Different mechanics of snap-trapping in the two closely related carnivorous plants, Dionaea muscipula and Aldrovanda vesiculosa

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- The carnivorous aquatic Waterwheel Plant (Aldrovanda
vesiculosa L.) and the closely related terrestrial Venus Flytrap
(Dionaea muscipula SOL. EX J. ELLIS) both feature elaborate
snap-traps, which shut after reception of an external mechanical
stimulus by prey animals. Traditionally, Aldrovanda is considered as a
miniature, aquatic Dionaea, an assumption which was already
established by Charles Darwin. However, videos of snapping traps from
both species suggest completely different closure mechanisms. Indeed,
the well- described snapping mechanism in Dionaea comprises abrupt
curvature inversion of the two trap lobes, while the closing movement
in Aldrovanda involves deformation of the trap midrib but not of the
lobes, which do not change curvature. In this paper, we present the
first detailed mechanical models for these plants, which are based on
the theory of thin solid membranes and explain this difference by
showing that the fast snapping of Aldrovanda is due to kinematic
amplification of the bending deformation of the midrib, while that of
Dionaea unambiguously relies on the buckling instability that affects
the two lobes.

Pair Creation Constrains Superluminal Neutrino Propagation

LK12734

- The OPERA collaboration claims that muon neutrinos with mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that superluminal neutrinos may lose energy rapidly via the bremsstrahlung of electron-positron pairs ( ! + e− + e+). For the claimed superluminal velocity and at the stated mean energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. This presents a significant challenge to the superluminal interpretation of the OPERA data. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of
high-energy neutrinos.

Impact craters: grains against grains

LH13515


- Nowadays it is well accepted that craters in the moons and planets were created by asteroid collisions. But, why some craters are completely flat and others show central peaks? The actual paradigm explains that central peaks arise due to the surface fluidization produced by the impact and/or the crater collapse. However, based on the granular nature of the asteroids we developed impact experiments of “granular projectiles” in sand, obtaining similar morphologies to those observed in celestial bodies. So we claim that the crater morphology is due to the granularity of the projectile: low-packed projectiles completely spread after collision producing bowl- shaped craters, high-packed projectiles confine the internal material during the impact giving rise to central peaks.

How a quintessential quantum test was fooled -- or why quantum physicists should always read the fine print

LH12960

- When it comes to pitting quantum theory against classical notions of
the world, there’s one experiment that physicists say makes quantum
theory the clear winner: a test of Bell’s inequalities. We have found
that it’s possible to fake quantum results using classical physics in
such a test, reminding us to be cautious about the assumptions in
experiments. Bell inequalities measure the strength of correlations
between two particles, or how much their behaviors are coordinated.
Quantum physics allows for stronger correlations than classical physics,
violating a Bell inequality. In our experiment, a typical apparatus for
measuring Bell violations by photons was cheated using bright pulses of
light to manipulate the output of single-photon detectors. Researchers
thinking ahead to quantum devices for communication and computation have
proposed incorporating tests of Bell inequalities in such devices to act
as safeguards. Our work highlights the practical challenges of such
schemes. It also reminds us that no Bell tests so far have been without
seemingly reasonable ‘fine print’ assumptions about how the experiments
worked. In our case, we exploited the so-called detection loophole. Our
attack was an evil intervention. We have no reason to think the Universe
conspired to trick past experiments, but one would prefer to eliminate
the need for fine print. Various experimental groups worldwide are
working towards this goal.

Switching the light fantastic

LH12759

- Quantum mechanics says that light consists of small indivisible packets of energy or quanta known as photons. In this paper, we show that the passage of a light beam through an optical fiber can be controlled by just a few quanta of energy (photons) in another light beam.

Photons are introverts by nature and usually don’t interact with each other, unless they are in large numbers. One of the holy grails of physics is single-photon all-optical switching, where one photon controls the passage of another photon through a medium. It is a critical goal for the development of future quantum information networks, promising ultrahigh speed computation and ultra-secure communication.

Our paper takes a significant step towards this goal by demonstrating all-optical switching with less than twenty photons and that too at fast timescales of around five billionths of a second. We confine the light, along with an atomic vapor, to the core of an optical fiber that has a size less than a tenth of the width of a human hair. This architecture forces light to strongly interact with the atoms, causing the absorption of photons of two different colors only if they are simultaneously present, but not if one type is absent.