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  • richardmitnick 2:49 pm on March 27, 2018 Permalink | Reply
    Tags: , , , Photon Sciences, , Quantum systems,   

    From University of Chicago: “UChicago scientists build trap to make tiny packages of light ‘collide’” 

    U Chicago bloc

    University of Chicago

    March 27, 2018
    Louise Lerner

    Study examines how to manipulate photons for quantum engineering.

    Asst. Prof. Jonathan Simon with the photon collider—the blue light is reflected by a precisely arranged set of mirrors to manipulate individual photons so that they ‘collide’ with one another. Photo by Jean Lachat.

    The universe is illuminated via photons, the tiny individual particles that make up light, but they don’t interact with each other. To make them see the light, a team of University of Chicago physicists built a trap to help photons bounce off each other.

    Their photon collider, described in the March 19 edition of Nature Physics, is the latest effort to make photons behave like other particles such as electrons—a step toward greater understanding and control of quantum systems, which may one day manifest as technology with new properties.

    Quantum systems behave according to the strange laws that govern the smallest particles in the universe, like electrons. Scientists are increasingly interested in exploring new ways to harness the particles’ odd behaviors, like being in two states at once, and then choosing one only when measured.

    Jonathan Simon, the Neubauer Family Assistant Professor of Physics and the James Franck Institute, is interested in how walls dividing matter and light begin to break down at this scale. Most electronic systems use electrons as the moving parts, but photons can display quantum properties just as easily as electrons—and photons’ quirks could both offer advantages as technologies and serve as models to understand the more slippery electrons. So his team wants to manipulate and stack photons to build matter out of light.

    (From left): Asst. Prof. Jonathan Simon, graduate student Ningyuan Jia and postdoctoral scholar Logan Clark with the photon collider. (Photo by Jean Lachat).

    “Essentially we want to make photon systems into a kind of quantum Legos—blown-up materials that you can more easily study and tease out basic quantum design principles,” said Simon, who is also a fellow of the Institute for Molecular Engineering.

    But because photons have no mass, no charge and no chill—they always want to travel at the speed of light—making them behave like other particles takes some delicate finagling.

    Two years ago, Simon’s lab figured out a way to make photons behave as though they were in a magnetic field. The next challenge was to make photons react to each others’ presence, which light normally doesn’t.

    In their lab, the scientists shine a weak laser to send a photon into a trap: a series of mirrors that keep it continuously bouncing around inside. The photon interacts with a cloud of rubidium atoms that are prepared so that once any atom in the cloud absorbs a photon, no other atom can. This repels other incoming photons behind them—as though they were “colliding.”

    This offers a new way to understand some of the more poorly understood quantum properties, like entanglement—the state in which two particles become linked and share the same state even at great distances.

    Scientists use a weak laser to send a photon into a series of mirrors, which keeps the photon continuously bouncing around inside. (Photo by Jean Lachat).

    “We don’t have much intuition about what kinds of entanglement lead to which properties,” Simon said, “so if we can understand an analogous system, that could give us some insight.”

    There’s also interest in using photon systems for ultra-secure communications and to make computers. The team’s next step, Simon said, is to combine this setup with their previous one, to produce a set of photons that both interact with each other and with magnetic fields.

    The first author on the study was UChicago graduate student Ningyuan Jia. Other co-authors were graduate students Albert Ryou (now at the University of Washington), Nathan Schine and Alexandros Georgakopoulos, as well as postdoctoral scholars Ariel Sommer (now at Lehigh University) and Logan Clark.

    See the full article here .

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  • richardmitnick 3:21 pm on December 13, 2017 Permalink | Reply
    Tags: , , , , , , Photon Sciences   

    From FNAL: “Photons continue to enlighten physicists” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    December 13, 2017
    Andy Beretvas
    Alessandra Lucà

    You may be familiar with particles of light, called photons. Physicists give the name “prompt photons” to those that are produced by two particles smashing together — hard collisions — as contrasted with those resulting from the decay of other particles. The Tevatron produced prompt photons by the hard collisions between protons and antiprotons.

    Knowing the likelihood that proton-antiproton collisions will produce prompt photons tells us something about the proton’s components, which are called quarks and gluons. In particular, we can learn about the density of quarks and gluons inside the colliding protons and get a better grasp on how they fragment into photons. These ingredients are all described in a theory called perturbative quantum chromodynamics.

    The cross section is presented as a function of the transverse energy of the photon.

    This plot compares three models — Pythia 6.216, Sherpa 1.4.1 and MCFM 6.8 — to the data.

    Prompt photons at hadron colliders constitute an important test of perturbative quantum chromodynamics (pQCD), and may also be found in signatures of new physics processes. A precise measurement of prompt photon production is important to probe theoretical models, as well as to gain a better understanding of final states that contain energetic photons.

    CDF physicists used the full Tevatron Run II data set, which contained 2.1 million collision events in the selected sample, to measure the prompt photons’ energies.

    FNAL/Tevatron CDF detector

    The researchers were particularly interested in the energy they carried in a direction perpendicular to the colliding beams, a property called transverse energy.

    The photons’ transverse energy tells you something about the process that produced it. Photons with less than 100 GeV of transverse energy were generated primarily by quarks and gluons scattering off each other. At higher energies, the dominant process was the annihilation of a quark with its antimatter counterpart.

    CDF conducted a similar study to this one in 2009. An important part of the measurement is that the photons should be isolated (the energy deposited near the photon is small). This time, a larger data set meant scientists could study a larger range of transverse photon energy, from 30 to 500 GeV. Moreover, a different statistical technique has been developed to better identify prompt photons; their identification is very challenging because of the huge background coming from other particles (mostly hadrons).

    The results are presented in the first figure: The likelihood of proton-antiproton collisions producing a prompt photon decreases with increasing transverse energy. Note the data covers six orders of magnitude. This provides a challenge for theorists to come up with models that predicts this behavior correctly over so large a range.

    Over the full range, data shows good agreement with the MCFM prediction. This model is a next-to-leading order pQCD calculation developed by Fermilab physicists John Campbell, Keith Ellis, Walter Giele and Ciaran Williams.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

  • richardmitnick 6:04 am on December 6, 2016 Permalink | Reply
    Tags: , Inorganic geochemistry, Molecular environmental science, Photon Sciences, ,   

    From Stanford: “Eureka moment leads to new method of studying environmental toxins” 

    Stanford University Name
    Stanford University

    March 31, 2016 [Stanford just saw fit to put this in social media.]
    Ker Than

    View of the TVA Kingston Fossil Plant fly ash spill. Work using X-ray beams is clarifying how pollutants bind or release from solid surfaces and move into groundwater. Photo: Brian Stansberry via Wikimedia Commons

    A technique for probing the surface of particles revealed how toxins move from the soil to groundwater.

    In 1986, Gordon Brown used SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) to visualize something no one had ever seen before: the exact way that atoms bond to a solid surface.


    The work stemmed from a eureka moment that Brown had during the doctoral defense of graduate student Kim Hayes but has since grown into one of the seminal works in inorganic geochemistry, and even spawned a new field of study — molecular environmental science.

    Knowing how charged ions interact with solid surfaces is crucial for understanding how toxic metal ions such as lead, arsenic and mercury or radioactive elements such as uranium may be released from particles in soils and sediments and into groundwater or vice versa. Using the techniques Brown’s team helped pioneer, scientists today can paint exquisitely detailed pictures of how metal ions bind to different solid surfaces, including those on nanoparticles.

    “You can determine what other atoms are around the pollutant ions of interest, the inter-atomic distances separating them and the number and types of chemical bonds that keep them bound to the surface,” says Brown, a professor of geological sciences and of photon science. “This is crucial for understanding how easily they move from one place to another.”

    Access mp4 video here .

    Synchrotron-generated X-rays like those produced at SSRL are ideal for this type of investigation for a number of reasons, says John Bargar, a senior scientist at SLAC and Brown’s former PhD student. For one thing, synchrotron X-rays are highly focused, much like laser beams. “All of the photons produced are condensed into either a pencil beam or a narrow fan,” Bargar says. “That means you can use nearly all of the photons that you’re making with very little waste.”

    Another advantage of synchrotron X-rays, Brown says, is that their extremely high intensity makes it possible to detect and study pollutant ions at the very low concentration levels typically found in many polluted environmental samples.

    Moreover, synchrotron X-rays are polarized, meaning their waves vibrate primarily in a single plane. By modifying the direction of polarization, scientists can create very powerful probes for studying chemical bonds in molecules.

    “A metal ion sitting inside a larger molecule is surrounded by many bonds. Oftentimes, we don’t want to interrogate all of those bonds at once,” Bargar says. “With polarized X-rays, we can selectively interrogate the bonds in a specific orientation.”

    Recently, Brown and Bargar have collaborated to study how organic matter and live microbial organisms affect the binding affinities of different environmental pollutants to solid surfaces. Bargar and Brown are also investigating ways to harness bacterial aggregations called biofilms to neutralize the effects of environmental pollutants. In addition, they are also using synchrotron X-rays at SSRL to look for more efficient ways of safely extracting oil and gas from tight shales via hydraulic fracturing, a process that is transforming the energy landscape of the United States.

    “The X-ray beams synchrotrons are able to generate today are about 15 orders of magnitude brighter than what was available when I was a graduate student. This has led to a revolution in all areas of science and engineering,” Brown says. “I could collect the data for my entire PhD thesis in one morning at SSRL now.”

    See the full article here .

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 6:59 am on May 8, 2015 Permalink | Reply
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    From MIT: “Electrons corralled using new quantum tool” 

    MIT News

    May 7, 2015
    David L. Chandler

    Image: Jon Wyrick/NIST

    “Whispering gallery” effect confines electrons, could provide basis for new electron-optics devices.

    Researchers have succeeded in creating a new “whispering gallery” effect for electrons in a sheet of graphene — making it possible to precisely control a region that reflects electrons within the material. They say the accomplishment could provide a basic building block for new kinds of electronic lenses, as well as quantum-based devices that combine electronics and optics.

    The new system uses a needle-like probe that forms the basis of present-day scanning tunneling microscopes (STM), enabling control of both the location and the size of the reflecting region within graphene — a two-dimensional form of carbon that is just one atom thick.

    The new finding is described in a paper appearing in the journal Science, co-authored by MIT professor of physics Leonid Levitov and researchers at the National Institute of Standards and Technology (NIST), the University of Maryland, Imperial College London, and the National Institute for Materials Science (NIMS) in Tsukuba, Japan.

    When the sharp tip of the STM is poised over a sheet of graphene, it produces a circular barrier on the sheet that “acts as a perfect curved mirror” for electrons, Levitov says, reflecting them along the curved surface until they begin to interfere with themselves. This controllable reflectivity and interference is similar, he adds, to so-called “whispering gallery” confinement modes that have been used in optical and acoustic systems — but these have not been tunable or adjustable.

    “In optics, whispering gallery resonators are known and useful,” Levitov says. “They provide high-quality cavities that find applications in sensing, spectroscopy, and communications. But the usual problem in optics is they’re not tunable.” Similarly, previous attempts to create quantum “corrals” for electrons have used atoms precisely positioned on a surface, which cannot be reconfigured easily.

    The confinement in this case is produced by the boundary between two different regions on the graphene surface, corresponding to the “p” and “n” regions in a transistor. In this case, a circular region just beneath the STM tip takes on one polarity, and the surrounding region the opposite polarity, creating a controllable circular junction between the two regions. Electrons inside sheets of graphene behave like particles of light; in this case, the circular junction acts as a curved mirror that can focus and control the electrons.

    It’s too early to predict what specific uses might be found for this phenomenon, Levitov says, but adds, “Any resonator can be used for a variety of things.”

    This electron resonator combines several good features. There’s clearly something special about having tunability and also high quality at the same time.”

    Philip Kim, a professor of physics at Harvard University who was not connected with this research, says it is “a very notable example of demonstrating novel electronic properties of graphene.” He adds, “Electrons in graphene behave like photons confined in a two-dimensional atomic sheet. This work unambiguously demonstrates that electrons confined in the potential created by scanning probe microscope exhibit a wave like resonance behavior, known as whispering gallery mode.”

    Because the new system is based on well-established STM technology, it could be developed relatively quickly into usable devices, Levitov suggests. And conveniently, the STM not only creates the whispering gallery effect, but also provides a means of observing the results, to study the phenomenon. “The tip does double-duty in this case,” he says.

    This could be a step toward the creation of electronic lenses, Levitov says — “a concept that intrigues graphene researchers.” In principle, these could provide a way of observing objects one-thousandth the size of those visible using light waves.

    Electronic lenses would represent a fundamentally different approach from existing electron microscopes, which bombard a surface with high-energy beams of electrons, obliterating any subtle effects within the objects being observed. Electron lenses, by contrast, would be able to observe the ambient low-energy electrons within the object itself.

    An appealing feature of the setup developed in NIST is that the boundary between the two surface regions, which can serve as a lens, is movable, since it is carried along with the STM tip when it is scanning the surface. This could make it possible to study “subtle things about how charge carriers behave at a microscopic level, that you can’t see from the outside,” Levitov says.

    The new work by Levitov and his colleagues provides one piece of such a system — and potentially of other advanced electro-optical systems, he says, such as negative-refraction materials that have been proposed as a kind of “invisibility cloak.” The new whispering-gallery mode for electrons is part of a toolbox that could lead to a whole family of new quantum-based electron-optics devices. It could also be used for high-fidelity sensing, since such resonators “can be used to enhance your sensitivity to very small signals,” Levitov says.

    Harvard’s Kim says that this work “is an important step toward building novel electronic applications, based on the unique relativistic quantum-mechanical behavior of electrons in graphene.”

    The research team also included graduate student Joaquin Rodriguez-Nieva from MIT; Yue Zhao, Jonathan Wyrick, Fabian Natterer, Nikolai Zhitenev, and Joseph Stroscio from NIST; Cyprian Lewandowski from Imperial College London; and Kenji Watanabe and Takashi Taniguchi from NIMS.

    See the full article here.

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  • richardmitnick 1:11 pm on March 27, 2015 Permalink | Reply
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    From BNL: “Physicists Solve Low-Temperature Magnetic Mystery” 

    Brookhaven Lab

    March 27, 2015
    Chelsea Whyte, (631) 344-8671 or Peter Genzer, (631) 344-3174

    Ignace Jarrige shown with the sample used in the experiment.

    Researchers have made an experimental breakthrough in explaining a rare property of an exotic magnetic material, potentially opening a path to a host of new technologies. From information storage to magnetic refrigeration, many of tomorrow’s most promising innovations rely on sophisticated magnetic materials, and this discovery opens the door to harnessing the physics that governs those materials.

    The work, led by Brookhaven National Laboratory physicist Ignace Jarrige, and University of Connecticut professor Jason Hancock, together with collaborators from Japan and Argonne National Laboratory, marks a major advance in the search for practical materials that will enable several types of next-generation technology. A paper describing the team’s results was published this week in the journal Physical Review Letters.

    The work is related to the Kondo Effect, a physical phenomenon that explains how magnetic impurities affect the electrical resistance of materials. The researchers were looking at a material called ytterbium-indium-copper-four (usually written using its chemical formula: YbInCu4).

    YbInCu4 has long been known to undergo a unique transition as a result of changing temperature. Below a certain temperature, the material’s magnetism disappears, while above that temperature, it is strongly magnetic. This transition, which has puzzled physicists for decades, has recently revealed its secret. “We detected a gap in the electronic spectrum, similar to that found in semiconductors like silicon, whose energy shift at the transition causes the Kondo Effect to strengthen sharply,” said Jarrige

    From Left to Right: Jason Hancock, Diego Casa, and Jung-ho Kim, shown with one of the instruments used in the experiment.

    Electronic energy gaps define how electrons move (or don’t move) within the material, and are the critical component in understanding the electrical and magnetic properties of materials. “Our discovery goes to show that tailored semiconductor gaps can be used as a convenient knob to finely control the Kondo Effect and hence magnetism in technological materials,” said Jarrige.

    To uncover the energy gap, the team used a process called Resonant Inelastic X-Ray Scattering (RIXS), a new experimental technique that is made possible by an intense X-ray beam produced at a synchrotron operated by the Department of Energy and located at Argonne National Laboratory outside of Chicago. By placing materials in the focused X-ray beam and sensitively measuring and analyzing how the X-rays are scattered, the team was able to uncover elusive properties such as the energy gap and connect them to the enigmatic magnetic behavior.

    The new physics identified through this work suggest a roadmap to the development of materials with strong “magnetocaloric” properties, the tendency of a material to change temperature in the presence of a magnetic field. “The Kondo Effect in YbInCu4 turns on at a very low temperature of 42 Kelvin (-384F),” said Hancock, “but we now understand why it happens, which suggests that it could happen in other materials near room temperature.” If that material is discovered, according to Hancock, it would revolutionize cooling technology.

    During the RIXS experiment, an X-ray beam is used to excite electrons inside the sample. The X-ray loses energy during the process and then is scattered out of the sample. A fine analysis of the scattered X-rays yields insight into the mechanism that controls the strength of the Kondo Effect.

    Household use of air conditioners in the US accounts for over $11 billion in energy costs and releases 100 million tons of carbon dioxide annually. Use of the magnetocaloric effect for magnetic refrigeration as an alternative to the mechanical fans and pumps in widespread use today could significantly reduce those numbers.

    In addition to its potential applications to technology, the work has advanced the state of the art in research. “The RIXS technique we have developed can be applied in other areas of basic energy science,” said Hancock, noting that the development is very timely, and that it may be useful in the search for “topological Kondo insulators,” materials which have been predicted in theory, but have yet to be discovered.

    See the full article here.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

  • richardmitnick 8:41 am on March 19, 2015 Permalink | Reply
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    From SLAC: “Scientists Watch Quantum Dots ‘Breathe’ in Response to Stress” 

    SLAC Lab

    March 18, 2015

    Nanocrystal Study at SLAC’s X-ray Laser Could Aid in the Design of New Materials

    In this illustration, intense X-rays produced at SLAC’s Linac Coherent Light Source strike nanocrystals of a semiconductor material. Scientists used the X-rays to study an ultrafast “breathing” response in the crystals induced quadrillionths of a second earlier by laser light. (SLAC National Accelerator Laboratory)

    Researchers at the Department of Energy’s SLAC National Accelerator Laboratory watched nanoscale semiconductor crystals expand and shrink in response to powerful pulses of laser light. This ultrafast “breathing” provides new insight about how such tiny structures change shape as they start to melt – information that can help guide researchers in tailoring their use for a range of applications.

    In the experiment using SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, researchers first exposed the nanocrystals to a burst of laser light, followed closely by an ultrabright X-ray pulse that recorded the resulting structural changes in atomic-scale detail at the onset of melting.

    SLAC LCLS Inside

    “This is the first time we could measure the details of how these ultrasmall materials react when strained to their limits,” said Aaron Lindenberg, an assistant professor at SLAC and Stanford who led the experiment. The results were published March 12 in Nature Communications.

    Getting to Know Quantum Dots

    The crystals studied at SLAC are known as “quantum dots” because they display unique traits at the nanoscale that defy the classical physics governing their properties at larger scales. The crystals can be tuned by changing their size and shape to emit specific colors of light, for example.

    So scientists have worked to incorporate them in solar panels to make them more efficient and in computer displays to improve resolution while consuming less battery power. These materials have also been studied for potential use in batteries and fuel cells and for targeted drug delivery.

    Scientists have also discovered that these and other nanomaterials, which may contain just tens or hundreds of atoms, can be far more damage-resistant than larger bits of the same materials because they exhibit a more perfect crystal structure at the tiniest scales. This property could prove useful in battery components, for example, as smaller particles may be able to withstand more charging cycles than larger ones before degrading.

    A Surprise in the ‘Breathing’ of Tiny Spheres and Nanowires

    In the LCLS experiment, researchers studied spheres and nanowires made of cadmium sulfide and cadmium selenide that were just 3 to 5 nanometers, or billionths of a meter, across. The nanowires were up to 25 nanometers long. By comparison, amino acids – the building blocks of proteins – are about 1 nanometer in length, and individual atoms are measured in tenths of nanometers.

    By examining the nanocrystals from many different angles with X-ray pulses, researchers reconstructed how they change shape when hit with an optical laser pulse. They were surprised to see the spheres and nanowires expand in width by about 1 percent and then quickly contract within femtoseconds, or quadrillionths of a second. They also found that the nanowires don’t expand in length, and showed that the way the crystals respond to strain was coupled to how their structure melts.

    In an earlier, separate study, another team of researchers had used LCLS to explore the response of larger gold particles on longer timescales.

    “In the future, we want to extend these experiments to more complex and technologically relevant nanostructures, and also to enable X-ray exploration of nanoscale devices while they are operating,” Lindenberg said. “Knowing how materials change under strain can be used together with simulations to design new materials with novel properties.”

    Participating researchers were from SLAC, Stanford and two of their joint institutes, the Stanford Institute for Materials and Energy Sciences (SIMES) and Stanford PULSE Institute; University of California, Berkeley; University of Duisburg-Essen in Germany; and Argonne National Laboratory. The work was supported by the DOE Office of Science and the German Research Council.

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

  • richardmitnick 7:13 pm on December 6, 2014 Permalink | Reply
    Tags: , Photon Sciences, ,   

    From Stanford: “Stanford engineers take big step toward using light instead of wires inside computers” 

    Stanford University Name
    Stanford University

    December 2, 2014
    Chris Cesare

    Stanford engineers have designed and built a prism-like device that can split a beam of light into different colors and bend the light at right angles, a development that could eventually lead to computers that use optics, rather than electricity, to carry data.

    They describe what they call an “optical link” in an article in Scientific Reports.

    The optical link is a tiny slice of silicon etched with a pattern that resembles a bar code. When a beam of light is shined at the link, two different wavelengths (colors) of light split off at right angles to the input, forming a T shape. This is a big step toward creating a complete system for connecting computer components with light rather than wires.

    This tiny slice of silicon, etched in Jelena Vuckovic’s lab at Stanford with a pattern that resembles a bar code, is one step on the way toward linking computer components with light instead of wires.

    “Light can carry more data than a wire, and it takes less energy to transmit photons than electrons,” said electrical engineering Professor Jelena Vuckovic, who led the research.

    In previous work her team developed an algorithm that did two things: It automated the process of designing optical structures and it enabled them to create previously unimaginable, nanoscale structures to control light.

    Now, she and lead author Alexander Piggott, a doctoral candidate in electrical engineering, have employed that algorithm to design, build and test a link compatible with current fiber optic networks.

    Creating a silicon prism

    The Stanford structure was made by etching a tiny bar code pattern into silicon that split waves of light like a small-scale prism. The team engineered the effect using a subtle understanding of how the speed of light changes as it moves through different materials.

    What we call the speed of light is how fast light travels in a vacuum. Light travels a bit more slowly in air and even more slowly in water. This speed difference is why a straw in a glass of water looks dislocated.

    A property of materials called the index of refraction characterizes the difference in speed. The higher the index, the more slowly light will travel in that material. Air has an index of refraction of nearly 1 and water of 1.3. Infrared light travels through silicon even more slowly: it has an index of refraction of 3.5.

    The Stanford algorithm designed a structure that alternated strips of silicon and gaps of air in a specific way. The device takes advantage of the fact that as light passes from one medium to the next, some light is reflected and some is transmitted. When light traveled through the silicon bar code, the reflected light interfered with the transmitted light in complicated ways.

    The algorithm designed the bar code to use this subtle interference to direct one wavelength to go left and a different wavelength to go right, all within a tiny silicon chip eight microns long.

    Both 1300-nanometer light and 1550-nanometer light, corresponding to and O-band wavelengths widely used in fiber optic networks, were beamed at the device from above. The bar code-like structure redirected C-band light one way and O-band light the other, right on the chip.

    Convex optimization

    The researchers designed these bar code patterns already knowing their desired function. Since they wanted C-band and O-band light routed in opposite directions, they let the algorithm design a structure to achieve it.

    “We wanted to be able to let the software design the structure of a particular size given only the desired inputs and outputs for the device,” Vuckovic said.

    To design their device they adapted concepts from convex optimization, a mathematical approach to solving complex problems such as stock market trading. With help from Stanford electrical engineering Professor Stephen Boyd, an expert in convex optimization, they discovered how to automatically create novel shapes at the nanoscale to cause light to behave in specific ways.

    “For many years, nanophotonics researchers made structures using simple geometries and regular shapes,” Vuckovic said. “The structures you see produced by this algorithm are nothing like what anyone has done before.”

    The algorithm began its work with a simple design of just silicon. Then, through hundreds of tiny adjustments, it found better and better bar code structures for producing the desired output light.

    Previous designs of nanophotonic structures were based on regular geometric patterns and the designer’s intuition. The Stanford algorithm can design this structure in just 15 minutes on a laptop computer.

    They have also used this algorithm to design a wide variety of other devices, like the super-compact “Swiss cheese” structures that route light beams to different outputs not based on their color, but based on their mode, i.e., based on how they look. For example, a light beam with a single lobe in the cross-section goes to one output, and a double lobed beam (looking like two rivers flowing side by side) goes to the other output. Such a mode router is equally as important as the bar code color splitter, as different modes are also used in optical communications to transmit information.

    The algorithm is the key. It gives researchers a tool to create optical components to perform specific functions, and in many cases such components didn’t even exist before. “There’s no way to analytically design these kinds of devices,” Piggott said.

    Media Contact

    Tom Abate, School of Engineering: (650) 736-2245, tabate@stanford.edu

    Dan Stober, Stanford News Service: (650) 721-6965, dstober@stanford.edu

    See the full article here.

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 7:38 pm on October 23, 2014 Permalink | Reply
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    From BNL: “National Synchrotron Light Source II Achieves ‘First Light'” 

    Brookhaven Lab

    October 23, 2014
    Chelsea Whyte, (631) 344-8671 or Peter Genzer, (631) 344-3174

    The National Synchrotron Light Source II detects its first photons, beginning a new phase of the facility’s operations. Scientific experiments at NSLS-II are expected to begin before the end of the year.

    A crowd gathered on the experimental floor of the National Synchrotron Light Source II to witness “first light,” when the x-ray beam entered a beamline for the first time at the facility.

    The brightest synchrotron light source in the world has delivered its first x-ray beams. The National Synchrotron Light Source II (NSLS-II) at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory achieved “first light” on October 23, 2014, when operators opened the shutter to begin commissioning the first experimental station (called a beamline), allowing powerful x-rays to travel to a phosphor detector and capture the facility’s first photons. While considerable work remains to realize the full potential of the new facility, first light counts as an important step on the road to facility commissioning.

    BNL NSLS-II Interior
    NSLS-II at BNL

    “This is a significant milestone for Brookhaven Lab, for the Department of Energy, and for the nation,” said Harriet Kung, DOE Associate Director of Science for Basic Energy Sciences. “The National Synchrotron Light Source II will foster new discoveries and create breakthroughs in crucial areas of national need, including energy security and the environment. This new U.S. user facility will advance the Department’s mission and play a leadership role in enabling and producing high-impact research for many years to come.”

    At 10:32 a.m. on October 23, a crowd of scientists, engineers, and technicians gathered around the Coherent Soft X-ray Scattering (CSX) beamline at NSLS-II, expectantly watching the video feed from inside a lead-lined hutch where the x-ray beam eventually struck the detector. As the x-rays hit the detector, cheers and applause rang out across the experimental hall for a milestone many years in the making.

    The team of scientists, engineers, and technicians at the Coherent Soft X-ray Scattering (CSX) beamline gathered around the control station to watch as group leader Stuart Wilkins (seated, front) opened the shutter between the beamline and the storage ring, allowing x-rays to enter the first optical enclosure for the first time.

    “This achievement begins an exciting new chapter of synchrotron science at Brookhaven, building on the remarkable legacy of NSLS, and leading us in new directions we could not have imagined before,” said Laboratory Director Doon Gibbs. “It’s a great illustration of the ways that national labs continually evolve and grow to meet national needs, and it’s a wonderful time for all of us. Everyone at the Lab, in every role, supports our science, so we can all share in the sense of excitement and take pride in this accomplishment.”

    NSLS-II first x-rays
    Inside the beamline enclosure, a phosphor detector (the rectangle at right) captured the first x-rays (in white) which hit the mark dead center.

    In the heart of the 590,000 square foot facility, an electron gun emits packets of the negatively charged particles, which travel down a linear accelerator into a booster ring. There, the electrons are brought to nearly the speed of light, and then steered into the storage ring, where powerful magnets guide the beam on a half-mile circuit around the NSLS-II storage ring. As the electrons travel around the ring, they emit extremely intense x-rays, which are delivered and guided down beamlines into experimental end stations where scientists will carry out experiments for scientific research and discovery. NSLS-II accelerator operators have previously stored beam in the storage ring, but they hadn’t yet opened the shutters to allow x-ray light to reach a detector until today’s celebrated achievement.

    “We have been eagerly anticipating this culmination of nearly a decade of design, construction, and testing and the sustained effort and dedication of hundreds of individuals who made it possible,” said Steve Dierker, Associate Laboratory Director for Photon Sciences. ‘We have more work to do, but soon researchers from around the world will start using NSLS-II to advance their research on everything from new energy storage materials to developing new drugs to fight disease. I’m very much looking forward to the discoveries that NSLS-II will enable, and to the continuing legacy of groundbreaking synchrotron research at Brookhaven.”

    NSLS-II, a third-generation synchrotron light source, will be the newest and most advanced synchrotron facility in the world, enabling research not possible anywhere else. As a DOE Office of Science User Facility, it will offer researchers from academia, industry, and national laboratories new ways to study material properties and functions with nanoscale resolution and exquisite sensitivity by providing state-of-the-art capabilities for x-ray imaging, scattering, and spectroscopy.

    Currently 30 beamlines are under development to take advantage of the high brightness of the x-rays at NSLS-II. Commissioning of the first group of seven beamlines will begin in the coming months, with first experiments beginning at the CSX beamline before the end of 2014.

    At the NSLS-II beamlines, scientists will be able to generate images of the structure of materials such as lithium-ion batteries or biological proteins at the nanoscale level—research expected to advance many fields of science and impact people’s quality of life in the years to come.

    NSLS-II will support the Department of Energy’s scientific mission by providing the most advanced tools for discovery-class science in condensed matter and materials science, physics, chemistry, and biology—science that ultimately will enhance national and energy security and help drive abundant, safe, and clean energy technologies.

    Media Contacts:
    Karen McNulty Walsh, 631 344-8350 or kmcnulty@bnl.gov
    Chelsea Whyte, 631 344-8671 or cwhyte@bnl.gov

    See the full article here.

    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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  • richardmitnick 6:22 am on October 21, 2014 Permalink | Reply
    Tags: , , Photon Sciences,   

    From SLAC: “Puzzling New Behavior Found in High-Temperature Superconductors” 

    SLAC Lab

    October 20, 2014

    Ultimate Goal: A Super-efficient Way to Conduct Electricity at Room Temperature

    Research by an international team led by SLAC and Stanford scientists has uncovered a new, unpredicted behavior in a copper oxide material that becomes superconducting – conducting electricity without any loss – at relatively high temperatures.

    This new phenomenon – an unforeseen collective motion of electric charges coursing through the material – presents a challenge to scientists seeking to understand its origin and connection with high-temperature superconductivity. Their ultimate goal is to design a superconducting material that works at room temperature.

    “Making a room-temperature superconductor would save the world enormous amounts of energy,” said Thomas Devereaux, leader of the research team and director of the Stanford Institute for Materials and Energy Sciences (SIMES), which is jointly run with SLAC. “But to do that we must understand what’s happening inside the materials as they become superconducting. This result adds a new piece to this long-standing puzzle.”

    The results are published Oct. 19 in Nature Physics.

    Delving Into Doping Differences

    The researchers used an emerging X-ray technique called resonant inelastic X-ray scattering, or RIXS, to measure how the properties of a copper oxide change as extra electrons are added in a process known as doping. The team used the Swiss Light Source’s RIXS instrument, which currently has the world’s highest resolution and can reveal atomic-scale excitations – rapid changes in magnetism, electrical charge and other properties – as they move through the material.

    Copper oxide, a ceramic that normally doesn’t conduct electricity at all, becomes superconducting only when doped with other elements to add or remove electrons and chilled to low temperatures. Intriguingly, the electron-rich version loses its superconductivity when warmed to about 30 degrees above absolute zero (30 kelvins) while the electron-poor one remains superconducting up to 120 kelvins (minus 244 degrees Fahrenheit). One of the goals of the new research is to understand why they behave so differently.

    The experiments revealed a surprising increase of magnetic energy and the emergence of a new collective excitation in the electron-rich compounds, said Wei-sheng Lee, a SLAC staff scientist and lead author on the Nature Physics paper. “It’s very puzzling that these new electronic phenomena are not seen in the electron-poor material,” he said.

    SLAC Staff Scientist Wei-sheng Lee (SLAC National Accelerator Laboratory)

    Lee added that it’s unclear whether the new collective excitation is related to the ability of electrons to pair up and effortlessly conduct electricity – the hallmark of superconductivity – or whether it promotes or limits high-temperature superconductivity. Further insight can be provided by additional experiments using next-generation RIXS instruments that will become available in a few years at synchrotron light sources worldwide.

    A Long, Tortuous Path

    This discovery is the latest step in the long and tortuous path toward understanding high-temperature superconductivity.

    Scientists have known since the late 1950s why certain metals and simple alloys become superconducting when chilled within a few degrees of absolute zero: Their electrons pair up and ride waves of atomic vibrations that act like a virtual glue to hold the pairs together. Above a certain temperature, however, the glue fails as thermal vibrations increase, the electron pairs split up and superconductivity disappears.

    Starting in 1986, researchers discovered a number of materials that are superconducting at higher temperatures. By understanding and optimizing how these materials work, they hope to develop superconductors that work at room temperature and above.

    Until recently, the most likely glue holding superconducting electron pairs together at higher temperatures seemed to be strong magnetic excitations created by interactions between electron spins. But a recent theoretical simulation by SLAC and Stanford researchers concluded that these high-energy magnetic interactions are not the sole factor in copper oxide’s high-temperature superconductivity. The new results confirm that prediction, and also complement a 2012 report on the behavior of electron-poor copper oxides by a team that included Lee, Devereaux and several other SLAC/Stanford scientists.

    “Theorists must now incorporate this new ingredient into their explanations of how high-temperature superconductivity works,” said Thorsten Schmitt, leader of the RIXS team at the Paul Scherrer Institute in Switzerland, who collaborated on the study.

    Other researchers involved in the study were from Columbia University, University of Minnesota, AGH University of Science and Technology in Poland, National Synchrotron Radiation Research Center and National Tsing Hua University in Taiwan, and the Chinese Academy of Sciences. Funding for the research came from the DOE Office of Science, U.S. National Science Foundation and Swiss National Science Foundation.

    See the full article, with animation video, here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 5:03 pm on September 10, 2014 Permalink | Reply
    Tags: , , , Photon Sciences,   

    From LBL: “Advanced Light Source Sets Microscopy Record” 

    Berkeley Logo

    Berkeley Lab

    September 10, 2014
    Lynn Yarris (510) 486-5375

    A record-setting X-ray microscopy experiment may have ushered in a new era for nanoscale imaging. Working at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), a collaboration of researchers used low energy or “soft” X-rays to image structures only five nanometers in size. This resolution, obtained at Berkeley Lab’s Advanced Light Source (ALS), a DOE Office of Science User Facility, is the highest ever achieved with X-ray microscopy.

    LBL Advanced Light Source

    Ptychographic image using soft X-rays of lithium iron phosphate nanocrystal after partial dilithiation. The delithiated region is shown in red.

    Using ptychography, a coherent diffractive imaging technique based on high-performance scanning transmission X-ray microscopy (STXM), the collaboration was able to map the chemical composition of lithium iron phosphate nanocrystals after partial dilithiation. The results yielded important new insights into a material of high interest for electrochemical energy storage.

    “We have developed diffractive imaging methods capable of achieving a spatial resolution that cannot be matched by conventional imaging schemes,” says David Shapiro, a physicist with the ALS. “We are now entering a stage in which our X-ray microscopes are no longer limited by our optics and we can image at nearly the wavelength of our X-ray light.”

    Shapiro is the lead and corresponding author of a paper reporting this research in Nature Photonics. The paper is titled “Chemical composition mapping with nanometer resolution by soft X-ray microscopy.” (See below for a full list of co-authors and their affiliations.)

    David Shapiro with the STXM instruments at ALS beamline (Photo by Roy Kaltschmidt)

    In ptychography (pronounced tie-cog-raphee), a combination of multiple coherent diffraction measurements is used to obtain 2D or 3D maps of micron-sized objects with high resolution and sensitivity. Because of the sensitivity of soft x-rays to electronic states, ptychography can be used to image chemical phase transformations and the mechanical consequences of those transformations that a material undergoes.

    “Until this work, however, the spatial resolution of ptychographic microscopes did not surpass that of the best conventional systems using X-ray zone plate lenses,” says Howard Padmore, leader of the Experimental Systems Group at the ALS and a co-author of the Nature Photonics paper. “The problem stemmed from the fact that ptychography was primarily developed on hard X-ray sources using simple pinhole optics for illumination. This resulted in a low scattering cross-section and low coherent intensity at the sample, which meant that exposure times had to be extremely long, and that mechanical and illumination stabilities were not good enough for high resolution.”

    Key to the success of Shapiro, and his collaborators were the use of soft X-rays which have wavelengths ranging between 1 to 10 nanometers, and a special algorithm that eliminated the effect of all incoherent background signals. Ptychography measurements were recorded with the STXM instruments at ALS beamline 11.0.2, which uses an undulator x-ray source, and ALS beamline, which uses a bending magnet source. A coherent soft X-ray beam would be focused onto a sample and scanned in 40 nanometer increments. Diffraction data would then be recorded on an X-ray CCD (charge-coupled device) that allowed reconstruction of the sample to very high spatial resolution.

    “Throughout the ptychography scans, we maintained the sample and focusing optic in relative alignment using an interferometric feedback system with a precision comparable to the wavelength of the X-ray illumination,” Shapiro says.

    Lithium iron phosphate is widely studied for its use as a cathode material in rechargeable lithium-ion batteries. In using their ptychography technique to map the chemical composition of lithium iron phosphate crystals, Shapiro and his collaborators found a strong correlation between structural defects and chemical phase propagation.

    “Surface cracking in these crystals was expected,” Shapiro says, “but there is no other means of visualizing the correlation of those cracks with chemical composition at these scales. The ability to visualize the coupling of the kinetics of a phase transformation with the mechanical consequences is critical to designing materials with ultimate durability.”

    Shapiro and his colleagues have already begun applying their ptychography technique to the study of catalytic and magnetic films, magnetotactic bacteria, polymer blends and green cements.
    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas.

    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas.

    For the chemical mapping of lithium iron phosphate they used the STXM instrument at ALS beamline which required up to 800 milliseconds of exposure to the X-ray beam for each scan. Next year, they anticipate using a new ALS beamline called COSMIC (COherent Scattering and MICroscopy), which will feature a high brightness undulator x-ray source coupled to new high-frame-rate CCD sensors that will cut beam exposure times to only a few milliseconds and provide spatial resolution at the wavelength of the radiation.

    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas. – See more at: http://newscenter.lbl.gov/2014/09/10/advanced-light-source-sets-microscopy-record/#sthash.6DLMbCxp.dpuf

    “If visible light microscopes could only achieve a resolution that was 50 times the wavelength of visible light, we would not be able to see most single celled organisms,” Shapiro says. “Where would the life sciences be with such a limitation? We are now approaching the point where we will have X-ray microscopes of comparable quality to today’s visible light instruments for the study of nanomaterials.”

    Co-authoring the Nature Photonics paper in addition to Shapiro and Padmore were Young-Sang Yu, Tolek Tyliszczak, Jordi Cabana, Rich Celestre, Weilun Chao, David Kilcoyne, Stefano Marchesini, Tony Warwick and Lee Yang of Berkeley Lab; Konstantin Kaznatcheev of Brookhaven National Laboratory; Shirley Meng of the University of San Diego; and Filipe Maia of Uppsala University in Sweden.

    This research was primarily supported by the DOE Office of Science.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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    DOE Seal

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