367 research outputs found
International summer school on hydrological drought and global change, Trieste, Italy, 22-27 June 2008
On quantum non-signalling boxes
A classical non-signalling (or causal) box is an operation on classical
bipartite input with classical bipartite output such that no signal can be sent
from a party to the other through the use of the box. The quantum counterpart
of such boxes, i.e. completely positive trace-preserving maps on bipartite
states, though studied in literature, have been investigated less intensively
than classical boxes. We present here some results and remarks about such maps.
In particular, we analyze: the relations among properties as causality,
non-locality and entanglement; the connection between causal and entanglement
breaking maps; the characterization of causal maps in terms of the
classification of states with fixed reductions. We also provide new proofs of
the fact that every non-product unitary transformation is not causal, as well
as for the equivalence of the so-called semicausality and semilocalizability
properties.Comment: 18 pages, 7 figures, revtex
Seasonal characteristics of the relationship between daily precipitation intensity and surface temperature
Past studies have argued that the intensity of extreme precipitation events should increase exponentially with temperature. This argument is based on the principle that the atmospheric moisture holding capacity increases according to the Clausius-Clapeyron equation and on the expectation that precipitation formation should follow accordingly. We test the latter assumption by investigating to what extent a relation with temperature can be observed intraseasonally in present-day climate. For this purpose, we use observed and simulated daily surface temperature and precipitation over Europe. In winter a general increase in precipitation intensity is indeed observed, while in summer we find a decrease in precipitation intensity with increasing temperature. We interpret these findings by making use of model results where we can distinguish separate precipitation types and investigate the moisture content in the atmosphere. In winter, the Clausius-Clapeyron relationship sets a limit to the increase in the large-scale precipitation with increasing temperature. Conversely, in summer the availability of moisture, and not the atmosphere's capacity to hold this moisture, is the dominant factor at the daily timescale. For convective precipitation, we find a peak like structure which is similar for all subregions, independent of the mean temperature, contrary to large-scale precipitation which has a more monotonic dependence on temperature
A class of 2^N x 2^N bound entangled states revealed by non-decomposable maps
We use some general results regarding positive maps to exhibit examples of
non-decomposable maps and 2^N x 2^N, N >= 2, bound entangled states, e.g. non
distillable bipartite states of N + N qubits.Comment: 19 pages, 1 figur
Environment Induced Entanglement in Markovian Dissipative Dynamics
We show that two, non interacting 2-level systems, immersed in a common bath,
can become mutually entangled when evolving according to a Markovian,
completely positive reduced dynamics.Comment: 4 pages, LaTex, no figures, added reference
Broadcast copies reveal the quantumness of correlations
We study the quantumness of bipartite correlations by proposing a quantity
that combines a measure of total correlations -- mutual information -- with the
notion of broadcast copies -- i.e., generally nonfactorized copies -- of
bipartite states. By analyzing how our quantity increases with the number of
broadcast copies, we are able to classify classical, separable, and entangled
states. This motivates the definition of the broadcast regularization of mutual
information, the asymptotic minimal mutual information per broadcast copy,
which we show to have many properties of an entanglement measure.Comment: 1 figure, 5 pages, more similar to the published versio
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