| Dec.
1, 2005
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Physicists Coax Six Atoms
into Quantum ‘Cat’ State
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.
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.
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
‘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
View
a high resolution version of this image.
|
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.
‘Long’
Distances Measured 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
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
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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