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Deang, Jennifer; Du, Qiang; Gunzburger, Max D. |
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Modeling and computation of random thermal fluctuations and material defects in the Ginzburg–Landau model for superconductivity |
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2002 |
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J. Comp. Phys. |
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181 |
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1 |
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45-67 |
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noise; superconductivity; finite element methods; fluctuations. |
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It is well known that thermal fluctuations and material impurities affect the motion of vortices in superconductors. These effects are modeled by variants of a time-dependent Ginzburg-Landau model containing either additive or multiplicative noise. Numerical computations are presented that illustrate the effects that noise has on the dynamics of vortex nucleation and vortex motion. For an additive noise model with relatively low variances, it is found that the vortices form a quasi-steady-state lattice in which the vortex core sizes remain roughly fixed but their positions vibrate. Two multiplicative noise models are considered. For one model having relatively long-range order, the sizes of the vortex cores vary in time and from one vortex to another. Finally, for the additive noise case, we show that as the variance of the noise tends to zero, solutions of the stochastic time-dependent Ginzburg-Landau equations converge to solutions of the corresponding equations with no noise. |
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RPLAB @ gujma @ |
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758 |
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Marsili, F.; Bitauld, D.; Fiore, A.; Gaggero, A.; Leoni, R.; Mattioli, F.; Divochiy, A.; Korneev, A.; Seleznev, V.; Kaurova, N.; Minaeva, O.; Goltsman, G. |
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Superconducting parallel nanowire detector with photon number resolving functionality |
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2009 |
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J. Modern Opt. |
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J. Modern Opt. |
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56 |
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2-3 |
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334-344 |
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PNR; SSPD; SNSPD; thin superconducting films; photon number resolving detector; multiplication noise; telecom wavelength; NbN |
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We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm-wide, few nm-thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3-4 nm thick NbN films grown on sapphire (substrate temperature TS=900C) or MgO (TS=400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one photon quantum efficiency can be estimated to be QE=3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise. |
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0950-0340 |
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701 |
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Kroug, M.; Cherednichenko, S.; Choumas, M.; Merkel, H.; Kollberg, E.; Hübers, H.-W.; Richter, H.; Loudkov, D.; Voronov, B.; Gol'Tsman, G. |
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HEB quasi-optical heterodyne receiver for THz frequencies |
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2001 |
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Proc. 12th Int. Symp. Space Terahertz Technol. |
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244-252 |
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HEB mixer, NbN, MgO, conversion gain bandwidth, noise temperature |
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San Diego, CA, USA |
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319 |
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Ryabchun, S. A.; Tretyakov, I. V.; Finkel, M. I.; Maslennikov, S. N.; Kaurova, N. S.; Seleznev, V. A.; Voronov, B. M.; Gol'tsman, G. N. |
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NbN phonon-cooled hot-electron bolometer mixer with additional diffusion cooling |
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2009 |
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Proc. 20th Int. Symp. Space Terahertz Technol. |
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Proc. 20th ISSTT |
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151-154 |
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HEB, mixer, bandwidth, noise temperatue, in-situ contacts, in situ contacts |
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Charlottesville, USA |
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590 |
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Karpov, A.; Miller, D.; Stern, J. A.; Bumble, B.; LeDuc, H. G.; Zmuidzinas, J. |
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Broadband SIS mixer for 1 THz Band |
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Conference Article |
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2009 |
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Proc. 20th Int. Symp. Space Terahertz Technol. |
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35-35 |
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SIS mixer, noise temperature |
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We report the development of a low noise and broadband SIS mixer aimed for 1 THz channel of the Caltech Airborne Submillimeter Interstellar Medium Investigations Receiver (CASIMIR), designed for the Stratospheric Observatory for Far Infrared Astronomy, (SOFIA). The mixer uses an array of 0.24 µm² Nb/Al-AlN/NbTiN SIS junctions with critical current density of 30-50 KA/cm². The junctions are shaped in order to optimize the suppression of the Josephson DC currents. We are using a double slot planar antenna to couple the mixer chip with the telescope beam. The RF matching microcircuit is made using Nb and gold films. The mixer IF circuit is designed to cover 4 – 8 GHz band. A test receiver with the new mixer has a low noise operation in a 0.87 – 1.12 THz band. The minimum DSB receiver noise measured at 1 THz is 260 K (Y=1.64), apparently the lowest reported up to date. The receiver noise corrected for the loss in the LO injection beam splitter and in the cryostat window is 200 K. The combination of a broad operation band of about 250 GHz with a low receiver noise is making the new mixer a useful element for application at SOFIA. We will discuss the prospective of a further improvement of the sensitivity and extension of the upper frequency of operation of SIS mixer. |
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