Focused Ion Beam Milling and Deposition of Tungsten Contacts on Exfoliated Graphene for Electronic Device Applications

We demonstrate a rapid-prototyping method for the fabrication of electrical structures from exfoliated graphene using focused ion beam (FIB) assisted deposition of tungsten and milling. Alignment accuracies of less than 250 nm are achieved without imaging of the graphene using the FIB beam. Parameters for the FIB assisted deposition on graphene have to be controlled exactly to avoid damage to the underlying graphene. Measured channel resistance of 58 k? shows a good electrical contact between deposited tungsten and graphene

Quantum mode filtering of non-Gaussian states for teleportation-based quantum information processing

We propose and demonstrate an effective mode-filtering technique of non-Gaussian states generated by photon-subtraction. More robust non-Gaussian states have been obtained by removing noisy low frequencies from the original mode spectrum. We show that non-Gaussian states preserve their non-classicality after quantum teleportation to a higher degree, when they have been mode-filtered. This is indicated by a stronger negativity $-0.033 \pm 0.005$ of the Wigner function at the origin, compared to $-0.018 \pm 0.007$ for states that have not been mode-filtered. This technique can be straightforwardly applied to various kinds of photon-subtraction protocols, and can be a key ingredient in a variety of applications of non-Gaussian states, especially teleportation-based protocols towards universal quantum information processing

Numerical Study on GRB-Jet Formation in Collapsars

Two-dimensional magnetohydrodynamic simulations are performed using the ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB jet, taking account of realistic equation of state, neutrino cooling and heating processes, magnetic fields, and gravitational force from the central black hole and self gravity. It is found that neutrino heating processes are not so efficient to launch a jet in this study. It is also found that a jet is launched mainly by B_\phi fields that are amplified by the winding-up effect. However, since the ratio of total energy relative to the rest mass energy in the jet is not so high as several hundred, we conclude that the jets seen in this study are not be a GRB jet. This result suggests that general relativistic effects, which are not included in this study, will be important to generate a GRB jet. Also, the accretion disk with magnetic fields may still play an important role to launch a GRB jet, although a simulation for much longer physical time (\sim 10-100 s) is required to confirm this effect. It is shown that considerable amount of 56Ni is synthesized in the accretion disk. Thus there will be a possibility for the accretion disk to supply sufficient amount of 56Ni required to explain the luminosity of a hypernova. Also, it is shown that neutron-rich matter due to electron captures with high entropy per baryon is ejected along the polar axis. Moreover, it is found that the electron fraction becomes larger than 0.5 around the polar axis near the black hole by \nu_e capture at the region. Thus there will be a possibility that r-process and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons will be ejected from the jet, which suggests that signals from the neutron decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ. High resolution version is available at http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd

Muonium as a shallow center in GaN

A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the [0001] direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c-axis. Its small ionization energy (=< 14 meV) and small hyperfine parameter (--10^{-4} times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.Comment: 4 figures, to be published in Phys. Rev. Letter

Nucleon scattering with higgsino and wino cold dark matter

Neutralinos that are mostly wino or higgsino are shown to be compatible with the recent DAMA annual modulation signal. The nucleon scattering rates for these dark matter candidates are typically an order of magnitude above the oft-considered bino. Although thermal evolution of higgsino and wino number densities in the early universe implies that they are not viable dark matter candidates, non-thermal sources, such as from gravitino or moduli decay in anomaly mediated supersymmetry breaking, suggest that they can be the dominant source of cold dark matter. Their stealthiness at high energy colliders gives even more impetus to analyze nucleon scattering detection methods. We also present calculations for their predicted scattering rate with Germanium detectors, which have yet to see evidence of WIMP scattering.Comment: 16 pages, LaTex, 4 figures, uses feynMF, minor changes made for PRD publicatio

Mediterranean cyclones in a changing climate. Results from JMA-GSM model

Póster elaborado para la 11th PLINIUS Conference in Mediterranean Storms celebrada del 7 al 11 de septiembre de 2009 en Barcelona.This work has been framed within the MEDEX project, and has had the support from MEDICANES/CGL2008-01271/CLI project, from Spanish Ministerio de Ciencia e Innovación

WMAP Data and Recent Developments in Supersymmetric Dark Matter

A brief review is given of the recent developments in the analyses of supersymmetric dark matter. Chief among these is the very accurate determination of the amount of cold dark matter in the universe from analyses using WMAP data. The implications of this data for the mSUGRA parameter space are analyzed. It is shown that the data admits solutions on the hyperbolic branch (HB) of the radiative breaking of the electroweak symmetry. A part of the hyperbolic branch lies in the so called inversion region where the LSP neutralino $\chi_1^0$ becomes essentially a pure Higgsino and degenerate with the next to the lightest neutralino $\chi_2^0$ and the light chargino $\chi_1^{\pm}$. Thus some of the conventional signals for the observation of supersymmetry at colliders (e.g., the missing energy signals) do not operate in this region. On the other hand the inversion region contains a high degree of degeneracy of $\chi_1^0$, $\chi_2^0$, $\chi_1^{\pm}$ leading to coannihilations which allow for the satisfaction of the WMAP relic density constraints deep on the hyperbolic branch. Further, an analysis of the neutralino-proton cross sections in this region reveals that this region can still be accessible to dark matter experiments in the future. Constraints from $g_{\mu}-2$ and from $B^0_s\to \mu^+\mu^-$ are discussed. Future prospects are also discussed.Comment: 15 pages Latex. Invited talk at the IV International Conference on Non-accelerator New Physics (NANP'03), Dubna, Russia, June 23-28, 200