  A recent study [Rosati, Dolcini, and Rossi, Appl. Phys. Lett. 106, 243101
(2015)] has predicted that, while in semiconducting single-walled carbon
nanotubes (SWNTs) an electronic wave packet experiences the typical spatial
diffusion of conventional materials, in metallic SWNTs its shape remains
essentially unaltered up to micron distances at room temperature, even in the
presence of the electron-phonon coupling. Here, by utilizing a Lindblad-based
density-matrix approach enabling us to account for both dissipation and
decoherence effects, we test such prediction by analyzing various aspects that
were so far unexplored. In particular, accounting for initial nonequilibrium
excitations, characterized by an excess energy $E_0$, and including both intra-
and interband phonon scattering, we show that for realistically high values of
$E_0$ the electronic diffusion is extremely small and nearly independent of its
energetic distribution, in spite of a significant energy-dissipation and
decoherence dynamics. Furthermore, we demonstrate that the effect is robust
with respect to the variation of the chemical potential. Our results thus
suggest that metallic SWNTs are a promising platform to realise quantum
channels for the non-dispersive transmission of electronic wave packets.
