Truth shines a light into dark places. But sometimes to find that truth in the first place, it’s better to stay in the dark. That’s what recent findings* at the National Institute of Standards and Technology (NIST) show about methods for testing the safety of nanoparticles. It turns out that previous tests indicating that some nanoparticles can damage our DNA may have been skewed by inadvertent light exposure in the lab.
Nanoparticles made of titanium dioxide are a common ingredient in paint, and they also are considered safe for use both on the body (in sunscreen, where they help block ultraviolet light) and even within it (in foodstuffs such as salad dressings to make them appear whiter). It is well known that in the presence of light and water, these particles can form dangerous, highly reactive chemicals called free radicals that can damage DNA. Because light does not reach the human body’s interior, scientists have long accepted that these nanoparticles would not damage cells by forming free radicals from light activation.
Titanium dioxide nanoparticles are widely used not only in paints but in sunscreen and even salad dressing.
However, some recent studies using cells suggest that titanium dioxide can damage DNA even in darkness—a disturbing possibility. Because such findings could have major health implications, the NIST team set out to determine whether light was indeed required for the nanoparticles to cause DNA damage.
“We didn’t set out to test the safety of the particles themselves—that’s for someone else to determine,” says NIST’s Elijah Petersen. “Our main concern is to ensure that scientists have enough knowledge to make accurate measurements. That way, tests will give accurate representations of reality.”
The NIST team exposed samples of DNA to titanium dioxide nanoparticles under three different conditions: Some samples were exposed in the presence of visible or ultraviolet light while others were kept carefully and intentionally in complete darkness from the moment of exposure to the time the DNA damage was measured. The team found that only when exposed to laboratory or ultraviolet light did the DNA form base lesions, a form of DNA damage associated with attack by radicals. Their conclusion? The culprit in earlier studies may be ambient light from the laboratory that inadvertently caused DNA damage.
“The results suggest that titanium dioxide nanoparticles do not damage DNA when kept in the dark,” Petersen says. “These findings show that experimental conditions, such as lighting, must be carefully controlled before drawing conclusions about nanoparticle effects on DNA.”
*E.J. Petersen, V. Reipa, S.S. Watson, D.L. Stanley, S.A Rabb and B.C. Nelson. The DNA damaging potential of photoactivated P25 titanium dioxide nanoparticles. Chemical Research in Toxicology, October 2014 issue, DOI: 10.1021/tx500340v.
Center researchers aim to understand how quantum systems can store, transport, process information
The University of Maryland (UMD) and the U.S. Department of Commerce’s National Institute of Standards and Technology (NIST) announced today the creation of the Joint Center for Quantum Information and Computer Science (QuICS), with the support and participation of the Research Directorate of the National Security Agency/Central Security Service (NSA/CSS). Scientists at the center will conduct basic research to understand how quantum systems can be effectively used to store, transport and process information.
This new center complements the fundamental quantum research performed at the work of the Joint Quantum Institute (JQI), which was established in 2006 by UMD, NIST and the NSA. Focusing on one of JQI’s original objectives to fully understand quantum information, QuICS will bring together computer scientists—who have expertise in algorithm and computational complexity theory and computer architecture—with quantum information scientists and communications scientists.
“This new endeavor builds on an already successful and fruitful collaboration at JQI,” said Acting Under Secretary of Commerce for Standards and Technology and Acting Director of NIST Willie May. “The new center will be a venue for groundbreaking basic research that will help to build our capacity for quantum research and train the next generation of researchers.”
UMD and NIST have a shared history of collaboration and cooperation in education, research and public service. They have long cooperated in building collaborative research consortia and programs that have resulted in extensive personal, professional and institutional relationships.
“By deepening our partnership with NIST, we now have all the ingredients in place to make major advances in quantum science,” said UMD President Wallace Loh. “This superb, world-class quantum program will team some of the best minds in physics, computer science and engineering to overcome the limitations of current computing systems.”
Dianne O’Leary, Distinguished University Professor Emerita in computer science at UMD, and Jacob Taylor, a NIST physicist and JQI Fellow, will serve as co-directors of the new center. Like the JQI, QuICS will be located on the UMD campus in College Park, Md.
The capabilities of today’s embedded and high-performance computer architectures have limited advances in critical areas, such as modeling the physical world, improving sensors and securing communications. Quantum computing could enable us to break through some of these barriers.
QuICS’ objectives will be to:
Develop a world-class research center that will build the scientific foundation for quantum information science to enable understanding of the relationships between information theory, computational complexity theory and nature, as well as the advances in computer science necessary to support potential quantum computing and communication devices and systems;
Maintain and enhance the nation’s leading role in quantum information science by expanding an already-powerful collaboration between UMD, NIST and NSA/CSS; and
Establish a unique, interdisciplinary center for the interchange of ideas among computer scientists, physicists and quantum information researchers.
Some of the topics QuICS researchers will initially examine include understanding how quantum mechanics informs computation and communication theories, determining what insights computer science can shed on quantum computing, investigating the consequences of quantum information theory for fundamental physics, and developing practical applications for theoretical advances in quantum computation and communication.
QuICS is expected to train scientists for future industrial and academic opportunities and provide U.S. industry with cutting-edge research results. By combining the strengths of UMD and NIST, QuICS will become an international center for excellence in quantum computer and information science.
QuICS will be the newest of 16 centers and labs within the University of Maryland Institute for Advanced Computer Studies (UMIACS). The center will bring together researchers from UMIACS; the UMD Departments of Physics and Computer Science; and the UMD Applied Mathematics & Statistics, and Scientific Computation program with NIST’s Information Technology and Physical Measurement laboratories.
About the University of Maryland
The University of Maryland is home to three quantum science research centers: the Joint Center for Quantum Information and Computer Science, the Joint Quantum Institute, and the Quantum Engineering Center. UMD has nation-leading computer science, physics and math departments, with particular strengths in the areas relevant to quantum science research.
In the 2015 Best Graduate Schools ranking by U.S. News & World Report, UMD’s Department of Physics ranked 14th, the Department of Computer Science ranked 15th, and Department of Mathematics ranked 17th. The atomic/molecular/optical physics specialty ranked 6th, the quantum physics specialty ranked 8th, and the applied math specialty ranked 10th. Visit UMD’s website to learn more.
As a non-regulatory agency of the U.S. Department of Commerce, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life. Visit NIST’s website for more information.
Rechargeable battery manufacturers may get a jolt from research performed at NIST and several other institutions, where a team of scientists has discovered a safe, inexpensive, sodium-conducting material that significantly outperforms all others in its class.
The team’s discovery is a sodium-based, complex metal hydride, a material with potential as a much cheaper alternative to the lithium-based conductors used in many rechargeable batteries. Because lithium is a comparatively rare commodity near the earth’s surface, the industry would prefer to build reusable batteries out of common ingredients that are both economical and inexhaustible.
The novel hydride—which has the formula Na2B10H10—might fit the bill, and not only because it is formed of the three easily obtainable elements of sodium, boron and hydrogen. There are other practical reasons as well: It is a stable inorganic solid, meaning it would pose fewer of the risks carried by many flammable liquids in traditional batteries, such as the potential for leaking or exploding. And compared to other sodium-based solids, it can enable more power output.
This last advantage stems from its unusual ability to conduct sodium ions exceptionally well when heated. At room temperature, the hydride’s atoms are tightly packed together. But when heated to near water’s boiling point, they repack to create numerous corridors through which the sodium ions can flow easily. Because charged ions are what carry electricity in a battery, this “phase change,” as physicists call it, allows the team’s material to outperform others.
“It’s more than 20 times better at doing its job than other known sodium-based complex hydrides in this temperature range,” says Terrence Udovic of the NIST Center for Neutron Research (NCNR). “It’s also as good as the best solid lithium-based hydride that has been measured, so it’s quite promising.”
Udovic had been exploring metal hydride materials as candidates for hydrogen storage, and while this particular compound performed poorly at that task, he hit upon the idea of testing it as an ion conductor. NCNR research hinted at its abilities, but clarifying them took an international effort among collaborators from Japan’s Tohoku Univ., Russia’s Institute of Metal Physics, the Univ. of Maryland and Sandia National Laboratories.
Udovic says that future work will involve chemically tweaking the hydride’s properties in order to optimize its performance. At this point, it would be necessary to operate a battery above the phase transition temperature, so one goal will be to bring the transition temperature down to as close to room temperature as possible—a goal he is confident is within reach.
“You could probably use this material in a battery right now,” he says. “But the lower the temperature required to make it work, the more useful it will be.”
Considered by some to be the next frontier of global economic development, nanotechnology has the potential to revolutionize industries like healthcare, information technology and energy systems.
A new study provides investors and stakeholders with a comprehensive guide to this nascent, rapidly growing industry. The study indicates that nanotechnology could provide important societal and economic benefits along with substantial financial rewards for investors.
“Already, nanotechnology has realized scientific success. Its next phase could lead to revolutionary advancements for treating diseases, purifying water and addressing environmental issues,” said Jon Lukomnik, IRRCi executive director.
“Most industries either are already incorporating nanomaterials into products or conducting research based on nanotechnology. This means companies should tell investors how they are using nanotechnology and taking appropriate precautions,” Si2 Executive Director Heidi Welsh added.
Nanotechnology is an emerging field that focuses on the understanding and control of matter at near-atomic scale. It crosses scientific disciplines and has the potential to affect virtually every aspect of daily life and every economic sector. At least 1,600 consumer products have entered the marketplace in the last eight years, and this is just a sliver of the products and processes already in use and under development.
By 2020, six million people worldwide may work with nanomaterials. Corporations now provide about half the funding for research on nano frontiers, catching up with governments led by the United States and 60 other countries such as Germany, France, Japan, Korea and China.
Abstract: Researchers at the National Institute of Standards and Technology (NIST) and the University of Michigan have demonstrated a technique based on the quantum properties of atoms that directly links measurements of electric field strength to the International System of Units (SI).*
NIST quantum probe enhances electric field measurements
Boulder, CO | Posted on October 8th, 2014
The new method could improve the sensitivity, precision and ease of tests and calibrations of antennas, sensors, and biomedical and nano-electronic systems and facilitate the design of novel devices.
Conventional electric field probes have limited frequency range and sensitivity, often disturb the field being measured, and require laboratory calibrations that are inherently imprecise (because the reference field depends on the geometry of the source). Furthermore, linking these measurements to SI units, the highest level of calibration, is a complex process.
NIST’s new electric-field probe spans enormous ranges. It can measure the strength of fields from 1 to 500 gigahertz, including the radio, microwave, millimeter-wave and sub-terahertz bands. It can measure fields up to 100 times weaker than conventional methods can (as weak as 0.8millivolts per meter, the SI unit of measure). Researchers used the new method to measure field strengths for a wide range of frequencies, and the results agreed with both numerical simulations and calculations.
Importantly, the new method can calibrate itself, as well as other instruments, because it is based on predictable quantum properties: vibrations in atoms as they switch between energy levels. This self-calibration feature improves measurement precision and may make traceable calibrations possible in the millimeter and sub-terahertz bands of the spectrum for the first time.
“The exciting aspect of this approach is that an atom is rich in the number of transitions that can be excited,” NIST project leader Chris Holloway says. “This results in a broadband measurement probe covering a frequency range of 1 to 500 gigahertz and possibly up to 1 terahertz.”
The NIST instrument currently is tabletop sized, but researchers are working on miniaturizing it using photonic structures.
The basic method has already been demonstrated for imaging applications.** Briefly, researchers use a red and a blue laser to prepare atoms contained in a cylinder to high-energy (“Rydberg”) states, which have novel properties such as extreme sensitivity and reactivity to electromagnetic fields. An antenna or other source generates an electric field, which, depending on its frequency, affects the spectrum of light absorbed by the atoms. By measuring this effect, researchers can calculate the field strength. Various atoms can be used—NIST uses rubidium or cesium—to measure field strength in different parts of the frequency spectrum.
Among possible applications, the NIST probe may be suitable for measuring and optimizing compatibility in densely packaged electronics that include radar and wireless communications and control links, and for integration into endoscopic probes with medical applications such as investigating implants in the body. The technique might also be included in a future “NIST on a chip” offering multiple measurement methods and standards in a portable form.
Importantly, the technique also enables, for the first time, calibrated measurements of frequencies above 100 GHZ, in the millimeter wave and sub-terahertz bands.*** This capability will be crucial for the development of advanced communications systems and climate change research, among other applications.
Five co-authors of the new paper are with the University of Michigan, which provided the blue laser and aided in the experiments. The project is funded in part by the Defense Advanced Research Projects Agency.
* C.L. Holloway, J.A. Gordon, S. Jefferts, A. Schwarzkopf, D. A. Anderson, S.A. Miller, N. Thaicharoen and G. Raithelet. Broadband Rydbergatom-based electric-field probe: From self-calibrated measurements to sub-wavelength imaging. IEEE Trans. on Antennas and Propagation. 99. Accepted for publication. DOI: 10.1109/TAP.2014.2360208.
*** J.A. Gordon, C.L. Holloway, A. Schwarzkopf, D. A. Anderson, S. Miller, N. Thaicharoen and G. Raithel. Millimeter wave detection via Autler-Townes splitting in rubidium Rydberg atoms. Applied Physics Letters, 2014. Vol. 105, Issue 2.DOI:10.1063/1.4890094.
Quantum Dot Photovoltaics: A New Breed of Solar Cells: Setting New Records for Efficiency
May 28, 2014
Solar-cell technology has advanced rapidly, as hundreds of groups around the world pursue more than two dozen approaches using different materials, technologies, and approaches to improve efficiency and reduce costs.
Now a team at MIT has set a new record for the most efficient quantum-dot cells—a type of solar cell that is seen as especially promising because of its inherently low cost, versatility, and light weight.
While the overall efficiency of this cell is still low compared to other types—about 9 percent of the energy of sunlight is converted to electricity—the rate of improvement of this technology is one of the most rapid seen for a solar technology. The development is described in a paper, published in the journal Nature Materials, by MIT professors Moungi Bawendi and Vladimir Bulović and graduate students Chia-Hao Chuang and Patrick Brown.
The new process is an extension of work by Bawendi, the Lester Wolfe Professor of Chemistry, to produce quantum dots with precisely controllable characteristics—and as uniform thin coatings that can be applied to other materials. These minuscule particles are very effective at turning light into electricity, and vice versa. Since the first progress toward the use of quantum dots to make solar cells, Bawendi says, “The community, in the last few years, has started to understand better how these cells operate, and what the limitations are.”
The new work represents a significant leap in overcoming those limitations, increasing the current flow in the cells and thus boosting their overall efficiency in converting sunlight into electricity.
Many approaches to creating low-cost, large-area flexible and lightweight solar cells suffer from serious limitations—such as short operating lifetimes when exposed to air, or the need for high temperatures and vacuum chambers during production.
By contrast, the new process does not require an inert atmosphere or high temperatures to grow the active device layers, and the resulting cells show no degradation after more than five months of storage in air.
Bulović, the Fariborz Maseeh Professor of Emerging Technology and associate dean for innovation in MIT’s School of Engineering, explains that thin coatings of quantum dots “allow them to do what they do as individuals—to absorb light very well—but also work as a group, to transport charges.” This allows those charges to be collected at the edge of the film, where they can be harnessed to provide an electric current.
The new work brings together developments from several fields to push the technology to unprecedented efficiency for a quantum-dot based system: The paper’s four co-authors come from MIT’s departments of physics, chemistry, materials science and engineering, and electrical engineering and computer science. The solar cell produced by the team has now been added to the National Renewable Energy Laboratories’ listing of record-high efficiencies for each kind of solar-cell technology.
The overall efficiency of the cell is still lower than for most other types of solar cells. But Bulović points out, “Silicon had six decades to get where it is today, and even silicon hasn’t reached the theoretical limit yet. You can’t hope to have an entirely new technology beat an incumbent in just four years of development.” And the new technology has important advantages, notably a manufacturing process that is far less energy-intensive than other types.
Chuang adds, “Every part of the cell, except the electrodes for now, can be deposited at room temperature, in air, out of solution. It’s really unprecedented.”
The system is so new that it also has potential as a tool for basic research. “There’s a lot to learn about why it is so stable. There’s a lot more to be done, to use it as a testbed for physics, to see why the results are sometimes better than we expect,” Bulović says.
A companion paper, written by three members of the same team along with MIT’s Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering, and three others, appears this month in the journal ACS Nano, explaining in greater detail the science behind the strategy employed to reach this efficiency breakthrough.
The new work represents a turnaround for Bawendi, who had spent much of his career working with quantum dots. “I was somewhat of a skeptic four years ago,” he says. But his team’s research since then has clearly demonstrated quantum dots‘ potential in solar cells, he adds.
Arthur Nozik, a research professor in chemistry at the University of Colorado who was not involved in this research, says, “This result represents a significant advance for the applications of quantum-dot films and the technology of low-temperature, solution-processed, quantum-dot photovoltaic cells. … There is still a long way to go before quantum-dot solar cells are commercially viable, but this latest development is a nice step toward this ultimate goal.”
Are you an inventor, entrepreneur, product developer, angel investor, scientist, engineer or post-doc in search of your future? Is your company looking for technology solutions to improve your products? Spend the day at the NIST Boulder Lab learning about new innovations and the resources available to help build businesses around them.
This event brings together innovative technologies, licensable inventions, research and engineering facilities, small business support resources at the Federal and state levels, and sources of funding—all under one roof, and all available for networking. This showcase is sponsored by the National Institute of Standards and Technology (NIST), National Oceanic and Atmospheric Administration (NOAA), the Colorado Manufacturers’ Edge (Manufacturing Extension Partnership) and the Colorado Office of Economic Development and International Trade.
The format of the showcase will include opening remarks by Congressman Jared Polis, brief morning presentations of NIST and NOAA research capabilities and commercially-viable inventions. Speakers will be available following their presentations as their time permits for networking with interested attendees to explore licensing and collaboration opportunities—no appointments necessary. For those identifying collaboration opportunities, NIST’s and NOAA’s CRADA and licensing experts will be available to advise and demystify the process of collaborating with Federal agencies. Over lunch and into the afternoon, showcase sponsors will introduce the wide variety of resources available to support small and start-up businesses in the greater Denver-Boulder area and will also be available for ad hoc networking and consultation.
Start-ups as well as small and medium sized firms will:
Get clarity on rights to intellectual property that arises under government collaborations.
Gain insight on how interdisciplinary science and engineering can create new innovations.
Learn how local resources can connect you with the business, financing and manufacturing support you need to grow your business.
If you are not registered, you will not be allowed on site. Registered attendees will receive security and campus instructions prior to the workshop.
Effective July 21, 2014, under the REAL ID Act of 2005, federal agencies, including NIST, can only accept a state-issued driver’s license or identification card for access to federal facilities if issued by states that are REAL ID compliant or have an extension. Driver’s licenses from the following states and territories are not compliant with the Real ID Act of 2005 and will not be accepted as identification: Alaska, Arizona, Oklahoma, Louisiana, Massachusetts, Maine, and American Samoa. For more information, please visit this page >>
NON U.S. CITIZENS PLEASE NOTE: All foreign national visitors who do not have permanent resident status and who wish to register for the above meeting must supply additional information. Failure to provide this information prior to arrival will result, at a minimum, in significant delays (up to 24 hours) in entering the facility. Authority to gather this information is derived from United States Department of Commerce Department Administrative Order (DAO) number 207-12. When registration is open, the required NIST-1260 form will be available as well.
Start Date: Thursday, October 9, 2014
Location: Building 1, NIST Boulder, 325 Broadway, Boulder, CO 80305
$26 registration fee. Registration will close COB October 6, 2014. All attendees must be pre-registered to gain entry to the NIST campus. Photo identification must be presented at the main gate to be admitted to the conference. International attendees are required to present a passport. Attendees must wear their conference badge at all times while on the campus. There is no on-site registration for meetings held at NIST.
In a rare case of having their cake and eating it too, scientists from the National Institute of Standards and Technology (NIST) and other institutions have developed a toolset that allows them to explore the complex interior of tiny, multi-layered batteries they devised. It provides insight into the batteries’ performance without destroying them—resulting in both a useful probe for scientists and a potential power source for micromachines.
The microscopic lithium-ion batteries are created by taking a silicon wire a few micrometers long and covering it in successive layers of different materials. Instead of a cake, however, each finished battery looks more like a tiny tree.
The analogy becomes obvious when you see the batteries attached by their roots to silicon wafers and clustered together by the million into “nanoforests,” as the team dubs them.
But it’s the cake-like layers that enable the batteries to store and discharge electricity, and even be recharged. These talents could make them valuable for powering autonomous MEMS – microelectromechanical machines – which have potentially revolutionary applications in many fields.
With so many layers that can vary in thickness, morphology and other parameters, it’s crucial to know the best way to build each layer to enhance the battery’s performance, as the team found in previous research.** But conventional transmission electron microscopy (TEM) couldn’t provide all the details needed, so the team created a new technique that involved multimode scanning TEM (STEM) imaging. With STEM, electrons illuminate the battery, which scatters them at a wide range of angles. To see as much detail as possible, the team decided to use a set of electron detectors to collect electrons in a wide range of scattering angles, an arrangement that gave them plenty of structural information to assemble a clear picture of the battery’s interior, down to the nanoscale level.
The promising toolset of electron microscopy techniques helped the researchers to home in on better ways to build the tiny batteries. “We had a lot of choices in what materials to deposit and in what thicknesses, and a lot of theories about what to do,” team member Vladimir Oleshko says. “But now, as a result of our analyses, we have direct evidence of the best approach.
outer layers. Credit: Oleshko/NIST
“MEMS manufacturers could make use of the batteries themselves, a million of which can be fabricated on a square centimeter of a silicon wafer. But the same manufacturers also could benefit from the team’s analytical toolset. Oleshko points out that the young, rapidly emerging field of additive manufacturing, which creates devices by building up component materials layer by layer, often needs to analyze its creations in a noninvasive way. For that job, the team’s approach might take the cake.
More information: V.P. Oleshko, T. Lam, D. Ruzmetov, P. Haney, H.J. Lezec, A.V. Davydov, S.Krylyuk, J.Cumings and A.A. Talin. “Miniature all-solid-state heterostructure nanowire Li-ion batteries as a tool for engineering and structural diagnostics of nanoscale electrochemical processes.” Nanoscale, DOI: 0.1039/c4nr01666a, Aug. 15, 2014.
Just as diamonds with perfect symmetry may be unusually brilliant jewels, the quantum world has a symmetrical splendor of high scientific value.
Confirming this exotic quantum physics theory, JILA physicists led by theorist Ana Maria Rey and experimentalist Jun Ye have observed the first direct evidence of symmetry in the magnetic properties—or nuclear “spins”—of atoms. The advance could spin off practical benefits such as the ability to simulate and better understand exotic materials exhibiting phenomena such as superconductivity (electrical flow without resistance) and colossal magneto-resistance (drastic change in electrical flow in the presence of a magnetic field).
Illustration of symmetry in the magnetic properties—or nuclear spins—of strontium atoms. JILA researchers observed that if two atoms have the same nuclear spin state (top), they interact weakly, and the interaction strength does not depend on which of the 10 possible nuclear spin states are involved. If the atoms have different nuclear spin states (bottom), they interact much more strongly, and, again, always with the same strength.
The JILA discovery, described in Science Express,* was made possible by the ultra-stable laser used to measure properties of the world’s most precise and stable atomic clock.** JILA is jointly operated by the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder.
“Spin symmetry has a very strong impact on materials science, as it can give rise to unexpected behaviors in quantum matter,” JILA/NIST Fellow Jun Ye says. “Because our clock is this good—really it’s the laser that’s this good—we can probe this interaction and its underlying symmetry, which is at a very small energy scale.”
The global quest to document quantum symmetry looks at whether key properties remain the same despite various exchanges, rotations or reflections. For example, matter and antimatter demonstrate fundamental symmetry: Antimatter behaves in many respects like normal matter despite having the charges of positrons and electrons reversed.
To detect spin symmetry, JILA researchers used an atomic clock made of 600 to 3,000 strontium atoms trapped by laser light. Strontium atoms have 10 possible nuclear spin configurations (also referred to as angular momentum), which influences magnetic behavior. In a collection of clock atoms there is a random distribution of all 10 states.
The researchers analyzed how atom interactions—their collisions—at the two electronic energy levels used as the clock “ticks” were affected by the spin state of the atoms’ nuclei. In most atoms, the electronic and nuclear spin states are coupled, so atom collisions depend on both electronic and nuclear states. But in strontium, the JILA team predicted and confirmed that this coupling vanishes, giving rise to collisions that are independent of nuclear spin states.
In the clock, all the atoms tend to be in identical electronic states. Using lasers and magnetic fields to manipulate the nuclear spins, the JILA researchers observed that, when two atoms have different nuclear spin states, no matter which of the 10 states they have, they will interact (collide) with the same strength. However, when two atoms have the same nuclear spin state, regardless of what that state is, they will interact much more weakly.
“Spin symmetry here means atom interactions, at their most basic level, are independent of their nuclear spin states,” Ye explains. “However, the intriguing part is that while the nuclear spin does not participate directly in the electronic-mediated interaction process, it still controls how atoms approach each other physically. This means that, by controlling the nuclear spins of two atoms to be the same or different, we can control interactions, or collisions.”
The new research adds to understanding of atom collisions in atomic clocks documented in previous JILA studies.*** Further research is planned to engineer specific spin conditions to explore novel quantum dynamics of a large collection of atoms.
JILA theorist Ana Maria Rey made key predictions and calculations for the study. Theorists at the University of Innsbruck in Austria and the University of Delaware also contributed. Funding was provided by NIST, the National Science Foundation, the Air Force Office of Scientific Research, and the Defense Advanced Research Projects Agency.
*X. Zhang, M. Bishof, S.L. Bromley, C.V. Kraus, M.S. Safronova, P. Zoller, A.M. Rey, J. Ye. Spectroscopic observation of SU(N)-symmetric interactions in Sr orbital magnetism. Science Express. Published online Aug. 21, 2104.