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  • richardmitnick 2:47 pm on March 15, 2019 Permalink | Reply
    Tags: , , Quantum Computing, Quantum information can be stored and exchanged using electron spin states., , Size matters in quantum information exchange even on the nanometer scale, The collaboration between researchers with diverse expertise was key to success., Two correlated electron pairs were coherently superposed and entangled over five quantum dots constituting a new world record within the community.   

    From Niels Bohr Institute: “Long-distance quantum information exchange – success at the nanoscale” 

    University of Copenhagen

    Niels Bohr Institute bloc

    From Niels Bohr Institute

    At the Niels Bohr Institute, University of Copenhagen, researchers have realized the swap of electron spins between distant quantum dots. The discovery brings us a step closer to future applications of quantum information, as the tiny dots have to leave enough room on the microchip for delicate control electrodes. The distance between the dots has now become big enough for integration with traditional microelectronics and perhaps, a future quantum computer. The result is achieved via a multinational collaboration with Purdue University and the University of Sydney, Australia, now published in Nature Communications.

    Size matters in quantum information exchange even on the nanometer scale.

    Quantum information can be stored and exchanged using electron spin states. The electrons’ charge can be manipulated by gate-voltage pulses, which also controls their spin. It was believed that this method can only be practical if quantum dots touch each other; if squeezed too close together the spins will react too violently, if placed too far apart the spins will interact far too slowly. This creates a dilemma, because if a quantum computer is ever going to see the light of day, we need both, fast spin exchange and enough room around quantum dots to accommodate the pulsed gate electrodes.

    Normally, the left and right dots in the linear array of quantum dots (Illustration 1) are too far apart to exchange quantum information with each other. Frederico Martins, postdoc at UNSW, Sydney, Australia, explains: “We encode quantum information in the electrons’ spin states, which have the desirable property that they don’t interact much with the noisy environment, making them useful as robust and long-lived quantum memories. But when you want to actively process quantum information, the lack of interaction is counterproductive – because now you want the spins to interact!” What to do? You can’t have both long lived information and information exchange – or so it seems. “We discovered that by placing a large, elongated quantum dot between the left dots and right dots, it can mediate a coherent swap of spin states, within a billionth of a second, without ever moving electrons out of their dots. In other words, we now have both fast interaction and the necessary space for the pulsed gate electrodes ”, says Ferdinand Kuemmeth, associate professor at the Niels Bohr Institute.

    1
    Researchers at the Niels Bohr Institute cooled a chip containing a large array of spin qubits below -273 Celsius. To manipulate individual electrons within the quantum-dot array, they applied fast voltage pulses to metallic gate electrodes located on the surface of the gallium-arsenide crystal (see scanning electron micrograph). Because each electron also carries a quantum spin, this allows quantum information processing based on the array’s spin states (the arrows on the graphic illustration). During the mediated spin exchange, which only took a billionth of a second, two correlated electron pairs were coherently superposed and entangled over five quantum dots, constituting a new world record within the community.

    Collaborations are an absolute necessity, both internally and externally.

    The collaboration between researchers with diverse expertise was key to success. Internal collaborations constantly advance the reliability of nanofabrication processes and the sophistication of low-temperature techniques. In fact, at the Center for Quantum Devices, major contenders for the implementation of solid-state quantum computers are currently intensely studied, namely semiconducting spin qubits, superconducting gatemon qubits, and topological Majorana qubits.

    All of them are voltage-controlled qubits, allowing researchers to share tricks and solve technical challenges together. But Kuemmeth is quick to add that “all of this would be futile if we didn’t have access to extremely clean semiconducting crystals in the first place”. Michael Manfra, Professor of Materials Engineering, agrees: “Purdue has put a lot of work into understanding the mechanisms that lead to quiet and stable quantum dots. It is fantastic to see this work yield benefits for Copenhagen’s novel qubits”.

    The theoretical framework of the discovery is provided by the University of Sydney, Australia. Stephen Bartlett, a professor of quantum physics at the University of Sydney, said: “What I find exciting about this result as a theorist, is that it frees us from the constraining geometry of a qubit only relying on its nearest neighbours”. His team performed detailed calculations, providing the quantum mechanical explanation for the counterintuitive discovery.

    Overall, the demonstration of fast spin exchange constitutes not only a remarkable scientific and technical achievement, but may have profound implications for the architecture of solid-state quantum computers. The reason is the distance: “If spins between non-neighboring qubits can be controllably exchanged, this will allow the realization of networks in which the increased qubit-qubit connectivity translates into a significantly increased computational quantum volume”, predicts Kuemmeth.

    See the full article here .


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    Niels Bohr Institute Campus

    Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

    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

     
  • richardmitnick 1:10 pm on March 10, 2019 Permalink | Reply
    Tags: A quantum computer would greatly speed up analysis of the collisions hopefully finding evidence of supersymmetry much sooner—or at least allowing us to ditch the theory and move on., And they’ve been waiting for decades. Google is in the race as are IBM Microsoft Intel and a clutch of startups academic groups and the Chinese government., , At the moment researchers spend weeks and months sifting through the debris from proton-proton collisions in the LCH trying to find exotic heavy sister-particles to all our known particles of matter., “This is a marathon” says David Reilly who leads Microsoft’s quantum lab at the University of Sydney Australia. “And it's only 10 minutes into the marathon.”, , , CERN-Future Circular Collider, For CERN the quantum promise could for instance help its scientists find evidence of supersymmetry or SUSY which so far has proven elusive., HL-LHC-High-Luminosity LHC, IBM has steadily been boosting the number of qubits on its quantum computers starting with a meagre 5-qubit computer then 16- and 20-qubit machines and just recently showing off its 50-qubit processor, In a bid to make sense of the impending data deluge some at CERN are turning to the emerging field of quantum computing., In a quantum computer each circuit can have one of two values—either one (on) or zero (off) in binary code; the computer turns the voltage in a circuit on or off to make it work., In theory a quantum computer would process all the states a qubit can have at once and with every qubit added to its memory size its computational power should increase exponentially., Last year physicists from the California Institute of Technology in Pasadena and the University of Southern California managed to replicate the discovery of the Higgs boson found at the LHC in 2012, None of the competing teams have come close to reaching even the first milestone., Quantum Computing, , , The quest has now lasted decades and a number of physicists are questioning if the theory behind SUSY is really valid., Traditional computers—be it an Apple Watch or the most powerful supercomputer—rely on tiny silicon transistors that work like on-off switches to encode bits of data., Venture capitalists invested some $250 million in various companies researching quantum computing in 2018 alone.,   

    From WIRED: “Inside the High-Stakes Race to Make Quantum Computers Work” 

    Wired logo

    From WIRED

    03.08.19
    Katia Moskvitch

    1
    View Pictures/Getty Images

    Deep beneath the Franco-Swiss border, the Large Hadron Collider is sleeping.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    But it won’t be quiet for long. Over the coming years, the world’s largest particle accelerator will be supercharged, increasing the number of proton collisions per second by a factor of two and a half.

    Once the work is complete in 2026, researchers hope to unlock some of the most fundamental questions in the universe. But with the increased power will come a deluge of data the likes of which high-energy physics has never seen before. And, right now, humanity has no way of knowing what the collider might find.

    To understand the scale of the problem, consider this: When it shut down in December 2018, the LHC generated about 300 gigabytes of data every second, adding up to 25 petabytes (PB) annually. For comparison, you’d have to spend 50,000 years listening to music to go through 25 PB of MP3 songs, while the human brain can store memories equivalent to just 2.5 PB of binary data. To make sense of all that information, the LHC data was pumped out to 170 computing centers in 42 countries [http://greybook.cern.ch/]. It was this global collaboration that helped discover the elusive Higgs boson, part of the Higgs field believed to give mass to elementary particles of matter.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    To process the looming data torrent, scientists at the European Organization for Nuclear Research, or CERN, will need 50 to 100 times more computing power than they have at their disposal today. A proposed Future Circular Collider, four times the size of the LHC and 10 times as powerful, would create an impossibly large quantity of data, at least twice as much as the LHC.

    CERN FCC Future Circular Collider map

    In a bid to make sense of the impending data deluge, some at CERN are turning to the emerging field of quantum computing. Powered by the very laws of nature the LHC is probing, such a machine could potentially crunch the expected volume of data in no time at all. What’s more, it would speak the same language as the LHC. While numerous labs around the world are trying to harness the power of quantum computing, it is the future work at CERN that makes it particularly exciting research. There’s just one problem: Right now, there are only prototypes; nobody knows whether it’s actually possible to build a reliable quantum device.

    Traditional computers—be it an Apple Watch or the most powerful supercomputer—rely on tiny silicon transistors that work like on-off switches to encode bits of data.

    ORNL IBM AC922 SUMMIT supercomputer, No.1 on the TOP500. Credit: Carlos Jones, Oak Ridge National Laboratory/U.S. Dept. of Energy

    Each circuit can have one of two values—either one (on) or zero (off) in binary code; the computer turns the voltage in a circuit on or off to make it work.

    A quantum computer is not limited to this “either/or” way of thinking. Its memory is made up of quantum bits, or qubits—tiny particles of matter like atoms or electrons. And qubits can do “both/and,” meaning that they can be in a superposition of all possible combinations of zeros and ones; they can be all of those states simultaneously.

    For CERN, the quantum promise could, for instance, help its scientists find evidence of supersymmetry, or SUSY, which so far has proven elusive.

    Standard Model of Supersymmetry via DESY

    At the moment, researchers spend weeks and months sifting through the debris from proton-proton collisions in the LCH, trying to find exotic, heavy sister-particles to all our known particles of matter. The quest has now lasted decades, and a number of physicists are questioning if the theory behind SUSY is really valid. A quantum computer would greatly speed up analysis of the collisions, hopefully finding evidence of supersymmetry much sooner—or at least allowing us to ditch the theory and move on.

    A quantum device might also help scientists understand the evolution of the early universe, the first few minutes after the Big Bang. Physicists are pretty confident that back then, our universe was nothing but a strange soup of subatomic particles called quarks and gluons. To understand how this quark-gluon plasma has evolved into the universe we have today, researchers simulate the conditions of the infant universe and then test their models at the LHC, with multiple collisions. Performing a simulation on a quantum computer, governed by the same laws that govern the very particles that the LHC is smashing together, could lead to a much more accurate model to test.

    Beyond pure science, banks, pharmaceutical companies, and governments are also waiting to get their hands on computing power that could be tens or even hundreds of times greater than that of any traditional computer.

    And they’ve been waiting for decades. Google is in the race, as are IBM, Microsoft, Intel and a clutch of startups, academic groups, and the Chinese government. The stakes are incredibly high. Last October, the European Union pledged to give $1 billion to over 5,000 European quantum technology researchers over the next decade, while venture capitalists invested some $250 million in various companies researching quantum computing in 2018 alone. “This is a marathon,” says David Reilly, who leads Microsoft’s quantum lab at the University of Sydney, Australia. “And it’s only 10 minutes into the marathon.”

    Despite the hype surrounding quantum computing and the media frenzy triggered by every announcement of a new qubit record, none of the competing teams have come close to reaching even the first milestone, fancily called quantum supremacy—the moment when a quantum computer performs at least one specific task better than a standard computer. Any kind of task, even if it is totally artificial and pointless. There are plenty of rumors in the quantum community that Google may be close, although if true, it would give the company bragging rights at best, says Michael Biercuk, a physicist at the University of Sydney and founder of quantum startup Q-CTRL. “It would be a bit of a gimmick—an artificial goal,” says Reilly “It’s like concocting some mathematical problem that really doesn’t have an obvious impact on the world just to say that a quantum computer can solve it.”

    That’s because the first real checkpoint in this race is much further away. Called quantum advantage, it would see a quantum computer outperform normal computers on a truly useful task. (Some researchers use the terms quantum supremacy and quantum advantage interchangeably.) And then there is the finish line, the creation of a universal quantum computer. The hope is that it would deliver a computational nirvana with the ability to perform a broad range of incredibly complex tasks. At stake is the design of new molecules for life-saving drugs, helping banks to adjust the riskiness of their investment portfolios, a way to break all current cryptography and develop new, stronger systems, and for scientists at CERN, a way to glimpse the universe as it was just moments after the Big Bang.

    Slowly but surely, work is already underway. Federico Carminati, a physicist at CERN, admits that today’s quantum computers wouldn’t give researchers anything more than classical machines, but, undeterred, he’s started tinkering with IBM’s prototype quantum device via the cloud while waiting for the technology to mature. It’s the latest baby step in the quantum marathon. The deal between CERN and IBM was struck in November last year at an industry workshop organized by the research organization.

    Set up to exchange ideas and discuss potential collab­orations, the event had CERN’s spacious auditorium packed to the brim with researchers from Google, IBM, Intel, D-Wave, Rigetti, and Microsoft. Google detailed its tests of Bristlecone, a 72-qubit machine. Rigetti was touting its work on a 128-qubit system. Intel showed that it was in close pursuit with 49 qubits. For IBM, physicist Ivano Tavernelli took to the stage to explain the company’s progress.

    IBM has steadily been boosting the number of qubits on its quantum computers, starting with a meagre 5-qubit computer, then 16- and 20-qubit machines, and just recently showing off its 50-qubit processor.

    IBM iconic image of Quantum computer

    Carminati listened to Tavernelli, intrigued, and during a much needed coffee break approached him for a chat. A few minutes later, CERN had added a quantum computer to its impressive technology arsenal. CERN researchers are now starting to develop entirely new algorithms and computing models, aiming to grow together with the device. “A fundamental part of this process is to build a solid relationship with the technology providers,” says Carminati. “These are our first steps in quantum computing, but even if we are coming relatively late into the game, we are bringing unique expertise in many fields. We are experts in quantum mechanics, which is at the base of quantum computing.”

    The attraction of quantum devices is obvious. Take standard computers. The prediction by former Intel CEO Gordon Moore in 1965 that the number of components in an integrated circuit would double roughly every two years has held true for more than half a century. But many believe that Moore’s law is about to hit the limits of physics. Since the 1980s, however, researchers have been pondering an alternative. The idea was popularized by Richard Feynman, an American physicist at Caltech in Pasadena. During a lecture in 1981, he lamented that computers could not really simulate what was happening at a subatomic level, with tricky particles like electrons and photons that behave like waves but also dare to exist in two states at once, a phenomenon known as quantum superposition.

    Feynman proposed to build a machine that could. “I’m not happy with all the analyses that go with just the classical theory, because nature isn’t classical, dammit,” he told the audience back in 1981. “And if you want to make a simulation of nature, you’d better make it quantum mechanical, and by golly it’s a wonderful problem, because it doesn’t look so easy.”

    And so the quantum race began. Qubits can be made in different ways, but the rule is that two qubits can be both in state A, both in state B, one in state A and one in state B, or vice versa, so there are four probabilities in total. And you won’t know what state a qubit is at until you measure it and the qubit is yanked out of its quantum world of probabilities into our mundane physical reality.

    In theory, a quantum computer would process all the states a qubit can have at once, and with every qubit added to its memory size, its computational power should increase exponentially. So, for three qubits, there are eight states to work with simultaneously, for four, 16; for 10, 1,024; and for 20, a whopping 1,048,576 states. You don’t need a lot of qubits to quickly surpass the memory banks of the world’s most powerful modern supercomputers—meaning that for specific tasks, a quantum computer could find a solution much faster than any regular computer ever would. Add to this another crucial concept of quantum mechanics: entanglement. It means that qubits can be linked into a single quantum system, where operating on one affects the rest of the system. This way, the computer can harness the processing power of both simultaneously, massively increasing its computational ability.

    While a number of companies and labs are competing in the quantum marathon, many are running their own races, taking different approaches. One device has even been used by a team of researchers to analyze CERN data, albeit not at CERN. Last year, physicists from the California Institute of Technology in Pasadena and the University of Southern California managed to replicate the discovery of the Higgs boson, found at the LHC in 2012, by sifting through the collider’s troves of data using a quantum computer manufactured by D-Wave, a Canadian firm based in Burnaby, British Columbia. The findings didn’t arrive any quicker than on a traditional computer, but, crucially, the research showed a quantum machine could do the work.

    One of the oldest runners in the quantum race, D-Wave announced back in 2007 that it had built a fully functioning, commercially available 16-qubit quantum computer prototype—a claim that’s controversial to this day. D-Wave focuses on a technology called quantum annealing, based on the natural tendency of real-world quantum systems to find low-energy states (a bit like a spinning top that inevitably will fall over). A D-Wave quantum computer imagines the possible solutions of a problem as a landscape of peaks and valleys; each coordinate represents a possible solution and its elevation represents its energy. Annealing allows you to set up the problem, and then let the system fall into the answer—in about 20 milliseconds. As it does so, it can tunnel through the peaks as it searches for the lowest valleys. It finds the lowest point in the vast landscape of solutions, which corresponds to the best possible outcome—although it does not attempt to fully correct for any errors, inevitable in quantum computation. D-Wave is now working on a prototype of a universal annealing quantum computer, says Alan Baratz, the company’s chief product officer.

    Apart from D-Wave’s quantum annealing, there are three other main approaches to try and bend the quantum world to our whim: integrated circuits, topological qubits and ions trapped with lasers. CERN is placing high hopes on the first method but is closely watching other efforts too.

    IBM, whose computer Carminati has just started using, as well as Google and Intel, all make quantum chips with integrated circuits—quantum gates—that are superconducting, a state when certain metals conduct electricity with zero resistance. Each quantum gate holds a pair of very fragile qubits. Any noise will disrupt them and introduce errors—and in the quantum world, noise is anything from temperature fluctuations to electromagnetic and sound waves to physical vibrations.

    To isolate the chip from the outside world as much as possible and get the circuits to exhibit quantum mechanical effects, it needs to be supercooled to extremely low temperatures. At the IBM quantum lab in Zurich, the chip is housed in a white tank—a cryostat—suspended from the ceiling. The temperature inside the tank is a steady 10 millikelvin or –273 degrees Celsius, a fraction above absolute zero and colder than outer space. But even this isn’t enough.

    Just working with the quantum chip, when scientists manipulate the qubits, causes noise. “The outside world is continually interacting with our quantum hardware, damaging the information we are trying to process,” says physicist John Preskill at the California Institute of Technology, who in 2012 coined the term quantum supremacy. It’s impossible to get rid of the noise completely, so researchers are trying to suppress it as much as possible, hence the ultracold temperatures to achieve at least some stability and allow more time for quantum computations.

    “My job is to extend the lifetime of qubits, and we’ve got four of them to play with,” says Matthias Mergenthaler, an Oxford University postdoc student working at IBM’s Zurich lab. That doesn’t sound like a lot, but, he explains, it’s not so much the number of qubits that counts but their quality, meaning qubits with as low a noise level as possible, to ensure they last as long as possible in superposition and allow the machine to compute. And it’s here, in the fiddly world of noise reduction, that quantum computing hits up against one of its biggest challenges. Right now, the device you’re reading this on probably performs at a level similar to that of a quantum computer with 30 noisy qubits. But if you can reduce the noise, then the quantum computer is many times more powerful.

    Once the noise is reduced, researchers try to correct any remaining errors with the help of special error-correcting algorithms, run on a classical computer. The problem is, such error correction works qubit by qubit, so the more qubits there are, the more errors the system has to cope with. Say a computer makes an error once every 1,000 computational steps; it doesn’t sound like much, but after 1,000 or so operations, the program will output incorrect results. To be able to achieve meaningful computations and surpass standard computers, a quantum machine has to have about 1,000 qubits that are relatively low noise and with error rates as corrected as possible. When you put them all together, these 1,000 qubits will make up what researchers call a logical qubit. None yet exist—so far, the best that prototype quantum devices have achieved is error correction for up to 10 qubits. That’s why these prototypes are called noisy intermediate-scale quantum computers (NISQ), a term also coined by Preskill in 2017.

    For Carminati, it’s clear the technology isn’t ready yet. But that isn’t really an issue. At CERN the challenge is to be ready to unlock the power of quantum computers when and if the hardware becomes available. “One exciting possibility will be to perform very, very accurate simulations of quantum systems with a quantum computer—which in itself is a quantum system,” he says. “Other groundbreaking opportunities will come from the blend of quantum computing and artificial intelligence to analyze big data, a very ambitious proposition at the moment, but central to our needs.”

    But some physicists think NISQ machines will stay just that—noisy—forever. Gil Kalai, a professor at Yale University, says that error correcting and noise suppression will never be good enough to allow any kind of useful quantum computation. And it’s not even due to technology, he says, but to the fundamentals of quantum mechanics. Interacting systems have a tendency for errors to be connected, or correlated, he says, meaning errors will affect many qubits simultaneously. Because of that, it simply won’t be possible to create error-correcting codes that keep noise levels low enough for a quantum computer with the required large number of qubits.

    “My analysis shows that noisy quantum computers with a few dozen qubits deliver such primitive computational power that it will simply not be possible to use them as the building blocks we need to build quantum computers on a wider scale,” he says. Among scientists, such skepticism is hotly debated. The blogs of Kalai and fellow quantum skeptics are forums for lively discussion, as was a recent much-shared article titled “The Case Against Quantum Computing”—followed by its rebuttal, “The Case Against the Case Against Quantum Computing.

    For now, the quantum critics are in a minority. “Provided the qubits we can already correct keep their form and size as we scale, we should be okay,” says Ray Laflamme, a physicist at the University of Waterloo in Ontario, Canada. The crucial thing to watch out for right now is not whether scientists can reach 50, 72, or 128 qubits, but whether scaling quantum computers to this size significantly increases the overall rate of error.

    3
    The Quantum Nano Centre in Canada is one of numerous big-budget research and development labs focussed on quantum computing. James Brittain/Getty Images

    Others believe that the best way to suppress noise and create logical qubits is by making qubits in a different way. At Microsoft, researchers are developing topological qubits—although its array of quantum labs around the world has yet to create a single one. If it succeeds, these qubits would be much more stable than those made with integrated circuits. Microsoft’s idea is to split a particle—for example an electron—in two, creating Majorana fermion quasi-particles. They were theorized back in 1937, and in 2012 researchers at Delft University of Technology in the Netherlands, working at Microsoft’s condensed matter physics lab, obtained the first experimental evidence of their existence.

    “You will only need one of our qubits for every 1,000 of the other qubits on the market today,” says Chetan Nayak, general manager of quantum hardware at Microsoft. In other words, every single topological qubit would be a logical one from the start. Reilly believes that researching these elusive qubits is worth the effort, despite years with little progress, because if one is created, scaling such a device to thousands of logical qubits would be much easier than with a NISQ machine. “It will be extremely important for us to try out our code and algorithms on different quantum simulators and hardware solutions,” says Carminati. “Sure, no machine is ready for prime time quantum production, but neither are we.”

    Another company Carminati is watching closely is IonQ, a US startup that spun out of the University of Maryland. It uses the third main approach to quantum computing: trapping ions. They are naturally quantum, having superposition effects right from the start and at room temperature, meaning that they don’t have to be supercooled like the integrated circuits of NISQ machines. Each ion is a singular qubit, and researchers trap them with special tiny silicon ion traps and then use lasers to run algorithms by varying the times and intensities at which each tiny laser beam hits the qubits. The beams encode data to the ions and read it out from them by getting each ion to change its electronic states.

    In December, IonQ unveiled its commercial device, capable of hosting 160 ion qubits and performing simple quantum operations on a string of 79 qubits. Still, right now, ion qubits are just as noisy as those made by Google, IBM, and Intel, and neither IonQ nor any other labs around the world experimenting with ions have achieved quantum supremacy.

    As the noise and hype surrounding quantum computers rumbles on, at CERN, the clock is ticking. The collider will wake up in just five years, ever mightier, and all that data will have to be analyzed. A non-noisy, error-corrected quantum computer will then come in quite handy.

    See the full article here .

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  • richardmitnick 10:16 am on February 28, 2019 Permalink | Reply
    Tags: "Immunising quantum computers against errors", , , Quantum Computing, Researchers at ETH Zürich have used trapped calcium ions to demonstrate a new method for making quantum computers immune to errors   

    From ETH Zürich: “Immunising quantum computers against errors” 

    ETH Zurich bloc

    From ETH Zürich

    Researchers at ETH Zürich have used trapped calcium ions to demonstrate a new method for making quantum computers immune to errors. To do so, they created a periodic oscillatory state of an ion that circumvents the usual limits to measurement accuracy.

    1
    In the ETH experiment, calcium ions are made to oscillate in such a way that their wave functions look like the teeth of a comb. The measurement uncertainty can thus be distributed over many such teeth, which in principle enables precise error detection. (Visualisations: Christa Flühmann / Shutterstock)

    When building a quantum computer, one needs to reckon with errors – in both senses of the word. Quantum bits or “qubits”, which can take on the logical values 0 and 1 at the same time and thus carry out calculations faster, are extremely susceptible to perturbations. A possible remedy for this is quantum error correction, which means that each qubit is represented “redundantly” in several copies, such that errors can be detected and eventually corrected without disturbing the fragile quantum state of the qubit itself. Technically this is very demanding. However, several years ago an alternative suggestion came up in which information isn’t stored in several redundant qubits, but rather in the many oscillatory states of a single quantum harmonic oscillator. The research group of Jonathan Home, professor at the Institute for Quantum Electronics at ETH Zurich, has now realised such a qubit encoded in an oscillator. Their results have been published in the scientific journal Nature.

    Periodic oscillatory states

    In Home’s laboratory, PhD student Christa Flühmann and her colleagues work with electrically charged calcium atoms that are trapped by electric fields. Using appropriately chosen laser beams, these ions are cooled down to very low temperatures at which their oscillations in the electric fields (inside which the ions slosh back and forth like marbles in a bowl) are described by quantum mechanics as so-called wave functions. “At that point things get exciting”, says Flühmann, who is first author of the Nature paper. “We can now manipulate the oscillatory states of the ions in such a way that their position and momentum uncertainties are distributed among many periodically arranged states.”

    Here, “uncertainty” refers to Werner Heisenberg’s famous formula, which states that in quantum physics the product of the measurement uncertainties of the position and velocity (more precisely: the momentum) of a particle can never go below a well-defined minimum. For instance, if one wants to manipulate the particle in order to know its position very well – physicists call this “squeezing” – one automatically makes its momentum less certain.

    Reduced uncertainty

    Squeezing a quantum state in this way is, on its own, only of limited value if the aim is to make precise measurements. However, there is a clever way out: if, on top of the squeezing, one prepares an oscillatory state in which the particle’s wave function is distributed over many periodically spaced positions, the measurement uncertainty of each position and of the respective momentum can be smaller than Heisenberg would allow. Such a spatial distribution of the wave function – the particle can be in several places at once, and only a measurement decides where one actually finds it – is reminiscent of Erwin Schrödinger’s famous cat, which is simultaneously dead and alive.

    This strongly reduced measurement uncertainty also means that the tiniest change in the wave function, for instance by some external disturbance, can be determined very precisely and – at least in principle – corrected. “Our realisation of those periodic or comb-like oscillatory states of the ion are an important step towards such an error detection”, Flühmann explains. “Moreover, we can prepare arbitrary states of the ion and perform all possible logical operations on it. All this is necessary for building a quantum computer. In a next step we want to combine that with error detection and error correction.”

    Applications in quantum sensors

    A few experimental obstacles have to be overcome on the way, Flühmann admits. The calcium ion first needs to be coupled to another ion by electric forces, so that the oscillatory state can be read out without destroying it. Still, even in its present form the method of the ETH researchers is of great interest for applications, Flühmann explains: “Owing to their extreme sensitivity to disturbances, those oscillatory states are a great tool for measuring tiny electric fields or other physical quantities very precisely.”

    See the full article here .

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    Stem Education Coalition

    ETH Zurich campus

    ETH Zürich is one of the leading international universities for technology and the natural sciences. It is well known for its excellent education, ground-breaking fundamental research and for implementing its results directly into practice.

    Founded in 1855, ETH Zürich today has more than 18,500 students from over 110 countries, including 4,000 doctoral students. To researchers, it offers an inspiring working environment, to students, a comprehensive education.

    Twenty-one Nobel Laureates have studied, taught or conducted research at ETH Zürich, underlining the excellent reputation of the university.

     
  • richardmitnick 10:22 am on February 23, 2019 Permalink | Reply
    Tags: , , , Quantum Computing, , , Semiconductor quantum dots,   

    From University of Cambridge: “Physicists get thousands of semiconductor nuclei to do ‘quantum dances’ in unison” 

    U Cambridge bloc

    From University of Cambridge

    22 Feb 2019
    Communications office

    1
    Theoretical ESR spectrum buildup as a function of two-photon detuning δ and drive time τ, for a Rabi frequency of Ω = 3.3 MHz on the central transition. Credit: University of Cambridge.

    A team of Cambridge researchers have found a way to control the sea of nuclei in semiconductor quantum dots so they can operate as a quantum memory device.

    Quantum dots are crystals made up of thousands of atoms, and each of these atoms interacts magnetically with the trapped electron. If left alone to its own devices, this interaction of the electron with the nuclear spins, limits the usefulness of the electron as a quantum bit – a qubit.

    Led by Professor Mete Atatüre from Cambridge’s Cavendish Laboratory, the researchers are exploiting the laws of quantum physics and optics to investigate computing, sensing or communication applications.

    “Quantum dots offer an ideal interface, as mediated by light, to a system where the dynamics of individual interacting spins could be controlled and exploited,” said Atatüre, who is a Fellow of St John’s College. “Because the nuclei randomly ‘steal’ information from the electron they have traditionally been an annoyance, but we have shown we can harness them as a resource.”

    The Cambridge team found a way to exploit the interaction between the electron and the thousands of nuclei using lasers to ‘cool’ the nuclei to less than 1 milliKelvin, or a thousandth of a degree above the absolute zero temperature. They then showed they can control and manipulate the thousands of nuclei as if they form a single body in unison, like a second qubit. This proves the nuclei in the quantum dot can exchange information with the electron qubit and can be used to store quantum information as a memory device. The results are reported in the journal Science.

    Quantum computing aims to harness fundamental concepts of quantum physics, such as entanglement and superposition principle, to outperform current approaches to computing and could revolutionise technology, business and research. Just like classical computers, quantum computers need a processor, memory, and a bus to transport the information backwards and forwards. The processor is a qubit which can be an electron trapped in a quantum dot, the bus is a single photon that these quantum dots generate and are ideal for exchanging information. But the missing link for quantum dots is quantum memory.

    Atatüre said: “Instead of talking to individual nuclear spins, we worked on accessing collective spin waves by lasers. This is like a stadium where you don’t need to worry about who raises their hands in the Mexican wave going round, as long as there is one collective wave because they all dance in unison.

    “We then went on to show that these spin waves have quantum coherence. This was the missing piece of the jigsaw and we now have everything needed to build a dedicated quantum memory for every qubit.”

    In quantum technologies, the photon, the qubit and the memory need to interact with each other in a controlled way. This is mostly realised by interfacing different physical systems to form a single hybrid unit which can be inefficient. The researchers have been able to show that in quantum dots, the memory element is automatically there with every single qubit.

    Dr Dorian Gangloff, one of the first authors of the paper [Science] and a Fellow at St John’s, said the discovery will renew interest in these types of semiconductor quantum dots. Dr Gangloff explained: “This is a Holy Grail breakthrough for quantum dot research – both for quantum memory and fundamental research; we now have the tools to study dynamics of complex systems in the spirit of quantum simulation.”

    The long term opportunities of this work could be seen in the field of quantum computing. Last month, IBM launched the world’s first commercial quantum computer, and the Chief Executive of Microsoft has said quantum computing has the potential to ‘radically reshape the world’.

    Gangloff said: “The impact of the qubit could be half a century away but the power of disruptive technology is that it is hard to conceive of the problems we might open up – you can try to think of it as known unknowns but at some point you get into new territory. We don’t yet know the kind of problems it will help to solve which is very exciting.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 1:29 pm on February 22, 2019 Permalink | Reply
    Tags: , , , , IBM Q, Quantum Computing   

    From Brookhaven National Lab: “Quantum Information Science Effort Expands at Brookhaven Lab” 

    From Brookhaven National Lab

    February 19, 2019
    Ariana Tantillo
    atantillo@bnl.gov

    The Computational Science Initiative is building its staff, capabilities, and programs in this emerging research area expected to revolutionize science and other fields.

    1
    Brookhaven Lab’s Computational Science Initiative recently formed a new Quantum Computing Group as one of the many ways it’s expanding its efforts in quantum information science. The group members are (left to right) Meifeng Lin, Dimitrios Katramatos, Eden Figueroa, Michael McGuigan, Yao-Lung (Leo) Fang, and Layla Hormozi. Lin and Hormozi are co-leading the group.

    An emerging and exciting research field known as quantum information science (QIS) is ramping up in the Computational Science Initiative (CSI) at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory.

    “Because of our extraordinary data management, analysis, and distribution requirements at Brookhaven Lab, we are always on the look out for new computational technologies that will enable us to continue to provide leading services,” said CSI Director Kerstin Kleese van Dam. “Quantum computing and networking are among these promising technologies, and we want to make sure we are at the forefront of this exciting new research and development.”

    From classical to quantum computing

    The computers we use today store and process information in the form of binary digits (bits) that encode a value of zero or one. The values represent two different states, such as off or on, true or false, and yes or no.

    2
    A schematic illustrating the difference between a bit (left) and qubit (right). A bit can be at either of the two poles of the imaginary sphere, while a qubit can be at any point within the volume of the sphere. Credit: IBM.

    By contrast, quantum computers use quantum bits, or qubits, that can exist as a zero and one at the same time. This newer form of computing takes advantage of the strange way that matter behaves at atomic and subatomic scales. In this quantum world, atoms and subatomic particles appear to exist in multiple states or places at the same time (quantum superposition) and can correlate their behavior across large distances (quantum entanglement). Because of these quantum mechanical phenomena, quantum computers can store much more information, perform calculations significantly faster, and use less energy than classical computers.

    A quantum community

    At Brookhaven Lab, CSI staff are evaluating and designing QIS systems and developing the system-level support and algorithms needed to fully exploit the new QIS architectures.

    “CSI has access to several online test systems, including the IBM Q quantum computer, and is actively using these systems for its research,” said Kleese van Dam.

    2
    Launched in 2016, IBM Q is a cloud platform that provides companies, universities, and research labs around the world with the ability to perform quantum computations online without having direct access to a quantum computer. Credit: IBM.

    In addition, CSI has been building relationships with leading experts in the field from various institutions, including the Massachusetts Institute of Technology (MIT), Princeton University, Harvard University, Tufts University, Stony Brook University, and the University of Toronto. Several of these experts now have joint appointments with Brookhaven, including MIT mechanical engineering and physics professor Seth Lloyd and Tufts associate physics professor Peter Love.

    In house, CSI is building its QIS expertise through educating existing staff, hiring new personnel, and hosting students, such as those participating in DOE’s Computational Science Graduate Fellowship. CSI researchers and external QIS experts are currently carrying out several joint QIS projects.

    Quantum solutions

    CSI computational scientists Shinjae Yoo and Layla Hormozi—who is co-leading CSI’s new Quantum Computing Group with computational scientist Meifeng Lin—and collaborators from Carnegie Mellon University, MIT, and Stony Brook are evaluating existing QIS architectures for state-of-the-art machine learning algorithms. In particular, they are identifying issues related to the programmability and performance of algorithms operating on QIS systems. Currently, the team is investigating strategies to overcome slow data loading speeds and to effectively encode data.


    A video describing why we need quantum computers and how the Q quantum computer works. Credit: IBM.

    “Input/output and error correction are serious challenges to using upcoming quantum computers,” said Yoo. “We are looking into how machine learning can help such challenges and how we can improve quantum machine learning algorithms.”

    Another team—including CSI computational scientist Michael McGuigan and collaborators from Boston University, Microsoft, MIT, Michigan State, Syracuse University, University of California, Santa Barbara, and University of Iowa (lead)—is developing the building blocks of quantum computing to solve basic questions in high-energy physics (HEP) and the early universe. In particular, the team is studying ways to efficiently map quantum field theories of the strong interactions—mathematical frameworks that describe the interactions between subatomic particles—to quantum computing hardware.

    3
    Proposed structure of the oxygen-evolving, or water-splitting, center of Photosystem II, a protein complex that executes the initial photosynthesis reaction. The center contains a cluster of manganese (Mn) ions, a calcium (Ca) ion, oxygen (O) atoms, and coordinating amino acids.

    Through a separate collaboration, Brookhaven Lab and Harvard University are developing quantum-based models of biomimetic photosynthesis. Chemical processes that replicate and optimize photosynthesis—the process by which plants convert solar energy into chemical energy—could be used to produce clean and sustainable fuels and other chemicals.

    “The natural protein co-factors that catalyze photosynthetic reactions involve multiple transition-metal atoms that exhibit strongly correlated electron behavior,” said CSI application architect and team member Hubertus van Dam. “An accurate description of this correlated behavior requires far more terms from different electron distributions than can ever be calculated on a conventional computer. Quantum computers enable the use of quantum matter to simulate the quantum behavior of these electrons much more efficiently.”

    CSI has also created the Northeast Quantum Systems Center (NEQsys), a partnership between Harvard, MIT, Princeton, Raytheon, Stony Brook, University of Toronto, Tufts, and Yale. By leveraging the wealth of quantum expertise at leading universities and in industry, this collaboration seeks to impact a broad range of areas—for example, theoretical and experimental materials science and condensed matter physics, devices and system software, and algorithms and computational applications.

    “This cross-cutting research effort will impact the entire quantum ecosystem,” explained Kleese van Dam. “CSI is providing knowledge integration across the hardware and software stack to impact work being conducted across the institutions.”

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 5:39 pm on February 15, 2019 Permalink | Reply
    Tags: An innovative way for different types of quantum technology to “talk” to each other using sound, ANL Advanced Photon Source, , “Spins”—a property of an electron that can be up or down or both, “The object is to couple the sound waves with the spins of electrons in the material”, , Quantum Computing, Sound waves let quantum systems ‘talk’ to one another,   

    From University of Chicago: “Sound waves let quantum systems ‘talk’ to one another” 

    U Chicago bloc

    From University of Chicago

    Feb 15, 2019
    Louise Lerner

    1
    An X-ray image of sound waves. Image courtesy of Kevin Satzinger and Samuel Whiteley

    Researchers at the University of Chicago and Argonne National Laboratory have invented an innovative way for different types of quantum technology to “talk” to each other using sound. The study, published Feb. 11 in Nature Physics, is an important step in bringing quantum technology closer to reality.

    Researchers are eyeing quantum systems, which tap the quirky behavior of the smallest particles as the key to a fundamentally new generation of atomic-scale electronics for computation and communication. But a persistent challenge has been transferring information between different types of technology, such as quantum memories and quantum processors.

    “We approached this question by asking: Can we manipulate and connect quantum states of matter with sound waves?” said senior study author David Awschalom, the Liew Family Professor with the Institute for Molecular Engineering and senior scientist at Argonne National Laboratory.

    One way to run a quantum computing operation is to use “spins”—a property of an electron that can be up, down or both. Scientists can use these like zeroes and ones in today’s binary computer programming language. But getting this information elsewhere requires a translator, and scientists thought sound waves could help.

    “The object is to couple the sound waves with the spins of electrons in the material,” said graduate student Samuel Whiteley, the co-first author on the paper. “But the first challenge is to get the spins to pay attention.” So they built a system with curved electrodes to concentrate the sound waves, like using a magnifying lens to focus a point of light.

    The results were promising, but they needed more data. To get a better look at what was happening, they worked with scientists at the Center for Nanoscale Materials at Argonne to observe the system in real time. Essentially, they used extremely bright, powerful X-rays from the lab’s giant synchrotron, the Advanced Photon Source, as a microscope to peer at the atoms inside the material as the sound waves moved through it at nearly 7,000 kilometers per second.

    ANL Advanced Photon Source

    “This new method allows us to observe the atomic dynamics and structure in quantum materials at extremely small length scales,” said Awschalom. “This is one of only a few locations worldwide with the instrumentation to directly watch atoms move in a lattice as sound waves passes through them.”

    2
    Argonne nanoscientist Martin Holt took X-ray images of the acoustic waves with the Hard X-ray Nanoprobe at the Center for Nanoscale Materials and Advanced Photon Source, both at Argonne. Image courtesy of Argonne National Laboratory.

    One of the many surprising results, the researchers said, was that the quantum effects of sound waves were more complicated than they’d first imagined. To build a comprehensive theory behind what they were observing at the subatomic level, they turned to Prof. Giulia Galli, the Liew Family Professor at the IME and a senior scientist at Argonne. Modeling the system involves marshalling the interactions of every single particle in the system, which grows exponentially, Awschalom said, “but Professor Galli is a world expert in taking this kind of challenging problem and interpreting the underlying physics, which allowed us to further improve the system.”

    It’s normally difficult to send quantum information for more than a few microns, said Whiteley—that’s the width of a single strand of spider silk. This technique could extend control across an entire chip or wafer.

    “The results gave us new ways to control our systems, and opens venues of research and technological applications such as quantum sensing,” said postdoctoral researcher Gary Wolfowicz, the other co-first author of the study.

    The discovery is another from the University of Chicago’s world-leading program in quantum information science and engineering; Awschalom is currently leading a project to build a quantum “teleportation” network between Argonne and Fermi National Accelerator Laboratory to test principles for a potentially unhackable communications system.

    The scientists pointed to the confluence of expertise, resources and facilities at the University of Chicago, Institute for Molecular Engineering and Argonne as key to fully exploring the technology.

    3
    An acoustic chip is used to generate and control sound waves. Photo courtesy of Kevin Satzinger

    “No one group has the ability to explore these complex quantum systems and solve this class of problems; it takes state-of-the-art facilities, theorists and experimentalists working in close collaboration,” Awschalom said. “The strong connection between Argonne and the University of Chicago enables our students to address some of the most challenging questions in this rapidly moving area of science and technology.”

    Other coauthors on the paper are Assoc. Prof. David Schuster, and Prof. Andrew Cleland; Argonne scientists Joseph Heremans and Martin Holt; graduate students Christopher Anderson, Alexandre Bourassa, He Ma and Kevin Satzinger; and postdoctoral researcher Meng Ye.

    The devices were fabricated in the Pritzker Nanofabrication Facility at the William Eckhardt Research Center. Materials characterization was performed at the UChicago Materials Research Science and Engineering Center.

    Funding: Air Force Office of Scientific Research, U.S. Department of Energy Office of Basic Energy Sciences, National Science Foundation, Department of Defense

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    University of Chicago

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

     
  • richardmitnick 4:15 pm on February 12, 2019 Permalink | Reply
    Tags: , , Chemist Francesco Evangelista-a winner of the Dirac Medal, , Emory University, Quantum Computing,   

    From Emory University- “A new spin on computing: Chemist leads $3.9 million DOE quest for quantum software” 

    From Emory University

    February 5, 2019
    Carol Clark

    1
    “Quantum computers are not just exponentially faster, they work in a radically different way from classical computers,” says chemist Francesco Evangelista, who is leading a project to develop quantum software He is a winner of the Dirac medal.

    When most people think of a chemistry lab, they picture scientists in white coats mixing chemicals in beakers. But the lab of theoretical chemist Francesco Evangelista looks more like the office of a tech start-up. Graduate students in jeans and t-shirts sit around a large, round table chatting as they work on laptops.

    “A ‘classical’ chemist is focused on getting a chemical reaction and creating new molecules,” explains Evangelista, assistant professor at Emory University. “As theoretical chemists, we want to understand how chemistry really works — how all the atoms involved interact with one another during a reaction.”

    Working at the intersection of math, physics, chemistry and computer science, the theorists develop algorithms to serve as simulation models for the molecular behaviors of atomic nuclei and electrons. They also develop software that enables them to feed these algorithms into “super” computers — nearly a million times faster than a laptop — to study chemical processes.

    The problem is, even super computers are taxed by the mind-boggling combinatorial complexity underlying reactions. That limits the pace of the research.

    “Computers have hit a barrier in terms of speed,” Evangelista says. “One way to make them more powerful is to make transistors smaller, but you can’t make them smaller than the width of a couple of atoms — the limit imposed by quantum mechanics. That’s why there is a race right now to make breakthroughs in quantum computing.”

    Evangelista and his graduate students have now joined that race.

    The Department of Energy (DOE) awarded Evangelista $3.9 million to lead research into the development of software to run the first generation of quantum computers. He is the principal investigator for the project, encompassing scientists at seven universities, to develop new methods and algorithms for calculating problems in quantum chemistry. The tools the team develops will be open access, made available to other researchers for free.

    Watch a video about Francesco Evangelista’s work,
    produced by the Camille & Henry Dreyfus Foundation:

    While big-data leaders — such as IBM, Google, Intel and Rigetti — have developed prototypes of quantum computers, the field remains in its infancy. Many technological challenges remain before quantum computers can fulfill their promise of speeding up calculations to crack major mysteries of the natural world.

    The federal government will play a strong supporting role in achieving this goal. President Trump recently signed a $1.2 billion law, the National Quantum Initiative Act, to fund advances in quantum technologies over the next five years.

    “Right now, it’s a bit of a wild west, but eventually people working on this giant endeavor are going to work out some of the current technological problems,” Evangelista says. “When that happens, we need to have quantum software ready and a community trained to use it for theoretical chemistry. Our project is working on programming codes that will someday get quantum computers to do the calculations we want them to do.”

    The project will pave the way for quantum computers to simulate chemical systems critical to the mission of the DOE, such as transition metal catalysts, high-temperature superconductors and novel materials that are beyond the realm of simulation on “classical” computers. The insights gained could speed up research into how to improve everything from solar power to nuclear energy.

    Unlike objects in the “classical” world, that we can touch, see and experience around us, nature behaves much differently in the ultra-small quantum world of atoms and subatomic particles.

    “One of the weird things about quantum mechanics is that you can’t say whether an electron is actually only here or there,” Evangelista says.

    He takes a coin from his pocket. “In the classical world, we know that an object like this quarter is either in my pocket or in your pocket,” Evangelista says. “But if this was an electron, it could be in both our pockets. I cannot tell you exactly where it is, but I can use a wave function to describe the likelihood of whether it is here or there.”

    To make things even more complicated, the behavior of electrons can be correlated, or entangled. When objects in our day-to-day lives, like strands of hair, become entangled they can be teased apart and separated again. That rule doesn’t apply at the quantum scale where entangled objects are somehow intimately connected even if they are apart in space.

    “Three electrons moving in three separate orbitals can actually be interacting with one another,” Evangelista says. “Somehow they are talking together and their motion is correlated like ballerinas dancing and moving in a concerted way.”

    2
    Graduate students in Evangelista’s lab are developing algorithms to simulate quantum software so they can run tests and adapt the design based on the results.

    Much of Evangelista’s work involves trying to predict the collective behavior of strongly correlated electrons. In order to understand how a drug interacts with a protein, for example, he needs to consider how it affects the hundreds of thousands of atoms in that protein, along with the millions of electrons within those atoms.

    “The problem quickly explodes in complexity,” Evangelista says. “Computationally, it’s difficult to account for all the possible combinations of ways the electrons could be interacting. The computer soon runs out of memory.”

    A classical computer stores memory in a line of “bits,” which are represented by either a “0” or a “1.” It operates on chunks of 64 bits of memory at a time, and each bit is either distinctly a 0 or a 1. If you add another bit to the line, you get just one more bit of memory.

    A quantum computer stores memory in quantum bits, or qubits. A single qubit can be either a 0 or a 1 — or mostly a 0 and part of a 1 — or any other combination of the two. When you add a qubit to a quantum computer, it increases the memory by a factor of two. The fastest quantum computers now available contain around 70 qubits.

    “Quantum computers are not just exponentially faster, they work in a radically different way from classical computers,” Evangelista says.

    For instance, a classical computer can determine all the consequences of a chess move by working one at a time through the chain of possible next moves. A quantum computer, however, could potentially determine all these possible moves in one go, without having to work through each step.

    While quantum computers are powerful, they are also somewhat delicate.

    “They’re extremely sensitive,” Evangelista says. “They have to be kept at low temperatures to maintain their coherence. In a typical setup, you also need a second computer kept at very low temperatures to drive the quantum computer, otherwise the heat from the wires coming out will destroy entanglement.”

    The potential error rate is one of the challenges of the DOE project to develop quantum software. The researchers need to determine the range of errors that can still yield a practical solution to a calculation. They will also develop standard benchmarks for testing the accuracy and computing power of new quantum hardware and they will validate prototypes of quantum computers in collaborations with industry partners Google and Rigetti.

    Just as they develop algorithms to simulate chemical processes, Evangelista and his graduate students are now developing algorithms to simulate quantum software so they can run tests and adapt the design based on the results.

    Evangelista pulled together researchers from other universities with a range of expertise for the project, including some who are new to quantum computing and others who are already experts in the field. The team includes scientists from Rice University, Northwestern, the University of Michigan, CalTech, the University of Toronto and Dartmouth.

    The long-range goal is to spur the development of more efficient energy sources, including solar power, by providing detailed data on phenomena such as the ways electrons in a molecule are affected when that molecule absorbs light.

    “Ultimately, such theoretical insights could provide a rational path to efforts like making solar cells more efficient, saving the time and money needed to conduct trial-and-error experiments in a lab,” Evangelista says.

    Evangelista also has ongoing collaborations with Emory chemistry professor Tim Lian, studying ways to harvest and convert solar energy into chemical fuels. In 2017, Evangelista won the Dirac Medal, one of the world’s most prestigious awards for theoretical and computational chemists under 40.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Emory University is a private research university in metropolitan Atlanta, located in the Druid Hills section of DeKalb County, Georgia, United States. The university was founded as Emory College in 1836 in Oxford, Georgia by the Methodist Episcopal Church and was named in honor of Methodist bishop John Emory. In 1915, the college relocated to metropolitan Atlanta and was rechartered as Emory University. The university is the second-oldest private institution of higher education in Georgia and among the fifty oldest private universities in the United States.

    Emory University has nine academic divisions: Emory College of Arts and Sciences, Oxford College, Goizueta Business School, Laney Graduate School, School of Law, School of Medicine, Nell Hodgson Woodruff School of Nursing, Rollins School of Public Health, and the Candler School of Theology. Emory University, the Georgia Institute of Technology, and Peking University in Beijing, China jointly administer the Wallace H. Coulter Department of Biomedical Engineering. The university operates the Confucius Institute in Atlanta in partnership with Nanjing University. Emory has a growing faculty research partnership with the Korea Advanced Institute of Science and Technology (KAIST). Emory University students come from all 50 states, 6 territories of the United States, and over 100 foreign countries.

     
  • richardmitnick 3:15 pm on February 2, 2019 Permalink | Reply
    Tags: IBM's Quantum Experience, Pauli exclusion principle- two electrons cannot occupy the same position in space at the same time, Quantum Computing, The discovery is another breakthrough at the frontier of quantum efforts at the University, three-laboratory quantum “teleporter”,   

    From University of Chicago: “Scientists tap into open-access quantum computer to tease out quantum secrets” 

    U Chicago bloc

    From University of Chicago

    Jan 31, 2019
    Louise Lerner

    U Chicago Researchers used IBM’s Quantum Experience, an open-access quantum computer, to test fundamental principles of quantum mechanics.

    UChicago, IME scientists use IBM Q to verify elusive quantum mechanics principles.

    The rules of quantum mechanics describe how atoms and molecules act very differently from the world around us. Scientists have made progress toward teasing out these rules—essential for finding ways to make new molecules and better technology—but some are so complex that they evade experimental verification.

    With the advent of open-access quantum computers, scientists at the University of Chicago saw an opportunity to do a very unusual experiment to test some of these quantum principles. Their study, which appeared Jan. 31 in Nature Communications Physics, taps into a quantum computer to discover fundamental truths about the quantum behavior of electrons in molecules.

    “Quantum computing is a really exciting realm to explore fundamental questions. It allows us to observe aspects of quantum theory that are absolutely untouchable with classical computers,” said Prof. David Mazziotti, professor of chemistry and author on the paper.

    One particular rule of quantum mechanics, called the Pauli exclusion principle, is that two electrons cannot occupy the same position in space at the same time. In many cases, a molecule’s electrons experience additional restrictions on their locations; these are known as the generalized Pauli constraints. “These rules inform the way that all molecules and matter form,” said Mazziotti.

    In this study, Mazziotti, Prof. David Shuster and graduate student Scott Smart created a set of algorithms that would ask IBM’s Q Experience computer to randomly generate quantum states in three-electron systems, and then measure where the electrons are most probably located.

    “Suppose that the generalized Pauli constraints were not true: In that scenario, about half of the quantum states would exhibit a violation,” said Smart, the first author on the paper. Instead, in the many quantum states formed, they found that violations of generalized Pauli constraints occurred very rarely in a pattern consistent with noise in the quantum circuit.

    The results provide strong experimental verification, the scientists said.

    “The simplest generalized Pauli constraints were discovered theoretically on a classical computer at IBM in the early 1970s, so it is fitting that for the first time they would be experimentally verified on an IBM quantum computer,” Mazziotti said.

    The discovery is another breakthrough at the frontier of quantum efforts at the University; recent efforts have included a three-laboratory quantum “teleporter,” steps toward more powerful quantum sensors, and a collaboration to develop algorithms for emerging quantum computers.

    An open question is how the generalized Pauli constraints may be useful for improving quantum technology. “They will potentially contribute to achieving more efficient quantum calculations as well as better error correction schemes—critical for quantum computers to reach their full potential,” Mazziotti said.

    The discovery is another breakthrough at the frontier of quantum efforts at the University; recent efforts have included a three-laboratory quantum “teleporter,” steps toward more powerful quantum sensors, and a collaboration to develop algorithms for emerging quantum computers.

    U Chicago three-laboratory quantum “teleporter”

    Argonne National Laboratory The Quantum Link is an ambitious project by Argonne, Fermilab and the University of Chicago to bring the property of entanglement into the real world.

    University of Chicago Prof. David Awschalom works in his lab at the with PhD students Kevin Miao (left) and Alexandre Bourassa.

    An open question is how the generalized Pauli constraints may be useful for improving quantum technology. “They will potentially contribute to achieving more efficient quantum calculations as well as better error correction schemes—critical for quantum computers to reach their full potential,” Mazziotti said.

    Citation:

    Experimental data from a quantum computer verifies the generalized Pauli exclusion principle. Smart et al, Nature Communications Physics, Jan. 31, 2018.

    IBM iconic image of Quantum computer

    See the full article here .
    See also from U Chicago here.

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    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    University of Chicago

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

     
    • Jodi Toubes 2:48 pm on February 3, 2019 Permalink | Reply

      Okay… I read the blog’s origin story. Not sure you wanted critique but I will just say, it was nice to read, I found one typo (in case you want to know)… At the start to the 6th paragraph, you have “Some where” instead of somewhere. Not sure if that was on purpose or a typo. Also, I thought it ended a little abruptly, but maybe you had just said all that you wanted to and didn’t need a softer ending. Very nice for anyone who is interested to see how the ScienceSprings blog came to be.

      love, me

      >

      Like

  • richardmitnick 10:27 am on January 7, 2019 Permalink | Reply
    Tags: Quantum Computing, Quantum computing steps further ahead with new projects at Sandia,   

    From Sandia Lab: “Quantum computing steps further ahead with new projects at Sandia” 


    From Sandia Lab

    January 7, 2019

    Neal Singer
    nsinger@sandia.gov
    505-845-7078

    Quantum computing is a term that periodically flashes across the media sky like heat lightning in the desert: brilliant, attention-getting and then vanishing from the public’s mind with no apparent aftereffects.

    Yet a multimillion dollar international effort to build quantum computers is hardly going away.

    1
    Sandia National Laboratories researchers are looking to shape the future of computing through a series of quantum information science projects. As part of the work, they will collaborate to design and develop a new quantum computer that will use trapped atomic ion technology. (Photo by Randy Montoya)

    And now, four new projects led by Sandia National Laboratories aim to bring the wiggly subject into steady illumination by creating:

    A quantum computing “testbed” with accessible components on which industrial, academic and government researchers can run their own algorithms.
    A suite of test programs to measure the performance of quantum hardware.
    Classical software to ensure reliable operation of quantum computing testbeds and coax the most utility from them.
    High-level quantum algorithms that explore connections with theoretical physics, classical optimization and machine learning.

    These three- to five-year projects are funded at $42 million by the Department of Energy’s Office of Science’s Advanced Scientific Computing Research program, part of Sandia’s Advanced Science and Technology portfolio.

    Quantum information science “represents the next frontier in the information age,” said U.S. Secretary of Energy Rick Perry this fall when he announced $218 million in DOE funding for the research. “At a time of fierce international competition, these investments will ensure sustained American leadership in a field likely to shape the long-term future of information processing and yield multiple new technologies that benefit our economy and society.”

    Partners on three of the four Sandia-led projects include the California Institute of Technology, Los Alamos National Laboratory, Dartmouth College, Duke University, the University of Maryland and Tufts University.

    Birth of a generally available quantum computer

    2
    Sandia National Laboratories researcher Mohan Sarovar is developing software for quantum testbeds. Sandia’s quantum computer will play a role analogous to those of graphics processing units in today’s high-performance computers. (Photo by Randy Wong)

    Design and construction of the quantum computer itself — formally known as the Quantum Scientific Computing Open User Testbed — under the direction of Sandia researcher Peter Maunz, is a $25.1 million, five-year project that will use trapped atomic ion technology.

    Trapped ions are uniquely suited to realize a quantum computer because quantum bits (qubits) — the quantum generalization of classical bits — are encoded in the electronic states of individual trapped atomic ions, said Maunz.

    “Because trapped ions are identical and suspended by electric fields in a vacuum, they feature identical, nearly perfect qubits that are well isolated from the noise of the environment and therefore can store and process information faithfully,” he said. “While current small-scale quantum computers without quantum error correction are still noisy devices, quantum gates with the lowest noise have been realized with trapped-ion technology.”

    A quantum gate is a fundamental building block of a quantum circuit operating on a small number of qubits.

    Furthermore, in trapped-ion systems, Maunz said, “It is possible to realize quantum gates between all pairs of ions in the same trap, a feature which can crucially reduce the number of gates needed to realize a quantum computation.”

    QSCOUT is intended to make a trapped-ion quantum computer accessible to the DOE scientific community. As an open platform, Maunz said, it will not only provide full information about all its quantum and classical processes, it will also enable researchers to investigate, alter and optimize the internals of the testbed, or even to propose more advanced implementations of the quantum operations.

    Because today’s quantum computers only have access to a limited number of qubits and their operation is still subject to errors, these devices cannot yet solve scientific problems beyond the reach of classical computers. Nevertheless, access to prototype quantum processors like QSCOUT should allow researchers to optimize existing quantum algorithms, invent new ones and assess the power of quantum computing to solve complex scientific problems, Maunz said.

    Proof of the pudding

    3
    Sandia National Laboratories researcher Robin Blume-Kohout is leading a team that will develop a variety of methods to ensure the performance of quantum computers in real-world situations. (Photo by Kevin Young)

    But how do scientists ensure that the technical components of a quantum testbed are performing as expected?

    A Sandia team led by quantum researcher Robin Blume-Kohout is developing a toolbox of methods to measure the performance of quantum computers in real-world situations.

    “Our goal is to devise methods and software that assess the accuracy of quantum computers,” said Blume-Kohout.

    The $3.7 million, five-year Quantum Performance Assessment project plans to develop a broad array of tiny quantum software programs. These range from simple routines like “flip this qubit and then stop,” to testbed-sized instances of real quantum algorithms for chemistry or machine learning that can be run on almost any quantum processor.

    These programs aren’t written in a high-level computer language, but instead are sequences of elementary instructions intended to run directly on the qubits and produce a known result.

    However, Blume-Kohout says, “because we recognize that quantum mechanics is also intrinsically somewhat random, some of these test programs are intended to produce 50/50 random results. That means we need to run test programs thousands of times to confirm that the result really is 50/50 rather than, say, 70/30, to check a quantum computer’s math.”

    The team’s goal is to use testbed results to debug processors like QSCOUT by finding problems so engineers can fix them. This demands considerable expertise in both physics and statistics, but Blume-Kohout is optimistic.

    “This project builds on what Sandia has been doing for five years,” he said. “We’ve tackled similar problems in other situations for the U.S. government.”

    For example, he said, the Intelligence Advanced Research Projects Activity reached out to Sandia to evaluate the results of the performers on its LogiQ program, which aims to improve the fidelity of quantum computing. “We expect be able to say with a certain measure of reliability, ‘Here are the building blocks you need to achieve a goal,’” Blume-Kohout said.

    Quantum and classical computing meet up

    Once the computer is built by Maunz’s group and its reliability ascertained by Blume-Kohout’s team, how will it be used for computational tasks?

    The Sandia-led, $7.8 million, four-year Optimization, Verification and Engineered Reliability of Quantum Computers project aims to answer this question. LANL and Dartmouth College are partners.

    Project lead and physicist Mohan Sarovar expects that the first quantum computer developed at Sandia will be a very specialized processor, playing a role analogous to that played by graphics processing units in high-performance computing.

    “Similarly, the quantum testbed will be good at doing some specialized things. It’ll also be ‘noisy.’ It won’t be perfect,” Sarovar said. “My project will ask: What can you use such specialized units for? What concrete tasks can they perform, and how can we use them jointly with specialized algorithms connecting classical and quantum computers?”

    The team intends to develop classical “middleware” aimed at making computational use of the QSCOUT testbed and similar near-term quantum computers.

    “While we have excellent ideas for how to use fully developed, fault-tolerant quantum computers, we’re not really sure what computational use the limited devices we expect to see created in the near future will be,” Sarovar said. “We think they will play the role of a very specialized co-processor within a larger, classical computational framework.” The project aims to develop tools, heuristics and software to extract reliable, useful answers from these near-term quantum co-processors.

    At the peak

    At the most theoretical level, the year-old, Sandia-led Quantum Optimization and Learning and Simulation (QOALAS) project’s team of theoretical physicists and computer scientists, headed by researcher Ojas Parekh, have produced a new quantum algorithm for solving linear systems of equations — one of the most fundamental and ubiquitous challenges facing science and engineering.

    The three-year, $4.5 million project, in addition to Sandia, includes LANL, the University of Maryland and Caltech.

    “Our quantum linear systems algorithm, created at LANL, has the potential to provide an exponential speedup over classical algorithms in certain settings,” said Parekh. “Although similar quantum algorithms were already known for solving linear systems, ours is much simpler.

    “For many problems in quantum physics we want to know what is the lowest energy state? Understanding such states can, for example, help us better understand how materials work. Classical discrete optimization techniques developed over the last 40 years can be used to approximate such states. We believe quantum physics will help us obtain better or faster approximations.”

    The team is working on other quantum algorithms that may offer an exponential speedup over the best-known classical algorithms. For example, said Parekh, “If a classical algorithm required 2100 steps — two times itself one hundred times, or 1,267,650,600,228,229,401,496,703,205,376 steps — to solve a problem, which is a number believed to be larger than all the particles in the universe, then the quantum algorithm providing an exponential speed-up would only take 100 steps. An exponential speedup is so massive that it might dwarf such practical hang-ups as, say, excessive noise.

    “Sooner or later, quantum will be faster,” he said.

    See the full article here .


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    Sandia Campus
    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 11:04 am on January 2, 2019 Permalink | Reply
    Tags: , , , , Physicists record “lifetime” of graphene qubits, , Quantum Computing,   

    From MIT News: “Physicists record ‘lifetime’ of graphene qubits” 

    MIT News
    MIT Widget

    From MIT News

    December 31, 2018
    Rob Matheson

    1
    Researchers from MIT and elsewhere have recorded the “temporal coherence” of a graphene qubit — how long it maintains a special state that lets it represent two logical states simultaneously — marking a critical step forward for practical quantum computing. Stock image

    First measurement of its kind could provide stepping stone to practical quantum computing.

    Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit — meaning how long it can maintain a special state that allows it to represent two logical states simultaneously. The demonstration, which used a new kind of graphene-based qubit, represents a critical step forward for practical quantum computing, the researchers say.

    Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1. But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

    The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

    Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks. Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing.

    In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials. These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

    The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

    “Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT. “In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

    There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

    A pristine graphene sandwich

    Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum). In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

    But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

    To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage. These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

    For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches. The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

    When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene. The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

    How voltage helps

    The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip. “Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

    Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

    For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

    But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

    See the full article here .


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