Superdense coding

Entangled states constitute a powerful natural resource for QIP. In this section, two of the most interesting applications are illustrated superdense coding and the teleport. 

The superdense coding is a process, in which two bits of classical information are transmitted using only one quantum bit. Here the example of exchange of information between two parties Alice and Bob, is described. Suppose that initially Alice and Bob share qubits in an entangled cat state ... 

Teleport is a process through which the state of a qubit is transferred to another, using the non-local properties of entangled states [17]. Differently from superdense coding, no qubit is transferred in teleport, but only a quantum state. 

In the simplest case of teleport, three qubits are involved, two with Alice (let s label them lira)) and one with Bob (labelled fc . As in the superdense coding process, initially Alice and Bob qubits, a) and b), are in a cat state. Alice wishes to transmit to Bob the unknown state of a third qubit, IV ) = a 0> -I- 8 1>. Of course, she cannot measure ir), for she would only get 0 or 1, with the probabilities a and p, respectively. The quantum circuit that describes the teleport process is illustrated in Figure 3.8, where the top line represents the qubit Alice wants to teleport to Bob ( V >), and the second and third lines, represent the entangled qubit pair, the second one with Alice and the third one with Bob. 

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