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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Jukna, A., Kitaygorsky, J., Pan, D., Cross, A., Perlman, A., Komissarov, I., et al. (2008). Dynamics of hotspot formation in nanostructured superconducting stripes excited with single photons. Acta Physica Polonica A, 113(3), 955–958.
Abstract: Dynamics of a resistive hotspot formation by near-infrared-wavelength single photons in nanowire-type superconducting NbN stripes was investigated. Numerical simulations of ultrafast thermalization of photon-excited nonequilibrium quasiparticles, their multiplication and out-diffusion from a site of the photon absorption demonstrate that 1.55 μm wavelength photons create in an ultrathin, two-dimensional superconducting film a resistive hotspot with the diameter which depends on the photon energy, and the nanowire temperature and biasing conditions. Our hotspot model indicates that under the subcritical current bias of the 2D stripe, the electric field penetrates the superconductor at the hotspot boundary, leading to suppression of the stripe superconducting properties and accelerated development of a voltage transient across the stripe.
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Корнеев, А. А., Минаева, О., Рубцова, И., Милостная, И., Чулкова, Г., Воронов, Б., et al. (2005). Сверхпроводящий однофотонный детектор на основе ультратонкой пленки NbN. Квантовая электроника, 35(8), 698–700.
Abstract: Представлены результаты исследований сверхпроводящих однофотонных детекторов, изготовленных из ультратонкой пленки NbN. Развитие технологического процесса изготовления детекторов, а также снижение рабочей температуры до 2 К позволили существенно увеличить квантовую эффективность: для видимого света (λ = 0.56 мкм) она составила 30%–40%, т.е. достигла предела, определяемого коэффициентом поглощения пленки. С ростом длины волны квантовая эффективность экспоненциально падает, составляя ~20% на λ=1.55 мкм и ~0.02% на λ = 5 мкм. При скорости темнового счета ~10-4s-1 экспериментально измеренная эквивалентная мощность шума составила 1.5 × 10-20 Вт/Гц-1/2; в дальнейшем она может быть уменьшена до рекордно низкого значения 5 × 10-21 Вт/Гц-1/2. Временное разрешение детектора равно 30 пс.
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Korneev, A., Minaeva, O., Rubtsova, I., Milostnaya, I., Chulkova, G., Voronov, B., et al. (2005). Superconducting single-photon ultrathin NbN film detector. Quantum Electronics, 35(8), 698–700.
Abstract: Superconducting single-photon ultrathin NbN film detectors are studied. The development of manufacturing technology of detectors and the reduction of their operating temperature down to 2 K resulted in a considerable increase in their quantum efficiency, which reached in the visible region (at 0.56 μm) 30%—40%, i.e., achieved the limit determined by the absorption coefficient of the film. The quantum efficiency exponentially decreases with increasing wavelength, being equal to ~20% at 1.55 μm and ~0.02% at 5 μm. For the dark count rate of ~10-4s-1, the experimental equivalent noise power was 1.5×10-20 W Hz-1/2; it can be decreased in the future down to the record low value of 5×10-21 W Hz-1/2. The time resolution of the detector is 30 ps.
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Pearlman, A., Cross, A., Slysz, W., Zhang, J., Verevkin, A., Currie, M., et al. (2005). Gigahertz counting rates of NbN single-photon detectors for quantum communications. IEEE Trans. Appl. Supercond., 15(2), 579–582.
Abstract: We report on the GHz counting rate and jitter of our nanostructured superconducting single-photon detectors (SSPDs). The devices were patterned in 4-nm-thick and about 100-nm-wide NbN meander stripes and covered a 10-/spl mu/m/spl times/10-/spl mu/m area. We were able to count single photons at both the visible and infrared telecommunication wavelengths at rates of over 2 GHz with a timing jitter of below 18 ps. We also present the model for the origin of the SSPD switching dynamics and jitter, based on the time-delay effect in the phase-slip-center formation mechanism during the detector photoresponse process. With further improvements in our readout electronics, we expect that our SSPDs will reach counting rates of up to 10 GHz. An integrated quantum communications receiver based on two fiber-coupled SSPDs and operating at 1550-nm wavelength is also presented.
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