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  • richardmitnick 8:01 am on May 10, 2019 Permalink | Reply
    Tags: "Q&A: SLAC/Stanford researchers prepare for a new quantum revolution", , , , , , , , , , Quantum squeezing, SLAC National Accelerator Laboratory, The most exciting opportunities in quantum control make use of a phenomenon known as entanglement   

    From SLAC National Accelerator Lab- “Q&A: SLAC/Stanford researchers prepare for a new quantum revolution” 

    From SLAC National Accelerator Lab

    May 9, 2019
    Manuel Gnida

    Monika Schleier-Smith and Kent Irwin explain how their projects in quantum information science could help us better understand black holes and dark matter.

    The tech world is abuzz about quantum information science (QIS). This emerging technology explores bizarre quantum effects that occur on the smallest scales of matter and could potentially revolutionize the way we live.

    Quantum computers would outperform today’s most powerful supercomputers; data transfer technology based on quantum encryption would be more secure; exquisitely sensitive detectors could pick up fainter-than-ever signals from all corners of the universe; and new quantum materials could enable superconductors that transport electricity without loss.

    In December 2018, President Trump signed the National Quantum Initiative Act into law, which will mobilize $1.2 billion over the next five years to accelerate the development of quantum technology and its applications. Three months earlier, the Department of Energy had already announced $218 million in funding for 85 QIS research awards.

    The Fundamental Physics and Technology Innovation directorates of DOE’s SLAC National Accelerator Laboratory recently joined forces with Stanford University on a new initiative called Q-FARM to make progress in the field. In this Q&A, two Q-FARM scientists explain how they will explore the quantum world through projects funded by DOE QIS awards in high-energy physics.

    Monika Schleier-Smith, assistant professor of physics at Stanford, wants to build a quantum simulator made of atoms to test how quantum information spreads. The research, she said, could even lead to a better understanding of black holes.

    Kent Irwin, professor of physics at Stanford and professor of photon science and of particle physics and astrophysics at SLAC, works on quantum sensors that would open new avenues to search for the identity of the mysterious dark matter that makes up most of the universe.

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    Monika Schleier-Smith and Kent Irwin are the principal investigators of three quantum information science projects in high-energy physics at SLAC. (Farrin Abbott/Dawn Harmer/SLAC National Accelerator Laboratory)

    What exactly is quantum information science?

    Irwin: If we look at the world on the smallest scales, everything we know is already “quantum.” On this scale, the properties of atoms, molecules and materials follow the rules of quantum mechanics. QIS strives to make significant advances in controlling those quantum effects that don’t exist on larger scales.

    Schleier-Smith: We’re truly witnessing a revolution in the field in the sense that we’re getting better and better at engineering systems with carefully designed quantum properties, which could pave the way for a broad range of future applications.

    What does quantum control mean in practice?

    Schleier-Smith: The most exciting opportunities in quantum control make use of a phenomenon known as entanglement – a type of correlation that doesn’t exist in the “classical,” non-quantum world. Let me give you a simple analogy: Imagine that we flip two coins. Classically, whether one coin shows heads or tails is independent of what the other coin shows. But if the two coins are instead in an entangled quantum state, looking at the result for one “coin” automatically determines the result for the other one, even though the coin toss still looks random for either coin in isolation.

    Entanglement thus provides a fundamentally new way of encoding information – not in the states of individual “coins” or bits but in correlations between the states of different qubits. This capability could potentially enable transformative new ways of computing, where problems that are intrinsically difficult to solve on classical computers might be more efficiently solved on quantum ones. A challenge, however, is that entangled states are exceedingly fragile: any measurement of the system – even unintentional – necessarily changes the quantum state. So a major area of quantum control is to understand how to generate and preserve this fragile resource.

    At the same time, certain quantum technologies can also take advantage of the extreme sensitivity of quantum states to perturbations. One application is in secure telecommunications: If a sender and receiver share information in the form of quantum bits, an eavesdropper cannot go undetected, because her measurement necessarily changes the quantum state.

    Another very promising application is quantum sensing, where the idea is to reduce noise and enhance sensitivity by controlling quantum correlations, for instance, through quantum squeezing.

    What is quantum squeezing?

    Irwin: Quantum mechanics sets limits on how we can measure certain things in nature. For instance, we can’t perfectly measure both the position and momentum of a particle. The very act of measuring one changes the other. This is called the Heisenberg uncertainty principle. When we search for dark matter, we need to measure an electromagnetic signal extremely well, but Heisenberg tells us that we can’t measure the strength and timing of this signal without introducing uncertainty.

    Quantum squeezing allows us to evade limits on measurement set by Heisenberg by putting all the uncertainty into one thing (which we don’t care about), and then measuring the other with much greater precision. So, for instance, if we squeeze all of the quantum uncertainty in an electromagnetic signal into its timing, we can measure its strength much better than quantum mechanics would ordinarily allow. This lets us search for an electromagnetic signal from dark matter much more quickly and sensitively than is otherwise possible.

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    Kent Irwin (at left with Dale Li) leads efforts at SLAC and Stanford to build quantum sensors for exquisitely sensitive detectors. (Andy Freeberg/SLAC National Accelerator Laboratory)

    What types of sensors are you working on?

    Irwin: My team is exploring quantum techniques to develop sensors that could break new ground in the search for dark matter.

    We’ve known since the 1930s that the universe contains much more matter than the ordinary type that we can see with our eyes and telescopes – the matter made up of atoms. Whatever dark matter is, it’s a new type of particle that we don’t understand yet. Most of today’s dark matter detectors search for relatively heavy particles, called weakly interacting massive particles, or WIMPs.

    PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ project at SURF, Lead, SD, USA

    But what if dark matter particles were so light that they wouldn’t leave a trace in those detectors? We want to develop sensors that would be able to “see” much lighter dark matter particles.

    There would be so many of these very light dark matter particles that they would behave much more like waves than individual particles. So instead of looking for collisions of individual dark matter particles within a detector, which is how WIMP detectors work, we want to look for dark matter waves, which would be detected like a very weak AM radio signal.

    In fact, we even call one of our projects “Dark Matter Radio.” It works like the world’s most sensitive AM radio. But it’s also placed in the world’s most perfect radio shield, made up of a material called a superconductor, which keeps all normal radio waves out. However, unlike real AM radio signals, dark matter waves would be able to go right through the shield and produce a signal. So we are looking for a very weak AM radio station made by dark matter at an unknown frequency.

    Quantum sensors can make this radio much more sensitive, for instance by using quantum tricks such as squeezing and entanglement. So the Dark Matter Radio will not only be the world’s most sensitive AM radio; it will also be better than the Heisenberg uncertainty principle would normally allow.

    What are the challenges of QIS?

    Schleier-Smith: There is a lot we need to learn about controlling quantum correlations before we can make broad use of them in future applications. For example, the sensitivity of entangled quantum states to perturbations is great for sensor applications. However, for quantum computing it’s a major challenge because perturbations of information encoded in qubits will introduce errors, and nobody knows for sure how to correct for them.

    To make progress in that area, my team is studying a question that is very fundamental to our ability to control quantum correlations: How does information actually spread in quantum systems?

    The model system we’re using for these studies consists of atoms that are laser-cooled and optically trapped. We use light to controllably turn on interactions between the atoms, as a means of generating entanglement. By measuring the speed with which quantum information can spread in the system, we hope to understand how to design the structure of the interactions to generate entanglement most efficiently. We view the system of cold atoms as a quantum simulator that allows us to study principles that are also applicable to other physical systems.

    In this area of quantum simulation, one major thrust has been to advance understanding of solid-state systems, by trapping atoms in arrays that mimic the structure of a crystalline material. In my lab, we are additionally working to extend the ideas and tools of quantum simulation in new directions. One prospect that I am particularly excited about is to use cold atoms to simulate what happens to quantum information in black holes.

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    Monika Schleier-Smith (at center with graduate students Emily Davis and Eric Cooper) uses laser-cooled atoms in her lab at Stanford to study the transfer of quantum information. (Dawn Harmer/SLAC National Accelerator Laboratory)

    What do cold atoms have to do with black holes?

    Schleier-Smith: The idea that there might be any connection between quantum systems we can build in the lab and black holes has its origins in a long-standing theoretical problem: When particles fall into a black hole, what happens to the information they contained? There were compelling arguments that the information should be lost, but that would contradict the laws of quantum mechanics.

    More recently, theoretical physicists – notably my Stanford colleague Patrick Hayden – found a resolution to this problem: We should think of the black hole as a highly chaotic system that “scrambles” the information as fast as physically possible. It’s almost like shredding documents, but quantum information scrambling is much richer in that the result is a highly entangled quantum state.

    Although precisely recreating such a process in the lab will be very challenging, we hope to look at one of its key features already in the near term. In order for information scrambling to happen, information needs to be transferred through space exponentially fast. This, in turn, requires quantum interactions to occur over long distances, which is quite counterintuitive because interactions in nature typically become weaker with distance. With our quantum simulator, we are able to study interactions between distant atoms by sending information back and forth with photons, particles of light.

    What do you hope will happen in QIS over the next few years?

    Irwin: We need to prove that, in real applications, quantum technology is superior to the technology that we already have. We are in the early stages of this new quantum revolution, but this is already starting to happen. The things we’re learning now will help us make a leap in developing future technology, such as universal quantum computers and next-generation sensors. The work we do on quantum sensors will enable new science, not only in dark matter research. At SLAC, I also see potential for quantum-enhanced sensors in X-ray applications, which could provide us with new tools to study advanced materials and understand how biomolecules work.

    Schleier-Smith: QIS offers plenty of room for breakthroughs. There are many open questions we still need to answer about how to engineer the properties of quantum systems in order to harness them for technology, so it’s imperative that we continue to broadly advance our understanding of complex quantum systems. Personally, I hope that we’ll be able to better connect experimental observations with the latest theoretical advances. Bringing all this knowledge together will help us build the technologies of the future.

    See the full article here .


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    Please help promote STEM in your local schools.

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    SLAC/LCLS


    SLAC/LCLS II projected view


    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 11:18 am on April 15, 2019 Permalink | Reply
    Tags: "SLAC’s high-speed ‘electron camera’ films molecular movie in HD", , , , , How a bond in the ring breaks and atoms jiggle around for extended periods of time., , Researchers have made the first high-definition “movie” of ring-shaped molecules breaking open in response to light, , SLAC National Accelerator Laboratory, The results demonstrate how our unique instruments for studying ultrafast processes complement each other, This allows us to ask new questions about fundamental processes stimulated by light., UED-ultrafast electron diffraction instrument   

    From SLAC National Accelerator Lab: “SLAC’s high-speed ‘electron camera’ films molecular movie in HD” 

    From SLAC National Accelerator Lab

    April 15, 2019

    Manuel Gnida
    mgnida@slac.stanford.edu
    (650) 926-2632

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    This illustration shows snapshots of the light-triggered transition of the ring-shaped 1,3-cyclohexadiene (CHD) molecule (background) to its stretched-out 1,3,5-hexatriene (HT) form (foreground). The snapshots were taken with SLAC’s high-speed “electron camera” – an instrument for ultrafast electron diffraction (UED). (Greg Stewart/SLAC National Accelerator Laboratory)

    With an extremely fast “electron camera” at the Department of Energy’s SLAC National Accelerator Laboratory, researchers have made the first high-definition “movie” of ring-shaped molecules breaking open in response to light. The results could further our understanding of similar reactions with vital roles in chemistry, such as the production of vitamin D in our bodies.


    Visualization of a molecular movie made with SLAC’s electron camera, in which researchers have captured in atomic detail how a ring-shaped molecule opens up in the first 800 millionths of a billionth of a second after being hit by a laser flash. Ring-opening reactions like this one play important roles in chemistry, such as the light-driven synthesis of vitamin D in our bodies. (Thomas Wolf/PULSE Institute)

    A previous molecular movie of the same reaction, produced with SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, for the first time recorded the large structural changes during the reaction.


    This video describes how the Linac Coherent Light Source, an X-ray free-electron laser at SLAC National Accelerator Laboratory, provided the first direct measurements of how a ring-shaped gas molecule unravels in the millionths of a billionth of a second after it is split open by light. The measurements were compiled in sequence to form the basis for computer animations showing molecular motion. (SLAC National Accelerator Laboratory)

    Now, making use of the lab’s ultrafast electron diffraction (UED) instrument, these new results provide high-resolution details – showing, for instance, how a bond in the ring breaks and atoms jiggle around for extended periods of time.

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    August 5, 2015- With SLAC’s new apparatus for ultrafast electron diffraction – one of the world’s fastest “electron cameras” – researchers can study motions in materials that take place in less than 100 quadrillionths of a second. A pulsed electron beam is created by shining laser pulses on a metal photocathode. The beam gets accelerated by a radiofrequency field and focused by a magnetic lens. Then it travels through a sample and scatters off the sample’s atomic nuclei and electrons, creating a diffraction image on a detector. Changes in these diffraction images over time are used to reconstruct ultrafast motions of the sample’s interior structure. (SLAC National Accelerator Laboratory)

    “The details of this ring-opening reaction have now been settled,” said Thomas Wolf, a scientist at the Stanford Pulse Institute of SLAC and Stanford University and leader of the research team. “The fact that we can now directly measure changes in bond distances during chemical reactions allows us to ask new questions about fundamental processes stimulated by light.”

    SLAC scientist Mike Minitti, who was involved in both studies, said, “The results demonstrate how our unique instruments for studying ultrafast processes complement each other. Where LCLS excels in capturing snapshots with extremely fast shutter speeds of only a few femtoseconds, or millionths of a billionth of a second, UED cranks up the spatial resolution of these snapshots. This is a great result, and the studies validate one another’s findings, which is important when making use of entirely new measurement tools.”

    LCLS Director Mike Dunne said, “We’re now making SLAC’s UED instrument available to the broad scientific community, in addition to enhancing the extraordinary capabilities of LCLS by doubling its energy reach and transforming its repetition rate. The combination of both tools uniquely positions us to enable the best possible studies of fundamental processes on ultrasmall and ultrafast scales.”

    The team reported their results today in Nature Chemistry.

    Molecular movie in HD

    This particular reaction has been studied many times before: When a ring-shaped molecule called 1,3-cyclohexadiene (CHD) absorbs light, a bond breaks and the molecule unfolds to form the almost linear molecule known as 1,3,5-hexatriene (HT). The process is a textbook example of ring-opening reactions and serves as a simplified model for studying light-driven processes during vitamin D synthesis.

    In 2015, researchers studied the reaction with LCLS, which resulted in the first detailed molecular movie of its kind and revealed how the molecule changed from a ring to a cigar-like shape after it was struck by a laser flash. The snapshots, which initially had limited spatial resolution, were brought further into focus through computer simulations.

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    Researchers created the first atomic-resolution movie of the ring-opening reaction of 1,3-cyclohexadiene (CHD) with an “electron camera” called UED. Bottom: The UED electron beam accurately measures the distances between pairs of atoms in the CHD molecule as the reaction proceeds. The distance between each pair is represented by a colored line in the graph. Variations in the distances as the molecule changes shape represent the molecular movie. Top: Visualization of the molecular structure corresponding to the distance distribution measured at about 380 femtoseconds into the reaction (dashed line at bottom). (David Sanchez/Stanford University)

    The new study used UED – a technique in which researchers send an electron beam with high energy, measured in millions of electronvolts (MeV), through a sample – to precisely measure distances between pairs of atoms.


    Taking snapshots of these distances at different intervals after an initial laser flash and tracking how they change allows scientists to create a stop-motion movie of the light-induced structural changes in the sample.

    The electron beam also produces strong signals for very dilute samples, such as the CHD gas used in the study, said SLAC scientist Xijie Wang, director of the MeV-UED instrument.

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    SLAC Megaelectronvolt Ultrasfast Electron Diffraction Instrument: MeV-UED

    “This allowed us to follow the ring-opening reaction over much longer periods of time than before.”

    Surprising details

    The new data revealed several surprising details about the reaction.

    They showed that the movements of the atoms accelerated as the CHD ring broke, helping the molecules rid themselves of excess energy and accelerating their transition to the stretched-out HT form.

    The movie also captured how the two ends of the HT molecule jiggled around as the molecules became more and more linear. These rotational motions went on for at least a picosecond, or a trillionth of a second.

    “I would have never thought these motions would last that long,” Wolf said. “It demonstrates that the reaction doesn’t end with the ring opening itself and that there is much more long-lasting motion in light-induced processes than previously thought.”

    A method with potential

    The scientists also used their experimental data to validate a newly developed computational approach for including the motions of atomic nuclei in simulations of chemical processes.

    “UED provided us with data that have the high spatial resolution needed to test these methods,” said Stanford chemistry professor and PULSE researcher Todd Martinez, whose group led the computational analysis. “This paper is the most direct test of our methods, and our results are in excellent agreement with the experiment.”

    In addition to advancing the predictive power of computer simulations, the results will help deepen our understanding of life’s fundamental chemical reactions, Wolf said: “We’re very hopeful our method will pave the way for studies of more complex molecules that are even closer to the ones used in life processes.”

    Other research institutions involved in this study were the University of York, UK; University of Nebraska-Lincoln; University of Potsdam, Germany; University of Edinburgh, UK; and Brown University. Large parts of this work were financially supported by the DOE Office of Science. SLAC’s MeV-UED instrument is part of LCLS, a DOE Office of Science user facility.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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 3:45 pm on April 12, 2019 Permalink | Reply
    Tags: "SLAC develops novel compact antenna for communicating where radios fail", A high Q piezoelectric resonator as a portable VLF transmitter, , SLAC National Accelerator Laboratory   

    From SLAC National Accelerator Lab: “SLAC develops novel compact antenna for communicating where radios fail” 

    From SLAC National Accelerator Lab

    April 12, 2019

    1
    A new type of pocket-sized antenna, developed at SLAC, could enable mobile communication in situations where conventional radios don’t work, such as under water, through the ground and over very long distances through air. (Greg Stewart/SLAC National Accelerator Laboratory)

    The 4-inch-tall device could be used in portable transmitters for rescue missions and other challenging applications demanding high mobility.

    The device emits very low frequency (VLF) radiation with wavelengths of tens to hundreds of miles. These waves travel long distances beyond the horizon and can penetrate environments that would block radio waves with shorter wavelengths. While today’s most powerful VLF technology requires gigantic emitters, this antenna is only four inches tall, so it could potentially be used for tasks that demand high mobility, including rescue and defense missions.

    “Our device is also hundreds of times more efficient and can transmit data faster than previous devices of comparable size,” said SLAC’s Mark Kemp, the project’s principal investigator. “Its performance pushes the limits of what’s technologically possible and puts portable VLF applications, like sending short text messages in challenging situations, within reach.”

    The SLAC-led team reported their results today in Nature Communications.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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 9:19 am on April 9, 2019 Permalink | Reply
    Tags: Children’s Museum of Indianapolis, Mission Jurassic, , SLAC National Accelerator Laboratory,   

    From SLAC National Accelerator Lab: “A mile-long graveyard of Jurassic fossils sparks a new international science collaboration” 

    From SLAC National Accelerator Lab

    March 28, 2019
    Ali Sundermier

    1
    Kimberly Calkins and Dallas Evans, lead curator of natural science and paleontology, with a sauropod femur at the upper sauropod quarry of The Jurassic Mile dig site. (Children’s Museum of Indianapolis)

    The Children’s Museum of Indianapolis announced plans this week for Mission Jurassic, a project that will support paleontological excavation of a fossil-rich plot of land in northern Wyoming. The project will bring together scientists from around the world, including the Department of Energy’s SLAC National Accelerator Laboratory, to reveal dramatic new secrets about the world of millions of years ago.

    “Mission Jurassic is a wonderful project because it’s not just an isolated fossil – it’s a suite of different organisms, including dinosaurs and plants, in a single location,” says SLAC scientist Nick Edwards. “We hope that through our involvement in this project, we will contribute some new information to the preservation, chemistry and maybe even the basic understanding of these extinct organisms, ancient ecosystems, and Earth history on the broader scale.”

    The Children’s Museum will serve as the Mission Jurassic leader. The project is made possible through a lead gift from Lilly Endowment Inc. Spearheaded by Phil Manning and Victoria Egerton of the University of Manchester in England, both scientists-in-residence at The Children’s Museum, more than 100 scientists from three countries will join forces to investigate the rare confluence of Jurassic Period fossils, trackways and fossilized plants. The site will provide clues that promise to tell a more complete story about the Jurassic Period.

    “We have been using SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) for over a decade to help map the subtle changes in chemistry that are a function of burial environments,” Manning says.

    SLAC SSRL Campus


    SLAC SSRL PEP collider map


    SLAC/SSRL

    “This work has real-world impact on how we might plan the long-term burial and disposal of waste in the 21st Century. We use the fossil record as a ‘hindsight laboratory’ that can better inform science on the mass transfer of compounds from the biosphere into the lithosphere”.

    The Jurassic Mile

    Project leaders are calling the fossil-rich, mile-square plot of land the Jurassic Mile. There are four main quarries within the multi-level, 640-acre site that offer a diverse assemblage of Morrison Formation articulated and semi-articulated dinosaurs. It has also yielded associated animals, fossil plants and dinosaur trackways of the Late Jurassic Period, 150 million years ago.

    Nearly 600 specimens weighing more than six tons have been collected from this site over the past two years, despite the fact that only a fraction of the site has been explored. They include the bones of an 80-foot-long sauropod (Brachiosaur) and 90-foot-long Diplodocid. A 6-foot-6-inch sauropod scapula (shoulder bone) and several blocks containing articulated bones are among the material collected during the 2018 field season. A 5-foot-1-inch femur was revealed at the announcement on March 25, 2019.

    Probing our world at the atomic level

    SLAC, a key partner working with the University of Manchester team, will shine bright X-rays onto the fossils at the SSRL, a DOE Office of Science user facility that produces X-ray beams perfectly tailored for probing the world at the atomic and molecular level. New imaging techniques being developed by the team have already resulted in multiple high-impact scientific publications.

    “Our primary instrument at SSRL is unique because it can do elemental imaging, which tells us where the elements are in fossils, and it can also do absorption spectroscopy, which tells us what chemical state they’re in,” says Uwe Bergmann, a distinguished staff scientist at SLAC. “It allows us to detect a wide range of important biological and geochemical elements, from light elements like phosphorous and sulfur all the way to the transition metals.”

    Specimens from the well-preserved fossil remains at the Jurassic Mile site will form the basis for a major expansion of The Children’s Museum of Indianapolis’ permanent Dinosphere exhibit that will add creatures from the Jurassic Period. The project is already utilizing cutting-edge science, from particle accelerators to some of the most powerful computers on the planet, to help resurrect the Jurassic dinosaurs and add momentum to the process of unearthing the lost world and forgotten lives.

    This article is based on a press release from The Children’s Museum of Indianapolis.

    From the press release, no image credits:

    3
    4

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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 10:05 am on April 4, 2019 Permalink | Reply
    Tags: A new method could turn random fluctuations in the intensity of laser pulses from a nuisance into an advantage facilitating studies of these fundamental interactions., In a computational process that borrows ideas from machine learning researchers can then turn these data into a visualization of the X-ray pulse’s effects on the sample., In addition we need to control the time delay between them very well., Pump-probe experiments therefore typically require that we first prepare well-defined short pulses that are less random, , SLAC National Accelerator Laboratory, Taking advantage of X-ray spikes-by repeating the experiment with varying time delays between the pulses researchers can make a stop-motion movie of the tiny fast motions., Taking ghostly snapshots-Daniel Ratner and his coworkers want to apply the technique of ghost imaging., The secret is applying a method known as “ghost imaging” which reconstructs what objects look like without ever directly recording their images., X-ray free-electron lasers (XFELs)   

    From SLAC National Accelerator Lab: “Ghostly X-ray images could provide key info for analyzing X-ray laser experiments” 

    From SLAC National Accelerator Lab

    April 3, 2019
    Manuel Gnida

    1
    SLAC researchers suggest using the randomness of subsequent X-ray pulses from an X-ray laser to study the pulses’ interactions with matter, a method they call pump-probe ghost imaging. (Greg Stewart/SLAC National Accelerator Laboratory)

    X-ray free-electron lasers (XFELs) produce incredibly powerful beams of light that enable unprecedented studies of the ultrafast motions of atoms in matter. To interpret data taken with these extraordinary light sources, researchers need a solid understanding of how the X-ray pulses interact with matter and how those interactions affect measurements.

    Now, computer simulations by scientists from the Department of Energy’s SLAC National Accelerator Laboratory suggest that a new method could turn random fluctuations in the intensity of laser pulses from a nuisance into an advantage, facilitating studies of these fundamental interactions. The secret is applying a method known as “ghost imaging,” which reconstructs what objects look like without ever directly recording their images.

    “Instead of trying to make XFEL pulses less random, which is the approach we most often pursue for our experiments, we actually want to use randomness in this case,” said James Cryan from the Stanford PULSE Institute, a joint institute of Stanford University and SLAC. “Our results show that by doing so, we can get around some of the technical challenges associated with the current method for studying X-ray interactions with matter.”

    The research team published their results in Physical Review X.

    Taking advantage of X-ray spikes

    Scientists commonly look at these interactions through pump-probe experiments, in which they send pairs of X-ray pulses through a sample. The first pulse, called the pump pulse, rearranges how electrons are distributed in the sample. The second pulse, called the probe pulse, investigates the effects these rearrangements have on the motions of the sample’s electrons and atomic nuclei. By repeating the experiment with varying time delays between the pulses, researchers can make a stop-motion movie of the tiny, fast motions.

    One of the challenges is that X-ray lasers generate light pulses in a random process, so that each pulse is actually a train of narrow X-ray spikes whose intensities vary randomly between pulses.

    “Pump-probe experiments therefore typically require that we first prepare well-defined, short pulses that are less random,” said SLAC’s Daniel Ratner, the study’s lead author. “In addition we need to control the time delay between them very well.”

    In the new approach, he said, “We wouldn’t have to worry about any of that. We would use X-ray pulses as they come out of the XFEL without further modifications.”

    In fact, in this new way of thinking each pair of spikes within a single X-ray pulse can be considered a pair of pump and probe pulses, so researchers could do many pump-probe measurements with a single shot of the XFEL.

    2
    Simulated profile of an X-ray pulse from an X-ray free-electron laser. It consists of a train of narrow spikes whose intensity (power) fluctuates randomly. SLAC researchers suggest using pairs of these spikes for pump-probe experiments that trigger and measure structural changes in a sample, turning a former nuisance into an advantage. This example highlights three pairs of spikes with different time delays between them. (DOI: 10.1103/PhysRevX.9.01104 [N/A])

    Taking ghostly snapshots

    To produce snapshots of a sample’s molecular motions with this method, Ratner and his coworkers want to apply the technique of ghost imaging.

    In conventional imaging, light falling on an object produces a two-dimensional image on a detector – whether the back of your eye, the megapixel sensor in your cell phone or an advanced X-ray detector. Ghost imaging, on the other hand, constructs an image by analyzing how random patterns of light shining onto the object affect the total amount of light coming off the object.

    “In our method, the random patterns are the fluctuating spike structures of individual XFEL pulses,” said co-author Siqi Li, a graduate student at SLAC and Stanford and lead author of a previous study that demonstrated ghost imaging using electrons [Physical Review Letters]. “To do the image reconstruction, we need to repeat the experiment many times – about 100,000 times in our simulations. Each time, we measure the pulse profile with a diagnostic tool and analyze the signal emitted by the sample.”

    In a computational process that borrows ideas from machine learning, researchers can then turn these data into a visualization of the X-ray pulse’s effects on the sample.

    3
    In conventional imaging (left), light falling on an object produces a two-dimensional image on a detector. Ghost imaging (right) constructs an image by analyzing how random patterns of light shining onto the object affect the total amount of light coming off the object. (Greg Stewart/SLAC National Accelerator Laboratory)

    A complementary tool

    So far, the new idea has been tested only in simulations and awaits experimental validation, for instance at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science user facility.

    SLAC LCLS

    Yet, the researchers are already convinced their method could complement conventional pump-probe experiments.

    “If future tests are successful, the method could strengthen our ability to look at very fundamental processes in XFEL experiments,” Ratner said. “It would also offer a few advantages that we would like to explore.” These include more stability, faster image reconstruction, less sample damage and the prospect of doing experiments at faster and faster timescales.

    Other co-authors of the paper are SLAC’s TJ Lane and Gennady Stupakov. The project was financially supported by the DOE Office of Science.

    See the full article here .


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    Please help promote STEM in your local schools.

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    SLAC/LCLS


    SLAC/LCLS II projected view


    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 10:57 am on February 9, 2019 Permalink | Reply
    Tags: , , , , Q-FARM will build upon Stanford and SLAC’s strong foundation in quantum science and engineering, QIS aims to harness the spookier properties of quantum mechanics: superposition-wave particle duality-entanglement, , , Quantum teleportation, SLAC National Accelerator Laboratory,   

    From Stanford University: “Q-FARM initiative to bolster quantum research at Stanford-SLAC 

    Stanford University Name
    From Stanford University

    February 8, 2019
    Ker Than

    1
    Patrick Hayden and Jelena Vuckovic will direct Stanford’s new Q-FARM initiative centered around experimental and theoretical quantum science and engineering. (Image credit: L.A. Cicero)

    There’s a new farm on the Farm.

    Stanford and SLAC National Accelerator Laboratory have launched a new Quantum Fundamentals, ARchitecture and Machines (Q-FARM) initiative to leverage and expand the university’s strengths in quantum science and engineering and to train the field’s next generation of scientists.

    “Our mission is not only to do research, it’s also to educate students, bring the community together, fill the gaps that we have in this space and connect to the world outside, both to industry and to other academic institutions,” said Q-FARM director Jelena Vuckovic, a professor of electrical engineering.

    Q-FARM emerged from Stanford’s long-range planning process as part of a team focused on understanding the natural world. The idea for it originated from faculty across departments who recognized that the university is uniquely positioned to become a leader in the field of quantum research, said Q-FARM deputy director Patrick Hayden, a professor of physics in the School of Humanities and Sciences.

    “I think it is very possible for Stanford to establish itself as the leading center in quantum science and engineering,” Hayden said. “We have advantages that other schools do not, including top-ranked science and engineering departments that are a short distance away from technology companies and SLAC, a renowned laboratory of the U.S. Department of Energy.”

    A second wave

    First formulated in the early 20th century, quantum mechanics deals with nature at its smallest scales. The theory describes with remarkable precision everything from the interactions between fundamental particles to the nature of chemical bonds and the electrical properties of materials. It even explains the origins of galaxies as tiny quantum ripples in spacetime that were stretched to enormous sizes during the first moments of the universe. Quantum mechanics is also the basis for some of our most transformative and ubiquitous technologies, including transistors and lasers.

    As influential as the theory has been, it’s poised to be even more impactful in the future. Beginning in the 1990s, quantum mechanics entered a “second wave” of discovery and innovation driven by theoretical and technological advances.

    On the theoretical front, quantum mechanics merged with computer science, mathematics and other branches of physics to give rise to a new field known as quantum information science (QIS). QIS aims to harness the spookier properties of quantum mechanics – superposition, wave-particle duality, entanglement – to manipulate information. Surprisingly, insights and techniques from QIS are proving useful not only for the design of quantum computers, algorithms and sensors but also for providing powerful new tools for investigating old questions in physics.

    “I finally feel, after all these years, that I’m at a stage in my life where things are as interesting as the things I missed because I came into physics too late,” said Leonard Susskind, a theoretical physicist at the Stanford Institute for Theoretical Physics. Susskind and Hayden are using quantum information to model black hole interiors and probe the nature of spacetime.

    As QIS has matured, so too has the ability of engineers to fabricate quantum-mechanical systems. Phenomena such as quantum teleportation that were once purely theoretical can now be created and studied in the lab. “This is what’s supposed to happen in science, that there is this feedback loop between theory and experiment, but it’s not always true,” Hayden said. “This is an area where it’s really happening and that’s very exciting.”

    A strong foundation

    Q-FARM will build upon Stanford and SLAC’s strong foundation in quantum science and engineering. The institutions include experts in the field, including Nobel laureate Robert Laughlin, and have played leading roles in a broad range of quantum research, including the discovery and characterization of new quantum materials, the use of quantum sensors to search for dark matter and exploration of the interface between QIS and fundamental physics.

    Furthermore, SLAC, as a multi-purpose DOE laboratory, brings unique facilities and expertise for QIS research that will complement Q-FARM on many fronts.

    Stanford and SLAC are also located in the heart of Silicon Valley, home to established companies like Google and to a long list of recent startups that are engaged in R&D efforts in quantum technologies. “Stanford has a history of strong interaction with Silicon Valley,” Hayden said. “All the big technology companies are investing in quantum computing. They are looking for the next major breakthrough in terms of computing power or communication power. Quantum mechanics seems to offer that.”

    Priorities

    With many world-leading research groups already established at Stanford, Q-FARM’s role will be to build bridges between them and create a community that can tackle the major emerging challenges in the area. Among Q-FARM’s initial priorities are the creation of postdoctoral and graduate fellowships and organizing research seminars where faculty, students and visiting scholars can present their research.

    Q-FARM will also focus on developing an educational program for undergraduate and graduate students to bolster the current curriculum. “We already have an excellent collection of classes, but we want to coordinate the program between physics and engineering so that we can better educate our students,” Vuckovic said.

    Demonstrating a united front on the research end will also help with faculty and student recruitment in an increasingly competitive field and attract some of the significant government funding that will target quantum research.

    In 2018, the U.S. Senate unanimously passed the National Quantum Initiative, which authorizes $1.275 billion to be spent over the next five years to fund American quantum information science research and to create multiple centers dedicated to quantum research and education.

    “Bringing one of those centers to Stanford and SLAC will help us maintain the strengths we already possess and establish ourselves more broadly in this field,” Vuckovic said.

    “If we can sustain this pace, Stanford will be the place where people who work in this field will want to be,” she added. “We have leading physics and leading engineering. We are in Silicon Valley. This is what makes us the right place to carry this forward.”

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Stanford University campus. No image credit

    Stanford University

    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

    Stanford University Seal

     
  • richardmitnick 10:32 am on February 9, 2019 Permalink | Reply
    Tags: Condenced-Matter Physics, , , , SLAC National Accelerator Laboratory,   

    From SLAC National Accelerator Lab: “First direct view of an electron’s short, speedy trip across a border” 

    From SLAC National Accelerator Lab

    February 8, 2019
    Glennda Chui

    1
    Electrons traveling between two layers of atomically thin material give off tiny bursts of electromagnetic waves in the terahertz spectral range. This glow, shown in red and blue, allowed researchers at SLAC and Stanford to observe and track the electrons’ ultrafast movements. (Greg Stewart/SLAC National Accelerator Laboratory)

    Watching electrons sprint between atomically thin layers of material will shed light on the fundamental workings of semiconductors, solar cells and other key technologies.

    Electrons flowing across the boundary between two materials are the foundation of many key technologies, from flash memories to batteries and solar cells. Now researchers have directly observed and clocked these tiny cross-border movements for the first time, watching as electrons raced seven-tenths of a nanometer – about the width of seven hydrogen atoms – in 100 millionths of a billionth of a second.

    Led by scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, the team made these observations by measuring tiny bursts of electromagnetic waves given off by the traveling electrons – a phenomenon described more than a century ago by Maxwell’s equations, but only now applied to this important measurement.

    “To make something useful, generally you need to put different materials together and transfer charge or heat or light between them,” said Eric Yue Ma, a postdoctoral researcher in the laboratory of SLAC/Stanford Professor Tony Heinz and lead author of a report in Science Advances.

    “This opens up a new way to measure how charge – in this case, electrons and holes – travels across the abrupt interface between two materials,” he said. “It doesn’t just apply to layered materials. For instance, it can also be used to look at electrons flowing between a solid surface and molecules that are attached to it, or even, in principle, between a liquid and a solid.”

    Too short, too fast – or were they?

    The materials used in this experiment are transition metal dichalcogenides, or TMDCs – an emerging class of semiconducting materials that consist of layers just a few atoms thick. There’s been an explosion of interest in TMDCs over the past few years as scientists explore their fundamental properties and potential uses in nanoelectronics and photonics.

    When two types of TMDC are stacked in alternating layers, electrons can flow from one layer to the next in a controllable way that people would like to harness for various applications.

    But until now, researchers who wanted to observe and study that flow had only been able to do it indirectly, by probing the material before and after the electrons had moved. The distances involved were just too short, and the electron speeds too fast, for today’s instruments to catch the flow of charge directly.

    At least that’s what they thought.

    Maxwell leads the way

    According to a famous set of equations named after physicist James Clerk Maxwell, pulses of current give off electromagnetic waves, which can vary from radio waves and microwaves to visible light and X-rays. In this case, the team realized that an electron’s journey from one TMDC layer to another should generate blips of terahertz waves – which fall between microwaves and infrared light on the electromagnetic spectrum – and that those blips could be detected with today’s state-of-the-art tools.

    “People had probably thought of this before, but dismissed the idea because they thought there was no way you could measure the current from electrons traveling such a small distance in such a small amount of material,” Ma said. “But if you do a back-of-the-envelope calculation, you see that if a current is really that fast you should be able to measure the emitted light, so we just tried.”

    Nudges from a laser

    The researchers, all investigators with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC, tested their idea on a TMDC material made of molybdenum disulfide and tungsten disulfide.

    Working with SLAC/Stanford Professor Aaron Lindenberg, Ma and fellow postdoc Burak Guzelturk hit the material with ultrashort pulses of optical laser light to get the electrons moving and recorded the terahertz waves they gave off with a technique called time-domain terahertz emission spectroscopy. Those measurements not only revealed how far and fast the electric current traveled between layers, Ma said, but also the direction it traveled in. When the same two materials were stacked in reverse order, the current flowed in exactly the same way but in the opposite direction.

    “With the demonstration of this new technique, many exciting problems can now be addressed,” said Heinz, who led the team’s investigation. “For example, rotating one of the two crystal layers with respect to the other is known to dramatically change the electronic and optical properties of the combined layers. This method will allow us to directly follow the rapid motion of electrons from one layer to the other and see how this motion is affected by the relative positioning of the atoms.”

    Major funding for this work came from the DOE Office of Science and the Gordon and Betty Moore Foundation. The samples of material the team studied were grown at North Carolina State University.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

     
  • richardmitnick 12:41 pm on December 13, 2018 Permalink | Reply
    Tags: , , , , SLAC National Accelerator Laboratory, Tangled magnetic fields power cosmic particle accelerators   

    From SLAC National Accelerator Lab: “Tangled magnetic fields power cosmic particle accelerators” 

    From SLAC National Accelerator Lab

    December 13, 2018
    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    Written by Manuel Gnida

    SLAC scientists find a new way to explain how a black hole’s plasma jets boost particles to the highest energies observed in the universe. The results could also prove useful for fusion and accelerator research on Earth.

    Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe. That’s the result of a new computational study by researchers from the Department of Energy’s SLAC National Accelerator Laboratory, which simulated particle emissions from distant active galaxies.

    1
    SLAC researchers have found a new mechanism that could explain how plasma jets emerging from the center of active galaxies, like the one shown in this illustration, accelerate particles to extreme energies. Computer simulations (circled area) showed that tangled magnetic field lines create strong electric fields in the direction of the jets, leading to dense electric currents of high-energy particles streaming away from the galaxy. (Greg Stewart/SLAC National Accelerator Laboratory)

    At the core of these active galaxies, supermassive black holes launch high-speed jets of plasma – a hot, ionized gas – that shoot millions of light years into space. This process may be the source of cosmic rays with energies tens of millions of times higher than the energy unleashed in the most powerful manmade particle accelerator.

    “The mechanism that creates these extreme particle energies isn’t known yet,” said SLAC staff scientist Frederico Fiúza, the principal investigator of a new study that will publish tomorrow in Physical Review Letters. “But based on our simulations, we’re able to propose a new mechanism that can potentially explain how these cosmic particle accelerators work.”

    The results could also have implications for plasma and nuclear fusion research and the development of novel high-energy particle accelerators.


    These movies show how distortions of the helical magnetic field of a cosmic jet (center) generate a strong electric field in the jet direction (left). The electric field boosts the energy of charged particles, effectively creating a dense electric current along the jet (right). (arXiv:1810.05154v1)

    Simulating cosmic jets

    Researchers have long been fascinated by the violent processes that boost the energy of cosmic particles. For example, they’ve gathered evidence that shock waves from powerful star explosions could bring particles up to speed and send them across the universe.

    Scientists have also suggested that the main driving force for cosmic plasma jets could be magnetic energy released when magnetic field lines in plasmas break and reconnect in a different way – a process known as “magnetic reconnection.”

    However, the new study suggests a different mechanism that’s tied to the disruption of the helical magnetic field generated by the supermassive black hole spinning at the center of active galaxies.

    “We knew that these fields can become unstable,” said lead author Paulo Alves, a research associate working with Fiúza. “But what exactly happens when the magnetic fields become distorted, and could this process explain how particles gain tremendous energy in these jets? That’s what we wanted to find out in our study.”

    However, the new study suggests a different mechanism that’s tied to the disruption of the helical magnetic field generated by the supermassive black hole spinning at the center of active galaxies.

    “We knew that these fields can become unstable,” said lead author Paulo Alves, a research associate working with Fiúza. “But what exactly happens when the magnetic fields become distorted, and could this process explain how particles gain tremendous energy in these jets? That’s what we wanted to find out in our study.”

    2
    Composite image of the active galaxy Centaurus A, showing lobes and jets extending millions of light years into space. (Optical: ESO/WFI; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; X-ray: NASA/CXC/CfA/R.Kraft et al.)

    To do so, the researchers simulated the motions of up to 550 billion particles – a miniature version of a cosmic jet – on the Mira supercomputer at the Argonne Leadership Computing Facility (ALCF) at DOE’s Argonne National Laboratory.

    MIRA IBM Blue Gene Q supercomputer at the Argonne Leadership Computing Facility

    Then, they scaled up their results to cosmic dimensions and compared them to astrophysical observations.

    From tangled field lines to high-energy particles

    The simulations showed that when the helical magnetic field is strongly distorted, the magnetic field lines become highly tangled and a large electric field is produced inside the jet. This arrangement of electric and magnetic fields can, indeed, efficiently accelerate electrons and protons to extreme energies. While high-energy electrons radiate their energy away in the form of X-rays and gamma rays, protons can escape the jet into space and reach the Earth’s atmosphere as cosmic radiation.

    “We see that a large portion of the magnetic energy released in the process goes into high-energy particles, and the acceleration mechanism can explain both the high-energy radiation coming from active galaxies and the highest cosmic-ray energies observed,” Alves said.

    Roger Blandford, an expert in black hole physics and former director of the SLAC/Stanford University Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), who was not involved in the study, said, “This careful analysis identifies many surprising details of what happens under conditions thought to be present in distant jets, and may help explain some remarkable astrophysical observations.”

    3
    In simulations of a miniature version of a cosmic jet, SLAC researchers have found that when the jet’s helical magnetic field (left) is strongly distorted, the magnetic field lines become highly tangled (middle), producing a large electric field (right) inside the jet that can efficiently accelerate electrons and protons to extreme energies. (arXiv:1810.05154v1)

    Next, the researchers want to connect their work even more firmly with actual observations, for example by studying what makes the radiation from cosmic jets vary rapidly over time. They also intend to do lab research to determine if the same mechanism proposed in this study could also cause disruptions and particle acceleration in fusion plasmas.

    This work was also co-authored by Jonathan Zrake, a former Kavli Fellow at KIPAC, who is now at Columbia University. The project was supported by the DOE Office of Science through its Early Career Research Program and an ALCC award for simulations on the Mira high-performance computer. ALCF is a DOE Office of Science user facility.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

     
  • richardmitnick 1:50 pm on November 7, 2018 Permalink | Reply
    Tags: , , , , , , , Researchers create most complete high-res atomic movie of photosynthesis to date, SLAC National Accelerator Laboratory, ,   

    From SLAC National Accelerator Lab: “Researchers create most complete high-res atomic movie of photosynthesis to date” 

    From SLAC National Accelerator Lab

    November 7, 2018

    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    In a major step forward, SLAC’s X-ray laser captures all four stable states of the process that produces the oxygen we breathe, as well as fleeting steps in between. The work opens doors to understanding the past and creating a greener future.

    1
    Using SLAC’s X-ray laser, researchers have captured the most complete high-res atomic movie to date of Photosystem II, a key protein complex in plants, algae and cyanobacteria responsible for splitting water and producing the oxygen we breathe. (Gregory Stewart, SLAC National Accelerator Laboratory)

    Despite its role in shaping life as we know it, many aspects of photosynthesis remain a mystery. An international collaboration between scientists at SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory and several other institutions is working to change that. The researchers used SLAC’s Linac Coherent Light Source (LCLS) X-ray laser to capture the most complete and highest-resolution picture to date of Photosystem II, a key protein complex in plants, algae and cyanobacteria responsible for splitting water and producing the oxygen we breathe. The results were published in Nature today.

    SLAC/LCLS

    Explosion of life

    When Earth formed about 4.5 billion years ago, the planet’s landscape was almost nothing like what it is today. Junko Yano, one of the authors of the study and a senior scientist at Berkeley Lab, describes it as “hellish.” Meteors sizzled through a carbon dioxide-rich atmosphere and volcanoes flooded the surface with magmatic seas.

    Over the next 2.5 billion years, water vapor accumulating in the air started to rain down and form oceans where the very first life appeared in the form of single-celled organisms. But it wasn’t until one of those specks of life mutated and developed the ability to harness light from the sun and turn it into energy, releasing oxygen molecules from water in the process, that Earth started to evolve into the planet it is today. This process, oxygenic photosynthesis, is considered one of nature’s crown jewels and has remained relatively unchanged in the more than 2 billion years since it emerged.

    “This one reaction made us as we are, as the world. Molecule by molecule, the planet was slowly enriched until, about 540 million years ago, it exploded with life,” said co-author Uwe Bergmann, a distinguished staff scientist at SLAC. “When it comes to questions about where we come from, this is one of the biggest.”

    A greener future

    Photosystem II is the workhorse responsible for using sunlight to break water down into its atomic components, unlocking hydrogen and oxygen. Until recently, it had only been possible to measure pieces of this process at extremely low temperatures. In a previous paper, the researchers used a new method to observe two steps of this water-splitting cycle [Nature]at the temperature at which it occurs in nature.

    Now the team has imaged all four intermediate states of the process at natural temperature and the finest level of detail yet. They also captured, for the first time, transitional moments between two of the states, giving them a sequence of six images of the process.

    The goal of the project, said co-author Jan Kern, a scientist at Berkeley Lab, is to piece together an atomic movie using many frames from the entire process, including the elusive transient state at the end that bonds oxygen atoms from two water molecules to produce oxygen molecules.

    “Studying this system gives us an opportunity to see how metals and proteins work together and how light controls such kinds of reactions,” said Vittal Yachandra, one of the authors of the study and a senior scientist at Berkeley Lab who has been working on Photosystem II for more than 35 years. “In addition to opening a window on the past, a better understanding of Photosystem II could unlock the door to a greener future, providing us with inspiration for artificial photosynthetic systems that produce clean and renewable energy from sunlight and water.”

    Sample assembly line

    For their experiments, the researchers grow what Kern described as a “thick green slush” of cyanobacteria — the very same ancient organisms that first developed the ability to photosynthesize — in a large vat that is constantly illuminated. They then harvest the cells for their samples.

    At LCLS, the samples are zapped with ultrafast pulses of X-rays [Science] to collect both X-ray crystallography and spectroscopy data to map how electrons flow in the oxygen-evolving complex of photosystem II. In crystallography, researchers use the way a crystal sample scatters X-rays to map its structure; in spectroscopy, they excite the atoms in a material to uncover information about its chemistry. This approach, combined with a new assembly-line sample transportation system [Nature Methods], allowed the researchers to narrow down the proposed mechanisms put forward by the research community over the years.

    Mapping the process

    Previously, the researchers were able to determine the room-temperature structure of two of the states at a resolution of 2.25 angstroms; one angstrom is about the diameter of a hydrogen atom. This allowed them to see the position of the heavy metal atoms, but left some questions about the exact positions of the lighter atoms, like oxygen. In this paper, they were able to improve the resolution even further, to 2 angstroms, which enabled them to start seeing the position of lighter atoms more clearly, as well as draw a more detailed map of the chemical structure of the metal catalytic center in the complex where water is split.

    This center, called the oxygen-evolving complex, is a cluster of four manganese atoms and one calcium atom bridged with oxygen atoms. It cycles through the four stable oxidation states, S0-S3, when exposed to sunlight. On a baseball field, S0 would be the start of the game when a player on home base is ready to go to bat. S1-S3 would be players on first, second, and third. Every time a batter connects with a ball, or the complex absorbs a photon of sunlight, the player on the field advances one base. When the fourth ball is hit, the player slides into home, scoring a run or, in the case of Photosystem II, releasing breathable oxygen.

    The researchers were able to snap action shots of how the structure of the complex transformed at every base, which would not have been possible without their technique. A second set of data allowed them to map the exact position of the system in each image, confirming that they had in fact imaged the states they were aiming for.

    1
    In photosystem II, the water-splitting center cycles through four stable states, S0-S3. On a baseball field, S0 would be the start of the game when a batter on home base is ready to hit. S1-S3 would be players waiting on first, second, and third. The center gets bumped up to the next state every time it absorbs a photon of sunlight, just like how a player on the field advances one base every time a batter connects with a ball. When the fourth ball is hit, the player slides into home, scoring a run or, in the case of Photosystem II, releasing the oxygen we breathe. (Gregory Stewart/SLAC National Accelerator Laboratory)

    Sliding into home

    But there are many other things going on throughout this process, as well as moments between states when the player is making a break for the next base, that are a bit harder to catch. One of the most significant aspects of this paper, Yano said, is that they were able to image two moments in between S2 and S3. In upcoming experiments, the researchers hope to use the same technique to image more of these in-between states, including the mad dash for home — the transient state, or S4, where two atoms of oxygen bond together — providing information about the chemistry of the reaction that is vital to mimicking this process in artificial systems.

    “The entire cycle takes nearly two milliseconds to complete,” Kern said. “Our dream is to capture 50-microsecond steps throughout the full cycle, each of them with the highest resolution possible, to create this atomic movie of the entire process.”

    Although they still have a way to go, the researchers said that these results provide a path forward, both in unveiling the mysteries of how photosynthesis works and in offering a blueprint for artificial sources of renewable energy.

    “It’s been a learning process,” said SLAC scientist and co-author Roberto Alonso-Mori. “Over the last seven years we’ve worked with our collaborators to reinvent key aspects of our techniques. We’ve been slowly chipping away at this question and these results are a big step forward.”

    In addition to SLAC and Berkeley Lab, the collaboration includes researchers from Umeå University, Uppsala University, Humboldt University of Berlin, the University of California, Berkeley, the University of California, San Francisco and the Diamond Light Source.

    Key components of this work were carried out at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), Berkeley Lab’s Advanced Light Source (ALS) and Argonne National Laboratory’s Advanced Photon Source (APS). LCLS, SSRL, APS, and ALS are DOE Office of Science user facilities. This work was supported by the DOE Office of Science and the National Institutes of Health, among other funding agencies.

    SLAC/SSRL

    LBNL/ALS

    ANL APS

    See the full article here .


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    Please help promote STEM in your local schools.

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    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.

     
  • richardmitnick 11:39 am on November 7, 2018 Permalink | Reply
    Tags: , , , , Dancing atoms in perovskite materials provide insight into how solar cells work, , , SLAC National Accelerator Laboratory,   

    From SLAC National Accelerator Lab: “Dancing atoms in perovskite materials provide insight into how solar cells work” 

    From SLAC National Accelerator Lab

    November 6, 2018
    Ali Sundermier

    1
    When the researchers scattered neutrons off the perovskite material (red beam) they were able to measure the energy the neutrons lost or gained (white and blue lines). Using this information, they were able to see the structure and motion of the atoms and molecules within the material (arrangement of blue and purple spheres). (Greg Stewart/SLAC National Accelerator Laboratory)

    A new study is a step forward in understanding why perovskite materials work so well in energy devices and potentially leads the way toward a theorized “hot” technology that would significantly improve the efficiency of today’s solar cells.

    A closer look at materials that make up conventional solar cells reveals a nearly rigid arrangement of atoms with little movement. But in hybrid perovskites, a promising class of solar cell materials, the arrangements are more flexible and atoms dance wildly around, an effect that impacts the performance of the solar cells but has been difficult to measure.

    In a paper published in the PNAS, an international team of researchers led by the U.S. Department of Energy’s SLAC National Accelerator Laboratory has developed a new understanding of those wild dances and how they affect the functioning of perovskite materials. The results could explain why perovskite solar cells are so efficient and aid the quest to design hot-carrier solar cells, a theorized technology that would almost double the efficiency limits of conventional solar cells by converting more sunlight into usable electrical energy.

    Piece of the puzzle

    Perovskite solar cells, which can be produced at room temperature, offer a less expensive and potentially better performing alternative to conventional solar cell materials like silicon, which have to be manufactured at extremely high temperatures to eliminate defects. But a lack of understanding about what makes perovskite materials so efficient at converting sunlight into electricity has been a major hurdle to producing even higher efficiency perovskite solar cells.

    “It’s really only been over the last five or six years that people have developed this intense interest in solar perovskite materials,” says Mike Toney, a distinguished staff scientist at SLAC’s Stanford Synchrotron Radiation Light Source (SSRL) who led the study.

    SLAC/SSRL

    “As a consequence, a lot of the foundational knowledge about what makes the materials work is missing. In this research, we provided an important piece of this puzzle by showing what sets them apart from more conventional solar cell materials. This provides us with scientific underpinnings that will allow us to start engineering these materials in a rational way.”

    Keeping it hot

    When sunlight hits a solar cell, some of the energy can be used to kick electrons in the material up to higher energy states. These higher-energy electrons are funneled out of the material, producing electricity.

    But before this happens, a majority of the sun’s energy is lost to heat with some fraction also lost during the extraction of usable energy or due to inefficient light collection. In many conventional solar cells, such as those made with silicon, acoustic phonons – a sort of sound wave that propagates through material – are the primary way that this heat is carried through the material. The energy lost by the electron as heat limits the efficiency of the solar cell.

    In this study, theorists from the United Kingdom, led by Imperial College Professor Aron Walsh and electronic structure theorists Jonathan Skelton and Jarvist Frost, provided a theoretical framework for interpreting the experimental results. They predicted that acoustic phonons traveling through perovskites would have short lifetimes as a result of the flexible arrangements of dancing atoms and molecules in the material.

    Stanford chemists Hema Karunadasa and Ian Smith were able to grow the large, specialized single crystals that were essential for this work. With the help of Peter Gehring, a physicist at the NIST Center for Neutron Research, the team scattered neutrons off these perovskite single crystals in a way that allowed them to retrace the motion of the atoms and molecules within the material. This allowed them to precisely measure the lifetime of the acoustic phonons.

    The research team found that in perovskites, acoustic phonons are incredibly short-lived, surviving for only 10 to 20 trillionths of a second. Without these phonons trucking heat through the material, the electrons might stay hot and hold onto their energy as they’re pulled out of the material. Harnessing this effect could potentially lead to hot-carrier solar cells with efficiencies that are nearly twice as high as conventional solar cells.

    In addition, this phenomenon could explain how perovskite solar cells work so well despite the material being riddled with defects that would trap electrons and dampen performance in other materials.

    “Since phonons in perovskites don’t travel very far, they end up heating the area surrounding the electrons, which might provide the boost the electrons need to escape the traps and continue on their merry way,” Toney says.

    Transforming energy production

    To follow up on this study, researchers at the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory will investigate this phenomenon in more complicated perovskite materials that are shown to be more efficient in energy devices. They would like to figure out how changing the chemical make-up of the material affects acoustic phonon lifetimes.

    “We need to fundamentally transform our energy system as quickly as possible,” says Aryeh Gold-Parker, who co-led the study as a PhD student at Stanford University and SLAC. “As we move toward a low-carbon future, a very important piece is having cheap and efficient solar cells. The hope in perovskites is that they’ll lead to commercial solar panels that are more efficient and cheaper than the ones on the market today.”

    The research team also included scientists from NIST; the University of Bath and Kings College London, both in the UK; and Yonsei University in Korea.

    SSRL is a DOE Office of Science user facility. This work was supported by the DOE’s Office of Science and the Solar Energy Technologies Office; the Engineering and Physical Sciences Research Council; the Royal Society; and the Leverhulme Trust.

    See the full article here .


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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.

     
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