3,722 research outputs found
Reply to Marinatto's comment on "Bell's theorem without inequalities and without probabilities for two observers"
It is shown that Marinatto's claim [Phys. Rev. Lett. 90, 258901 (2003)] that
the proof of "Bell's theorem without inequalities and without probabilities for
two observers" [A. Cabello, Phys. Rev. Lett. 86, 1911 (2001)] requires four
spacelike separated observers rather than two is unjustified.Comment: REVTeX4, 1 pag
Bell's theorem without inequalities and without unspeakable information
A proof of Bell's theorem without inequalities is presented in which distant
local setups do not need to be aligned, since the required perfect correlations
are achieved for any local rotation of the local setups.Comment: REVTeX4, 4 pages, 1 figure; for Asher Peres' Festschrift, to be
published in Found. Phy
Implications of quantum automata for contextuality
We construct zero-error quantum finite automata (QFAs) for promise problems
which cannot be solved by bounded-error probabilistic finite automata (PFAs).
Here is a summary of our results:
- There is a promise problem solvable by an exact two-way QFA in exponential
expected time, but not by any bounded-error sublogarithmic space probabilistic
Turing machine (PTM).
- There is a promise problem solvable by an exact two-way QFA in quadratic
expected time, but not by any bounded-error -space PTMs in
polynomial expected time. The same problem can be solvable by a one-way Las
Vegas (or exact two-way) QFA with quantum head in linear (expected) time.
- There is a promise problem solvable by a Las Vegas realtime QFA, but not by
any bounded-error realtime PFA. The same problem can be solvable by an exact
two-way QFA in linear expected time but not by any exact two-way PFA.
- There is a family of promise problems such that each promise problem can be
solvable by a two-state exact realtime QFAs, but, there is no such bound on the
number of states of realtime bounded-error PFAs solving the members this
family.
Our results imply that there exist zero-error quantum computational devices
with a \emph{single qubit} of memory that cannot be simulated by any finite
memory classical computational model. This provides a computational perspective
on results regarding ontological theories of quantum mechanics \cite{Hardy04},
\cite{Montina08}. As a consequence we find that classical automata based
simulation models \cite{Kleinmann11}, \cite{Blasiak13} are not sufficiently
powerful to simulate quantum contextuality. We conclude by highlighting the
interplay between results from automata models and their application to
developing a general framework for quantum contextuality.Comment: 22 page
Six-qubit permutation-based decoherence-free orthogonal basis
There is a natural orthogonal basis of the 6-qubit decoherence-free (DF)
space robust against collective noise. Interestingly, most of the basis states
can be obtained from one another just permuting qubits. This property: (a) is
useful for encoding qubits in DF subspaces, (b) allows the implementation of
the Bennett-Brassard 1984 (BB84) protocol in DF subspaces just permuting
qubits, which completes a the method for quantum key distribution using DF
states proposed by Boileau et al. [Phys. Rev. Lett. 92, 017901 (2004)], and (c)
points out that there is only one 6-qubit DF state which is essentially new
(not obtained by permutations) and therefore constitutes an interesting
experimental challenge.Comment: REVTeX4, 5 page
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
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
Two Party Non-Local Games
In this work we have introduced two party games with respective winning
conditions. One cannot win these games deterministically in the classical world
if they are not allowed to communicate at any stage of the game. Interestingly
we find out that in quantum world, these winning conditions can be achieved if
the players share an entangled state. We also introduced a game which is
impossible to win if the players are not allowed to communicate in classical
world (both probabilistically and deterministically), yet there exists a
perfect quantum strategy by following which, one can attain the winning
condition of the game.Comment: Accepted in International Journal of Theoretical Physic
State-independent quantum violation of noncontextuality in four dimensional space using five observables and two settings
Recently, a striking experimental demonstration [G. Kirchmair \emph{et al.},
Nature, \textbf{460}, 494(2009)] of the state-independent quantum mechanical
violation of non-contextual realist models has been reported for any two-qubit
state using suitable choices of \emph{nine} product observables and \emph{six}
different measurement setups. In this report, a considerable simplification of
such a demonstration is achieved by formulating a scheme that requires only
\emph{five} product observables and \emph{two} different measurement setups. It
is also pointed out that the relevant empirical data already available in the
experiment by Kirchmair \emph{et al.} corroborate the violation of the NCR
models in accordance with our proof
Optimization of Convolutional Neural Network ensemble classifiers by Genetic Algorithms
Breast cancer exhibits a high mortality rate and it is the most invasive cancer in women. An analysis from histopathological images could predict this disease. In this way, computational image processing might support this task. In this work a proposal which employes deep learning convolutional neural networks is presented. Then, an ensemble of networks is considered in order to obtain an enhanced recognition performance of the system by the consensus of the networks of the ensemble. Finally, a genetic algorithm is also considered to choose the networks that belong to the ensemble. The proposal has been tested by carrying out several experiments with a set of benchmark images.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Greenberger-Horne-Zeilinger-like proof of Bell's theorem involving observers who do not share a reference frame
Vaidman described how a team of three players, each of them isolated in a
remote booth, could use a three-qubit Greenberger-Horne-Zeilinger state to
always win a game which would be impossible to always win without quantum
resources. However, Vaidman's method requires all three players to share a
common reference frame; it does not work if the adversary is allowed to
disorientate one player. Here we show how to always win the game, even if the
players do not share any reference frame. The introduced method uses a 12-qubit
state which is invariant under any transformation
(where , where is a
unitary operation on a single qubit) and requires only single-qubit
measurements. A number of further applications of this 12-qubit state are
described.Comment: REVTeX4, 6 pages, 1 figur
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