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D. Henrich, L. Rehm S. Dörner, M. Hofherr, K. Il'in, A. Semenov, and M. Siegel |
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Detection efficiency of a spiral-nanowire superconducting single-photon detector |
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2012 |
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Critical current, Nanoscale devices, Superconducting photodetectors. |
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We investigate the detection efficiency of a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction in sharp turns of the nanowire than the conventional meander design. Detector samples with different nanowire width from 300 to 100 nm are patterned from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC at 4.2 K for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-1700 nm and the cut-off wavelength of the hot-spot plateau is determined. In the optical range, the spiral detector reaches a detection efficiency of 27.6%, which is ~1.5 times the value of the meander. In the infrared range the detection efficiency is more than doubled. |
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D. Henrich, L. Rehm S. Dörner, M. Hofherr, K. Il'in, A. Semenov, and M. Siegel |
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RPLAB @ seleznev @ |
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880 |
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Beck, Matthias; Leiderer, Paul; Kabanov, Viktor V.; Gol'tsman, Gregory; Helm, Manfred; Demsar, Jure |
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Energy-gap dynamics of a superconductor NbN studied by time-resolved terahertz spectroscopy |
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2012 |
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INIS |
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INIS |
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45 |
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12 |
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1-3 |
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NbN energy gap |
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Using time-resolved terahertz (THz) spectroscopy we performed direct studies of the photoinduced suppression and recovery of the SC gap in a conventional SC 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 important microscopic constants: the Cooper pair-breaking rate via phonon absorption and the bare quasiparticle recombination rate. From the latter we were able to extract the dimensionless electron-phonon coupling constant, λ=1.1±0.1, in excellent agreement with theoretical estimates. The technique also allowed us to determine the absorbed energy required to suppress SC, which in NbN equals the thermodynamic condensation energy (in cuprates the two differ by an order of magnitude). Finally, we present the first studies of dynamics following resonant excitation with intense narrow band THz pulses tuned to above and below the superconducting gap. These suggest an additional process, particularly pronounced near Tc, that could be attributed to amplification of SC via effective quasiparticle cooling. |
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1383 |
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Korotkov, Alexander N. |
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Entanglement preservation: The Sleeping Beauty approach |
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2012 |
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Nature Physics |
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Nat. Phys. |
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8 |
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2 |
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107-108 |
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fromIPMRAS |
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Two-qubit entanglement can be preserved by partially measuring the qubits to leave them in a 'lethargic' state. The original state is restored using quantum measurement reversal after the qubits have travelled through a decoherence channel. |
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RPLAB @ gujma @ |
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814 |
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Vercruyssen, N.; Verhagen, T. G. A.; Flokstra, M. G.; Pekola, J. P.; Klapwijk, T. M. |
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Evanescent states and nonequilibrium in driven superconducting nanowires |
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2012 |
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Phys. Rev. B |
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Phys. Rev. B |
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85 |
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224503(1-10) |
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Al HEB, Al superconducting nanowire, global state, bimodal state, quasiclassical kinetic equations, Usadel equation |
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We study the nonlinear response of current transport in a superconducting diffusive nanowire between normal reservoirs. We demonstrate theoretically and experimentally the existence of two different superconducting states appearing when the wire is driven out of equilibrium by an applied bias, called the global and bimodal superconducting states. The different states are identified by using two-probe measurements of the wire, and measurements of the local density of states with tunneling probes. The analysis is performed within the framework of the quasiclassical kinetic equations for diffusive superconductors. |
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898 |
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Hase, Muneaki; Katsuragawa, Masayuki; Constantinescu, Anca Monia; Petek, Hrvoje |
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Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon |
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2012 |
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Nature Photonics |
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Nat. Photon. |
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6 |
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243–247 |
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fromIPMRAS |
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High-order nonlinear light–matter interactions in gases enable the generation of X-ray and attosecond light pulses, metrology and spectroscopy1. Optical nonlinearities in solid-state materials are particularly interesting for combining optical and electronic functions for high-bandwidth information processing2. Third-order nonlinear optical processes in silicon have been used to process optical signals with bandwidths greater than 1 GHz (ref. 2). However, fundamental physical processes for a silicon-based optical modulator in the terahertz bandwidth range have not yet been explored. Here, we demonstrate ultrafast phononic modulation of the optical index of silicon by irradiation with intense few-cycle femtosecond pulses. The anisotropic reflectivity modulation by the resonant Raman susceptibility at the fundamental frequency of the longitudinal optical phonon of silicon (15.6 THz) generates a frequency comb up to seventh order. All-optical >100 THz frequency comb generation is realized by harnessing the coherent atomic motion of the silicon crystalline lattice at its highest mechanical frequency. |
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794 |
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Ghali, Mohsen; Ohtani1, Keita; Ohno, Yuzo; Ohno, Hideo |
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Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field |
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2012 |
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Nature Communications |
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Nat. Comm. |
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3 |
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661 |
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6 |
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fromIPMRAS |
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Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05. |
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RPLAB @ gujma @ |
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769 |
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Tuchak, A. N.; Gol’tsman, G. N.; Kitaeva, G. K.; Penin, A. N.; Seliverstov, S. V.; Finkel, M. I.; Shepelev, A. V.; Yakunin, P. V. |
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Generation of nanosecond terahertz pulses by the optical rectification method |
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2012 |
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JETP Lett. |
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JETP Lett. |
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96 |
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2 |
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94-97 |
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optical rectification, lithium niobate crystal |
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The possibility of the generation of quasi-cw terahertz radiation by the optical rectification method for broad-band Fourier unlimited nanosecond laser pulses has been experimentally demonstrated. The broadband radiation of a LiF dye-center laser is used as a pump source of a nonlinear optical oscillator. The energy efficiency of terahertz optical frequency conversion in a periodically polarized lithium niobate crystal is 4 × 10−9 at a pump power density of 7 MW/cm2. |
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0021-3640 |
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1377 |
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Usmani, Imam; Clausen, Christoph; Bussières, Félix; Sangouard, Nicolas; Afzelius, Mikael; Gisin, Nicolas |
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Heralded quantum entanglement between two crystals |
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2012 |
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Nature Photonics |
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Nat. Photon. |
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6 |
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4 |
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234-237 |
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fromIPMRAS |
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Quantum networks must have the crucial ability to entangle quantum nodes. A prominent example is the quantum repeater, which allows the distance barrier of direct transmission of single photons to be overcome, provided remote quantum memories can be entangled in a heralded fashion. Here, we report the observation of heralded entanglement between two ensembles of rare-earth ions doped into separate crystals. A heralded single photon is sent through a 50/50 beamsplitter, creating a single-photon entangled state delocalized between two spatial modes. The quantum state of each mode is subsequently mapped onto a crystal, leading to an entangled state consisting of a single collective excitation delocalized between two crystals. This entanglement is revealed by mapping it back to optical modes and by estimating the concurrence of the retrieved light state. Our results highlight the potential of crystals doped with rare-earth ions for entangled quantum nodes and bring quantum networks based on solid-state resources one step closer. |
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RPLAB @ gujma @ |
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793 |
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De Luca, M.; Gupta, H.; Neufeld, D.; Gerin, M.; Teyssier, D.; Drouin, B. J.; Pearson, J. C.; Lis, D. C.; Monje, R.; Phillips, T. G.; Goicoechea, J. R.; Godard, B.; Falgarone, E.; Coutens, A.; Bell, T. A. |
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Herschel/HIFI discovery of HCL+ in the interstellar medium |
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2012 |
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Astrophys. J. Lett. |
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751 |
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2 |
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L37 |
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HEB mixer applications, HIFI, Herschel |
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The radical ion HCl+, a key intermediate in the chlorine chemistry of the interstellar gas, has been identified for the first time in the interstellar medium with the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared. The ground-state rotational transition of H35Cl+, 2Π3/2 J = 5/2-3/2, showing Λ-doubling and hyperfine structure, is detected in absorption toward the Galactic star-forming regions W31C (G10.6-0.4) and W49N. The complex interstellar absorption features are modeled by convolving in velocity space the opacity profiles of other molecular tracers toward the same sources with the fine and hyperfine structure of HCl+. This structure is derived from a combined analysis of optical data from the literature and new laboratory measurements of pure rotational transitions, reported in the accompanying Letter by Gupta et al. The models reproduce well the interstellar absorption, and the frequencies inferred from the astronomical observations are in exact agreement with those calculated using spectroscopic constants derived from the laboratory data. The detection of H37Cl+ toward W31C, with a column density consistent with the expected 35Cl/37Cl isotopic ratio, provides additional evidence for the identification. A comparison with the chemically related molecules HCl and H2Cl+ yields an abundance ratio of unity with both species (HCl+ : H2Cl+ : HCl ~ 1). These observations also yield the unexpected result that HCl+ accounts for 3%-5% of the gas-phase chlorine toward W49N and W31C, values several times larger than the maximum fraction (~1%) predicted by chemical models. |
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1092 |
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Minaeva, O.; Fraine, A.; Korneev, A.; Divochiy, A.; Goltsman, G.; Sergienko, A. |
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High resolution optical time-domain reflectometry using superconducting single-photon detectors |
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2012 |
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Frontiers in Opt. 2012/Laser Sci. XXVIII |
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Frontiers in Opt. 2012/Laser Sci. XXVIII |
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Fw3a.39 |
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SSPD, SNSPD, Photodetectors; Fiber characterization; Light beams; Optical time domain reflectometry; Photon counting; Single mode fibers; Single photon detectors; Superconductors |
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We discuss the advantages and limitations of single-photon optical time-domain reflectometry with superconducting single-photon detectors. The higher two-point resolution can be achieved due to superior timing performance of SSPDs in comparison with InGaAs APDs. |
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Optical Society of America |
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