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 flow of superconducting flux 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.
|
Quantity |
Quantum |
Magnitude |
|
Voltage |
Magnetic flux quantum |
h/2e |
|
Current |
Single electon |
e |
|
Resistance |
Resistance quantum |
e2/h |
|
Time and Frequency |
Atomic transition of a Cs atom |
9.12631770 GHz |
|
Length |
Wavelength of a HeNe laser |
632.99139822 nm |
|
Constant |
Symbol |
Magnitude |
|
Planck constabt |
h |
6.625 0693 x 10-34 J s |
|
Elementary charge |
e |
1.602 176 53 x 10-19 C |
|
ltzmann constant |
kB |
1.380 6505 x 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 definitive 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 first 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 definition 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.}