Metamaterials Put the Brakes on Light Signals
Light normally travels at a speed of about 300 thousand kilometers per second, or seven times around the Earth every second. A collaboration of physicists from the Vrije Universiteit Brussel, Belgium, and Iowa State University, Iowa, has now devised a way to slow down electromagnetic signals a hundred fold with metamaterials.
Light is the preferred carrier for transmitting large amounts of information around the globe, but its high speed makes it difficult to route this data to various destinations. When optical packets must be switched, most fiber-optic systems convert the signals to electrical pulses, so that the data can be temporarily stored, rerouted, and then reconverted to optical signals. This conversion, however, limits the data capacity of communication systems such as the internet significantly.
Avoiding the conversion from optical to electrical format requires slowing down the speed of light. Currently, the most successful way to do so is by the use of a quantum mechanical effect in metal vapors called electromagnetically induced transparency. Unfortunately, this technique requires complicated and expensive equipment to create the proper conditions, e.g., to cool the metal atoms to a temperature close to the absolute zero.
In Physical Review Letters, Philippe Tassin and coauthors describe a metamaterial design in which an effect very similar to electromagnetically induced transparency can be observed. Metamaterials are materials that contain—typically metallic—elements that are carefully designed to achieve materials with desired optical properties such as a slow speed of light.
The proposed “slow-light” metamaterial would work at room temperature and does not need additional equipment apart from the metamaterial itself. It can currently be manufactured to work with microwaves and terahertz waves; slowing down visible light with the proposed technique will first require more advances in the fabrication technology of metamaterials.
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LS11445
Frequency beats -but only for a while
Frequency beating -the periodic increase and decrease of intensity
perceived when two sinusoidal signals are superimposed- is one of the
most fundamental and useful phenomena in physics. This yields the
familiar acoustic beats of airplanes in WWII movies and it is also the
basis of many ingenious detection techniques. In this paper, the authors
consider the situation where, rather than being externally imposed, the
periodic signals are internally generated. This happens in nonlinear
spatially extended systems undergoing a pattern-forming instability and
the author take an optical cavity containing a photonic-crystal fiber as
an example. In some circumstances, they find, beating lasts only for a
while, leaving a simple harmonic oscillation for the rest of the time.
The number of beats is arbitrary and depends only on the initial
conditions. The phenomenon is analogous to the appearance of localized
dissipative structures in other spatially extended systems encountered
in chemistry, optics and biology.
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LY11386B
Sign change of equilibrium superconducting Hall coefficient due to gap
anisotropy
The magnetic Lorentz force is among the fundamental forces in physics
characterized by a unique property to deflect charged particles, causing
the Hall effect on dissipative currents in metals and semiconductors. In
this paper, we show theoretically that the force works even on
supercurrents without dissipation to induce finite charge distribution
and the resulting electric field in equilibrium superconductors. An
analytic expression is obtained for the corresponding Hall coefficient
of clean type-II superconductors with simultaneously incorporating the
Fermi-surface and gap anisotropies. It has the same sign and magnitude
at zero temperature as the normal state for an arbitrary pairing, having
no temperature dependence specifically for the isotropic s-wave pairing.
The gap anisotropy may bring a considerable temperature dependence in
the Hall coefficient and can lead to its sign change as a function of
temperature, as exemplified for a model d-wave pairing with a
two-dimensional Fermi surface. The sign change may be observed in some
high-Tc superconductors.
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LV10908
A Laboratory Probe of the Particle Nature of Dark Energy
The GammeV collaboration presents the results from the second component of
their experimental suite; a test of chameleon dark energy. This is the
first dedicated laboratory test of a dark energy model. With chameleon
dark energy, the observed acceleration of the universe is caused by a
light scalar particle that has evaded other terrestrial experiments. This
is due to the fact that the properties of the chameleon particle---namely
its mass---depend upon the environment. We exploit this effect to trap
these chameleon particles in a jar. Chameleon particles that are
generated from the interaction of laser light and a magnetic field bounce
off of the walls of our vacuum chamber, including the optical windows at
each end. When the laser is turned off, the jar empties as the chameleons
reconvert to detectable photons. This afterglow is a telltale signature
of the chameleon particle. While no signal was found, the resulting
limits constrain the properties of the chameleon particle, including its
coupling to photons and its mass, for a range of chameleon dark energy
models.
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LV11596
Ultracold neutrons reveal the robustness of Berry's geometric phase
Devising fault-tolerant methods for the manipulation of fragile quantum
states is a major challenges in the field of quantum information processing.
In this paper, we demonstrate that the Berry phase can potentially be used
for this purpose since it remains widely unaffected by fluctuations induced
by the environment. Berry's phase is based on the curvature of Hilbert
space, the space of quantum states, in close analogy to the precession of
Foucault's pendulum which is determined by the curved surface of earth. This
geometric origin leads to its interesting behavior with respect to noise.
We have built a setup to store ultracold neutrons and manipulate their spin
by controlled variations of magnetic fields. By generating additional
fluctuations on top of the control fields, we could measure the resulting
uncertainty in the Berry phase for state manipulations of different
duration. We have verified that the uncertainty in the Berry phase vanishes
as the manipulation time increases. Hence, for long operations Berry's phase
is not influenced by noise.
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LP11321E
Biological systems work flexibly using mechanisms that are totally
different from those of artificial machines.
Although artificial neural networks have been studied with a view to
mimicking brain functions,
they lack certain key features of biological systems including
adaptability and robustness against environmental change.
In this paper, we incorporated stochastic processes into artificial networks
in order to overcome these shortcomings.
Using ring circuits based on the principle of stochastic resonance and an
excitable threshold system,
we created attractors that represent quasi-equilibrium states into which a
system settles
until disrupted by environmental change.
Furthermore, noise-driven attractor stabilization and switching were
embodied
by electronic circuits that introduced a brain-mimicking inhibitory
connection.
Noise works as a power source to stabilize and switch attractors, and
endows the system with hysteresis behavior that resembles that of stereopsis
and
binocular rivalry in the human visual cortex.
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AY10391
Ring resonator goes quantum
Ring resonator is commonly used in many devices in optical
communications, as well as many frontier quantum optics experiments.
A ring resonator supports two counter-propagating modes, the
whispering gallery modes, that makes the transport properties of
light through such component an interesting and rich plethora.
Now the researchers at Stanford University provides a fully quantum
mechanical analytic results for single-photon transport through a
ring resonator. Among their results, they found there exists a
critical coupling condition for such system that an on-resonance
incoming single photon would be blocked completely, in spite of the
presence of dissipations and imperfections of the resonator. In view
of the increasing attentions on single-photon generation, controlling
and traffic regulating, their theory should be a timely work for
fields such as quantum information processing and quantum communication.
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AU10216
*Towards water-soluble fullerenes: what happens next*
Highly hydroxylated fullerene C60 derivatives (fullerenols) are especially
important in medical sciences because they form water-soluble substances and
may be used in drug delivery applications. Despite the diverse therapeutic
use of fullerenols, little is known on the electron distribution and spatial
arrangement of their molecular structures. For this reason, we have employed
density-functional-theory methods to unveil the structural features and
electronic properties of fullerenols as a function of the hydroxylation. Our
recent published results showed that fullerenols with more numerous hydroxyl
groups (e.g., C60(OH)24) can exhibit a kind of electronic confinement effect
able to reduce the interaction of the carbon cage with the environment. In
other words, the great number of hydroxyl groups adsorbed on the fullerene
surface can protect it of immediate reaction as is it occurs for the
pristine fullerene C60 in aqueous solution.
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LW11249
Nano Test Tube
As test tubes go, it doesn't get any smaller than a single-walled carbon
nanotube. The confinement offered by a nanotube constrains chemical
reactions. We show such nanochemistry enables electron doping through
the 1D van Hove singularity of single-walled carbon nanotubes. This
yields enhanced density of conduction states, providing a model base for
challenging fundamental physics. "Screening", in physics, is the damping
of electric fields
by the presence of mobile charge
electronic excitations from the carbon 1s core level to 1D quantized
states of initial semiconducting tubes, we demonstrate that their
increased density of conduction states leads to enhanced core hole
screening. This fact illustrates the importance of many body effects in
understanding core level excitation process in carbon nanotubes. Using
1D quantum confinement of carbon nanotubes as a probe, our archetypical
nanochemistry addresses a fundamental physics issue and highlights how
such advances could determine future nanoscience.
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LU11744
Digging for buried microstructures, or why a new liver cancer medicine works
Buried nanoscopic crystalline domains embedded in solid biodegradable
polymer microspheres, have been detected and characterized by
nonlinear light scattering spectroscopy, which is a combination of
light scattering and nonlinear optics. We find that inside the 20 -50
micron sized spheres, which are key to a promising new treatment for
an incurable form of liver cancer, there is a distribution of
crystalline domains with sizes below 600 nm. This finding explains
the apparent structural robustness of the microspheres that seems to
be crucial in the understanding of the working mechanism of the
treatment: In the proposed medicine the crystalline domains can form
a host matrix for the necessary medicinal complex. The ability to
look inside a solid matrix without cutting open the material opens up
new avenues for the study of heterogeneities in chemistry and
physics, such as the monitoring of crystal nucleation and growth, or
the detection of small amounts of biological crystals (such as
proteins and biopolymers).
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BT10815
Engineering deterministic aperiodic structures for nanoplasmonics
The ability to control, enhance and extract
sub-wavelength (sub-_) optical radiation from
engineered nanostructures is at the core of
nanophotonics/nano-electronics integration.
An efficient scheme for local-field enhancement,
input/output coupling and precise addressing of
sub-_ radiation at the nanoscale is essential to
benefit from the extreme downscaling of state of
the art nano-optoelectronics components such as
light-emitting quantum structures, nano-tubes,
single molecule detectors and plasmonics devices.
Crucial to this picture is the development of a
novel engineering approach for the control of
electromagnetic sub-_ field enhancement at the
nanoscale. This has the potential to enable a
variety of novel nanoplasmonics active devices
offering large radiative-rate enhancements of
quantum dots, efficient photon injection and
extraction at the nanoscale, enhanced sensing
capabilities and unprecedented nonlinearities for
on-chip switching and frequency generation.
Crucial to this vision is the development of
novel rational approach for "engineering optical
fields at the nanoscale".
Presently, the best approaches to generate
nanoscale electromagnetic giant fields rely on
random "roughening" of metal surfaces by etching
or by colloidal synthesis of nanoparticles
resulting in aggregates statistically described
by non-periodic fractal objects and morphologies.
However, despite non-periodic statistical fractal
aggregates and rough metal surfaces led to the
successful generation of giant fields with
applications in single molecule spectroscopy,
they lack reproducibility and simple engineering
design rules for deterministic optimization.
The study of Deterministic Aperiodic Structures
of metal nanoparticles overcomes the fundamental
limitation of randomness by uniquely enabling
controllable spatial localization of
sub-wavelength plasmonic modes combined with wide
frequency spectra, which can be accurately
engineered. This approach is uniquely suited for
the establishment of predictive theories and
accurate design rules to understand and control
highly localized electromagnetic fields in
nanofabricated plasmonic-photonic devices such as
Fibonacci quasi-crystals [1-4] and more complex
deterministic structures with far richer spectral
properties [5,6].
Central to this novel approach is the development
of electromagnetic models for the accurate and
efficient solution of large-scale aperiodic
systems of interacting nanoparticles. This
provides significant challenges to classical
computational electromagnetics (CEM) techniques.
Conventional numerical approaches based on
discretized grids, such as Finite Difference Time
Domain (FDTD), Finite Difference (FD), and Finite
Elements (FE) becomes very inefficient and
inaccurate for the solution of large-scale
aperiodic systems with nanoscale features, which
require prohibitive computational power.
Despite the field of aperiodic deterministic
nanoplasmonics structures is still in its
infancy, our original modeling, computation
[1,2,4,7] and experimental work [3,5] has
demonstrated the onset of plasmonic band-gaps and
localized field states in metal nanoparticle
chains and arrays, unveiling the fundamental
connection between aperiodic morphologies and
eigenmode spectral and localization properties.
We envision that in the near-future the study of
deterministic aperiodic order will become a
primary paradigm in nanophotonics and
nanoplasmonics design technologies, where it
could open novel pathways for the demonstration
of nanoscale optical sensors, engineered SERS
substrates with single molecule sensitivity, and
a variety of active nanoplasmonics devices
enabled by the manipulation of localized
electromagnetic fields at the nanoscale.
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LT11942A
Chaotic shock waves of a Bose-Einstein condensate
The harmonically confined Bose-Einstein condensate (BEC) has been studied widely, however, the exact solution of the system has not been reported yet. It is demonstrated that the well-known Smale-horseshoe chaos exists in the time evolution of the one-dimensional (1D) BEC driven by the time-periodic harmonic or inverted-harmonic potential. The first exact solution of the system is constructed , which describes the matter shock waves with chaotic or periodic amplitudes and phases. When the periodic driving is switched off and the number of condensed atoms is conserved, we obtained the exact stationary states and non-stationary states. The former contains the stable `non-propagated' shock wave, and in the latter the shock wave alternately collapses and grows for the harmonic trapping or propagates with exponentially increased shock-front speed for the antitrapping. It is revealed that existence of chaos play a role for suppressing the blast of matter wave. The results suggest a method for preparing the exponentially accelerated BEC shock waves or the stable stationary states. The chaotic shock wave as a new type of superfluid turbulence warrants further investigation.
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LY11450
Origin of electromagnons in multiferroics
In most materials electricity and magnetism do not strongly interact so
that mixed magneto-electric devices are not yet a part of the
electronics industry. Similarly, the electromagnetic response (i.e., to
light) is generally separate – the magnetic field of light can excite
magnetic resonances and light’s electric field can excite lattice
vibrations. In multiferroic materials, where magnetism and
ferroelectricity coexist, it is possible to excite mixed spin and
lattice vibrations with electromagnetic waves. These excitations are
called electromagnons.
Based on a study of the absorption spectrum of the multiferroic compound
TbMnO_3 as a function of magnetic field, temperature, and polarization
of light we propose a theory for the origin of these electromagnon
excitations in the whole multiferroic family RMnO_3. Interestingly, we
find that the mechanism responsible for electromagnons is different from
the one that couples static magnetism and ferroelectricity. Our model
also explains the appearance of ferroelectricity in another family of
multiferroic materials with collinear magnetic structures - the so
called E-phase. Our results show how to strongly couple spin and lattice
excitations, and that this mechanism can exist in non-multiferroic
materials. Therefore, in principle, this effect could be useful for
spintronic applications that take advantage of this coupling even at
room temperature, something that is not possible in the current families
of multiferroic materials where these effects exist only at cryogenic
temperatures.
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LN11455ER
Polymer Adsorbtion
A recent computational method developed by University of Minnesota
researchers may open the door to substantial improvements in a broad
range of technologies that depend on polymer adsorption.
The ability of polymers---molecules composed of hundreds of repeat
units---to stick to surfaces is critical to numerous processes such
as coating, lubrication, and drug delivery. When adsorbed to a surface,
polymers undergo random changes in their conformation and
position thanks to bombardment by much smaller solvent molecules,
a phenomenon known as Brownian motion. Describing these dynamics
in an accurate way has remained a long-standing challenge due to
their complexity. University of Minnesota researchers have developed
a method to exactly describe the most difficult
aspect of the random motion: hydrodynamic interactions---the
solvent-mediated interaction of one part of the polymer with another part
and with the surface. Their results make clear for the first time the
role of these interactions, and allow for systematic investigation of the
effects of polymer and solvent properties on this complex behavior.
The method is expected to ultimately enable the design of
surfaces to precisely control the dynamics of adsorbed polymers, which in
turn may lead to stronger coatings, better lubricants, and more
effective drug
delivery strategies.
