Josephson constant
ElectromagneticExact
= 483 597.8484… × 109 Hz V−1
- Value
- 483 597.8484… × 109 Hz V−1
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
NIST prints this exact value cut to 10 digits. ConstantID recomputes it from the defining constants: 4.835 978 484 169 836 324 476 582 850 55 × 1014…
Use in a calculation
# Josephson constant, CODATA 2022 (NIST)
K_J = 4.8359784841698363244765828505452814e14 # Hz V^-1, exact
# SciPy: scipy.constants.physical_constants['Josephson constant']What it is
The frequency-to-voltage ratio of the Josephson effect: a junction between two superconductors, driven by microwaves of frequency f, develops voltage steps of exactly f/K_J. Voltage standards around the world are built on it, and since 2019 its value is exact.
It is built only from constants that have exact values since 20 May 2019, so it is exact too; CODATA 2018 was the first adjustment to list it that way.
Equations
- definition
- Josephson voltage steps
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 483 597.8484… × 109 | exact | exact |
| 2018 | 483 597.8484… × 109 | exact | −1.4 σ of 2014 |
| 2014 | 483 597.8525(30) × 109 | 6.2 × 10−9 | −1.6 σ of 2010 |
| 2010 | 483 597.870(11) × 109 | 2.3 × 10−8 | −1.8 σ of 2006 |
| 2006 | 483 597.891(12) × 109 | 2.5 × 10−8 | +0.3 σ of 2002 |
| 2002 | 483 597.879(41) × 109 | 8.5 × 10−8 | −1.0 σ of 1998 |
| 1998 | 483 597.898(19) × 109 | 3.9 × 10−8 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).