1,718 research outputs found
Blazar observations above 60 GeV: the Influence of CELESTE's Energy Scale on the Study of Flares and Spectra
The CELESTE atmospheric Cherenkov detector ran until June 2004. It has
observed the blazars Mrk 421, 1ES 1426+428 and Mrk 501. We significantly
improved our understanding of the atmosphere using a LIDAR, and of the optical
throughput of the detector using stellar photometry. The new data analysis
provides better background rejection. We present our light curve for Mrk 421
for the 2002-2004 season and a comparison with X-ray data and the 2004
observation of 1ES 1426+428. The new analysis will allow a more sensitive
search for a signal from Mrk 501.Comment: 7 pages, 7 figures, proc. of the 35th COSPAR Scientific Assembly held
in Paris, France, July 200
Universal Quantum Computation in a Neutral Atom Decoherence Free Subspace
In this paper, we propose a way to achieve protected universal computation in
a neutral atom quantum computer subject to collective dephasing. Our proposal
relies on the existence of a Decoherence Free Subspace (DFS), resulting from
symmetry properties of the errors. After briefly describing the physical system
and the error model considered, we show how to encode information into the DFS
and build a complete set of safe universal gates. Finally, we provide numerical
simulations for the fidelity of the different gates in the presence of
time-dependent phase errors and discuss their performance and practical
feasibility.Comment: 7 pages, 8 figure
Quantum optical non-linearities induced by Rydberg-Rydberg interactions: a perturbative approach
In this article, we theoretically study the quantum statistical properties of
the light transmitted through or reflected from an optical cavity, filled by an
atomic medium with strong optical non-linearity induced by Rydberg-Rydberg van
der Waals interactions. Atoms are driven on a two-photon transition from their
ground state to a Rydberg level via an intermediate state by the combination of
a weak signal field and a strong control beam. By using a perturbative
approach, we get analytic results which remain valid in the regime of weak
feeding fields, even when the intermediate state becomes resonant. Therefore
they allow us to investigate quantitatively new features associated with the
resonant behaviour of the system. We also propose an effective non-linear
three-boson model of the system which, in addition to leading to the same
analytic results as the original problem, sheds light on the physical processes
at work in the system
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