omplex quantum system, like an atom, a molecule, a crystal, or even a fragment of DNA, as may be already envisioned by some futurists. It is beyond the scope of this chapter to address this issue and analyze, even superficially, what type of protocol and resources would be required to achieve quNit teleportation, in terms of shared entangled states and exchange of classical bits. We may, however, venture one step further in the description by considering the teleportation of two qubits. This description should suffice to illustrate the complexity of teleporting more than one qubit, and also to satisfy a legitimate curiosity about the potentials of teleporting an ensemble of quantum states. A proposed circuit for the simultaneous teleportation of two qubits (9), 19'> from Alice is shown in Fig. 18.10, as an original, symmetrical variant of that shown in Gottesman and Chuang (1999). As seen from the figure, Alice and Bob share a 4-qubit entangled resource, 1x), which I shall specify later. The two boxes labeled B, with two cbit outputs each, correspond to Bell-state measurements. The rest of the circuit includes three controlled- and controlled-Z gates with Alice's four cbits as control signals, to be communicated to Bob via a classical channel. The circuit output, as received remotely by Bob, is defined as 1/> = C43/9)3/9')4 with |q' controlling 19)3. To retrieve 19), |q'), Bob simply needs to pass the two qubits through the same CNOT gate, as shown at the very right of Fig. 18.10. A possible circuit implementation to generate the entangled state 1x) is illustrated in Fig. 18.11. The circuit is seen to use two identical EPR-Bell states 1Boo) and one CNOT gate. Labeling the four quantum wires in Fig. 18.11 one to From D. Gottesman and I. L. Chuang, Quantum teleportation is a universal computational primitive. Nature, (1999), 390-3, http://arxiv.org/PS_cache/quant-ph/pdf/9908/9908010v1.pdf 18.5 Quantum teleportation Figure 18.11 Possible circuit implementation for generating the entangled state 1x) in Fig. 18.10. fo