It has long been recognized that the basic units in science - such as the second and the kilogram - should be defined in terms of fundamental physical phenomena. However, it took over a century for the metre and the second to be defined in terms of the quantum properties of atoms. And it was only in 1990 that reproducible standards of voltage and resistance were linked to quantum phenomena.
Now Mark Keller and co-workers at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, have developed a technique to set up a new standard for capacitance that is based on the quantum tunnelling of single electrons (Science 1999 285 1706).
Terry Quinn of the International Bureau of Weights and Measures in Sèvres, France describes why this technique could represent a significant step forward in electrical metrology in the November issue of Physics World magazine.