Séminaires
On the redefinition of the kilogram: Recent advances -- Richard Davis (BIPM)
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Europe/Paris
Description
As is well known, the kilogram is the last remaining base unit of the Système international d’unités (SI) still to be defined by an artifact. Manufactured in the 19th century, the artifact kilogram is conserved and used at the BIPM. In fact, other base units of the SI are defined in terms of the kilogram: the ampere and the mole. For a great many years, chemists have preferred a standard of mass based on 12C. This has led to the wide use of the (non-SI) unified atomic mass unit (u). Electrical units of voltage and resistance are presently realized to very high precision using quantum-based standards based on the Josephson and quantized Hall effects. These quantum electrical standards rely on values of the Planck constant (h) and the fundamental electrical charge (e). Unfortunately, the SI values of both these constants depend at present on experimental traceability to the artifact kilogram. Clearly, the kilogram should be redefined as soon as possible in terms of a physical constant; but how can this be accomplished to everyone’s satisfaction? The presentation will discuss these issues, with emphasis on those experiments which link the artifact kilogram to fundamental physical constants with highest accuracy.