David Kirkpatrick

July 22, 2010

The first beneficiaries of quantum computing?

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 5:12 pm

Chemists. Who’d a thunk that one. It’s not totally there yet, but quantum chemistry may transform the field.

From the link:

There’s no shortage of scientists waiting to get their hands on quantum computers. Cryptographers, in particular, are licking their lips in anticipation.

But there’s another group who are already beginning to benefit from the first few iterations of quantum computing devices: chemists.

Various scientists have pointed out that it is possible to study the properties of a particular quantum system using another controllable quantum system.

This kind of quantum simulation has huge implications for chemistry. No longer would it be necessary to mess around with real atoms, ions and molecules in messy experiments with test tubes and bunsen burners.

Instead it ought to be possible to perfectly simulate what goes on using a quantum computer set up in the right way. That’s the theory anyway. The practice is inevitably more tricky.

July 8, 2010

Latest on quantum computing

There’s been a mini-flurry of quantum computing news of late, and here’s the latest. Even though quantum computing news is both fun and interesting it’s best to keep in mind we are nowhere close to actually building anything the average person would consider a quantum computer. The payoff for all this research and development, however, is worth the effort and certainly worth keeping track of.

From the second link:

One of the more interesting runners in the race to build scalable quantum computers is the idea of using point-like defects in a diamond lattice that have been filled with a nitrogen atom. The nitrogen interloper provides an extra electron which can be used to generate photons or to store quantum information.

The big advantage of these so-called nitrogen vacancies is that they’re easy to see (because they can be made to emit photons) which means they can be relatively easily addressed. They are also well isolated from many types of environmental interference and so can store qubits for relatively long periods of up to several hundred microseconds.

But the problem is how to make them en masse. Until now, the fastest way was to fire nitrogen atoms one by one through an aperture into a thin layer of diamond. That makes for slow going if you need hundreds of thousands of them in a single layer.

Now David Toyli at the University of California, Santa Barbara, and few buddies have demonstrated a much faster technique. Their approach is to cover the diamond with a thin layer of resist, through which they then blast an array of holes using electron beam lithography.

July 3, 2010

Toward quantum computing

This news comes from the University of Maryland offering another advancement toward a quantum computer — something that is ways off yet — that involves nanotechnology.

The release:

UM Scientists Advance Quantum Computing & Energy Conversion Tech

COLLEGE PARK, Md. — Using a unique hybrid nanostructure, University of Maryland researchers have shown a new type of light-matter interaction and also demonstrated the first full quantum control of qubit spin within very tiny colloidal nanostructures (a few nanometers), thus taking a key step forward in efforts to create a quantum computer.

Published in the July 1 issue of Nature, their research builds on work by the same Maryland research team published in March in the journal Science (3-26-10). According to the authors and outside experts, the new findings further advance the promise these new nanostructures hold for quantum computing and for new, more efficient, energy generation technologies (such as photovoltaic cells), as well as for other technologies that are based on light-matter interactions like biomarkers.

“The real breakthrough is that we use a new technology from materials science to ‘shed light’ on light-matter interactions and related quantum science in ways that we believe will have important applications in many areas, particularly energy conversion and storage and quantum computing,” said lead researcher Min Ouyang, an assistant professor in the department of physics and in the university’s Maryland NanoCenter. “In fact, our team already is applying our new understanding of nanoscale light-matter interactions and advancement of precise control of nanostructures to the development of a new type of photovoltaic cell that we expect to be significantly more efficient at converting light to electricity than are current cells.”

Ouyang and the other members of the University of Maryland team — research scientist Jiatao Zhang, and students Kwan Lee and Yun Tang — have created a patent-pending process that uses chemical thermodynamics to produce, in solution, a broad range of different combination materials, each with a shell of structurally perfect mono-crystal semiconductor around a metal core. In the research published in this week’s Nature, the researchers used hybrid metal/semiconductor nanostructures developed through this process to experimentally demonstrate “tunable resonant coupling” between a plasmon (from metal core) and an exciton (from semiconductor shell), with a resulting enhancement of the Optical Stark Effect. This effect was discovered some 60 years ago in studies of the interaction between light and atoms that showed light can be applied to modify atomic quantum states.

Nanostructures, Large Advances
“Metal-semiconductor heteronanostructures have been investigated intensely in the last few years with the metallic components used as nanoscale antennas to couple light much more effectively into and out of semiconductor nanoscale, light-emitters,” said Garnett W. Bryant, leader of the Quantum Processes and Metrology Group in the Atomic Physics Division of the National Institute of Standards and Technology (NIST). “The research led Min Ouyang shows that a novel heteronanostructure with the semiconductor surrounding the metallic nanoantenna can achieve the same goals. Such structures are very simple and much easier to make than previously attempted, greatly opening up possibilities for application. Most importantly, they have demonstrated that the light/matter coupling can be manipulated to achieve coherent quantum control of the semiconductor nanoemitters, a key requirement for quantum information processing,” said Bryant, who is not involved with this research. Bryant also is a scientist in the Joint Quantum Institute, a leading center of quantum science research that is a partnership between NIST and the University of Maryland.

Ouyang and his colleagues agree that their new findings were made possible by their crystal-metal hybrid nanostructures, which offer a number of benefits over the epitaxial structures used for previous work. Epitaxy has been the principle way to create single crystal semiconductors and related devices. The new research highlights the new capabilities of these UM nanostructures, made with a process that avoids two key constraints of epitaxy — a limit on deposition semiconductor layer thickness and a rigid requirement for “lattice matching.”

The Maryland scientists note that, in addition to the enhanced capabilities of their hybrid nanostructures, the method for producing them doesn’t require a clean room facility and the materials don’t have to be formed in a vacuum, the way those made by conventional epitaxy do. “Thus it also would be much simpler and cheaper for companies to mass produce products based on our hybrid nanostructures,” Ouyang said.

UM: Addressing Big Issues, Exploring Big Ideas
Every day University of Maryland faculty and student researchers are making a deep impact on the scientific, technological, political, social, security and environmental challenges facing our nation and world. Working in partnership with federal agencies, and international and industry collaborators, they are advancing knowledge and solutions in a areas such as climate change, global security, energy, public health, information technology, food safety and security, and space exploration.

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Schematic of hybrid core-shell growth process

“Tailoring light-matter-spin interactions in colloidal hetero-nanostructures” Jiatao Zhang, Yun Tang, Kwan Lee, Min Ouyang, Nature, July 1, 2010.

This work was supported by the Office of Naval Research, the National Science Foundation (NSF), and Beckman Foundation. Facility support was from Maryland Nanocenter and its Nanoscale Imaging, Spectroscopy, and Properties Laboratory, which is supported in part by the NSF as a Materials Research Science and Engineering Centers shared experiment facility.

June 16, 2010

One step closer to quantum computing

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 12:40 am

Alternative computing is always an fascinating topic, and the sheer processing power potential for quantum computers makes that field particularly interesting.

From the link:

Quantum computers can solve in a matter of moments problems that would take ordinary computers years to work out. But thus far, these computers exist only as state-of-the-art experimental setups in a few physics laboratories.

Now, Elena Kuznetsova, a post-doctoral researcher in UConn’s Department of Physics, has proposed a new type of quantum computer that could bring the technology one step closer to becoming a reality.

“The main excitement about quantum computers,” says Kuznetsova, “ comes from their potential ability to solve certain problems exponentially faster compared to classical computers, such as factoring a large number into its primes, which would allow us to break cryptographic codes. These problems cannot be solved using a  in the foreseeable future.”

May 12, 2010

Semi-conductor nanocrystals and quantum computing

Another step toward quantum computing.

The release:

Quantum move toward next generation computing

McGill researchers make important contribution to the development of quantum computing

This release is available in French.

IMAGE: These images show the electrostatic energy given off when electrons are added to a quantum dot. They were made with an atomic-force microscope.

Click here for more information.

Physicists at McGill University have developed a system for measuring the energy involved in adding electrons to semi-conductor nanocrystals, also known as quantum dots – a technology that may revolutionize computing and other areas of science. Dr. Peter Grütter, McGill’s Associate Dean of Research and Graduate Education, Faculty of Science, explains that his research team has developed a cantilever force sensor that enables individual electrons to be removed and added to a quantum dot and the energy involved in the operation to be measured.

Being able to measure the energy at such infinitesimal levels is an important step in being able to develop an eventual replacement for the silicon chip in computers – the next generation of computing. Computers currently work with processors that contain transistors that are either in an on or off position – conductors and semi-conductors – while quantum computing would allow processors to work with multiple states, vastly increasing their speed while reducing their size even more.

Although popularly used to connote something very large, the word “quantum” itself actually means the smallest amount by which certain physical quantities can change. Knowledge of these energy levels enables scientists to understand and predict the electronic properties of the nanoscale systems they are developing.

“We are determining optical and electronic transport properties,” Grütter said. “This is essential for the development of components that might replace silicon chips in current computers.”

IMAGE: These images show the electrostatic energy given off when electrons are added to a quantum dot. They were made with an atomic-force microscope.

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The electronic principles of nanosystems also determine their chemical properties, so the team’s research is relevant to making chemical processes “greener” and more energy efficient. For example, this technology could be applied to lighting systems, by using nanoparticles to improving their energy efficiency. “We expect this method to have many important applications in fundamental as well as applied research,” said Lynda Cockins of McGill’s Department of Physics.

The principle of the cantilever sensors sounds relatively simple. “The cantilever is about 0.5 mm in size (about the thickness of a thumbnail) and is essentially a simple driven, damped harmonic oscillator, mathematically equivalent to a child’s swing being pushed,” Grütter explained. “The signal we measure is the damping of the cantilever, the equivalent to how hard I have to push the kid on the swing so that she maintains a constant height, or what I would call the ‘oscillation amplitude.’ “

Dr. Aashish Clerk, Yoichi Miyahara, and Steven D. Bennett of McGill’s Dept. of Physics, and scientists at the Institute for Microstructural Sciences of the National Research Council of Canada contributed to this research, which was published online late yesterday afternoon in the Proceedings of the National Academy of Sciences. The research received funding from the Natural Sciences and Engineering Research Council of Canada, le Fonds Québécois de le Recherche sur la Nature et les Technologies, the Carl Reinhardt Fellowship, and the Canadian Institute for Advanced Research.

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May 1, 2010

Quantum computing news

I wouldn’t call this an astounding breakthrough, but sometimes a shift in focus — like this research into alternative materials for quantum computers — can lead to seismic changes in the field down the road.

The release:

UCSB scientists look beyond diamond for quantum computing

IMAGE: David Awschalom is a researcher at University of California – Santa Barbara.

Click here for more information.

(Santa Barbara, Calif.) –– A team of scientists at UC Santa Barbara that helped pioneer research into the quantum properties of a small defect found in diamonds has now used cutting-edge computational techniques to produce a road map for studying defects in alternative materials.

Their new research is published in the online edition of the Proceedings of the National Academy of Sciences (PNAS), and will soon be published in the print edition of the journal. The findings may enable new applications for semiconductors ––materials that are the foundation of today’s information technology. In particular, they may help identify alternative materials to use for building a potential quantum computer.

“Our results are likely to have an impact on experimental and theoretical research in diverse areas of science and technology, including semiconductor physics, materials science, magnetism, and quantum device engineering,” said David D. Awschalom, UCSB physics professor and one of two lead investigators on this project. “Ironically, while much of semiconductor technology is devoted to eliminating the defects that interfere with how today’s devices operate, these defects may actually be useful for future quantum technologies.”

IMAGE: Chris Van de Walle is a researcher at University of California – Santa Barbara.

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According to PNAS, the researchers have developed a set of screening criteria to find specific atomic defects in solids that could act as quantum bits (qubits) in a potential quantum computer. As a point of reference, they use a system whose quantum properties they themselves have recently helped to discern, the NV or nitrogen-vacancy center defect in diamond. This defect, which the team has shown can act as a very fast and stable qubit at room temperature, consists of a stray nitrogen atom alongside a vacancy in the otherwise perfect stacking of carbon atoms in a diamond.

Electrons trapped at the defect’s center interact with light and microwaves in a predictable way, allowing information to be stored in and read out from the orientation of their quantum-mechanical spins.

The drawback to using diamond, however, is that the material is expensive and difficult to grow and process into chips. This raises the question of whether there may be defects in other materials that have similar properties and could perform equally well.

In this week’s publication, the researchers enumerate specific screening criteria to identify appropriate defects in materials that could be useful for building a quantum computer. Experimental testing of all the potential candidates might take decades of painstaking research, explained Awschalom. To address this problem, the UCSB group employed advanced computational methods to theoretically examine the characteristics of potential defect centers in many different materials, providing a sort of road map for future experiments.

UCSB’s Chris G. Van de Walle, professor of materials and one of the senior investigators on the project, remarked: “We tap into the expertise that we have accumulated over the years while examining ‘bad’ defects, and channel it productively into designing ‘good’ defects; i.e., those that have the necessary characteristics to equal or even outperform the NV center in diamond.” This expertise is backed up by advanced theoretical and computational models that enable the reliable prediction of the properties of defects, a number of which are proposed and examined in the paper.

Awschalom added: “We anticipate this work will stimulate additional collaborative activities among theoretical physicists and materials engineers to accelerate progress towards quantum computing based on semiconductors.”

Current computers are based on binary logic: each bit can be either “one” or “zero.” In contrast, each qubit in a quantum computer is continuously variable between these two states and hence offers infinitely more possibilities to be manipulated and combined with other qubits to produce a desired computational result. “It has been well established that, in theory, quantum computers can tackle some tasks that are completely beyond the capabilities of binary computers,” said Awschalom. “The challenge has been to identify real physical systems that can serve as qubits for future machines.”

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April 22, 2010

Quantum computing improvement

This is the first quantum computing post in a couple of months. This is a promising finding.

The release:

Bizarre matter could find use in quantum computers

Rice physicists: Odd electron mix has fault-tolerant quantum registry

IMAGE: From left, Rice physicist Rui-Rui Du, graduate students Chi Zhang and Yanhua Dai, and former postdoctoral researcher Tauno Knuuttila (not pictured) have found that odd groupings of ultracold electrons could…

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HOUSTON — (April 21, 2010) — There are enticing new findings this week in the worldwide search for materials that support fault-tolerant quantum computing. New results from Rice University and Princeton University indicate that a bizarre state of matter that acts like a particle with one-quarter electron charge also has a “quantum registry” that is immune to information loss from external perturbations.

The research appeared online April 21 in Physical Review Letters. The team of physicists found that ultracold mixes of electrons caught in magnetic traps could have the necessary properties for constructing fault-tolerant quantum computers — future computers that could be far more powerful than today’s computers. The mixes of electrons are dubbed “5/2 quantum Hall liquids” in reference to the unusual quantum properties that describe their makeup.

“The big goal, the whole driving force, besides deep academic curiosity, is to build a quantum computer out of this,” said the study’s lead author Rui-Rui Du, professor of physics at Rice. “The key for that is whether these 5/2 liquids have ‘topological’ properties that would render them immune to the sorts of quantum perturbations that could cause information degradation in a quantum computer.”

Du said the team’s results indicate the 5/2 liquids have the desired properties. In the parlance of condensed-matter physics, they are said to represent a “non-Abelian” state of matter.

Non-Abelian is a mathematical term for a system with “noncommutative” properties. In math, commutative operations, like addition, are those that have the same outcome regardless of the order in which they are carried out. So, one plus two equals three, just as two plus one equals three. In daily life, commutative and noncommutative tasks are commonplace. For example, when doing the laundry, it doesn’t matter if the detergent is added before the water or the water before the detergent, but it does matter if the clothes are washed before they’re placed in the dryer.

“It will take a while to fully understand the complete implications of our results, but it is clear that we have nailed down the evidence for ‘spin polarization,’ which is one of the two necessary conditions that must be proved to show that the 5/2 liquids are non-Abelian,” Du said. “Other research teams have been tackling the second condition, the one-quarter charge, in previous experiments.”

The importance of the noncommutative quantum properties is best understood within the context of fault-tolerant quantum computers, a fundamentally new type of computer that hasn’t been built yet.

Computers today are binary. Their electrical circuits, which can be open or closed, represent the ones and zeros in binary bits of information. In quantum computers, scientists hope to use “quantum bits,” or qubits. Unlike binary ones and zeros, the qubits can be thought of as little arrows that represent the position of a bit of quantum matter. The arrow might represent a one if it points straight up or a zero if it points straight down, but it could also represent any number in between. In physics parlance, these arrows are called quantum “states.” And for certain complex calculations, being able to represent information in many different states would present a great advantage over binary computing.

The upshot of the 5/2 liquids being non-Abelian is that they have a sort of “quantum registry,” where information doesn’t change due to external quantum perturbations.

“In a way, they have internal memory of their previous state,” Du said.

The conditions needed to create the 5/2 liquids are extreme. At Rice, Tauno Knuuttila, a former postdoctoral research scientist in Du’s group, spent several years building the “demagnetization refrigerator” needed to cool 5-millimeter squares of ultrapure semiconductors to within one-10,000th of a degree of absolute zero. It took a week for Knuuttila to simply cool the nearly one-ton instrument to the necessary temperature for the Rice experiments.

The gallium arsenide semiconductors used in the tests are the most pure on the planet. They were created by Loren Pfieiffer, Du’s longtime collaborator at Princeton and Bell Labs. Rice graduate student Chi Zhang conducted additional tests at the National High Magnetic Field Laboratory in Tallahassee, Fla., to verify that the 5/2 liquid was spin- polarized.

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Study co-authors include Zhang, Knuuttila, Pfeiffer, Princeton’s Ken West and Rice’s Yanhua Dai. The research is supported by the Department of Energy, the National Science Foundation and the Keck Foundation.

February 15, 2010

A little nano bling …

… may lead to some serious nanotech applications in medicine, data protection and supercomputing.

The release:

Digging deep into diamonds, applied physicists advance quantum science and technology

Diamond nanowire device could lead to new class of diamond nanomaterials suitable for quantum cryptography, quantum computing, and magnetic field imaging

IMAGE: A diamond-based nanowire device. Researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just “one-of-a-kind ” designs,…

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CAMBRIDGE, Mass., By creating diamond-based nanowire devices, a team at Harvard has taken another step towards making applications based on quantum science and technology possible.

The new device offers a bright, stable source of single photons at room temperature, an essential element in making fast and secure computing with light practical.

The finding could lead to a new class of nanostructured diamond devices suitable for quantum communication and computing, as well as advance areas ranging from biological and chemical sensing to scientific imaging.

Published in the February 14th issue of Nature Nanotechnology, researchers led by Marko Loncar, Assistant Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), found that the performance of a single photon source based on a light emitting defect (color center) in diamond could be improved by nanostructuring the diamond and embedding the defect within a diamond nanowire.

Scientists, in fact, first began exploiting the properties of natural diamonds after learning how to manipulate the electron spin, or intrinsic angular momentum, associated with the nitrogen vacancy (NV) color center of the gem. The quantum (qubit) state can be initialized and measured using light.

The color center “communicates” by emitting and absorbing photons. The flow of photons emitted from the color center provides a means to carry the resulting information, making the control, capture, and storage of photons essential for any kind of practical communication or computation. Gathering photons efficiently, however, is difficult since color-centers are embedded deep inside the diamond.

“This presents a major problem if you want to interface a color center and integrate it into real-world applications,” explains Loncar. “What was missing was an interface that connects the nano-world of a color center with macro-world of optical fibers and lenses.”

The diamond nanowire device offers a solution, providing a natural and efficient interface to probe an individual color center, making it brighter and increasing its sensitivity. The resulting enhanced optical properties increases photon collection by nearly a factor of ten relative to natural diamond devices.

“Our nanowire device can channel the photons that are emitted and direct them in a convenient way,” says lead-author Tom Babinec, a graduate student at SEAS.

Further, the diamond nanowire is designed to overcome hurdles that have challenged other state-of-the-art systems—such as those based on fluorescent dye molecules, quantum dots, and carbon nanotubes—as the device can be readily replicated and integrated with a variety of nano-machined structures.

The researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just “one-of-a-kind” designs, the realization of quantum networks and systems, which require the integration and manipulation of many devices in parallel, is more likely.

“We consider this an important step and enabling technology towards more practical optical systems based on this exciting material platform,” says Loncar. “Starting with these synthetic, nanostructured diamond samples, we can start dreaming about the diamond-based devices and systems that could one day lead to applications in quantum science and technology as well as in sensing and imaging.”

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Loncar and Babinec’s co-authors included research scholar Birgit Hausmann, graduate student Yinan Zhang, and postdoctoral student Mughees Khan, all at SEAS; graduate student Jero Maze in the Department of Physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University.

The researchers acknowledge the following support: Nanoscale Interdisciplinary Research Team (NIRT) grant from National Science Foundation (NSF), the NSF-funded Nanoscale Science and Engineering Center at Harvard (NSEC); the Defense Advanced Research Projects Agency (DARPA); and a National Defense Science and Engineering Graduate Fellowship and National Science Foundation Graduate Fellowship. All devices have been fabricated at the Center for Nanoscale Systems (CNS) at Harvard.

February 7, 2010

Another step closer to quantum computers

Here’s the release from Friday:

Princeton scientist makes a leap in quantum computing

A major hurdle in the ambitious quest to design and construct a radically new kind of quantum computer has been finding a way to manipulate the single electrons that very likely will constitute the new machines’ processing components or “qubits.”

Princeton University’s Jason Petta has discovered how to do just that — demonstrating a method that alters the properties of a lone electron without disturbing the trillions of electrons in its immediate surroundings. The feat is essential to the development of future varieties of superfast computers with near-limitless capacities for data.

Petta, an assistant professor of physics, has fashioned a new method of trapping one or two electrons in microscopic corrals created by applying voltages to minuscule electrodes. Writing in the Feb. 5 edition of Science, he describes how electrons trapped in these corrals form “spin qubits,” quantum versions of classic computer information units known as bits. Other authors on the paper include Art Gossard and Hong Lu at the University of California-Santa Barbara.

Previous experiments used a technique in which electrons in a sample were exposed to microwave radiation. However, because it affected all the electrons uniformly, the technique could not be used to manipulate single electrons in spin qubits. It also was slow. Petta’s method not only achieves control of single electrons, but it does so extremely rapidly — in one-billionth of a second.

“If you can take a small enough object like a single electron and isolate it well enough from external perturbations, then it will behave quantum mechanically for a long period of time,” said Petta. “All we want is for the electron to just sit there and do what we tell it to do. But the outside world is sort of poking at it, and that process of the outside world poking at it causes it to lose its quantum mechanical nature.”

When the electrons in Petta’s experiment are in what he calls their quantum state, they are “coherent,” following rules that are radically different from the world seen by the naked eye. Living for fractions of a second in the realm of quantum physics before they are rattled by external forces, the electrons obey a unique set of physical laws that govern the behavior of ultra-small objects.

Scientists like Petta are working in a field known as quantum control where they are learning how to manipulate materials under the influence of quantum mechanics so they can exploit those properties to power advanced technologies like quantum computing. Quantum computers will be designed to take advantage of these characteristics to enrich their capacities in many ways.

In addition to electrical charge, electrons possess rotational properties. In the quantum world, objects can turn in ways that are at odds with common experience. The Austrian theoretical physicist Wolfgang Pauli, who won the Nobel Prize in Physics in 1945, proposed that an electron in a quantum state can assume one of two states — “spin-up” or “spin-down.” It can be imagined as behaving like a tiny bar magnet with spin-up corresponding to the north pole pointing up and spin-down corresponding to the north pole pointing down.

An electron in a quantum state can simultaneously be partially in the spin-up state and partially in the spin-down state or anywhere in between, a quantum mechanical property called “superposition of states.” A qubit based on the spin of an electron could have nearly limitless potential because it can be neither strictly on nor strictly off.

New designs could take advantage of a rich set of possibilities offered by harnessing this property to enhance computing power. In the past decade, theorists and mathematicians have designed algorithms that exploit this mysterious superposition to perform intricate calculations at speeds unmatched by supercomputers today.

Petta’s work is using electron spin to advantage.

“In the quest to build a quantum computer with electron spin qubits, nuclear spins are typically a nuisance,” said Guido Burkard, a theoretical physicist at the University of Konstanz in Germany. “Petta and coworkers demonstrate a new method that utilizes the nuclear spins for performing fast quantum operations. For solid-state quantum computing, their result is a big step forward.”

Petta’s spin qubits, which he envisions as the core of future quantum logic elements, are cooled to temperatures near absolute zero and trapped in two tiny corrals known as quantum wells on the surface of a high-purity, gallium arsenide chip. The depth of each well is controlled by varying the voltage on tiny electrodes or gates. Like a juggler tossing two balls between his hands, Petta can move the electrons from one well to the other by selectively toggling the gate voltages.

Prior to this experiment, it was not clear how experimenters could manipulate the spin of one electron without disturbing the spin of another in a closely packed space, according to Phuan Ong, the Eugene Higgins Professor of Physics at Princeton and director of the Princeton Center for Complex Materials.

Other experts agree.

“They have managed to create a very exotic transient condition, in which the spin state of a pair of electrons is in that moment entangled with an almost macroscopic degree of freedom,” said David DiVencenzo, a research staff member at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y.

Petta’s research also is part of the fledgling field of “spintronics” in which scientists are studying how to use an electron’s spin to create new types of electronic devices. Most electrical devices today operate on the basis of another key property of the electron — its charge.

There are many more challenges to face, Petta said.

“Our approach is really to look at the building blocks of the system, to think deeply about what the limitations are and what we can do to overcome them,” Petta said. “But we are still at the level of just manipulating one or two quantum bits, and you really need hundreds to do something useful.”

As excited as he is about present progress, long-term applications are still years away. “It’s a one-day-at-a-time approach,” Petta said.

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November 22, 2009

Getting closer to quantum computing

The latest in quantum computing news:

UCSB physicists move 1 step closer to quantum computing

IMAGE: This is David Awschalom from the University of California — Santa Barbara.

Click here for more information.

 

(Santa Barbara, Calif.) –– Physicists at UC Santa Barbara have made an important advance in electrically controlling quantum states of electrons, a step that could help in the development of quantum computing. The work is published online today on the Science Express Web site.

The researchers have demonstrated the ability to electrically manipulate, at gigahertz rates, the quantum states of electrons trapped on individual defects in diamond crystals. This could aid in the development of quantum computers that could use electron spins to perform computations at unprecedented speed.

Using electromagnetic waveguides on diamond-based chips, the researchers were able to generate magnetic fields large enough to change the quantum state of an atomic-scale defect in less than one billionth of a second. The microwave techniques used in the experiment are analogous to those that underlie magnetic resonance imaging (MRI) technology.

The key achievement in the current work is that it gives a new perspective on how such resonant manipulation can be performed. “We set out to see if there is a practical limit to how fast we can manipulate these quantum states in diamond,” said lead author Greg Fuchs, a postdoctoral researcher at UCSB. “Eventually, we reached the point where the standard assumptions of magnetic resonance no longer hold, but to our surprise we found that we actually gained an increase in operation speed by breaking the conventional assumptions.”

While these results are unlikely to change MRI technology, they do offer hope for the nascent field of quantum computing. In this field, individual quantum states take on the role that transistors perform in classical computing.

IMAGE: This is postdoctoral researcher Greg Fuchs in the lab of UCSB’s Center for Spintronics and Quantum Computation.

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“From an information technology standpoint, there is still a lot to learn about controlling quantum systems,” said David Awschalom, principal investigator and professor of physics, electrical and computer engineering at UCSB. “Still, it’s exciting to stand back and realize that we can already electrically control the quantum state of just a few atoms at gigahertz rates –– speeds comparable to what you might find in your computer at home.”

 

 

 

 

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The work was performed at UCSB’s Center for Spintronics and Quantum Computation, directed by Awschalom. Co-authors on the paper include David. M. Toyli and F. Joseph Heremans, both of UCSB. Slava V. Dobrovitski of Ames Laboratory and Iowa State University contributed to the paper.

July 31, 2009

Quantum computing — a breakthrough and a warning

The potential power of quantum computing is astonishing, and a lot of research is going into creating quantum computers. Of course there’s always a dark side to anything — a quantum computer that realizes the full potential of the technology will also render current security and encryption obsolete overnight.

This post is a about a breakthrough involving the building blocks of matter and how that adds to quantum computing research, and also a cautionary tale from a researcher who is preparing for the security needs when the first quantum computer arises.

First the warning:

So far, so good, despite an occasional breach. But our security and our data could be compromised overnight when the first quantum computer is built, says Dr. Julia Kempe of Tel Aviv University‘s Blavatnik School of Computer Science. These new computers, still in the theoretical stage, will be many times more powerful than the computers that protect our data now.

Laying the groundwork to keep governments, companies and individuals safe, Dr. Kempe is working to understand the power of quantum computers by designing algorithms that fit them. At the same time, she is figuring out the limits of quantum computers, something especially important so we can build safety systems against quantum hackers.

“If a very rich person worked secretly to fund the building of a quantum computer, there is no reason in principle that it couldn’t be used for malevolent power within the next decade,” she says. “Governments, large corporations, entrepreneurs and common everyday people will have no ability to protect themselves. So we have to plan ahead.”

And now the breakthrough:

Discovery about behavior of building block of nature could lead to computer revolution

A team of physicists from the Universities of Cambridge and Birmingham have shown that electrons in narrow wires can divide into two new particles called spinons and a holons.

The electron is a fundamental building block of nature and is indivisible in isolation, yet a new experiment has shown that electrons, if crowded into narrow wires, are seen to split apart.

The electron is responsible for carrying electricity in wires and for making magnets. These two properties of magnetism and electric charge are carried by electrons which seem to have no size or shape and are impossible to break apart.

However, what is true about the properties of a single electron does not seem to be the case when electrons are brought together. Instead the like-charged electrons repel each other and need to modify the way they move to avoid getting too close to each other. In ordinary metals this does not usually make much difference to their behaviour. However, if the electrons are put in a very narrow wire the effects are exacerbated as they find it much harder to move past each other.

In 1981, physicist Duncan Haldane conjectured theoretically that under these circumstances and at the lowest temperatures the electrons would always modify the way they behaved so that their magnetism and their charge would separate into two new types of particle called spinons and holons.

The challenge was to confine electrons tightly in a ‘quantum wire’ and bring this wire close enough to an ordinary metal so that the electrons in that metal could ‘jump’ by quantum tunneling into the wire. By observing how the rate of jumping varies with an applied magnetic field the experiment reveals how the electron, on entering the quantum wire, has to fall apart into spinons and holons. The conditions to make this work comprised a comb of wires above a flat metal cloud of electrons. The Cambridge physicists, Yodchay Jompol and Chris Ford, clearly saw the distinct signatures of the two new particles as the Birmingham theorists, Tim Silk and Andy Schofield, had predicted.

Dr Chris Ford from the University of Cambridge’s Cavendish Laboratory says, ‘We had to develop the technology to pass a current between a wire and a sheet only 30 atomic widths apart.

‘The measurements have to be made at extremely low temperatures, about a tenth of a degree above absolute zero.

‘Quantum wires are widely used to connect up quantum “dots”, which may in the future form the basis of a new type of computer, called a quantum computer. Thus understanding their properties may be important for such quantum technologies, as well as helping to develop more complete theories of superconductivity and conduction in solids in general. This could lead to a new computer revolution.’

Professor Andy Schofield from the University of Birmingham’s School of Physics and Astronomy says, ‘The experiment to test this is based on an idea I had together with three colleagues almost 10 years ago. At that time the technology required to implement the experiment was still a long way off.

‘What is remarkable about this new experiment is not just the clarity of the observation of the spinon and holon, which confirms some earlier studies, but that the spinon and holon are seen well beyond the region that Duncan Haldane originally conjectured.

‘Our ability to control the behaviour of a single electron is responsible for the semiconductor revolution which has led to cheaper computers, iPods and more. Whether we will be able to control these new particles as successfully as we have the single electron remains to be seen. What it does reveal is that bringing electrons together can lead to new properties and even new particles.’

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 Notes to Editors

1. The paper is published in Science 10.1126/science.1171769 at http://dx.doi.org/10.1126/science.1171769

2. The experiment was performed in Cambridge’s Cavendish Laboratory with theoretical support from scientists at the University of Birmingham’s School of Physics and Astronomy.

July 8, 2009

Quantum computing progress

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 2:47 pm

Via KurzweilAI.net — Quantum computing holds a lot of promise, not so much reality so far. Any news on progress is always good news.

Quantum computer closer: Optical transistor made from single molecule
gizmag, July 6, 2009

An optical transistor has been created from a single hydrocarbon molecule called dibenzanthanthrene by ETH Zurich researchers.

 
Read Original Article>>

July 3, 2009

The latest in quantum computing

Filed under: Science, Technology — Tags: , , — David Kirkpatrick @ 3:45 pm

Hot on the heels of a post about photonic computing, here’s the latest in quantum computing — using matter qubits for quantum memory.

From the second link:

Physicists Peter Maunz and coauthors from the University of Maryland Department of Physics and National Institute of Standards and Technology in College Park, Maryland, and the University of Michigan in Ann Arbor, Michigan, published their study in a recent issue of Physical Review Letters.

“Our work demonstrates a probabilistic remote entangling quantum gate,” Maunz told PhysOrg.com. “Remote entangling gates are an essential building block for quantum repeaters which facilitate quantum communication over long distances. Furthermore, the remote link established by the entangling gate could be used to interconnect remote quantum processors and thus could be an important additional possibility to scale a future quantum computer.”

As the scientists explain, their quantum gate works by entangling two ytterbium ions, each confined in its own trap positioned one meter apart. The scientists suspended the ions into either a one or a zero state using . The use of ion traps prevents anything from interacting with the ytterbium. This allows the ions to hold states of both zero and one simultaneously so that the ions function as qubits.

April 9, 2009

Quantum computing news

The final release dump post. As always I prefer providing you the entire release rather than rework it into something different. Any commentary or strong feelings on the release makes it into the intro, but usually it’s just news that I find interesting, cool or maybe just funny. Quantum computing news is always interesting and very, very cool.

The release:

Quantum computers will require complex software to manage errors

IMAGE: While rudimentary is a fair description of this early computer, the National Bureau of Standards — SEAC, built in 1950 –prototype quantum computers have not even reached its level of…

Click here for more information. 

Highlighting another challenge to the development of quantum computers, theorists at the National Institute of Standards and Technology (NIST) have shown* that a type of software operation, proposed as a solution to fundamental problems with the computers’ hardware, will not function as some designers had hoped.

Quantum computers—if they can ever be realized—will employ effects associated with atomic physics to solve otherwise intractable problems. But the NIST team has proved that the software in question, widely studied due to its simplicity and robustness to noise, is insufficient for performing arbitrary computations. This means that any software the computers use will have to employ far more complex and resource-intensive solutions to ensure the devices function effectively.

Unlike a conventional computer’s binary on-off switches, the building blocks of quantum computers, known as quantum bits, or “qubits,” have the mind-bending ability to exist in both “on” and “off” states simultaneously due to the so-called “superposition” principle of quantum physics. Once harnessed, the superposition principle should allow quantum computers to extract patterns from the possible outputs of a huge number of computations without actually performing all of them. This ability to extract overall patterns makes the devices potentially valuable for tasks such as codebreaking.

One issue, though, is that prototype quantum processors are prone to errors caused, for example, by noise from stray electric or magnetic fields. Conventional computers can guard against errors using techniques such as repetition, where the information in each bit is copied several times and the copies are checked against one another as the calculation proceeds. But this sort of redundancy is impossible in a quantum computer, where the laws of the quantum world forbid such information cloning.

To improve the efficiency of error correction, researchers are designing quantum computing architectures so as to limit the spread of errors. One of the simplest and most effective ways of ensuring this is by creating software that never permits qubits to interact if their errors might compound one another. Quantum software operations with this property are called “transversal encoded quantum gates.” NIST information theorist Bryan Eastin describes these gates as a solution both simple to employ and resistant to the noise of error-prone quantum processors. But the NIST team has proved mathematically that transversal gates cannot be used exclusively, meaning that more complex solutions for error management and correction must be employed.

Eastin says their result does not represent a setback to quantum computer development because researchers, unable to figure out how to employ transversal gates universally, have already developed other techniques for dealing with errors. “The findings could actually help move designers on to greener pastures,” he says. “There are some avenues of exploration that are less tempting now.”

 

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* B. Eastin and E. Knill. Restrictions on transversal quantum gate sets. Physical Review Letters, 102, 110502, March 20, 2009.

March 20, 2009

Toward quantum computing

Filed under: Technology — Tags: , , , , — David Kirkpatrick @ 5:00 pm

Quantum computers are the next gigantic leap in processing power. Here’s another step in that direction.

Via KurzweilAI.net:

Scientists make quantum leap in developing faster computers
PhysOrg.com, Mar. 19, 2009

Scientists at the Universities of Manchester and Edinburgh have created a molecular device that could act as a building block for future generations of superfast, non-silicon based computers.

It uses magnetic molecules, which could be used as qubits, combined with molecular machines that enable them to move.

 
Read Original Article>>

December 26, 2008

The top ten quantum articles of 2008

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 1:27 pm

From KurzweilAI.net — This story comes from New Scientist Physics & Math and covers things quantum such as antimatter, quantum computing.

A year in the quantum world
New Scientist Physics & Math, Dec. 26, 2008

Four radical routes to a theory of everything, The great antimatter mystery, Anyons: the breakthrough quantum computing needs?, and Matter is merely vacuum fluctuations are among the year’s top 10 in-depth articles about the quantum world.

 
Read Original Article>>

December 7, 2008

Making headway toward quantum networks

Quantum computing is coming. Get ready.

The release:

New record for information storage and retrieval lifetime advances quantum networks

Quantum memory boost

IMAGE: Ran Zhao and Yaroslav Dudin, graduate students in the Georgia Tech School of Physics, adjust optics in a system used to study quantum memory.

Click here for more information. 

Physicists have taken a significant step toward creation of quantum networks by establishing a new record for the length of time that quantum information can be stored in and retrieved from an ensemble of very cold atoms. Though the information remains usable for just milliseconds, even that short lifetime should be enough to allow transmission of data from one quantum repeater to another on an optical network.

The new record – 7 milliseconds for rubidium atoms stored in a dipole optical trap – is scheduled to reported December 7 in the online version of the journal Nature Physics by researchers at the Georgia Institute of Technology. The previous record for storage time was 32 microseconds, a difference of more than two orders of magnitude.

“This is a really significant step for us, because conceptually it allows long memory times necessary for long-distance quantum networking,” said Alex Kuzmich, associate professor in the Georgia Tech School of Physics and a co-author of the paper. “For multiple architectures with many memory elements, several milliseconds would allow the movement of light across a thousand kilometers.”

The keys to extending the storage time included the use of a one-dimensional optical lattice to help confine the atoms and selection of an atomic phase that is insensitive to magnetic effects. The research was sponsored by the National Science Foundation, the A.P. Sloan Foundation and the U.S. Office of Naval Research.

IMAGE: A research group from the Georgia Institute of Technology poses with optical equipment used to study quantum memory.

Click here for more information. 

The general purpose of quantum networking or quantum computing is to distribute entangled qubits – two correlated data bits that are either “0” or “1” – over long distances. The qubits would travel as photons across existing optical networks that are part of the global telecommunications system.

Because of loss in the optical fiber that makes up networks, repeaters must be installed at regular intervals – about every 100 kilometers – to boost the signal. Those repeaters will need quantum memory to receive the photonic signal, store it briefly and then produce a photonic signal that will carry the information to the next node, and on to its final destination.

For their memory, the Georgia Tech researchers used an ensemble of rubidium-87 atoms that is cooled to almost absolute zero to minimize atomic motion. To store information, the entire atomic ensemble is exposed to laser light carrying a signal, which allows each atom to participate in the storage as part of a “collective excitation.”

In simple terms, each atom “sees” the incoming signal – which is a rapidly oscillating electromagnetic field – slightly differently. Each atom is therefore imprinted with phase information that can later be “read” from the ensemble with another laser.

IMAGE: Associate professor Alex Kuzmich and research scientist Stewart Jenkins, both from the Georgia Tech School of Physics, adjust optics in a system used to study quantum memory.

Click here for more information. 

Even though they are very cold, the atoms of the ensemble are free to move in a random way. Because each atom stores a portion of the quantum information and that data’s usefulness depends on each atom’s location in reference to other atoms, significant movement of the atoms could destroy the information.

“The challenge for us in implementing these long-lived quantum memories is to preserve the phase imprinting in the atomic ensemble for as long as possible,” explained Stewart Jenkins, a School of Physics research scientist who participated in the research. “It turns out that is difficult to do experimentally.”

To extend the lifetime of their memory, the Georgia Tech researchers took two approaches. The first was to confine the atoms using an optical lattice composed of laser beams. Because of the laser frequencies chosen, the atoms are attracted to specific locations within the lattice, though they are not held tightly in place.

Because the ensemble atoms are affected by environmental conditions such as magnetism, the second strategy was to use atoms that had been pumped to the so-called “clock transition state” that is relatively insensitive to magnetic fields.

“The most critical aspect to getting these long coherence times was the optical lattice,” Jenkins explained. “Although atoms had been confined in optical lattices before, what we did was to use this tool in the context of implementing quantum memory.”

Other research teams have stored quantum information in single atoms or ions. This simpler approach allows longer storage periods, but has limitations, he said.

“The advantage of using these ensembles as opposed to single atoms is that if we shine into them a ‘read’ laser field, because these atoms have a particular phase imprinted on them, we know with a high degree of probability that we are going to get a second photon – the idler photon – coming out in a particular direction,” Jenkins explained. “That allows us to put a detector in the right location to read the photon.”

Though the work significantly advances quantum memories, practical quantum networks probably are at least a decade away, Kuzmich believes.

“In practice, you will need to make robust repeater nodes with hundreds of memory elements that can be quickly manipulated and coupled to the fiber,” he said. “There is likely to be slow progress in this area with researchers gaining better and better control of quantum systems. Eventually, they will get good enough so we can make a jump to having systems that can work outside the laboratory environment.”

 

###

 

In addition to Kuzmich and Jenkins, the research team included Ran Zhao, Yaroslav Dudin, Corey Campbell, Dzmitry Matsukevich, and Brian Kennedy, a professor in the School of Physics.

November 14, 2008

Atomic quantum computing

One more bullet for the quantum computing arsenal.

From the PhysOrg link:

“There are a number of different proposals for quantum computing,” Andrew Daley tells PhysOrg.com. “These include solid state or semiconductor as well as atomic and molecular systems. We are considering atomic systems, and more specifically alkaline earth metals.”

Daley is a physicist in the Institute for Theoretical Physics at the University of Innsbruck and the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Austria. He, along with Martin Boyd and Jun Ye at the University of Colorado, and Peter Zoller at Innsbruck, are proposing a quantum computing scheme that would make use of overlaying optical lattices to store information as well as perform computations. Much of this work was performed when the authors were guests at the California Institute of Technology in Pasadena, and their ideas are shared in Physical Review Letters: “Quantum Computing with Alkaline-Earth-Metal Atoms.”

Electrons play a vital role in quantum computing with atoms, and when atoms are controlled with light, the electrons are also controlled. “That’s what makes alkali atoms nice to deal with,” says Daley. “They only have one valence electron, which makes the system really simple.” He then points out that alkaline earth metals offer an advantage over alkali atoms: “There are two electrons weakly bound. Even though the system is a little more complicated, there are some very nice properties.”

October 22, 2008

Moving toward quantum computing

Making headway, it seems. This is amazing — storing information inside the nucleus of an atom!

From the link:

The problem: How do you isolate a quantum bit from a noisy environment to protect the deli-cate quantum information, while at the same time allowing it to interact with the outside world so that it can be manipulated and measured?

The team, with scientists and engineers from Oxford and Princeton universities and Lawrence Berkeley National Laboratory, reported a solution to this problem in the Oct. 23 issue of the journal Nature.

The team’s plan was to devise a hybrid system using both the electron and nucleus of an atom of phosphorous embedded in a silicon crystal. Each behaves as a tiny quantum magnet capa-ble of storing quantum information, but inside the crystal the electron is more than a million times bigger than the nucleus, with a magnetic field that is a thousand times stronger. This makes the electron well-suited for manipulation and measurement, but not so good for storing information, which can become rapidly corrupted. This is where the nucleus comes in: when the information in the electron is ready for storage, it is moved into the nucleus where it can survive for much longer times.

Go below the fold for a release from October 23 on this story.

(more…)

September 25, 2008

Quantum computing and more

We’re getting closer to harnessing quantum mechanics to create supercomputers and other devices.

From the link:

The brave new world of quantum technology may be a big step closer to reality thanks to a team of University of Calgary researchers that has come up with a unique new way of testing quantum devices to determine their function and accuracy. Their breakthrough is reported in today’s edition of Science Express, the advanced online publication of the prestigious journal Science.

“Building quantum machines is difficult because they are very complex, therefore the testing you need to do is also very complex,” said Barry Sanders, director of the U of C’s Institute for Quantum Information Science and a co-author of the paper. “We broke a bunch of taboos with this work because we have come up with an entirely new way of testing that is relatively simple and doesn’t require a lot of large and expensive diagnostic equipment.”

Similar to any electronic or mechanical device, building a quantum machine requires a thorough understanding of how each part operates and interacts with other parts if the finished product is going to work properly. In the quantum realm, scientists have been struggling to find ways to accurately determine the properties of individual components as they work towards creating useful quantum systems. The U of C team has come up with a highly-accurate method for analyzing quantum optical processes using standard optical techniques involving lasers and lenses.

September 3, 2008

Advances toward quantum computing

News from PhysOrg:

MIT researchers may have found a way to overcome a key barrier to the advent of super-fast quantum computers, which could be powerful tools for applications such as code breaking. Ever since Nobel Prize-winning physicist Richard Feynman first proposed the theory of quantum computing more than two decades ago, researchers have been working to build such a device.

One approach involves superconducting devices that, when cooled to temperatures of nearly absolute zero (-459 degrees F, -273 degrees C), can be made to behave like artificial atoms – nanometer-scale “boxes” in which the electrons are forced to exist at specific, discrete energy levels (picture an elevator that can stop at the floors of a building but not in between). But traditional scientific techniques for characterizing – and therefore better understanding – atoms and molecules do not necessarily translate easily to artificial atoms, said William Oliver of MIT Lincoln Laboratory’s Analog Device Technology Group and MIT’s Research Laboratory for Electronics (RLE).

In the Sept. 4 issue of Nature, Oliver and colleagues have reported a technique that could fill that gap. Oliver’s co-authors are lead author David Berns, a graduate student in physics and RLE; Mark Rudner, also a graduate student in physics; Sergio Valenzuela, a research affiliate at MIT’s Francis Bitter Magnet Laboratory; Karl Berggren, the Emanuel E. Landsman Career Development Associate Professor in the Department of Electrical Engineering and Computer Science (EECS); Professor Leonid Levitov of physics; and EECS Professor Terry Orlando. The work is a hallmark of the increased collaboration between researchers on the MIT campus and at Lincoln Laboratory.

August 6, 2008

Making headway toward quantum computing

From KurzweilAI.net:

Breakthrough In Quantum Mechanics: Superconducting Electronic Circuit Pumps Microwave Photons
ScienceDaily, Aug. 5, 2008

Researchers at UC Santa Barbara have used a superconducting electronic circuit known as a Josephson phase qubit to store up to six microwave photons in a superconducting microwave resonator.

The research could help in the quest to build a quantum computer.
 
Read Original Article>>

April 7, 2008

Supercomputing news

Two bits from KurzweilAI.net. First is a qutrit breakthrough making strides toward quantum computing.

The second is on a DARPA challenge for research projects offering “dramatic improvements” in areas including quantum computing.

Qutrit breakthrough brings quantum computers closer
Physics arXiv blog, April 4, 2008University of Queensland scientists have built and tested quantum logic gates that are vastly more powerful than those that have gone before by exploiting the higher dimensions available in quantum mechanics.For example, a qubit can be encoded in a photon‘s polarization. But a photon has other dimensions which can also be used to carry information, such as its arrival time, photon number or frequency. By exploiting these, a photon can easily be used as a much more powerful three level system called a qutrit.That allows a dramatic reduction in the number of gates necessary to perform a specific task. Using only three of the higher-dimension logic gates, the team has built and tested a Toffoli logic gate that could only have been constructed using 6 conventional logic gates. And they say that a computer made up of 50 conventional quantum logic gates could be built using only 9 of theirs.

 
Read Original Article>>

Uncle Sam searches for a quantum leap
NewScientist news service, April 1, 2008Under its new QuEST (Quantum Entanglement Science and Technology) program, DARPA has issued a request for proposal for research projects that address “”dramatic improvements” in “the nature, establishment, control, or transport of multi-qubit entanglement.”Applications might include parallel computing power in a quantum computer and secure communications using quantum cryptography
Read Original Article>>

March 27, 2008

Atomic property of carbon nanotubes affects quantum computing

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 6:10 pm

Electrons in carbon nanotubes have intertwined spins and orbits and this information has an effect on quantum computing.

From KurzweilAI.net:

Electron spin and orbits in carbon nanotubes are coupled
PhysOrg.com, Mar. 26, 2008Cornell physicists have found that the spin of an electron in a carbonnanotube is coupled — that is, interacts with — the electron‘s orbit.

The finding means researchers will have to change the way they read out or change spin in using nanotubes in quantum computing, but offers a new way to manipulate the spin, by manipulating the orbit.

Until now, physicists believed that the four possible states of an electron in a carbonnanotube–spin up or down, and orbit clockwise or counterclockwise–must be equivalent.
Read Original Article>>

February 27, 2008

Nanotechnology advances in quantum computing

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 11:52 pm

More cool nanotech. This time from the KurzweilAI.net newsletter. For reference, a qubit is a unit of quantum information.

Physicists Demonstrate Qubit-Qutrit Entanglement
PhysOrg.com, Feb. 26, 2008An international team of physicists entangled a qubit with its 3D equivalent, the “qutrit,” demonstrating a new way to handle higher-dimensional quantum information carriers.

Qubit-qutrit entanglement could lead to advantages in quantum computing, such as increased security and more efficient quantum gates, and enable novel tests of quantum mechanics. A qutrit is the quantum informationanalogue of the classical trit and carries more information: it exists in superpositions of its three basics states, while a qubit can exist in superpositions of its two states.
Read Original Article>>

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