconducting hot electron bolometer mixer for middle IR range. In Proc. 16th Int. Crimean Microwave and Telecommunication Technology (Vol. 2, pp. 686–687).
Abstract: The developed directly lens coupled hot electron bolometer (HEB) mixer was based on 5 nm superconducting NbN deposited on GaAs substrate. The layout of the structure, including 30x20 mcm^2 active area coupled with a 50 Ohm coplanar line, was patterned by photolithography. The responsivity of the mixer was measured in a direct detection mode in the 25-64 THz frequency range. The noise performance of the mixer and the directivity of the receiver were investigated in a heterodyne mode. A 10.6 mum wavelength CW CO2 laser was utilized as a local oscillator.
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