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Dec. 1, 2005

  In This Issue:
bullet Physicists Coax Six Atoms into Quantum ‘Cat’ State
bullet

Nano-Cages ‘Fill Up’ with Hydrogen

bullet ‘Jammed Networks’ May Clear the Way to Better Materials
bullet ‘Long’ Distances Measured with Picometer Accuracy
bullet Grant Advances Web Portal for U.S./China Standards
bullet NIST Assists with Testing of Crash Avoidance System

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Physicists Coax Six Atoms into Quantum ‘Cat’ State

NIST researchers have succeeded in coaxing six ions into an unusual quantum “cat” state in which their nuclei are collectively spinning clockwise and counterclockwise at the same time.

NIST researchers have succeeded in coaxing six ions into an unusual quantum “cat” state in which their nuclei are collectively spinning clockwise and counterclockwise at the same time. View an animation simulating six entangled ions in simultaneous "cat" states.

Image credit: Bill Pietsch, Astronaut 3 Media Group Inc.

View a high resolution version of this image.

Scientists at the National Institute of Standards and Technology (NIST) have coaxed six atoms into spinning together in two opposite directions at the same time, a so-called Schrödinger “cat” state that obeys the unusual laws of quantum physics. The ambitious choreography could be useful in applications such as quantum computing and cryptography, as well as ultra-sensitive measurement techniques, all of which rely on exquisite control of nature’s smallest particles.

The experiment, which was unusually challenging even for scientists accustomed to crossing the boundary between the macroscopic and quantum worlds, is described in the Dec. 1 issue of Nature.* NIST scientists entangled six beryllium ions (charged atoms) so that their nuclei were collectively spinning clockwise and counterclockwise at the same time. Entanglement, which Albert Einstein called “spooky action at a distance,” occurs when the quantum properties of two or more particles are correlated. The NIST work, along with a paper by Austrian scientists published in the same issue of Nature, breaks new ground for entanglement of multiple particles in the laboratory. The previous record was five entangled photons, the smallest particles of light.

“It is very difficult to control six ions precisely for a long enough time to do an experiment like this,” says physicist Dietrich Leibfried, lead author of the NIST paper.

The ability to exist in two states at once is another peculiar property of quantum physics known as “superposition.” The NIST ions were placed in the most extreme superposition of spin states possible with six ions. All six nuclei are spinning in one direction and the opposite direction simultaneously or what physicists call Schrödinger cat states. The name was coined in a famous 1935 essay in which German physicist Erwin Schrödinger described an extreme theoretical case of being in two states simultaneously, namely a cat that is both dead and alive at the same time.

Schrödinger’s point was that cats are never observed in such states in the macroscopic “real world,” so there seems to be a boundary where the strange properties of quantum mechanics—the rule book for nature’s smallest particles—give way to everyday experience. The NIST work, while a long way from full entanglement of a real cat’s roughly 1026 atoms, extends the domain where Schrödinger cat states can exist to at least six atoms. The Austrian team used a different approach to entangle more ions (eight) but in a less sensitive state.

For further information, see www.nist.gov/public_affairs/releases/cat_states.htm.

* D. Leibfried, E. Knill, S. Seidelin, J. Britton, R.B. Blakestad, J. Chiaverini, D. Hume, W.M. Itano, J.D. Jost, C. Langer, R. Ozeri, R. Reichle, and D.J. Wineland. Creation of a six atom 'Schrödinger cat' state. Nature. Dec. 1, 2005, 639-642.

Media Contact:
Laura Ost, laura.ost@nist.gov, (301) 975-4034

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Nano-Cages ‘Fill Up’ with Hydrogen

Neutron-scattering image reveals where hydrogen molecules (red-green circles) connect to a metal organic framework (MOF), a type of custom-made compound eyed for hydrogen storage applications.
Neutron-scattering image reveals where hydrogen molecules (red-green circles) connect to a metal organic framework (MOF), a type of custom-made compound eyed for hydrogen storage applications. The ball-and-stick model of the MOF is superimposed on the neutron image.

Image credit: T. Yildirim/NIST

View a high resolution version of this image.

A “cagey” strategy to stack more hydrogen in nanoscale scaffoldings made of zinc-based boxes may yield a viable approach to storing hydrogen and, ultimately, replacing fossil fuels in future automobiles, according to new results from National Institute of Standards and Technology (NIST) researchers.

Using beams of neutrons as probes, NIST scientists determined where hydrogen latches onto the lattice-like arrangement of zinc and oxygen clusters in a custom-made material known as a metal-organic framework, or MOF. Called MOF5, the particular nanoscale material studied by Taner Yildirim and Michael Hartman has four types of docking sites, including a “surprising” three-dimensional network of “nano-cages” that appears to form after other sites load up with hydrogen.

This finding, reported in Physical Review Letters,* suggests that MOF materials might be engineered to optimize both the storage of hydrogen and its release under normal vehicle operating conditions. It also suggests that MOFs might be used as templates for interlinking hydrogen nano-cages, creating materials with unusual properties due to a phenomenon known as quantum confinement. In a sense, this discovery is a bonus.

Yildirim and Hartman found that the two most stable sites in the scaffolding already offer considerable room for storing hydrogen, accounting for the interest MOFs already have attracted. Earlier studies reported that, at about –200 degrees Celsius, MOF5 could hold less than 2 percent of its weight in hydrogen.

The NIST research indicates ample room for improvement. At very low temperatures, hydrogen uptake approached 10 percent of the material’s weight. (The FreedomCar and Fuel Partnership involving the Department of Energy and the nation’s “Big 3” automakers has set a level of about 6 percent as a minimum capacity for economically viable hydrogen storage.) The bulk of the hydrogen was held in nanometer-scale cavities inside the box-like arrangements of zinc and oxygen clusters.

“Neutron diffraction measurements clearly show that the molecules are packed in a fashion similar to the way apples or oranges fill a bowl,” Yildirim explains. The unexpected nano-cages introduce the potential for spillover capacity, so to speak.

Hydrogen storage levels of 10 percent are encouraging, but these results were achieved at impractically low temperatures. Yildirim and Hartman say they hope better understanding of how hydrogen molecules tether to MOFs will ultimately lead to improved materials suitable for practical applications.

The research was carried out at the NIST Center for Neutron Research and partially supported by the U.S. Department of Energy. More information can be obtained at http://www.ncnr.nist.gov/staff/taner/h2.

*T. Yildirim and M.R. Hartman, Direct observation of hydrogen adsorption sites and nano-cage formation in metal-organic frameworks (MOF). Phys. Rev. Lett., 95, 215504 (2005).

Media Contact:
Mark Bello, mark.bello@nist.gov, (301) 975-3776

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‘Jammed Networks’ May Clear the Way for Better Materials

Video sequences reveal how different additives affect the behavior of a plastic material (PMMA) when heated under fire-like conditions. Top two rows show behavior during heating, and the bottom shows the final residue. Unmodified PMMA (left) behaves like a liquid, bubbling vigorously and leaving almost no residue. Adding a tiny dash (0.5 wt percent) of single-walled carbon nanotubes (center) nearly eliminated bubbling; the residue was slightly thinner than the original sample, and it had a smooth undulating surface. Numerous small “islands” formed during heating of the material with multi-walled carbon nanotubes (MWNTs) and vigorous bubbling was observed among islands. With continued heating, islands eventually coagulated, forming large islands separated by deep cracks.

Image credit: NIST

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Jammed networks may cause upheaval in phone systems, but among wispy carbon nanotubes or nanofibers, a similar phenomenon may greatly improve flammability resistance and, perhaps, other properties in polymers, report researchers from the National Institute of Standards and Technology and the University of Pennsylvania.

Results achieved with two types of carbon nanotubes (single- and multi-walled) and with carbon nanofibers could help to eliminate trial-and-error in designing and producing nanocomposite materials with flame-retarding and other desired properties optimized for applications in areas ranging from packaging and electronics to construction and aerospace. The work appears in the December issue of Nature Materials.*

Nanoparticle fillers—especially clays—have been shown to reduce the flammability of plastics and other polymers. Previous work on these nanoclay flame retardants, says NIST fire researcher Takashi Kashiwagi, indicates that the additives are most effective when they migrate to form a continuous surface layer, creating a “heat shield” on top of the more flammable polymer matrix. The shield, he explains, suppresses the “vigorous bubbling” that can occur as the matrix breaks down.

However, if the plate-like nanoclay particles cluster into islands, heat escapes through cracks between them, compromising their performance as flame retardants.

To get around this problem, Kashiwagi and colleagues chose to investigate carbon nanotubes and nanofibers, which tend to be narrower and longer than nanoclays. These structures also have been shown to enhance strength, electrical conductivity and other material properties. The researchers reasoned that the extended, sinuous geometry of the tiny tubes and fibers might lend itself to forming a “continuous, network-structured protective layer” that is free of cracks.

When the researchers heated polymethyl methacrylate (PMMA)—a clear plastic—dispersed with carbon nanotubes or nanofibers, the material behaved like a gel. In a process dictated by their type, concentration and other factors, the nano additives dispersed throughout the PMMA matrix and eventually achieved a “mechanically stable network structure.” The researchers say the “jammed networks” formed as the nanocomposites underwent a change in identity, a transition from liquid to solid. The shift occurred at an optimal composition that the team called the “gel concentration.”

For single-walled carbon nanotubes—sheets of carbon atoms rolled into cylinders—top fire retardant performance was achieved when the fillers made up only 0.5 percent of the total mass of the material. For multi-walled carbon nanotubes, which are nested sets of carbon cylinders, the gel concentration was 1 percent. Both types of nanotubes have the potential to surpass nanoclays as effective fire retardants, says NIST materials scientist Jack Douglas.

Results suggest that the gel concentration also may mark the point at which other nanotube-enabled improvements in material properties are maximized, Douglas adds.

*T. Kashiwagi, F. Du, J.F. Douglas, K.I. Winey, R.H. Harris Jr., and J.R. Shields. Nanoparticle networks reduce the flammability of polymer nanocomposites. Nature Materials, December 2005, 928-933.

Media Contact:
Mark Bello, mark.bello@nist.gov, (301) 975-3776

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‘Long’ Distances Measured with Picometer Accuracy

Laser light is sent into the chamber through an optical fiber and stored between two highly reflective mirrors (left and bottom arrows), which form an optical cavity. By measuring the frequency of the light, which is tuned to match specific properties of the cavity, a scientist can determine changes in the lower mirror's position with picometer accuracy.

This NIST vacuum chamber is used to measure millimeter distances more accurately than ever before. Laser light is sent into the chamber through an optical fiber and stored between two highly reflective mirrors (left and bottom arrows), which form an optical cavity. By measuring the frequency of the light, which is tuned to match specific properties of the cavity, a scientist can determine changes in the lower mirror's position with picometer accuracy.

Image credit: J. Lawall/NIST

View a high resolution version of this image.

A new laser-based method for measuring millimeter distances more accurately than ever before—with an uncertainty of 10 picometers (trillionths of a meter)—has been developed and demonstrated by a physicist at the National Institute of Standards and Technology (NIST). This is akin to measuring the distance from New York to Los Angeles with an uncertainty of just 1 millimeter. The technique may have applications in nanotechnology, remote sensing and industries such as semiconductor fabrication.

Laser light is typically used to measure distances by counting the number of wavelengths (the distance between successive peaks of the wave pattern) of light between two points. Because the wavelength is very short (633 nanometers for the red light most often used), the method is intrinsically very precise.

Modern problems in nanotechnology and device fabrication, however, require uncertainty far below 633 nm.

A more precise method, described in the December issue of the Journal of the Optical Society of America A,* involves measuring the frequency of laser light rather than the wavelength. The laser light is stored between two highly reflective mirrors, to create the optical analog of an organ pipe. The length of an organ pipe can be measured by driving the pipe with sound waves of a known frequency (pitch). The sound emitted by the pipe is loudest when it is driven at one of its “natural” frequencies, commonly called harmonics. When one or more of these frequencies is identified, the pipe length can be determined. In the NIST work, light is transmitted through both mirrors only when the frequency of the light matches a harmonic frequency. This frequency can be used to determine the distance between the mirrors.

While this approach has been used previously for the measurement of short distances (of the order of 1 micrometer), the new work extends it 25,000-fold by demonstrating a range of 25 millimeters. (Ultimately, the design should accommodate a range of up to 50 mm.) In addition, the NIST approach described in the paper excites two harmonics of the optical system, rather than one, a redundancy that increases the range while achieving picometer accuracy.

*J.R. Lawall. Fabry-Perot metrology for displacements up to 50 mm. Journal of the Optical Society of America A. December 2005.

Media Contact:
Laura Ost, laura.ost@nist.gov, (301) 975-4034

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Grant Advances Web Portal for U.S./China Standards

The National Institute of Standards and Technology (NIST) has awarded a $250,000 matching grant to support the development of an American National Standards Institute (ANSI)-sponsored U.S./China Standards Portal. The Web site will provide online educational materials on the Chinese and U.S. standards systems, as well as translated titles and scopes of up to 1,000 selected standards used in each of the two nations.

Standards-related issues are a significant concern among U.S. businesses competing in the Chinese market. In a recent survey of members of the U.S.-China Business Council, standards ranked sixth among the top 10 concerns of U.S. companies, up from eighth a year earlier.

Developed in consultation with ANSI members and constituents, the U.S./China Standards Portal will feature translations of key bibliographic information pertaining to 1,000 of China’s mandatory national standards and Chinese translations for a comparable number of U.S. standards. The free site will include information on the structure and operation of the standards systems in both nations.

ANSI anticipates the site will be operational by the third quarter of 2006.

NIST intends to provide additional funding for enhancements to the portal. The additional funds also would help to support an “Options for Action” Summit meeting, tentatively scheduled for the summer of 2006.

Organized by ANSI and NIST, this high-level meeting for standards developers and industry and government representatives will focus on the development of timetables and actions that can be taken to make the U.S. more competitive internationally in the standards arena. Participants will devise methods to coordinate and leverage the resources of individual organizations to respond more effectively to external standards-related challenges to innovation and competitiveness.

Embodied in safety and other regulations or specified by customers, standards influence an estimated 80 percent of global merchandise trade. Occasionally, some of these technical requirements, which range in scope from specific types of products to organizational management and quality systems, may pose market-entry barriers to merchandise and services exported by other nations.

Media Contact:
Mark Bello (NIST), mark.bello@nist.gov, (301) 975-3776
Stacy Leistner (ANSI), sleistne@ansi.org
, (212) 642-4931

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NIST Assists with Testing Crash Avoidance System

Researchers at the National Institute of Standards and Technology (NIST) are assisting the Department of Transportation (DOT) by developing tests for a crash avoidance system that could substantially reduce the number of rear-end, road departure and lane change accidents. About 1,836,000 such accidents occur annually, or 48 percent of police-reported cases a year.

DOT’s “Integrated Vehicle-Based Safety System” (IVBSS) for light vehicles and trucks is a single crash avoidance system under development that combines technologies used in separate warning systems. It is intended to simultaneously detect and warn drivers of any of three different forms of crashes at different speeds and in specified driving situations. The integration of individual systems is expected to increase safety benefits, improve overall system performance, reduce system cost, and enhance consumer and fleet acceptance.

NIST has designed preliminary test procedures that address DOT’s needs. An IVBSS developer, under contract with DOT, will use the NIST tests to measure the performance of the safety system, as well as its components, such as sensors and warning algorithms. NIST-derived performance tests will include ways to determine the system’s ability (1) to warn drivers of possible collisions between the front of their vehicles and the rear of a stationary lead vehicle or decelerating vehicle; (2) to detect a moving vehicle in adjacent lanes and the host car’s drift toward them, (3) to identify the presence of parked cars, guardrails or other roadside objects and determine the available maneuvering room.

NIST will observe the contractor’s tests during the multiyear development effort, as well as conduct its own independent tests and report the results to DOT. DOT will use the data to decide whether warning system performance is adequate to proceed with installing the new system in about 10 vehicles for tests on the highway. DOT plans to complete the field operational test in approximately four years. Afterward, fully integrated warning systems may become available as options on U.S. automobiles.

Media Contact: John Blair, john.blair@nist.gov, (301) 975-4261


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Editor: Gail Porter

Date created:12/1/05
Date updated: 12/1/05
Contact: inquiries@nist.gov