41,420 research outputs found
Spin squeezing: transforming one-axis-twisting into two-axis-twisting
Squeezed spin states possess unique quantum correlation or entanglement that
are of significant promises for advancing quantum information processing and
quantum metrology. In recent back to back publications [C. Gross \textit{et al,
Nature} \textbf{464}, 1165 (2010) and Max F. Riedel \textit{et al, Nature}
\textbf{464}, 1170 (2010)], reduced spin fluctuations are observed leading to
spin squeezing at -8.2dB and -2.5dB respectively in two-component atomic
condensates exhibiting one-axis-twisting interactions (OAT). The noise
reduction limit for the OAT interaction scales as , which
for a condensate with atoms, is about 100 times below standard
quantum limit. We present a scheme using repeated Rabi pulses capable of
transforming the OAT spin squeezing into the two-axis-twisting type, leading to
Heisenberg limited noise reduction , or an extra 10-fold
improvement for .Comment: 4 pages, 3 figure
Dynamo quenching due to shear flow
We provide a theory of dynamo (α effect) and momentum transport in three-dimensional magnetohydrodynamics. For the first time, we show that the α effect is reduced by the shear even in the absence of magnetic field. The α effect is further suppressed by magnetic fields well below equipartition (with the large-scale flow) with different scalings depending on the relative strength of shear and magnetic field. The turbulent viscosity is also found to be significantly reduced by shear and magnetic fields, with positive value. These results suggest a crucial effect of shear and magnetic field on dynamo quenching and momentum transport reduction, with important implications for laboratory and astrophysical plasmas, in particular, for the dynamics of the Sun
Parton Distributions at Hadronization from Bulk Dense Matter Produced at RHIC
We present an analysis of , , and spectra from
Au+Au collisions at GeV in terms of distributions of
effective constituent quarks at hadronization. Consistency in quark ratios
derived from various hadron spectra provides clear evidence for hadron
formation dynamics as suggested by quark coalescence or recombination models.
We argue that the constituent quark distribution reflects properties of the
effective partonic degrees of freedom at hadronization. Experimental data
indicate that strange quarks have a transverse momentum distribution flatter
than that of up/down quarks consistent with hydrodynamic expansion in partonic
phase prior to hadronization. After the AMPT model is tuned to reproduce the
strange and up/down quark distributions, the model can describe the measured
spectra of hyperons and mesons very well where hadrons are formed
through dynamical coalescence.Comment: 5 pages, 3 figures, two more paragraph added to address the referee's
comment, figure updated to include the KET scale. Accepted version to appear
in Phys. Rev.
Production of , , and in hadronic decays
A coherent study of the production of (, 2, 3 corresponding to
, , and ) in is
reported based on a previously proposed glueball and nonet mixing
scheme, and a factorization for the decay of , where
denotes the isoscalar vector mesons and , and denotes
pseudoscalar mesons. The results show that the decays are very
sensitive to the structure of those scalar mesons, and suggest a glueball in
the GeV region, in line with Lattice QCD. The presence of significant
glueball mixings in the scalar wavefunctions produces peculiar patterns in the
branching ratios for , which are in good agreement
with the recently published experimental data from the BES collaboration.Comment: Version accepted by PRD; Numerical results in Tab IV and VI changed
due to correction of an error in quoting an experimental datum; Conclusion is
not change
Preasymptotic Convergence of Randomized Kaczmarz Method
Kaczmarz method is one popular iterative method for solving inverse problems,
especially in computed tomography. Recently, it was established that a
randomized version of the method enjoys an exponential convergence for
well-posed problems, and the convergence rate is determined by a variant of the
condition number. In this work, we analyze the preasymptotic convergence
behavior of the randomized Kaczmarz method, and show that the low-frequency
error (with respect to the right singular vectors) decays faster during first
iterations than the high-frequency error. Under the assumption that the inverse
solution is smooth (e.g., sourcewise representation), the result explains the
fast empirical convergence behavior, thereby shedding new insights into the
excellent performance of the randomized Kaczmarz method in practice. Further,
we propose a simple strategy to stabilize the asymptotic convergence of the
iteration by means of variance reduction. We provide extensive numerical
experiments to confirm the analysis and to elucidate the behavior of the
algorithms.Comment: 20 page
- …