Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Current Status of the Quantum Metrology Triangle



Mark W. Keller


The quantum metrology triangle is a test of the consistency of three quantum electrical standards: the single-electron tunneling current standard, the Josephson voltage standard, and the quantum Hall resistance standard. This paper considers what is known about each of these effects separately in terms of 1) theory, 2) empirical tests of universality, and 3) ``direct'' tests involving fundamental constants. The current status of each of the three ``legs'' of the triangle is quite different, with the single-electron leg being the weakest by far. This leads to the conclusion that a recent experimental result for the triangle should be interpreted primarily in terms of corrections to the quantum of charge transferred by single-electron devices.


Keller, M. (2008), Current Status of the Quantum Metrology Triangle, Metrologia, [online], (Accessed May 28, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created January 18, 2008, Updated January 27, 2020