  The spectrum of 1-state and 2-states per line quantum buses is used to
determine the effective $V_{ab}(N)$ electronic coupling between emitter and
receiver states through the bus as a function of the number $N$ of parallel
lines in the bus. When the calculation of $V_{ab}(N)$ is spectrally difficult,
an Heisenberg-Rabi time dependent quantum exchange process can be triggered
through the bus by preparing a specific initial non-stationanry state and
identifying a target state to capture the effective oscillation frequency
$\Omega_{ab}(N)$ between those. For $\Omega_{ab}(N)$ (for $V_{ab}(N)$), two
different regimes are observed as a function of $N$: linear and $\sqrt{N}$ more
moderate increases. This state preparation was remplaced by electronically
coupling the quantum bus to two semi-infinite electrodes. The native quantum
transduction process at work in this tunnel junction is not faithfully
following the $\Omega_{ab}(N)$ variations with $N$. Due to normalisation to
unity of the electronic transparency of the quantum bus and to the low pass
filter character of the transduction, large $\Omega_{ab}(N)$ cannot be followed
by the tunnel junction. At low coupling and when $N$ is small enough not to
compensate the small through line coupling, an $N^2$ power law is preserved for
$\Omega_{ab}(N)$. The limitations of the quantum transduction in a tunnel
junction is pointing how the broadly used concept of electrical contact between
a metallic nanopad and a molecular wire can be better described as a quantum
transduction process.
