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Task of this metrology project is the implementation of a new capacitance
standard which is based on the quantization of electrical charge in units of
the elementary charge e.
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The basic idea of the experiment is to charge a capacitor with a well-known number of n electrons and to measure the resulting electrical
voltage U. Thus, the capacitance C of the capacitor is determined by
C = ne / U. Accurate "counting" of the electrons occurs with the help of
a special Single-Electron Tunneling (SET) circuit, a so-called SET-pump.
If the voltage U is measured by using a Josephson voltage standard
(U = ifh / 2e), the capacitance C can be expressed exclusively in terms
of the fundamental constants e and h, the frequency f and integer
numbers (n and i). Thus, the experiment enables electrical capacitance
metrology on quantum basis, as it is already usual for the electrical
voltage U (using the Josephson effect) and the electrical resistance R
(using the quantum Hall effect).
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Quantum-Based
Capacitance Standard
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If the experiment is performed with a relative uncertainty of 10-7
(0.1 ppm), it opens a way to realize the "quantum metrological triangle"
which is a consistency test for the three electrical quantum effects
involved. The results of this experiment will impact on a future system of
units which will be based on fundamental constants.
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Quantum Metrological
Triangle
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© Physikalisch-Technische Bundesanstalt
Page created: 2006-09-28, last update:20.2.2008 , Susanne Gruber |
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