One-atom thick film absorbs light completely

LE13613

 - Black bodies are idealized objects capable of absorbing all
light impinging into them. In this paper, we engineer a black body made
of a single layer of carbon atoms (graphene). Our design achieves total
light absorption for selected colors, which can be easily tuned by means
of electrical connections placed nearby. This study has direct
application to improved photodetection, particularly in the difficult
range of infrared detection, for security sensing, nocturnal imaging,
etc. It has also direct application to infrared lighting, with great
potential for manufacturing sources with unprecedented levels of
brightness in this range of the optical spectrum, which has been
difficult to cover so far. Our design can also be used to collect
infrared light for improved photovoltaics, because this part of the
solar spectrum is generally lost due to the unavailability of good
infrared absorbers as ours. And there are several other directions of
application, including bionsensing, chemical detection, etc. And last
but not least, the new black bodies have fundamental interest as a
unique structure that is capable of absorbing light completely within
record-thin one-atom layer (the graphene) that is just several thousand
times thinner than the ligh wavelength.

TIMELIKE ENTANGLEMENT AND TELEPORTATION

AJ10688

 - It has been known since the 1970's that quantum entanglement exists
between regions of empty space at a given time – this underlies many
exotic phenomena such as the evaporation of black holes.  In this
paper, we show that the same type of empty-space entanglement also
exists between different times at a single location in space, and that
this “timelike entanglement” can, in principle, be used as a resource
for quantum technology.  We show how a particle detector operating at
11:45am could in principle be made to share quantum entanglement with
another particle detector at the same location in space at exactly
12:15pm, but at no other times (e.g. not 12:10 or 12:20).  The
now-standard technology of quantum teleportation uses ordinary
entanglement as a resource for moving qubits of information from one
point to another in space – we propose that the use of timelike
entanglement could be used to teleport qubits of information from one
time to another, without being present during the time in between.

APS Physics News Ticker on Hiatus . . .

. . . until January 3, 2012.

Sensors using sound amplification by light

LF13479A

- The quest to measure exceedingly small motions of test masses for gravitational wave detectors has, over the past 40 years, led to the development of successive generations of ever more sensitive instruments limited by the laws of nature. Physicists studying kilometer scale laser interferometer gravitational wave detectors have turned a problem - triple resonance of two light fields with a single sound field - into a new instrument. They have experimentally shown that the instrument can measure a tiny vibration as small as a thousandth of the diameter of the nucleus of a gold atom...about one part in 10 to the power of 17 of a meter! They show that simple improvements can make the instrument 1000-fold more sensitive.

The new instrument operates by shining laser light onto a flexible mirror. When the light reflects off the mirror, the mirror recoils and the tiny recoil is enough to convert the light into a new light beam of a slightly different colour, and in a pattern that allows it to build up by resonance as it reflects back and forth between the flexible mirror and a second mirror. This resonance enhances the conversion of the vibration to the new light. By measuring the intensity of the new light, the mirror vibration is measured to extreme accuracy. The trick in making this deceptively simple concept work is the tuning of the resonance for the new light, which the team achieves by using a secondary laser to precisely deform one of the mirrors.

In a slight variation the same instrument can amplify radio waves and turn these into light, or measure tiny magnetic fields down to a millionth of the strength of the earth’s magnetic field.

The researchers plan to make a sensor for airborne detection of magnetic minerals, as well as tiny devices usable in space for measuring the composition of asteroids that could be mined and used in future space exploration.

Melting Ice Avalanches

LG13252

- This letter describes a novel experiment exploring melting in ice-bearing granular flows such as rock fall from mountain faces previously stabilised by permafrost or collapse of glacier séracs. It is proposed that collisions between ice particles as they flow over each other cause the particles' surfaces to melt, even at temperatures well below freezing. The melted layer not only alters the friction between particles, but it leads to the formation of liquid bridges between neighbouring particles. Our experiment employs a narrow Perspex drum, half filled with ice particles, situated in a temperature controlled laboratory. As the drum rotates, a continual avalanche of ice particles is formed. By regulating the temperature of the experiment the energy required to melt the particle surfaces, the degree of melting and the moisture content of the granular ice avalanche are all controlled. This work shows that melting through collisions enhances ice avalanche velocities and defines a parameter space for detailed exploration of these processes. It pioneers a new approach to analyzing the evolving hazard posed by rock and ice avalanches.

Do quantum states truly jump instantly?

LG14011A

- Among the strange properties of quantum states is their behavior when a measurement is performed: according to the so-called orthodox interpretation they change instantly (collapse). In this work we assume that this collapse may last for a non-vanishing time and suggest a procedure to estimate its duration. This is important because the status of objective reality of quantum states is far from being consensual among physicists. Two competing views stand out: either the state is a mathematical tool that gives statistical information on sets of systems, being ultimately meaningless for a single particle; or it is an "existing" thing for each system, at the same footing as the velocity of a particle or the electric field generated by a charge. In the first scenario it is natural to conceive the collapse as a gain of information, which can, in principle, be sudden. However, if the quantum state is to be considered a physical entity, not only a mental construct, the idea of instantaneous collapse is, at least, awkward. Thus, accessing the time scale of collapse would deepen our knowledge on the very nature of quantum theory.

Artificial intelligence to search for new compounds

LF13329

- By combining quantum chemistry with artificial intelligence, researchers have achieved a scientific breakthrough expected to aid in exploring chemical compound space, i.e. the virtual space populated by all possible chemical compounds. The interdisciplinary team dramatically increased the speed of calculating energies of small molecules with quantum chemical accuracy. Quantum chemical methods permit scientists to calculate molecular properties on a computer from first principles (i.e., without having to conduct any experiments)—they are necessary for many chemical applications such as catalysis, or the discovery of novel materials. Previously, such calculations demanded intensive computational resources. Machine Learning, on the other hand, generates predictive models based on examples. While common in daily life, such as in Google's internet search engines or Amazon's book suggestions, it is also used in scientific domains, such as genetic research or brain computer interfaces. When applied to quantum chemistry, thousands of quantum chemical reference energies have been calculated in order to learn a molecular model. The resulting artificial intelligence machine permits the prediction of molecular properties with comparable accuracy within milliseconds, instead of hours. Such speed-up paves the way for highly accurate calculations of unprecedentedly many molecules.

Superluminal neutrino experiment faces more theoretical challenges

LK13037

- Indications from the OPERA collaboration that neutrinos may travel faster than light shocked the world as it may break the Einstein’s relativity theory. However, this result is facing new challenges from theoretical considerations, as shown in a paper to be published in Physical Review Letters. The kinematics related with neutrinos is changed if it is superluminal, so that neutrinos with energy greater than 5 GeV are even not able to be generated by decay of π mesons, which is the process to generate neutrinos at OPERA. This is clearly conflict with the fact that neutrinos of about 40GeV have been detected in the experiment. Further, the study shows that the neutrino spectrum is modified as the superluminal neutrinos lose energy quickly by radiating electron-positron pairs. By studying the neutrino spectrum measured at IceCube the superluminality of neutrinos is constrained to be about 7 orders smaller than that measured at OPERA.

Quantum integrated circuits go 3D

LG13182


- We developed a electronic quantum-bit (qubit) circuit, a computational base of a quantum computer, that can attain quantum coherence an order of magnitude longer than any previously reported quantum integrated circuits. A large-scale quantum computer has abilities to perform computation and store quantum information, which are impossible with a classical computer. The number of possible operations in a quantum computer is determined by its coherence time for which the state of the quantum computer maintains its quantum nature. In this paper, the improvement in the coherence time owes to our new three-dimensional (3D) circuit quantum electrodynamics (QED) architecture that uses wireless connection between the superconducting qubit and a three-dimensional superconducting cavity. This creates a clean environment for the qubit to achieve long coherence. Our work advances one big step towards realizing an electronic large-scale quantum computer with the improved
coherence demonstrated in our 3D technology.

Obstacles can speed granular flow

LG14037

- The flow of particles through a bottleneck is prone to spontaneously developing clogs, which are able to arrest the flow and produce a rapid dissipation of the kinetic energy of all the particles in the system. This behavior is observed in different scenarios such as grains discharging from a silo, people escaping from a room, bubbles passing through an orifice and vehicle traffic in a highway.

We present experimental results on the effect that inserting an obstacle just above the outlet of a silo has on the clogging process. We find that, if the obstacle position is properly selected, the probability that the granular flow is arrested can be reduced by a factor of one hundred. This dramatic effect occurs without any remarkable modification of the flow rate or the packing fraction above the outlet, which are discarded as the cause of the change in the clogging probability. Hence, inspired by previous results of pedestrian crowd dynamics, we propose that the physical mechanism behind the clogging reduction is a pressure decrease in the region of arch formation.

Hunting very rare gases

LE13320

- This research reports on the lowest concentration of a gas of simple molecules ever measured by laser spectroscopy. A radiocarbon-containing ubiquitous molecule (14C16O2) was detected at pressures below 1 femtobar, corresponding to a concentration of 43 parts per million of billions (43x10-15), thus setting a new benchmark in trace gas sensing. Our result directly challenges accelerator mass spectrometry that, for more than 30 years, has been the only option for radioisotope-based dating of artifacts of biological origin. Moreover, detection of very dilute and elusive molecules can give a new drive to very diverse fields, as climate changes monitoring, medical research, energy plants monitoring, detection of hazardous substances for homeland security or even fundamental physics research, all in a table-top set-up.

Observation of quantum motion of a nanomechanical resonator

LJ12981

- According to quantum mechanics, a mechanical resonator cooled to its ground state will continue to exhibit fluctuations in position. This so-called zero-point motion, a type of quantum noise, previously demonstrated for trapped ions, has now been directly measured for a chip-scale nanomechanical resonator cooled near its quantum ground state. In a paper to be published in PRL physicists, use a fabricated silicon nanomechanical resonator coupled to laser light, to both cool, and read-out the motion of mechanical system. This method of cooling, called electromagnetic back-action cooling, has been of interest for some time, as an effective means to remove all thermal noise from a mechanical resonator. Such cooling methods have only recently been successful at achieving this task, but only using read-out techniques ill-suited for observing the remaining quantum noise of motion. Using two lasers, one for back-action cooling, and the other for a two-shot read-out scheme, physicists have now measured the quantum motion of a nanomechanical system. By carefully measuring the rates at which the mechanical system can emit, and absorb energy from its surround environment, the authors demonstrate an asymmetry with no classical analogue, and provide a self-calibrated method of thermometry of the nanomechanical resonator.

How to design a surface that never gets dirty

EG10952

- Surface fouling is a major, still unresolved problem, harmful to countless industrial and biomedical applications. For example, the accumulation of unwanted particles may cause clogging and failure of medical devices, such as implants and stents, whereas the formation of biofilms by microorganisms can promote rapid spreading of dangerous diseases and can even hamper the speed of ships. In this paper, we use numerical simulations to probe how tiny, hair-like posts covering surfaces be can designed to effectively mitigate the deposition of microscopic particles suspended in a flowing fluid. We show that posts are tilted against the fluid stream create circulatory microflows that push solid particles, such as dust and bacteria, away from the wall, thereby reducing their deposition and accumulation. The action of these anti-fouling posts is purely hydrodynamic and does not require any external control or actuation, thereby enabling the creation of environmentally-safe surface coatings with anti-bacterial and self-cleaning capabilities.

The birth of our universe from superstring theory

LH13109

- Numerical simulation of superstring theory suggests a totally new picture of how our universe began. According to the standard Big Bang scenario, our universe was extremely small when it began about 14 billion years ago. Therefore, in order to study how it actually began, one needs to extend Einstein's general theory of relativity to make it consistent with quantum mechanics. One of the most promising approaches is superstring theory, which enables quantum description of gravity as well as all the fundamental interactions and the matters in a unified fashion. However, the theory requires the space-time to have (9+1)-dimensions, and how to reconcile this fact with the observed (3+1)-dimensional universe has been a big mistery. It is difficult to address this issue in conventional formulations of the theory based on Feynman diagrams due to their inability to take full account of strong coupling dynamics of superstrings. In this paper a new formulation of superstring theory based on large matrices is used to overcome this problem. Numerical simulation suggests that the space was indeed nine-dimensional up to some critical time, after which only three out of nine spatial directions started to expand.

Hydrodynamics of writing with ink

LE12903

- Writing with ink involves the supply of liquid from a pen on to a porous hydrophilic solid surface, paper. The resulting line width depends on the pen speed and the physicochemical properties of the ink and of paper. Here we quantify the dynamics of this process using a combination of experiment and theory. Our experiments are carried out using a minimal pen: a long narrow tube that serves as a reservoir of liquid, which can write on a model of paper: a hydrophilic micropillar array. A minimal theory for the rate of wicking or spreading of the liquid is given by balancing capillary force that drives the liquid flow and viscous force exerted by the substrate. This allows us to quantitatively predict the shape of the front and the width of the line laid out by the pen, the results corroborated by experiments.

Faster-than-light neutrinos may leave trails at the LHC

DKR1045

- Is Einstein's venerated theory of special relativity challenged by
neutrinos? Our work suggests that the LHC may help provide the answer.

The OPERA experiment, at the Gran Sasso Laboratory in Italy, has reported
observation of neutrinos that travel faster than light. This result, if
confirmed, would violate one of the defining laws of special relativity --
a pillar of fundamental physics for over a century-- that forbids
superluminal (faster-than-light) travel. If neutrinos, which are extremely
elusive by nature, can travel at superluminal speeds it has been predicted
that they would emit easy-to-detect particles, such as electron
anti-electron pairs, along their paths. In our paper, we suggest looking
for these conspicuous trails that would be left in the wake of neutrinos
-- if they traversed the LHC detectors faster than light -- as a way of
testing the superluminal neutrino hypothesis implied by the OPERA results.
The requisite neutrinos can originate from decays of top quarks that are
copiously produced at the LHC.

Why it is hard to see Schroedinger's Cat

LH12959

- Why do we not see quantum physical effects in our daily lives? This question was raised already by Schroedinger, one of the founding fathers of quantum physics, in his famous cat paradox. One answer is that quantum superposition states, such as the cat being both dead and alive at the same time, are very fragile. When the cat interacts with its environment even just a tiny bit, the superposition is destroyed.

This effect is known as decoherence, and it has been studied intensively over the last few decades. But it turns out that decoherence is not the only reason why quantum effects are hard to see. In a recent paper in Physical Review Letters, researchers point out an even more basic difficulty: seeing quantum effects requires extremely precise measurements. Studying a concrete example for such a "cat" motivated by recent experiments, a particular quantum state involving a large number of photons, they show that in order to see the quantum nature of this state, one has to be able to count the number of photons in it perfectly. This becomes more and more difficult as the total number of photons is increased.

Distinguishing one photon from two photons is within reach of current technology, but distinguishing a million photons from a million plus one is not. This shows that seeing Schroedinger's cat is hard also because it would require exceptionally good eyesight.

Leonardo's Rule of Tree Branching

LE13207

- Leonardo da Vinci observed in his notebooks that "all the branches of a tree at every stage of its height when put together are equal in thickness to the trunk." There have been surprisingly few assessments of this rule, but the available data indicate that the Leonardo rule holds for a large number of species. Despite this scarcity of experimental evidence, it is safe to state that Leonardo's rule has not been disproved. As a matter of fact, it is so natural to the eye that it is routinely used in computer-generated trees. In this Letter, it is proposed that this rule is a consequence of the tree skeleton having a self-similar structure and the branch diameters being adjusted to resist wind-induced loads.

Radical Role Reversal

LE13164

- It is an elementary principle of chemistry that radicals, i.e. atoms or molecules with an unpaired electron orbiting their nucleus, are highly reactive, while closed-shell species, i.e. atoms and molecules where the electrons are all paired, are relatively stable. In this paper, atoms and ions are produced and confined at ultracold temperatures in a novel hybrid trap, dubbed the MOTION trap. By carefully monitoring the interaction of the ultracold atoms and ions in this trap, it is observed that at these ultracold temperatures closed-shell species can in fact be thousands of times more reactive than radicals. This role-reversal is found to be the consequence of the underlying quantum dynamics driving the chemical reaction, which are normally obscured at room temperature. Given that reactions of the type observed in this work are important for determining astrophysical processes and in planned hybrid atom-ion devices, this work highlights both the need for a renewed effort in laboratory astrophysics and fully-quantum chemical reaction calculations on a case-by-case basis to guide the next generation of atom-ion device design.

How hard is it to generate a complex birdsong?

EH10901

- Behavior emerges from the interaction between a nervous system and a peripheral bio-mechanical device executing those instructions. In that perspective, how much of the complexity is coded in the driving commands, and how much emerges in the physical device? In this work we study the acoustically challenging song the Zebra finch, and test the hypothesis that much of its acoustic complexity is due to the nonlinear nature of the avian vocal organ. We test it by reconstructing the parameters of a simple model, and comparing those results with direct measurements of the physiological parameters driving the vocal organ. Simple instructions, driving the nonlinear device, generate the most peculiar and acoustically rich song of the Zebra finch.

High-brightness multi-wavelength remote laser for detecting multiple hazard gases in air

LE13721AR

- Since the first ruby laser was demonstrated in 1960, there have been enormous requirements for a variety of coherent light sources in a broad spectrum of fields covering science and engineering. In environmental science, there has been a large amount of research effort aiming at measuring atmospheric trace species over a long distance. The ability to control the generation of coherent light source with different frequencies at a designed location would provide a new strategy to meet the pressing needs of various environmental issues from monitoring global warming and stratospheric ozone depletion to early detection of nuclear reactor radiation leak and biological treat agents in air. To date, a multi-wavelength remote laser in air that allows for dynamically switching the operating wavelength has not yet been achieved, although this type of laser is certainly of high importance for detecting multiple hazard gases. Here, we demonstrate a harmonic-seeded switchable multi-wavelength laser in air driven by intense mid-infrared femtosecond laser pulses. Furthermore, population inversion in the multi-wavelength remote laser occurs at an unexpected ultrafast time-scale (i.e., less than ~200 fs) owing to direct formation of excited molecular nitrogen ions by strong-field ionization of inner-valence electrons. The bright multi-wavelength laser in air opens the perspective for remote detection of multiple pollutants based on nonlinear spectroscopy.

New way to pack marbles and buckyballs

LJ12785ER


- Spherical objects inside a cylinder can now be packed more efficiently than ever. With a suitable template, the densest packings can surprisingly be obtained from a very simple deposition procedure. The findings will have a broad range of applications in physics, from the macro- to the nano-scale, and also in commercial packaging.

Indications of a spatial variation of the fine structure constant

LV12409

- One of the most cherished principles in science - the constancy of physics – apparently may not be true. A new study, using data from the world’s largest optical telescopes, suggests that one of the four fundamental forces of Nature, electromagnetism - measured by the so-called fine-structure constant and denoted by the symbol alpha - seems to vary across the Universe.

The very first hints that alpha might not be constant arose in 1999 from data collected with the Keck Observatory in Hawaii but there was insufficient data to explore any dependence on location in the Universe. Now, newer data from the European Southern Observatory’s “Very Large Telescope” in Chile suggests a “preferred direction” in the Universe, along which alpha varies, slightly, but significantly.

The discovery, if confirmed, has profound implications for our understanding of space and time and violates one of the fundamental principles underlying Einstein's General Relativity theory. The continuous drift in alpha may also imply a much larger universe than our observable patch, possibly infinite and also offer a natural explanation for a question that puzzled scientists for decades: why do the laws of physics seem to be so finely-tuned for the existence of life?

Peering Out from Under an Invisibility Cloak

PRE 84, 046607 (2011)

- Most invisibility cloak designs have one serious drawback - they make it impossible for anyone hiding under the cloak to see what's going on in the outside world. Researchers have now come up with an approach that, in theory, should allow us to make cloaks that allow you to peek out while remaining entirely hidden. In effect, they propose making a tiny tear in the cloak, and then stitching the hole with a two types of materials chosen to effectively cancel each other out when seen from the outside, while still allowing light to enter. Although the invisibility cloak design currently exists only on paper, it theoretically ensures that aspiring Harry Potters remain invisible while keeping an eye on the Voldemorts and Snapes all around them.

Self-organizing patterns help to conceal secret communication

EF10894


- Steganography is a science of hiding data in a communication in such a way that only the sender and the receiver know of its existence. In this paper, we propose a steganographic communication algorithm based on self-organizing patterns. The dot-skeleton representation of the secret image is embedded into the initial random perturbation around the unstable stationary state. The pattern of stripes is allowed to evolve for a pre-determined number of forward time steps and is transmitted to the receiver. The receiver has to generate the identical initial perturbation (without the dot-skeleton representation of the secret image). The difference between the pattern produced by the receiver and the pattern received via the communication channel reveals the secret image.

Complex nonlinear pattern formation processes govern the formation of stripes interconnecting dot-skeleton points in the difference image. The proposed communication system is fully functional when grayscale levels of the dot-skeleton representation of the secret are well below the noise level of the initial random perturbation. The ability of the proposed scheme to hide information and to avoid suspicion outperforms traditional steganographic techniques if the security of communication is considered as a primary objective.