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| Author |
Maslennikov, S. |
| Title |
RF heating efficiency of the terahertz superconducting hot-electron bolometer |
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Journal Article |
| Year |
2014 |
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arXiv |
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arXiv |
| Volume |
1404.5276 |
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1-4 |
| Keywords |
superconducting hot-electron bolometer mixer, HEB, NbN, distributed model, HEB model, HEB mixer model, heat balance equa-tions, conversion gain, RF heating efficiency, noise temperature, simulation, Euler method |
| Abstract |
We report results of the numerical solution by the Euler method of the system of heat balance equations written in recurrent form for the superconducting hot-electron bolometer (HEB) embedded in an electrical circuit. By taking into account the dependence of the HEB resistance on the transport current we have been able to calculate rigorously the RF heating efficiency, absorbed local oscillator (LO) power and conversion gain of the HEB mixer. We show that the calculated conversion gai nis in excellent agreement with the experimental results, and that the substitution of the calculated RF heating efficiency and absorbed LO power into the expressions for the conversion gain and noise temperature given by the analytical small-signal model of the HEB yields excellent agreement with the corresponding measured values |
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RPLAB @ atomics90 @ |
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954 |
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| Author |
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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Journal Article |
| Year |
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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Sprengers, J.P.; Gaggero, A.; Sahin, D.; Nejad, S. Jahanmiri; Mattioli, F.; Leoni, R.; Beetz, J.; Lermer, M.; Kamp, M.; Höfling, S.; Sanjines, R.; Fiore A. |
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Waveguide single-photon detectors for integrated quantum photonic circuits |
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Conference Article |
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2011 |
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arXiv |
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arXiv |
| Volume |
1108.5107 |
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1-11 |
| Keywords |
optical waveguides, waveguide SSPD |
| Abstract |
The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work on quantum photonic circuits has used external sources and detectors. Here we propose an approach to a fully-integrated quantum photonic circuit on a semiconductor chip, and demonstrate a key component of such circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (20%) at telecom wavelengths, high timing accuracy (60 ps), response time in the ns range, and are fully compatible with the integration of single-photon sources, passive networks and modulators. |
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