A B|0)); which can be summarized in the general form: 'mm') 1/>/ with 1/su = Zm' Xm |q) being the qubit accessible to Bob. It is clear that without any knowledge of the two bits m, m', Bob is not able to make any sense of his qubit other than performing meaningless random-measurement guesses. Bob cannot have any certainty either of Alice's measurement, through any prior agreement between them. No such agreement is possible, since by definition any of Alice's measurement of any of the four pure states 'mm') has 1/4 chance of being successful. Alice and Bob could agree that only the measurement |00) will be systematically performed, which already represents one bit of advance information. Alice must then tell Bob if the measurement succeeded, and this is another bit of information, resulting in m, m' = 0, 0. Only then can Bob be certain that = The key conclusion is that for successful qubit teleportation, Bob needs the two classical bits m, m' from Alice. Should the QT apparatus use qubits instead of cbits to control Bob's gates, the conclusion remains the same: Alice's qubits |m), |m') must be transmitted over the distance separating her from Bob. Any physical channel supporting qubits can be used for this transmission (for instance an optical fiber or a radio link), but the communication cannot be faster than the speed of light. 1 In any physical medium, the speed of an electromagnetic (EM) wave is given by C = co/n, where n > 1 is the medium's refractive index and CO is the speed of light in absolute vacuum. Thus, the condition C < CO is always satisfied for any EM-wave transmission. Qubit measurements, coding, and teleportation Alice Alice Figure 18.10 Circuit implementation for simultaneous quantum teleportation of two qubits. What about the possibility of teleporting an arbitrary number N of different qubits simultaneously or, even better, teleporting at once an N-qubit, also called quNit or, equivalently, qudit, for d-qubit? The second case would achieve the "dream" of tele- porting to another location any c