3,326 research outputs found
Multi-Photon Quantum Key Distribution Based on Double-Lock Encryption
This paper presents a multi-stage, multi-photon quantum key distribution
protocol based on the double-lock cryptography. It exploits the asymmetry in
the detection strategies between the legitimate users and the eavesdropper. The
security analysis of the protocol is presented with coherent states under the
intercept-resend attack, the photon number splitting attack, and the
man-in-the-middle attack. It is found that the mean photon number can be much
larger than one. This complements the recent interest in multi-photon quantum
communication protocols that require a pre-shared key between the legitimate
users
Operator-sum representation of time-dependent density operators and its applications
We show that any arbitrary time-dependent density operator of an open system
can always be described in terms of an operator-sum representation regardless
of its initial condition and the path of its evolution in the state space, and
we provide a general expression of Kraus operators for arbitrary time-dependent
density operator of an -dimensional system. Moreover, applications of our
result are illustrated through several examples.Comment: 4 pages, no figure, brief repor
Neutrino Mass Sum-rules in Flavor Symmetry Models
Four different neutrino mass sum-rules have been analyzed: these frequently
arise in flavor symmetry models based on the groups A_4, S_4 or T', which are
often constructed to generate tri-bimaximal mixing. In general, neutrino mass
can be probed in three different ways, using beta decay, neutrino-less double
beta decay and cosmology. The general relations between the corresponding three
neutrino mass observables are well known. The sum-rules lead to relations
between the observables that are different from the general case and therefore
only certain regions in parameter space are allowed. Plots of the neutrino mass
observables are given for the sum-rules, and analytical expressions for the
observables are provided. The case of deviations from the exact sum-rules is
also discussed, which can introduce new features. The sum-rules could be used
to distinguish some of the many models in the literature, which all lead to the
same neutrino oscillation results.Comment: 22 pages, 10 figures; matches the version published in Nuclear
Physics
Tri-Bimaximal Neutrino Mixing from Discrete Symmetry in Extra Dimensions
We discuss a particularly symmetric model of neutrino mixings where, with
good accuracy, the atmospheric mixing angle theta_{23} is maximal, theta_{13}=0
and the solar angle satisfies sin^2(theta_{12})=1/3 (Harrison-Perkins-Scott
(HPS) matrix). The discrete symmetry A_4 is a suitable symmetry group for the
realization of this type of model. We construct a model where the HPS matrix is
exactly obtained in a first approximation without imposing ad hoc relations
among parameters. The crucial issue of the required VEV alignment in the scalar
sector is discussed and we present a natural solution of this problem based on
a formulation with extra dimensions. We study the corrections from higher
dimensionality operators allowed by the symmetries of the model and discuss the
conditions on the cut-off scales and the VEVs in order for these corrections to
be completely under control. Finally, the observed hierarchy of charged lepton
masses is obtained by assuming a larger flavour symmetry. We also show that,
under general conditions, a maximal theta_{23} can never arise from an exact
flavour symmetry.Comment: 24 pages, 1 figure, misprints corrected and references adde
Higher Spin Black Holes from CFT
Higher spin gravity in three dimensions has explicit black holes solutions,
carrying higher spin charge. We compute the free energy of a charged black hole
from the holographic dual, a 2d CFT with extended conformal symmetry, and find
exact agreement with the bulk thermodynamics. In the CFT, higher spin
corrections to the free energy can be calculated at high temperature from
correlation functions of W-algebra currents.Comment: 24 pages; v2 reference adde
Quantum uniqueness
In the classical world one can construct two identical systems which have
identical behavior and give identical measurement results. We show this to be
impossible in the quantum domain. We prove that after the same quantum
measurement two different quantum systems cannot yield always identical
results, provided the possible measurement results belong to a non orthogonal
set. This is interpreted as quantum uniqueness - a quantum feature which has no
classical analog. Its tight relation with objective randomness of quantum
measurements is discussed.Comment: Presented at 4th Feynman festival, June 22-26, 2009, in Olomouc,
Czech Republic
New high-pressure phase of HfTiO4 and ZrTiO4 ceramics
We studied the high-pressure effects on the crystalline structure of
monoclinic HfTiO4 and ZrTiO4. We found that the compressibility of these
ceramics is highly non-isotropic, being the b-axis the most compressible one.
In addition, the a-axis is found to have a small and negative compressibility.
At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition
in HfTiO4 (ZrTiO4), coexisting the low- and high-pressure phases in a broad
pressure range. The new high-pressure phase has a monoclinic structure which
involves an increase in the Ti-O coordination and a collapse of the cell
volume. The equation of state for the low-pressure phase is also determined.Comment: 16 pages, 5 figures, 26 references, Article in Pres
Operator entanglement of two-qubit joint unitary operations revisited: Schmidt number approach
Operator entanglement of two-qubit joint unitary operations is revisited.
Schmidt number is an important attribute of a two-qubit unitary operation, and
may have connection with the entanglement measure of the unitary operator. We
found the entanglement measure of two-qubit unitary operators is classified by
the Schmidt number of the unitary operators. The exact relation between the
operator entanglement and the parameters of the unitary operator is clarified
too.Comment: To appear in the Brazilian Journal of Physic
A note on entropic uncertainty relations of position and momentum
We consider two entropic uncertainty relations of position and momentum
recently discussed in literature. By a suitable rescaling of one of them, we
obtain a smooth interpolation of both for high-resolution and low-resolution
measurements respectively. Because our interpolation has never been mentioned
in literature before, we propose it as a candidate for an improved entropic
uncertainty relation of position and momentum. Up to now, the author has
neither been able to falsify nor prove the new inequality. In our opinion it is
a challenge to do either one.Comment: 2 pages, 2 figures, 2 references adde
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