Symbol sigma_z

Its job in the formula

sigm$a_z$ is part of the quantity the equation computes from the expression on the right.

Where the article explains it

Then $\langle$ f|$\psi$$\rangle$ = $\tfrac12(1-i)$ and $\langle$ f|$\sigma_z$|$\psi$$\rangle$ = $\tfrac12(1+i)$ , so the weak value of $\sigma_z$ is

Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

Open the illustrated subscripts: which member of a family? guide →