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Quantum Electrical Metrology AC-DC Difference Standards and Measurement Techniques Pulse Metrology and Time Domain Measurements Return
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Division Contact: James K. Olthoff The kilogram is the only remaining International System of Units (SI) base unit whose definition is based on a physical artifact rather than on fundamental properties of nature. Environmental contamination or material loss from surface cleaning or other unknown mechanisms are causing the mass of the kilogram to vary by about 3 parts in 108 per century relative to sister prototypes. This observed drift highlights a significant shortcoming of the SI system. The measured values of many physical constants are based on mass, and these constants are regularly used in quantum-based measurement systems, such as the Josephson effect, which are becoming more significant to the growth of international technology and trade accreditation. Thus, with a time-drifting mass standard, adjustments to the value of physical constants must be made periodically to maintain the consistency of the SI system. Moreover, each future change will adversely affect a continuously growing technology base that relies increasingly on electronic testing, quality control, and environmental monitoring. The adoption of the electronic kilogram as the mass standard will improve the consistency of the SI and also will provide better determinations of many fundamental physical constants, such as the charge and mass of the electron, that serve the general scientific and technological communities. The equivalence of electrical and mechanical power provides a convenient route to the measurement of mass in terms of other quantum mechanically defined measurement units. The apparatus at our electronic kilogram facility is a balance that compares both kinds of power in a virtual measurement that is unaffected by the dissipative forces of friction and electromagnetic heating. The experimental observables are length, time, voltage, and resistance. We measure these quantities with respect to fundamental and invariant quantum phenomena: atomic clocks, lasers, the Josephson effect, and the quantum Hall effect, respectively. The goal of this project is to realize the SI unit of voltage and to provide an alternative definition of the SI unit of mass that is based on measured quantities determined by fundamental physical constants of nature. Contacts: Richard L. Steiner and Michael H. Kelley We have developed an X-ray detector with outstanding energy resolution required for precise X-ray microanalysis. Such an X-ray detector, with an energy resolution of a few electron volts, can be made using the rapid change in resistance of a superconductor near its transition temperature to sense the X-ray-induced temperature rise of electrons in a normal metal film held at about 0.1 K. Such ultrasensitive microcalorimeters offer enormous potential to materials analysis in the semiconductor and other industries and promise remarkable advances for optical and infrared detectors. While single microcalorimeters have attracted a great deal of attention worldwide, applications involving arrays are being pursued vigorously. When applied to defect analysis in the semiconductor industry, arrays will speed data acquisition many thousand-fold. The arrays also will make possible imaging in the X-ray though infrared regions of the electromagnetic spectrum and are of particular excitement to the National Aeronautics and Space Administration. Use of a transition-edge detector also can greatly improve thermal comparisons between ac and dc electrical voltages. At present such comparisons are done with room temperature instruments, but the cryogenic detectors are expected to improve the sensitivity of the ac/dc thermal conversion measurements by a factor of between 10 and 100 over room temperature detectors. Contact: Kent D. Irwin Ultra-small nanoscale electronic devices operated at cryogenic temperatures offer unique capabilities that impact both fundamental metrology and industrial instrumentation. This project is developing a revolutionary new fundamental quantum-based standard for capacitance. Using ultra-small (less than 100-nanometer) tunnel junctions operated at ultralow temperature (0.05 K), the device pumps electrons onto a capacitor one-by-one at a rate determined by an external clock. This device operates at a metrologically important level with an error rate less than about 1 part in 108. Using similar principles, work is under way to develop a superconducting version of the single electron pump. The superconducting charge pump should be able to operate at significantly higher clock speeds, producing an important increase in the current from the device. Single electron devices also can be used to produce single photons on demand by the recombination of single electrons and holes in a quantum dot. Work to build such a single photon source is also under way. High-temperature superconductivity (HTS) has opened the possibility for operating superconducting electronic instrumentation at temperatures accessible with present-day cryocoolers. HTS devices will expand the applicability of superconductors to unique standards, such as the Josephson volt, and measurement apparatus, such as superconducting quantum interference devices (SQUIDs). We have developed fabrication, testing capabilities, and theoretical competence for HTS devices in the areas of microwave and terahertz metrology and technology. We work with the HTS communication industry to measure and improve the power-handling capabilities of HTS devices as well as to improve microwave measurement and characterization techniques for HTS films and devices. We also evaluate and improve HTS Josephson junctions for use in terahertz detectors, and other devices to meet the measurement and application needs of industry. We also fabricate microelectromechanical (MEMS) systems for a number of applications. For example, thermally isolated regions are micromachined onto the surface of wafers for microcalorimeter arrays. The technology offers the possibility of multi-level circuits incorporating the sensors on one level and multiplexing on another. Collaborations with the Time and Frequency Division (Physics Laboratory) have led to fabrication of micromachined ion traps for atomic clocks and quantum computing and with the Magnetic Technology Division for magnetic instruments. Contact: David A. Rudman Manufacturers of precision electronic components and instrumentation need intrinsic electrical standards with accuracy above that achievable by traditional electrical metrology and artifact standards. The characterization and calibration of modern digital voltmeters, reference standards, and analog-to-digital and digital-to-analog converters require the development of new and improved intrinsic standards for the measurement of ac and dc voltage. Target customers are electronic instrument makers, Department of Defense contractors, and national and military standards laboratories. This project pioneered the development of practical Josephson voltage standards and, by encouraging the commercialization of these standards, has allowed U.S. industry to lead the world market for dc Josephson voltage systems and components. Continuing work is designed to make these systems faster, applicable to time-varying voltages, easier to use, and more reliable. Recently, we have delivered a new generation of programmable voltage standards that can change rapidly to any specified output voltage under computer control. An even newer quantum-based arbitrary waveform generator has been developed so that intercomparison with conventional ac voltage standards is possible. Finally, Josephson standards are being applied to calibrate a thermometer based on the thermal noise generated in a resistor. Such noise thermometers may prove to be a fundamental new measure of temperature. Contact: Samuel
P. Benz All voltage measurements performed in the United States, whether for the purpose of direct voltage reading or for the determination of another parameter (such as temperature), rely on traceability to international standards through the U.S. legal volt. Because of the length of the calibration chain that connects measurements by an end user with the U.S. legal volt, it is common for the measurement uncertainty of the end user to exceed the NIST primary uncertainty by a factor of 100 or more. The continued development and deployment by the U.S. electronics instrumentation industries of increasingly sophisticated and accurate instrumentation places ever-increasing demands for higher accuracy voltage metrology, both in calibration and testing laboratories and on production lines and factory floors. Consequently, we are continuously pressed both to reduce our measurement uncertainty at the beginning of this chain and to develop improved mechanisms for dissemination to the end user. Through maintenance, development, and dissemination of the U.S. legal volt, this project provides the base for voltage metrology that enables the U.S. electronics instrumentation industry to compete successfully in the global market. To maintain and disseminate the U.S. legal volt, we have established a representation of the SI unit of voltage via the Josephson effect and have developed the measurement systems required to measure and transfer that voltage to other electronic systems and chemical or electronic standards. To continually achieve the lowest possible uncertainty, we must perform regular checks for subtle systematic errors in both the Josephson voltage standard systems and the subsequent transfer systems. We also must perform regular comparison checks between our systems and maintain long-term observations of well-characterized check standards. We must periodically verify our consistency with the international community through very careful international comparisons. We perform research on the physical and statistical limitations of metrology equipment and protocols both presently in use and under development in order to support future technological advances. Our goal is to maintain the U.S. legal volt and to provide for the dissemination of an internationally consistent, accurate, reproducible, and traceable voltage standard, tied to the SI units, and readily and continuously available for U.S. science and industry. Contacts: Yi-hua
Tang and Michael
H. Kelley The U.S. electronics instrumentation industry maintains a position of world leadership through the development and deployment of increasingly sophisticated multifunction, high-precision, and low-maintenance instruments. The ready availability of accurate and reliable precision electrical metrology is a critical need of continued instrumentation development. In addition, the U.S. electrical power industry relies on precise and accurate electrical metrology in both the distribution and metering of electrical power. To meet present challenges and in anticipation of increasing needs of future instruments, we are focused on maintaining and disseminating a reliable unit of resistance. Because reliable and stable resistance standards have been available for many years, many electrical measurements (e.g., at very high/low current levels) are converted to resistance measurements. Because of this very broad customer need, resistance dissemination is required to support a wide variety of impedance measurements, a wide range of resistance levels and frequency, and with very high levels of accuracy. Our measurement activities enable U.S. industry to demonstrate and verify the accuracy of electrical measurements and the performance of high-precision instrumentation in a competitive world environment. Maintenance of the U.S. legal ohm requires research and the pursuit of scientific breakthroughs in quantum metrology to maintain a local representation of the unit and requires close collaboration with other national metrology institutes, including participation in international metrology comparisons to ensure international consistency of electrical measurements. To provide the continued improvement in our programs required in the competitive world environment, we are pursuing several objectives. The goal of this project is to maintain the U.S. legal ohm and to provide for the dissemination of an internationally consistent, accurate, reproducible, and traceable resistance standard that is readily and continuously available for U.S. science and industry. Contacts: Randolph
E. Elmquist and Michael
H. Kelley Our goals are to maintain the farad and tie the U.S. legal farad to the International System of Units (SI), to support NIST's impedance measurement services, and to ensure the critically needed access of the U.S. industrial base to internationally consistent, reliable, reproducible, and traceable electrical measurements. We tie the U.S. legal system of electrical units to the SI through the realization of the SI unit of capacitance. Because of the central role played by our experimental effort in maintaining both the consistency of the electrical units and the equivalence of electrical measurements within the United States to those of other nations, it is essential that this unit be determined with the highest possible accuracy and precision. This work also forms the foundation of our measurement services for electrical impedance, specifically capacitance and inductance artifact standards, ensuring the sound metrological basis for all impedance measurements, both nationally and internationally and ensuring that the claims of measurement accuracy by U.S. industries are recognized and accepted worldwide. We tie the U.S. legal system of electrical units to the International System of Units with smaller uncertainties than those of any other nation and provide the United States with a very solid basis for the measurement of electrical quantities. The central facility is the NIST calculable capacitor, with which the measurement of capacitance is effectively achieved through a measurement of length. Both the calculable capacitor and the chain of high precision measurements that transfers the SI unit to the calibration laboratories must be maintained and improved. We also conduct international comparisons with other national metrology laboratories to ensure measurement consistency. Contacts: Yicheng Wang and Gerald Fitzpatrick Concepts developed mostly over the past five to 10 years promise computing of revolutionary power and completely secure distribution of information. Using a Josephson junction, we have developed a new approach to quantum bits. A significant advantage of this approach, compared with others, is that the devices can be produced lithographically, like any other integrated circuit. As a result, the concept is thought to be extendable beyond concept demonstration to at least small-scale computers. A great deal of fundamental work remains to be done before quantum computing is even conceptually practical, e.g., the qubits must be connected to form gates that perform logic functions. Finally, the gates must be connected to perform more complex logic functions required of actual computing. Nevertheless, our fabrication and cryogenic facilities are perhaps the most ideal place to develop this exciting fundamental new technology. Another quantum information concept is used to distribute cryotographic keys in a way that was thought to be unbreakable according to the laws of physics. One approach uses coupled pairs of photons, said to be entangled. Unfortunately, the technology for perfectly generating such photons does not yet exist. We have, therefore, developed a photon counter that accurately determines the number of photons in a very weak pulse of light. This instrument has proven to be of vital importance to several research groups in the United States and has attracted international attention. Contact: John Martinis and Sae Woo Nam Our goal project is to develop applications of single-electron tunneling (SET) technologies that are relevant to high-precision electrical metrology. We address three different needs: the development of a fundamental representation of capacitance; development of a fundamental representation of electrical current; and development of general applications of SET devices. The present representation of the International System of Units (SI) farad is through silica-based artifact capacitors. Although these capacitors are of high quality, they are susceptible to drift over time, and their accuracy may depend on other parameters such as temperature, pressure, and frequency. The metrology community, including both the national standards laboratories and domestic secondary calibration laboratories, needs a capacitance representation based on fundamental physical principles and not on properties of individual physical artifacts. At present, there is no fundamental representation of current; the representation of current is via the representations of voltage and resistance. Though these representations are based on fundamental physical principles and are of high quality, the representation of current is dependent upon them. An independent representation of current could provide significant additional confidence in the coherency of the representations of the SI electrical units through closure of the "metrology triangle," V = IR with all measurements based on fundamental constants. Integrated circuit (IC) applications of SET effects are becoming more important, either deliberately, for example, single-electron memory or quantum computing, or accidentally as design rules continue to shrink. One very important practical problem with implementing SET-based device integration is the "charge offset" phenomenon. This phenomenon makes it difficult or impossible to integrate multiple SET-based devices together, thus engendering problems for the IC industry. That industry needs devices, which are resistant to the charge offset. This project is addressing these needs through the development of single-electron tunneling technologies. SET devices are being developed that will allow the reliable and reproducible control of individual electrons and will provide a standard of charge through control of these fundamental particles. Contacts: Neil M. Zimmerman and Michael H. Kelley Terahertz technology fits into the electromagnetic spectrum between microwaves and the infrared. While this region of the spectrum is relatively undiscovered, many scientific and commercial applications are uniquely possible at terahertz frequencies (1012 Hz). This project focuses on providing the metrological tools needed by industry to exploit this technology. Activities under way include the development of a prototype concealed weapons detection system. The system uses a wafer-scale array of more than 120 antenna-coupled bolometers. It is expected to be useful in a portal design, for example for passengers entering an airport. Another system uses terahertz bolometer arrays to analyze problems in plasmas in semiconductor manufacturing. The plasmas typically contain a number of molecular and ionic species, whose concentrations and temperatures can be accurately monitored by spectroscopy on their pure rotational transitions, which lie in the terahertz range. As a demonstration, a NIST deposition system is being equipped with such a monitor. To further advance this still-evolving technology, we have developed, and continue to perfect, tiny lithographed antennas to match the small wavelengths in the terahertz range. One program pursued the novel use of a large array of inexpensive antenna-coupled diodes worn on a military person's backpack as a source of power. We also are pursuing cryogenic detectors having ultimate sensitivity. Contact: Erich
N. Grossman AC-DC Difference Standards and Measurement Techniques Thermal voltage and current converters offer the most accurate and broadband method for measuring ac voltage and current for applications in communications, power generation, aerospace, and defense. Thermal transfer standards are calibrated by NIST in terms of reference converters, which themselves have been characterized by reference to the NIST primary standards-special multijunction thermal converters whose performance is known. These primary and working standards, in common use throughout the metrology community, employ thermal converters fabricated from wire elements. We are studying new methods for the manufacture of film thermal converter structures made by the use of photolithography on silicon substrates. The application of this new technology may result in improved performance and reduction in the cost of thermal converters. Contacts: Joseph
R. Kinard and Michael
H. Kelley Pulse Metrology and Time Domain Measurements NIST has an active program to provide a basis for characterizing both the time domain and frequency domain performance of sampling and digitizing systems, including analog/digital converters, sampling oscilloscopes, and waveform recorders. Project objectives are to develop standards, test methods, and analysis techniques for waveform acquisition devices and to expand and improve the present time domain waveform measurement services to support high-performance samplers and digitizers, as well as fast pulse and impulse sources, operating over frequencies from dc to 50 GHz. Theoretical and experimental research establishes test methods, reference waveforms, and state-of-the-art sampling technology to support these systems. Research areas include opto-electronic and electro-optical techniques for sampling and pulse generation in the 1- to 5-picosecond regime; advanced signal processing methods, including deconvolution, phase-plane compensation and spectral estimation; and ultrahigh accuracy techniques to support modern sigma-delta sampling technology. Contact: Nicholas
G. Paulter, Jr. and Gerald
Fitzpatrick Electrical measurements are critical to the operation of electrical power systems in many ways; they are fundamentally important to the control of power flow, the maintenance of reliability and quality, and the revenue metering of electrical power. Our research supports the high reliability of electric power delivery, public safety, and fairness in the sale of electric power to customers. Also, the dawn of deregulation of the electric power industry has opened the door to new electricity suppliers who use non-traditional technologies that may introduce harmonic power flows into the power system. The development of wideband current and power measurement systems at NIST support both the characterization of distortion in the electric power delivered to customers and the verification of accurate meter operation in the presence of harmonic distortion. The proliferation
of power electronic controllers for motors introduces distortions that
degrade the quality of electric power in distribution systems. Sensitive
electronic equipment must be protected from degradation of power quality.
Our research supports the identification of sources and also the mitigation
of its deleterious effects. The new era of electric power industry deregulation
has utilities looking toward new technologies to help maintain outstanding
high reliability in face of a changing complexion of electric power generation
and delivery systems. These new technologies include magneto-optic measurement
devices that offer great advantages over conventional instrumentation
not only for metering in high voltage transmission and distribution systems,
but also for monitoring power quality and the condition of power equipment.
We conduct research to support verification of the accuracy and usefulness
of these optical devices. Efficiency requirements on distribution transformers
have been introduced to save energy by limiting their allowable power
losses. We are designing portable, cost-effective, power-loss measurement
systems in support of transformer manufacturers who need to meet the efficiency
requirements.
Date
created:November
8, 2001 |