139 research outputs found
Stabilizing two-qubit entanglement with engineered synthetic squeezing
It is well known that qubits immersed in a squeezed vacuum environment
exhibit many exotic phenomena, including dissipative entanglement
stabilization. Here, we show that these effects only require interference
between excitation and decay processes, and can be faithfully mimicked without
non-classical light using simple classical temporal modulation. We present
schemes that harnesses this idea to stabilize entanglement between two remote
qubits coupled via a transmission line or waveguide, where either the
qubit-waveguide coupling is modulated, or the qubits are directly driven. We
analyze the resilience of these approaches against various imperfections, and
also characterize the trade-off between the speed and quality of entanglement
stabilization. Our protocols are compatible with state of the art cavity QED
systems.Comment: 16 pages, 6 figure
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Laser welding of a beryllium/tantalum collimator
This report describes the methods utilized in the fabrication of a collimator from 0.001 inch thick beryllium and tantalum foil. The laser welding process proved to be an acceptable method for joining the beryllium in a standing edge joint configuration
SPI Measurements of Galactic 26Al
The precision measurement of the 1809 keV gamma-ray line from Galactic
Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge
detector camera. We aim for determination of the detailed shape of this
gamma-ray line, and its variation for different source regions along the plane
of the Galaxy. Data from the first part of the core program observations of the
first mission year have been inspected. A clear detection of the \Al line at
about 5--7 significance demonstrates that SPI will deepen \Al studies.
The line intensity is consistent with expectations from previous experiments,
and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more
consistent with RHESSI's recent value. Only preliminary statements can be made
at this time, however, due to the multi-component background underlying the
signal at \about 40 times higher intensity than the signal from Galactic
Al.Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL
volume
The Galactic 26Al Problem and The Close Binary SNIb/c Solution?
The origin of the long-lived radioactive 26Al, which has been observed in the
Galactic interstellar medium from its 1.809 MeV decay gamma-ray line emission,
has been a persistent problem for over twenty years. Wolf-Rayet (WR) winds were
thought to be the most promising source, but their calculated 26Al yields are
not consistent with recent analyses of the 1.809 MeV emission from the nearest
WR star and nearby OB associations. The expected 26Al yield from the WR star
exceeds by as much as a factor of 3, that set by the 2-sigma upper limit on the
1.809 MeV emission, while the WR yields in the OB associations are only about
1/3 of that required by the 1.809 MeV emission. We suggest that a solution to
these problems may lie in 26Al from a previously ignored source: explosive
nucleosynthesis in the core collapse SNIb/c supernovae of WR stars that have
lost most of their mass to close binary companions. Recent nucleosynthetic
calculations of SNIb/c suggest that their 26Al yields depend very strongly on
the final, pre-supernova mass of the WR star, and that those with final masses
around 6 to 8 solar masses are expected to produce as much as 0.01 solar masses
of 26Al per supernova. Such binary SNIb/c make up only a small fraction of the
current SNIb/c and only about 1% of all Galactic core collapse supernovae. They
appear to be such prolific sources that the bulk of the present 26Al in the
Galaxy may come from just a few hundred close binary SNIb/c and the intense
1.809 MeV emission from nearby OB associations may come from just one or two
such supernova.Comment: Accepted for publication in Astrophysical Journal Letters, 611,10
August 200
Light Element Evolution and Cosmic Ray Energetics
Using cosmic-ray energetics as a discriminator, we investigate evolutionary
models of LiBeB. We employ a Monte Carlo code which incorporates the delayed
mixing into the ISM both of the synthesized Fe, due to its incorporation into
high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the
transport of the cosmic rays. We normalize the LiBeB production to the integral
energy imparted to cosmic rays per supernova. Models in which the cosmic rays
are accelerated mainly out of the average ISM significantly under predict the
measured Be abundance of the early Galaxy, the increase in [O/Fe] with
decreasing [Fe/H] notwithstanding. We suggest that this increase could be due
to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated
out of supernova ejecta enriched superbubbles, the measured Be abundances are
consistent with a cosmic-ray acceleration efficiency that is in very good
agreement with the current epoch data. We also find that neither the above
cosmic-ray origin models nor a model employing low energy cosmic rays
originating from the supernovae of only very massive progenitors can account
for the Li data at values of [Fe/H] below 2.Comment: latex 19 pages, 2 tables, 10 eps figures, uses aastex.cls natbib.sty
Submitted to the Astrophysical Journa
Possible Evidence For Axino Dark Matter In The Galactic Bulge
Recently, the SPI spectrometer on the INTEGRAL satellite observed strong 511
keV line emission from the galactic bulge. Although the angular distribution
(spherically symmetric with width of \sim 9 degree) of this emission is
difficult to account for with traditional astrophysical scenarios, light dark
matter particles could account for the observation. In this letter, we consider
the possibility that decaying axinos in an R-parity violating model of
supersymmetry may be the source of this emission. We find that \sim 1-300 MeV
axinos with R-parity violating couplings can naturally produce the observed
emission.Comment: 4 pages, 1 figure. Version accepted by Physical Review
Rossi X-Ray Timing Explorer Guest Investigator Program
Rossi X-ray Timing Explorer (RXTE) observations of the bright supernova remnant Cas A have revealed a hard power law component above 10 keV in addition to two thermal components inferred from ASCA measurements of the many line centroids from low-Z elements. The power law can be shown to be consistent with synchrotron emission from radio to hard x-rays by electrons of up to 4 x 10(exp 13) eV. Measurement of the 1157 keV line by CGRO (Compton Gamma Ray Observatory) from SC-44 in the chain of decay of Ti-44 predicts that the two Ti-44 lines at 68 and 78 keV should appear at the CGRO intensity. RXTE has placed upper limits on such lines that are marginally consistent with the CGRO measurement. Implications of these results on sites for cosmic ray acceleration and nucleosynthesis are discussed
Electron-positron Annihilation Lines and Decaying Sterile Neutrinos
If massive sterile neutrinos exist, their decays into photons and/or
electron-positron pairs may give rise to observable consequences. We consider
the possibility that MeV sterile neutrino decays lead to the diffuse positron
annihilation line in the Milky Way center, and we thus obtain bounds on the
sterile neutrino decay rate s from relevant
astrophysical/cosmological data. Also, we expect a soft gamma flux of ph cm s from the Milky Way
center which shows up as a small MeV bump in the background photon spectrum.
Furthermore, we estimate the flux of active neutrinos produced by sterile
neutrino decays to be cm s passing through the earth.Comment: Accepted for publication in Astrophysics & Space Scienc
On the Origin of Cosmic Magnetic Fields
We review the literature concerning how the cosmic magnetic fields pervading
nearly all galaxies actually got started. some observational evidence involves
the chemical abundance of the light elements Be and B, while another one is
based on strong magnetic fields seen in high red shift galaxies. Seed fields,
whose strength is of order 10^{-20} gauss, easily sprung up in the era
preceding galaxy formation. Several mechanisms are proposed to amplify these
seed fields to microgauss strengths. The standard mechanism is the Alpha-Omega
dynamo theory. It has a major difficulty that makes unlikely to provide the
sole origin. The difficulty is rooted in the fact that the total flux is
constant. This implies that flux must be removed from the galactic discs. This
requires that the field and flux be separated, for otherwise interstellar mass
must be removed from the deep galactic gravitational and then their strength
increased by the alpha omega theory.Comment: 90 pages and 6 figures; accepted for publication in Reports of
Progress in Physics as an invited revie
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