In Search of Rogue Wave Sources

LU13570 - New experiments presented in this paper reveal that extreme wave events, or “rogue waves” on the surface of a vertically vibrated liquid are caused by the interaction between oscillating solitons. Such solitons, also known as oscillons, have been found in a variety of physical systems such as granular medium, non-Newtonian fluids, optical media and plasmon oscillons in nanoparticle arrays. New observations made in the water surface ripple and reported here suggest that oscillons interact within a lattice and that such interaction causes their horizontal mobility and merger which leads to the formation of closed regions, or craters. Rogue waves, or strong vertical jets originate from the centers of such craters. The probability of large wave events greatly increases when oscillons move faster on the surface of water. These results will be useful in understanding physics of the rogue wave generation in other nonlinear systems.

Testing Stressed Viruses

LK13179 - One of the big questions about materials at the nanoscale is whether macroscopic theories can be applied to nano-sized systems. To answer this question, we focus on self-assembling, viral nanoparticles to test the predictions of elasticity theory. Of all known viruses those with icosahedral symmetry are the most common. Their structure can be described by folding a hexagonal lattice into a sphere-like configuration. By doing so defects with 5-fold symmetry are created at the icosahedral vertices.  According to elasticity theory these vertices should be under a permanent pre-stress, a prediction which never has been verified experimentally. Here we compare naturally occurring viruses with those that have missing proteins at their vertices, and test the hypothesis that the latter particles are stress-free. Deforming the viruses by Atomic Force Microscopy and comparing our results to detailed simulations has verified our hypothesis about pre-stress. This is the first time that the predictions about pre-stressed vertices in viral particles has been demonstrated experimentally and is a huge support for the use of continuum elasticity to describe nanometer sized objects.

Experimental Violation of Heisenberg's Uncertainty Principle

LU13293 - While there is a rigorously proven relationship about uncertainties intrinsic to any quantum system, often referred to as "Heisenberg's Uncertainty Principle," Heisenberg originally formulated his ideas in terms of a relationship between the precision of a measurement and the disturbance it must create. Although this latter relationship is not rigorously proven, it is commonly believed
(and taught) as an aspect of the broader uncertainty principle. Here, we experimentally observe
a violation of Heisenberg's \measurement-disturbance relationship", using weak measurements to
characterize a quantum system before and after it interacts with a measurement apparatus. Our
experiment implements a 2010 proposal of Lund and Wiseman to con rm a revised measurement-
disturbance relationship derived by Ozawa in 2003. Its results have broad implications for the
foundations of quantum mechanics and for practical issues in quantum mechanics.

Leading the Way to Lead-Free Piezoelectrics

LQ13398 - Energy and environment are two pressing global challenges.  Piezoelectric materials enable the conversion between electrical and mechanical energies, and have been used in many important applications, such as devices for ultrasound medical imaging and for energy harvesting from vibrations.  In the past six decades, lead-containing ceramics (greater than 60% weight of lead) have dominated the piezoelectric technology even though they pose a serious threat to the environment and human health.  For best piezoelectric performances, the compositions are fine tuned to be at the so-called morphotropic phase boundaries and the ceramics go through a poling processing where they are exposed to a highest possible electric field.  A recent discovery (to be published in the September 6 issue of Physical Review Letters) breaks the ice for new lead-free piezoelectrics.  The original approach of poling to the highest possible field is incorrect and the composition is not necessary to be at the morphotropic phase boundary.  Such a fundamental alteration to the long-standing paradigm adds a new dimension to the development of high-performance lead-free piezoelectrics.  

Learning from an Eggshell

LU13685  - If you squeeze an eggshell along its major axis, the shell is strikingly rigid and it is extremely challenging to break it with our bare hands. Conversely, if the eggshell is compressed along its equator, the resulting deflections are larger and, past a critical load one is typically able to fracture it. In our paper, we have rationalized this difference in the rigidity of an eggshell depending on the shell-load orientation to be due to the local geometry near the points of indentation. We have introduced a predictive framework for the rigidity of thin elastic shells which can also account for the situation when the shell is over-pressurized. Our concept of Geometry-Induced Rigidity can be used in reverse, as a precision non-destructive tool, to measure parameters of a shell (e.g. thickness) upon knowing the geometry of the underlying surface and the local mechanical response. The scale-invariance of Geometry-Induced Rigidity suggests that our framework should find uses across length scales: from the mechanical testing of viral capsids through Atomic Force Microscopy, to ocular tonometry procedures or in the design of architectural shells. All this work was inspired by the remarkable physics of an elegant eggshell!

Jet impact on a soap film

LG14014E - We experimentally investigate the impact of a liquid jet on a soap film. We observe that the jet never breaks the film and that two  qualitatively different steady regimes may occur. The first one is a refraction-like behavior obtained at small incidence angles when the jet crosses the film and is deflected by the film-jet interaction. For larger incidence angles, the jet is absorbed by the film, giving rise to a new class of flow in which the jet undulates along the film with a characteristic wavelength. Besides its fundamental interest, this study presents a new way to guide a micro-metric flow of liquid in the inertial regime and to probe foam stability submitted to violent perturbations at the soap film scale.

Geometric Mechanics of Curved Crease Origami

LT13067 - Origami has been widely applied to fields in structural engineering, architecture, and design, contributing to solutions of many practical problems of these fields. Although the idea that a sheet of paper can be folded along an arbitrary curve seems unfamiliar, such folds have been incorporated into origami sculptures for quite some time, and are also seen in decorative and functional boxes such as the McDonald's Fries Box. Though the crease of an open closed fold lies flat on the plane, a closed crease buckles dramatically and appears mechanically stiff. Previous work has described the geometry of curved folds. For the first time, we have presented an analytical and simulation model of the mechanics of curved fold origami. We show that it is the interaction between the geometry of the fold, the mechanical tendency to avoid in-plane stretching, and the bending energy of the sheets that produce both the three-dimensional shapes observed and the mechanical stiffness.

Slime Mold Vein Networks Give Hint To Cure Cancer

LQ13471  - Slime molds are omnipresent in nature. They feed on organic material and avoid direct sunlight. The typical damp-fresh smell in the woods is emanating from them. These slimy creatures appear primitive, yet they have developed a sophisticated strategy to transport food and deliver environmental information. They use an intricate system of veins organized in a network. Most unexpectedly, slime molds give us a hint to cure cancer. Their smart mechanism of network formation is so general that it can be applied to analyze the development of blood supply via vessel in tumors. Thus, the effectiveness of different therapies in hindering tumor growth could be tested. In order to arrive at this conclusion researchers have used exact mathematical tools from topology. This branch of mathematics deals with  the ways general objects are connected independent of their shape. 

Sorting out blood flow

LT13043 - Blood contains many different types of cells, each with specific functions in the body. As blood flows, these cells segregate, with the white blood cells (WBCs) and platelets preferentially found near blood vessel walls. This phenomenon, called margination, allows for efficient immune surveillance by the WBCs and rapid response to vessel wall injuries by platelets. Our work demonstrates how the physical properties of different cells lead to this important observation. As the stiff WBCs and platelets collide with the more flexible red blood cells during flow, they are pushed aside while having little effect on the motion of the red blood cells, a process that ultimately leads to the trapping of WBCs and platelets near the vessel walls. A simple model of blood flow that accounts only for these collisions and the flow-induced repulsion of the cells from the vessel walls is able to match results from detailed numerical simulations. The understanding provided by this study will be helpful in designing effective drug delivery particles that target the vascular walls for treatment of cancer or atherosclerosis. Margination has also been employed in biomimetic microfluidic devices to separate WBCs and platelets from whole blood, which could be helpful in treating leukemia or for platelet rich plasma therapy (used by athletes for healing injuries). The principles established in our study will aid the development of these devices.

Image processing of two photons

LT13248A - The where-about of two photons along a one-dimensional line can be generally described by the probability of the two photons to have a certain combination of positions along the line. This is a two-dimensional distribution, as is, for example, the intensity distribution that makes up a classical image. There are many ways in which an image can be processed and manipulated. Could such methods be used for controlling the spatial distribution of two photons, even if it represents a highly non-classical, quantum state of light?

In this work we show that one of the most frequently used image processing techniques, namely, spatial frequency shaping, or "Fourier processing", can be adapted for the spatial manipulation of highly non-classical states of photon pairs. As an example, we demonstrate the retrieval of the two-photon quantum phase using an analog of classical phase-contrast microscopy. As many more Fourier processing algorithms can be applied, we believe that this opens up a new avenue for the manipulation of non-classical light.      

New Quantum Computer Blueprint

Physical Review X - We develop a layered quantum-computer architecture, which is a systematic framework for tackling the individual challenges of developing a quantum computer while constructing a cohesive device design. We discuss many of the prominent techniques for implementing circuit-model quantum computing and introduce several new methods, with an emphasis on employing surface-code quantum error correction. In doing  so, we propose a new quantum-computer architecture based on optical control of quantum dots. The time scales of physical-hardware operations and logical, error-corrected quantum gates differ by several orders of magnitude. By dividing functionality into layers, we can design and analyze subsystems independently, demonstrating the value of our layered architectural approach. Using this concrete hardware platform, we provide resource analysis for executing fault-tolerant quantum algorithms for integer factoring and quantum simulation, finding that the quantum-dot architecture we study could solve such problems on the time scale of days.

Light-controlled metamaterial optics

LR13197 - We suggest and verify experimentally a novel practical approach for dynamic noncontact tuning of composite structures. This approach allows metamaterials to acquire almost any desirable spatially inhomogeneous properties by interacting with visual light patterns projected onto the metamaterial, which may lead to a new generation of electromagnetic composites whose local properties can be tuned continuously. More specifically, our approach works by applying a hand-crafted light profile to an array of light-tunable magnetic meta-atoms. The illumination affects the magnetic resonances of the meta-atoms individually. Thus, for the first time we achieve a practical design of a metamaterial in which the constitutive parameters may be changed at will and gradually within a material volume. We fabricate the first reconfigurable light-tunable metamaterial that under different illumination profiles can operate as a controllable beam deflector or/and focusing or defocusing reflector.

No Maxwell’s Demon at work in Ranque-Hilsch vortex tubes

PRL - The long-standing problem of how a vortex tube simultaneously produces hot and cold  air streams with nothing more than the injection of a high-speed peripheral air stream has been unravelled in this paper by simplification of the device to its lowest single element – a duct rotating about a central outlet delivering air from its periphery.  This simple case shows unequivocally that a pressure gradient driving air flow against a centrifugal gravitational field results in the air giving up kinetic and internal energy as angular propulsion, resulting in a temperature reduction at the central outlet.  The theory presented is based on thermodynamic principles and shows that the maximum temperature drop is a function of the velocity of the gas at the periphery of the tube.  The article also shows that the effect is easily scaled up.

Studying the Light Response of Living Photoreceptor Cells

LN12705 -  Eyes of living organisms represent advanced light harvesting systems, developed through hundreds of millions years of evolution. Some of their features are comparable or even superior to existing man-made photodetection devices. For example, rod photoreceptor cells of the retina, which are responsible for night vision and form the focus of the present study, represent miniaturized photodetectors containing a photosensitive element (rhodopsin pigment) along with a ‘‘built-in’’ chemical power supply (ATP produced by mitochondria). They have sensitivity down to single-photon level, and demonstrate a remarkable low noise operation. Understanding such properties of nature-given photodetectors stimulates considerable interest in interfacing them with sources of nonclassical light, such as light with a ‘‘fixed’’ number of photons, and ‘‘squeezed’’ light. We analyzed the electrophysiological response of an isolated rod photoreceptor of the  African Clawed Frog (Xenopus laevis) under stimulation by coherent and pseudothermal light sources. Using the suction-electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.

Proteins in cell membranes studied using string theory to help unravel the mystery of sneezing

LQ13362  - We see how forces arising from thermal fluctuations could affect proteins embedded in cellular membranes by applying conformal field theory methods originally developed by string theorists.  Our research is inspired by an astonishing recent discovery that cell membranes can separate into two fluid regions (the way oil and water separate, but in two dimensions), forming microscopic fractal puddles of each in the membranes of living cells. We find that fluctuations in this complicated two-dimensional soup lead to long-range attractive forces between proteins preferring the same type of puddle, and repulsion between proteins preferring dissimilar puddles. These forces could help explain many mysteries in the experimentally observed behavior of membrane proteins.  For example, they may be important in clumping together the proteins that detect and respond to allergens in pollen, initiating a complex sequence of events that eventually makes you sneeze.

Smooth change from liquid to solid in granular media

LQ13873 - A shaken confined granular system presents a very unusual solid-liquid-like phase transition; it occurs above a certain heating threshold and, as this paper shows, it can be either abrupt or continuous. For equilibrium systems it is believed that a liquid-solid transition is always abrupt: a disordered liquid state cannot change smoothly to an ordered solid state because of their different symmetries. However, recent studies show that confined equilibrium systems, like water nano-films, can behave differently. In this paper, we show that a shaken non-equilibrium confined granular system also differs from the classical image. The transition can be either abrupt or smooth depending on the vertical height and filling density, meaning that one can go smoothly from one state to the other by changing a control parameter. In the experiments, density fluctuations do not present strong variations at the transition, whereas the way grains are locally ordered varies strongly, either abruptly or continuously. In the second case, grains smoothly order in a square symmetry in highly fluctuating domains. The associated fluctuations, characteristic size and relaxation time seem to diverge at the transition in a way described by the non-equilibrium theory of phase transitions.

What will happen when a bubble is close to a flexible soft boundary?

ER10845 -The interaction between an oscillating bubble and a flexible soft boundary is an important phenomenon, which is commonly found in nature, marine industrial applications, and medical treatments. The behavior of an oscillating bubble is greatly dependent on the characteristics of a boundary that it is placed near to.  If the boundary is rigid, the bubble moves towards it; whereas if the boundary is a free surface, the bubble migrates away from it. The behavior of the bubble near a flexible soft boundary would fall in-between these mentioned limiting cases and is more complex.  We investigate the physical behavior of the interaction between a bubble and a flexible soft boundary numerically and experimentally. The results from this study may provide physical insights into the complex physics of bubble-rubber interaction. The understanding is possibly applicable in biomedicine for drug delivery to tissue, which is a soft material. It is also probably useful in the marine industry where ultrasonic bubbles are generated for the defouling of the ship surfaces which has been coated with an elastic material. There is also potential interest in underwater explosion near an elastic structure. 

With whom do you want to share rumors, a blabbermouth or a person of few words?

EG10922 - On a social network, it seems better to transfer information preferentially toward those who have many social links ("blabbermouths") because they have larger impact on the network.  However, at the same time they can be bottlenecks for spreading information since information tends to concentrate on these blabbermouths and becomes redundant.  This paper shows that to achieve a faster spread over the network, it is indeed better to spread information preferentially toward those who have few social links (reverse preferential).

The Abraham force: the end of a century in hiding?

ASJ1069 - A century after Abraham predicted his elusive force we propose a conceptually simple way to see it in the laboratory. The rival theories of Abraham and Minkowski, both presented around 1910, seemed to give slightly different predictions for the physics of light travelling inside, say, glass or water. In particular, Abraham says that fields that change with time will give a little extra push to the material compared to what Minkowski predicts: the Abraham force. It's proved very hard to think of ways to detect this force, however, it existence is still in question. Using a series of intense and very short laser pulses, we show theoretically that the Abraham force could be detected in a way that is, at least conceptually, very simple. When a light pulse enters an optical fiber, the Abraham force would give a small "kick", setting the fiber in motion. As the pulse exits, a "kick" in the opposite direction makes it stop, but in the meantime the fiber has moved a tiny distance. Repeat this process enough times, and the distance becomes measurable. By winding a long fiber onto a cylinder and using a rapid repetition of short laser pulses, the Abraham force makes the cylinder rotate if it hangs by a thin thread. The rotation could be made so large as to be visible to the naked eye. And if the Abraham force isn't there, the cylinder will rotate in the opposite direction.

Quantum wires: prime numbers make the difference

LP12825 - Imagine a bunch of people forming a line. By talking to each of the their neighbours, they help Alice, at one end, in passing a message to Bob, at the other end. Like a sort of bucket brigade. If all do their job correctly, the message should reach Bob independently of the number of people in line. However, if we substitute people with (interacting) “talking” quantum particles, a new analysis shows that this is not the case, and that the number of people is crucial. Lines of this type are called quantum wires: they model the transfer of information between quantum particles and appear in a variety of nanodevices engineered and natural. It is known since a decade that perfect communication in quantum wires is impossible beyond three particles. But now we know that if we include an arbitrarily small imperfection, and if we wait long enough, then the message is very likely to reach Bob, exactly when the length of the wire is very special: a power of two, a prime or twice a prime. This peculiar phenomenon is due to interference effects. So, if the wire is composed by 9 particles, which is not one of these numbers, Alice better invites an extra particle to join the line and then get to 10 – which is twice a prime. The result opens up the possibility of employing quantum dynamics to design “natural algorithms” for probing the arithmetic structure of numbers

Asymmetric Higgsino Dark Matter

LP12845 - In the supersymmetric framework, prior to the electroweak phase transition, the existence of a baryon asymmetry implies the existence of a higgsino asymmetry. We investigate whether the higgsino could be a viable asymmetric dark matter candidate. We find that this is indeed possible. Thus, supersymmetry can provide the observed dark matter abundance and, furthermore, relate it with the baryon asymmetry, in which case the puzzle of why the baryonic and dark matter mass densities are similar would be explained. To accomplish this task, two conditions are required. First, the gauginos, squarks and sleptons must all be very heavy, such that the only electroweak-scale superpartners are the higgsinos. With this spectrum, supersymmetry does not solve the fi ne-tuning problem. Second, the temperature of the electroweak phase transition must be low, in the (1-10) GeV range. This condition requires an extension of the minimal supersymmetric standard model.

Zippy harmonic oscillators

LT13019 AND LT13077 - How fast can one transport a particle in a harmonic well from one place to another and come to a dead stop? With precise control, the particle can be transported arbitrarily fast and still return to its initial quantum mechanical state. So far, most experiments have been performed adiabatically, on time-scales much longer than one oscillation period. Now two research groups have cooled trapped ions to their quantum mechanical ground state and transported them over hundreds of micrometers (10,000s of  times the extent of the particle wave packet), in as few as 5 oscillation cycles. The rapid acceleration leads to excitation during transport, but the experiments show that the deceleration can be controlled well enough to return the ions to their ground state. Besides exploring a new regime of quantum transport, this work also has practical implications: Some proposals for scaling quantum information processing with trapped ions require ion transport inside a complicated array structure. So far, transport durations were long compared to those of quantum logic operations on the ions. The recent diabatic experiments  put these time scales on the same level, thereby significantly reducing the processing overhead.

Spread of microorganisms in the soil labyrinth

A network of soil pore space.

LQ13682 - Soil hosts a stunning wealth of biological activity of microbes -bacteria, fungi, protozoa...- that plays an essential role in processes such as plant growth, climate change, or soil-borne epidemics. Such microorganisms inhabit the soil pore space which is a complex maze-like network of interconnected microchannels of different shapes and lengths (see the attached figure). Despite the qualitative insight provided by experiments dealing with 2D thin sections of soil, the effect of soil structure on microbial spread is nowadays poorly understood. For instance, it is not known to what an extent the soil structural heterogeneity affects the ability of microbes to invade large portions of soil . In our Letter, we use 3D radiographs of soil and mathematical network models to show that the extreme complexity of the soil labyrinth has a prominent effect on microbial invasion. One of the most remarkable results is that neglecting the structural complexity of soil would typically lead to a substantial underestimation of microbial invasion. Invasions in complex soil labyrinths are typically larger than in more homogeneous habitats because of the presence of relatively long channels that may act as bridges for microbial transmission between distant parts of soil.

The weakest link

LR12838 - How do arches break under vibration? It turns out that arches sporting a neat, clean shape resist better than those with geometrical imperfections. In a recent experiment, physicists first create arches in a vertical layer of small spheres and then submit them to controlled perturbations. After considering several geometrical features of the arches such as size or aspect ratio, they conclude that the danger is concentrated at places where the arch departs from a perfect, uniform shape. Worse still, if one of the beads is hanging from its neighbors due to friction, odds are high that the arch will break just there, as observed in high-speed recordings. Moreover, the more prominent the defect, the easier it is to shatter the arch. Other variables, such as the number of beads, only affect the robustness to the extent that they influence the probability of finding a defect. The researchers also point to the forces between the spheres and the friction coefficient of the material as issues deserving a closer look. Apart from the obvious hits for designing stronger structures, this could also help in getting weaker ones - which could be interesting, for instance, to avoid clogging in particulate flows.

Acoustic mirage: Do you believe what you hear?

BJ12067 - In China, there is a famous saying "Words are but wind, but seeing is believing." This means that only the eyes see that is the fact while the ear heard is not the truth. Here, an intriguing acoustic mirage is present by using an acoustic concentrator, in which what you hear is not the actual, but an illusion. We design the acoustic concentrator made of gradient negative-refraction medium, which is a class of composite materials with anomalous acoustic properties varying along the radial direction. The concentrator shell functions as a magnifying superlens for sound, and projects zoom-in acoustic image at a shifted position. Thus the human auditory system will be misled and we cannot identify the location or origin of a heard sound. Based on the mirage effect, we go a step further and describe how to acoustically transform a particular object into another: the object can be made heard as another object at will. Then, do you believe what you hear?