\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\hfil\begin{tikzpicture}

\draw(-1,0)--++(4,0)--++(0,4)--++(-4,0)--cycle;

\draw[line width=4pt](0,0)--++(0,4);
\draw[line width=4pt](1,0)..controls(1,2)and(2,2)..(2,0);
\draw[line width=4pt](1,4)..controls(1,2)and(2,2)..(2,4);

\end{tikzpicture}

\end{document}
