In quantum information theory, classical-quantum channels are considered to be channels whose input is the realizations $x\in\mathcal{X}$ of a classical random variable to a quantum state $\rho_x^B$, that is
$$W:x\rightarrow\rho_x^B$$
where each quantum state $\rho_x$ is described by a positive semi-definite operator with unit trace. This kind of channels are useful due to the fact that they arise in the reality, such as an optic fiber communication link, and so codes taking into account the impact of quantum mechanics can be constructed to make the link perform better.
I was wondering if someone can give reference about more examples of real life communication scenarios where this kind of channels can be useful to describe them apart from the optical link example that is the most typical one.
