2,125 research outputs found
Angular EPR paradox
The violation of local uncertainty relations is a valuable tool for detecting
entanglement, especially in multi-dimensional systems. The orbital angular
momentum of light provides such a multi-dimensional system. We study quantum
correlations for the conjugate variables of orbital angular momentum and
angular position. We determine an experimentally testable criterion for the
demonstration of an angular version of the EPR paradox. For the interpretation
of future experimental results from our proposed setup, we include a model for
the indeterminacies inherent to the angular position measurement. For this
measurement angular apertures are used to determine the probability density of
the angle. We show that for a class of aperture functions a demonstration of an
angular EPR paradox, according to our criterion, is to be expected.Comment: 21 pages, 9 figures, to be published in J. Mod. Opt. special issue on
quantum imagin
On local-hidden-variable no-go theorems
The strongest attack against quantum mechanics came in 1935 in the form of a
paper by Einstein, Podolsky and Rosen. It was argued that the theory of quantum
mechanics could not be called a complete theory of Nature, for every element of
reality is not represented in the formalism as such. The authors then put forth
a proposition: we must search for a theory where, upon knowing everything about
the system, including possible hidden variables, one could make precise
predictions concerning elements of reality. This project was ultimatly doomed
in 1964 with the work of Bell Bell, who showed that the most general local
hidden variable theory could not reproduce correlations that arise in quantum
mechanics. There exist mainly three forms of no-go theorems for local hidden
variable theories. Although almost every physicist knows the consequences of
these no-go theorems, not every physicist is aware of the distinctions between
the three or even their exact definitions. Thus we will discuss here the three
principal forms of no-go theorems for local hidden variable theories of Nature.
We will define Bell inequalities, Bell inequalities without inequalities and
pseudo-telepathy. A discussion of the similarities and differences will follow.Comment: 7 pages, no figure, replaced "Bell inequalities" with "Bell theorems"
and updated the reference
Quantum information with continuous variables
Quantum information is a rapidly advancing area of interdisciplinary
research. It may lead to real-world applications for communication and
computation unavailable without the exploitation of quantum properties such as
nonorthogonality or entanglement. We review the progress in quantum information
based on continuous quantum variables, with emphasis on quantum optical
implementations in terms of the quadrature amplitudes of the electromagnetic
field.Comment: accepted for publication in Reviews of Modern Physic
Bell's Theorem Versus Local Realism in a Quaternionic Model of Physical Space
In the context of EPR-Bohm type experiments and spin detections confined to spacelike hypersurfaces, a local, deterministic and realistic model within a Friedmann-Robertson-Walker spacetime with a constant spatial curvature (S^3 ) is presented that describes simultaneous measurements of the spins of two fermions emerging in a singlet state from the decay of a spinless boson. Exact agreement with the probabilistic predictions of quantum theory is achieved in the model without data rejection, remote contextuality, superdeterminism or backward causation. A singularity-free Clifford-algebraic representation of S^3 with vanishing spatial curvature and non-vanishing torsion is then employed to transform the model in a more elegant form. Several event-by-event numerical simulations of the model are presented, which confirm our analytical results with the accuracy of 4 parts in 10^4 . Possible implications of our results for practical applications such as quantum security protocols and quantum computing are briefly discussed
Counterfactual Reasoning, Realism and Quantum Mechanics: Much Ado About Nothing?
I purport to show why old and new claims on the role of counterfactual
reasoning for the EPR argument and the Bell theorem are unjustified: once the
logical relation between locality and counterfactual reasoning is clarified,
the use of the latter does no harm and the nonlocality result can well follow
from the EPR premises. To show why, I critically review (i) incompleteness
arguments that Einstein developed before the EPR paper, and (ii) more recent
claims that equate the use of counterfactual reasoning with the assumption of a
strong form of realism.Comment: arXiv admin note: text overlap with arXiv:1501.04618 by other author
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