(color online) Circuits for the projective measurements onto bases . The circuits at top left, top right, bottom left, and bottom right simulate the projective measurements onto , and respectively. There are two two-qubit operations in these circuits. The first one is the swap operation, which is depicted in Fig. 4. The other one is a controlled unitary operation, . The one-qubit operations are the Hadamard gate H and the gate that appeared in the circuit for one qubit tomography. At the end of each circuit, we measure each qubit with the projective measurement {|0⟩⟨0|, |1⟩⟨1|}.