180 research outputs found
Experimental Falsification of Leggett's Non-Local Variable Model
Bell's theorem guarantees that no model based on local variables can
reproduce quantum correlations. Also some models based on non-local variables,
if subject to apparently "reasonable" constraints, may fail to reproduce
quantum physics. In this paper, we introduce a family of inequalities, which
allow testing Leggett's non-local model versus quantum physics, and which can
be tested in an experiment without additional assumptions. Our experimental
data falsify Leggett's model and are in agreement with quantum predictions.Comment: 5 pages, 3 figures, 1 tabl
Experimental Test of Relativistic Quantum State Collapse with Moving Reference Frames
An experimental test of relativistic wave-packet collapse is presented. The
tested model assumes that the collapse takes place in the reference frame
determined by the massive measuring detectors. Entangled photons are measured
at 10 km distance within a time interval of less than 5 ps. The two apparatuses
are in relative motion so that both detectors, each in its own inertial
reference frame, are first to perform the measurement. The data always
reproduces the quantum correlations and thus rule out a class of collapse
models. The results also set a lower bound on the "speed of quantum
information" to 0.66 x 10^7 and 1.5 x 10^4 times the speed of light in the
Geneva and the background radiation reference frames, respectively. The very
difficult and deep question of where the collapse takes place - if it takes
place at all - is considered in a concrete experimental context.Comment: 4 pages + 2 ps figure
Quantum correlations versus Multisimultaneity: an experimental test
Multisimultaneity is a causal model of relativistic quantum physics which
assigns a real time ordering to any set of events, much in the spirit of the
pilot-wave picture. Contrary to standard quantum mechanics, it predicts a
disappearance of the correlations in a Bell-type experiment when both analysers
are in relative motion such that, each one in its own inertial reference frame,
is first to select the output of the photons. We tested this prediction using
acousto-optic modulators as moving beam-splitters and interferometers separated
by 55 m. We didn't observe any disappearance of the correlations, thus refuting
Multisimultaneity.Comment: 4 pages, 3 figures, RevTex 4 versio
Realistic loophole-free Bell test with atom-photon entanglement
The establishment of nonlocal correlations, obtained through the violation of
a Bell inequality, is not only important from a fundamental point of view, but
constitutes the basis for device-independent quantum information technologies.
Although several nonlocality tests have been performed so far, all of them
suffered from either the locality or the detection loopholes. Recent studies
have suggested that the use of atom-photon entanglement can lead to Bell
inequality violations with moderate transmission and detection efficiencies. In
this paper we propose an experimental setup realizing a simple atom-photon
entangled state that, under realistic experimental parameters available to
date, achieves a significant violation of the Clauser-Horn-Shimony-Holt
inequality. Most importantly, the violation remains when considering typical
detection efficiencies and losses due to required propagation distances.Comment: 21 pages, 5 figures, 3 table, to appear in Nature Com
Can a falling tree make a noise in two forests at the same time?
It is a commonplace to claim that quantum mechanics supports the old idea
that a tree falling in a forest makes no sound unless there is a listener
present. In fact, this conclusion is far from obvious. Furthermore, if a
tunnelling particle is observed in the barrier region, it collapses to a state
in which it is no longer tunnelling. Does this imply that while tunnelling, the
particle can not have any physical effects? I argue that this is not the case,
and moreover, speculate that it may be possible for a particle to have effects
on two spacelike separate apparatuses simultaneously. I discuss the measurable
consequences of such a feat, and speculate about possible statistical tests
which could distinguish this view of quantum mechanics from a ``corpuscular''
one. Brief remarks are made about an experiment underway at Toronto to
investigate these issues.Comment: 9 pp, Latex, 3 figs, to appear in Proc. Obsc. Unr. Conf.; Fig 2
postscript repaired on 26.10.9
Sperm design and variation in the New World blackbirds (Icteridae)
Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilizing selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed
Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km
For more than 80 years, the counterintuitive predictions of quantum theory
have stimulated debate about the nature of reality. In his seminal work, John
Bell proved that no theory of nature that obeys locality and realism can
reproduce all the predictions of quantum theory. Bell showed that in any local
realist theory the correlations between distant measurements satisfy an
inequality and, moreover, that this inequality can be violated according to
quantum theory. This provided a recipe for experimental tests of the
fundamental principles underlying the laws of nature. In the past decades,
numerous ingenious Bell inequality tests have been reported. However, because
of experimental limitations, all experiments to date required additional
assumptions to obtain a contradiction with local realism, resulting in
loopholes. Here we report on a Bell experiment that is free of any such
additional assumption and thus directly tests the principles underlying Bell's
inequality. We employ an event-ready scheme that enables the generation of
high-fidelity entanglement between distant electron spins. Efficient spin
readout avoids the fair sampling assumption (detection loophole), while the use
of fast random basis selection and readout combined with a spatial separation
of 1.3 km ensure the required locality conditions. We perform 245 trials
testing the CHSH-Bell inequality and find . A
null hypothesis test yields a probability of that a local-realist
model for space-like separated sites produces data with a violation at least as
large as observed, even when allowing for memory in the devices. This result
rules out large classes of local realist theories, and paves the way for
implementing device-independent quantum-secure communication and randomness
certification.Comment: Raw data will be made available after publicatio
Adaptive phenotypic plasticity in the Midas cichlid fish pharyngeal jaw and its relevance in adaptive radiation
Phenotypic evolution and its role in the diversification of organisms is a central topic in evolutionary biology. A neglected factor during the modern evolutionary synthesis, adaptive phenotypic plasticity, more recently attracted the attention of many evolutionary biologists and is now recognized as an important ingredient in both population persistence and diversification. The traits and directions in which an ancestral source population displays phenotypic plasticity might partly determine the trajectories in morphospace, which are accessible for an adaptive radiation, starting from the colonization of a novel environment. In the case of repeated colonizations of similar environments from the same source population this "flexible stem" hypothesis predicts similar phenotypes to arise in repeated subsequent radiations. The Midas Cichlid (Amphilophus spp.) in Nicaragua has radiated in parallel in several crater-lakes seeded by populations originating from the Nicaraguan Great Lakes. Here, we tested phenotypic plasticity in the pharyngeal jaw of Midas Cichlids. The pharyngeal jaw apparatus of cichlids, a second set of jaws functionally decoupled from the oral ones, is known to mediate ecological specialization and often differs strongly between sister-species. We performed a common garden experiment raising three groups of Midas cichlids on food differing in hardness and calcium content. Analyzing the lower pharyngeal jaw-bones we find significant differences between diet groups qualitatively resembling the differences found between specialized species. Observed differences in pharyngeal jaw expression between groups were attributable to the diet's mechanical resistance, whereas surplus calcium in the diet was not found to be of importance. The pharyngeal jaw apparatus of Midas Cichlids can be expressed plastically if stimulated mechanically during feeding. Since this trait is commonly differentiated - among other traits - between Midas Cichlid species, its plasticity might be an important factor in Midas Cichlid speciation. The prevalence of pharyngeal jaw differentiation across the Cichlidae further suggests that adaptive phenotypic plasticity in this trait could play an important role in cichlid speciation in general. We discuss several possibilities how the adaptive radiation of Midas Cichlids might have been influenced in this respect
Testing foundations of quantum mechanics with photons
The foundational ideas of quantum mechanics continue to give rise to
counterintuitive theories and physical effects that are in conflict with a
classical description of Nature. Experiments with light at the single photon
level have historically been at the forefront of tests of fundamental quantum
theory and new developments in photonics engineering continue to enable new
experiments. Here we review recent photonic experiments to test two
foundational themes in quantum mechanics: wave-particle duality, central to
recent complementarity and delayed-choice experiments; and Bell nonlocality
where recent theoretical and technological advances have allowed all
controversial loopholes to be separately addressed in different photonics
experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review
articl
Automated smoother for the numerical decoupling of dynamics models
<p>Abstract</p> <p>Background</p> <p>Structure identification of dynamic models for complex biological systems is the cornerstone of their reverse engineering. Biochemical Systems Theory (BST) offers a particularly convenient solution because its parameters are kinetic-order coefficients which directly identify the topology of the underlying network of processes. We have previously proposed a numerical decoupling procedure that allows the identification of multivariate dynamic models of complex biological processes. While described here within the context of BST, this procedure has a general applicability to signal extraction. Our original implementation relied on artificial neural networks (ANN), which caused slight, undesirable bias during the smoothing of the time courses. As an alternative, we propose here an adaptation of the Whittaker's smoother and demonstrate its role within a robust, fully automated structure identification procedure.</p> <p>Results</p> <p>In this report we propose a robust, fully automated solution for signal extraction from time series, which is the prerequisite for the efficient reverse engineering of biological systems models. The Whittaker's smoother is reformulated within the context of information theory and extended by the development of adaptive signal segmentation to account for heterogeneous noise structures. The resulting procedure can be used on arbitrary time series with a nonstationary noise process; it is illustrated here with metabolic profiles obtained from <it>in-vivo </it>NMR experiments. The smoothed solution that is free of parametric bias permits differentiation, which is crucial for the numerical decoupling of systems of differential equations.</p> <p>Conclusion</p> <p>The method is applicable in signal extraction from time series with nonstationary noise structure and can be applied in the numerical decoupling of system of differential equations into algebraic equations, and thus constitutes a rather general tool for the reverse engineering of mechanistic model descriptions from multivariate experimental time series.</p
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