  We investigate the two-plasmon spontaneous decay of a quantum emitter near
single-walled carbon nanotubes (SWCNT) and graphene-coated wires (GCWs). We
demonstrate efficient, enhanced generation of two-plasmon entangled states in
SWCNTs due to the strong coupling between tunable guided plasmons and the
quantum emitter. We predict two-plasmon emission rates more than twelve orders
of magnitude higher than in free-space, with average lifetimes of a few dozens
of nanoseconds. Given their low dimensionality, these systems could be more
efficient for generating and detecting entangled plasmons in comparison to
extended graphene. Indeed, we achieve tunable spectrum of emission in GCWs,
where sharp resonances occur precisely at the plasmons' minimum excitation
frequencies. We show that, by changing the material properties of the GCW's
dielectric core, one could tailor the dominant modes and frequencies of the
emitted entangled plasmons while keeping the decay rate ten orders of magnitude
higher than in free-space. By unveiling the unique properties of two-plasmon
spontaneous emission processes in the presence of low dimensional carbon-based
nanomaterials, our findings set the basis for a novel material platform with
applications to on-chip quantum information technologies.
