- #1
maximus123
- 50
- 0
Hello,
I have a problem where I'm given the following
[itex]H=-\frac{\hbar\Omega}{2}\sigma_x\quad\quad\quad\textrm{and}\quad\quad\quad\Psi(0)=\left|0\right\rangle\quad[/itex]
Where
[itex]\sigma_x=\begin{pmatrix}0 & 1\\1&0\end{pmatrix}\quad\quad\quad\textrm{and}\quad\quad\quad\left|0\right\rangle=\begin{pmatrix}1\\0\end{pmatrix}[/itex]
And in general
[itex]\Psi(t)=\textrm{exp}\left[-i\frac{H}{\hbar}t\right]\Psi(0)[/itex]
So
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle[/itex]
The problem is I need to get from here to
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle=\begin{pmatrix}\textrm{cos}(\Omega t/2)\,\,\,&i\textrm{sin}(\Omega t/2)\\i\textrm{sin}(\Omega t/2)\,\,\,&\textrm{cos}(\Omega t/2)\end{pmatrix}\begin{pmatrix}1\\0\end{pmatrix}\\\\\\
\quad\quad\quad\quad\quad\quad\quad\quad\quad\,\,\,\,=\begin{pmatrix}cos(\Omega t/2)\\isin(\Omega t/2)\end{pmatrix}
[/itex]
I can't work out how to get to this cos and sine matrix. I tried this
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle=\left\lbrace\textrm{cos}\left(\frac{\Omega t}{2}\sigma_x\right)+i\textrm{sin}\left(\frac{\Omega t}{2}\sigma_x\right)\right\rbrace\left|0\right\rangle\\\\
\quad\quad\quad\quad\quad\quad\quad\quad\quad=\left\lbrace\textrm{cos}\begin{pmatrix}0 & \frac{\Omega t}{2}\\\frac{\Omega t}{2} & 0\end{pmatrix}+i\textrm{sin}\begin{pmatrix}0 & \frac{\Omega t}{2}\\\frac{\Omega t}{2} & 0\end{pmatrix}\right\rbrace\begin{pmatrix}1\\0\end{pmatrix}[/itex]
Beyond this I cannot see how to get from here to
[itex]\begin{pmatrix}\textrm{cos}(\Omega t/2)\,\,\,&i\textrm{sin}(\Omega t/2)\\i\textrm{sin}(\Omega t/2)\,\,\,&\textrm{cos}(\Omega t/2)\end{pmatrix}\begin{pmatrix}1\\0\end{pmatrix}[/itex]
Any help would be really appreciated
I have a problem where I'm given the following
[itex]H=-\frac{\hbar\Omega}{2}\sigma_x\quad\quad\quad\textrm{and}\quad\quad\quad\Psi(0)=\left|0\right\rangle\quad[/itex]
[itex]\sigma_x=\begin{pmatrix}0 & 1\\1&0\end{pmatrix}\quad\quad\quad\textrm{and}\quad\quad\quad\left|0\right\rangle=\begin{pmatrix}1\\0\end{pmatrix}[/itex]
[itex]\Psi(t)=\textrm{exp}\left[-i\frac{H}{\hbar}t\right]\Psi(0)[/itex]
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle[/itex]
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle=\begin{pmatrix}\textrm{cos}(\Omega t/2)\,\,\,&i\textrm{sin}(\Omega t/2)\\i\textrm{sin}(\Omega t/2)\,\,\,&\textrm{cos}(\Omega t/2)\end{pmatrix}\begin{pmatrix}1\\0\end{pmatrix}\\\\\\
\quad\quad\quad\quad\quad\quad\quad\quad\quad\,\,\,\,=\begin{pmatrix}cos(\Omega t/2)\\isin(\Omega t/2)\end{pmatrix}
[/itex]
I can't work out how to get to this cos and sine matrix. I tried this
[itex]\Psi(t)=\textrm{exp}\left[i\frac{\Omega t}{2}\sigma_x\right]\left|0\right\rangle=\left\lbrace\textrm{cos}\left(\frac{\Omega t}{2}\sigma_x\right)+i\textrm{sin}\left(\frac{\Omega t}{2}\sigma_x\right)\right\rbrace\left|0\right\rangle\\\\
\quad\quad\quad\quad\quad\quad\quad\quad\quad=\left\lbrace\textrm{cos}\begin{pmatrix}0 & \frac{\Omega t}{2}\\\frac{\Omega t}{2} & 0\end{pmatrix}+i\textrm{sin}\begin{pmatrix}0 & \frac{\Omega t}{2}\\\frac{\Omega t}{2} & 0\end{pmatrix}\right\rbrace\begin{pmatrix}1\\0\end{pmatrix}[/itex]
Beyond this I cannot see how to get from here to
[itex]\begin{pmatrix}\textrm{cos}(\Omega t/2)\,\,\,&i\textrm{sin}(\Omega t/2)\\i\textrm{sin}(\Omega t/2)\,\,\,&\textrm{cos}(\Omega t/2)\end{pmatrix}\begin{pmatrix}1\\0\end{pmatrix}[/itex]