From Ohm to Quantum Ohm
Paper Authors: Dean G. Jarrett and Albert F. Rigosi
Presenter: Dean G. Jarrett
National Institute of Standards and Technology
Gaithersburg, MD 20899
From the time of the founding of the National Bureau of Standards (NBS) in 1901 to the present,
resistance measurements have been among the research activities to realize electrical units at the
National Institute of Standards and Technology (NIST). The U. S. representation of the ohm has seen
many changes over the past 125 years including three adjustments (1948, 1990, 2019), advances in
standards and instrumentation, the discovery of the quantum Hall effect, and realization of the ohm by
fundamental constants. The standards and instrumentation have leveraged advances in technology and
evolved to support the many needs for resistance measurements over wider ranges with reduced
uncertainties. From the mercury ohm of the early days to the development of ultra-stable wire wound
resistance standards, to the quantum graphene standards of today and tomorrow: resistance metrology
has been a part of the research activities at NIST and the other national metrology institutes (NMIs) for
over a century. Looking towards the future, resistance measurements at NIST today focus on graphene
as a next generation of quantum resistance standard, the measurement needs of U. S. industry, and new
demands for resistance measurements and standards in applications ranging from low-current sensing
technologies to high current needs in the delivery of electric power. The historical past will be reviewed
and the present status presented with an outlook towards the future of the NIST Quantum Ohm.
Intro
The ohm, the unit of electrical resistance, has a rich and complex history, evolving over centuries from
early experiments to the sophisticated quantum standards of today. This report will explore that history,
highlighting key milestones, redefinitions, and the ongoing quest for increasingly accurate and reliable
resistance measurements.
Early Developments
The general idea of electrical resistance began to take shape in the 19th century, with Georg Simon
Ohm’s work. In 1827, Ohm discovered the empirical relationship V = IR, which quantified the
relationship between voltage (V), current (I), and resistance (R). This foundational law provided the basis
for measuring electrical resistance. Later in the 19th century, scientists like Gauss (1833) and Weber
(1851) contributed to the understanding of electrical quantities by showing that such quantities could be
measured in terms of mechanical units.
