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  • richardmitnick 8:20 am on October 17, 2014 Permalink | Reply
    Tags: , , Quantum Computing,   

    From MIT: “Superconducting circuits, simplified” 


    MIT News

    October 17, 2014
    Larry Hardesty | MIT News Office

    Computer chips with superconducting circuits — circuits with zero electrical resistance — would be 50 to 100 times as energy-efficient as today’s chips, an attractive trait given the increasing power consumption of the massive data centers that power the Internet’s most popular sites.

    chip
    Shown here is a square-centimeter chip containing the nTron adder, which performed the first computation using the researchers’ new superconducting circuit. Photo: Adam N. McCaughan

    Superconducting chips also promise greater processing power: Superconducting circuits that use so-called Josephson junctions have been clocked at 770 gigahertz, or 500 times the speed of the chip in the iPhone 6.

    But Josephson-junction chips are big and hard to make; most problematic of all, they use such minute currents that the results of their computations are difficult to detect. For the most part, they’ve been relegated to a few custom-engineered signal-detection applications.

    In the latest issue of the journal Nano Letters, MIT researchers present a new circuit design that could make simple superconducting devices much cheaper to manufacture. And while the circuits’ speed probably wouldn’t top that of today’s chips, they could solve the problem of reading out the results of calculations performed with Josephson junctions.

    The MIT researchers — Adam McCaughan, a graduate student in electrical engineering, and his advisor, professor of electrical engineering and computer science Karl Berggren — call their device the nanocryotron, after the cryotron, an experimental computing circuit developed in the 1950s by MIT professor Dudley Buck. The cryotron was briefly the object of a great deal of interest — and federal funding — as the possible basis for a new generation of computers, but it was eclipsed by the integrated circuit.

    “The superconducting-electronics community has seen a lot of devices come and go, without any real-world application,” McCaughan says. “But in our paper, we have already applied our device to applications that will be highly relevant to future work in superconducting computing and quantum communications.”

    Superconducting circuits are used in light detectors that can register the arrival of a single light particle, or photon; that’s one of the applications in which the researchers tested the nanocryotron. McCaughan also wired together several of the circuits to produce a fundamental digital-arithmetic component called a half-adder.

    Resistance is futile

    Superconductors have no electrical resistance, meaning that electrons can travel through them completely unimpeded. Even the best standard conductors — like the copper wires in phone lines or conventional computer chips — have some resistance; overcoming it requires operational voltages much higher than those that can induce current in a superconductor. Once electrons start moving through an ordinary conductor, they still collide occasionally with its atoms, releasing energy as heat.

    Superconductors are ordinary materials cooled to extremely low temperatures, which damps the vibrations of their atoms, letting electrons zip past without collision. Berggren’s lab focuses on superconducting circuits made from niobium nitride, which has the relatively high operating temperature of 16 Kelvin, or minus 257 degrees Celsius. That’s achievable with liquid helium, which, in a superconducting chip, would probably circulate through a system of pipes inside an insulated housing, like Freon in a refrigerator.

    A liquid-helium cooling system would of course increase the power consumption of a superconducting chip. But given that the starting point is about 1 percent of the energy required by a conventional chip, the savings could still be enormous. Moreover, superconducting computation would let data centers dispense with the cooling systems they currently use to keep their banks of servers from overheating.

    Cheap superconducting circuits could also make it much more cost-effective to build single-photon detectors, an essential component of any information system that exploits the computational speedups promised by quantum computing.

    Engineered to a T

    The nanocryotron — or nTron — consists of a single layer of niobium nitride deposited on an insulator in a pattern that looks roughly like a capital “T.” But where the base of the T joins the crossbar, it tapers to only about one-tenth its width. Electrons sailing unimpeded through the base of the T are suddenly crushed together, producing heat, which radiates out into the crossbar and destroys the niobium nitride’s superconductivity.

    A current applied to the base of the T can thus turn off a current flowing through the crossbar. That makes the circuit a switch, the basic component of a digital computer.

    After the current in the base is turned off, the current in the crossbar will resume only after the junction cools back down. Since the superconductor is cooled by liquid helium, that doesn’t take long. But the circuits are unlikely to top the 1 gigahertz typical of today’s chips. Still, they could be useful for some lower-end applications where speed isn’t as important as energy efficiency.

    Their most promising application, however, could be in making calculations performed by Josephson junctions accessible to the outside world. Josephson junctions use tiny currents that until now have required sensitive lab equipment to detect. They’re not strong enough to move data to a local memory chip, let alone to send a visual signal to a computer monitor.

    In experiments, McCaughan demonstrated that currents even smaller than those found in Josephson-junction devices were adequate to switch the nTron from a conductive to a nonconductive state. And while the current in the base of the T can be small, the current passing through the crossbar could be much larger — large enough to carry information to other devices on a computer motherboard.

    “I think this is a great device,” says Oleg Mukhanov, chief technology officer of Hypres, a superconducting-electronics company whose products rely on Josephson junctions. “We are currently looking very seriously at the nTron for use in memory.”

    “There are several attractions of this device,” Mukhanov says. “First, it’s very compact, because after all, it’s a nanowire. One of the problems with Josephson junctions is that they are big. If you compare them with CMOS transistors, they’re just physically bigger. The second is that Josephson junctions are two-terminal devices. Semiconductor transistors are three-terminal, and that’s a big advantage. Similarly, nTrons are three-terminal devices.”

    “As far as memory is concerned,” Mukhanov adds, “one of the features that also attracts us is that we plan to integrate it with magnetoresistive spintronic devices, mRAM, magnetic random-access memories, at room temperature. And one of the features of these devices is that they are high-impedance. They are in the kilo-ohms range, and if you look at Josephson junctions, they are just a few ohms. So there is a big mismatch, which makes it very difficult from an electrical-engineering standpoint to match these two devices. NTrons are nanowire devices, so they’re high-impedance, too. They’re naturally compatible with the magnetoresistive elements.”

    McCaughan and Berggren’s research was funded by the National Science Foundation and by the Director of National Intelligence’s Intelligence Advanced Research Projects Activity.

    See the full article here.

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  • richardmitnick 3:55 pm on October 3, 2014 Permalink | Reply
    Tags: , , , Quantum Computing,   

    From Princeton via Huff Post: “Physicists Observe New Particle That’s Also Its Own ‘Antiparticle'” 

    Princeton University
    Princeton University

    Huffington Post
    10/03/2014
    Macrina Cooper-White

    After decades of searching, physicists at Princeton University say they’ve observed an elusive particle that behaves both like matter and antimatter.

    Yes, the discovery is an exciting step forward for particle physics, but it may also help advance the creation of powerful quantum computers.

    team
    Team not identifed

    In the early 20th century, as quantum theory emerged, scientists predicted that most common particles, like electrons, had mysterious “antimatter” counterparts with the same mass and opposite charge. Scientists even thought that if a particle came in contact with its “antiparticle,” the two would annihilate one another.

    Italian physicist Ettore Majorana first hypothesized in 1937 that one particle — called the “Majorana fermion” — could serve as its very own antimatter particle, and scientists have been searching for that particle ever since.

    iron
    An experiment revealing the atomic structure of an iron wire on a lead surface. The zoomed-in portion of the image depicts the probability of the wire containing the Majorana fermion. The image pinpoints the particle to the end of the wire, which is where it had been predicted to based on years of theoretical calculations.

    For their study, the Princeton researchers designed a simple experiment to observe what they call “emergent particles” which can be found within a material — rather than in the vacuum of a giant collider, where the Higgs boson was discovered.

    “This is more exciting and can actually be practically beneficial,” Ali Yazdani, a physics professor at the university who led the research team, said a written statement, “because it allows scientists to manipulate exotic particles for potential applications, such as quantum computing.”

    The researchers placed a thin, long chain of pure magnetic iron atoms on a superconductor made of lead. Then they cooled the materials to -457 degrees Fahrenheit and peered at them through a two-story-tall scanning-tunneling microscope. Just check out the video above.

    What did the researchers find? An electrically neutral signal at the ends of the iron wires, which is considered to be the “key signature” of the elusive Majorana fermion. The researchers say the fermion’s observed properties make it a good candidate for building quantum bits in computers.

    “One of the first steps in making a quantum computer is to make a quantum bit,” Yazdani said in an email to the Huffington Post, “The ideal quantum bit should [be] one that you can control but it does not interact with its environment, so as to be changed.”

    While other scientists find the study intriguing, many believe further research should be conducted to confirm the results.

    “We should keep in mind possible alternative explanations — even if there are no immediately obvious candidates,” Jason Alicea, a physicist at the California Institute of Technology, who did not participate in this research, told Scientific American.

    The research was published online on Oct. 2 in the journal Science.

    See the full article, with video, here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 7:27 am on September 30, 2014 Permalink | Reply
    Tags: , , Quantum Computing   

    From physicsworld: “Quantum data are compressed for the first time” 

    physicsworld
    physicsworld.com

    Sep 29, 2014
    Jon Cartwright

    A quantum analogue of data compression has been demonstrated for the first time in the lab. Physicists working in Canada and Japan have squeezed quantum information contained in three quantum bits (qubits) into two qubits. The technique could pave the way for a more effective use of quantum memories and offers a new method of testing quantum logic devices.

    image
    Three for two: physicists have compressed quantum data

    Compression of classical data is a simple procedure that allows a string of information to take up less space in a computer’s memory. Given an unadulterated string of, for example, 1000 binary values, a computer could simply record the frequency of the 1s and 0s, which might require just a dozen or so binary values. Recording the information about the order of those 1s and 0s would require a slightly longer string, but it would probably still be shorter than the original sequence.

    Quantum data are rather different, and it is not possible to simply determine the frequencies of 1s and 0s in a string of quantum information. The problem comes down to the peculiar nature of qubits, which, unlike classical bits, can be a 1, a 0 or some “superposition” of both values. A user can indeed perform a measurement to record the “one-ness” of a qubit, but such a measurement would destroy any information about that qubit’s “zero-ness”. What is more, if a user then measures a second qubit prepared in an identical way, he or she might find a different value for its “one-ness” – because qubits do not specify unique values but only the probability of measurement outcomes. This latter trait would seem to preclude the possibility of compressing even identical qubits, because there is no way of predicting what classical values they will ultimately manifest as.

    A way forward

    In 2010 physicists Martin Plesch and Vladimír Bužek of the Slovak Academy of Sciences in Bratislava realized that, while it is not possible to compress quantum data to the same extent as classical data, some compression can be achieved. As long as the quantum nature of a string of identically prepared qubits is preserved, they said, it should be possible to feed them through a circuit that records only their probabilistic natures. Such a recording would require exponentially fewer qubits, and would allow a user to easily store the quantum information in a quantum memory, which is currently a limited resource. Then at some later time, the user could decide what type of measurement to perform on the data.

    “This way you can store the qubits until you know what question you’re interested in,” says Aephraim Steinberg of the University of Toronto. “Then you can measure x if you want to know x; and if you want to know z, you can measure z – whereas if you don’t store the qubits, you have to choose which measurements you want to do right now.”

    Now, Steinberg and his colleagues have demonstrated working quantum compression for the first time with photon qubits. Because photon qubits are currently very difficult to process in quantum logic gates, Steinberg’s group resorted to a technique known as measurement-based quantum computing, in which the outcomes of a logic gate are “built in” to qubits that are prepared and entangled at the same source. The details are complex, but the researchers managed to transfer the probabilistic nature of three qubits into two qubits.

    A nice trick

    Plesch says that this is the first time that compression of quantum data has been realized, and believes Steinberg and colleagues have come up with a “nice trick” to make it work. “This approach is, however, hard to scale to a larger number of qubits,” Plesch adds. “Having said that, I consider the presented work as a very nice proof-of-concept for the future.”

    Steinberg thinks that larger-scale quantum compression might be possible with different types of qubits, such as trapped ions, which have so far proved easier to manage in large ensembles. A practical use for the process would be in testing quantum devices using a process known as quantum tomography, in which many identically prepared qubits are sent through a quantum device to check that it is functioning properly. With quantum compression, says Steinberg, one could perform the tomography experiment and then decide later what aspect of the device you wanted to test.

    But in the meantime, says Steinberg, the demonstration provides another perspective on the strangeness of the quantum world. “If you had a book filled just with ones, you could simply tell your friend that it’s a book filled with ones,” he says. “But quantum mechanically, that’s already not true. Even if I gave you a billion identically prepared photons, you could get different information from each one. To describe their states completely would require infinite classical information.”

    The research will be described in Physical Review Letters.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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  • richardmitnick 4:41 pm on September 20, 2014 Permalink | Reply
    Tags: , , , Quantum Computing, ,   

    From Princeton: “‘Solid’ light could compute previously unsolvable problems” 

    Princeton University
    Princeton University

    Sep 08, 2014
    John Sullivan

    Researchers at Princeton University have begun crystallizing light as part of an effort to answer fundamental questions about the physics of matter.

    The researchers are not shining light through crystal – they are transforming light into crystal. As part of an effort to develop exotic materials such as room-temperature superconductors, the researchers have locked together photons, the basic element of light, so that they become fixed in place.

    “It’s something that we have never seen before,” said Andrew Houck, an associate professor of electrical engineering and one of the researchers. “This is a new behavior for light.”

    The results raise intriguing possibilities for a variety of future materials. But the researchers also intend to use the method to address questions about the fundamental study of matter, a field called condensed matter physics.

    “We are interested in exploring – and ultimately controlling and directing – the flow of energy at the atomic level,” said Hakan Türeci, an assistant professor of electrical engineering and a member of the research team. “The goal is to better understand current materials and processes and to evaluate materials that we cannot yet create.”

    The team’s findings, reported online on Sept. 8 in the journal Physical Review X, are part of an effort to answer fundamental questions about atomic behavior by creating a device that can simulate the behavior of subatomic particles. Such a tool could be an invaluable method for answering questions about atoms and molecules that are not answerable even with today’s most advanced computers.

    light

    In part, that is because current computers operate under the rules of classical mechanics, which is a system that describes the everyday world containing things like bowling balls and planets. But the world of atoms and photons obeys the rules of quantum mechanics, which include a number of strange and very counterintuitive features. One of these odd properties is called “entanglement” in which multiple particles become linked and can affect each other over long distances.

    The difference between the quantum and classical rules limits a standard computer’s ability to efficiently study quantum systems. Because the computer operates under classical rules, it simply cannot grapple with many of the features of the quantum world. Scientists have long believed that a computer based on the rules of quantum mechanics could allow them to crack problems that are currently unsolvable. Such a computer could answer the questions about materials that the Princeton team is pursuing, but building a general-purpose quantum computer has proven to be incredibly difficult and requires further research.

    Another approach, which the Princeton team is taking, is to build a system that directly simulates the desired quantum behavior. Although each machine is limited to a single task, it would allow researchers to answer important questions without having to solve some of the more difficult problems involved in creating a general-purpose quantum computer. In a way, it is like answering questions about airplane design by studying a model airplane in a wind tunnel – solving problems with a physical simulation rather than a digital computer.

    In addition to answering questions about currently existing material, the device also could allow physicists to explore fundamental questions about the behavior of matter by mimicking materials that only exist in physicists’ imaginations.

    To build their machine, the researchers created a structure made of superconducting materials that contains 100 billion atoms engineered to act as a single “artificial atom.” They placed the artificial atom close to a superconducting wire containing photons.

    By the rules of quantum mechanics, the photons on the wire inherit some of the properties of the artificial atom – in a sense linking them. Normally photons do not interact with each other, but in this system the researchers are able to create new behavior in which the photons begin to interact in some ways like particles.

    “We have used this blending together of the photons and the atom to artificially devise strong interactions among the photons,” said Darius Sadri, a postdoctoral researcher and one of the authors. “These interactions then lead to completely new collective behavior for light – akin to the phases of matter, like liquids and crystals, studied in condensed matter physics.”

    Türeci said that scientists have explored the nature of light for centuries; discovering that sometimes light behaves like a wave and other times like a particle. In the lab at Princeton, the researchers have engineered a new behavior.

    “Here we set up a situation where light effectively behaves like a particle in the sense that two photons can interact very strongly,” Türeci said. “In one mode of operation, light sloshes back and forth like a liquid; in the other, it freezes.”

    The current device is relatively small, with only two sites where an artificial atom is paired with a superconducting wire. But the researchers say that by expanding the device and the number of interactions, they can increase their ability to simulate more complex systems – growing from the simulation of a single molecule to that of an entire material. In the future, the team plans to build devices with hundreds of sites with which they hope to observe exotic phases of light such as superfluids and insulators.

    “There is a lot of new physics that can be done even with these small systems,” said James Raftery, a graduate student in electrical engineering and one of the authors. “But as we scale up, we will be able to tackle some really interesting questions.”

    Besides Houck, Türeci, Sadri and Raftery, the research team included Sebastian Schmidt, a senior researcher at the Institute for Theoretical Physics at ETH Zurich, Switzerland. Support for the project was provided by: the Eric and Wendy Schmidt Transformative Technology Fund; the National Science Foundation; the David and Lucile Packard Foundation; the U.S. Army Research Office; and the Swiss National Science Foundation.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 8:30 pm on September 9, 2014 Permalink | Reply
    Tags: , , , Quantum Computing   

    From Kavli: “Tiny Graphene Drum Could Form Future Quantum Memory” 

    KavliFoundation

    The Kavli Foundation

    09/09/2014
    No Writer Credit

    Scientists from TU Delft’s Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential to be used as sensors in devices such as mobile phones. Using their unique mechanical properties, these drums could also act as memory chips in a quantum computer. The researchers present their findings in an article in the August 24th edition of Nature Nanotechnology. The research was funded by the FOM Foundation, the EU Marie-Curie program, and NWO.

    Graphene drums

    drum
    Graphene Drum

    Graphene is famous for its special electrical properties, but research on the one-layer thin graphite was recently expanded to explore graphene as a mechanical object. Thanks to their extreme low mass, tiny sheets of graphene can be used the same was as the drumhead of a musician. In the experiment, scientists use microwave-frequency light to ‘play’ the graphene drums, to listen to its ‘nano sound’, and to explore the way graphene in these drums moves.

    Optomechanics

    Dr. Vibhor Singh and his colleagues did this by using a 2D crystal membrane as a mirror in an ‘optomechanical cavity’. “In optomechanics you use the interference pattern of light to detect tiny changes in the position of an object. In this experiment, we shot microwave photons at a tiny graphene drum. The drum acts as a mirror: by looking at the interference of the microwave photons bouncing off of the drum, we are able to sense minute changes in the position of the graphene sheet of only 17 femtometers, nearly 1/10000th of the diameter of an atom.”, Singh explains.

    Amplifier

    The microwave ‘light’ in the experiment is not only good for detecting the position of the drum, but can also push on the drum with a force. This force from light is extremely small, but the small mass of the graphene sheet and the tiny displacements they can detect mean that the scientist can use these forces to ‘beat the drum’: the scientists can shake the graphene drum with the momentum of light. Using this radiation pressure, they made an amplifier in which microwave signals, such as those in your mobile phone, are amplified by the mechanical motion of the drum.

    Memory

    The scientists also show you can use these drums as ‘memory chips’ for microwave photons, converting photons into mechanical vibrations and storing them for up to 10 milliseconds. Although that is not long by human standards, it is a long time for a computer chip. “One of the long-term goals of the project is explore 2D crystal drums to study quantum motion. If you hit a classical drum with a stick, the drumhead will start oscillating, shaking up and down. With a quantum drum, however, you can not only make the drumhead move up and then down, but also make it into a ‘quantum superposition’, in which the drum head is both moving up and moving down at the same time ”, says research group leader Dr. Gary Steele. “This ‘strange’ quantum motion is not only of scientific relevance, but also could have very practical applications in a quantum computer as a quantum ‘memory chip’”.

    In a quantum computer, the fact that quantum ‘bits’ that can be both in the state 0 and 1 at the same time allow it to potentially perform computations much faster than a classical computer like those used today. Quantum graphene drums that are ‘shaking up and down at the same time’ could be used to store quantum information in the same way as RAM chips in your computer, allowing you to store your quantum computation result and retrieve it at a later time by listening to its quantum sound.

    See the full article, with video, here.

    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

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  • richardmitnick 6:41 pm on April 9, 2014 Permalink | Reply
    Tags: , , , , Quantum Computing   

    From M.I.T.: “New ‘switch’ could power quantum computing” 

    April 9, 2014
    Peter Dizikes | MIT News Office

    A light lattice that traps atoms may help scientists build networks of quantum information transmitters.

    Using a laser to place individual rubidium atoms near the surface of a lattice of light, scientists at MIT and Harvard University have developed a new method for connecting particles — one that could help in the development of powerful quantum computing systems.

    qc

    The new technique, described in a paper published today in the journal Nature, allows researchers to couple a lone atom of rubidium, a metal, with a single photon, or light particle. This allows both the atom and photon to switch the quantum state of the other particle, providing a mechanism through which quantum-level computing operations could take place.

    Moreover, the scientists believe their technique will allow them to increase the number of useful interactions occurring within a small space, thus scaling up the amount of quantum computing processing available.

    “This is a major advance of this system,” says Vladan Vuletić, a professor in MIT’s Department of Physics and Research Laboratory for Electronics (RLE), and a co-author of the paper. “We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom.”

    That is, photons can have two polarization states, and interaction with the atom can change the photon from one state to another; conversely, interaction with the photon can change the atom’s phase, which is equivalent to changing the quantum state of the atom from its “ground” state to its “excited” state. In this way the atom-photon coupling can serve as a quantum switch to transmit information — the equivalent of a transistor in a classical computing system. And by placing many atoms within the same field of light, the researchers may be able to build networks that can process quantum information more effectively.

    “You can now imagine having several atoms placed there, to make several of these devices — which are only a few hundred nanometers thick, 1,000 times thinner than a human hair — and couple them together to make them exchange information,” Vuletić adds.

    Using a photonic cavity

    Quantum computing could enable the rapid performance of calculations by taking advantage of the distinctive quantum-level properties of particles. Some particles can be in a condition of superposition, appearing to exist in two places at the same time. Particles in superposition, known as qubits, could thus contain more information than particles at classical scales, and allow for faster computing.

    However, researchers are in the early stages of determining which materials best allow for quantum-scale computing. The MIT and Harvard researchers have been examining photons as a candidate material, since photons rarely interact with other particles. For this reason, an optical quantum computing system, using photons, could be harder to knock out of its delicate alignment. But since photons rarely interact with other bits of matter, they are difficult to manipulate in the first place.

    In this case, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers — less than a wavelength of light — from the edge of the cavity. At such small distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place.

    Other methods of producing a similar outcome have been considered before — such as, in effect, dropping atoms into the light and then finding and trapping them. But the researchers found that they had greater control over the particles this way.

    “In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić says.

    The result is what he calls a “hybrid quantum system,” where individual atoms are coupled to microscopic fabricated devices, and in which atoms and photons can be controlled in productive ways. The researchers also found that the new device serves as a kind of router separating photons from each other.

    “The idea is to combine different things that have different strengths and weaknesses in such a way to generate something new,” Vuletić says, adding: “This is an advance in technology. Of course, whether this will be the technology remains to be seen.”

    ‘Still amazing’ to hold onto one atom

    The paper, Nanophotonic quantum phase switch with a single atom, is co-authored by Vuletić; Tobias Tiecke, a postdoc affiliated with both RLE and Harvard; Harvard professor of physics Mikhail Lukin; Harvard postdoc Nathalie de Leon; and Harvard graduate students Jeff Thompson and Bo Liu.

    The collaboration between the MIT and Harvard researchers is one of two advances in the field described in the current issue of Nature. Researchers at the Max Planck Institute of Quantum Optics in Germany have concurrently developed a new method of producing atom-photon interactions using mirrors, forming quantum gates, which change the direction of motion or polarization of photons.

    “The Harvard/MIT experiment is a masterpiece of quantum nonlinear optics, demonstrating impressively the preponderance of single atoms over many atoms for the control of quantum light fields,” says Gerhard Rempe, a professor at the Max Planck Institute of Quantum Optics who helped lead the German team’s new research, and who has read the paper by the U.S.-based team. “The coherent manipulation of an atom coupled to a photonic crystal resonator constitutes a breakthrough and complements our own work … with an atom in a dielectric mirror resonator.”

    Rempe adds that he thinks both techniques will be regarded as notable “achievements on our way toward a robust quantum technology with stationary atoms and flying photons.”

    If the research techniques seem a bit futuristic, Vuletić says that even as an experienced researcher in the field, he remains slightly awed by the tools at his disposal.

    “For me what is still amazing, after working in this for 20 years,” Vuletić reflects, “is that we can hold onto a single atom, we can see it, we can move it around, we can prepare quantum superpositions of atoms, we can detect them one by one.”

    Funding for the research was provided in part by the National Science Foundation, the MIT-Harvard Center for Ultracold Atoms, the Natural Sciences and Engineering Research Council of Canada, the Air Force Office of Scientific Research, and the Packard Foundation.

    See the full article here.


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  • richardmitnick 3:44 pm on December 5, 2013 Permalink | Reply
    Tags: , , , , Quantum Computing   

    From Berkeley Lab: “Berkeley Lab Researchers Create a Nonlinear Light-generating Zero-Index MetaMaterial” 


    Berkeley Lab

    Holds Promise for Future Quantum Networks and Light Sources

    December 05, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    The Information Age will get a major upgrade with the arrival of quantum processors many times faster and more powerful than today’s supercomputers. For the benefits of this new Information Age 2.0 to be fully realized, however, quantum computers will need fast and efficient multi-directional light sources. While quantum technologies remain grist for science fiction, a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have taken an important step towards efficient light generation, the foundation for future quantum networks.

    graph
    In this graphic showing four-wave mixing in a positive/negative-index (upper) and zero-index (lower) metamaterial, forward-propagating FWM is much stronger than backward FWM for the positive/negative-index material but about the same in both directions for the zero-index metamaterial. (Image courtesy of Zhang group)

    In a study led by Xiang Zhang, a faculty scientist with Berkeley Lab’s Materials Sciences Division, the research team used a unique optical metamaterial with a refractive index of zero to generate phase mismatch–free nonlinear light, meaning the generated light waves move through the material gaining strength in all directions. This phase mismatch-free quality holds promise for quantum computing and networking, and future light sources based on nonlinear optics – the phenomena that occur when interactions with light modify a material’s properties.

    “In our demonstration of nonlinear dynamics in an optical metamaterial with zero-index refraction, equal amounts of nonlinearly generated waves are observed in both forward and backward propagation directions,” says Zhang. “The removal of phase matching in nonlinear optical metamaterials may lead to applications such as efficient multidirectional light emissions for novel light sources and the generation of entangled photons for quantum networking.”

    Zhang is the corresponding author of a paper in Science that describes this research. The paper is titled Phase Mismatch–Free Nonlinear Propagation in Optical Zero-Index Materials. Co-authors are Haim Suchowski, Kevin O’Brien, Zi Jing Wong, Alessandro Salandrino and Xiaobo Yin.

    team
    From left Xiang Zhang, Haim Suchowski, Zi Jing Wong, Kevin O’Brien and Alessandro Salandrino have created a nonlinear light-generating zero-index metamaterial that holds promise for future quantum networks and light sources. (Photo by Roy Kaltschmidt)

    Zhang, who holds the Ernest S. Kuh Endowed Chair Professor of Mechanical Engineering at the University of California (UC) Berkeley, where he also directs the National Science Foundation’s Nano-scale Science and Engineering Center, is one of the world’s foremost authorities in metamaterials research.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 6:46 pm on November 4, 2013 Permalink | Reply
    Tags: , , , , Quantum Computing   

    From Berkeley Lab: “Diamond Imperfections Pave the Way to Technology Gold” 


    Berkeley Lab

    November 04, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    From supersensitive detections of magnetic fields to quantum information processing, the key to a number of highly promising advanced technologies may lie in one of the most common defects in diamonds. Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have taken an important step towards unlocking this key with the first ever detailed look at critical ultrafast processes in these diamond defects.

    Using two-dimensional electronic spectroscopy on pico- and femto-second time-scales, a research team led by Graham Fleming, Vice Chancellor for Research at UC Berkeley and faculty scientist with Berkeley Lab’s Physical Biosciences Division, has recorded unprecedented observations of energy moving through the atom-sized diamond impurities known as nitrogen-vacancy (NV) centers. An NV center is created when two adjacent carbon atoms in a diamond crystal are replaced by a nitrogen atom and an empty gap.

    “Our use of 2D electronic spectroscopy allowed us to essentially map the flow of energy through the NV center in real time and observe critical quantum mechanical effects,” Fleming says. “The results hold broad implications for magnetometry, quantum information, nanophotonics, sensing and ultrafast spectroscopy.”

    lab
    Vanessa Huxter, former member of Graham Fleming’s research group and now a professor at the University of Arizona, was a key member of the research team that provided unprecedented observations of ultrafast processes in diamond NV centers. (Photo by Beatriz Verdugo, University of Arizona)

    See the full article here.

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  • richardmitnick 6:39 pm on September 16, 2013 Permalink | Reply
    Tags: , , , Quantum Computing   

    From Berkeley Lab: “On the Road to Fault-Tolerant Quantum Computing” 


    Berkeley Lab

    Collaboration at Berkeley Lab’s Advanced Light Source Induces High Temperature Superconductivity in a Toplogical Insulator

    September 16, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    Reliable quantum computing would make it possible to solve certain types of extremely complex technological problems millions of times faster than today’s most powerful supercomputers. Other types of problems that quantum computing could tackle would not even be feasible with today’s fastest machines. The key word is “reliable.” If the enormous potential of quantum computing is to be fully realized, scientists must learn to create “fault-tolerant” quantum computers. A small but important step toward this goal has been achieved by an international collaboration of researchers from China’s Tsinghua University and the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) working at the Advanced Light Source (ALS).

    Using premier beams of ultraviolet light at the ALS, a DOE national user facility for synchrotron radiation, the collaboration has reported the first demonstration of high-temperature superconductivity in the surface of a topological insulator – a unique class of advanced materials that are electrically insulating on the inside but conducting on the surface. Inducing high-temperature superconductivity on the surface of a topological insulator opens the door to the creation of a pre-requisite for fault-tolerant quantum computing, a mysterious quasiparticle known as the “Majorana zero mode.”

    “We have shown that by interfacing a topological insulator, bismuth selenide, with a high temperature superconductor, BSCCO (bismuth strontium calcium copper oxide), it is possible to induce superconductivity in the topological surface state,” says Alexei Fedorov, a staff scientist for ALS beamline 12.0.1, where the induced high temperature superconductivity of the topological insulator heterostructure was confirmed. “This is the first reported demonstration of induced high temperature superconductivity in a topological surface state.”

    state
    This schematic of a bismuth selenide/BSCCO cuprate (Bi2212) heterostructure shows a proximity-induced high-temperature superconducting gap on the surface states of the bismuth selenide topological insulator. No image credit.

    See the full article here.

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  • richardmitnick 3:07 pm on February 8, 2013 Permalink | Reply
    Tags: , , Quantum Computing,   

    From Caltech: “Creating New Quantum Building Blocks” 

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    Caltech

    “Scientists have long dreamed of creating a quantum computer—a device rooted in the bizarre phenomena that transpire at the level of the very small, where quantum mechanics rules the scene. It is believed that such new computers could process currently unsolvable problems in seconds.

    Researchers have tried using various quantum systems, such as atoms or ions, as the basic, transistor-like units in simple quantum computation devices. Now, laying the groundwork for an on-chip optical quantum network, a team of researchers, including Andrei Faraon from the California Institute of Technology (Caltech), has shown that defects in diamond can be used as quantum building blocks that interact with one another via photons, the basic units of light.

    photon

    The device is simple enough—it involves a tiny ring resonator and a tunnel-like optical waveguide, which both funnel light. Both structures, each only a few hundred nanometers wide, are etched in a diamond membrane and positioned close together atop a glass substrate. Within the resonator lies a nitrogen-vacancy center (NV center)—a defect in the structure of diamond in which a nitrogen atom replaces a carbon atom, and in which a nearby spot usually reserved for another carbon atom is simply empty. Such NV centers are photoluminescent, meaning they absorb and emit photons.

    ‘These NV centers are like the building blocks of the network, and we need to make them interact—like having an electrical current connecting one transistor to another,’ explains Faraon, lead author on a paper describing the work in the New Journal of Physics. “In this case, photons do that job.'”

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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