Does the size really matter?
It is well known that dynamics of atoms in nanocrystalline materials is remarkably different from their bulk counterparts. The anomalous features are usually attributed to small nanograins with enhanced surface-to-volume ratio. To further reveal the origin of those anomalies we investigated the atomic dynamics of nanocrystalline Fe90Zr7B3 alloy at various phases of crystallization. The atomic vibrations of the nanograins were separated from those of the interfaces for a wide range of grain size and interface thickness. Surprisingly, the results show that the atomic vibrations of the nanograins do not vary with their size even down to 2 nm, and still closely resemble those of the bulk. The known vibrational anomalies originate from the interface atoms and the degree of deviation from bulk dynamics is proportional to the interface fraction.
A practical implication of these results is that in order to optimize particular thermodynamic properties of the nanocrystalline materials one has to control precisely the fraction of the interfaces rather than the size of the nanograins.
***
LM11721
Galactic magnetic fields could originate at the epoch of reheating after inflation
The origin of the microgauss magnetic fields observed in galaxies and clusters
of galaxies is still a mystery. In this paper we propose that they could be produced
at the electroweak transition after a period of low-scale hybrid inflation. We show
how the non-equilibrium processes occurring at the epoch of reheating of the
Universe may give rise to a significant fraction of energy density in the form of
helical magnetic field lines, whose correlation length grows via inverse cascade
in the primordial plasma. These magnetic fields would be seen today in galaxies
and clusters of galaxies, but not in the cosmic microwave background. The
detection of a helical component of cosmological magnetic fields would give yet
another signature, together with the predicted Gravitational Wave Background,
of the violent processes occurring at the Big Bang.
***
LQ11037
Active cooling of massive objects
Several groups worldwide are investigating the possibility of cooling macroscopic mechanical resonators towards the quantum mechanical ground state, using active feedback or laser cooling techniques. A possible outcome of this research could be the observation of quantum behaviour in a macroscopic object. In this paper, we demonstrate that these techniques can be efficiently applied to resonators much more massive than previously analysed systems. In particular, we cooled the resonant modes of the cryogenic gravitational wave detector AURIGA, a 2 ton aluminium bar resonator whose motion is detected by a very sensitive SQUID-based position sensor. Starting from a temperature of 4.2 K, we were able to achieve by active feedback a minimum equivalent temperature of 0.17 mK, which is even lower than the temperature previously reported for much smaller systems. This experiment suggests that, using this technique, it could be possible to cool even massive human-scale resonators towards the quantum ground state.
***
LQ11568
QUANTUM MOTION SOLVED ON CURVED SURFACES WITH ELECTRIC AND MAGNETIC FIELDS
We derive the quantum dynamical equation for a charged particle moving on a curved surface in the presence of an electric and magnetic field.
It is evident that both the geometry of the surface and the applied fields influence the motion of a particle, but, up to now, it was not clear if these factors couple with each other.
We find that it is not the case: the effect of the fields is independent from the surface curvature.
In addition, we demonstrate that, also with fields, the motion of the particle on the surface is not affected by the dynamics along the direction perpendicular to it.
Applying our results, it has been possible to obtain the quantum equation of motion on surfaces of frontier interest for nanosciences, such as spheres, cylinders and tori.
Our new equation will be useful both for the interpretation of experimental results and theoretical predictions involving curved structures immersed in fields, for example in the analysis of new effects in low-dimensional nanostrucures.
The results are the outcome of the collaboration between two young researchers, a solid-state physicist and a field-theorist: this is a proof of how fruitful is the interplay of competences among different areas of physics.
***
LM11290
Probing colored light and ghosts by gentle warming
Sometimes victory of a long-distance racer depends on what is usually
considered to be not a even a physical issue. This is the strength of
the racer's spirit. The colored gluons and quarks -- basic building
blocks of the theory of strong interactions -- emerge naturally with
other objects, ghosts. We demonstrate that the long-distance
propagation of warmed gluons is intimately related to proliferation of
the ghosts. The gluons are massless intensity of the colored "light" of
gluons created by a static quarks falls off as the inverse square of
the distance from the source. The same as for ordinary light. Color is
seen however only at short distances, less than about one femtometer
(one quadrillionth of a meter, 10^{-15}). At long distances only
colorless hadrons, or bound states of quarks and gluons are
observed. This phenomenon is known as color confinement.
In our work we show theoretically that slightly warmed gluons
and ghosts offer a new kind of conspiracy implied by confinement
of color. We demonstrate that the warm colored ghosts propagate
for long distances and the falloff of the intensity of the ghosts
and gluons obeys a certain relation.
***
LN11310
Electronegativity Identification of Novel Superhard Materials
The hardness of materials can be identified via electronegativity. The search for superhard materials is a huge challenge to scientists. Furthermore, people are also facing many new challenges to precisely measure the hardness of synthesized superhard materials. In this letter, the nature of hardness is systematically studied from the viewpoint of electronegativity, one of the most widely used parameters in chemistry, physics and materials science. We find that materials hardness is essentially determined by the electron-holding energy of constituent bonds per unit volume. The hardness of various materials can be satisfactorily predicted solely in terms of electronegativity and crystal structure. A number of bonds which can or cannot form a superhard material are qualitatively distinguished. Our work provides a new approach to design novel superhard materials from the general viewpoint of electronegativity, which will inspire people to further explore new superhard materials.
***
LP11122
"Quantum bit measurement reaches computing regime"
Very precise state measurements necessary to create a working Quantum Computer (QC) have recently been achieved in the lab. The QC uses information encoded in quantum bits ("qubits") which can exist in a quantum "superposition" of the states 0 and 1, in contrast to conventional bits which can only be in one of these states at any time. If built, the QC could exploit the quantum phenomena of superposition and "entanglement" to solve certain problems that are intractable on any conceivable conventional machine. To make an error-free computation, the state of most of the qubits in the computer must be read out with very high accuracy both during the computational process and to determine the final answer. This paper reports the high fidelity measurement of qubits stored in a single trapped Calcium atom. The state of the atom was repeatedly measured with a mistake occurring less than once in every 10000 tests. This 99.99% fidelity is high enough for a working QC and is believed to be currently the best measurement of any physical qubit. This achievement is particularly exciting given recent insights into the power of quantum measurement, which can be the driving force at the very heart of a quantum algorithm.
***
LL11113
ITER operational regime in a simple small experiment
The ITER experiment is now being built in Cadarache, France, with the goal of showing the feasibility of producing controlled thermonuclear fusion energy. Its success will critically depend on reaching an operational regime where matter and heat are highly confined, the so called H-mode regime. Although the discovery of such a high confinement regime dates back to the '80s, the underlying physical mechanisms have not been fully understood yet. In particular, the fact that the H mode is achieved only in big fusion-relevant devices has made its dynamics always very difficult to diagnose and control. In the present paper, a theoretical prediction is made that an H mode-like regime can also be achieved in a simpler and smaller sized device with easy diagnostics access. The relative simplicity of the considered configuration has allowed the theoretical exploration of the properties of this operational regime in great detail.
***
LM11031
Calcium as the Superior Coating Metal in Functionalization of Carbon Fullerenes
for High-Capacity Hydrogen Storage
There has been an expanding effort of the scientific community searching
for the most promising materials for high-capacity hydrogen storage,
with carbon-based nanostructures representing one important class of
systems under intensive study. Because molecular hydrogen and pristine
carbon nanostructures such as fullerenes or nanotubes are both
sufficiently stable and relatively inert, a variety of surface
modification schemes have been proposed in the recent literature to
enhance the binding of molecular hydrogen, such as by doping (Ref. A),
coating (Refs. B and C, D), or charging (Ref. E), but each scheme having
severe limitations or running into disappointments. Our paper shows that
Ca as a coating element satisfies all the requirements to functionalize
fullerenes (and related carbon nanostructures) as potential high storage
media. Even more pleasantly, Ca turns out to be (probably) the only
coating element in the periodic table to deliver the desired
functionality, making this contribution truly refreshing in an otherwise
somewhat frustrated community.
The attached figure shows that the optimized organometallic complex of
Ca32C60 can contains 92 H2, which corresponds to a hydrogen uptake of
8.4wt%.
