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Parrott, Edward P. J.; Zeitler, J. Axel; Fris<cc><152>c<cc><152>ic<cc><81>, Tomislav; Pepper, Michael; Jones, William; Day, Graeme M.; Gladden, Lynn F. |
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Testing the sensitivity of terahertz spectroscopy to changes in molecular and supramolecular structure: a study of structurally similar cocrystals |
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2009 |
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Crystal Growth & Design |
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Crystal Growth & Design |
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9 |
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3 |
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1452-1460 |
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supramolecular recognition, infrared, terahertz, IR, THz, TDS |
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Terahertz time-domain-spectroscopy (THz-TDS) has emerged as a versatile spectroscopic technique, and an alternative to powder X-ray diffraction in the characterization of molecular crystals. We tested the ability of terahertz spectroscopy to distinguish between chiral and racemic hydrogen-bonded cocrystals that are similar in molecular and supramolecular structure. Terahertz spectroscopy readily distinguished between the isostructural cocrystals of theophylline with chiral and racemic forms of malic acid which are almost identical in molecular structure and supramolecular architecture. Similarly, the cocrystals of theophylline with chiral and racemic forms of tartaric acid, which are similar at the molecular level but dissimilar in crystal packing, were distinguished unequivocally. The investigation of the same cocrystals using X-ray powder diffraction and Raman spectroscopy suggested that THz-TDS is comparable in sensitivity to diffraction methods and more sensitive than Raman spectroscopy to changes in cocrystal architecture. The differences in spectra acquired by THz-TDS could be further enhanced by cooling the samples to 109 K. |
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1528-7483 |
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567 |
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Hadfield, Robert H. |
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Title |
Single-photon detectors for optical quantum information applications |
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2009 |
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Nature Photonics |
Abbreviated Journal |
Nature Photonics |
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3 |
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696-705 |
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SPD |
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The past decade has seen a dramatic increase in interest in new single-photon detector technologies. A major cause of this trend has undoubtedly been the push towards optical quantum information applications such as quantum key distribution. These new applications place extreme demands on detector performance that go beyond the capabilities of established single-photon detectors. There has been considerable effort to improve conventional photon-counting detectors and to transform new device concepts into workable technologies for optical quantum information applications. This Review aims to highlight the significant recent progress made in improving single-photon detector technologies, and the impact that these developments will have on quantum optics and quantum information science. |
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RPLAB @ gujma @ |
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678 |
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Sahu, Mitrabhanu; Bae, Myung-Ho; Rogachev, Andrey; Pekker, David; Wei, Tzu-Chieh; Shah, Nayana; Goldbart, Paul M.; Bezryadin, Alexey |
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Individual topological tunnelling events of a quantum field probed through their macroscopic consequences |
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2009 |
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Nature Phys. |
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Nature Phys. |
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5 |
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503-508 |
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phase slips, superconducting nanowires |
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Phase slips are topological fluctuations that carry the superconducting order-parameter field between distinct current-carrying states. Owing to these phase slips, superconducting nanowires acquire electrical resistance. In such wires, it is well known that at higher temperatures phase slips occur through the process of thermal barrier-crossing by the order-parameter field. At low temperatures, the general expectation is that phase slips should proceed through quantum tunnelling events, which are known as quantum phase slips. However, resistive measurements have produced evidence both for and against the occurrence of quantum phase slips. Here, we report evidence for the observation of individual quantum phase-slip events in homogeneous ultranarrow wires at high bias currents. We accomplish this through measurements of the distribution of switching currents for which the width exhibits a rather counter-intuitive, monotonic increase with decreasing temperature. Importantly, measurements show that in nanowires with larger critical currents, quantum fluctuations dominate thermal fluctuations up to higher temperatures. |
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Recommended by Klapwijk |
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928 |
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Driessen, E. F. C.; Braakman, F. R.; Reiger, E. M.; Dorenbos, S. N.; Zwiller, V.; de Dood, M. J. A. |
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Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors |
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2009 |
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Eur. Phys. J. Appl. Phys. |
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47 |
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10701 |
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SSPD, SNSPD |
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We measured the single-photon detection efficiency of NbN superconducting single-photon detectors as a function of the polarization state of the incident light for different wavelengths in the range from 488 nm to 1550 nm. The polarization contrast varies from ~% at 488 nm to~0% at 1550 nm, in good agreement with numerical calculations. We use an optical-impedance model to describe the absorption for polarization parallel to the wires of the detector. For the extremely lossy NbN material, the absorption can be kept constant by keeping the product of layer thickness and filling factor constant. As a consequence, the maximum possible absorption is independent of filling factor. By illuminating the detector through the substrate, an absorption efficiency of ~0% can be reached for a detector on Si or GaAs, without the need for an optical cavity. |
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RPLAB @ alex_kazakov @ |
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1062 |
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Marsili, F.; Bitauld, D.; Fiore, A.; Gaggero, A.; Leoni, R.; Mattioli, F.; Divochiy, A.; Korneev, A.; Seleznev, V.; Kaurova, N.; Minaeva, O.; Goltsman, G. |
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Superconducting parallel nanowire detector with photon number resolving functionality |
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2009 |
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J. Modern Opt. |
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J. Modern Opt. |
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56 |
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2-3 |
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334-344 |
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PNR; SSPD; SNSPD; thin superconducting films; photon number resolving detector; multiplication noise; telecom wavelength; NbN |
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We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm-wide, few nm-thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3-4 nm thick NbN films grown on sapphire (substrate temperature TS=900C) or MgO (TS=400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one photon quantum efficiency can be estimated to be QE=3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise. |
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0950-0340 |
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RPLAB @ gujma @ |
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701 |
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