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  • richardmitnick 1:10 pm on December 6, 2019 Permalink | Reply
    Tags: "A platform for stable quantum computing, a playground for exotic physics", , , , , Quantum Physics, Topological insulators are materials that can conduct electricity on their surface or edge but not in the middle.   

    From Harvard Gazette: “A platform for stable quantum computing, a playground for exotic physics” 

    Harvard University

    From Harvard Gazette

    December 5, 2019
    Leah Burrows

    A close-up view of a quantum computer. Courtesy of Harvard SEAS

    Recent research settles a long-standing debate.

    Move over Godzilla vs. King Kong. This is the crossover event you’ve been waiting for — at least if you’re a condensed-matter physicist. Harvard University researchers have demonstrated the first material that can have both strongly correlated electron interactions and topological properties.

    Not sure what that means? Don’t worry, we’ll walk you through it. But the important thing to know is that this discovery not only paves the way for more stable quantum computing, but also creates an entirely new platform to explore the wild world of exotic physics.

    The research was published in Nature Physics.

    Let’s start with the basics. Topological insulators are materials that can conduct electricity on their surface or edge, but not in the middle. The strange thing about these materials is that no matter how you cut them, the surface will always be conducting and the middle always insulating. These materials offer a playground for fundamental physics, and are also promising for a number of applications in special types of electronics and quantum computing.

    Since the discovery of topological insulators, researchers around the world have been working to identify materials with these powerful properties.

    “A recent boom in condensed-matter physics has come from discovering materials with topologically protected properties,” said Harris Pirie, a graduate student in the Department of Physics and first author of the paper.

    One potential material, samarium hexaboride, has been at the center of a fierce debate among condensed-matter physicists for more than a decade. At issue: Is it or isn’t it a topological insulator?

    “Over the last 10 years, a bunch of papers have come out saying yes and a bunch of papers have come out saying no,” said Pirie. “The crux of the issue is that most topological materials don’t have strongly interacting electrons, meaning the electrons move too quickly to feel each other. But samarium hexaboride does, meaning that electrons inside this material slow down enough to interact strongly. In this realm, the theory gets fairly speculative and it’s been unclear whether or not it’s possible for materials with strongly interacting properties to also be topological. As experimentalists, we’ve been largely operating blind with materials like this.”

    In order to settle the debate and figure out, once and for all, whether it’s possible to have both strongly interacting and topological properties, the researchers first needed to find a well-ordered patch of samarium hexaboride surface on which to perform the experiment.

    A simulation of electrons scattering off atomic defects in samarium hexaboride. By observing the waves, the researchers could figure out the momentum of the electrons in relation to their energy. Video courtesy of Harris Pirie/Harvard University

    It was no easy task, considering the majority of the material surface is a craggy, disordered mess. The researchers used ultrahigh precision measurement tools developed in the lab of Jenny Hoffman, the Clowes Professor of Science and senior author of the paper, to find a suitable, atomic-scale patch of samarium hexaboride.

    Next, the team set out to determine if the material was topologically insulating by sending waves of electrons through the material and scattering them off of atomic defects — like dropping a pebble into a pond. By observing the waves, the researchers could figure out the momentum of the electrons in relation to their energy.

    “We found that the momentum of the electrons is directly proportional to their energy, which is the smoking gun of a topological insulator,” said Pirie. “It’s really exciting to be finally moving into this intersection of interacting physics and topological physics. We don’t know what we’ll find here.”

    As it relates to quantum computing, strongly interacting topological materials may be able to protect qubits from forgetting their quantum state, a process called decoherence.

    “If we could encode the quantum information in a topologically protected state, it is less susceptible to external noise that can accidentally switch the qubit,” said Hoffman. “Microsoft already has a large team pursuing topological quantum computation in composite materials and nanostructures. Our work demonstrates a first in a single topological material that harnesses strong electron interactions that might eventually be used for topological quantum computing.”

    “The next step will be to use the combination of topologically protected quantum states and strong interactions to engineer novel quantum states of matter, such as topological superconductors,” said Dirk Morr, professor of physics at the University of Illinois, Chicago, and the senior theorist on the paper. “Their extraordinary properties could open unprecedented possibilities for the implementation of topological quantum bits.”

    This research was co-authored by Yu Liu, Anjan Soumyanarayanan, Pengcheng Chen, Yang He, M.M. Yee, P.F.S. Rosa, J.D. Thompson, Dae-Jeong Kim, Z. Fisk, Xiangfeng Wang, Johnpierre Paglione, and M.H. Hamidian.

    See the full article here .


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    Harvard University campus
    Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

  • richardmitnick 9:58 am on September 25, 2019 Permalink | Reply
    Tags: , Quantum Physics, The many-worlds interpretation   

    From Curiosity: “The Many-Worlds Interpretation Says There Are Infinite Timelines and Infinite Yous” 

    Curiosity Makes You Smarter

    From From Curiosity

    April 26, 2017 [Just now in social media]
    Ashley Hamer


    Quantum physics is mind-bending, counterintuitive, and close to impossible to understand. It’s so complicated that a theory saying our reality is just one of an infinite web of infinite timelines is one that’s actually simpler than what most quantum physicists believe. That neat-and-tidy explanation is known as the many-worlds interpretation, and it has caused plenty of controversy in physics circles.

    Split the Difference

    In the 1950s, a student at Princeton University named Hugh Everett III was studying quantum mechanics. He learned about the Copenhagen interpretation, which says that at the very, very smallest level — what we mean when we say quantum — matter exists not just as a particle and not just as a wave, but in all possible states at once (all of those states together is called its wave function; the phenomenon of existing in all of those states at once is called superposition). It also says that when you observe a quantum object, you break that superposition and it essentially “chooses” one state to be in. He also learned about the Heisenberg Uncertainty Principle, which says that because we affect a quantum object’s behavior through observation, we can never be completely certain where it is or what it’s doing at any given time.

    Everett understood these principles, but he took issue with one part: What if, instead of a quantum object “choosing” a state when you observe it — say, it becomes a particle instead of a wave — there was an actual split in the universe that created separate timelines? According to Everett’s theory, in this timeline, the object is a particle, but there’s another timeline where it’s a wave. Even more baffling, this implies that quantum phenomena aren’t the only things that split the universe into separate timelines. For everything that happens, every action you take or decide not to take, there are infinite other timelines — worlds, if we may — where something else took place. That’s the many-worlds interpretation of quantum physics. It may not seem like it, but it’s actually simpler than the Copenhagen interpretation — it doesn’t strike an arbitrary line between the quantum world and everything else, because everything behaves in the same way. It also removes randomness from the picture, which helps the math work out nicely.


    Many Worlds Means Big Implications

    Not all physicists subscribe to this theory — a recent poll found that the majority are Copenhagen all the way — but a growing minority do. Sean Carroll, for one. He explains that many objections to the theory arise because people come at it from a classical physics point of view. “In classical mechanics … it’s quite a bit of work to accommodate extra universes, and you better have a good reason to justify putting in that work,” he writes. “That is not what happens in quantum mechanics. The capacity for describing multiple universes is automatically there. We don’t have to add anything.”

    If the many-worlds interpretation is true, what does this say about the nature of reality? It says there are infinite versions of you living in infinite alternate timelines. There’s a version of you that got out of bed on a different side this morning, one that ate a different breakfast, one that has differently colored hair, one that’s a different gender, one that’s a foot taller, one that’s a psychopath, one that — we can hardly stomach it! — didn’t decide to read this article. That might make you feel less than unique. On the contrary, the you that you are right now is the only you there will ever be. The moment you do anything, the universe splits and you’re a you that’s living in a different timeline than the you that didn’t take that action. Wild, isn’t it?

    See the full article here .


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    Experience Curiosity on our website, through our apps and across social media. We designed Curiosity with your busy life in mind. Our editors find interesting and important topics that you’ll want to know more about, and introduce you to the best ways to keep learning.

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  • richardmitnick 2:41 pm on August 27, 2019 Permalink | Reply
    Tags: "Department of Energy awards Fermilab $3.5 million for quantum science", Cryogenic engineering, , , QuantISED-Quantum Information Science-Enabled Discovery program, , , Quantum Physics,   

    From Fermi National Accelerator Lab: “Department of Energy awards Fermilab $3.5 million for quantum science” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    August 27, 2019
    Edited by Leah Hesla

    The U.S. Department of Energy has awarded researchers at its Fermi National Accelerator Laboratory more than $3.5 million to boost research in the fast-emerging field of Quantum Information Science.

    “Few pursuits have the revolutionary potential that quantum science presents,” said Fermilab Chief Research Officer Joe Lykken. “Fermilab’s expertise in quantum physics and cryogenic engineering is world-class, and combined with our experience in conventional computing and networks, we can advance quantum science in directions that not many other places can.”

    As part of a number of grants to national laboratories and universities offered through its Quantum Information Science-Enabled Discovery (QuantISED) program, DOE’s recent round of funding to Fermilab covers three initiatives related to quantum science. It also funds Fermilab’s participation in a fourth initiative led by Argonne National Laboratory.

    The DOE QuantISED grants will fund initiatives related to quantum computing. These include the simulation of advanced quantum devices that will improve quantum computing simulations and the development of novel electronics to work with large arrays of ultracold qubits.

    For a half-century, Fermilab researchers have closely studied the quantum realm and provided the computational and engineering capabilties needed to zoom in on nature at its most fundamental level. The projects announced by the Department of Energy will build on those capabilities, pushing quantum science and technology forward and leading to new discoveries that will enhance our picture of the universe at its smallest scale.

    “Fermilab is well-versed in engineering, algorithmic development and recruiting massive computational resources to explore quantum-scale phenomena,” said Fermilab Head of Quantum Science Panagiotis Spentzouris. “Now we’re wrangling those competencies and capabilities to advance quantum science in many areas, and in a way that only a leading physics laboratory could.”

    The Fermilab-led initiatives funded through these DOE QuantISED grants are:

    Large Scale Simulations of Quantum Systems on High-Performance Computing with Analytics for High-Energy Physics Algorithms
    Lead principal investigator: Adam Lyon, Fermilab

    The large-scale simulation of quantum computers has plenty in common with simulations in high-energy physics: Both must sweep over a large number of variables. Both organize their inputs and outputs similarly. And in both cases, the simulation has to be analyzed and consolidated into results. Fermilab scientists, in collaboration with scientists at Argonne National Laboratory, will use tools from high-energy physics to produce and analyze simulations using high-performance computers at the Argonne Leadership Computing Facility. Specifically, they will simulate the operation of a qubit device that uses superconducting cavities (which are also used as components in particle accelerators) to maintain quantum information over a relatively long time. Their results will determine the device’s impact on high-energy physics algorithms using an Argonne-developed quantum simulator.

    Partner institution: Argonne National Laboratory

    Research Technology for Quantum Information Systems
    Lead principal investigator: Gustavo Cancelo, Fermilab

    One of the main challenges in quantum information science is designing an architecture that solves problems of massive interconnection, massive data processing and heat load. The electronics must be able to operate and interface with other electronics operating both at 4 kelvins and at near absolute zero. Fermilab scientists and engineers are designing novel electronic circuits as well as massive control and readout electronics to be compatible with quantum devices, such as sensors and quantum qubits. These circuits will enable many applications in the quantum information science field.

    Partner institutions: Argonne National Laboratory, Massachusetts Institute of Technology, University of Chicago

    MAGIS-100 – co-led by Stanford University and Fermilab
    Lead Fermilab principal investigator: Rob Plunkett

    Fermilab will host a new experiment to test quantum mechanics on macroscopic scales of space and time. Scientists on the MAGIS-100 experiment will drop clouds of ultracold atoms down a 100-meter-long vacuum pipe on the Fermilab site, and use a stable laser to create an atom interferometer which will look for dark matter made of ultralightweight particles. They will also advance a technique for gravitational-wave detection at relatively low frequencies.

    This is a joint venture under the collaboration leadership of Stanford University Professor Jason Hogan, who is funded by grant GBMF7945 from the Gordon and Betty Moore Foundation. Rob Plunkett of Fermilab serves as the project manager.

    Other participating institutions: Northern Illinois University, Northwestern University, Stanford University, Johns Hopkins University, University of Liverpool


    Fermilab was also funded to participate in another initiative led by Argonne National Laboratory:

    Quantum Sensors for Wide Band Axion Dark Matter Detection
    Lead principal investigator: Peter Barry, Argonne

    Researchers are searching high and low for dark matter, the mysterious substance that makes up a quarter of our universe. One theory proposes that it could be made of particles called axions, which would signal their presence by converting into particles of light, called photons. Fermilab researchers are part of a team developing specialized detectors that look for photons in the terahertz range — at frequencies just below the infrared. The development of these detectors will widen the range of frequencies where axions may be discovered. To bring the faint signals to the fore, the team is using supersensitive quantum amplifiers.

    Other participating institutions: National Institute of Standards and Technology, University of Colorado

    See the full here.


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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

  • richardmitnick 11:59 am on July 28, 2019 Permalink | Reply
    Tags: A quantum particle can have a range of possible states known as a “superposition.”, “Quantum-classical transition.”, But why can’t we see a quantum superposition?, , Darwin-Survival of the Fittest, Many independent observers can make measurements of a quantum system and agree on the outcome—a hallmark of classical behavior., Quantum Darwinism, , Quantum Physics, The definite properties of objects that we associate with classical physics—position and speed say—are selected from a menu of quantum possibilities., The process is loosely analogous to natural selection in evolution., The vexing question then becomes: How do quantum probabilities coalesce into the sharp focus of the classical world?, This doesn’t really mean it is in several states at once; rather it means that if we make a measurement we will see one of those outcomes., This process by which “quantumness” disappears into the environment is called decoherence.,   

    From WIRED: “Quantum Darwinism Could Explain What Makes Reality Real” 

    Wired logo

    From WIRED

    Philip Ball

    Contrary to popular belief, says physicist Adán Cabello, “quantum theory perfectly describes the emergence of the classical world.” Olena Shmahalo/Quanta Magazine

    It’s not surprising that quantum physics has a reputation for being weird and counterintuitive. The world we’re living in sure doesn’t feel quantum mechanical. And until the 20th century, everyone assumed that the classical laws of physics devised by Isaac Newton and others—according to which objects have well-defined positions and properties at all times—would work at every scale. But Max Planck, Albert Einstein, Niels Bohr and their contemporaries discovered that down among atoms and subatomic particles, this concreteness dissolves into a soup of possibilities. An atom typically can’t be assigned a definite position, for example—we can merely calculate the probability of finding it in various places. The vexing question then becomes: How do quantum probabilities coalesce into the sharp focus of the classical world?

    Physicists sometimes talk about this changeover as the “quantum-classical transition.” But in fact there’s no reason to think that the large and the small have fundamentally different rules, or that there’s a sudden switch between them. Over the past several decades, researchers have achieved a greater understanding of how quantum mechanics inevitably becomes classical mechanics through an interaction between a particle or other microscopic system and its surrounding environment.

    One of the most remarkable ideas in this theoretical framework is that the definite properties of objects that we associate with classical physics—position and speed, say—are selected from a menu of quantum possibilities in a process loosely analogous to natural selection in evolution: The properties that survive are in some sense the “fittest.” As in natural selection, the survivors are those that make the most copies of themselves. This means that many independent observers can make measurements of a quantum system and agree on the outcome—a hallmark of classical behavior.

    This idea, called quantum Darwinism (QD), explains a lot about why we experience the world the way we do rather than in the peculiar way it manifests at the scale of atoms and fundamental particles. Although aspects of the puzzle remain unresolved, QD helps heal the apparent rift between quantum and classical physics.

    Chaoyang Lu (left) and Jian-Wei Pan of the University of Science and Technology of China in Hefei led a recent experiment that tested quantum Darwinism in an artificial environment made of interacting photons. Chaoyang Lu

    Only recently, however, has quantum Darwinism been put to the experimental test. Three research groups, working independently in Italy, China and Germany, have looked for the telltale signature of the natural selection process by which information about a quantum system gets repeatedly imprinted on various controlled environments. These tests are rudimentary, and experts say there’s still much more to be done before we can feel sure that QD provides the right picture of how our concrete reality condenses from the multiple options that quantum mechanics offers. Yet so far, the theory checks out.

    Survival of the Fittest

    At the heart of quantum Darwinism is the slippery notion of measurement—the process of making an observation. In classical physics, what you see is simply how things are. You observe a tennis ball traveling at 200 kilometers per hour because that’s its speed. What more is there to say?

    In quantum physics that’s no longer true. It’s not at all obvious what the formal mathematical procedures of quantum mechanics say about “how things are” in a quantum object; they’re just a prescription telling us what we might see if we make a measurement. Take, for example, the way a quantum particle can have a range of possible states, known as a “superposition.” This doesn’t really mean it is in several states at once; rather, it means that if we make a measurement we will see one of those outcomes. Before the measurement, the various superposed states interfere with one another in a wavelike manner, producing outcomes with higher or lower probabilities.

    But why can’t we see a quantum superposition? Why can’t all possibilities for the state of a particle survive right up to the human scale?

    The answer often given is that superpositions are fragile, easily disrupted when a delicate quantum system is buffeted by its noisy environment. But that’s not quite right. When any two quantum objects interact, they get “entangled” with each other, entering a shared quantum state in which the possibilities for their properties are interdependent. So say an atom is put into a superposition of two possible states for the quantum property called spin: “up” and “down.” Now the atom is released into the air, where it collides with an air molecule and becomes entangled with it. The two are now in a joint superposition. If the atom is spin-up, then the air molecule might be pushed one way, while, if the atom is spin-down, the air molecule goes another way—and these two possibilities coexist. As the particles experience yet more collisions with other air molecules, the entanglement spreads, and the superposition initially specific to the atom becomes ever more diffuse. The atom’s superposed states no longer interfere coherently with one another because they are now entangled with other states in the surrounding environment—including, perhaps, some large measuring instrument. To that measuring device, it looks as though the atom’s superposition has vanished and been replaced by a menu of possible classical-like outcomes that no longer interfere with one another.

    This process by which “quantumness” disappears into the environment is called decoherence. It’s a crucial part of the quantum-classical transition, explaining why quantum behavior becomes hard to see in large systems with many interacting particles. The process happens extremely fast. If a typical dust grain floating in the air were put into a quantum superposition of two different physical locations separated by about the width of the grain itself, collisions with air molecules would cause decoherence—making the superposition undetectable—in about 10−31 seconds. Even in a vacuum, light photons would trigger such decoherence very quickly: You couldn’t look at the grain without destroying its superposition.

    Surprisingly, although decoherence is a straightforward consequence of quantum mechanics, it was only identified in the 1970s, by the late German physicist Heinz-Dieter Zeh. The Polish-American physicist Wojciech Zurek further developed the idea in the early 1980s and made it better known, and there is now good experimental support for it.

    Wojciech Zurek, a theoretical physicist at Los Alamos National Laboratory in New Mexico, developed the quantum Darwinism theory in the 2000s to account for the emergence of objective, classical reality. Los Alamos National Laboratory

    But to explain the emergence of objective, classical reality, it’s not enough to say that decoherence washes away quantum behavior and thereby makes it appear classical to an observer. Somehow, it’s possible for multiple observers to agree about the properties of quantum systems. Zurek, who works at Los Alamos National Laboratory in New Mexico, argues that two things must therefore be true.

    First, quantum systems must have states that are especially robust in the face of disruptive decoherence by the environment. Zurek calls these “pointer states,” because they can be encoded in the possible states of a pointer on the dial of a measuring instrument. A particular location of a particle, for instance, or its speed, the value of its quantum spin, or its polarization direction can be registered as the position of a pointer on a measuring device. Zurek argues that classical behavior—the existence of well-defined, stable, objective properties—is possible only because pointer states of quantum objects exist.

    What’s special mathematically about pointer states is that the decoherence-inducing interactions with the environment don’t scramble them: Either the pointer state is preserved, or it is simply transformed into a state that looks nearly identical. This implies that the environment doesn’t squash quantumness indiscriminately but selects some states while trashing others. A particle’s position is resilient to decoherence, for example. Superpositions of different locations, however, are not pointer states: Interactions with the environment decohere them into localized pointer states, so that only one can be observed. Zurek described this “environment-induced superselection” of pointer states in the 1980s [Physical Review D].

    But there’s a second condition that a quantum property must meet to be observed. Although immunity to interaction with the environment assures the stability of a pointer state, we still have to get at the information about it somehow. We can do that only if it gets imprinted in the object’s environment. When you see an object, for example, that information is delivered to your retina by the photons scattering off it. They carry information to you in the form of a partial replica of certain aspects of the object, saying something about its position, shape and color. Lots of replicas are needed if many observers are to agree on a measured value—a hallmark of classicality. Thus, as Zurek argued in the 2000s, our ability to observe some property depends not only on whether it is selected as a pointer state, but also on how substantial a footprint it makes in the environment. The states that are best at creating replicas in the environment—the “fittest,” you might say—are the only ones accessible to measurement. That’s why Zurek calls the idea quantum Darwinism [Nature Physics].

    It turns out that the same stability property that promotes environment-induced superselection of pointer states also promotes quantum Darwinian fitness, or the capacity to generate replicas. “The environment, through its monitoring efforts, decoheres systems,” Zurek said, “and the very same process that is responsible for decoherence should inscribe multiple copies of the information in the environment.”

    Information Overload

    It doesn’t matter, of course, whether information about a quantum system that gets imprinted in the environment is actually read out by a human observer; all that matters for classical behavior to emerge is that the information get there so that it could be read out in principle. “A system doesn’t have to be under study in any formal sense” to become classical, said Jess Riedel, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, and a proponent of quantum Darwinism.

    “QD putatively explains, or helps to explain, all of classicality, including everyday macroscopic objects that aren’t in a laboratory, or that existed before there were any humans.”

    About a decade ago, while Riedel was working as a graduate student with Zurek, the two showed theoretically that information from some simple, idealized quantum systems is “copied prolifically into the environment,” Riedel said, “so that it’s necessary to access only a small amount of the environment to infer the value of the variables.” They calculated [Physical Review Letters] that a grain of dust one micrometer across, after being illuminated by the sun for just one microsecond, will have its location imprinted about 100 million times in the scattered photons.

    It’s because of this redundancy that objective, classical-like properties exist at all. Ten observers can each measure the position of a dust grain and find that it’s in the same location, because each can access a distinct replica of the information. In this view, we can assign an objective “position” to the speck not because it “has” such a position (whatever that means) but because its position state can imprint many identical replicas in the environment, so that different observers can reach a consensus.

    What’s more, you don’t have to monitor much of the environment to gather most of the available information—and you don’t gain significantly more by monitoring more than a fraction of the environment. “The information one can gather about the system quickly saturates,” Riedel said.

    This redundancy is the distinguishing feature of QD, explained Mauro Paternostro, a physicist at Queen’s University Belfast who was involved in one of the three new experiments. “It’s the property that characterizes the transition towards classicality,” he said.

    Quantum Darwinism challenges a common myth about quantum mechanics, according to the theoretical physicist Adán Cabello of the University of Seville in Spain: namely, that the transition between the quantum and classical worlds is not understood and that measurement outcomes cannot be described by quantum theory. On the contrary, he said, “quantum theory perfectly describes the emergence of the classical world.”

    Just how perfectly remains contentious, however. Some researchers think decoherence and QD provide a complete account of the quantum-classical transition. But although these ideas attempt to explain why superpositions vanish at large scales and why only concrete “classical” properties remain, there’s still the question of why measurements give unique outcomes. When a particular location of a particle is selected, what happens to the other possibilities inherent in its quantum description? Were they ever in any sense real? Researchers are compelled to adopt philosophical interpretations of quantum mechanics precisely because no one can figure out a way to answer that question experimentally.

    Into the Lab

    Quantum Darwinism looks fairly persuasive on paper. But until recently that was as far as it got. In the past year, three teams of researchers have independently put the theory to the experimental test by looking for its key feature: how a quantum system imprints replicas of itself on its environment.

    The experiments depended on the ability to closely monitor what information about a quantum system gets imparted to its environment. That’s not feasible for, say, a dust grain floating among countless billions of air molecules. So two of the teams created a quantum object in a kind of “artificial environment” with only a few particles in it. Both experiments—one by Paternostro [Physical Review A] and collaborators at Sapienza University of Rome, and the other by the quantum-information expert Jian-Wei Pan [https://arxiv.org/abs/1808.07388] and co-authors at the University of Science and Technology of China—used a single photon as the quantum system, with a handful of other photons serving as the “environment” that interacts with it and broadcasts information about it.

    Both teams passed laser photons through optical devices that could combine them into multiply entangled groups. They then interrogated the environment photons to see what information they encoded about the system photon’s pointer state—in this case its polarization (the orientation of its oscillating electromagnetic fields), one of the quantum properties able to pass through the filter of quantum Darwinian selection.

    A key prediction of QD is the saturation effect: Pretty much all the information you can gather about the quantum system should be available if you monitor just a handful of surrounding particles. “Any small fraction of the interacting environment is enough to provide the maximal classical information about the observed system,” Pan said.

    The two teams found precisely this. Measurements of just one of the environment photons revealed a lot of the available information about the system photon’s polarization, and measuring an increasing fraction of the environment photons provided diminishing returns. Even a single photon can act as an environment that introduces decoherence and selection, Pan explained, if it interacts strongly enough with the lone system photon. When interactions are weaker, a larger environment must be monitored.

    Fedor Jelezko, director of the Institute for Quantum Optics at Ulm University in Germany. Ulm University

    A team led by Jelezko probed the state of a nitrogen “defect” inside a synthetic diamond (shown mounted on the right) by monitoring surrounding carbon atoms. Their findings confirmed predictions of a theory known as quantum Darwinism.
    Ulm University

    The third experimental test of QD, led by the quantum-optical physicist Fedor Jelezko at Ulm University in Germany in collaboration with Zurek and others, used a very different system and environment, consisting of a lone nitrogen atom substituting for a carbon atom in the crystal lattice of a diamond—a so-called nitrogen-vacancy defect. Because the nitrogen atom has one more electron than carbon, this excess electron cannot pair up with those on neighboring carbon atoms to form a chemical bond. As a result, the nitrogen atom’s unpaired electron acts as a lone “spin,” which is like an arrow pointing up or down or, in general, in a superposition of both possible directions.

    This spin can interact magnetically with those of the roughly 0.3 percent of carbon nuclei present in the diamond as the isotope carbon-13, which, unlike the more abundant carbon-12, also has spin. On average, each nitrogen-vacancy spin is strongly coupled to four carbon-13 spins within a distance of about 1 nanometer.

    By controlling and monitoring the spins using lasers and radio-frequency pulses, the researchers could measure how a change in the nitrogen spin is registered by changes in the nuclear spins of the environment. As they reported in a preprint last September, they too observed the characteristic redundancy predicted by QD: The state of the nitrogen spin is “recorded” as multiple copies in the surroundings, and the information about the spin saturates quickly as more of the environment is considered.

    Zurek says that because the photon experiments create copies in an artificial way that simulates an actual environment, they don’t incorporate a selection process that picks out “natural” pointer states resilient to decoherence. Rather, the researchers themselves impose the pointer states. In contrast, the diamond environment does elicit pointer states. “The diamond scheme also has problems, because of the size of the environment,” Zurek added, “but at least it is, well, natural.”

    Generalizing Quantum Darwinism

    So far, so good for quantum Darwinism. “All these studies see what is expected, at least approximately,” Zurek said.

    Riedel says we could hardly expect otherwise, though: In his view, QD is really just the careful and systematic application of standard quantum mechanics to the interaction of a quantum system with its environment. Although this is virtually impossible to do in practice for most quantum measurements, if you can sufficiently simplify a measurement, the predictions are clear, he said: “QD is most like an internal self-consistency check on quantum theory itself.”

    But although these studies seem consistent with QD, they can’t be taken as proof that it is the sole description for the emergence of classicality, or even that it’s wholly correct. For one thing, says Cabello, the three experiments offer only schematic versions of what a real environment consists of. What’s more, the experiments don’t cleanly rule out other ways to view the emergence of classicality. A theory called “spectrum broadcasting,” for example, developed by Pawel Horodecki at the Gdańsk University of Technology in Poland and collaborators, attempts to generalize QD. Spectrum broadcast theory (which has only been worked through for a few idealized cases) identifies those states of an entangled quantum system and environment that provide objective information that many observers can obtain without perturbing it. In other words, it aims to ensure not just that different observers can access replicas of the system in the environment, but that by doing so they don’t affect the other replicas. That too is a feature of genuinely “classical” measurements.

    Horodecki and other theorists have also sought to embed QD in a theoretical framework that doesn’t demand any arbitrary division of the world into a system and its environment, but just considers how classical reality can emerge from interactions between various quantum systems. Paternostro says it might be challenging to find experimental methods capable of identifying the rather subtle distinctions between the predictions of these theories.

    Still, researchers are trying, and the very attempt should refine our ability to probe the workings of the quantum realm. “The best argument for performing these experiments probably is that they are good exercise,” Riedel said. “Directly illustrating QD can require some very difficult measurements that will push the boundaries of existing laboratory techniques.” The only way we can find out what measurement really means, it seems, is by making better measurements.

    See the full article here .


    Please help promote STEM in your local schools.

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  • richardmitnick 8:53 am on July 17, 2019 Permalink | Reply
    Tags: "Quantum control with light paves way for ultra-fast computers", , , , Quantum Physics   

    From Iowa State University via Futurity: “Quantum control with light paves way for ultra-fast computers” 

    From Iowa State University



    July 16th, 2019
    Mike Krapfl-Iowa State


    Terahertz light can control some of the essential quantum properties of superconducting states, report researchers.

    Jigang Wang patiently explains his latest discovery in quantum control that could lead to superfast computing based on quantum mechanics: He mentions light-induced superconductivity without energy gap. He brings up forbidden supercurrent quantum beats. And he mentions terahertz-speed symmetry breaking.

    Then he backs up and clarified all that. After all, the quantum world of matter and energy at terahertz and nanometer scales—trillions of cycles per second and billionths of meters—is still a mystery to most of us.

    “I like to study quantum control of superconductivity exceeding the gigahertz, or billions of cycles per second, bottleneck in current state-of-the-art quantum computation applications,” says Wang, a professor of physics and astronomy at Iowa State University. “We’re using terahertz light as a control knob to accelerate supercurrents.”

    A bit more explanation

    Superconductivity is the movement of electricity through certain materials without resistance. It typically occurs at very, very cold temperatures. Think -400 Fahrenheit for “high-temperature” superconductors.

    Terahertz light is light at very, very high frequencies. Think trillions of cycles per second. It’s essentially extremely strong and powerful microwave bursts firing at very short time frames.

    It all sounds esoteric and strange. But the new method could have very practical applications.

    “Light-induced supercurrents chart a path forward for electromagnetic design of emergent materials properties and collective coherent oscillations for quantum engineering applications,” Wang and his coauthors write in a paper in Nature Photonics.

    In other words, the discovery could help physicists “create crazy-fast quantum computers by nudging supercurrents,” Wang writes in a summary of the research team’s findings.

    Controlling quantum physics

    Finding ways to control, access, and manipulate the special characteristics of the quantum world and connect them to real-world problems is a major scientific push these days. The National Science Foundation has included the “Quantum Leap” in its “10 big ideas” for future research and development.

    “By exploiting interactions of these quantum systems, next-generation technologies for sensing, computing, modeling, and communicating will be more accurate and efficient,” says a summary of the science foundation’s support of quantum studies. “To reach these capabilities, researchers need understanding of quantum mechanics to observe, manipulate, and control the behavior of particles and energy at dimensions at least a million times smaller than the width of a human hair.”

    The researchers are advancing the quantum frontier by finding new macroscopic supercurrent flowing states and developing quantum controls for switching and modulating them.

    A summary of the research team’s study says experimental data they obtained from a terahertz spectroscopy instrument indicates terahertz light-wave tuning of supercurrents is a universal tool “and is key for pushing quantum functionalities to reach their ultimate limits in many cross-cutting disciplines” such as those mentioned by the science foundation.

    And so, the researchers write, “We believe that it is fair to say that the present study opens a new arena of light-wave superconducting electronics via terahertz quantum control for many years to come.”

    The Army Research Office supports Wang’s research. Additional researchers from Iowa State, the University of Wisconsin-Madison, and the University of Alabama at Birmingham contributed to the work.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Iowa State University is a public, land-grant university, where students get a great academic start in learning communities and stay active in 800-plus student organizations, undergrad research, internships and study abroad. They learn from world-class scholars who are tackling some of the world’s biggest challenges — feeding the hungry, finding alternative fuels and advancing manufacturing.

    Iowa Agricultural College and Model Farm (now Iowa State University) was officially established on March 22, 1858, by the legislature of the State of Iowa. Story County was selected as a site on June 21, 1859, and the original farm of 648 acres was purchased for a cost of $5,379. The Farm House, the first building on the Iowa State campus, was completed in 1861, and in 1862, the Iowa legislature voted to accept the provision of the Morrill Act, which was awarded to the agricultural college in 1864.

    Iowa State University Knapp-Wilson Farm House. Photo between 1911-1926

    Iowa Agricultural College (Iowa State College of Agricultural and Mechanic Arts as of 1898), as a land grant institution, focused on the ideals that higher education should be accessible to all and that the university should teach liberal and practical subjects. These ideals are integral to the land-grant university.

    The first official class entered at Ames in 1869, and the first class (24 men and 2 women) graduated in 1872. Iowa State was and is a leader in agriculture, engineering, extension, home economics, and created the nation’s first state veterinary medicine school in 1879.

    In 1959, the college was officially renamed Iowa State University of Science and Technology. The focus on technology has led directly to many research patents and inventions including the first binary computer (the ABC), Maytag blue cheese, the round hay baler, and many more.

    Beginning with a small number of students and Old Main, Iowa State University now has approximately 27,000 students and over 100 buildings with world class programs in agriculture, technology, science, and art.

    Iowa State University is a very special place, full of history. But what truly makes it unique is a rare combination of campus beauty, the opportunity to be a part of the land-grant experiment, and to create a progressive and inventive spirit that we call the Cyclone experience. Appreciate what we have here, for it is indeed, one of a kind.

  • richardmitnick 9:17 am on July 16, 2019 Permalink | Reply
    Tags: , “Photonic” and “spintronic” materials that transfer digitized information based on the spin of photons or electrons respectively is also made possible thanks to these results., , , Quantum Physics, , Weyl semimetals- a class of quantum materials have bulk quantum states whose electrical properties can be controlled using light., With quantum computing all platforms are light-based so it’s the photon which is the carrier of quantum information.   

    From Penn Today: “Unique electrical properties in quantum materials can be controlled using light” 

    From Penn Today

    July 15, 2019
    Erica K. Brockmeier

    Insights from quantum physics have allowed engineers to incorporate components used in circuit boards, optical fibers, and control systems in new applications ranging from smartphones to advanced microprocessors. But, even with significant progress made in recent years, researchers are still looking for new and better ways to control the uniquely powerful electronic properties of quantum materials.

    A new study from Penn researchers found that Weyl semimetals, a class of quantum materials, have bulk quantum states whose electrical properties can be controlled using light. The project was led by Ritesh Agarwal and graduate student Zhurun Ji in the School of Engineering and Applied Science in collaboration with Charles Kane, Eugene Mele, and Andrew M. Rappe in the School of Arts and Sciences, along with Zheng Liu from Nanyang Technological University. Penn’s Zachariah Addison, Gerui Liu, Wenjing Liu, and Heng Gao, and Nanyang’s Peng Yu, also contributed to the work. Their findings were published in Nature Materials.

    A hint of these unconventional photogalvanic properties, or the ability to generate electric current using light, was first reported by Agarwal in silicon. His group was able to control the movement of electrical current by changing the chirality, or the inherent symmetry of the arrangement of silicon atoms, on the surface of the material.

    “At that time, we were also trying to understand the properties of topological insulators, but we could not prove that what we were seeing was coming from those unique surface states,” Agarwal explains.

    A microscopic image of multiple electrodes on a sheet of Weyl semimetal, with red and blue arrows depicting the circular movement of the light-induced electrical current by either left- (blue) or right-circularly polarized light (right). (Photo: Zhurun Ji)

    Then, while conducting new experiments on Weyl semimetals, where the unique quantum states exist in the bulk of the material, Agarwal and Ji got results that didn’t match any theories that could explain how the electrical field was moving when activated by light. Instead of the electrical current flowing in a single direction, the current moved around the semimetal in a swirling circular pattern.

    Agarwal and Ji turned to Kane and Mele to help develop a new theoretical framework that could explain what they were seeing. After conducting new, extremely thorough experiments to iteratively eliminate all other possible explanations, the physicists were able to narrow the possible explanations to a single theory related to the structure of the light beam.

    “When you shine light on matter, it’s natural to think about a beam of light as laterally uniform,” says Mele. “What made these experiments work is that the beam has a boundary, and what made the current circulate had to do with its behavior at the edge of the beam.”

    Using this new theoretical framework, and incorporating Rappe’s insights on the electron energy levels inside the material, Ji was able to confirm the unique circular movements of the electrical current. The scientists also found that the current’s direction could be controlled by changing the light beam’s structure, such as changing the direction of its polarization or the frequency of the photons.

    “Previously, when people did optoelectronic measurements, they always assume that light is a plane wave. But we broke that limitation and demonstrated that not only light polarization but also the spatial dispersion of light can affect the light-matter interaction process,” says Ji.

    This work allows researchers to not only better observe quantum phenomena, but it provides a way to engineer and control unique quantum properties simply by changing light beam patterns. “The idea that the modulation of light’s polarization and intensity can change how an electrical charge is transported could be powerful design idea,” says Mele.

    Future development of “photonic” and “spintronic” materials that transfer digitized information based on the spin of photons or electrons respectively is also made possible thanks to these results. Agarwal hopes to expand this work to include other optical beam patterns, such as “twisted light,” which could be used to create new quantum computing materials that allow more information to be encoded onto a single photon of light.

    “With quantum computing, all platforms are light-based, so it’s the photon which is the carrier of quantum information. If we can configure our detectors on a chip, everything can be integrated, and we can read out the state of the photon directly,” Agarwal says.

    Agarwal and Mele emphasize the “heroic” effort made by Ji, including an additional year’s measurements made while running an entirely new set of experiments that were crucial to the interpretation of the study. “I’ve rarely seen a graduate student faced with that challenge who was able not only to rise to it but to master it. She had the initiative to do something new, and she got it done,” says Mele.

    This research was supported by Office of Naval Research (Grant N00014-17-1-2661), U.S. Army Research Office (Grant W911NF- 17-1-0436), U.S. Department of Energy (grants DE FG02 84ER45118 and DE-FG02-07ER46431), and a National Science Foundation Materials Research Science and Engineering Centers seed grant.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Penn campus

    Academic life at Penn is unparalleled, with 100 countries and every U.S. state represented in one of the Ivy League’s most diverse student bodies. Consistently ranked among the top 10 universities in the country, Penn enrolls 10,000 undergraduate students and welcomes an additional 10,000 students to our world-renowned graduate and professional schools.

    Penn’s award-winning educators and scholars encourage students to pursue inquiry and discovery, follow their passions, and address the world’s most challenging problems through an interdisciplinary approach.

  • richardmitnick 2:06 pm on July 15, 2019 Permalink | Reply
    Tags: , , , Quantum Physics   

    From PBS NOVA: “Bring “Spooky Action at a Distance” into the Classroom with NOVA Resources” 

    From PBS NOVA

    July 15, 2019

    Quantum physics impacts the technology students use every day. Use these resources from NOVA broadcasts, NOVA Digital, and What the Physics!? to introduce quantum concepts to your classroom.


    Imagine you have a pair of quantum dice. You put the dice in your cup, throw them, and they are both a “six.” You do it again, and they’re both a “three.” You do it again, and they’re both a “one.” No matter how many times you throw the dice, they are always the same number. This is a seemingly random process, but quantum entanglement ensures that these dice will always act in unison.

    The thought of tackling quantum entanglement in your classroom can be intimidating. Even Albert Einstein was skeptical of the concept, calling it “spooky action at a distance,” and didn’t think it was possible. If this was a tough sell for Einstein, how can you teach this idea to middle and high school students?

    Quantum physics are the laws that govern subatomic particles. It can help explain the movements, interactions, and behaviors of very small things like photons and electrons. How small are particles in the subatomic world? Imagine something a million times smaller than the width of a human hair, or making a soccer ball into the size of the Earth and moving inside. This is how we can understand the scale of the world of atoms and subatomic particles.

    Quantum physics is rooted in probability. An electron doesn’t have a specific location in space until it is looked for or detected. When we picture an atom, we often imagine its electrons orbiting the atom’s nucleus in clear defined paths. However, electrons are not the ever-present tiny spheres we imagine them to be. They are really a “fuzzy wave of probability,” ready to be in an infinite amount of locations around the nucleus of an atom until we look at it. The simple act of observing an electron changes the electron’s location.

    Quantum entanglement takes this idea one step further, and is a phenomenon where two particles act in unison, no matter the distances between them. Unlike a row of dominoes that rely on the actions of each previous domino to be knocked down over time, entangled particles change instantly once one is detected, no matter how far apart they may be. For example, if a particle on Earth is entangled with a particle in the Andromeda galaxy, they will change at the exact same time once a change is made to one of the particles.

    While quantum physics pertains to the smallest units in the universe, the ways in which it impacts our daily lives are immense. Quantum theory played a role in the Manhattan Project and the atom bomb and in the development of lasers and transistors. Our increasingly digital world relies on quantum entanglement to send encrypted messages and quantum computers with massive processing power to solve problems a normal computer could never accomplish.

    Quantum physics impacts the technology students use every day. Use these resources from NOVA broadcasts, NOVA Digital, and What the Physics!? to introduce quantum concepts to your students.

    Einstein’s Quantum Riddle Resources

    Quantum Entanglement: Conceptualize quantum entanglement, the idea that particles can instantaneously influence each other even when they are spatially separated, in this video from NOVA: Einstein’s Quantum Riddle.

    Wave Particle Duality of Electrons: Conceptualize the nonintuitive idea that electrons can behave both as a wave and a particle (wave–particle duality) in this video from NOVA: Einstein’s Quantum Riddle.

    Collecting Evidence for Quantum Entanglement: Learn why different experimental designs were needed to collect evidence for quantum entanglement in this media gallery of videos from NOVA: Einstein’s Quantum Riddle.

    What the Physics!? Resources

    Seeing Quantum with the Naked Eye: How can you train yourself to be a quantum detector? You can detect quantum mechanics all over—if you know how to look for it. In this episode of What the Physics!? find out how simply squinting at a lamp reveals the quantum nature of light.

    The Biggest Puzzle in Physics: Sometimes the biggest puzzle in physics seems like the worst relationship in the universe. Quantum mechanics and general relativity are the two best theories in physics, but they have never been able to get along. Find out why in this episode of What the Physics!?

    NOVA Digital Resources

    Quantum Confidential: Watch how a technique called quantum cryptography could save a state secret from falling into enemy hands in this video from NOVA Digital.

    Quantum Physics to Protect Votes: Voters want to be assured that every election is fraud-proof and hack-free. With the help of quantum mechanics, it’s possible to do just that — encrypt and transmit a vote in ways that can’t be tampered with.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

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

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

    From SLAC National Accelerator Lab

    May 9, 2019
    Manuel Gnida

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

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

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

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

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

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

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

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

    What exactly is quantum information science?

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

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

    What does quantum control mean in practice?

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

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

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

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

    What is quantum squeezing?

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

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

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

    What types of sensors are you working on?

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

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

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

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

    LBNL LZ project at SURF, Lead, SD, USA

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

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

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

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

    What are the challenges of QIS?

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

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

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

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

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

    What do cold atoms have to do with black holes?

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition


    SLAC/LCLS II projected view

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

  • richardmitnick 5:44 pm on April 17, 2019 Permalink | Reply
    Tags: , , Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum, , , Quantum Physics,   

    From Scientific American: “Cosmologist Lee Smolin says that at certain key points, the scientific worldview is based on fallacious reasoning” 

    Scientific American

    From Scientific American

    April 17, 2019
    Jim Daley

    Lee Smolin, author of six books about the philosophical issues raised by contemporary physics, says every time he writes a new one, the experience completely changes the direction his own research is taking. In his latest book, Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum, Smolin, a cosmologist and quantum theorist at the Perimeter Institute for Theoretical Physics in Ontario, tackles what he sees as the limitations in quantum theory.

    Credit: Perimeter Institute

    “I want to say the scientific worldview is based on fallacious reasoning at certain key points,” Smolin says. In Einstein’s Unfinished Revolution, he argues one of those key points was the assumption that quantum physics is a complete theory. This incompleteness, Smolin argues, is the reason quantum physics has not been able to solve certain questions about the universe.

    “Most of what we do [in science] is take the laws that have been discovered by experiments to apply to parts of the universe, and just assume that they can be scaled up to apply to the whole universe,” Smolin says. “I’m going to be suggesting that’s wrong.”

    Join Smolin at the Perimeter Institute as he discusses his book and takes the audience on a journey through the basics of quantum physics and the experiments and scientists who have changed our understanding of the universe. The discussion, “Einstein’s Unfinished Revolution,” is part of Perimeter’s public lecture series and will take place on Wednesday, April 17, at 7 P.M. Eastern time. Online viewers can participate in the discussion by tweeting to @Perimeter using the #piLIVE hashtag.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

  • richardmitnick 1:12 pm on April 9, 2019 Permalink | Reply
    Tags: "In quantum breakthrough scientists demonstrate ‘one-way street’ for energy flow", , , , , Quantum Physics,   

    From University of Chicago: “In quantum breakthrough, scientists demonstrate ‘one-way street’ for energy flow” 

    U Chicago bloc

    From University of Chicago

    Apr 4, 2019
    A. A. Clerk

    Copyright shutterstock.com

    In a new study, scientists found a method to create a controllable one-way channel for the flow of vibrational energy and heat.

    A basic rule in our lives is that if energy can flow in one direction, then it can also flow in the reverse direction. For example, if you open a window and yell at someone outside, you also can hear if they yell back. But what if there was a way to create a “one-way street” for mechanical energy that only allows heat and sound to flow in one direction?

    Finding new ways to break this basic symmetry has sparked the interest of scientists and engineers in recent years; such one-way streets could be extremely useful in applications ranging from quantum computing to cooling in electronics and devices.

    A breakthrough experiment involving researchers with the Institute for Molecular Engineering at the University of Chicago and Yale University demonstrated that by using light to mediate the interaction between mechanical systems, they can create a controllable, one-way channel for the flow of vibrational energy and heat.

    The study, published April 3 in Nature, was based on an idea developed earlier by the University of Chicago team [Physical Review X] and proves that the basic theory works. It also shows that the ideas can be implemented in a simple, compact system that could be incorporated in new devices.

    Schematic image of the experimental device. Credit: Jack Sankey

    “This is a really exciting resource that can be used in both classical and quantum contexts,” said study co-author Aashish Clerk, a professor in molecular engineering at the University of Chicago who developed the theory. “This research could open the door for many new studies.”

    Breaking symmetry by using light

    The principle that says energy and information exchange between two systems via a two-way street is known as “reciprocity,” and it is a fundamental rule in most physical systems. Breaking this symmetry is crucial in a number of different applications. For example, by preventing a backward flow of energy, one could protect a delicate signal source from corruption, or cool a system by preventing unwanted heating.

    It’s especially important in quantum computation, in which scientists harness quantum phenomena to enable powerful new kinds of information processing. Breaking this symmetry ensures delicate quantum processors are not destroyed during the readout process.

    In their experiment, researchers used a tiny vibrating membrane as the mechanical system. Much like a drumhead, this membrane could vibrate in several distinct ways, each with a distinct resonant frequency.

    The researchers’ goal was to engineer a one-way flow of energy between two of these vibrational modes. To do this, the membrane was placed in a structure called an optical cavity, with two parallel mirrors designed to trap light. By shining light on the cavity using lasers, the researchers were able to use light as a medium for transferring mechanical energy between two vibrational modes. When the lasers were tuned carefully (in a way predicted by Clerk’s theory), this transfer mechanism was completely directional.

    From theory to lab to the quantum level

    The experiment was based on basic theoretical concepts developed by Clerk and his former postdoc Anja Metelmann (now at the Freie University in Berlin).

    “You can come up with a lot of ideas that are exciting in terms of the basic theory and concepts, but often there is a gap between these abstract ideas and what you can actually build and realize in the lab,” Clerk said. “To me, it is exciting that our proposal was realized, and that the experimentalists had enough control over their system to make it work.”

    The approach used in the experiment to achieve a one-way interaction—mechanical vibrations interacting with light—could pave the way for designing new devices targeting a variety of applications, ranging from mitigating heat flow to new kinds of communication systems. These unusual one-way interactions also have interesting fundamental implications.

    As a theoretical physicist who focuses on quantum systems, Clerk is particularly interested in studying arrays where many quantum systems interact with one another in a unidirectional manner. This could be a powerful way to generate the unusual kinds of quantum states that are needed for quantum communication and quantum computation.

    Other authors on the paper include Jack Harris, Haitan Xu and Luyao Jiang of Yale University.

    Clerk is working with the Polsky Center for Entrepreneurship and Innovation at the University of Chicago to advance his discoveries.

    See the full article here .


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