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  • richardmitnick 10:07 am on July 13, 2017 Permalink | Reply
    Tags: , Electron valley states, , , , Qubits,   

    From UCLA: “Technique for measuring and controlling electron state is a breakthrough in quantum computing” 

    UCLA bloc

    UCLA

    July 06, 2017
    Meghan Steele Horan

    1
    UCLA professor HongWen Jiang (center) and graduate students Blake Freeman and Joshua Schoenfield affixing a quantum dot device to the gold plate of a cooling chamber. Nick Penthorn.

    During their research for a new paper on quantum computing, HongWen Jiang, a UCLA professor of physics, and Joshua Schoenfield, a graduate student in his lab, ran into a recurring problem: They were so excited about the progress they were making that when they logged in from home to their UCLA desktop — which allows only one user at a time — the two scientists repeatedly knocked each other off of the remote connection.

    The reason for their enthusiasm: Jiang and his team created a way to measure and control the energy differences of electron valley states in silicon quantum dots, which are a key component of quantum computing research. The technique could bring quantum computing one step closer to reality.

    “It’s so exciting,” said Jiang, a member of the California NanoSystems Institute. “We didn’t want to wait until the next day to find out the outcome.”

    Quantum computing could enable more complex information to be encoded on much smaller computer chips, and it holds promise for faster, more secure problem-solving and communications than today’s computers allow.

    In standard computers, the fundamental components are switches called bits, which use 0s and 1s to indicate that they are off or on. The building blocks of quantum computers, on the other hand, are quantum bits, or qubits.

    The UCLA researchers’ breakthrough was being able to measure and control a specific state of a silicon quantum dot, known as a valley state, an essential property of qubits. The research was published in Nature Communications.

    “An individual qubit can exist in a complex wave-like mixture of the state 0 and the state 1 at the same time,” said Schoenfield, the paper’s first author. “To solve problems, qubits must interfere with each other like ripples in a pond. So controlling every aspect of their wave-like nature is essential.”

    Silicon quantum dots are small, electrically confined regions of silicon, only tens of nanometers across, that can trap electrons. They’re being studied by Jiang’s lab — and by researchers around the world — for their possible use in quantum computing because they enable scientists to manipulate electrons’ spin and charge.

    Besides electrons’ spin and charge, another of their most important properties is their “valley state,” which specifies where an electron will settle in the non-flat energy landscape of silicon’s crystalline structure. The valley state represents a location in the electron’s momentum, as opposed to an actual physical location.

    Scientists have realized only recently that controlling valley states is critical for encoding and analyzing silicon-based qubits, because even the tiniest imperfections in a silicon crystal can alter valley energies in unpredictable ways.

    “Imagine standing on top of a mountain and looking down to your left and right, noticing that the valleys on either side appear to be the same but knowing that one valley was just 1 centimeter deeper than the other,” said Blake Freeman, a UCLA graduate student and co-author of the study. “In quantum physics, even that small of a difference is extremely important for our ability to control electrons’ spin and charge states.”

    At normal temperatures, electrons bounce around, making it difficult for them to rest in the lowest energy point in the valley. So to measure the tiny energy difference between two valley states, the UCLA researchers placed silicon quantum dots inside a cooling chamber at a temperature near absolute zero, which allowed the electrons to settle down. By shooting fast electrical pulses of voltage through them, the scientists were able to move single electrons in and out of the valleys. The tiny difference in energy between the valleys was determined by observing the speed of the electron’s rapid switching between valley states.

    After manipulating the electrons, the researchers ran a nanowire sensor very close to the electrons. Measuring the wire’s resistance allowed them to gauge the distance between an electron and the wire, which in turn enabled them to determine which valley the electron occupied.

    The technique also enabled the scientists, for the first time, to measure the extremely small energy difference between the two valleys — which had been impossible using any other existing method.

    In the future, the researchers hope to use more sophisticated voltage pulses and device designs to achieve full control over multiple interacting valley-based qubits.

    “The dream is to have an array of hundreds or thousands of qubits all working together to solve a difficult problem,” Schoenfield said. “This work is an important step toward realizing that dream.”

    The research was supported by the U.S. Army Research Office.

    See the full article here .

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    UC LA Campus

    For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

    We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

    This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

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  • richardmitnick 8:59 am on June 29, 2017 Permalink | Reply
    Tags: A 100-dimensional quantum system from the entanglement of two subatomic particles, , , Multi-coloured photons in 100 dimensions may make quantum computers stronger, , Qubits, Qutrits   

    From COSMOS: “Multi-coloured photons in 100 dimensions may make quantum computers stronger” 

    Cosmos Magazine bloc

    COSMOS

    29 June 2017
    Andrew Masterson

    1
    An illustration showing high-dimensional color-entangled photon states from a photonic chip, manipulated and transmitted via telecommunications systems.
    Michael Kues.

    By using manipulating the frequency of entangled photons, researchers have found a way to make more stable tools for quantum computing from off-the-shelf equipment.

    Researchers using off-the-shelf telecommunications equipment have created a 100-dimensional quantum system from the entanglement of two subatomic particles.

    The system can be controlled and manipulated to perform high-level gateway functions – a critical component of any viable quantum computer – the scientists report in the journal Nature.

    The team, led by Michael Kues of the University of Glasgow, effectively created a quantum photon generator on a chip. The tiny device uses a micro-ring resonator generate entangled pairs of photons from a laser input.

    The entanglement is far from simple. Each photon is composed of a superposition of several different colours, all expressed simultaneously, giving the photon several dimensions. The expression of any individual colour – or frequency, if you like – is mirrored across the two entangled photons, regardless of the distance between them.

    The complexity of the photon pairs represents a major step forward in manipulating quantum entities.

    Almost all research into quantum states, for the purpose of developing quantum computing, has to date focussed on qubits: artificially created subatomic particles that exist in a superposition two possible states. (They are the quantum equivalent of standard computing ‘bits’, basic units that are capable only of being switched between 1 and 0, or yes/no, or on/off.)

    Kues and colleagues are instead working with qudits, which are essentially qubits with superpositions comprising three or more states.

    In 2016, Russian researchers showed that qudit-based quantum computing systems were inherently more stable than their two dimensional predecessors.

    The Russians, however, were working with a subset of qudits called qutrits, which comprise a superposition of three possible states. Kues and his team upped the ante considerably, fashioning qudits comprising 10 possible states – one for each of the colours, or frequencies, of the photon – giving an entangled pair a minimum of 100.

    And that’s just the beginning. Team member Roberto Morandotti of the University of Electronic Science and Technology of China, in Chengdu, suggests that further refinement will produce entangled two-qudit systems containing as many as 9000 dimensions, bringing a robustness and complexity to quantum computers that is at present unreachable.

    Kues adds that perhaps the most attractive feature of his team’s achievement is that it was done using commercially available components. This means that the strategy can be quickly and easily adapted by other researchers in the field, potentially ushering in a period of very rapid development.

    See the full article here .

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  • richardmitnick 11:31 am on May 29, 2017 Permalink | Reply
    Tags: , , Doped diamond, , Qubits,   

    From COSMOS: “Doped diamond may lead to everyday quantum computers” 

    Cosmos Magazine bloc

    COSMOS

    29 May 2017
    Andrew Masterson

    1
    Precise placement of atoms in a diamond lattice may be a handy technique for quantum computer manufacture. Victor Habbick Visions / Getty

    Quantum computers are still halfway mythical, but they are moving closer to reality step by tiny step.

    One of the most widely favoured structures for building viable quantum computers is a diamond surface dotted with irregularities only a couple of atoms wide.

    The problem researchers face, however, is making sure those irregularities – essentially atom-scale holes and accompanying bits of atom-wide foreign material – are drilled into the diamond substrate in exactly the right spot.

    A report at Nature Communications by a team from MIT, Harvard University, and Sandia National Laboratories, in the US, covers a new method of doing so, creating the “defects” in the diamond crystal structure within 50 nanometres of their optimal locations.

    The precise placement of the irregularities – known as “dopant-vacancies” in the business – is a critical outcome if quantum computers are ever to end up on the market.

    This is because the combination of a tiny hole and a couple of atoms of non-diamond matter – nitrogen, for instance – can be engineered to act as a qubit, the fundamental element of quantum computing.

    At the heart of a qubit is a subatomic particle that can simultaneously occupy a number of contradictory states – on, off, and a “superposition” of both together, for instance. The combination of the hole, the foreign atoms, and the light refracted through the diamond combine to create an elegant qubit.

    At least, theoretically. To date, most experimental work has been done using nitrogen dopant-vacancies. These have the advantage of being able to maintain superposition longer than other candidates, but emit light across a broad range of frequencies, making information retrieval difficult.

    The MIT-Harvard-Sandia team, led by Tim Schröder, experimented instead with silicon-based defects, which emit light in a much narrower range. That advantage, however, comes with its own challenge: the silicon dopant-vacancies need to be chilled to within a few thousands of a degree above absolute zero if they are to maintain a superposition for any length of time.

    That remains a challenge still to be met, however. The import of the current study, published in the journal Nature Communications, lies in the increase in the accuracy of positioning the defects in the diamond.

    To achieve this, scientists at MIT and Harvard first created a sliver of diamond only 200 nanometres thick. Onto this they etched tiny cavities.

    The substrate was then sent to the Sandia laboratories, where each cavity was bombarded with 20 to 30 silicon ions. The process led to only about two percent of the cavities attracting silicon residents.

    Back at MIT a second new process was employed. The diamond sliver was heated to 1000 ºC, at which temperature its component lattice became malleable, allowing the researchers to align more cavities with more silicon particles – taking the total number of dopant-vacancies to 20%.

    Most of the irregularities thus produced were within 50 nanometres of their optimal position, and shone at around 85% of optimal brightness.

    A quantum computer in every household is still a long way off, but this study marks a potentially important step in the journey.

    See the full article here .

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  • richardmitnick 4:23 pm on January 2, 2017 Permalink | Reply
    Tags: , Electron-photon small-talk could have big impact on quantum computing, , , Qubits   

    From Princeton: “Electron-photon small-talk could have big impact on quantum computing” 

    Princeton University
    Princeton University

    December 22, 2016
    Catherine Zandonella

    In a step that brings silicon-based quantum computers closer to reality, researchers at Princeton University have built a device in which a single electron can pass its quantum information to a particle of light. The particle of light, or photon, can then act as a messenger to carry the information to other electrons, creating connections that form the circuits of a quantum computer.

    The research, published today in the journal Science and conducted at Princeton and HRL Laboratories in Malibu, California, represents a more than five-year effort to build a robust capability for an electron to talk to a photon, said Jason Petta, a Princeton professor of physics.

    1
    Princeton Professor of Physics Jason Petta, from left, and physics graduate students David Zajac and Xiao Mi, have built a device that is a step forward for silicon-based quantum computers, which when built will be able to solve problems beyond the capabilities of everyday computers. The device isolates an electron so that can pass its quantum information to a photon, which can then act as a messenger to carry the information to other electrons to form the circuits of the computer. (Photo by Denise Applewhite, Office of Communications)

    “Just like in human interactions, to have good communication a number of things need to work out — it helps to speak the same language and so forth,” Petta said. “We are able to bring the energy of the electronic state into resonance with the light particle, so that the two can talk to each other.”

    The discovery will help the researchers use light to link individual electrons, which act as the bits, or smallest units of data, in a quantum computer. Quantum computers are advanced devices that, when realized, will be able to perform advanced calculations using tiny particles such as electrons, which follow quantum rules rather than the physical laws of the everyday world.

    Each bit in an everyday computer can have a value of a 0 or a 1. Quantum bits — known as qubits — can be in a state of 0, 1, or both a 0 and a 1 simultaneously. This superposition, as it is known, enables quantum computers to tackle complex questions that today’s computers cannot solve.

    Simple quantum computers have already been made using trapped ions and superconductors, but technical challenges have slowed the development of silicon-based quantum devices. Silicon is a highly attractive material because it is inexpensive and is already widely used in today’s smartphones and computers.

    2
    The qubit consists of a single electron that is trapped below the surface of a silicon chip (gray). The green, pink and purple wires on top of the silicon structure deliver precise voltages to the qubit. The purple plate reduces electronic interference that can destroy the qubit’s quantum information. By adjusting the voltages in the wires, the researchers can trap a single electron in a double quantum dot and adjust its energy so that it can communicate its quantum information to a nearby photon. (Photo courtesy of the Jason Petta research group, Department of Physics)

    The researchers trapped both an electron and a photon in the device, then adjusted the energy of the electron in such a way that the quantum information could transfer to the photon. This coupling enables the photon to carry the information from one qubit to another located up to a centimeter away.

    Quantum information is extremely fragile — it can be lost entirely due to the slightest disturbance from the environment. Photons are more robust against disruption and can potentially carry quantum information not just from qubit to qubit in a quantum computer circuit but also between quantum chips via cables.

    For these two very different types of particles to talk to each other, however, researchers had to build a device that provided the right environment. First, Peter Deelman at HRL Laboratories, a corporate research-and-development laboratory owned by the Boeing Company and General Motors, fabricated the semiconductor chip from layers of silicon and silicon-germanium. This structure trapped a single layer of electrons below the surface of the chip. Next, researchers at Princeton laid tiny wires, each just a fraction of the width of a human hair, across the top of the device. These nanometer-sized wires allowed the researchers to deliver voltages that created an energy landscape capable of trapping a single electron, confining it in a region of the silicon called a double quantum dot.

    The researchers used those same wires to adjust the energy level of the trapped electron to match that of the photon, which is trapped in a superconducting cavity that is fabricated on top of the silicon wafer.

    Prior to this discovery, semiconductor qubits could only be coupled to neighboring qubits. By using light to couple qubits, it may be feasible to pass information between qubits at opposite ends of a chip.

    The electron’s quantum information consists of nothing more than the location of the electron in one of two energy pockets in the double quantum dot. The electron can occupy one or the other pocket, or both simultaneously. By controlling the voltages applied to the device, the researchers can control which pocket the electron occupies.

    “We now have the ability to actually transmit the quantum state to a photon confined in the cavity,” said Xiao Mi, a graduate student in Princeton’s Department of Physics and first author on the paper. “This has never been done before in a semiconductor device because the quantum state was lost before it could transfer its information.”

    4
    A fully packaged device for trapping and manipulating single electrons and photons. A series of on-chip electrodes (lower left and upper right) lead to the formation of a double quantum dot that confines a single electron below the surface of the chip. The photon, which is free to move within the full 7-millimeter span of the cavity, exchanges quantum information with the electron inside the double quantum dot. (Photo courtesy of the Jason Petta research group, Department of Physics)

    The success of the device is due to a new circuit design that brings the wires closer to the qubit and reduces interference from other sources of electromagnetic radiation. To reduce this noise, the researchers put in filters that remove extraneous signals from the wires that lead to the device. The metal wires also shield the qubit. As a result, the qubits are 100 to 1,000 times less noisy than the ones used in previous experiments.

    Jeffrey Cady, a 2015 graduate, helped develop the filters to reduce the noise as part of his undergraduate senior thesis, and graduate student David Zajac led the effort to use overlapping electrodes to confine single electrons in silicon quantum dots.

    Eventually the researchers plan to extend the device to work with an intrinsic property of the electron known as its spin. “In the long run we want systems where spin and charge are coupled together to make a spin qubit that can be electrically controlled,” Petta said. “We’ve shown we can coherently couple an electron to light, and that is an important step toward coupling spin to light.”

    David DiVincenzo, a physicist at the Institute for Quantum Information in RWTH Aachen University in Germany, who was not involved in the research, is the author of an influential 1996 paper outlining five minimal requirements necessary for creating a quantum computer. Of the Princeton-HRL work, in which he was not involved, DiVincenzo said: “It has been a long struggle to find the right combination of conditions that would achieve the strong coupling condition for a single-electron qubit. I am happy to see that a region of parameter space has been found where the system can go for the first time into strong-coupling territory.”

    Funding for this research was provided by Army Research Office grant No. W911NF-15-1-0149, the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF4535, and the National Science Foundation (DMR-1409556 and DMR-1420541). The material is based upon work supported by the U.S. Department of Defense under contract H98230-15-C0453.

    The paper, Strong Coupling of a Single Electron in Silicon to a Microwave Photon by X. Mi, J. V. Cady, D. M. Zajac, P. W. Deelman, J. R. Petta, was published in the journal Science online on Thursday, Dec. 22.

    See the full article here .

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  • richardmitnick 3:16 pm on December 23, 2016 Permalink | Reply
    Tags: and Google, , , Intel and Competitors IBM, , , Qubits   

    From MIT Tech Review: “Intel Bets It Can Turn Everyday Silicon into Quantum Computing’s Wonder Material” 

    MIT Technology Review
    MIT Technology Review

    December 21, 2016
    Tom Simonite

    The world’s largest chip company sees a novel path toward computers of immense power.

    1
    Researchers at TU Delft in the Netherlands use equipment like this to test quantum computing devices at supercool temperatures, in a collaboration with chip maker Intel. No image credit.

    Sometimes the solution to a problem is staring you in the face all along. Chip maker Intel is betting that will be true in the race to build quantum computers—machines that should offer immense processing power by exploiting the oddities of quantum mechanics.

    Competitors IBM, Microsoft, and Google are all developing quantum components that are different from the ones crunching data in today’s computers. But Intel is trying to adapt the workhorse of existing computers, the silicon transistor, for the task.

    Intel has a team of quantum hardware engineers in Portland, Oregon, who collaborate with researchers in the Netherlands, at TU Delft’s QuTech quantum research institute, under a $50 million grant established last year. Earlier this month Intel’s group reported that they can now layer the ultra-pure silicon needed for a quantum computer onto the standard wafers used in chip factories.

    This strategy makes Intel an outlier among industry and academic groups working on qubits, as the basic components needed for quantum computers are known. Other companies can run code on prototype chips with several qubits made from superconducting circuits (see Google’s Quantum Dream Machine). No one has yet advanced silicon qubits that far.

    A quantum computer would need to have thousands or millions of qubits to be broadly useful, though. And Jim Clarke, who leads Intel’s project as director of quantum hardware, argues that silicon qubits are more likely to get to that point (although Intel is also doing some research on superconducting qubits). One thing in silicon’s favor, he says: the expertise and equipment used to make conventional chips with billions of identical transistors should allow work on perfecting and scaling up silicon qubits to progress quickly.

    Intel’s silicon qubits represent data in a quantum property called the “spin” of a single electron trapped inside a modified version of the transistors in its existing commercial chips. “The hope is that if we make the best transistors, then with a few material and design changes we can make the best qubits,” says Clarke.

    Another reason to work on silicon qubits is that they should be more reliable than the superconducting equivalents. Still, all qubits are error prone because they work on data using very weak quantum effects (see Google Researchers Make Quantum Components More Reliable).

    The new process that helps Intel experiment with silicon qubits on standard chip wafers, developed with the materials companies Urenco and Air Liquide, should help speed up its research, says Andrew Dzurak, who works on silicon qubits at the University of New South Wales in Australia. “To get to hundreds of thousands of qubits, we will need incredible engineering reliability, and that is the hallmark of the semiconductor industry,” he says.

    Companies developing superconducting qubits also make them using existing chip fabrication methods. But the resulting devices are larger than transistors, and there is no template for how to manufacture and package them up in large numbers, says Dzurak.

    Chad Rigetti, founder and CEO of Rigetti Computing, a startup working on superconducting qubits similar to those Google and IBM are developing, agrees that this presents a challenge. But he argues that his chosen technology’s head start will afford ample time and resources to tackle the problem.

    Google and Rigetti have both said that in just a few years they could build a quantum chip with tens or hundreds of qubits that dramatically outperforms conventional computers on certain problems, even doing useful work on problems in chemistry or machine learning.

    No sciencde papers cited.

    See the full article here .

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    The mission of MIT Technology Review is to equip its audiences with the intelligence to understand a world shaped by technology.

     
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