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  • richardmitnick 11:57 am on September 5, 2017 Permalink | Reply
    Tags: "Minuscule jitters may hint at quantum collapse mechanism, Classical Mechanics, , , ,   

    From Science News: “Minuscule jitters may hint at quantum collapse mechanism” 

    ScienceNews bloc

    ScienceNews

    September 1, 2017
    Emily Conover

    Data match prediction for wave function theory, but more experiments are needed.

    1
    A tiny, shimmying cantilever wiggles a bit more than expected in a new experiment. The excess jiggling of the miniature, diving board–like structure might hint at why the strange rules of quantum mechanics don’t apply in the familiar, “classical” world. But that potential hint is still a long shot: Other sources of vibration are yet to be fully ruled out, so more experiments are needed.

    Quantum particles can occupy more than one place at the same time, a condition known as a superposition (SN: 11/20/10, p. 15). Only once a particle’s position is measured does its location become definite. In quantum terminology, the particle’s wave function, which characterizes the spreading of the particle, collapses to a single location (SN Online: 5/26/14).

    In contrast, larger objects are always found in one place. “We never see a table or chair in a quantum superposition,” says theoretical physicist Angelo Bassi of the University of Trieste in Italy, a coauthor of the study, to appear in Physical Review Letters. But standard quantum mechanics doesn’t fully explain why large objects don’t exist in superpositions, or how and why wave functions collapse.

    Extensions to standard quantum theory can alleviate these conundrums by assuming that wave functions collapse spontaneously, at random intervals. For larger objects, that collapse happens more quickly, meaning that on human scales objects don’t show up in two places at once.

    Now, scientists have tested one such theory by looking for one of its predictions: a minuscule jitter, or “noise,” imparted by the random nature of wave function collapse. The scientists looked for this jitter in a miniature cantilever, half a millimeter long. After cooling the cantilever and isolating it to reduce external sources of vibration, the researchers found that an unexplained trembling still remained.

    In 2007, physicist Stephen Adler of the Institute for Advanced Study in Princeton, N.J., predicted that the level of jitter from wave function collapse would be large enough to spot in experiments like this one. The new measurement is consistent with Adler’s prediction. “That’s the interesting fact, that the noise matches these predictions,” says study coauthor Andrea Vinante, formerly of the Institute for Photonics and Nanotechnologies in Trento, Italy. But, he says, he wouldn’t bet on the source being wave function collapse. “It is much more likely that it’s some not very well understood effect in the experiment.” In future experiments, the scientists plan to change the design of the cantilever to attempt to isolate the vibration’s source.

    The result follows similar tests performed with the LISA Pathfinder spacecraft, which was built as a test-bed for gravitational wave detection techniques. Two different studies found no excess jiggling Physical Review D] of free-falling weights [Physical Review D] within the spacecraft. But the new cantilever experiment tests for wave function collapse occurring at different rate and length scales than those previous studies.

    ESA/LISA Pathfinder

    Two different studies found no excess jiggling of free-falling weights within the spacecraft. But the new cantilever experiment tests for wave function collapse occurring at different rate and length scales than those previous studies.

    Theories that include spontaneous wave function collapse are not yet accepted by most physicists. But interest in them has recently become more widespread, says physicist David Vitali of the University of Camerino in Italy, “sparked by the fact that technological advances now make fundamental tests of quantum mechanics much easier to conceive.” Focusing on a simple system like the cantilever is the right approach, says Vitali, who was not involved with the research. Still, “a lot of things can go wrong or can be not fully controlled.”

    To conclude that wave function collapse is the cause of the excess vibrations, every other possible source will have to be ruled out. So, Adler says, “it’s going to take a lot of confirmation to check that this is a real effect.”

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

    Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

    Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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  • richardmitnick 11:47 am on September 11, 2015 Permalink | Reply
    Tags: , Classical Mechanics, Mott transition, , ,   

    From phys.org: “Team announces breakthrough observation of Mott transition in a superconductor” 

    physdotorg
    phys.org

    September 11, 2015
    Joost Bruysters

    1

    An international team of researchers, including the MESA+ Institute for Nanotechnology at the University of Twente in The Netherlands and the U.S. Department of Energy’s Argonne National Laboratory, announced today in Science the observation of a dynamic Mott transition in a superconductor.

    The discovery experimentally connects the worlds of classical and quantum mechanics and illuminates the mysterious nature of the Mott transition. It also could shed light on non-equilibrium physics, which is poorly understood but governs most of what occurs in our world. The finding may also represent a step towards more efficient electronics based on the Mott transition.

    Since its foundations were laid in the early part of the 20th century, scientists have been trying to reconcile quantum mechanics with the rules of classical or Newtonian physics (like how you describe the path of an apple thrown into the air—or dropped from a tree). Physicists have made strides in linking the two approaches, but experiments that connect the two are still few and far between; physics phenomena are usually classified as either quantum or classical, but not both.

    One system that unites the two is found in superconductors, certain materials that conduct electricity perfectly when cooled to very low temperatures. Magnetic fields penetrate the superconducting material in the form of tiny filaments called vortices, which control the electronic and magnetic properties of the materials.

    These vortices display both classical and quantum properties, which led researchers to study them for access to one of the most enigmatic phenomena of modern condensed matter physics: the Mott insulator-to-metal transition.

    The Mott transition occurs in certain materials that according to textbook quantum mechanics should be metals, but in reality turn insulators. A complex phenomenon controlled by the interactions of many quantum particles, the Mott transition remains mysterious—even whether or not it’s a classical or quantum phenomenon is not quite clear. Moreover, scientists have never directly observed a dynamic Mott transition, in which a phase transition from an insulating to a metallic state is induced by driving an electrical current through the system; the disorder inherent in real systems disguises Mott properties.

    At the University of Twente, researchers built a system containing 90,000 superconducting niobium nano-sized islands on top of a gold film. In this configuration, the vortices find it energetically easiest to settle into energy dimples in an arrangement like an egg crate—and make the material act as a Mott insulator, since the vortices won’t move if the applied electric current is small.

    2

    When they applied a large enough electric current, however, the scientists saw a dynamic Mott transition as the system flipped to become a conducting metal; the properties of the material had changed as the current pushed it out of equilibrium.

    The vortex system behaved exactly like an electronic Mott transition driven by temperature, said Valerii Vinokur, an Argonne Distinguished Fellow and corresponding author on the study. He and study co-author Tatyana Baturina, then at Argonne, analyzed the data and recognized the Mott behavior.

    “This experimentally materializes the correspondence between quantum and classical physics,” Vinokur said. “We can controllably induce a phase transition between a state of locked vortices to itinerant vortices by applying an electric current to the system,” said Hans Hilgenkamp, head of the University of Twente research group. “Studying these phase transitions in our artificial systems is interesting in its own right, but may also provide further insight in the electronic transitions in real materials.”

    The system could further provide scientists with insight into two categories of physics that have been hard to understand: many-body systems and out-of-equilibrium systems.

    “This is a classical system that which is easy to experiment with and provides what looks like access to very complicated many-body systems,” said Vinokur. “It looks a bit like magic.”

    As the name implies, many-body problems involve a large number of particles interacting; with current theory they are very difficult to model or understand.

    1

    “Furthermore, this system will be key to building a general understanding of out-of-equilibrium physics, which would be a major breakthrough in physics,” Vinokur said.

    The Department of Energy named five great basic energy scientific challenges of our time; one of them is understanding and controlling out-of-equilibrium phenomena. Equilibrium systems—where there’s no energy moving around—are now understood quite well. But nearly everything in our lives involves energy flow, from photosynthesis to digestion to tropical cyclones, and we don’t yet have the physics to describe it well. Scientists think a better understanding could lead to huge improvements in energy capture, batteries and energy storage, electronics and more.

    As we seek to make electronics faster and smaller, Mott systems also offer a possible alternative to the silicon transistor. Since they can be flipped between conducting and insulating with small changes in voltage, they may be able to encode 1s and 0s at smaller scales and higher accuracy than silicon transistors.

    ‘Initially, we were studying the structures for completely different reasons, namely to investigate the effects of inhomogeneities on superconductivity,” Hilgenkamp said. “After discussing with Valerii Vinokur at Argonne, we looked more specifically into our data and were quite amazed to see that it revealed so nicely the details of the transition between the state of locked and moving vortices. There are many ideas for follow up studies, and we look forward to our continued collaboration.”

    The results were printed in the study Critical behavior at a dynamic vortex insulator-to-metal transition, released today in Science. Other co-authors are associated with the Siberian Branch of Russian Academy of Science, the Rome International Center for Materials Science Superstripes, Novosibirsk State University, the Moscow Institute of Physics and Technology and Queen Mary University of London.

    See the full article here .

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    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 4:29 pm on May 28, 2015 Permalink | Reply
    Tags: , Classical Mechanics, , ,   

    From NOVA: “Ultracold Experiment Could Solve One of Physics’s Biggest Contradictions” 

    PBS NOVA

    NOVA

    28 May 2015
    Allison Eck

    1
    A vortex structure emerges within a rotating Bose-Einstein condensate.

    There’s a mysterious threshold that’s predicted to exist beyond the limits of what we can see. It’s called the quantum-classical transition.

    If scientists were to find it, they’d be able to solve one of the most baffling questions in physics: why is it that a soccer ball or a ballet dancer both obey the Newtonian laws while the subatomic particles they’re made of behave according to quantum rules? Finding the bridge between the two could usher in a new era in physics.

    We don’t yet know how the transition from the quantum world to the classical one occurs, but a new experiment, detailed in Physical Review Letters, might give us the opportunity to learn more.

    The experiment involves cooling a cloud of rubidium atoms to the point that they become virtually motionless. Theoretically, if a cloud of atoms becomes cold enough, the wave-like (quantum) nature of the individual atoms will start to expand and overlap with one another. It’s sort of like circular ripples in a pond that, as they get bigger, merge to form one large ring. This phenomenon is more commonly known as a Bose-Einstein condensate, a state of matter in which subatomic particles are chilled to near absolute zero (0 Kelvin or −273.15° C) and coalesce into a single quantum object. That quantum object is so big (compared to the individual atoms) that it’s almost macroscopic—in other words, it’s encroaching on the classical world.

    The team of physicists cooled their cloud of atoms down to the nano-Kelvin range by trapping them in a magnetic “bowl.” To attempt further cooling, they then shot the cloud of atoms upward in a 10-meter-long pipe and let them free-fall from there, during which time the atom cloud expanded thermally. Then the scientists contained that expansion by sending another laser down onto the atoms, creating an electromagnetic field that kept the cloud from expanding further as it dropped. It created a kind of “cooling” effect, but not in the traditional way you might think—rather, the atoms have a lowered “effective temperature,” which is a measure of how quickly the atom cloud is spreading outward. At this point, then, the atom cloud can be described in terms of two separate temperatures: one in the direction of downward travel, and another in the transverse direction (perpendicular to the direction of travel).

    Here’s Chris Lee, writing for ArsTechnica:

    “This is only the start though. Like all lenses, a magnetic lens has an intrinsic limit to how well it can focus (or, in this case, collimate) the atoms. Ultimately, this limitation is given by the quantum uncertainty in the atom’s momentum and position. If the lensing technique performed at these physical limits, then the cloud’s transverse temperature would end up at a few femtoKelvin (10-15). That would be absolutely incredible.

    A really nice side effect is that combinations of lenses can be used like telescopes to compress or expand the cloud while leaving the transverse temperature very cold. It may then be possible to tune how strongly the atoms’ waves overlap and control the speed at which the transition from quantum to classical occurs. This would allow the researchers to explore the transition over a large range of conditions and make their findings more general.”

    Jason Hogan, assistant professor of physics at Stanford University and one of the study’s authors, told NOVA Next that you can understand this last part by using the Heisenberg Uncertainty Principle. As a quantum object’s uncertainty in momentum goes down, its uncertainty in position goes up. Hogan and his colleagues are essentially fine-tuning these parameters along two dimensions. If they can find a minimum uncertainty in the momentum (by cooling the particles as much as they can), then they could find the point at which the quantum-to-classical transition occurs. And that would be a spectacular discovery for the field of particle physics.

    See the full article here.

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
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