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  • richardmitnick 11:05 am on May 16, 2019 Permalink | Reply
    Tags: Laser Technology, , Phonon lasers, , The optical tweezer   

    From The Conversation: “Laser of sound promises to measure extremely tiny phenomena” 

    Conversation
    From The Conversation

    May 16, 2019
    Mishkat Bhattacharya
    Associate Professor of Physics and Astronomy, Rochester Institute of Technology

    Nick Vamivakas
    Associate Professor of Quantum Optics & Quantum Physics, University of Rochester

    1
    The crests (bright) and troughs (dark) of waves spread out after they were produced. The picture applies to both light and sound waves. Titima Ongkantong

    Most people are familiar with optical lasers through their experience with laser pointers. But what about a laser made from sound waves?

    What makes optical laser light different from a light bulb or the sun is that all the light waves emerging from it are moving in the same direction and are pretty much in perfect step with each other. This is why the beam coming out of the laser pointer does not spread out in all directions.

    In contrast, rays from the sun and light from a light bulb go in every direction. This is a good thing because otherwise it would be difficult to illuminate a room; or worse still, the Earth might not receive any sunlight. But keeping the light waves in step – physicists call it coherence – is what makes a laser special. Sound is also made of waves.

    Recently there has been considerable scientific interest in creating phonon lasers in which the oscillations of light waves are replaced by the vibrations of a tiny solid particle. By generating sound waves that are perfectly synchronized, we figured out how to make a phonon laser – or a “laser for sound.”

    In work we recently published in the journal Nature Photonics, we have constructed our phonon laser using the oscillations of a particle – about a hundred nanometers in diameter – levitated using an optical tweezer.

    2
    A red laser beam from a high-power lab laser. Doug McLean/Shutterstock.com

    Waves in sync

    An optical tweezer is simply a laser beam which goes through a lens and traps a nanoparticle in midair, like the tractor beam in “Star Wars.” The nanoparticle does not stay still. It swings back and forth like a pendulum, along the direction of the trapping beam.

    Since the nanoparticle is not clamped to a mechanical support or tethered to a substrate, it is very well isolated from its surrounding environment. This enables physicists like us to use it for sensing weak electric, magnetic and gravitational forces whose effects would be otherwise obscured.

    To improve the sensing capability, we slow or “cool” the nanoparticle motion. This is done by measuring the position of the particle as it changes with time. We then feed that information back into a computer that controls the power in the trapping beam. Varying the trapping power allows us to constrain the particle so that it slows down. This setup has been used by several groups around the world in applications that have nothing to do with sound lasers. We then took a crucial step that makes our device unique and is essential for building a phonon laser.

    This involved modulating the trapping beam to make the nanoparticle oscillate faster, yielding laser-like behavior: The mechanical vibrations of the nanoparticle produced synchronized sound waves, or a phonon laser.

    The phonon laser is a series of synchronized sound waves. A detector can monitor the phonon laser and identify changes in the pattern of these sound waves that reveal the presence of a gravitational or magnetic force.

    It might appear that the particle becomes less sensitive because it is oscillating faster, but the effect of having all the oscillations in sync actually overcomes that effect and makes it a more sensitive instrument.

    3
    An artist’s depiction of optical tweezers (pink) holding the nanoparticle in midair, while allowing it to move back and forth and create sound waves. A. Nick Vamivakas and Michael Osadciw, University of Rochester illustration, CC BY-SA

    Possible applications

    It is clear that optical lasers are very useful. They carry information over optical fiber cables, read bar codes in supermarkets and run the atomic clocks which are essential for GPS.

    We originally developed the phonon laser as a tool for detecting weak electric, magnetic and gravitational fields, which affect the sound waves in a way we can detect. But we hope that others will find new uses for this technology in communication and sensing, such as the mass of very small molecules.

    On the fundamental side, our work leverages current interest in testing quantum physics theories about the behavior of collections of billion atoms – roughly the number contained in our nanoparticle. Lasers are also the starting point for creating exotic quantum states like the famous Schrodinger cat state, which allows an object to be in two places at the same time. Of course the most exciting uses of the optical tweezer phonon laser may well be ones we cannot currently foresee.

    See the full article here .

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    The Conversation launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

     
  • richardmitnick 10:45 am on May 14, 2019 Permalink | Reply
    Tags: , “Tractor beam”, “What I want to do is understand these complex biological processes using the laws and tools of physics.”, , For Lee these multidisciplinary projects reflect the essence of his chosen calling: biophysics., Laser Technology, Lee is also able to generate ultra-high resolution images of neuron development for research aimed at finding improved treatments for degenerative diseases., Lee is principal investigator on a $1.5 million Department of Energy project—with his Rutgers team (Shishir Chundawat; Eric Lam; and Laura Fabris), Lee says “I became determined to understand biological processes through the simple universal and beautiful principles of physics.”, Lee’s device allows him to examine live plant cells in “unprecedented molecular detail” for a project that could help break new ground in the development of biofuels., , Rutgers physicist Sang-Hyuk Lee, , The development of optical tweezers goes back decades., The instrument uses a focused laser beam to trap hold and move microscopic objects that previously had been too tiny to touch.   

    From Rutgers University: “Once a Dream of Science Fiction, a Laser Tweezer Helps a Rutgers Biophysicist Boldly Go Where Molecules Move” 

    Rutgers smaller
    Our Great Seal.

    From Rutgers University

    THIS POST IS DEDICATED TO L.Z. OF RUTGERS UNIVERSITY PHYSICS AND H.P.

    5.14.19
    John Chadwick

    Sang-Hyuk Lee integrates two Nobel Prize-winning innovations.

    1
    Sang-Hyuk Lee

    “An old dream of science fiction,” the Nobel Prize Committee said in its praise of the invention.

    Like the “tractor beam” of vintage Star Trek episodes others observed.

    The futuristic device they’re talking about is optical tweezers.

    Invented by Arthur Ashkin, one of three pioneers in laser physics to win the 2018 Nobel Prize in Physics, the instrument uses a focused laser beam to trap, hold, and move microscopic objects that previously had been too tiny to touch.

    2
    Sang-Hyuk Lee with Nobel Prize winning device, “tractor beam”

    The revolutionary tool is essential to the work of a Rutgers professor who recently brought the technology to the university. Sang-Hyuk Lee, of the Department of Physics and Astronomy, School of Arts and Sciences, has also added advanced microscopy techniques to make the device capable of examining and visualizing molecules at the tiniest level.

    He is using the innovative instrument for several federally-funded research projects that combine elements of physics and biology.

    Lee’s device allows him to examine live plant cells in “unprecedented molecular detail” for a project that could help break new ground in the development of biofuels. He is also able to generate ultra-high resolution images of neuron development for research aimed at finding improved treatments for degenerative diseases.

    For Lee, these multidisciplinary projects reflect the essence of his chosen calling: biophysics.

    “A biophysicist is bridging the gap between two worlds,” he says. “What I want to do is understand these complex biological processes using the laws and tools of physics.”

    The optical tweezers provide him with the perfect tool for that mission.

    The development of optical tweezers goes back decades. Ashkin, who was the head of laser science at Bell Labs in Holmdel, N.J., from 1963 to 1987, set out to build an instrument capable of grabbing particles, atoms, molecules, and living cells with “laser beam fingers,” according to NobelPrize.org. A major breakthrough came in 1987, when Ashkin succeeded in capturing living bacteria without harming them.

    Optical tweezers can move and manipulate particles smaller than a micron. A single strand of human hair is about 75 microns in width.

    Lee became intrigued by the technology while working on his doctorate at New York University under David Grier, a physicist who created more complex versions of optical tweezers by adding digital holography. Lee was also influenced by, and later worked as a post-doc for Carlos Bustamante, a biophysicist at the University of California, Berkeley, who used optical tweezers to stretch a single DNA molecule to measure the force holding it together.

    “His work completely changed my views of biology,” Lee says. “I became determined to understand biological processes through the simple, universal, and beautiful principles of physics.”

    After arriving at Rutgers in 2015, Lee designed and built the mammoth instrument that’s now housed within a glass enclosure in a laboratory at the Institute for Quantitative Biomedicine on Busch Campus. The device is far more versatile than commercially available models because Lee integrated a number of advanced optics techniques, including use of multiple lasers, and a technology known as super resolution fluorescence microscopy, which won the 2014 Nobel in Chemistry for producing higher resolution image than what conventional light microscopes could achieve.

    “So, we can get super-resolution image of intra-cellular structures while we exert measure force on individual molecules,” he says. “Our instrument is a one-of-a-kind, home-built microscope.”

    Physics Chair Robert Bartynski agrees. And he said the application of laser physics to contemporary problems in biology is opening an exciting new chapter in interdisciplinary science.

    4
    Nobel Prize winning device, “Tractor Beam”

    “The optical tweezers technology that Sang-Hyuk has developed at Rutgers give us a singular capability that expands our understanding of how biomolecules move in and around cells to carry out critical tasks,” Bartynski said. “The ability to manipulate and visualize individual molecules with these advanced optical techniques, will give unprecedented insights into the physics behind key biological processes

    Lee is principal investigator on a $1.5 million Department of Energy project—with his Rutgers team (Shishir Chundawat, Eric Lam and Laura Fabris), along with collaborators at Vanderbilt University and Oak Ridge National Laboratory—that seeks to understand how cell walls in plants are formed—knowledge that may accelerate the development of genetically engineered crops for use as renewable fuels and have broad impact on molecular and cellular biology fields in general.

    He is also involved in a National Science Foundation-funded project—with Nada N. Boustany, a Rutgers professor of biomedical engineering serving as principal investigator—that could help improve treatments for degenerative neural diseases or nerve injury due to trauma.

    Lee describes his research focus as “single-molecule biophysics,” the study of individual biomolecules to understand how they carry out their functions in living cells.

    “The application to important biology problems is still in its infancy,” he says. “This emerging field has tremendous potential.

    See the full article here .


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    rutgers-campus

    Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

    Founded in 1766, Rutgers teaches across the full educational spectrum: preschool to precollege; undergraduate to graduate; postdoctoral fellowships to residencies; and continuing education for professional and personal advancement.

    As a ’67 graduate of University college, second in my class, I am proud to be a member of

    Alpha Sigma Lamda, National Honor Society of non-tradional students.

     
  • richardmitnick 8:01 am on May 10, 2019 Permalink | Reply
    Tags: "Q&A: SLAC/Stanford researchers prepare for a new quantum revolution", , , , , Laser Technology, , , , , Quantum squeezing, , 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.

    1
    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.

    2
    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.

    3
    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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    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., Laser Technology, Researchers have made the first high-definition “movie” of ring-shaped molecules breaking open in response to light, , , 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

    1
    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.

    3
    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.

    4
    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.

    3
    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 .


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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 8:46 am on April 11, 2019 Permalink | Reply
    Tags: Laser Technology, New system-Line VISAR was developed at Lawrence Livermore Labs, , , VISAR- Velocity Interferometer System for Any Reflector, Z Machine   

    From Sandia Lab: “New device in Z machine measures power for nuclear fusion” 

    From Sandia Lab

    April 10, 2019
    Neal Singer
    nsinger@sandia.gov
    505-845-7078

    Sandia Z machine

    1
    Sandia National Laboratories mechanical technologist Kenny Velasquez makes adjustments during the final installation of the hardware inside the chamber of the Z Line VISAR in preparation for the commissioning shot at Z machine in December 2018. (Photo by Michael Jones)

    If you’re chasing the elusive goal of nuclear fusion and think you need a bigger reactor to do the job, you first might want to know precisely how much input energy emerging from the wall plug is making it to the heart of your machine.

    If somewhere during that journey you could reduce internal losses, you might not need a machine as big as you thought.

    To better determine energy leaks at Sandia’s powerful Z machine — where remarkable gains in fusion outputs have occurred over the last two and a half decades, including a tripling of output in 2018 — a joint team from Sandia and Lawrence Livermore national laboratories have installed an upgraded laser diagnostic system.

    The quest to accurately understand how much power makes it into Z’s fusion reaction has become more pressing as Z moves into producing the huge number of neutrons that now are only a factor of 40 below the milestone where energy output equals energy input, a desirable state known as scientific break-even. The Z machine’s exceptionally large currents — about 26 megamperes — directly compress fusion fuel to the extreme conditions needed for fusion reactions to occur.

    Laboratory fusion reactions — the joining of the nuclei of atoms — have both civilian and military purposes. Data used in supercomputer simulations offer information about nuclear weapons without underground tests, an environmental, financial and political plus. The more powerful the reaction, the better the data.

    And, over the longer term, the vision of achieving an extraordinarily high-yield, stable and relatively clean energy source is the ambition of many researchers in the fusion field.

    A little help from our lasers

    The laser diagnostic system that Sandia developed to help achieve these improvements was originally called VISAR, for Velocity Interferometer System for Any Reflector. VISAR takes information about available power gathered from an area the size of a pencil point.

    The new system, called Line VISAR, was developed later at Lawrence Livermore. It analyzes information gleaned within the larger scope made available through a line, instead of a point, source.

    Both innovations bounce a laser beam off a moving target at the center of Z. But there’s a big difference between the two techniques.

    VISAR uses a fiber cable to send a laser pulse from a stable outside location to the center of the machine. There, the pulse is reflected from a point on a piece of metal about the size of a dime called a flyer plate. The flyer plate, acting like a mirror, bounces the laser signal back along the cable. But because the flyer plate is propelled forward by Z’s huge electromagnetic pulse by a distance of roughly a millimeter in a few hundred nanoseconds, the returning pulse is slightly out of phase with the input version.

    Measuring the phase difference between the two waves determines the velocity achieved by the flyer plate in that period. That velocity, combined mathematically with the mass of the flyer plate, is then used to estimate how much energy has driven the plate. Because the plate sits at the heart of the machine, this figure is nearly identical to the energy causing fusion reactions at the center of the machine. This observation was the objective of VISAR.

    But the point target could not account for distortions in the flyer plate itself caused by the enormous pressures created by the electromagnetic field driving its motion.

    Try optics

    Lawrence Livermore’s improvement to the device, now installed at Z, was to send a laser beam along an optical beam path instead of a fiber cable. Passing through lenses and bouncing off mirrors, Line VISAR returns a visual picture of the pulse hitting the entire flyer plate, rather than returning a single electrical signal from a single point on the flyer plate.

    Researchers study the contrast between the phase-changed Line VISAR picture and an unchanged reference picture and then sliced along a line so that an ultra-high-speed movie with a reduced but workable amount of data can be recorded. By analyzing the movie, which shows the expansion and deformation of the flyer plate along the line, researchers uncover a truer picture of the amount of energy available at the heart of the machine.

    “Because you have spatial resolution, it tells you more precisely where current loss occurs,” said Clayton Myers, who’s in charge of experiments at Z using Line VISAR.

    Sandia and Lawrence Livermore technicians modified the Line VISAR to work at Z, where everything busily happens at the heart of a machine that shakes coffee cups in buildings several hundred feet away when it fires, compared with the relative calm of the firings at the National Ignition Facility at Lawrence Livermore, where banks of lasers sit removed from the otherwise tranquil sphere in which firings take place.


    National Ignition Facility at LLNL

    “The Sandia team was tasked with integrating the various Line VISAR components into the existing infrastructure of the Z machine,” Myers said. “This meant, among other things, engineering a 50-meter beam transport system that provided a buffer between the instrument and its Z target.”

    Nevertheless, the last optic of Line VISAR at Z must be replaced for every shot because it faces near-instant destruction from the energy delivered as Z fires.

    How does the new detection system work?

    “Wonderfully,” said Myers. “I can hardly believe the precision of the data we’re getting.”

    See the full article here .


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    Sandia Campus
    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 8:57 am on March 31, 2019 Permalink | Reply
    Tags: "Physicists predict a way to squeeze light from the vacuum of empty space", , Laser Technology, ,   

    From Science Magazine: “Physicists predict a way to squeeze light from the vacuum of empty space” 

    AAAS
    From Science Magazine

    Mar. 29, 2019
    Adrian Cho

    1
    Charged particles zipping through water in a nuclear reactor produce Cherenkov radiation. Credit: Argonne National Laboratory/Wikimedia commons (CC BY-SA 2.0)

    2
    Cherenkov Radiation. Credit Nuclear-Power.net

    Talk about getting something for nothing. Physicists predict that just by shooting charged particles through an electromagnetic field, it should be possible to generate light from the empty vacuum. In principle, the effect could provide a new way to test the fundamental theory of electricity and magnetism, known as quantum electrodynamics, the most precise theory in all of science. In practice, spotting the effect would require lasers and particle accelerators far more powerful than any that exist now.

    “I’m quite confident about [the prediction] simply because it combines effects that we understand pretty well,” says Ben King, a laser-particle physicist at the University of Plymouth in the United Kingdom, who was not involved in the new analysis. Still, he says, an experimental demonstration “is something for the future.”

    Physicists have long known that energetic charged particles can radiate light when they zip through a transparent medium such as water or a gas. In the medium, light travels slower than it does in empty space, allowing a particle such as an electron or proton to potentially fly faster than light. When that happens, the particle generates an electromagnetic shockwave, just as a supersonic jet creates a shockwave in air. But whereas the jet’s shockwave creates a sonic boom, the electromagnetic shockwave creates light called Cherenkov radiation. That effect causes the water in the cores of nuclear reactors to glow blue, and it’s been used to make particle detectors.

    However, it should be possible to ditch the material and produce Cherenkov light straight from the vacuum, predict Dino Jaroszynski, a physicist at the University of Strathclyde in Glasgow, U.K., and colleagues. The trick is to shoot the particles through an extremely intense electromagnetic field instead.

    According to quantum theory, the vacuum roils with particle-antiparticle pairs flitting in and out of existence too quickly to observe directly. The application of a strong electromagnetic field can polarize those pairs, however, pushing positive and negative particles in opposite directions. Passing photons then interact with the not-quite-there pairs so that the polarized vacuum acts a bit like a transparent medium in which light travels slightly slower than in an ordinary vacuum, Jaroszynski and colleagues calculate.

    Putting two and two together, an energetic charged particle passing through a sufficiently strong electromagnetic field should produce Cherenkov radiation, the team reports in a paper in press at Physical Review Letters. Others had suggested vacuum Cherenkov radiation should exist in certain situations, but the new work takes a more fundamental and all-encompassing approach, says Adam Noble, a physicist at Strathclyde.

    Spotting vacuum Cherenkov radiation would be tough. First, the polarized vacuum slows light by a tiny amount. The electromagnetic fields in the strongest pulses of laser light reduce light’s speed by about a millionth of a percent, Noble estimates. In comparison, water reduces light’s speed by 25%. Second, charged particles in an electromagnetic field spiral and emit another kind of light called synchroton radiation that, in most circumstances, should swamp the Cherenkov radiation.

    Still, in principle, it should be possible to produce vacuum Cherenkov radiation by firing high-energy electrons or protons through overlapping pulses from the world’s highest intensity lasers, which can pack a petawatt, or 1015 watts, of power. However, Jaroszynski and colleagues calculate that in such fields, even particles from the world’s highest energy accelerators would produce much more synchrotron radiation than Cherenkov radiation.

    Space could be another place to look for the effect. Extremely high-energy protons passing through the intense magnetic field of a spinning neutron star—also known as a pulsar—should produce more Cherenkov radiation than synchrotron radiation, the researchers predict. However, pulsars don’t produce many high-energy protons, says Alice Harding, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the particles that do enter a pulsar’s magnetic field should quickly lose energy and spiral instead of zipping across it. “I’m not terribly excited about the prospect for pulsars,” she says.

    Nevertheless, King says, experimenters might see the effect someday. Physicists in Europe are building a trio of 10 petawatt lasers in Romania, Hungary, and the Czech Republic, and their counterparts in China are developing a 100 petawatt laser.

    2
    A laser in Shanghai, China, has set power records yet fits on tabletops. Credit: KAN ZHAN

    Scientists are also trying to create compact laser-driven accelerators that might produce highly energetic particle beams far more cheaply. If those things come together, physicists might be able to spot vacuum Cherenkov radiation, King says.

    Others are devising different ways to use high-power lasers to probe the polarized vacuum. The ultimate aim of such work is to test quantum electrodynamics in new ways, King says. Experimenters have confirmed the theory’s predictions are accurate to within a few parts in a billion. But the theory has never been tested in the realm of extremely strong fields, King says, and such tests are now becoming possible. “The future of this field is quite exciting.”

    See the full article here .


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  • richardmitnick 9:48 am on March 30, 2019 Permalink | Reply
    Tags: , Cubits, Laser Technology, , ,   

    From Pennsylvania State University: “Extremely accurate measurements of atom states for quantum computing” 

    Penn State Bloc

    From Pennsylvania State University

    25 March 2019

    David Weiss
    dsweiss@phys.psu.edu
    (814) 863-3076

    Sam Sholtis
    samsholtis@psu.edu
    814-865-1390

    1
    New method allows extremely accurate measurement of the quantum state of atomic qubits—the basic unit of information in quantum computers. Atoms are initially sorted to fill two 5×5 planes (dashed yellow grid marks their initial locations). After the first images are taken, microwaves are used to put the atoms into equal superpositions of two spin states. A shift to the left or right in the final images corresponds to detection in one spin state or the other. Associated square patterns denote atom locations (cyan: initial position, orange and blue: shifted positions). Credit: Weiss Laboratory, Penn State

    A new method allows the quantum state of atomic “qubits”—the basic unit of information in quantum computers—to be measured with twenty times less error than was previously possible, without losing any atoms. Accurately measuring qubit states, which are analogous to the one or zero states of bits in traditional computing, is a vital step in the development of quantum computers. A paper describing the method by researchers at Penn State appears March 25, 2019 in the journal Nature Physics.

    “We are working to develop a quantum computer that uses a three-dimensional array of laser-cooled and trapped cesium atoms as qubits,” said David Weiss, professor of physics at Penn State and the leader of the research team. “Because of how quantum mechanics works, the atomic qubits can exist in a ‘superposition’ of two states, which means they can be, in a sense, in both states simultaneously. To read out the result of a quantum computation, it is necessary to perform a measurement on each atom. Each measurement finds each atom in only one of its two possible states. The relative probability of the two results depends on the superposition state before the measurement.”

    To measure qubit states, the team first uses lasers to cool and trap about 160 atoms in a three-dimensional lattice with X, Y, and Z axes. Initially, the lasers trap all of the atoms identically, regardless of their quantum state. The researchers then rotate the polarization of one of the laser beams that creates the X lattice, which spatially shifts atoms in one qubit state to the left and atoms in the other qubit state to the right. If an atom starts in a superposition of the two qubit states, it ends up in a superposition of having moved to the left and having moved to the right. They then switch to an X lattice with a smaller lattice spacing, which tightly traps the atoms in their new superposition of shifted positions. When light is then scattered from each atom to observe where it is, each atom is either found shifted left or shifted right, with a probability that depends on its initial state. The measurement of each atom’s position is equivalent to a measurement of each atom’s initial qubit state.

    “Mapping internal states onto spatial locations goes a long way towards making this an ideal measurement,” said Weiss. “Another advantage of our approach is that the measurements do not cause the loss of any of the atoms we are measuring, which is a limiting factor in many previous methods.”

    The team determined the accuracy of their new method by loading their lattices with atoms in either one or the other qubit states and performing the measurement. They were able to accurately measure atom states with a fidelity of 0.9994, meaning that there were only six errors in 10,000 measurements, a twenty-fold improvement on previous methods. Additionally, the error rate was not impacted by the number of qubits that the team measured in each experiment and because there was no loss of atoms, the atoms could be reused in a quantum computer to perform the next calculation.

    “Our method is similar to the Stern-Gerlach experiment from 1922—an experiment that is integral to the history of quantum physics,” said Weiss. “In the experiment, a beam of silver atoms was passed through a magnetic field gradient with their north poles aligned perpendicular to the gradient. When Stern and Gerlach saw half the atoms deflect up and half down, it confirmed the idea of quantum superposition, one of the defining aspects of quantum mechanics. In our experiment, we also map the internal quantum states of atoms onto positions, but we can do it on an atom by atom basis. Of course, we do not need to test this aspect of quantum mechanics, we can just use it.”

    In addition to Weiss, the research team at Penn State includes Tsung-Yao Wu, Aishwarya Kumar, and Felipe Giraldo. The research was supported by the U.S. National Science Foundation.

    See the full article here .

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    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

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  • richardmitnick 8:43 am on March 29, 2019 Permalink | Reply
    Tags: , , Laser Technology, , SUSY-Supersymmetry   

    From CERN Courier: “First light for Supersymmetry” 


    From CERN Courier

    8 March 2019

    1
    SUSY engineering

    Ideas from supersymmetry have been used to address a longstanding challenge in optics – how to suppress unwanted spatial modes that limit the beam quality of high-power lasers. Mercedeh Khajavikhan at the University of Central Florida in the US and colleagues have created a first supersymmetric laser array, paving the way towards new schemes for scaling up the radiance of integrated semiconductor lasers.

    Supersymmetry (SUSY) is a possible additional symmetry of space–time that would enable bosonic and fermionic degrees of freedom to be “rotated” between one another. Devised in the 1970s in the context of particle physics, it suggests the existence of a mirror-world of supersymmetric particles and promises a unified description of all fundamental interactions. “Even though the full ramification of SUSY in high-energy physics is still a matter of debate that awaits experimental validation, supersymmetric techniques have already found their way into low-energy physics, condensed matter, statistical mechanics, nonlinear dynamics and soliton theory as well as in stochastic processes and BCS-type theories, to mention a few,” write Khajavikhan and collaborators in Science.

    The team applied the SUSY formalism first proposed by Ed Witten of the Institute for Advanced Study in Princeton to force a semiconductor laser array to operate exclusively in its fundamental transverse mode. In contrast to previous schemes developed to achieve this, such as common antenna-feedback methods, SUSY introduces a global and systematic method that applies to any type of integrated laser array, explains Khajavikhan. “Now that the proof of concept has been demonstrated, we are poised to develop high-power electrically pumped laser arrays based on a SUSY design. This can be applicable to various wavelengths, ranging from visible to mid-infrared lasers.”

    To demonstrate the concept, the Florida-based team paired the unwanted modes of the main laser array (comprising five coupled ridge-waveguide cavities etched from quantum wells on an InP wafer) with a lossy superpartner (an array of four waveguides left unpumped). Optical strategies were used to build a superpartner index profile with propagation constants matching those of the four higher-order modes associated with the main array, and the performance of the SUSY laser was assessed using a custom-made optical setup. The results indicated that the existence of an unbroken SUSY phase (in conjunction with a judicious pumping of the laser array) can promote the in-phase fundamental mode and produce high-radiance emission.

    “This is a remarkable example of how a fundamental idea such as SUSY may have a practical application, here increasing the power of lasers,” says SUSY pioneer John Ellis of King’s College London. “The discovery of fundamental SUSY still eludes us, but SUSY engineering has now arrived.”

    See the full article here .


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 10:14 am on March 18, 2019 Permalink | Reply
    Tags: "Exotic “second sound” phenomenon observed in pencil lead", , , Laser Technology, , , There’s good reason to believe that second sound might be more pronounced in graphene even at room temperature., Transient thermal grating   

    From MIT News: “Exotic “second sound” phenomenon observed in pencil lead” 

    MIT News
    MIT Widget

    From MIT News

    March 14, 2019
    Jennifer Chu

    1
    Researchers find evidence that heat moves through graphite similar to the way sound moves through air. Image: Christine Daniloff

    At relatively balmy temperatures, heat behaves like sound when moving through graphite, study reports.

    The next time you set a kettle to boil, consider this scenario: After turning the burner off, instead of staying hot and slowly warming the surrounding kitchen and stove, the kettle quickly cools to room temperature and its heat hurtles away in the form of a boiling-hot wave.

    We know heat doesn’t behave this way in our day-to-day surroundings. But now MIT researchers have observed this seemingly implausible mode of heat transport, known as “second sound,” in a rather commonplace material: graphite — the stuff of pencil lead.

    At temperatures of 120 kelvin, or -240 degrees Fahrenheit, they saw clear signs that heat can travel through graphite in a wavelike motion. Points that were originally warm are left instantly cold, as the heat moves across the material at close to the speed of sound. The behavior resembles the wavelike way in which sound travels through air, so scientists have dubbed this exotic mode of heat transport “second sound.”

    The new results represent the highest temperature at which scientists have observed second sound. What’s more, graphite is a commercially available material, in contrast to more pure, hard-to-control materials that have exhibited second sound at 20 K, (-420 F) — temperatures that would be far too cold to run any practical applications.

    The discovery, published today in Science, suggests that graphite, and perhaps its high-performance relative, graphene, may efficiently remove heat in microelectronic devices in a way that was previously unrecognized.

    “There’s a huge push to make things smaller and denser for devices like our computers and electronics, and thermal management becomes more difficult at these scales,” says Keith Nelson, the Haslam and Dewey Professor of Chemistry at MIT. “There’s good reason to believe that second sound might be more pronounced in graphene, even at room temperature. If it turns out graphene can efficiently remove heat as waves, that would certainly be wonderful.”

    The result came out of a long-running interdisciplinary collaboration between Nelson’s research group and that of Gang Chen, the Carl Richard Soderberg Professor of Mechanical Engineering and Power Engineering. MIT co-authors on the paper are lead authors Sam Huberman and Ryan Duncan, Ke Chen, Bai Song, Vazrik Chiloyan, Zhiwei Ding, and Alexei Maznev.

    “In the express lane”

    Normally, heat travels through crystals in a diffusive manner, carried by “phonons,” or packets of acoustic vibrational energy. The microscopic structure of any crystalline solid is a lattice of atoms that vibrate as heat moves through the material. These lattice vibrations, the phonons, ultimately carry heat away, diffusing it from its source, though that source remains the warmest region, much like a kettle gradually cooling on a stove.

    The kettle remains the warmest spot because as heat is carried away by molecules in the air, these molecules are constantly scattered in every direction, including back toward the kettle. This “back-scattering” occurs for phonons as well, keeping the original heated region of a solid the warmest spot even as heat diffuses away.

    However, in materials that exhibit second sound, this back-scattering is heavily suppressed. Phonons instead conserve momentum and hurtle away en masse, and the heat stored in the phonons is carried as a wave. Thus, the point that was originally heated is almost instantly cooled, at close to the speed of sound.

    Previous theoretical work in Chen’s group had suggested that, within a range of temperatures, phonons in graphene may interact predominately in a momentum-conserving fashion, indicating that graphene may exhibit second sound. Last year, Huberman, a member of Chen’s lab, was curious whether this might be true for more commonplace materials like graphite.

    Building upon tools previously developed in Chen’s group for graphene, he developed an intricate model to numerically simulate the transport of phonons in a sample of graphite. For each phonon, he kept track of every possible scattering event that could take place with every other phonon, based upon their direction and energy. He ran the simulations over a range of temperatures, from 50 K to room temperature, and found that heat might flow in a manner similar to second sound at temperatures between 80 and 120 K.

    Huberman had been collaborating with Duncan, in Nelson’s group, on another project. When he shared his predictions with Duncan, the experimentalist decided to put Huberman’s calculations to the test.

    “This was an amazing collaboration,” Chen says. “Ryan basically dropped everything to do this experiment, in a very short time.”

    “We were really in the express lane with this,” Duncan adds.

    Upending the norm

    Duncan’s experiment centered around a small, 10-square-millimeter sample of commercially available graphite.

    Using a technique called transient thermal grating, he crossed two laser beams so that the interference of their light generated a “ripple” pattern on the surface of a small sample of graphite. The regions of the sample underlying the ripple’s crests were heated, while those that corresponded to the ripple’s troughs remained unheated. The distance between crests was about 10 microns.

    Duncan then shone onto the sample a third laser beam, whose light was diffracted by the ripple, and its signal was measured by a photodetector. This signal was proportional to the height of the ripple pattern, which depended on how much hotter the crests were than the troughs. In this way, Duncan could track how heat flowed across the sample over time.

    If heat were to flow normally in the sample, Duncan would have seen the surface ripples slowly diminish as heat moved from crests to troughs, washing the ripple pattern away. Instead, he observed “a totally different behavior” at 120 K.

    Rather than seeing the crests gradually decay to the same level as the troughs as they cooled, the crests actually became cooler than the troughs, so that the ripple pattern was inverted — meaning that for some of the time, heat actually flowed from cooler regions into warmer regions.

    “That’s completely contrary to our everyday experience, and to thermal transport in almost every material at any temperature,” Duncan says. “This really looked like second sound. When I saw this I had to sit down for five minutes, and I said to myself, ‘This cannot be real.’ But I ran the experiment overnight to see if it happened again, and it proved to be very reproducible.”

    According to Huberman’s predictions, graphite’s two-dimensional relative, graphene, may also exhibit properties of second sound at even higher temperatures approaching or exceeding room temperature. If this is the case, which they plan to test, then graphene may be a practical option for cooling ever-denser microelectronic devices.

    “This is one of a small number of career highlights that I would look to, where results really upend the way you normally think about something,” Nelson says. “It’s made more exciting by the fact that, depending on where it goes from here, there could be interesting applications in the future. There’s no question from a fundamental point of view, it’s really unusual and exciting.”

    This research was funded in part by the Office of Naval Research, the Department of Energy, and the National Science Foundation.

    See the full article here .


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:25 pm on March 15, 2019 Permalink | Reply
    Tags: "New state of matter discovered that could lead to better quantum engineering", , , Catch and visualize electrons in a high-temperature iron-based superconducting material which interact as a new state of matter not observed in equilibrium, Laser Technology, University of Alabama Birmingham   

    From University of Alabama Birmingham: “New state of matter discovered that could lead to better quantum engineering” 

    From University of Alabama Birmingham

    March 05, 2019
    Alicia Rohan

    1
    Ames Laboratory researchers used laser pulses of less than a trillionth of a second in much the same way as flash photography, in order to take a series of snapshots. Called terahertz spectroscopy, this technique can be thought of as “laser strobe photography” where many quick images reveal the subtle movement of electron pairings inside the materials using long wavelength far-infrared light. Credit: US Department of Energy, Ames Laboratory

    A team of experimentalists at the U.S. Department of Energy’s Ames Laboratory and theoreticians at University of Alabama Birmingham discovered a remarkably long-lived new state of matter in an iron pnictide superconductor, which reveals a laser-induced formation of collective behaviors that compete with superconductivity.

    Using intense lasers with extremely short pulses in a way equivalent to strobe photography, theoretical and computational physicists at the University of Alabama at Birmingham collaborated with experimentalists at Ames National Lab and Iowa State University to catch and visualize electrons in a high-temperature iron-based superconducting material, which interact as a new state of matter not observed in equilibrium.

    Switching on this state of matter with its unusual, quantum properties takes intense laser pulses, like a flash, hitting the cooled superconductor. Then, a second light pulse triggers an ultrafast camera to take images of this state and observe collective behaviors competing with superconductivity that, when fully understood and tuned, could one day have implications for faster, heat-free, quantum computing, information storage and communication — or what is called “quantum engineering.”

    “The discovery of this new switching scheme and quantum state was full of challenges,” said Ilias Perakis, Ph.D., chair of the UAB College of Arts and Sciences Department of Physics. “To find new emergent electron matter beyond solids, liquids and gases, today’s condensed matter physicists can no longer fully rely on traditional, slow, thermodynamic tuning knobs such as changing temperatures, pressures, chemical compositions or magnetic fields.”

    The UAB advanced computation team of postdoctoral research fellow Martin Mootz, Ph.D., and Perakis developed a model and simulations that made it possible for Jigang Wang’s laser spectroscopy group at Iowa State University and the United States Department of Energy’s Ames Laboratory to identify the experimental signatures of the new quantum state. The experimental signatures were driven by intense laser excitation and are not observed in equilibrium.
    Conducting electricity without resistance

    The new switching scheme developed by this collaboration uses short pulsed light particles to selectively bombard the superconductor energy gap for less than a trillionth of a second. This suddenly switches the superconductor, which at ultracold temperatures can conduct electricity without resistance, to a state of matter not observed under equilibrium conditions.

    The scientific journal Physical Review Letters recently published a paper describing this discovery. This paper follows a recent publication in the journal Nature Materials and is part of an ongoing project funded by the U.S. Department of Energy. In most cases, exotic states of matter such as the one described in this research paper are unstable and short-lived. In this case, the state of matter is metastable, or without decay to a stable state for an order of magnitude longer than conventional equilibration pathways.

    A remaining challenge for the researchers is to figure out how to control and further stabilize the hidden state, and whether this is suitable for the implementation, for example, of quantum logic operations. That could enable researchers to apply and even harness coherence and dynamics of the hidden state for practical functions — such as quantum computing — and for fundamental tests of bizarre quantum mechanics phenomena now used for “quantum engineering.”

    “We aim to create a sustainable innovation and entrepreneurship ecosystem in Birmingham, powered by UAB research and education on advanced materials and computation, and necessary for enabling the ‘Silicon Valley of the South’ sometime in the near future,” Perakis said. “Today, almost all technologies that underpin the global economy and health care depend on advanced materials and computation, in one way or the other.”
    Engine of progress

    Perakis states that the discovery and understanding of new quantum materials with unique properties is an engine of progress for Birmingham and the nation as a whole. Demand for novel materials designed to respond in desired ways under extreme conditions and external stimuli is rapidly rising for applications in key technologies and industries.

    For example, the very recent launch of a National Quantum Initiative by President Donald Trump and Congress recognizes that multifunctional devices based on “quantum phenomena” will be an engine for future economic growth. Quantum phenomena are already being incorporated into technologies for next-generation computers, sensors and detectors that demonstrate superior performance characteristics.

    Quantum device capabilities envisioned include enhanced resolution in imaging, sensors and detectors; advanced cryptography for more secure communication; and significantly larger computational capabilities at speeds far greater than those possible at present. These and other advances require a more detailed interdisciplinary effort to understand how materials behave under extreme and non-equilibrium conditions. This is the focus of the UAB Department of Physics, supported by a grant from the U.S. Department of Energy and others.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Alabama at Birmingham (UAB) is a public research university in Birmingham, Alabama. Developed from an academic extension center established in 1936, the institution became a four-year campus in 1966 and a fully autonomous institution in 1969. Today, it is one of three institutions in the University of Alabama System and, along with the University of Alabama, an R1 research institution. In the fall of 2015, 19,656 students from more than 110 countries were enrolled at UAB pursuing studies in 140 programs of study in 12 academic divisions leading to bachelor’s, master’s, doctoral, and professional degrees in the social and behavioral sciences, the liberal arts, business, education, engineering, and health-related fields such as medicine, dentistry, optometry, nursing, and public health.

    The UAB Health System, one of the largest academic medical centers in the United States, is affiliated with the university. UAB Hospital sponsors residency programs in medical specialties, including internal medicine, neurology, surgery, radiology, and anesthesiology. UAB Hospital is the only Level I trauma center in Alabama.

    UAB is the state’s largest employer, with more than 21,000 faculty and staff and over 53,000 jobs at the university and in the health system. An estimated 10 percent of the jobs in the Birmingham-Hoover Metropolitan Area and 1 in 33 jobs in the state of Alabama are directly or indirectly related to UAB. The university’s overall annual economic impact was estimated to be $4.6 billion in 2010.

     
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