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Author Miller, Aaron J.; Lita, Adriana E.; Calkins, Brice; Vayshenker, Igor; Gruber, Steven M.; Nam, Sae Woo openurl 
  Title Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent Type Journal Article
  Year 2011 Publication Optics Express Abbreviated Journal (up) Opt. Express  
  Volume 19 Issue 10 Pages 9102-9110  
  Keywords TES  
  Abstract We present a compact packaging technique for coupling light from a single-mode telecommunication fiber to cryogenic single-photon sensitive devices. Our single-photon detectors are superconducting transition-edge sensors (TESs) with a collection area only a factor of a few larger than the area of the fiber core which presents significant challenges to low-loss fiber-to-detector coupling. The coupling method presented here has low loss, cryogenic compatibility, easy and reproducible assembly and low component cost. The system efficiency of the packaged single-photon counting detectors is verified by the “triplet method” of power-source calibration along with the “multiple attenuator” method that produces a calibrated single-photon flux. These calibration techniques, when used in combination with through-wafer imaging and fiber back-reflection measurements, give us confidence that we have achieved coupling losses below 1 % for all devices packaged according to the self-alignment method presented in this paper.  
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  Call Number RPLAB @ gujma @ Serial 666  
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Author Huang, Kevin C. Y.; Jun, Young Chul; Seo, Min-Kyo; Brongersma, Mark L. openurl 
  Title Power flow from a dipole emitter near an optical antenna Type Journal Article
  Year 2011 Publication Optics Express Abbreviated Journal (up) Opt. Express  
  Volume 19 Issue 20 Pages 19084-19092  
  Keywords optical antennas  
  Abstract Current methods to calculate the emission enhancement of a quantum emitter coupled to an optical antenna of arbitrary geometry rely on analyzing the total Poynting vector power flow out of the emitter or the dyadic Green functions from full-field numerical simulations. Unfortunately, these methods do not provide information regarding the nature of the dominant energy decay pathways. We present a new approach that allows for a rigorous separation, quantification, and visualization of the emitter output power flow captured by an antenna and the subsequent reradiation power flow to the far field. Such analysis reveals unprecedented details of the emitter/antenna coupling mechanisms and thus opens up new design strategies for strongly interacting emitter/antenna systems used in sensing, active plasmonics and metamaterials, and quantum optics.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 743  
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Author Hu, Xiaolong; Dauler, Eric A.; Molnar, Richard J.; Berggren, Karl K. openurl 
  Title Superconducting nanowire single-photon detectors integrated with optical nano-antennae Type Journal Article
  Year 2011 Publication Optics Express Abbreviated Journal (up) Opt. Express  
  Volume 19 Issue 1 Pages 17-31  
  Keywords optical antennas  
  Abstract Optical nano-antennae have been integrated with semiconductor lasers to intensify light at the nanoscale and photodiodes to enhance photocurrent. In quantum optics, plasmonic metal structures have been used to enhance nonclassical light emission from single quantum dots. Absorption and detection of single photons from free space could also be enhanced by nanometallic antennae, but this has not previously been demonstrated. Here, we use nano-optical transmission effects in a one-dimensional gold structure, combined with optical cavity resonance, to form optical nano-antennae, which are further used to couple single photons from free space into a 80-nm-wide superconducting nanowire. This antenna-assisted coupling enables a superconducting nanowire single-photon detector with 47% device efficiency at the wavelength of 1550 nm and 9-μm-by-9-μm active area while maintaining a reset time of only 5 ns. We demonstrate nanoscale antenna-like structures to achieve exceptional efficiency and speed in single-photon detection.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 745  
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Author Bulaevskii, L. N.; Graf, M. J.; Batista, C. D.; Kogan, V. G. openurl 
  Title Vortex-induced dissipation in narrow current-biased thin-film superconducting strips Type Journal Article
  Year 2011 Publication Phys. Rev. B Abbreviated Journal (up) Phys. Rev. B  
  Volume 83 Issue 14 Pages 9  
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  Abstract A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness d on the order of the coherence length ξ and of width w much narrower than the Pearl length Λâ‰<ab>wâ‰<ab>ξ. At high bias currents I*<I<Ic the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here Ic is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate I* to be roughly Ic/3. Furthermore, we argue that such “hot” vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between I* and Ic. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below I*, that is, in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing.  
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  Notes SSPD Approved no  
  Call Number RPLAB @ gujma @ Serial 688  
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Author Beck, M.; Klammer, M.; Lang, S.; Leiderer, P.; Kabanov, V. V.; Gol'tsman, G. N.; Demsar, J. doi  openurl
  Title Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy Type Journal Article
  Year 2011 Publication Phys. Rev. Lett. Abbreviated Journal (up) Phys. Rev. Lett.  
  Volume 107 Issue 17 Pages 4  
  Keywords NbN thin film, energy gap dynamics  
  Abstract Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, λ=1.1±0.1, which is in excellent agreement with theoretical estimates.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 641  
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