A Pauli channel is defined as a convex combination of Pauli operators, i.e. $\epsilon_{Pauli} (\rho)=\sum_{j} q_j\sigma_j\rho \sigma_j$, where $0 \leq q_j \leq 1$ and $\sum_j q_j=1$. Now, I want to transmit firstly a pure state qubit through it, and then a Bell state. How do I start working on this?