6,273 research outputs found
Soft and Hard Pomeron in the Structure Function of the Proton at Low x and Low Q^2
We study inclusive electroproduction on the proton at low and low
using a soft and a hard Pomeron. The contribution of the soft Pomeron is based
on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross
section can be calculated by means of a gauge invariant gluon field strength
correlator. To model the hard Pomeron exchange we phenomenologically extend the
leading order evolution of a power-behaved structure function, , proposed by L\'opez and Yndur\'ain. This extension allows to
consider both the case and the region of higher on the basis of
the same parametrization. A good simultaneous fit to the data on and on
the cross section of real photoproduction is obtained for
. With four parameters we achieve a for 222 data points. In addition, we use our model of the inclusive
interaction to compute the longitudinal structure function
.Comment: 18 pages, Latex, 6 PS-figures, Regge-exchange neglected, more details
concerning the soft Pomeron included, section on the longitudinal structure
function added, all conclusions unchanged, final version to appear in Eur.
Phys. J.
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
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How to be a deontic buck-passer
Deontic, as opposed to evaluative buck-passing theories seem to be easier to accept, since there appears to be an intimate connection between deontic properties, such as âoughtâ, ârequirementâ, and âpermissionâ on the one hand, and normative reasons on the other. However, it is far from obvious what, precisely, the connection consists in, and this topic has suffered from a paucity of discussion. This paper seeks to address that paucity by providing a novel deontic buck-passing view, one that avoids the pitfalls both of the most straightforward view on the matter (what I call the âstandard viewâ) as well as a recently articulated view, due to Matt Bedke. It does so by appealing first to the distinction between a reason for, and a reason against, and uses this distinction to clarify what are taken to be two fundamental, but distinct, deontic propertiesâought and requirement. The resulting view allows us to capture these properties, the structural relations between them, and does so in a way that avoids making supererogation impossible
Iron deficiency anaemia in bantu infants, and its association wiht kwashiorkor
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Atomic cluster state build up with macroscopic heralding
We describe a measurement-based state preparation scheme for the efficient
build up of cluster states in atom-cavity systems. As in a recent proposal for
the generation of maximally entangled atom pairs [Metz et al., Phys. Rev. Lett.
97, 040503 (2006)], we use an electron shelving technique to avoid the
necessity for the detection of single photons. Instead, the successful fusion
of smaller into larger clusters is heralded by an easy-to-detect macroscopic
fluorescence signal. High fidelities are achieved even in the vicinity of the
bad cavity limit and are essentially independent of the concrete size of the
system parameters.Comment: 14 pages, 12 figures; minor changes, mainly clarification
Virginia Techâs Innovative College Librarian Program
In 1994, Virginia Polytechnic Institute and State University (Virginia Tech) Libraries founded a College Librarian Program. Begun with four librarians serving four colleges, it has since grown to include eleven librarians providing comprehensive library services to the six of Virginia Tech\u27s eight colleges not served by branch libraries. Other authors have described the early history of the program or outlined some of its specific elements. By reviewing how the program came to be, by analyzing the choice points it presents, especially from an administrative perspective, and by discussing its benefits and costs from a university point of view, the authors hope to illuminate an exciting and potentially beneficial approach that other large institutions might seek to adapt to their own missions
Robust Entanglement through Macroscopic Quantum Jumps
We propose an entanglement generation scheme that requires neither the
coherent evolution of a quantum system nor the detection of single photons.
Instead, the desired state is heralded by a {\em macroscopic} quantum jump.
Macroscopic quantum jumps manifest themselves as a random telegraph signal with
long intervals of intense fluorescence (light periods) interrupted by the
complete absence of photons (dark periods). Here we show that a system of two
atoms trapped inside an optical cavity can be designed such that a dark period
prepares the atoms in a maximally entangled ground state. Achieving fidelities
above 0.9 is possible even when the single-atom cooperativity parameter C is as
low as 10 and when using a photon detector with an efficiency as low as eta =
0.2.Comment: 5 pages, 4 figures, more detailed discussion of underlying physical
effect, references update
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