- #1
Tales Roberto
- 7
- 0
Homework Statement
Consider the wave packet [tex]\psi\left(x\right)=\Psi\left(x,t=0\right)[/tex] given by [tex]\psi=Ce^{\frac{ip_{0}x}{h}-\frac{\left|x\right|}{2\Delta x}[/tex] where C is a normalization constant:
(a) Normalize [tex]\psi\left(x\right) [/tex] to unity
(b) Obtain the corresponding momentum space wave function [tex]\phi\left(p_{x}\right)[/tex] and verify that it is normalized to unity according to: [tex]\int^{\infty}_{-\infty}\left|\phi\left(p_{x}\right)\right|^{2} dp_{x}=1[/tex]
(c) Suggest a reasonable definition of the width [tex]\Delta p_{x}[/tex] and show that [tex]\Delta x \Delta p_{x} \geq h [/tex]
The Attempt at a Solution
(a) is easy to solve and we find that [tex] C=\frac{1}{\sqrt{2\Delta x}} [/tex] assuming that C is real. This way [tex]\psi=\frac{1}{\sqrt{2\Delta x}}e^{\frac{ip_{0}x}{h}-\frac{\left|x\right|}{2\Delta x}[/tex]
I attempt to use Fourier Transform to calculate (b):
[tex]\phi\left(p_{x}\right)=\left(2\Pi h \right)^{-\frac{1}{2}} \int e^{\frac{-ip_{x}x}{h}} \psi dx[/tex]
[tex]\phi\left(p_{x}\right)=\left(4\Pi h \right\Delta x)^{-\frac{1}{2}} \int e^{\frac{-i\left(p_{x}-p_{0}\right)x}{h}} e^{\frac{-\left|x\right|}{2\Delta x}} dx[/tex]
[tex]\phi\left(p_{x}\right)=\left(4\Pi h \right\Delta x)^{-\frac{1}{2}} \left[\int_{0}^{\infty} e^{-\left(\frac{ip}{h}} + \frac{1}{2\Delta x}\right)x} dx + \int_{-\infty}^{0} e^{-\left(\frac{ip}{h} - \frac{1}{2\Delta x}\right)x} dx\right][/tex]
where [tex]p=p_{x} - p_{0}[/tex]. To simplify let's write:
[tex]\beta_{1}=\left(\frac{ip}{h}} + \frac{1}{2\Delta x}\right)[/tex] [tex]\beta_{2}=\left(\frac{ip}{h} - \frac{1}{2\Delta x}\right)[/tex]
Then:
[tex]\phi\left(p_{x}\right)=\left(4\Pi h \right\Delta x)^{-\frac{1}{2}} \left[\int_{0}^{\infty} e^{-\beta_{1}x} dx + \int_{-\infty}^{0} e^{-\beta_{2}x} dx\right][/tex]
This integral does not converge since arguments are complex. My "feeling" is that my solution is completely wrong, please help!