45,401 research outputs found
Class of bipartite quantum states satisfying the original Bell inequality
In a general setting, we introduce a new bipartite state property sufficient
for the validity of the perfect correlation form of the original Bell
inequality for any three bounded quantum observables. A bipartite quantum state
with this property does not necessarily exhibit perfect correlations. The class
of bipartite states specified by this property includes both separable and
nonseparable states. We prove analytically that, for any dimension d>2, every
Werner state, separable or nonseparable, belongs to this class.Comment: 6 pages, v.2: one reference added, the statement on Werner states
essentially extended; v.3: details of proofs inserte
Threshold bounds for noisy bipartite states
For a nonseparable bipartite quantum state violating the
Clauser-Horne-Shimony-Holt (CHSH) inequality, we evaluate amounts of noise
breaking the quantum character of its statistical correlations under any
generalized quantum measurements of Alice and Bob. Expressed in terms of the
reduced states, these new threshold bounds can be easily calculated for any
concrete bipartite state. A noisy bipartite state, satisfying the extended CHSH
inequality and the perfect correlation form of the original Bell inequality for
any quantum observables, neither necessarily admits a local hidden variable
model nor exhibits the perfect correlation of outcomes whenever the same
quantum observable is measured on both "sides".Comment: 9 pages; v.2: minor editing corrections; to appear in J. Phys. A:
Math. Ge
Causal Quantum Theory and the Collapse Locality Loophole
Causal quantum theory is an umbrella term for ordinary quantum theory
modified by two hypotheses: state vector reduction is a well-defined process,
and strict local causality applies. The first of these holds in some versions
of Copenhagen quantum theory and need not necessarily imply practically
testable deviations from ordinary quantum theory. The second implies that
measurement events which are spacelike separated have no non-local
correlations. To test this prediction, which sharply differs from standard
quantum theory, requires a precise theory of state vector reduction.
Formally speaking, any precise version of causal quantum theory defines a
local hidden variable theory. However, causal quantum theory is most naturally
seen as a variant of standard quantum theory. For that reason it seems a more
serious rival to standard quantum theory than local hidden variable models
relying on the locality or detector efficiency loopholes.
Some plausible versions of causal quantum theory are not refuted by any Bell
experiments to date, nor is it obvious that they are inconsistent with other
experiments. They evade refutation via a neglected loophole in Bell experiments
-- the {\it collapse locality loophole} -- which exists because of the possible
time lag between a particle entering a measuring device and a collapse taking
place. Fairly definitive tests of causal versus standard quantum theory could
be made by observing entangled particles separated by light
seconds.Comment: Discussion expanded; typos corrected; references adde
On the probabilistic description of a multipartite correlation scenario with arbitrary numbers of settings and outcomes per site
We consistently formalize the probabilistic description of multipartite joint
measurements performed on systems of any nature. This allows us: (1) to specify
in probabilistic terms the difference between nonsignaling, the Einstein-
Podolsky-Rosen (EPR) locality and Bell's locality; (2) to introduce the notion
of an LHV model for an S_{1}x...xS_{N}-setting N-partite correlation
experiment, with outcomes of any spectral type, discrete or continuous, and to
prove both general and specific "quantum" statements on an LHV simulation in an
arbitrary multipartite case; (3) to classify LHV models for a multipartite
quantum state, in particular, to show that any N-partite quantum state, pure or
mixed, admits an Sx1x...x1 -setting LHV description; (4) to evaluate a
threshold visibility for a noisy bipartite quantum state to admit an S_{1}xS_
{2}-setting LHV description under any generalized quantum measurements of two
parties. In a sequel to this paper, we shall introduce a single general
representation incorporating in a unique manner all Bell-type inequalities for
either joint probabilities or correlation functions that have been introduced
or will be introduced in the literature.Comment: 26 pages; added section Conclusions and some references for section
Quantum Equilibrium and the Origin of Absolute Uncertainty
The quantum formalism is a ``measurement'' formalism--a phenomenological
formalism describing certain macroscopic regularities. We argue that it can be
regarded, and best be understood, as arising from Bohmian mechanics, which is
what emerges from Schr\"odinger's equation for a system of particles when we
merely insist that ``particles'' means particles. While distinctly
non-Newtonian, Bohmian mechanics is a fully deterministic theory of particles
in motion, a motion choreographed by the wave function. We find that a Bohmian
universe, though deterministic, evolves in such a manner that an {\it
appearance} of randomness emerges, precisely as described by the quantum
formalism and given, for example, by ``\rho=|\psis|^2.'' A crucial ingredient
in our analysis of the origin of this randomness is the notion of the effective
wave function of a subsystem, a notion of interest in its own right and of
relevance to any discussion of quantum theory. When the quantum formalism is
regarded as arising in this way, the paradoxes and perplexities so often
associated with (nonrelativistic) quantum theory simply evaporate.Comment: 75 pages. This paper was published a long time ago, but was never
archived. We do so now because it is basic for our recent article
quant-ph/0308038, which can in fact be regarded as an appendix of the earlier
on
Randomised positive control trial of NSAID and antimicrobial treatment for calf fever caused by pneumonia
One hundred and fifty-four preweaning calves were followed between May and October 2015. Calves were fitted with continuous monitoring temperature probes (TempVerified FeverTag), programmed so a flashing light emitting diode (LED) light was triggered following six hours of a sustained ear canal temperature of ≥39.7°C. A total of 83 calves (61.9 per cent) developed undifferentiated fever, with a presumptive diagnosis of pneumonia through exclusion of other calf diseases. Once fever was detected, calves were randomly allocated to treatment groups. Calves in group 1 (NSAID) received 2 mg/kg flunixin meglumine (Allevinix, Merial) for three consecutive days and group 2 (antimicrobial) received 6 mg/kg gamithromycin (Zactran, Merial). If fever persisted for 72 hours after the initial treatment, calves were given further treatment (group 1 received antimicrobial and group 2 received NSAID). Calves in group 1 (NSAID) were five times more likely (P=0.002) to require a second treatment (the antimicrobial) after 72 hours to resolve the fever compared with the need to give group 2 (antimicrobial) calves a second treatment (NSAID). This demonstrates the importance of ongoing monitoring and follow-up of calves with respiratory disease. However, of calves with fever in group 1 (NSAID), 25.7 per cent showed resolution following NSAID-only treatment with no detrimental effect on the development of repeated fever or daily live weight gain. This suggests that NSAID alone may be a useful first-line treatment, provided adequate attention is given to ongoing monitoring to identify those cases that require additional antimicrobial treatment
Multiparticle Interference, GHZ Entanglement, and Full Counting Statistics
We investigate the quantum transport in a generalized N-particle Hanbury
Brown--Twiss setup enclosing magnetic flux, and demonstrate that the Nth-order
cumulant of current cross correlations exhibits Aharonov-Bohm oscillations,
while there is no such oscillation in all the lower-order cumulants. The
multiparticle interference results from the orbital Greenberger-Horne-Zeilinger
entanglement of N indistinguishable particles. For sufficiently strong
Aharonov-Bohm oscillations the generalized Bell inequalities may be violated,
proving the N-particle quantum nonlocality.Comment: 4 pages, 1 figure, published versio
Generalized Bell Inequality Experiments and Computation
We consider general settings of Bell inequality experiments with many
parties, where each party chooses from a finite number of measurement settings
each with a finite number of outcomes. We investigate the constraints that Bell
inequalities place upon the correlations possible in a local hidden variable
theories using a geometrical picture of correlations. We show that local hidden
variable theories can be characterized in terms of limited computational
expressiveness, which allows us to characterize families of Bell inequalities.
The limited computational expressiveness for many settings (each with many
outcomes) generalizes previous results about the many-party situation each with
a choice of two possible measurements (each with two outcomes). Using this
computational picture we present generalizations of the Popescu-Rohrlich
non-local box for many parties and non-binary inputs and outputs at each site.
Finally, we comment on the effect of pre-processing on measurement data in our
generalized setting and show that it becomes problematic outside of the binary
setting, in that it allows local hidden variable theories to simulate maximally
non-local correlations such as those of these generalised Popescu-Rohrlich
non-local boxes.Comment: 16 pages, 2 figures, supplemental material available upon request.
Typos corrected and references adde
Light Element Abundance Inhomogeneities in Globular Clusters: Probing Star Formation and Evolution in the Early Milky Way
Abundance patterns of the elements C, N, and O are sensitive probes of
stellar nucleosynthesis processes and, in addition, O abundances are an
important input for stellar age determinations. Understanding the nature of the
observed distribution of these elements is key to constraining protogalactic
star formation history. Patterns deduced from low-resolution spectroscopy of
the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or
first shell-hydrogen burning phases in the oldest ensembles known, the Galactic
globular star clusters, are reviewed. New results for faint stars in NGC 104
(47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and
CH strengths found among luminous evolved stars is also present in stars
nearing the end of their main-sequence lifetimes. In the absence of known
mechanisms to mix newly synthesized elements from the interior to the
observable surface layers of such unevolved stars, those particular
inhomogeneities imply that the original material from which the stars formed
some 15 billion years ago was chemically inhomogeneous in the C and N elements.
However, in other clusters, observations of abundance ratios and C isotope
ratios suggest that alterations to surface chemical compositions are produced
as stars evolve from the main sequence through the red giant branch. Thus, the
current observed distributions of C, N, and O among the brightest stars (those
also observed most often) may not reflect the true distribution from which the
protocluster cloud formed. The picture which is emerging of the C, N and O
abundance patterns within globular clusters may be one whichComment: 12 pages in uuencoded compressed postscript (including figures), to
appear in the Canadian Journal of Physics (Special Issue in Honor of G.
Herzberg
Bell's Jump Process in Discrete Time
The jump process introduced by J. S. Bell in 1986, for defining a quantum
field theory without observers, presupposes that space is discrete whereas time
is continuous. In this letter, our interest is to find an analogous process in
discrete time. We argue that a genuine analog does not exist, but provide
examples of processes in discrete time that could be used as a replacement.Comment: 7 pages LaTeX, no figure
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