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  • richardmitnick 10:09 am on August 29, 2016 Permalink | Reply
    Tags: , , Quantum Computing   

    From physicsworld.com: “Nonlinear optical quantum-computing scheme makes a comeback” 

    physicsworld
    physicsworld.com

    Aug 29, 2016
    Hamish Johnston

    A debate that has been raging for 20 years about whether a certain interaction between photons can be used in quantum computing has taken a new twist, thanks to two physicists in Canada. The researchers have shown that it should be possible to use “cross-Kerr nonlinearities” to create a cross-phase (CPHASE) quantum gate. Such a gate has two photons as its input and outputs them in an entangled state. CPHASE gates could play an important role in optical quantum computers of the future.

    Photons are very good carriers of quantum bits (qubits) of information because the particles can travel long distances without the information being disrupted by interactions with the environment. But photons are far from ideal qubits when it comes to creating quantum-logic gates because photons so rarely interact with each other.

    One way around this problem is to design quantum computers in which the photons do not interact with each other. Known as “linear optical quantum computing” (LOQC), it usually involves preparing photons in a specific quantum state and then sending them through a series of optical components, such as beam splitters. The result of the quantum computation is derived by measuring certain properties of the photons.

    Simpler quantum computers

    One big downside of LOQC is that you need lots of optical components to perform basic quantum-logic operations – and the number quickly becomes very large to make an integrated quantum computer that can perform useful calculations. In contrast, quantum computers made from logic gates in which photons interact with each other would be much simpler – at least in principle – which is why some physicists are keen on developing them.

    This recent work on cross-Kerr nonlinearities has been carried out by Daniel Brod and Joshua Combes at the Perimeter Institute for Theoretical Physics and Institute for Quantum Computing in Waterloo, Ontario. Brod explains that a cross-Kerr nonlinearity is a “superidealized” interaction between two photons that can be used to create a CPHASE quantum-logic gate.

    This gate takes zero, one or two photons as input. When the input is zero or one photon, the gate does nothing. But when two photons are present, the gate outputs both with a phase shift between them. One important use of such a gate is to entangle photons, which is vital for quantum computing.

    The problem is that there is no known physical system – trapped atoms, for example – that behaves exactly like a cross-Kerr nonlinearity. Physicists have therefore instead looked for systems that are close enough to create a practical CPHASE. Until recently, it looked like no appropriate system would be found. But now Brod and Combes argue that physicists have been too pessimistic about cross-Kerr nonlinearities and have shown that it could be possible to create a CPHASE gate – at least in principle.

    From A to B via an atom

    Their model is a chain of interaction sites through which the two photons propagate in opposite directions. These sites could be pairs of atoms, in which the atoms themselves interact with each other. The idea is that one photon “A” will interact with one of the atoms in a pair, while the other photon “B” interacts with the other atom. Because the two atoms interact with each other, they will mediate an interaction between photons A and B.

    Unlike some previous designs that implemented quantum error correction to protect the integrity of the quantum information, this latest design is “passive” and therefore simpler.

    Brod and Combes reckon that a high-quality CPHASE gate could be made using five such atomic pairs. Brod told physicsworld.com that creating such a gate in the lab would be difficult, but if successful it could replace hundreds of components in a LOQC system.

    As well as pairs of atoms, Brod says that the gate could be built from other interaction sites such as individual three-level atoms or optical cavities. He and Combes are now hoping that experimentalists will be inspired to test their ideas in the lab. Brod points out that measurements on a system with two interaction sites would be enough to show that their design is valid.

    The work is described in Physical Review Letters. Brod and Combes have also teamed-up with Julio Gea-Banacloche of the University of Arkansas to write a related paper that appears in Physical Review A. This second work looks at their design in more detail.

    See the full article here .

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  • richardmitnick 12:35 pm on August 16, 2016 Permalink | Reply
    Tags: , , China launched the world’s first quantum satellite on 16 August, Quantum Computing   

    From Nature: “Chinese satellite is one giant step for the quantum internet” 

    Nature Mag
    Nature

    16 August 2016
    Elizabeth Gibney

    Craft that launched in August is first in a wave of planned quantum space experiments.

    1
    China’s 600-kilogram quantum satellite contains a crystal that produces entangled photons. Cai Yang/Xinhua via ZUMA Wire

    Update: China launched the world’s first quantum satellite on 16 August. The Quantum Experiments at Space Scale (QUESS) satellite, which lifted off from the Jiuquan Satellite Launch Center in northern China at 1:40 a.m. local time, successfully entered orbit at an altitude of 500 kilometres.

    China is poised to launch the world’s first satellite designed to do quantum experiments. A fleet of quantum-enabled craft is likely to follow.

    First up could be more Chinese satellites, which will together create a super-secure communications network, potentially linking people anywhere in the world. But groups from Canada, Japan, Italy and Singapore also have plans for quantum space experiments.

    “Definitely, I think there will be a race,” says Chaoyang Lu, a physicist at the University of Science and Technology of China in Hefei, who works with the team behind the Chinese satellite. The 600-kilogram craft, the latest in a string of Chinese space-science satellites, will launch from Jiuquan Satellite Launch Center in August. The Chinese Academy of Sciences and the Austrian Academy of Sciences are collaborators on the US$100-million mission.

    Quantum communications are secure because any tinkering with them is detectable. Two parties can communicate secretly — by sharing a encryption key encoded in the polarization of a string of photons, say — safe in the knowledge that any eavesdropping would leave its mark.

    So far, scientists have managed to demonstrate quantum communication up to about 300 kilometres. Photons travelling through optical fibres and the air get scattered or absorbed, and amplifying a signal while preserving a photon’s fragile quantum state is extremely difficult. The Chinese researchers hope that transmitting photons through space, where they travel more smoothly, will allow them to communicate over greater distances.

    At the heart of their satellite is a crystal that produces pairs of entangled photons, whose properties remain entwined however far apart they are separated. The craft’s first task will be to fire the partners in these pairs to ground -stations in Beijing and Vienna, and use them to generate a secret key.

    During the two-year mission, the team also plans to perform a statistical measurement known as a Bell test to prove that entanglement can exist between particles separated by a distance of 1,200 kilometres. Although quantum theory predicts that entanglement persists at any distance, a Bell test would prove it.

    The team will also attempt to ‘teleport’ quantum states, using an entangled pair of photons alongside information transmitted by more conventional means to reconstruct the quantum state of a photon in a new location.

    “If the first satellite goes well, China will definitely launch more,” says Lu. About 20 satellites would be required to enable secure communications throughout the world, he adds.

    The teams from outside China are taking a different tack. A collaboration between the National University of Singapore (NUS) and the University of Strathclyde, UK, is using cheap 5-kilogram satellites known as cubesats to do quantum experiments. Last year, the team launched a cubesat that created and measured pairs of ‘correlated’ photons in orbit; next year, it hopes to launch a device that produces fully entangled pairs.

    Costing just $100,000 each, cubesats make space-based quantum communications accessible, says NUS physicist Alexander Ling, who is leading the project.

    A Canadian team proposes to generate pairs of entangled photons on the ground, and then fire some of them to a microsatellite that weighs less than 30 kilograms. This would be cheaper than generating the photons in space, says Brendon Higgins, a physicist at the University of Waterloo, who is part of the Canadian Quantum Encryption and Science Satellite (QEYSSat) team. But delivering the photons to the moving satellite would be a challenge. The team plans to test the system using a photon receiver on an aeroplane first.

    An even simpler approach to quantum space science, pioneered by a team at the University of Padua in Italy led by Paolo Villoresi, involves adding reflectors and other simple equipment to regular satellites. Last year, the team showed that photons bounced back to Earth off an existing satellite maintained their quantum states and were received with low enough error rates for quantum cryptography (G. Vallone et al. Phys. Rev. Lett. 115, 040502; 2015). In principle, the researchers say, the method could be used to generate secret keys, albeit at a slower rate than in more-complex set-ups.

    Researchers have also proposed a quantum experiment aboard the International Space Station (ISS) that would simultaneously entangle the states of two separate properties of a photon — a technique known as hyperentanglement — to make teleportation more reliable and efficient.

    As well as making communications much more secure, these satellite systems would mark a major step towards a ‘quantum internet’ made up of quantum computers around the world, or a quantum computing cloud, says Paul Kwiat, a physicist at the University of Illinois at Urbana–Champaign who is working with NASA on the ISS project.

    The quantum internet is likely to involve a combination of satellite- and ground-based links, says Anton Zeilinger, a physicist at the Austrian Academy of Sciences in Vienna, who argued unsuccessfully for a European quantum satellite before joining forces with the Chinese team. And some challenges remain. Physicists will, for instance, need to find ways for satellites to communicate with each other directly; to perfect the art of entangling photons that come from different sources; and to boost the rate of data transmission using single photons from megabits to gigabits per second.

    If the Chinese team is successful, other groups should find it easier to get funding for quantum satellites, says Zeilinger. The United States has a relatively low profile when it comes to this particular space race, but Zeilinger suggests that it could be doing more work on the topic that is classified.

    Eventually, quantum teleportation in space could even allow researchers to combine photons from satellites to make a distributed telescope with an effective aperture the size of Earth — and enormous resolution. “You could not just see planets,” says Kwiat, “but in principle read licence plates on Jupiter’s moons.”

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 9:22 am on August 5, 2016 Permalink | Reply
    Tags: , , Quantum Computing   

    From Harvard: “New way to model molecules” 

    Harvard University

    Harvard University

    August 4, 2016
    Peter Reuell

    1
    Alan Aspuru-Guzik is among the co-authors of a new study that shows how quantum computers can be used to understand chemistry, a breakthrough that could lead to the development of new materials with unique properties.

    In study, quantum computer simulates their behavior accurately, which can greatly speed up research

    Imagine a future in which hyper-efficient solar panels provide renewable sources of energy, improved water filters quickly remove toxins from drinking water, and the air is scrubbed clean of pollution and greenhouse gases. That could become a reality with the right molecules and materials.

    Scientists from Harvard and Google have taken a major step toward making the search for those molecules easier, demonstrating for the first time that a quantum computer could be used to model the electron interactions in a complex molecule. The work is described in a new paper published in the journal Physical Review X by Professor Alán Aspuru-Guzik from the Department of Chemistry and Chemical Biology and several co-authors.

    “There are a number of applications that a quantum computer would be useful for: cryptography, machine learning, and certain number-theory problems,” Aspuru-Guzik said. “But one that has always been mentioned, even from the first conceptions of a quantum computer, was to use it to simulate matter. In this case, we use it to simulate chemistry.”

    “There are millions or even trillions of possible molecules,” said Jonathan Romero Fontalvo, a Ph.D. student in Aspuru-Guzik’s lab and one of the lead authors of the study. “If you are an experimentalist hoping to find a new molecule for a drug, you need to consider a huge number of possibilities, and you need to synthesize and test them all. That is extremely costly and requires a great deal of time and effort.”

    Classical computers can model simple molecules, but they lack the horsepower needed to model all the possible interactions that take place in more complex molecules.

    A molecule like cholesterol, Aspuru-Guzik said, is all but impossible to model exactly in traditional systems because it would require decades to describe how its electrons interact.

    Though Aspuru-Guzik and colleagues had described an algorithm to model molecules using quantum computers more than a decade ago, quantum computing resources were limited at the time, meaning the team was only able to test certain parts of the algorithm.

    The new study not only marks the first time the entire algorithm has been tested in a scalable manner, but also implements it with a new algorithm, dubbed the variational quantum eigensolver. Even more importantly, Aspuru-Guzik said, both algorithms were implemented in a scalable approach, meaning that while they were tested on a small molecule, they would work equally well on a larger, more complex compound.

    “We were actually able to compare our old algorithm against the new one,” he said. “The machine is so powerful we can do that. And because it’s scalable, the same algorithm we would run against any molecule in this case was run against a small molecule.”

    Using the algorithm, Aspuru-Guzik and colleagues are able to model the electronic structure of a given molecule, and then to “read” that information, giving them precise data about behavior and interactions.

    Armed with that information, he said, researchers can understand whether a molecule will possess the properties desired — whether it will bind to an enzyme or protein, whether it will catalyze certain reactions, and whether a material will possess specific traits.

    “This is arguably the most valuable application for a quantum computer,” he continued. “Commercially, the market for fine chemicals is estimated to be worth $3 trillion. A number of other teams, including researchers at Microsoft and national labs, have made this area a priority.”

    But without quantum computers, Aspuru-Guzik said, that search would amount to little more than a guessing game.

    That is why “I like to call this a disruptive innovation,” he said. “All the methods we have now are approximations, which means if we want to discover a new battery or a better LED, our calculations will sometimes fail. But the change a quantum computer brings is that the answer is exact. Period. That trust will allow us to discover molecules much quicker, make molecules that are much more interesting, and explore chemical spaces significantly faster. When I started at Harvard in 2006, I never imagined that 10 years later we would be at this point.”

    The future is likely to bring hardware advances.

    “We are currently fabricating a new generation of quantum chips that will enable much larger calculations,” said co-author Ryan Babbush, a quantum engineer at Google. “We are optimistic that these chips will be large enough to model small transition metal complexes, which are notoriously difficult for classical computers.”

    The study has implications to other areas of study, such as machine learning.

    “I very much like to think of variational quantum algorithms as a quantum generalization of neural networks,” Google co-author Hartmut Neven said. “Naturally we expect quantum neural networks to be more capable than their classical counterparts in describing quantum systems. An interesting open question is whether they will also prove superior in learning classical data.”

    Harvard’s Office of Technology Development has filed several patent applications relating to the software that drives Aspuru-Guzik’s quantum computing platforms.

    The study was funded by the Luis W. Alvarez Postdoctoral Fellowship in Computing Sciences at Lawrence Berkeley National Laboratory, the Air Force Office of Scientific Research, the Army Research Office, the Office of Naval Research, and the National Science Foundation.

    See the full article here .

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

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

     
  • richardmitnick 8:26 am on July 28, 2016 Permalink | Reply
    Tags: , Quantum Computing,   

    From SA: “Chinese Satellite Is One Giant Step for the Quantum Internet” 

    Scientific American

    Scientific American

    July 27, 2016
    Elizabeth Gibney

    1
    At the heart of their satellite is a crystal that produces pairs of entangled photons, whose properties remain entwined however far apart they are separated. Credit: Vasiliy Yakobchuk/Thinkstock (MARS)

    China is poised to launch the world’s first satellite designed to do quantum experiments. A fleet of quantum-enabled craft is likely to follow.

    First up could be more Chinese satellites, which will together create a super-secure communications network, potentially linking people anywhere in the world. But groups from Canada, Japan, Italy and Singapore also have plans for quantum space experiments.

    “Definitely, I think there will be a race,” says Chaoyang Lu, a physicist at the -University of Science and Technology of China in Hefei, who works with the team behind the Chinese satellite. The 600-kilogram craft, the latest in a string of Chinese space-science satellites, will launch from Jiuquan Satellite Launch Center in August. The Chinese Academy of Sciences and the Austrian Academy of Sciences are collaborators on the $100-million mission.

    Quantum communications are secure because any tinkering with them is detectable. Two parties can communicate secretly — by sharing a encryption key encoded in the polarization of a string of photons, say — safe in the knowledge that any eavesdropping would leave its mark.

    So far, scientists have managed to demonstrate quantum communication up to about 300 kilometers. Photons travelling through optical fibers and the air get scattered or absorbed, and amplifying a signal while preserving a photon’s fragile quantum state is extremely difficult. The Chinese researchers hope that transmitting photons through space, where they travel more smoothly, will allow them to communicate over greater distances.

    At the heart of their satellite is a crystal that produces pairs of entangled photons, whose properties remain entwined however far apart they are separated. The craft’s first task will be to fire the partners in these pairs to ground -stations in Beijing and Vienna, and use them to generate a secret key.

    During the two-year mission, the team also plans to perform a statistical measurement known as a Bell test to prove that entanglement can exist between particles separated by a distance of 1,200 kilometers. Although quantum theory predicts that entanglement persists at any distance, a Bell test would prove it.

    The team will also attempt to ‘teleport’ quantum states, using an entangled pair of photons alongside information transmitted by more conventional means to reconstruct the quantum state of a photon in a new location.

    “If the first satellite goes well, China will definitely launch more,” says Lu. About 20 satellites would be required to enable secure communications throughout the world, he adds.

    The teams from outside China are taking a different tack. A collaboration between the National University of Singapore (NUS) and the University of Strathclyde, UK, is using cheap 5-kilogram satellites known as cubesats to do quantum experiments. Last year, the team launched a cubesat that created and measured pairs of ‘correlated’ photons in orbit; next year, it hopes to launch a device that produces fully entangled pairs.

    Costing just $100,000 each, cubesats make space-based quantum communications accessible, says NUS physicist Alexander Ling, who is leading the project.

    A Canadian team proposes to generate pairs of entangled photons on the ground, and then fire some of them to a microsatellite that weighs less than 30 kilograms. This would be cheaper than generating the photons in space, says Brendon Higgins, a physicist at the University of Waterloo, who is part of the Canadian Quantum Encryption and Science Satellite (QEYSSat) team. But delivering the photons to the moving satellite would be a challenge. The team plans to test the system using a photon receiver on an aeroplane first.

    An even simpler approach to quantum space science, pioneered by a team at the University of Padua in Italy led by Paolo Villoresi, involves adding reflectors and other simple equipment to regular satellites. Last year, the team showed that photons bounced back to Earth off an existing satellite maintained their quantum states and were received with low enough error rates for quantum cryptography (G. Vallone et al. Phys. Rev. Lett. 115, 040502; 2015). In principle, the researchers say, the method could be used to generate secret keys, albeit at a slower rate than in more-complex set-ups.

    Researchers have also proposed a quantum experiment aboard the International Space Station (ISS) that would simultaneously -entangle the states of two separate properties of a photon — a technique known as hyperentanglement — to make teleportation more reliable and efficient.

    As well as making communications much more secure, these satellite systems would mark a major step towards a ‘quantum internet’ made up of quantum computers around the world, or a quantum computing cloud, says Paul Kwiat, a physicist at the University of Illinois at Urbana–Champaign who is working with NASA on the ISS project.

    The quantum internet is likely to involve a combination of satellite- and ground-based links, says Anton Zeilinger, a physicist at the Austrian Academy of Sciences in Vienna, who argued unsuccessfully for a European quantum satellite before joining forces with the Chinese team. And some challenges remain. Physicists will, for instance, need to find ways for satellites to communicate with each other directly; to perfect the art of entangling photons that come from different sources; and to boost the rate of data transmission using single photons from megabits to gigabits per second.

    If the Chinese team is successful, other groups should find it easier to get funding for quantum satellites, says Zeilinger. The United States has a relatively low profile when it comes to this particular space race, but Zeilinger suggests that it could be doing more work on the topic that is classified.

    Eventually, quantum teleportation in space could even allow researchers to combine photons from satellites to make a distributed telescope with an effective aperture the size of Earth — and enormous resolution. “You could not just see planets,” says Kwiat, “but in principle read licence plates on Jupiter’s moons.”

    See the full article here .

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

     
  • richardmitnick 8:03 pm on July 24, 2016 Permalink | Reply
    Tags: , , Quantum Computing,   

    From Science Alert: “Google’s quantum computer just accurately simulated a molecule for the first time” 

    ScienceAlert

    Science Alert

    22 JUL 2016
    DAVID NIELD

    1

    It’s a quantum world, we’re just living in it.

    Google’s engineers just achieved a milestone in quantum computing: they’ve produced the first completely scalable quantum simulation of a hydrogen molecule.

    That’s big news, because it shows similar devices could help us unlock the quantum secrets hidden in the chemistry that surrounds us.

    Researchers working with the Google team were able to accurately simulate the energy of hydrogen H2 molecules, and if we can repeat the trick for other molecules, we could see the benefits in everything from solar cells to medicines.

    These types of predictions are often impossible for ‘classical’ computers or take an extremely long time – working out the energy of something like a propane (C3H8) molecule would take a supercomputer in the region of 10 days.

    To achieve the feat, Google’s engineers teamed up with researchers from Harvard University, Lawrence Berkeley National Labs, UC Santa Barbara, Tufts University, and University College London in the UK.

    “While the energies of molecular hydrogen can be computed classically (albeit inefficiently), as one scales up quantum hardware it becomes possible to simulate even larger chemical systems, including classically intractable ones,” writes Google Quantum Software Engineer Ryan Babbush.

    Chemical reactions are quantum in nature, because they form highly entangled quantum superposition states. In other words, each particle’s state can’t be described independently of the others, and that causes problems for computers used to dealing in binary values of 1s and 0s.

    Enter Google’s universal quantum computer, which deals in qubits – bits that themselves can be in a state of superposition, representing both 1 and 0 at the same time.

    To run the simulation, the engineers used a supercooled quantum computing circuit called a variational quantum eigensolver (VQE) – essentially a highly advanced modelling system that attempts to mimic our brain’s own neural networks on a quantum level.

    2
    Credit: Google

    When the results of the VQE were compared against the actual released energy of the hydrogen molecule, the curves matched almost exactly, as you can see in the graph above.

    Babbush explains that going from qualitative and descriptive chemistry simulations to quantitative and predictive ones “could modernise the field so dramatically that the examples imaginable today are just the tip of the iceberg”.

    We’re dealing with the very first steps of modelling reality, and Google says we could start to see applications in all kinds of systems involving chemistry: improved batteries, flexible electronics, new types of materials, and more.

    One potential use is modelling the way bacteria produce fertiliser. The way humans produce fertiliser is extremely inefficient in terms of the environment, and costs 1-2 percent of the world’s energy per year – so any improvements in understanding the chemical reactions involved could produce massive gains.

    It’s still early days though, and while we’ve described Google’s hardware as a quantum computer for simplicity’s sake, there’s still an ongoing debate over whether we’ve cracked the quantum computing code just yet.

    Some say Google’s machine is still a prototype, part-quantum computer rather than the real deal. But while the scientists discuss the ins and outs of that argument, at least we’re starting to reap the benefits of the technology – and can look forward to a near future where computing power is almost unimaginable.

    The findings are published in Physical Review X.

    See the full article here .

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  • richardmitnick 10:52 am on July 13, 2016 Permalink | Reply
    Tags: Quantum Computing, ,   

    From UC Santa Barbara- “Entanglement : Chaos” 

    UC Santa Barbara Name bloc

    July 11, 2016
    Sonia Fernandez

    1
    A quantum qubit array. Photo Credit: Michael Fang/Martinis Lab

    2
    Experimental link between quantum entanglement (left) and classical chaos (right) found using a small quantum computer. Photo Credit: Courtesy Image

    3
    The Google and UCSB researchers, from left to right: Jimmy Chen, John Martinis, Pedram Roushan, Yu Chen, Anthony Megrant and Charles Neill. Photo Credit: Sonia Fernandez

    Using a small quantum system consisting of three superconducting qubits, researchers at UC Santa Barbara and Google have uncovered a link between aspects of classical and quantum physics thought to be unrelated: classical chaos and quantum entanglement. Their findings suggest that it would be possible to use controllable quantum systems to investigate certain fundamental aspects of nature.

    “It’s kind of surprising because chaos is this totally classical concept — there’s no idea of chaos in a quantum system,” Charles Neill, a researcher in the UCSB Department of Physics and lead author of a paper that appears in Nature Physics. “Similarly, there’s no concept of entanglement within classical systems. And yet it turns out that chaos and entanglement are really very strongly and clearly related.”

    Initiated in the 15th century, classical physics generally examines and describes systems larger than atoms and molecules. It consists of hundreds of years’ worth of study including Newton’s laws of motion, electrodynamics, relativity, thermodynamics as well as chaos theory — the field that studies the behavior of highly sensitive and unpredictable systems. One classic example of a chaotic system is the weather, in which a relatively small change in one part of the system is enough to foil predictions — and vacation plans — anywhere on the globe.

    At smaller size and length scales in nature, however, such as those involving atoms and photons and their behaviors, classical physics falls short. In the early 20th century quantum physics emerged, with its seemingly counterintuitive and sometimes controversial science, including the notions of superposition (the theory that a particle can be located in several places at once) and entanglement (particles that are deeply linked behave as such despite physical distance from one another).

    And so began the continuing search for connections between the two fields.

    All systems are fundamentally quantum systems, according Neill, but the means of describing in a quantum sense the chaotic behavior of, say, air molecules in an evacuated room, remains limited.

    Imagine taking a balloon full of air molecules, somehow tagging them so you could see them and then releasing them into a room with no air molecules, noted co-author and UCSB/Google researcher Pedram Roushan. One possible outcome is that the air molecules remain clumped together in a little cloud following the same trajectory around the room. And yet, he continued, as we can probably intuit, the molecules will more likely take off in a variety of velocities and directions, bouncing off walls and interacting with each other, resting after the room is sufficiently saturated with them.

    “The underlying physics is chaos, essentially,” he said. The molecules coming to rest — at least on the macroscopic level — is the result of thermalization, or of reaching equilibrium after they have achieved uniform saturation within the system. But in the infinitesimal world of quantum physics, there is still little to describe that behavior. The mathematics of quantum mechanics, Roushan said, do not allow for the chaos described by Newtonian laws of motion.

    To investigate, the researchers devised an experiment using three quantum bits, the basic computational units of the quantum computer. Unlike classical computer bits, which utilize a binary system of two possible states (e.g., zero/one), a qubit can also use a superposition of both states (zero and one) as a single state. Additionally, multiple qubits can entangle, or link so closely that their measurements will automatically correlate. By manipulating these qubits with electronic pulses, Neill caused them to interact, rotate and evolve in the quantum analog of a highly sensitive classical system.

    The result is a map of entanglement entropy of a qubit that, over time, comes to strongly resemble that of classical dynamics — the regions of entanglement in the quantum map resemble the regions of chaos on the classical map. The islands of low entanglement in the quantum map are located in the places of low chaos on the classical map.

    “There’s a very clear connection between entanglement and chaos in these two pictures,” said Neill. “And, it turns out that thermalization is the thing that connects chaos and entanglement. It turns out that they are actually the driving forces behind thermalization.

    “What we realize is that in almost any quantum system, including on quantum computers, if you just let it evolve and you start to study what happens as a function of time, it’s going to thermalize,” added Neill, referring to the quantum-level equilibration. “And this really ties together the intuition between classical thermalization and chaos and how it occurs in quantum systems that entangle.”

    The study’s findings have fundamental implications for quantum computing. At the level of three qubits, the computation is relatively simple, said Roushan, but as researchers push to build increasingly sophisticated and powerful quantum computers that incorporate more qubits to study highly complex problems that are beyond the ability of classical computing — such as those in the realms of machine learning, artificial intelligence, fluid dynamics or chemistry — a quantum processor optimized for such calculations will be a very powerful tool.

    “It means we can study things that are completely impossible to study right now, once we get to bigger systems,” said Neill.

    See the full article here .

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

     
  • richardmitnick 12:19 pm on July 8, 2016 Permalink | Reply
    Tags: , , Quantum Computing   

    From Penn State: “New, better way to build circuits for world’s first useful quantum computers” 

    Penn State Bloc

    Pennsylvania State University

    June 25, 2016
    Barbara K. Kennedy

    1
    The research team led by David Weiss at Penn State University performed a specific single quantum operation on individual atoms in a P-S-U pattern on three separate planes stacked within a cube-shaped arrangement. The team then used light beams to selectively sweep away all the atoms that were not targeted for that operation. The scientists then made pictures of the results by successively focusing on each of the planes in the cube. The photos, which are the sum of 20 implementations of this process, show bright spots where the atoms are in focus, and fuzzy spots if they are out of focus in an adjacent plane — as is the case for all the light in the two empty planes. The photos also show both the success of the technique and the comparatively small number of targeting errors.
    Image: David Weiss lab, Penn State University

    The era of quantum computers is one step closer as a result of research published in the current issue of the journal Science. The research team has devised and demonstrated a new way to pack a lot more quantum computing power into a much smaller space and with much greater control than ever before. The research advance, using a 3-dimensional array of atoms in quantum states called quantum bits — or qubits — was made by David S. Weiss, professor of physics at Penn State University, and three students on his lab team. He said, “Our result is one of the many important developments that still are needed on the way to achieving quantum computers that will be useful for doing computations that are impossible to do today, with applications in cryptography for electronic data security and other computing-intensive fields.”

    The new technique uses both laser light and microwaves to precisely control the switching of selected individual qubits from one quantum state to another without altering the states of the other atoms in the cubic array. The new technique demonstrates the potential use of atoms as the building blocks of circuits in future quantum computers.

    The scientists invented an innovative way to arrange and precisely control the qubits, which are necessary for doing calculations in a quantum computer. “Our paper demonstrates that this novel approach is a precise, accurate, and efficient way to control large ensembles of qubits for quantum computing,” Weiss said.

    The paper in Science [no link provided] describes the new technique, which Weiss’s team plans to continue developing further. The achievement also is expected to be useful to scientists pursuing other approaches to building a quantum computer, including those based on other atoms, on ions, or on atom-like systems in 1 or 2 dimensions. “If this technique is adopted in those other geometries, they would also get this robustness,” Weiss said.

    To corral their quantum atoms into an orderly 3-D pattern for their experiments, the team constructed a lattice made by beams of light to trap and hold the atoms in a cubic arrangement of five stacked planes — like a sandwich made with five slices of bread — each with room for 25 equally spaced atoms. The arrangement forms a cube with an orderly pattern of individual locations for 125 atoms. The scientists filled some of the possible locations with qubits consisting of neutral cesium atoms — those without a positive or a negative charge. Unlike the bits in a classical computer, which typically are either zeros or ones, each of the qubits in the Weiss team’s experiment has the difficult-to-imagine ability to be in more than one state at the same time — a central feature of quantum mechanics called quantum superposition.

    Weiss and his team then use another kind of light tool — crossed beams of laser light — to target individual atoms in the lattice. The focus of these two laser beams, called “addressing” beams, on a targeted atom shifts some of that atom’s energy levels by about twice as much as it does for those of any of the other atoms in the array, including those that were in the path of one of the addressing beams on its way to the target. When the scientists then bathe the whole array with a uniform wash of microwaves, the state of the atom with the shifted energy levels is changed, while the states of all the other atoms are not.

    “We have set more qubits into different, precise quantum superpositions at the same time than in any previous experimental system,” Weiss said. The scientists also designed their system to be very insensitive to the exact details of the alignments or the power of those light beams they use — which Weiss said is a good thing because “you don’t want to be dependent upon exactly what the intensity of the light is or exactly what the alignment is.”

    One of the ways that the scientists demonstrated their ability to change the quantum state of individual atoms was by changing the states of selected atoms in three of the stacked planes within the cubic array in order to draw the letters P, S, and U — the letters that represent Penn State University. “We changed the quantum superposition of the PSU atoms to be different from the quantum superposition of the other atoms in the array,” Weiss said. “We have a pretty high-fidelity system. We can do targeted selections with a reliability of about 99.7%, and we have a plan for making that more like 99.99%.”

    Among the goals that Weiss has for his team’s future research is to get the qubits to “have entangled quantum wave functions where the state of one particle is implicitly correlated with the state of the other particles around it.” Weiss said that this entangled connection between qubits is a critical element needed for quantum computing. He said he hopes that building on the techniques demonstrated in his team’s prototype system eventually will enable his lab to demonstrate high-quality entangling operations for quantum computing. “Filling the cube with exactly one atom per site and setting up entanglements between atoms at any of the sites that we choose are among our nearer-term research goals,” Weiss said.

    In addition to Weiss, the other members of the Penn State research team are Yang Wang, Aishwarya Kumar, and Tsung-Yao Wu, all graduate students. The research was funded by the U.S. National Science Foundation.

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  • richardmitnick 8:41 am on June 28, 2016 Permalink | Reply
    Tags: , , Quantum Computing   

    From livescience: “Quantum Computer Could Simulate Beginnings of the Universe” 

    Livescience

    June 27, 2016
    Charles Q. Choi

    1
    Researchers simulated the creation of elementary particle pairs out of the vacuum by using a quantum computer.
    Credit: IQOQI/Harald Ritsch

    Quantum mechanics suggest that seemingly empty space is actually filled with ghostly particles that are fluctuating in and out of existence. And now, scientists have for the first time made an advanced machine known as a quantum computer simulate these so-called virtual particles.

    This research could help shed light on currently hidden aspects of the universe, from the hearts of neutron stars to the very first moments of the universe after the Big Bang, researchers said.

    Quantum mechanics suggests that the universe is a fuzzy, surreal place at its smallest levels. For instance, atoms and other particles can exist in states of flux known as superpositions, where they can seemingly each spin in opposite directions simultaneously, and they can also get entangled — meaning they can influence each other instantaneously no matter how far apart they are separated. Quantum mechanics also suggests that pairs of virtual particles, each consisting of a particle and its antiparticle, can wink in and out of seemingly empty vacuum and influence their surroundings.

    Quantum mechanics underlies the standard model of particle physics, which is currently the best explanation for how all the known elementary particles, such as electrons and protons, behave.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    However, there are still many open questions regarding the standard model of particle physics, such as whether or not it can help explain cosmic mysteries such as dark matter and dark energy — both of which have not been directly detected by astronomers, but are inferred based on their gravitational effects.

    The interactions between elementary particles are often described with what is known as gauge theories. However, the real-time dynamics of particles in gauge theories are extremely difficult for conventional computers to compute, except in the simplest of cases. As a result, scientists have instead turned to experimental devices known as quantum computers.

    “Our work is a first step towards developing dedicated tools that can help us to gain a better understanding of the fundamental interactions between the elementary constituents in nature,” study co-lead author Christine Muschik told Live Science. Muschik is a theoretical physicist at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Innsbruck, Austria.

    Whereas classical computers represent data as ones and zeroes — binary digits known as “bits,” symbolized by flicking switch-like transistors either on or off — quantum computers use quantum bits, or qubits, that are in superpositions — meaning that they are on and off at the same time. This enables a qubit to carry out two calculations simultaneously. In principle, quantum computers could work much faster than regular computers at solving certain problems because the quantum machines can analyze every possible solution at once.

    In their new study, scientists built a quantum computer using four electromagnetically trapped calcium ions. They controlled and manipulated these four qubits with laser pulses.

    The researchers had their quantum computer simulate the appearance and disappearance of virtual particles in a vacuum, with pairs of qubits representing pairs of virtual particles — specifically, electrons and positrons, the positively charged antimatter counterparts of electrons. Laser pulses helped simulate how powerful electromagnetic fields in a vacuum can generate virtual particles, the scientists said.

    “This is one of the most complex experiments that has ever been carried out in a trapped-ion quantum computer,” study co-author Rainer Blatt, an experimental physicist at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Innsbruck, Austria, said in a statement.

    This work shows that quantum computers can simulate high-energy physics — showing how particles might behave at energy levels that are much too high to be easily generated on Earth. “The field of experimental quantum computing is growing very fast, and many people ask the question, What is a small-scale quantum computer good for?” study co-lead author Esteban Martinez, an experimental physicist at the University of Innsbruck in Austria, told Live Science. “Unlike other applications, you don’t need millions of quantum bits to do these simulations — tens might be enough to tackle problems that we cannot yet attack using classical approaches.”

    The problem the researchers had their quantum simulator analyze was simple enough for classical computers to compute, which showed that the quantum simulator’s results matched predictions with great accuracy. This suggests that quantum simulators could be used on more complex gauge-theory problems in the future, and the machines could even see new phenomena.

    “Our proof-of-principle experiment represents a first step toward the long-term goal of developing future generations of quantum simulators that will be able to address questions that cannot be answered otherwise,” Muschik said.

    In principle, desktop quantum simulators could help model the kind of extraordinarily high-energy physics currently studied using expensive atom smashers, such as the Large Hadron Collider at CERN.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    “These two approaches complement one another perfectly,” study co-author Peter Zoller, a theoretical physicist at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Innsbruck, said in a statement. “We cannot replace the experiments that are done with particle colliders. However, by developing quantum simulators, we may be able to understand these experiments better one day.”

    “Moreover, we can study new processes by using quantum simulation — for example, in our experiment, we also investigated particle entanglement produced during pair creation, which is not possible in a particle collider,” Blatt said in a statement.

    Ultimately, quantum simulators may help researchers simulate the dynamics within the dead stars known as neutron stars, or investigate “questions relating to interactions at very high energies and high densities describing early-universe physics,” Muschik said.

    The scientists detailed their findings in the June 23 issue of the journal Nature.

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  • richardmitnick 9:46 am on June 26, 2016 Permalink | Reply
    Tags: , Quantum Computing,   

    From Science Alert: “Physicists just used a quantum computer to simulate antimatter creation” 

    ScienceAlert

    Science Alert

    24 JUN 2016
    BEC CREW

    1
    A quantum trap. Credit: Institut für Experimentalphysik

    For the first time, physicists have used a primitive quantum computer to simulate the spontaneous creation of particle-antiparticle pairs.

    This marks the first full simulation of a high-energy physics experiment – something that our current computers are incapable of running – and could give physicists the opportunity to investigate how quarks bind together into protons and neutrons, and how these fundamental particles of the Universe form atomic nuclei.

    Quantum computers are set to revolutionise computing in the future, because they’re not limited to the 1s and 0s of binary code bits, used in the computers of today. Instead, quantum computers use qubits, which can essentially each take the state of 0, 1, or a ‘superposition’ of the two.

    So rather than having bits that can only be 1 or 0 at any given moment, qubits can be anything and everything. This means they can perform many calculations simultaneously, giving them the potential for unprecedented processing power.

    How unprecedented? Well, Google’s D-Wave 2 ‘quantum computer’ is 100 million times faster than your laptop, and many physicists argue that it’s not even a proper quantum computer.

    As Mary-Ann Russon reports for the International Business Times, back in 2014, an international team of computer scientists published a paper in Science showing that the D-Wave 2 failed certain benchmark tests, which means it was faster than regular computers in some tests, but actually slower in others.

    The D-Wave 2 now works with twice as many qubits, but no one has been able to independently verify its quantum behaviour.

    But there are tried-and-tested quantum computers out there – they’re just really primitive. To simulate antimatter creation, a team of Austrian physicists used one that traps four calcium ions in a row with powerful electromagnetic fields, turning them into qubits floating in a vacuum.

    When strategically placed laser pulses were fired at the qubits, the resulting quantum fluctuations in energy allowed the researchers to mathematically calculate if that energy had been converted into matter, creating electron particles and their antiparticles partners, positrons.

    “They manipulated the ions’ spins – their magnetic orientations – using laser beams,” Davide Castelvecchi reports for Nature. “This coaxed the ions to perform logic operations, the basic steps in any computer calculation.”

    The team ran several sequences of 100 steps – each taking no more than a few milliseconds to complete, and then observed the state of the ions using a digital camera. They could tell by the location and the orientation of the ions if the process had created a particle or antiparticle in that spot.

    The experiment was a pretty simple one, performed on a really primitive quantum computer, “but their calculations confirmed the predictions of a simplified version of quantum electrodynamics, the established theory of the electromagnetic force”, says Castelvecchi.

    If this could be scaled up, it would allow physicists to test the outcomes predicted in theoretical physics like never before.

    “The stronger the field, the faster we can create particles and antiparticles,” one of the team, Esteban Martinez from the University of Innsbruck, told Nature.

    The only problem? Scaling quantum computers up is complicated as hell, and while Google’s D-Wave 2 is now claimed to have over 1,000 qubits working inside, critics still can’t agree on if its behaviour is truly quantum at all.

    But with experiments like this, we’re finally catching a glimpse of what science might be like with full-blown quantum computers in our corner, so hopefully that will give scientists the push they need to figure this one out.

    The research has been published in Nature.


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  • richardmitnick 12:31 pm on June 9, 2016 Permalink | Reply
    Tags: , Google Moves Closer to a Universal Quantum Computer, Quantum Computing,   

    From SA: “Google Moves Closer to a Universal Quantum Computer” 

    Scientific American

    Scientific American

    June 9, 2016
    Philip Ball, Nature Magazine

    1
    Corporate headquarters complex of Google in Mountain View, California. Credit: Brooks Kraft LLC/Corbis via Getty Images

    For 30 years, researchers have pursued the universal quantum computer, a device that could solve any computational problem, with varying degrees of success. Now, a team in California and Spain has made an experimental prototype of such a device that can solve a wide range of problems in fields such as chemistry and physics, and has the potential to be scaled up to larger systems.

    Both IBM and a Canadian company called D-Wave have created functioning quantum computers using different approaches. But their devices are not easily scalable to the many quantum bits (qubits) needed for solving problems that classical computers cannot.

    Computer scientists at Google’s research laboratories in Santa Barbara, California, and physicists at the University of California at Santa Barbara and the University of the Basque Country in Bilbao, Spain, describe their new device online in Nature.

    “It’s terrific work in many respects, and is filled with valuable lessons for the quantum computing community,” says Daniel Lidar, a quantum-computing expert at the University of Southern California in Los Angeles.

    The Google prototype combines the two main approaches to quantum computing. One approach constructs the computer’s digital circuits using qubits in particular arrangements geared to solve a specific problem. This is analogous to a tailor-made digital circuit in a conventional microprocessor made from classical bits.

    Much of quantum computing theory is based on this approach, which includes methods for correcting errors that might otherwise derail a calculation. So far, practical implementations have been possible only with a handful of qubits.

    Analog approach

    The other approach is called adiabatic quantum computing (AQC). Here, the computer encodes a given problem in the states of a group of qubits, gradually evolving and adjusting the interactions between them to “shape” their collective quantum state and reach a solution. In principle, just about any problem can be encoded into the same group of qubits.

    This analog approach is limited by the effects of random noise, which introduces errors that cannot be corrected as systematically as in digital circuits. And there’s no guarantee that this method can solve every problem efficiently, says computer scientist Rami Barends, a member of the Google team.

    Yet only AQC has furnished the first commercial devices — made by D-Wave in Burnaby, British Columbia — which sell for about $15 million apiece. Google owns a D-Wave device, but Barends and colleagues think that there’s a better way to do AQC.

    In particular, they want to find some way to implement error correction. Without it, scaling up AQC will be difficult, because errors accumulate more quickly in larger systems. The team thinks the first step to achieving that is to combine the AQC method with the digital approach’s error-correction capabilities.

    Virtual chemistry

    To do that, the Google team uses a row of nine solid-state qubits, fashioned from cross-shaped films of aluminium about 400 micrometers from tip to tip. These are deposited onto a sapphire surface. The researchers cool the aluminium to 0.02 degrees kelvin, turning the metal into a superconductor with no electrical resistance. Information can then be encoded into the qubits in their superconducting state.

    The interactions between neighboring qubits are controlled by ‘logic gates’ that steer the qubits digitally into a state that encodes the solution to a problem. As a demonstration, the researchers instructed their array to simulate a row of magnetic atoms with coupled spin states — a problem thoroughly explored in condensed-matter physics. They could then look at the qubits to determine the lowest-energy collective state of the spins that the atoms represented.

    This is a fairly simple problem for a classical computer to solve. But the new Google device can also handle so-called ‘non-stoquastic’ problems, which classical computers cannot. These include simulations of the interactions between many electrons, which are needed for accurate computer simulations in chemistry. The ability to simulate molecules and materials at the quantum level could be one of the most valuable applications of quantum computing.

    This new approach should enable a computer with quantum error correction, says Lidar. Although the researchers did not demonstrate that here, the team has previously shown how that might be achieved on its nine-qubit device.

    “With error correction, our approach becomes a general-purpose algorithm that is, in principle, scalable to an arbitrarily large quantum computer,” says Alireza Shabani, another member of the Google team.

    The Google device is still very much a prototype. But Lidar says that in a couple of years, devices with more than 40 qubits could become a reality.

    “At that point,” he says, “it will become possible to simulate quantum dynamics that is inaccessible on classical hardware, which will mark the advent of ‘quantum supremacy’.”

    See the full article here .

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

     
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