Two qubits are prepared in the Bell state illustrated in (4). Alice takes one
qubit and Bob takes the other. By sending a single qubit to Bob, Alice can
subsequently communicate two bits of classical information to Bob. Alice
follows the following rules, if she wants to send information to Bob.
| To Send | Apply the transformation to her qubit |
| 00 | Don't apply anything to the qubit |
| 01 | Apply the phase flip (Z) |
| 10 | Apply the Not gate (X) |
| 11 | Apply the iY gate |
The state of the qubit after these transformation is one of the four Bell states previously discussed. Alice transmits her qubit to Bob. Bob then measures the entangled pair against the Bell orthonormal basis, thus enabling him to determine which of the four possible classical bit strings Alice sent him.