File:Quantum Fourier transform on n qubits.svg

\documentclass[10pt]{article}

\usepackage[hang,small,bf]{caption}    % fancy captions

\usepackage{tikz}	
\usetikzlibrary{backgrounds,fit,decorations.pathreplacing}  % TikZ libraries

\newcommand{\ket}[1]{\ensuremath{\left|#1\right\rangle}} % Dirac Kets
\begin{document}

\begin{figure}[h]  
\centerline{     
\begin{tikzpicture}[thick]     
%     
% `operator' will only be used by Hadamard (H) gates here.     
% `phase' is used for controlled phase gates (dots).     
% `surround' is used for the background box.     
\tikzstyle{operator} = [draw,fill=white,minimum size=1.5em]      
\tikzstyle{phase} = [fill,shape=circle,minimum size=5pt,inner sep=0pt]  
%\tikzstyle{surround} = [fill=red!10,thick,draw=white,rounded corners=2mm] 	
\tikzstyle{phase1} = [draw=black,shape=circle,minimum size=8pt,inner sep=0pt]  
\tikzstyle{phase3} = [fill,shape=circle,minimum size=0pt,inner sep=0pt]  
%
% columna     
\node at (-2,0) (q1) {\ket{x_{1}}};     
\node at (-2,-1) (q2) {\ket{x_{2}}}; 
\node at (-2,-2) (q3) {\vdots}; 
\node at (-2,-3) (q5) {\ket{x_{n-1}}};     
\node at (-2,-4) (q6) {\ket{x_{n}}}; 
%        
% Column 1 
\node[operator] at (-1,0) (q7) {H} edge [-] (q1);     
% Columna 2
\node at (0,-2) (q4) {\vdots};
\node[operator] at (0,0) (q8) {$R_{2}$} edge [-] (q7);
\node[phase] at (0,-1) (q9) {} edge [-] (q8) edge [-] (q2);
%
%Columna 3
\node at (1,0) (q10) {\dots} edge [-] (q8); 
\node at (1,-1) (q11) {\dots} edge [-] (q9); 
%
%          
%    
% Column 4  
\node[operator] at (2,0) (q12) {$R_{n-1}$} edge [-] (q10);
\node[phase] at (2,-3) (q13) {} edge [-] (q12) edge [-] (q5);
\node[phase3] at (2,-1) (q14) {} edge [-] (q11);  
%Columna 5
\node[operator] at (3.2,0) (q15) {$R_{n}$} edge [-] (q12);
\node[phase] at (3.2,-4) (q16) {} edge [-] (q15) edge [-] (q6);
%Columna 6
\node[operator] at (4,-1) (q17) {H} edge [-] (q11);
%columna 7
\node at (5,-1) (q18) {\dots} edge [-] (q17); 
%columna 8
\node[operator] at (6,-1) (q19) {$R_{n-2}$} edge [-] (q18);
\node[phase] at (6,-3) (q20) {} edge [-] (q19) edge [-] (q13);
%columna 9/10
\node[operator] at (7.5,-1) (q21) {$R_{n-1}$} edge [-] (q19);
\node[phase] at (7.5,-4) (q22) {} edge [-] (q21) edge [-] (q16);
%columna 11
\node at (9,-1) (q23) {\dots} edge [-] (q21); 
\node at (9,-3) (q24) {\dots} edge [-] (q20);
\node at (9,-4) (q25) {\dots} edge [-] (q22);
%columna 12
\node[operator] at (10,-3) (q26) {H} edge [-] (q24);
% columna 13
\node[operator] at (11,-3) (q27) {$R_{2}$} edge [-] (q26);
\node[phase] at (11,-4) (q28) {} edge [-] (q27) edge [-] (q25);
%columna 14
\node[operator] at (12,-4) (q29) {H} edge [-] (q28);
%columna 15
\node at (14.2,0) (q31) {\ket{0}+$e^{2\pi i0.x_{1}x_{2}..x_{n}}$\ket{1}} edge [-] (q15);     
\node at (14.2,-1) (q32) {\ket{0}+$e^{2\pi i0.x_{2}..x_{n}}$\ket{1}} edge [-] (q23); 
\node at (14.2,-2) (q33) {\vdots}; 
\node at (14.2,-3) (q35) {\ket{0}+$e^{2\pi i0.x_{n-1}..x_{n}}$\ket{1}} edge [-] (q27);     
\node at (14.2,-4) (q36) {\ket{0}+$e^{2\pi i0.x_{n}}$\ket{1}} edge [-] (q29);
%
\end{tikzpicture}  
} 
\end{figure}
\end{document}