Conductance quantum
ElectromagneticExact
= 7.748 091 729… × 10−5 S
- Value
- 7.748 091 729… × 10−5 S
- 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: 7.748 091 729 863 650 646 680 823 323 31 × 10−5…
Use in a calculation
# conductance quantum, CODATA 2022 (NIST)
conductance_quantum = 7.7480917298636506466808233233087639e-5 # S, exact
# SciPy: scipy.constants.physical_constants['conductance quantum']What it is
The conductance of a single perfect one-dimensional channel for electrons, counting both spin directions. Atomic-scale wires and quantum point contacts conduct in steps of G₀.
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
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 | 7.748 091 729… × 10−5 | exact | exact |
| 2018 | 7.748 091 729… × 10−5 | exact | −1.1 σ of 2014 |
| 2014 | 7.748 091 7310(18) × 10−5 | 2.3 × 10−10 | −1.4 σ of 2010 |
| 2010 | 7.748 091 7346(25) × 10−5 | 3.2 × 10−10 | +6.5 σ of 2006 |
| 2006 | 7.748 091 7004(53) × 10−5 | 6.8 × 10−10 | −1.3 σ of 2002 |
| 2002 | 7.748 091 733(26) × 10−5 | 3.4 × 10−9 | +1.3 σ of 1998 |
| 1998 | 7.748 091 696(28) × 10−5 | 3.6 × 10−9 |
“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).