Consider an operator $${\displaystyle A}$$. The expectation value is then $${\displaystyle \langle A\rangle =\langle \psi |A|\psi \rangle }$$ in Dirac notation with $${\displaystyle |\psi \rangle }$$ a normalized state … See more

• Rayleigh quotient
• Uncertainty principle
• Virial theorem See more

In quantum theory, an experimental setup is described by the observable $${\displaystyle A}$$ to be measured, and the See more

As an example, consider a quantum mechanical particle in one spatial dimension, in the configuration space representation. … See more

The expectation value, in particular as presented in the section "Formalism in quantum mechanics", is covered in most elementary textbooks … See more