Josephson constant

(physics) The quantity K_J = 2e/h, which appears in the equations for the alternating-current Josephson effect, where e is the magnitude of the charge of the electron and h is Planck's constant. The conventional value of this quantity adopted by international agreement on January 1, 1990, to establish a standard for the volt, K_J-90 = 493,597.9 gigahertz per volt.

[Etymology: B. D. Josephson; UK 1940- ] fundamental constant. Symbol K_J. The quotient of frequency divided by the potential difference corresponding to the n = 1 step in the Josephson effect, used in the determination of the volt etc.
[Hartland A. Contemp. Phys. Vol. 29, 477 (1988) http://www.npl.co.uk/npl/publications/electricity/] The conventional value, agreed in 1988 for implementation in 1990, is K_J-90 = 483 597.9 GHz·V^-1. The true value, denoted K_J, is evaluated as 483 597.879(41) × 10⁹ Hz·V^-1 with relative standard uncertainty 8.5 × 10^-8.
[Mohr P. J., Taylor B. N. CODATA Recommended Values of the Fundamental Physical Constants: 2002 (to be published)]
[Mohr P. J., Taylor B. N. Rev. Mod. Phys. Vol. 72:351-495 (2000)]
[Mohr P. Phys. Today Vol. 53:7, 11-16 (2000)]
[For latest recommended values, see http://physics.nist.gov/cuu/Constants/index.html]