Alice then transmits a single photon in the state specified to Bob, using the quantum channel.

Alice sends over a public quantum channel to Bob.

She sends the second qubit of each pair over a noisy quantum channel to a receiver Bob.

There are, however, a few issues with this description of the quantum channel.

Importantly, the classical information can be sent after the quantum channel has ceased to exist.

The send particle is destroyed in the measurement and thus is not actually moved from one location to another to create the quantum channel.

Let be a quantum channel that can cause at most one phase flip.

Let be a quantum channel that can arbitrarily corrupt a single qubit.

General dense coding schemes can be formulated in the language used to describe quantum channels.

The level of imperfection is modelled by noisy quantum channels.