直積演算子
I z = 1 / 2 ( 1 0 0 0 0 1 0 0 0 0 − 1 0 0 0 0 − 1 ) {\displaystyle I_{z}=1/2{\begin{pmatrix}1&0&0&0\\0&1&0&0\\0&0&-1&0\\0&0&0&-1\end{pmatrix}}}
S x = 1 / 2 ( 0 1 0 0 1 0 0 0 0 0 0 1 0 0 1 0 ) {\displaystyle S_{x}=1/2{\begin{pmatrix}0&1&0&0\\1&0&0&0\\0&0&0&1\\0&0&1&0\end{pmatrix}}}
S y = i / 2 ( 0 − 1 0 0 1 0 0 0 0 0 0 − 1 0 0 1 0 ) {\displaystyle S_{y}=i/2{\begin{pmatrix}0&-1&0&0\\1&0&0&0\\0&0&0&-1\\0&0&1&0\end{pmatrix}}}
S z = 1 / 2 ( 1 0 0 0 0 − 1 0 0 0 0 1 0 0 0 0 − 1 ) {\displaystyle S_{z}=1/2{\begin{pmatrix}1&0&0&0\\0&-1&0&0\\0&0&1&0\\0&0&0&-1\end{pmatrix}}}