University of Electro-Communications

About: University of Electro-Communications is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Laser & Robot. The organization has 8041 authors who have published 16950 publications receiving 235832 citations. The organization is also known as: UEC & Denki-Tsūshin Daigaku.

Current-driven resonant excitation of magnetic vortices.

Abstract: A magnetic vortex core in a ferromagnetic circular nanodot has a resonance frequency originating from the confinement of the vortex core. By the micromagnetic simulation including the spin-transfer torque, we show that the vortex core can be resonantly excited by an ac (spin-polarized) current through the dot and that the resonance frequency can be tuned by the dot shape. The resistance measurement under the ac current successfully detects the resonance at the frequency consistent with the simulation.

Quantum Hypothesis Testing and the Operational Interpretation of the Quantum Rényi Relative Entropies

Abstract: We show that the new quantum extension of Renyi’s α-relative entropies, introduced recently by Muller-Lennert et al. (J Math Phys 54:122203, 2013) and Wilde et al. (Commun Math Phys 331(2):593–622, 2014), have an operational interpretation in the strong converse problem of quantum hypothesis testing. Together with related results for the direct part of quantum hypothesis testing, known as the quantum Hoeffding bound, our result suggests that the operationally relevant definition of the quantum Renyi relative entropies depends on the parameter α: for α < 1, the right choice seems to be the traditional definition $${{D_\alpha^{(old)}} (\rho \| \sigma) :=\frac{1}{\alpha-1} \,\,{\rm log\,\,Tr}\,\, \rho^{\alpha} \sigma^{1-\alpha}}$$ , whereas for α > 1 the right choice is the newly introduced version $${D_\alpha^{(new)}} (\rho \| \sigma) := \frac{1}{\alpha-1}\,{\rm log\,\,Tr}\,\big(\sigma^{\frac{1-\alpha}{2 \alpha}}\rho \sigma^{\frac{1-\alpha}{2 \alpha}}\big)^{\alpha}$$ .On the way to proving our main result, we show that the new Renyi α-relative entropies are asymptotically attainable by measurements for α > 1. From this, we obtain a new simple proof for their monotonicity under completely positive trace-preserving maps.

An efficient branch-and-bound algorithm for finding a maximum clique

Abstract: We present an exact and efficient branch-and-bound algorithm for finding a maximum clique in an arbitrary graph. The algorithm is not specialized for any particular kind of graph. It employs approximate coloring and appropriate sorting of vertices to get an upper bound on the size of a maximum clique. We demonstrate by computational experiments on random graphs with up to 15,000 vertices and on DIMACS benchmark graphs that our algorithm remarkably outperforms other existing algorithms in general. It has been successfully applied to interesting problems in bioinformatics, image processing, the design of quantum circuits, and the design of DNA and RNA sequences for biomolecular computation.

Linewidth of the Raman features of individual single-wall carbon nanotubes

Abstract: In this work we analyze the room-temperature linewidth for several Raman features (i.e., the radial breathing mode, the G band, the D band, and the ${G}^{\ensuremath{'}}$ band) observed for individual isolated single-wall carbon nanotubes (SWNTs). Temperature-dependent measurements on SWNT bundles and isolated SWNTs show that anharmonic effects are not important for linewidth broadening at room temperature. Measurements on a large number of samples (170 isolated SWNTs) allow us to filter out the effect from extrinsic SWNT properties (e.g., defects, tube deformations, substrate roughness) and to obtain information about intrinsic properties related to phonon and electron dispersion relations, curvature and Breit-Wigner-Fano effects, single- vs double-resonance Raman scattering processes, and the resonance condition itself through a linewidth analysis. We also use observations at the single-nanotube level to understand linewidth effects in SWNT bundles.