445 research outputs found
Determination of hidden variable models reproducing the spin-singlet
The experimental violation of Bell inequality establishes necessary but not
sufficient conditions that any theory must obey. Namely, a theory compatible
with the experimental observations can satisfy at most two of the three
hypotheses at the basis of Bell's theorem: free will, no-signaling, and
outcome-Independence. Quantum mechanics satisfies the first two hypotheses but
not the latter. Experiments not only violate Bell inequality, but show an
excellent agreement with quantum mechanics. This fact restricts further the
class of admissible theories. In this work, the author determines the form of
the hidden-variable models that reproduce the quantum mechanical predictions
for a spin singlet while satisfying both the hypotheses of free will and
no-signaling. Two classes of hidden-variable models are given as an example,
and a general recipe to build infinitely many possible models is provided.Comment: Slightly revised version, 7 pages, no figures, to appear in PRA.
Final version, removed extra references no longer cite
Nonlocality with less Complementarity
In quantum mechanics, nonlocality (a violation of a Bell inequality) is
intimately linked to complementarity, by which we mean that consistently
assigning values to different observables at the same time is not possible.
Nonlocality can only occur when some of the relevant observables do not
commute, and this noncommutativity makes the observables complementary. Beyond
quantum mechanics, the concept of complementarity can be formalized in several
distinct ways. Here we describe some of these possible formalizations and ask
how they relate to nonlocality. We partially answer this question by describing
two toy theories which display nonlocality and obey the no-signaling principle,
although each of them does not display a certain kind of complementarity. The
first toy theory has the property that it maximally violates the CHSH
inequality, although the corresponding local observables are pairwise jointly
measurable. The second toy theory also maximally violates the CHSH inequality,
although its state space is classical and all measurements are mutually
nondisturbing: if a measurement sequence contains some measurement twice with
any number of other measurements in between, then these two measurements give
the same outcome with certainty.Comment: 6 pages, published versio
Bell's inequality and the coincidence-time loophole
This paper analyzes effects of time-dependence in the Bell inequality. A
generalized inequality is derived for the case when coincidence and
non-coincidence [and hence whether or not a pair contributes to the actual
data] is controlled by timing that depends on the detector settings. Needless
to say, this inequality is violated by quantum mechanics and could be violated
by experimental data provided that the loss of measurement pairs through
failure of coincidence is small enough, but the quantitative bound is more
restrictive in this case than in the previously analyzed "efficiency loophole."Comment: revtex4, 3 figures, v2: epl document class, reformatted w slight
change
Pre- and post-selected ensembles and time-symmetry in quantum mechanics
An expression is proposed for the quantum mechanical state of a pre- and
post-selected ensemble, which is an ensemble determined by the final as well as
the initial state of the quantum systems involved. It is shown that the
probabilities calculated from the proposed state agree with previous
expressions, for cases where they both apply. The same probabilities are found
when they are calculated in the forward- or reverse-time directions. This work
was prompted by several problems raised by Shimony recently in relation to the
state, and time symmetry, of pre- and post-selected ensembles.Comment: RevTex4, 17 pages, no fig
The Biomineralization in Social Wasps (Vespinae): The Presence of Statoliths
In social wasps granular aggregates occur mainly in the head region and the body integument. In the former location they are present both on the outer and inner side of the frons. On the outer side of the frons, in a groove traversing its center, there is a deep pit surrounded by a membrane which forms a cyst-like sac. In the pit of the hornet Vespa orientalis (Linne, 1771), there are aggregates comprising silicon (Sl), potassium (K), calcium (Ca) and iron (Fe), which are arranged in morula-like fashion. A granular material is secreted at the base of sensory hairs (sensilla), distributed on both sides of the groove, as well as along their shafts. Aggregates of sillcon and calcium are also present on the inner side of the frons.
The integumental aggregates are comprised of yellow pigment granules. In the abdominal region these granules, which are concentrated in yellow stripes, assume a quasi-cylindrical shape, measuring 0.6-0.8 ÎĽmin length and 0.3-0.4 ÎĽmin diameter. Their structure is affected by caste, age, exposure to sunlight, and drugs introduced through feeding. Feeding on colchicine induces degeneration of the granules, whereas feeding on xanthines renders them refractory to the destructive action of colchicine. Their main metallic element is K.
We postulate that 1) the granules on both sides of the frons are part of a tympanic and static organ; 2) the yellow granules (YG) dispersed all over the external surface of the body possess properties of organic semiconductors; 3) 1 and 2 are piezoelectric, and are involved both in gravity orientation and transposition from photo to geotaxis
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Bell inequalities for random fields
The assumptions required for the derivation of Bell inequalities are not
usually satisfied for random fields in which there are any thermal or quantum
fluctuations, in contrast to the general satisfaction of the assumptions for
classical two point particle models. Classical random field models that
explicitly include the effects of quantum fluctuations on measurement are
possible for experiments that violate Bell inequalities.Comment: 18 pages; 1 figure; v4: Essentially the published version; extensive
improvements. v3: Better description of the relationship between classical
random fields and quantum fields; better description of random field models.
More extensive references. v2: Abstract and introduction clarifie
Comment on "Consistency, amplitudes, and probabilities in quantum theory"
In a recent article [Phys. Rev. A 57, 1572 (1998)] Caticha has concluded that
``nonlinear variants of quantum mechanics are inconsistent.'' In this note we
identify what it is that nonlinear quantum theories have been shown to be
inconsistent with.Comment: LaTeX, 5 pages, no figure
Lorentz transformations of open systems
We consider open dynamical systems, subject to external interventions by
agents that are not completely described by the theory (classical or quantal).
These interventions are localized in regions that are relatively spacelike.
Under these circumstances, no relativistic transformation law exists that
relates the descriptions of the physical system by observers in relative
motion. Still, physical laws are the same in all Lorentz frames.Comment: Final version submitted to J. Mod. Opt. (Proc. of Gdansk conference
Quantum Preferred Frame: Does It Really Exist?
The idea of the preferred frame as a remedy for difficulties of the
relativistic quantum mechanics in description of the non-local quantum
phenomena was undertaken by such physicists as J. S. Bell and D. Bohm. The
possibility of the existence of preferred frame was also seriously treated by
P. A. M. Dirac. In this paper, we propose an Einstein-Podolsky-Rosen-type
experiment for testing the possible existence of a quantum preferred frame. Our
analysis suggests that to verify whether a preferred frame of reference in the
quantum world exists it is enough to perform an EPR type experiment with pair
of observers staying in the same inertial frame and with use of the massive EPR
pair of spin one-half or spin one particles.Comment: 5 pp., 6 fig
- …