First Electrical Cable Built of a Single Molecule

BER1188B

- Can single molecules be deployed as reliable and effective conductors in the future electronic devices? Seeking the answer to this question we succeeded for the first time to create an electric cable from a single molecule in a systematic and reproducible way. The obtained wires are only 10 Ångstrom (1 nanometer) long, but they represent a prototypical example of a true molecular conductor clamped to the electrodes via the two well-defined “crocodile” clamps of atomic size. We create the wires by lifting one end of the single molecule lying on the atomically clean metal surface with the sharp metal tip vibrating with sub-Ångstom amplitudes. The vibrating tip on one hand plays a role of the second electric contact used for the conductance measurements at the same time it allows us to measure the stiffness of the wire thus controlling its conformation during the liftoff process.

Soda cans squeeze sound on tighter spots

LD13104


- On top of being convenient soda containers, cans are also good acoustic
resonators. Anyone can verify this by blowing air inside an empty can: an
almost pure tone can be heard. In this letter, we prove that a packed
bunch of soda cans behaves as a new sonic material with fascinating
properties. Subject to various tones, the ensemble of cans responds
collectively and creates complex sound patterns. Very interestingly, those
patterns oscillate on spatial dimensions of the order of a soda can, that
is, much smaller than the wavelength of the acoustic waves that excite
them. Generating broad spectrum sounds with low cost computer
loudspeakers, we demonstrate that 1 meter wavelength audible acoustic
waves can be squeezed thanks to the cans onto spots as tight as a few
centimetres. This experiment opens up the possibility to control acoustic
power or send audio messages on dimensions much smaller than the
wavelength. Our approach, evidenced with soda cans for the sake of
simplicity, is very general. It can be realized using many resonator and
is valid for acoustic and elastic waves at any frequency. We believe it
opens up exciting possibilities for the control of audible sound in new
exotic ways, but also more pragmatically for the design of smart sensors,
actuators and MEMS.

Stressed Workers Lead to Relaxed Colleagues

LC13228

- We study the nature of workplace stress from the aspects of human-human interactions. We investigated the distribution of Center for Epidemiological Studies Depression Scale scores, a measure of the degree of stress, in workplaces. We found that the degree of stress people experience when around other highly stressed people tends to be low, and vice versa. A simulation based on a model describing micro-level human-human interaction reproduced this observed phenomena and revealed that the energy state of a face-to-face communication network correlates with workplace stress macroscopically.

Bacteria Swim Faster in Groups

LD13593

- It is a well known fact that in nature many animals exhibit collective behaviours to move more efficiently and save energy. For example, birds fly in flocks when they migrate, fish swim together when they feed, and cyclists ride in a close group during a race to dramatically reduce drag. However, little is known about what happens when we consider collective behaviour in the microscopic world of bacteria. In particular, whether collective swimming is also the most efficient way of moving at the micro-scales, where viscous effects are dominant, is a question that until recently had no answer.

The mystery has been solved by researchers who investigated the collective swimming of bacteria. By measuring the three-dimensional velocity field, they discovered that by moving together bacteria can swim three times as fast, and that the mass transport in the suspension can be considerably improved.

Surprisingly, to achieve this enormous increase in speed, the bacteria used only a tiny amount of additional energy. The study was the first to discover that also for microorganisms collective swimming is the most energy-efficient way of moving and of absorbing oxygen and nutrients in nature.

A record-size quantum computing register

LC13841

- Quantum computing holds the revolutionary promise of exponentially speeding up such calculations as integer factoring and the simulation of quantum mechanical systems. Building a practical quantum computer will require a scalable number of individual quantum memory units ("Qbits" or "Qmodes"), all individually addressable and controllable with no error. In this paper, we demonstrated an experimental breakthrough: the generation of a record-size quantum register of 60 Qmodes, in 15 independently entangled (i.e. specifically correlated) sets, called cluster states. This massively scalable implementation of a quantum register was all-optical and based on an exotic laser, an optical parametric oscillator, which emitted quantum electromagnetic fields (the Qmodes) at equally spaced optical frequencies over an "optical frequency comb." Technical constraints limited the measured number of generated Qmodes to the reported 60 but we estimated the actual size of our quantum register to be of 180 to 600 Qmodes. This work is a major step toward entangling all these Qmodes together in a single cluster state, in order to achieve a scalable platform for a quantum computer.

Time-reversed optical parametric oscillation

LC13088

- The invention of the antilaser has attracted recently a considerable
attention from the scientific community and general media as well. The
antilaser is a device that acts like a laser in reverse and is thus
capable of completely absorbing coherent light beams instead of
scattering them as most other things do. Such a device might provide a
way to build miniature silicon optical switches or lead to new types
of photonic sensors.

In this Letter the author has shown rather generally that the main
idea of time-reversing a laser to perfectly annihilate coherent light
quanta is not peculiar to a laser system, and can be applied to other
kinds of optical instabilities. In particular, the time-reversed
process of optical parametric oscillation in a nonlinear crystal can
realize a kind of coherent perfect absorber for colored incident
signal and idler fields. In this device, two coherent light waves of
different colours can be fully annihilated in the crystal. As compared
to the antilaser, here photons are not converted into heat or some
internal energy of the medium, rather they are converted into photons
of a different colour. The idea of time reversing a generic kind of
optical instability is expected to be fruitful to built up a novel
class of optical devices similar to the antilaser but operating with
e.g. multicoloured light.

Solid-State Refrigerators and Materials to Convert Waste Heat to Energy

BB11707

- Innovations could improve the conversion of waste heat to energy.

By substituting some of the indium in CuInSe2 with manganese the thermoelectric properties of CuInSe2 have been improved by over two orders of magnitude. Thermoelectric materials work in two ways, by creating either electricity (Seebeck effect) or a temperature gradient (Peltier effect). These improved thermoelectric substances may be key in converting waste heat to energy, for example in automobile engines. Additionally, these materials may prove useful in developing new solid-state refrigerators, due to their advantages of being more compact, portable and environmentally friendly as compared to traditional liquid, ozone-depleting refrigerants. In this work, increased electrical conductivity has been observed in CuInSe2 by adding manganese, thus the thermoelectric figure of merit (ZT) of the material is increased. At the same time, the addition of manganese disrupts the normal atom locations in the material, resulting in a decrease in the thermal conductivity. This is exciting because most often the improvement in one of these properties is at the expense of the other. This work demonstrates that CuInSe2-based systems could be viable thermoelectric materials if the electrical conductivity could be even further enhanced. The improved system would be of interest to the automobile industry, for example, for the purpose of converting waste heat in the internal combustion engine to electricity.

Turbidity breaks the diffraction barrier

LB13391

“Turbidity” caused by multiple scattering is normally considered detrimental to optical imaging. For example, translucent media such as biological tissues and a ground glass make an object underneath invisible. In our study, we developed a method of extracting the original image information from the multiple scattering. This enabled us to see through the turbid media. More importantly, we made a counter-intuitive finding that optical turbidity, rather than being a hindrance to imaging, can in fact dramatically improve both the spatial resolution and the field of view of the target images. In essence, our method turns a turbid medium into a unique and unconventional lens. We believe that this will lead to great important applications in deep-tissue biological imaging and super-resolution imaging.

Figure caption:

Live cell imaging under a rat skin tissue. (a) the image of a microglia cell hidden under a skin tissue. (b) reconstructed image from (a).

A trick for visual stabilization in a hovering bird

EBJ1059

- Using fundamental mechanics principles, we interpret the complicated phenomenon of visual stabilization in a flying bird. For birds, mechanisms of visual stabilization are of great significance because blurred vision resulting from vigorous body vibrations caused by wing flapping could seriously jeopardize their survival. Most relevant studies have attributed the bird’s vision stabilization to their nervous and musculoskeletal systems that sense and reduce the vibrations. In our study, however, we found that a flapping passerine exploits a trick to fix the eyes: the production of a lift force exerted posterior to the center of mass of the bird’s body. This trick concurrently results in rotational and translational displacements of the bird's body. Such a complicated body motion does not deteriorate the stability of the eye; instead, the eye remains stabilized because the displacement caused by body translation becomes an offset due to the displacement caused by body rotation. This trick for visual stabilization can offer bio-inspired guidance for engineers to enhance the visual stability of surveillance cameras incorporated in micro aerial vehicles.

Cancer Cells as Fractals: possible new way of cancer diagnostics

LB12649


- Here it was shown that the surface of human cervical epithelial cells demonstrates substantially different fractal behavior when the cell becomes cancerous. Fractals are "self-similar" irregular shapes that repeat their pattern when zoomed in or out. These complex disorderly patterns are typically formed under far-from-equilibrium conditions, or emerge from chaos. Examples of fractal shape range from the large-scale structure of the Universe to the shape of trees and snowflakes. This paper demonstrated that the surface of human cancer cells could be treated as fractal. Analyzing the adhesion images of individual cells obtained with atomic force microscopy, it was found that cancer cells demonstrate a simple fractal behavior, whereas normal cells could only be approximated at best as multifractal. This leads to an unusually high accuracy in identification of cancer at the single cell level. Although some difference in the surface of cancer cell was expected, the observed unambiguous divergence of the fractal behavior was a surprise. This may shed light on the nature of cancer from a new physics prospective. Furthermore, it can be used for early detection of cervical cancer with accuracy surpassing the existing methods.

St. Elmo’s fire helps emerging organic electronics

LD13757

- For centuries, sailors observed St. Elmo’s fire on ship masts before a storm: this intriguing phenomenon visualizes strong increase of the electric field at sharp conducting edges. Here we find that a remarkably similar effect appears in organic electronic devices at micro-scales, and it may be controlled to improve the device performance.

Everyday electronics is expected to be revolutionized by the introduction of organic polymer semiconductors, which are new “green” materials with unique properties and low cost. These soft polymers can be transformed in-situ from an insulating to highly conducting state via electrochemical doping. When voltage is applied, doping zones spread in the polymers in a manner similar to flame fronts. However, electrochemical doping is rather slow, which represents a serious obstacle for many technical applications. In this paper we obtain a new fundamental effect, doping front instability, which speeds up the process considerably. We find that small humps at a doping front produce local increase of the electric field, similar to St. Elmo’s fire, which, in turn, leads to further growth of the humps. As a result, the front becomes strongly corrugated and moves much faster. This new effect exhibits deep similarities to the speed-up of corrugated flames in car engines and in powerful star explosions, Supernovae.

At the Edge: Why Drops Spread

LA13026


- The spreading of a liquid drop on a solid surface is a simple everyday phenomenon, yet much of the process is complex and remains under investigation. Hydrodynamic analysis of the spreading leads to a non-physical singularity at the contact line, or the triple point where air, solid, and liquid meet. In 1919, Sir William Bates Hardy discovered that the edge of a spreading drop emits a microscopically thin layer of fluid, invisible to the naked eye. The existence of this "precursor film" relieves the singularity issue. In the mid-1980s, Pierre-Gilles de Gennes and coworkers developed a theoretical model for the precursor film, considering intermolecular forces close to the contact line. Since then, physicists have striven to capture experimental evidence of its behavior and characteristics. However, due to the film's nano-scale features, it has been a challenge to overcome the limitations of many detection techniques. Researchers have recently measured the dynamic evolution of the precursor film using fluorescence microscopy. This work is the first to provide experimental support for the theory governing the precursor film's behavior with respect to time and space.

Trapping single electrons without barriers

LD12982

- In the last 20 years, many circuits have been realized where single electrons are trapped in small regions delimited by thin insulating barriers. Based on electron trapping, controlled transport of single electrons has been achieved, and spectroscopic measurements of quantum dots and molecules have been developed.

In our experiment, we show that single electrons can also be trapped without barriers. Our trap is an atomic-size contact between two superconductors with different macroscopic phases. Whereas most electrons are paired at the temperature of the experiment, we find that unpaired electrons tend to be trapped at the atomic contact and stay there for more than 100µs. The trapping of an electron is revealed by the suppression of the supercurrent that flows between the superconductors. The dynamics of trapping and untrapping displays surprising features yet to be understood.

While trapping single electrons in superconductors can be detrimental to the functioning of qubits and detectors, it could open the way to individual spin manipulation and to superconducting spin qubits.

Nanomagnetism takes energy efficiency to the limit

LC13625

- How efficient can a computer built out of magnets be? It turns out, the answer is maximally efficient. In our paper, we show that magnetic computers are able to process information at the theoretical upper limit of energy efficiency - great news for mobile devices and other energy-constrained computer applications. Some background: in 1961, Rolf Landauer of IBM discovered that any information processor – no matter how it is built – requires a minimum amount of energy to carry out a computation. This mysterious quantity is now called the Landauer limit. While the Landauer limit represents a clear technological goal for energy efficient computers, most existing computers consume far more energy than this. Enter nanomagnets. Our calculations reveal that computers built from these tiny magnetic elements use up the exact amount of energy required by the Landauer limit – nothing more. This result establishes that nanomagnetic computers are the first known technology capable of attaining the long-theorized maximum of computational energy efficiency.

Reducing Blood Viscosity with Magnetic Fields

Blood viscosity is a major player in heart disease. When blood viscosity increases, it damages blood vessel and increases the risk of heart attacks. Currently, the only method is to take drugs like Aspirin that has, however, several unwanted side effects. Here we report our new finding that blood viscosity can be reduced with magnetic fields of 1 Tesla or above in the blood flow direction. One magnetic field pulse of 1.3 Tesla lasting about one minute can reduce the blood viscosity by 20-30%. After the exposure, in absence of magnetic field, the blood viscosity slowly moves up, but takes a couple of hours to return to the original value. The process is repeatable. Reapplying the magnetic field reduces the blood viscosity again. By selecting the magnetic field strength and duration, we can keep the blood viscosity within the normal range at around 1 cp. In addition, such viscosity reduction does not affect red cells’ normal function. This technology has high potential for physical therapy.

Probing Atoms to Understand the Coexistence of Superconductivity and Magnetism

LB13449

- Superconductivity and magnetism seem antagonistic and only coexist under very restricted conditions. Explaining their coexistence requires a detailed understanding of the interaction between magnetism and superconductivity down to the atomic scale. Researchers have for the first time utilized atom probe tomography (APT) to directly image the three-dimensional atomic arrangement in newly discovered Fe-based superconductors that exhibit both antiferromagnetism and superconductivity. APT, a cutting-edge analytical microscopy technique that allows atom-by atom mapping of a material, revealed that dopants form nanoscale clusters. Complementary advanced quantum-mechanics based simulations demonstrated that these clusters underpin the unique properties of this material. These exciting results, soon to appear in Physical Review Letters, demonstrate the potential of combining nanoscale materials characterization and advanced simulations to unveil the fundamentals and advance superconductor science, exactly 100 years after its discovery, and facilitate the design of future generations of superconductor devices.

Dengue epidemics and human mobility

EB10856

- In this work we explore the effects of human mobility on the
dispersion of a vector borne disease. We combine an already presented
stochastic model for dengue with a simple representation of the daily
motion of humans on a schematic city of 20x20 blocks with 100
inhabitants in each block. The pattern of motion of the individuals is
described in terms of complex networks in which links connect
different blocks and the link length distribution is in accordance
with recent findings on human mobility. It is shown that human
mobility can turn out to be the main driving force of the disease
dispersal.

Did a Supernova Explode Near Earth in the Recent Past?

LZ12656

- Recent measurements of soil samples brought back from the Moon by NASA astronauts suggest that a supernova may have exploded near our solar system 2 to 3 million years ago. Elevated radioactivity was detected in a sample from the lunar surface. This radioactivity is thought to represent debris from the supernova explosion that was deposited on the lunar surface as the debris passed through the solar system. Similar evidence for this event has previously been found in a rock sample recovered from deep in the Pacific Ocean on Earth. Supernova explosions are a relatively common event in the universe, but finding direct evidence of such an explosion on a planetary body is challenging. Explosion of a nearby supernova could have biological effects on Earth, and it is important to determine if Earth has in fact been subjected to such events in the past.

Scratching as a Fracture Process: From Butter to Steel

LZ12125

- We present results of a hybrid experimental and theoretical investigation of the fracture scaling in scratch tests and show that scratching is a fracture dominated process. Validated for paraffin wax, cement paste, Jurassic limestone and steel, we derive a model that provides a quantitative means to relate quantities measured in scratch tests to fracture properties of materials at multiple scales. The scalability of scratching for different probes and depths opens new venues towards miniaturization of our technique, to extract fracture properties of materials at even smaller length scales.

Baryonic Z' explanation for the CDF Wjj excess

LD13219

- A new force may have been found in a recent CDF result. The CDF
collaboration has announced an exciting observation of a suspicious
bump in W+2 jet production. If this excess holds up, it could be a
discovery of new physics beyond the standard model of particle
physics. We showed that a new force of nature, mediated by a baryonic
Z’ suggested 15 years ago, can explain this excess. This baryonic Z'
boson is very different from the usual Z boson as it only couples to
quarks that carry baryon numbers. With this special property it
survives all other constraints imposed on Z' bosons.

Further tests for Z’ include looking for excess in similar channels
such as photon + 2jet and Z + 2 jet. This baryonic Z' can come from
some specific versions of grand unified theory (GUT) or some entirely
new type of models. If this observation is real and a baryonic Z’ is
confirmed with more data, it will give a significant implication to
the final theory of particle physics.

Randy Moths on the Edge

LX12269

- Male moths can sense and locate females releasing sex pheromones from more than a mile away. This involves the male working on pheromone concentrations across several orders of magnitude - from very small concentration when they are far away to large concentrations on their final approach. It has recently been suggested that this kind of sensory dynamic range can arise in brain networks if their dynamics are close to a critical point analogous with a phase transition in physics (e.g. between solid and liquid). In our paper we describe how such a critical point could arise in, and explain the dynamic range of, the inhibitory neurons that lie at the base of the male moths antennae (the invertebrate equivalent of a nose). Interestingly this large dynamic range in the response to pheromones disappears when the male moth has mated or as a natural part of their diurnal rhythms. Consequently our work really does suggest that the brains of sexually motivated virgin male moths are literally "on the edge" when searching for females.

Superconducting Circuits from Gravity

LA13386

Using Einstein's general relativity, traditionally a theory of gravity, we
construct a model of a Josephson junction and find that it agrees with
results from condensed matter physics.

A Josephson junction is made by sandwiching a non-superconductor between
two superconductors. Superconducting electrons can 'tunnel' through the
non-superconducting barrier and produce a current. These junctions are
well-understood by condensed matter physics and have wide applications in
electronic circuits.

Recently, using tools from string theory, a gravity model of a
superconductor was found. It was created in hopes of understanding one of
the biggest puzzles in condensed matter: high temperature
superconductivity. We test this model by using it to build a Josephson
junction. We then calculate the behavior of the current across the
junction, and find that it matches the expectations from condensed matter
physics.

Surface plasmons can be imprinted on metal nanostructures for subsequent imaging

LA13268

- An unusual observation turned into a scientific breakthrough when researchers investigating the optical properties of nanomaterials discovered a new type of high resolution microscopy for imaging the electric fields of nanostructures.

Optical nanomaterials are mainly based on surface plasmon resonances – the property whereby, in metallic nanostructures, light can collectively excite surface electron waves. With the help of plasmons, light can be captured, modified and even stored in nanostructures. This emerging nanotechnology could find applications in curing cancer, biochemical sensing, solar cells, optical computing, negative refractive index materials, and even invisibility. The imaging of surface plasmons provides a direct way to map and understand the local electric fields that are responsible for the unusual electromagnetic properties of optical nanomaterials; the imaging of surface plasmons, however, is quite challenging. Generally speaking, while there are methods to image plasmons with high resolution, they come at a considerable increase in both cost and complexity.

Now, researchers have demonstrated that upon illuminating nanostructures made of nickel or palladium, the resulting surface plasmon pattern is imprinted on the structures themselves, allowing for subsequent imaging with standard surface probe techniques, such as scanning electron microscopy or atomic force microscopy. The imprinting method is quite unique, combining aspects of both imaging and writing techniques. The combination offers a resolution on plasmons that is, in principle, only limited by that of the atomically-sensitive surface probe techniques.

New wireless devices based on current-induced torques

BA11499

- Current flowing through a magnetic material can alter its magnetization
by spin torque, whereby the spins of the electrons flowing in the
current exert a torque on the magnetization. This mechanism can induce
high-frequency precession of the magnetization. The effect can be used
to make high-frequency wireless devices for future mobile phones,
devices that are significantly smaller and consume less power than the
current state-of-art current technology based, for example, on standard
quartz crystal resonators. In this work, we demonstrate that a very
tiny magnetic tunnel junction device, in which two magnetic layers
(CoFeB) are separated by an oxide barrier (MgO) can emit strong
microwave signals with GHz frequencies. The novelty of our results is
that we are able to demonstrate microwave emission from both the top
magnetic layer, which is called free layer, and the bottom magnetic
layer which is called fixed layer. We show that the precession frequency
of the free layer changes linearly with bias voltage due to the linear
variation of perpendicular component of spin torque. In contrast, the
precession frequency of the fixed layer changes quadratically as a
result of heating effects. By changing the applied field magnitude it is
possible to control which layer is excited and hence to manipulate the
behavior of the frequency with bias voltage. Thus our work provides an
important step towards making next generation wireless devices.

Quantum walking over rough terrain: How obstacles influence the propagation of quantum particles

LA12856

- Quantum physics allows particles to spread quadratically faster than their classical counterparts in a discrete, uniform environment. We have implemented an experimental setup that demonstrates how the dynamics drastically change, if temporal and spatial inhomogeneities are introduced. Fast fluctuations in time lead to a full suppression of the quantum behavior, forcing the particle to act entirely classically. On the other hand, spatial disorders result in a stagnation of the propagation, thus trapping the quantum particle around its initial position, which is in high contrast to
any classical description. Quantum walks serve as underlying theoretical model to explain processes in a variety of different physical systems, as for example, the energy transfer in photosynthesis. The dynamics in such biological systems are hard to measure and highly influenced by disorder and thermal fluctuations. Using controllable photonic quantum networks, we were now able to simulate similar environmental influences and carry out detailed studies of their impact on quantum systems. The experiment not only confirms the theoretical predictions, but opens up new routes for quantum simulations and information processing in mesoscopic structures based on coherent state transfer.