Elezov, M. S., Semenov, A. V., An, P. P., Tarkhov, M. A., Goltsman, G. N., Kardakova, A. I., et al. (2013). Investigating the detection regimes of a superconducting single-photon detector. J. Opt. Technol., 80(7), 435.
Abstract: The detection regimes of a superconducting single-photon detector have been investigated. A technique is proposed for determining the regions in which “pure regimes” predominate. Based on experimental data, the dependences of the internal quantum efficiency on the bias current are determined in the one-, two-, and three-photon detection regimes.
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Kovalyuk, V., Hartmann, W., Kahl, O., Kaurova, N., Korneev, A., Goltsman, G., et al. (2013). Absorption engineering of NbN nanowires deposited on silicon nitride nanophotonic circuits. Opt. Express, 21(19), 22683–22692.
Abstract: We investigate the absorption properties of U-shaped niobium nitride (NbN) nanowires atop nanophotonic circuits. Nanowires as narrow as 20nm are realized in direct contact with Si3N4 waveguides and their absorption properties are extracted through balanced measurements. We perform a full characterization of the absorption coefficient in dependence of length, width and separation of the fabricated nanowires, as well as for waveguides with different cross-section and etch depth. Our results show excellent agreement with finite-element analysis simulations for all considered parameters. The experimental data thus allows for optimizing absorption properties of emerging single-photon detectors co-integrated with telecom wavelength optical circuits.
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Peltonen, J. T., Astafiev, O. V., Korneeva, Y. P., Voronov, B. M., Korneev, A. A., Charaev, I. M., et al. (2013). Coherent flux tunneling through NbN nanowires. Phys. Rev. B, 88(22), 220506 (1 to 5).
Abstract: We demonstrate evidence of coherent magnetic flux tunneling through superconducting nanowires patterned in a thin highly disordered NbN film. The phenomenon is revealed as a superposition of flux states in a fully metallic superconducting loop with the nanowire acting as an effective tunnel barrier for the magnetic flux, and reproducibly observed in different wires. The flux superposition achieved in the fully metallic NbN rings proves the universality of the phenomenon previously reported for InOx. We perform microwave spectroscopy and study the tunneling amplitude as a function of the wire width, compare the experimental results with theories, and estimate the parameters for existing theoretical models.
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