LH10916
Nanoquakes are stirring up microflows
At small scales, fluids behave quite different.
Physical effects, being negligible in the world of the daily life become
more and more dominant when things get tiny. Surface tension for example
beats gravity. Inertia means nothing. Squeezed into micron size tubes,
water suddenly appears as viscous as honey, making controlled pumping a
difficult task. Swimming and propulsion requires special techniques,
which have been sucessfully tackled by bacteria and other creatures
living under microflow conditions. Even simple exercises like the mixing
of two fluids resemble the kneading of a pizza dough if working in the
microfluidic regime. Mixing, however, is extremely important for
microfluidic applications like a complete lab on a chip. Without mixing,
all reactions rely on slow diffusion processes, only.
Launching and sweeping narrow beams of surface acoustic waves on a
piezoelectric substrate, scientists at the University of
Augsburg/Germany now gave a twist to restive micrcoflows: Being the
nanometer analogue of an earthquake, a surface acoustic wave transmits
part of it¿s energy to the fluid, creating intense streaming in an
externally controllable direction and amplitude. This way, complex
spatio-temporal flow patterns are excited in the liquid, enabling the
controlled folding of the tiny material lines and induce rapid mixing -
just like a baker would roll and fold the pastry. Theoretically well
described and understood, optimum mixing conditions now may be predicted
and designed for a given microfluidic device.
***
LH10890
Extreme and rare events, i.e.~deadly earthquakes, tsunamis, floods,
etc..., are of great interest and have motivated the development of a
statistical theory of extremes. In a context far from such
disasters, we bring those techniques to the study of quantum
eigenstates and wave functions, more generally. There an extreme
event depends on the largest/smallest intensities in real space or
some physically important basis. Macroscopic phenomena such as giant
rogue ocean surface waves may be considered as well.
We treat the class of states found for random complex wave functions
or chaotic quantum eigenstates in the absence of time reversal
symmetry, for example, quantum eigenstates for a stadium shaped
billiard table with a weak applied magnetic field. In our work we
show how to compute the distribution of these extreme quantum events
exactly. The surprisingly simple analysis reduces to the "broken
stick distribution" used by mathematical ecologists, which has a slow
convergence toward the appropriate universal statistics followed by
many of the previously considered macroscopic extreme events.
***
LH11386
Polariton lasing in a semiconductor micropillar
At the origin of fascinating phenomena like lasing and Bose Einstein
condensation is the property of bosons to accumulate in a single quantum
state. In the present paper we demonstrate lasing with very special
bosons, namely the discrete light-matter states of semiconductor
micropillars. Semiconductor micropillars are optical cavities where
light is confined in a volume comparable to that of human red blood cell
(of the order of 20 µm3). Very thin layers (quantum wells) are located
where the cavity optical field is maximum and trap optically excited
carriers. As a result, the interaction between light and matter is so
strong that entangled light-matter particles (polaritons) are formed.
Polaritons behave as bosons and combine the dynamics of excitons with
the coherence properties of light: they undergo a sharp threshold at
which they collapse in a single quantum state, and occupancies as large
as 10000 are observed. As a result, coherent laser-like emission is
observed. This new type of lasers presents a threshold power 100 times
smaller than conventional lasing in the same system. Moreover it is a
model solid-state system to reveal new properties of a quantum state
macroscopically occupied with a matter wave.
***
LG10986
A soliton is a special kind of wave which holds itself together as a
stable self-localized structure, instead of spreading and decaying like
ripples on a pond. This paper reports application of this fundamental
concept of nonlinear science to a state-of the art semiconductor laser.
Hence the new device, termed a Cavity Soliton Laser, could be of great
relevance for both science and technology.
The authors demonstrate multiple microlasers, each about 10 microns across,
within a 200 micron diameter Vertical-Cavity Surface-Emitting Laser
(VCSEL). The VCSEL current is kept so low that lasing requires external
feedback, and furthermore that the light organizes itself into solitonic
structures with the right shape, frequency and amplitude to be
self-sustaining. These microlasers are bistable similar to electronic
flip-flops and can be set and reset with an external control beam anywhere
in the active area. Due to the self-localization there is no need for
micro-fabrication of individual emitters.
Interesting future directions include the interaction of these solitons,
exploiting their freedom of frequency, phase and polarization, and
miniaturization for applications in all-optical processing for future
photonic networks. The investigations are part of a European project
FunFACS directed on Fundamentals, Functionalities and Applications of
Cavity Solitons (www.funfacs.org).
***
LL11069
Dancing vortex in airy-fairy way
A vortex can dance like a fairy, and even get into a tangle, in a
superfluid. In the present paper, we report that a vortex becomes
stretched and entangled by attaching to an oscillating obstacle,
triggering turbulence. In a superfluid, a vortex is so stable to form a
ring and propagate due to vortex flow like a smoke ring does. The
turbulence of a superfluid is controllable, as observed in this
report. This work sheds light on turbulence, which has been a great
mystery in nature.
Figure caption:
Dancing vortices (fig-a.jpg) develop to turbulence (fig-b.jpg). The gold
sphere is an oscillating obstacle. You can also see this simulation in
***
LF11123
A new look at the binding forces that hold materials and molecules together
Many-electron correlations are essential for determining the structure and dynamics of all condensed matter systems. However it is very difficult to probe them directly by conventional spectroscopic techniques and isolate them from other effects. A newly proposed two-dimensional coherent optical spectroscopy targets these tiny but critical correlations among particles. Particle correlations can be easily singled out by new signals that vanish by quantum interference when correlations are absent. This technique can help understand and visualize quantum microscopic processes such as electron-hole dynamics in semiconductors, and chemical reactions and can also help manipulate macroscopic quantum systems such as superconductors and Bose-Einstein condensates. It can further facilitate the design of novel materials and next generation of semiconductor devices.
***
LK11590
Loschmidt cooling by time reversal of atomic matter waves
The statistical theory of gases developed by Boltzmann leads to
macroscopic irreversibility and entropy growth even if
dynamical equations of motion are time reversible.
This contradiction was pointed out by Loschmidt
and is now known as the Loschmidt paradox.
The reply of Boltzmann relied on the technical difficulty
of velocity reversal for material particles: a story tells that
he simply said ``then go and do it!''.
The modern resolution of this famous dispute came with
the development of the theory of
dynamical chaos where small perturbations grow exponentially
with time, making the motion practically irreversible.
However, the quantum evolution remains stable and reversible
in presence of small perturbations. This allowed to realize
experimental implementations of time reversibility for quantum dynamics
or propagating waves with spin systems (spin echo technique),
acoustic and electromagnetic waves,
resulting in various technological applications.
But till now the time reversal of matter waves
has not been performed so far.
In this paper we present a concrete experimental proposal of
an effective time reversal of atomic matter waves
in the regime of quantum chaos.
Surprisingly, a significant fraction of the time reversed atoms
becomes cooled down by several orders of magnitude during the process.
The proposed scheme of this Loschmidt cooling
can be implemented with existing experimental setups
for cold atoms in optical lattices.
***
LH10876
The Parts Determine the Whole, Except for Schrodinger's Cat
In quantum mechanics, the whole is greater than the sum of its parts,
and quantum entanglement sees to it that consideration of the affairs
of a number of individual particles almost never tells the story about
the collection as a whole. Nevertheless, the state of affairs of a
collection of particles (the whole) is determined by the states of
larger subcollections (the parts) for all but a small class of
extremely entangled states, the identity of which has been unknown
until now. In this paper, we show that the extremely entangled states
of a collection of quantum bits (simple particles that can only be
found in one of two states, say up or down), are none other than
Schrodinger Cat states, special types of highly correlated states in
which all quantum bits are up (cat alive) or all quantum bits are down
(cat dead). Thus, the Schrodinger Cat states possess a higher degree
of correlation than other quantum states, and appear to play a
privileged role in the theory of quantum entanglement.
***
LE11341
The next earthquake magnitude can be predicted
Since the Omori discovery in 1894, it is universally accepted that
seismicity is a process clustered in time and space: after big events a large
number of quakes occurs closely in time and space. On the other hand,
magnitudes are generally supposed to be independent and therefore the
magnitude of the next earthquake is unpredictable.
In this paper we conversely show that clustering in magnitude does exist:
big quakes preferentially occur after big ones.
This suggests
that an earthquake alters the system state in such a way to influence
the energy released in subsequent events.
The time and space scales of this process appear to be controlled by the
magnitude difference between correlated events.
In particular, two events
of magnitude $m_1$ and $m_2$ are correlated on a time scale
$\tau \propto 10^{m_1-m_2}$ and over a distance $r \sim \tau^(1/3)$.
This approach allows to construct seismic hazard maps reproducing the
spatio-temporal occurrence of the last 30 years California earthquakes.
In the attached figure, we plot the probability $P$ to have $m \ge 3$
earthquakes during January 2007 because of past seismicity.
Recorded events (yellow stars) are closely located near the maximums of $P$.
