In This Issue...
NIST Achieves Record-Low Error Rate for Quantum Information Processing with One Qubit
Thanks to advances in experimental design, physicists at the National Institute of Standards and Technology (NIST) have achieved a record-low probability of error in quantum information processing with a single quantum bit (qubit)—the first published error rate small enough to meet theoretical requirements for building viable quantum computers.
A quantum computer could potentially solve certain problems that are intractable using today's technology, even supercomputers. The NIST experiment with a single beryllium ion qubit, described in a forthcoming paper,* is a milestone for simple quantum logic operations. However, a working quantum computer also will require two-qubit logic operations with comparably low error rates.
"One error per 10,000 logic operations is a commonly agreed upon target for a low enough error rate to use error correction protocols in a quantum computer," explains Kenton Brown, who led the project as a NIST postdoctoral researcher. "It is generally accepted that if error rates are above that, you will introduce more errors in your correction operations than you are able to correct. We've been able to show that we have good enough control over our single-qubit operations that our probability of error is 1 per 50,000 logic operations."
The NIST experiment was performed on 1,000 unique sequences of logic operations randomly selected by computer software. Sequences of 10 different lengths, ranging from one to 987 operations, were repeated 100 times each. The measured results were compared to perfect theoretical outcomes. The maximum length of the sequences was limited by the hardware used to control the experiment.
The record low error rate was made possible by two major changes in the group's experimental setup. First, scientists manipulated the ion using microwaves instead of the usual laser beams. A microwave antenna was incorporated into the ion trap, with the ion held close by, hovering 40 micrometers above the trap surface. The use of microwaves reduced errors caused by instability in laser beam pointing and power, as well as spontaneous ion emissions. Second, the ion trap was placed inside a copper vacuum chamber and cooled to 4.2 K with a helium bath to reduce errors caused by magnetic field fluctuations in the lab.
Brown now works at the Georgia Institute of Technology. Co-author Christian Ospelkaus contributed to the research while at NIST and is now at research institutions in Germany. The research was supported in part by the Intelligence Advanced Research Projects Activity, the National Security Agency, the Defense Advanced Research Projects Agency and the Office of Naval Research.
* K.R. Brown, A.C. Wilson, Y. Colombe, C. Ospelkaus, A.M. Meier, E. Knill, D. Leibfried and D. J. Wineland. 2011. Single-qubit gate error below 10-4 in a trapped ion. Physical Review A Forthcoming. Preprint available at: http://arxiv.org/abs/1104.2552.
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Researchers Expand Capabilities of Miniature Analyzer for Complex Samples
It’s not often that someone can claim that going from a positive to a negative is a step forward, but that’s the case for a team of scientists from the National Institute of Standards and Technology (NIST) and private industry. In a recent paper,* the group significantly extended the reach of their novel microfluidic system for analyzing the chemical components of complex samples. The new work shows how the system, meant to analyze real-world, crude mixtures such as dirt or whole blood, can work for negatively charged components as well as it has in the past for positively charged ones.
In previous work,** NIST researchers Elizabeth Strychalski and David Ross, in collaboration with Alyssa Henry of Applied Research Associates Inc. (Alexandria, Va.), demonstrated the use of a technique called GEMBE (for “gradient elution moving boundary electrophoresis”) for analyzing complex samples. The NIST-developed system combines a simple microfluidic structure (two reservoirs connected by a microchannel), electrophoresis (which uses electricity to move sample components through a fluid) and pressure-driven flow.
Analyzing complex samples can be difficult because components in these samples (such as the fat globules in milk or proteins in blood) can “foul” or contaminate microfluidic channels. The traditional solution has been to remove contaminants with costly, time-consuming sample preparation prior to analysis.
GEMBE solves this problem by pumping fluid through the microchannel using a controlled pressure in the direction opposite to electrophoresis. This opposing pressure-driven flow acts as a "fluid gate" between the sample reservoir and the microchannel. Gradually reducing the pressure of the counterflow opens the "gate" a little bit at a time. A specific sample component is detected when the pressure flow becomes weak enough—i.e. the "gate" opens wide enough—that the component’s electrophoretic motion pushes it against the pressure-driven flow and into the channel for detection. In this way, different components enter the channel at different times, based on their particular electrophoretic motion. Most importantly, the channel doesn’t become fouled because the unwanted components in the sample are held out.
“Previously, we validated the GEMBE technique by quantitatively analyzing components from complex samples in solution that were cationic [positively charged] and could, therefore, be separated relatively easily from anionic [negatively charged] contaminants in a mixture,” Strychalski says. “However, we needed a way to make GEMBE work when both the desired components and the contaminants are negatively charged.”
For some samples, Strychalski says, this was achieved by choosing a different solution pH to change the electrophoretic motion of the unwanted components. In other cases, the addition of commercially available surface coatings to the sample did the trick without compromising the ease and robustness of the GEMBE technique.
“Additives can be selected that will interact with material in the sample that we don’t want to study,” Strychalski explains. “If we choose the right coating, it will slow the electrophoretic motion of contaminants relative to the desired components. This prevents the former from interfering with analysis while still allowing the latter to enter the microchannel for detection.”
Strychalski and her colleagues plan to continue refining the GEMBE system, including an effort to define which surface coatings optimize the technique for specific components in a variety of complex samples.
* E.A. Strychalski, A.C. Henry and D. Ross. Expanding the capabilities of microfluidic gradient elution moving boundary electrophoresis for complex systems. Analytical Chemistry, Vol. 83, No. 16, pp 6316–6322. Aug. 15, 2011.
** See “‘No Muss, No Fuss’ Miniaturized Analysis for Complex Samples Developed” in NIST Tech Beat, Nov. 17, 2009, at www.nist.gov/public_affairs/tech-beat/tb20091117.cfm#gembe.
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Iron ‘Veins’ Are Secret of Promising New Hydrogen Storage Material
With a nod to biology, scientists at the National Institute of Standards and Technology (NIST) have a new approach to the problem of safely storing hydrogen in future fuel-cell-powered cars. Their idea: molecular scale "veins" of iron permeating grains of magnesium like a network of capillaries. The iron veins may transform magnesium from a promising candidate for hydrogen storage into a real-world winner.
Hydrogen has been touted as a clean and efficient alternative to gasoline, but it has one big drawback: the lack of a safe, fast way to store it onboard a vehicle. According to NIST materials scientist Leo Bendersky, iron-veined magnesium could overcome this hurdle. The combination of lightweight magnesium laced with iron could rapidly absorb—and just as importantly, rapidly release—sufficient quantities of hydrogen so that grains made from the two metals could form the fuel tank for hydrogen-powered vehicles.
"Powder grains made of iron-doped magnesium can get saturated with hydrogen within 60 seconds," says Bendersky, "and they can do so at only 150 degrees Celsius and fairly low pressure, which are key factors for safety in commercial vehicles."
Grains of pure magnesium are reasonably effective at absorbing hydrogen gas, but only at unacceptably high temperatures and pressures can they store enough hydrogen to power a car for a few hundred kilometers—the minimum distance needed between fill-ups. A practical material would need to hold at least 6 percent of its own weight in hydrogen gas and be able to be charged safely with hydrogen in the same amount of time as required to fill a car with gasoline today.
The NIST team used a new measurement technique they devised that uses infrared light to explore what would happen if the magnesium were evaporated and mixed together with small quantities of other metals to form fine-scale mixtures. The team found that iron formed capillary-like channels within the grains, creating passageways for hydrogen transport within the metal grains that allow hydrogen to be drawn inside extremely fast. According to Bendersky, the magnesium-iron grains could hold up to 7 percent hydrogen by weight.
Bendersky adds that the measurement technique could be valuable more generally, as it can reveal details of how a material absorbs hydrogen more effectively than the more commonly employed technique of X-ray diffraction—a method that is limited to analyzing a material's averaged properties.
* Z. Tan, C. Chiu, E.J. Heilweil and L.A. Bendersky. Thermodynamics, kinetics and microstructural evolution during hydrogenation of iron-doped magnesium this films. International Journal of Hydrogen Energy, 36 (2011), pp. 9702-9713, DOI: 10.1016/j.ijhydene.2011.04.196
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Better 'Photon Loops' May Be Key to Computer and Physics Advances
Surprisingly, transmitting information-rich photons thousands of miles through fiber-optic cable is far easier than reliably sending them just a few nanometers through a computer circuit. However, it may soon be possible to steer these particles of light accurately through microchips because of research* performed at the Joint Quantum Institute of the National Institute of Standards and Technology (NIST) and the University of Maryland, together with Harvard University.
The scientists behind the effort say the work not only may lead to more efficient information processors on our desktops, but also could offer a way to explore a particularly strange effect of the quantum world known as the quantum Hall effect in which electrons can interfere with themselves as they travel in a magnetic field. The corresponding physics is rich enough that its investigation has already resulted in three Nobel Prizes, but many intriguing theoretical predictions about it have yet to be observed.
The advent of optical fibers a few decades ago made it possible for dozens of independent phone conversations to travel long distances along a single glass cable by, essentially, assigning each conversation to a different color—each narrow strand of glass carrying dramatic amounts of information with little interference.
Ironically, while it is easy to send photons far across a town or across the ocean, scientists have a harder time directing them to precise locations across short distances—say, a few hundred nanometers—and this makes it difficult to employ photons as information carriers inside computer chips.
"We run into problems when trying to use photons in microcircuits because of slight defects in the materials chips are made from," says Jacob Taylor, a theoretical physicist at NIST and JQI. "Defects crop up a lot, and they deflect photons in ways that mess up the signal."
These defects are particularly problematic when they occur in photon delay devices, which slow the photons down to store them briefly until the chip needs the information they contain. Delay devices are usually constructed from a single row of tiny resonators, so a defect among them can ruin the information in the photon stream. But the research team perceived that using multiple rows of resonators would build alternate pathways into the delay devices, allowing the photons to find their way around defects easily.
As delay devices are a vital part of computer circuits, the alternate-pathway technique may help overcome obstacles blocking the development of photon-based chips, which are still a dream of computer manufacturers. While that application would be exciting, lead author Mohammad Hafezi says the prospect of investigating the quantum Hall effect with the same technology also has great scientific appeal.
"The photons in these devices exhibit the same type of interference as electrons subjected to the quantum Hall effect," says Hafezi, a research associate at JQI. "We hope these devices will allow us to sidestep some of the problems with observing the physics directly, instead allowing us to explore them by analogy."
*M. Hafezi, E.A. Demler, M.D. Lukin and J.M. Taylor. Robust optical delay lines with topological protection. Nature Physics, Aug. 21, 2011, DOI: 10.1038/NPHYS2063.
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Ion Armageddon: Measuring the Impact Energy of Highly Charged Ions
Much like a meteor impacting a planet, highly charged ions hit really hard and can do a lot of damage, albeit on a much smaller scale. And much like geologists determine the size and speed of the meteor by looking at the hole it left, physicists can learn a lot about a highly charged ion's energy by looking at the divots it makes in thin films.
Building upon their work for which they were recently awarded a patent,* scientists at the National Institute of Standards and Technology (NIST) and Clemson University have measured the energy of highly charged ion impacts on a thin film surface for the first time in detail.** Understanding how ions discharge their energy upon impact will help researchers to make better predictive models of how the particles affect surfaces.
The question isn't trivial. Ions are used in exactly that way for a variety of micro- and nanoscale production processes, techniques such as ion milling and etching. Better predictive models may also help researchers curtail ionic erosion where it would be a bad thing, such as inside a fusion reactor.
The research team used xenon atoms from which they had stripped all but 10 of the atoms' original 54 electrons. Making an atom so highly ionized takes a lot of energy—about 50,000 electron volts. The atom soaks up all the energy that went into freeing the electrons until it is capable of imparting more energy, and thus more damage, than could be done with kinetic energy—mass and speed—alone.
"When the highly charged ion is finally released and hurtles into its target, most of its energy, about 60 percent, blows back in the 'splash' and dissipates into the vacuum," says Josh Pomeroy. "According to our measurements, 27 percent of the remaining 40 percent of the ion's energy goes into changing the shape of the material—making divots."
Pomeroy says that the remaining 13 percent is most likely converted to heat.
The group first began looking into nanoscale pitting of thin films to help improve the performance of data storage hard drives, which used aluminum oxide thin films as an insulator between magnetic plates. They used ions to pockmark the surface of these films and showed that the depth of the pitting could be determined by measuring minute changes in electrical conductance through the film.
The original motivation for the work has abated, but the group's method and materials remain useful for measuring the energy transfer of highly charged ions and calibrating industrial systems using high-energy ion beams.
* United States Patent 7,914,915, "Highly charged ion modified oxide device and method of making same." Inventors: J.M. Pomeroy, H. Grube and A. Perrella. Issued March 29, 2011.
** R.E. Lake, J.M. Pomeroy, H. Grube and C.E. Sosolik. Charge state dependent energy deposition by ion impact. Physical Review Letters. August 5, 2011. http://prl.aps.org/abstract/PRL/v107/i6/e063202.
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Survey of Baldrige Examiners Reveals Current Perceptions of Performance
Management and non-management personnel across a broad cross-section of U.S. organizations see eye-to-eye on mission, customer focus and commitment to success but differ significantly in their views on how to best measure quality of work and customer satisfaction. These are a few of the findings from a recent survey of nearly 500 members of the 2011 Board of Examiners for the Malcolm Baldrige National Quality Award.
Baldrige examiners are experts from industry, educational institutions, health care providers, government at all levels and non-profit organizations who volunteer many hours reviewing applications for the award, conducting site visits and providing each applicant with an extensive feedback report citing strengths and opportunities to improve. The Baldrige Performance Excellence Program asked this year’s examiners to assess their own organizations using either the program’s “Are We Making Progress?” or “Are We Making Progress as Leaders?” questionnaires, depending on whether or not the examiners worked in management. These survey instruments* are based on the Baldrige Criteria for Performance Excellence and allow an organization to gauge its progress in achieving high performance and define where improvements are needed to reach that goal.
The questionnaires ask employee respondents to gauge their level of agreement with statements related to the Baldrige criteria, such as, “I know who my most important customers are.” Managers are quizzed on their perceptions of their organizations (“Our employees know who their most important customers are.”). The 173 employees and 294 leaders taking the surveys were in strong and positive agreement, regardless of institution, on a number of factors, including understanding of the organization’s mission, clear identification of most important customers and strong commitment to success. Both groups also matched up on areas where they perceived that the organization was not performing well, such as actively seeking input for long-range planning, using good processes to perform tasks and removing obstacles in the way of progress.
Perhaps most interesting were the areas where employees and leaders differed significantly in their perceptions. These included knowing how to measure work quality (78 percent of employees felt they had such knowledge while only 51 percent of leaders agreed that they did), using work quality measures to make improvements (74 percent of employees said that they did while only 43 percent of leaders recognized that ability), and feeling that customers were satisfied with work performed (85 percent of employees felt their work achieved this status while just 69 percent of leaders agreed). The one statement with a large response discrepancy where the leaders agreed more than the employees—84 percent to 69 percent—was “My boss and my organization care about me.”
“The survey results indicate a lot of opportunity exists for better communication between leaders and employees, as well as improving performance measurement and overall organizational performance,” says Harry Hertz, director of the Baldrige Performance Excellence Program.
To see the complete results of the 2011 Examiners Survey, go to www.nist.gov/baldrige/publications/progress.cfm for the employee responses and www.nist.gov/baldrige/publications/progress_leaders.cfm for those of the leaders. Both sites also include results from an earlier survey of examiners to compare and contrast current perceptions of performance with those in the past.
* To access either or both of the two self-assessment tools, go to www.nist.gov/baldrige/enter/self.cfm.
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NIST/JQI Researcher Ian Spielman to Receive 2011 Junior BEC Award
Ian Spielman, a physicist at the National Institute of Standards and Technology (NIST) and fellow of the Joint Quantum Institute, a collaborative enterprise of NIST and the University of Maryland, was selected to receive the Junior BEC Award 2011 by the award committee of the biannual Bose-Einstein Condensation Conference for "the first experimental realization of synthetic magnetic fields and spin-orbit couplings in atomic Bose-Einstein condensates."
An atomic-gas Bose-Einstein condensate (BEC) is a state of matter encountered at extremely low temperatures, on the order of 100 nanokelvins or less—more than one billion times colder than room temperature. BECs are nearly perfect quantum mechanical systems in which physicists can, among other things, study poorly understood phenomena important for materials with technological applications, without all the complexities of material systems.
The technique of creating "synthetic" fields, pioneered by Spielman and his colleagues, not only paves the way for using electrically neutral atoms to explore the complex natural phenomena involving charged particles in magnetic fields, but also may contribute to an exotic new form of quantum computing.
The Junior BEC Award goes to young scientists for high-quality independent research performed early in their careers. Winners receive €2,500 and a certificate detailing their achievements. TOPTICA Photonics AG, a privately held manufacturer of lasers and associated products, sponsors the prize.
To read more about the work for which Spielman was recognized, see the Dec. 15, 2009, NIST news announcement, "JQI Researchers Create 'Synthetic Magnetic Fields' for Neutral Atoms", online at www.nist.gov/pml/div684/synthetic_121509.cfm, and the March 15, 2011, NIST Tech Beat article, "First Demonstration of 'Spin-Orbit Coupling' in Ultracold Atomic Gases" at www.nist.gov/public_affairs/tech-beat/tb20110315.cfm#coupling.The awards will be presented at the Bose-Einstein Conference in Sant Feliu, Spain, Sept. 10-16, 2011. This will be the first presentation of the BEC Awards. The 2011 Senior BEC Award will go to Gora Shlyapnikov of the Université Paris-Sud, France, and the University of Amsterdam.
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