\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}\begin{array}{ccc}
\left | \phi_{b,x} \right>=\left\{\begin{array}{c}
\frac{1}{\sqrt{2}}(\left | 0 \right>+\left | 1 \right>) \,\,\,\,\,\, b=0,\, x=0\\
\frac{1}{\sqrt{2}}(\left | 0 \right>-\left | 1 \right>) \,\,\,\,\,\, b=0,\, x=1\\
\frac{1}{\sqrt{2}}(\left | 0 \right>+\left | 2 \right>) \,\,\,\,\,\, b=1,\, x=0\\
\frac{1}{\sqrt{2}}(\left | 0 \right>-\left | 2 \right>) \,\,\,\,\,\, b=1,\, x=1
\end{array}\right.
\end{array}\end{equation*}
\end{document}