Classical information channel

• In quantum teleportation, a classical channel together with a previously prepared entangled quantum state are used to transmit quantum information between two parties. Neither the classical channel nor the previously prepared quantum state alone can do this task.
• In quantum cryptography, a classical channel is used along with a quantum channel in protocols for quantum key exchange.
• In quantum communication, the information rate of a noisy quantum channel can be increased when used together with a noise-free classical channel. In particular, some very noisy quantum channels cannot transmit quantum information if used alone but can transmit it if used together with a classical channel.