Editing Elementary charge (section)

=== From the Josephson and von Klitzing constants ===
Another accurate method for measuring the elementary charge is by inferring it from measurements of two effects in [[quantum mechanics]]: The [[Josephson effect]], voltage oscillations that arise in certain [[superconducting]] structures; and the [[quantum Hall effect]], a quantum effect of electrons at low temperatures, strong magnetic fields, and confinement into two dimensions. The [[Josephson constant]] is
<math display="block">K_\text{J} = \frac{2e}{h},</math>
where ''h'' is the [[Planck constant]]. It can be measured directly using the [[Josephson effect]].

The [[von Klitzing constant]] is
<math display="block">R_\text{K} = \frac{h}{e^2}.</math>
It can be measured directly using the [[quantum Hall effect]].

From these two constants, the elementary charge can be deduced:
<math display="block">e = \frac{2}{R_\text{K} K_\text{J}}.</math>