9,018 research outputs found
Coherent Storage of Temporally Multimode Light Using a Spin-Wave Atomic Frequency Comb Memory
We report on coherent and multi-temporal mode storage of light using the full
atomic frequency comb memory scheme. The scheme involves the transfer of
optical atomic excitations in Pr3+:Y2SiO5 to spin-waves in the hyperfine levels
using strong single-frequency transfer pulses. Using this scheme, a total of 5
temporal modes are stored and recalled on-demand from the memory. The coherence
of the storage and retrieval is characterized using a time-bin interference
measurement resulting in visibilities higher than 80%, independent of the
storage time. This coherent and multimode spin-wave memory is promising as a
quantum memory for light.Comment: 17 pages, 5 figure
Angular dependence of core hole screening in LiCoO2: A DFT+U calculation of the oxygen and cobalt K-edge x-ray absorption spectra
Angular dependent core-hole screening effects have been found in the cobalt
K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and
parameter-free GGA+U calculations. The Co 1s core-hole on the absorber causes
strong local attraction. The core-hole screening on the nearest neighbours
cobalt induces a 2 eV shift in the density of states with respect to the
on-site 1s-3d transitions, as detected in the Co K pre-edge spectrum. Our DFT+U
calculations reveal that the off-site screening is different in the
out-of-plane direction, where a 3 eV shift is visible in both calculations and
experiment. The detailed analysis of the inclusion of the core-hole potential
and the Hubbard parameter U shows that the core-hole is essential for the
off-site screening, while U improves the description of the angular dependent
screening effects. In the case of oxygen K-edge, both the core-hole potential
and the Hubbard parameter improve the relative positions of the spectral
features
Storage of up-converted telecom photons in a doped crystal
We report on an experiment that demonstrates the frequency up-conversion of
telecommunication wavelength single-photon-level pulses to be resonant with a
: crystal. We convert
the telecom photons at to using a
periodically-poled potassium titanyl phosphate nonlinear waveguide. The maximum
device efficiency (which includes all optical loss) is inferred to be
(internal efficiency
) with a signal to noise ratio exceeding 1 for
single-photon-level pulses with durations of up to 560ns. The converted
light is then stored in the crystal using the atomic frequency comb scheme with
storage and retrieval efficiencies exceeding for
predetermined storage times of up to . The retrieved light is
time delayed from the noisy conversion process allowing us to measure a signal
to noise ratio exceeding 100 with telecom single-photon-level inputs. These
results represent the first demonstration of single-photon-level optical
storage interfaced with frequency up-conversion
Quaterpyridine Ligands for Panchromatic Ru(II) Dye Sensitizers
A new general synthetic access to carboxylated quaterpyridines (qpy), of interest as ligands for panchromatic dyesensitized solar cell organometallic sensitizers, is presented. The strategic step is a Suzuki−Miyaura cross-coupling reaction,
which has allowed the preparation of a number of representative unsubstituted and alkyl and (hetero)aromatic substituted qpys.
To bypass the poor inherent stability of 2-pyridylboronic acid derivatives, we successfully applied N-methyliminodiacetic acid
(MIDA) boronates as key reagents, obtaining the qpy ligands in good yields up to (quasi)gram quantities. The structural,
spectroscopic (NMR and UV−vis), electrochemical, and electronic characteristics of the qpy have been experimentally and
computationally (DFT) investigated. The easy access to the bis-thiocyanato Ru(II) complex of the parent species of the qpy
series, through an efficient route which bypasses the use of Sephadex column chromatography, is shown. The bis-thiocyanato
Ru(II) complex has been spectroscopically (NMR and UV−vis), electrochemically, and computationally investigated, relating its
properties to those of previously reported Ru(II)−qpy complexes.“This document is the Accepted Manuscript version of a Published Work that appeared in final form in [The Journal of Organic Chemistry], copyright © American Chemical Society after peer review and technical editing by the publisher
On the High-dimensional Bak-Sneppen model
We report on extensive numerical simulations on the Bak-Sneppen model in high
dimensions. We uncover a very rich behavior as a function of dimensionality.
For d>2 the avalanche cluster becomes fractal and for d \ge 4 the process
becomes transient. Finally the exponents reach their mean field values for
d=d_c=8, which is then the upper critical dimension of the Bak Sneppen model.Comment: 4 pages, 3 eps figure
Finite dimensional corrections to mean field in a short-range p-spin glassy model
In this work we discuss a short range version of the -spin model. The
model is provided with a parameter that allows to control the crossover with
the mean field behaviour. We detect a discrepancy between the perturbative
approach and numerical simulation. We attribute it to non-perturbative effects
due to the finite probability that each particular realization of the disorder
allows for the formation of regions where the system is less frustrated and
locally freezes at a higher temperature.Comment: 18 pages, 5 figures, submitted to Phys Rev
Critical exponents of the anisotropic Bak-Sneppen model
We analyze the behavior of spatially anisotropic Bak-Sneppen model. We
demonstrate that a nontrivial relation between critical exponents tau and
mu=d/D, recently derived for the isotropic Bak-Sneppen model, holds for its
anisotropic version as well. For one-dimensional anisotropic Bak-Sneppen model
we derive a novel exact equation for the distribution of avalanche spatial
sizes, and extract the value gamma=2 for one of the critical exponents of the
model. Other critical exponents are then determined from previously known
exponent relations. Our results are in excellent agreement with Monte Carlo
simulations of the model as well as with direct numerical integration of the
new equation.Comment: 8 pages, three figures included with psfig, some rewriting, + extra
figure and table of exponent
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