822 research outputs found
Key Distillation and the Secret-Bit Fraction
We consider distillation of secret bits from partially secret noisy
correlations P_ABE, shared between two honest parties and an eavesdropper. The
most studied distillation scenario consists of joint operations on a large
number of copies of the distribution (P_ABE)^N, assisted with public
communication. Here we consider distillation with only one copy of the
distribution, and instead of rates, the 'quality' of the distilled secret bits
is optimized, where the 'quality' is quantified by the secret-bit fraction of
the result. The secret-bit fraction of a binary distribution is the proportion
which constitutes a secret bit between Alice and Bob. With local operations and
public communication the maximal extractable secret-bit fraction from a
distribution P_ABE is found, and is denoted by Lambda[P_ABE]. This quantity is
shown to be nonincreasing under local operations and public communication, and
nondecreasing under eavesdropper's local operations: it is a secrecy monotone.
It is shown that if Lambda[P_ABE]>1/2 then P_ABE is distillable, thus providing
a sufficient condition for distillability. A simple expression for
Lambda[P_ABE] is found when the eavesdropper is decoupled, and when the honest
parties' information is binary and the local operations are reversible.
Intriguingly, for general distributions the (optimal) operation requires local
degradation of the data.Comment: 12 page
Surface solitons in two-dimensional chirped photonic lattices
We study surface modes in semi-infinite chirped two-dimensional photonic
lattices in the frame- work of an effective discrete nonlinear model. We
demonstrate that the lattice chirp can change dramatically the conditions for
the mode localization near the surface, and we find numerically the families of
surface modes, in linear lattices, and discrete surface solitons, in nonlinear
lattices. We demonstrate that, in a sharp contrast to one-dimensional discrete
surface solitons, in two-dimensional lattices the mode threshold power is
lowered by the action of both the surface and lattice chirp. By manipulating
with the lattice chirp, we can control the mode position and its localization.Comment: 12 pages, 7 figure
From Bell's Theorem to Secure Quantum Key Distribution
Any Quantum Key Distribution (QKD) protocol consists first of sequences of
measurements that produce some correlation between classical data. We show that
these correlation data must violate some Bell inequality in order to contain
distillable secrecy, if not they could be produced by quantum measurements
performed on a separable state of larger dimension. We introduce a new QKD
protocol and prove its security against any individual attack by an adversary
only limited by the no-signaling condition.Comment: 5 pages, 2 figures, REVTEX
Multicolor vortex solitons in two-dimensional photonic lattices
We report on the existence and stability of multicolor lattice vortex
solitons constituted by coupled fundamental frequency and second-harmonic waves
in optical lattices in quadratic nonlinear media. It is shown that the solitons
are stable almost in the entire domain of their existence, and that the
instability domain decreases with the increase of the lattice depth. We also
show the generation of the solitons, and the feasibility of the concept of
lattice soliton algebra.Comment: 18 pages,6 figures. To appear in Physical Review
Soliton eigenvalue control with optical lattices
We address the dynamics of higher-order solitons in optical lattices, and
predict their self-splitting into the set of their single-soliton constituents.
The splitting is induced by the potential introduced by the lattice, together
with the imprinting of a phase tilt onto the initial multisoliton states. The
phenomenon allows the controllable generation of several coherent solitons
linked via their Zakharov-Shabat eigenvalues. Application of the scheme to the
generation of correlated matter waves in Bose-Einstein condensates is
discussed.Comment: 13 pages, 4 figures, to appear in Physical Review Letter
Bright solitons from defocusing nonlinearities
We report that defocusing cubic media with spatially inhomogeneous
nonlinearity, whose strength increases rapidly enough toward the periphery, can
support stable bright localized modes. Such nonlinearity landscapes give rise
to a variety of stable solitons in all three dimensions, including 1D
fundamental and multihump states, 2D vortex solitons with arbitrarily high
topological charges, and fundamental solitons in 3D. Solitons maintain their
coherence in the state of motion, oscillating in the nonlinear potential as
robust quasi-particles and colliding elastically. In addition to numerically
found soliton families, particular solutions are found in an exact analytical
form, and accurate approximations are developed for the entire families,
including moving solitons.Comment: 13 pages, 6 figures, to appear in Physical Review
Nonlinear switching of low-index defect modes in photonic lattices
We address nonlinear signal switching between two low-index defect channels
induced in periodic optical lattices. In contrast to conventional directional
couplers, where the guiding mechanism is total internal reflection or
refraction, in such Bragg-type coupler, the guidance is of a photonic-bandgap
origin. The coupling length in the low-index coupler is controlled by the
lattice parameters and by the channel spacing. In the nonlinear regime the
Bragg-type coupler behaves as an all-optical switch, exhibiting a remarkable
difference of switching power for focusing versus defocusing nonlinearity.Comment: 13 pages, 4 figures, to appear in Physical Review
Soliton topology versus discrete symmetry in optical lattices
We address the existence of vortex solitons supported by azimuthally
modulated lattices and reveal how the global lattice discrete symmetry has
fundamental implications on the possible topological charges of solitons. We
set a general ``charge rule'' using group-theory techniques, which holds for
all lattices belonging to a given symmetry group. Focusing in the case of
Bessel lattices allows us to derive also a overall stability rule for the
allowed vortex solitons.Comment: 4 pages, 3 figures. To appear in Phys. Rev. Let
The Impact of Migrations on the Health Services for Rare Diseases in Europe: The Example of Haemoglobin Disorders
Migration from different parts of the world to several European countries leads to the introduction of haemoglobinopathy genes into the population, which creates several demanding needs for prevention and treatment services for Hb disorders. In this paper we examined the degree to which European health services have responded to such challenges and in particular to health services necessary to address the needs of patients with thalassaemia and sickle cell disease (SCD). Information on available services was obtained from international organizations, collaborated European project, and the Thalassaemia International Federation (TIF) Databases, which include information from published surveys, registries, field trips, and delegation visits to countries and regions by expert advisors, local associations, and other collaborators' reports. Results show that countries with traditional strong prevention and treatment programs are well prepared to face the above challenges, while others are urgently needed to address these problems in a systematic way. The Thalassaemia International Federation (TIF) is committed to monitor the progress, raise awareness, and support the promotion of more immigrant-oriented health policies to ensure their integration in society and their access to appropriate, adequate, and timely health services
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