44,466 research outputs found
Distilling common randomness from bipartite quantum states
The problem of converting noisy quantum correlations between two parties into
noiseless classical ones using a limited amount of one-way classical
communication is addressed. A single-letter formula for the optimal trade-off
between the extracted common randomness and classical communication rate is
obtained for the special case of classical-quantum correlations. The resulting
curve is intimately related to the quantum compression with classical side
information trade-off curve of Hayden, Jozsa and Winter. For a general
initial state we obtain a similar result, with a single-letter formula, when we
impose a tensor product restriction on the measurements performed by the
sender; without this restriction the trade-off is given by the regularization
of this function. Of particular interest is a quantity we call ``distillable
common randomness'' of a state: the maximum overhead of the common randomness
over the one-way classical communication if the latter is unbounded. It is an
operational measure of (total) correlation in a quantum state. For
classical-quantum correlations it is given by the Holevo mutual information of
its associated ensemble, for pure states it is the entropy of entanglement. In
general, it is given by an optimization problem over measurements and
regularization; for the case of separable states we show that this can be
single-letterized.Comment: 22 pages, LaTe
Geometric functionals of fractal percolation
Fractal percolation exhibits a dramatic topological phase transition,
changing abruptly from a dust-like set to a system spanning cluster. The
transition points are unknown and difficult to estimate. In many classical
percolation models the percolation thresholds have been approximated well using
additive geometric functionals, known as intrinsic volumes. Motivated by the
question whether a similar approach is possible for fractal models, we
introduce corresponding geometric functionals for the fractal percolation
process . They arise as limits of expected functionals of finite
approximations of . We establish the existence of these limit functionals
and obtain explicit formulas for them as well as for their finite
approximations.Comment: 42 pages, 8 figure
High-temperature oxidation and erosion-resistant refractory coatings
Various refractory coating systems were evaluated for rocket nozzle applications by actual rocket test firings. A reference is noted which identifies failure mechanisms and gives results of the firing tests for 18 coating systems. Iridium, iridium-rhenium, and hafnium oxide-zirconium oxide coatings show most promising results
Cycles of construing in radicalization and deradicalization: a study of Salafist Muslims.
© Taylor & Francis Group, LLC.This article explores radicalization and deradicalization by considering the experiences of six young Tunisian people who had become Salafist Muslims. Their responses to narrative interviews and repertory grid technique are considered from a personal construct perspective, revealing processes of construing and reconstruing, as well as relevant aspects of the structure and content of their construct systems. In two cases, their journeys involved not only radicalization but self-deradicalization, and their experiences are drawn on to consider implications for deradicalization.Peer reviewedFinal Accepted Versio
Long-term Evolution and Stability of Saturnian Small Satellites: Aegaeon, Methone, Anthe, and Pallene
Aegaeon, Methone, Anthe, and Pallene are four Saturnian small moons,
discovered by the Cassini spacecraft. Although their orbital characterization
has been carried on by a number of authors, their long-term evolution has not
been studied in detail so far. In this work, we numerically explore the
long-term evolution, up to yr, of the small moons in a system formed by
an oblate Saturn and the five largest moons close to the region: Janus,
Epimetheus, Mimas, Enceladus, and Tethys. By using frequency analysis we
determined the stability of the small moons and characterize, through diffusion
maps, the dynamical behavior of a wide region of geometric phase space, vs
, surrounding them. Those maps could shed light on the possible initial
number of small bodies close to Mimas, and help to better understand the
dynamical origin of the small satellites. We found that the four small moons
are long-term stable and no mark of chaos is found for them. Aegaeon, Methone,
and Anthe could remain unaltered for at least Myr, given the current
configuration of the system. They remain well-trapped in the corotation
eccentricity resonances with Mimas in which they currently librate. However,
perturbations from nearby resonances, such as Lindblad eccentricity resonances
with Mimas, seem responsible for largest variations observed for Methone and
Anthe. Pallene remains in a non-resonant orbit and it is the more stable, at
least for 64 Myr. Nonetheless, it is affected by a quasi-resonance with Mimas,
which induces long-term orbital oscillations of its eccentricity and
inclination.Comment: 17 pages, 12 figures, 5 tables. Accepted for publication in MNRA
The quantum capacity with symmetric side channels
We present an upper bound for the quantum channel capacity that is both
additive and convex. Our bound can be interpreted as the capacity of a channel
for high-fidelity quantum communication when assisted by a family of channels
that have no capacity on their own. This family of assistance channels, which
we call symmetric side channels, consists of all channels mapping symmetrically
to their output and environment. The bound seems to be quite tight, and for
degradable quantum channels it coincides with the unassisted channel capacity.
Using this symmetric side channel capacity, we find new upper bounds on the
capacity of the depolarizing channel. We also briefly indicate an analogous
notion for distilling entanglement using the same class of (one-way) channels,
yielding one of the few entanglement measures that is monotonic under local
operations with one-way classical communication (1-LOCC), but not under the
more general class of local operations with classical communication (LOCC).Comment: 10 pages, 4 figure
Wigner function and quantum kinetic theory in curved space-time and external fields
A new definition of the Wigner function for quantum fields coupled to curved
space--time and an external Yang--Mills field is studied on the example of a
scalar and a Dirac fields. The definition uses the formalism of the tangent
bundles and is explicitly covariant and gauge invariant. Derivation of
collisionless quantum kinetic equations is carried out for both quantum fields
by using the first order formalism of Duffin and Kemmer. The evolution of the
Wigner function is governed by the quantum corrected Liouville--Vlasov equation
supplemented by the generalized mass--shell constraint. The structure of the
quantum corrections is perturbatively found in all adiabatic orders. The lowest
order quantum--curvature corrections coincide with the ones found by Winter.Comment: 41 page
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