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Eigenvalues and Eigenfunctions | Quantum Mechanics

Eigenvalues and Eigenfunctions

If an operator  operating on a function:

$\psi_{n}(x)$

gives

$Â\psi_{n}(x) = Â\psi_{n}(x),$

then

$\psi_{n}(x)$

is called the eigenfunction of  corresponding to eigenvalue $\lambda$ and the above equation is known as the eigenvalue equation of operator Â.

Example:

$Â = \frac{d^{2}}{dx^{2}}$ and $\psi_{n}(x) = \alpha e^{-2x}$

$\Longrightarrow Â\psi_{n}(x)= \frac{d^{2}}{dx^{2}} (\alpha e^{-2x}) = 4\alpha e^{-2x} = 4\psi_{n}(x)$

$\psi_{n}(x)$ is an eigenfunction of  corresponding to eigenvalue 4.

If the commutator bracket of two operators  and $\hat{B}$ is equal to zero

i.e. $[Â,\hat{B}] = 0,$

then the physical observables corresponding to these operators are simultaneously accurately measurable and they have a complete set of simultaneous eigenfunctions.

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