File:Reversible circuit composition.svg

\documentclass[11pt]{article}
\input{Qcircuit}
\thispagestyle{empty}
\begin{document}
\begin{align*}
 \Qcircuit @C=1em @R=.1em {
  & \multigate{4}{f} & \qw              & \qw\\
  & \ghost{f}        & \qw              & \qw\\
  & \ghost{f}        & \multigate{6}{g} & \qw\\
  & \ghost{f}        & \ghost{g}        & \qw\\
  & \ghost{f}        & \ghost{g}        & \qw\\
  & \qw              & \ghost{g}        & \qw\\
  & \qw              & \ghost{g}        & \qw\\
  & \qw              & \ghost{g}        & \qw\\
  & \qw              & \ghost{g}        & \qw \gategroup{1}{2}{9}{3}{.5em}{--}\\
 }
\end{align*}
\end{document}