  We study multi-qubit quantum channels that can be represented as a product of
one-mode fermionic attenuation channels. An explicit formula for the classical
capacity $C_1$ and for the minimum output entropy $S_{min}$ of these channels
is proposed. We compute $S_{min}$ analytically for any number of qubits under
assumption that the minimum is achieved on a Gaussian input. Apart from that, a
simple numerical method for evaluating $S_{min}$ is developed. The method is
applicable to any channels that are sufficiently noisy. For fermionic product
channels the proposed formula for $S_{min}$ agrees with the numerical results
with a precision about $10^{-9}$.
