Production of SET chips at the
PTB’s clean room centre. The chip’s
capacity to transport and count
electrons – a quantum effect called
‘single electron tunneling’ – could
make it the foundation of a novel
definition of the ampere as of 2011,
linking the base unit to the charge
of an electron.
The screen shows the 1 x 1 mm
central area of one chip.

[A] ‘The AMPERE is that con-
stant current which, if maintained
in two straight parallel conductors of
infinite length, of negligible circular
cross-section, and placed 1 metre
apart in vacuum, would produce
between these conductors a force
equal to 2·10–7 newton per meter
of length.’