New Electrical Standards

by David Bradley

Dr John Gallop of the National Physical Laboratory also pointed out how metrology has developed over the last thirty five years, emphasising the development of an unexpected plethora of simple quantum electrical standards that can realise all three of the classical electrical measurements - voltage, resistance, and current. First, came a voltage standard based on the Josephson alternating current effect. This was followed a decade later by the quantised Hall effect, based on the von Klitzing constant which allows the unit of electrical resistance, the ohm, to be maintained very precisely. It became apparent twenty years ago that a quantum current standard might also be possible.

These three - voltage, resistance, and current, - taken together, define the Quantum Electrical Triangle of standards, explained Gallop. Today all three units are defined in terms of different combinations of just two quantities - the value of the charge on an electron and the Planck constant.

He summarised the modern physics of condensed matter systems at low temperatures that underpins the three modern standards and showed the stark contrast between the classical views of current, voltage and resistance with which physics worked for two hundred years.

While the present standards increasingly rely on quantum understanding, in the future ultra-low temperature and nanoscale measurements will allow truly quantum mechanical versions of the standards to be developed. Such an improvement in knowledge might yet unify voltage, resistance, and current in a single standard.

Read on... Weighing up the new kilogram