Sharing All of The World

The ideal clock is merely a convenient fiction, as theorists from the University of Warsaw (UW) and University of Nottingham (UN) have shown. In a study published in the journal Classical and Quantum Gravity they demonstrate that in systems moving with enormous accelerations, building a clock that would precisely measure the passage of time is impossible for fundamental reasons.
"In both theories of relativity, special and general, it is tacitly assumed that it is always possible to construct an ideal clock -- one that will accurately measure the time elapsed in the system, regardless of whether the system is at rest, moving at a uniform speed, or accelerating. It turns out, however, that when we talk about really fast accelerations, this postulate simply cannot apply," says Dr. Andrzej Dragan from the Faculty of Physics, University of Warsaw.
The simplest clocks are unstable elementary particles, for example muons (particles with similar properties to electrons but 200 times more massive). Usually, muons decay into an electron, muon neutrino, and an electron antineutrino. By measuring the decay times and averaging the results for muons moving slowly and those moving at nearly the speed of light, we can observe the famous slowing down of the passage of time: the faster the muons are moving, the less likely the experimenter is to see them decay. Velocity therefore affects the clocks' observed tempo.
What about acceleration? Experiments were performed at CERN in the late 1970s, measuring the decay time of muons undergoing circular motion accelerations even as great as billions of billions of times the acceleration of Earth's gravity (10^18 g). Such acceleration was found to have no impact on the disintegration times.
The Polish-British group of theorists from the universities of Warsaw and Nottingham, on the other hand, were looking at the description of unstable particles moving in accelerating motion in a straight line. The key point for their analysis turned out to be a fascinating effect predicted in 1976 by the Canadian physicist William Unruh.
"Contrary to intuition, the concept of a particle is not completely independent of the observer. We all know the Doppler Effect, for example, which causes a photon emitted by a moving source to appear bluer to an observer toward which the source is approaching, but redder to one it is receding from. The Unruh effect is somewhat similar, except that the results are more spectacular: in an certain area of space, a non-accelerating observer sees a quantum field vacuum, whereas an accelerating observer sees many particles," explains Dr. Dragan.
The equation describing the Unruh effect says that the number of particles visible within a quantum field varies depending on the acceleration experienced by an observer: the greater the acceleration, the more of them there are. These non-inertial effects may be due to the movement of the observer, but their source can also be a gravitational field. Interestingly, the Unruh effect is very akin to the famous Hawking radiation emitted by black holes.
The unstable particles which the physicists from the universities of Warsaw and Nottingham treated as a fundamental clocks in their analysis decay as a result of interactions with other quantum fields. The theory says that if such a particle remains in a space filled with a vacuum it decays at a different pace than when in the vicinity of many other particles interacting with it. Thus if in a system of extreme acceleration more particles can be seen as a result of the Unruh effect, the average decay times of particles such as muons should change.
"Our calculations showed that above certain very large accelerations there simply must be time disorders in the decay of elementary particles. And if the disturbances affect fundamental clocks such as muons, then any other device built on the principles of quantum field theory will also be disrupted. Therefore, perfectly precise measurements of proper time are no longer possible. This fact has further consequences, because losing the ability to accurately measure the passage of time also means problems with the measurements of distance," explains Dr. Dragan.
Until now it has been assumed that the concepts of time and space may lose their traditional senses only when certain phenomena predicted by hypothetical theories of quantum gravity begin to play a vital role. It is believed that the necessary conditions prevailed in the vicinity of the Big Bang.
"In our paper, we show that for problems with the measurements of space-time to arise, such extreme conditions are not needed at all. Time, and therefore space, most likely cease to be accurately measurable even in today's Universe, provided that we try to carry out the measurements in systems moving with great acceleration," notes Dr. Dragan.
The results from the physicists from Warsaw and Nottingham mean that at sufficiently high accelerations, the operational capabilities of any theory built on the notion of time, and thus also space, will be disrupted. This raises interesting questions. If in extremely accelerating systems we cannot build a clock that measures time accurately, is this exclusively a fundamental flaw in our measurement methods? Or maybe something is happening directly to time itself? And do properties which cannot be measured accurately even make physical sense?
Modern accelerators can accelerate particles with accelerations several orders of magnitude higher than in the experiments of the 70s. Thus today we can carry out experiments in which the Unruh effect should be visible -- and so changes in the decay time of particles triggered by acceleration should be observable, too. The conclusions of the Polish-British group of physicists on ideal clocks will thus soon be verified.
"If our predictions are confirmed experimentally, many things related to our understanding of space-time, the passage of time, and its measurement methods will have to be rethought from scratch. It could be... interesting," concludes Dr. Dragan with a smile.

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In an article published in the Oct. 5 issue of Physical Review Letters, a team of University of Chicago physicists explains how to tune a laser to make atoms attract or repel each other in an exotic state of matter called a Bose-Einstein condensate.
"This realizes a goal that has been pursued for the past 20 years," said Cheng Chin, professor in physics at the University of Chicago, who led the team. "This exquisite control over interactions in a many-body system has great potential for the exploration of exotic quantum phenomena and engineering of novel quantum devices."
Many research groups in the United States and Europe have tried various ideas over the last decade. It was Logan Clark, a graduate student in Chin's group, who came up with the first practical solution. He has now demonstrated the idea in the lab with cesium atoms chilled to temperatures just billionths of a degree above absolute zero, and the technique can be widely applied to other atomic species.
Clark compared the process to a billiards game, when one ball encounters another. "Normally, as soon as the surfaces touch, the balls repel each other and bounce away," Clark said. In Chin's lab, cesium atoms replace the billiard balls, and ordinarily they repel each other when they collide. But by turning up the laser while operating at a "magic" wavelength, Clark showed that the repulsion between atoms can be converted into attraction.
"The atoms exhibit fascinating behavior in this system," he said. By exposing different parts of the sample to different laser intensities, "We can choose to make the atoms attract or repel each other, or pass right through each other without colliding."
Alternatively, by oscillating their interactions, analogous to making the billiard balls rapidly grow and shrink while they roll, the atoms stick to each other in pairs.
The researchers explained two fundamental ways that lasers influence the atomic motion. One is to create potentials, like a bump or valley on the billiard table, proportional to laser intensity. The new way is to alter how billiard balls collide.
"We want our laser to control collisions, but we don't want it to create any hills or valleys," Clark said. When the laser is tuned to a "magic wavelength," the beam creates no hills or valleys, but only affects collisions.
"This is because the magic wavelength happens to be in between two excited states of the atom, so they 'magically' cancel each other out," he said.
Magic is a concept that has no place in science, though the word does enjoy fairly common use among atomic physicists. "Generally it is used to refer to a wavelength at which two effects cancel or are equal, in particular when this cancellation or equality is useful for some technological goal," Clark said.

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This existential question has been raised by a series of experiments conducted recently at the Large Hadron Collider and the Relativistic Heavy Ion Collider that smash various atomic particles together at nearly the speed of light in order to create tiny drops of primordial soup: the quark-gluon plasma (QGP) that cosmologists are convinced dominated the universe microseconds after the Big Bang before the universe cooled down enough for atoms to form. In fact, the flow characteristic of these droplets is a major topic at a scientific conference, Quark Matter 2015, taking place this week in Kobe, Japan.
As part of the Large Hadron Collider's CMS detector team, Professor of Physics Julia Velkovska, post-doctoral fellow Shenguan Tuo and assistant research professor Shengli Huang at Vanderbilt University have been at the middle of these discoveries.
In 2010, the LHC successfully created sub-atomic blobs of QGP by colliding lead ions together. Smashing these two massive ions -- each containing hundreds of protons and neutrons -- had generated the tremendous temperatures, more than 250,000 times hotter than the core of the sun, that are required for the primordial state of matter to form.
(Unfortunately, the physicists don't have a direct way to measure the number of particles in the quark-gluon plasma, so they use the number of subatomic particles that are created when the plasma evaporates as a measure of their size.)
"Lead ions are very large, each containing hundreds of protons and neutrons. When you smash them together at very high speed, they generate blobs of plasma that produce thousands of particles when they cool down," said Velkovska. "But when the LHC switched to proton-lead ion collisions, we didn't think the collisions would contain enough energy to produce the plasma."
However, Tuo, as part of his doctoral thesis, made detailed measurements of the behavior of the particles produced by these smaller proton-lead collisions and discovered that they were in fact producing liquid droplets that were about one tenth the size of those produced in the lead-lead collisions.
"Everyone was surprised when we began finding evidence for liquid behavior," said Tuo. "It caused some very intense debates."
One of the key properties of a liquid is the ability to flow. Looked at from the point of view of the individual particles in a liquid, the ability to flow means that each particle is exerting an attractive force on its neighbors that is strong enough to effect their movement but not strong enough to lock them together like they are in a solid. So their movements are coordinated and, when released from a container, they retain information about the container's shape. Tuo's measurements showed that small numbers of particles produced in the proton-lead collisions originated on the ellipsoidal surfaces of small QGP droplets.
Because of the computational difficulty involved, physicists normally look for these correlations between pairs of particles, but Velkovska, Tuo and their CMS collaborators took it several steps further. They searched for correlations between groups of four, six and eight particles. In some cases, they went to the extraordinary length of computing the correlations between all the particles in a given collision.
"These measurements confirmed that we were seeing this coherent behavior even in droplets producing as few as 100 to 200 particles," Tuo said. The results were published in Physical Review Letters in June. But that wasn't the end of the story.
The recreation of the quark gluon plasma (QGP) dates back to 2005. Velkovska and her Vanderbilt colleagues -- physics professors Victoria Greene and Charlie Maguire -- were members of the PHENIX science team at RHIC, located at Brookhaven National Laboratory, when they announced that they had created this new state of matter by colliding gold ions together at relativistic velocities. The big surprise was that this primordial material behaved like a liquid, rather than a gas.
To see what happened at even higher energies, the Vanderbilt group joined the CMS science team at the LHC located at the European Laboratory for Nuclear and Particle Physics in Geneva. The more powerful particle collider succeeded in duplicating the RHIC results, first as expected, by smashing lead ions together and then, unexpectedly, in the proton-lead collisions.
The proton-lead results prompted the scientists in the PHENIX team to re-analyze data that had been collected at RHIC in 2000, when the collider had smashed deuterium ions (proton-neutron pairs) and gold ions together at much lower energies than those in the LHC. The re-analysis, led by Shengli Huang, found that the proton-neutron pairs formed two hot spots in the gold ion when they collided which then merged into an elongated drop of QGP.
The RHIC researchers decided to test this further by adding a new run that collided helium ions (two protons and a neutron) with gold ions, and found that the same thing happened, except that three hot spots formed and merged into the QGP droplet. The results were just published in Physical Review Letters.
"Although the LHC collisions release 25 times more energy than the RHIC collisions, we don't see much difference in the droplet-formation process: Once you have reached the threshold, adding more energy doesn't seem to have much effect," said Velkovska. "I guess you can't get more perfect than perfect!"
Not only have the physicists found that the quark-gluon plasma is a liquid, the physicists have also established that it is nearly a perfect liquid: That is a liquid with zero viscosity that flows without any resistance. If you swish a perfect liquid in a glass and set the glass down, then the liquid will continue to swirl around as long as it is not disrupted.
Curiously, the phenomenon that most closely resembles the properties of the hottest known liquid is one of the coldest known liquids: lithium atoms that have been cooled to temperatures one-billionth of a degree above absolute zero using a device called a laser trap. When released from the trap these ultra-cold atoms also behave as a perfect liquid with near-zero viscosity.
"These are both strongly coupled systems. This appears to be an emergent property of such systems," Velkovska has concluded.

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Their final product, described this week in the Journal of Applied Physics, from AIP Publishing, was an acoustical "metamaterial" with an effective density near zero (DNZ). This work could help to endow a transmission network with coveted properties such as high transmission around sharp corners, high-efficient wave splitting, and acoustic cloaking.
"It's as if the entire [interior] space is missing," said Xiaojun Liu, a professor in the physics department at Nanjing University's Collaborative Innovation Center of Advanced Microstructures.
"We were curious about whether we could make a simple but compact density-near-zero metamaterial from just a few tiny membranes," Liu said, "and, if so, can we further manipulate sound and make acoustic invisibility cloaks and other strange functional devices?"
Previous prototypes had attempted to achieve density-near-zero by using coiled structures and phononic crystals to create "Dirac cones," but required large physical dimensions, complex geometric structures, and the difficult feat of slowing sound waves to extremely low velocities within scattering cylinders to be effective -- limiting their practical applications.
Their current paper proposes a physical, minimalist realization of their original density-near-zero idea, consisting of 0.125 mm-thick polyethylene membranes perforated with 9-millimeter-radius holes in a square grid inside of a metal waveguide, a physical structure for guiding sound waves. The intensive resonances of the membranes significantly reduce the structure's effective mass density, which is a measure of its dynamic response to incident sound waves. By Newton's second law, this reduction causes the average acceleration of the structure to approach infinity, which gives rise to sound tunneling.
When sound at a frequency of 990 Hz is then conducted and rapidly accelerated through the material, the membranes act as a tunnel for sound, encapsulating the waves into local subwavelength regions. This arrangement allows the sound waves to pass through without accumulating a phase change or distorting the wavefront -- analogous to the quantum tunneling effect, in which a particle crosses through a potential energy barrier otherwise insurmountable by classical mechanics.
For future applications, the metamaterial would likely be integrated into acoustic circuits and structures. When implemented in a wave splitter, the researchers found an 80 percent increase in the efficiency of energy transmission, regardless of the wave's incident angle.
Additionally, the researchers are able to tune the frequency of the metamaterial network by altering the membrane's tension and physical dimensions, which they were unable to do in previous prototypes.
Liu and his colleagues have already used the membrane network to fabricate a planar hyperlens, a device which magnifies one and two-dimensional objects on the subwavelength scale to compensate for the losses of acoustic waves carrying fine details of images as they pass a lens. This can allow scientists to see fine features of objects such as tumors, or minute flaws within airplane wings in industrial testing, that may otherwise be unobservable due to an instrument's diffractive limit. Additional planned applications include using smart acoustic structures, such as logic gates that can control acoustic waves by altering their propagation, for communication systems in environmental conditions too extreme for conventional electronic devices and photonic structures.
"The vanishing mass density we've demonstrated is definitely more than a mathematical trick," said Liu.

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Researchers in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering used this insight to invent something totally new: they've combined two promising solar cell materials together for the first time, creating a new platform for LED technology.
The team designed a way to embed strongly luminescent nanoparticles called colloidal quantum dots (the chocolate chips) into perovskite (the oatmeal cookie). Perovskites are a family of materials that can be easily manufactured from solution, and that allow electrons to move swiftly through them with minimal loss or capture by defects.
The work is published in the international journal Nature on July 15, 2015.
"It's a pretty novel idea to blend together these two optoelectronic materials, both of which are gaining a lot of traction," says Xiwen Gong, one of the study's lead authors and a PhD candidate working with Professor Ted Sargent. "We wanted to take advantage of the benefits of both by combining them seamlessly in a solid-state matrix."
The result is a black crystal that relies on the perovskite matrix to 'funnel' electrons into the quantum dots, which are extremely efficient at converting electricity to light. Hyper-efficient LED technologies could enable applications from the visible-light LED bulbs in every home, to new displays, to gesture recognition using near-infrared wavelengths.
"When you try to jam two different crystals together, they often form separate phases without blending smoothly into each other," says Dr. Riccardo Comin, a post-doctoral fellow in the Sargent Group. "We had to design a new strategy to = convince these two components to forget about their differences and to rather intermix into forming a unique crystalline entity."
The main challenge was making the orientation of the two crystal structures line up, called heteroexpitaxy. To achieve heteroepitaxy, Gong, Comin and their team engineered a way to connect the atomic 'ends' of the two crystalline structures so that they aligned smoothly, without defects forming at the seams. "We started by building a nano-scale scaffolding 'shell' around the quantum dots in solution, then grew the perovskite crystal around that shell so the two faces aligned," explained coauthor Dr. Zhijun Ning, who contributed to the work while a post-doctoral fellow at UofT and is now a faculty member at ShanghaiTech.
The resulting heterogeneous material is the basis for a new family of highly energy-efficient near-infrared LEDs. Infrared LEDs can be harnessed for improved night-vision technology, to better biomedical imaging, to high-speed telecommunications.
Combining the two materials in this way also solves the problem of self-absorption, which occurs when a substance partly re-absorbs the same spectrum of energy that it emits, with a net efficiency loss. "These dots in perovskite don't suffer reabsorption, because the emission of the dots doesn't overlap with the absorption spectrum of the perovskite," explains Comin.
Gong, Comin and the team deliberately designed their material to be compatible with solution-processing, so it could be readily integrated with the most inexpensive and commercially practical ways of manufacturing solar film and devices. Their next step is to build and test the hardware to capitalize on the concept they have proven with this work.
"We're going to build the LED device and try to beat the record power efficiency reported in the literature," says Gong.
This work was supported by the Ontario Research Fund Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the King Abdullah University of Science & Technology (KAUST).

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The researchers report in the journal Science July 16 the first observation of Weyl fermions, which, if applied to next-generation electronics, could allow for a nearly free and efficient flow of electricity in electronics, and thus greater power, especially for computers, the researchers suggest.
Proposed by the mathematician and physicist Hermann Weyl in 1929, Weyl fermions have been long sought by scientists because they have been regarded as possible building blocks of other subatomic particles, and are even more basic than the ubiquitous, negative-charge carrying electron (when electrons are moving inside a crystal). Their basic nature means that Weyl fermions could provide a much more stable and efficient transport of particles than electrons, which are the principle particle behind modern electronics. Unlike electrons, Weyl fermions are massless and possess a high degree of mobility; the particle's spin is both in the same direction as its motion -- which is known as being right-handed -- and in the opposite direction in which it moves, or left-handed.
"The physics of the Weyl fermion are so strange, there could be many things that arise from this particle that we're just not capable of imagining now," said corresponding author M. Zahid Hasan, a Princeton professor of physics who led the research team.
The researchers' find differs from the other particle discoveries in that the Weyl fermion can be reproduced and potentially applied, Hasan said. Typically, particles such as the famous Higgs boson are detected in the fleeting aftermath of particle collisions, he said. The Weyl fermion, however, was discovered inside a synthetic metallic crystal called tantalum arsenide that the Princeton researchers designed in collaboration with researchers at the Collaborative Innovation Center of Quantum Matter in Beijing and at National Taiwan University.
The Weyl fermion possesses two characteristics that could make its discovery a boon for future electronics, including the development of the highly prized field of efficient quantum computing, Hasan explained.
For a physicist, the Weyl fermions are most notable for behaving like a composite of monopole- and antimonopole-like particles when inside a crystal, Hasan said. This means that Weyl particles that have opposite magnetic-like charges can nonetheless move independently of one another with a high degree of mobility.
The researchers also found that Weyl fermions can be used to create massless electrons that move very quickly with no backscattering, wherein electrons are lost when they collide with an obstruction. In electronics, backscattering hinders efficiency and generates heat. Weyl electrons simply move through and around roadblocks, Hasan said.
"It's like they have their own GPS and steer themselves without scattering," Hasan said. "They will move and move only in one direction since they are either right-handed or left-handed and never come to an end because they just tunnel through. These are very fast electrons that behave like unidirectional light beams and can be used for new types of quantum computing."
Prior to the Science paper, Hasan and his co-authors published a report in the journal Nature Communications in June that theorized that Weyl fermions could exist in a tantalum arsenide crystal. Guided by that paper, the researchers used the Princeton Institute for the Science and Technology of Materials (PRISM) and Laboratory for Topological Quantum Matter and Spectroscopy in Princeton's Jadwin Hall to research and simulate dozens of crystal structures before seizing upon the asymmetrical tantalum arsenide crystal, which has a differently shaped top and bottom.
The crystals were then loaded into a two-story device known as a scanning tunneling spectromicroscope that is cooled to near absolute zero and suspended from the ceiling to prevent even atom-sized vibrations. The spectromicroscope determined if the crystal matched the theoretical specifications for hosting a Weyl fermion. "It told us if the crystal was the house of the particle," Hasan said.
The Princeton team took the crystals passing the spectromicroscope test to the Lawrence Berkeley National Laboratory in California to be tested with high-energy accelerator-based photon beams. Once fired through the crystal, the beams' shape, size and direction indicated the presence of the long-elusive Weyl fermion.
First author Su-Yang Xu, a postdoctoral research associate in Princeton's Department of Physics, said that the work was unique for encompassing theory and experimentalism.
"The nature of this research and how it emerged is really different and more exciting than most of other work we have done before," Xu said. "Usually, theorists tell us that some compound might show some new or interesting properties, then we as experimentalists grow that sample and perform experiments to test the prediction. In this case, we came up with the theoretical prediction ourselves and then performed the experiments. This makes the final success even more exciting and satisfying than before."
In pursuing the elusive particle, the researchers had to pull from a number of disciplines, as well as just have faith in their quest and scientific instincts, Xu said.
"Solving this problem involved physics theory, chemistry, material science and, most importantly, intuition," he said. "This work really shows why research is so fascinating, because it involved both rational, logical thinking, and also sparks and inspiration."
Weyl, who worked at the Institute for Advanced Study, suggested his fermion as an alternative to the theory of relativity proposed by his colleague Albert Einstein. Although that application never panned out, the characteristics of his theoretical particle intrigued physicists for nearly a century, Hasan said. Actually observing the particle was a trying process -- one ambitious experiment proposed colliding high-energy neutrinos to test if the Weyl fermion was produced in the aftermath, he said.
The hunt for the Weyl fermion began in the earliest days of quantum theory when physicists first realized that their equations implied the existence of antimatter counterparts to commonly known particles such as electrons, Hasan said.
"People figured that although Weyl's theory was not applicable to relativity or neutrinos, it is the most basic form of fermion and had all other kinds of weird and beautiful properties that could be useful," he said.
"After more than 80 years, we found that this fermion was already there, waiting. It is the most basic building block of all electrons," he said. "It is exciting that we could finally make it come out following Weyl's 1929 theoretical recipe."
Ashvin Vishwanath, a professor of physics at the University of California-Berkeley who was not involved in the study, commented, "Professor Hasan's experiments report the observation of both the unusual properties in the bulk of the crystal as well as the exotic surface states that were theoretically predicted. While it is early to say what practical implications this discovery might have, it is worth noting that Weyl materials are direct 3-D electronic analogs of graphene, which is being seriously studied for potential applications."
Other co-authors were Chenglong Zhang, Zhujun Yuan and Shuang Jia from Peking University; Raman Sankar and Fangcheng Chou from the National Taiwan University; Guoqing Chang, Chi-Cheng Lee, Shin-Ming Huang, BaoKai Wang and Hsin Lin from the National University of Singapore; Jie Ma from Oak Ridge National Laboratory; and Arun Bansil from Northeastern University. BaoKai Wang is also affiliated with Northeastern University, and Shuang Jia is affiliated with the Collaborative Innovation Center of Quantum Matter in Beijing.
The paper, "Discovery of Weyl fermions and topological Fermi arcs," was published online by Science on July 16. The work was supported by the Gordon and Betty Moore Foundations Emergent Phenomena in Quantum Systems (EPiQS) Initiative (grant no. GBMF4547); the Singapore National Research Foundation (grant no. NRF-NRFF2013-03); the National Basic Research Program of China (grant nos. 2013CB921901 and 2014CB239302); the U.S. Department of Energy (grant no. DE-FG-02-05ER462000); and the Taiwan Ministry of Science and Technology (project no. 102-2119-M- 002-004).

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"Our method is the first to image electric fields near the surface of a sample quantitatively with atomic precision on the sub-nanometre scale," says Dr. Ruslan Temirov from Forschungszentrum Jülich. Such electric fields surround all nanostructures like an aura. Their properties provide information, for instance, on the distribution of charges in atoms or molecules.
For their measurements, the Jülich researchers used an atomic force microscope. This functions a bit like a record player: a tip moves across the sample and pieces together a complete image of the surface. To image electric fields up until now, scientists have used the entire front part of the scanning tip as a Kelvin probe. But the large size difference between the tip and the sample causes resolution difficulties -- if we were to imagine that a single atom was the same size as a head of a pin, then the tip of the microscope would be as large as the Empire State Building.
Single molecule as a sensor
In order to improve resolution and sensitivity, the scientists in Jülich attached a single molecule as a quantum dot to the tip of the microscope. Quantum dots are tiny structures, measuring no more than a few nanometres across, which due to quantum confinement can only assume certain, discrete states comparable to the energy level of a single atom.
The molecule at the tip of the microscope functions like a beam balance, which tilts to one side or the other. A shift in one direction or the other corresponds to the presence or absence of an additional electron, which either jumps from the tip to the molecule or does not. The "molecular" balance does not compare weights but rather two electric fields that act on the mobile electron of the molecular sensor: the first is the field of a nanostructure being measured, and the second is a field surrounding the tip of the microscope, which carries a voltage.
"The voltage at the tip is varied until equilibrium is achieved. If we know what voltage has been applied, we can determine the field of the sample at the position of the molecule," explains Dr. Christian Wagner, a member of Temirov's Young Investigators group at Jülich's Peter Grünberg Institute (PGI-3). "Because the whole molecular balance is so small, comprising only 38 atoms, we can create a very sharp image of the electric field of the sample. It's a bit like a camera with very small pixels."
Universally applicable
A patent is pending for the method, which is particularly suitable for measuring rough surfaces, for example those of semiconductor structures for electronic devices or folded biomolecules. "In contrast to many other forms of scanning probe microscopy, scanning quantum dot microscopy can even work at a distance of several nanometres. In the nanoworld, this is quite a considerable distance," says Christian Wagner. Until now, the technique developed in Jülich has only been applied in high vacuum and at low temperatures: essential prerequisites to carefully attach the single molecule to the tip of the microscope.
"In principle, variations that would work at room temperature are conceivable," believes the physicist. Other forms of quantum dots could be used as a sensor in place of the molecule, such as those that can be realized with semiconductor materials: one example would be quantum dots made of nanocrystals like those already being used in fundamental research.

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For many decades silicon has formed the basis of modern electronics. To date silicon technology could provide ever tinier transistors for smaller and smaller devices. But the size of silicon transistors is reaching its physical limit. Also, consumers would like to have flexible devices, devices that can be incorporated into clothing and the likes. However, silicon is hard and brittle. All this has triggered a race for new materials that might one day replace silicon.
Black arsenic phosphorus might be such a material. Like graphene, which consists of a single layer of carbon atoms, it forms extremely thin layers. The array of possible applications ranges from transistors and sensors to mechanically flexible semiconductor devices. Unlike graphene, whose electronic properties are similar to those of metals, black arsenic phosphorus behaves like a semiconductor.
Phosphorene vs. graphene
A cooperation between the Technical University of Munich and the University of Regensburg on the German side and the University of Southern California (USC) and Yale University in the United States has now, for the first time, produced a field effect transistor made of black arsenic phosphorus. The compounds were synthesized by Marianne Koepf at the laboratory of the research group for Synthesis and Characterization of Innovative Materials at the TUM. The field effect transistors were built and characterized by a group headed by Professor Zhou and Dr. Liu at the Department of Electrical Engineering at USC.
The new technology developed at TUM allows the synthesis of black arsenic phosphorus without high pressure. This requires less energy and is cheaper. The gap between valence and conduction bands can be precisely controlled by adjusting the arsenic concentration. "This allows us to produce materials with previously unattainable electronic and optical properties in an energy window that was hitherto inaccessible," says Professor Tom Nilges, head of the research group for Synthesis and Characterization of Innovative Materials.
Detectors for infrared
With an arsenic concentration of 83 percent the material exhibits an extremely small band gap of only 0.15 electron volts, making it predestined for sensors which can detect long wavelength infrared radiation. LiDAR (Light Detection and Ranging) sensors operate in this wavelength range, for example. They are used, among other things, as distance sensors in automobiles. Another application is the measurement of dust particles and trace gases in environmental monitoring.
A further interesting aspect of these new, two-dimensional semiconductors is their anisotropic electronic and optical behavior. The material exhibits different characteristics along the x- and y-axes in the same plane. To produce graphene like films the material can be peeled off in ultra thin layers. The thinnest films obtained so far are only two atomic layers thick.
This work was supported by the Office of Naval Research (ONR), the Air Force Office of Scientific Research (AFOSR), the Center of Excellence for Nanotechnologies (CEGN) of King Abdul-Aziz City for Science and Technology (KACST), the German Research Council (DFG) and the TUM Graduate School.

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According to QCD, quarks possess one of three charges that allow them to pair in various combinations, such as mesons--elementary particles composed of one quark and its corresponding antiquark. Force carrier particles, known as gluons, hold the quarks together by exchanging and mediating the strong forc e, one of the four fundamental forces. This structure is the foundation of all matter in the universe, but much is still unknown about why QCD works the way it does.
Currently, scientists are searching for the existence of mesons that don't fit the traditional patterns. If a meson is found to weigh more than expected, something else must be going on. After all, one plus one can't equal three. Scientists call these hypothetical particles exotic mesons and believe that gluons play an important role in their structure. Their existence has long been theorized, but exotic mesons have not yet been observed in the laboratory or predicted with precision from first principles.
Robert Edwards, a researcher and senior staff member at the US Department of Energy's (DOE's) Jefferson Laboratory (JLab), hopes to change that. Edwards is the principal investigator for a group at the Oak Ridge Leadership Computing Facility (OLCF), a DOE Office of Science User Facility located at Oak Ridge National Laboratory. His team has been using the OLCF's Jaguar and Titan supercomputers for several years to map out different combinations of particles.
Last year, they were awarded an Advanced Scientific Computing Research (ASCR) Leadership Computing Challenge (ALCC) allocation to run lattice quantum chromodynamics (LQCD) calculations that can accurately analyze the interactions between quarks and gluons in a vacuum across both space and time.
Climbing a hill
"A way to think of this is like knocking a billiard ball across a hilly area to get from point A to point B. We repeat these calculations over several different instances of these hilly areas," Edwards said, noting that the hillsides represent fluctuations in the gluon field. "These are the different configurations of gluon fields, and those snapshots are what we generated in previous INCITE allocations running on Jaguar and Titan."
The team's ALCC project focused on running quarks through the gluon field and analyzing how their position in space-time is affected by the different configurations.
Because of the unique properties of QCD, the team can't take advantage of classical mathematical methods.
"There are no other choices but to try to solve everything numerically. You write down the theory for the standard model of particle physics and say, 'OK, that's what we're going to put in the computer.' So they put space-time on the computer," said Jack Wells, director of science for the National Center for Computational Sciences, home to OLCF. "The idea is, here's space and time represented as a lattice, or grid, of points. In the limit that the grid size is large and the lattice spacing is small, we'll get the right answer."
LQCD calculations use statistical sampling in much the same way that pollsters predict who will win an election. You don't have to survey every single person. You just have to have a large enough sample size to have confidence. The larger the sample, the better it reflects reality.
Increasing the size of these snapshots has been the group's focus over the past few years. As a result, the lattices on which the gluons are represented mathematically have become very large. The team has finished its work on lattice sizes up to 403 -- 256. That is 40 sites in each of the three space dimensions and 256 sites in the time direction for a total of 16 million sites.
The researchers hope that this greater level of realism will allow them to be the first to predict exotic mesons from first principles. Their research will give greater insight into how quarks and gluons bind to form such states and increase our understanding of the fundamental strong force.
Edwards' ALCC project wrapped up on June 30 with all proposed computational tasks achieved; the project used 350 million hours on Titan, the largest annual project usage of OLCF resources to date.
Enter JLab
An additional goal of the group has to been to give theoretical underpinnings to GlueX, a $50 million nuclear physics photon detector in JLab's new Hall D.
Edwards said the GlueX detector will try to answer two fundamental questions experimentally. "One, do these [exotic] mesons even exist? That's just a basic question. And two, how would you actually find them experimentally? For that, you need to know how they decay, because they only exist for a short period of time."
It has been difficult for researchers to observe these particles experimentally because they can't observe the individual pieces--quarks, antiquarks, and gluons--by themselves. Unlike the other fundamental forces, such as gravity, the strong force only increases with distance. If you try to pull elementary particles apart, the fields holding them together eventually snap, and another quark and antiquark pair is produced out of the vacuum.
Because of this phenomenon, known as confinement, scientists have to look at the makeup of mesons and other elementary particles in a roundabout way. In an electron accelerator, photons are shot into a proton target. Edwards likens it to "thwacking a bell" that starts ringing and sending off vibrations, or resonances. When that resonance decays, it breaks down into other particles that are picked up by detectors like GlueX. The nuclear physicists at JLab then try to reverse engineer these particles to determine what was in the initial state.
Edwards' team hopes to help better calibrate these physical experiments by determining the energy spectrum of exotic resonances as well as by predicting what the properties of these exotic mesons might be so JLab researchers have a better idea of where to look for them.
"I don't like to use the 'B' word often," Edwards said, "but this ALCC allocation has allowed a breakthrough advance for us. Now, the race is on. GlueX is starting to take measurements and goes into full production in the fall."

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The above post is reprinted from materials provided by DOE/Oak Ridge National Laboratory. Note: Materials may be edited for content and length.

This can be especially true for scientists who study old and delicate items, where preservation and pulverization for analysis battle in the scientists' minds. Many items of historical significance have been destroyed or ruined in the effort to study them.
At a number of Department of Energy laboratories, however, scientists are using new techniques and new technologies to study specimens -- from sound recordings, to bird eggs, to dinosaur bones -- in an effort to investigate their targets without annihilating them.
For example, physicist Carl Haber of Lawrence Berkeley National Laboratory made use of sophisticated mathematical techniques that he helped develop in designing particle detectors for the Large Hadron Collider at the European Center for Nuclear Research (CERN) to capture sound from old recordings.
He and Vitaliy Fadeyev, then a Berkeley Lab postdoc, now a faculty member at the University of California, Santa Cruz, used an electron microscope to capture an image of an old sound recording, and then applied complex algorithms, similar to those used in sophisticated particle detectors, to generate clear sounds from the image. The technology allowed the two to listen to the 1950s hit "Goodnight Irene."
The same techniques will be used to recover Native American voices recorded more than 100 years ago. This summer, Haber is partnering with UC Berkeley to scan 2,700 wax cylinder recordings of Native American tribes in California to re-create the songs they sang and the words they spoke. These wax cylinders are very fragile. When successful, we will have an opportunity to actually listen to digital recordings of Native American history.
DOE's big x-ray light sources have also proved to be extremely effective at non-invasive characterization of samples, including archeological items and assorted artifacts. Various x-ray techniques provided by DOE light sources allow scientists to identify certain molecules, radiation, electron activity, and other characteristics of these objects that provide a comprehensive history and understanding of the object itself, without causing it damage.
Currently, the Office of Science User Facilities operates five x-ray light sources at national laboratories across the country.
Argonne National Laboratory is home to the Advanced Photon Source (APS), a DOE Office of Science User Facility and one of only four third-generation, hard x-ray synchrotron radiation light sources in the world. The brightness and energy of x-ray beams are critical for research. Higher brightness means more x-rays can be focused onto a smaller, laser-like spot, allowing researchers to gather more data in greater detail in less time.
APS facility user and Benedictine University microbial ecologist Monica Tischler measured the heavy metals in avian museum specimens. Using the APS, Tischler has found a way to quantify the metals that birds have encountered in their environment and that have been deposited in the egg shells. These data enable researchers to track trends of climate change, pollution, and ecology through an elemental analysis of the eggs. Using non-destructive, light-source techniques, Tischler could have her egg and study it, too.
Scientists at University of Manchester, with the assistance of the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC National Laboratory, were able to use high resolution x-ray scanning to detect traces of copper, zinc, and strontium in 150 million-year-old dinosaur bones. The abundance of these metals, essential elements of bone maintenance enzymes, provided insights into how dinosaurs healed.
In general, it is very difficult to understand the healing process of animal bones, let alone bones of extinct animals, but SSRL enabled researchers to study these bones at the atomic and molecular levels.

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The above post is reprinted from materials provided by Department of Energy, Office of Science. Note: Materials may be edited for content and length.

Scientists, engineers and technicians at the U.S. Department of Energy's Fermi National Accelerator Laboratory have achieved for high-energy neutrino experiments a world record: a sustained 521-kilowatt beam generated by the Main Injector particle accelerator. More than 1,000 physicists from around the world will use this high-intensity beam to more closely study neutrinos and fleeting particles called muons, both fundamental building blocks of our universe.
The record beam power surpasses that of the 400-plus-kilowatt beam sent to neutrino experiments from particle accelerators at CERN.
Setting this world record is an initial step for the Fermilab accelerator complex as it will gradually increase beam power over the coming years. The next goal for the laboratory's two-mile-around Main Injector accelerator -- the final and most powerful in Fermilab's accelerator chain -- is to deliver 700-kilowatt beams to the laboratory's various experiments. Ultimately, Fermilab plans to make additional upgrades to its accelerator complex over the next decade, achieving beam power in excess of 1,000 kilowatts, also referred to as 1 megawatt.
"We have the world's highest-power beam for neutrinos, and we're only going up from here," said Ioanis Kourbanis, head of the Main Injector Department at Fermilab.
Laboratory-made neutrino experiments start by accelerating a beam of particles, typically protons, and then smashing them into a target to create neutrinos. Scientists then use particle detectors to "catch" as many of those neutrinos as possible and record their interactions. Neutrinos rarely engage with matter: Only one out of every trillion emerging from the proton beam will interact in an experiment's detector. The more particles in that beam, the more opportunities researchers will have to study these rare interactions.
The amped-up particle beam provided by the Main Injector enriches the lab's neutrino supply, positioning Fermilab to become the primary laboratory for accelerator-based neutrino research. Neutrinos are also made in stars and in Earth's core, and they pass through everything -- people and planets alike.
"The idea is that if you build a more intense beam, neutrino scientists from around the world will beat a path to your door," said Fermilab Deputy Director Joe Lykken. "This is exactly what's happening."
Fermilab currently operates four neutrino experiments: MicroBooNE, MINERvA, MINOS+ and the laboratory's largest-to-date neutrino experiment, NOvA, which sends particles from Fermilab's suburban Chicago location to a far detector 500 miles away in Ash River, Minnesota. The laboratory is working with scientists from around the world on expanding its short-baseline neutrino program and would also serve as host to the proposed flagship Long-Baseline Neutrino Facility and Deep Underground Neutrino Experiment, or DUNE. Scientists aim to address basic questions about the mass and properties of each kind of neutrino as well as the role neutrinos played in the evolution of the universe.
"Reaching this milestone is a fantastic achievement for Fermilab; beam power is everything in our field," said DUNE co-spokesperson Mark Thomson of the University of Cambridge. "The ability for Fermilab to deliver, yet again, gives the international neutrino community huge confidence in the future U.S.-hosted neutrino program."
Fermilab is also preparing to operate two experiments for studying muons, short-lived particles that could reveal secrets about the earliest moments of the universe. The increased beam power will also benefit the Fermilab Test Beam Facility, one of the few facilities in the world that provides muons, pions and other particles that researchers can use to test their particle detectors.
Since 2011, Fermilab has made significant upgrades to its accelerators and reconfigured the complex to provide the best possible particle beams for neutrino and muon experiments. With the dedicated work of the Fermilab Accelerator Division, the Main Injector is on track to nearly double its Tevatron-era beam power by 2016.
"Fermilab's beamline has been a tremendous driver of neutrino science for many years, and the continued improvements to the intensity mean that it will remain a driver for many years to come," said Indiana University's Mark Messier, co-spokesperson for the NOvA experiment.

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The above post is reprinted from materials provided by Fermi National Accelerator Laboratory (Fermilab). Note: Materials may be edited for content and length.