# Linear superposition of solutions is a solution of TDSE

1. Jan 11, 2012

### Silversonic

1. The problem statement, all variables and given/known data

Consider two normalised, orthogonal solutions of the TDSE

(Note all my h's here are meant to be h-bar, I'm not sure how to get a bar through them).

$\Psi_1 = \psi_1 (x) e^{-E_1 it/h}$

$\Psi_2 = \psi_2 (x) e^{-E_2 it/h}$

Consider the wavefunction

$\Phi = \sqrt{\frac{1}{3}}\Psi_1 + \sqrt{\frac{2}{3}}\Psi_2$

Which is also a normalised solution to the TDSE. Any linear superposition of solutions to the TDSE is also a solution.

2. Relevant equations

The TDSE is;

$\widehat{H}\Phi = ih\frac{\delta}{\delta t}\Phi$

3. The attempt at a solution

This isn't a question, I've just gone to pursue the statement that the linear superposition is also a solution. I can't see to show it though.

Using $\Phi = \sqrt{\frac{1}{3}}\Psi_1 + \sqrt{\frac{2}{3}}\Psi_2$

$\widehat{H}\Phi = ih\frac{\delta}{\delta t}\Phi = \sqrt{\frac{1}{3}}E_1\psi_1 (x) e^{-E_1 it/h} + \sqrt{\frac{2}{3}}E_2\psi_2 (x) e^{-E_2 it/h}$

Which I cannot manage to get in to the form

$(\sqrt{\frac{1}{3}}E_1 + \sqrt{\frac{2}{3}}E_2)\Phi$

Which is the form is should be in if it was a solution surely?

2. Jan 12, 2012

### ehild

Any linear combination of two solutions is also a solution of the TDSE. But the linear combination of two eigenfunctions is not an eigenfunction if functions belonging to different energies are involved.

Show that Φ is a solution by substituting into the TDSE.

Show that it is normalized.

ehild