5,859 research outputs found
Observing collapse in two colliding dipolar Bose-Einstein condensates
We study the collision of two Bose-Einstein condensates with pure dipolar
interaction. A stationary pure dipolar condensate is known to be stable when
the atom number is below a critical value. However, collapse can occur during
the collision between two condensates due to local density fluctuations even if
the total atom number is only a fraction of the critical value. Using full
three-dimensional numerical simulations, we observe the collapse induced by
local density fluctuations. For the purpose of future experiments, we present
the time dependence of the density distribution, energy per particle and the
maximal density of the condensate. We also discuss the collapse time as a
function of the relative phase between the two condensates.Comment: 6 pages, 7 figure
Partonic Pole Matrix Elements for Fragmentation
A model-independent analysis of collinear three-parton correlation functions
for fragmentation is performed. By investigating their support properties it is
shown, in particular, that the so-called partonic pole matrix elements vanish.
This sheds new light on the understanding of transverse single spin asymmetries
in various hard semi-inclusive reactions. Moreover, it gives additional strong
evidence for the universality of transverse-momentum-dependent fragmentation
functions.Comment: 4 pages, 2 figures; minor changes, matches journal versio
MMHelper: An automated framework for the analysis of microscopy images acquired with the mother machine
This is the final version. Available from Nature Research via the DOI in this record.Live-cell imaging in microfluidic devices now allows the investigation of cellular heterogeneity within microbial populations. In particular, the mother machine technology developed by Wang et al. has been widely employed to investigate single-cell physiological parameters including gene expression, growth rate, mutagenesis, and response to antibiotics. One of the advantages of the mother machine technology is the ability to generate vast amounts of images; however, the time consuming analysis of these images constitutes a severe bottleneck. Here we overcome this limitation by introducing MMHelper (https://doi.org/10.5281/zenodo.3254394), a publicly available custom software implemented in Python which allows the automated analysis of brightfield or phase contrast, and any associated fluorescence, images of bacteria confined in the mother machine. We show that cell data extracted via MMHelper from tens of thousands of individual cells imaged in brightfield are consistent with results obtained via semi-automated image analysis based on ImageJ. Furthermore, we benchmark our software capability in processing phase contrast images from other laboratories against other publicly available software. We demonstrate that MMHelper has over 90% detection efficiency for brightfield and phase contrast images and provides a new open-source platform for the extraction of single-bacterium data, including cell length, area, and fluorescence intensity.Royal SocietyWellcome TrustMRCBBSR
Effect of frequency mismatched photons in quantum information processing
Many promising schemes for quantum information processing (QIP) rely on
few-photon interference effects. In these proposals, the photons are treated as
being indistinguishable particles. However, single photon sources are typically
subject to variation from device to device. Thus the photons emitted from
different sources will not be perfectly identical, and there will be some
variation in their frequencies. Here, we analyse the effect of this frequency
mismatch on QIP schemes. As examples, we consider the distributed QIP protocol
proposed by Barrett and Kok, and Hong-Ou-Mandel interference which lies at the
heart of many linear optical schemes for quantum computing. In the distributed
QIP protocol, we find that the fidelity of entangled qubit states depends
crucially on the time resolution of single photon detectors. In particular,
there is no reduction in the fidelity when an ideal detector model is assumed,
while reduced fidelities may be encountered when using realistic detectors with
a finite response time. We obtain similar results in the case of Hong-Ou-Mandel
interference -- with perfect detectors, a modified version of quantum
interference is seen, and the visibility of the interference pattern is reduced
as the detector time resolution is reduced. Our findings indicate that problems
due to frequency mismatch can be overcome, provided sufficiently fast detectors
are available.Comment: 14 pages, 8 figures. Comments welcome. v2: Minor changes. v3: Cleaned
up 3 formatting error
Relations between generalized and transverse momentum dependent parton distributions
Recent work suggests non-trivial relations between generalized parton
distributions on the one hand and (naive time-reversal odd) transverse momentum
dependent distributions on the other. Here we review the present knowledge on
such type of relations. Moreover, as far as spectator model calculations are
concerned, the existing results are considerably extended. While various
relations between the two types of parton distributions can be found in the
framework of spectator models, so far no non-trivial model-independent
relations have been established.Comment: 25 pages, 9 figures; Eq. (B17) and typos corrected, identical with
journal versio
Production of entanglement in Raman three-level systems using feedback
We examine the theoretical limits of the generation of entanglement in a
damped coupled ion-cavity system using jump-based feedback. Using Raman
transitions to produce entanglement between ground states reduces the necessary
feedback bandwidth, but does not improve the overall effect of the spontaneous
emission on the final entanglement. We find that the fidelity of the resulting
entanglement will be limited by the asymmetries produced by vibrations in the
trap, but that the concurrence remains above 0.88 for realistic ion trap sizes.Comment: 8 pages, 8 figure
Generalized polarizabilities of the nucleon studied in the linear sigma model (II)
In a previous paper virtual Compton scattering off the nucleon has been
investigated in the one-loop approximation of the linear sigma model in order
to determine the 3 scalar generalized polarizabilities. We have now extended
this work and calculated the 7 vector polarizabilities showing up in the
spin-dependent amplitude of virtual Compton scattering. The results fulfill 3
model-independent constraints recently derived. Compared to the constituent
quark model there exist enormous differences for some of the vector
polarizabilities. At vanishing three-momentum of the virtual photon, the
analytical results of the sigma model and of chiral perturbation theory can be
related. The influence of the exchange in the channel has been
discussed in some detail. Besides, the vector polarizabilities determine 2
linear combinations of the third order spin-polarizabilities appearing in real
Compton scattering.Comment: 17 pages, 4 figures, latex2e (Revtex), submitted to Z. Phys.
Localization of a dipolar Bose-Einstein condensate in a bichromatic optical lattice
By numerical simulation and variational analysis of the Gross-Pitaevskii
equation we study the localization, with an exponential tail, of a dipolar
Bose-Einstein condensate (DBEC) of Cr atoms in a three-dimensional
bichromatic optical-lattice (OL) generated by two monochromatic OL of
incommensurate wavelengths along three orthogonal directions. For a fixed
dipole-dipole interaction, a localized state of a small number of atoms () could be obtained when the short-range interaction is not too attractive
or not too repulsive. A phase diagram showing the region of stability of a DBEC
with short-range interaction and dipole-dipole interaction is given
Structure analysis of the virtual Compton scattering amplitude at low energies
We analyze virtual Compton scattering off the nucleon at low energies in a
covariant, model-independent formalism.
We define a set of invariant functions which, once the irregular nucleon pole
terms have been subtracted in a gauge-invariant fashion, is free of poles and
kinematical zeros.
The covariant treatment naturally allows one to implement the constraints due
to Lorentz and gauge invariance, crossing symmetry, and the discrete
symmetries.
In particular, when applied to the reaction,
charge-conjugation symmetry in combination with nucleon crossing generates four
relations among the ten originally proposed generalized polarizabilities of the
nucleon.Comment: 19 pages, LaTeX2e/RevTeX, no figures, original sections IV.-VI.
removed, to be discussed in a separate publication, none of the conclusions
change
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