English: This quantum circuit implements Deutsch's algorithm. Given a unitary "oracle" operator ${\displaystyle U_{f}\in {\mathcal {L}}(\mathbb {C} ^{2}\otimes \mathbb {C} ^{2})}$ such that ${\displaystyle U_{f}|x,y\rangle =|x,y\oplus f(x)\rangle }$ for all ${\displaystyle x,y\in \{{\texttt {0}},{\texttt {1}}\}}$, the measurement gate in the upper-right determines whether or not ${\displaystyle f({\texttt {0}}){\stackrel {?}{=}}f({\texttt {1}})}$ using a single query. The bottom wire can be safely measured and/or discarded at the end of the algorithm.

This image was generated with the following LaTeX code:

\documentclass[tikz]{standalone}
\usepackage{quantikz}
\begin{document}
\begin{quantikz}[row sep=2mm,column sep=2mm]
\lstick{\ket{\texttt{0}}} & \qw & \gate{H} & \gate[2][2cm]{U_f} \gateinput{$x$} \gateoutput{$x$} & \gate{H} & \meter{} \\
\lstick{\ket{\texttt{0}}} & \gate{X} & \gate{H} & \gateinput{$y$} \gateoutput{$y \oplus f(x)$} & \trash{}
\end{quantikz}
\end{document}