147,430 research outputs found
Comparison of different measures for quantum discord under non-Markovian noise
Two geometric measures for quantum discord were recently proposed by Modi et
al. [Phys. Rev. Lett. 104, 080501 (2010)] and Dakic et al. [Phys. Rev. Lett.
105, 190502 (2010)]. We study the similarities and differences for total
quantum correlations of Bell-diagonal states using these two geometry-based
quantum discord and the original quantum discord. We show that, under
non-Markovian dephasing channels, quantum discord and one of the geometric
measures stay constant for a finite amount of time, but not the other geometric
measure. However, all the three measures share a common sudden change point.
Our study on critical point of sudden transition might be useful for keeping
long time total quantum correlations under decoherence.Comment: 10 pages, 3 figures submitted for publicatio
A new three-parameter correlation for gamma-ray bursts with a plateau phase in the afterglow
Gamma ray bursts (GRBs) have great advantages for their huge burst energies,
luminosities and high redshifts in probing the Universe. A few interesting
luminosity correlations of GRBs have been used to test cosmology models.
Especially, for a subsample of long GRBs with known redshifts and a plateau
phase in the afterglow, a correlation between the end time of the plateau phase
(in the GRB rest frame) and the corresponding X-ray luminosity has been found.
In this paper, we re-analyze the subsample and found that a significantly
tighter correlation exists when we add a third parameter, i.e. the isotropic
-ray energy release, into the consideration. Additionally, both long
and intermediate duration GRBs are consistent with the same three-parameter
correlation equation. It is argued that the new three-parameter correlation is
consistent with the hypothesis that the subsample of GRBs with a plateau phase
in the afterglow be associated with the birth of rapidly rotating magnetars,
and that the plateau be due to the continuous energy-injection from the
magnetar. It is suggested that the newly born millisecond magnetars associated
with GRBs might provide a good standard candle in the Universe.Comment: 11 pages, 3 figures, 1 table; A&A, in pres
Impact of Resonant Magnetic Perturbations on Zonal Modes, Drift-Wave Turbulence and the L-H Transition Threshold
We study the effects of Resonant Magnetic Perturbations (RMPs) on turbulence,
flows and confinement in the framework of resistive drift-wave turbulence. This
work was motivated, in parts, by experiments reported at the IAEA 2010
conference [Y. Xu {\it et al}, Nucl. Fusion \textbf{51}, 062030] which showed a
decrease of long-range correlations during the application of RMPs. We derive
and apply a zero-dimensional predator-prey model coupling the Drift-Wave Zonal
Mode system [M. Leconte and P.H. Diamond, Phys. Plasmas \textbf{19}, 055903] to
the evolution of mean quantities. This model has both density gradient drive
and RMP amplitude as control parameters and predicts a novel type of transport
bifurcation in the presence of RMPs. This model allows a description of the
full L-H transition evolution with RMPs, including the mean sheared flow
evolution. The key results are: i) The L-I and I-H power thresholds \emph{both}
increase with RMP amplitude |\bx|, the relative increase of the L-I threshold
scales as \Delta P_{\rm LI} \propto |\bx|^2 \nu_*^{-2} \gyro^{-2}, where
is edge collisionality and \gyro is the sound gyroradius. ii) RMPs
are predicted to \emph{decrease} the hysteresis between the forward and
back-transition. iii) Taking into account the mean density evolution, the
density profile - sustained by the particle source - has an increased turbulent
diffusion compared with the reference case without RMPs which provides one
possible explanation for the \emph{density pump-out} effect.Comment: 30 pages, IAEA-based articl
Annealing-induced Fe oxide nanostructures on GaAs
We report the evolution of Fe oxide nanostructures on GaAs(100) upon pre- and post-growth annealing conditions. GaAs nanoscale pyramids were formed on the GaAs surface due to wet etching and thermal annealing. An 8.0-nm epitaxial Fe film was grown, oxidized, and annealed using a gradient temperature method. During the process the nanostripes were formed, and the evolution has been demonstrated using transmission and reflection high energy electron diffraction, and scanning electron microscopy. These nanostripes; exhibited uniaxial magnetic anisotropy. The formation of these nanostructures is attributed to surface anisotropy, which in addition could explain the observed uniaxial magnetic anisotropy
Why not Merge the International Monetary Fund (IMF) with the International Bank for Reconstruction and Development (World Bank)
Motivation: Cellular Electron CryoTomography (CECT) is an emerging 3D imaging technique that visualizes subcellular organization of single cells at sub-molecular resolution and in near-native state. CECT captures large numbers of macromolecular complexes of highly diverse structures and abundances. However, the structural complexity and imaging limits complicate the systematic de novo structural recovery and recognition of these macromolecular complexes. Efficient and accurate reference-free subtomogram averaging and classification represent the most critical tasks for such analysis. Existing subtomogram alignment based methods are prone to the missing wedge effects and low signal-to-noise ratio (SNR). Moreover, existing maximum-likelihood based methods rely on integration operations, which are in principle computationally infeasible for accurate calculation. Results: Built on existing works, we propose an integrated method, Fast Alignment Maximum Likelihood method (FAML), which uses fast subtomogram alignment to sample sub-optimal rigid transformations. The transformations are then used to approximate integrals for maximum-likelihood update of subtomogram averages through expectation-maximization algorithm. Our tests on simulated and experimental subtomograms showed that, compared to our previously developed fast alignment method (FA), FAML is significantly more robust to noise and missing wedge effects with moderate increases of computation cost. Besides, FAML performs well with significantly fewer input subtomograms when the FA method fails. Therefore, FAML can serve as a key component for improved construction of initial structuralmodels frommacromolecules captured by CECT
Nuclear spin qubits in a trapped-ion quantum computer
Physical systems must fulfill a number of conditions to qualify as useful
quantum bits (qubits) for quantum information processing, including ease of
manipulation, long decoherence times, and high fidelity readout operations.
Since these conditions are hard to satisfy with a single system, it may be
necessary to combine different degrees of freedom. Here we discuss a possible
system, based on electronic and nuclear spin degrees of freedom in trapped
ions. The nuclear spin yields long decoherence times, while the electronic
spin, in a magnetic field gradient, provides efficient manipulation, and the
optical transitions of the ions assure a selective and efficient initialization
and readout.Comment: 7 page
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