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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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Minaeva, O.; Divochiy, A.; Korneev, A.; Sergienko, A. V.; Goltsman, G. N. |
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High speed infrared photon counting with photon number resolving superconducting single-photon detectors (SSPDs) |
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Conference Article |
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2009 |
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CLEO/Europe – EQEC |
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CLEO/Europe – EQEC |
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SSPD, SNSPD |
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A review of development and characterization of the nanostructures consisting of several meander sections, all connected in parallel was presented. Such geometry leads to a significant decrease of the kinetic inductance, without a decrease of the SSPD active area. A new type of SSPDs possess the QE of large-active- area devices, but, simultaneously, allows achieving short response times and the GHz-counting rate. This new generation of superconducting detectors has another significant advantage for quantum key distribution, they have a photon number resolving capability and can distinguish more photons. |
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1399 |
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Esteban, Eduin; Serna, Hernandez |
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Quantum key distribution protocol with private-public key |
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Journal Article |
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2009 |
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arXiv |
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arXiv |
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3 |
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quantum cryptography; QKD; protocol |
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A quantum cryptographic protocol based in public key cryptography combinations and private key cryptography is presented. Unlike the BB84 protocol 1 and its many variants 2,3 two quantum channels are used. The present research does not make reconciliation mechanisms of information to derive the key. A three related system of key distribution are described. |
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arXiv: 0908.2146 |
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RPLAB @ gujma @ |
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756 |
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Ovchinnikov, Yu. N.; Varlamov, A. A. |
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Fluctuation-dissipative phenomena in a narrow superconducting channel carrying current below critical |
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2009 |
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arXiv |
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0910.2659v1 |
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1-4 |
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superconducting nanowire, resistance calculation |
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The theory of current transport in a narrow superconducting channel accounting for thermal fluctuations is developed. These fluctuations result in the appearance of small but finite dissipation in the sample. The value of corresponding voltage is found as the function of temperature (close to transition temperature) and arbitrary bias current. It is demonstrated that the value of the activation energy (exponential factor in the Arrenius law) when current approaches to the critical one is proportional to (1-J/Jc)^(5/4). This result is in concordance with the one for the affine phenomenon of the Josephson current decay due to the thermal phase fluctuations, where the activation energy proportional (1-J/J_c)^(3/2)(the difference in the exponents is related to the additional current dependence of the order parameter). Found dependence of the activation energy on current explains the enormous discrepancy between the theoretically predicted before and the experimentally observed broadening of the resistive transition. |
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arXiv:0910.2659v1; 4 pages, 3 figures |
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931 |
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Sekine, Norihiko; Hosako, Iwao |
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Intensity modulation of terahertz quantum cascade lasers under external light injection |
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2009 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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95 |
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201106(1-3) |
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QCL modulation, THz, terahertz |
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We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation. |
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