Turing Machine

\usetikzlibrary{automata, positioning}

\begin{tikzpicture}[shorten >=1pt, node distance=3cm, on grid, auto]
  \node[state, initial] (q0) {$q_0$};
  \node[state] (q1) [right=of q0] {$q_1$};
  \node[state] (q2) [right=of q1] {$q_2$};
  \node[state, accepting] (qa) [below=2cm of q1] {$q_a$};

  \path[->]
  (q0) edge node{$0/X, R$} (q1)
  (q1) edge[loop above] node{$0/0, R$} ()
  edge node{$1/Y, L$} (q2)
  (q2) edge[loop above] node{$0/0, L$} ()
  edge node{$X/X, R$} (q0)
  (q0) edge node[left]{$Y/Y, R$} (qa);
\end{tikzpicture}