Equilibrium magnetisation structures in ferromagnetic nanorings

The ground state of the ring-shape magnetic nanoparticle is studied. Depending on the geometrical and magnetic parameters of the nanoring, there exist different magnetisation configurations (magnetic phases): two phases with homogeneous magnetisation (easy-axis and easy-plane phases) and two inhomogeneous (planar vortex phase and out-of-plane one). The existence of a new intermediate out-of-plane vortex phase, where the inner magnetisation is not strongly parallel to the easy axis, is predicted. Possible transitions between different phases are analysed using the combination of analytical calculations and micromagnetic simulations.Comment: LaTeX, 19 pages, 11 figure

Relativistic Einstein-Podolsky-Rosen correlation and Bell's inequality

We formulate the Einstein-Podolsky-Rosen (EPR) gedankenexperiment within the framework of relativistic quantum theory to analyze a situation in which measurements are performed by moving observers. We point out that under certain conditions the perfect anti-correlation of an EPR pair of spins in the same direction is deteriorated in the moving observers' frame due to the Wigner rotation, and show that the degree of the violation of Bell's inequality prima facie decreases with increasing the velocity of the observers if the directions of the measurement are fixed. However, this does not imply a breakdown of non-local correlation since the perfect anti-correlation is maintained in appropriately chosen different directions. We must take account of this relativistic effect in utilizing in moving frames the EPR correlation and the violation of Bell's inequality for quantum communication.Comment: 33 pages, 6 figure

Nonunitary quantum circuit

A quantum circuit is generalized to a nonunitary one whose constituents are nonunitary gates operated by quantum measurement. It is shown that a specific type of one-qubit nonunitary gates, the controlled-NOT gate, as well as all one-qubit unitary gates constitute a universal set of gates for the nonunitary quantum circuit, without the necessity of introducing ancilla qubits. A reversing measurement scheme is used to improve the probability of successful nonunitary gate operation. A quantum NAND gate and Abrams-Lloyd's nonlinear gate are analyzed as examples. Our nonunitary circuit can be used to reduce the qubit overhead needed to ensure fault-tolerant quantum computation.Comment: 19 pages, 6 figures; added a referenc

Bell's inequality with Dirac particles

We study Bell's inequality using the Bell states constructed from four component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo vector which is relativistic invariant operator. By using Lorentz transformation, in both Bell states and spin operator, we obtain an observer independent Bell's inequality, so that it is maximally violated as long as it is violated maximally in the rest frame.Comment: 7 pages. arXiv admin note: text overlap with arXiv:quant-ph/0308156 by other author

Chandra Snapshot Observations of Low-Luminosity AGNs with a Compact Radio Source

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness (RO = L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2, AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert galaxies, quasars and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio loud.Comment: 15 pages, accepted for publication in Ap

Spin decoherence by spacetime curvature

A decoherence mechanism caused by spacetime curvature is discussed. The spin state of a particle is shown to decohere if only the particle moves in a curved spacetime. In particular, when a particle is near the event horizon of a black hole, an extremely rapid spin decoherence occurs for an observer who is static in a Killing time, however slow the particle's motion is.Comment: 13 pages, 2 figure

Direct Observation of Non-Monotonic dx2-y2-Wave Superconducting Gap in Electron-Doped High-Tc Superconductor Pr0.89LaCe0.11CuO4

We performed high-resolution angle-resolved photoemission spectroscopy on electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4 to study the anisotropy of the superconducting gap. The observed momentum dependence is basically consistent with the dx2-y2-wave symmetry, but obviously deviates from the monotonic dx2-y2 gap function. The maximum gap is observed not at the zone boundary, but at the hot spot where the antiferromagnetic spin fluctuation strongly couples to the electrons on the Fermi surface. The present experimental results unambiguously indicate the spin-mediated pairing mechanism in electron-doped high-Tc superconductors.Comment: 4 pages, 4 figure

The Ionizing Source of the Nucleus of NGC1097

We present new observations in X-ray and optical/ultraviolet of the nucleus of NGC1097, known for the abrupt appearance of broad, double-peaked Balmer lines in its spectrum in 1991. These new observations are used to construct the spectral energy distribution (SED) of the central engine. From the SED we infer that this AGN is radio-loud and has a bolometric luminosity L_Bol ~ 10^42 erg/s, implying a low Eddington ratio of L_Bol/L_Edd ~ 10^{-4}. These results suggest that the central ionizing source is an advection-dominated accretion flow (ADAF) in the form of an ellevated structure which photoionizes an outer thin disk. We fit a simplified ADAF model to the SED and obtain limits on the values of the mass accretion rate Mdot and accretion efficiency \eta, namely Mdot/Mdot_Edd >= 10^{-3} and \eta <= 10^{-2}. We identify an energy budget problem: if the central photoionizing source is isotropic, the covering factor of the line-emitting portion of the thin accretion disk is ~ 6, i. e. the central source accounts for only 20% of the energy emitted in the double-peaked Balmer lines.Comment: 4 pages, 3 figures, to appear in the proceedings of "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. Th. Storchi Bergmann, L.C. Ho, and H.R. Schmit

Five-dimensional SYM from undeformed ABJM

We expand undeformed ABJM theory around the vacuum solution that was found in arxiv:0909.3101. This solution can be interpreted as a circle-bundle over a two-dimensional plane with a singularity at the origin. By imposing periodic boundary conditions locally far away from the singularity, we obtain a local fuzzy two-torus over which we have a circle fibration. By performing fluctuation analysis we obtain five-dimensional SYM with the precise value on the coupling constant that we would obtain by compactifying multiple M5 branes on the vacuum three-manifold. In the resulting SYM theory we also find a coupling to a background two-form.Comment: 23 page