Magnetic flux quantum
ElectromagneticExact
= 2.067 833 848… × 10−15 Wb
- Value
- 2.067 833 848… × 10−15 Wb
- 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: 2.067 833 848 461 929 323 081 115 412 15 × 10−15…
Use in a calculation
# magnetic flux quantum, CODATA 2022 (NIST)
Phi_0 = 2.0678338484619293230811154121474973e-15 # Wb, exact
# SciPy: scipy.constants.physical_constants['mag. flux quantum']What it is
The magnetic flux through a superconducting ring can only change in steps of Φ₀ = h/2e; the 2 is there because the current is carried by pairs of electrons. SQUID magnetometers count these quanta.
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 | 2.067 833 848… × 10−15 | exact | exact |
| 2018 | 2.067 833 848… × 10−15 | exact | +1.3 σ of 2014 |
| 2014 | 2.067 833 831(13) × 10−15 | 6.3 × 10−9 | +1.6 σ of 2010 |
| 2010 | 2.067 833 758(46) × 10−15 | 2.2 × 10−8 | +1.8 σ of 2006 |
| 2006 | 2.067 833 667(52) × 10−15 | 2.5 × 10−8 | −0.3 σ of 2002 |
| 2002 | 2.067 833 72(18) × 10−15 | 8.7 × 10−8 | +1.0 σ of 1998 |
| 1998 | 2.067 833 636(81) × 10−15 | 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).