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Amundsen, Morten; Linder, Jacob |
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General solution of 2D and 3D superconducting quasiclassical systems: coalescing vortices and nanodisk geometries |
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2015 |
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arXiv:1512.00030 [cond-mat.supr-con] |
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quasiclassical Usadel equation, finite elements method |
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In quasiclassical Keldysh theory, the Green function matrix g<cb><2021> is used to compute a variety of physical quantities in mesoscopic systems. However, solving the set of non-linear differential equations that provide g<cb><2021> becomes a challenging task when going to higher spatial dimensions than one. Such an extension is crucial in order to describe physical phenomena like charge/spin Hall effects and topological excitations like vortices and skyrmions, none of which can be captured in one-dimensional models. We here present a numerical finite element method which solves the 2D and 3D quasiclassical Usadel equation, without any linearisation, relevant for the diffusive regime. We show the application of this on two model systems with non-trivial geometries: (i) a bottlenecked Josephson junction with external flux and (ii) a nanodisk ferromagnet deposited on top of a superconductor. We demonstrate that it is possible to control externally not only the geometrical array in which superconducting vortices arrange themselves, but also to cause coalescence and thus tune the number of vortices. The finite element method presented herein could pave the way for gaining insight in physical phenomena which so far have remained largely unexplored due to the complexity of solving the full quasiclassical equations in higher dimensions. |
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1066 |
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Kurochkin, V. L.; Zverev, A. V.; Kurochkin, Y. V.; Ryabtsev, I. I.; Neizvestnyi, I. G.; Ozhegov, R. V.; Gol’tsman, G. N.; Larionov, P. A. |
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Long-distance fiber-optic quantum key distribution using superconducting detectors |
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Conference Article |
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2015 |
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Proc. Optoelectron. Instrum. |
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Proc. Optoelectron. Instrum. |
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51 |
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6 |
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548-552 |
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QKD, SSPD, SNSPD |
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This paper presents the results of experimental studies on quantum key distribution in optical fiber using superconducting detectors. Key generation was obtained on an experimental setup based on a self-compensation optical circuit with an optical fiber length of 101.1 km. It was first shown that photon polarization encoding can be used for quantum key distribution in optical fiber over a distance in excess of 300 km. |
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8756-6990 |
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1342 |
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Kahl, O.; Ferrari, S.; Kovalyuk, V.; Goltsman, G. N.; Korneev, A.; Pernice, W. H. P. |
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Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths |
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2015 |
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Sci. Rep. |
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Sci. Rep. |
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5 |
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10941 (1 to 11) |
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optical waveguides; waveguide integrated SSPD; waveguide SSPD; nanophotonics |
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Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present efficiencies close to unity at 1550nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noiseequivalent powers in the 10–19W/Hz–1/2 range and the timing jitter is as low as 35ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms. |
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PMID:26061283; PMCID:PMC4462017 |
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RPLAB @ kovalyuk @ |
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946 |
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Korneev, Alexander; Golt'sman, Gregory; Pernice, Wolfram |
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Photonic integration meets single-photon detection |
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2015 |
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Laser Focus World |
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Laser Focus World |
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51 |
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5 |
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47-50 |
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optical waveguide SSPD, SNSPD |
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By embedding superconducting nanowire single-photon detectors (SNSPDs) in nanophotonic circuits, these waveguide-integrated detectors are a key building block for future on-chip quantum computing applications. |
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RPLAB @ akorneev @ |
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1126 |
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Smirnov, K.; Vachtomin, Y.; Divochiy, A.; Antipov, A.; Goltsman, G. |
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The limitation of noise equivalent power by background radiation for infrared superconducting single photon detectors coupled to standard single mode optical fibers |
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2015 |
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Rus. J. Radio Electron. |
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Rus. J. Radio Electron. |
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5 |
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NbN SSPD |
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We investigated the minimum level of the dark count rates and noise equivalent power of superconducting single photon detectors coupled to standard single mode optical fibers. We found that background radiation limits the minimum level of the dark count rates. We also proposed the effective method for reducing background radiation out of the required spectral range of the detector. Measured noise equivalent power of detector reaches 8.9×10-19 W×Hz1/2 at a wavelength of 1.55 μm and quantum efficiency 35%. |
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14 pages |
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