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Beck, M.; Klammer, M.; Rousseau, I.; Gol’tsman, G. N.; Diamant, I.; Dagan, Y.; Demsar, J. |
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Probing superconducting gap dynamics with THz pulses |
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Conference Article |
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2015 |
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CLEO |
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CLEO |
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SM3H.3 (1 to 2) |
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superconducting gap; electric fields; femtosecond pulses; near infrared radiation; picosecond pulses; superconductors; thin films |
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We studied superconducting gap dynamics in a BCS superconductor NbN and electron doped cuprate superconductor PCCO following excitation with near-infrared (NIR) and narrow band THz pulses. Systematic studies on PCCO imply very selective electron-phonon coupling. |
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Optical Society of America |
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1345 |
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Takemoto, K.; Nambu, Y.; Miyazawa, T.; Sakuma, Y.; Yamamoto, T.; Yorozu, S.; Arakawa, Y. |
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Quantum key distribution over 120 km using ultrahigh purity single-photon source and superconducting single-photon detectors |
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2015 |
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Sci. Rep. |
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5 |
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14383 |
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SSPD, SNSPD applications, quantum key distribution, QKD |
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Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks. |
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1104 |
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Amundsen, Morten; Linder, Jacob |
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General solution of 2D and 3D superconducting quasiclassical systems: coalescing vortices and nanodisk geometries |
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2015 |
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arXiv:1512.00030 [cond-mat.supr-con] |
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quasiclassical Usadel equation, finite elements method |
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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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1066 |
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Gayduchenko, I.; Kardakova, A.; Fedorov, G.; Voronov, B.; Finkel, M.; Jiménez, D.; Morozov, S.; Presniakov, M.; Goltsman, G. |
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Response of asymmetric carbon nanotube network devices to sub-terahertz and terahertz radiation |
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2015 |
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J. Appl. Phys. |
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J. Appl. Phys. |
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118 |
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19 |
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194303 |
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terahertz detectors, asymmetric carbon nanotubes, CNT |
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Demand for efficient terahertz radiation detectors resulted in intensive study of the asymmetric carbon nanostructures as a possible solution for that problem. It was maintained that photothermoelectric effect under certain conditions results in strong response of such devices to terahertz radiation even at room temperature. In this work, we investigate different mechanisms underlying the response of asymmetric carbon nanotube (CNT) based devices to sub-terahertz and terahertz radiation. Our structures are formed with CNT networks instead of individual CNTs so that effects probed are more generic and not caused by peculiarities of an individual nanoscale object. We conclude that the DC voltage response observed in our structures is not only thermal in origin. So called diode-type response caused by asymmetry of the device IV characteristic turns out to be dominant at room temperature. Quantitative analysis provides further routes for the optimization of the device configuration, which may result in appearance of novel terahertz radiation detectors. |
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0021-8979 |
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1169 |
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Goltsman, G. N.; Samartsev, V. V.; Vinogradov, E. A.; Naumov, A. V.; Karimullin, K. R. |
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Title |
New generation of superconducting nanowire single-photon detectors |
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2015 |
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EPJ Web of Conferences |
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EPJ Web of Conferences |
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103 |
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01006 (1 to 2) |
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SSPD, SNSPD |
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We present an overview of recent results for new generation of infrared and optical superconducting nanowire single-photon detectors (SNSPDs) that has already demonstrated a performance that makes them devices-of-choice for many applications. SNSPDs provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, SNSPDs are also compatible with an integrated optical platform as a crucial requirement for applications in emerging quantum photonic technologies. By embedding SNSPDs in nanophotonic circuits we realize waveguide integrated single photon detectors which unite all desirable detector properties in a single device. |
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2100-014X |
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