9,864 research outputs found
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 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 and if protons or heavy nuclei were accelerated to ultra-relativistic
energies of order . We show that the charged scalar
mesons like and heavy vector mesons like , which have several
decay modes onto , 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 . 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
cm is about 70 cmVs 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
Population-only decay map for n-qubit n-partite inseparability detection
We introduce a new positive linear map for a single qubit. This map is a
decay only in populations of a single-qubit density operator. It is shown that
an n-fold product of this map may be used for a detection of n-partite
inseparability of an n-qubit density operator (i.e., detection of impossibility
of representing a density operator in the form of a convex combination of
products of density operators of individual qubits). This product map is also
investigated in relation to a variant of the entanglement detection method
mentioned by Laskowski and Zukowski.Comment: 5 pages, 1 figure, RevTex4, v2 minor grammatical changes, typos
correcte
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