1,046 research outputs found
Analytical solutions for optimal photon absorption into inhomogeneous spin memories
We investigate for optimal photon absorption a quantum electrodynamical model
of an inhomogeneously-broadened spin ensemble coupled to a single-mode cavity.
We consider a one-photon input pulse and obtain a simple one-parameter form for
its optimal shape for absorption in the spin ensemble. Solutions to this
problem are developed without using perturbation theory concerning the spin
ensemble. Furthermore, we exploit the possibility of modulating the frequency
and coupling rate of the resonator. We show some optimal scenarios and
demonstrate the usefulness of our approach for the design of efficient quantum
memories. In particular, we find the optimal cooperativity for different
parameters and identify cases where absorption with a success probability
larger than is achieved.Comment: 18 pages, 20 figure
Large-Eddy Simulations of Fluid and Magnetohydrodynamic Turbulence Using Renormalized Parameters
In this paper a procedure for large-eddy simulation (LES) has been devised
for fluid and magnetohydrodynamic turbulence in Fourier space using the
renormalized parameters. The parameters calculated using field theory have been
taken from recent papers by Verma [Phys. Rev. E, 2001; Phys. Plasmas, 2001]. We
have carried out LES on grid. These results match quite well with direct
numerical simulations of . We show that proper choice of parameter is
necessary in LES.Comment: 12 pages, 4 figures: Proper figures inserte
Mobile quantum gravity sensor with unprecedented stability
Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39nm/s2, long-term stability of 0.5nm/s2 and short-term noise of 96nm/s2/√Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.Peer Reviewe
Moments of Nucleon Generalized Parton Distributions in Lattice QCD
Calculation of moments of generalized parton distributions in lattice QCD
requires more powerful techniques than those previously used to calculate
moments of structure functions. Hence, we present a novel approach that
exploits the full information content from a given lattice configuration by
measuring an overdetermined set of lattice observables to provide maximal
statistical constraints on the generalized form factors at a given virtuality,
t. In an exploratory investigation using unquenched QCD configurations at
intermediate sea quark masses, we demonstrate that our new technique is
superior to conventional methods and leads to reliable numerical signals for
the n=2 flavor singlet generalized form factors up to 3 GeV^2. The contribution
from connected diagrams in the flavor singlet sector to the total quark angular
momentum is measured to an accuracy of the order of one percent.Comment: 16 pages, 8 figures, LaTeX, minor elaboration of formalism and
singular value decomposition for non-specialists and addition of several
reference
Nuclear deformation and neutron excess as competing effects for pygmy dipole strength
The electromagnetic dipole strength below the neutron-separation energy has
been studied for the xenon isotopes with mass numbers A = 124, 128, 132, and
134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung
facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIgS facility at
Triangle Universities Nuclear Laboratory Durham. The systematic study gained
new information about the influence of the neutron excess as well as of nuclear
deformation on the strength in the region of the pygmy dipole resonance. The
results are compared with those obtained for the chain of molybdenum isotopes
and with predictions of a random-phase approximation in a deformed basis. It
turned out that the effect of nuclear deformation plays a minor role compared
with the one caused by neutron excess. A global parametrization of the strength
in terms of neutron and proton numbers allowed us to derive a formula capable
of predicting the summed E1 strengths in the pygmy region for a wide mass range
of nuclides.Comment: 5 pages, subimtted to Physical Review Letter
Dual Superconductor Scenario of Confinement: A Systematic Study of Gribov Copy Effects
We perform a study of the effects from maximal abelian gauge Gribov copies in
the context of the dual superconductor scenario of confinement, on the basis of
a novel approach for estimation of systematic uncertainties from incomplete
gauge fixing. We present numerical results, in SU(2) lattice gauge theory,
using the overrelaxed simulated annealing gauge fixing algorithm. We find
abelian and non-abelian string tensions to differ significantly, their ratio
being 0.92(4) at BETA = 2.5115. An approximate factorization of the abelian
potential into monopole and photon contributions has been confirmed, the former
giving rise to the abelian string tension.Comment: 35 pages uucompressed LaTeX with 10 encapsuled postscript figure
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