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  • richardmitnick 4:58 pm on November 14, 2017 Permalink | Reply
    Tags: , , , , , Quantum Circuits Company, , Quantum Mechanics, , Robert Schoelkopf is at the forefront of a worldwide effort to build the world’s first quantum computer,   

    From NYT: “Yale Professors Race Google and IBM to the First Quantum Computer” 

    New York Times

    The New York Times

    NOV. 13, 2017
    CADE METZ

    1
    Prof. Robert Schoelkopf inside a lab at Yale University. Quantum Circuits, the start-up he has created with two of his fellow professors, is located just down the road. Credit Roger Kisby for The New York Times

    Robert Schoelkopf is at the forefront of a worldwide effort to build the world’s first quantum computer. Such a machine, if it can be built, would use the seemingly magical principles of quantum mechanics to solve problems today’s computers never could.

    Three giants of the tech world — Google, IBM, and Intel — are using a method pioneered by Mr. Schoelkopf, a Yale University professor, and a handful of other physicists as they race to build a machine that could significantly accelerate everything from drug discovery to artificial intelligence. So does a Silicon Valley start-up called Rigetti Computing. And though it has remained under the radar until now, those four quantum projects have another notable competitor: Robert Schoelkopf.

    After their research helped fuel the work of so many others, Mr. Schoelkopf and two other Yale professors have started their own quantum computing company, Quantum Circuits.

    Based just down the road from Yale in New Haven, Conn., and backed by $18 million in funding from the venture capital firm Sequoia Capital and others, the start-up is another sign that quantum computing — for decades a distant dream of the world’s computer scientists — is edging closer to reality.

    “In the last few years, it has become apparent to us and others around the world that we know enough about this that we can build a working system,” Mr. Schoelkopf said. “This is a technology that we can begin to commercialize.”

    Quantum computing systems are difficult to understand because they do not behave like the everyday world we live in. But this counterintuitive behavior is what allows them to perform calculations at rate that would not be possible on a typical computer.

    Today’s computers store information as “bits,” with each transistor holding either a 1 or a 0. But thanks to something called the superposition principle — behavior exhibited by subatomic particles like electrons and photons, the fundamental particles of light — a quantum bit, or “qubit,” can store a 1 and a 0 at the same time. This means two qubits can hold four values at once. As you expand the number of qubits, the machine becomes exponentially more powerful.

    Todd Holmdahl, who oversees the quantum project at Microsoft, said he envisioned a quantum computer as something that could instantly find its way through a maze. “A typical computer will try one path and get blocked and then try another and another and another,” he said. “A quantum computer can try all paths at the same time.”

    The trouble is that storing information in a quantum system for more than a short amount of time is very difficult, and this short “coherence time” leads to errors in calculations. But over the past two decades, Mr. Schoelkopf and other physicists have worked to solve this problem using what are called superconducting circuits. They have built qubits from materials that exhibit quantum properties when cooled to extremely low temperatures.

    With this technique, they have shown that, every three years or so, they can improve coherence times by a factor of 10. This is known as Schoelkopf’s Law, a playful ode to Moore’s Law, the rule that says the number of transistors on computer chips will double every two years.

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    Professor Schoelkopf, left, and Prof. Michel Devoret working on a device that can reach extremely low temperatures to allow a quantum computing device to function. Credit Roger Kisby for The New York Times

    “Schoelkopf’s Law started as a joke, but now we use it in many of our research papers,” said Isaac Chuang, a professor at the Massachusetts Institute of Technology. “No one expected this would be possible, but the improvement has been exponential.”

    These superconducting circuits have become the primary area of quantum computing research across the industry. One of Mr. Schoelkopf’s former students now leads the quantum computing program at IBM. The founder of Rigetti Computing studied with Michel Devoret, one of the other Yale professors behind Quantum Circuits.

    In recent months, after grabbing a team of top researchers from the University of California, Santa Barbara, Google indicated it is on the verge of using this method to build a machine that can achieve “quantum supremacy” — when a quantum machine performs a task that would be impossible on your laptop or any other machine that obeys the laws of classical physics.

    There are other areas of research that show promise. Microsoft, for example, is betting on particles known as anyons. But superconducting circuits appear likely to be the first systems that will bear real fruit.

    The belief is that quantum machines will eventually analyze the interactions between physical molecules with a precision that is not possible today, something that could radically accelerate the development of new medications. Google and others also believe that these systems can significantly accelerate machine learning, the field of teaching computers to learn tasks on their own by analyzing data or experiments with certain behavior.

    A quantum computer could also be able to break the encryption algorithms that guard the world’s most sensitive corporate and government data. With so much at stake, it is no surprise that so many companies are betting on this technology, including start-ups like Quantum Circuits.

    The deck is stacked against the smaller players, because the big-name companies have so much more money to throw at the problem. But start-ups have their own advantages, even in such a complex and expensive area of research.

    “Small teams of exceptional people can do exceptional things,” said Bill Coughran, who helped oversee the creation of Google’s vast internet infrastructure and is now investing in Mr. Schoelkopf’s company as a partner at Sequoia. “I have yet to see large teams inside big companies doing anything tremendously innovative.”

    Though Quantum Circuits is using the same quantum method as its bigger competitors, Mr. Schoelkopf argued that his company has an edge because it is tackling the problem differently. Rather than building one large quantum machine, it is constructing a series of tiny machines that can be networked together. He said this will make it easier to correct errors in quantum calculations — one of the main difficulties in building one of these complex machines.

    But each of the big companies insist that they hold an advantage — and each is loudly trumpeting its progress, even if a working machine is still years away.

    Mr. Coughran said that he and Sequoia envision Quantum Circuits evolving into a company that can deliver quantum computing to any business or researcher that needs it. Another investor, Canaan’s Brendan Dickinson, said that if a company like this develops a viable quantum machine, it will become a prime acquisition target.

    “The promise of a large quantum computer is incredibly powerful,” Mr. Dickinson said. “It will solve problems we can’t even imagine right now.”

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  • richardmitnick 10:05 am on November 8, 2017 Permalink | Reply
    Tags: A computer for completely new problems, , Basel researchers lead the field, , Collaboration with industrial partner IBM, , Quantum Mechanics,   

    From U Basel: “The second revolution in quantum physics” 

    u-basel-bloc

    U Basel

    11.8.17
    Dominik Zumbühl

    1
    Dominik Zumbühl, U Basel

    Quantum physics promises to deliver revolutionary new technologies such as the quantum computer – with far-reaching consequences for the economy and society. For many years, the University of Basel has been playing a pioneering role in quantum research.

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    Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons

    07-09-2017
    We have demonstrated a quantum memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency, and with an acceptance bandwidth of δf=0.66 GHz. This memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. These results were published in Physical Review Letters 119, 060502.

    In the first third of the 20th century, physicists such as Max Planck, Albert Einstein, Erwin Schrödinger, and Werner Heisenberg fundamentally changed the way we understand nature. With the development of quantum mechanics, a theory was emerging that would challenge human understanding and intuition. Its pioneers were simultaneously astonished and bewildered, and used thought experiments to try to illustrate the paradoxical consequences of the new theory. In the most famous example, Schrödinger describes a cat that, according to the laws of quantum physics, is alive and dead at the same time. However absurd ideas like this may seem, quantum theory is now seen as one of the greatest achievements in science and has revolutionized the way we see the world.

    Over the last 20 years or so, quantum physics has given rise to a second revolution. With a steady stream of new experiments, scientists have shown that we can use the crazy world of quantum physics to do useful things that would be impossible in classical physics.

    Today, highly sensitive quantum sensors allow us to measure magnetic fields faster and more accurately than ever before. In the near future, quantum physics could pave the way for secure communication channels. In the past, medical diagnostic devices such as magnetic resonance imaging (MRI) scanners have been developed based on the laws of quantum physics.

    A computer for completely new problems

    Quantum physics offers breathtaking potential for innovation. Against this backdrop, physicists at the University of Basel are pursuing the vision of a computer that takes advantage of the laws of quantum mechanics.

    A quantum computer can perform a large number of computing operations in parallel. It is therefore incredibly fast and solves problems in a matter of hours that would take today’s supercomputers billions of years. Whereas the latest supercomputers contain a billion transistors, a quantum computer would contain a billion quantum bits (qubits). While classical bits can adopt only states of 0 or 1, qubits allow you to define more than just two states. In the future, their sheer computing power could allow us to answer questions we have not even dared to ask yet. It is conceivable, for example, that we will be able to create molecules and therefore materials with previously unknown properties: new types of pharmaceutical active substances, for example. Or superconductors for transporting electricity without loss at room temperature. Or chlorophyll-like substances that convert sunlight into useful energy. Until now, innovative substances tended to be discovered by chance. However, in the future, quantum computers could allow scientists to design materials with desirable properties in a targeted manner.

    The quantum computer is a highly promising innovation. Its realization is now the subject of work by leading researchers from Harvard to Tokyo. One promising implementation is based on an idea, formulated 20 years ago by the physicist Daniel Loss, that the angular momentum (spin) of individual electrons can be used as the smallest information carrier in a quantum computer. In laboratories around the world, qubits of this kind are considered the most promising candidates for building a quantum computer. The idea’s originator, Daniel Loss, works in Basel and devotes his time to developing a Basel qubit. Manufactured from a semiconducting material, this qubit is extremely small and fast. As silicon is a thoroughly tried-and-tested material for computer chips, silicon qubits offer key advantages over other qubit concepts. Developing a qubit is the overarching objective of Basel’s physics department, where 12 professors are channeling the expertise of their research teams into achieving this common goal.

    Basel researchers lead the field

    Let me state clearly the magnitude of the challenge: the Department of Physics at the University of Basel is not an industrial laboratory seeking to build a quantum computer in the next few months or years. Rather, we are carrying out research on the foundations of the quantum computer. Research of this kind is very time-consuming but has the potential to bring about genuine innovations. It is worth remembering that, after the transistor was discovered in 1947, it took half a century for personal computers and mobile phones to make their way into our everyday lives and to turn the world of work upside down. With regard to the quantum computer, the marathon has only just begun. Today, companies like Microsoft, Google, and Intel are pinning their hopes on the quantum computer as they realize that the increasing miniaturization of classical CMOS chips is reaching its limits. Basel’s ambition is to be among the front-runners.

    So far, we’ve been making great progress. In recent years, Basel’s physicists have secured eight of the prestigious grants from the European Research Council (ERC), with the last two going to our professors Jelena Klinovaja and Ilaria Zardo. This success demonstrates the excellence of our research portfolio. Many young researchers are attracted to the brilliance of the quantum research carried out in Basel. Operating since autumn 2016, the PhD school for “Quantum Computing and Quantum Technologies” currently brings together 20 doctoral researchers. In addition, generous support from the Georg H. Endress Foundation will allow us to set up a cross-border postdoc cluster in cooperation with the University of Freiburg from January 2018. As a result, there will be ten additional scientists working in the field of quantum computing. This initiative is modeled on foundations in the US that provide funding for postdocs at top centers of research.

    Collaboration with industrial partner IBM

    There are some critical decisions that we currently have to make in the field of quantum physics in order to further strengthen this strategic focus at the University of Basel. These include participation in the EU’s billion-euro flagship project on quantum technologies, which is planned to begin next year. At present, we are preparing an application for a National Centre of Competence in Research (NCCR) from the Swiss National Science Foundation with Basel as the leading house on the topic of scalable quantum computing.

    For this NCCR, we have chosen the IBM Zurich Research Laboratory as our main, coleading partner, together with other universities as partners. Our goal is to build silicon spin qubits. In 12 years, the ambitious target is to have a fully scalable logical qubit consisting of ca. 15 physical qubits. Although this is not yet a complete quantum computer, it does provide a copy-paste blueprint for a quantum chip.

    When the first concepts for a quantum computer emerged, they did so in Europe. With this as our starting point, we now have the opportunity to build the foundation of a new Silicon Valley. Research on the quantum computer is an investment in a future technology and therefore in Switzerland’s industrial base. Our laboratories are also currently home to a rising generation of experts who can understand, shape and disseminate this emergent technology. Only with their help can we succeed in turning the second revolution of quantum physics to the advantage of society as a whole.

    See the full article here .

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    u-basel-campus

    Purposes

    The University of Basel fosters the development of critically thinking and tolerant individuals who are capable of taking initiative and taking on responsibility. It is the aim of the University to enable these individuals to deepen their knowledge and field-specific academic training and further education.

    Through research and teaching, the University imparts the insights past down over the ages in addition to producing new knowledge. It is guided by the principle of meaningfulness and purpose rather than feasibility.

    The University is aware of the duties arising from knowledge, fulfilling these duties through critical reflection and the services it provides. It takes its own position concerning problems facing society.

    The University realizes its aims by taking responsibility with respect to future generations, the society that supports them, the international academic community and the culture that is passed down from generation to generation.

     
  • richardmitnick 8:11 am on October 30, 2017 Permalink | Reply
    Tags: , Mach-Zehnder interferometer, , Quantum Mechanics, Scienced Mag   

    From Science: “Quantum experiment in space confirms that reality is what you make it” 

    ScienceMag
    Science Magazine

    Oct. 27, 2017
    Adrian Cho

    1
    To test quantum theory, physicists used the Matera Laser Ranging Observatory in southern Italy, which usually tracks satellites to monitor tiny changes in Earth’s shape. Quantum Future Research Group, University of Padova – DEI, Padova Italy – 2017

    An odd space experiment has confirmed that, as quantum mechanics says, reality is what you choose it to be. Physicists have long known that a quantum of light, or photon, will behave like a particle or a wave depending on how they measure it. Now, by bouncing photons off satellites, a team has confirmed that an observer can make that decision even after a photon has made its way almost completely through the experiment—seemingly well past the point at which it would become either a wave or a particle. Such delayed-choice experiments might someday probe the fuzzy frontier between quantum theory and relativity, researchers say.

    Other researchers have demonstrated the same counterintuitive effect in the laboratory. But the new work shows that a photon’s nature remains undefined even over thousands of kilometers, says Philippe Grangier, a physicist at the Institute of Optics in Palaiseau, France, who collaborated on an earlier test. “It’s a very nice experiment that demonstrates their ability to do quantum physics in space.”

    A photon can act like a bulletlike particle or rippling wave—but not both at once—depending on how experimenters decide to measure it. In the late 1970s, famed theoretician John Archibald Wheeler realized that experimenters could even delay the choice until the photon had made its way almost completely through an apparatus configured to emphasize one property or the other, thus proving that the photon’s behavior isn’t predetermined.

    Wheeler imagined sending photons one at a time through a so-called Mach-Zehnder interferometer, which accentuates light’s wave nature. Using a mirrorlike “beam splitter,” the interferometer splits the entering photon’s quantum wave in half and sends the two waves along different paths, like people walking opposite ways around the block. A second beam splitter then recombines the waves, which interfere with each other to shunt the photon toward either one of a pair of detectors. Which detector is triggered depends on the difference in the two paths’ lengths, as expected for interfering waves.

    ____________________________________________________________________________________

    Wave or particle?

    A photon ordinarily takes both paths through a Mach-Zehnder interferometer, and wavelike interference can then shunt it toward one detector or the other. Remove the second beam splitter and, like a particle, the photon must take one path or the other and is equally likely to hit either detector.

    It is explained that if a photon is introduced between the beam splitter and either of the mirrors, it will be detected at one of the two detectors at random. However, if it is introduced before the beam splitter, it will always appear at the same detector. From this follows that the (unobservable) split histories of the photon influence where it will be detected, so an explanation like splitting and interference of universes is necessary.

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    https://physics.stackexchange.com/questions/274379/outcome-of-mach-zehnder-interferometer-experiment

    ______________________________________________________________________________________

    Remove the second beam splitter and interference becomes impossible. Instead, the first beam splitter sends the photon down one path or the other, like a particle. As the paths cross where the second beam splitter would have been, the detectors click with equal probabilities regardless of the paths’ lengths. Wheeler realized that experimenters could even wait to remove the second beam splitter until after the photon had passed the first beam splitter. That assertion suggests, weirdly, that a decision in the present determines an event in the past: whether the photon split like a wave or took one path like a particle. Quantum theory avoids the issue by assuming that, until measured, the photon remains both a particle and a wave.

    Now, a team led by Francesco Vedovato and Paolo Villoresi of the University of Padua in Italy has performed a version of the experiment using the 1.5-meter telescope at the Matera Laser Ranging Observatory in southern Italy to bounce photons off satellites thousands of kilometers away. At such distances, physicists cannot make light take two parallel paths, Villoresi notes, as the spreading beams would overlap and merge. Instead, they send a photon through a Mach-Zehnder interferometer on Earth that has paths of very different lengths. The difference in path lengths splits the single pulse into two, separated in time by 3.5 nanoseconds, which the telescope then shoots skyward.

    Once the pulses return, the experimenters run them back through the interferometer. The apparatus can either undo the time shift so that the two pulses overlap and interfere like waves or double it so that no interference is possible. Of course, the physicists must choose which thing happens. When the pulses first leave the interferometer, they have different polarizations. To undo the time shift, physicists must first use a very fast electronic polarization to change their polarization in a certain way. To double the time shift, they simply leave their polarizations alone.

    When experimenters make the pulses overlap, the photon triggers one detector or another with a probability that depends on the satellite’s recession speed, as expected for interfering waves. When the pulses cannot interfere, then the photon, like a particle, ends up in either detector with a 50-50 probability regardless of the satellite’s speed. Crucially, physicists choose which measurement to make after the light pings off the satellite halfway through its 10-millisecond round-trip, they report 25 October in Science Advances. Again, the delayed decision seems to reach back in time, defining how the photon behaved after it left the first beam splitter.

    The experiment isn’t the most stringent test of Wheeler’s idea, notes Jean-François Roch, a physicist at the École Normale Supérieure in Paris, who in 2007 led a more faithful test. For example, to see the light at all over such long distances, Villoresi and colleagues must fire pulses containing many photons, instead of the individual photons Wheeler specified. Still, Roch says, the experiment is a noteworthy example of taking “quantum optics” out of the lab and into space. In May, physicists in China used a satellite to establish a weird quantum connection called entanglement between two photons sent to widely separated cities.

    Delayed-choice experiments could help probe the boundary between relativity—which requires that cause precede effect—and quantum theory, Roch says. Even though, strictly speaking, the effect does not violate causality, it still raises a tension by suggesting that a measurement in the present shapes what can be inferred about the past. “This area where you mix quantum mechanics and relativity is still relatively unexplored,” Roch says, “and this is the sort of experiment that raised the possibility of probing the link” between the two.

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  • richardmitnick 4:12 pm on October 26, 2017 Permalink | Reply
    Tags: , , Light bounced off satellites confirms quantum weirdness, , Quantum Mechanics,   

    From COSMOS: “Light bounced off satellites confirms quantum weirdness” 

    Cosmos Magazine bloc

    COSMOS Magazine

    26 October 2017
    Andrew P Street

    If light falls in a beam splitter in a forest, does it choose a path? It depends on what happens next, it would appear.

    1
    Bouncing photons off satellites has confirmed quantum weirdness in space — and time. QAI Publishing/UIG via Getty Images

    Anyone hoping that the frustratingly counterintuitive nature of the quantum realm was about to become less inexplicable, brace yourself: the wave-particle duality of light is still as baffling as ever.

    This is confirmed by new research in which scientists fired photons thousands of kilometres into space, bounced them off a fast moving satellite, and watched which of their two possible forms they assumed on return.

    That light behaves as both a particle and a wave has been known since the 1920s, when experiments demonstrated that light entering a plate with two vertical slits would show a classical interference pattern with itself when it reached a screen behind the plate, exactly as one would expect if light were a wave.

    The problem was that if individual detectors were placed at the slits, experimenters found that a single photon would enter one slit but not the other, thereby behaving like a particle. Furthermore, light thus measured would not show an interference pattern.

    That light seemed to know what experimenters were doing and change its behaviour accordingly is one of the many unsettling conclusions of quantum physics – but it gets weirder with the idea that light somehow makes its decision retroactively.

    The late American physicist John Wheeler first posited what became known as the “delayed choice” experiment as part of a series of thought experiments he began publishing in 1978. His Gedankenexperiments went one step further than the classical double slit. The photons were not observed going through the plate, but instead were measured afterwards.

    He theorised that they would still behave as particles, despite not “knowing” they were being measured until after passing through the plate. Experiments conducted in 2007 by French scientists confirmed this was precisely what happened.

    An even more ambitious thought experiment used light from a distant quasar being gravitationally lensed through gravity, raising the notion that a photon “chose” to behave either as a particle or wave based on the actions of an experiment carried out many millions of years after it was created.

    And this peculiar time-bending behaviour was confirmed in a paper published this week in Science Advances.

    An Italian team led by Francesco Vedovato from the Università degli Studi di Padova performed an elegant variation of Wheeler’s original concept by firing a pulsed laser into a beam splitter which directed the light to satellites in low Earth orbit. These reflected the light back to Earth, with the choice to activate a second beam splitter made by the team while the light was in transit – much like the light from Wheeler’s hypothetical quasar.

    The result from the ground stations was exactly as predicted: the light exhibited either wave-like or particle-like behaviour depending on the actions of the observers. And while low Earth orbit is not exactly the vast distances proposed by Wheeler, it appears to confirm that the quantum universe still behaves in disturbingly weird ways.

    Vedovato and his colleagues see exciting practical applications arising from the realisation of Wheeler’s thought experiment on such a large scale. Although they experienced quite a high level of photon loss because of the distance and complexities of the journey, the findings, they write, open the door for further “applications of quantum mechanics involving hyper-entangled states, around the planet and beyond.”

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  • richardmitnick 2:44 pm on October 23, 2017 Permalink | Reply
    Tags: A new species of traversable wormhole has emerged, , , , Black holes and wormholes, Carl Sagan and Kip Thorne, , Many theorists believe in black hole interiors but in order to understand them they must discover the fate of information that falls inside, , Quantum Mechanics, The paradox has loomed since 1974 when the British physicist Stephen Hawking determined that black holes evaporate, The repulsive negative energy in the wormhole’s throat can be generated from the outside by a special quantum connection between the pair of black holes that form the wormhole’s two mouths, The wormhole also safeguards unitarity — the principle that information is never lost, While traversable wormholes won’t revolutionize space travel according to Preskill the new wormhole discovery provides “a promising resolution” to the black hole firewall question by suggesting   

    From Quanta: “Newfound Wormhole Allows Information to Escape Black Holes” 

    Quanta Magazine
    Quanta Magazine

    October 23, 2017
    Natalie Wolchover

    1
    Tomáš Müller for Quanta Magazine

    In 1985, when Carl Sagan was writing the novel Contact, he needed to quickly transport his protagonist Dr. Ellie Arroway from Earth to the star Vega. He had her enter a black hole and exit light-years away, but he didn’t know if this made any sense. The Cornell University astrophysicist and television star consulted his friend Kip Thorne, a black hole expert at the California Institute of Technology (who won a Nobel Prize earlier this month). Thorne knew that Arroway couldn’t get to Vega via a black hole, which is thought to trap and destroy anything that falls in. But it occurred to him that she might make use of another kind of hole consistent with Albert Einstein’s general theory of relativity: a tunnel or “wormhole” connecting distant locations in space-time.

    While the simplest theoretical wormholes immediately collapse and disappear before anything can get through, Thorne wondered whether it might be possible for an “infinitely advanced” sci-fi civilization to stabilize a wormhole long enough for something or someone to traverse it. He figured out that such a civilization could in fact line the throat of a wormhole with “exotic material” that counteracts its tendency to collapse. The material would possess negative energy, which would deflect radiation and repulse space-time apart from itself. Sagan used the trick in Contact, attributing the invention of the exotic material to an earlier, lost civilization to avoid getting into particulars. Meanwhile, those particulars enthralled Thorne, his students and many other physicists, who spent years exploring traversable wormholes and their theoretical implications. They discovered that these wormholes can serve as time machines, invoking time-travel paradoxes — evidence that exotic material is forbidden in nature.

    Now, decades later, a new species of traversable wormhole has emerged, free of exotic material and full of potential for helping physicists resolve a baffling paradox about black holes. This paradox is the very problem that plagued the early draft of Contact and led Thorne to contemplate traversable wormholes in the first place; namely, that things that fall into black holes seem to vanish without a trace. This total erasure of information breaks the rules of quantum mechanics, and it so puzzles experts that in recent years, some have argued that black hole interiors don’t really exist — that space and time strangely end at their horizons.

    The flurry of findings started last year with a paper [Journal not named] that reported the first traversable wormhole that doesn’t require the insertion of exotic material to stay open. Instead, according to Ping Gao and Daniel Jafferis of Harvard University and Aron Wall of Stanford University, the repulsive negative energy in the wormhole’s throat can be generated from the outside by a special quantum connection between the pair of black holes that form the wormhole’s two mouths. When the black holes are connected in the right way, something tossed into one will shimmy along the wormhole and, following certain events in the outside universe, exit the second. Remarkably, Gao, Jafferis and Wall noticed that their scenario is mathematically equivalent to a process called quantum teleportation, which is key to quantum cryptography and can be demonstrated in laboratory experiments.

    John Preskill, a black hole and quantum gravity expert at Caltech, says the new traversable wormhole comes as a surprise, with implications for the black hole information paradox and black hole interiors. “What I really like,” he said, “is that an observer can enter the black hole and then escape to tell about what she saw.” This suggests that black hole interiors really exist, he explained, and that what goes in must come out.

    ____________________________________________________________________

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    Lucy Reading-Ikkanda/Quanta Magazine
    ____________________________________________________________________

    The new wormhole work began in 2013, when Jafferis attended an intriguing talk at the Strings conference in South Korea. The speaker, Juan Maldacena, a professor of physics at the Institute for Advanced Study in Princeton, New Jersey, had recently concluded, based on various hints and arguments, that “ER = EPR.” That is, wormholes between distant points in space-time, the simplest of which are called Einstein-Rosen or “ER” bridges, are equivalent (albeit in some ill-defined way) to entangled quantum particles, also known as Einstein-Podolsky-Rosen or “EPR” pairs. The ER = EPR conjecture, posed by Maldacena and Leonard Susskind of Stanford, was an attempt to solve the modern incarnation of the infamous black hole information paradox by tying space-time geometry, governed by general relativity, to the instantaneous quantum connections between far-apart particles that Einstein called “spooky action at a distance.”

    The paradox has loomed since 1974, when the British physicist Stephen Hawking determined that black holes evaporate — slowly giving off heat in the form of particles now known as “Hawking radiation.” Hawking calculated that this heat is completely random; it contains no information about the black hole’s contents. As the black hole blinks out of existence, so does the universe’s record of everything that went inside. This violates a principle called “unitarity,” the backbone of quantum theory, which holds that as particles interact, information about them is never lost, only scrambled, so that if you reversed the arrow of time in the universe’s quantum evolution, you’d see things unscramble into an exact re-creation of the past.

    Almost everyone believes in unitarity, which means information must escape black holes — but how? In the last five years, some theorists, most notably Joseph Polchinski of the University of California, Santa Barbara, have argued that black holes are empty shells with no interiors at all — that Ellie Arroway, upon hitting a black hole’s event horizon, would fizzle on a “firewall” and radiate out again.

    Many theorists believe in black hole interiors (and gentler transitions across their horizons), but in order to understand them, they must discover the fate of information that falls inside. This is critical to building a working quantum theory of gravity, the long-sought union of the quantum and space-time descriptions of nature that comes into sharpest relief in black hole interiors, where extreme gravity acts on a quantum scale.

    The quantum gravity connection is what drew Maldacena, and later Jafferis, to the ER = EPR idea, and to wormholes. The implied relationship between tunnels in space-time and quantum entanglement posed by ER = EPR resonated with a popular recent belief that space is essentially stitched into existence by quantum entanglement. It seemed that wormholes had a role to play in stitching together space-time and in letting black hole information worm its way out of black holes — but how might this work? When Jafferis heard Maldacena talk about his cryptic equation and the evidence for it, he was aware that a standard ER wormhole is unstable and non-traversable. But he wondered what Maldacena’s duality would mean for a traversable wormhole like the ones Thorne and others played around with decades ago. Three years after the South Korea talk, Jafferis and his collaborators Gao and Wall presented their answer. The work extends the ER = EPR idea by equating, not a standard wormhole and a pair of entangled particles, but a traversable wormhole and quantum teleportation: a protocol discovered in 1993 [Physical Review Letters]that allows a quantum system to disappear and reappear unscathed somewhere else.

    When Maldacena read Gao, Jafferis and Wall’s paper, “I viewed it as a really nice idea, one of these ideas that after someone tells you, it’s obvious,” he said. Maldacena and two collaborators, Douglas Stanford and Zhenbin Yang, immediately began exploring the new wormhole’s ramifications for the black hole information paradox; their paper appeared in April. Susskind and Ying Zhao of Stanford followed this with a paper about wormhole teleportation in July. The wormhole “gives an interesting geometric picture for how teleportation happens,” Maldacena said. “The message actually goes through the wormhole.”


    Video: David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics. Filming by Petr Stepanek. Editing and motion graphics by MK12. Music by Steven Gutheinz.

    Diving Into Wormholes

    In their paper, “Diving Into Traversable Wormholes,” published in Fortschritte der Physik, Maldacena, Stanford and Yang consider a wormhole of the new kind that connects two black holes: a parent black hole and a daughter one formed from half of the Hawking radiation given off by the parent as it evaporates. The two systems are as entangled as they can be. Here, the fate of the older black hole’s information is clear: It worms its way out of the daughter black hole.

    During an interview this month in his tranquil office at the IAS, Maldacena, a reserved Argentinian-American with a track record of influential insights, described his radical musings. On the right side of a chalk-dusty blackboard, Maldacena drew a faint picture of two black holes connected by the new traversable wormhole. On the left, he sketched a quantum teleportation experiment, performed by the famous fictional experimenters Alice and Bob, who are in possession of entangled quantum particles a and b, respectively. Say Alice wants to teleport a qubit q to Bob. She prepares a combined state of q and a, measures that combined state (reducing it to a pair of classical bits, 1 or 0), and sends the result of this measurement to Bob. He can then use this as a key for operating on b in a way that re-creates the state q. Voila, a unit of quantum information has teleported from one place to the other.

    Maldacena turned to the right side of the blackboard. “You can do operations with a pair of black holes that are morally equivalent to what I discussed [about quantum teleportation]. And in that picture, this message really goes through the wormhole.”

    4
    Juan Maldacena, a professor of physics at the Institute for Advanced Study. Sasha Maslov for Quanta Magazine

    Say Alice throws qubit q into black hole A. She then measures a particle of its Hawking radiation, a, and transmits the result of the measurement through the external universe to Bob, who can use this knowledge to operate on b, a Hawking particle coming out of black hole B. Bob’s operation reconstructs q, which appears to pop out of B, a perfect match for the particle that fell into A. This is why some physicists are excited: Gao, Jafferis and Wall’s wormhole allows information to be recovered from black holes. In their paper, they set up their wormhole in a negatively curved space-time geometry that often serves as a useful, if unrealistic, playground for quantum gravity theorists. However, their wormhole idea seems to extend to the real world as long as two black holes are coupled in the right way: “They have to be causally connected and then the nature of the interaction that we took is the simplest thing you can imagine,” Jafferis explained. If you allow the Hawking radiation from one of the black holes to fall into the other, the two black holes become entangled, and the quantum information that falls into one can exit the other.

    The quantum-teleportation format precludes using these traversable wormholes as time machines. Anything that goes through the wormhole has to wait for Alice’s message to travel to Bob in the outside universe before it can exit Bob’s black hole, so the wormhole doesn’t offer any superluminal boost that could be exploited for time travel. It seems traversable wormholes might be permitted in nature as long as they offer no speed advantage. “Traversable wormholes are like getting a bank loan,” Gao, Jafferis and Wall wrote in their paper: “You can only get one if you are rich enough not to need it.”

    A Naive Octopus

    While traversable wormholes won’t revolutionize space travel, according to Preskill the new wormhole discovery provides “a promising resolution” to the black hole firewall question by suggesting that there is no firewall at black hole horizons. Preskill said the discovery rescues “what we call ‘black hole complementarity,’ which means that the interior and exterior of the black hole are not really two different systems but rather two very different, complementary ways of looking at the same system.” If complementarity holds, as is widely assumed, then in passing across a black hole horizon from one realm to the other, Contact’s Ellie Arroway wouldn’t notice anything strange. This seems more likely if, under certain conditions, she could even slide all the way through a Gao-Jafferis-Wall wormhole.

    The wormhole also safeguards unitarity — the principle that information is never lost — at least for the entangled black holes being studied. Whatever falls into one black hole eventually exits the other as Hawking radiation, Preskill said, which “can be thought of as in some sense a very scrambled copy of the black hole interior.”

    Taking the findings to their logical conclusion, Preskill thinks it ought to be possible (at least for an infinitely advanced civilization) to influence the interior of one of these black holes by manipulating its radiation. This “sounds crazy,” he wrote in an email, but it “might make sense if we can think of the radiation, which is entangled with the black hole — EPR — as being connected to the black hole interior by wormholes — ER. Then tickling the radiation can send a message which can be read from inside the black hole!” He added, “We still have a ways to go, though, before we can flesh out this picture in more detail.”

    Indeed, obstacles remain in the quest to generalize the new wormhole findings to a statement about the fate of all quantum information, or the meaning of ER = EPR.

    5
    A sketch known as the “octopus” that expresses the ER = EPR idea.

    https://arxiv.org/abs/1306.0533 [hep-th]

    In Maldacena and Susskind’s paper proposing ER = EPR, they included a sketch that’s become known as the “octopus”: a black hole with tentacle-like wormholes leading to distant Hawking particles that have evaporated out of it. The authors explained that the sketch illustrates “the entanglement pattern between the black hole and the Hawking radiation. We expect that this entanglement leads to the interior geometry of the black hole.”

    But according to Matt Visser, a mathematician and general-relativity expert at Victoria University of Wellington in New Zealand who has studied wormholes since the 1990s, the most literal reading of the octopus picture doesn’t work. The throats of wormholes formed from single Hawking particles would be so thin that qubits could never fit through. “A traversable wormhole throat is ‘transparent’ only to wave packets with size smaller than the throat radius,” Visser explained. “Big wave packets will simply bounce off any small wormhole throat without crossing to the other side.”

    Stanford, who co-wrote the recent paper with Maldacena and Yang, acknowledged that this is a problem with the simplest interpretation of the ER = EPR idea, in which each particle of Hawking radiation has its own tentacle-like wormhole. However, a more speculative interpretation of ER = EPR that he and others have in mind does not suffer from this failing. “The idea is that in order to recover the information from the Hawking radiation using this traversable wormhole,” Stanford said, one has to “gather the Hawking radiation together and act on it in a complicated way.” This complicated collective measurement reveals information about the particles that fell in; it has the effect, he said, of “creating a large, traversable wormhole out of the small and unhelpful octopus tentacles. The information would then propagate through this large wormhole.” Maldacena added that, simply put, the theory of quantum gravity might have a new, generalized notion of geometry for which ER equals EPR. “We think quantum gravity should obey this principle,” he said. “We view it more as a guide to the theory.”

    In his 1994 popular science book, Black Holes and Time Warps, Kip Thorne celebrated the style of reasoning involved in wormhole research. “No type of thought experiment pushes the laws of physics harder than the type triggered by Carl Sagan’s phone call to me,” he wrote; “thought experiments that ask, ‘What things do the laws of physics permit an infinitely advanced civilization to do, and what things do the laws forbid?’”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 7:29 am on October 9, 2017 Permalink | Reply
    Tags: Back in 1905 Einstein had helped pioneer quantum theory with his revolutionary discovery that light has the characteristics of both a wave and a particle, Bohr found a flaw in Einstein’s logic, But does this also mean “spooky action at a distance” is real?, , Einstein and Bohr continued to debate the issue for the rest of their lives, , Einstein was the first to publicly support de Broglie’s bold hypothesis, Einstein-Podolsky-Rosen paradox, Einstein: “God does not play dice with the universe”, Einstein’s hopes of finding hidden variables that would take the uncertainty out of quantum theory were dashed, Erwin Schrödinger, Fifth Solvay Congress in Brussels, Instant action violated Einstein’s theory of relativity: nothing can travel faster than the speed of light, Louis de Broglie, , , Quantum Mechanics, The Copenhagen theory held that subatomic particles were ruled by chance   

    From COSMOS: “Einstein, Bohr and the origins of entanglement” Wonderful article on this debate between Einstein and Bohr 

    Cosmos Magazine bloc

    COSMOS Magazine

    06 October 2017
    Robyn Arianrhod

    Two of history’s greatest physicists argued for decades over one of the deepest mysteries of quantum mechanics. Today, their successors are opening new fronts in the battle to understand ‘spooky action at a distance’.

    1
    Niels Bohr and Albert Einstein at the Fifth Solvay Congress. American Institute Of Physics / Getty Images

    It all began in October 1927, at the Fifth Solvay Congress in Brussels. It was Louis de Broglie’s first congress, and he had been “full of pleasure and curiosity” at the prospect of meeting Einstein, his teenage idol. Now 35, de Broglie happily reported: “I was particularly struck by his mild and thoughtful expression, by his general kindness, by his simplicity, and by his friendliness.”

    Back in 1905, Einstein had helped pioneer quantum theory with his revolutionary discovery that light has the characteristics of both a wave and a particle. Niels Bohr later explained this as “complementarity”: depending on how you observe light, you will see either wave or particle behaviour. As for de Broglie, he had taken Einstein’s idea into even stranger territory in his 1924 PhD thesis: if light waves could behave like particles, then perhaps particles of matter could also behave like waves! After all, Einstein had shown that energy and matter were interchangeable, via E = mc2.

    Einstein was the first to publicly support de Broglie’s bold hypothesis. By 1926, Erwin Schrödinger had developed a mathematical formula to describe such “matter waves”, which he pictured as some kind of rippling sea of smeared-out particles. But Max Born showed that Schrödinger’s waves are, in effect, “waves of probability”. They encode the statistical likelihood that a particle will show up at a given place and time based on the behaviour of many such particles in repeated experiments. When the particle is observed, something strange appears to happen. The wave-function “collapses” to a single point, allowing us to see the particle at a particular position.

    Born’s probability wave also fitted neatly with Werner Heisenberg’s recently proposed “uncertainty principle”. Heisenberg had concluded that in the quantum world it is not possible to obtain exact information about both the position and the momentum of a particle at the same time. He imagined the very act of measuring a quantum particle’s position, say by shining a light on it, gave it a jolt that changed its momentum, so the two could never be precisely measured at once.

    When the world’s leading physicists gathered in Brussels in 1927, this was the strange state of quantum physics.

    The official photograph of the participants shows 28 besuited, sober-looking men, and one equally serious woman, Marie Curie. But fellow physicist Paul Ehrenfest’s private photo of intellectual adversaries Bohr and Einstein captures the spirit of the conference: Bohr looks intensely thoughtful, hand on his chin, while Einstein is leaning back looking relaxed and dreamy. This gentle, contemplative picture belies the depth of the famous clash between these two intellectual titans – a clash that hinged on the extraordinary concept of quantum entanglement.

    At the congress, Bohr presented his view of quantum mechanics for the first time. Dubbed the Copenhagen interpretation, in honour of Bohr’s home city, it combined his own idea of particle-wave complementarity with Born’s probability waves and Heisenberg’s uncertainty principle.

    Most of the attendees readily accepted this view, but Einstein was perturbed. It was one thing for groups of particles to be ruled by chance; indeed Einstein had explained the jittery motion of pollen in apparently still water (dubbed Brownian motion) by invoking the random group behaviour of water molecules. Individual molecules, though, would still be ruled by Newton’s laws of motion; their exact movements could in principle be calculated.

    By contrast, the Copenhagen theory held that subatomic particles were ruled by chance.

    Einstein began his attack in the time-honoured tradition of reductio ad absurdum – arguing that the logical extension of quantum theory would lead to an absurd outcome.

    After several sleepless nights, Bohr found a flaw in Einstein’s logic. Einstein did not retreat: he was sure he could convince Bohr of the absurdity of this strange new theory. Their debate flowed over into the Sixth Solvay Congress in 1930, and on until Einstein felt he finally had the pieces in place to checkmate Bohr at the seventh congress in 1933. Two weeks before that, however, Nazi persecution forced Einstein to flee to the United States. The planned checkmate would have to wait.

    When it came, it was deceptively simple. In 1935 at Princeton, Einstein and two collaborators, Boris Podolsky and Nathan Rosen, published what became known as the Einstein-Podolsky-Rosen paradox [Physical Review Journals Archive], or EPR for short. Podolsky wrote up the thought experiment in a mathematical form, but let me illustrate it with jellybeans.

    Suppose you have a red and a green jellybean in a box. The box seals off the jellybeans from all others: technically speaking, the pair form an “isolated system”, and they are “entangled” in the sense that the colour of one jellybean gives information about the other. You can see this by asking a friend to close her eyes and pick a jellybean at random. If she picks red, you know the remaining sweet is green.

    This is key to EPR: by knowing the colour of your friend’s jellybean, you can know the colour of your own without “disturbing” it by looking at it. But in trying to bypass the supposed observer-effect in this way, EPR had also inadvertently uncovered the strange idea of “entanglement”. The term was coined by Schrödinger after he read the EPR paper .

    So now apply this technique to two electrons. Instead of a colour, each one has an intrinsic property called “spin”. Imagine something like the spin axis of a gyroscope. If two electrons are prepared together in the lab so that they have zero total spin, then the principle of conservation of angular momentum means that if one of the electrons has its spin axis up, the other electron’s axis must be down. The electrons are entangled, just as the jellybeans were.

    2

    With jellybeans, the colour of your friend’s chosen sweet is fixed, whether or not she actually observes it. With electrons, by contrast, until your friend makes her observation, quantum theory simply says there is a 50% chance its spin is up, and 50% it is down.

    The EPR attempt to strike at the heart of quantum theory now goes like this. Perhaps the spin of your friend’s electron was in fact determined before she picked it out. However, like a watermark that can’t be detected until a special light is shone on it, the spin state is only revealed when she looks at it. Quantum spin, then, involves a “hidden variable”, yet to be described by quantum theory. Alternatively, if quantum mechanics is correct and complete, then the theory defies common sense – because as soon as your friend checks the spin of her electron, your electron appears to respond instantly, because if hers is “up” then yours will be “down”.

    This is because the correlation between the two spins was built into the experiment when the electrons were first entangled, just as putting the two jellybeans in a box ensures the colour of your jellybean will be “opposite” that of your friend’s. The implications are profound. Even if your friend moved to the other side of the galaxy, your electron would “know” that it must manifest the opposite spin in the instant she makes her observation.

    Of course, instant action violated Einstein’s theory of relativity: nothing can travel faster than the speed of light. Hence Einstein dubbed this absurd proposition “spooky action at a distance”.

    But there was more. Spin is not the only property your friend could have chosen to observe. What EPR showed, then, is that the physical nature of your electron seems to have no identity of its own. Rather, it depends on how your friend chooses to observe her electron. As Einstein put it: “Do you really believe the Moon is there only when you look at it?” The EPR paper concluded: “No reasonable definition of reality could be expected to permit this.” Ergo, the authors believed, quantum theory had some serious problems.

    Bohr was stumped by EPR. He ditched the idea that the act of measurement jolted the state of the particle. (Indeed, later experiments would show that uncertainty is not solely the result of an interfering observer; it is an inherent characteristic of particles.)

    But he did not abandon the uncertainty at the heart of quantum mechanics. Instead of trying to wrestle with the real world implications, he concluded [Physical Review Journals Archive] that we can only speak of what we observe – at the beginning of the experiment and the end when your friend’s electron is definitely “up”, say. We cannot speak about what happens in between.

    Einstein and Bohr continued to debate the issue for the rest of their lives. What they really disagreed about was the nature of reality. Bohr believed that nature was fundamentally random. Einstein did not. “God does not play dice with the universe,” he declared.

    Nevertheless, Einstein knew that quantum theory accurately described the results of real as opposed to thought experiments. So most physicists considered that Bohr had won. They focused on applying quantum theory, and questions about the EPR paradox and entanglement became a niche interest.

    In 1950, Chien-Shiung Wu and Irving Shaknov [Physical Review Journals Archive] found oddly linked behaviour in pairs of photons. They didn’t know it at the time but it was the first real-world observation of quantum entanglement.

    ___________________________________________________________________________
    Some suggest that something like a ‘wormhole’ – a tunnel in spacetime between two widely separated black holes, a consequence of general relativity theory first deduced by Einstein and Rosen – may be the mechanism underlying entanglement.
    ___________________________________________________________________________

    Later, David Bohm realised [Physical Review Journals Archive] Wu and Shaknov’s discovery was an opportunity to take entanglement out of the realm of thought experiments and into the lab. Following Bohm, in 1964 John Bell translated the two EPR alternatives into a mathematical relationship that could be tested. But it was left to other experimenters – most famously Alain Aspect in 1981 [Physical Review Letters] – to carry out the tests.

    Einstein’s hopes of finding hidden variables that would take the uncertainty out of quantum theory were dashed. There seemed no escaping the bizarre consequences of EPR and the reality of entanglement.

    But does this also mean “spooky action at a distance” is real? Entanglement in electrons has been demonstrated at distances of a kilometre or two. But so far that’s too short a distance to know if faster-than-light interactions between them were involved. Things may soon become clearer: at the time of writing, Chinese scientists have just announced the successful transmission of entangled photons [Science] from an orbiting satellite over distances of more than 1,200 km.

    On the other hand, some physicists have recently taken up Einstein’s side of the argument. For instance, in 2016 Bengt Nordén, of Chalmers University in Sweden, published a paper [Cambridge Quarterly Reviews of Biophysics] entitled, Quantum entanglement: facts and fiction – how wrong was Einstein after all? Against Bohr’s better judgement, such physicists are once again asking about the meaning of reality, and wondering what is causing the weird phenomenon of entanglement.

    Some even suggest that something like a “wormhole” – a tunnel in spacetime between two widely separated black holes, a consequence of general relativity theory first deduced by Einstein and Rosen – may be the mechanism underlying entanglement. The mythical faster-than-light tachyon is another possible contender.

    But nearly everyone agrees that whatever is going on between entangled particles, experimenters can only communicate their observations of entangled particles at light speed or less.

    Entanglement is no longer a philosophical curio: not only are physicists using it to encrypt information and relying on it to underpin the design of tomorrow’s quantum computers, they are once again grappling with the hard questions about the nature of reality that entanglement raises.

    Ninety years after the Fifth Solvay Congress, Einstein’s thought experiments continue to drive science onwards.

    See the full article here .

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  • richardmitnick 9:10 pm on October 7, 2017 Permalink | Reply
    Tags: (3-D) quantum gas atomic clock, , , JILA physicists have created an entirely new design for an atomic clock, , , , Quantum gas, Quantum Mechanics   

    From NIST: “JILA’s 3-D Quantum Gas Atomic Clock Offers New Dimensions in Measurement” 


    NIST

    October 05, 2017

    Laura Ost
    laura.ost@nist.gov
    (303) 497-4880

    1
    JILA

    4
    CU Boulder

    1
    JILA’s three-dimensional (3-D) quantum gas atomic clock consists of a grid of light formed by three pairs of laser beams. A stack of two tables is used to configure optical components around a vacuum chamber. Shown here is the upper table, where lenses and other optics are mounted. A blue laser beam excites a cube-shaped cloud of strontium atoms located behind the round window in the middle of the table. Strontium atoms fluorescence strongly when excited with blue light. Credit: G.E. Marti/JILA

    JILA physicists have created an entirely new design for an atomic clock, in which strontium atoms are packed into a tiny three-dimensional (3-D) cube at 1,000 times the density of previous one-dimensional (1-D) clocks. In doing so, they are the first to harness the ultra-controlled behavior of a so-called “quantum gas” to make a practical measurement device.

    With so many atoms completely immobilized in place, JILA’s cubic quantum gas clock sets a record for a value called “quality factor” and the resulting measurement precision. A large quality factor translates into a high level of synchronization between the atoms and the lasers used to probe them, and makes the clock’s “ticks” pure and stable for an unusually long time, thus achieving higher precision.

    Until now, each of the thousands of “ticking” atoms in advanced clocks behave and are measured largely independently. In contrast, the new cubic quantum gas clock uses a globally interacting collection of atoms to constrain collisions and improve measurements. The new approach promises to usher in an era of dramatically improved measurements and technologies across many areas based on controlled quantum systems.

    The new clock is described in the Oct. 6 issue of Science.

    “We are entering a really exciting time when we can quantum engineer a state of matter for a particular measurement purpose,” said physicist Jun Ye of the National Institute of Standards and Technology (NIST). Ye works at JILA, which is jointly operated by NIST and the University of Colorado Boulder.

    The clock’s centerpiece is an unusual state of matter called a degenerate Fermi gas (a quantum gas for Fermi particles), first created in 1999 by Ye’s late colleague Deborah Jin. All prior atomic clocks have used thermal gases. The use of a quantum gas enables all of the atoms’ properties to be quantized, or restricted to specific values, for the first time.

    “The most important potential of the 3-D quantum gas clock is the ability to scale up the atom numbers, which will lead to a huge gain in stability,” Ye said. “Also, we could reach the ideal condition of running the clock with its full coherence time, which refers to how long a series of ticks can remain stable. The ability to scale up both the atom number and coherence time will make this new-generation clock qualitatively different from the previous generation.”

    Until now, atomic clocks have treated each atom as a separate quantum particle, and interactions among the atoms posed measurement problems. But an engineered and controlled collection, a “quantum many-body system,” arranges all its atoms in a particular pattern, or correlation, to create the lowest overall energy state. The atoms then avoid each other, regardless of how many atoms are added to the clock. The gas of atoms effectively turns itself into an insulator, which blocks interactions between constituents.

    The result is an atomic clock that can outperform all predecessors. For example, stability can be thought of as how precisely the duration of each tick matches every other tick, which is directly linked to the clock’s measurement precision. Compared with Ye’s previous 1-D clocks, the new 3-D quantum gas clock can reach the same level of precision more than 20 times faster due to the large number of atoms and longer coherence times.

    The experimental data show the 3-D quantum gas clock achieved a precision of just 3.5 parts error in 10 quintillion (1 followed by 19 zeros) in about 2 hours, making it the first atomic clock to ever reach that threshold (19 zeros). “This represents a significant improvement over any previous demonstrations,” Ye said.

    The older, 1-D version of the JILA clock was, until now, the world’s most precise clock. This clock holds strontium atoms in a linear array of pancake-shaped traps formed by laser beams, called an optical lattice. The new 3-D quantum gas clock uses additional lasers to trap atoms along three axes so that the atoms are held in a cubic arrangement. This clock can maintain stable ticks for nearly 10 seconds with 10,000 strontium atoms trapped at a density above 10 trillion atoms per cubic centimeter. In the future, the clock may be able to probe millions of atoms for more than 100 seconds at a time.

    Optical lattice clocks, despite their high levels of performance in 1-D, have to deal with a tradeoff. Clock stability could be improved further by increasing the number of atoms, but a higher density of atoms also encourages collisions, shifting the frequencies at which the atoms tick and reducing clock accuracy. Coherence times are also limited by collisions. This is where the benefits of the many-body correlation can help.

    The 3-D lattice design—imagine a large egg carton—eliminates that tradeoff by holding the atoms in place. The atoms are fermions, a class of particles that cannot be in the same quantum state and location at once. For a Fermi quantum gas under this clock’s operating conditions, quantum mechanics favors a configuration where each individual lattice site is occupied by only one atom, which prevents the frequency shifts induced by atomic interactions in the 1-D version of the clock.

    JILA researchers used an ultra-stable laser to achieve a record level of synchronization between the atoms and lasers, reaching a record-high quality factor of 5.2 quadrillion (5.2 followed by 15 zeros). Quality factor refers to how long an oscillation or waveform can persist without dissipating. The researchers found that atom collisions were reduced such that their contribution to frequency shifts in the clock was much less than in previous experiments.

    “This new strontium clock using a quantum gas is an early and astounding success in the practical application of the ‘new quantum revolution,’ sometimes called ‘quantum 2.0’,” said Thomas O’Brian, chief of the NIST Quantum Physics Division and Ye’s supervisor. “This approach holds enormous promise for NIST and JILA to harness quantum correlations for a broad range of measurements and new technologies, far beyond timing.”

    Depending on measurement goals and applications, JILA researchers can optimize the clock’s parameters such as operational temperature (10 to 50 nanokelvins), atom number (10,000 to 100,000), and physical size of the cube (20 to 60 micrometers, or millionths of a meter).

    Atomic clocks have long been advancing the frontier of measurement science, not only in timekeeping and navigation but also in definitions of other measurement units and other areas of research such as in tabletop searches for the missing “dark matter” in the universe.

    The National Bureau of Standards, now NIST, invented the first atomic clock in 1948.

    3
    Dr. Harold Lyons (right), inventor of the ammonia absorption cell atomic clock, observes, while Dr. Edward U. Condon, the director of the National Bureau of Standards, examines a model of the ammonia molecule (1949).

    The work is supported by NIST, the Defense Advanced Research Projects Agency and the National Science Foundation.

    See the full article here.

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    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.
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  • richardmitnick 1:46 pm on October 5, 2017 Permalink | Reply
    Tags: , Dark Matter Radio, Every particle can also behave like a wave, Quantum Mechanics, ,   

    From Symmetry: “A radio for dark matter” 

    Symmetry Mag

    Symmetry

    10/05/17
    Manuel Gnida

    Instead of searching for dark matter particles, a new device will search for dark matter waves.

    1
    Artwork by Colleen Ehrhart

    2

    The dark matter radio disc jockeys. Front row, from left: Carl Dawson, Hsiao-Mei “Sherry” Cho and Saptarshi Chaudhuri. Back row, from left: Arran Phipps, Stephen Kuenstner and Kent Irwin. Not pictured: Dale Li and Peter Graham. Dawn Harmer/SLAC

    Researchers are testing a prototype “radio” that could let them listen to the tune of mysterious dark matter particles.

    Dark matter is an invisible substance thought to be five times more prevalent in the universe than regular matter. According to theory, billions of dark matter particles pass through the Earth each second. We don’t notice them because they interact with regular matter only very weakly, through gravity.

    So far, researchers have mostly been looking for dark matter particles. But with the dark matter radio, they want to look for dark matter waves.

    Direct detection experiments for dark matter particles use large underground detectors. Researchers hope to see signals from dark matter particles colliding with the detector material. However, this only works if dark matter particles are heavy enough to deposit a detectable amount energy in the collision.

    “If dark matter particles were very light, we might have a better chance of detecting them as waves rather than particles,” says Peter Graham, a theoretical physicist at the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. “Our device will take the search in that direction.”

    The dark matter radio makes use of a bizarre concept of quantum mechanics known as wave-particle duality: Every particle can also behave like a wave.

    Take, for example, the photon: the massless fundamental particle that carries the electromagnetic force. Streams of them make up electromagnetic radiation, or light, which we typically describe as waves—including radio waves.

    The dark matter radio will search for dark matter waves associated with two particular dark matter candidates. It could find hidden photons—hypothetical cousins of photons with a small mass. Or it could find axions, which scientists think can be produced out of light and transform back into it in the presence of a magnetic field.

    “The search for hidden photons will be completely unexplored territory,” says Saptarshi Chaudhuri, a Stanford graduate student on the project. “As for axions, the dark matter radio will close gaps in the searches of existing experiments.”

    Intercepting dark matter vibes

    A regular radio intercepts radio waves with an antenna and converts them into sound. What sound depends on the station. A listener chooses a station by adjusting an electric circuit, in which electricity can oscillate with a certain resonant frequency. If the circuit’s resonant frequency matches the station’s frequency, the radio is tuned in and the listener can hear the broadcast.

    The dark matter radio works the same way. At its heart is an electric circuit with an adjustable resonant frequency. If the device were tuned to a frequency that matched the frequency of a dark matter particle wave, the circuit would resonate. Scientists could measure the frequency of the resonance, which would reveal the mass of the dark matter particle.

    The idea is to do a frequency sweep by slowly moving through the different frequencies, as if tuning a radio from one end of the dial to the other.

    The electric signal from dark matter waves is expected to be very weak. Therefore, Graham has partnered with a team led by another KIPAC researcher, Kent Irwin. Irwin’s group is developing highly sensitive magnetometers known as superconducting quantum interference devices, or SQUIDs, which they’ll pair with extremely low-noise amplifiers to hunt for potential signals.

    In its final design, the dark matter radio will search for particles in a mass range of trillionths to millionths of an electronvolt. (One electronvolt is about a billionth of the mass of a proton.) This is somewhat problematic because this range includes kilohertz to gigahertz frequencies—frequencies used for over-the-air broadcasting.

    “Shielding the radio from unwanted radiation is very important and also quite challenging,” Irwin says. “In fact, we would need a several-yards-thick layer of copper to do so. Fortunately we can achieve the same effect with a thin layer of superconducting metal.”

    One advantage of the dark matter radio is that it does not need to be shielded from cosmic rays. Whereas direct detection searches for dark matter particles must operate deep underground to block out particles falling from space, the dark matter radio can operate in a university basement.

    The researchers are now testing a small-scale prototype at Stanford that will scan a relatively narrow frequency range. They plan on eventually operating two independent, full-size instruments at Stanford and SLAC.

    “This is exciting new science,” says Arran Phipps, a KIPAC postdoc on the project. “It’s great that we get to try out a new detection concept with a device that is relatively low-budget and low-risk.”

    The dark matter disc jockeys are taking the first steps now and plan to conduct their dark matter searches over the next few years. Stay tuned for future results.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:18 pm on October 3, 2017 Permalink | Reply
    Tags: , , New faculty to advance quantum matter research, , , Quantum Mechanics   

    From P.I. : “New faculty to advance quantum matter research” 

    Perimeter Institute
    Perimeter Institute

    October 2, 2017
    Tenille Bonoguore

    1
    Beni Yoshida

    2
    Yin-Chen He

    3
    Timothy Hsieh

    The research pursued by three new Faculty members at Perimeter Institute will advance understanding in a highly promising field.

    Three exceptional young researchers are set to join the faculty of Perimeter Institute, where they will bring new expertise to efforts to better understand, and one day exploit, quantum effects and condensed matter.

    Beni Yoshida – a former Perimeter postdoctoral researcher and “It from Qubit” Simons Fellow – is already at Perimeter. He will be joined in spring 2018 by Timothy Hsieh, currently a Gordon and Betty Moore Fellow and associate specialist at the Kavli Institute for Theoretical Physics, and Yin-Chen He, a Gordon and Betty Moore Fellow at Harvard University.

    All three study various aspects of condensed matter, which is being widely pursued as a solution to many challenges, from computing limits to efficient energy transmission. Together, they will lead the Institute’s new Quantum Matter Initiative.

    Perimeter Director Neil Turok described the appointments as a coup for the Institute, providing a leap forward in condensed matter research, one of the fastest-growing areas of physics today.

    “Quantum materials are expected to enable entirely new technologies with a host of potential applications,” Turok said. “With three exceptional young theorists joining our faculty, each bringing complementary skills and insights, Perimeter is preparing to engage with and support these exciting developments.”

    Yoshida studied and worked at MIT, and Caltech before coming to Perimeter in 2015. A specialist in quantum information theory, condensed matter, and black holes, his current work focuses on topological orders and quantum chaos.

    For Yoshida, the transition from postdoctoral fellow to faculty member promises exciting potential not just for his research but also for future collaborations. His research lies between three fields – quantum information, condensed matter, and string theory – all of which are represented in Perimeter’s faculty.

    “This field is relatively young. There are many brilliant young researchers and it’s a very energetic field. I want to bring more of those young talents here,” Yoshida said.

    “Perimeter is very interdisciplinary. I can learn from people with diverse interests. Of course, I was very happy to do research as a postdoc, but now I have more opportunity to make contributions to both PI and also to science, by bringing very smart students and postdocs. That’s probably most exciting.”

    Hsieh studied physics and mathematics at Harvard before earning his PhD in physics from MIT in 2015. A prediction he co-authored in 2013 – that a material called tin-telluride is a topological crystalline insulator – was experimentally confirmed by multiple groups and has spawned significant theoretical and experimental interest in its phenomenology.

    Hsieh said he was looking forward to exploring quantum materials, entanglement, and dynamics in Perimeter’s interdisciplinary environment.

    Yin-Chen He is a condensed matter researcher interested in spin liquids, topological phases, and topological phase transitions. He received his PhD from Shanghai’s Fudan University in 2014, and prior to moving to Harvard in 2016, worked at the Max Planck Institute in Dresden.

    “PI and I share a mutual interest in doing original, path-breaking research rather than following the main trends of the field,” He said.

    “PI has highly interdisciplinary research fields in theoretical physics as well as very active research members, and I am very much looking forward to being part of it.”

    See the full article here .

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    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 9:46 am on September 28, 2017 Permalink | Reply
    Tags: , , , Quantum Mechanics, , , Technical University of Dresden, The spin Hall effect, The spin Nernst effect, The spin Peltier effect, The spin Seebeck effect, Turning up the heat on electrons reveals an elusive physics phenomenon, When things heat up spinning electrons go their separate ways   

    From ScienceNews: “Turning up the heat on electrons reveals an elusive physics phenomenon” 

    ScienceNews bloc

    ScienceNews

    September 26, 2017
    Emily Conover

    Spin Nernst effect could help scientists design new gadgets that store data using quantum property of spin.

    1
    WHIRL AWAY Electrons in platinum move in different directions depending on their spin when the metal is heated at one end. Scientists have observed this phenomenon, called the spin Nernst effect, for the first time. Creativity103/Flickr (CC BY 2.0)

    When things heat up, spinning electrons go their separate ways.

    Warming one end of a strip of platinum shuttles electrons around according to their spin, a quantum property that makes them behave as if they are twirling around. Known as the spin Nernst effect, the newly detected phenomenon was the only one in a cadre of related spin effects that hadn’t previously been spotted, researchers report online September 11 in Nature Materials.

    “The last missing piece in the puzzle was spin Nernst and that’s why we set out to search for this,” says study coauthor Sebastian Goennenwein, a physicist at the Technical University of Dresden in Germany.

    The effect and its brethren — with names like the spin Hall effect, the spin Seebeck effect and the spin Peltier effect — allow scientists to create flows of electron spins, or spin currents. Such research could lead to smaller and more efficient electronic gadgets that use electrons’ spins to store and transmit information instead of electric charge, a technique known as “spintronics.”

    In the spin Nernst effect, named after Nobel laureate chemist Walther Nernst, heating one end of a metal causes electrons to flow toward the other end, bouncing around inside the material as they go. Within certain materials, that bouncing has a preferred direction: Electrons with spins pointing up (as if twirling counterclockwise) go to the right and electrons with spins pointing down (as if twirling clockwise) go to the left, creating an overall spin current. Although the effect had been predicted, no one had yet observed it.

    Finding evidence of the effect required disentangling it from other heat- and charge-related effects that occur in materials. To do so, the researchers coupled the platinum to a layer of a magnetic insulator, a material known as yttrium iron garnet. Then, they altered the direction of the insulator’s magnetization, which changed whether the spin current could flow through the insulator. That change slightly altered a voltage measured along the strip of platinum. The scientists measured how this voltage changed with the direction of the magnetization to isolate the fingerprints of the spin Nernst effect.

    “The measurement was a tour de force; the measurement was ridiculously hard,” says physicist Joseph Heremans of Ohio State University in Columbus, who was not involved with the research. The effect could help scientists to better understand materials that may be useful for building spintronic devices, he says. “It’s really a new set of eyes on the physics of what’s going on inside these devices.”

    A relative of the spin Nernst effect called the spin Hall effect is much studied for its potential use in spintronic devices. In the spin Hall effect, an electric field pushes electrons through a material, and the particles veer off to the left and right depending on their spin. The spin Nernst effect relies on the same basic physics, but uses heat instead of an electric field to get the particles moving.

    “It’s a beautiful experiment. It shows very nicely the spin Nernst effect,” says physicist Greg Fuchs of Cornell University. “It beautifully unifies our understanding of the interrelation between charge, heat and spin transport.”

    See the full article here .

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