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Author Kahl, O.; Ferrari, S.; Kovalyuk, V.; Vetter, A.; Lewes-Malandrakis, G.; Nebel, C.; Korneev, A.; Goltsman, G.; Pernice, W. url  openurl
  Title Spectrally resolved single-photon imaging with hybrid superconducting – nanophotonic circuits Type Miscellaneous
  Year 2016 Publication (up) arXiv Abbreviated Journal arXiv  
  Volume Issue Pages 1-20  
  Keywords waiveguide SSPD, SNSPD, imaging  
  Abstract The detection of individual photons is an inherently binary mechanism, revealing either their absence or presence while concealing their spectral information. For multi-color imaging techniques, such as single photon spectroscopy, fluorescence resonance energy transfer microscopy and fluorescence correlation spectroscopy, wavelength discrimination is essential and mandates spectral separation prior to detection. Here, we adopt an approach borrowed from quantum photonic integration to realize a compact and scalable waveguide-integrated single-photon spectrometer capable of parallel detection on multiple wavelength channels, with temporal resolution below 50 ps and dark count rates below 10 Hz. We demonstrate multi-detector devices for telecommunication and visible wavelengths and showcase their performance by imaging silicon vacancy color centers in diamond nanoclusters. The fully integrated hybrid superconducting-nanophotonic circuits enable simultaneous spectroscopy and lifetime mapping for correlative imaging and provide the ingredients for quantum wavelength division multiplexing on a chip.  
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  Notes Approved no  
  Call Number Serial 1334  
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Author Arutyunov, K. Y.; Ramos-Álvarez, A.; Semenov, A. V.; Korneeva, Y. P.; An, P. P.; Korneev, A. A.; Murphy, A.; Bezryadin, A.; Gol’tsman, G. N. url  openurl
  Title Quasi-1-dimensional superconductivity in highly disordered NbN nanowires Type Miscellaneous
  Year 2016 Publication (up) arXiv Abbreviated Journal  
  Volume Issue Pages  
  Keywords narrow NbN nanowires, BCS  
  Abstract The topic of superconductivity in strongly disordered materials has attracted a significant attention. In particular vivid debates are related to the subject of intrinsic spatial inhomogeneity responsible for non-BCS relation between the superconducting gap and the pairing potential. Here we report experimental study of electron transport properties of narrow NbN nanowires with effective cross sections of the order of the debated inhomogeneity scales. We find that conventional models based on phase slip concept provide reasonable fits for the shape of the R(T) transition curve. Temperature dependence of the critical current follows the text-book Ginzburg-Landau prediction for quasi-one-dimensional superconducting channel Ic~(1-T/Tc)^3/2. Hence, one may conclude that the intrinsic electronic inhomogeneity either does not exist in our structures, or, if exist, does not affect their resistive state properties.  
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  Notes Duplicated as 1332 Approved no  
  Call Number Serial 1338  
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Author Sidorova, M.; Semenov, A.; Korneev, A.; Chulkova, G.; Korneeva, Y.; Mikhailov, M.; Devizenko, A.; Kozorezov, A.; Goltsman, G. url  openurl
  Title Electron-phonon relaxation time in ultrathin tungsten silicon film Type Miscellaneous
  Year 2018 Publication (up) arXiv Abbreviated Journal  
  Volume Issue Pages  
  Keywords WSi film  
  Abstract Using amplitude-modulated absorption of sub-THz radiation (AMAR) method, we studied electron-phonon relaxation in thin disordered films of tungsten silicide. We found a response time ~ 800 ps at critical temperature Tc = 3.4 K, which scales as minus 3 in the temperature range from 1.8 to 3.4 K. We discuss mechanisms, which can result in a strong phonon bottle-neck effect in a few nanometers thick film and yield a substantial difference between the measured time, characterizing response at modulation frequency, and the inelastic electron-phonon relaxation time. We estimate the electron-phonon relaxation time to be in the range ~ 100-200 ps at 3.4 K.  
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  Notes Duplicated as 1341 Approved no  
  Call Number Serial 1340  
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Author Sidorova, M. V.; Kozorezov, A. G.; Semenov, A. V.; Korneev, A. A.; Chulkova, G. M.; Korneeva, Y. P.; Mikhailov, M. Y.; Devizenko, A. Y.; Goltsman, G. N. url  openurl
  Title Non-bolometric bottleneck in electron-phonon relaxation in ultra-thin WSi film Type Miscellaneous
  Year 2018 Publication (up) arXiv Abbreviated Journal  
  Volume Issue Pages  
  Keywords WSi films, diffusion constant, SSPD, SNSPD  
  Abstract We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in tau{e-ph} = 140-190 ps at TC = 3.4 K, supporting the results of earlier measurements by independent techniques.  
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  Notes Duplicated as 1305 Approved no  
  Call Number Serial 1341  
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Author Murphy, A.; Semenov, A.; Korneev, A.; Korneeva, Y.; Gol’tsman, G.; Bezryadin, A. url  openurl
  Title Dark counts initiated by macroscopic quantum tunneling in NbN superconducting photon detectors Type Miscellaneous
  Year 2014 Publication (up) arXiv Abbreviated Journal  
  Volume Issue Pages  
  Keywords NbN SSPD  
  Abstract We perform measurements of the switching current distributions of three w = 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter 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.  
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  Notes Approved no  
  Call Number murphy2014dark Serial 1356  
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Author Jian Wei; David Olaya; Boris Karasik; Sergey Pereverzev; Andrei Sergeev; Michael Gershenson url  openurl
  Title Ultra-sensitive hot-electron nanobolometers for terahertz astrophysics Type Journal Article
  Year 2007 Publication (up) ArXiv e-prints Abbreviated Journal  
  Volume 710 Issue Pages  
  Keywords cond-mat.other; astro-ph; cond-mat.mes-hall  
  Abstract The background-limited spectral imaging of the early Universe requires spaceborne terahertz (THz) detectors with the sensitivity 2-3 orders of magnitude better than that of the state-of-the-art bolometers. To realize this sensitivity without sacrificing operating speed, novel detector designs should combine an ultrasmall heat capacity of a sensor with its unique thermal isolation. Quantum effects in thermal transport at nanoscale put strong limitations on the further improvement of traditional membrane-supported bolometers. Here we demonstrate an innovative approach by developing superconducting hot-electron nanobolometers in which the electrons are cooled only due to a weak electron-phonon interaction. At T<0.1K, the electron-phonon thermal conductance in these nanodevices becomes less than one percent of the quantum of thermal conductance. The hot-electron nanobolometers, sufficiently sensitive for registering single THz photons, are very promising for submillimeter astronomy and other applications based on quantum calorimetry and photon counting.  
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  Notes arXiv:0710.5474v1; 19 pages, 3 color figures Approved no  
  Call Number RPLAB @ s @ Serial 407  
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Author Bell, M.; Sergeev, A.; Mitin, V.; Bird, J.; Verevkin, A.; Gol'tsman, G. openurl 
  Title One-dimensional resistive states in quasi-two-dimensional superconductors Type Journal Article
  Year 2007 Publication (up) arXiv:0709.0709v1 [cond-mat.supr-con] Abbreviated Journal  
  Volume Issue Pages 1-11  
  Keywords  
  Abstract We investigate competition between one- and two-dimensional topological excitations – phase slips and vortices – in formation of resistive states in quasi-two-dimensional superconductors in a wide temperature range below the mean-field transition temperature T(C0). The widths w = 100 nm of our ultrathin NbN samples is substantially larger than the Ginzburg-Landau coherence length ξ = 4nm and the fluctuation resistivity above T(C0) has a two-dimensional character. However, our data shows that the resistivity below T(C0) is produced by one-dimensional excitations, – thermally activated phase slip strips (PSSs) overlapping the sample cross-section. We also determine the scaling phase diagram, which shows that even in wider samples the PSS contribution dominates over vortices in a substantial region of current/temperature variations. Measuring the resistivity within seven orders of magnitude, we find that the quantum phase slips can only be essential below this level.  
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  Notes Approved no  
  Call Number RPLAB @ atomics90 @ Serial 948  
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Author Amundsen, Morten; Linder, Jacob url  openurl
  Title General solution of 2D and 3D superconducting quasiclassical systems: coalescing vortices and nanodisk geometries Type Journal Article
  Year 2015 Publication (up) arXiv:1512.00030 [cond-mat.supr-con] Abbreviated Journal  
  Volume Issue Pages  
  Keywords quasiclassical Usadel equation, finite elements method  
  Abstract 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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  Notes Approved no  
  Call Number Serial 1066  
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