19,853 research outputs found
VLBI observations of SN2011dh: imaging of the youngest radio supernova
We report on the VLBI detection of supernova SN2011dh at 22GHz using a subset
of the EVN array. The observations took place 14 days after the discovery of
the supernova, thus resulting in a VLBI image of the youngest radio-loud
supernova ever. We provide revised coordinates for the supernova with
milli-arcsecond precision, linked to the ICRF. The recovered flux density is a
factor 2 below the EVLA flux density reported by other authors at the same
frequency and epoch of our observations. This discrepancy could be due to
extended emission detected with the EVLA or to calibration problems in the VLBI
and/or EVLA observations.Comment: Letter. Accepted in A&
Entanglement cost of mixed states
We compute the entanglement cost of several families of bipartite mixed
states, including arbitrary mixtures of two Bell states. This is achieved by
developing a technique that allows us to ascertain the additivity of the
entanglement of formation for any state supported on specific subspaces. As a
side result, the proof of the irreversibility in asymptotic local manipulations
of entanglement is extended to two-qubit systems.Comment: 4 pages, no figures, (v4) new results, including a new method to
determine E_c for more general mixed states, presentation changed
significantl
Fidelity balance in quantum operations
I derive a tight bound between the quality of estimating the state of a
single copy of a -level system, and the degree the initial state has to be
altered in course of this procedure. This result provides a complete analytical
description of the quantum mechanical trade-off between the information gain
and the quantum state disturbance expressed in terms of mean fidelities. I also
discuss consequences of this bound for quantum teleportation using nonmaximally
entangled states.Comment: 4 pages, REVTeX. Revised versio
Genralized Robustness of Entanglement
The robustness of entanglement results of Vidal and Tarrach considered the
problem whereby an entangled state is mixed with a separable state so that the
overall state becomes non-entangled. In general it is known that there are also
cases when entangled states are mixed with other entangled states and where the
sum is separable. In this paper, we treat the more general case where entangled
states can be mixed with any states so that the resulting mixture is
unentangled. It is found that entangled pure states for this generalized case
have the same robustness as the restricted case of Vidal and Tarrach.Comment: Final version. Editorial changes and references added to independent
wor
HST/STIS Optical Transit Transmission Spectra of the hot-Jupiter HD209458b
We present the transmission spectra of the hot-Jupiter HD209458b taken with
the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Our
analysis combines data at two resolutions and applies a complete pixel-by-pixel
limb-darkening correction to fully reveal the spectral line shapes of
atmospheric absorption features. Terrestrial-based Na I and H I contamination
are identified which mask the strong exoplanetary absorption signature in the
Na core, which we find reaches total absorption levels of ~0.11% in a 4.4 Ang
band. The Na spectral line profile is characterized by a wide absorption
profile at the lowest absorption depths, and a sharp transition to a narrow
absorption profile at higher absorption values. The transmission spectra also
shows the presence of an additional absorber at ~6,250 Ang, observed at both
medium and low resolutions. We performed various limb-darkening tests,
including using high precision limb-darkening measurements of the sun to
characterize a general trend of Atlas models to slightly overestimate the
amount of limb-darkening at all wavelengths, likely due to the limitations of
the model's one-dimensional nature. We conclude that, despite these
limitations, Atlas models can still successfully model limb-darkening in high
signal-to-noise transits of solar-type stars, like HD209458, to a high level of
precision over the entire optical regime (3,000-10,000 Ang) at transit phases
between 2nd and 3rd contact.Comment: 18 pages, 11 figures, Accepted to Ap
Corrigendum to "The upper atmosphere of the exoplanet HD209458b revealed by the sodium D lines: Temperature-pressure profile, ionization layer and thermosphere" [2011, A&A, 527, A110]
An error was detected in the code used for the analysis of the HD209458b
sodium profile (Vidal-Madjar et al. 2011). Here we present an updated T-P
profile and briefly discuss the consequences.Comment: Published in Astronomy & Astrophysics, 533, C
15 years of VLBI observations of two compact radio sources in Messier 82
We present the results of a second epoch of 18cm global Very Long-Baseline
Interferometry (VLBI) observations, taken on 23 February 2001, of the central
kiloparsec of the nearby starburst galaxy Messier 82. These observations
further investigate the structural and flux evolution of the most compact radio
sources in the central region of M82. The two most compact radio objects in M82
have been investigated (41.95+575 and 43.31+592). Using this recent epoch of
data in comparison with our previous global VLBI observations and two earlier
epochs of European VLBI Network observations we measure expansion velocities in
the range of 1500-2000km/s for 41.95+575, and 9000-11000km/s for 43.31+592
using various independent methods. In each case the measured remnant expansion
velocities are significantly larger than the canonical expansion velocity
(500km/s) of supernova remnants within M82 predicted from theoretical models.
In this paper we discuss the implications of these measured expansion
velocities with respect to the high density environment that the SNR are
expected to reside in within the centre of the M82 starburst.Comment: Accepted for publication in MNRAS, 9 pages, 8 figure
Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation
We present indications of thermalization and cooling of quasi-particles, a
precursor for quantum condensation, in a plasmonic nanoparticle array. We
investigate a periodic array of metallic nanorods covered by a polymer layer
doped with an organic dye at room temperature. Surface lattice resonances of
the array---hybridized plasmonic/photonic modes---couple strongly to excitons
in the dye, and bosonic quasi-particles which we call
plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density
through optical pumping, we observe thermalization and cooling of the strongly
coupled PEP band in the light emission dispersion diagram. For increased
pumping, we observe saturation of the strong coupling and emission in a new
weakly coupled band, which again shows signatures of thermalization and
cooling.Comment: 8 pages, 5 figures including supplemental material. The newest
version includes new measurements and corrections to the interpretation of
the result
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