98,766 research outputs found
A complete characterisation of the heralded noiseless amplification of photons
Heralded noiseless amplifcation of photons has recently been shown to provide
a means to overcome losses in complex quantum communication tasks. In
particular, to overcome transmission losses that could allow for the violation
of a Bell inequality free from the detection loophole, for Device Independent
Quantum Key Distribution (DI-QKD). Several implementations of a heralded photon
amplifier have been proposed and the first proof of principle experiments
realised. Here we present the first full characterisation of such a device to
test its functional limits and potential for DI-QKD. This device is tested at
telecom wavelengths and is shown to be capable of overcoming losses
corresponding to a transmission through of single mode telecom
fibre. We demonstrate heralded photon amplifier with a gain and a
heralding probability , required by DI-QKD protocols that use the
Clauser-Horne-Shimony-Holt (CHSH) inequality. The heralded photon amplifier
clearly represents a key technology for the realisation of DI-QKD in the real
world and over typical network distances.Comment: 9 pages, 4 figure
Leaky vessels as a potential source of stromal acidification in tumours
Malignant tumours are characterised by higher rates of acid production and a lower extracellular pH than normal tissues. Previous mathematical modelling has indicated that the tumour-derived production of acid leads to a gradient of low pH in the interior of the tumour extending to a normal pH in the peritumoural tissue. This paper uses mathematical modelling to examine the potential of leaky vessels as an additional source of stromal acidification in tumours. We explore whether and to what extent increasing vascular permeability in vessels can lead to the breakdown of the acid gradient from the core of the tumour to the normal tissue, and a progressive acidification of the peritumoural stroma. We compare our mathematical simulations to experimental results found in vivo with a tumour implanted in the mammary fat pad of a mouse in a window chamber construct. We find that leaky vasculature can cause a net acidification of the normal tissue away from the tumour boundary, though not a progressive acidification over time as seen in the experiments. Only through progressively increasing the leakiness can the model qualitatively reproduce the experimental results. Furthermore, the extent of the acidification predicted by the mathematical model is less than as seen in the window chamber, indicating that although vessel leakiness might be acting as a source of acid, it is not the only factor contributing to this phenomenon. Nevertheless, tumour destruction of vasculature could result in enhanced stromal acidification and invasion, hence current therapies aimed at buffering tumour pH should also examine the possibility of preventing vessel disruption
Instabilities leading to vortex lattice formation in rotating Bose-Einstein condensates
We present a comprehensive theoretical study of vortex lattice formation in
atomic Bose-Einstein condensates confined by a rotating elliptical trap. We
consider rotating solutions of the classical hydrodynamic equations, their
response to perturbations, as well as time-dependent simulations. We
discriminate three distinct, experimentally testable, regimes of instability:
{\em ripple}, {\em interbranch}, and {\em catastrophic}. Under
symmetry-breaking perturbations these instabilities lead to lattice formation
even at zero temperature. While our results are consistent with previous
theoretical and experimental results, they shed new light on lattice formation.Comment: 5 pages, 2 figure
Relativistic Coulomb Green's function in -dimensions
Using the operator method, the Green's functions of the Dirac and
Klein-Gordon equations in the Coulomb potential are derived for
the arbitrary space dimensionality . Nonrelativistic and quasiclassical
asymptotics of these Green's functions are considered in detail.Comment: 9 page
Hydrogen dynamics and light-induced structural changes in hydrogenated amorphous silicon
We use accurate first principles methods to study the network dynamics of
hydrogenated amorphous silicon, including the motion of hydrogen. In addition
to studies of atomic dynamics in the electronic ground state, we also adopt a
simple procedure to track the H dynamics in light-excited states. Consistent
with recent experiments and computer simulations, we find that dihydride
structures are formed for dynamics in the light-excited states, and we give
explicit examples of pathways to these states. Our simulations appear to be
consistent with aspects of the Staebler-Wronski effect, such as the
light-induced creation of well separated dangling bonds.Comment: 9 pages, 8 figures, submitted to PR
High efficiency coupling of photon pairs in practice
Multi-photon and quantum communication experiments such as loophole-free Bell
tests and device independent quantum key distribution require entangled photon
sources which display high coupling efficiency. In this paper we put forward a
simple quantum theoretical model which allows the experimenter to design a
source with high pair coupling efficiency. In particular we apply this approach
to a situation where high coupling has not been previously obtained: we
demonstrate a symmetric coupling efficiency of more than 80% in a highly
frequency non-degenerate configuration. Furthermore, we demonstrate this
technique in a broad range of configurations, i.e. in continuous wave and
pulsed pump regimes, and for different nonlinear crystals
The largest oxigen bearing organic molecule repository
We present the first detection of complex aldehydes and isomers in three
typical molecular clouds located within 200pc of the center of our Galaxy.
We find very large abundances of these complex organic molecules (COMs) in
the central molecular zone (CMZ), which we attribute to the ejection of COMs
from grain mantles by shocks. The relative abundances of the different COMs
with respect to that of CH3OH are strikingly similar for the three sources,
located in very different environments in the CMZ. The similar relative
abundances point toward a unique grain mantle composition in the CMZ. Studying
the Galactic center clouds and objects in the Galactic disk having large
abundances of COMs, we find that more saturated molecules are more abundant
than the non-saturated ones. We also find differences between the relative
abundance between COMs in the CMZ and the Galactic disk, suggesting different
chemical histories of the grain mantles between the two regions in the Galaxy
for the complex aldehydes. Different possibilities for the grain chemistry on
the icy mantles in the GC clouds are briefly discussed. Cosmic rays can play an
important role in the grain chemistry. With these new detections, the molecular
clouds in the Galactic center appear to be one of the best laboratories for
studying the formation of COMs in the Galaxy.Comment: 20 pages, 4 figures, accepted in Ap
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