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August 19, 2008

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Light Touch: Controlling the Behavior of Quantum Dots

STM image
schematic of NIST-JQI set up

(Top) Cross-section scanning tunneling microscope (STM) image shows indium arsenide quantum dot regions embedded in gallium arsenide. Each 'dot' is approximately 30 nanometers long–faint lines are individual rows of atoms. (Color added for clarity.) Credit: J.R. Tucker
(Bottom) Schematic of NIST-JQI experimental set up. Orienting the resonant laser at a right angle to the quantum dot light minimizes scattering. Credit: Solomon/NIST

View hi-resolution image of top image | View hi-resolution image of bottom image

Researchers from the National Institute of Standards and Technology (NIST) and the Joint Quantum Institute (JQI), a collaborative center of the University of Maryland and NIST, have reported a new way to fine-tune the light coming from quantum dots by manipulating them with pairs of lasers. Their technique, published in Physical Review Letters,* could significantly improve quantum dots as a source of pairs of “entangled” photons, a property with important applications in quantum information technologies. The accomplishment could accelerate development of powerful advanced cryptography applications, projected to be a key 21st-century technology.

Entangled photons are a peculiar consequence of quantum mechanics. Tricky to generate, they remain interconnected even when separated by large distances. Merely observing one instantaneously affects the properties of the other. The entanglement can be used in quantum communication to pass an encryption key that is by its nature completely secure, as any attempt to eavesdrop or intercept the key would be instantly detected. One goal of the NIST-JQI team is to develop quantum dots as a convenient source of entangled photons.

Quantum dots are nanoscale regions of a semiconductor material similar to the material in computer processors but with special properties due to their tiny dimensions. Though they can be composed of tens of thousands of atoms, quantum dots in many ways behave almost as if they were single atoms. Unfortunately, almost is not good enough when it comes to the fragile world of quantum cryptography and next-generation information technologies. When energized, a quantum dot emits photons, or “particles” of light, just as a solitary atom does. But imperfections in the shape of a quantum dot cause what should be overlapping energy levels to separate. This ruins the delicate balance of the ideal state required to emit entangled photons.

To overcome this problem, the NIST-JQI team uses lasers to precisely control the energy levels of quantum dots, just as physicists have been doing with actual single atoms since the mid-1970s and, much more recently, with the artificial quantum dot variety. With their customized set-up, which includes two lasers—one shining from above the quantum dot and the other illuminating it from the side—the researchers were able to manipulate energy states in a quantum dot and directly measure its emissions. By adjusting the intensity of the laser beams, they were able to correct for imperfection-caused variations and generate more ideal signals. In so doing, the team was the first to demonstrate that laser-tuned quantum dots can efficiently generate photons one at a time, as required for quantum cryptography and other applications.

While the device currently still requires quite cold temperatures and sits in a liquid helium bath, it is compact enough to fit in the palm of your hand—an elegant setup that could be eventually implemented in quantum cryptography applications.

* A. Muller, W. Fang, J. Lawall and G.S. Solomon. Emission spectrum of a dressed exciton-biexciton complex in semiconductor quantum dot. Physical Review Letters, 101, 027401 (2008), posted online July 11, 2008.

Media Contact: Mark Bello,, (301) 975-3776



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Candy-Coating Keeps Proteins Sweet

image of protein ribbon

In this image, a ribbon of protein stands in the foreground against a computer-simulation of a stress field in a glassy material (like a sugar-glass) in the background. Researchers at NIST have developed a fast, inexpensive and effective method for evaluating the sugars pharmaceutical companies use to stabilize protein-drugs for storage at room temperature.

Credit: NIST

Sugar-frosting isn’t just for livening up boring bran flakes; it can also preserve important therapeutic proteins. Researchers at the National Institute of Standards and Technology (NIST) have developed a fast, inexpensive and effective method for evaluating the sugars pharmaceutical companies use to stabilize protein-drugs for storage at room temperature. The group presented their findings* at the 236th American Chemical Society National Meeting and Exposition.

Protein-based drugs such as insulin and vaccines must be stabilized after manufacturing in order to be used safely. For the past 30 years, researchers have been preserving therapeutic proteins by freeze-drying them and coating them with a thin layer of various formulations of glass-like sugars that act to stabilize their molecular structures. This allows them to be safely stored for extended periods of time. Pharmaceutical companies, though they have general guidelines, develop their formulations essentially by trial and error and have to wait up to two years to see if the glasses are suitable. The new methods will help pharmaceutical companies make the best choice about which formulations to test and make it easier to stabilize drugs at room temperature. Room-temperature storage is vital when the pharmaceuticals are to be used in areas of the world where controlled storage conditions are not available.

The new findings build upon previous work** at NIST in which the team used neutron scattering to determine that rapidly solidified sugars preserve such proteins best when they suppress molecular motions lasting a nanosecond or less. Their latest experiments center on the hydrogen bonding that makes the sugars rigid. They have shown that the lifetimes of these bond networks can be measured directly with a fluorescent probe. This method is much more convenient than using neutrons and could be used for routine formulation evaluation.

Hydrogen bonds are responsible for many of water’s properties; they make water a liquid at room temperature. All biological fluids, which are composed mostly of water, are also defined by their hydrogen bonds. Without these bonds, proteins would unfold, and life as we know it would be impossible. Sugars used to safeguard protein-based drugs act like cement, taking the place of water by bonding to the proteins and locking them in place. By rapidly freezing liquid sugar, its molecules have no time to form the usual orderly crystal patterns typically found in sugars that are solids at room temperature. Lead NIST researcher Marc Cicerone says that the randomly ordered sugar molecules fit the encased proteins like a glove, “stiffening” molecular motions that cause the proteins to chemically degrade.

Using the fluorescent probe, the team can now tell within minutes after freeze-drying the protein whether the formulation will be stable, reducing the time and expense associated with the “wait and see” method currently in use.

“Instead of needing relaxation measurements that require using neutron scattering—a national facility with limited time availability—we have developed a widely accessible solution in the form of readily available steady-state fluorescence measurements,” Cicerone says. “This will allow pharmaceutical companies to adopt the new metrology we’ve developed.”

When applied, the team’s findings should help to increase the availability of viable medicines in places where refrigeration is scarce or unavailable.

* M. T. Cicerone and J. M. Johnson. Hydrogen bond network lifetime as an indicator of protein stability in pharmaceutical preparations. Biophysical & Biomolecular Symposium: Current Challenges in Protein Formulations. 236th ACS National Meeting, Philadelphia, Penn., Monday, Aug. 18, 2008.

** See “Keeping Drugs Stable without Refrigeration.”

Media Contact: Mark Esser,, (301) 975-8735



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NIST Requests Comments on Next Generation C/A Process for Information Systems

The National Institute of Standards and Technology (NIST) has released for public review and comment a major revision to its security certification and accreditation (C&A) guidelines for federal information systems. A substantial rewrite of the original document, the new Guide for Security Authorization of Federal Information Systems: A Security Lifecycle Approach, represents a significant step toward developing a common approach to information security across the Federal government, including civilian, defense, and intelligence agencies, according to NIST security experts.

When finalized, the revised guide will replace NIST Special Publication 800-37, which was issued in 2004 under the title Guide for the Security Certification and Accreditation of Federal Information Systems. Like the original, the revised guide maps out a basic framework for managing the risks that arise from the operation and use of federal information systems, the measures taken to address or reduce risk, and a formal managerial process for accepting known risks and granting—or withdrawing—authorization to operate information systems. The guide emphasizes the need to treat information security as a dynamic process, with established procedures to monitor, reassess and update security measures to maintain the authorized security state of an information system. The revised security authorization process is designed to be tightly integrated into enterprise architectures and ongoing system development life cycle processes, promotes the concept of near real-time risk management, capitalizes on investments in technology including automated support tools, and takes advantage of over three decades of lessons learned in previous approaches to certification and accreditation.

Since 2003, NIST has developed and published information security standards and guidelines under the Federal Information Security Management Act (FISMA). While the NIST methodology for analyzing, documenting and authorizing the security of information systems is widely followed by federal agencies operating non-national security systems, other frameworks have coexisted with it for national security systems, including the Department of Defense Information Assurance Certification and Accreditation Process (DIACAP) and the National Information Assurance Certification and Accreditation Process (NIACAP). This first revision to SP 800-37 is the result of an interagency effort that is part of a C&A Transformation Initiative working toward a convergence of information security standards, guidelines and best practices across the government’s civilian, defense and intelligence agencies. NIST is participating in this effort along with the Office of the Director of National Intelligence (DNI), the Department of Defense (DOD) and the Committee on National Security Systems (CNSS). Future updates to NIST FISMA publications will continue this convergence towards common standards and procedures.

Copies of the initial public draft of SP 800-37 Revision 1 are available from the NIST Computer Security Resource Center at NIST is requesting comments on the draft by Sept. 30, 2008.

Media Contact: Michael Baum,, (301) 975-2763



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Quick Links

Stop the Waste: Making Measurements Measure Up to Standards

Information standards enable common activities. For instance, bring your laptop anywhere in the world and you will quickly and cheaply find a wireless Internet connection—due to the globally adopted WiFi standards. On the other hand, bring your U.S. cell phone overseas and you may spend lots of time and money in frustration before you can finally call your friends and colleagues again—because of the absence of globally adopted cell phone standards.

Researchers at the National Institute of Standards and Technology (NIST) are working to enable “WiFi-quality” information standards for manufacturing metrology systems. In this pursuit, NIST researchers and their industry partners have developed DMIS (Dimensional Measurement Interface Standard), which is a language for performing dimensional measurements. DMIS allows measurement program portability without requiring expensive translators.

Also, essential to achieving a “WiFi-quality” standard is to define a standards certification program. NIST is playing an essential role: The NIST-developed DMIS testing software is the heart and soul of a new DMIS certification program.

The Dimensional Metrology Standards Consortium (on the Web at is joining with NIST to sponsor an exhibit Sept. 8-13 at the International Manufacturing Technology Show 2008 to demonstrate the value of DMIS certification. They will show how a variety of manufacturing measurement software—certified using the NIST DMIS testing software—can operate seamlessly with little waste. The demonstration will be held in Chicago’s McCormick Place, Booth D-4338. At the booth, DMIS software programs from three vendors will take turns operating two coordinate measuring machines from different suppliers, each measuring a battery housing component.



Oxygen Data is a Best Seller for Atmospheric Research

The paper currently holding the top spot for most downloaded paper in the Journal of Molecular Spectroscopy is the densely titled “Experimental intensity and lineshape parameters of the oxygen A-band using frequency-stabilized cavity ring-down spectroscopy.” A collaborative effort of researchers at the National Institute of Standards and Technology, the NASA Jet Propulsion Laboratory at the California Institute of Technology and the Instytut Fizyki at the Uniwersytet Mikolaja Kopernika in Poland, the paper reports some of the most accurate measurements ever made of the properties of oxygen. The data were gathered to support the Orbiting Carbon Observatory, a satellite designed to measure the sources and sinks of carbon dioxide in the atmosphere due to be launched in January 2009.

The reference data on the oxygen spectrum will help the satellite measure the pathlength of solar light passing through the Earth’s atmosphere, the pressure of the air beneath it, and enable it to detect changes in carbon dioxide concentrations by as little as 1 part in 300. The attempt to make such accurate measurements of carbon dioxide in the atmosphere is unprecedented. The information gathered on this mission should bring researchers another step closer to discovering how carbon dioxide influences global warming.

More information on the NASA mission may be seen at

The paper “Experimental intensity and lineshape parameters of the oxygen A-band using frequency-stabilized cavity ring-down spectroscopy” is viewable online at

(Return to NIST News Page)

Editor: Michael Baum

Date created: August 19, 2008
Date updated: August 19, 2008