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  • richardmitnick 9:53 am on February 27, 2020 Permalink | Reply
    Tags: Quantum Mechanics, , "Penn Engineers Ensure Quantum Experiments Get Off to the Right Start", Quantum experiments that utilize a defect within diamond to store information have to contend with uncertainty- specifically the number of electrons trapped at that defect when the experiment begins., Penn Engineers have devised a system to reset the starting conditions and test them to see whether they are correct and automatically start the experiment if they are all in a matter of microseconds., Initialization is one of the key fundamental requirements for doing almost any kind of quantum-information processing., (NV)-nitrogen-vacancy center in the diamond., Quantum experiments that utilize a defect within diamond to store information have to contend with uncertainty.   

    From Penn Engineering: “Penn Engineers Ensure Quantum Experiments Get Off to the Right Start” 

    From University of Pennsylvania Engineering

    Feb 17, 2020

    Quantum experiments that utilize a defect within diamond to store information have to contend with uncertainty, specifically, the number of electrons trapped at that defect when the experiment begins. Penn Engineers have now developed an initialization procedure that addresses this problem. (Illustration: Ann Sizemore Blevins)

    Tzu-Yung Huang, Lee Bassett and David Hopper in the Quantum Engineering Laboratory. (Image: Penn Engineering)

    The quantum mechanical properties of electrons are beginning to open the door to a new class of sensors and computers with abilities far beyond what their counterparts based in classical physics can accomplish. Quantum states are notoriously difficult to read or write, however, and to make things worse, uncertainty about those states’ starting conditions can make experiments more laborious or even impossible.

    Now, Penn Engineers have devised a system to reset those starting conditions, test them to see whether they are correct, and automatically start the experiment if they are, all in a matter of microseconds.

    This new “initialization procedure” will save quantum researchers the time and effort of re-running experiments to statistically account for uncertain starting states, and enable new kinds of measurements that require exact starting conditions to be run at all.

    Lee Bassett, assistant professor in the Department of Electrical and Systems Engineering and director of the Quantum Engineering Laboratory, along with lab members David Hopper and Joseph Lauigan, led a recent study demonstrating this new initialization procedure. Lab member Tzu-Yung Huang also contributed to the study.

    It was published in the journal Physical Review Applied.

    “Initialization is one of the key, fundamental requirements for doing almost any kind of quantum-information processing,” Bassett says. “You need to be able to deterministically set your quantum state before you can do anything useful with it, but the dirty little secret is that, in almost all quantum architectures, that initialization is not perfect.”

    “Some of the time,” Hopper says, “we can accept that uncertainty, and by running an experimental protocol many thousands of times, come up with a measurement we’re ultimately confident in. But there are other experiments we’d like to do where this type of averaging over multiple runs won’t work.”

    The particular type of uncertainty the researchers investigated has to do with a commonly used quantum system known as a nitrogen-vacancy (NV) center in diamond. These NV centers are defects that naturally occur within diamond, where the regular lattice of carbon atoms is occasionally disrupted with a nitrogen atom and a vacant spot next to it. The electron clouds of neighboring atoms overlap at this empty space, creating a “trapped molecule” in the diamond that can be probed with a laser, allowing researchers to measure, or alter, the electrons’ quantum property known as “spin.”

    The electrons trapped at an NV center form a “qubit” — the basic unit of quantum information — that can be used to sense local fields, store quantum superposition states, and even perform quantum computations.

    “Electrons are excellent magnetic sensors,” Bassett says, “and they can even detect the tiny magnetic fields associated with carbon nuclei surrounding the defect. Those nuclei can serve as qubits themselves and be controlled using the central electron to build up the entangled quantum states that form the basis of quantum computers. They also couple to photons, which are used to transmit quantum information over long distances. So NV centers really merge the three main areas of quantum science: sensing, communication and computation.”

    As promising as NV centers are, researchers still must contend with an uncertain variable: the number of electrons that are trapped at the NV center when an experiment starts, as electrons can hop in and out of the defect when it is illuminated with a laser. An initialization procedure that guarantees a predictable number of electrons every time would reduce the amount of time it takes to successfully run an experiment, or enable experiments where uncertain starting conditions can’t be statistically corrected for after the fact.

    “The NV center is like a box with a coin inside,” Lauigan says. “If we want to do our experiment only when the coin is on heads, we have to shake the box, check the coin, and repeat until we find that it landed the right way up. That’s the initialization procedure.”

    To execute this initialization, the researchers used a pair of lasers, photon detectors and specialized hardware that could handle the precise timing necessary.

    “We shine a green laser at the NV center, which basically ‘flips the coin’ and mixes up the number of electrons that are trapped in the defect,” Hopper says. “Then we come in with a red laser, and depending on the number of electrons that are there, the defect will either emit a photon or remain dark.”

    “Once we detect the photon that tells us the right number of electrons are in the defect, specialized circuitry automatically starts the experiment,” Huang says. “This all happens in about 500 nanoseconds; there isn’t time to have the signal analyzed by a normal computer, so it all has to happen on these specialized chips called field programmable gate arrays.”

    The researchers leveraged the power of advanced classical electronics to better control a particular quantum sensing system. They showed that, thanks to ideal starting conditions, their device can detect a tiny oscillating magnetic field of only 1.3 nanoteslas in one second of measurements, which is a sensitivity record for room-temperature quantum sensors based on single NV centers.

    The researchers’ initialization procedure may also help hasten progress on new quantum architectures for computation and communication. Diamond is typically composed of two stable isotopes of carbon, carbon-12 and carbon-13. The former is the most common, but every few tenths of a nanometer, there is an atom of the latter. And because carbon-13 has an extra neutron, it exhibits nuclear spin and can be used as a qubit.

    An NV center can be a “handle” for controlling those nuclear-spin qubits in a quantum computer, but in this situation the ability to precisely initialize its state becomes crucial. The errors associated with poor initialization multiply, and it quickly becomes impossible to perform a complex calculation. The type of real-time measurement and control used by the team in this work is a major step towards implementing more sophisticated error-correcting protocols in these quantum devices.

    In the near term, the improved sensing ability will be useful in determining the locations of carbon-13 atoms in the diamond lattice.

    “Finding all of those special carbon atoms is a laborious process, since there are so many atoms and each measurement takes a very long time,” Hopper says. “When we started this project, our goal was to see what was making those measurements take so long and whether there was any way to shorten it.”

    The research was supported by the National Science Foundation under awards ECCS-1553511 and ECCS-1842655.

    See the full article here .


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  • richardmitnick 9:54 am on February 24, 2020 Permalink | Reply
    Tags: , Quantum Mechanics, , "Correcting the “jitters” in quantum devices", “Noise” — random fluctuations that can eradicate the data stored in such devices.   

    From MIT News: “Correcting the “jitters” in quantum devices” 

    MIT News

    From MIT News

    February 18, 2020
    David L. Chandler

    In a diamond crystal, three carbon atom nuclei (shown in blue) surround an empty spot called a nitrogen vacancy center, which behaves much like a single electron (shown in red). The carbon nuclei act as quantum bits, or qubits, and it turns out the primary source of noise that disturbs them comes from the jittery “electron” in the middle. By understanding the single source of that noise, it becomes easier to compensate for it, the researchers found. Image: David Layden.

    A new study suggests a path to more efficient error correction, which may help make quantum computers and sensors more practical.

    Labs around the world are racing to develop new computing and sensing devices that operate on the principles of quantum mechanics and could offer dramatic advantages over their classical counterparts. But these technologies still face several challenges, and one of the most significant is how to deal with “noise” — random fluctuations that can eradicate the data stored in such devices.

    A new approach developed by researchers at MIT could provide a significant step forward in quantum error correction. The method involves fine-tuning the system to address the kinds of noise that are the most likely, rather than casting a broad net to try to catch all possible sources of disturbance.

    The analysis is described in the journal Physical Review Letters, in a paper by MIT graduate student David Layden, postdoc Mo Chen, and professor of nuclear science and engineering Paola Cappellaro.

    “The main issues we now face in developing quantum technologies are that current systems are small and noisy,” says Layden. Noise, meaning unwanted disturbance of any kind, is especially vexing because many quantum systems are inherently highly sensitive, a feature underlying some of their potential applications.

    And there’s another issue, Layden says, which is that quantum systems are affected by any observation. So, while one can detect that a classical system is drifting and apply a correction to nudge it back, things are more complicated in the quantum world. “What’s really tricky about quantum systems is that when you look at them, you tend to collapse them,” he says.

    Classical error correction schemes are based on redundancy. For example, in a communication system subject to noise, instead of sending a single bit (1 or 0), one might send three copies of each (111 or 000). Then, if the three bits don’t match, that shows there was an error. The more copies of each bit get sent, the more effective the error correction can be.

    The same essential principle could be applied to adding redundancy in quantum bits, or “qubits.” But, Layden says, “If I want to have a high degree of protection, I need to devote a large part of my system to doing these sorts of checks. And this is a nonstarter right now because we have fairly small systems; we just don’t have the resources to do particularly useful quantum error correction in the usual way.” So instead, the researchers found a way to target the error correction very narrowly at the specific kinds of noise that were most prevalent.

    The quantum system they’re working with consists of carbon nuclei near a particular kind of defect in a diamond crystal called a nitrogen vacancy center. These defects behave like single, isolated electrons, and their presence enables the control of the nearby carbon nuclei.

    But the team found that the overwhelming majority of the noise affecting these nuclei came from one single source: random fluctuations in the nearby defects themselves. This noise source can be accurately modeled, and suppressing its effects could have a major impact, as other sources of noise are relatively insignificant.

    “We actually understand quite well the main source of noise in these systems,” Layden says. “So we don’t have to cast a wide net to catch every hypothetical type of noise.”

    The team came up with a different error correction strategy, tailored to counter this particular, dominant source of noise. As Layden describes it, the noise comes from “this one central defect, or this one central ‘electron,’ which has a tendency to hop around at random. It jitters.”

    That jitter, in turn, is felt by all those nearby nuclei, in a predictable way that can be corrected.

    “The upshot of our approach is that we’re able to get a fixed level of protection using far fewer resources than would otherwise be needed,” he says. “We can use a much smaller system with this targeted approach.”

    The work so far is theoretical, and the team is actively working on a lab demonstration of this principle in action. If it works as expected, this could make up an important component of future quantum-based technologies of various kinds, the researchers say, including quantum computers that could potentially solve previously unsolvable problems, or quantum communications systems that could be immune to snooping, or highly sensitive sensor systems.

    “This is a component that could be used in a number of ways,” Layden says. “It’s as though we’re developing a key part of an engine. We’re still a ways from building a full car, but we’ve made progress on a critical part.”

    “Quantum error correction is the next challenge for the field,” says Alexandre Blais, a professor of physics at the University of Sherbrooke, in Canada, who was not associated with this work. “The complexity of current quantum error correcting codes is, however, daunting as they require a very large number of qubits to robustly encode quantum information.”

    Blais adds, “We have now come to realize that exploiting our understanding of the devices in which quantum error correction is to be implemented can be very advantageous. This work makes an important contribution in this direction by showing that a common type of error can be corrected for in a much more efficient manner than expected. For quantum computers to become practical we need more ideas like this.​”

    The research was supported by the U.S. Army Research Office and the National Science Foundation.

    See the full article here .

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  • richardmitnick 4:40 pm on February 18, 2020 Permalink | Reply
    Tags: , , , , MIP-multiprover interactive proof, , , Quantum Mechanics,   

    From Science News: “How a quantum technique highlights math’s mysterious link to physics” 

    From Science News

    February 17, 2020
    Tom Siegfried

    Verifying proofs to very hard math problems is possible with infinite quantum entanglement.

    A technique that relies on quantum entanglement (illustrated) expands the realm of mathematical problems for which the solution could (in theory) be verified. inkoly/iStock/Getty Images Plus.

    It has long been a mystery why pure math can reveal so much about the nature of the physical world.

    Antimatter was discovered in Paul Dirac’s equations before being detected in cosmic rays. Quarks appeared in symbols sketched out on a napkin by Murray Gell-Mann several years before they were confirmed experimentally. Einstein’s equations for gravity suggested the universe was expanding a decade before Edwin Hubble provided the proof. Einstein’s math also predicted gravitational waves a full century before behemoth apparatuses detected those waves (which were produced by collisions of black holes — also first inferred from Einstein’s math).

    Nobel laureate physicist Eugene Wigner alluded to math’s mysterious power as the “unreasonable effectiveness of mathematics in the natural sciences.” Somehow, Wigner said, math devised to explain known phenomena contains clues to phenomena not yet experienced — the math gives more out than was put in. “The enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious and … there is no rational explanation for it,” Wigner wrote in 1960.

    But maybe there’s a new clue to what that explanation might be. Perhaps math’s peculiar power to describe the physical world has something to do with the fact that the physical world also has something to say about mathematics.

    At least that’s a conceivable implication of a new paper that has startled the interrelated worlds of math, computer science and quantum physics.

    In an enormously complicated 165-page paper, computer scientist Zhengfeng Ji and colleagues present a result that penetrates to the heart of deep questions about math, computing and their connection to reality. It’s about a procedure for verifying the solutions to very complex mathematical propositions, even some that are believed to be impossible to solve. In essence, the new finding boils down to demonstrating a vast gulf between infinite and almost infinite, with huge implications for certain high-profile math problems. Seeing into that gulf, it turns out, requires the mysterious power of quantum physics.

    Everybody involved has long known that some math problems are too hard to solve (at least without unlimited time), but a proposed solution could be rather easily verified. Suppose someone claims to have the answer to such a very hard problem. Their proof is much too long to check line by line. Can you verify the answer merely by asking that person (the “prover”) some questions? Sometimes, yes. But for very complicated proofs, probably not. If there are two provers, though, both in possession of the proof, asking each of them some questions might allow you to verify that the proof is correct (at least with very high probability). There’s a catch, though — the provers must be kept separate, so they can’t communicate and therefore collude on how to answer your questions. (This approach is called MIP, for multiprover interactive proof.)

    Verifying a proof without actually seeing it is not that strange a concept. Many examples exist for how a prover can convince you that they know the answer to a problem without actually telling you the answer. A standard method for coding secret messages, for example, relies on using a very large number (perhaps hundreds of digits long) to encode the message. It can be decoded only by someone who knows the prime factors that, when multiplied together, produce the very large number. It’s impossible to figure out those prime numbers (within the lifetime of the universe) even with an army of supercomputers. So if someone can decode your message, they’ve proved to you that they know the primes, without needing to tell you what they are.

    Someday, though, calculating those primes might be feasible, with a future-generation quantum computer. Today’s quantum computers are relatively rudimentary, but in principle, an advanced model could crack codes by calculating the prime factors for enormously big numbers.

    That power stems, at least in part, from the weird phenomenon known as quantum entanglement. And it turns out that, similarly, quantum entanglement boosts the power of MIP provers. By sharing an infinite amount of quantum entanglement, MIP provers can verify vastly more complicated proofs than nonquantum MIP provers.

    It is obligatory to say that entanglement is what Einstein called “spooky action at a distance.” But it’s not action at a distance, and it just seems spooky. Quantum particles (say photons, particles of light) from a common origin (say, both spit out by a single atom) share a quantum connection that links the results of certain measurements made on the particles even if they are far apart. It may be mysterious, but it’s not magic. It’s physics.

    Say two provers share a supply of entangled photon pairs. They can convince a verifier that they have a valid proof for some problems. But for a large category of extremely complicated problems, this method works only if the supply of such entangled particles is infinite. A large amount of entanglement is not enough. It has to be literally unlimited. A huge but finite amount of entanglement can’t even approximate the power of an infinite amount of entanglement.

    As Emily Conover explains in her report for Science News, this discovery proves false a couple of widely believed mathematical conjectures. One, known as Tsirelson’s problem, specifically suggested that a sufficient amount of entanglement could approximate what you could do with an infinite amount. Tsirelson’s problem was mathematically equivalent to another open problem, known as Connes’ embedding conjecture, which has to do with the algebra of operators, the kinds of mathematical expressions that are used in quantum mechanics to represent quantities that can be observed.

    Refuting the Connes conjecture, and showing that MIP plus entanglement could be used to verify immensely complicated proofs, stunned many in the mathematical community. (One expert, upon hearing the news, compared his feces to bricks.) But the new work isn’t likely to make any immediate impact in the everyday world. For one thing, all-knowing provers do not exist, and if they did they would probably have to be future super-AI quantum computers with unlimited computing capability (not to mention an unfathomable supply of energy). Nobody knows how to do that in even Star Trek’s century.

    Still, pursuit of this discovery quite possibly will turn up deeper implications for math, computer science and quantum physics.

    It probably won’t shed any light on controversies over the best way to interpret quantum mechanics, as computer science theorist Scott Aaronson notes in his blog about the new finding. But perhaps it could provide some sort of clues regarding the nature of infinity. That might be good for something, perhaps illuminating whether infinity plays a meaningful role in reality or is a mere mathematical idealization.

    On another level, the new work raises an interesting point about the relationship between math and the physical world. The existence of quantum entanglement, a (surprising) physical phenomenon, somehow allows mathematicians to solve problems that seem to be strictly mathematical. Wondering why physics helps out math might be just as entertaining as contemplating math’s unreasonable effectiveness in helping out physics. Maybe even one will someday explain the other.

    See the full article here .


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  • richardmitnick 3:10 pm on February 17, 2020 Permalink | Reply
    Tags: , , , , , , , Quantum Mechanics, Shedding new light on the internal structure of atomic nuclei.   

    From KTH Royal Institute of Technology via phys.org: “Exotic atomic nuclei reveal traces of new form of superfluidity” 


    From KTH Royal Institute of Technology



    Published Feb 17, 2020
    David Callahan

    The team behind the discovery of the new form of superfluidity: from left, Bo Cederwall, professor of physics at KTH Royal Institute of Technology, Xiaoyu Liu, Wei Zhang, Aysegül Ertoprak, Farnaz Ghazi Moradi and Özge Aktas.Published Feb 17, 2020

    Recent observations of the internal structure of the rare isotope ruthenium-88 shed new light on the internal structure of atomic nuclei, a breakthrough which could also lead to further insights into how some chemical elements in nature and their isotopes are formed.

    Led by Bo Cederwall, Professor of Experimental Nuclear Physics at KTH Royal Institute of Technology, an international research team identified new rotational states in the extremely neutron-deficient, deformed, atomic nucleus 88Ru. The results suggest that the structure of this exotic nuclear system is heavily influenced by the presence of strongly-coupled neutron-proton pairs.

    “Such a structure is fundamentally different from the normal conditions observed in atomic nuclei, where neutrons and protons interact in pairs in separate systems, forming a near-superfluid state,” Cederwall says.

    The results may also suggest alternative explanations for how the production of different chemical elements, and in particular their most neutron-poor isotopes, proceeds in the nucleosynthesis reactions in certain stellar environments such as neutron star-red giant binaries, he says.

    The discovery, which was published February 12 in the journal, Physical Review Letters, results from an experiment at the Grand Accélérateur National d’Ions Lourds (GANIL), France, using the Advanced Gamma Tracking Array (AGATA) [below].

    The researchers used nuclear collisions to create highly unstable atomic nuclei with equal numbers of neutrons and protons. Their structure was studied by using sensitive instruments, including AGATA, detecting the radiation they emit in the form of high-energy photons, neutrons, protons and other particles.

    The Advanced Gamma Tracking Array (AGATA), which researchers from KTH used to study unstable atomic nuclei generated at the Grand Accélérateur National d’Ions Lourds.

    According to the Standard Model of particle physics describing the elementary particles and their interactions, there are two general types of particles in nature; bosons and fermions, which have integer and half-integer spins, respectively. Examples of fermions are fundamental particles like the electron and the electron neutrino but also composite particles like the proton and the neutron and their fundamental building blocks, the quarks. Examples of bosons are the fundamental force carriers; the photon, the intermediate vector bosons, the gluons and the graviton.

    The properties of a system of particles differ considerably depending on whether it is based on fermions or bosons. As a result of the Pauli principle of quantum mechanics, in a system of fermions (such as an atomic nucleus) only one particle can hold a certain quantum state at a certain point in space and time. For several fermions to appear together, at least one property of each fermion, such as its spin, must be different. At low temperature systems of many fermions can exhibit condensates of paired particles manifested as superfluidity for uncharged particles (for example, the superfluid 3He), and superconductivity for charged particles, such as electrons in a superconductor below the critical temperature. Bosons, on the other hand, can condense individually with an unlimited number of particles in the same state, so-called Bose-Einstein condensates.

    In most atomic nuclei that are close to the line of beta stability and in their ground state, or excited to an energy not too high above it, the basic structure appears to be based on pair-correlated condensates of particles with the same isospin quantum number but with opposite spins. This means that neutrons and protons are paired separately from each other. These isovector pair correlations give rise to properties similar to superfluidity and superconductivity. In deformed nuclei, this structure is for example revealed as discontinuities in the rotational frequency when the rotational excitation energy of the nucleus is increased.

    Such discontinuities, which were discovered already in the early 1970s by KTH Professor emeritus Arne Johnson, have been labeled “backbending”. The backbending frequency is a measure of the energy required to break a neutron or proton pair and therefore also reflects the energy released by the formation of a pair of nucleons in the nucleus. There are long-standing theoretical predictions that systems of neutron-proton pairs can be mixed with, or even replace, the standard isovector pair correlations in exotic atomic nuclei with equal numbers of protons and neutrons. The nuclear structure resulting from the isoscalar component of such pair correlations is different from that found in “ordinary” atomic nuclei close to stability. Among different possible experimental observables, the backbending frequency in deformed nuclei is predicted to increase significantly compared with nuclei with different numbers of neutrons and protons.

    The KTH research group has previously observed evidence of strong neutron-proton correlations in the spherical nuclear nucleus 92Pd, which was published in the journal Nature (B. Cederwall et al., Nature, volume 469, p 68-71 (2011)). The ruthenium isotope 88Ru, with 44 neutrons and 44 protons, is deformed and exhibits a rotation-like structure that has now been observed up to higher spin, or rotational frequency, than previously possible. The new measurement provides a different angle on nuclear pair correlations compared with the previous work. By confirming the theoretical predictions of a shift towards higher backbending frequency it provides complementary evidence for the occurrence of strong isoscalar pair correlations in the heaviest nuclear systems with equal numbers of neutrons and protons.

    See the full article here .


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  • richardmitnick 2:24 pm on February 3, 2020 Permalink | Reply
    Tags: , “We have found a new way to switch the electrical conduction in materials from on to off” said lead author Berend Zwartsenberg, New quantum switch turns metals into insulators, , Quantum Mechanics,   

    From University of British Columbia: “New quantum switch turns metals into insulators” 

    U British Columbia bloc

    From University of British Columbia

    Feb 3, 2020
    Sachi Wickramasinghe
    UBC Media Relations
    Tel: 604-822-4636
    Cel: 604-754-8289

    Artist’s impression of the dissolving of the electronic “traffic jam.” The red atoms are different in their quantum nature and allow transport of electrons in their surroundings. Credit: SBQMI

    Most modern electronic devices rely on tiny, finely-tuned electrical currents to process and store information. These currents dictate how fast our computers run, how regularly our pacemakers tick and how securely our money is stored in the bank.

    In a study published in Nature Physics, researchers at the University of British Columbia have demonstrated an entirely new way to precisely control such electrical currents by leveraging the interaction between an electron’s spin (which is the quantum magnetic field it inherently carries) and its orbital rotation around the nucleus.

    “We have found a new way to switch the electrical conduction in materials from on to off,” said lead author Berend Zwartsenberg, a Ph.D. student at UBC’s Stewart Blusson Quantum Matter Institute (SBQMI). “Not only does this exciting result extend our understanding of how electrical conduction works, it will help us further explore known properties such as conductivity, magnetism and superconductivity, and discover new ones that could be important for quantum computing, data storage and energy applications.”

    Flipping the switch on metal-insulator transitions

    Broadly, all materials can be categorized as metals or insulators, depending on the ability of electrons to move through the material and conduct electricity.

    However, not all insulators are created equally. In simple materials, the difference between metallic and insulating behavior stems from the number of electrons present: an odd number for metals, and an even number for insulators. In more complex materials, like so-called Mott insulators, the electrons interact with each other in different ways, with a delicate balance determining their electrical conduction.

    In a Mott insulator, electrostatic repulsion prevents the electrons from getting too close to one another, which creates a traffic jam and limits the free flow of electrons. Until now, there were two known ways to free up the traffic jam: by reducing the strength of the repulsive interaction between electrons, or by changing the number of electrons.

    The SBQMI team explored a third possibility: was there a way to alter the very quantum nature of the material to enable a metal-insulator transition to occur?

    Using a technique called angle-resolved photoemission spectroscopy, the team examined the Mott insulator Sr2IrO4, monitoring the number of electrons, their electrostatic repulsion, and finally the interaction between the electron spin and its orbital rotation.

    “We found that coupling the spin to the orbital angular momentum slows the electrons down to such an extent that they become sensitive to one another’s presence, solidifying the traffic jam.” said Zwartsenberg. “Reducing spin-orbit coupling in turn eases the traffic jam and we were able to demonstrate a transition from an insulator to a metal for the first time using this strategy.”

    “This is a really exciting result at the fundamental physics level, and expands the potential of modern electronics,” said co-author Andrea Damascelli, principal investigator and scientific director of SBQMI. “If we can develop a microscopic understanding of these phases of quantum matter and their emergent electronic phenomena, we can exploit them by engineering quantum materials atom-by-atom for new electronic, magnetic and sensing applications.”

    See the full article here .


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  • richardmitnick 2:45 pm on January 30, 2020 Permalink | Reply
    Tags: "An ultrafast microscope for the quantum world", An attosecond is a billionth of a billionth of a second., , From Max Planck Institute for Solid State Research, , , Quantum Mechanics, Researchers need a high-speed camera that exposes each frame of an “electron video” for just a few hundred attoseconds., Scanning tunnelling microscope   

    From Max Planck Institute for Solid State Research: “An ultrafast microscope for the quantum world” 

    From Max Planck Institute for Solid State Research

    January 24, 2020

    Dr. Manish Garg
    Max Planck Institute for Solid State Research, Stuttgart
    +49 711 689-1639
    +49 711 689-1637

    Prof. Dr. Klaus Kern
    Max Planck Institute for Solid State Research, Stuttgart
    +49 711 689-1660

    Resolution taken to the extreme: Using a combination of ultrashort laser pulses (red) and a scanning tunnelling microscope, researchers at the Max Planck Institute for Solid State Research are filming processes in the quantum world. They focus the laser flashes on the tiny gap between the tip of the microscope and the sample surface, thus solving the tunneling process in which electrons (blue) overcome the gap between the tip and the sample. In this way, they achieve a temporal resolution of several hundred attoseconds when they image quantum processes such as an electronic wave packet (coloured wave) with atomic spatial resolution. © Dr. Christian Hackenberger

    The operation of components for future computers can now be filmed in HD quality, so to speak. Manish Garg and Klaus Kern, researchers at the Max Planck Institute for Solid State Research in Stuttgart, have developed a microscope for the extremely fast processes that take place on the quantum scale. This microscope – a sort of HD camera for the quantum world – allows the precise tracking of electron movements down to the individual atom. It should therefore provide useful insights when it comes to developing extremely fast and extremely small electronic components, for example.

    The processes taking place in the quantum world represent a challenge for even the most experienced of physicists. For example, the things taking place inside the increasingly powerful components of computers or smartphones not only happen extremely quickly but also within an ever-smaller space. When it comes to analysing these processes and optimising transistors, for example, videos of the electrons would be of great benefit to physicists. To achieve this, researchers need a high-speed camera that exposes each frame of this “electron video” for just a few hundred attoseconds. An attosecond is a billionth of a billionth of a second; in that time, light can only travel the length of a water molecule. For a number of years, physicists have used laser pulses of a sufficiently short length as an attosecond camera.

    In the past, however, an attosecond image delivered only a snapshot of an electron against what was essentially a blurred background. Now, thanks to the work of Klaus Kern, Director at the Max Planck Institute for Solid State Research, and Manish Garg, a scientist in Kern’s Department, researchers can now also identify precisely where the filmed electron is located down to the individual atom.

    Ultrashort laser pulses combined with a scanning tunnelling microscope.

    To do this, the two physicists use ultrashort laser pulses in conjunction with a scanning tunnelling microscope. The latter achieves atomic-scale resolution by scanning a surface with a tip that itself is ideally made up of just a single atom. Electrons tunnel between the tip and the surface – that is, they cross the intervening space even though they actually don’t have enough energy to do so. As the effectiveness of this tunnelling process depends strongly on the distance the electrons have to travel, it can be used to measure the space between the tip and a sample and therefore to depict even individual atoms and molecules on a surface. Until now, however, scanning tunnelling microscopes did not achieve sufficient temporal resolution to track electrons.

    “By combining a scanning tunnelling microscope with ultrafast pulses, it was easy to use the advantages of the two methods to compensate for their respective disadvantages,” says Manish Garg. The researchers fire these extremely short pulses of light at the microscope tip – which is positioned with atomic precision – to trigger the tunnelling process. As a result, this high-speed camera for the quantum world can now also achieve HD resolution.

    Paving the way for light-wave electronics, which is millions of times faster.

    With the new technique, physicists can now measure exactly where electrons are at a specific time down to the individual atom and to an accuracy of a few hundred attoseconds. For example, this can be used in molecules that have had an electron catapulted out of them by a high-energy pulse of light, leading the remaining negative charge carriers to rearrange themselves and possibly causing the molecule to enter into a chemical reaction with another molecule. “Filming electrons in molecules live, and on their natural spatial and temporal scale, is vital in order to understand chemical reactivity, for example, and the conversion of light energy within charged particles, such as electrons or ions,” says Klaus Kern, Director at the Max Planck Institute for Solid State Research.

    Moreover, the technique not only allows researchers to track the path of electrons through the processors and chips of the future, but can also lead to a dramatic acceleration of the charge carriers: “In today’s computers, electrons oscillate at a frequency of a billion hertz,” says Klaus Kern. “Using ultrashort light pulses, it may be possible to increase their frequency to a trillion hertz.” With this turbo booster for light waves, researchers could clear the way for light-wave electronics, which is millions of times faster than current computers. Therefore, the ultrafast microscope not only films processes in the quantum world, but also acts as the Director by interfering with these processes.

    Science paper:
    M. Garg et al, “Attosecond coherent manipulation of electrons in tunneling microscopy”

    See the full article here .

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    The Max Planck Institute for Solid State Research (German: Max-Planck-Institut für Festkörperforschung) was founded in 1969 and is one of the 82 Max Planck Institutes of the Max Planck Society. It is located on a campus in Stuttgart, together with the Max Planck Institute for Intelligent Systems.

    Research at the Max Planck Institute for Solid State Research is focused on the physics and chemistry of condensed matter, including especially complex materials and nanoscale science. In both of these fields, electronic and ionic transport phenomena are of particular interest.

    MPG campus

    The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

    According to its primary goal, the Max Planck Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014)[2] Max Planck Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

    The Max Planck Institutes focus on excellence in research. The Max Planck Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the Max Planck institutes fifth worldwide in terms of research published in Nature journals (after Harvard, MIT, Stanford and the US NIH). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by the Chinese Academy of Sciences, the Russian Academy of Sciences and Harvard University. The Thomson Reuters-Science Watch website placed the Max Planck Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.

  • richardmitnick 11:04 am on January 27, 2020 Permalink | Reply
    Tags: "Finding solutions amidst fractal uncertainty and quantum chaos", , Dyatlov is now studying how the behavior of quantum systems over long time periods corresponds to that of classical systems., Math professor Semyon Dyatlov explores the relationship between classical and quantum physics., , Quantum Mechanics, Semyon Dyatlov   

    From MIT News: “Finding solutions amidst fractal uncertainty and quantum chaos” 

    MIT News

    From MIT News

    January 25, 2020
    Jonathan Mingle

    Semyon Dyatlov. Image: M. Scott Brauer

    Math professor Semyon Dyatlov explores the relationship between classical and quantum physics.

    Semyon Dyatlov calls himself a “mathematical physicist.”

    He’s an associate editor of the journal Probability and Mathematical Physics. His PhD dissertation advanced understanding of wave decay in black hole spacetimes. And much of his research focuses on developing new ways to understand the correspondence between classical physics (which describes light as rays that travel in straight lines and bounce off surfaces) and quantum systems (wherein light has wave-particle duality).

    So it may come as a surprise that, as a student growing up in Siberia, he didn’t study physics in depth.

    “Much of my work is deeply related to physics, even though I didn’t receive that much physics education as a student,” he says. “It took when I started working as a mathematician to slowly start understanding things like general relativity and modern particle physics.”

    A math-loving family, and inspiring mentors

    His mathematical education, however, has been extensive — and started early.

    Dyatlov was raised in a family of mathematicians. One of his two brothers is an applied mathematician. Both of his parents have math degrees. He grew up a five-minute walk away from the campus of Novosibirsk State University (NSU), a major academic research center in Siberia, where his father still teaches.

    “From a young age I was exposed to all kinds of mathematics,” he says. “There were journals and books lying around our house. I was very lucky that I both liked mathematics and was born into a family where a lot of mathematics was going on.”

    He can even trace his interest in microlocal analysis — his field of specialty today as an associate professor of mathematics at MIT — to conversations with his older brother decades ago. These talks sparked a fascination with partial differential equations, which Dyatlov studied as an undergraduate at NSU, where both his brother and father received their PhDs.

    Dyatlov went on to pursue graduate studies at the University of California at Berkeley. There his trajectory was influenced by a course he took during his first year with Professor Maciej Zworski on the theory of scattering resonances, which he explains are “pure states for systems in which energy can scatter to infinity.”

    It would prove to be a fruitful encounter. Zworski became Dyatlov’s dissertation advisor; a decade later, they are still collaborating. In addition to the many papers that they have written together, they co-authored a new textbook published by the American Mathematical Society in September.

    Zworski, who received both his bachelor’s degree and PhD in math from MIT, gave Dyatlov a particular problem to tackle early in his graduate studies.

    “There was back then a bit of a mystery surrounding how to apply scattering theory methods to black holes,” he recalls. The problem, which related to this mystery, grew into his dissertation’s detailed exploration of exponential wave decay in the context of general relativity.

    Of luck, collaboration, and “trapped trajectories”

    In December 2013, Dyatlov began a postdoc at MIT; by 2015 he had been hired as an assistant professor of mathematics. He is now an associate professor and was awarded tenure in 2019.

    “I sometimes feel I just got lucky many times,” Dyatlov says of his professional journey, from growing up in a family of mathematicians to finding influential mentors and collaborators like Zworski.

    Dyatlov is now studying how the behavior of quantum systems over long time periods corresponds to that of classical systems. Some of his recent research focuses on spectral gaps for open quantum chaotic systems.

    To help beginning students conceptualize it, he offers the analogy of striking a bell: “How does the shape of a bell determine how long its sound is sustained?” (Sometimes he uses MIT math department mugs instead.)

    The shape of the bell determines how long the sound is sustained. The difference lies in both the pitch of the sound, and in how long it can be heard. “You can study both,” he says, “but a natural question to ask is, no matter how you hit the bell, how long does it take for the sound to die out?”

    Classical physics might characterize what’s happening with the bell (or mug) as a phenomenon similar to light bouncing off a mirror: The sound bounces once off the bell and then escapes to infinity.

    “Mathematically what you hope to see is some exponential decay of energy, of the solution to a corresponding wave equation,” he explains. What interests Dyatlov is the rate of this decay, and whether, in some situations, there may not be any exponential decay at all.

    His recent work delves into what happens with these trajectories under conditions of “quantum chaos.”

    “Say you have waves bouncing off, and everything else escapes but you have a system — say the inside of a bowl — where these classical trajectories never leave. The thing that I study is a situation where you have in your system a fractal set of trapped trajectories,” he says.

    These trapped trajectories form a fractal set that appears “out of nowhere,” he says. “The fact that fractal sets appear from this was known well before my work, but it was still a surprise to me when I looked at it. Here, a fractal set appears naturally in a problem where you didn’t put in a fractal set.”

    That work led to his development of what he terms the “fractal uncertainty principle.” The classical uncertainty principle says you can’t pinpoint both the position and momentum of a quantum particle. Dyatlov posited a form of this principle for this fractal set of trapped trajectories.

    “I figured out one might be able to solve this wave decay question — this question about partial differential equations, about classical-quantum correspondence, about wave dynamics, and chaotic dynamics — but the component you need is this new kind of fractal uncertainty principle,” he says.

    Translation and toolboxes

    Pursuing this question required him to branch out into different fields of math, which lay outside his own training. In that pursuit, he caught another “lucky break:” MIT professor of mathematics Larry Guth suggested he talked with Joshua Zahl, a postdoc who had been thinking independently about a related question, from his own field of additive combinatorics. Applying their respective techniques, they developed a proof for exponential decay in some specific fractal sets and wrote a paper together on the subject. A couple years later — in yet another “lucky” collaboration — Dyatlov worked with the late Jean Bourgain, a renowned mathematician at the Institute for Advanced Study, to prove the fractal uncertainty principle for the general case of these sets.

    “You have your toolbox, and you try to get as much out of it as you can for a problem,” he says, but sometimes you have to seek out new tools. “MIT is a great place for that.”

    That act of reaching across fields is fundamental to the practice of mathematics, he says. The book that he recently published with Zworski opens with a quote from Goethe: “Mathematicians are Frenchmen of sorts: Whatever one says to them they translate into their own language and then it becomes something entirely different.”

    Dyatlov sees a connection between this epigraph and his own forays into the correspondence between math and physics.

    “It’s an ironic take on that,” he says. “There’s a natural repelling force for math and physics to diverge into separate fields, because we do things so differently. Experimental physicists have to respect the reality of situation, and have to think about what you can model in a lab. As a mathematician, you focus on things you can prove. You have to distill and translate the physical phenomena into theorems.”

    “It’s up to people in communities to create an attracting force to work together and bridge this divide.”

    See the full article here .

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    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 3:42 pm on January 26, 2020 Permalink | Reply
    Tags: "A quantum strategy could verify the solutions to unsolvable problems — in theory", , , , Quantum Mechanics,   

    From Science News: “A quantum strategy could verify the solutions to unsolvable problems — in theory” 

    From Science News

    January 24, 2020
    Emily Conover

    A new study has resolved questions in physics, computer science and mathematics.

    Entanglement, a type of quantum linkage between distant objects, could allow for the verification of solutions to unsolvable problems, computer scientists report. Jurik Peter/Shutterstock

    Computer scientists’ daydreams have revealed the power of quantum mechanics.

    Imagine meeting omniscient beings who claim to have the solution to a complex problem that no computer could ever solve. You’d probably be at a loss to check the answer. But now, computer scientists report that quantum mechanics provides a way to quickly verify the solutions to an incredibly broad class of problems, including some that are impossible to solve in the first place.

    Although the result doesn’t have obvious practical applications, its theoretical ramifications have had a ripple effect, answering unsolved questions in physics and mathematics, scientists report in a paper posted January 13 at arXiv.org. “It has so many implications for all these areas. It’s a huge deal no matter how you look at it,” says theoretical computer scientist Scott Aaronson of the University of Texas at Austin, who was not involved with the new study.

    In computer science, some problems are difficult to solve but have solutions that are easy to check. So researchers classify questions according to how hard it is for computers to verify purported answers.

    On its own, a computer can go only so far in verifying solutions. But scientists have a few tricks up their sleeves. They concoct scenarios where a “prover” — a computer or person who claims to have a solution to a problem — is peppered with questions by the person who is attempting to check the solution, the “verifier.”

    Imagine, for example, that you have a friend who claims to have deduced how to tell the difference between Pepsi and Coke, even though you can’t distinguish between the two. To confirm this claim, you — the verifier — might prepare a cup of either Pepsi or Coke and query your friend — the prover — on which one it is. If your friend consistently gives the right answer to such questions, you’d be convinced that the cola-identification quandary had been solved.

    Known as an interactive proof, this strategy can reveal additional information that would allow computer scientists to verify solutions to problems that are too difficult for a computer to convince the scientists of independently. Still more powerful interactive proofs involve multiple provers. That scenario is a bit like a police interrogation of two suspects, isolated in separate rooms, who can’t coordinate their answers to trick an investigator.

    The class of problems that can be verified in this way is “big, but not ridiculously big,” says study coauthor Thomas Vidick, a theoretical computer scientist at Caltech. To check the solutions to an even larger variety of problems, scientists can imagine adding another twist: The provers share a quantum connection called entanglement, which causes two seemingly independent objects to behave in correlated ways (SN: 4/25/18).

    Until now, it was not known how many problems were verifiable with quantum entanglement. The new result reveals that it’s “an unbelievably huge number of problems,” says Aaronson.

    That huge group is called recursively enumerable, or RE, problems. “It contains all problems that are solvable by computers and then some,” says coauthor Henry Yuen, a computer scientist at the University of Toronto. “That’s a crazy thing.” It’s the “and then some” that is really mind-boggling. No computer would be able to solve those problems outright, but if two entangled omniscient beings had a solution, they could convince you it was correct. Of course, enacting the verification technique in the real world is made implausible by the lack of omniscient beings to offer up the answers.

    The result is summed up in the succinct equality, MIP* = RE, where MIP* stands for Multi-prover Interactive Proof with quantum entanglement. Every problem in RE is also in MIP*, and vice versa.

    Although not yet peer-reviewed, the study is being taken very seriously, says computer scientist Lance Fortnow of the Illinois Institute of Technology in Chicago. “I would bet that it’s probably correct…. There’s no reason to think it’s wrong.”

    And the result is a triple threat: It solved three problems at once. In addition to revealing that MIP* equals RE, it simultaneously answered two other open questions, one in physics and one in math. The first is a quantum physics puzzle called Tsirelson’s problem, which asks whether the types of quantum correlations that could be produced using an infinite amount of entanglement could be approximated with a very large, but finite amount of entanglement. The answer, the study reveals, is no: Sometimes you can’t even come close to replicating infinite entanglement with finite entanglement.

    In mathematics, the study settles Connes’ embedding conjecture, a long-standing idea that is mathematically equivalent to Tsirelson’s problem. It likewise deals with the question of whether a finite approximation can necessarily replicate something truly infinite. Again, the answer is no.

    “It’s an incredible achievement; it’s just really exciting,” says mathematician William Slofstra of the University of Waterloo in Canada. “It’s a fulfillment of something we’ve wanted for a long time.”

    See the full article here .


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  • richardmitnick 4:45 pm on January 23, 2020 Permalink | Reply
    Tags: Advances in quantum networking and quantum computing, Frequency beam splitter, Frequency tritter which splits a beam of light into three different frequencies instead of two., Off-the-shelf devices can deliver impressive control at the single-photon level., Optics & Photonics News, , Photons travel at the speed of light., Photons: single particles of light that can act as qubits, Quantum Mechanics, Quantum optical frequency combs,   

    From Oak Ridge National Laboratory: “Quantum experiments explore power of light for communications, computing” 


    From Oak Ridge National Laboratory

    January 23, 2020

    Researchers in ORNL’s Quantum Information Science group summarized their significant contributions to quantum networking and quantum computing in a special issue of Optics & Photonics News. Credit: Christopher Tison and Michael Fanto/Air Force Research Laboratory.

    A team from the Department of Energy’s Oak Ridge National Laboratory has conducted a series of experiments to gain a better understanding of quantum mechanics and pursue advances in quantum networking and quantum computing, which could lead to practical applications in cybersecurity and other areas.

    ORNL quantum researchers Joseph Lukens, Pavel Lougovski, Brian Williams, and Nicholas Peters—along with collaborators from Purdue University and the Technological University of Pereira in Colombia—summarized results from several of their recent academic papers in a special issue of the Optical Society’s Optics & Photonics News [above], which showcased some of the most significant results from optics-related research in 2019. Their entry was one of 30 selected for publication from a pool of 91.

    Conventional computer “bits” have a value of either 0 or 1, but quantum bits, called “qubits,” can exist in a superposition of quantum states labeled 0 and 1. This ability makes quantum systems promising for transmitting, processing, storing, and encrypting vast amounts of information at unprecedented speeds.

    To study photons—single particles of light that can act as qubits—the researchers employed light sources called quantum optical frequency combs that contain many precisely defined wavelengths. Because they travel at the speed of light and do not interact with their environment, photons are a natural platform for carrying quantum information over long distances.

    Interactions between photons are notoriously difficult to induce and control, but these capabilities are necessary for effective quantum computers and quantum gates, which are quantum circuits that operate on qubits. Nonexistent or unpredictable photonic interactions make two-photon quantum gates much more difficult to develop than standard one-photon gates, but the researchers reached several major milestones in recent studies that addressed these challenges.

    For example, they made adjustments to existing telecommunications equipment used in optics research to optimize them for quantum photonics. Their results revealed new ways to use these resources for both traditional and quantum communication.

    “Using this equipment to manipulate quantum states is the technological underpinning of all these experiments, but we did not expect to be able to move in the other direction and improve classical communication by working on quantum communication,” Lukens said. “These interesting and unanticipated findings have appeared as we delve deeper into this research area.”

    One such tool, a frequency beam splitter, divides a single beam of light into two frequencies, or colors, of light.

    “Imagine you have a beam of light going down an optical fiber that has a particular frequency, say, red,” Lukens said. “Then, after going through the frequency beam splitter, the photon will leave as two frequencies, so it will be both red and blue.”

    The members of this team were the first researchers to successfully design a quantum frequency beam splitter with standard lightwave communications technology. This device takes in red and blue photons simultaneously, then produces energy in either the red or the blue frequency. By using this method to deliberately change the frequencies of photons, the team tricked the stubborn particles into beneficial interactions based on quantum interference, the phenomenon of photons interfering with their own trajectories.

    “It turned out that off-the-shelf devices can deliver impressive control at the single-photon level, which people didn’t know was possible,” Lougovski said.

    Additionally, the researchers completed the first demonstration of a frequency tritter, which splits a beam of light into three different frequencies instead of two. Their results indicated that multiple quantum information processing operations can run at the same time without introducing errors or damaging the data.

    Another key accomplishment was the team’s design and demonstration of a coincidence-basis controlled-NOT gate, which enables one photon to control a frequency shift in another photon. This device completed a universal quantum gate set, meaning any quantum algorithm can be expressed as a sequence within those gates.

    “Quantum computing applications require much more impressive control levels than any sort of classical computing,” Lougovski said.

    The team also encoded quantum information in multiple independent values known as degrees of freedom within a single photon, which allowed them to observe quantum entanglement-like effects without needing two separate particles. Entanglement usually involves two linked particles in which changes made to the state of one particle also apply to the other.

    Finally, the researchers have completed quantum simulations of real-world physics problems. In collaboration with scientists at the Air Force Research Laboratory, they are now developing tiny, specialized silicon chips similar to those common in microelectronics in pursuit of even better photonic performance.

    “In theory, we can get all these operations onto a single photonic chip, and we see a lot of potential for doing similar quantum experiments on this new platform,” Lukens said. “That’s the next step to really move this technology forward.”

    Future quantum computers will allow scientists to simulate incredibly complex scientific problems that would be impossible to study on current systems, even supercomputers. In the meantime, the team’s findings could help researchers embed photonic systems into current high-performance computing resources.

    “We have a very diverse and talented team,” Lougovski said. “The most important thing is we’re getting results.”

    This research was funded by ORNL’s Laboratory Directed Research and Development program.

    See the full article here .

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    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.


  • richardmitnick 8:18 am on January 22, 2020 Permalink | Reply
    Tags: "High-precision distributed sensing using an entangled quantum network", , , , , Quantum Mechanics, Quantum-enhanced metrology, Squeezed light and homodyne detection, Technical University of Denmark, , Using an entangled quantum network to sense an averaged phase shift among multiple distributed nodes., We wanted to estimate the average of multiple optical phase shifts.   

    From Technical University of Denmark and University of Copenhagen via phys.org: “High-precision distributed sensing using an entangled quantum network” 


    From Technical University of Denmark


    From University of Copenhagen


    January 21, 2020
    Ingrid Fadelli

    The experimental setup used in the study. Credit: Jonas S. Neergaard-Nielsen.

    Quantum-enhanced metrology has been an active area of research for several years now due to its many possible applications, ranging from atomic clocks to biological imaging. Past physics research established that having a non-classical probe, such as squeezed light or an entangled spin state, can have significant benefits compared to classical probes. This idea was explored further in several recent works, some of which also considered the benefits of examining multiple distinct samples with non-classical probes.

    Inspired by these studies, researchers at the Technical University of Denmark and the University of Copenhagen have recently carried out an experiment investigating the advantages of using an entangled quantum network to sense an averaged phase shift among multiple distributed nodes. Their paper, published in Nature Physics,introduces a series of techniques that could help to collect more precise measurements in a variety of areas.

    “Recent studies showed that having non-classical correlations between probes addressing different samples could lead to a gain compared to having non-correlated probes,” Johannes Borregaard, the researcher who initiated the project, told Phys.org. “This inspired us to investigate whether such advantages could be demonstrated already using present technology.”

    In their study, Borregaard and his colleagues focused on squeezed light and homodyne detection, which are now established sensing techniques. The overall goal of the experiment was to measure a global property of multiple spatially separated objects and investigate whether probing these objects simultaneously with entangled light led to more precise results than probing them individually. The researchers found that the use of a quantum network to probe the objects simultaneously enabled phase sensing with far higher precision than that attainable when examining probes individually.

    Outline of the scheme for distributed phase sensing. Squeezed light (sqz) is distributed via beam-splitters to the phase samples under study. The phases imprinted on the squeezed probes are detected with homodyne detectors and these measurements are subsequently combined to form the average phase shift. Due to the quantum correlations between the probes, this average phase shift can be obtained with higher precision than if the samples were probed independently. Credit: Jonas S. Neergaard-Nielsen.

    “In this particular demonstration, we wanted to estimate the average of multiple optical phase shifts,” Xueshi Guo, lead author of the paper, told Phys.org. “We measured the phase shifts (which we set with wave plates to a known value) by sending a weak laser beam through and detecting the change in the light’s phase quadrature with homodyne detectors.”

    To generate entangled light and distribute it among different sites, the researchers used a fairly simple method. First, they created a phase-squeezed state of light, which is a standard non-classical quantum state. Then they divided it into multiple beams using beam splitters.

    This resulted in light probes with reduced noise in the phase quadrature, but only when all probes were measured simultaneously. This is precisely the property required to attain a better signal-to-noise ratio in the estimation of the average phase without increasing the energy (i.e., number of photons) in the probe states.

    “In the experiment we had four phase samples in total,” Guo explained. “The gain that can be achieved by using entanglement is then theoretically limited to a factor of 2. However, as the number of samples increases, so does the achievable gain.”

    Image showing the source of squeezed light in the experiment (i.e., an optical parametric oscillator). Credit: Jonas S. Neergaard-Nielsen.

    The researchers found that the advantage of using distributed quantum sensing truly becomes significant when a property of many objects connected in an optical network is to be measured. To successfully attain an increase in precision, however, the losses in the network and detectors need to be kept low, otherwise the quantum advantage vanishes.

    “The key achievement of our study is the experimental demonstration of the advantages associated with using multi-mode entanglement for distributed sensing,” Borregaard said. “Previous theoretical studies had predicted such advantages, but they often considered highly idealized scenarios and experimentally very challenging probe states or detection techniques. Our work cements that such advantages are accessible even with present noisy technology.”

    In the future, the techniques demonstrated by Borregaard, Guo and their colleagues could have important implications for a number of different areas of research and technology development. For instance, they could help to enhance the sensitivity of molecular tracking tools, atomic clocks, and optical magnetometry techniques.

    Although only further investigations will determine how much each of these applications can benefit from the methods introduced by the researchers, this recent study offers valuable insight into how quantum-enhanced metrology can be achieved using readily available technologies, such as squeezed light generation and homodyne detection. In their future work, the researchers plan to continue investigating the use of multi-mode squeezed light in other contexts, in particular for optical quantum computing applications.

    “In our experiment, we did not actually use the optimal probe states and measurement methods allowed by quantum theory, so it would be exciting to demonstrate the distributed sensing problem with those resources,” Jonas S. Neergaard-Nielsen, another researcher involved in the study, told Phys.org. “Furthermore, it could be interesting to distribute the entangled light to far-away locations in an installed fiber network to show the real-world applicability of the scheme.”

    See the full article here .


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    About Science X in 100 words
    Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide.


    DTU develops technology for people. With our international elite research and study programmes, we are helping to create a better world and to solve the global challenges formulated in the UN’s 17 Sustainable Development Goals.

    Hans Christian Ørsted founded DTU in 1829 with a clear vision to develop and create value using science and engineering to benefit society. That vision lives on today.

    The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

    The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient.

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