Pauli Matrices

${\sigma }_1=\left(\begin{array}{cc}0& 1\\ 1& 0\end{array}\right){\sigma }_2=\left(\begin{array}{cc}0& -i\\ i& 0\end{array}\right){\sigma }_3=\left(\begin{array}{cc}1& 0\\ 0& -1\end{array}\right)$