8,226 research outputs found
Classification of local realistic theories
Recently, it has shown that an explicit local realistic model for the values
of a correlation function, given in a two-setting Bell experiment (two-setting
model), works only for the specific set of settings in the given experiment,
but cannot construct a local realistic model for the values of a correlation
function, given in a {\it continuous-infinite} settings Bell experiment
(infinite-setting model), even though there exist two-setting models for all
directions in space. Hence, two-setting model does not have the property which
infinite-setting model has. Here, we show that an explicit two-setting model
cannot construct a local realistic model for the values of a correlation
function, given in a {\it only discrete-three} settings Bell experiment
(three-setting model), even though there exist two-setting models for the three
measurement directions chosen in the given three-setting experiment. Hence,
two-setting model does not have the property which three-setting model has.Comment: To appear in Journal of Physics A: Mathematical and Theoretica
Kochen-Specker theorem as a precondition for secure quantum key distribution
We show that (1) the violation of the Ekert 91 inequality is a sufficient
condition for certification of the Kochen-Specker (KS) theorem, and (2) the
violation of the Bennett-Brassard-Mermin 92 (BBM) inequality is, also, a
sufficient condition for certification of the KS theorem. Therefore the success
in each QKD protocol reveals the nonclassical feature of quantum theory, in the
sense that the KS realism is violated. Further, it turned out that the Ekert
inequality and the BBM inequality are depictured by distillable entanglement
witness inequalities. Here, we connect the success in these two key
distribution processes into the no-hidden-variables theorem and into witness on
distillable entanglement. We also discuss the explicit difference between the
KS realism and Bell's local realism in the Hilbert space formalism of quantum
theory.Comment: 4 pages, To appear in Phys. Rev.
Comment on ``All quantum observables in a hidden-variable model must commute simultaneously"
Malley discussed {[Phys. Rev. A {\bf 69}, 022118 (2004)]} that all quantum
observables in a hidden-variable model for quantum events must commute
simultaneously. In this comment, we discuss that Malley's theorem is indeed
valid for the hidden-variable theoretical assumptions, which were introduced by
Kochen and Specker. However, we give an example that the local hidden-variable
(LHV) model for quantum events preserves noncommutativity of quantum
observables. It turns out that Malley's theorem is not related with the LHV
model for quantum events, in general.Comment: 3 page
Multipartite positive-partial-transpose inequalities exponentially stronger than local reality inequalities
We show that positivity of {\it every} partial transpose of -partite
quantum states implies new inequalities on Bell correlations which are stronger
than standard Bell inequalities by a factor of . A violation of
the inequality implies the system is in a bipartite distillable entangled
state. It turns out that a family of -qubit bound entangled states proposed
by D\"ur {[Phys. Rev. Lett. {\bf 87}, 230402 (2001)]} violates the inequality
for .Comment: 4 pages, To appear in Phys. Rev.
Bell inequality with an arbitrary number of settings and its applications
Based on a geometrical argument introduced by Zukowski, a new multisetting
Bell inequality is derived, for the scenario in which many parties make
measurements on two-level systems. This generalizes and unifies some previous
results. Moreover, a necessary and sufficient condition for the violation of
this inequality is presented. It turns out that the class of non-separable
states which do not admit local realistic description is extended when compared
to the two-setting inequalities. However, supporting the conjecture of Peres,
quantum states with positive partial transposes with respect to all subsystems
do not violate the inequality. Additionally, we follow a general link between
Bell inequalities and communication complexity problems, and present a quantum
protocol linked with the inequality, which outperforms the best classical
protocol.Comment: 8 pages, To appear in Phys. Rev.
Two Nucleon-States in a Chiral Quark-Diquark Model
We study the ground and first excited states of nucleons in a chiral
quark-diquark model. We include two quark-diquark channels of the
scalar-isoscalar and axial-vector-isovector types for the nucleon states. The
diquark correlation violating the spin-flavor SU(4) symmetry allows to
treat the two quark-diquark channels independently. Hence the two states appear
as the superpositions of the two quark-diquark channels; one is the nucleon and
the other is a state which does not appear in the SU(4) quark models.
With a reasonable choice of model parameters, the mass of the excited state
appears at around 1.5 GeV, which we identify with the Roper resonance N(1440).Comment: 11 pages, 5 figures. Errors are corrected. Conclusions are not
affecte
Estudo da diversidade de begomovirus em tomateiro cultivado na região da caatinga do Brasil.
O presente trabalho teve como objetivo analisar a diversidade de begomovirus infectando tomateiro no Nordeste brasileiro.Resumo 673-
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