241 research outputs found
Two-particle entanglement as a property of three-particle entangled states
In a recent article [Phys. Rev. A 54, 1793 (1996)] Krenn and Zeilinger
investigated the conditional two-particle correlations for the subensemble of
data obtained by selecting the results of the spin measurements by two
observers 1 and 2 with respect to the result found in the corresponding
measurement by a third observer. In this paper we write out explicitly the
condition required in order for the selected results of observers 1 and 2 to
violate Bell's inequality for general measurement directions. It is shown that
there are infinitely many sets of directions giving the maximum level of
violation. Further, we extend the analysis by the authors to the class of
triorthogonal states |Psi> = c_1 |z_1>|z_2>|z_3> + c_2 |-z_1>|-z_2>|-z_3>. It
is found that a maximal violation of Bell's inequality occurs provided the
corresponding three-particle state yields a direct ("all or nothing")
nonlocality contradiction.Comment: REVTeX, 7 pages, no figure
Independent Set Reconfiguration in Cographs
We study the following independent set reconfiguration problem, called
TAR-Reachability: given two independent sets and of a graph , both
of size at least , is it possible to transform into by adding and
removing vertices one-by-one, while maintaining an independent set of size at
least throughout? This problem is known to be PSPACE-hard in general. For
the case that is a cograph (i.e. -free graph) on vertices, we show
that it can be solved in time , and that the length of a shortest
reconfiguration sequence from to is bounded by , if such a
sequence exists.
More generally, we show that if is a graph class for which (i)
TAR-Reachability can be solved efficiently, (ii) maximum independent sets can
be computed efficiently, and which satisfies a certain additional property,
then the problem can be solved efficiently for any graph that can be obtained
from a collection of graphs in using disjoint union and complete join
operations. Chordal graphs are given as an example of such a class
Bayesian Nash Equilibria and Bell Inequalities
Games with incomplete information are formulated in a multi-sector
probability matrix formalism that can cope with quantum as well as classical
strategies. An analysis of classical and quantum strategy in a multi-sector
extension of the game of Battle of Sexes clarifies the two distinct roles of
nonlocal strategies, and establish the direct link between the true quantum
gain of game's payoff and the breaking of Bell inequalities.Comment: 6 pages, LaTeX JPSJ 2 column format, changes in sections 1, 3 and 4,
added reference
A feasible quantum optical experiment capable of refuting noncontextuality for single photons
Elaborating on a previous work by Simon et al. [PRL 85, 1783 (2000)] we
propose a realizable quantum optical single-photon experiment using standard
present day technology, capable of discriminating maximally between the
predictions of quantum mechanics (QM) and noncontextual hidden variable
theories (NCHV). Quantum mechanics predicts a gross violation (up to a factor
of 2) of the noncontextual Bell-like inequality associated with the proposed
experiment. An actual maximal violation of this inequality would demonstrate
(modulo fair sampling) an all-or-nothing type contradiction between QM and
NCHV.Comment: LaTeX file, 8 pages, 1 figur
Reconfiguring Independent Sets in Claw-Free Graphs
We present a polynomial-time algorithm that, given two independent sets in a
claw-free graph , decides whether one can be transformed into the other by a
sequence of elementary steps. Each elementary step is to remove a vertex
from the current independent set and to add a new vertex (not in )
such that the result is again an independent set. We also consider the more
restricted model where and have to be adjacent
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