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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Schuck, C., Pernice, W. H. P., Minaeva, O., Li, M., Gol'tsman, G., Sergienko, A. V., et al. (2013). Matrix of integrated superconducting single-photon detectors with high timing resolution. IEEE Trans. Appl. Supercond., 23(3), 2201007.
Abstract: We demonstrate a large grid of individually addressable superconducting single photon detectors on a single chip. Each detector element is fully integrated into an independent waveguide circuit with custom functionality at telecom wavelengths. High device density is achieved by fabricating the nanowire detectors in traveling wave geometry directly on top of silicon-on-insulator waveguides. Our superconducting single photon detector matrix includes detector designs optimized for high detection efficiency, low dark count rate, and high timing accuracy. As an example, we exploit the high timing resolution of a particularly short nanowire design to resolve individual photon round-trips in a cavity ring-down measurement of a silicon ring resonator.
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Gol’tsman, G., Okunev, O., Chulkova, G., Lipatov, A., Dzardanov, A., Smirnov, K., et al. (2001). Fabrication and properties of an ultrafast NbN hot-electron single-photon detector. IEEE Trans. Appl. Supercond., 11(1), 574–577.
Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film’s supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.
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Murphy, A., Semenov, A., Korneev, A., Korneeva, Y., Gol'tsman, G., & Bezryadin, A. (2015). Three temperature regimes in superconducting photon detectors: quantum, thermal and multiple phase-slips as generators of dark counts. Sci. Rep., 5, 10174 (1 to 10).
Abstract: We perform measurements of the switching current distributions of three w approximately 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijarvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.
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Korneev, A. A., Korneeva, Y. P., Mikhailov, M. Y., Pershin, Y. P., Semenov, A. V., Vodolazov, D. Y., et al. (2015). Characterization of MoSi superconducting single-photon detectors in the magnetic field. IEEE Trans. Appl. Supercond., 25(3), 2200504 (1 to 4).
Abstract: We investigate the response mechanism of nanowire superconducting single-photon detectors (SSPDs) made of amorphous MoxSi1-x. We study the dependence of photon count and dark count rates on bias current in magnetic fields up to 113 mT at 1.7 K temperature. The observed behavior of photon counts is similar to the one recently observed in NbN SSPDs. Our results show that the detecting mechanism of relatively high-energy photons does not involve the vortex penetration from the edges of the film, and on the contrary, the detecting mechanism of low-energy photons probably involves the vortex penetration from the film edges.
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