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Sáysz, W., Guziewicz, M., Bar, J., Wegrzecki, M., Grabiec, P., Grodecki, R., et al. (2008). Superconducting NbN nanostructures for single photon quantum detectors. In Proc. 7-th Int. Conf. Ion Implantation and Other Applications of Ions and Electrons (160).
Abstract: Practical quantum systems such as quantum communication (QC) or quantum measurement systems require detectors with high speed, high sensitivity, high quantum efficiency (QE), and short deadtimes along with precise timing characteristics and low dark counts. Superconducting single photon detectors (SSPDs) based on ultrathin meander type NbN nanostripes (operated at T=2-5K) are a new and highly promising type of devices fulfilling above requirements. In this paper we present results of the SSPDs nanostructure technological optimization. The base for our detector is thin-film (4nm) NbN layer deposited on 350- P m-thick sapphire substrate The active element of the detector is a meander- nanostructure made of 4-nm-thick and 100-nm-wide NbN stripe, covering 10 u 10 P m 2 area with the filling factor ~0,5. The NbN superconducting films were deposited on sapphire substrates by DC reactive magnetron sputtering whereas the meander element of the detector was patterned by the direct electron-beam lithography followed by reactive-ion etching. To enhance the SSPD efficiency at Ȝ = 1.55 P m, we have performed an approach to increase the absorption of the detector by integrating it with optical resonant cavity. An optical microcavity optimized for absorption of 1.55 P m photons was designed as an one-mirror resonator consisting of a Ȝ/4 dielectric layer and a metallic mirror. The microcavity was deposited on the top of the NbN SSPD meander. The resonator was formed by the dielectric SiO 2 layer and metal mirror made of gold or palladium. Microcavity layers were deposited using a magnetron sputtering system.
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Jukna, A., Kitaygorsky, J., Pan, D., Cross, A., Perlman, A., Komissarov, I., et al. (2008). Dynamics of hotspot formation in nanostructured superconducting stripes excited with single photons. Acta Physica Polonica A, 113(3), 955–958.
Abstract: Dynamics of a resistive hotspot formation by near-infrared-wavelength single photons in nanowire-type superconducting NbN stripes was investigated. Numerical simulations of ultrafast thermalization of photon-excited nonequilibrium quasiparticles, their multiplication and out-diffusion from a site of the photon absorption demonstrate that 1.55 μm wavelength photons create in an ultrathin, two-dimensional superconducting film a resistive hotspot with the diameter which depends on the photon energy, and the nanowire temperature and biasing conditions. Our hotspot model indicates that under the subcritical current bias of the 2D stripe, the electric field penetrates the superconductor at the hotspot boundary, leading to suppression of the stripe superconducting properties and accelerated development of a voltage transient across the stripe.
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Dauler, E. A., Robinson, B. S., Kerman, A. J., Yang, J. K. W., Rosfjord, E. K. M., Anant, V., et al. (2007). Multi-element superconducting nanowire single-photon detector. IEEE Trans. Appl. Supercond., 17(2), 279–284.
Abstract: A multi-element superconducting nanowire single photon detector (MESNSPD) is presented that consists of multiple independently-biased superconducting nanowire single photon detector (SNSPD) elements that form a continuous active area. A two-element SNSPD has been fabricated and tested, showing no measurable crosstalk between the elements, sub-50-ps relative timing jitter, and four times the maximum counting rate of a single SNSPD with the same active area. The MESNSPD can have a larger active area and higher speed than a single-element SNSPD and the input optics can be designed so that the detector provides spatial, spectral or photon number resolution.
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Zinoni, C., Alloing, B., Li, L. H., Marsili, F., Fiore, A., Lunghi, L., et al. (2007). Single-photonics at telecom wavelengths using nanowire superconducting single photon detectors. In CLEO/QELS (QTuF6 (1 to 2)). Optical Society of America.
Abstract: Novel single-photon detectors based on NbN superconducting nanostructures promise orders-of- magnitude improvement over InGaAs APDs. We demonstrate this improved performance for the first time by measuring the g(2)(τ) on single photon states produced by a quantum dot at telecom wavelength.
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Kerman, A. J., Dauler, E. A., Yang, J. K. W., Rosfjord, K. M., Anant, V., Berggren, K. K., et al. (2007). Constriction-limited detection efficiency of superconducting nanowire single-photon detectors. Appl. Phys. Lett., 90(10), 101110 (1 to 3).
Abstract: We investigate the source of the large variations in the observed detection efficiencies of superconducting nanowire single-photon detectors between many nominally identical devices. Through both electrical and optical measurements, we infer that these variations arise from “constrictions:” highly localized regions of the nanowires where the effective cross-sectional area for superconducting current is reduced. These constrictions limit the bias-current density to well below its critical value over the remainder of the wire, and thus prevent the detection efficiency from reaching the high values that occur in these devices when they are biased near the critical current density.
This work is sponsored by the United States Air Force under Contract No. FA8721-05-C-0002.
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