77,218 research outputs found
Noise robustness in the detection of non separable random unitary maps
We briefly review a recently proposed method to detect properties of quantum
noise processes and quantum channels. We illustrate in detail the method for
detecting non separable random unitary channels and consider in particular the
explicit examples of the CNOT and CZ gates. We analyse their robustness in the
presence of noise for several quantum noise models.Comment: 10 pages, 1 figur
Detection methods to rule out completely co-positive and bi-entangling operations
In this work we extend the quantum channel detection method developed in
[Phys. Rev. A 88, 042335 (2013)] and [Phys. Script. T153, 014044 (2013)] in
order to detect other interesting convex sets of quantum channels. First we
work out a procedure to detect non completely co-positive maps. Then we focus
on the set of so-called bi-entangling operations and show how a map outside
this set can be revealed. In both cases we provide explicit examples showing
the theoretical technique and the corresponding experimental procedure.Comment: 6 pages, 2 figure
IBVPs for Scalar Conservation Laws with Time Discontinuous Fluxes
The initial boundary value problem for a class of scalar non autonomous
conservation laws in one space dimension is proved to be well posed and stable
with respect to variations in the flux. Targeting applications to traffic, the
regularity assumptions on the flow are extended to a merely
dependence on time. These results ensure, for instance,
the well posedness of a class of vehicular traffic models with time dependent
speed limits. A traffic management problem is then shown to admit an optimal
solution
Note on lattice regularization and equal-time correlators for parton distribution functions
We show that a recent interesting idea to circumvent the difficulties with
the continuation of parton distribution functions to the Euclidean region, that
consists in looking at equal time correlators between proton states of infinite
momentum, encounters some problems related to the power divergent mixing
pattern of DIS operators, when implemented within the lattice regularization.Comment: 15 pages, no figures, Physical Review D (2017
Radio-X-ray Synergy to discover and Study Jetted Tidal Disruption Events
Observational consequences of tidal disruption of stars (TDEs) by
supermassive black holes (SMBHs) can enable us to discover quiescent SMBHs,
constrain their mass function, study formation and evolution of transient
accretion disks and jet formation. A couple of jetted TDEs have been recently
claimed in hard X-rays, challenging jet models, previously applied to
-ray bursts and active galactic nuclei. It is therefore of paramount
importance to increase the current sample. In this paper, we find that the best
strategy is not to use up-coming X-ray instruments alone, which will yield
between several (e-Rosita) and a couple of hundreds (Einstein Probe) events per
year below redshift one. We rather claim that a more efficient TDE hunter will
be the Square Kilometer Array (SKA) operating {\it in survey mode} at 1.4 GHz.
It may detect up to several hundreds of events per year below with
a peak rate of a few tens per year at . Therefore, even if the
jet production efficiency is {\it not } as assumed here, the predicted
rates should be large enough to allow for statistical studies. The
characteristic TDE decay of , however, is not seen in radio, whose
flux is quite featureless. {\it Identification} therefore requires localization
and prompt repointing by higher energy instruments. If radio candidates would
be repointed within a day by future X-ray observatories (e.g. Athena and
LOFT-like missions), it will be possible to detect up to X-ray
counterparts, almost up to redshift . The shortcome is that only for
redshift below the trigger times will be less than 10 days from
the explosion. In this regard the X-ray surveys are better suited to probe the
beginning of the flare, and are therefore complementary to SKA.Comment: Astrophysical Journal (revised version
Circular polarization signals of cloudy (exo)planets
The circular polarization of light that planets reflect is often neglected
because it is very small compared to the linear polarization. It could,
however, provide information on a planet's atmosphere and surface, and on the
presence of life, because homochiral molecules that are the building blocks of
life on Earth are known to reflect circularly polarized light.
We compute , the degree of circular polarization, for light that is
reflected by rocky (exo)planets with liquid water or sulfuric acid solution
clouds, both spatially resolved across the planetary disk and, for planets with
patchy clouds, integrated across the planetary disk, for various planetary
phase angles .
The optical thickness and vertical distribution of the atmospheric gas and
clouds, the size parameter and refractive index of the cloud particles, and
all influence . Spatially resolved, varies between (the sign indicates the polarization direction). Only for small gas
optical thicknesses above the clouds do significant sign changes (related to
cloud particle properties) across the planets' hemispheres occur. For patchy
clouds, the disk--integrated is typically smaller than ,
with maximums for between and , and
to . As expected, the disk--integrated is virtually zero at
and 180. The disk--integrated is also very small
at .
Measuring circular polarization signals appears to be challenging with
current technology. The small atmospheric circular polarization signal could,
however, allow the detection of circular polarization due to homochiral
molecules. Confirmation of the detectability of such signals requires better
knowledge of the strength of circular polarization signals of biological
sources.Comment: 15 pages, 11 figures, Accepted for publication in Astronomy and
Astrophysic
Non Local Conservation Laws in Bounded Domains
The well posedness for a class of non local systems of conservation laws in a
bounded domain is proved and various stability estimates are provided. This
construction is motivated by the modelling of crowd dynamics, which also leads
to define a non local operator adapted to the presence of a boundary. Numerical
integrations show that the resulting model provides qualitatively reasonable
solutions
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