1,938 research outputs found
Quantum state-independent contextuality requires 13 rays
We show that, regardless of the dimension of the Hilbert space, there exists
no set of rays revealing state-independent contextuality with less than 13
rays. This implies that the set proposed by Yu and Oh in dimension three [Phys.
Rev. Lett. 108, 030402 (2012)] is actually the minimal set in quantum theory.
This contrasts with the case of Kochen-Specker sets, where the smallest set
occurs in dimension four.Comment: 8 pages, 2 tables, 1 figure, v2: minor change
Minimal true-implies-false and true-implies-true sets of propositions in noncontextual hidden variable theories
An essential ingredient in many examples of the conflict between quantum
theory and noncontextual hidden variables (e.g., the proof of the
Kochen-Specker theorem and Hardy's proof of Bell's theorem) is a set of atomic
propositions about the outcomes of ideal measurements such that, when outcome
noncontextuality is assumed, if proposition is true, then, due to
exclusiveness and completeness, a nonexclusive proposition () must be
false (true). We call such a set a {\em true-implies-false set} (TIFS) [{\em
true-implies-true set} (TITS)]. Here we identify all the minimal TIFSs and
TITSs in every dimension , i.e., the sets of each type having the
smallest number of propositions. These sets are important because each of them
leads to a proof of impossibility of noncontextual hidden variables and
corresponds to a simple situation with quantum vs classical advantage.
Moreover, the methods developed to identify them may be helpful to solve some
open problems regarding minimal Kochen-Specker sets.Comment: 9 pages, 7 figure
Twin inequality for fully contextual quantum correlations
Quantum mechanics exhibits a very peculiar form of contextuality. Identifying
and connecting the simplest scenarios in which more general theories can or
cannot be more contextual than quantum mechanics is a fundamental step in the
quest for the principle that singles out quantum contextuality. The former
scenario corresponds to the Klyachko-Can-Binicioglu-Shumovsky (KCBS)
inequality. Here we show that there is a simple tight inequality, twin to the
KCBS, for which quantum contextuality cannot be outperformed. In a sense, this
twin inequality is the simplest tool for recognizing fully contextual quantum
correlations.Comment: REVTeX4, 4 pages, 1 figur
Proposed experiment for the quantum "Guess my number" protocol
An experimental realization of the entanglement-assisted "Guess my number"
protocol for the reduction of communication complexity, introduced by Steane
and van Dam, would require producing and detecting three-qubit GHZ states with
an efficiency eta > 0.70, which would require single photon detectors of
efficiency sigma > 0.89. We propose a modification of the protocol which can be
translated into a real experiment using present-day technology. In the proposed
experiment, the quantum reduction of the multi-party communication complexity
would require an efficiency eta > 0.05, achievable with detectors of sigma >
0.47, for four parties, and eta > 0.17 (sigma > 0.55) for three parties.Comment: REVTeX4, 4 pages, 1 figur
Compact set of invariants characterizing graph states of up to eight qubits
The set of entanglement measures proposed by Hein, Eisert, and Briegel for
n-qubit graph states [Phys. Rev. A 69, 062311 (2004)] fails to distinguish
between inequivalent classes under local Clifford operations if n > 6. On the
other hand, the set of invariants proposed by van den Nest, Dehaene, and De
Moor (VDD) [Phys. Rev. A 72, 014307 (2005)] distinguishes between inequivalent
classes, but contains too many invariants (more than 2 10^{36} for n=7) to be
practical. Here we solve the problem of deciding which entanglement class a
graph state of n < 9 qubits belongs to by calculating some of the state's
intrinsic properties. We show that four invariants related to those proposed by
VDD are enough for distinguishing between all inequivalent classes with n < 9
qubits.Comment: REVTeX4, 9 pages, 1 figur
Diagrama Pareto y manual para la elaboración y el uso de la interfaz para el registro de los reciclables separados en la empresa Grupo SARRE
El diagrama Pareto y el manual para la elaboración y el uso de la interfaz para el Registro de los Reciclables Separados en la empresa Grupo SARRE, es un proyecto que busca identificar aquellos reciclables que más se venden en la planta con ayuda de dos indicadores: Separación de Reciclables (kg/mes) y Costo total ($/mes). Para así poder jerarquizarlos y saber cuáles
residuos representan el 20% más significativo para Grupo SARRE. Por último, obtienen dos resultados y/o productos: Una tabla de jerarquización y un diagrama Pareto 80-20 para enfocar en aquello que sea de mayor utilidad para la empresa. Se trata de priorizar y trabajar con el 20% de los esfuerzos, para obtener el 80% de los resultados. Además, se elaboró una
interfaz para gestionar los residuos que se separan para empezar a tener un control de los reciclables que se separan en la planta.ITESO, A.C
Experimental fully contextual correlations
Quantum correlations are contextual yet, in general, nothing prevents the
existence of even more contextual correlations. We identify and test a
noncontextuality inequality in which the quantum violation cannot be improved
by any hypothetical postquantum theory, and use it to experimentally obtain
correlations in which the fraction of noncontextual correlations is less than
0.06. Our correlations are experimentally generated from the results of
sequential compatible tests on a four-state quantum system encoded in the
polarization and path of a single photon.Comment: REVTeX4, 6 pages, 3 figure
Minimum detection efficiency for a loophole-free atom-photon Bell experiment
In Bell experiments, one problem is to achieve high enough photodetection to
ensure that there is no possibility of describing the results via a local
hidden-variable model. Using the Clauser-Horne inequality and a two-photon
non-maximally entangled state, a photodetection efficiency higher than 0.67 is
necessary. Here we discuss atom-photon Bell experiments. We show that, assuming
perfect detection efficiency of the atom, it is possible to perform a
loophole-free atom-photon Bell experiment whenever the photodetection
efficiency exceeds 0.50.Comment: REVTeX4, 4 pages, 1 figur
Memory cost of quantum contextuality
The simulation of quantum effects requires certain classical resources, and
quantifying them is an important step in order to characterize the difference
between quantum and classical physics. For a simulation of the phenomenon of
state-independent quantum contextuality, we show that the minimal amount of
memory used by the simulation is the critical resource. We derive optimal
simulation strategies for important cases and prove that reproducing the
results of sequential measurements on a two-qubit system requires more memory
than the information carrying capacity of the system.Comment: 18 pages, no figures, v2: revised for clarit
Finite-precision measurement does not nullify the Kochen-Specker theorem
It is proven that any hidden variable theory of the type proposed by Meyer
[Phys. Rev. Lett. {\bf 83}, 3751 (1999)], Kent [{\em ibid.} {\bf 83}, 3755
(1999)], and Clifton and Kent [Proc. R. Soc. London, Ser. A {\bf 456}, 2101
(2000)] leads to experimentally testable predictions that are in contradiction
with those of quantum mechanics. Therefore, it is argued that the existence of
dense Kochen-Specker-colorable sets must not be interpreted as a nullification
of the physical impact of the Kochen-Specker theorem once the finite precision
of real measurements is taken into account.Comment: REVTeX4, 5 page
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