Simulating Capacitances to Silicon Quantum Dots: Breakdown of the Parallel Plate Capacitor Model

Many electrical applications of quantum dots rely on capacitively coupled gates; therefore, to make reliable devices we need those gate capacitances to be predictable and reproducible. We demonstrate in silicon nanowire quantum dots that gate capacitances are reproducible to within 10% for nominally identical devices. We demonstrate the experimentally that gate capacitances scale with device dimensions. We also demonstrate that a capacitance simulator can be used to predict measured gate capacitances to within 20%. A simple parallel plate capacitor model can be used to predict how the capacitances change with device dimensions; however, the parallel plate capacitor model fails for the smallest devices because the capacitances are dominated by fringing fields. We show how the capacitances due to fringing fields can be quickly estimated.Comment: 4 pages, 3 figures, to be published in IEEE Trans. Nan

Protected Rabi oscillation induced by natural interactions among physical qubits

For a system composed of nine qubits, we show that natural interactions among the qubits induce the time evolution that can be regarded, at discrete times, as the Rabi oscillation of a logical qubit. Neither fine tuning of the parameters nor switching of the interactions is necessary. Although straightforward application of quantum error correction fails, we propose a protocol by which the logical Rabi oscillation is protected against all single-qubit errors. The present method thus opens a simple and realistic way of protecting the unitary time evolution against noise.Comment: In this revised manuscript, new sections V, VI, VII and new appendices A, B, C have been added to give detailed discussions. 13 pages, 4 figure

Hydrodynamical effects in internal shock of relativistic outflows

We study both analytically and numerically hydrodynamical effects of two colliding shells, the simplified models of the internal shock in various relativistic outflows such as gamma-ray bursts and blazars. We pay particular attention to three interesting cases: a pair of shells with the same rest mass density (``{\it equal rest mass density}''), a pair of shells with the same rest mass (``{\it equal mass}''), and a pair of shells with the same bulk kinetic energy (``{\it equal energy}'') measured in the intersteller medium (ISM) frame. We find that the density profiles are significantly affected by the propagation of rarefaction waves. A split-feature appears at the contact discontinuity of two shells for the ``equal mass'' case, while no significant split appears for the ``equal energy'' and ``equal rest mass density'' cases. The shell spreading with a few ten percent of the speed of light is also shown as a notable aspect caused by rarefaction waves. The conversion efficiency of the bulk kinetic energy to internal one is numerically evaluated. The time evolutions of the efficiency show deviations from the widely-used inellastic two-point-mass-collision model.Comment: 29 pages, 16 figures, accepted by Ap

Deterministic implementation of weak quantum cubic nonlinearity

We propose a deterministic implementation of weak cubic nonlinearity, which is a basic building block of a full scale CV quantum computation. Our proposal relies on preparation of a specific ancillary state and transferring its nonlinear properties onto the desired target by means of deterministic Gaussian operations and feed-forward. We show that, despite the imperfections arising from the deterministic nature of the operation, the weak quantum nonlinearity can be implemented and verified with the current level of technology.Comment: 4 pages, 2 figure

Meson Synchrotron Emission from Central Engines of Gamma-Ray Bursts with Strong Magnetic Fields

Gamma-ray bursts (GRBs) are presumed to be powered by still unknown central engines for the timescales in the range $1ms \sim$ a few s. We propose that the GRB central engines would be a viable site for strong meson synchrotron emission if they were the compact astrophysical objects such as neutron stars or rotating black holes with extremely strong magnetic fields $H \sim10^{12} - 10^{17}G$ and if protons or heavy nuclei were accelerated to ultra-relativistic energies of order $\sim 10^{12}-10^{22}eV$. We show that the charged scalar mesons like $\pi^{\pm}$ and heavy vector mesons like $\rho$, which have several decay modes onto $\pi^{\pm}$, could be emitted with high intensity a thousand times larger than photons through strong couplings to ultra-relativistic nucleons. These meson synchrotron emission processes eventually produce a burst of very high-energy cosmic neutrinos with $10^{12} eV \leq E_{\nu}$. These neutrinos are to be detected during the early time duration of short GRBs.Comment: 12 pages, 4 figures. Accepted for publication in the Astrophysical Journal Letter

Hole Transport in p-Type ZnO

A two-band model involving the A- and B-valence bands was adopted to analyze the temperature dependent Hall effect measured on N-doped \textit{p}-type ZnO. The hole transport characteristics (mobilities, and effective Hall factor) are calculated using the ``relaxation time approximation'' as a function of temperature. It is shown that the lattice scattering by the acoustic deformation potential is dominant. In the calculation of the scattering rate for ionized impurity mechanism, the activation energy of 100 or 170 meV is used at different compensation ratios between donor and acceptor concentrations. The theoretical Hall mobility at acceptor concentration of $7 \times 10^{18}$ cm$^3$ is about 70 cm$^2$V$^{-1}$s$^{-1}$ with the activation energy of 100 meV and the compensation ratio of 0.8 at 300 K. We also found that the compensation ratios conspicuously affected the Hall mobilities.Comment: 5page, 5 figures, accepted for publication in Jpn. J. Appl. Phy

Relativistic Dynamos in Magnetospheres of Rotating Compact Objects

The kinematic evolution of axisymmetric magnetic fields in rotating magnetospheres of relativistic compact objects is analytically studied, based on relativistic Ohm's law in stationary axisymmetric geometry. By neglecting the poloidal flows of plasma in simplified magnetospheric models, we discuss self-excited dynamos due to the frame-dragging effect (originally pointed out by Khanna & Camenzind), and we propose alternative processes to generate axisymmetric magnetic fields against ohmic dissipation. The first process (which may be called induced excitation) is caused by the help of a background uniform magnetic field in addition to the dragging of inertial frames. It is shown that excited multipolar components of poloidal and azimuthal fields are sustained as stationary modes, and outgoing Poynting flux converges toward the rotation axis. The second one is self-excited dynamo through azimuthal convection current, which is found to be effective if plasma rotation becomes highly relativistic with a sharp gradient in the angular velocity. In this case no frame-dragging effect is needed, and the coupling between charge separation and plasma rotation becomes important. We discuss briefly the results in relation to active phenomena in the relativistic magnetospheres.Comment: 16 pages, AASLaTeX macros v4.

Stochastic Binary Modeling of Cells in Continuous Time as an Alternative to Biochemical Reaction Equations

We have developed a coarse-grained formulation for modeling the dynamic behavior of cells quantitatively, based on stochasticity and heterogeneity, rather than on biochemical reactions. We treat each reaction as a continuous-time stochastic process, while reducing each biochemical quantity to a binary value at the level of individual cells. The system can be analytically represented by a finite set of ordinary linear differential equations, which provides a continuous time course prediction of each molecular state. In this letter, we introduce our formalism and demonstrate it with several examples.Comment: 10pages, 3 figure

Coordination of flagella on filamentous cells of Escherichia coli

Video techniques were used to study the coordination of different flagella on single filamentous cells of Escherichia coli. Filamentous, nonseptate cells were produced by introducing a cell division mutation into a strain that was polyhook but otherwise wild type for chemotaxis. Markers for its flagellar motors (ordinary polyhook cells that had been fixed with glutaraldehyde) were attached with antihook antibodies. The markers were driven alternately clockwise and counterclockwise, at angular velocities comparable to those observed when wild-type cells are tethered to glass. The directions of rotation of different markers on the same cell were not correlated; reversals of the flagellar motors occurred asynchronously. The bias of the motors (the fraction of time spent spinning counterclockwise) changed with time. Variations in bias were correlated, provided that the motors were within a few micrometers of one another. Thus, although the directions of rotation of flagellar motors are not controlled by a common intracellular signal, their biases are. This signal appears to have a limited range