Quantum metrology and fundamental constants: international school at Les Houches Physics Centre, 1st to 12 October 2007.
> Highlights (291 Ko)
Electrical quantities are defined in the International System of Units (SI) in relation to the ampere, but practical realization of these definitions with a high degree of accuracy is very difficult and does not meet the requirements of modern instruments, which require increasingly stable and reproducible electrical standards. Over the last 20 years, work on the quantum effects of electron transport has shown the feasibility of replacing material standards with more stable and reproducible quantum standards and has made quantum electrical metrology possible. Measuring these standards involves universal physical constants, such as the electron charge e and the Planck constant h.
Since the early 1990s, the International Comittee for Weights and Measures (CIPM) has recommended using the Josephson effect (JE) and the quantum Hall effect (QHE) to develop voltage and resistance standards respectively. More recently, the single-electron tunnelling (SET) effect has opened up new possibilities for developing a current standard. In this context, the new quantum standards offer hitherto unequalled levels of reproducibility.
LNE has launched studies to define the properties of nanometric devices used to maintain voltage and resistance units. Since the quantum phenomena involved are observed in specific experimental conditions, special cryogenic current comparators (CCCs) have been developed at the Laboratory.
LNE is also carrying out innovative studies on programmable Josephson arrays and on the development of Hall bar arrays using advanced lithography techniques. A quantum current standard (based on the single-electron tunnelling effect) is also being finalized in the context of the metrological triangle experiment, which consists in developing a quantum Ohm's law from the three effects (JE, QHE and SET). The principal goal of this experiment is to test, with a relative uncertainty of 10-8, the consistency of the constants and their implied values in the three quantum phenomena. It should eventually be possible to represent certain electrical units in terms of universal constants (h, e ).