2,160 research outputs found
Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond
The nitrogen-vacancy (NV) color center in diamond is an atom-like system in
the solid-state which specific spin properties can be efficiently used as a
sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of
the NV center levels which can be measured using Optically Detected Magnetic
Resonance (ODMR). In this work, we exploit the ODMR signal of an ensemble of NV
centers in order to quantitatively map the vectorial structure of a magnetic
field produced by a sample close to the surface of a CVD diamond hosting a thin
layer of NV centers. The reconstruction of the magnetic field is based on a
maximum-likelihood technique which exploits the response of the four intrinsic
orientations of the NV center inside the diamond lattice. The sensitivity
associated to a 1 {\mu}m^2 area of the doped layer, equivalent to a sensor
consisting of approximately 10^4 NV centers, is of the order of 2
{\mu}T/sqrt{Hz}. The spatial resolution of the imaging device is 400 nm,
limited by the numerical aperture of the optical microscope which is used to
collect the photoluminescence of the NV layer. The versatility of the sensor is
illustrated by the accurate reconstruction of the magnetic field created by a
DC current inside a copper wire deposited on the diamond sample.Comment: 11 pages, 5 figures, figure 4 added, results unchange
Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample
We show that the orientation of nitrogen-vacancy (NV) defects in diamond can
be efficiently controlled through chemical vapor deposition (CVD) growth on a
(111)-oriented diamond substrate. More precisely, we demonstrate that
spontaneously generated NV defects are oriented with a ~ 97 % probability along
the [111] axis, corresponding to the most appealing orientation among the four
possible crystallographic axes. Such a nearly perfect preferential orientation
is explained by analyzing the diamond growth mechanism on a (111)-oriented
substrate and could be extended to other types of defects. This work is a
significant step towards the design of optimized diamond samples for quantum
information and sensing applications.Comment: 6 pages, 4 figure
Light-by-light scattering sum rules constraining meson transition form factors
Relating the forward light-by-light scattering to energy weighted integrals
of the \gamma* \gamma -fusion cross sections, with one real photon (\gamma) and
one virtual photon (\gamma*), we find two new exact super-convergence
relations. They complement the known super-convergence relation based on the
extension of the GDH sum rule to the light-light system. We also find a set of
sum rules for the low-energy photon-photon interaction. All of the new
relations are verified here exactly at leading order in scalar and spinor QED.
The super-convergence relations, applied to the \gamma* \gamma -production of
mesons, lead to intricate relations between the \gamma \gamma -decay widths or
the \gamma* \gamma -transition form factors for (pseudo-) scalar, axial-vector
and tensor mesons. We discuss the phenomenological implications of these
results for mesons in both the light-quark sector and the charm-quark sector.Comment: 32 pages, 7 figure
Rare decay Z --> neutrino antineutrino photon photon via quartic gauge boson couplings
We present a detailed calculation of the rare decay Z --> neutrino
antineutrino photon photon via the quartic neutral gauge boson coupling
Z-Z-photon-photon in the framework of the effective Lagrangian approach. The
current experimental bound on this decay mode is then used to constrain the
coefficients of this coupling. It is found that the bounds obtained in this
way, of the order of , are weaker than the ones obtained from the
analysis of triple-boson production at LEP-2Comment: 5 pages, 2 figures, to appear in Physical Review D Brief Report
A qualitative optimization technique for biophysical neuron models with many parameters
We present a novel computational technique that enables more efficient optimization of qualitative features in biophysical neural models
R^2 Dark Matter
There is a non-trivial four-derivative extension of the gravitational
spectrum that is free of ghosts and phenomenologically viable. It is the so
called -gravity since it is defined by the only addition of a term
proportional to the square of the scalar curvature. Just the presence of this
term does not improve the ultraviolet behaviour of Einstein gravity but
introduces one additional scalar degree of freedom that can account for the
dark matter of our Universe.Comment: 6 pages, 1 figure, to appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
Engineered arrays of NV color centers in diamond based on implantation of CN- molecules through nanoapertures
We report a versatile method to engineer arrays of nitrogen-vacancy (NV)
color centers in dia- mond at the nanoscale. The defects were produced in
parallel by ion implantation through 80 nm diameter apertures patterned using
electron beam lithography in a PMMA layer deposited on a diamond surface. The
implantation was performed with CN- molecules which increased the NV defect
formation yield. This method could enable the realization of a solid-state
coupled-spin array and could be used for positioning an optically active NV
center on a photonic microstructure.Comment: 12 pages, 3 figure
Bosonic Quartic Couplings at LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W-
gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q
q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After
a careful study of the backgrounds and how to extract them from the data, we
show that the process p p -> j j gamma l+ l- is potentially the most sensitive
to deviations from the Standard Model, improving the sensitivity to anomalous
couplings by up to a factor 10^4 (10^2) with respect to the present direct
(indirect) limits.Comment: 18 pages, 2 figures, revised versio
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