44,764 research outputs found
Correlation-induced suppression of decoherence in capacitively coupled Cooper-pair boxes
Charge fluctuations from gate bias and background traps severely limit the
performance of a charge qubit in a Cooper-pair box (CPB). Here we present an
experimentally realizable method to control the decoherence effects of these
charge fluctuations using two strongly capacitively coupled CPBs. This
coupled-box system has a low-decoherence subspace of two states. Our results
show that the inter-box Coulomb correlation can help significantly suppress
decoherence of this two-level system, making it a promising candidate as a
logical qubit, encoded using two CPBs.Comment: 5 pages, 2 figures. Phys. Rev. B, in pres
The Grad-Shafranov Reconstruction of Toroidal Magnetic Flux Ropes: Method Development and Benchmark Studies
We develop an approach of Grad-Shafranov (GS) reconstruction for toroidal
structures in space plasmas, based on in-situ spacecraft measurements. The
underlying theory is the GS equation that describes two-dimensional
magnetohydrostatic equilibrium as widely applied in fusion plasmas. The
geometry is such that the arbitrary cross section of the torus has rotational
symmetry about the rotation axis , with a major radius . The magnetic
field configuration is thus determined by a scalar flux function and a
functional that is a single-variable function of . The algorithm is
implemented through a two-step approach: i) a trial-and-error process by
minimizing the residue of the functional to determine an optimal
axis orientation, and ii) for the chosen , a minimization process
resulting in the range of . Benchmark studies of known analytic solutions
to the toroidal GS equation with noise additions are presented to illustrate
the two-step procedures and to demonstrate the performance of the numerical GS
solver, separately. For the cases presented, the errors in and are
9 and 22\%, respectively, and the relative percent error in the
numerical GS solutions is less than 10\%. We also make public the computer
codes for these implementations and benchmark studies.Comment: submitted to Sol. Phys. late Dec 2016; under review; code will be
made public once review is ove
Empirical Parameterization of Nucleon-Nucleon Elastic Scattering Amplitude at High Beam Momenta for Glauber Calculations and Monte Carlo Simulations
A parameterization of the nucleon-nucleon elastic scattering amplitude is
needed for future experiments with nucleon and nuclear beams in the beam
momentum range of 2 -- 50 GeV/c/nucleon. There are many parameterizations of
the amplitude at 25--50 GeV/c, and at 5 GeV/c. Our
paper is aimed to cover the range between 5 -- 50 GeV/c.
The amplitude is used in Glauber calculations of various cross sections and
Monte Carlo simulations of nucleon-nucleon scatterings. Usually, the
differential nucleon-nucleon elastic scattering cross sections are described by
an exponential expression. Corresponding experimental data on interactions
at 0.005 (GeV/c) and 0.125 (GeV/c) have been fit. We
propose formulae to approximate the beam momentum dependence of these
parameters in the momentum range considered. The same was done for
interactions at 0.5 (GeV/c). Expressions for the momentum
dependence of the total and elastic cross sections, and the ratio of real to
imaginary parts of the amplitude at zero momentum transfer are also given for
and collisions. These results are sufficient for a first
approximation of the Glauber calculations. For more exact calculations we fit
the data at 0.005 (GeV/c) without restrictions on the maximum value
of using an expression based on two coherent exponential. The parameters
of the fits are found for the beam momentum range 2 -- 50 GeV/c.Comment: 14 pages, 10 figure
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