Computing operator in bra-ket within momentum space

1. Oct 13, 2011

Void123

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

$<e^{ip'x}|x^{2}|e^{ipx}>$

2. Relevant equations

3. The attempt at a solution

Its pretty obvious that its difficult to integrate in position-space, so I rewrite x in momentum space (i.e. the second-order differential operator with respect to p).

If that is the case, is this correct (which is the part I'm not sure about):

$C \int^{-\infty}_{-\infty} e^{ip'x}\frac{∂^{2}}{∂p^{2}}e^{ipx} dp$

(hbar is absorbed into the constant on the side)

Or do I have to fourier transform $e^{ip'x}$ and $e^{ipx}$?

Thanks.

2. Oct 13, 2011

susskind_leon

$e^{ipx}$ is the wavefunction given in position space, so if you want to integrate in momentum space, you need to express the wavefunctions in momentum space as well, which should be $\delta(p_1-p)$