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Ovchinnikov YN, Varlamov AA. Fluctuation-dissipative phenomena in a narrow superconducting channel carrying current below critical. arXiv. 2009;0910.2659v1:1–4.
Abstract: The theory of current transport in a narrow superconducting channel accounting for thermal fluctuations is developed. These fluctuations result in the appearance of small but finite dissipation in the sample. The value of corresponding voltage is found as the function of temperature (close to transition temperature) and arbitrary bias current. It is demonstrated that the value of the activation energy (exponential factor in the Arrenius law) when current approaches to the critical one is proportional to (1-J/Jc)^(5/4). This result is in concordance with the one for the affine phenomenon of the Josephson current decay due to the thermal phase fluctuations, where the activation energy proportional (1-J/J_c)^(3/2)(the difference in the exponents is related to the additional current dependence of the order parameter). Found dependence of the activation energy on current explains the enormous discrepancy between the theoretically predicted before and the experimentally observed broadening of the resistive transition.
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Stucki D, Walenta N, Vannel F, Thew RT, Gisin N, Zbinden H, et al. High rate long-distance quantum key distribution over 250 km of ultra low loss fibres. New J. Phys.. 2009;11(7):075003.
Abstract: We present a fully automated quantum key distribution prototype running at 625 MHz clock rate. Taking advantage of ultra low loss fibres and low-noise superconducting detectors, we can distribute 6,000 secret bits per second over 100 km and 15 bits per second over 250km.
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Minaeva O, Divochiy A, Korneev A, Sergienko AV, Goltsman GN. High speed infrared photon counting with photon number resolving superconducting single-photon detectors (SSPDs). In: CLEO/Europe – EQEC.; 2009.
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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Driessen EFC, Braakman FR, Reiger EM, Dorenbos SN, Zwiller V, de Dood MJA. Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors. Eur. Phys. J. Appl. Phys.. 2009;47:10701.
Abstract: We measured the single-photon detection efficiency of NbN superconducting single-photon detectors as a function of the polarization state of the incident light for different wavelengths in the range from 488 nm to 1550 nm. The polarization contrast varies from ~% at 488 nm to~0% at 1550 nm, in good agreement with numerical calculations. We use an optical-impedance model to describe the absorption for polarization parallel to the wires of the detector. For the extremely lossy NbN material, the absorption can be kept constant by keeping the product of layer thickness and filling factor constant. As a consequence, the maximum possible absorption is independent of filling factor. By illuminating the detector through the substrate, an absorption efficiency of ~0% can be reached for a detector on Si or GaAs, without the need for an optical cavity.
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Sahu M, Bae M-H, Rogachev A, Pekker D, Wei T-C, Shah N, et al. Individual topological tunnelling events of a quantum field probed through their macroscopic consequences. Nature Phys. 2009;5:503–8.
Abstract: Phase slips are topological fluctuations that carry the superconducting order-parameter field between distinct current-carrying states. Owing to these phase slips, superconducting nanowires acquire electrical resistance. In such wires, it is well known that at higher temperatures phase slips occur through the process of thermal barrier-crossing by the order-parameter field. At low temperatures, the general expectation is that phase slips should proceed through quantum tunnelling events, which are known as quantum phase slips. However, resistive measurements have produced evidence both for and against the occurrence of quantum phase slips. Here, we report evidence for the observation of individual quantum phase-slip events in homogeneous ultranarrow wires at high bias currents. We accomplish this through measurements of the distribution of switching currents for which the width exhibits a rather counter-intuitive, monotonic increase with decreasing temperature. Importantly, measurements show that in nanowires with larger critical currents, quantum fluctuations dominate thermal fluctuations up to higher temperatures.
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Sekine N, Hosako I. Intensity modulation of terahertz quantum cascade lasers under external light injection. Appl Phys Lett. 2009;95:201106(1–3).
Abstract: We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation.
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Ryabchun SA, Tretyakov IV, Pentin IV, Kaurova NS, Seleznev VA, Voronov BM, et al. Low-noise wide-band hot-electron bolometer mixer based on an NbN film. Radiophys. Quant. Electron.. 2009;52(8):576–82.
Abstract: We develop and study a hot-electron bolometer mixer made of a two-layer NbN–Au film in situ deposited on a silicon substrate. The double-sideband noise temperature of the mixer is 750 K at a frequency of 2.5 THz. The conversion efficiency measurements show that at the superconducting transition temperature, the intermediate-frequency bandwidth amounts to about 6.5 GHz for a mixer 0.112 μm long. These record-breaking characteristics are attributed to the improved contacts between a sensitive element and a helical antenna and are reached due to using the in situ deposition of NbN and Au layers at certain stages of the process.
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Baryshev AM, Wild W, Likhachev SF, Vdovin VF, Goltsman GN, Kardashev NS. Main parameters and instrumentation of Millimetron space mission [abstract]. In: Proc. 20th Int. Symp. Space Terahertz Technol.; 2009. 108.
Abstract: Millimetron (official RosKosmos name ”Spectrum-M”) is a part of ambitious program called Spectrum intended to cover the whole electromagnetic spectrum with world class facilities. It is an approved mission included in Russian space program with the launch date in 2017..2019 time frame. The Millimetron satellite has a deployable 12 m diameter antenna with inner solid 4..6 m dish and a rim of petals. The mirror design is largely based on Radioastron mission concept that will be launched in 2009. If the antenna is passively cooled by radiation to open space, it would operate at approx. 50 K surface temperature, due to presence of a deployable three layer radiation screen. As a goal, there is a consideration of active cooling of antenna to 4 K, but this will depend on resources available to the project. Lagrangian libration point L2 considered for Millimetron orbit. There are four groups of scientific instruments envisioned: SVLBI instruments Space-Earth VLBI. It will allow to achieve unprecedented spatial resolution. Millimetron mission will attempt to achieve a mm/submm wave SVLBI. For that purpose, a SVLBI instrument covering selected ALMA bands and a standard VLBI band is envisioned, accompanied by a maser reference oscillator, a data digitizing and memory system, and a high speed data transmission link to ground. The ALMA bands can be extended to cover water lines if detector technology allows. Type of detector – heterodyne. Photometer/polarimeter. Recent progress in direct detector cameras with low spectral resolution, allows to propose a large format (5-10 kPixel) photometer camera on board of Millimetron mission. This camera can cover 0.1 – 2 THz region (with adequate amount of pixels per each subband). Wide band moderate resolution imaging spectrometer. Wide band moderate R = 1000 imaging spectrometer type instrument similar to SPICA SAFARI is planned, taking advantage of large cooled dish. It will cover the adequate spectral range allowable by antenna and will also work below 1 THz, as no ground instrument can have a cold main dish. High resolution spectrometer. For high resolution spectroscopy a heterodyne instrument is proposed, conceptually similar to HIFI on Herschel. This instrument will cover interesting frequency spots in 0.5..4 THz frequency range (using central part of antenna for higher frequency). It is sure that advances in LO and mixer technology will allow this frequency coverage.
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Gol'tsman BM, Kutasov VA, Luk'yanova LN. Mechanism of formation of texture and its influence on the strength of thermoelectric p-Bi0.5Sb1.5Te3. Phys Sol St. 2009;51(4):747–9.
Abstract: It is established that, in preparing p-Bi0.5Sb1.5Te3 by vertical zone melting, in addition to the directional texture (characteristic of materials exhibiting a highly anisotropic growth rate) in which the cleavage planes of crystal grains are parallel to the direction of propagation of the crystallization front, other texture types can arise, in which the orientation of grain cleavage planes is ordered in a cross-sectional plane of the ingot. Two types of such textures, “radial†and “circular,†were observed. In a radial texture, the lines of intersection of grain cleavage planes with a cross-sectional plane of the ingot are oriented along radii of this cross section and, in a circular texture, these lines of intersection are oriented approximately perpendicular to a radius crossing the grain. The formation of a radial texture is associated with rotation of the ampoule with the crystallizing substance about its vertical axis causing centrifugal flows of the melt. The formation of a circular texture is associated with the orientation effect of the ampoule walls and with circular motion of the melt during torsional oscillations of the ampoule about the vertical axis. Ingots with a radial texture exhibit much lower resistance to splitting along their axis than ingots with a circular texture do. An explanation is provided for this fact.
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Wild W, Kardashev NS, Likhachev SF, Babakin NG, Arkhipov VY, Vinogradov IS, et al. Millimetron—a large Russian-European submillimeter space observatory. Exp Astron. 2009;23(1):221–44.
Abstract: Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution.
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