LH11777
CROSSED RATCHETS FOR 2D DOMAIN WALLS
A domain wall moving across a magnetic thin film with an array of asymmetric holes has been found to be subject to two crossed ratchet effects of opposite sign. This results in an inversion of domain wall rectification as a function of magnetic field that provides the basis of a novel memory effect.
The propagation of domain walls in thin magnetic films with pinning is a problem of great interest because it provides both the basis for many magnetic devices and an excellent experimental system to study the physics of driven elastic interfaces, such as ferroelectric domain walls, contact lines of liquids menisci, dislocations, fractures and so on. When the pinning potential is asymmetric, propagation can be favored in one direction giving rise to a ratchet effect. Up to now, these studies have been performed restricting wall motion to a narrow 1D path so that the wall behaves as a point particle in an asymmetric potential.
In this paper, domain wall motion in a 2D extended film has been considered. In this geometry, the domain wall is an elastic line that can distort all along its length in response to a 2D asymmetric pinning potential. The competition between elasticity and pinning results in the existence of two crossed ratchet effects of opposite sign depending on whether a flat or a kinked wall is moving: one favors the forward motion of a flat wall while the other acts on the upward/downward kink propagation favoring net backward wall motion at low fields. Due to the interplay between both ratchets, the system keeps memory of the sign of the last saturating state, opening the possibility for applications in memory devices.
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LJ10995
GRAVITATIONAL ENERGY AS DARK ENERGY: EINSTEIN'S UNFINISHED REVOLUTION?
A new solution is derived giving a potentially viable model of
the Universe without exotic dark energy or modifications to gravity.
The biggest problem in cosmology, dark energy, is solved by deeper
understanding of unexplored territory in Einstein's original theory -
the fact that space itself is dynamical, carrying energy in its fabric.
The author replaces the Friedmann-Lemaitre solutions of our standard
cosmology, which date from the 1920s. These old solutions assume that
matter is a smooth featureless fluid, even though the present-day universe
is very lumpy, with clusters of galaxies strung in bubble walls around
huge voids. The new solution uses an average of Einstein's equations that
accounts for the void structure. The author returns to first principles in
reinterpreting cosmological observations. Gradients in spatial curvature
can give rise to gradients in gravitational energy, with the result that
the clocks of observers in galaxies - which broke away from the expansion
of the universe over 10 billion years ago - eventually tick slower than
clocks at an average location in freely-expanding space; giving apparent
cosmic acceleration. These paradigm-challenging claims are backed up by
two other papers [New J. Phys. 9 (2007) 377, and arxiv:0709.2535,
Astrophys. J. Letters in press] where observational tests are performed,
and new best-fit parameters for the universe derived.
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LH11535
Ordinarily, we think of a liquid becoming a glass as the temperature is decreased. By contrast, this paper reveals that a model liquid, composed of silica nanoparticles in a binary fluid, becomes a glass not only on cooling but also on heating! Although initially surprising, this behavior is, in fact, predicted by recent theories, and leads us another step towards cracking the glass puzzle.
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LG11546
Compressing stars
In this work, purely stellar matter was compressed for the first time.
"Pieces of star"» are exotic beam of 56 Nickel, created in laboratory.
Thanks to a revolutionary gaseous target called MAYA, they reach an
excited state, the giant monopole resonance, in which nuclei " breath"
through a compression-dilatation mode. This breakthrough, which is also
valid for neutron-rich exotic nuclei, paves the way to the exploration
of the equation of state of asymmetric nuclear matter, which plays a
pivotal role in compression-explosion scenarios of supernovae, or in the
structure of pulsars and neutrons stars compressed by the gravitational
attraction.
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LK11641
Mechanical Response of Molecular Swimmers? It depends!
The concept of a ``stochastic motor'' for molecular swimmers is
introduced in this paper, and it is shown that the force-velocity
response of a nanoswimmer depends on where the force is exerted.
As technological advances allow us to fabricate smaller and smaller
autonomous self-propelled devices, it is clear that at some point
directed propulsion could not come from pre-specified deterministic
periodic deformation of the swimmer's body and we need to develop
strategies to extract a net directed motion from a series of random
transitions in the conformation space of the swimmer. We have
constructed a motor based on this concept and used it to propel a
simple low Reynolds number swimmer, namely, the three-sphere swimmer
model. When the detailed-balanced is broken and the motor is driven
out of equilibrium, it can propel the swimmer in the required
direction. Moreover, we have found that when such a system is put
under the effect of an external load, the way stress is distributed
across the swimmer's body will determine the efficiency of the
different legs of the reaction cycle, and hence the net swimming
velocity. This shows that for such designed small swimmers, the
concept of a generic force--velocity response breaks down, which
might have intriguing implications for designing molecular swimmers.
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LH11233
Observation of squeezed light with 10dB quantum noise reduction
In this paper we report on the first detection of a squeezed laser beam with a quantum noise reduction of a factor of 10 below the shot noise level. The experiment was performed at the Albert-Einstein-Institute Hannover, Germany (Max-Planck-Institute for Gravitational Physics and Institute for Gravitational Physics at the Leibniz Universitaet Hannover, www.aei.uni-hannover.de, www.squeezed-light.de). After 20 years of intensive research doubts arose whether strong squeezing can ever be realized as required for eminent applications. Here we show experimentally that such strong squeezing of light's quantum noise is possible. Furthermore, thorough analysis reveals that even higher squeezing factors will be feasible in our setup.
Squeezed states of light offer a broad spectrum of applications. In quantum communication and quantum information strong squeezed light offers an extra high transmission bandwidth. Quantum teleportation and the generation of entangled states are further applications, which have already been demonstrated in proof of principle experiments. Another important field of application are the high precision laser interferometers built for the detection of gravitational waves. These instruments have now reached a technical standard at which squeezed light becomes a key technology. Squeezing the quantum noise of these detectors provides a sensitivity improvement without increasing the thermal load inside the interferometers. This is especially essential for the realization of future cryogenically cooled detectors with even higher sensitivities. The first implementation of the squeezed light technique in gravitational wave detectors is already in preparation.
We expect that our observation of 10dB squeezing of light's quantum noise has a significant impact on quantum communication and information, the development of quantum memories, the generation of entanglement and high precision metrology. Progress in these fields that was not envisaged so far might now be possible.
