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  • richardmitnick 10:28 am on July 3, 2020 Permalink | Reply
    Tags: "Towards Lasers Powerful Enough to Investigate a New Kind of Physics", , Institut national de la recherche scientifique INRS Quebec, , Physics   

    From Institut national de la recherche scientifique INRS Quebec: “Towards Lasers Powerful Enough to Investigate a New Kind of Physics” 

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    From Institut national de la recherche scientifique INRS Quebec

    July 2, 2020
    Audrey-Maude Vézina

    In a paper that made the cover of the journal Applied Physics Letters, an international team of researchers has demonstrated an innovative technique for increasing the intensity of lasers. This approach, based on the compression of light pulses, would make it possible to reach a threshold intensity for a new type of physics that has never been explored before: quantum electrodynamics phenomena.

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    Since the invention of frequency drift amplification in 1985 by Donna Strickland and Gérard Mourou, laser power has increased phenomenally, to finally reach a limit in the last years. Many research groups are amplifying the energy of the laser to increase its power, but this approach is expensive and requires beams and optics that are very large, more than a metre in size.

    Researchers Jean-Claude Kieffer of the Institut national de la recherche scientifique (INRS), E. A. Khazanov of the Institute of Applied Physics of the Russian Academy of Sciences and Gérard Mourou, Professor Emeritus of the Ecole Polytechnique in France, who was awarded the Nobel Prize in Physics in 2018, have chosen another direction to achieve a power of around 10^23 Watts (W). Rather than increasing the energy of the laser, they decrease the pulse duration to only a few femtoseconds. This would keep the system within a reasonable size and keep operating costs down.

    To generate the shortest possible pulse, the researchers are exploiting the effects of non-linear optics. “A laser beam is sent through an extremely thin and perfectly homogeneous glass plate. The particular behaviour of the wave inside this solid medium broadens the spectrum and allows for a shorter pulse when it is recompressed at the exit of the plate,” explains Jean-Claude Kieffer, co-author of the study published online on 15 June 2020 in the journal Applied Physics Letters.

    Installed in the Advanced Laser Light Source (ALLS) facility at INRS, the researchers limited themselves to an energy of 3 joules for a 10-femtosecond pulse, or 300 terawatts (1012W).

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    Advanced Laser Light Source (ALLS) Université du Québec – Institut national de la recherche scientifique (INRS), Varennes, Québec

    They plan to repeat the experiment with an energy of 13 joules over 5 femtoseconds, or an intensity of 3 petawatts (1015 W). “We would be among the first in the world to achieve this level of power with a laser that has such short pulses,” says Professor Kieffer.

    “If we achieve very short pulses, we enter relativistic problem classes. This is an extremely interesting direction that has the potential to take the scientific community to new horizons,” says Professor Kieffer. “It was a very nice piece of work solidifying the paramount potential of this technique,” concludes Gérard Mourou.

    See the full article here.

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  • richardmitnick 7:49 am on July 3, 2020 Permalink | Reply
    Tags: "Europeans Decide on Particle Strategy", , , , , , , , , Physics   

    From “Physics”: “Europeans Decide on Particle Strategy” 

    About Physics

    From “Physics”

    July 2, 2020
    Michael Schirber

    The CERN Council approved a strategy update that prioritizes a 100-km circular collider, while still developing other options for future particle physics projects.

    1
    A map depicting where the 100-km-long Future Circular Collider could be built in relation to CERN’s existing accelerator infrastructure.

    European particle physicists have updated their strategy for the coming decades. Beyond current commitments, the community advocates pursuing a new facility at the CERN site outside Geneva—a circular collider with a circumference of 100 kilometers. Such a machine could serve a dual purpose: to act initially as a “Higgs factory” where electrons and positrons smash together at energies up to 350 GeV, and to later scope out the high-energy frontier by colliding protons at up to 100-TeV energies. The feasibility of this so-called Future Circular Collider (FCC) is still an open question, which is why the strategy also calls for continued research and development into accelerator technology, such as plasma acceleration and muon colliders.

    Following a two-year-long process, the European Strategy for Particle Physics Update was unanimously endorsed on June 19 by the CERN Council, which is the governing body of the CERN facility. The Update outlines a number of current and future priorities. In the near-term, the main initiatives for Europe are the high-luminosity upgrade of CERN’s Large Hadron Collider (LHC) and continuing support of international neutrino experiments, such as the forthcoming Deep Underground Neutrino Experiment (DUNE) in the US.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    But beyond that, many questions remain. “CERN needs to have a project for after the LHC,” says Halina Abramowicz, chair of the European Strategy Group, from Tel Aviv University in Israel.

    The main objective of any post-LHC endeavor will be to look for new particles or phenomena that go beyond the standard model of particle physics.

    Standard Model of Particle Physics, Quantum Diaries

    Physicists are still in the dark as to what this “new physics” will be, so the best way forward is to study the Higgs boson with greater precision, Abramowicz says. The Higgs is unique in that it should interact with all particles, even ones that physicists haven’t detected yet. “The Higgs does not differentiate: if there is something out there, it will couple to it,” Abramowicz explains.

    CERN CMS Higgs Event May 27, 2012

    CERN ATLAS Higgs Event June 12, 2012

    Precision measurements of Higgs physics can be done with an electron-positron collider, but the exact design of such a Higgs factory is still undecided. The International Linear Collider (ILC) is one option, but the proposed host, Japan, has not yet committed to the project.


    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

    Researchers at CERN have been developing the Compact Linear Collider (CLIC), which could potentially smash electrons and positrons at energies as high as 3 TeV.

    CERN CLIC collider


    CERN CLIC Collider annotated

    However, uncertainty about the energy where new physics might appear led the Strategy Group to decide on the FCC concept as the best option to pursue. The large ring-shaped tunnel could accommodate a Higgs factory and then later shift to colliding protons at energies 7 times greater than those of the LHC.

    But pursuing the FCC won’t be straightforward. “The FCC would be the machine that physicists most want,” says Ursula Bassler, the president of the CERN Council. “However, we do not know if it’s technically and financially feasible.” Preliminary estimates suggest that such a collider would cost around 20 billion dollars, so involvement by countries outside of Europe will likely be necessary. “The scope and the science and technology challenges of such a Higgs factory would require a long-term global collaboration of the kind that the US is currently engaged in with the LHC and DUNE,” says Fermilab’s Marcela Carena, who was the US representative for the strategy’s Physics Preparatory Group.

    One possible wrinkle is that Chinese physicists have proposed the Circular Electron Positron Collider (CEPC), whose design is similar in size and scope to that of the FCC.

    China Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

    “I think there is a competition between China and Europe,” Bassler says. “However, there’s also a lot of collaboration going on.” As long as neither side has committed to a project, she thinks it can help spur innovation to have different groups working on the same research track.

    Abramowicz stresses that the FCC is not the final word. By continuing research and development into accelerator technology, she believes particle physicists can remain flexible in the face of new developments in the scientific and political worlds. “From the input we received, it’s clear that particle physicists are very excited about the FCC, but they do realize that it’s not a given. So they want to make sure that we have alternatives.”

    Bassler is happy the process is complete. “In the beginning, every time I met a physicist at CERN cafeteria, I heard a different strategy.” She feels the community has now converged on a common roadmap, in which the first step will be a thorough feasibility study of the FCC concept. At the same time, US particle physicists will be working on “Snowmass”—a community exercise led by the American Physical Society, which aims to draw up a particle physics vision for 2021. “The timing of the European Strategy Update fits well with the launch of the Snowmass process,” Carena says.

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

     
  • richardmitnick 8:31 am on July 1, 2020 Permalink | Reply
    Tags: "LHCb discovers a new type of tetraquark at CERN", , , , , , , Physics   

    From CERN LHCb: “LHCb discovers a new type of tetraquark at CERN” 

    Cern New Bloc

    Cern New Particle Event


    From CERN LHCb

    1 July, 2020

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    Illustration of a tetraquark composed of two charm quarks and two charm antiquarks, detected for the first time by the LHCb collaboration at CERN. (Image: CERN)

    The LHCb collaboration has observed a type of four-quark particle never seen before. The discovery, presented at a recent seminar at CERN and described in a paper posted today on the arXiv preprint server, “Observation of structure in the J/ψ-pair mass spectrum“, is likely to be the first of a previously undiscovered class of particles.

    The finding will help physicists better understand the complex ways in which quarks bind themselves together into composite particles such as the ubiquitous protons and neutrons that are found inside atomic nuclei.

    Quarks typically combine together in groups of twos and threes to form particles called hadrons. For decades, however, theorists have predicted the existence of four-quark and five-quark hadrons, which are sometimes described as tetraquarks and pentaquarks, and in recent years experiments including the LHCb have confirmed the existence of several of these exotic hadrons. These particles made of unusual combinations of quarks are an ideal “laboratory” for studying one of the four known fundamental forces of nature, the strong interaction that binds protons, neutrons and the atomic nuclei that make up matter. Detailed knowledge of the strong interaction is also essential for determining whether new, unexpected processes are a sign of new physics or just standard physics.

    “Particles made up of four quarks are already exotic, and the one we have just discovered is the first to be made up of four heavy quarks of the same type, specifically two charm quarks and two charm antiquarks,” says the outgoing spokesperson of the LHCb collaboration, Giovanni Passaleva. “Up until now, the LHCb and other experiments had only observed tetraquarks with two heavy quarks at most and none with more than two quarks of the same type.”

    “These exotic heavy particles provide extreme and yet theoretically fairly simple cases with which to test models that can then be used to explain the nature of ordinary matter particles, like protons or neutrons. It is therefore very exciting to see them appear in collisions at the LHC for the first time,” explains the incoming LHCb spokesperson, Chris Parkes.

    The LHCb team found the new tetraquark using the particle-hunting technique of looking for an excess of collision events, known as a “bump”, over a smooth background of events. Sifting through the full LHCb datasets from the first and second runs of the Large Hadron Collider, which took place from 2009 to 2013 and from 2015 to 2018 respectively, the researchers detected a bump in the mass distribution of a pair of J/ψ particles, which consist of a charm quark and a charm antiquark. The bump has a statistical significance of more than five standard deviations, the usual threshold for claiming the discovery of a new particle, and it corresponds to a mass at which particles composed of four charm quarks are predicted to exist.

    As with previous tetraquark discoveries, it is not completely clear whether the new particle is a “true tetraquark”, that is, a system of four quarks tightly bound together, or a pair of two-quark particles weakly bound in a molecule-like structure. Either way, the new tetraquark will help theorists test models of quantum chromodynamics, the theory of the strong interaction.

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    This is the first observation of this unusual combination of heavy quarks. Indeed all the exotic hadrons observed so far have at most two heavy quarks and none of them is made of more than two quarks of the same type.

    See the full article here .

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    LHCb
    CERN LHCb New II

    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

     
  • richardmitnick 10:17 am on June 28, 2020 Permalink | Reply
    Tags: "Case for Axion Origin of Dark Matter Gains Traction", , Institute for Advanced Study, , Physics   

    From Institute for Advanced Study: “Case for Axion Origin of Dark Matter Gains Traction” 


    From Institute for Advanced Study

    June 26, 2020
    Lee Sandberg
    lsandberg@ias.edu
    609-455-4398

    1
    The axion field rapidly runs over the potential barriers and eventually begins oscillations when sufficiently slowed down by friction.

    In a new study of axion motion, researchers propose a scenario known as “kinetic misalignment” that greatly strengthens the case for axion/dark matter equivalence. The novel concept answers key questions related to the origins of dark matter and provides new avenues for ongoing detection efforts. This work, published in Physical Review Letters, was conducted by researchers at the Institute for Advanced Study, University of Michigan, and UC Berkeley.

    The existence of dark matter has been confirmed by several independent observations, but its true identity remains a mystery. According to this study, axion velocity provides a key insight into the dark matter puzzle. Previous research efforts have successfully accounted for the abundance of dark matter in the universe; however certain factors, such as the underproduction of axions with stronger ordinary matter interactions, remained unexplored.

    By assigning a nonzero initial velocity to the axion field, the team discovered a mechanism—termed kinetic misalignment—producing far more axions in the early universe than conventional mechanisms. The motion, generated by breaking of the axion shift symmetry, significantly modifies the conventional computation of the axion dark matter abundance. Additionally, these dynamics allow axion dark matter to react more strongly with ordinary matter, exceeding the prediction of the conventional misalignment mechanism.

    “The extensive literature on the axion was built upon the assumption that the axion field is initially static in the early universe,” stated Keisuke Harigaya of the Institute for Advanced Study. “Instead, we discovered that the axion field may be initially dynamic as a consequence of theories of quantum gravity with axions.”

    Two members of the research team, Keisuke Harigaya and Raymond Co, previously explored the concept of axion dynamics in the study “Axiogenesis,” [Physical Review Letters] which explained how the excess of matter over antimatter could be due to a nonzero initial velocity of the QCD axion field. This study also provided a framework for generating new insights into the questions surrounding dark matter.

    “This new kinetic misalignment mechanism predicts an axion with a larger interaction strength and may be discovered in planned experimental searches,” stated Raymond Co of the University of Michigan. “Our discovery of new axion dynamics thus opens up unexplored research avenues for theoretical and experimental particle physics and cosmology.”

    To date, the axion has proven incredibly versatile. The particle was originally proposed to solve the mystery of why neutrons do not interact with an electric field despite having charged constituents. Former IAS Professor Frank Wilczek, who coined the term axion, published his landmark findings in 1978 in Physical Review Letters while a Member of the Institute for Advanced Study’s School of Natural Sciences.

    See the full article here.

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    The Institute, established in 1930, began with twenty-three Members in the School of Mathematics with Albert Einstein as one of its first Professors. Since then, the Institute’s community of scholars has grown to include more than eight thousand historians, mathematicians, natural scientists, and social scientists. A Faculty of some thirty permanent Professors selects and mentors the roughly two hundred Members who arrive each year from around the world, about 60 percent from outside the United States, typically from more than thirty different countries.

     
  • richardmitnick 2:51 pm on June 26, 2020 Permalink | Reply
    Tags: "New Research Deepens Mystery of Particle Generation in Proton Collisions", , , , , , , Physics, RHICf   

    From Brookhaven National Lab: “New Research Deepens Mystery of Particle Generation in Proton Collisions” 

    From Brookhaven National Lab

    June 23, 2020

    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350

    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    ____________________________________
    The following news release was issued by the RHICf collaboration. The RHICf experiment is installed in the “forward” direction (along the beamline) in the same particle interaction region as the STAR detector [below] at the Relativistic Heavy Ion Collider (RHIC) [below], a DOE Office of Science user facility for nuclear physics research at Brookhaven National Laboratory. The RHICf experiment collected data from RHIC’s polarized proton collisions to explore further details of asymmetries observed in collisions at RHIC—particularly a preference for certain particles to emerge from these spin-polarized collisions in a particular direction. This new result adds to the puzzling story of what causes this “transverse spin asymmetry”—an open question for physicists since the 1970s. These and other results from RHIC’s polarized proton collisions will eventually contribute to solving this question. For more information about research at RHIC, contact Karen McNulty Walsh, (631) 344-8350, kmcnulty@bnl.gov.
    ____________________________________

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    The RHICf experiment is installed in the “forward” direction (along the beamline) in the same particle interaction region as the STAR detector at the Relativistic Heavy Ion Collider (RHIC), a DOE Office of Science user facility for nuclear physics research at Brookhaven National Laboratory.

    A group of researchers including scientists from the RIKEN Nishina Center for Accelerator-Based Science, University of Tokyo, Nagoya University, and the Japan Atomic Energy Agency (JAEA) used the spin-polarized Relativistic Heavy Ion Collider (RHIC) [below]—a DOE Office of Science user facility for nuclear physics research at Brookhaven National Laboratory in the United States—to show that, in polarized proton-proton collisions, neutral pions emitted in the very forward area of collisions—where direct interactions involving quarks and gluons are not applicable—still have a large degree of left-right asymmetry. This finding suggests that the previous consensus regarding the generation of particles in such collisions needs to be reevaluated.

    Understanding the mechanism through which particles are created in collisions involving protons has relevance for understanding cosmic ray showers, where particles entering Earth’s atmosphere from outer space create particle “showers” that help us learn about astronomical phenomena that take place in the extreme environment of the universe. However, it is very difficult to study the details of how particles are created, as the force that binds protons in the nucleus and that bind quarks and gluons into protons—the strong interaction or nuclear force—is very strong compared to other forces such as the electromagnetic force and gravity. One avenue for exploring these challenging questions has involved an attribute of protons called “spin,” which can be understood by analogy to the way a toy top rotates on its axis. The spin of protons can be artificially aligned in a process that is called “polarization.”

    In the 1970s, accelerator experiments at Argonne National Laboratory in the United States revealed that the pions generated toward the front of collisions involving polarized protons had large left-right asymmetry. The energy of the polarized protons used in these experiments was about 10 billion electron volts (GeV). Experiments at higher energies—including one at 200 GeV using the polarized proton beam at Fermi National Accelerator Laboratory (FNAL) in the United States and at RHIC at Brookhaven National Laboratory (BNL) in the United States, where two beams of 100 GeV protons moving in opposite directions were collided—showed that the left-right asymmetry persisted even with high-energy polarized protons. A consensus emerged that this asymmetry was caused by direct interactions among the quarks and gluons in the protons, based on a theory called perturbative quantum chromodynamics (QCD).

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    Understanding the mechanism through which particles are created in collisions involving protons like those at RHIC has relevance for understanding cosmic ray showers created by particles entering Earth’s atmosphere. (Image credit: Simon Swordy (U. Chicago), NASA)

    However, with additional experiments at RHIC, findings began to emerge that challenged the consensus. According to Yuji Goto, one of the authors of the current work, “At the energy of RHIC, quarks and gluons are scattered, and various particles are generated in the form of a jet. When the left-right asymmetry of the jet generated forward of the collision position at RHIC was examined, it was found that, contrary to expectations, the overall jet and the pions contained in the jet did not show a left-right asymmetry. This suggested that the cause of the left-right asymmetry was not the direct scattering of quarks and gluons.”

    In order to further investigate, the researchers conducted experiments, published in Physical Review Letters, where they used an electromagnetic calorimeter detector previously used in the Large Hadron Collider at CERN—known as the LHCf experiment there and the RHICf experiment at RHIC—to take a detailed look at the gamma rays generated by pion decays at the very forward region of the collision. They found, however, that the left-right asymmetry in neutral pions persists even in that very narrow area.

    CERN LHCf

    BNL RHICf detector

    More information on the RHICf experiment is available at http://crportal.isee.nagoya-u.ac.jp/RHICf/.

    See the full article here .


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    BNL Campus

    Brookhaven campus

    BNL Center for Functional Nanomaterials

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL Phenix Detector

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

     
  • richardmitnick 10:21 am on June 26, 2020 Permalink | Reply
    Tags: "Dance Electron Dance: Scientists Use Light to Choreograph Electronic Motion in 2D Materials", , , How electrons move and interact within materials, , , Moiré superlattices provide a unique method for introducing exotic electronic behavior in materials where they don’t typically exist., , Physics, Using light to choreograph electron spin.   

    From Lawrence Berkeley National Lab: “Dance, Electron, Dance: Scientists Use Light to Choreograph Electronic Motion in 2D Materials” 


    From Lawrence Berkeley National Lab

    June 26, 2020
    Theresa Duque
    tnduque@lbl.gov
    (510) 424-2866

    Study led by Berkeley Lab, UC Berkeley could advance understanding of electron interactions for quantum devices.

    1
    Microscope image of the TMD moiré superlattice device. (Credit: Emma Regan/Berkeley Lab)

    A team of scientists led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley has demonstrated a powerful new technique that uses light to measure how electrons move and interact within materials. With this technique, the researchers observed exotic states of matter in stacks of atomically thin semiconductors called transition metal dichalcogenide (TMD) moiré superlattices.

    Their study, which was published in the journal Nature, is the first to prove that interactions between electrons play a significant role in how charge flows in TMD moiré superlattices.

    “Moiré superlattices provide a unique method for introducing exotic electronic behavior in materials where they don’t typically exist,” said lead author Emma Regan, a doctoral researcher in Berkeley Lab’s Materials Sciences Division and the UC Berkeley physics department. “Understanding and engineering electronic behavior in quantum materials may provide new approaches for electronic devices in the future.”

    In most materials, electrons move fast and rarely interact. But in previous studies, other researchers have shown that a moiré superlattice – which creates an energy landscape for electrons – can slow the electrons down enough that they feel interactions between each other.

    “We suspected that these electron-electron interactions in TMD moiré superlattices are very strong – even stronger than what you would find in stacks of graphene,” said Regan.

    Typically, physicists investigate electron-electron interactions by attaching wires to a material and measuring how easily electrical current flows. But in stacks of TMDs, electrons don’t flow easily between the wires and the material, which makes it difficult to understand how the electrons interact.

    So the researchers turned to light instead.

    The research team, led by senior author Feng Wang, fabricated the TMD moiré superlattice from atomically thin layers of tungsten diselenide and tungsten disulfide – two common semiconductors known for their ability to efficiently absorb and emit light. They then formed a device just 25 nanometers (25 billionths of a meter) thick by sandwiching the tungsten diselenide/tungsten disulfide moiré superlattice between boron nitride and graphene.

    In Wang’s ultrafast nano-optics lab, the researchers shone lasers on the TMD device to observe how electrons flowed in the superlattice as they varied the number of electrons injected into the material. Wang is a faculty scientist in Berkeley Lab’s Materials Sciences Division and professor of physics at UC Berkeley.

    Using light to choreograph electron spin

    3
    Electrons resting in the moire superlattice at different electron densities. Wigner crystal states are shown left and center. Typical insulating state is shown right. (Credit: Emma Regan/Berkeley Lab)

    As expected, the researchers uncovered evidence of very strong electron-electron interactions in the TMD moiré superlattice device.

    In one experiment, for example, the device suddenly became electrically insulating – the electrons stopped moving – when they added enough electrons to fill each unit cell in the moiré superlattice.

    This behavior is common in a material with strong electron-electron interactions, Regan said. “Since the electrons interact strongly, they prefer not to sit at the same position because this will increase their energy. If all of the unit cells are already occupied, then the electrons stop moving around,” she explained.

    So Regan and co-authors were surprised to see similar insulating behavior in the TMD moiré superlattice device when there were fewer electrons in the material, and not all the superlattice unit cells were occupied.

    “Electron interactions were so strong in the TMD moiré superlattice that electrons also avoided sitting on neighboring sites,” she said. “These states are called generalized Wigner crystal states and haven’t been seen in any other moiré superlattice system.”

    TMDs have a unique property where different polarizations of light can excite electrons to spin up or spin down, so the researchers used a laser to inject electrons with “spin up” or “spin down” into the material, probing their behavior with a second laser. “Direct optical access to the electron spin is special because it helps us understand the details of these exotic states,” Regan said.

    “This study is very exciting because we were able to demonstrate strong electron-electron interactions in TMD moiré superlattices, which also have fascinating and useful optical properties,” she added. “This work weds traditional correlated electron physics with 2D TMD materials – two communities that usually don’t overlap.”

    The researchers hope to further develop their technique to take optical measurements of electron spin at tiny scales of distance and timing.

    Researchers from the Kavli Institute at Cornell for Nanoscale Science; Huazhong University of Science and Technology, and the University of the Chinese Academy of Sciences, China; Arizona State University; Lund University, Sweden; and the National Institute for Materials Science, Japan, also contributed to the study.

    The work was supported by the DOE Office of Science. Additional funding was provided by the U.S. Army Research Office.

    See the full article here .

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    LBNL Molecular Foundry

    Bringing Science Solutions to the World
    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

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

    University of California Seal

     
  • richardmitnick 9:57 am on June 26, 2020 Permalink | Reply
    Tags: , , , , Physics, ,   

    From KEK Inter-University Research Institute Corporation: “SuperKEKB collider achieves the world’s highest luminosity” 

    From KEK Inter-University Research Institute Corporation

    2020/06/26

    1
    Fig. 1 The instantaneous luminosity of SuperKEKB measured at 5-minute intervals from Fall 2019 to June 22, 2020. Values are on-line measurements and contain an approximate 1% error.

    Japan’s High Energy Accelerator Research Organization (KEK) has been steadily improving the performance of its flagship electron-positron collider, SuperKEKB, since it produced its first electron-positron collisions in April 2018.

    The SuperKEKB electron-positron collider in Tsukuba, Japan

    At 20:34 on 15th June 2020, SuperKEKB achieved the world’s highest instantaneous luminosity for a colliding-beam accelerator, setting a record of 2.22×1034cm-2s-1. Previously, the KEKB collider, which was SuperKEKB’s predecessor and was operated by KEK from 1999 to 2010, had achieved the world’s highest luminosity, reaching 2.11×1034cm-2s-1. KEKB’s record was surpassed in 2018, when the LHC proton-proton collider at the European Organization for Nuclear Research (CERN) overtook the KEKB luminosity at 2.14×1034cm-2s-1. SuperKEKB’s recent achievement returns the title of world’s highest luminosity colliding-beam accelerator to KEK.(*)

    (*)The current record is 2.40×1034cm-2s-1, obtained at 00:53 JST on June 21st.

    In the coming years, the luminosity of SuperKEKB will be increased to approximately 40 times the new record. This exceptionally high luminosity is to be achieved mainly by using a beam collision method called the “nano-beam scheme”, developed by Italian physicist Pantaleo Raimondi. Raimondi’s innovation enables significant increases in luminosity by using powerful magnets to squeeze the two beams in both the horizontal and vertical directions. Substantially decreasing the beam sizes increases the luminosity, which varies inversely with the cross-sectional area of the colliding beams.

    SuperKEKB is the first collider in the world to realize the nano-beam scheme. In the beam operation of SuperKEKB, we keep increasing the luminosity by squeezing the beams ever harder, while solving various problems associated with the squeezing. Currently, the vertical height of the beams at the collision point is about 220 nanometers, and this will decrease to approximately 50 nanometers (about 1/1000 the width of a human hair) in the future.

    Another factor that determines luminosity is the product of the two beam currents, which is proportional to the product of the numbers of electrons and positrons stored in the collider. KEK physicists and accelerator operators continue to increase the beam currents, while mitigating various high-current problems, such as stray background particles that introduce noise in the Belle II detector. SuperKEKB achieved the new luminosity record with a product of beam currents that was less than 25% that of KEKB. This demonstrates the superiority of the SuperKEKB design. In the future, we aim to increase the beam current product to about four times the value achieved by KEKB.

    In order to adopt the nano-beam scheme and increase the beam current, KEKB underwent significant upgrades that turned it into SuperKEKB. These included a new beam pipe, new superconducting final-focusing magnets, a positron damping ring, and an advanced injector. The most recent improvement was completed in April 2020, with the introduction of the “crab waist”, first used at the DAΦNE accelerator in Frascati, Italy, in 2010, and which reduces the beam size and stabilizes collisions.

    The success of SuperKEKB relies also on contributions from overseas. As an example, the superconducting final-focusing magnets were built in cooperation with Brookhaven National Laboratory and Fermi National Accelerator Laboratory in the U.S. under the U.S.-Japan Science and Technology Cooperation Program. Other major contributions under this program were the development of a collision-point orbit feedback system (SLAC National Accelerator Laboratory) and an X-ray beam size monitor (University of Hawaii and SLAC National Accelerator Laboratory). Researchers from CERN (Switzerland), IJCLab (France), IHEP (China)as well as SLAC(U.S.) have participated in accelerator research and operation under KEK’s Multinational Partnership Project (MNPP-01).There are also contributions from many other foreign research institutes. Other important contributions have come through the Belle II experiment collaboration, such as the diamond-based radiation monitor and beam abort system (INFN and University of Trieste, Italy), and the luminosity monitoring system developed at BINP (Russia).

    SuperKEKB brings its electron and positron beams into collision at the center of the Belle II particle detector. The detector has been built and is operated by the Belle II collaboration, an international group of approximately 1,000 physicists and engineers from 119 universities and laboratories located in 26 countries and regions around the world. Belle II physicists use the detector to explore fundamental physics phenomena, by studying the production and decay processes of particles produced in the collisions, primarily B mesons, D mesons, and tau leptons. To within the precision of current measurements, the behavior of particles such as these is well described by the theory known as the Standard Model. However, the Standard Model fails to address key questions, such as the mystery of the matter-dominated universe and the existence of dark matter. Therefore, new physical laws are needed to explain these observations. Signals of such “new physics” may arise in decay processes that are very rarely observed. Maximizing the discovery potential of Belle II for such signals requires a large number of electron-positron collisions, necessitating a very high-luminosity collider, such as SuperKEKB.

    Collecting data for about 10 years, the Belle II experiment will accumulate 50 times more particle collisions than its predecessor, the Belle experiment. The large data set, containing about 50 billion B-meson pairs and similar numbers of charm mesons and tau leptons, will enable Belle II physicists to explore nature at a much deeper level than was previously possible. The data will also be used in sensitive searches for very weakly interacting particles that may help answer some of the outstanding mysteries of the universe.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    KEK-Accelerator Laboratory

    KEK, the High Energy Accelerator Research Organization, is one of the world’s leading accelerator science research laboratories, using high-energy particle beams and synchrotron light sources to probe the fundamental properties of matter. With state-of-the-art infrastructure, KEK is advancing our understanding of the universe that surrounds us, its mechanisms and their control. Our mission is:

    • To make discoveries that address the most compelling questions in a wide range of fields, including particle physics, nuclear physics, materials science, and life science. We at KEK strive to make the most effective use of the funds entrusted by Japanese citizens for the benefit of all, by adding to knowledge and improving the technology that protects the environment and serves the economy, academia, and public health; and

    • To act as an Inter-University Research Institute Corporation, a center of excellence that promotes academic research by fulfilling the needs of researchers in universities across the country and by cooperating extensively with researchers abroad; and

    • To promote national and international collaborative research activities by providing advanced research facilities and opportunities. KEK is committed to be in the forefront of accelerator science in Asia-Oceania, and to cooperate closely with other institutions, especially with Asian laboratories.

    Established in 1997 in a reorganization of the Institute of Nuclear Study, University of Tokyo (established in 1955), the National Laboratory for High Energy Physics (established in 1971), and the Meson Science Laboratory of the University of Tokyo (established in 1988), KEK serves as a center of excellence for domestic and foreign researchers, providing a wide variety of research opportunities. In addition to the activities at the Tsukuba Campus, KEK is now jointly operating a high-intensity proton accelerator facility (J-PARC) in Tokai village, together with the Japan Atomic Energy Agency (JAEA). Over 600 scientists, engineers, students and staff perform research activities on the Tsukuba and Tokai campuses. KEK attracts nearly 100,000 national and international researchers every year (total man-days), and provides excellent research facilities and opportunities to many students and post-doctoral fellows each year.

     
  • richardmitnick 7:24 am on June 26, 2020 Permalink | Reply
    Tags: "Experiment at CERN makes the first observation of rare events producing three massive force carriers simultaneously", , , , , , , Physics, The simultaneous production of three W or Z bosons- subatomic "mediator particles" that carry the weak interaction.   

    From Caltech: “Experiment at CERN makes the first observation of rare events producing three massive force carriers simultaneously” 

    Caltech Logo

    From Caltech

    June 25, 2020
    Emily Velasco
    626‑395‑6487
    evelasco@caltech.edu

    1
    Caltech

    Modern physics knows a great deal about how the universe works, from the grand scale of galaxies down to the infinitesimally small size of quarks and gluons. Still, the answers to some major mysteries, such as the nature of dark matter and origin of gravity, have remained out of reach.

    Caltech physicists and their colleagues using the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland, the largest and most powerful particle accelerator in existence, and its Compact Muon Solenoid (CMS) experiment have made a new observation of very rare events that could help take physics beyond its current understanding of the world.

    LHC

    CERN map

    CERN LHC Maximilien Brice and Julien Marius Ordan

    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector

    CMS

    CERN/CMS

    LHCb

    CERN/LHCb detector

    The new observation involves the simultaneous production of three W or Z bosons, subatomic “mediator particles” that carry the weak interaction—one of the four known fundamental forces—which is responsible for the phenomenon of radioactivity as well as an essential ingredient in the sun’s thermonuclear processes.

    Bosons are a class of particles that also include photons, which make up light; the Higgs boson, which is thought to be responsible for giving mass to matter; and gluons, which bind nuclei together. The W and Z bosons are similar to each other in that they both carry the weak force but are different in that the Z boson has no electric charge. The existence of these bosons, along with other subatomic particles like gluons and neutrinos, is explained by what is known as the Standard Model of particle physics.

    Caltech graduate student Zhicai Zhang (MS ’18), a member of the High Energy Physics research team led by Harvey Newman, the Marvin L. Goldberger Professor of Physics, and Maria Spiropulu, the Shang-Yi Ch’en Professor of Physics, is one of the principal contributors to the new observation, working together with other team members.

    The events producing the trios of bosons occur when intense bunches of high-energy protons that have been accelerated to nearly the speed of light are brought into a head-on collision at a few points along the circular path of the LHC. When two protons collide, the quarks and gluons in the protons are forced apart, and as that happens, W and Z bosons can pop into existence; in very rare cases, they appear as triplets: WWW, WWZ, WZZ, and ZZZ. Such triplets of W and Z bosons, Newman says, are only produced in one out of 10 trillion proton-proton collisions.

    These events are recorded using the CMS, which surrounds one of the collision points along the LHC’s path. Zhang says these events are 50 times rarer than those used to discover the Higgs boson.

    “With the LHC creating an enormous number of collisions, we can see things that are very rare, like the production of these bosons,” Newman says.

    It is possible for the W and Z bosons to self-interact, allowing W and Z bosons to create still more W and Z bosons; these may manifest themselves as events with two or three massive bosons. Still, this creation is rare, so the more bosons that are produced, the less frequent the production happens. The production of two massive bosons has previously been observed and measured with good precision at the LHC.

    The creation of these bosons was not the specific goal of the experiment, Newman says. By collecting enough data, including many events with boson triplets and other rare events, researchers will be able to test the Standard Model’s predictions with increasing precision and may eventually find and be able to study the new interactions that lie beyond it.

    “We know from observing the rotation and distribution of galaxies that there must be dark matter exerting its gravitational influence, but dark matter doesn’t fit into the Standard Model. There is no room in it for dark particles, nor does it include gravity, and it simply does not work at the energy scales typical of the early universe in the first moments after the Big Bang. We know that there is a more fundamental yet-to-be-discovered theory than the Standard Model,” Newman says.

    The next three-year experimental run, scheduled for 2021–24, is already being prepared. At the end of that run, the equipment will be upgraded to increase its data-collection capacity 30-fold. “There is a lot of unrealized potential. The masses of data we have already collected still represent only a few percent of what we expect to collect following major upgrades of both CMS and the LHC, at the High Luminosity LHC that is scheduled to run for 10 years beginning in 2027. We are only at the very beginning of this 30-year physics program,” he says.

    A paper describing their findings, titled, “Observation of heavy triboson production in leptonic final states in proton-proton collisions at √s = 13 TeV” is available at CERN [ http://cds.cern.ch/record/2714899 ].

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 10:34 am on June 25, 2020 Permalink | Reply
    Tags: "‘Twisted’ sound experiment helps confirm 50-year-old science theory", A 50-year-old theory that began as speculation about how an alien civilisation could use a black hole to generate energy has been experimentally verified for the first time in a Glasgow research lab., , , , Physics, Roger Penrose and Yakov Zel’dovich, They built a system which uses small ring of speakers to create a twist in the sound waves analogous to the twist in the light waves proposed by Zel’dovich., University of Glasgow’s School of Physics and Astronomy   

    From University of Glasgow: “‘Twisted’ sound experiment helps confirm 50-year-old science theory” 

    U Glasgow bloc

    From University of Glasgow

    22 Jun 2020

    A 50-year-old theory that began as speculation about how an alien civilisation could use a black hole to generate energy has been experimentally verified for the first time in a Glasgow research lab.

    In 1969, British physicist Roger Penrose suggested that energy could be generated by lowering an object into the black hole’s ergosphere – the outer layer of the black hole’s event horizon, where an object would have to move faster than the speed of light in order to remain still.

    Penrose predicted that the object would acquire a negative energy in this unusual area of space. By dropping the object and splitting it in two so that one half falls into the black hole while the other is recovered, the recoil action would measure a loss of negative energy – effectively, the recovered half would gain energy extracted from the black hole’s rotation. The scale of the engineering challenge the process would require is so great, however, that Penrose suggested only a very advanced, perhaps alien, civilisation would be equal to the task.

    Two years later, another physicist named Yakov Zel’dovich suggested the theory could be tested with a more practical, earthbound experiment. He proposed that ’twisted’ light waves, hitting the surface of a rotating metal cylinder turning at just the right speed, would end up being reflected with additional energy extracted from the cylinder’s rotation thanks to a quirk of the rotational doppler effect.

    But Zel’dovich’s idea has remained solely in the realm of theory since 1971 because, for the experiment to work, his proposed metal cylinder would need to rotate at least a billion times a second – another insurmountable challenge for the current limits of human engineering.

    Now, researchers from the University of Glasgow’s School of Physics and Astronomy have finally found a way to experimentally demonstrate the effect that Penrose and Zel’dovich proposed by twisting sound instead of light – a much lower frequency source, and thus much more practical to demonstrate in the lab.

    In a new paper published today in Nature Physics, the team describe how they built a system which uses small ring of speakers to create a twist in the sound waves analogous to the twist in the light waves proposed by Zel’dovich.

    1

    2
    The experiment. (Cromb et al., Nature Physics, 2020)

    Those twisted sound waves were directed towards a rotating sound absorber made from a foam disc. A set of microphones behind the disc picked up the sound from the speakers as it passed through the disc, which steadily increased the speed of its spin.

    What the team were looking to hear in order to know that Penrose and Zel’dovich’s theories were correct was a distinctive change in the frequency and amplitude of the sound waves as they travelled through the disc, caused by that quirk of the doppler effect.

    Marion Cromb, a PhD student in the University’s School of Physics and Astronomy, is the paper’s lead author. Marion said: “The linear version of the doppler effect is familiar to most people as the phenomenon that occurs as the pitch of an ambulance siren appears to rise as it approaches the listener but drops as it heads away. It appears to rise because the sound waves are reaching the listener more frequently as the ambulance nears, then less frequently as it passes.

    “The rotational doppler effect is similar, but the effect is confined to a circular space. The twisted sound waves change their pitch when measured from the point of view of the rotating surface. If the surface rotates fast enough then the sound frequency can do something very strange – it can go from a positive frequency to a negative one, and in doing so steal some energy from the rotation of the surface.”

    As the speed of the spinning disc increases during the researchers’ experiment, the pitch of the sound from the speakers drops until it becomes too low to hear. Then, the pitch rises back up again until it reaches its previous pitch – but louder, with amplitude of up to 30% greater than the original sound coming from the speakers.

    Marion added: “What we heard during our experiment was extraordinary. What’s happening is that the frequency of the sound waves is being doppler-shifted to zero as the spin speed increases. When the sound starts back up again, it’s because the waves have been shifted from a positive frequency to a negative frequency. Those negative-frequency waves are capable of taking some of the energy from the spinning foam disc, becoming louder in the process – just as Zel’dovich proposed in 1971.”

    Professor Daniele Faccio, also of the University of Glasgow’s School of Physics and Astronomy, is a co-author on the paper. Prof Faccio added: “We’re thrilled to have been able to experimentally verify some extremely odd physics a half-century after the theory was first proposed. It’s strange to think that we’ve been able to confirm a half-century-old theory with cosmic origins here in our lab in the west of Scotland, but we think it will open up a lot of new avenues of scientific exploration. We’re keen to see how we can investigate the effect on different sources such as electromagnetic waves in the near future.”

    The research team’s paper, titled ‘Amplification of waves from a rotating body’, is published in Nature Physics. The research was supported by funding from the Engineering and Physical Sciences Research Council (EPSRC) and the European Union’s Horizon 2020 programme.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Glasgow campus

    The University of Glasgow (Scottish Gaelic: Oilthigh Ghlaschu, Latin: Universitas Glasguensis) is the fourth oldest university in the English-speaking world and one of Scotland’s four ancient universities. It was founded in 1451. Along with the University of Edinburgh, the University was part of the Scottish Enlightenment during the 18th century. It is currently a member of Universitas 21, the international network of research universities, and the Russell Group.

    In common with universities of the pre-modern era, Glasgow originally educated students primarily from wealthy backgrounds, however it became a pioneer[citation needed] in British higher education in the 19th century by also providing for the needs of students from the growing urban and commercial middle class. Glasgow University served all of these students by preparing them for professions: the law, medicine, civil service, teaching, and the church. It also trained smaller but growing numbers for careers in science and engineering.[4]

    Originally located in the city’s High Street, since 1870 the main University campus has been located at Gilmorehill in the West End of the city.[5] Additionally, a number of university buildings are located elsewhere, such as the University Marine Biological Station Millport on the Island of Cumbrae in the Firth of Clyde and the Crichton Campus in Dumfries.

    Alumni or former staff of the University include philosopher Francis Hutcheson, engineer James Watt, philosopher and economist Adam Smith, physicist Lord Kelvin, surgeon Joseph Lister, 1st Baron Lister, seven Nobel laureates, and two British Prime Ministers.

     
  • richardmitnick 9:54 am on June 23, 2020 Permalink | Reply
    Tags: "Keeping Time at NIST", , , Physics   

    From NIST: “Keeping Time at NIST” 


    From NIST

    June 23, 2020
    Mark Esser

    Einstein is reported to have once said that time is what a clock measures. Some say that what we experience as time is really our experience of the phenomenon of entropy, the second law of thermodynamics. Entropy, loosely explained, is the tendency for things to become disorganized. Hot coffee always goes cold. It never reheats itself. Eggs don’t unscramble themselves. Your room gets messy and you have to expend energy to clean it, until it gets messy again.

    Here at NIST, we don’t worry about any of these philosophical notions of time. For us, time is the interval between two events. That could be the rising and setting of the sun, the swing of a pendulum from one side to another, or the back-and-forth vibration of a small piece of quartz. For the most precise measurement of the second, we look at the electromagnetic waves that an atom releases and consider the very short time it takes two successive peaks of the wave to hit a detector. This “frequency” — the number of wave cycles that hit a detector per second — can be used to precisely define very brief time intervals.

    James Clerk Maxwell, the father of electromagnetic theory, was the first person to suggest that we might use the frequencies of atomic radiation as a kind of invariant natural pendulum, but he was talking about this in the mid-19th century, long before we could exert any kind of control over individual atoms. We would have to wait a century for NIST’s Harold Lyons to build the world’s first atomic clock.

    1
    NIST Director Edward Condon (left) and clock inventor Harold Lyons contemplate the ammonia molecule upon which the clock was based.

    Lyons’ atomic clock, which he and his team debuted in 1949, was actually based on the ammonia molecule, but the principle is essentially the same. Inside a chamber, a gas of atoms or molecules fly into a device that emits microwave radiation. The emitter creates microwave radiation with a narrow range of frequencies. When the emitter hits the right frequency, it energizes a maximum number of atoms. The atoms want to lose that energy as quickly as possible, and that loss of energy is manifested as microwaves with a specific frequency. The time it takes a defined number of wavelengths of those microwaves to hit a detector is what we call a second.

    Lyons’ clock, while revolutionary, wasn’t any better at keeping time than doing so by astronomical observations. The first clock that used cesium and was accurate enough to be used as a time standard was built by NIST’s counterpart in the U.K., the National Physical Laboratory, in 1955. NIST’s first cesium clock accurate enough to be used as a time standard, NBS-2, was built a few years later in 1958 and went into service as the U.S. official time standard on January 1, 1960. It had an uncertainty of one second in every 3,000 years, meaning that it kept time to within 1/3,000 of a second per year, pretty good compared to an average quartz watch, which might gain or lose a second every month.

    The atomic second based on the cesium clock was defined in the International System of Units as the duration of 9,192,631,770 cycles of radiation in 1967. It remains so defined to this day.

    While the definition has stayed the same, atomic clocks sure haven’t. Atomic clocks have been continually improved, becoming more and more stable and accurate until the hot clock design reached its peak with the NIST-7, which would neither gain nor lose one second in 6 million years.

    Why do we say “hot” clock? That’s because until the 1990s, the temperature of the cesium inside these clocks was a little more than room temperature. At those temperatures, cesium atoms move at around 130 meters per second, pretty fast. So fast, in fact, that it was hard to get a read on them. The clocks simply didn’t have much time to maximize their fluorescence and get a more accurate and stable signal. What we needed to do was give our detectors more time to get the best signal by slowing down the atoms. But how do you slow down an atom? With laser cooling, of course.

    But how can lasers cause something to cool down? Aren’t lasers hot? The answer is: It depends. The science of slowing down atoms with lasers was pioneered by Bill Phillips and his colleagues, a feat for which they shared the 1997 Nobel Prize in Physics. Very basically what they did was use a specially tuned array of lasers to bombard the atoms with photons from all angles. These photons are like pingpong balls compared to the bowling-ball-like atoms, but if you have enough of them, they can arrest the motion of the cesium atoms, slowing them from about 130 meters per second to a few centimeters per second, giving the clock plenty of time to get a good read on their signal and vastly improving the accuracy and precision of the clock.

    The first clock to use this new technology, NIST-F1, called a fountain clock, was put into service in 1999 and originally offered a threefold improvement over its predecessor, keeping time to within 1/20,000,000 of a second per year. NIST continued to enhance the design of NIST-F1 and subsequent fountain clocks until the accuracies approached one second every 100,000,000 years.

    2
    In the JILA/NIST strontium atomic clock, a few thousand atoms of strontium are held in an “optical lattice,” a 30-by-30 micrometer column of about 400 pancake-shaped regions formed by intense laser light. Credit: The Ye group and Brad Baxley, JILA

    Not ones to rest on our laurels, NIST and its partner institutions, including JILA, are also working on a series of experimental clocks that operate at optical frequencies with trillions of clock “ticks” per second. One of these clocks, the strontium atomic clock, is accurate to within 1/15,000,000,000 of a second per year. This is so accurate that it would not have gained or lost a second if the clock had started running at the dawn of the universe.

    But why do we need such accurate clocks? One thing that wouldn’t exist without such accurate time is the Global Positioning System, or GPS. Each satellite in the GPS network has atomic clocks aboard that beam signals to users below about their position and the time they sent the signal. By measuring the amount of time it takes for the signal to get to you from four different satellites, the receiver in your car or in your phone can figure out where you are to within a few meters or less.

    Such accurate time is also used to timestamp financial transactions so that we know exactly when trades are happening, which can mean the difference between making a fortune and going broke. Accurate time is also necessary for synchronizing communications signals so that, for instance, your call isn’t lost as you travel between cellphone towers.

    And as new, even more accurate clocks are invented, it’s assured that we will find uses for them. In the meantime, you’ll have to settle for knowing where you are anywhere on Earth at any given time while talking on your cellphone on your way to an appointment. Even if you arrive a few millionths of a second late, we won’t give you a hard time about it.

    See the full article here.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    NIST Campus, Gaitherberg, MD, USA

    NIST Mission, Vision, Core Competencies, and Core Values

    NIST’s mission

    To promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
    NIST’s vision

    NIST will be the world’s leader in creating critical measurement solutions and promoting equitable standards. Our efforts stimulate innovation, foster industrial competitiveness, and improve the quality of life.
    NIST’s core competencies

    Measurement science
    Rigorous traceability
    Development and use of standards

    NIST’s core values

    NIST is an organization with strong values, reflected both in our history and our current work. NIST leadership and staff will uphold these values to ensure a high performing environment that is safe and respectful of all.

    Perseverance: We take the long view, planning the future with scientific knowledge and imagination to ensure continued impact and relevance for our stakeholders.
    Integrity: We are ethical, honest, independent, and provide an objective perspective.
    Inclusivity: We work collaboratively to harness the diversity of people and ideas, both inside and outside of NIST, to attain the best solutions to multidisciplinary challenges.
    Excellence: We apply rigor and critical thinking to achieve world-class results and continuous improvement in everything we do.

     
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