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Lobanov, Y.; Tong, E.; Blundell, R.; Hedden, A.; Voronov, B.; Gol'tsman, G. |
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Large-signal frequency response of an HEB mixer: from 300 MHz to terahertz |
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2011 |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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628-631 |
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waveguide NbN HEB mixers |
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We present a study of the large signal frequency response of an HEB mixer over a wide frequency range. In our experiments, we have subjected the HEB mixer to incident electromagnetic radiation from 0.3 GHz to 1 THz. The mixer element is an NbN film deposited on crystalline quartz. The mixer chip is mounted in a waveguide cavity, coupled to free space with a diagonal horn. At microwave frequencies, electromagnetic radiation is applied through the coaxial bias port of the mixer block. At higher frequencies the input signal passes via the diagonal horn feed. At each frequency, the incident power is varied and a family of I-V curves is recorded. From the curves we identify 3 distinct regimes of operation of the mixer separated by the phonon relaxation frequency and the superconducting energy gap frequency observed at about 3 GHz and 660 GHz respectively. In this paper, we will present observed curves and discuss the results of our experiment. |
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RPLAB @ gujma @ |
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719 |
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Lobanov, Y.V.; Tong, C.-Y.E.; Hedden, A.S.; Blundell, R.; Voronov, B.M.; Gol'tsman, G.N. |
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Direct measurement of the gain and noise bandwidths of HEB mixers |
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2011 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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645-648 |
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waveguide NbN HEB mixers |
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The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement. |
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720 |
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Васильева, И. А.; Компанеец, В. В.; Красная, Ж. А.; Чижикова, З. А. |
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Проявление внутримолекулярных вибронных взаимодействий в тонкоструктурных спектрах флуоресценции и возбуждения флуоресценции полиеновых δ-диметиламинокетонов |
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2011 |
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Оптический журнал |
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Опт. ж. |
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78 |
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5 |
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3-8 |
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спектры флуоресценции; вибрационный анализ; адиабатическое гармоническое приближение; бесфононная линия; фононное крыло |
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Проведен вибрационный анализ спектров флуоресценции и возбуждения флуоресценции, полученных методом Шпольского при 4,2 K. Рассчитаны параметры внутримолекулярных взаимодействий двух δ-диметиламинокетонов. Для определения интегральных интенсивностей вибронных полос в спектрах с тонкой структурой на интенсивном сплошном фоне выполнено моделирование спектров путем представления полосы каждого из вибронных переходов бесфононной линией и фононным крылом с определенными параметрами (полуширинами, фактором Дебая–Валлера). Показано, что нарушение зеркальной симметрии в сопряженных спектрах флуоресценции и возбуждения флуоресценции этих двух соединений может быть обÑŠяснено интерференцией франк-кондоновского и герцберг-теллеровского взаимодействий. |
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RPLAB @ gujma @ |
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721 |
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Antipov, Andrei; Bell, Matt; Yasar, Mesut; Mitin, Vladimir; Scharmach, William; Swihart, Mark; Verevkin, Aleksandr; Sergeev, Andrei |
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Luminescence of colloidal CdSe/ZnS nanoparticles: high sensitivity to solvent phase transitions |
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2011 |
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Nanoscale Research Letters |
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Nan. Res. Lett. |
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6 |
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7 |
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We investigate nanosecond photoluminescence processes in colloidal core/shell CdSe/ZnS nanoparticles dissolved in water and found strong sensitivity of luminescence to the solvent state. Several pronounced changes have been observed in the narrow temperature interval near the water melting point. First of all, the luminescence intensity substantially (approximately 50%) increases near the transition. In a large temperature scale, the energy peak of the photoluminescence decreases with temperature due to temperature dependence of the energy gap. Near the melting point, the peak shows N-type dependence with the maximal changes of approximately 30 meV. The line width increases with temperature and also shows N-type dependence near the melting point. The observed effects are associated with the reconstruction of ligands near the ice/water phase transition. |
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RPLAB @ gujma @ |
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722 |
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Wiechers, C.; Lydersen, L.; Wittmann, C.; Elser, D.; Skaar, J.; Marquardt, Ch; Makarov, V.; Leuchs, G. |
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After-gate attack on a quantum cryptosystem |
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2011 |
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New J. Phys. |
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13 |
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1 |
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14 |
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quantum cryptography; hacking; interception; attack; SPD; APD; QKD |
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We present a method to control the detection events in quantum key distribution systems that use gated single-photon detectors. We employ bright pulses as faked states, timed to arrive at the avalanche photodiodes outside the activation time. The attack can remain unnoticed, since the faked states do not increase the error rate per se. This allows for an intercept-resend attack, where an eavesdropper transfers her detection events to the legitimate receiver without causing any errors. As a side effect, afterpulses, originating from accumulated charge carriers in the detectors, increase the error rate. We have experimentally tested detectors of the system id3110 (Clavis2) from ID Quantique. We identify the parameter regime in which the attack is feasible despite the side effect. Furthermore, we outline how simple modifications in the implementation can make the device immune to this attack. |
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RPLAB @ gujma @ |
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730 |
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