THE ELECTRONICS AND ELECTRICAL

ENGINEERING LABORATORY

One of NIST’s seven Measurement and Standards Laboratories, EEEL conducts research, provides measurement services, and helps set standards in support of: the fundamental electronic technologies of semiconductors, magnetics, and superconductors; information and communications technologies, such as fi ber optics, photonics, microwaves, electronic displays, and electronics manufacturing supply chain collaboration; forensics and security measurement instrumentation; fundamental and practical physical standards and measurement services for electrical quantities; maintaining the quality and integrity of electrical power systems; and the development of nanoscale and microelectromechanical devices. EEEL provides support to law enforcement, corrections, and criminal justice agencies, including homeland security. EEEL consists of four programmatic divisions and two matrixmanaged offi ces:Semiconductor Electronics DivisionOptoelectronics DivisionQuantum Electrical Metrology DivisionElectromagnetics DivisionOffi ce of Microelectronics ProgramsOffi ce of Law Enforcement StandardsThis document describes the technical programs of the Quantum Electrical Metrology Division. Similar documents describing the other Divisions and Offi ces are available. Contact NIST/EEEL, 100 Bureau Drive, MS 8100, Gaithersburg, MD 20899-8100, Telephone: (301) 975-2220, On the Web: www.eeel.nist.gov
ELECTRONICS AND ELECTRICAL

ENGINEERING LABORATORY

QUANTUM ELECTRICAL

METROLOGY DIVISION

PROGRAMS, ACTIVITIES, AND

ACCOMPLISHMENTS

NISTIR 7370

January 2007

U.S. DEPARTMENT OF COMMERCE

Carlos M. Gutierrez, Secretary

Technology Administration

Robert Cresanti, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

William Jeffrey, Director
Any mention of commercial products is for information only; it does not imply recommendation or endorsement by the National Institute of Standards and Technology nor does it imply 

that the products mentioned are necessarily the best available for the purpose.
Quantum Electrical Metrology Division iii 

CONTENTS

Welcome..................................................................................................................................iv

Quantum Standards ..................................................................................................................1

 Quantum Voltage Metrology ...........................................................................................2

 Voltage Metrology ............................................................................................................7

 AC-DC Difference Standards and Measurement Techniques ........................................10

 Single Electronics for Standards and Metrology ............................................................14

 Metrology of the Ohm ....................................................................................................20

 Farad and Impedance Metrology ....................................................................................23

 The Electronic Kilogram ................................................................................................27

 Quantum-Based Noise Thermometry ............................................................................30

Quantum Measurements ........................................................................................................35

 Electric Power Metrology ..............................................................................................36

 Quantum Computing Using Integrated Josephson Junction Circuits .............................39

 Quantum Sensors ............................................................................................................44

 Magnetic Sensors & Quantum Materials .......................................................................51

Appendix A: Topics Covered by Organizational Units.........................................................55

Appendix B: Quantum Electrical Metrology Division Calibration Services ........................57

Appendix C: Quantum Electrical Metrology Division Staff and Phone Numbers ...............58

Appendix D: Post-Doctoral Research Associateships ..........................................................60
iv Electronics and Electrical Engineering Laboratory

WELCOME

The Quantum Electrical Metrology Division unites fundamental electrical metrology and 

leading-edge quantum-based metrology research to create a dynamic organization poised to 

lead quantum metrology into the future. The Division consists of three groups: Fundamental 

Electrical Measurements, Applied Electrical Metrology, and Quantum Devices. The fi rst two 

groups are located in Gaithersburg, MD and boast of a proud 100-year history of precision 

electrical metrology. The Quantum Devices Group located in Boulder, CO brings a 35-year 

history of creating world-leading quantum-based standards and measurements. The Division 

works to provide the world’s best electrically-based measurements and standards.

This document is organized into two main sections, Quantum Standards, and Quantum Measurements. Within those sections each Division project is described without reference to its 

geographical location. Appendix A describes the organizational location of all the research 

projects in the Division. Appendix B lists all of the measurement services offered by the Division, and Appendix C is a Division staff list for readers wishing to phone or e-mail us to learn 

more about a topic. We are always interested in new post-doctoral associates, and Appendix D 

describes many research opportunities in the Quantum Electrical Metrology Division.

We always strive to serve our customer’s needs, and I hope that this document provides you 

with the information you need to better interact with our research staff. We appreciate your 

interest and welcome your comments. We also invite you to visit our web page at http://www.

eeel.nist.gov/817/.

Thank you.

James K. Olthoff, Chief

Quantum Electrical Metrology Division

Electronics and Electrical Engineering Laboratory

National Institute of Standard and Technology
Quantum Electrical Metrology Division 1

QUANTUM STANDARDS

At the National Institute of Standards and Technology, our ultimate objective is to create what 

we call intrinsic standards. As part of the Electronics and Electrical Engineering Laboratory the 

Quantum Electrical Metrology Division concentrates primarily on intrinsic electrical standards. 

Such standards can be widely used by any careful operators to give results that are ultimately 

as accurate as those produced within NIST by our expert metrologists.

An intrinsic standard that is based on quantum effects is particularly attractive. Such effects offer 

tiny rulers permitting counting the number of quanta that make up a quantity to be measured. 

The quantum effects we use are the counting rate of fl ow of superconducting fl ux quanta or the 

much larger resistance quanta in the quantum Hall effect. We are also developing techniques 

for counting individual electrons. All of these effects occur at very low temperatures close to 

absolute zero.

Other organizations at NIST use atomic transitions to measure time and frequency of the wavelength of light from a certain laser to measure length.

QUANTUM STANDARDS

Quantity Quantum Magnitude

Voltage Magnetic fl ux quantum h/2e

Current Single electron e

Resistance Resistance quantum e2

/h

Time and frequency Atomic transition of a Cs atom 9.192631770 GHz

Length Wavelength of a HeNe laser 632.99139822 nm

FUNDAMENTAL CONSTANTS

Constant Symbol Magnitude

Planck constant h 6.626 0693 × 10-34 J s

Elementary charge e 1.602 176 53 × 10-19 C

Boltzmann constant kB 1.380 6505 × 10-23 J k-1

The Quantum Electrical Metrology Division uses intrinsic standards that occur in condensed 

matter systems. Two of these, superconductivity and the quantum Hall effect, are macroscopic 

quantum systems. They are particularly convenient because in some cases it is not necessary 

to have particularly small structures to isolate the quantum. Both have been developed to make 

defi nitive measurements of voltage and resistance. 

At present the Division is pursuing two standards that are not for electrical standards but that 

depend on our experience with electrical measurements. The fi rst is a potential new standard 

of mass based on the equivalence of gravitational forces and electrical forces. If fully successful, this work may lead to an “electronic kilogram” in which the unit of mass is based on 

electrical quantities. In the second the temperature-dependent electrical noise of a resistance 

is compared with the quantum-based ac voltage standard to measure temperature. If this work 

is fully successful it might lead to a defi nition of temperature in terms of electrical quantities 

— an “electronic Kelvin.”

In this section we discuss our progress with quantum standards and our uses of them. These 

standards are for voltage, both constant and time-varying, current and capacitance, resistance, 

capacitance, and inductance.
2 Electronics and Electrical Engineering Laboratory

QUANTUM VOLTAGE METROLOGY

GOALS

To meet the nation’s voltage metrology needs by 

developing state-of-the-art voltage standard systems and precision measurement techniques that 

are founded on quantum-based superconducting 

circuit and system technology so that internationally consistent, accurate, and reproducible voltage measurements are readily and continuously 

available for U.S. industrial, governmental, and 

scientifi c applications.

CUSTOMER NEEDS

The demands of modern technology for accurate 

voltage calibrations have exceeded the capability 

of classical artifact standards. To meet current 

needs, an international agreement signed in 1990 

redefi ned the practical volt in terms of the voltage 

generated by a superconductive integrated circuit 

developed at NIST and the Physikalisch-Technische Bundesanstalt in Germany. This circuit 

contains thousands of superconducting Josephson 

junctions, all connected in a series array and biased 

at a microwave frequency. The voltage developed 

by each junction depends only on the frequency and 

a fundamental physical constant; thus, the circuit 

never needs to be calibrated. This allows any standards or commercial laboratory to generate highly 

accurate voltages without the need to calibrate an 

artifact standard. This advance has improved the 

uniformity of voltage measurements around the 

world by about a hundredfold. These systems are 

now essential for meeting legal and accreditation 

requirements in commercial, governmental, and 

military activities.

The U.S. electronics instrumentation industry 

maintains its world position through the development and deployment of increasingly accurate, 

fl exible, easy-to-use instruments. Providing U.S. 

industry with quantum voltage standard systems 

gives these customers immediate realization of the 

highest possible in-house accuracy. These customers also benefi t dramatically by eliminating their 

dependence on less accurate reference standards 

that require frequent calibration.

We also support the standards community by applying quantum-based voltage metrology to new areas 

and by developing voltage standard systems with 

new capabilities, including lower cost, increased 

functionality, and ease of use. This is especially 

true in the area of ac voltage metrology where 

we have developed the world’s fi rst ac Josephson 

voltage standard system for arbitrary waveform 

synthesis. Other customers are the superconductive electronics community and the U.S. military, 

which we support through development of novel 

superconductive circuits, cryogenic packaging, and 

high-performance systems, and also by providing 

technical expertise.

Burm Baek, Nicolas Hadacek, Paul Dresselhaus, 

Charlie Burroughs, Sam Benz, Michio Watanabe, and 

Yonuk Chong, at NIST-Boulder labs.

A 1 centimeter × 1 centimeter superconducting 

integrated circuit with over 132,000 triple-stacked 

SNS Josephson junctions for the 5.0 Volt high-resolution programmable voltage standard operating at 

18.5 GHz.

Technical Contact:

Sam Benz

Staff-Years (FY 2006):

3 professionals

3 guest researchers

TECHNICAL STRATEGY

Over the past 25 years, we have developed superconductive Josephson junction array technology 

for quantum voltage standard systems. Groundbreaking work at NIST led to commercialization 

of the fi rst practical dc Josephson voltage standard 

system. Recent improvements in system design 

and operation have led to a traveling Josephson 
Quantum Electrical Metrology Division 3

Schematic diagram depicting a 4-junction stacked 

series array with molybdenum-disilicide normal metal 

barriers, superconducting niobium electrodes, and 

silicon dioxide insulating dielectric.

voltage standard system that is compact, low cost, 

and transportable for calibration of Zener reference 

standards. The technology for this conventional 

Josephson voltage standard system has been completely transferred to the private sector, where 

systems are produced and supported by a number 

of small companies.

In order to create a new generation of voltage 

standards, we developed a novel superconductor-normal metal-superconductor (SNS) junction 

technology that adds the features of stability and 

programmability to the accuracy of conventional 

Josephson voltage standards. This gave rise to the 

fi rst Programmable Josephson Voltage Standard 

(PJVS) systems with 1 V output voltage. This was 

the fi rst practical system to have the unique feature 

that the quantum-defi ned voltage steps are intrinsically stable, which is essential for some calibrations 

and many applications. As a result, PJVS systems 

have been delivered to, and installed in, a number of 

metrology experiments – namely the Watt-balance 

experiments at NIST and Switzerland’s Federal 

Offi ce of Metrology (OFMET), where their accuracy, stability and noise immunity have reduced 

the uncertainty of the experimental measurements. 

In order to support the maintenance and dissemination of the Volt, a one-volt programmable voltage 

standard system is also now in use in the NIST 

primary voltage calibration laboratory. 

In order to increase the junction density of arrays 

and thereby the output voltage for all our quantum-based voltage standard circuits, we invented 

a nanoscale junction fabrication technology in 

which the spacing between junctions is reduced 

from 7 μm to less than 50 nm. Over many years we 

explored various fabrication methods and materials 

before determining the optimal method of vertically stacking the junctions on top of each other 

in three dimensions. We found a number of useful 

junction barrier materials, in particular molybdenum-disilicide and niobium-silicide, that could be 

etched contiguously with niobium electrodes. To 

form the junction stacks we developed a deep vertical etching process using an inductively coupled 

plasma etcher to make tall stacks. Stacks as tall as 

15 junctions have been demonstrated and uniform 

electrical characteristics of arrays have been measured using Nb-electrodes as thin as 5 nm. The 

stacked-junction technology has now matured to 

the point where we have made useful PJVS circuits 

with over 130,000 junctions operating uniformly 

on a single chip. Such nano-stacked junction arrays 

are now the basis for all of our next generation dc 

and ac Josephson voltage standard systems.

Scanning electron microscope image of an 8-junction stack with niobium-silicide barriers and niobium 

electrodes. The image shows that the nano-stacked 

junctions can be vertically etched which is critical for 

achieving uniformity of the electrical characteristics. 

(Image by Burm Baek, NIST)

Our present goals are to further improve NIST 

electrical measurement capabilities by applying 

quantum voltage standards to both existing and 

new areas, in particular, in dc and ac metrology, 

60 Hz power applications, and electronic-based 

precision thermometry. Our most challenging and 

long-term goal is to demonstrate a 10 V PJVS 

system that is essentially a turn-key system that 

does not require an expert to operate. Such a system 

would be preferable for many applications that are 

not fulfi lled using the existing 10 V conventional 

Josephson voltage standards. This challenging 

task requires signifi cant development of array 

technology, microwave integrated circuits, electronic instrumentation, and cryogenic packaging. 

We have demonstrated circuits that have reached 

voltages as high as 5 V. This was accomplished by 
4 Electronics and Electrical Engineering Laboratory

PLANS

Our present goal is to increase the output voltage 

and measurement bandwidth of the acJVS to 1 V and 

1 MHz. We recently demonstrated 220 mV rms (311 

mV peak) output voltage circuits that are even closer 

to realizing this goal and were possible through the 

development of high-density arrays and novel tapered 

transmission line circuits. Future research and creative 

breakthroughs in electronics and circuit design are 

required to expand the output range to 1 V and the 

output bandwidth to 1 MHz. A low-voltage version of the 

acJVS has also been developed as a precision pseudonoise voltage source to calibrate the measurement 

electronics of a novel Johnson noise thermometry 

system. The thermometry application is described in 

detail in the Johnson noise thermometry chapter of this 

book.

Finally, in order to improve calibrations of 60 Hz 

power meters, we have renewed our interest in using 

the PJVS system as an ac standard for frequencies 

below 1 kHz. Since higher voltages are possible 

with this system, we can use the PJVS as a multi-bit 

digital-to-analog converter by rapidly switching array 

segments to appropriate constant voltage steps. The 

new quantum-based power standard will use two 

PJVS systems (one for voltage and one for current) 

to produce precision 60 Hz sinusoidal reference 

signals. Using step-wise approximation synthesis, the 

PJVS systems produce sine waves with calculable 

rms voltage and spectral content. This work is in 

collaboration with the Applied Electrical Metrology 

Group, and they are developing novel divider and 

amplifi er techniques to implement comparison between 

the 120 V calibration and 1.2 V PJVS signals. Our 

goal is to reduce all error sources and uncertainty 

contributions from the PJVS-synthesized waveforms to 

be a few parts in 107

, so that the overall uncertainty in 

the power standard will be a few parts in 106

. 

•

•

increasing the number of junctions in each array 

through the development of new junction barrier 

materials and nano-stacked junction technology. 

Achieving 10 V PJVS circuits requires improved 

microwave designs.

Over the past 10 years we also have been developing 

the necessary technology to make a practical and 

automated ac Josephson voltage standard (acJVS) 

system. We call this same system the Josephson 

arbitrary waveform synthesizer (JAWS) when it is 

used to synthesize non-sinusoidal waveforms. The 

concept for this new device was co-invented by 

NIST and Northrop-Grumman researchers in 1996, 

and is essentially a digital-to-analog converter that 

is capable of synthesizing arbitrary waveforms and, 

like the previously described dc-only systems, exploits the perfectly quantized pulses of Josephson 

junctions. Present ac voltage calibrations are done 

using ac-dc thermal voltage converters, which 

thermally compare the root-mean-square voltage of 

an ac signal with a known and accurate dc signal. 

The new quantum-based acJVS is a perfect voltage 

source and will provide an entirely new instrument 

and methodology for ac voltage metrology. The 

precision, stable and accurate arbitrary waveforms 

will also be useful for calibrating other scientifi c 

instruments, such as ac voltmeters, spectrum analyzers, amplifi ers, and fi lters. The biggest challenge 

has been to reach practical output voltages of at 

least one-quarter volt. 

In 2006, we completed the fi rst acJVS system, 

which is now installed in the NIST Voltage Calibration Lab and can generate arbitrary waveforms 

up to 100 mV rms and frequencies up to 100 kHz. 

This is the world’s fi rst quantum-mechanically 

accurate ac voltage standard source with practical output voltage at audio frequencies. Precision 

measurements with the acJVS demonstrated the 

accuracy of these synthesized voltage waveforms 

from dc up to 100 kHz over the full voltage range. 

This new measurement capability was achieved 

by using superconducting integrated circuits with 

nano-stacked Josephson junction arrays, better onchip fi lters, and a well-controlled output transmission line. This work was undertaken specifi cally to 

improve NIST’s low-voltage ac calibration service, 

and we anticipate a 10- to 100-fold reduction in 

calibration uncertainties in this 1 mV to 100 mV 

range.

Charles Burroughs with the Programmable Josephson 

Voltage Standard system showing (left to right) the low 

thermal probe, the microwave and high-speed bias 

electronics, and the computer.
Quantum Electrical Metrology Division 5

Paul Dresselhaus holds silicon wafer containing 

superconducting integrated circuits and shows the current-voltage characteristics of a Josephson junction 

array.

ACCOMPLISHMENTS

Demonstrated accurate 100 mVrms synthesized quantum-based voltage waveforms from dc 

up to 100 kHz. This new measurement capability 

was achieved by using superconducting integrated 

circuits with nano-stacked Josephson junction arrays, better on-chip fi lters, and a well-controlled 

output transmission line. This work was undertaken 

in order to improve our low-voltage ac calibration 

service.

Investigated new JJ barriers, WSi2

, TiSi2, 

NbxSi1-x which have led to new high-speed Josephson applications.

Further increased programmable voltage 

standard output with longer triple-stacked arrays. 

The record voltage is now 5 V with a useful 1 mA 

current range. This result gives us confi dence that 

we have a practical path to reach 10 V, which is 

essential for making a turn-key quantum voltage 

standard system that will revolutionize voltage 

metrology.

Duplicated, automated, and delivered a 100 

mVrms acJVS system to voltage calibration lab in 

Gaitherburg. Performed the fi rst direct quantumbased measurements on the two lowest voltage 

ranges of a Fluke transfer standard.

Synthesized and measured 60 Hz 1.5 V rms 

sine waves with PJVS arrays for quantum-based 

power calibration EEEL Director’s Reserve program. Measured harmonic content agrees with the 

expected quantum-accurate synthesized voltages.

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Demonstrated precision measurements of a 

commercial analog-to-digital-converter with a 

record 220 mV rms (311 mV peak) sine waves and 

arbitrary waveforms.

RECENT PUBLICATIONS

S. P. Benz, C. J. Burroughs, P. D. Dresselhaus, T. E. Lipe and 

J. R. Kinard, “An AC Josephson Voltage Standard for AC-DC 

Transfer Standard Measurements,” to appear in IEEE Trans. 

Inst. Meas., vol. 56, no. 2 (in press).

C. J. Burroughs, S. P. Benz, P. D. Dresselhaus, Y. Chong, B. 

Waltrip, T. Nelson, J. M. Williams, D. Henderson, P.Patel, L. 

Palafox, and R. Behr, “Development of a 60 Hz Power Standard 

using SNS Programmable Josephson Voltage Standards,” to 

appear in IEEE Trans. Inst. Meas., vol. 56, no. 2 (in press).

S. P. Benz, C. J. Burroughs, P. D. Dresselhaus, T. E. Lipe and J. 

R. Kinard, “100 mV ac-dc transfer standard measurements with 

a pulse-driven ac Josephson voltage standard,” 2006 Conference 

on Precision Electromagnetic Measurements Digest, presented 

10–14 July 2006, Torino, Italy, pp. 678-679. 

C. J. Burroughs, S. P. Benz, P. D. Dresselhaus, Y. Chong, B. 

Waltrip, T. Nelson, J. M. Williams, D. Henderson, P.Patel, L. 

Palafox, and R. Behr, “Development of a 60 Hz Power Standard 

using SNS Programmable Josephson Voltage Standards,” 2006 

Conference on Precision Electromagnetic Measurements Digest, presented 10–14 July 2006, Torino, Italy, pp. 682-683. 

B. Baek, Paul D. Dresselhaus, and Samuel P. Benz, “Co-sputtered Amorphous Nbx

Si1-x Barriers for Josephson-Junction 

Circuits,” to appear in IEEE Trans. Appl. Supercond., 2006.

M. Watanabe, P. D. Dresselhaus, and S. P. Benz, “Resonancefree Low-pass Filters for the ac Josephson Voltage Standard,” 

IEEE Trans. Appl. Supercond., vol. 16, no. 1, pp. 49-53, March 

2006.

Y. Chong, N. Hadacek, P. D. Dresselhaus, C. J. Burroughs, B. 

Baek, and S. P. Benz, “Josephson junctions with nearly superconducting metal silicide barriers,” Appl. Phys. Lett., vol. 87, 

222511, December 2005.

P. D. Dresselhaus, Y. Chong, N. Hadacek, B. Baek, M. Watanabe, C. J. Burroughs, and S. P. Benz, “Silicide Barrier SNS 

Junctions for AC Josephson Voltage Standards,” in Proceedings of the 10th International Superconductive Electronics 

Conference, ISEC’05, September 5–9, 2005, Noordwijkerhout, 

Netherlands.

S. P. Benz, C. J. Burroughs, P. D. Dresselhaus, N. Hadacek, 

and Y. Chong, and, “Progress Toward Practical AC and DC 

Josephson Voltage Standards at NIST,” in Proceedings of the 

6th International Seminar on Electrical Metrology, VI Semetro, 

21-23 September 2005, Rio de Janeiro, Brazil, pp. 32-34.

Y. Chong, P. D. Dresselhaus, and S. P. Benz, “Electrical properties of Nb-MoSi2

-Nb Josephson junctions,” Appl. Phys. Lett., 

vol. 86, 232505, 6 June 2005.

N. Hadacek, P. D. Dresselhaus, Y. Chong, S. P. Benz, and J. 

E. Bonevich, “Fabrication and Measurement of Tall Stacked 

Arrays of SNS Josephson Junctions,” IEEE Trans. Appl. Supercond., vol. 15, no. 2, pp. 110-113, June 2005.

C. J. Burroughs, S. P. Benz, P. D. Dresselhaus, Y. Chong, 

and H. Yamamori, “Flexible Cryo-packages for Josephson 

Devices,” IEEE Trans. Appl. Supercond., vol. 15, no. 2, pp. 

465-468, June 2005.

■
6 Electronics and Electrical Engineering Laboratory

P. D. Dresselhaus, Y. Chong, and S. P. Benz, “Stacked NbMoSi2-Nb Josephson Junctions for ac Voltage Standards,” 

IEEE Trans. Appl. Supercond., vol. 15, no. 2, pp. 449-452, 

June 2005.

Y. Chong, C. J. Burroughs, P. D. Dresselhaus, N. Hadacek, H. 

Yamamori, and S. P. Benz, “Practical High-Resolution Programmable Josephson Voltage Standards using Double- and 

Triple-Stacked MoSi2

-Barrier Junctions,” IEEE Trans. Appl. 

Supercond., vol. 15, no. 2, pp. 461-464, June 2005.

C. J. Burroughs, S. P. Benz, P. D. Dresselhaus, and Y. Chong, 

“Precision Measurements of AC Josephson Voltage Standard 

Operating Margins,” IEEE Trans. Inst. Meas., vol. 54, no. 2, 

pp. 624-627, April 2005.

Y. Chong, C. J. Burroughs, P. D. Dresselhaus, N. Hadacek, H. 

Yamamori, and S. P. Benz, “2.6 V high-resolution programmable Josephson voltage standard circuits using double-stacked 

MoSi2

-barrier junctions,” IEEE Trans. Inst. Meas., vol. 54, no. 

2, pp. 616-619, April 2005.
Quantum Electrical Metrology Division 7

VOLTAGE METROLOGY

GOALS

To maintain the U.S. legal volt and to provide for 

the dissemination of an internationally consistent, 

accurate, reproducible, and traceable voltage 

standard that is tied to the SI units and is readily 

and continuously available for the U.S. scientifi c, 

industrial base and government laboratories.

CUSTOMER NEEDS

All voltage measurements performed in the U.S., 

whether for the purpose of direct voltage readings 

or for the determination of another parameter 

(such as temperature) through the use of a transducer that converts that parameter into a voltage 

signal, rely on the consistency of 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 industry 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 fl oors. Consequently, NIST is continuously 

pressed to reduce 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 robust base for voltage metrology that enables 

the U.S. electronics instrumentation industry to 

compete successfully in the global market and supports scientifi c research in high accuracy voltage 

measurements ever needed.

TECHNICAL STRATEGY

A representation of the SI unit of voltage has been 

established via the Josephson effect, to maintain 

and disseminate the U.S. legal volt. The measurement systems required to measure and transfer that 

voltage to other electronic systems and to chemical 

or electronic standards have been developed. To 

continually achieve the lowest possible uncertainty, 

project members: 1) perform regular checks for 

subtle systematic errors in the Josephson voltage standard systems and the subsequent transfer 

systems, 2) perform regular direct or indirect 

comparisons between NIST systems, 3) maintain 

long-term observations of well-characterized check 

standards, and 4) periodically verify our consistency with the international community through 

very careful international comparisons. Research 

continues 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.

In recent years, an increasing number of Josephson 

voltage standards have been deployed both around 

the world and throughout the U.S. It has proven 

very diffi cult to verify in the fi eld the performance 

of voltage metrology systems based upon Josephson standards because the accuracy of these 

measurements is limited by the performance of the 

Zener voltage references used as transfer standards. 

Because the ultimate performance of Josephson 

voltage systems should be much better than that 

which can be verifi ed using these standards, a traveling compact Josephson voltage standard (CJVS) 

has been developed, along with measurement 

protocols appropriate for its use in comparisons 

between Josephson voltage systems in geographically separated locations. The elimination of the 

problems associated with traveling Zener standards 

has reduced the uncertainty of Josephson voltage 

comparisons by an order of magnitude compared to 

that using a Zener MAP. Direct array comparison 

will be used to further improve the uncertainty of 

JVS comparisons. NIST is collaborating with the 

National Research Council, Canada and private 

industry to develop an alternative protocol for 

making JVS comparisons available to other NMIs 

and industry labs.

The NIST voltage calibration service has implemented a programmable Josephson voltage 

standard (PJVS) to replace the cell banks and 

incorporated it into the daily calibration service. 

This implementation has reduced the number of 

transfers necessary to link the calibration bench to 

the Josephson voltage standard. The PJVS can be 

used to verify other NIST JVS systems operation 

by providing a stable voltage up to 2.5 V with an 

uncertainty of a few parts in 1010. Further improvement of the programmable voltage standard by 

using a newly designed array with a higher current 

and voltage margin is in progress. The fi nal goal 

is to deliver a system with better specifi cations for 

applications such as direct array comparison, the 

electronic mass and the metrology triangle. 

Technical Contact: 

Yi-hua Tang 

Staff-Years (FY 2006):

1 professional
8 Electronics and Electrical Engineering Laboratory

With the implementation of the compact Josephson 

voltage standard and programmable Josephson 

voltage standard, we will be able to serve our 

customers’ needs in voltage dissemination with 

reliability, effi ciency and accuracy, and to meet the 

most demanding requirements for voltage measurements in scientifi c research and development.

PLANS

Establish the viability of using the 1 V 

programmable JVS for regular calibrations.

Perform a series of comparisons using the NIST 

compact Josephson voltage standard with other 

national metrology institutes and with high-level 

industrial metrology laboratories. 

Upgrade the hardware and software of the compact 

Josephson voltage standard to develop an alternative 

protocol for direct array comparisons. 

Continuous improvement of programmable 

array design and fabrication for applications in volt 

maintenance, the electronic mass and the metrology 

triangle. 

ACCOMPLISHMENTS

The 7th interlaboratory comparison (ILC) 

of Josephson Voltage Standards (JVS) at 10 V, 

sponsored by the National Conference of Standard 

Laboratories International (NCSLI), took place 

from April to October 2005 with 15 participating 

labs. NIST was the pivot lab and implemented 

the CJVS in the JVS ILC. A traveling NIST JVS 

system and NIST protocol were used to make fi ve 

comparisons with the sub-pivot labs. The use of the 

CJVS in the ILC 2005 improved the uncertainty 

of the sub-pivot comparisons by about an order of 

magnitude to 2 to 3 parts in 109

 and also provided 

a more direct link between NIST and the other 

nine participants in the ILC. Because the sub-pivot 

comparisons are made in-situ, uncertainty from 

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•

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non-linear drift, transportation and environmental 

effects is largely eliminated. Small system errors 

of a few parts in 109

 can be detected and corrected 

with a CJVS comparison. The discovery of system 

problems at three of the fi fteen laboratories in the 

ILC 2005 demonstrates the value of intercomparisons of Josephson voltage systems. 

The National Research Council’s (NRC) 

Josephson voltage standard (JVS) has been directly compared with the compact, transportable 

Josephson array standard of the National Institute 

of Standards and Technology (NIST) at 10 V. A 

simplifi ed biasing technique for both arrays has 

been developed for this direct comparison. The 

difference between the NRC JVS and the NIST 

CJVS at 10 V was found to be 0.3 nV with an expanded uncertainty of 3.8 nV or 3.8 x 10-10 at 95% 

confi dence. This is a substantial reduction over 

comparisons using Zener references. The results 

of this comparison augment the confi dence and 

traceability of the 7th interlaboratory comparison 

(ILC) of Josephson Voltage Standards (JVS) at 

10 V sponsored by the National Conference of 

Standard Laboratories International (NCSLI). 

A bilateral JVS comparison was carried out in 

March 2006 with CENAM. This is the fi rst time 

that the NIST CJVS has been used in a Sistema Interamericano de Metrologia (SIM) comparison. A 

request to list the result in the SIM key comparison 

database SIM.EM.BIPM-K11.b has been submitted to SIM. The result of the comparison was very 

satisfying. The difference between the CENAM 

JVS and the NIST CJVS at 10 V was found to be 

-38 nV with an expanded uncertainty of 42 nV at 

95% confi dence or 4.2 x 10-9. This is a factor of 

9.7 improvement compared to the uncertainty that 

CENAM achieved in the NCSLI JVS ILC 1999, the 

last intercomparison that CENAM participated in. 

This is the fi rst time a CENAM JVS intercomparison reached an uncertainty of few parts in 109

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NCSLI JVS ILC 2005 results.

SIM.EM:BIPM-K11.b comparison between NIST and 

CENAM JVS.
Quantum Electrical Metrology Division 9

A JVS Working Group (JVSWG) consisting 

of 15 NCSLI JVS ILC participants and other interested labs was formed after the NCSL JVS ILC 

2005 to address common issues within the JVS 

community and to promote collaboration among the 

group members. Two group meetings have been 

held; one at the MSC 2006 and the other at NCSLI 

2006. One teleconference was accomplished in 

February. At these meetings the results of the recent 

JVS ILC 2005 and issues concerning the new WINDOWS JVS software were reported and discussed. 

The JVSWG has proved to be a useful forum that is 

benefi cial to its members by promoting guidelines 

and assistance with the maintenance and healthy 

operation of member JVS systems. 

CALIBRATIONS

Voltage calibrations (17 calibration reports, 50 

outputs) were performed from October 1, 2005 to 

August 30, 2006. The generated division income 

was approximately $41K.

COLLABORATIONS

NRC, Collaboration in developing an alternative protocol for JVS direct comparison 

NRC, Peer review of NRC dc voltage metrology to meet ISO 17025 technical requirements

NCSLI, Implementation of NIST compact JVS 

for ILC to improve uncertainty

CENAM, Bilateral JVS comparison using 

NIST CJVS for SIM.EM:BIPM-K11.b

CENAM, Peer review of CENAM’s dc voltage 

metrology to meet ISO 17025 technical requirements

INMETRO, Training its staff to prepare for 

INMETRO-BIPM JVS comparison

NPL-India, Host a guest researcher for training 

in JVS operation and volt dissemination 

STANDARDS COMMITTEE

PARTICIPATION

Yi-hua Tang, coordinator of the NCSLI JVS 

JVS Working Group

Yi-hua Tang, participant in NCSLI Intrinsic / 

Derived Standards Committee for revising the 

Recommended Practice of Intrinsic and Derived 

Standards (RISP) catalog. 

RECENT PUBLICATIONS

Y. Tang “An Overview of Josephson Voltage Standard Interlaboratory Comparison,” Proc. 2006 Natl. Conf. of Standards 

Laboratories Intl. Workshop and Symp. (NCSLI), Aug.6-10, 

2006, Nashville, TN (Aug. 2006). 

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B. Wood, Y. Tang and C. A. Hamilton, “Direct Josephson Array 

Voltage Comparison between NRC and NIST,” Digest of Conf. 

on Precision Electromagnetic Measurements (CPEM2006), July 

9- July 14, 2006, Torino, Italy, pp. 14-15 (July 2006).

Y.Tang , C. A. Hamilton, D. Deaver, H. Parks, and B. Wood, “ 

The Seventh Intercomparison of Josephson Voltage Standards in 

North America,” Digest of Conf. on Precision Electromagnetic 

Measurements (CPEM2006), July 9- July 14, 2006, Torino, 

Italy, pp. 188-189 (July 2006).

J. Sims and Y. Tang, “Implementation of Programmable Josephson Voltage Standard to NIST Voltage Dissemination System,” 

NCSLI MEASURE, Vol. 1, No. 2, 42-46, June 2006.

Y. Tang, C. Hamilton, H. Parks, D. Deaver and B. Wood, “Experimental Design of NCSLI 2005 Josephson Voltage Standard 

Interlaboratory Comparison,” NCSLI MEASURE, Vol. 1, No. 

1, pp. 36- 40, March 2006.

Y. Tang, “Applications of the Programmable Josephson Voltage 

Standard in Voltage Metrology,” Proc. VI SEMETRO, Sep. 

21-23, 2005, Rio de Geneiro, Brazil. 

J. Sims and Y. Tang, “Implementation of Programmable 

Josephson Voltage Standard to NIST Voltage Dissemination 

System,” Proc. 2005 Natl. Conf. of Standards Laboratories Intl. 

Workshop and Symp. (NCSLI), Aug.7-11, 2005, Washington 

D.C., (Aug. 2005). 

Y. Tang, C. Hamilton, H. Parks, D. Deaver and B. Wood, 

“Experimental Design of NCSLI 2005 Josephson Voltage 

Standard Interlaboratory Comparison,” Proc. 2005 Natl. Conf. 

of Standards Laboratories Intl. Workshop and Symp. (NCSLI), 

Aug.7-11, 2005, Washington D.C., (Aug. 2005). 

Y. Tang , S.L. Kupferman and M. T. Salazar, “Interlaboratory 

Comparison Using a Transport Josephson Voltage Standard 

System,” IEEE Trans. Instrum. Meas. Vol.54, pp. 398-403, 

February 2005.

T. J. Witt and Y. Tang, “Investigations of Noise in Measurements 

of Electronic Voltage Standards,” IEEE Trans. Instrum. Meas. 

Vol.54, pp 567-570, April 2005.
10 Electronics and Electrical Engineering Laboratory

AC-DC DIFFERENCE STANDARDS AND

MEASUREMENT TECHNIQUES

GOALS

To provide U.S. industry with the essential link 

between the dc and corresponding ac electrical 

standards, by maintaining and improving the U.S. 

national standards of ac-dc difference that are used 

to provide calibrations and measurement services 

for thermal converters and shunts.

CUSTOMER NEEDS

Increasingly accurate, easier-to-use instruments 

and devices for precision ac voltage and current measurements are being developed by U.S. 

electronic instrumentation and test equipment 

manufacturers for use in a wide variety of industrial 

and scientifi c applications throughout the world. 

These instruments are beginning to press the best 

available uncertainties, especially for calibration 

of ac waveforms at high currents and for ac voltages below 100 mV. The need continues for better 

calibration tools with which to verify accuracy 

claims, achieve consistency, and to help avoid 

international trade barriers based on technical diffi culties. Examples of specifi c customer requirements are cited below.

Instrument manufacturers have developed new 

methods for calibrating thermal transfer standards 

at voltages less than 100 mV. The new methods 

will result in uncertainties close to what NIST gives 

for routine calibrations, and is likely to require 

signifi cant reductions in the uncertainty of NIST 

calibrations at the very lowest voltage levels to 

support these instruments.

US military and industrial laboratories require 

highly accurate calibrations of thermal converters at frequencies greater than 1 MHz. Potential 

discontinuation of the RF-dc calibration service 

because of funding concerns would mean that NIST 

customers would no longer have ready access to 

required calibrations. 

The U. S. Army primary standards laboratory 

uses the same primary standards for ac current 

metrology as NIST. New standards are required 

to replace these aging, failing, devices. In addition, 

the U. S. Air Force primary standards laboratory is 

seeking improved thermal converters for measurements at frequencies up to 100 MHz.

The U.S. Air Force primary standards laboratory calibrates 100 A current amplifi ers for their 

secondary laboratories. Although these amplifi ers 

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are specifi ed to 100 kHz at 100 A, NIST presently 

supports only 100 A measurements to 10 kHz. The 

Air Force requires an expansion of the frequency 

range for high-current calibrations. The Air Force 

also requires improved devices for measuring ac 

voltages from 100 mV to 2 V with smaller uncertainties than existing devices.

NIST’s international obligations include 

assisting other National Metrology Institutes 

(NMIs) improve their metrology capabilities. For 

example, the National Institute of Standards in 

Egypt requires signifi cant improvements in their 

measurement service for ac-dc difference in order 

to be recognized in the international arena.

In 2008, the Quantum Electrical Metrology 

Division will host the 2008 Conference on Precision Electromagnetic Measurements. This is 

an extremely important and visible international 

conference on electrical metrology. Members of 

the staff will serve as guest editors for the IEEE 

Transactions on Instrumentation and Measurement 

special issue for CPEM 2008. This task is vital to 

the success of the conference.

Research and development are required to maintain and to expand NIST calibration and special 

test services for thermal converters and shunts, 

especially for calibrating high current shunts and 

high voltage converters. In addition, research and 

development of an intrinsic standard for ac voltage is required to successfully address the problem 

of maintaining extremely accurate calibrations at 

voltages below 100 mV.

TECHNICAL STRATEGY

To address manufacturer’s requirements for highly 

accurate calibrations of thermal transfer standards 

at voltage levels below 100 mV, NIST is developing 

the world’s fi rst intrinsic standard for ac voltage. 

This system, based on pulse-driven Josephson arrays, will allow us to calibrate thermal converters 

at voltages down to 2 mV with unprecedented 

accuracy. Linking with our existing multijunction 

thermal converter (MJTC) standards at 100 mV, 

the combination of ac JVS and MJTCs will provide 

standards for thermal converter calibrations from 2 

mV to 2 V without requiring the scaling techniques 

that increase the uncertainties at these low voltage 

levels. Combined with the inclusion of Fluke 792A 

calibrations at all voltage levels into the AC-DC 

Difference Project, this ac Josephson Voltage Stan-

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Technical Contact:

Thomas E. Lipe

Staff-Years (FY 2006):

3 professionals
Quantum Electrical Metrology Division 11

dard (ac JVS) will give us the ability to span the 

entire voltage range of 2 mV to 1000 V in a single 

calibration service, leading to signifi cantly reduced 

uncertainties and greater effi ciency (and therefore 

reduced turnaround time and lower costs) for our 

calibration customers.

To maintain the ability to support the US military 

and industrial calibration laboratories at frequencies greater than 1 MHz, we are transferring the 

RF-dc calibration service from NIST Division 818 

in Boulder, CO to the AC-DC Difference Project 

in Gaithersburg. In addition to maintaining the service, having both the low-frequency (up to 1 MHz) 

and high-frequency service in the same project will 

strengthen the link between the services at 1 MHz, 

resulting in lower uncertainties and costs, and better customer support. We will also undertake the 

documentation of the RF-dc service to bring it into 

compliance with the NIST ISO 17025 self-declaration. In addition, development work has begun on 

high-frequency MJTCs.

To address the requirement for maintaining the 

NIST calibration service for ac currents above 

500 mA, a collaboration between personnel in the 

NIST AC-DC Difference Project and the Quantum Devices Group fabrication facility at NIST 

Boulder is designing and fabricating new thermal 

converters based on thin-fi lm fabrication technology. Prototypes of these devices indicate that, in 

addition to being more effi cient and economical 

to produce than traditional wire thermal converters, these devices have signifi cantly improved 

performance with respect to the earlier designs. 

These thin-fi lm thermal converters will replace the 

legacy standards for ac current metrology at NIST, 

as well as provide required replacements for aging 

standards at the Army laboratory. To achieve current measurements up to 10 A, a multi-converter 

module is being fabricated.

To address the Air Force requirements for an expansion of the frequency range for 100 A current 

shunts, NIST is continuing to assess the stability of 

the 100 A shunts comprising the working standards 

for high current. An additional set of high-current 

shunts was recently acquired to aid in the scaling 

process from 10 A to 100 A, and a set of two-stage 

current transformers is being used to check the 

frequency fl atness of the shunts.

To support NIS, a collaboration has been formed 

between NIST scientists and National Institute of 

Standards, Egypt (NIS) personnel. An exchange 

of standards and personnel is required for this 

collaboration.

To support IEEE publication of metrology-related 

information, staff in the AC-DC Difference Project 

will serve as guest editors for the IEEE Transactions on Instrumentation and Measurement, in 

Torino, Italy, July 8-14, 2006.

PLANS

Bring the ac JVS online and integrate it into the acdc difference calibration service as a metrology tool.

Transfer the RF-dc difference calibration service 

from NIST Division 818 in Boulder, CO to the AC-DC 

Difference Project in Gaithersburg, MD. Produce plans 

for fabricating high-frequency thin-fi lm MJTCs.

Continue fabrication of thin-fi lm, high-current 

MJTCs and multiconverter modules for currents up to 

10 A.

Begin calibration service for ac current shunts at 

100 kHz up to 100 A.

Acquire approval for reduced ac current calibration 

uncertainties.

Begin documentation of RF-dc calibration service, 

in anticipation of uncertainty reductions

Exchange thermal transfer standards with NIS, and 

visit NIS in Cairo, Egypt.

Provide personnel for Associate Guest Editor for the 

CPEM 2006 Special Issue of the IEEE Transactions on 

Instrumentation and Measurement.

Begin an interlaboratory intercomparison of 

MJTC voltage converters, fabricated by NIST and 

Sandia National Laboratories, and including the DoD 

laboratories, Kennedy Space Center, and Sandia 

National Laboratories. NIST will be the pilot laboratory.

ACCOMPLISHMENTS

The ac JVS being used as a research tool in 

Boulder, CO, was duplicated, tested in Boulder, 

and delivered to NIST in Gaithersburg, MD for 

development into a metrology system. The system 

has been tested at voltages down to 2 mV, and at 

frequencies up to 1 MHz at 100 mV and 50 mV. 

Measurements on a thermal transfer standard using the ac JVS at 100 mV indicate that the ac JVS 

agrees with traditional measurement techniques 

to well within the uncertainty of the traditional 

measurements. In fact, these measurements are 

probably serving more as a check on the voltage 

scaling methods than a check on the ac JVS.

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12 Electronics and Electrical Engineering Laboratory

The RF-dc difference calibration service was 

successfully transferred from NIST in Boulder, 

CO to Gaithersburg, MD. The increased effi ciency 

of including this service in the AC-DC Project 

has already resulted in lower calibration prices. 

George Free, Thomas Lipe, and Joseph Kinard 

began documentation of this calibrations service 

with the CPEM 2006 paper “Characterization of 

RF-DC Transfer Difference for Thermal Voltage 

Converters with Built-in Tees in the Frequency 

Range 1 MHz to 1GHz.” In addition, we provided 

a calibrated TVC for development of a peak-topeak detector calibration service using the NIST 

Sampling Waveform Analyzer.

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Photograph of the ac JVS System.

Comparison of a thermal transfer standard measured 

using the ac JVS (in grounded and fl oating modes) 

and a calibration made by traditional methods. The 

uncertainty bars are the expanded uncertainties of the 

traditional calibration.

Comparison of traditional 100 MHz thermal converter 

(right) with a TVC with an integrated tee structure.

Thomas Lipe and Joseph Kinard were trained 

on the Denton sputtering machine in the NIST 

Nanofab facility. We will use this tool to deposit 

the thermocouple metals for high current MJTCs, 

before they are completed in the Quantum Devices 

facility in Boulder, Co. In addition, we are planning to host a guest scientist, Luciana Scarioni 

from Venezuela, to collaborate on fabricating additional MJTCs. She has extensive experience in 

MJTC fabrication, and is an expert in clean room 

operations.

To support the collaboration with NIS, we sent 

two sets of thermal transfer standards to Egypt for 

an intercomparison with NIS. Joseph Kinard then 

traveled to NIS to evaluate their methodology, 

and to present several technical talks on ac-dc 

difference. Considerable improvement in the NIS 

capability in the ac-dc difference area has resulted 

from this collaboration. The equipment purchases 

and travel was made possible by a grant from the 

State Department. Mamdouh Halawa from NIS 

will visit NIST in September to collaborate in 

modeling transmission line structures for MJTCs 

and the ac JVS.

We began evaluating candidates for the interlaboratory comparison (ILC) of MJTCs. Since 

these devices are among the most accurate thermal 

converters in the world, this ILC will enable the 

participants to check their calibration systems and 

methodologies to unprecedented accuracies. The 

participants (the U.S. military primary laboratories, 

Sandia National Laboratories, and Kennedy Space 

Center) were chosen because all possess MJTCs of 

the NIST/Sandia type. NIST will serve as the pilot 

laboratory for the ILC, and will contribute one of 

the traveling standards. The U.S. Air Force will 

contribute the other. This is very likely the fi rst 

ILC of MJTCs outside of NMIs.

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Quantum Electrical Metrology Division 13

Parameter space for ac-dc transfer measurements of 

thermal voltage converters, including the RF-dc calibration service, and expanded service at low voltage.

Thomas Lipe served (with Yi-hua Tang) as coAssociate guest editor for the CPEM 2006 Special 

Issue of the IEEE Transactions on Instrumentation 

and Measurement, in Torino, Italy, July 8-14, 2006. 

He will serve as co-Guest Editor of the CPEM 2008 

Special Issue (Boulder, CO).

Draft B of CCEM-K11 (international intercomparison of thermal transfer standards at 10 

mV and 100 mV) was made available in 2006. 

The results show that NIST is exceptionally close 

to the reference value at both voltage and at all 

frequencies.

The addition of the RF-dc calibration service 

and calibrations below 100 mV has signifi cantly 

expanded the parameter space for voltage calibrations. It is now among the largest parameter 

spaces in the world serviced by one calibration 

laboratory.

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COLLABORATIONS

Mamdouh Halawa (National Institute of Standards, Egypt), to improve the NIS ac-dc calibration 

capabilities, funded by the Joint U.S.-Egypt Science and Technology Board.

Michael Surdu (Science and Technology Center, Ukraine), to improve ac voltage and impedance 

metrology, particularly in Ukraine.

During 2006, Thomas Lipe served as NVLAP 

assessor to Southern California Edison, and acted 

as NVLAP technical reviewer for Fluke 5790A 

wideband calibration accreditation for John Fluke 

Manufacturing Company.

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CALIBRATIONS

As of August 20, the AC-DC Project had completed 

20 calibration jobs of 589 points, with revenues of 

about $78,000, with another $28,000 in process.

SELECTED PUBLICATIONS

George M. Free, Thomas E. Lipe, and Joseph R. Kinard, “Characterization of RF-DC Transfer Difference for Thermal Voltage 

Converters with Built-in Tees in the Frequency Range 1 MHz 

to 1GHz,” CPEM 2006 Conference Digest, Torino, Italy, July 

8-14, 2006, pp. 248-249.

Samuel P. Benz, Charles J. Burroughs, P. D. Dresselhaus, T. 

E. Lipe, and J. R. Kinard, “100 mV AC-DC Transfer Standard 

Measurements with a Pulse-Driven AC Josephson Voltage 

Standard,” CPEM 2006 Conference Digest, Torino, Italy, July 

8-14, 2006, pp. 678-679.

Thomas E. Lipe, Joseph R. Kinard, and June E. Sims, “Improvements in the NIST Calibration Service for Thermal 

Transfer Standards,” Proceedings of the 2006 NCSLI Workshop and Symposium, August 7-10, 2006, Nashville, TN, on 

CD-ROM.

Thomas E. Lipe, Joseph R. Kinard, Charles J. Burroughs, Paul 

D. Dresselhaus, and Samuel P. Benz, “Improvements in the 

NIST Calibration Service for Low-Voltage Thermal Transfer 

Standards,” Proceedings of the 2005 NCSLI Workshop and 

Symposium, August 7-11, 2006, Washington, DC, on CDROM.

Charles J, Burroughs, Paul D. Dresselhaus, Samuel P. Benz, 

Thomas E. Lipe, and Joseph R. Kinard, “100 mV AC-DC 

Transfer Standard Measurements Using an AC Josephson 

Voltage Standard,” Proceedings of the 2005 NCSLI Workshop 

and Symposium, August 7-11, 2006, Washington, DC, on 

CD-ROM.

Joseph R. Kinard, Thomas E. Lipe, and Svetlana Avramov-Zamurovic, “Determination of Frequency Coeffi cients for Thermal 

Voltage Converters and Digital Voltmeters by Comparison to 

Inductive Voltage Dividers,” CPEM 2004 Conference Digest, 

London, UK, June 26-30, 2004, pp. 463-464.

Hector Laiz, Thomas F. Wunsch, Joseph R. Kinard, Thomas 

E. Lipe, “1 A and 120 mA Thin-Film Multijunction Thermal 

Converters,” IEEE Trans. Instrum. Meas. Vol. IM-54, no. 2, 

pp. 803-806, April, 2005.

Hector Laiz, Thomas F. Wunsch, Joseph R. Kinard, Thomas 

E. Lipe, “1 A and 120 mA Thin-Film Multijunction Thermal 

Converters,” CPEM 2004 Conference Digest, London, UK, 

June 26-30, 2004, pp. 457-458.

Joseph R. Kinard, Thomas E. Lipe, and Svetlana Avramov-Zamurovic, “Determination of Frequency Coeffi cients for Thermal 

Voltage Converters and Digital Voltmeters by Comparison to 

Inductive Voltage Dividers,” Proceedings of the NCSLI Workshop and Symposium, Salt Lake City, UT, July 12-16, 2004. 

Hector Laiz, Thomas F. Wunsch, Joseph R. Kinard, Thomas E. 

Lipe, “1 A and 120 mA Thin-Film Multijunction Thermal Converters,” Proceeding of the NCSLI Workshop and Symposium, 

Salt Lake City, UT, July 12-16 2004.
14 Electronics and Electrical Engineering Laboratory

SINGLE ELECTRONICS FOR STANDARDS AND

METROLOGY

GOALS

To develop novel integrated circuits for standards 

and metrology based on the unique properties of 

electronic devices that can manipulate and detect 

individual electrons.

Portions of this project are located in both Boulder, 

Colorado, and Gaithersburg, Maryland.

CUSTOMER NEEDS

This project addresses three different needs: a 

fundamental representation of capacitance, a fundamental representation of electrical current, and 

general applications of single-electron tunneling 

(SET) devices, with a particular emphasis on future 

integrated nano-electronics.

For the fi rst need: NIST is working on the development of intrinsic standards based on fundamental 

physical principles, such as the volt, based on the 

Josephson effect, and the ohm, based on the quantum Hall effect. The present representation of the 

SI farad is through silica-based artifact capacitors. 

Although these capacitors are of high quality, they 

are susceptible to drift in time and they 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 that is based on 

fundamental physical principles and not on properties of individual physical artifacts.

For the second need: 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 signifi cant additional confi dence 

in the coherency of the representations of the SI 

electrical units through closure of the “metrology 

triangle” V = I R with all measurements based on 

fundamental constants.

For the third need: Various classes of future nanoelectronics beyond CMOS are projected to work 

with one or a few electrons. These include molecular electronics, semiconductor-based integrated 

circuits using single-electron memory or logic, and 

quantum computing (QC). For example, in QC, 

we are using our expertise to elucidate properties 

of transfer of superconducting “Cooper pairs,” 

which are the basic mechanism for one realization 

of QC circuits. As another example, one endemic 

problem in single-electron logic is the “charge 

offset” phenomenon, which makes it diffi cult or 

impossible to integrate multiple SET-based devices 

together; again, we are using our expertise to attack this problem. In all three cases, our project 

has the capability to offer early guidance to these 

burgeoning fi elds, to assist companies in pursuing 

productive areas, and rejecting problematic ones. 

Because these fi elds are not yet mature, our relatively small efforts can yield large payoffs for the 

customers as they progress.

TECHNICAL STRATEGY

Our basic strategy for this project is to develop 

important applications in our areas of world-leading expertise. These areas, which are all intimately 

related to the single-electron tunneling transistor 

and other SET devices, include:

Advanced fabrication of nanoscale metal devices (features as small as 20 nm) using our clean 

room facility in Boulder, CO.

Cryogenic measurement equipment, including 

custom fi ltering, and low-noise electronics.

Fundamentals of SET physics in metal-based 

devices and Si-based devices.

CAPACITANCE STANDARD

At present, the most mature application of SET 

devices within the project is using SET devices to 

develop an electron-counting capacitance standard 

(ECCS). By depositing a counted number, N, of 

electrons (of order 108

) onto the plate of a capacitor 

(of value approximately 1 pF) and measuring the 

resulting voltage (approximately 1 V), one can calibrate the capacitance, C, through the defi nition of 

capacitance, C = Q / V, with the charge determined 

by the number of electrons, Q = N e.

A prototype of the ECCS has been demonstrated 

with repeatability on the order of 1 part in 107 and 

a relative standard uncertainty of 1 part in 106. The 

major tasks remaining are to continue to reduce 

the uncertainty and to develop a robust system for 

possible widespread use.

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Technical Contact:

Mark Keller

Neil Zimmerman

Staff-Years (FY 2006):

3 NIST staff

2 post-docs

1 guest researcher
Quantum Electrical Metrology Division 15

CURRENT STANDARD

Using the expertise described earlier, we are pursuing three tracks toward a current standard based on 

counted electrons:

Superconducting Single Cooper Pair Tunneling (SCPT) devices combine the physics of 

single-electron devices and Josephson junctions. 

Our fi rst application of this new technology will 

be to develop a SCPT charge pump. Because superconducting tunneling is a coherent process, in 

principle the SCPT pump should be able to operate 

at signifi cantly higher frequencies, allowing larger 

currents to be produced with metrological accuracy. 

To build the SCPT pump will require signifi cant 

advances in the fundamental understanding of how 

these devices work. This work will also have direct 

impact on worldwide progress towards using these 

devices for quantum computing.

Si-based SET pumps, turnstiles, and CCD’s offer signifi cant promising avenues as well. Because 

the typical device capacitance is at least a factor of 

ten smaller than the non-superconducting pump, 

they offer a concomitant increase in speed and thus 

current value. Also, because they lack the charge 

offset problem, we can parallelize a large number 

of pumps to increase the current.

Passive counting using the rf-SET: Using rf 

techniques, we can perform electrometry up to 100 

MHz. This will allow us to attempt to monitor the 

charge passing through a single junction with an 

unprecedented combination of speed and precision. 

This technique offers the possibility of multiplexing 

a number of these charge sources to build a larger 

current source (100 pA to 1 nA).

One of the primary motivations for developing 

larger currents is our work to close the metrology 

triangle. This experiment can not be performed at 

the required accuracy with the currents presently 

available from single-electron pumps.

ULTRA-SENSITIVE CHARGE

ELECTROMETRY FOR MOLECULAR

ELECTRONICS/BIOLOGICAL

APPLICATIONS

SET devices also can be used as tools to measure 

the performance of other devices that operate with 

individual electrons.

We are pursuing the study of electrostatic charge 

reconfiguration of self-assembled monolayers 

(SAM) by fabricating and assembling a “nano-gap” 

capacitor. This device, made using Si microma-

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chining, allows us to make a capacitor with a gap 

of only 50 nm, but an area of (80 mm)2

; this area is 

large enough to give us a measurable signal, while 

the gap is small enough to measure charge motion 

over 1 nm or less.

PLANS

Combine a new generation of electron counting 

devices with various other improvements to allow the 

ECCS to reach an uncertainty of 1 part in 107

.

Use the improved ECCS to test for possible 

corrections to the basic formulae relating SET current 

and Josephson voltage to the fundamental constants e 

and h. 

Quantify and evaluate the differences in charge 

offset between metal-based and Si-based SET devices; 

suggest ways of improving the performance of the 

metal-based ones.

Produce a prototype device with parallel SET 

electron pumps.

Verify Cooper pair pump operation. This involves 

studies of individual elements, including eliminating 

quasiparticle poisoning, verifying the suppression of 

the Josephson coupling energy in a high impedance 

environment.

Produce prototype passive counting device with 

10 MHz bandwidth. Determine practical limits of 

passive counting bandwidth and suggest strategies for 

multiplexing for larger currents.

Pursue individual elements, including larger-current 

SET-based current source, resistor, null detector, and 

control/monitoring electronics.

Close metrology triangle to within 0.02 ppm via the 

current-through-a-resistor method.

Develop a robust repeatable nano-gap capacitor.

Verify or refute the belief in the molecular 

electronics fi eld that nonlinearities in the transport are 

due to charge motion in the molecules.

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16 Electronics and Electrical Engineering Laboratory

Atomic force microscope image of an electron counter, the heart of a new capacitance standard based 

on counting electrons. The standard, shown in the 

schematic, consists of the electron counter, a capacitor, and a single-electron electrometer to monitor the 

process (not shown). The electron counter, based on 

seven nanometer-scale tunnel junctions in series, can 

“pump” electrons onto the capacitor with an error 

rate of less than 1 electron in 108.

ACCOMPLISHMENTS

Electron Counting Capacitance Standard 

Demonstrated – At present, the most advanced 

application for SET devices within the project is a 

new capacitance standard based on the fundamental 

defi nition of capacitance. A prototype of an Electron Counting Capacitance Standard (ECCS) has 

been demonstrated, with a repeatability of 1 part 

in 107 and a relative standard uncertainty of 1 part 

in106. This brings to fruition a decade of research 

aimed at creating this standard and shows the way 

toward even better performance in the future. The 

components of the standard are an electron counter, 

a capacitor, and an electrometer to monitor the process, as illustrated in the fi gure below. The electron 

counter, shown in the Atomic Force Microscope 

image below, is based on seven nanometer-scale 

tunnel junctions in series. It can “pump” electrons 

onto the capacitor with an error rate of less than one 

electron in 108

. The electron pumping is monitored 

with an SET-based electrometer fabricated on the 

same chip as the pump, with a charge sensitivity 

better than 10-2 electrons. The capacitor operates 

at cryogenic temperatures and uses vacuum as the 

dielectric, resulting in a frequency-independent 

capacitance. To operate the ECCS approximately 

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100 million electrons are placed, one at a time, 

on the capacitor. The voltage across the capacitor 

is then measured, resulting in a calibration of the 

cryogenic capacitor. This capacitance can then be 

transferred to room temperature using a standard ac 

bridge measurement technique. The fi gure below 

shows the result of pumping electrons on and off 

the capacitor, with a 20 second pause when fully 

charged to measure the voltage. The result is a 

value of capacitance in terms of the charge of the 

electron.

Demonstration of pumping electrons on and off a 

prototype capacitance standard.

Quasiparticle Poisoning in Cooper Pair 

Transistors Elucidated – In collaboration with 

Professor Michel Devoret (Yale), we have performed a number of experiments which verifi ed 

a model for erratic quasiparticle tunneling in superconducting Cooper pair transistors (these are 

the superconducting versions of the SET). This 

phenomena, quasiparticle “poisoning,” will limit 

the operation of the superconducting Cooper pair 

pump as well as charge-based qubits. Our work 

showed that the gap energies in the leads versus 

the island played a signifi cant role in determining 

these poisoning rates.

In addition, we have confi rmed a “remote poisoning” phenomena, whereby a voltage-biased junction device can cause poisoning in other devices on 

the same chip, even if it is electrically isolated. This 

has important implications for the electrometry that 

we will use in the Cooper pair pump, as well as in 

charge-based qubits.

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Quantum Electrical Metrology Division 17

Switching current histograms (z-axis) vs. gate polarization charge on a superconducting Cooper pair 

transistor. The double peaks for fi xed gate polarization 

indicate that quasiparticles are poisoning the transistor island.

rf-SET demonstrated – In collaboration with 

Konrad Lehnert at JILA, we have assembled and 

demonstrated operation of a rf-SET at NIST, a version of an SET electrometer read out by microwave 

refl ectometry. This approach greatly increases the 

bandwidth of the electrometer (to 3 MHz in our 

present setup) and improves the charge resolution 

(to 50 me/Hz1/2). This is the basic technology we 

will use to perform the passive electron counting 

experiments. Future work will focus on expanding 

the bandwidth and narrowing the charge resolution 

to perform better than the quantum limit.

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Using techniques similar to the rf-SET measurement, 

we have measured the modulation of the Josephson 

inductance of a Cooper pair transistor while biased 

on the supercurrent branch. In this example, when a 

quasiparticle enters the transistor island, the Josephson inductance shifts causing a change in refl ected 

power. In this plot, when a quasiparticle has entered 

the island (the “odd state”), the refl ected power 

increases. With this technique we can observe these 

quasiparticle tunneling events in the time domain as a 

telegraph signal.

Real-Time Observation of Quasiparticle 

Poisoning Using a Novel rf Measurement Mode

– Conventional operation of the rf-SET involves 

biasing the device on the quasiparticle branch 

of the current-voltage characteristic. This quasiparticle current creates quasiparticles in remote 

devices (which may be charge qubits or Cooper 

pair pumps), that may prevent successful operation. 

Recently, we have successfully demonstrated that 

it is possible to measure the Josephson inductance 

of a Cooper pair transistor while it is biased on the 

supercurrent branch. Using the same techniques as 

in the rf-SET, we have measured the quasiparticle 

poisoning in a single Cooper pair transistor in the 

time domain. Since this technique operates on the 

supercurrent branch we expect minimal generation 

of quasiparticles. 

SET Electronics Developed to Probe GaAs 

Quantum Dots for Single Photon Source – The 

past two years have produced signifi cant progress 

towards the development of a single-photon turnstile, a device designed to generate single photons 

on demand using semiconductor quantum dots 

(QD) and single-electron principles. A key step 

towards this goal is to measure the tunneling of 

single electrons onto individual quantum dots. 

We have succeeded in making these measurements by integrating an SET electrometer over a 

low density fi eld of GaAs quantum dots (grown 

by Rich Mirin of the Optoelectronics Division). 

A schematic cross-section of the device is shown 

below, along with a scanning electron micrograph 

of the SET electrometer. Such nanoscale device 

integration is diffi cult and required extensive process development. Using these devices, we have 

clearly identifi ed the addition of single electrons 

onto single quantum dots located below the SET. 

We have counted up to 3 electrons added to a single 

dot, and have measured the energy spectrum associated with adding electrons on this dot. This work 

has led to a recent publication showing how adding 

a gate electrode to the QD structure can improve 

its performance as a source of single photons for 

quantum cryptography.

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18 Electronics and Electrical Engineering Laboratory

a) Schematic cross-section of our SET electrometer 

integrated on a GaAs chip containing self-assembled 

quantum dots. b) SEM micrograph of an SET electrometer. We have identifi ed single electron tunneling 

events into individual quantum dots located beneath 

the electrometer.

Si-based Pumps, Turnstiles, CCDs Demonstrated – Our work in collaboration with a group 

in NTT (Nippon Telephone and Telegraph), Japan, 

has made a great deal of progress in investigating 

Si-based devices that can control the motion of 

single electrons. In the past two years, we have 

demonstrated such control in three different types 

of devices, pumps, turnstiles, and CCDs. The most 

promising device for the future is the CCD, both 

because we have recently demonstrated in subsequent work that such devices can be made with 

improved reliability and homogeneity, and because 

we demonstrated that this device has the potential 

to run at higher speed. In one of our publications, 

we showed that the CCD can pump single electrons 

at rates as fast as 100 MHz, corresponding to 15 

pA; this is an improvement by about a factor of 

fi ve over previous results in metal-based pumps. 

However, we have to note that we were not able to 

do detailed error rate measurements in the CCDs; 

this work is now occurring.

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The pumping current in a CCD versus control voltage. 

The plateaus correspond to pumping 1e, 2e, ..., per 

cycle; note that the plateaus are at the same level for 

frequencies between 5 and 100 MHz.

We have also recently fi nished our fi rst theoretical 

analysis of error mechanisms and error rates in 

Si-based turnstiles and CCDs. From a fundamental 

point of view, the most interesting result was the 

elucidation of a new mechanism, the “dynamical 

error.” This error can results from the inability of 

the quantum dot to form the Coulomb blockade 

quickly enough; research into this mechanism 

should advance fundamental understanding of 

Coulomb blockade. By considering in addition 

thermal, frequency, and heating errors, we predicted that with devices accessible at present we 

should be able to achieve 0.01 ppm error rates at 

frequencies up to 200 MHz. Of course, we need to 

perform the experimental work to verify or refute 

these predictions.

More recently, we have done a detailed study of the 

SET transistor behavior of several different devices 

made using the CCD architecture. In addition to 

an interesting array of fundamental properties, we 

found that in three different devices the parameters 

(specifi cally, a variety of cross capacitances) vary 

by no more than 15 percent between the devices. In 

previous fabrications using the pattern-dependent 

oxidation process, the homogeneity was no better than 50 percent, and sometimes much worse. 

This substantial improvement in homogeneity 

makes it much more likely that we should be able 

to integrate devices for general applications, and 

specifi cally to parallelize a number of CCDs to get 

a higher value of current.

COLLABORATIONS

NIST/JILA, passive electron counting for 

current standard

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Quantum Electrical Metrology Division 19

NIST Semiconductor Electronics Division, 

Si-based SET devices

NIST Optoelectronics Division, single-photon 

competence project

Nippon Telegraph and Telephone, Si-based 

SET devices

Center for Integrated Nanotechnologies, Sandia National Laboratory, single-photon devices

SELECTED PUBLICATIONS

O. Naaman and J. Aumentado, “Time-domain measurements of 

quasiparticle tunneling rates in a single-Cooper-pair transistor,” 

Phys. Rev. B 73, 172504 (2006).

O. Naaman and J. Aumentado, “Poisson Transition Rates from 

Time-Domain Measurements with a Finite Bandwidth,” Phys. 

Rev. Lett. 96, 100201 (2006).

K. D. Osborn and M. W. Keller, “Single-photon pump,” to appear in Appl. Phys. Lett. (2006).

Akira Fujiwara, Neil M. Zimmerman, Yukinori Ono, Yasuo 

Takahashi, “Current quantization due to single-electron transfer in Si-wire charge-coupled devices,” Appl. Phys. Lett. 84, 

1323 (2004).

Neil M. Zimmerman, Emmanouel Hourdakis, Yukinori Ono, 

Akira Fujiwara, Yasuo Takahashi, “Error Mechanisms and Rates 

in Tunable-Barrier Single-Electron Turnstiles and CCD’s,” J. 

Appl. Phys. 96, 5254 (2004).

K. D. Osborn, M. W. Keller, and R. P. Mirin, “Single-electron 

transistor spectroscopy of InGaAs self-assembled quantum 

dots,” Physica E 21, 501-505 (2004).

J. Aumentado, M. W. Keller, J. M. Martinis, and M. H. Devoret, 

“Nonequilibrium Quasiparticles and 2e Periodicity in SingleCooper-Pair Transistors,” Phys. Rev. Lett. 92, 066802 (2004).

Yukinori Ono, Neil M. Zimmerman, Kenji Yamazaki and Yasuo 

Takahashi, “Turnstile Operation Using a Silicon Dual-Gate 

Single-Electron Transistor,” Jpn. J. Appl. Phys 42, L1109 - 11 

(2003).

X. Jehl, M. W. Keller, R. L. Kautz, J. Aumentado, and J. M. 

Martinis, “Counting Errors in a Voltage-Biased Electron Pump,” 

Phys. Rev. B 67, 165331 (2003).

Neil M. Zimmerman, Mahmoud A. El Sabbagh, and Yicheng 

Wang, “Larger Value and SI Measurement of the Improved 

Cryogenic Capacitor for the Electron-Counting Capacitance 

Standard.” IEEE Transactions on Instrumentation and Measurement 52, 608 - 11 (2003).

M. W. Keller, “Standards of current and capacitance based on 

single-electron tunneling devices,” Recent Advances in Metrology and Fundamental Constants - FERMI School CXLVI, 

Varenna, Italy, ed. T.J. Quinn, S. Leschiutta, and P. Tavella, IOS 

Press, Amsterdam, pp. 291-316, (2001).

M. W. Keller, A. L. Eichenberger, J. M. Martinis, N. M. Zimmerman, “A capacitance standard based on counting electrons,” 

Science, 285, 1706 (1999).

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20 Electronics and Electrical Engineering Laboratory

METROLOGY OF THE OHM

GOALS

To maintain the U.S. legal ohm and to provide for 

the dissemination of an internationally consistent, 

accurate, reproducible, scalable, and traceable resistance standard that is readily and continuously 

available for the U.S. scientifi c, industrial base, and 

government laboratories.

CUSTOMER NEEDS

The U.S. electronics instrumentation industry, 

along with military and aerospace industries, 

maintains a position of world leadership through 

the development and deployment of increasingly 

sophisticated multi-function, high-precision and 

low-maintenance instruments. To meet the present challenging needs, and in anticipation of the 

increasingly strict demands of advanced scientifi c 

processes, this project develops instruments and 

standards that enable the dissemination of over 20 

decades of resistance values. Resistance standards 

provide references for electrical measurements at 

very high and low current levels and are used to 

support a wide variety of impedance, temperature, 

strain, and power measurements, over a wide 

range of frequency, at very high levels of accuracy. Through this very broad customer base, the 

activities of this project support innovation and 

enable U.S. industry to demonstrate and verify 

in a cost-effective way the accuracy of electrical 

measurements and the performance of high-precision instrumentation in a competitive world 

environment.

Precision shunt resistors provide high-current capability for power and industrial applications.

TECHNICAL STRATEGY

Highly directed research and involvement with our 

customers demonstrates our interest in performing 

at levels that exceed expectations. These customers 

value NIST calibrations because of our reputation 

as a “science foremost” and “customers fi rst” institution, and the Division 817 technical strategy 

refl ects these values. 

As part of a National Measurement Institute (NMI), 

we pursue scientifi c breakthroughs in quantum metrology to maintain an accurate local representation 

of the unit of resistance. We pursue collaboration 

with other NMIs, and participate in international 

metrology comparisons to ensure consistency of 

electrical measurements. 

In FY 2006 we initiated and piloted a regional 

comparison of dc resistance between laboratories of 

SIM nations. NIST developed methods to analyze 

data and link the SIM results to CCEM Key Comparison results through NIST and NRC (Canada). 

The comparison package traveled fi rst to South 

America and will complete another three circuits 

of laboratories, each time returning to NIST for the 

pilot lab measurements, before the comparison is 

completed in February 2007.

We are conducting tests on two new Cryogenic 

Current Comparator (CCC) systems for resistance 

scaling. A four-decade CCC developed for and in 

collaboration with Sandia National Labs will allow Sandia to provide ratios accurate to 1 part in a 

hundred million in support of automated resistance 

bridges and to maintain their very low uncertainty 

levels. Sandia engineers developed and produced 

multi-layer circuit boards for this system, which 

helped lower the development cost for this and 

future CCC systems built by NIST. A second, new 

design of high-resistance (HR) CCC bridge has 

been tested at 1 megohm, and electronics is being 

developed for scaling from the QHR standard to 10 

megohm and other high resistance levels.

Non-commercial CCC systems have replaced 

room-temperature current comparators in many 

NMIs because they allow much lower uncertainty 

in resistance scaling. Commercialization of CCC 

systems has ceased for the time being after the 

fi rst few such systems failed to operate successfully over the long term at NMIs. We are working 

to initiate a collaboration to construct a number 

of NIST-design HR CCCs, which could be used 

at NMIs as well as U.S. DoD primary calibration 

facilities.

Technical Contact:

Randolph Elmquist

Staff-Years (FY 2006):

3 professionals

1 technician
Quantum Electrical Metrology Division 21

PLANS

Prepare and pilot the fi rst Regional Metrology 

Organization (RMO) Key Comparison of dc resistance 

within SIM, at resistance ranges of 1 ohm, 1 megohm, 

and 1 gigaohm. SIM constitutes the RMO for major 

NMIs in the Western Hemisphere

Using new capabilities to monitor and measure 

characteristics of large numbers of precision 1 ohm 

resistance standards, determine how the different 

construction methods and materials contribute to more 

stable, predictable behavior under many different 

conditions and stresses encountered in the laboratory 

and in transport. 

 In order to accommodate customer requests to 

calibrate higher resistance values, Construct new 

standards, upgrade detection systems, and complete 

automated fully-guarded switching systems to enable 

100 teraohm measurements with 0.05% or better 

uncertainty. 

Initiate collaborations with several NMIs to develop 

CCC systems to compare high value standard resistors 

directly against the QHR standard with lower noise, 

better uncertainty, and at a wider range of resistance 

levels. These methods will test our theoretical models 

of cryogenic current comparators, and help reach the 

Johnson noise level of 1 megohm and 10 megohm 

room-temperature resistors. 

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Visit by M. Kraft and R. Elmquist to Navy NAVAIR 

facility, which this year has installed a new QHR 

standard.

ACCOMPLISHMENTS

At this year’s NCSL conference we presented 

three papers on: 1) the major role of NIST in international comparisons, 2) how to make precise and 

repeatable tests using high-current shunts, and 3) 

the effects of changes in temperature and pressure 

on precision one ohm resistance standards. Staff 

members also visited the Army Metrology lab at 

Redstone Arsenal and the Navy NAVAIR Calibration lab in San Diego to observe and offer help on 

metrology problems. These activities not only serve 

our customers but also help them to make informed 

decisions about how to use NIST calibration services and to improve their programs.

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The Electronic Kilogram Experiment laboratory required more frequent 100 ohm CCC transfers 

in order to support fi nal results for CPEM-2006. 

These measurements allowed the EKE lab to 

maintain two 100 ohm standards on-site with 5 

parts in 109

 uncertainty, in order to cross-check 

the standards after transfers. These represent the 

lowest uncertainty dissemination of resistances 

presently available.

With other researchers in Division 812 and 

817, we are updating and expanding our calibration service check-standard database and testing 

this resource in the Ohm and Power & Energy 

projects. Development will provide more search 

features, better security, and more control of data 

by researchers.

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Two automated 1 ohm measurement systems allow 

precise customer tests and characterization studies.

Fifteen Thomas 1 ohm resistors and fi ve newer 

1 ohm resistors of similar quality were characterized using controlled, variable temperature and 

pressure chambers. These standards are calibrated 

by NIST as references for low resistance DCC and 

CCC bridges, and for international comparisons. 

Two oral papers on this study have been presented: 

CPEM’06, “Recent Investigations into the Temperature and Pressure Characteristics of Precision 

1 Ohm Resistors at the National Institute of Standards and Technology,” and NCSLI’06, “Temperature and Pressure Coeffi cients of Thomas 1 Ohm 

Resistors.” George Jones received the “Best Paper 

Award” at NCSLI’06 for this contribution. 

CALIBRATIONS

Over 250 calibrations were performed with approximately $325,000 division income received 

(October 1, 2005 to September 30, 2006).

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22 Electronics and Electrical Engineering Laboratory

2006 SIM resistance comparison standards and transport package.

COLLABORATIONS

Argentina, Brazil, Canada, Mexico, Uruguay, 

and the U. S. are participating in the SIM resistance 

regional comparison.

A project to build, test, and install a 10-to-1 

ratio CCC for DoE’s Sandia Primary Standards 

laboratory is near completion.

Studies of 1 ohm precision resistors have been 

broadened to include Evanohm standards constructed by B. Pritchard of NMI Australia. Pritchard 

will be a guest Researcher at NIST beginning in 

February, 2007.

A program to construct HR CCC systems 

is being arranged with INTI (Argentina), NMI 

(Australia). Several other NMIs have been invited 

to participate.

SELECTED PUBLICATIONS

G. R. Jones, R. E. Elmquist, “Recent Investigations Into the 

Temperature and Pressure Characteristics of Precision 1 Ohm 

Resistors at the National Institute of Standards and Technology,” 

IEEE Trans. Instrum. Meas. (to be published).

G. R. Jones, R. E. Elmquist, “Temperature and Pressure Coeffi cients of Thomas 1 Ohm Resistors,” NCSLI Workshop & 

Symposium, NCSL International Workshop and Symposium, 

Aug 06-10, 2006, Nashville, Tennessee (to be published in 

Measures).

M. E. Kraft, “Measurement Techniques of Low Value High 

Current Single Range Current Shunts 15 Amps to 3000 Amps,” 

Conference Proceedings of NCSL International Workshop and 

Symposium, NCSL International Workshop and Symposium, 

Aug 06-10, 2006, Nashville, Tennessee (to be published in 

Measures).

R. E. Elmquist, E. Hourdakis, D. G. Jarrett, and Neil M. Zimmerman, “Direct Resistance Comparisons from the QHR to 

100 Megohm Using a Cryogenic Current Comparator,” to be 

published in IEEE Trans. Instrum. Meas. (Special Issue on 

Selected Papers CPEM 2004).

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D. G. Jarrett, R. E. Elmquist, “Settling Times of High-Value 

Standard Resistors,” to be published in IEEE Trans. Instrum. 

Meas. (Special Issue on Selected Papers CPEM 2004).

Randolph E. Elmquist, Dean G. Jarrett, George R. Jones, Jr., 

Marlin E. Kraft, Scott H. Shields, and Ronald F. Dziuba, “NIST 

Measurement Service for DC Standard Resistors,” Natl. Inst. 

Stand. Technol. Tech. Note 1458 (Dec. 2003).

D. G. Jarrett and R. F. Dziuba, “CCEM-K2 Key Comparison of 

10 MΩ and 1 GΩ Resistance Standards,” IEEE Trans. Instrum. 

Meas. 52, No. 2, pp. 474-477 (Apr 2003).

R. E. Elmquist, N. M. Zimmerman, and W. H. Huber, “Using 

a High-value Resistor in Triangle Comparisons of Electrical 

Standards,” IEEE Trans. Instrum. Meas. 52, No. 2, pp. 590-

593 (Apr 2003).

N. F. Zhang, N. Sedransk, and D. G. Jarrett, “Statistical Uncertainty Analysis of CCEM-K2 Comparison of Resistance 

Standards,” IEEE Trans. Instrum. Meas. 52, No. 2, pp. 491-494 

(Apr 2003).

R. F. Dziuba and D. G. Jarrett, “CCEM-K2 Key Comparison of 

Resistance Standards at 10 MΩ and 1 GΩ,” Appendix B of Mutual Recognition Arrangement Bureau International des Poids 

et Mesures (BIPM) Report, also in Appendix B of the Bureau 

International des Poids et Mesures (BIPM) Key Comparison 

and Calibration Database http://www.bipm.org/pdf/fi nal_reports/EM/K2/CCEMK2.pdf (also link from Metrologia, 2002, 

39, Tech. Suppl., 01001).

D. G. Jarrett, “Analysis of a Dual-Balance High-Resistance 

Bridge at 10 TΩ,” IEEE Trans. Instrum. Meas. Special Issue 

on Selected Papers CPEM 2000, 50, No. 2, pp. 249-254 (Apr 

2001).
Quantum Electrical Metrology Division 23

FARAD AND IMPEDANCE METROLOGY

GOALS

To provide the world’s best basis for accurate impedance measurements. To achieve this by maintaining the Farad and tying the U.S. legal Farad 

to the international system of units, supporting 

and improving NIST’s impedance measurement 

services, and ensuring the critically needed access 

of the U.S. industrial base to internationally consistent, reliable, reproducible, and traceable electrical 

measurements. 

Technical Contacts:

Yicheng Wang

Staff-Years (FY 2006):

2.6 Professionals

1.5 Technicians

0.8 Contractor

“...the research you 

are doing related to the 

frequency response 

of the fused-silica 

standards, some of 

which you shared with 

us, has also raised 

eyebrows and left 

positive impacts both 

here and with others I 

just met at the NCSLI...”

Steve Kaplan, Vice President, 

Andeen-Hagerling, Inc. Yicheng Wang sets up an automated system for 

determining the frequency dependence of fused-silica 

capacitors.

CUSTOMER NEEDS

This project ties the U.S. legal system of electrical units to the International System of Units 

(SI) through the realization of the SI unit of capacitance. This work also forms the foundation 

of NIST’s measurement services for electrical 

impedance, 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. The need 

continues for better representation of capacitance 

and also for better test and calibration tools at NIST 

with which to objectively verify claims of improved 

performance specifi cations, to achieve consistency, 

and to help avoid technical trade barriers. 

TECHNICAL STRATEGY

The primary facility for connecting the U.S. legal 

system of electrical units to the international system 

of units is the NIST calculable capacitor, in 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, 

improved, and compared with other national 

metrology laboratories to ensure measurement 

consistency on an international level.

Over the last few decades, NIST has successfully 

invested in two key quantum representations of 

electrical quantities: both the Quantum Hall Resistance (QHR) and Josephson Voltage standards 

have now achieved measurement uncertainties 

approaching parts in 109

. These quantum standards, however, represent only a few points in a 

multi-dimensional world of electrical measurements. The crucial link between the fundamental 

electrical standards and commercial electronic 

instrumentation is provided by precision AC measurement standards. The current NIST expertise of 

AC measurements centers on transformer-based 

analog bridges and circuits and is largely limited 

to a single frequency at 1592 Hz, which has been 

achieved through a long, focused effort to realize 

the SI electrical units of the farad and the ohm. 

A combination of well-established transformer 

techniques and the AC signal generation and detection based on modern Digital Signal Processing 

(DSP) techniques has the potential to extend our 

expertise to provide best-in-the-world measurement capability over the frequency range from 

DC to 100 kHz.

AC measurements linking the calculable capacitor 

to the set of standards that comprise the National 

Farad Bank have been performed only at 1592 Hz 

and 1000 Hz. However, customer standards are 

often calibrated at other frequencies; as a result, the 

uncertainty provided for customer calibrations was 

signifi cantly increased to account for differences in 

the capacitance unit due to frequency dependence. 

In order to better support customers’ needs in the 

broader frequency range from 50 Hz to 20,000 Hz, 

the frequency dependence and dissipation factor of 

the Farad Bank need to be determined. 

Consistency between resistance and impedance 

measurement services from NIST is expected by 

the instrumentation industry and DoD laboratories. 

An improved RC link is also needed to realize 

the farad from the QHR standard, if the proposed 

redefi nition of the SI occurs in the near future, 

and to advance basic research such as closing the 

quantum metrology triangle. The current strategy 
24 Electronics and Electrical Engineering Laboratory

for closing the metrology triangle via an electron 

counting capacitance standard requires an accurate link between the Farad Bank and the QHR 

standard. 

Development of wideband impedance measurement services requires reference standards that can 

be characterized over the impedance and frequency 

ranges of interest. NIST has developed a system to 

characterize commercial four-terminal-pair (4TP) 

capacitance standards from 1 pF to 1 nF over the 

frequency range from 1 kHz to 10 MHz. This 

system is being used to offer special tests for 4TP 

capacitors as well as provide reference standards 

for general impedance measurements using a commercial LCR meter. A bootstrapping technique using the LCR meter and an inductive voltage divider 

(IVD) can be used to extend the characterization 

from the 1 nF standard to higher-valued capacitance 

standards up to 10 μF. 

PLANS

Complete development and characterization 

of reference standards for, and optimize scaling 

capabilities for dissemination of, dissipation factor 

measurements of capacitors from 50 Hz to 20 kHz.

Complete SIM capacitance comparison report within 

6 months of receipt of all participant data.

Develop a DSP-based ac waveform generator and 

synchronous detector for applications of precision ac 

measurements, including ac bridges.

Demonstrate the applications of DSP techniques to 

fully automate an existing single frequency, 2-terminalpair capacitance bridge in the audio frequency range.

Modernize a quad bridge to link a 1 nF capacitor 

with a 100 kΩ resistor at 1592 Hz to improve the 

RC link between the dc QHR and the Farad Bank 

and provide a foundation for future ac resistance 

measurement services.

Implement dissipation factor measurement services 

for fused-silica capacitors in the audio frequency range. 

Perform regular Farad Bank measurements and 

calibrations of the Farad Bank against the calculable 

capacitor.

Perform calibration and special test workload as 

well as international inter-comparisons as required. 

Perform regular calibration and check standard 

measurements necessary for the maintenance of the 

present measurement systems and standards.

ACCOMPLISHMENTS

Major advances have been achieved in determination of frequency dependence of capacitors. 

Frequency dependences of capacitance standards 

have to be determined in order to provide traceabili-

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ty of capacitance calibrations at various frequencies 

demanded by customers and to enable consistency 

check among the three fundamental electrical units: 

the volt, the ohm, and the ampere, by closing the 

Quantum Metrology Triangle (QMT). Using a 

combination of a 1 pF “cross capacitor” having a 

negligible frequency dependence due to surface 

fi lms and a 10 pF nitrogen dielectric capacitor with 

a very small residual inductance as references, we 

have measured the frequency dependence of 10 pF 

and 100 pF reference fused-silica capacitors from 

50 Hz to 20 kHz. This achievement has allowed 

us to greatly improve and expand the capacitance 

calibration services at NIST. It has also enabled 

EEEL researchers to set an upper bound on the 

frequency dependence of a cryogenic vacuumgap capacitor which is a key component of the 

QMT experiment and then to close the QMT with 

uncertainty of 1 ppm. 

We have established references for dissipation 

factor measurements of 10 pF fused-silica capacitance standards from 50 Hz to 20 kHz, using a 

toroidal cross capacitor and a 10 pF nitrogen-fi lled 

capacitor as the references. Precise dissipation 

factor measurements for capacitance standards are 

needed for characterization of dielectric materials, 

traceability of energy and power measurements, 

and characterization of precision attenuators (e.g., 

the input stage of the Agilent 3458A). As commercial instruments become ever more sophisticated, 

leading manufacturers in the U. S. are demanding 

better calibration support from NIST. 

Developed and characterized a programmable 

capacitance standard to provide accurately-known 

capacitance values over fi ve orders of magnitude 

from 100 pF to 10 μF with a resolution of 1 pF. 

The potential applications of a well-characterized 

programmable capacitance standard are numerous. 

NIST measurement support for high-accuracy 

capacitance calibrations has traditionally been 

limited to decade values from 1 pF to 1000 pF. 

The programmable reference capacitor will be 

used to test the linearity of commercial precision 

capacitance bridges to support the calibration of 

non-cardinal and high-valued capacitance standards. Used in conjunction with a programmable 

resistance standard, presently under construction, 

the programmable capacitor will be used to synthesize arbitrary impedances to support generalized 

impedance calibrations. The development of this 

standard was presented at the 2006 Conference on 

Precision Electromagnetic Measurements. A plot 

showing the stability and temperature controller 

effectiveness of the programmable capacitance 

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Quantum Electrical Metrology Division 25

standard over a two-day period is given in the 

fi gure below. The two large spikes in the fi gure 

correspond to times where the temperature controller was turned off and the fl at segments of the 

curve correspond to times where the controller was 

turned back on.

Stability data of the programmable capacitor at 0.1 uF 

and 1 kHz.

Established a special test for four-terminalpair capacitance standards of values from 10 nF 

to 100 μF at frequencies from 100 Hz to 100 kHz. 

New commercial capacitance bridges and impedance meters are becoming more and more accurate. This capability was established to satisfy the 

need for U.S. industry to calibrate more accurate 

impedance meters. An uncertainty analysis has 

been achieved up to 100 nF. A poster presentation on aspects of this work was given at the 2006 

Conference on Precision Electromagnetic Measurements. A complete description of the system 

has been drafted and will soon be published as a 

NIST TechNote.

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Andrew Koffman performs a special test for a fourterminal-pair capacitance standard.

Completed the key international comparison 

for inductive voltage dividers (CCEM-K7). The 

existing NIST IVD calibration system was used 

along with the new straddling bridge to determine 

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the in-phase and quadrature errors of the precision 

IVD used for a CCEM-sponsored international 

comparison. Results indicate that agreement between the two systems is better than 3 parts in 

108

 for in-phase error components and better than 

5 parts in 108 for quadrature error components. 

The results of the worldwide comparison have 

been disseminated. NIST measurements agreed 

well with the reference values to within the NIST 

uncertainties. NIST was one of only four labs out 

of the 17 participants whose results agreed with 

the reference values to within stated uncertainties 

at all 44 measurement points.

Served as pilot laboratory for SIM capacitance 

key comparison SIM-EM.K4 and supplemental 

comparisons SIM-EM.S4 and SIM-EM.S3, and 

completed protocol documentation and all measurements. The CCEM K4 key comparison for 

capacitance standards was completed in 2000 with 

NIST serving as the pilot laboratory. As the only 

country with a working calculable capacitor in 

the Americas, NIST has the obligation to provide 

the link between SIM and CCEM for capacitance 

measurements. In partial fulfi llment of this obligation, NIST is serving as the pilot lab for an 

international comparison of capacitance measurements between many of the National Metrology 

Labs in North, Central, and South America. All 

measurements have been completed and the traveling standards have been returned to NIST. The 

fi nal pilot measurements have been completed. 

When all participating laboratories have submitted 

measurement results, data evaluation and report 

generation will follow.

Documentation of the improved capacitance 

calibration services is drafted and the MCOM 

review process will begin before FY06 yearend. 

NIST low frequency three-terminal fused-silica 

and nitrogen dielectric standard capacitor calibration services have been improved and expanded in 

frequency from the previous 100 Hz, 400 Hz, and 

1000 Hz to 20 frequencies from 50 Hz to 20 kHz 

using a commercial automatic capacitance bridge 

as a transfer standard.

CALIBRATIONS

224 tests were performed on 94 artifacts for 54 

customers for impedance standards and inductive 

voltage dividers, providing income to the Division 

of approximately $175,000 (October 1, 2005 to 

August 31, 2006)

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26 Electronics and Electrical Engineering Laboratory

COLLABORATIONS

Yicheng Wang collaborated with Michael 

Moldover of CSTL in an SBIR Phase II project to 

develop an atomic standard of pressure based on 

capacitance metrology.

Andrew Koffman and Bryan Waltrip collaborated with the Measurement Standards Center at 

Agilent Technologies Japan in the production of 

the 4TP Capacitance Scaling System.

Yicheng Wang collaborated with Rae Duk Lee 

of KRISS, South Korea on developing transportable capacitance standards for dissipation factor 

measurements.

SELECTED PUBLICATIONS

N.M. Zimmerman, B.J. Simmonds, and Y. Wang, “An upper 

bound to the frequency dependence of the cryogenic vacuumgap capacitor,” Metrologia, 43 (Oct. 2006).

Y. Wang, A. Koffman, and G. FitzPatrick, “Dissipation factors 

of fused-silica capacitors in the audio frequency range,” Digest 

of Conference on Precision Electromagnetic Measurements 

(CPEM 2006), (Torino, Italy, July 9-14, 2006), p. 654-655.

N.M. Zimmerman, B.J. Simonds, Y. Wang, “Frequency dependence of the cryogenic capacitor in the ECCS,” Digest of Conference on Precision Electromagnetic Measurements (CPEM 

2006), (Torino, Italy, July 9-14, 2006), p. 160-161.

R. Gavioso, E.F. May, J.W. Schmidt, M.R. Moldover, and Y. 

Wang, “Towards an electromagnetic pressure standard: Dielectric permittivity of Helium and Argon measured with quasispherical microwave resonators and cross-capacitors,” Digest 

of Conference on Precision Electromagnetic Measurements 

(CPEM 2006), (Torino, Italy, July 9-14, 2006), p. 30-31.

S. Avramov-Zamurovic, B.C. Waltrip, and A.D. Koffman, 

“A Calibration Procedure for a Programmable Capacitance 

Standard,” 2006 CPEM Conference Digest, Turin, Italy, July 

9-14, 2006.

S. Avramov-Zamurovic, A.D. Koffman, and B.C. Waltrip, 

“Evaluation of Inductive Voltage Dividers and 10 nF Capacitors 

in a Capacitance Calibration Method,” 2006 CPEM Conference 

Digest, Turin, Italy, July 9-14, 2006.

Yicheng Wang and Scott Shields, “Improved capacitance measurements with respect to a 1 pF cross-capacitor from 200 to 

2000 Hz,” IEEE Trans. Instr. Meas. 54, 542 (2005).

A. Koffman, Y. Wang, and S. Shields, “Optimizing the use of 

commercial capacitance bridges in fused-silica standard capacitor calibrations at NIST,” 2005 NCSLI proceedings.

X. Li, L. Ling, X. Hua, G.S. Oehrlein, Yicheng Wang, A. V. 

Vasenkov, and M.J. Kushner, “Properties of C4

F8 inductively 

coupled plasmas. I. Studies of Ar/c-C4

F8 magnetically confi ned 

plasmas for etching of SiO2,” J. Vac. Sci. Technol. A, 22, 500 

(2004).

L. Ling, X. Hua, X. Li, G.S. Oehrlein, F.G. Celii, K.H.R. Kirmse, P. Jiang, Yicheng Wang, and H.M. Anderson, “Study of 

C4

F8/CO and C4F8/Ar/CO plasmas for highly selective etching 

of organosilicate glass over Si3N4 and SiC,” J. Vac. Sci. Technol. 

A, 22, 236 (2004).

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M.E. Cage, A.M. Jeffery, S.H. Shields, “Initial NIST AC QHR 

Measurements,” J. Res. NIST, 109, 391 (2004).

Yicheng Wang and L. Lee, “A digitally programmable capacitance standard,” Rev. Sci. Instrum. 75, 1158 (2004).
Quantum Electrical Metrology Division 27

THE ELECTRONIC KILOGRAM

GOALS

To realize the electrical unit of voltage and to provide an alternative defi nition of the unit of mass 

that is based on measured quantities determined by 

fundamental physical constants of nature.

To enhance NIST’s ability to measure and disseminate improved mass standards made of materials 

suitable for air to vacuum transfers.

CUSTOMER NEEDS

The kilogram is the only remaining base unit in the 

International System of Units (SI) whose defi nition 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 signifi cant 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 signifi cant 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 will also provide better determinations of many 

fundamental physical constants, such as the charge 

and mass of the electron, that serve the general 

scientifi c and technological communities.

The International Committee for Weights and Measures (CIPM), on the recommendation of the Consultative Committee on Units (CCU), has adopted 

a resolution to the General Committee of Weights 

and Measures (CGPM), to consider a redefi nition 

of the kilogram in 2011, provided suitable results 

have been reproduced. Since any new defi nition of 

the kilogram will likely involve measurements of 

mass standards in vacuum, new methods to transfer 

from and maintain mass standards in vacuum must 

be explored. Thus the Electronic Kilogram project 

and the related Alternative Approach to Mass Metrology projects are researching these issues.

Technical Contact:

Richard L. Steiner

Staff-Years (FY 2006):

2.0 professionals

TECHNICAL STRATEGY

The equivalence of electrical and mechanical 

power provides a convenient route to the measurement of mass in terms of other quantum mechanically defi ned measurement units. The apparatus at 

the Electronic Kilogram facility is a force balance 

connected to an induction coil in a large magnetic 

fi eld. Confi gured as either an electric generator 

or motor, both kinds of power are measured in a 

way that is unaffected by the dissipative forces of 

friction and electromagnetic heating. The experimental observables are time, length, voltage, and 

resistance, measured with respect to fundamental 

and invariant quantum phenomena, respectively: 

atomic clocks, lasers, the Josephson effect, and the 

quantum Hall effect.

The entire experiment is a complex mesh of mechanical and electronic components controlled by 

computer. The systems are not only for watt data 

acquisition but also include reference standards, 

servo control, and environmental monitoring. All 

systems need to perform accurately and consistently 24 hours a day. Some peripheral systems include 

a programmable Josephson array voltage standard, 

a gravimeter, an ac resistance temperature bridge, a 

temperature controller for the building, and a current controller for the magnetic fi eld solenoid. Even 

though the apparatus has been rebuilt and improved 

since 1998, a number of additional improvements 

Ed Williams, Richard Steiner, and Dave Newell with 

the NIST watt balance.
28 Electronics and Electrical Engineering Laboratory

are recognized as necessary for better instrument 

performance, easier operational use, and as preventative maintenance. The work in 2006 is expected 

to maximize and report on the performance of the 

present system. Future years envision the design 

of a new system, enhanced and user friendly, for 

use as the U.S. kilogram mass standard, located in 

the Advanced Metrology Laboratory.

PLANS

Better values of the Planck constant at about 

0.02 μW/W uncertainty, to meet the conditions specifi ed 

in Recommendation 1 (CI-2005), adopted by the 

International Committee for Weights and Measures 

(CIPM), calling for preparative steps towards new 

defi nitions of the kilogram, the ampere, the Kelvin 

and the mole in terms of fundamental constants, for 

possible adoption by the 24th General Committee of 

Weights and Measures (CGPM) in 2011.

A new electronic kilogram system in the Advanced 

Metrology Laboratory, designed for use as the next 

generation U.S. national mass standard.

ACCOMPLISHMENTS

Electronic Kilogram – A result for the Planck 

constant was published in March 2005, reporting 

a combined standard relative uncertainty (CSRU) 

of 52 μW/W, the fi rst result since 1998, after completely rebuilding the apparatus. 

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Improved analysis of the Type B systematic 

error sources led to a better result with a CSRU of 

36 μW/W (see fi gure at left), presented and submitted for publication in July 2006 at the Conference on Precision Electromagnetic Measurements 

(CPEM-2006). The two results are both within the 

lower of the two combined uncertainties, and agree 

with the 1998 result.

Two publications by Mills, et. al., presented 

arguments for redefining several SI units: the 

kilogram, ampere, Kelvin, and mole. The fi rst, 

calling for immediate redefi nition of the kilogram, 

initiated Recommendation 1 (CI-2005) of the 

CIPM for redefi ning and linking these units to 

fundamental constants as early as 2011. The second called for completely redefi ning these units in 

terms fundamental constants. Both papers sparked 

major international discussions within the various 

Consultative Committees that are concerned with 

these units.

R. Steiner, E. Williams, and D. Newell were 

awarded a Gold Medal in 2006 by the Department 

of Commerce, for their research work on the Electronic Kilogram.

Alternative Mass Metrology – A vacuum-toair mass balance has been designed. It involves 

magnetically suspending a mass inside a vacuum 

chamber and measuring its mass against one in 

air. The initial magnetic suspension has been 

achieved.

COLLABORATIONS

R. Steiner and E. Williams are collaborating via 

periodic workshops with NPL-UK, METAS-Switzerland, and LNE-France, and the BIPM as part 

of the Consultative Committee for Electricity and 

Magnetism (CCEM) group on the watt balance 

realization of the kilogram. 

E. Williams is scheduled to go on a 6 month sabbatical to LNE in November 2006. 

Edwin Williams is collaborating with the Mass 

Group of the Manufacturing Engineering laboratory on the Alternative Mass Metrology competence project.

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Laboratory Values of the Planck Constant. 
Quantum Electrical Metrology Division 29

Schematic diagram of the NIST watt balance.

SELECTED PUBLICATIONS

R. L Steiner, E. R. Williams, R. Liu, and D. B. Newell,, “Uncertainty improvements of the NIST Electronic Kilogram,” 

IEEE Transactions On Instrumentation And Measurement, (to 

be published Apr. 2007).

I. M. Mills, P. J. Mohr, T. J. Quinn, B. N. Taylor and E. R. Williams, “Redefi nition of the kilogram, ampere, Kelvin and mole: 

a proposed approach to implementing CIPM recommendation 

1 (CI-2005),” Metrologia, 43, 227-246 (2006).

I. M. Mills, P. J. Mohr, T. J. Quinn, B. N. Taylor and E. R. Williams, “Redefi nition of the kilogram: a decision whose time has 

come,” Metrologia, 42, 71–80 (2005).

R.L. Steiner, E.R. Williams, D.B. Newell and R. Liu “Towards 

an Electronic Kilogram: an improved measurement of the 

Planck constant and electron mass,” Metrologia,, 42, 431-441 

(2005) .

R. L Steiner, D. B. Newell, E. R. Williams, R. Liu, and P. 

Gournay, “The NIST project for the Electronic Realization of 

the Kilogram,” IEEE Transactions On Instrumentation And 

Measurement, 54, 846-849 (2005).

R. L. Steiner, E. R. Williams, and D. B. Newell, “Details of the 

1998 watt balance experiment determining the Planck constant,” 

J. Res. Natl. Inst. Stand. Technol., 110, 1-26 (2005).
30 Electronics and Electrical Engineering Laboratory

QUANTUM-BASED NOISE THERMOMETRY

GOALS

To create an intrinsic quantum-based electronic 

temperature standard to support the NIST Chemical 

Science and Technology Laboratory efforts toward 

reducing uncertainty in the ITS-90 temperature 

scale and to develop a novel method for determining the Boltzmann constant.

Sae Woo Nam tests the cross-correlation electronics 

for the Johnson noise thermometry system. A gallium 

triple-point cell at 302.916 K is behind him.

CUSTOMER NEEDS

Existing precision thermometry methods use gasbased and fi xed-point methods to achieve the lowest uncertainties below parts in 105

. Unfortunately, 

these methods are limited to specifi c fi xed temperatures and require considerable effort. Another 

method that compares electrical and thermal noise 

power, called Johnson noise thermometry (JNT), 

would provide a novel approach to precision thermometry and, through the use of quantum-based 

voltage standards, has the potential to improve the 

realization of the Kelvin Thermodynamic Temperature Scale, especially with regard to linearity.

In addition, a quantum-based JNT system would 

also provide a novel route to a re-determination of 

the Boltzmann constant, k. This latter goal is particularly timely because there are plans to redefi ne 

in 2011 four of the SI units (including the Kelvin 

in terms of k) in terms of fundamental physical 

constants so that they are universal, permanent, 

and invariant in time. The NIST quantum-based 

JNT approach to create an “electronic Kelvin” is 

analogous to the watt-balance program to realize 

an “electronic kilogram,” which compares electrical and mechanical power for the determination of 

Planck’s constant, h.

Our customers and collaborators include the NIST 

Chemical Science and Technology Laboratory, 

temperature calibration laboratories including other 

national measurement institutes, and industrial 

applications that require long-term temperature 

stability or have temperature sensors in diffi cult 

or remote locations.

In order to meet these customer needs and fundamental metrology goals, we created a quantum-based electronic temperature standard that is 

unique in the world by developing new technology 

in a number of different areas. Most importantly, 

we constructed the world’s fi rst quantum voltage 

noise source (QVNS) as well as state-of-the-art 

low-noise cross-correlation electronics, which is 

calibrated by the QVNS. We developed pseudonoise voltage waveforms and synthesis techniques 

for comparison with the voltage noise of resistors 

in triple point cells of both gallium and water. We 

also devised a novel ratiometric method that uses 

the QVNS to compare the voltage noise of resistors 

at different temperatures. 

TECHNICAL STRATEGY

The goal of the NIST Johnson noise thermometry 

program is to build an electronic temperature 

standard based on the quantized voltage pulses of 

superconducting Josephson junctions. 

In a JNT system, the temperature T is inferred 

from measurement of the Johnson noise voltage 

VT across a calibrated resistance R. The meansquared voltage noise is given by the Nyquist 

formula where Δf is the measurement bandwidth. Cross-correlation techniques are 

typically used to measure these extremely small 

voltages to remove the error introduced by amplifi er noise. In 1999, John Martinis realized that the 

Josephson Arbitrary Waveform Synthesizer being 

developed by the Quantum Voltage Project might 

be able to produce a stable, accurate, pseudo-noise 

voltage to provide a better means of calibrating the 

low-noise cross-correlation electronics. A stable, 

programmable, and intrinsically accurate noise 

source, based on the quantum accuracy of Josephson junctions, would provide a number of key 

Technical Contact:

Sam Benz

Staff-Years (FY 2006):

1 professional

1 guest researcher
Quantum Electrical Metrology Division 31

advantages: (1) direct calibration of the cross-correlation electronics, (2) matching of the calibration 

voltage noise to that of the sense resistor, while (3) 

simultaneously matching the source impedance to 

both the sense resistance and the output transmission-line impedance. These features, which are 

mutually exclusive using conventional methods, 

reduce the measurement uncertainty, increase the 

measurement bandwidth, and decrease the measurement time for the entire JNT system.

During the JNT development program, the Quantum Voltage Project developed a QVNS that is ideally suited for these measurements and is based on 

digital-to-analog waveform synthesis techniques. 

The QVNS superconducting integrated circuit is 

based on technology and research developed for 

ac Josephson voltage standards. However, development of the QVNS also provided new insights and 

precision measurement expertise that improved and 

benefi ted the ac Josephson program.

Our goal is to achieve uncertainties of better than a 

few parts in 105

 for temperatures in the range of a 

several hundred Kelvin. At these temperatures the 

noise signals are small, on the order of 1 nV/Hz1⁄2

for a 100 ohm resistor. In order to achieve small 

measurement uncertainties for such low-voltage 

signals, the noise power spectral density must be 

integrated for a long time and over a wide bandwidth. Thus the QVNS must be stable for long 

integration times but does not need to generate large 

voltages. We devised a special method of biasing 

the QVNS that meets these requirements and allows 

it to be much simpler than the Josephson arbitrary 

waveform synthesizer, where the primary focus is 

to obtain the highest possible voltages. 

We also constructed custom cross-correlation electronics for the JNT program. Two pairs of voltage 

leads are measured with separate low-noise amplifi er channels. Each signal is fi rst measured with an 

ac-coupled differential FET, followed by an antialias fi lter with a cutoff frequency at 2 MHz. The 

resulting amplifi ed and fi ltered signals are digitized 

at 50 MHz by a 14-bit analog-to-digital converter. 

Field-programmable gate arrays (FPGAs) at the 

output of the digitizers then digitally fi lter the 

signal with a low-pass frequency of 100 kHz. The 

digitally fi ltered data are transmitted via a 50 megabit/s optical link to a custom PCI card installed in a 

computer. Each channel transmits 2.08333 million 

samples per second which is the effective sampling 

frequency of the signal. In the present system, a 

dual-CPU computer is used to calculate two 221 

point fast Fourier transforms (FFTs) in real-time 

(less than one second). The cross-correlation and 

auto-correlation power spectra are then calculated, 

accumulated, and stored for later analysis.

Sam Benz optimizes the operating margins for the 

Josephson arbitrary-waveform synthesizer. 

ACCOMPLISHMENTS

Sae Woo Nam, Wes Tew (NIST Chemical 

Sciences and Technology Laboratory), and Sam 

Benz have performed many comparisons between 

the Johnson noise voltage of resistors at known 

temperatures and the synthesized pseudo-noise 

waveforms of the quantum voltage noise source. 

The resistor temperatures are controlled using 

either a gallium fi xed-point cell or a water triple 

point cell. Measurements are made using the custom built cross-correlation electronics system. The 

computer-controlled optically interfaced system 

correctly samples, stores, and processes the waveforms in real time. This correlation electronics is 

different from other systems because it digitally 

processes the signal in an FPGA before sending it 

to a computer. This is necessary to reduce the data 

rate to the computer. 

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32 Electronics and Electrical Engineering Laboratory

Log-log plot showing the measured spectrum of a 

QVNS-synthesized pseudo-noise waveform. The 

spectrum was measured with the JNT cross-correlation electronics and shows the power (V2

) spectrum Sxy

of the 1258 tones synthesized by the QVNS. Each bin 

has a width of 1 Hz and is an average of 200 samples. 

The power spectrum is in arbitrary units based on the 

digitizer bins.

Paul Dresselhaus fabricated numerous circuits 

specifi cally to improve the performance and optimize the circuits for the JNT program. Benz has 

tested the circuits with appropriate pseudo-noise 

waveforms and demonstrated proper cross-correlation using an HP FFT spectrum analyzer. Benz also 

performed extensive measurements of input-output 

coupling for the JNT circuits and devised a novel 

unipolar bias method to decrease the coupling by 

about 40 dB. Other improvements include novel 

QVNS circuits with smaller common mode signals and implementation of Charlie Burrough’s 

fl ip-chip on fl ex packaging. These results allowed 

us to take the next step and measure the arrays at 

much smaller voltages and higher bandwidth using 

Nam’s cross-correlation electronics.

Nam, Benz, Dresselhaus, and Charlie Burroughs, in collaboration with Wes Tew of the Chemistry Laboratory, have continued development of 

the Johnson noise thermometry system, especially 

with regard to improvements in the measurement 

circuits and electronics. Unwanted distortion was 

observed when the accurate QVNS signal was 

measured with the cross correlation electronics. 

This distortion was signifi cantly reduced by using 

inductive chokes on the input of the electronics. 

The cause of the distortion appeared to be mixing 

in the fi rst FET amplifi er from the high-frequency, 

100-400 MHz, quantization tones in the QVNS 

waveform. Other major sources of distortion that 

were uncovered through measurements of the accurate QVNS synthesized waveforms were due to 

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poor contacts and interconnections between the 

signal sources and the amplifi ers; poor interfaces 

rectify the waveform and produce measurable harmonic distortion. Unique waveforms, with either 

odd-only or even-only harmonics, were developed 

to elucidate and remove these errors. By constructing a second QNVS system, and making comparisons between them using both inputs to the JNT 

electronics, we were able to remove all distortion 

within the dynamic range of the electronics. 

Comparisons between different QVNS cryoprobes also increased our understanding of the 

high-frequency transfer function characteristics. 

Calculations showed that small differences in the 

transfer functions of the QVNS probes were caused 

by different transmission line leads. Calculations 

showed that this effect could not account for the 

transfer function differences between the QVNS 

and noise resistor probes. We fi nally realized, 

and confi rmed through further calculations, that 

there is a fundamental difference between the 

QVNS and resistor output circuits that results in 

a signifi cantly higher effective capacitance in the 

resistor circuits that progressively mismatches the 

two transfer functions at high higher frequencies. 

By increasing the QVNS output resistance by 

about 65%, we successfully matched the transfer 

functions of the QVNS and resistor circuits up to 

about 600 kHz. This truly matches the transmission 

lines for the fi rst time, contrary to our original assumptions about impedance matching at the start 

of this program.

Having greatly reduced the errors from distortion and transmission lines, we can now investigate 

voltage noise over a much wider frequency range. 

In preliminary measurements we’ve demonstrated 

that we can closely match the two transmission 

lines of the Josephson and triple-point resistor 

sources, causing the ratio to remain fl at over most 

of the measurement bandwidth. Control of the 

ratio’s frequency dependence is shown in Figure 

4, where the grey data points show the ratio when 

the transmission lines are nearly matched. In this 

measurement, the absolute error in measuring temperature or determining “k/h” was approximately 

50 ppm. This is 3-times better than previous temperature measurements. These preliminary results 

suggest that with only a 10-fold further improvement in the measurement uncertainty, we can have 

an impact on Boltzmann’s constant at a few parts 

per million. 

The next step toward lower uncertainty involves improving the measurement electronics 

to reduce intrinsic nonlinearities, lower the noise 

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Quantum Electrical Metrology Division 33

fl oor, and extend battery lifetime. These improvements will allow the measurement electronics to 

complete much longer integration times (>2 days). 

We also must perform extensive measurements and 

calculations to model the transmission line effects. 

We also plan to investigate improvements in common mode rejection of the front amplifi er stage and 

in the switching network.

Measured power spectral density ratios vs. frequency 

(kHz) showing control of the frequency dependence. 

The black points show the large frequency dependence 

in the ratio when the transmission lines (between the 

noise sources and the correlation electronics) are mismatched. The gray points show a nearly constant ratio 

up to 600 kHz with matched transmission lines.

In FY04 we delivered cross correlation electronics to the CSTL temperature calibration laboratory. This system is in use for making high temperature JNT measurements with the goal to reduce 

uncertainty in the ITS-90 temperature scale in the 

range 273 K to 1000 K through comparisons with 

a calibrated platinum resistance thermometer

In FY05 signifi cant improvements in the JNT 

system were discovered by comparing two different 

Josephson systems. Poor contacts and interconnects were the primary culprit causing undesirable 

distortion. Unfortunately, this competence program 

ended before water/gallium comparisons could be 

obtained using the improved system.

In September of FY06 we installed the Quantum Voltage Noise Source in CSTLs Thermometry 

Lab and performed record-breaking Johnson Noise 

Thermometry measurements at temperatures above 

500 K.

PLANS

This year we plan to make signifi cant improvements 

to the cross correlation electronics, including better 

preamplifi ers and battery chargers that allow us to 

make longer continuous measurements.

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With further improvements and removal systematic 

errors for the electronics, transmission lines and 

measurement circuits, we hope to reduce our 

measurement uncertainty to less than 20 parts per 

million.

COLLABORATIONS

We are collaborating with Weston Tew and John 

Labensky of the Process Measurements Division 

(836) in the NIST Chemical Science and Technology Laboratory.

•

Sae Woo Nam, Wes Tew, and Sam Benz with the quantized voltage noise source. 

Dr. D. Rod White from the Measurement Standards 

Laboratory in Lower Hutt, New Zealand is also 

consulting and collaborating with us, bringing 

many years of expertise in Johnson noise thermometry.

SELECTED PUBLICATIONS

W.L. Tew, J.R. Labenski, S.W. Nam, S.P. Benz, P.D. Dresselhaus, and C.J. Burroughs, “Johnson noise thermometry near the 

zinc freezing point using resistance-based scaling,” submitted 

to the Sixteenth Symposium on Thermophysical Properties, 30 

July–4 Aug. 2006, Boulder, CO. 

J.R. Labenski, W.L. Tew, S.W. Nam, S.P. Benz, P.D. Dresselhaus, and C.J. Burroughs, “Resistance-based scaling of LF- and 

MF-band thermal noise powers,” 2006 Conference on Precision 

Electromagnetic Measurements Digest, presented 10–14 July 

2006, Torino, Italy, pp. 404-405. 

W. L. Tew, S. W. Nam, S. P. Benz, P. Dresselhaus, John Martinis, 

and H. M. Hashemian, New Technologies for Noise Thermometry with Applications in Harsh and-or Remote Operating 

Environments, Presented at The 51st International Instrumentation Symposium in Knoxville Tennessee, The Instrumentation, 

Systems and Automation Society, May 2005.

S. Nam, S. Benz, P. Dresselhaus, C. Burroughs, W. L. Tew, 

D. R. White, J. M. Martinis, “Johnson Noise Thermometry 

using a Quantum Voltage Noise Source for Calibration,” IEEE 

Transactions on Instrumentation and Measurement, Vol. 54, 

No. 2, pp. 653-657 (April 2005). 
34 Electronics and Electrical Engineering Laboratory

S. Nam, S. Benz, P.D. Dresselhaus, and J. Martinis, “Johnson 

noise thermometry measurements using a quantized voltage 

noise source for calibration,” IEEE Transactions on Instrumentation and Measurement, Vol. 52, No. 2, pp. 550-554 

(April 2003). 

S.P. Benz, P.D. Dresselhaus, and J. Martinis, “An ac Josephson 

source for Johnson noise thermometry,” IEEE Transactions on 

Instrumentation and Measurement, Vol. 52, No. 2, pp. 545-549 

(April 2003). 

S. W. Nam , S. P. Benz, J. M. Martinis, P.D. Dresselhaus, W. 

L. Tew, and D. R. White, “A ratiometric method for Johnson 

noise thermometry using a quantized voltage noise source,” 

Temperature: Its Measurement and Control In Science and 

Industry, Vol. 7, Part 1, pp. 37-42, Edited by Dean C. Ripple, 

Proceedings of The Eighth International Temperature Symposium, (AIP Conference Proceedings Vol. 684: Melville, New 

York 2003).

S. P. Benz, J. M. Martinis, S. W. Nam, W. L. Tew, and D. R. 

White, “A new approach to Johnson noise thermometry using a 

Josephson quantized voltage source for calibration,” in Proceedings of TEMPMEKO 2001, the 8th International Symposium 

on Temperature and Thermal Measurements in Industry and 

Science, B. Fellmuth, J. Seidel, and G. Scholz, Eds., Berlin: 

VDE Verlag, April 2002, pp. 37-44.
Quantum Electrical Metrology Division 35

QUANTUM MEASUREMENTS

In earlier parts of this Technical Accomplishments Book for the Quantum Electrical Metrology Division, we discuss standards based either directly or indirectly on naturally occurring 

quanta.

In this section we present measurements, but not standards, many of which are achieved using 

quantum systems. Predominantly the system used is superconductivity, which is a macroscopic 

quantum system. Superconductors are particularly attractive for electrical metrology because 

they can carry current with very low loss, and with zero loss if the current is constant.

For measurements for quantum communications we use superconducting microcalorimeters 

to count single photons, the quanta of light. We use similar devices for X-ray microanalysis 

of materials and as ultra-sensitive or ultra-accurate detectors of infrared and X-ray radiation. 

Other superconducting detectors are use for terahertz frequency radiation. Our measurements 

of high-frequency electrical pulses and electrical power are based on fundamental standards 

that in turn rely on superconductors.

In a completely different way we are using superconductivity to contribute to a major NIST and 

international effort to realize the concept of quantum computing. If a quantum computer can 

be practically realized, it may be capable of vastly more computational power than any other 

known computing technique. It is of potentially profound national importance. As a result, 

NIST is investing heavily in this area because it is a very challenging measurement problem. 

Measurements are NIST’s expertise and we are able to make essential contributions to this 

exciting technology.

Quantum computing is completely different from the computing we know. It relies on the manipulation of the wave functions that are the basis of quantum systems. The measurement of the 

output from a quantum computer is performed at the very fundamental limit of measurements, 

based on the Heisenberg uncertainty principle. As a result we are striving to realize measurement of unprecedented delicacy, using approaches that surely will be of use much broader than 

just quantum computing as we progress through the 21st century.
36 Electronics and Electrical Engineering Laboratory

ELECTRIC POWER METROLOGY

GOALS

Our goals are to provide the electric power industry 

with the world’s best basis of precision electrical 

measurements in power and energy to ensure fair 

and accurate revenue billing; to provide electrical 

standards, tests, and services that underpin the reliable operation of the electrical power grid; and to 

assess and develop new measurement technologies 

for the increased reliability and quality of the U.S. 

electric power system. 

PMUs – a key component of electric power grid 

modernization. The fi gure shows the NIST Calibration 

System for PMUs. The PMUs are the two instruments 

on top of the cabinet. 

CUSTOMER NEEDS

The major needs of the U.S. electric power industry 

supported by this project are the equitable sale of 

electric power and energy, and reliable transmission and distribution of high quality electric power. 

Both require accurate and traceable measurements 

of electrical quantities. 

Electrical energy revenue metering throughout the 

U.S. is traceable to NIST calibrations and results 

in annual revenues exceeding $280 billion. We 

provide measurement traceability through calibration services for power and energy meters that 

ensure accuracy in measuring electric power and 

in monitoring power grid operation. 

In addition, we support the reliable operation of 

the power grid. The U.S. electric power industry 

continues to play the major role in public safety, 

economic stability, and quality of life. Because 

it underpins many other infrastructures, electric 

power is the infrastructure we most readily notice 

when a disruption occurs, even if it is only momentary. In the wake of the major electric power 

outages in 1996 and 2003, the U.S. Department of 

Energy (DoE) has sponsored grid modernization 

efforts that entail a revolutionary change in control 

of the power grid, with the long-range goal of removing system operators from the control loop and 

replacing them with completely automatic control 

systems. This will be achieved through synchronized measurements of system conditions derived 

from quantities known as phasors (voltage and 

current amplitudes and phases). The website for 

the Eastern Interconnect Phasor Project (EIPP) is 

http://phasors.pnl.gov/EIPP_RT_Resources made 

using Phasor Measurement Units (PMUs). The 

major benefi ts of these efforts will be improved 

grid reliability and effi ciency that lower costs to 

consumers, and reduced magnitude of the disruptions due to instantaneous location of faults. PMUbased control systems will also promote the use of 

alternative power generators by ensuring reliability 

as these new devices are added to the grid. We 

provide the basis for objective evaluation of PMU 

performance through the development of standards, 

test protocols, and measurement services. 

TECHNICAL STRATEGY

This project maintains the U.S. standards for power 

and energy and disseminates them through measurement services for electric meters used by utilities and meter manufacturers to ensure the accurate 

sale of electric power in the U.S. Improvements 

in the accuracies we provide to our customers and 

internal streamlining of our services adds value for 

our customers. For example, we are developing a 

power calibration system that is based upon Josephson arrays that will allow us to reduce uncertainties 

to a few ppm for power calibrations.

International comparisons of measurement capabilities are essential for the equivalence of 

calibrations at all the National Metrology Institutes 

(NMIs), allowing customers to use only one calibration to sell their product worldwide. To ensure 

the accurate measurement of power throughout 

the Americas, we are serving as the pilot lab for 

an intercomparison among the member countries 

of the regional organization of NMIs for North 

and South America, the Sistema Interamericano 

de Metrologia (SIM). 

The accuracies of power and energy measurement 

services that we provide depend in part upon accuracies of the digital multimeters (DMMs) we use 

Technical Contact:

Thomas Nelson

Staff-Years (FY 2006):

3.5 NIST staff

1 NIST associate 

1 technician
Quantum Electrical Metrology Division 37

in our measurement systems. To achieve the best 

accuracies for our own measurement systems and 

to meet the demands of manufacturers and users for 

DMM measurements traceable to national electrical 

standards, we also provide measurement services 

for DMMs. We will pilot a SIM intercomparison 

for DMMs in 2007. 

To improve power grid monitoring and control, a 

common calibration reference for devices requiring Coordinated Universal Time (UTC) timing 

references from GPS sources is required. We have 

established a SynchroMetrology Laboratory which 

will serve to calibrate PMUs and to develop and disseminate test procedures for use by manufacturers 

and utilities to assure interoperability and accuracy 

of time-coordinated metrology. The initial development of this laboratory is a calibration service 

for PMUs, to assure compliance of PMUs with 

the IEEE synchrophasor standard, C37.118. An 

Interagency Agreement between NIST and the U.S. 

DoE provides substantial support for this project. 

In collaboration with the North American Electric 

Utilities and DoE-sponsored Eastern Interconnect 

Phasor Project (EIPP), we are leading a working 

group to develop a testing Guide for PMUs. Future needs of the Electric Power Utilities require 

the assurance of interoperability of PMUs under 

dynamic conditions of the electric power grid. 

In collaboration with utilities and the standards 

community we are developing testing procedures 

and providing feedback to PMU manufacturers 

on the performance of their devices under various 

dynamic conditions. 

Not only is reliability important to utilities and 

end users of electric power, but the quality of 

electric power is also important. Our meter measurement services are typically performed at a 

single frequency, namely the 50 or 60 Hz power 

frequency. To improve our capability and meet 

the needs of electrical equipment manufacturers 

and utilities for measurements of distorted power 

that contains harmonics of the power frequency, 

a new sampling test system has been constructed 

and is being used to participate in an international 

comparison of harmonic power measurements. The 

system developed is based upon a NIST-developed 

sampling waveform analyzer (SWA) with custom 

probes that make highly accurate measurements 

of arbitrary waveform parameters from the basic 

root-mean-square (rms) values to crest factor, 

signal-to-noise ratio (SNR), harmonic distortion, 

etc. The SWA has a frequency response fl atter than 

any commercially-available instrument and this 

allows traceability to the national dc volt standard 

and enables accurate waveform sampling from 

power-line frequencies to 5 GHz. In addition to the 

distorted power measurements, application areas 

for the SWA include ac voltage, characterization 

of voltage pulses, and radiofrequency calibrators. 

A newly redesigned version of the mainframe 

unit, SWA II, is now being tested in the laboratory. The new system offers several signifi cant 

performance improvements including a tenfold 

increase in sampling time achieved through optimized effi ciency in the Markov signal averaging 

and increased data record length, better accuracy 

through optical isolation of the digital circuitry, and 

a considerable decrease in the physical size and 

cost of the system. The reduced cost is of interest 

to the primary standards laboratories (PSLs) of 

the U.S. Air Force, Army, and Navy, and Sandia 

National Laboratories. We have already delivered 

SWA systems that give them in-house capability 

to calibrate their ac measurement standards and 

they are interested in the improved SWA II. We 

will also use it to provide dedicated support for 

another NIST special test measurement service in 

voltage pulse characterization, the 65250S service, 

Fast Repetitive Pulse Settling Error.

Fuel cells are used as electrical power sources in 

many applications from electric vehicles to spacecraft. Much work needs to be done in determining 

which designs and manufacturing processes result 

in the best fuel cell performance and lowest cost. To 

help answer these questions, we have set up a fuel 

cell testbed to assess fuel cell performance. 

The new test stand for performance evaluation of fuel 

cells. The cells can be evaluated under controlled 

conditions to assess how manufacturing processes and 

design affect electrical performance. 

“The aggregate annual 

economic impact [for 

not having adequate 

measurements and 

standards in place for the 

electric power industry] 

ranges from $3.1 billion 

to $6.5 billion.”

 “Changing Measurements 

and Standards Needs in a 

Deregulated Electric Utility 

Industry,” NIST Planning 

Report 00-2
38 Electronics and Electrical Engineering Laboratory

PLANS

PMU Performance Evaluation

Develop a measurement service for performance 

testing of commercial PMUs.

Serve as leader of the EIPP PMU testing working 

group and complete the Guide for PMU testing under 

static conditions. 

Develop test methods for measuring performance of 

PMUs under dynamic conditions.

Improved Measurement Services

Incorporate the NIST-developed quantum watt 

source into the power and energy calibration system. 

Complete the SIM energy comparison and publish 

the results

Develop the waveform sampling-based calibration 

system for distorted power sources and other ac 

waveform standards, such as the Fluke 5790A 

Automated AC Measurement Standard.

New Project Areas

Test prototype fuel cell performance to determine 

infl uence of design and manufacturing parameters.

ACCOMPLISHMENTS

We developed special calibration procedure 

for PMUs relative to the parameters specifi ed in 

IEEE Standard C37.118 together with the North 

American electric utilities and power equipment 

manufacturers collaborating in the Eastern Interconnect Phasor Project (EIPP). This standard 

ensures that PMUs from multiple vendors will 

all interact correctly with the stability monitoring 

system being developed. In collaboration with the 

EIPP, we developed a special calibration service 

to calibrate the PMU parameters specifi ed in the 

IEEE Standard.

We constructed a precision thermally-stabilized calculable shunt for measuring currents from 

0.1 to 10 amperes for frequencies up to 1 MHz. 

This shunt exhibits less than 1 ppm of resistance 

change with currents between 0.3 and 10 amperes. 

This shunt was used in a ac shunt comparison with 

NRC-Canada up to 10 kHz and the agreement was 

better than 6 ppm.

We demonstrated the feasibility of making 

peak-to-peak waveform measurements up to 500 

MHz with uncertainties less than 3 % using a SWAbased waveform sampling system. The Peak-toPeak Detectors measurement service, 53430S and 

53431S, which previously relied upon inferring 

peak-to-peak from root-mean-square measurement of a pure sinusoidal signal, will soon switch 

over to a waveform sampling technique using the 

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NIST SWA, allowing more accurate peak-to-peak 

measurements to be made.

We set up fuel cell test bed for performance 

testing of single cells and to correlate the impact 

of variation in manufacturing processes on electrical output. 

CALIBRATIONS

Calibrations are typically performed for about 35 

companies and government agencies annually, for 

total fees of nearly $100,000. 

COMMITTEE PARTICIPATION

ANSI/NEMA Electricity Metering Committee 

(C12): T. L. Nelson serves as the chair.

IEEE Electricity Metering Subcommittee: T. L. 

Nelson serves as secretary.

Eastern Interconnect Phasor Project - G.N. Stenbakken is a member of the EIPP Performance 

Requirement Task Team and is the leader of the 

PMU System Testing and Calibration Guide Task 

Team. 

IEEE Instrumentation and Measurement (I&M) 

Society TC-10 Waveform Generation, Measurement and Analysis Committee, D.I. Bergman is 

a member. 

IEEE Power Engineering Society Power Systems 

Instrumentation and Measurement (PSIM) Committee, G.J. FitzPatrick chairs the committee.

SELECTED PUBLICATIONS

D. I. Bergman and G. N. Stenbakken, “Phase-Plane-Derived 

Distortion Modeling of a Fast and Accurate Digitizing Sampler,” 

IEEE Trans. Instrum. Meas, vol. 55, no. 4, August 2006.

NIST Support of Phasor Measurements to Increase Reliability of the North-American Electric Power Grid, IEEE 

Power Engineering Society General Meeting, June 18-22, 2006, 

PESGM2006-000586.PDF.

K. L. Stricklett, O. Petersons, and C. R. Hagwood, “Operating Characteristics of the Proposed Sampling Plan for Testing 

Distribution Transformers,” NIST Technical Note 1456, 24 

pages (May 2004)

E. So, D. Angelo, B. Waltrip, T. Nelson, T. Tsuchiyama and 

T. Takodoro, “Intercomparison of Calibration Systems for AC 

Shunts up to Audio Frequencies,” Conference Digest 2004, Conference on Precision Electromagnetic Measurements (CPEM 

2004), pp. 35 (June 2004)

E. So, R. Arseneau, D. Bennett, T.L. Nelson, and B.C. Waltrip, 

“NRC - NIST Intercomparison of Calibration Systems for 

Current Transducers with a Voltage Output at Power Frequencies,” Conference Digest 2002 Conference on Precision 

Electromagnetic Measurements, (CPRM 2002), pp. 544 – 544 

(June 2002).

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Quantum Electrical Metrology Division 39

QUANTUM COMPUTING USING INTEGRATED

JOSEPHSON JUNCTION CIRCUITS

GOALS

To develop techniques for making highly coherent 

quantum systems using integrated circuits. This 

includes developing new high fi delity measurements techniques for quantum systems. Ultimately, 

we want to make large-scale quantum information 

processing systems a reality.

Ray Simmonds probes the resistance of Josephson 

junctions on a new wafer of quantum bits.

CUSTOMER NEEDS

The integrated circuit components of classical 

computers are rapidly approaching the so-called 

“quantum limit.” Instead of avoiding quantum effects, we have the opportunity to exploit them as a 

means for more effective computation. A quantum 

computer has the ability to use the intrinsic properties of quantum systems to naturally perform parallel processing during a calculation. This allows a 

quantum computer to solve problems considered 

intractable for classical computers. Three such 

problems are of considerable interest: discrete 

logarithms, factorization, and search algorithms 

for large databases. The practical signifi cance of 

building a successful large scale quantum computer 

is tremendous: 

It could provide a powerful tool for encryption. 

A quantum computer is seen as the only instrument 

that could break the most secure encryption codes 

in use today. This application is an immensely 

important subject for national security. 

It could be used to solve highly complex 

(many-body) problems in a reasonable amount of 

time. This will become increasingly important for 

the chemical and biological sciences. 

It could provide rapid search engines to help 

navigate us through the information age. 

It could allow us to simulate large quantum 

systems effi ciently.

In a conventional computer, information is often 

stored as electrical charge on tiny capacitors. The 

presence or absence of charge on a single capacitor represents a (classical) bit which can store two 

(classical) information states “0” and “1.” All logical computations are done using groups and combinations of this binary information. A quantum bit 

or “qubit” is described in terms of two quantum 

states denoted by “|0>” and “|1>”. Remarkably, a 

quantum bit can be placed in a state that is a mixture 

of both “|0>” and “|1>”! Even more remarkable 

is the fact that multiple qubits can be placed in a 

massive mixture of all combinations of their possible states, a phenomenon known as entanglement. 

Entanglement is the magic of quantum mechanics 

and allows a quantum computer to stir up quantum information in order to produce a meaningful 

calculation with incredible speed. 

Whether or not quantum computing becomes 

practical, our work will produce new knowledge 

for the precise measurement of quantum systems. 

Through our research with quantum mechanical 

superconducting circuits, we are learning how to 

custom design, fabricate, and operate quantum 

systems. Through direct control and measurements we are developing new ways to utilize the 

quantum mechanics. We have already shown (as 

described below) the ability to detect previously 

unknown nanoscale quantum systems which could 

never be seen before. Ultimately, we are exploring 

untouched regimes of nature and may fi nd ways 

to direct unforeseen advancements in nanotechnology.

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Technical Contact:

Raymond W. Simmonds

Staff-Years (FY 2006):

1 professional

1 technician

4 post-doc researchers

4 graduate students

The integrated circuit 

components of classical 

computers are rapidly 

approaching the socalled “quantum limit.” 

Instead of avoiding 

quantum effects, we 

should exploit them as a 

means for more effective 

computation. Ultimately 

our work will produce 

new knowledge for the 

precise measurement of 

quantum systems.
40 Electronics and Electrical Engineering Laboratory

TECHNICAL STRATEGY

The strategy of this effort is to develop a highly 

coherent set of quantum bits which can be isolated, 

controlled, coupled and measured. These are the 

building blocks for quantum computing. Along 

these lines, we have developed a high impedance 

current bias and measurement scheme for controlling a Josephson “phase” qubit, while providing 

suffi cient isolation from the external environment. 

Josephson junctions are electrical circuit elements 

which resemble capacitors. They are made from 

two pieces of metal separated by a thin insulating 

barrier. When the metal electrodes become superconductors at low temperatures (in this case, the 

superconducting temperature is about 1 K while 

the measurement temperature is below 0.030 K 

or 30 mK) current can fl ow through this capacitor due to the quantum mechanical mixture of the 

superconducting wavefunctions on either side of 

the junction. Each wavefunction is described with 

the help of a quantum mechanical “phase” whose 

gradient is related to the zero-resistance fl ow of 

superconducting (Cooper) pairs of electrons. The 

current that fl ows through the Josephson junction is 

proportional to the sine of the quantum mechanical 

phase difference δ across the junction. A qubit is 

made by including a Josephson junction in a superconducting loop, as shown in the fi gure at right. 

Microwave current lines are capacitively coupled 

to the junction while a dc bias coil is placed some 

distance from the “qubit loop.” For an applied 

magnetic fl ux through the loop, the potential energy 

stored in the Josephson junction as a function of 

the superconducting phase difference δ is shown 

in the fi gure at right. The fl ux bias is chosen so 

that the qubit states, |0> and |1>, are formed in the 

left (~cubic) well. One can imagine these states as 

very rapid phase or current oscillations in this well. 

The |1> state is measured by an induced tunneling 

event to states in the (~quadratic) right well. This 

changes the fl ux in the qubit loop by roughly a 

fl ux quantum, a relatively large fl ux difference that 

can easily be detected using a pulsed dc SQUID 

magnetometer.

(a) The phase qubit schematic circuit. (b) The potential energy at a particular fl ux bias applied to the qubit 

loop. An example of qubit spectroscopy for two qubits 

showing the transition frequency ω10 for various fl ux 

biases to the qubit loop. Notice the small “splittings” 

indicative of microscopic quantum systems residing 

within the tunnel junction coupling to our superconducting quantum bit. Top inset shows Rabi oscillations 

away from resonators.

The qubit transition frequency ω10, which is directly 

related to the energy level separation of the |0> and 

|1> state, is measured spectroscopically as a function of the applied fl ux bias to the qubit loop. First 

we prepare the qubit in the |0> (ground) state. If 

we apply a microwave drive current at frequency 

ω and ω = ω10, then the qubit will make a transition to the |1> state, otherwise it will remain in 

the ground state. If we sweep the value of ω and 

measure the occupation probability of state |1>, 

we can determine the precise value for ω10 at that 

particular fl ux bias. We measure the occupation of 

the |1> state using a “fast” qubit state measurement 

technique. This is done by applying a quick dc fl ux 

pulse to the qubit loop so that the potential barrier 

ΔU is lowered just enough so that, if occupied, the 

By gaining the ability 

to control quantum 

systems directly, we are 

exploring untouched 

regimes of Nature 

and may fi nd ways 

to direct un-for-seen 

advancements in 

nanotechnology.

Through the fi rst 

ever simultaneous 

measurement of two 

superconducting qubits, 

we have witnessed two 

coupled phase qubits 

entangle themselves 

by performing coherent 

state oscillations.
Quantum Electrical Metrology Division 41

|1> state has a high probability for tunneling to the 

right well and will be detected using the SQUID. 

This procedure is done for many different values 

of the fl ux bias in order to determine the energy 

level separation or transition frequency ω10 as a 

function of the qubit loop fl ux bias. If we know the 

transition frequency ω10, then we are able to fully 

control the state of the qubit. Varying the fl ux bias, 

simply allows us to operate the qubit at different 

frequencies (typically from 7 to 10 GHz).

An example of “qubit spectroscopy” is shown in 

the fi gure below. We fi nd the expected decrease in 

the transition frequency with fl ux bias as the current 

through the junction approaches its critical or maximum current. Notice (in the lower inset) that there 

are “gaps” or “splittings” in the spectra. We have 

identifi ed these spurious resonators as nanoscopic 

two level systems within the junction’s insulating 

barrier. Away from any spurious resonators, we 

have applied microwaves on resonance (ω = ω10) 

to performed coherent state oscillations, known as 

“Rabi oscillations”, between the |0> and |1> state 

(upper inset). Near spurious resonators, we have 

found coupled interactions between the qubit and 

the resonator as described briefl y in Accomplishments. Although these resonators are undesirable in 

an ideal qubit, so far they have been useful for testing coupled interactions and estimating the limits of 

(a) A fabricated coupled qubit circuit. (b) Simultaneous measurement of two coupled qubits during state 

oscillations.

coherence in solid state nanosystems. An effort is 

being lead by David Pappas to improve the quality 

of Josephson junctions by growing epitaxial tunnel 

barriers to remove these nanoscopic defects. 

Our long term strategy is to produce highly coherent superconducting qubits for building small 

systems to successfully perform error tolerant 

quantum logic operations. With these building 

blocks, we should be able to quickly take advantage 

of existing integrated circuit technology to make 

progress towards a full scale superconducting 

quantum computer.

PLANS

The development of the phase qubit was just a 

start. This program is interested in understanding 

decoherence sources and producing high quality 

superconducting qubits. We plan to study all three 

types of qubits: charge, fl ux, and phase as well as 

harmonic oscillators or microwave resonators which 

also operate in the quantum regime. We will also 

extend these investigations to qubits coupled to 

harmonic oscillators and coupled qubits.

ACCOMPLISHMENTS

Although this project began only four years ago, 

we have made signifi cant progress over this short 

period of time. Our work on coupled qubits has 

shown that two-qubit gates should be feasible. We 

have developed high quality harmonic oscillators 

or microwave resonators in order to investigate 

energy loss from dielectric materials. Our research 

has led the way to understanding how to improve 

future qubits by eliminating dielectric materials 

in the fabrication of qubits. We have managed to 

improve the materials and design properties of our 

qubits to more than double their coherence times. 

Most signifi cantly we have developed a frequency 

tunable Josephson junction resonator which allows 

us to asses the quality of Josephson junction in an 

entirely new way. Many of our accomplishments 

over the past year are included in the list below.

Discovered spurious resonators within 

Josephson tunnel junctions. Using our new 

improved qubit we have developed spectroscopic 

measurements of the qubit transition frequency 

over a wide range of possible operating fl ux biases. 

In doing so, we discovered nanoscopic spurious 

resonators within the tunnel junctions of the qubit. 

Elimination of these resonators in future Josephson 

junctions could improve the performance of all

superconducting devices.

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42 Electronics and Electrical Engineering Laboratory

(a) The Josephson junction resonator circuit. (b) An 

example of spectroscopy showing “splittings” from the 

two-level defects in the single Josephson junction.

Developed a new, faster method to readout 

the phase qubit. We have implemented a new qubit 

state measurement technique that is an order of 

magnitude faster than our former method. In less 

than 5 ns, a fl ux bias pulse is applied to the qubit 

so that the |1> state, if occupied, rapidly tunnels 

to the right well. This new advance has allowed 

us to monitor rapid qubit state variations such as 

the coupled interactions between phase qubits and 

other quantum systems. 

Coupled qubit interactions. Through the 

fi rst ever simultaneous measurement of two superconducting qubits, we have recently witnessed 

two coupled phase qubits entangle themselves by 

performing coherent state oscillations. This is a 

tremendous step forward! Soon, we hope to have 

the ability to perform simple logic operations 

between two qubits, the building blocks for a full 

scale quantum computer.

Dielectric loss reduce energy relaxation 

times. Dielectric loss from two-level defects was 

shown to be a dominant decoherence source in 

superconducting quantum bits. Depending on 

the qubit design, dielectric loss from insulating 

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materials or the tunnel junction can lead to short 

coherence times. We have shown that a variety of 

microwave and qubit measurements are well modeled by loss from resonant absorption of two-level 

defects. Our results demonstrate that this loss can 

be signifi cantly reduced by using better dielectrics 

and fabricating junctions of small area and by removing dielectric material completely. Redesigned 

phase qubits reducing the amount of dielectric and 

using an improved dielectric have improved energy 

relaxation rates by a factor of 20.

Josephson junction resonator. We have 

developed a unique microwave resonator using a 

single Josephson junction as a tunable inductance 

in the circuit. This flux tunable circuit allows 

spectroscopic measurements for frequencies that 

vary over a range >1 GHz. Information can be 

gathered to test the quality of Josephson junctions 

in terms of individual nanoscopic defects as well 

as excess energy loss. This device very similar to 

a phase qubit but is extremely simple to fabricate 

and operate, and it allows us to obtain a maximum 

amount of information. Moreover, this device 

operates as a low loss fl uxometer ideal for future 

qubit readout. 

COLLABORATIONS

David Pappas – Quantum Metrology Division, 

NIST, Boulder, Epitaxial Josephson junctions with 

new materials.

John Martinis – University of California, 

Santa Barbara, Measurement electronics and qubit 

development.

Dale Van Harlingen – University of Illinois, 

Urbana-Champaign, 1/f noise measurements of 

Josephson junctions.

Lev Ioffe – Rutgers University, Theoretical 

study of two-level systems

SELECTED PUBLICATIONS

S. Oh, K. Cicak, J. S. Kline, M. A. Sillanpää, K. D. Osborn, J. D. 

Whittaker, R. W. Simmonds, D. P. Pappas, “Elimination of two 

level fl uctuators in superconducting quantum bits by an epitaxial 

tunnel barrier,” Phys. Rev. B 74, 100502 (2006).

J.M. Martinis, K. B. Cooper, R McDermott, M Steffen, M 

Ansmann, K. D. Osborn, K Cicak, S. Oh, D. P. Pappas, R. W. 

Simmonds, C. C. Yu, “Decoherence in Josephson qubits from 

dielectric loss,” Phys. Rev. Lett. 95, 210503 (2005).

R. McDermott, R. W. Simmonds, M. Steffen, K. B. Cooper, 

K. Cicak, K. D. Osborn, S. Oh, D. P. Pappas, J. M. Martinis, 

“Simultaneous state measurement of coupled Josephson phase 

qubits,” Science 307,1299 (2005).

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Quantum Electrical Metrology Division 43

K. B. Cooper, Matthias Steffen, R. McDermott, R. W. Simmonds, Seongshik Oh, D. A. Hite, D. P. Pappas, John M. Martinis, “Observation of quantum oscillations between a Josephson 

phase qubit and a microscopic resonator using fast readout,” 

Phys. Rev. Lett. 95, 066089 (2004).

R. W. Simmonds, K. M. Lang, D. A. Hite, D. P. Pappas, John 

M. Martinis, “Decoherence in Josephson Phase Qubits from 

Junction Resonators,” Phys. Rev. Lett. 93, 077003 (2004).
44 Electronics and Electrical Engineering Laboratory

QUANTUM SENSORS

The development of sensors based on the quantum 

mechanical phenomenon of superconductivity can 

dramatically improve the sensitivity of measurements across the electromagnetic spectrum, from 

dc magnetic fields to microwaves all the way 

through gamma rays. By operating at temperatures 

below 1 Kelvin, photon detectors based on superconductivity are achieving unparalleled sensitivity, and they are beginning to bring about a broad 

revolution in many areas. Superconducting X-ray 

spectrometers are providing new capabilities in 

materials analysis for the semiconductor industry. 

Gamma-ray sensors that can provide more than an 

order of magnitude better spectral resolution are 

aiding in analyzing nuclear materials for nuclear 

non-proliferation, and may be used material to stop 

them from being smuggled across international 

borders. In the future, improved detectors for measuring the polarization of microwaves will probe 

the fi rst moments of the universe by measuring 

the pattern that gravity waves from the Big Bang 

imprinted on the cosmic microwave background.

GOALS

The Quantum Sensors Project develops sensors 

based on quantum phenomena for spectroscopy, 

imaging, and other precision measurements for 

wavelengths from dc through gamma rays. We integrate these sensors with custom superconducting 

and room temperature electronics, cryogenic structures, and software to create complete measurement 

systems. We work with collaborators in industry, 

academia, and other government agencies to apply 

this measurement capability to applications including materials analysis, particle physics, astronomy, 

cosmology, and homeland defense.

We are developing sensors that operate at extremely 

low temperatures, and that take advantage of quantum phenomena, including quantum interference 

(SQUIDs), quantum phase transitions (superconducting transition-edge sensors), and quantum 

tunneling (normal-insulator-superconductor tunnel 

junctions).

The Quantum Sensors Project has been a world 

leader in developing these new detector systems. 

We have developed transition edge sensors (TES) 

for use in a variety of applications. These devices 

utilize a strip of superconducting material, biased 

in its transition from normal to superconducting 

states, as an extremely sensitive thermometer. 

This thermometer is attached to an absorber that 

is isolated from a cold (~100 mK) heat sink by a 

micromachined structure. The heat deposited by 

incident photons is then measured to accurately 

determine their energy. 

Many applications require large arrays of quantum 

sensors. However, it is diffi cult to route individual 

wires from many different pixels to room temperature readout electronics. Practical implementation 

of large superconducting detector arrays requires 

that the signals be multiplexed at the cold stage. 

We have developed large-format superconducting 

integrated circuits based on SQUID switches that 

make it possible to read out many pixels in one 

output channel. 

Applications for superconducting detectors include 

high-resolution X-ray spectroscopy for materials analysis for the semiconductor industry, high 

resolution gamma-ray spectroscopy to analyze 

nuclear materials to assist in nuclear non-proliferation and border security, and submillimeter 

and microwave detector arrays for astronomy and 

cosmological physics. In each of these areas the 

Quantum Sensors Project is developing detector 

systems that will redefi ne the measurement abilities 

of currently available technology, often by orders 

of magnitude. Our goal is to continue developing 

groundbreaking detector systems for both industry 

and research groups.

CUSTOMER NEEDS

Improved X-ray detector technology is one of the 

most important metrology needs for the semiconductor industry. The 2005 International Technology 

Roadmap for Semiconductors recognize that superconducting X-ray detectors provide important new 

capability in resolving overlapping X-ray peaks: 

“Such new X-ray detectors will allow resolution 

of slight chemical shifts in X-ray peaks providing chemical information such as local bonding 

environments. These advances over traditional 

energy-dispersive spectrometers (EDS) and some 

wavelength dispersive spectrometers can enable 

particle and defect analysis on SEMs located in 

the clean room.” The transition-edge sensor (TES) 

microcalorimeter X-ray detector developed at 

NIST has been identifi ed as a primary means of realizing these detector advances, which will greatly 

improve in-line and off-line metrology tools that 

currently use semiconductor EDS. At present, these 

metrology tools fail to provide fast and unambiguous analysis for smaller nanoparticles. Improved 

“NIST-Boulder has 

been a world leader 

in the development 

of superconducting 

detectors, and has 

produced working 

systems and components 

for X-ray microanalysis, 

X-ray astronomy, and farinfrared astronomy based 

on this technology...In 

short, a large fraction 

of the cutting-edge 

astronomical research 

currently being performed 

by US astronomers is 

directly supported by the 

NIST lab’s production of 

these devices... future 

astrophysics research 

would suffer greatly in the 

event that NIST-Boulder’s 

capability is lost.”

Catherine Pilachowski, 

President of the American 

Astronomical Society 

Technical Contact:

Kent Irwin

Staff-Years (FY 2006):

15
Quantum Electrical Metrology Division 45

EDS detectors such as the TES microcalorimeter 

are necessary to extend the capabilities of existing 

SEM-based instruments to meet the analytical requirements for future technology generations. With 

commercialization and continued development, 

microcalorimeter EDS should be able to meet both 

the near-term and the longer-term requirements of 

the semiconductor industry for improved particle 

analysis.

In addition, the astronomy community has an everincreasing need for instruments capable of supplying extremely high energy-sensitivity coupled 

with large-format arrays for imaging and photon 

collection. TES detector arrays promise to greatly 

expand the abilities of astronomers to study objects 

ranging from solar fl ares to supernova remnants to 

the formation of galaxies. The Quantum Sensor 

project has formed collaborations to transfer our 

TES technology into astronomical instruments 

with several institutions, including NASA, Stanford 

University, the Lockheed-Martin Solar Astrophysics Laboratory and the UK Astronomy Technology 

Center.

TECHNICAL STRATEGY

The ability to detect photons with high-energy 

resolution and near-unity quantum efficiency 

promises to dramatically improve the fi eld of X-ray 

microanalysis. Improved energy-dispersive X-ray 

spectroscopy will be used to solve a wide range 

of problems in materials analysis. For instance, 

in semiconductor manufacturing, improved X-ray 

materials analysis is needed to identify nanoscale 

contaminant particles on wafers and to analyze very 

thin layers of materials and minor constituents.

To make this technology available to the materials analysis community, NIST is working on the 

commercialization of these inventions. Additionally, NIST’s Chemical Science and Technology 

Laboratory is using a prototype microcalorimeter 

system constructed by our group to improve its own 

materials-analysis capability.

The transition-edge-sensor (TES)-based X-ray 

microcalorimeter developed in our group has been 

shown to have world-record energy resolution and 

to have wide application in many areas of X-ray 

microanalysis. In trying to deliver maximum benefi t of this technology to industrial and scientifi c 

users of microanalysis, we are concentrating our 

efforts in three areas: support of existing systems, 

development of improved and simplifi ed single 

detector pixels, and development of arrays of detectors as a means of increasing X-ray collection 

area and count rate.

The low operation temperature of TES microcalorimeters (~100 mK) necessitates a fairly complex 

arrangement of cryogenic and electronic elements 

in order to construct a complete X-ray spectrometer. In this case, we have developed superconducting electronics to read out the detectors, compact 

adiabatic demagnetization refrigerators to simplify 

cooling the detectors to millikelvin operating temperatures, and room-temperature electronics to 

process the output signals. 

An important part of our effort is to provide support to our existing customers, including the users 

of the prototype microcalorimeter system in the 

Chemical Science and Technology Laboratory in 

Gaithersburg, Maryland. We continue to provide 

expertise and training in detector and SQUID 

(readout electronic) operation and optimization, 

and operation of millikelvin refrigerators to CSTL, 

including consultations and site visits. Additionally we continue to make improvements to the 

components in the spectrometer system.

While the performance of the detectors we have 

made is much better than existing detectors, additional improvements in energy resolution (particularly at higher energies) are both theoretically 

possible and desirable by the user community. 

Improvements in energy resolution require new 

understanding of the limitations on performance 

of microcalorimeter detectors. We have begun to 

explore novel detector geometries and materials, 

and to develop the nonequilibrium thermodynamic 

theory of resistive bolometers to better explain 

measured noise.

For many X-ray microanalysis applications, improvements in count-rate and collection area are 

far more important than further improvements in 

energy resolution. This can be achieved by the 

creation of multipixel arrays of detectors. In addition to the fabrication diffi culties in making such 

arrays, the cold- and room-temperature electronics 

to read out the arrays must also be created.
46 Electronics and Electrical Engineering Laboratory

256-pixel TES X-ray calorimeter array and SQUID 

multiplexer electronics for X-ray material analysis 

and astronomy.

Another signifi cant focus of the project is the development of gamma-ray detectors for the analysis 

of nuclear materials. One of the most pressing international priorities is to control the dissemination 

of nuclear materials that could be used in attacks 

by terrorists or rogue states. Nuclear materials 

contain unstable isotopes, which emit X-rays and 

gamma rays. The characteristic energies of these 

photons provide a fi ngerprint of which radioactive 

isotopes are present. Unfortunately, some isotopes 

that occur in benign applications emit gamma rays 

with energies that are very similar to those emitted by materials used in weapons, which leads to 

ambiguous identifi cations and false alarms. This 

problem has been vexing the U.S., which is installing thousands of radiation portal monitors to 

detect the gamma rays emitted by nuclear materials carried by vehicles crossing the Canadian and 

Mexican borders. One of our most signifi cant fears 

is that terrorists might smuggle highly enriched 

(weapons-grade) uranium into the country to build 

a crude Hiroshima-style atomic bomb. The primary 

signature of highly enriched uranium is the 185.7 

kiloelectron-volt (keV) gamma ray from uranium235. This gamma ray, however, has almost the 

same energy as the 186.1 keV gamma ray emitted 

from the radium-226 in clay in cat litter and other 

materials, making it very diffi cult to distinguish the 

two. This so-called kitty-litter problem is the largest 

source of false alarms at the U.S. border.

The Quantum Sensors Project is developing 

gamma-ray detectors based on TES technology that 

have more than ten times better energy resolution 

than conventional detectors. These detectors can 

resolve more lines in the complicated gamma-ray 

spectra of nuclear materials such as uranium and 

plutonium isotopic mixtures (see fi gure below). 

The devices are being developed specifi cally to 

help in the verifi cation of international nonproliferation treaties, by determining the plutonium 

content of spent nuclear fuel. But they can also 

distinguish between the radium-226 in cat litter and 

the uranium-235 in highly enriched uranium. If a 

conventional hand-held detector or portal monitor 

were to detect a gamma-ray signal, one of the superconducting devices could be used as a follow-up 

tool to distinguish unambiguously between these 

two isotopes, thus eliminating many false alarms.

Spectrum taken with NIST gamma-ray detector array. 

When superconducting detectors are used to measure 

the spectrum of radiation from a plutonium-uranium isotopic mixture, the photons from the different 

isotopes are clearly resolved, allowing unambiguous 

identifi cation of the isotopes that are present (black 

lines). In a spectrum taken with a conventional highpurity germanium (HPGe) detector (gray line), the 

lines are not resolved, and the determination of the 

isotopic composition is more diffi cult.

The astronomy community has long been the driving force behind improvements in photon detection 

systems at all wavelengths. Because of TES detectors’ extremely good sensitivity, they are obvious 

candidates to solve many problems faced by this 

community. The same X-ray detectors used in our 

microanalysis efforts, for example, are well suited 

to analyzing the X-ray spectra of supernova remnants and solar fl ares. By redesigning these detectors, they may be used as bolometers to measure 

far infrared and submillimeter radiation on groundbased telescopes, allowing astronomers to probe 

the evolution of galaxies and search for planets 

around other stars. Finally, quantum sensors will 

be important for the precision measurement of the 

polarization of the cosmic microwave background, 

which will make it possible to measure the signal 

of gravity waves from the Big Bang itself.
Quantum Electrical Metrology Division 47

The Quantum Sensors Project has collaborations 

with several institutions to deploy our detectors for 

use in astronomical applications. As these collaborations push the technical abilities of our detectors, 

they often drive us to create improvements that are 

then applied to our more commercial applications, 

such as X-ray microanalysis.

Many of the requirements for X-ray astronomy 

are identical to those for our X-ray microanalysis 

project: high energy resolution, large arrays, high 

counting rates and multiplexed readout. We have 

two principal collaborators in this area: NASA’s 

Laboratory for High Energy Astrophysics (LHEA) 

and the Lockheed-Martin Solar Astrophysics Laboratory (LMSAL).

NASA has an ongoing program to study X-ray 

astrophysics as part of its Structure and Evolution 

of the Universe theme. Following on its successful 

Chandra mission, Constellation-X is the next generation of X-ray astronomy telescopes. To accomplish its goals, Constellation-X will need to have 

an imaging array of X-ray spectrometers to place at 

the focal plane of an orbiting X-ray telescope.

A similar telescope is planned by LMSAL to study 

the mechanisms behind solar fl ares and coronal 

mass ejections (CMEs). CMEs cause signifi cant 

fi nancial impact around the world, as they disrupt 

satellites in Earth orbit and can knock out power 

grids on the ground. Scientists hope to understand 

and possibly predict these solar phenomenon by 

study the spectra of solar fl ares, and LMSAL is 

working with the Quantum Sensor project to develop TES detectors for this purpose.

In the infrared regime, our TES bolometers have 

achieved world-record sensitivity. This impressive 

result confi rms the utility of TES technology for 

this application as well. For several years, we have 

been involved in a collaboration with Laboratory 

for Astronomy & Solar Physics (LASP), at NASA’s 

Goddard Space Flight Center, to develop far-infrared bolometers. A result on early result of this 

collaboration was the Fabry-Perot Interferometer 

Bolometer Research Experiment (FIBRE), the 

fi rst multiplexed TES bolometer array, which was 

deployed on the Caltech Submillimeter observatory 

at Mauna Kea, Hawaii. 

In addition, the Quantum Sensor project, in collaboration with the United Kingdom’s Astronomy 

Technology Center, is developing both sensors and 

readout technology for the second Submillimeter 

Common User Bolometer Array (SCUBA-2). The 

SCUBA-2 instrument is designed to detect radiation from astronomical sources at wavelengths of 

450 μm and 850 μm and will be installed on the 

James Clerk Maxwell Telescope (JCMT) in Hawaii. This array will be, by orders of magnitude, 

the largest bolometer array ever deployed, having over 10,000 individual pixels. It will allow 

astronomers to map the sky at speeds 100-1000 

times faster than previously achieved.

The detector systems discussed above all share a 

common technical requirement: large arrays of TES 

detectors. This requirement brings with it the complication of reading out such large arrays. These 

arrays will all operate at temperatures below 1 K. 

If each pixel in the array requires a separate readout 

all the way to the room temperature electronics, 

then the heat load on the array’s refrigeration system will rapidly become unmanageably large. A 

system to multiplex the readout of these detectors 

at the cold stage of their refrigerator is thus required 

to reduce the number of wires from the cold stage 

to warmer parts of the cryostat.

Fortunately, TES devices are low impedance, 

which allows them to be read out by superconducting SQUIDs. Because SQUIDS, in their unbiased 

“off” state, are superconducting, they may be effectively multiplexed without adding the noise of 

each individual SQUID to the whole.

The Quantum Sensor project has been at the forefront of SQUID multiplexing for several years now. 

Our fi rst-generation 8-channel SQUID MUX was 

successfully deployed with the FIBRE far-infrared 

bolometer array on the CSO telescope on Mauna 

Kea, Hawaii. We have now built upon that success 

by developing a second generation, 32-channel 

SQUID MUX that has better bandwidth and 2 

orders of magnitude lower power dissipation than 

the fi rst design. The fi rst fabrication run yielded devices that work at the design specifi cations. These 

MUX chips should have suffi cient performance to 

multiplex X-ray TES detectors, which are much 

faster than the infrared bolometers in FIBRE. We 

are now building full 1,280-pixel multiplexed arrays for the SCUBA-2 project.
48 Electronics and Electrical Engineering Laboratory

A hybridized TES subarray for the SCUBA-2 instrument. The array consists of a 1,280-pixel SQUID 

multiplexer wafer bump bonded to a 1,280-pixel TES 

bolometer array.

NIST has a long tradition of exploiting physical 

phenomena that occur at ultralow temperatures 

to produce electronic devices with properties that 

cannot be achieved by conventional electronics. 

For instance, NIST has developed Transition-Edge 

Sensor (TES) X-ray sensors which operate at 

temperatures near 100 mK and provide improved 

analytical capabilities to the semiconductor industry. The development of two-stage Adiabatic 

Demagnetization Refrigerators (ADRs) has made 

these low operating temperatures signifi cantly 

more accessible. Nonetheless, even a two-stage 

ADR adds considerable complexity, size, and 

expense to an analytical station. To overcome 

this challenge, NIST has begun development of a 

thin-fi lm refrigerator which is capable of cooling 

sensors from 300 mK to 100 mK. 

The refrigerator consists of Normal-InsulatorSuperconductor (NIS) tunnel junction. Current 

fl ow through the insulating barrier separating the 

electrodes preferentially removes the hottest electrons from the normal electrode, thereby producing 

cooling. When coupled to a Helium-3 cryostat, 

NIS coolers may provide a signifi cantly smaller, 

cheaper, and less complex means of reaching 100 

mK temperatures. 

PLANS

We have provided the Chemical Science and 

Technology Laboratory (CSTL) of NIST with a complete 

prototype microcalorimeter system for collaborative use 

in studying problems of interest to our customers. We 

will continue to provide support and improvements for 

this system.

•

We will develop models of single-pixel 

microcalorimeter performance to assist in improving 

detector sensitivity, and will fabricate and test novel 

detector designs based on these models.

We will further develop arrays of X-ray 

microcalorimeter detectors to demonstrate the increase 

in collection area and count rate achievable through 

arrays. We will work with NASA to develop these arrays 

for use in the Constellation-X project.

We will develop arrays of detectors optimized for 

imaging infrared bolometry, along with the necessary 

wiring, SQUID MUX and room temperature DSP 

electronics to read the array.

ACCOMPLISHMENTS

We have developed an extremely high energy 

resolution X-ray detector and demonstrated a 

complete X-ray spectroscopy system. This detector and spectrometer have been made possible by 

broad expertise within the Division in such fi elds 

as superconductivity, device fabrication including 

silicon micromachining, superconducting electronics, cryogenic engineering, and low-noise, 

room-temperature electronics. Without expertise 

in all of these areas, the complete systems that 

have provided the compelling demonstrations for 

the power of this technology would not have been 

possible.

This system holds the world record for energy 

resolution for an EDS detector of 2.37 eV ± 0.12 eV 

at 5900 eV, which is over 30 times better than the 

best high-resolution semiconductor-based detectors 

currently available. We have used the system to 

identify submicrometer particles of materials such 

as W on Si substrates, an identifi cation problem that 

is impossible with standard EDS detectors and of 

great importance to the semiconductor industry. 

It has also demonstrated energy shifts in the EDS 

X-ray spectra of materials such as Al, Fe, and Ti, 

depending on their chemical bonding state, thus 

allowing differentiation between a particle of Al 

and Al2O3, for example.

We have fabricated gamma ray detector arrays 

with the world record energy resolution for an EDS 

detector of 25 eV at 103 keV (see fi gure). This 

energy resolution was achieved in a 14-pixel multiplexed array. Gamma ray detectors with ultra-high 

energy resolution will provide superior capabilities 

for nuclear materials analysis.

•

•

•

■

■

■
Quantum Electrical Metrology Division 49

World record 25 eV energy resolution achieved with 

NIST microcalorimeter at 103 keV.

We have fabricated the fi rst on-chip, solid-state 

microrefrigerator using Normal metal-insulatorsuperconductor (NIS) tunnel junctions integrated 

with superconducting transition-edge sensors. 

Presently, cryogenic instruments that operate near 

100 mK use complex, expensive adiabatic demagnetization refrigerators and dilution refrigerators. 

We have fabricated an NIS refrigerator designed to 

operate at bath temperatures of 300 mK, which is 

accessible with relatively simple and inexpensive 

3He refrigerators. The normal metal in the junction 

is an Al thin fi lm doped with ferromagnetic impurities (Mn) in order to suppress superconductivity. 

These sensors are integrated with TES detectors, 

making it possible for them to operate from a lower 

temperature.

We demonstrated the fi rst multiplexed readout 

of an X-ray microcalorimeter array. This breakthrough establishes a clear path to the instrumentation of kilopixel microcalorimeter arrays, which 

will have wide-ranging implications for fi elds as 

diverse as materials analysis and X-ray astronomy. 

A challenge in the development of large arrays of 

X-ray microcalorimeters, which measure the energy, or color, of X-rays with high resolution, is that 

providing an amplifi er channel for each detector in 

the array requires too many wires to be connected 

to the cryogenic detectors. Time-division SQUID 

multiplexing, a scheme in which the signals from 

many detectors are read out through a single amplifi er, is one way to conquer this challenge. In the 

■

■

experiment, we measured the energy resolution of 

four microcalorimeters, using both conventional 

and multiplexed readout techniques. 

We have demonstrated the fi rst microwave 

SQUID multiplexer. This breakthrough opens a 

path to reading out very large arrays of SQUIDs 

for magnetoencephalography and non-destructive 

evaluation, and CCD-scale arrays of low-temperature detectors. In this circuit, the outputs of many 

SQUID amplifi ers are simultaneously monitored 

by a single high electron mobility transistor 

(HEMT) amplifi er channel. Each SQUID amplifi er 

is placed in a high-Q resonant circuit with a different resonant frequency, and excited by a comb of 

microwave signals at each of the resonant frequencies. The amplitude of the refl ected microwave 

signals at each frequency is a function of the input 

signal at each SQUID. In an initial experiment, we 

demonstrated the low-noise readout of SQUIDs 

using this microwave refl ectometer approach, and 

multiplexed two SQUIDs simultaneously near 500 

MHz. Future work will focus on operation at 5 GHz 

and developing technology for much larger SQUID 

arrays. Because of the large bandwidth available 

with microwave measurements, it should be possible in the future to read out many thousands of 

SQUIDs in a single coaxial cable, and instrument 

arrays of SQUIDs with thousands or millions of 

pixels.

We have delivered science-grade parts for the 

fi rst full, 1,280-pixel multiplexed submillimeter 

bolometer subarrays for the SCUBA-2 project. 

These parts are now being hybridized, and will lead 

to a signifi cant step forward for the community.

COLLABORATIONS

UK Astronomy Technology Center, SCUBA2 

camera

University of Edinburgh /Scottish Microelectronics 

Centre, SCUBA2 camera

Raytheon Vision Systems Inc., SCUBA2 camera

University of Cardiff, SCUBA2 camera

NIST Division 837, X-ray microcalorimeter for 

microanalysis

Intel, X-ray microanalysis using our microcalorimeter system

Lockheed Martin, X-ray detector development for 

solar physics

Stanford University, X-ray detector development 

for solar physics

■

■
50 Electronics and Electrical Engineering Laboratory

Jet Propulsion Laboratory, SQUID multiplexer 

for IR detectors

NASA Goddard Space Flight Center, SQUID 

multiplexer for IR detectors

NASA Goddard Space Flight Center, X-ray microcalorimeter arrays

NASA Goddard Space Flight Center, Magnetic 

Microcalorimeters

JILA, Microwave SQUID multiplexer

Star Cryoelectronics, X-ray detector development

SELECTED PUBLICATIONS

Time-division multiplexing of high-resolution TES X-ray 

microcalorimeters: Four pixels and beyond, W.B. Doriese, J.A. 

Beall, S. Deiker, W.D. Duncan, L. Ferreira, G.C. Hilton, K.D. 

Irwin, C.D. Reintsema, J.N. Ullom, L.R. Vale, and Y. Xu, Appl. 

Phys. Lett. (in press).

Microwave refl ectometer readout for large-format superconductor-insulator-normal metal bolometer arrays, D. R. Schmidt, A. 

M. Clark, W. Duncan, K. D. Irwin, N. Miller, J. N. Ullom, and 

K. W. Lehnert (submitted to Applied Physics Letters).

Seeing with Superconductors, Kent D. Irwin, Scientifi c American, November, 2006, pp. 86-94.

Transition-Edge Sensors, K.D. Irwin and G. C. Hilton, in 

Cryogenic Particle Detection, C. Enss (Ed.), Topics Appl. Phys. 

99, 63-149 (2005), Springer-Verlag Berlin Heidelberg 2005, 

ISBN: 3-540-20113-0.

Electron Probe Microanalysis with Cryogenic Detectors, D.E. 

Newbury, K.D. Irwin, G.C. Hilton, D.A. Wollman, J.A. Small 

and J.M. Martinis, in Cryogenic Particle Detection, C. Enss 

(Ed.), Topics Appl. Phys. 99, 267-312 (2005), Springer-Verlag 

Berlin Heidelberg 2005, ISBN: 3-540-20113-0.

Practical electron-tunneling refrigerator, A. M. Clark, A. Williams, S. T. Ruggiero, M. L. ven den Berg, and J. N. Ullom, 

Appl. Phys. Lett. 84 (4); 625-627; 26 January 2004.

Characterization and reduction of unexplained noise in superconducting transition-edge sensors, J.N. Ullom, W.B. Doriese, 

G.C. Hilton, J.A. Beall, S. Deiker, W.D. Duncan, L.Ferreira, 

K.D. Irwin, C.D. Reintsema, and L.R. Vale, Appl. Phys. Lett. 

84(21): 4206-4208 (May 24, 2004).

Cryogenics on a Chip. J.P. Pekola, R.J. Schoelkopf, and J.N. 

Ullom, Physics Today 57(5): 41, May 2004.

Transition edge sensor using dilute AlMn alloys, S.W. Deiker, 

W. Doriese, G.C. Hilton, K.D. Irwin, W. H. Rippard, J.N. 

Ullom, L.R. Vale, S.T. Ruggiero, J.N. Ullom, L.R. Vale, S.T. 

Ruggiero, A. Williams, and B.A. Young, Appl. Phys. Lett. 85 

(11) 2137-2139 (2004).

Microwave SQUID multiplexer, K.D. Irwin and K.W. Lehnert, 

Appl. Phys. Lett. 85 (11) 2107-2109 (2004).

A Prototype System for SQUID Multiplexing of Large-Format 

Transition-Edge Sensor Arrays, C.D. Reintsema, J. Beyer, 

S.W. Nam, S. Deiker, G.C. Hilton, K.D. Irwin, J.M. Martinis, 

J. Ullom, L.R. Vale, M. MacIntosh, Rev. Sci. Instrum. 74(10): 

4500-4580 (Oct. 2003).
Quantum Electrical Metrology Division 51

MAGNETIC SENSORS & QUANTUM MATERIALS

GOALS

This project addresses measurement needs in 

characterization of magnetic sensors, advanced 

applications of magnetic sensors, and national security. We are developing magnetoresistive arrays 

and readout electronics that can image magnetic 

fi elds for biomedical research, forensic analysis of 

magnetic recording media, and current distributions 

in integrated circuits for nondestructive evaluation. 

We also develop advanced electron tunneling barriers for superconducting Josephson junctions for 

future quantum computers. 

CUSTOMER NEEDS

Magnetic Sensors — Magnetoresistive magnetic 

fi eld sensors have wide application in research and 

industry. Currently, cryogenic superconducting 

quantum interference devices (SQUIDs) are used 

for the measurement of ultra-low magnetic fi elds. 

They provide important information in many areas 

of basic research, medical magnetic fi eld monitoring, and security. However, it is necessary to 

develop devices operating at room temperature that 

are scalable, linear, and have comparable sensitivity 

to realize the maximum benefi t of such devices. 

The most promising candidates for development 

are magnetoresistive technologies. Magnetic noise 

is a critical problem in the development of these 

devices; such noise can be two orders of magnitude 

higher than the intrinsic Johnson, shot, and 1/f 

noise of the device. New materials, measurement 

techniques, and device architectures are required 

to characterize and reduce the effect of low- and 

high-frequency magnetic fl uctuations. 

Magnetic Forensics — In the late 1990s, in a collaboration with the National Telecommunications 

and Information Administration, we developed 

basic magnetic imaging technology to retrieve 

data from damaged or altered magnetic tapes and 

computer disks by rastering samples with a single 

sensor to build up an image. We fi rst demonstrated 

the approach by recovering data from scraps of 

aircraft “black-box” tape that were too short to be 

played in a conventional tape deck. For several 

years, the Federal Bureau of Investigation (FBI) 

used a prototype of the magnetic imaging system. 

Because the system was slow, it was used only for 

testing and special cases. There has been a need 

for new, faster methods to authenticate magnetic 

recording tape.

Quantum Computing — Promising candidates 

for quantum computing devices are quantum bits 

(qubits) based on Josephson junctions. These junctions are used in magnetic detectors (SQUIDS), 

voltage standards, and other superconducting 

electronic devices; techniques for their fabrication 

have been investigated in some detail. However, 

qubits have far more stringent noise requirements 

that are now only barely satisfi ed by current fabrication technology. A signifi cant limitation to the 

performance of these devices is the generation 

of defects in the oxide interlayers. The structural 

origin of these defects is not well established, but is 

likely a consequence of both the amorphous nature 

of the oxides and the preparation methods. 

TECHNICAL STRATEGY

Magnetic Sensors — In 2004 we embarked on a 

NIST “Competence” program with the Materials 

Science and Engineering Laboratory, the Physics Laboratory, and the Information Technology 

Laboratory on low-noise magnetic sensors. The 

program includes development of new amorphous 

and nanocrystalline materials, imaging of magnetic 

domains, noise measurement in sensor devices, and 

micromagnetic modeling. 

Magnetic Forensics — We are fabricating linear 

arrays of 256 sensors to scan magnetic recording 

tape in a single pass. The sensors make use of the 

magnetoresistance effect, where their electrical 

resistance changes in response to magnetic fi elds 

detected from the tape. Software converts the 

sensor resistance measurements to visual images 

that have a resolution of about 240 dots per square 

centimeter (1520 dpi). Systems that are of interest 

include cassette, VHS, and digital audio tapes. 

Quantum Computing — State-of-the-art Josephson junctions employing superconducting Al or Nb 

electrodes and native-oxide tunnel barriers typically are fabricated by use of sputter deposition onto 

thermally oxidized Si wafers for microelectronics 

fabrication. However, spurious resonant states 

arising from microstructural defects in the tunnel 

barrier promote decoherence in Josephson qubits. 

These resonances may originate from defects and 

inhomogeneous oxidation during the tunnel barrier formation. Crystalline oxides contain three 

to four orders of magnitude fewer defects in the 

frequency range of interest for Josephson qubits. 

Our capability to prepare and then process samples 

in ultrahigh vacuum is critical to the development 

Technical Contact:

David Pappas

Staff-Years (FY 2006):

1 professional

3 post-docs
52 Electronics and Electrical Engineering Laboratory

of defect-free, crystalline tunneling barriers. We are 

now developing a process to grow epitaxial Re on 

crystalline sapphire (Al2O3) substrates.

PLANS

Install 256 imaging system at FBI Audio Forensics 

Laboratory in Quantico, VA. Train forensics agents on 

its use.

Fabrication low-dielectric Al2

O3 qubit and investigate 

measurement fi delity.

Fabricate V/MgO/V tunnel junctions and optimize for 

low subgap conductance

Fabricate NbN thin fi lms with high Tc (>9 K) and 

investigate effi cacy in single photon transition threshold 

detector.

ACCOMPLISHMENTS

New Zig-Zag Magnetoresistive Field Sensors Developed — We have developed new “zigzag” magnetoresistive sensors that, because of their 

shape, are sensitive to magnetic fi elds parallel to 

their axes but insensitive to fi elds perpendicular. 

The thin-fi lm devices are also able to distinguish 

positive and negative fi elds because their resistance 

is an odd function of fi eld.

In general, anisotropic magnetoresistive sensors 

must be biased, with their magnetization at an angle 

with respect to the current direction. Our new sensors are fabricated in a zig-zag pattern that pins the 

magnetization at alternating positive and negative 

45 degrees to the direction of the current fl ow (see 

fi gure below). This novel approach provides a builtin magnetization bias determined by the corrugation of the edges. Since the angle of magnetization 

of the magnetic domains is controlled only by the 

sensor shape, and not by adjacent biasing fi elds, the 

devices may be scaled to nanometric dimensions. 

When the sensor is exposed to a magnetic fi eld 

oriented in the direction of the current, the angle of 

magnetization relative to the current in both sets of 

the domains decreases. This results in an increase 

of electrical resistance in each domain and in the 

entire device. For magnetic fi elds in the negative 

current direction, the magnetization angle increases 

and the resistance decreases. For magnetic fi elds 

in the perpendicular axis, the magnetization angle 

increases in one set of magnetic domains and de-

•

•

•

•

■

creases in the other, resulting in no net change in 

device resistance. 

Images of Erased Tapes — We conducted 

high-resolution magnetic imaging measurements 

on erased audio tape for the FBI as part of its participation in a study by the National Archives and 

Records Administration (NARA) on the feasibility 

of recovering audio from an 18.5 minute gap in a 

tape from the Nixon White House.

NARA’s 6-millimeter-wide test tapes had been 

recorded and then erased in a manner similar to 

that of the Nixon tapes. As described by NARA, 

the test tapes were “recorded on an original Nixon 

White House Sony 800B tape recorder, then erased 

on Rosemary Woods’ UHER 5000.” Tests were 

made of both an erased audio recording and an 

erased blank section of tape. The FBI could fi nd 

no trace of the recording or erasure marks using a 

standard imaging technique with a ferromagnetic 

fl uid. However, we were able to detect an extra 

noise band on the outside edge of the erased section 

of the audio tape that was not evident on the erased 

section of blank tape. The noise band was scanned 

at high resolution and converted to an audio signal. 

It consisted of only very low frequency sounds, 

with no trace of audible speech. In a press release 

dated May 8, 2003, Archivist of the United States 

John W. Carlin said, “I am fully satisfi ed that we 

have explored all of the avenues to attempt to recover the sound on this tape. The candidates were 

highly qualifi ed and used the latest technology in 

their pursuit.” 

New System Sees Crimes on Audiotape

— We developed a real-time magnetic imaging 

system that enables criminal investigators to see 

signs of tampering in audiotapes — erasing, overrecording, and other alterations — while listening 

to the tapes. An upgraded system was delivered to 

the FBI in Sept. 2006. The upgrades included increasing the resolution by a factor of 4 (to 256 sensors from 64), the capability to scan both VHS and 

cassette tapes, on-the-fl y image capture, complete 

computer control of the cassette tape transport, and 

the capability to digitize the audio directly from the 

acquired image (either real-time or in post-processing). A sample image is shown below.

■

■

Magnetization of a 10 μm long zig-zag shaped magnetic element.

Magnetic image of ~ 2 seconds of audio cassette tape 

where an overrecored event occurred. On the top left 

is new data,the top right is old data. The erased gap 

in center top is the area between the erase head and 

write head.
Quantum Electrical Metrology Division 53

At the heart of the technology is a cassette player 

modifi ed with an array of 256 customized magnetic 

sensors that detects and maps the microscopic 

magnetic fi elds on audiotapes as they are played. 

The array is connected to a desktop computer 

programmed to convert the magnetic data into a 

displayable image. Authentic, original tapes produce images with non-interrupted, predictable patterns, whereas erase and record functions produce 

characteristic “smudges” in an image that correlate 

to “pops” and “thumps” in the audio signal. The 

original markings specifi c to different types of tape 

players are not present on tape copies. An examiner 

can use this new system to help determine the authenticity of a tape and also help determine whether 

that tape is a copy. The benefi ts of the system are its 

speed in correlating sounds with magnetic marks 

on tape, and the fact that it makes an image without 

damaging the tape. 

Improved Superconducting Tunnel Junctions Using Epitaxial Underlayers — In collaboration with the Quantum Computing Measurements 

Project, we studied the growth of tunnel junction 

base electrodes to investigate the role that crystalline quality plays in device performance. We 

found that there is a strong correlation between the 

morphology of oxidized base electrodes and the 

lowering of subgap currents, and through the use 

of epitaxial seed layers, junctions with even lower 

subgap currents were obtained. In order to accomplish this, we engineered Josephson junctions with 

increasingly improved crystalline quality and were 

able to correlate the microstructure of the junctions 

with low-frequency transport measurements. Our 

data indicate a strong correlation between improved 

crystallinity of the tunnel barrier and reduced subgap leakage currents. 

In order to test the properties of these materials, we 

have fabricated quantum bits using the crystalline 

Al2O3 as a tunnel barrier. We have found an 80% 

reduction in the density of the spectral splittings 

that indicate the existence of two-level fl uctuators 

(TLFs) in amorphous tunnel barriers (see following 

fi gure). The residual 20 % TLFs can be attributed 

to interfacial effects that may be further reduced 

by different electrode materials. These results show 

that decoherence sources in the tunnel barrier of Josephson qubits can be identifi ed and eliminated.

■

Comparison of spectra taken from qubits with amorphous (a) and crystalline (b) barriers.

RECENT PUBLICATIONS

R.R. Owings, F.C.S. da Silva, D.P. Pappas, “Investigation of a 

thin fi lm magnetic moment reference material,” NIST Journal 

of Research (in press).

Seongshik Oh, Katarina Cicak, Jeffrey S. Kline, Mika A. 

Sillanpää, Kevin D. Osborn, Jed D. Whittaker, Raymond W. 

Simmonds, and David P. Pappas, “Elimination of two level 

fl uctuators in superconducting quantum bits by an epitaxial 

tunnel barrier,” Physical Review B 74, 100502R (2006).

Pappas D.P., Nazarov A.V., Stevenson D., Voran S., Read M.E., 

Gormley E.M., Cash J., Marr K., Ryan J.J., “Second-harmonic 

magnetoresistive imaging to authenticate and recover data from 

magnetic storage media,” B. L. Zink, K. D. Irwin, G. C. Hilton, 

J. N. Ullom, D. P. Pappas, “Erium-doped gold sensor fi lms for 

magnetic microcalorimeter X-ray detectors,” Journal of Applied 

Physics 99, 08B303 (2006).

Oh S., Hite D.A., Cicak K., Osborn K.D., Simmonds R.W., 

McDermott R., Cooper K.B., Steffen M., Martinis J.M., Pappas 

D.P., “Epitaxial growth of rhenium with sputtering,” Thin Solid 

Films 496 (2): 389-394 Feb. 21, 2006.

D. P. Pappas, A. Nazarov, D. Stevenson, S. Voran, M. E. Read, E. 

M. Gormley, J. Cash, K. Marr, and J. Ryan, “Second Harmonic 

Magneto-Resistive Imaging to Authenticate and Recover Data 

from Magnetic Storage Media,” Journal of Electronic Imaging 

14 (1): Art. No. 013015 Jan.-Mar. 2005.

Pappas D.P., Arnold C.S., “Application of W-Re thermocouples 

for in situ ultrahigh vacuum use over a wide temperature range,” 

Review of Scientifi c Instruments 76 (1): Art. No. 016104, 

Jan. 2005.

(a)

(b)
54 Electronics and Electrical Engineering Laboratory

Stutzke NA, Russek SE, Pappas DP, Tondra M, “Low-frequency 

noise measurements on commercial magnetoresistive magnetic 

fi eld sensors,” Journal of Applied Physics 97 (10): Art. No. 

10Q107 Part 3, May 15, 2005.

Martinis JM, Cooper KB, McDermott R, Steffen M, Ansmann 

M, Osborn KD, Cicak K, Oh S, Pappas DP, Simmonds RW, 

Yu CC, “Decoherence in Josephson qubits from dielectric 

loss,” Physical Review Letters 95 (21): Art. No. 210503, Nov. 

18, 2005.

Oh S, Cicak K, McDermott R, Cooper KB, Osborn KD, Simmonds RW, Steffen M, Martinis JM, Pappas DP, “Low-leakage 

superconducting tunnel junctions with a single-crystal Al2O3 

barrier,” Superconductor Science & Technology 18 (10): 1396-

1399, Oct. 2005.

McDermott R, Simmonds RW, Steffen M, Cooper KB, Cicak 

K, Osborn KD, Oh S, Pappas DP, Martinis JM, “Simultaneous 

state measurement of coupled Josephson phase qubits,” Science 

307 (5713): 1299-1302, Feb. 25 2005.

R. W. Simmonds, K. M. Lang, D. A. Hite, S. Nam, D. P. Pappas, and J. M. Martinis, “Decoherence in Josephson Phase 

Qubits from Junction Resonators,” Physics Review Letters. 

93, 077003/1-4 (August 2004).

K. M. Lang, D. A. Hite, R. W. Simmonds, R. McDermott, D. P. 

Pappas, and J. M. Martinis, “Conducting Atomic Force Microscopy for Nanoscale Tunnel Barrier Characterization,” Review 

Scientifi c Instrumentation 75, 2726-2731 (August 2004).

Cooper KB, Steffen M, McDermott R, Simmonds RW, Oh S, 

Hite DA, Pappas DP, Martinis JM, Observation of quantum 

oscillations between a Josephson phase qubit and a microscopic 

resonator using fast readout,” Physical Review Letters 93 (18): 

Art. No. 180401, Oct. 29 2004.

D. P. Pappas, F. da Silva, R. N. Clarke, J. Unguris, W. C. Uhlig, 

and A. Kos, “Zigzag Shaped Magnetic Sensors,” Applied Physics Letters 85 (24): 6022-6024, Dec. 13 2004.

M. G. Pini, A. Rettori, D. P. Pappas, A. V. Anisimov, and A. P. 

Popov, “Surface Magnetic Canting in a Nonuniform Film,” J. 

Magn. Magn. Mater. 272-276, 1152-1153 (May 2004).

B. L. Zink, K. D. Irwin, G. C. Hilton, D. P. Pappas, J. N. Ullom, 

and M. E. Huber, “Lithographically Patterned Magnetic Calorimeter X-ray Detectors with Integrated SQUID Readout,” Nucl. 

Instrum. Methods Phys. Res. A 520, 52-55 (March 2004).

Nazarov AV, da Silva FCS, Pappas DP, “Arrays of magnetoresistive sensors for nondestructive testing,” Journal of Vacuum 

Science & Technology A 22 (4): 1375-1378, Jul.-Aug. 2004.
Quantum Electrical Metrology Division 55

APPENDIX A: TOPICS COVERED BY

ORGANIZATIONAL UNITS

The following table shows which organizational unit(s) work on each of the research topics covered in this book. For information on the staff of the organizational units, please see 

Appendix C.

Topic Group Name Project Name Project Leader

QUANTUM STANDARDS

Quantum Voltage

Fundamental 

Electrical

Measurements

Voltage Metrology Yi-hua Tang

Quantum Devices Quantum Voltage Samuel Benz

AC-DC Difference 

Standards and 

Measurement 

Techniques

Fundamental Electrical 

Measurements

AC-DC Difference 

Standards and

Measurement 

Techniques

Thomas Lipe

Single Electronics 

for Standards and 

Metrology

Fundamental Electrical 

Measurements

Single Electron 

Tunneling Neil Zimmerman

Quantum Devices Quantum Information

And Measurements Robert Schwall

Metrology of the Ohm Fundamental Electrical 

Measurements

Metrology of the 

Ohm Rand Elmquist

Farad and Impedance 

Metrology

Applied Electrical 

Metrology

Farad and Impedance 

Metrology Yicheng Wang

The Electronic 

Kilogram

Fundamental Electrical 

Measurements

The Electronic 

Kilogram Richard Steiner

Josephson-based Noise 

Thermometry Quantum Devices Quantum Voltage Samuel Benz

Electric Power 

Metrology

Applied Electrical 

Metrology

Electric Power 

Metrology Thomas Nelson

QUANTUM MEASUREMENTS

Quantum Computing 

Using Integrated 

Josephson Junction 

Circuits

Quantum Devices Quantum Information 

and Measurements Robert Schwall

Magnetic Sensors & 

Quantum Materials Quantum Devices

Advanced Magnetic 

and Quantum 

Materials

David Pappas

Quantum Sensors Quantum Devices Quantum Sensors Kent Irwin
56 Electronics and Electrical Engineering Laboratory
Quantum Electrical Metrology Division 57

APPENDIX B: QUANTUM ELECTRICAL METROLOGY

DIVISION CALIBRATION SERVICES

The Quantum Electrical Metrology Division provides a number of for-fee calibration services 

of electrical standards. Below is an abbreviated listing of those services. More information, 

including a fee schedule can be found in the NIST Calibration Services Users Guide SP250 

available from the Calibration Program at NIST, (301) 975-2002, calibrations@nist.gov, or on 

the Web at: http://ts.nist.gov/ (click on “Calibrations,” then “Electromagnetic”).

Information about the availability and shipping requirements for the Quantum Electrical Metrology Division services listed below may be obtained by contacting Denise D. Prather, (301) 

975-4221, denise.prather@nist.gov. Technical information may be obtained by contacting the 

specifi c technical representatives listed below for each service.

A. Resistance Measurements

 A.1 DC Resistance Standards ............................ Randolph E. Elmquist (301) 975-6591

 and Measurements

 A.2 High-Voltage Standard ...................................Gerald J. FitzPatrick (301) 975-8922

 Resistors

B. Impedance Measurements

 (Except Resistors)

 B.1 Low-Frequency Capacitance ......................... Andrew D. Koffman (301) 975-4518

 and Inductance Measurements ................................Yicheng Wang (301) 975-4278

 and Standards

C. Voltage Measurements

 C.1 DC Voltage Measurements ..........................................Yi-hua Tang (301) 975-4691

 and Standards

 C.2 AC Voltage Measurements .....................................Mark E. Parker (301) 975-2413

 David I. Bergman (301) 975-4664

 C.3 AC-DC Thermal Voltage and ................................Thomas E. Lipe (301) 975-4251

 Current Converters (to 1 GHz)

D. Precision Ratio Measurements

 D.1 Inductive Dividers ......................................................Scott Shields (301) 975-2432

 D.2 Resistance Dividers ........................................Gerald J. FitzPatrick (301) 975-8922

E. Phase Meters and Standards and ..................................Mark E. Parker (301) 975-2413

VOR Measurements ...................................................... Nile M. Oldham (301) 975-2408

F. Power and Energy Measurements ...........................Thomas L. Nelson (301) 975-2986

Low-Frequency
58 Electronics and Electrical Engineering Laboratory

APPENDIX C: QUANTUM ELECTRICAL METROLOGY

DIVISION STAFF AND PHONE NUMBERS

(OCTOBER 2006)

DIVISION OFFICE 

2431 Olthoff, James (Chief)

2400 Grove, Sharon (Secretary)

4044 Tasker, Amy (Administrative Offi cer)

4941 Dorsey, Roy

4221 Prather, Denise 

4223 Belecki, Norman

FUNDAMENTAL ELECTRICAL

MEASUREMENTS (817.01) 

(GAITHERSBURG)

4228 Newell, David (Group Leader)

2737 Williamson, Laura (Secretary)

METROLOGY OF THE OHM

6591 Elmquist, Randolph (Project Leader)

4240 Jarrett, Dean

4225 Jones, George

4239 Kraft, Marlin

VOLTAGE METROLOGY

4691 Tang, Yi-hua (Project Leader)

4238 Sims, June

4246 Jaiswal, Shiv Kumar

THE ELECTRONIC KILOGRAM

4226 Steiner, Richard (Project Leader)

6555 Williams, Edwin

6556 Liu, Ruimin

SINGLE ELECTRON TUNNELING (SET)

5887 Zimmerman, Neil (Project Leader)

4690 Hourdakis, Emanouel

AC-DC DIFFERENCE STANDARDS

AND MEASUREMENT TECHNIQUES

4251 Lipe, Thomas (Project Leader)

4250 Kinard, Joseph

APPLIED ELECTRICAL METROLOGY

(817.02) (GAITHERSBURG)

8922 FitzPatrick, Gerald (Group Leader)

2403 Lainez, Zulma (Secretary)

FARAD AND IMPEDANCE METROLOGY

4278 Wang, Yicheng (Project Leader)

4518 Koffman, Andrew

2441 Palm, Robert

4232 Shields, Scott

2438 Waltrip, Bryan

3922 Avramov-Zamurovic, Svetlana

4237 Chang, Yui-May

4231 Lee, Lai

ELECTRIC POWER METROLOGY

2986 Nelson, Thomas (Project Leader)

4464 Bergman, David

2413 Parker, Mark

2440 Stenbakken, Gerard

2438 Waltrip, Bryan

2412 Laug, Owen 

2413 Fulcomer, Michael

2407 Oldham, Nile

2417 Petersons, Oskars

2406 Souders, Michael

2416 Zhou, Ming

QUANTUM DEVICES (817.03) 

(BOULDER)

5081 Rudman, David (Group Leader)

4724 Filla, Mary (Secretary)

3776 Harris, Richard

QUANTUM VOLTAGE

5258 Benz, Sam (Project Leader)

4760 Baek, Burm

3906 Burroughs, Charlie

5211 Dresselhaus, Paul

4218 Hadacek, Nicolas

3740 Hamilton, Clark
Quantum Electrical Metrology Division 59

QUANTUM VOLTAGE (CONTINUED)

5335 Kieler, Oliver

5312 Landim, Regis

5310 Rogalla, Horst

4853 Veening, Thijs

QUANTUM SENSORS

5911 Irwin, Kent (Project Leader)

5989 Beall, James

4463 Doriese, William

3811 Duncan, William

4391 Ferriera, Lisa

5679 Hilton, Gene

4380 Horansky, Robert

3402 Huber, Martin

4834 Mates, Ben

4576 Miller, Nathan

4794 O’Neil, Galen

4983 Rahman, Rezwan

5052 Reintsema, Carl

4743 Schmidt, Dan

4985 Sultan, Rubina

4408 Ullom, Joel

5121 Vale, Leila

7894 Xu, Yizi

4320 Zink, Barry

QUANTUM INFORMATION AND MEASUREMENTS

4732 Schwall, Robert (Project Leader)

4832 Allman, Shane

4858 Altomare, Fabio

4137 Aumentado, Jose

5344 Bergren, Norman

4606 Cicak, Katarina

3391 Kautz, Richard

5430 Keller, Mark

4378 Lang, Kristine

3021 Naaman, Ofer

4325 Osborn, Kevin

4995 Park, Jae

4410 Sillanpaa, Mika

4403 Simmonds, Ray

4772 Sirois, Adam

4905 Spietz, Lafe

4617 Strong, Josh

4826 Whittaker, Jed

ADVANCED MAGNETIC & QUANTUM

MATERIALS

3374 Pappas, David (Project Leader)

3873 DaSilva, Fabio

3374 Fardi, Hamid

4651 Halloran, Sean

4795 Kline, Jeffrey

4655 Oh, Seongshik

4726 Yuan, Lu

QUANTUM FABRICATION FACILITY

5081 Rudman, David

5989 Beall, James

5049 Crews, Margaret

7064 Koch, Jonathan

Email Address for all staff is:

Firstname.lastname@nist.gov (Gaithersburg)

Firstname.lastname@boulder.nist.gov 

(Boulder)

Telephone Numbers for all staff are:

301-975-XXXX (for Gaithersburg)

303-497-XXXX (for Boulder)
60 Electronics and Electrical Engineering Laboratory

APPENDIX D: POST-DOCTORAL RESEARCH

ASSOCIATESHIPS

The National Institute of Standards and Technology (NIST), in cooperation with the National 

Research Council, offers awards for postdoctoral research in the fi elds described in this booklet. 

These awards provide a select group of scientists and engineers an opportunity for research in 

many of the areas that are of deep concern to the scientifi c and technological community of the 

nation. NIST, with direct responsibilities for the nation’s measurement network, involves its 

laboratories in the most modern developments in the physical, engineering, and mathematical 

sciences and the technological developments that proceed from them.

These activities, comprising a broad spectrum of interests in basic and applied science, engineering, and technology, involve many disciplines. NIST affords great freedom and an opportunity 

for both interdisciplinary research and research in well-defi ned disciplines.

The technical activities of NIST are conducted in its laboratories, which are based in Gaithersburg, a large complex of modern laboratory buildings in a Maryland suburb of metropolitan 

Washington, DC, and at a modern, equally well-equipped facility in Boulder, Colorado. NIST 

has a staff of approximately 3,000 people, of which more than 55% are technical personnel.

Included on the following pages are the opportunities available in the Quantum Electrical Metrology Division. They are listed separately for the two locations in the Division, Boulder and 

Gaithersburg. For each opportunity a reference number is provided as well as the location.

Interested applicants should contact the advisors shown. All opportunities for NIST and application materials can be found at the National Research Council web site at http://www4.nas.

edu/pga/rap.nsf/. There are two competitions per year with fi nal applications due by February 

1 and August 1. Forty awards are made in the February competition and 20 in August. Please 

allow at least a month in advance of the deadlines to contact the advisor and prepare the application because a research proposal is required.

OPPORTUNITIES IN BOULDER, COLORADO

A CAPACITANCE STANDARD BASED ON COUNTING ELECTRONS

50.81.42.B4762 Boulder CO 80303

Adviser Information:

Keller, Mark William

(303) 497-5430

keller@boulder.nist.gov 

Modern metrology is moving toward quantum measurement standards, such as atomic clocks, 

that provide a natural basis for our system of units. We are currently working toward a method 

for determining capacitance in terms of the electron charge. We do this simply by placing N 

electrons onto a capacitor, measuring the resulting voltage V, and thus determining C = Ne/V, 

where e is the electron charge. We use a unique cryogenic, vacuum-gap capacitor, and the 

electrons are counted using single-electron tunneling (SET) devices operating at temperatures 

below 1 K. The current version of the standard has an estimated uncertainty of less than 1 partper-million when compared with NIST’s primary standard. Future work in this area will focus 

on determining the ultimate uncertainty of this method, more direct comparisons with primary 

standards, and the construction of a robust, automated version of the standard. The development 

of this new standard is expected to have impacts spanning practical metrology, our knowledge 

of fundamental constants, and the fundamental basis of electrical units. Facilities include a clean 
Quantum Electrical Metrology Division 61

room for fabricating SET devices, a custom cryostat for the capacitance standard, and custom 

capacitance bridges for making accurate comparisons with other standards.

APPLICATIONS OF SUPERCONDUCTING INTEGRATED CIRCUITS AND JOSEPHSON

JUNCTION ARRAYS

50.81.42.B4376 Boulder CO 80303

Adviser Information:

Benz, Samuel P.

(303) 497-5258

benz@boulder.nist.gov

Dresselhaus, Paul D.

(303) 497-5211

haus@boulder.nist.gov

We are studying and developing Josephson junctions for use in voltage standard and other 

applications of integrated superconductive circuits. Our project leads the fi eld in their implementation into systems. Some of these systems include voltage standards, digital-to-analog 

converters, and arbitrary waveform synthesizers. One current focus is on the construction of 

a pulse-quantized arbitrary waveform synthesizer to be used as an ac and dc voltage standard 

source and for other applications that require digitally synthesized waveforms with precise 

control of voltage, frequency, and phase. Another focus is the fabrication and study of lumped 

arrays of stacked Josephson junctions. These three-dimensional circuits will be implemented 

in the next generation voltage standard. Applicants should be interested in some or all of the 

following areas: nanofabrication, superconductive device physics, broadband (dc-20 GHz) 

circuit design and construction, digital waveform synthesis, and cryogenic packaging.

HIGH-RESOLUTION MICROCALORIMETERS FOR X-RAY MICROANALYSIS

50.81.42.B3588 Boulder CO 80303

Adviser Information:

Hilton, Gene C.

(303) 497-5679

hilton@boulder.nist.gov

Irwin, Kent David

(303) 497-5911

irwin@boulder.nist.gov

Reintsema, Carl D.

(303) 497-5052

reintsema@boulder.nist.gov

As the size scale of microelectronics continues to shrink well below 1 μm, current semiconductor-based energy-dispersive spectrometers (EDS) on scanning electron microscopes can no 

longer provide the resolution needed to evaluate these structures. We are developing a highresolution microcalorimeter-based EDS that provides revolutionary new capabilities for X-ray 

microanalysis. Microcalorimeter EDS provides more than an order of magnitude improvement 

in energy resolution (to 2 eV) compared to commercial semiconductor EDS, with good collection area (4 mm2 effective area with the use of an X-ray polycapillary optic lens) and count 

rate (500 s-1). The spectrometer system consists of a superconducting transition-edge sensor 

microcalorimeter cooled by a compact adiabatic demagnetization refrigerator and instrumented 
62 Electronics and Electrical Engineering Laboratory

by a SQUID current amplifi er. These unique superconducting electronics are fabricated in our 

state-of-the-art clean room. Using our microcalorimeter EDS mounted on a scanning electron 

microscope, we have resolved closely spaced X-ray peaks in complicated spectra and have 

made the fi rst energy-dispersive chemical shift measurements. The excellent performance of 

this system enables a wide range of research opportunities in X-ray microanalysis, including 

improved particle analysis, chemical bonding state analysis, and synchrotron-based measurements. Work is also underway to dramatically increase the collection area and count rate of 

the system using arrays of detectors read out with superconducting multiplexer, which will 

dramatically increase throughput and open new applications in real-time, in-process monitoring and process-stream monitoring.

PHYSICS AND APPLICATIONS OF SINGLE ELECTRON TUNNELING DEVICES

50.81.42.B3586 Boulder CO 80303

Adviser Information:

Keller, Mark William

(303) 497-5430

mark.keller@boulder.nist.gov 

Single electron tunneling (SET) devices are based on nanofabricated tunnel junctions operated 

at temperatures below 1 K, where the charging energy for a single electron dominates thermal 

fl uctuations. By using gate voltages to control the charging energy, individual tunneling events 

can be manipulated very precisely, allowing control of individual electrons. We have developed 

and now routinely operate devices in which the error per tunnel event is of order 1 part per 

billion, a world’s best by several orders of magnitude. Our research goals are to understand the 

fundamental physics of SET phenomena and to construct practical SET circuits for applications 

in metrology and other areas. Examples include electron pumps for accurate electron counting, 

new SET transistors for ultrasensitive electrometry, and SET-based direct measurements of the 

properties of single molecules for use in molecular electronics. Facilities include electron-beam 

lithography, extensive microfabrication, micromachining and vacuum deposition equipment, 

and two dilution refrigerators equipped for measurements up to GHz frequencies.

QUANTUM COMPUTING USING SUPERCONDUCTING DEVICES

50.81.42.B4764 Boulder CO 80303

Adviser Information:

Schwall, Robert E.

(303) 497-4732

schwall@boulder.nist.gov

Simmonds, Raymond

(303) 497-4403

simmonds@boulder.nist.gov

A new class of powerful computation algorithms have been proposed based on logic operations using quantum mechanical systems or quantum bits (qbits). Experimental implementation 

will require qbit coherence times long enough to perform single qbit manipulations, controlled 

interactions of multiple qbits, and state measurements. While the most dramatic progress to 

date has been made with trapped-ion systems, solid-state quantum devices should in principle 

have distinct advantages for the creation of a practical large-scale “quantum computer.” Using 

our state-of-the-art superconducting fabrication facility, we have improved the operation of a 

Josephson junction based phase qubit by incorporating it into a superconducting loop. This 
Quantum Electrical Metrology Division 63

has allowed us to further decouple the qubit from its environment and has eliminated quasiparticle-heating effects. Recent improvements in the fabrication of the Josephson junctions have 

produced a dramatic increase in the overall performance of qubits. Research opportunities 

include materials characterization for Josephson junctions, fabricating novel superconducting 

qubit devices, exploring the physics of coherence and coupling between qubits, and engineering multi-qubit devices. Our goal is to fabricate high quality Josephson junction based qubits 

for the eventual use in a 100 to 1000 qubit quantum computer.

SUPERCONDUCTING DETECTORS FOR X-RAY THROUGH MILLIMETER PHOTONS

50.81.42.B3587 Boulder CO 80303

Adviser Information:

Irwin, Kent David

(303) 497-5911

irwin@boulder.nist.gov

Reintsema, Carl D.

(303) 497-5052

reintsema@boulder.nist.gov

Hilton, Gene C.

(303) 497-5679

hilton@boulder.nist.gov

Cryogenic detectors and electronics provide unprecedented sensitivity and energy resolution for 

the detection of photons. We are developing novel low-temperature (100 mK) superconducting microcalorimeters and bolometers for the detection of photons from X-rays to millimeter 

waves. These devices, fabricated in our state-of-the-art clean room, consist of superconducting 

transition-edge sensors on micromachined structures. They are read out using unique highspeed, low-noise SQUID preamplifi ers designed and fabricated here. Using these devices, we 

have demonstrated the highest energy resolution achieved with an energy-dispersive X-ray 

detector, and one of the most sensitive detectors of incident infrared/submillimeter power. We 

are employing these detectors in a system for X-ray microanalysis of materials on a scanning 

electron microscope. We are also developing arrays of X-ray microcalorimeters and infrared/

submillimeter bolometers for astronomy and other applications. Research opportunities include 

improving our understanding of the nonequilibrium superconducting processes underlying 

the performance of superconducting detectors, developing novel micromachined structures to 

integrate detector arrays, developing and testing detector arrays, developing multiplexed superconducting integrated circuits for the readout of large arrays, and developing the fi rst uses 

of these detectors in astronomy and other applications.

SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE DEVELOPMENT

50.81.42.B5189 Boulder CO 80303

Adviser Information:

Irwin, Kent David

(303) 497-5911

irwin@boulder.nist.gov

Reintsema, Carl D.

(303) 497-5052

reintsema@boulder.nist.gov
64 Electronics and Electrical Engineering Laboratory

Hilton, Gene C.

(303) 497-5679

hilton@boulder.nist.gov

We are developing superconducting electronics for applications in the measurement of electromagnetic signals. Our main focus is on the development of superconducting quantum interference device (SQUID) circuits to multiplex signals from superconducting microcalorimeters and 

bolometers. SQUID multiplexers are a practical requirement for the successful deployment of 

large-format cryogenic detector arrays for X-ray microanalysis and X-ray through millimeterwave astronomy. We are also investigating other novel directions including the SQUID operational amplifi er and the development of susceptometers for magnetic calorimeters. Research 

opportunities involve improving the noise and bandwidth of these devices, fabricating SQUID 

circuits in our state-of-the-art superconducting fabrication facility, developing high-performance 

room-temperature electronics to drive our superconducting circuits, and exploring the device 

physics of SQUID circuits.

OPPORTUNITIES IN GAITHERSBURG, MD

“ELECTRONIC KILOGRAM” – THE SI DETERMINATION OF THE RATIO OF THE

MECHANICAL WATT TO THE ELECTRICAL WATT

50.81.11.B1491 Gaithersburg MD 20899

Adviser Information:

Steiner, Richard L.

(301) 975-4226

richard.steiner@nist.gov

Williams, Edwin R.

(301) 975-4206

williams@nist.gov

This experiment uses an electromagnetic force balance to measure the unit of power, the Watt, 

with a 0.01 ppm uncertainty, by determining the practical relation of the units Volt (Josephson 

effect) and Ohm (Quantum Hall effect) in terms of their theoretical representations in the SI 

units Meter (laser), Second (atomic clock), and Kilogram (artifact standard). This determines 

the Planck constant and the electron mass and has the potential to electronically monitor and 

redefi ne the Kilogram, the last artifact-based unit. Monitoring the Kilogram is a signifi cant 

goal pursued by only a few of the best international standards laboratories. The broad range of 

precision measurements involves force and mass (mechanical design, local gravity determination), velocity and position (optical interferometry), and voltage and current (electromagnetism, superconductivity). Applicants need a strong familiarity in classical electromagnetism, 

mechanics, electronics, and optics, while experience with superconductivity, electromagnetic 

interference, vibration isolation, and instrumentation programming is also useful.

CAPACITANCE STANDARDS AND AC MEASUREMENTS

50.81.11.B5185 Gaithersburg MD 20899

Adviser Information:

Wang, Yicheng

(301) 975-4278

yicheng.wang@nist.gov

The Quantum Electrical Metrology Division ties the US legal system of electrical units for capacitance, inductance, and resistance to the SI system of units. First, we realize the SI farad from 
Quantum Electrical Metrology Division 65

the SI meter through the calculable capacitor whose capacitance depends on only one length. 

We then realize the SI henry from a Maxwell-Wien bridge and the SI ohm from a quadrature 

bridge. However, routine calibrations demanded by the evolving industry call for research beyond these classical experiments used for the realization of the electrical units. Current research 

focuses on the frequency dependence, in the audio frequency range from 50 Hz to 20 kHz, of 

capacitance standards including the calculable capacitor, toroidal cross capacitors, and fusedsilica capacitors. In close collaboration with other staff, we are also pursuing two alternative 

representations of the farad: (1) an ac Quantum Hall Resistor with a quadrature bridge and (2) 

a single electron pump with a cryogenic capacitor. To fully take advantage of these quantum 

effects, classical precision ac bridge methods must be re-examined and automated whenever 

possible.

FUNDAMENTAL CONSTANTS, PRECISION MEASUREMENTS, AND ELECTRICAL UNITS

50.81.11.B1490 Gaithersburg MD 20899

Adviser Information:

Williams, Edwin R.

(301) 975-4206

williams@nist.gov

Steiner, Richard L.

(301) 975-4226

richard.steiner@nist.gov

The Division is engaged in research on methods to improve accuracies of fundamental physical 

constants and to develop better and more accurate techniques for measuring and maintaining 

basic electric units. Research includes developing nuclear magnetic resonance-based current 

and voltage standards, and measurements of absolute ampere, absolute volt, absolute farad 

and ohm, quantized-Hall resistance, and fi ne-structure constant. We are particularly interested 

in refi ning our current techniques and/or initiating new experiments to increase knowledge of 

these quantities or other constants of comparable importance, especially those involving the 

electrical units.

PHYSICS OF JOSEPHSON JUNCTIONS AT MICROWAVE FREQUENCIES AND PRECISION

VOLTAGE MEASUREMENT

50.81.11.B1494 Gaithersburg MD 20899

Adviser Information:

Steiner, Richard L.

(301) 975-4226

richard.steiner@nist.gov

The physics of Josephson junctions, driven at microwave or millimeter wave frequencies of 

15-20 and 70-95 GHz, has important applications to ultrahigh precision voltage measurements 

in support of several other experiments. Adversely affecting the desired voltage stability are 

behaviors such as complex frequency response in series-array Josephson junctions, noise induced instability of the quantized voltage steps, and the generation of Shapiro voltage steps 

at fractional values. Related applications in voltage measurement include the characterization 

of noise or externally induced (pressure, humidity) effects in electronic, Zener-diode based, 

instrumentation at nanovolt levels for normal measurement frequencies (10 mHz-1 kHz), and 

nonlinear, unpredictable behavior for longer times (1 mHz and below).
66 Electronics and Electrical Engineering Laboratory

Research facilities include several Josephson array voltage calibration systems; temperature 

and humidity test chamber; low noise, phase-locking microwave sources; a high-resolution 

spectrum analyzer; an assortment of high-precision voltage, frequency, and electrical reference 

instrumentation; and various waveguide-equipped probes and magnetically shielded Dewars 

for cryogenic measurements.

QUANTUM HALL EFFECT

50.81.11.B1496 Gaithersburg MD 20899

Adviser Information:

Elmquist, Randolph Ellis

(301) 975-6591

elmquist@nist.gov

The Quantum Electrical Metrology Division is involved in a continuing research program on the 

quantum Hall effect, with emphasis placed on using it to maintain the US legal unit of resistance 

and to determine the fi ne structure constant to the highest possible accuracy. Any experiments 

that would further the understanding of the quantum Hall effect or explore its limitations would 

be of interest. Such experiments could include temperature and current dependence, current 

distribution (edge and bulk effects), voltage quantization (breakdown effect), and ac quantized 

Hall resistance measurements that lead to ac impedance standards. Theoretical studies are also 

needed in all of these areas.

The apparatus consists of two 16-T persistent-current superconducting magnets, a top-loading He-3 refrigerator, a variable temperature insert, and automated quantized Hall resistance 

measurement systems with parts-per-billion uncertainties.

In support of this research, a clean-room sample preparation facility has been installed that is 

equipped with a micrometer photo-mask aligner, wire bonder, annealing oven, and probe test 

station as required for the defi nition, mounting, ohmic contracting, and room-temperature testing of semiconductor samples for quantum Hall experiments.

RESISTANCE COMPARISONS FOR FUNDAMENTAL ELECTRICAL STANDARDS

50.81.11.B5186 Gaithersburg MD 20899

Adviser Information:

Elmquist, Randolph Ellis

(301) 975-6591

elmquist@nist.gov

Converting single-electron tunneling (SET) devices into next-generation usable precision 

electronic will require precise cryogenic current-multiplication and a better understanding 

of highly resistive thin fi lms. Our work would be aided by fabrication of improved thin-fi lm 

resistance-material devices and studies of mesoscopic processes contributing to resistive noise 

at low temperature. This research would contribute to development of a precision three-way 

comparison of the SET current, lead to better measurements of Planck’s constant, and improve 

the uncertainty of precision SET-based current sources.
Quantum Electrical Metrology Division 67

SINGLE ELECTRON EFFECTS

50.81.11.B1492 Gaithersburg MD 20899

Adviser Information:

Zimmerman, Neil M.

(301) 975-5887

neilz@nist.gov

In nanoscale electronic circuits, we can observe Coulomb blockade or single electron tunneling 

(SET) effects. For metrological applications, the basic device is the single electron pump, which 

allows control of electrical fl ow in units of 1 e. This device enables accurate measurements of 

electrical current or charge. The Quantum Electrical Metrology Division studies such effects 

and their implications for precision metrology of the electrical units. We are pursuing two goals, 

both in close collaboration with our Boulder location. The fi rst involves using the electron 

pump to charge up a cryogenic capacitor. Then, by comparison to the Calculable Capacitor and 

Josephson Volt experiments, we will make metrological measurements of the electrical charge, 

e, or the fi ne structure constant. Our second goal is to investigate ways to increase the value of 

the current, for use as a direct current standard. Our current approach is to use Si-based SET 

pumps, which hold the potential to be parallelized.

THE ELECTRONICS AND ELECTRICAL

ENGINEERING LABORATORY

One of NIST’s seven Measurement and Standards Laboratories, EEEL conducts research, provides measurement services, and helps set standards in support of: the fundamental electronic technologies of semiconductors, magnetics, and superconductors; information and communications technologies, such as fi ber optics, photonics, microwaves, electronic displays, and electronics manufacturing supply chain collaboration; forensics and security measurement instrumentation; fundamental and practical physical standards and measurement services for electrical quantities; maintaining the quality and integrity of electrical power systems; and the development of nanoscale and microelectromechanical devices. EEEL provides support to law enforcement, corrections, and criminal justice agencies, including homeland security. EEEL consists of four programmatic divisions and two matrixmanaged offi ces:Semiconductor Electronics DivisionOptoelectronics DivisionQuantum Electrical Metrology DivisionElectromagnetics DivisionOffi ce of Microelectronics ProgramsOffi ce of Law Enforcement StandardsThis document describes the technical programs of the Quantum Electrical Metrology Division. Similar documents describing the other Divisions and Offi ces are available. Contact NIST/EEEL, 100 Bureau Drive, MS 8100, Gaithersburg, MD 20899-8100, Telephone: (301) 975-2220, On the Web: www.eeel.nist.gov