LS11836
Is realism really realistic?
Bell showed that it is impossible to explain all of the predictions of
quantum mechanics using a theory which still satisfies the basic
concepts of locality and realism, but which (if not both) is violated is
still an open question. In our forthcoming Physical Review Letter we ask how plausible realism -- the
idea that external reality exists prior to and independent of
observations -- is, by considering the amount of resources it consumes.
Einstein, who himself supported a realistic explanation of quantum
mechanics, believed in existence of "hidden variables" (HV) which could
deterministically predict the result of quantum measurement. Dakic et
al. have constructed an explicit realistic model in which the number of
HV states scales polynomially with the number of quantum measurements,
and this defines the resources of the realistic theory. Moreover, in
the limit of large number of measurements, they confirm the result of
Montina, that no successful realistic theory could use less HV states
than the one in which every quantum state is associated with a HV. This
shows that, for any given system size, realistic theories cannot
describe nature more efficiently than quantum theory itself. The paper
extends the work of Hardy, who showed that, even for the simplest
quantum system like electron spin or photon polarisation, realism is
extremely resource demanding, requiring infinitely many HV states to
explain all possible measurements.
***
EV10257
Tension-regulated Dynamics of Semiflexible Polymers
Rheological properties of mammalian cells are governed by the mechanical
tension borne by their cytoskeleton and by a weak power-law
viscoelasticity. These two features are closely associated in living
cells for reasons that are largely unknown. In this study, we
hypothesize that the tension dependence of power-law viscoelasticity of
cells originates from individual semifelxible polymers of the
cytoskeleton. We develop a stochastic model of a semiflexible polymer
subjected to different levels of tension. Assuming that the chain
dynamics is thermally driven, we use a Monte-Carlo algorithm to obtain
numerical simulations of the chain’s creep behavior. We find that the
chain’s creep response follows a power-law such that the creep rate
decreases with increasing tension in a manner that is consistent with
experimental data from living cells. The power-law creep results from a
finite-speed propagation of the free energy from end points towards the
center of the chain, while its dependence on tension results from the
chain’s stiffening behavior. These results suggest that the observed
complexities of cell rheology already exist at the level of single
tensed cytoskeletal polymer chains.
***
LE11482B
Linear piezomagnetism and its promising applications
In this paper, we present a new mechanism to be employed in the modern
magnetoelectric devices. In particular, we propose to fabricate
heterostructures formed by piezoelectric materials and magnetic
antiperovskites. We show that in the Mn-based antiperovskites the magnetic
moment can be induced by applying a small external biaxial strain. Thus,
these materials demonstrate distinct piezomagnetic properties, which is
another attractive aspect of this study (in general, piezomagnetic
materials are uncommon). Moreover, we show that the piezomagnetic effect
is linear, i.e. the magnetization produced as a result of the external
stress is a linear function of the latter. Besides, we show that the
direction of the induced magnetization reverses with the direction of the
applied strain, which makes our results of particular interest for
utilizing for electrical control of the magnetization in memory cells.
Finally, we emphasize that our estimates of the magnetoelectric coefficient
(which is one of the main parameter used to estimate how good the
magnetoelectric device is) give a promising large value comparable to the
one recently reported in BiFeO3/CoFe2O4 nanocomposites.
***
LU11304
"Realization of Arrays of Single Molecular Rotors with Fixed Rotation Axis"
We have developed a novel method for controlling the rotation of
single molecules, and have demonstrated the self-assembly of single
molecular rotors into large scale arrays for the first time.
Biological molecular motors, which convert chemical energy into
mechanical motions, are the essential agents of movement in living
organisms. In recent years, scientists have been studying on
artificial molecular motors which can convert various types of
energies into mechanical motions. The ongoing efforts will probably
open up a new molecular scale world composed of various
well-controlled molecular motors. At present stage, one of the most
important issues for the artificial molecular motors is how to achieve
a high level of control over the energy conversion. In our work, we
have found out a method for controlling single molecular rotors. We
show that the molecular rotation can be well controlled by designing
the molecular contact to a surface. In addition to that, our success
in fabricating the large-scale array of molecular rotors reveal a
possibility of integrating single molecular rotors into complex
molecular machines. This finding has established a solid route to
connect a single molecular rotor to a single Au atom of Au(111)
surface. This kind of rotating molecule together with the Au adatom of
an electrode can principally create electro-radiation, and if
introducing a magnetic atom into the molecule for example, the FePc,
can make the electricity, and finally lead to formation of practically
single-molecular electric generator and/or radiator devices.
***
LU11894
Can quantum effects break a complex network?
We study the propagation of waves in complex networks and show that quantum
effects can cause a novel type of phase transition from propagating waves
to localized waves. We find this transition simulating different network
topologies and suggest corresponding optical experiments.
The internet, for example, is changing towards an optical network, since
new contents require faster connections with optical devices. Can an
optical network break into small clusters although the engineers have
correctly connected all devices?
We show in this Letter that such a breakdown could be caused by quantum
effects if coherent light and coherent beam splitters were used and the
network topology fulfilled some requirements. Firstly the proportion of
nodes with a high number of links has to be small and secondly the
proportion of nodes connected in triangles (clustering) has to be large.
The good news is that the internet will be stable, since its topology is
sufficiently stable and current technology does not operate with coherent
light waves. However, the new type of quantum phase transition we show by
simulations is also relevant for understanding metal-insulator transitions
(Anderson transition) in electronic devices.
***
LT11072B
A magnetic field can unexpectedly enhance for many orders of
magnitude the penetration through barriers separating different
metals. The effect can be used for control of nano-devices.
***
LU11259
Photon localization transition in layered materials
Layered media are ubiquitous in geological, biological, electronic, and photonic settings. In this paper, we carry out the first study of the impact of nonuniformity within the layers upon transport. We find a crossover from localized towards diffusive propagation in stacks of glass cover slips with increasing sample thickness or layer nonuniformity. In thin samples, transmission falls exponentially as a consequence of Anderson localization arising from constructive interference of waves returning to points within the sample. As the sample thickness increases, however, the spatial coherence of the wave is lost since the wave passes through particular layers at different transverse locations at which the later thickness of the layer is different because of transverse disorder. Average transport can be then be better described as the random walk or diffusion of photons. The transition reflects a continuous change in dimensionality of wave transport from one to three dimensions with increasing sample thickness. The crossover occurs at a thickness at which the lateral spread of the wave equals the transverse coherence length in the transmitted speckle pattern, which is the typical extent of bright spots in the transmitted beam.
***
LQ11008
Construction at molecular scales - how reversibility helps virus shells
assemble
Molecular self-assembly is a little understood phenomenon (both
experimentally and theoretically) that plays an important role in nature
as well as in nanotechnology. An example is the growth of viral capsids,
the polyhedral protein shells that package spherical viruses. The paper
describes new insight into the underlying mechanism that has emerged
from molecular dynamics simulations based on a simplified model. Contrary
to expectation, self-assembly appears be a highly reversible process in
which partially assembled shells readily gain and lose members, with
just a slight bias towards growth; only the complete shells are
thermodynamically stable. This reversibility is a consequence of the
thermal fluctuations that are important at molecular scales (but not
directly experienced at the more familiar macroscopic level).
Reversibility helps undo any incorrect assembly steps, thereby ensuring
a robust, high-yield process. Furthermore, despite the wide variety of
possible partial shells, only a very small fraction of those structures
having the lowest energies actually appear on the assembly pathway.
***
LR11360
The life time of quantum partnership
When two distant quantum systems interact to form a couple,
they can establish correlations much stronger, but also
much more fragile, than ever possible in a classical
relationship. Scientists at the university of Freiburg have
now derived a universal law to infer the lifetime of these
quantum correlations -- often lumped together under the
label "entanglement" -- when perturbed by noise. Such
perturbations are the main obstacle for the construction of
a quantum computer, the computational power of which is
fuelled by entanglement. The Freiburg formula helps to
identify the time scale on which quantum algorithms need to
converge before entanglement fades away due to noise.
Importantly, the new result does not only apply to the
smallest quantum mechanical toy models, but also for large
quantum registers needed to run a quantum computer which
deserves the name.
***
BU10789
How one electron can change the measure of everything
This paper presents the study of the interaction of an electron with the electromagnetic field in the process of electron transport through a quantum dot. This tiny drop of conducting material can be put in such a state that the addition of even one electron would violate the famous energy conservation law. But according to quantum mechanics an electron can, in a virtual sense, hop on the dot then spread as a wave and exit on the other side. The results obtained for the probability of this process will be used in the proposed new Système International d’Unites (SI).
Systems of measurements have been improving since ancient times as the demands for accurate measurements in trade continually increased. While the current SI underpins the global economy, the proposed new SI aims to be location independent even throughout the Universe. It will be based on a set of fundamental physical constants and on two important laws of physics. These two laws will be experimentally tested by a team in France, using the device called the R-pump, which accurately transports electrons, and which the present author has proposed in earlier work with colleagues in Holland and Germany.
***
BVR1076
A Relativistic Particle Loosing its Twin
Relativity ensures every particle is accompanied by its own
anti-particle. Well, when arriving at the edge of the universe, we
found that these relativistic twins may break apart. While it is tough
to make such a long trip in our universe, it is relatively easy to
explore all sorts of relativistic effects in graphene, a recently
discovered material made of single-layer graphite in your pencils.
Interactions among electrons in graphene give rise to a particle named
"magnon", which describes how spin disturbances propagate in the
two-dimensional flatland. Remarkably, we spot a new type of magnon
near the edge of graphene with lower excitation energy compared with
their cousins in the bulk. It is surprising that the edge magnon does
not have antiparticle while its cousins in the bulk always appear in
twin pairs as predicted by relativity theory. This highlights the
importance to investigate the relativistic effects near the edge of
graphene. Meanwhile, it also indicates that the interplay between the
electronic interactions and the open boundaries plays an important
role in relativistic systems.
***
LU11895
AN OPTMAL CONTROL PULSE SEQUENCE PROVED UNIVERSAL
An optimal pulse sequence which consists of the minimum number of pulses
for dynamically decoupling a spin or qubit from its environment to a given
precision was first discovered by Uhrig for a special bosonic environment
model. In this paper, we have proved that the Uhrig pulse sequences apply
to all kinds of qubit-environment models, laying a foundation for optimal
dynamical decoupling in high-precision spin resonance spectroscopy and
quantum information processing. A corollary is that the Uhrig sequences
can serve as a core superimposed with additional pulses satisfying certain
symmetry requirements, which paves the road for controlling spins or
qubits while simultaneously combating the environment noises.
