vations, the QT circuits shown in the literature either use representations of Fig. 18.7 or of Fig. 18.8, or of both (the two outputs of any of Alice's measurement connecting to Bob's gates). Two other legitimate questions are whether it is possible to use EPR-Bell states different from 1Boo), and how Alice and Bob can set up an EPR-Bell state to share. Concerning the first question, the answer is yes, which is left as an exercise to show. In that case, however, the classical bits to be transmitted to Bob are different from m, m' and Alice must use a logic look-up table to transform m, m' into the right combinations, which depends on which EPR-Bei state has been used. Apart from this minor complication, the QT principle using the three EPR-Bell states 1,B01), 1B10), 1B11) remains strictly identical. The answer to the second question is provided in Fig. 18.9. Both Alice and Bob must supply a qubit |0) of their own, for Alice to use as an ancilla qubit, and for Bob to use as a target qubit. The Hadamard-CNOT circuit shaded in the figure corresponds to that of Fig. 18.3, which, as we have seen, generates the entangled state 1,Boo), when input with the two qubits |0), |0). As a summary and conclusion, we have learnt that it is possible to achieve the teleportation of a single unknown qubit through a quantum channel. For the two ends of the channel (Alice and Bob) the requirement is to share one EPR pair and two classical 18.5 Quantum teleportation X Z - 19 Figure 18.9 Full implementation of quantum teleportation circuit with ancilla and target qubits |0), |0) at input. bits of information. The fact that Alice must communicate the two classical bits to Bob shows that QT cannot operate faster than the speed of light, which is in agreement with a fundamental principle of the theory of relativity. However, we have seen that Alice's measurements instantaneously collapse the system into any of the four 3-qubit states given by Eq. (18.23), namely, |00)(a|0) + B|1)); |01)(x|1) + B|0)); (18.24) [10)(a|0) - B|1)); (11)(a|1) - 