Physikalisch-Technische Bundesanstalt

Tasks

In the department „Electrical Quantum Metrology“ macroscopic quantum effects are utilized to relate the electrical units

• ampere (A) and coulomb (C) for the quantities electrical current and charge
  
  
• volt (V) for the quantity voltage
  
  
• ohm (Ω) for the quantity resistance

to fundamental constants and to reproduce them with extremely low uncertainties.

The maintenance and dissemination of the unit of resistance, ohm (Ω), is based on the
quantum Hall effect. By operating quantum Hall resistors with ac-current it is possible to relate
an ac-impedance directly to fundamental constants which allows to reproduce the unit of
capacitance, the Farad (F), on the basis of these constants.

The maintenance and dissemination of the unit volt is based on the Josephson effect. Switchable
Josephson arrays allow the reproduction of practically arbitrary voltages (up to 10 Volt) with
quantum precision, as well as the synthesis of low frequency ac-voltages.

The reproduction of the units ampere and coulomb based on the effect of single electron tunneling
is still under development. It may allow to define in future the unit ampere by fixing the value of the
fundamental constant e, the ‚elementary charge’. Newly developed classical methods can already
now be used for traceable measurements of small currents which are measured at levels of 10 pA
and less with a worldwide unrivalled low uncertainty.

Working Groups

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