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  • richardmitnick 7:47 am on September 2, 2019 Permalink | Reply
    Tags: "Physicists Have Finally Built a Quantum X-Ray Device", , Bar Ilon University, PDC-parametric down-conversion, , Quantum enhancement, Quantum entanglement, Quantum illumination, Quantum imaging, , , X-ray PDC,   

    From Bar Ilon University and Riken via Science Alert: “Physicists Have Finally Built a Quantum X-Ray Device” 

    2

    From Bar Ilon University

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    From RIKEN

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    ScienceAlert

    Science Alert

    2 SEP 2019
    MICHELLE STARR

    1
    (APS/Alan Stonebraker)

    A team of researchers has just demonstrated quantum enhancement in an actual X-ray machine, achieving the desirable goal of eliminating background noise for precision detection.

    The relationships between photon pairs on quantum scales can be exploited to create sharper, higher-resolution images than classical optics. This emerging field is called quantum imaging, and it has some really impressive potential – particularly since, using optical light, it can be used to show objects that can’t usually be seen, like bones and organs.

    Quantum correlation describes a number of different relationships between photon pairs. Entanglement is one of these, and is applied in optical quantum imaging.

    But the technical challenges of generating entangled photons in X-ray wavelengths are considerably greater than for optical light, so in the building of their quantum X-ray, the team took a different approach.

    They used a technique called quantum illumination to minimise background noise. Usually, this uses entangled photons, but weaker correlations work, too. Using a process called parametric down-conversion (PDC), the researchers split a high-energy – or “pump” – photon into two lower-energy photons, called a signal photon and an idler photon.

    “X-ray PDC has been demonstrated by several authors, and the application of the effect as a source for ghost imaging has been demonstrated recently,” the researchers write in their paper.

    “However, in all previous publications, the photon statistics have not been measured. Essentially, to date, there is no experimental evidence that photons, which are generated by X-ray PDC, exhibit statistics of quantum states of radiation. Likewise, observations of the quantum enhanced measurement sensitivity have never been reported at X-ray wavelengths.”

    The researchers achieved their X-ray PDC with a diamond crystal. The nonlinear structure of the crystal splits a beam of pump X-ray photons into signal and idler beams, each with half the energy of the pump beam.

    Normally, this process is very inefficient using X-rays, so the team scaled up the power. Using the SPring-8 synchrotron in Japan, they shot a 22 KeV beam of X-rays at their crystal, which split into two beams, each carrying 11 KeV.

    SPring-8 synchrotron


    SPring-8 synchrotron, located in Hyōgo Prefecture, Japan

    The signal beam is sent towards the object to be imaged – in the case of this research, a small piece of metal with three slits – with a detector on the other side. The idler beam is sent straight to a different detector. This is set up so that each beam hits its respective detector at the same place and at the same time.

    “The perfect time-energy relationship we observed could only mean that the two photons were quantum correlated,” said physicist Sason Sofer of Bar-Ilan University in Israel.

    For the next step, the researchers compared their detections. There were only around 100 correlated photons per point in the image, and around 10,000 more background photons. But the researchers could match each idler to a signal, so they could actually tell which photons in the image were from the beam, thus easily separating out the background noise.

    They then compared these images to images taken using regular, non-correlated photons – and the correlated photons clearly produced a much sharper image.

    It’s early days yet, but it’s definitely a step in the right direction for what could be a greatly exciting tool. Quantum X-ray imaging could have a number of uses outside the range of current X-ray technology.

    One promise is that it could lower the amount of radiation required for X-ray imaging. This would mean that samples easily damaged by X-rays could be imaged, or samples that require low temperatures; less radiation would mean less heat. It could also enable physicists to X-ray atomic nuclei to see what’s inside.

    Obviously, since these quantum X-rays require a hardcore particle accelerator, medical applications are currently off the table. The team has demonstrated that it can be done, but scaling down is going to be tricky.

    Currently, determining whether the photons are entangled is the next step. That would require the photons’ arrival at the detectors to be measured within attosecond scales, which is beyond our current technology.

    Still, this is a pretty amazing achievement.

    “We have demonstrated the ability to utilise the strong time-energy correlations of photon pairs for quantum enhanced photodetection. The procedure we have presented possesses great potential for improving the performances of X-ray measurements,” the researchers write.

    “We anticipate that this work will open the way for more quantum enhanced x-ray regime detection schemes, including the area of diffraction and spectroscopy.”

    The research has been published in Physical Review X.

    See the full article here .


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    RIKEN campus

    RIKEN is Japan’s largest comprehensive research institution renowned for high-quality research in a diverse range of scientific disciplines. Founded in 1917 as a private research foundation in Tokyo, RIKEN has grown rapidly in size and scope, today encompassing a network of world-class research centers and institutes across Japan.

     
  • richardmitnick 9:50 am on July 29, 2019 Permalink | Reply
    Tags: "Engineering a Fast Two-Qubit Gate in Silicon", , “We were able to bring the qubit’s electrons closer or further apart effectively turning on and off the interaction between them- a prerequisite for a quantum gate” said Yu He., , Long coherence times- the ability to hang onto delicate quantum information for more than instant., , Quantum entanglement, Qubits transistor and leads, Scanning tunneling microscope hydrogen lithography, The big problem has been getting these atoms close enough together to “talk” to one another in a quantum-mechanical sense.,   

    From UNSW via Optics & Photonics: “Engineering a Fast Two-Qubit Gate in Silicon” 

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    From University of New South Wales

    Optics & Photonics

    7.29.19
    Stewart Wills

    In a tour-de-force of atom-scale engineering, a research team at the University of New South Wales (UNSW), Australia, has demonstrated a two-qubit gate between coupled donor atom qubits in silicon—the first time, according to the researchers, that such a feat has been accomplished (Nature). The work potentially overcomes one significant hurdle in building quantum computers with atom-based qubits on a silicon platform.

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    The research team behind the UNSW work on atom-based qubits in silicon included (left to right) co-lead-authors Sam Gorman and Yu He, team leader Michelle Simmons, Ludwik Kranz, Joris Keizer and Daniel Keith. [Image: UNSW Sydney]

    Bringing atom qubits to silicon

    Atom- and ion-based qubits have some notable attractions as candidates for quantum computing. A particular plus is these systems’ long coherence times, the ability to hang onto delicate quantum information for more than instant. This and other advantages have made assemblages of ions or atoms trapped in lattices of laser beams a key locus of advances in quantum research, with some standout recent accomplishments, for example, in quantum simulation.

    Technologists and engineers would like to bring some of those same advantages of atom-based qubits to silicon. In principle, that would mean that efforts to build quantum computers could leverage the infrastructure and techniques honed over decades in fashioning semiconductors for classical computers.

    Moreover, as Michelle Simmons, the leader of the UNSW team, noted in a press release accompanying the research, electron-spin qubits donated by single atoms “hold the world record” for qubits in silicon under several metrics. Previous work has shown, for example, that such qubits in silicon can have coherence times in the seconds, with potential gate fidelities (and, hence, coherent control) on the order of 99.9%.

    The big problem has been getting these atoms close enough together to “talk” to one another in a quantum-mechanical sense—through phenomena such as entanglement—and thus form quantum-computational logic gates, while still maintaining the ability to control and measure each atom qubit individually. As a result, while a number of research teams have demonstrated two-qubit gates in silicon using qubits bigger than individual atoms, such as quantum dots, the same feat hadn’t yet been achieved for individual-atoms-based qubits until the recent work by the UNSW team.

    STM hydrogen lithography

    To create such a two-qubit gate between atom-based qubits, Simmons and her team used a technique, scanning tunneling microscope (STM) hydrogen lithography, that the research group has been honing for some 20 years.

    The method begins with a natural silicon substrate—the surface of which, through a number of high-temperature chemical steps, the researchers then coat with a layer of monoatomic hydrogen. Next, the tip of an STM is used to individually pick off hydrogen atoms from that surface, creating an atom-scale lithographic mask on the surface, with nanometer precision. Finally, the surface is exposed to a phosphorous–hydrogen gas at 350 °C, leaving behind phosphorous in the exposed areas.

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    The UNSW team’s STM hydrogen lithography technique allowed it to construct a two-qubit logic gate consisting of phosphorous atoms placed a mere 13 nm apart, along with associated circuitry. [Image: UNSW Sydney Media Office]

    Qubits, transistor and leads

    By applying this method, the team was able to deposit phosphorous atom qubits—a left qubit consisting of two phosphorous atoms, and a right qubit including three—separated by a mere 13 nm. (The left–right asymmetry between the number of donor atoms was engineered intentionally, according to the paper, in part to increase the tunability of the exchange interaction between the qubits.)

    The researchers also used the technique to lay down associated circuitry for a quantum gate between the two qubits. That circuitry included source and drain leads, as well as a nearby single-electron transistor that serves, through weak tunnel-coupling with the qubits, as an electron reservoir and charge sensor.

    The team then popped the fabricated device into 50-mK dilution refrigerator, and tested its ability to implement a particular quantum logic gate—a so-called (SWAP)½ gate—on a variety of electron spin basis states from the donor atoms. The team was able to read out the gate results with 94% fidelity.

    “We were able to bring the qubit’s electrons closer or further apart, effectively turning on and off the interaction between them, a prerequisite for a quantum gate,” Yu He, one of the paper’s two lead co-authors (along with Sam Gorman), said in a press release. And the gate operation was blazingly fast, with the two-qubit SWAP exchange happening in a mere 800 ps.

    Exquisite engineering

    In an email to OPN, Simmons noted that one of the key points of the paper was the exquisite engineering that the technique allows. “We engineer the atoms to be [around] 13nm apart, to create entanglement,” she said, “but at the same time have the control to independently measure one qubit with high fidelity, without altering the neighboring qubit despite their close proximity.”

    Simmons added that the fact that the platform uses only phosphorous and silicon atoms allows (as the team had shown in previous work) “very low noise quantum circuitry.” That’s because the system “[gets] rid of any dielectrics of different materials, which typically cause charge noise and/or irregularities at the interfaces found in semiconductor quantum dots.”

    In the paper, the team noted that in the long run, the hope is that, by leveraging these techniques, the group can “utilize the hallmark long coherence times that are normally associated with ion trap qubits together with the scalability of the silicon material system to realize a large-scale quantum processor.” Simmons told OPN that she and her colleagues are “excited about the possibilities,” but also noted that the work is still at an early stage. “Watch this space,” she said.

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    Joris Keizer, Michelle Simmons and Yu He in the lab. [Image: UNSW Sydney Media Office]

    See the full article here .

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  • 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 entanglement, , 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

    07.28.19
    Philip Ball

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    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.

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    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.

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    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.

    6
    Fedor Jelezko, director of the Institute for Quantum Optics at Ulm University in Germany. Ulm University

    7
    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 .

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  • richardmitnick 9:14 am on July 13, 2019 Permalink | Reply
    Tags: , , Quantum entanglement, , , University of Glasgow   

    From University of Glasgow via Science Alert: “Scientists Just Unveiled The First-Ever Photo of Quantum Entanglement” 

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    From University of Glasgow

    via

    ScienceAlert

    Science Alert

    13 JUL 2019
    FIONA MACDONALD

    1
    (University of Glasgow)

    In an incredible first, scientists have captured the world’s first actual photo of quantum entanglement – a phenomenon so strange Einstein famously described it as ‘spooky action at a distance’.

    The image was captured by physicists at the University of Glasgow in Scotland, and it’s so breathtaking we can’t stop staring.

    It might not look like much, but just stop and think about it for a second: this fuzzy grey image is the first time we’ve seen the particle interaction that underpins the strange science of quantum mechanics and forms the basis of quantum computing.

    Quantum entanglement occurs when two particles become inextricably linked, and whatever happens to one immediately affects the other, regardless of how far apart they are. Hence the ‘spooky action at a distance’ description.

    This particular photo shows entanglement between two photons – two particles of light. They’re interacting and for a brief moment sharing physical states.

    Paul-Antoine Moreau, first author on the paper where the image was unveiled, told the BBC the image was “an elegant demonstration of a fundamental property of nature”.

    To capture the incredible photo, Moreau and a team of physicists created a system that blasted out streams of entangled photons at what they described as ‘non-conventional objects’.

    The experiment actually involved capturing four images of the photons under four different phase transitions. You can see the full image below:

    2
    (Moreau et al., Science Advances, 2019)

    What you’re looking at here is actually a composite of multiple images of the photons as they go through a series of four phase transitions.

    Basically, the physicists split the entangled photons up and ran one beam through a liquid crystal material known as β-Barium Borate, triggering four phase transitions.

    At the same time they captured photos of the entangled pair going through the same phase transitions, even though it hadn’t passed through the liquid crystal.

    You can see the setup below, the entangled beam of photons comes from the bottom left, one half of the entangled pair splits to the left and passes through the four phase filters. The others that go straight ahead didn’t go through the filters, but underwent the same phase changes.

    3
    (Moreau et al., Science Advances, 2019)

    The camera was able to capture images of these at the same time, showing that they’d both shifted the same way despite being split. In other words, they were entangled.

    While Einstein made quantum entanglement famous, the late physicist John Stewart Bell helped define quantum entanglement and established a test known as ‘Bell inequality’. Basically, if you can break Bell inequality, you can confirm true quantum entanglement.

    “Here, we report an experiment demonstrating the violation of a Bell inequality within observed images,” the team write in Science Advances.

    “This result both opens the way to new quantum imaging schemes … and suggests promise for quantum information schemes based on spatial variables.”

    The research was published in Science Advances.

    See the full article here .

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    U Glasgow campus

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

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

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

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

     
  • richardmitnick 11:11 am on July 6, 2019 Permalink | Reply
    Tags: Quantum entanglement, ,   

    From Science Alert: “If You Thought Quantum Mechanics Was Weird, You Need to Check Out Entangled Time” 

    ScienceAlert

    From Science Alert

    6 JULY 2019
    ELISE CRULL

    1
    (bestdesigns/iStock)

    In the summer of 1935, the physicists Albert Einstein and Erwin Schrödinger engaged in a rich, multifaceted and sometimes fretful correspondence about the implications of the new theory of quantum mechanics.

    The focus of their worry was what Schrödinger later dubbed entanglement: the inability to describe two quantum systems or particles independently, after they have interacted.

    Until his death, Einstein remained convinced that entanglement showed how quantum mechanics was incomplete. Schrödinger thought that entanglement was the defining feature of the new physics, but this didn’t mean that he accepted it lightly.

    “I know of course how the hocus pocus works mathematically,” he wrote to Einstein on 13 July 1935. “But I do not like such a theory.”

    Schrödinger’s famous cat, suspended between life and death, first appeared in these letters, a byproduct of the struggle to articulate what bothered the pair.

    The problem is that entanglement violates how the world ought to work. Information can’t travel faster than the speed of light, for one.

    But in a 1935 paper, Einstein and his co-authors showed how entanglement leads to what’s now called quantum nonlocality, the eerie link that appears to exist between entangled particles.

    If two quantum systems meet and then separate, even across a distance of thousands of lightyears, it becomes impossible to measure the features of one system (such as its position, momentum and polarity) without instantly steering the other into a corresponding state.

    Up to today, most experiments have tested entanglement over spatial gaps.

    The assumption is that the ‘nonlocal’ part of quantum nonlocality refers to the entanglement of properties across space. But what if entanglement also occurs across time? Is there such a thing as temporal nonlocality?

    The answer, as it turns out, is yes.

    Just when you thought quantum mechanics couldn’t get any weirder, a team of physicists at the Hebrew University of Jerusalem reported in 2013 that they had successfully entangled photons that never coexisted.

    Previous experiments involving a technique called ‘entanglement swapping’ had already showed quantum correlations across time, by delaying the measurement of one of the coexisting entangled particles; but Eli Megidish and his collaborators were the first to show entanglement between photons whose lifespans did not overlap at all.

    Here’s how they did it.

    First, they created an entangled pair of photons, ‘1-2’ (step I in the diagram below). Soon after, they measured the polarisation of photon 1 (a property describing the direction of light’s oscillation) – thus ‘killing’ it (step II).

    2
    (Provided)

    Photon 2 was sent on a wild goose chase while a new entangled pair, ‘3-4’, was created (step III). Photon 3 was then measured along with the itinerant photon 2 in such a way that the entanglement relation was ‘swapped’ from the old pairs (‘1-2’ and ‘3-4’) onto the new ‘2-3’ combo (step IV).

    Some time later (step V), the polarisation of the lone survivor, photon 4, is measured, and the results are compared with those of the long-dead photon 1 (back at step II).

    The upshot? The data revealed the existence of quantum correlations between ‘temporally nonlocal’ photons 1 and 4. That is, entanglement can occur across two quantum systems that never coexisted.

    What on Earth can this mean? Prima facie, it seems as troubling as saying that the polarity of starlight in the far-distant past – say, greater than twice Earth’s lifetime – nevertheless influenced the polarity of starlight falling through your amateur telescope this winter.

    Even more bizarrely: maybe it implies that the measurements carried out by your eye upon starlight falling through your telescope this winter somehow dictated the polarity of photons more than 9 billion years old.

    Lest this scenario strike you as too outlandish, Megidish and his colleagues can’t resist speculating on possible and rather spooky interpretations of their results.

    Perhaps the measurement of photon 1’s polarisation at step II somehow steers the future polarisation of 4, or the measurement of photon 4’s polarisation at step V somehow rewrites the past polarisation state of photon 1.

    In both forward and backward directions, quantum correlations span the causal void between the death of one photon and the birth of the other.

    Just a spoonful of relativity helps the spookiness go down, though.

    In developing his theory of special relativity, Einstein deposed the concept of simultaneity from its Newtonian pedestal.

    As a consequence, simultaneity went from being an absolute property to being a relative one. There is no single timekeeper for the Universe; precisely when something is occurring depends on your precise location relative to what you are observing, known as your frame of reference.

    So the key to avoiding strange causal behaviour (steering the future or rewriting the past) in instances of temporal separation is to accept that calling events ‘simultaneous’ carries little metaphysical weight.

    It is only a frame-specific property, a choice among many alternative but equally viable ones – a matter of convention, or record-keeping.

    The lesson carries over directly to both spatial and temporal quantum nonlocality.

    Mysteries regarding entangled pairs of particles amount to disagreements about labelling, brought about by relativity.

    Einstein showed that no sequence of events can be metaphysically privileged – can be considered more real – than any other. Only by accepting this insight can one make headway on such quantum puzzles.

    The various frames of reference in the Hebrew University experiment (the lab’s frame, photon 1’s frame, photon 4’s frame, and so on) have their own ‘historians’, so to speak.

    While these historians will disagree about how things went down, not one of them can claim a corner on truth. A different sequence of events unfolds within each one, according to that spatiotemporal point of view.

    Clearly, then, any attempt at assigning frame-specific properties generally, or tying general properties to one particular frame, will cause disputes among the historians.

    But here’s the thing: while there might be legitimate disagreement about which properties should be assigned to which particles and when, there shouldn’t be disagreement about the very existence of these properties, particles, and events.

    These findings drive yet another wedge between our beloved classical intuitions and the empirical realities of quantum mechanics.

    As was true for Schrödinger and his contemporaries, scientific progress is going to involve investigating the limitations of certain metaphysical views.

    Schrödinger’s cat, half-alive and half-dead, was created to illustrate how the entanglement of systems leads to macroscopic phenomena that defy our usual understanding of the relations between objects and their properties: an organism such as a cat is either dead or alive. No middle ground there.

    Most contemporary philosophical accounts of the relationship between objects and their properties embrace entanglement solely from the perspective of spatial nonlocality.

    But there’s still significant work to be done on incorporating temporal nonlocality – not only in object-property discussions, but also in debates over material composition (such as the relation between a lump of clay and the statue it forms), and part-whole relations (such as how a hand relates to a limb, or a limb to a person).

    For example, the ‘puzzle’ of how parts fit with an overall whole presumes clear-cut spatial boundaries among underlying components, yet spatial nonlocality cautions against this view. Temporal nonlocality further complicates this picture: how does one describe an entity whose constituent parts are not even coexistent?

    Discerning the nature of entanglement might at times be an uncomfortable project. It’s not clear what substantive metaphysics might emerge from scrutiny of fascinating new research by the likes of Megidish and other physicists.

    In a letter to Einstein, Schrödinger notes wryly (and deploying an odd metaphor): “One has the feeling that it is precisely the most important statements of the new theory that can really be squeezed into these Spanish boots – but only with difficulty.”

    We cannot afford to ignore spatial or temporal nonlocality in future metaphysics: whether or not the boots fit, we’ll have to wear ’em.

    See the full article here .


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  • richardmitnick 8:41 am on June 5, 2019 Permalink | Reply
    Tags: "Stanford joins collaboration to explore 'ultra-quantum matter'", , Quantum entanglement, , , The Simons Collaboration on Ultra-Quantum Matter   

    From Stanford University: “Stanford joins collaboration to explore ‘ultra-quantum matter'” 

    Stanford University Name
    From Stanford University

    June 3, 2019
    Ker Than

    1

    The Simons Collaboration on Ultra-Quantum Matter brings together physicists from 12 institutions to “understand, classify and realize” new forms of ultra-quantum matter in the lab.

    Stanford physicist Shamit Kachru is a member of a new collaboration that aims to unravel the mystery of entangled quantum matter — macroscopic assemblages of atoms and electrons that seem to share the same seemingly telepathic link as entangled subatomic particles.

    The Simons Collaboration on Ultra-Quantum Matter is funded by the Simons Foundation and led by Harvard physics Professor Ashvin Vishwanath. It is part of the Simons Collaborations in Mathematics and Physical Sciences program, which aims to “stimulate progress on fundamental scientific questions of major importance in mathematics, theoretical physics and theoretical computer science.” The Simons Collaboration on Ultra-Quantum Matter will be one of 12 such collaborations ranging across these fields.

    Ultra-quantum matter, or UQM, exhibit non-intuitive quantum properties that were once thought to arise only in very small systems. One key property is “non-local entanglement,” in which two physically separated groups of atoms can share joint properties, so that measuring one affects the measurement outcome of the other. UQM should exhibit entirely new physical properties, a better understanding of which could lead to new types of quantum information storage systems and quantum materials.

    The Simons Collaboration on Ultra-Quantum Matter brings together physicists from 12 institutions to “understand, classify and realize” new forms of ultra-quantum matter in the lab. To achieve this, the collaboration includes physicists working in different domains, including condensed matter and high energy theorists, as well as atomic and quantum information experts. Kachru’s own background is in string theory, theoretical cosmology, and condensed matter physics.

    A confluence of factors makes this a particularly exciting time to study UQM, said Kachru, who is the Wells Family Director of the Stanford Institute for Theoretical Physics (SITP) and the chair of the physics department.

    “Many of the cutting-edge questions in quantum field theory now seem to involve highly quantum condensed matter systems,” Kachru said. “These systems are often best studied using elegant and clean mathematical techniques, and there is a promise of genuine contact between high level theory and experiment. I can’t imagine better people to teach me about issues and opportunities here than the collaboration members, who are leading experts in all aspects of UQM.”

    Kachru also looks forward to working again with former Stanford graduate student and collaboration member, John McGreevy, who was Kachru’s first PhD advisee and is now a professor of physics at the University of California, San Diego.

    Ultra-Quantum Matter is an $8M four-year award funded by the Simons Foundation and renewable for three additional years. It will support researchers from the following institutions: Caltech, Harvard, the Institute for Advanced Study, MIT, Stanford, University of California Santa Barbara, University of California San Diego, the University of Chicago, the University of Colorado Boulder, the University of Innsbruck, University of Maryland and University of Washington.

    A UQM meeting of the new collaboration is scheduled to take place at Stanford in May of 2020.

    See the full article here .


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    Stanford University campus. No image credit

    Stanford University

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
  • richardmitnick 11:42 am on May 17, 2019 Permalink | Reply
    Tags: Articles about them inevitably refer to entanglement- a property of quantum physics that makes all these magical devices possible., , , Quantum computers; quantum cryptography; and quantum (insert name here) are often in the news these days., Quantum entanglement,   

    From University of Toronto: “Remote connections? U of T expert on detangling entanglement in quantum physics” 

    U Toronto Bloc

    From University of Toronto

    April 26, 2019
    Amar Vutha

    1
    Entanglement is a “quantum correlation” between the properties of particles (image by Shutterstock)

    Quantum computers, quantum cryptography and quantum (insert name here) are often in the news these days. Articles about them inevitably refer to entanglement, a property of quantum physics that makes all these magical devices possible.

    Einstein called entanglement “spooky action at a distance,” a name that has stuck and become increasingly popular. Beyond just building better quantum computers, understanding and harnessing entanglement is also useful in other ways.

    For example, it can be used to make more accurate measurements of gravitational waves, and to better understand the properties of exotic materials. It also subtly shows up in other places: I have been studying how atoms bumping into each other become entangled, to understand how this affects the accuracy of atomic clocks.

    But what is entanglement? Is there some way to understand this “spooky” phenomenon? I will try to explain it by bringing together two notions from physics: conservation laws and quantum superpositions.

    Conservation laws

    Conservation laws are some of the deepest and most pervasive concepts in all of physics. The law of conservation of energy states that the total amount of energy in an isolated system remains fixed (although it can be converted from electrical energy to mechanical energy to heat, and so on). This law underlies the workings of all of our machines, whether they are steam engines or electric cars. Conservation laws are a kind of accounting statement: You can exchange bits of energy around, but the total amount has to stay the same.

    Conservation of momentum (momentum being mass times velocity) is the reason why, when two ice skaters with different masses push off from each other, the lighter one moves away faster than the heavier. This law also underlies the famous dictum that “every action has an equal and opposite reaction.” Conservation of angular momentum is why – going back to ice skaters again – a whirling figure skater can spin faster by drawing her arms closer to her body.

    2
    France’s Gabriella Papadakis and Guillaume Cizeron demonstrate the effects of conservation laws during the 2019 ISU European Figure Skating Championships in Belarus (photo by Shutterstock)

    These conservation laws have been experimentally verified to work across an extraordinary range of scales in the universe, from black holes in distant galaxies all the way down to the tiniest spinning electrons.

    Quantum addition

    Picture yourself on a nice hike through the woods. You come to a fork in the trail, but you find yourself struggling to decide whether to go left or right. The path to the left looks dark and gloomy but is reputed to lead to some nice views, while the one to the right looks sunny but steep. You finally decide to go right, wistfully wondering about the road not taken. In a quantum world, you could have chosen both.

    For systems described by quantum mechanics (that is, things that are sufficiently well isolated from heat and external disturbances), the rules are more interesting. Like a spinning top, an electron for example can be in a state where it spins clockwise, or in another state where it spins anticlockwise. Unlike a spinning top though, it can also be in a state that is [clockwise spinning] + [anticlockwise spinning].

    The states of quantum systems can be added together and subtracted from each other. Mathematically, the rules for combining quantum states can be described in the same way as the rules for adding and subtracting vectors. The word for such a combination of quantum states is a superposition. This is really what is behind strange quantum effects that you may have heard about, such as the double-slit experiment, or particle-wave duality.


    PBS Studios: The Double-Slit Experiment. 13 minutes

    Say you decide to force an electron in the [clockwise spinning] + [anticlockwise spinning] superposition state to yield a definite answer. Then the electron randomly ends up either in the [clockwise spinning] state or in the [anticlockwise spinning] state. The odds of one outcome versus the other are easy to calculate (with a good physics book at hand). The intrinsic randomness of this process may bother you if your worldview requires the universe to behave in a completely predictable way, but … c’est la (experimentally tested) vie.

    Conservation laws and quantum mechanics

    Let’s put these two ideas together now, and apply the law of conservation of energy to a pair of quantum particles.

    Imagine a pair of quantum particles (say atoms) that start off with a total of 100 units of energy. You and your friend separate the pair, taking one each. You find that yours has 40 units of energy. Using the law of conservation of energy, you deduce that the one your friend has must have 60 units of energy. As soon as you know the energy of your atom, you immediately also know the energy of your friend’s atom. You would know this even if your friend never revealed any information to you. And you would know this even if your friend was off on the other side of the galaxy at the time you measured the energy of your atom. Nothing spooky about it (once you realize this is just correlation, not causation).

    But the quantum states of a pair of atoms can be more interesting. The energy of the pair can be partitioned in many possible ways (consistent with energy conservation, of course). The combined state of the pair of atoms can be in a superposition, for example: [your atom: 60 units; friend’s atom: 40 units] + [your atom: 70 units; friend’s atom: 30 units].

    This is an entangled state of the two atoms. Neither your atom, nor your friend’s, has a definite energy in this superposition. Nevertheless, the properties of the two atoms are correlated because of conservation of energy: Their energies always add up to 100 units.

    For example, if you measure your atom and find it in a state with 70 units of energy, you can be certain that your friend’s atom has 30 units of energy. You would know this even if your friend never revealed any information to you. And thanks to energy conservation, you would know this even if your friend was off on the other side of the galaxy.

    Nothing spooky about it.The Conversation

    See the full article here .


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    Stem Education Coalition

    Founded in 1827, the University of Toronto has evolved into Canada’s leading institution of learning, discovery and knowledge creation. We are proud to be one of the world’s top research-intensive universities, driven to invent and innovate.

    Our students have the opportunity to learn from and work with preeminent thought leaders through our multidisciplinary network of teaching and research faculty, alumni and partners.

    The ideas, innovations and actions of more than 560,000 graduates continue to have a positive impact on the world.

     
  • richardmitnick 3:39 pm on April 11, 2019 Permalink | Reply
    Tags: “Our quantum memories operate at room temperature., , BNL Scientific Data and Computing Center, DOE ESnet, Northeast Quantum Systems Center, Putting U.S. quantum networking research on the international map, Quantum entanglement, quantum entanglement is limited by decoherence, , The entanglement sources are portable and can be easily mounted in standard data center computer server racks that are connected to regular fiber distribution panels., This makes it natural to expand the test to principles of quantum repeaters which are the technological key to achieving quantum communication over hundreds of kilometers.”, Unlike digital transmissions in communication networks, Viable quantum repeaters will allow Figueroa and his team to scale up their ongoing experiments within “local-area” quantum networks to a distributed or “wide-area” version   

    From Stoney Brook University – SUNY and BNL: “Research Team Builds Quantum Network with Long-Distance Entanglement” 

    Brookhaven National Lab

    Stoney Brook bloc

    From Stoney Brook University – SUNY

    April 8, 2019
    Charity Plata
    cplata@bnl.gov

    Scientists from Stony Brook University, the U.S. Department of Energy’s Brookhaven National Laboratory, and DOE’s Energy Sciences Network (ESnet) are collaborating on an experiment that puts U.S. quantum networking research on the international map.

    Researchers, including Stony Brook’s Eden Figueroa, have built a quantum network testbed that connects several buildings on the Brookhaven Lab campus using unique portable quantum entanglement sources and an existing DOE ESnet communications fiber network—a significant step in building a large-scale quantum network that can transmit information over long distances.

    1
    Stony Brook’s Eden Figueroa describes the inner workings of the quantum network hardware at Brookhaven National Laboratory as Robinson Pino, acting director of Computational Science Research and Partnerships (SciDAC) Division overseen by DOE’s Advanced Scientific Computing Research program office, looks on.

    “In quantum mechanics, the physical properties of entangled particles remain associated, even when separated by vast distances. Thus, when measurements are performed on one side, it also affects the other,” said Kerstin Kleese van Dam, director of Brookhaven Lab’s Computational Science Initiative (CSI). “To date, this work has been successfully demonstrated with entangled photons separated by approximately 11 miles. This is one of the largest quantum entanglement distribution networks in the world, and the longest-distance entanglement experiment in the United States.”

    This quantum networking testbed project includes staff from CSI and Brookhaven’s Instrumentation Division and Physics Department, as well as faculty and students from Stony Brook University. The project also is part of the Northeast Quantum Systems Center. One distinct aspect of the team’s work that sets it apart from other quantum networks being run in China and Europe—both long-committed to quantum information science pursuits—is that the entanglement sources are portable and can be easily mounted in standard data center computer server racks that are connected to regular fiber distribution panels.

    The team successfully installed a portable quantum-entangled photon source in a server rack housed within the BNL Scientific Data and Computing Center, where the Lab’s central networking hub is located. With this connectivity, entangled photons now can be distributed to every building on the Lab’s campus using existing Brookhaven and ESnet fiber infrastructure. ESnet’s fibers have been introduced in paths between buildings to enable the distribution and study of entanglement over increasingly longer distances. The portable entanglement sources also are compatible with existing quantum memories, atom-filled glass cells that can store quantum information. Normally kept at super-cold temperatures, these cells can be stimulated using lasers to control the atomic states within them.

    In work sponsored by DOE’s Small Business Innovation Research program (SBIR), the Brookhaven-Stony Brook-ESnet testbed features portable quantum memories that can operate at room temperature. Such quantum memories, engineered for quantum networking on a large scale, have been a longtime “pet project” for Eden Figueroa, a joint appointee with Brookhaven’s CSI and Instrumentation Division and a Stony Brook University professor who leads its Quantum Information Technology group. He serves as lead investigator of the quantum networking testbed project.

    “The demonstration aims to combine entanglement with compatible atomic quantum memories,” Figueroa said. “Our quantum memories have the advantage of operating at room temperature rather than requiring subfreezing cold. This makes it natural to expand the test to principles of quantum repeaters, which are the technological key to achieving quantum communication over hundreds of kilometers.”

    Quantum networks send light pulses (photons) through the fiber, which requires the light to be periodically amplified as it travels through the lines. However, unlike digital transmissions in communication networks, quantum entanglement is limited by decoherence, where entangled photons, for example, revert to classical states because interactions with the environment cause them to lose the ability to remain entangled. This limits these fragile quantum states from being sent over large distances.

    Viable quantum repeaters will allow Figueroa and his team to scale up their ongoing experiments within “local-area” quantum networks to a distributed, or “wide-area,” version. In anticipation of this, the team is constructing the necessary optical connections to link Brookhaven Lab’s quantum network to ones that already exist at Stony Brook and Yale universities.

    “Realizing the quantum network with entangled photon sources mounted in server racks, portable quantum memories, and operable repeaters will mark the first real quantum communication network in the world that truly connects quantum computing processors and memories using photonic quantum entanglement,” Figueroa said. “It will mark a sea change in communications that can impact the world.”

    Funding for this quantum networking testbed project has been provided by SBIR, the Empire State Development Corporation, and Brookhaven Lab’s Laboratory Directed Research and Development program.

    See the full article here .

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    Stoney Brook campus

    Stony Brook University-SUNY’s reach extends from its 1,039-acre campus on Long Island’s North Shore–encompassing the main academic areas, an 8,300-seat stadium and sports complex and Stony Brook Medicine–to Stony Brook Manhattan, a Research and Development Park, four business incubators including one at Calverton, New York, and the Stony Brook Southampton campus on Long Island’s East End. Stony Brook also co-manages Brookhaven National Laboratory, joining Princeton, the University of Chicago, Stanford, and the University of California on the list of major institutions involved in a research collaboration with a national lab.

    And Stony Brook is still growing. To the students, the scholars, the health professionals, the entrepreneurs and all the valued members who make up the vibrant Stony Brook community, this is a not only a great local and national university, but one that is making an impact on a global scale.

     
  • richardmitnick 9:02 am on March 15, 2019 Permalink | Reply
    Tags: "Can entangled qubits be used to probe black holes?", JQI at UMD, , Quantum entanglement, ,   

    From UC Berkeley: “Can entangled qubits be used to probe black holes?” 

    From UC Berkeley

    March 6, 2019
    Robert Sanders
    rlsanders@berkeley.edu

    1
    Someday, entangled quantum bits, or qubits, may allow us to explore the mysterious interior of a black hole, as represented in this artistic rendering. (Graphic by E. Edwards/Joint Quantum Institute)

    Physicists have used a seven-qubit quantum computer to simulate the scrambling of information inside a black hole, heralding a future in which entangled quantum bits might be used to probe the mysterious interiors of these bizarre objects.

    Scrambling is what happens when matter disappears inside a black hole. The information attached to that matter — the identities of all its constituents, down to the energy and momentum of its most elementary particles — is chaotically mixed with all the other matter and information inside, seemingly making it impossible to retrieve.

    This leads to a so-called “black hole information paradox,” since quantum mechanics says that information is never lost, even when that information disappears inside a black hole.

    So, while some physicists claim that information falling through the event horizon of a black hole is lost forever, others argue that this information can be reconstructed, but only after waiting an inordinate amount of time — until the black hole has shrunk to nearly half its original size. Black holes shrink because they emit Hawking radiation, which is caused by quantum mechanical fluctuations at the very edge of the black hole and is named after the late physicist Stephen Hawking.

    Unfortunately, a black hole the mass of our sun would take about 10^67 years to evaporate — far, far longer than the age of the universe.

    2
    Can you extract information from a black hole? As part of a thought experiment, Alice, a physicist, drops a qubit into a black hole and asks whether Bob can reconstruct the qubit using only the outgoing Hawking radiation. (Graphic by Emily Elisa Edwards, University of Maryland)

    However, there is a loophole — or rather, a wormhole — out of this black hole. It may be possible to retrieve this infalling information significantly faster by measuring subtle entanglements between the black hole and the Hawking radiation it emits.

    Two bits of information — like the quantum bits, or qubits, in a quantum computer — are entangled when they are so closely linked that the quantum state of one automatically determines the state of the other, no matter how far apart they are. Physicists sometimes refer to this as “spooky action at a distance,” and measurements of entangled qubits can lead to the “teleportation” of quantum information from one qubit to another.

    “One can recover the information dropped into the black hole by doing a massive quantum calculation on these outgoing Hawking photons,” said Norman Yao, a UC Berkeley assistant professor of physics and a faculty scientist at Lawrence Berkeley National Laboratory. “This is expected to be really, really hard, but if quantum mechanics is to be believed, it should, in principle, be possible. That’s exactly what we are doing here, but for a tiny three-qubit `black hole’ inside a seven-qubit quantum computer.”

    By dropping an entangled qubit into a black hole and querying the emerging Hawking radiation, you could theoretically determine the state of a qubit inside the black hole, providing a window into the abyss.

    Yao, who is a member of Berkeley Lab’s Quantum Algorithms Team, and his colleagues at the University of Maryland and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, will report their results in a paper appearing in the March 7 issue of the journal Nature.

    Teleportation

    Yao, who is interested in understanding the nature of quantum chaos, learned from friend and colleague Beni Yoshida, a theorist at the Perimeter Institute, that recovering quantum information falling into a black hole is possible if the information is scrambled rapidly inside the black hole. The more thoroughly it is mixed throughout the black hole, the more reliably the information can be retrieved via teleportation. Based on this insight, Yoshida and Yao proposed last year an experiment to provably demonstrate scrambling on a quantum computer.

    3
    A seven-qubit quantum computer circuit built by University of Maryland physicists uses quantum teleportation to detect information scrambling. This is analogous to information propagation through a traversable wormhole, which would allow Bob to identify the qubit that Alice threw into the black hole. (Graphic by Emily Elisa Edwards, University of Maryland)

    “With our protocol, if you measure a teleportation fidelity that is high enough, then you can guarantee that scrambling happened within the quantum circuit,” Yao said. “So, then we called up my buddy, Chris Monroe.”

    Monroe, a physicist at the University of Maryland in College Park who heads one of the world’s leading trapped-ion quantum information groups, decided to give it a try. His group implemented the protocol proposed by Yoshida and Yao and effectively measured an out-of-time-ordered correlation function.

    Called OTOCs, these peculiar correlation functions are created by comparing two quantum states that differ in the timing of when certain kicks or perturbations are applied. The key is being able to evolve a quantum state both forward and backward in time to understand the effect of that second kick on the first kick.

    Monroe’s group created a scrambling quantum circuit on three qubits within a seven-qubit trapped-ion quantum computer and characterized the resulting decay of the OTOC. While the decay of the OTOC is typically taken as a strong indication that scrambling has occurred, to prove that they had to show that the OTOC didn’t simply decay because of decoherence — that is, that it wasn’t just poorly shielded from the noise of the outside world, which also causes quantum states to fall apart.

    Yao and Yoshida proved that the greater the accuracy with which they could retrieve the entangled or teleported information, the more stringently they could put a lower limit on the amount of scrambling that had occurred in the OTOC. This is because, if information is successfully teleported from one atom to another, it means that the state of the first atom is spread out across all of the atoms — something that only happens if the information is scrambled. If the information was lost, successful teleportation would not be possible. For an arbitrary process whose scrambling properties might not be known, this method could be used to test whether — or even how much — it scrambles.

    Monroe and his colleagues measured a teleportation fidelity of approximately 80 percent, meaning that perhaps half of the quantum state was scrambled and the other half decayed by decoherence. Nevertheless, this was enough to demonstrate that genuine scrambling had indeed occurred in this three-qubit quantum circuit.

    “One possible application for our protocol is related to the benchmarking of quantum computers, where one might be able to use this technique to diagnose more complicated forms of noise and decoherence in quantum processors,” Yao said. “The ability to diagnose how noise affects quantum simulations is key to building better fault-tolerant algorithms and getting accurate answers from current noisy quantum computers.”

    Yao is also working with a UC Berkeley group led by Irfan Siddiqi to demonstrate scrambling in a different quantum system, superconducting qutrits: quantum bits that have three, rather than two, states. Siddiqi is a UC Berkeley professor of physics and a faculty scientist at Berkeley Lab, where he is leading the effort to build an advanced quantum computing test bed.

    “At its core, this is a qubit or qutrit experiment, but the fact that we can relate it to cosmology is because we believe the dynamics of quantum information is the same,” he said. “The U.S. is launching a billion-dollar quantum initiative, and understanding the dynamics of quantum information connects many areas of research within this initiative: quantum circuits and computing, high energy physics, black hole dynamics, condensed matter physics and atomic, molecular and optical physics. The language of quantum information has become pervasive for our understanding of all these different systems.”

    “Regardless of whether real black holes are very good scramblers, studying quantum scrambling in the lab could provide useful insights for the future development of quantum computing or quantum simulation,” Monroe said.

    Aside from Yao, Yoshida and Monroe, other co-authors are graduate student Tommy Schuster of UC Berkeley and graduate student and first author Kevin Landsman, Caroline Figgatt and Norbert Linke of Maryland’s Joint Quantum Institute. The work was supported by the Department of Energy’s Office of Advanced Scientific Computing Research and Office of High Energy Physics and National Science Foundation.

    RELATED INFORMATION

    Ion experiment aces quantum scrambling test (JQI)
    Verified Quantum Information Scrambling (Nature) [above]
    Disentangling Scrambling and Decoherence via Quantum Teleportation (Physical Review X)
    Norman Yao’s website

    See the full article here .

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  • richardmitnick 4:19 pm on March 6, 2019 Permalink | Reply
    Tags: An atom-defect hybrid quantum system, , , Coherence in quantum behavior, If you can see things on smaller scales with better sensitivity than anybody else you’re going to find new physics, In the experiment we will have an atom on the diamond surface that couples to a shallow subsurface NV center inside the material in a highly controlled cryogenic and ultra-high vacuum environment, Key to this technology is the nitrogen-vacancy (NV) center in diamond an extensively studied point defect in diamond’s carbon atom lattice, , Quantum entanglement, , , The physical and materials knowledge gained by mastering the interface of such a hybrid system would contribute to the development of quantum computing systems, The technique is reminiscent of molecular beam epitaxy (MBE) a method of “growing” a material atom-by-atom on a substrate, This project is a “natural fit” for UC Santa Barbara say the researchers due to the campus’s strengths in both physics and materials sciences, To Hold Without Touching,   

    From UC Santa Barbara: “Sensing Disturbances in the Force” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    March 5, 2019
    Sonia Fernandez

    UC Santa Barbara researchers receive U.S. Department of Energy grant to build atom-defect hybrid quantum sensor.

    1

    It will be a feat of engineering and physics at the smallest scales, but it could open the biggest doors — to new science and more advanced technologies. UC Santa Barbara physicists Ania Jayich and David Weld, and materials scientist Kunal Mukherjee, are teaming up to build an atom-defect hybrid quantum system — a sensor technology that would use the power of quantum science to unlock the mysteries of the atomic and subatomic world.

    “We’re at this tipping point where we know there’s a lot of impactful and fundamentally exciting things we can do,” said Jayich, whose research investigates quantum effects at the nanoscale. The $1.5 million grant from the Department of Energy’s Office of Basic Sciences will kickstart the development of a system that will allow researchers an unusually high level of control over atoms while simultaneously leaving their “quantumness” untouched.

    “In this whole field of quantum technology, that has been the big challenge,” Jayich said. In the quirky and highly unintuitive world of quantum mechanics, she explained, objects can exist in a superposition of many places at once, and entangled elements separated by thousands of miles can be inextricably linked — phenomena which, in turn, have opened up new and powerful possibilities for areas such as sensing, computing and the deepest investigations of nature.

    However, the coherence that is the signature of these quantum behaviors — a state of information that is the foundation of quantum technology — is exceedingly fragile and fleeting.

    “Quantum coherence is such a delicate phenomenon,” Jayich said. “Any uncontrolled interaction with the environment will kill it. And that’s the whole challenge behind advancing this field — how do we preserve the very delicate quantumness of an atom or defect, or anything?” To study a quantum element such as an atom, one would have to interrogate it, she explained, but the act of measuring can also destroy its quantum nature.

    To Hold Without Touching

    Fortunately, Jayich and colleagues see a way around this conundrum.

    “It’s a hybrid atomic- and solid-state system,” Jayich said. Key to this technology is the nitrogen-vacancy (NV) center in diamond, an extensively studied point defect in diamond’s carbon atom lattice. The NV center is comprised of a vacancy created by a missing carbon atom next to another vacancy that is substituted with a nitrogen atom. With its several unpaired electrons, it is highly sensitive to and interactive with external perturbations, such as the minute magnetic or electric fields that would occur in the presence of individual atoms of interest.

    “In the proposed experiment, we would have an atom on the diamond surface that couples to a shallow, subsurface NV center inside the material, in a highly controlled, cryogenic and ultra-high vacuum environment,” Jayich explained. The diamond surface provides a natural trapping that allows researchers to more easily hold the atom in place — a challenge for many quantum scientists who want to trap individual atoms. Further, upon reading the state of the defect, one could understand the quantum properties of the atom under interrogation — without touching the atom itself and destroying its coherence.

    Previous methods aimed at interrogating individual adatoms (adsorbed atoms) relied on passing current through the atoms and necessitated metal surfaces, both of which, according to Jayich, reduce quantum coherence times.

    “The past several decades of work in atomic physics have resulted in tools that allow exquisite quantum control of all degrees of freedom of atomic ensembles, but typically only when the atoms are gently held in a vacuum far away from all other matter,” added Weld. “This experiment seeks to extend this level of control into a much messier but also much more technologically relevant regime, by manipulating and sensing individual atoms that are chemically bonded to a solid surface.”

    With the hybrid system, Jayich said, it would be “very easy to talk to the NV center defect with light, and the atoms have the benefit of retaining quantum information for very long periods of time. So we have a system where we leverage the best of both worlds — the best of the atom and the best of the defect — and put them together in a way that’s functional.”

    A Foundation for Future Quantum Tech

    Looking forward, the state-of-the-art spatial resolution and sensitivity of this atom-defect hybrid quantum system could offer researchers the deepest look at the workings of individual atoms, or structures of molecules at nanometer- and Angstrom scales.

    “If you can see things on smaller scales with better sensitivity than anybody else, you’re going to find new physics,” Jayich said. The connections of microscopic structure to macroscopic behavior in materials synthesis could be elucidated. Quantum phenomena in condensed matter systems could be probed. Proteins that have evaded structural determination — such as membrane proteins — could be studied.

    This project is a “natural fit” for UC Santa Barbara, say the researchers, due to the campus’s strengths in both physics and materials sciences. The technique is reminiscent of molecular beam epitaxy (MBE), a method of “growing” a material atom-by-atom on a substrate.

    “There is a strong tradition of materials deposition at UCSB, ranging from metals, semiconductors to novel electronic materials,” Mukherjee said of the campus’s long record of materials growth and world-class MBE facilities. Among the first few atoms they intend to study are rare-earth types such as holmium or dysprosium “as they have unpaired electrons which are protected from environmental interactions by the atomic structure,” noted Mukherjee, adding that he is “particularly excited” about the challenge of removing the atoms from and resetting the diamond surface without breaking vacuum.

    Additionally, the physical and materials knowledge gained by mastering the interface of such a hybrid system would contribute to the development of quantum computing systems. According to Jayich, future practicable quantum computers would likely be a hybrid of several elements, similar to how conventional computers are a mix of magnetic, electronic and solid-state components.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    UC Santa Barbara Seal
    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

     
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